Huntington's Disease Society of America

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2-DG 2-deoxy-D-glucose. - A substance that helps induce autophagy and thus decrease huntingtin protein aggregation. Also has been shown to increase levels of HSP-70 and GRP-78.
3-hydroxykynurenin (3HK) - A free radical generator that is present in increased amounts in humans with HD and HD mice.
3-NP - Abbreviation for 3-nitroproprionic acid.
3-nitroproprionic acid (3-NP) - An inhibitor of complex II of the mitochondrial electron transport chain. It binds to a site in the complex II protein, preventing it from performing its usual function.
5-lipoxygenase - An enzyme that leads to the production of leukotrienes, which are chemicals that contribute significantly to inflammation.
5-hydroxyindoleacetic acid (5-HIAA) - A molecule that is made from serotonin. It is present in decreased levels in the brains of HD mice.

A

A2A receptor - A receptor present in nerve cells of the striatum that becomes more active in the presence of mutant huntingtin.
acetaldehyde - A natural element found in alcohol that produces damaging free radicals.
acetaminophen - A compound that relieves mild pain and reduces fever. Acetaminophen has also been found to be suitable for people who can't take aspirin because of aspirin-related allergic reactions or stomach irritation. In addition, acetaminophen is safe for use by infants, children and teens. Common brand names include Tylenol® and Tempra®.
acetylcholine - A neurotransmitter active in the parasympathetic nervous system. It is strongly linked to memory and learning ability.
acetyl-CoA - In cellular metabolism, the substance that enters the Kreb’s cycle to be further broken down to produce energy
acetyl group - A chemical group that is added and taken off of histones. Acetylation of histones allows transciption to occur, and deacetylation inhibits transcription.
acidic - Adjective used to describe a substance or solution that has an abundance of positive hydrogen ions.
acne - A skin inflammation affecting approximately 80% of those between the ages of 12 and 24. Located in each hair follicle or tiny pit in the skin is a gland that lubricates the skin. If some oil gets trapped in the gland, bacteria multiply in the pit and the skin becomes inflamed.
active molecule - Some molecules must be chemically changed in the body to act on their targets. The active molecule is a modified version of the original molecule that is able to perform some role or function.
active site - The region on the surface of an enzyme where the substrate binds and the chemical reaction occurs.
acyl-CoA - A product of fatty acid activation. Acyl-CoA is subsequently carried by carnitine into the mitochondria for beta-oxidation. All of this is done in the context of fat breakdown for energy usage.
acyl-CoA synthetase - An enzyme that converts a fatty acid to acyl-coA for subsequent beta oxidation.
ADAS - Abbreviation for Alzheimer’s Disease Assessment Scale.
AD - Abbreviation for Alzheimer's disease.
adenine - One of the four nitrogenous bases found in DNA; pairs with the base thymine; often abbreviated as the letter "A"; see Figure B-3.
adenosine diphosphate (ADP) - A compound of adenosine containing two phosphate groups, ADP is used to synthesize ATP with the energy released in cell respiration. When ATP is used for cellular activities, ADP is re-formed.
adenosine triphosphate (ATP) - ATP is the major carrier of high-energy phosphate bonds and is the body’s primary form of energy “currency.” The breakdown of ATP by the following reaction releases a great deal of energy which the cell uses for its various activities: ATP + H2O --> ADP + Pi.
ADHD - Attention Deficit Hyperactive Disorder, is a neurological disorder initially appearing in childhood with symptoms such as hyperactivity, forgetfulness, poor impulse control, and distractibility.
ADP - Abbreviation for adenosine diphosphate.
adrenal cortex - The outer portion of the adrenal gland. The adrenal cortex secretes steroids that have multiple effects.
adrenal glands - Glands situated above each kidney. Each adrenal gland consists of a cortex (outer wall) that secretes important steroid hormones and a medulla (inner part) that secretes stress hormones.
adrenal medulla - The inner portion of the adrenal gland. The adrenal medulla secretes the stress hormones noradrenaline and adrenaline.
adrenaline - A molecule that acts as both a hormone and neurotransmitter. Adrenaline is synthesized during times of stress and produces various effects that include increased heart rate, sweating, and increased metabolism. Also referred to as epinephrine.
adrenocorticotropin hormone (ACTH) - A stress hormone released by the hypothalamus in response to a stressor.
adult form - Another term for adult-onset HD.
adult-onset - Referring to when the symptoms of the disease strike (onset) in adulthood (contrast with congenital). In adult-onset HD, the symptoms start to appear after age 20.
adult-onset HD - The form of Huntington’s disease which has an age of onset at or after age 20. (Contrast with juvenile HD.) Also referred to as the adult form of HD.
adult stem cells - Multipotent stem cells that are found in adult tissue.
adult stem cell plasticity - The ability of an adult stem cell from one tissue to generate specialized cells of another tissue (e.g., a blood stem cell that could produce a nerve cell).
aerobic respiration - The process in which glucose is converted into CO2 and H2O in the presence of oxygen, releasing large amounts of ATP. This process includes the krebs cycle, electron transport chain, and oxidative phosphorylation.
aggresome - A region of the cell where protein aggregates collect.
akathisia - A drug-induced side effect often caused by antipsychotic drugs. Symptoms include feelings of restlessness and urges to move about when sitting or standing.
ALA - Abbreviation for alpha-linolenic acid.
aldosterone - A steroid (mineralocorticoid) released from the adrenal cortex that maintains salt and fluid balance in the body. The end result of its release is an increase in blood pressure.
allele - One of the different versions of a gene. All alleles for a particular gene code for the same trait, but they influence the trait in different ways. For example, different alleles for the hair color gene correspond to different hair colors.
alpha helix - A three-dimensional structure of a protein that takes on a coiled, cylindrical shape.
alpha-linolenic acid - An essential fatty acid. ALA is an omega-3 fatty acid that serves as the parent compound in the synthesis of other omega-3 fatty acids in the body.
alpha-tocopherol - The form of vitamin E most commonly found in the human body. It acts as an antioxidant and protects cell membranes and other fat-containing cell parts.
alpha-tocotrienol - One of the eight different forms of vitamin E. It has been shown to protect nerve cells from glutamate-induced oxidative stress.
alpha wave - A type of brain wave; occurs at relaxed, quiet times.
ALS - Abbreviation for Amyotrophic Lateral Sclerosis.
altered - A term used on this site to describe a protein or gene that is somehow different from the most frequently occurring form (e.g., altered huntingtin protein, altered Huntington gene). An altered protein or gene is sometimes described as being “mutant.”
Alzheimer’s disease - A neurodegenerative disease that causes progressive memory loss and severe dementia in advanced cases. Alzheimer’s disease is associated with certain abnormalities in brain tissue, involving a particular protein, beta-amyloid. The gene encoding amyloid has been located and cloned from chromosome 21.
Alzheimer’s Disease Assessment Scale (ADAS) - An 11-part test that takes 30 minutes to complete. The ADAS is used to assess the language and memory skills of people with Alzheimer’s disease.
amenorrhea - The absence or abnormal stoppage of menstrual periods; a risk factor for osteoporosis.
amino acid - A small molecule that is the building block of proteins.
aminotransferase - Increases in concentration of this enzyme sometimes result in the elevation of toxic ammonia levels. Riluzole has occasionally been known to cause this increase.
amitriptyline - Amitriptyline hydrochloride is an antidepressant drug. It affects serotonin and noradrenaline reuptake. Used to treat depression in all stages of life.
amniocentesis - A medical procedure in which cells from the fetus are obtained from the fluid within the innermost fetal membrane.
Amyloid - Another term for beta-amyloid
amyloid fibrils - Another term for beta-amyloid fibrils.
amyloid plaques - Another term for beta-amyloid plaques.
Amyotrophic Lateral Sclerosis (ALS) - A progressive and fatal disorder affecting nerve cells that involves overactivation of glutamate receptors.
anabolism - Used to describe a process that builds up larger molecules from smaller molecules. Anabolism is a constructive process where small molecules are assembled into larger molecules.
anaerobic respiration - Smaller amounts of ATP are released when glucose is broken down in the absence of oxygen. Most organisms do fermentation as their primary method of ATP generation when oxygen is not present.
analog - A drug whose physical structure is related to that of another drug. Although they have similar physical properties, analogs can have very different chemical and biological properties.
angiogenesis - The process of new blood vessel formation.
androgen receptor (AR) - Receptors that have binding sites for the steroid androgen. Androgen receptors are altered in people with spinobulbar muscular atrophy (SBMA).
animal models - Non-human animals used in laboratories to study the biology of HD, usually having HD genes and related symptoms. For more on animal models, click {http://www.stanford.edu/group/hopes/rltdsci/studyhd/y6.html|here}
antagonist - a substance that blocks a receptor from binding to a neurotransmitter or hormone.
anterior horn - Gray matter in the spinal cord that contains motor nerve cell bodies. Also referred to as the ventral horn.
anterior pituitary - The anterior pituitary comprises the anterior lobe of the pituitary gland and is part of the endocrine system. Under the influence of the hypothalamus, the anterior pituitary produces and secretes several peptide hormones that regulate many physiological processes including stress, growth, and reproduction.
anti-apoptotic - Having the quality of preventing or delaying the programmed death of a cell.
antigen - A substance that triggers an immune response.
anti-glutamate - A property of drugs that prevents nerve cell death by inhibiting glutamate toxicity.
anti-hypertensive drugs - Drugs that reduce blood pressure.
anti-inflammatory - Reducing inflammation. Many substances, including the drug aspirin, have anti-inflammatory effects.
anti-inflammatory cytokines - Cytokines such as IL-10, IL-4, and IL-12 that are involved in the reduction of inflammatory reactions.
anti-tumor drug - A drug that is capable of either stopping or slowing the abnormal growth of tissue. Because the presence of tumors is one of the primary characteristics of cancer, anti-tumor drugs are often used to treat cancer.
antiandrogenic therapy - The use of chemicals or drugs to inhibit the substances that produce the male hormone testosterone.
antibiotic - A substance usually produced by a fungus or bacteria that can kill other microorganisms. Often prescribed for bacterial infections.
antibody - A protein that is produced when the immune system detects a substance that is believed to be foreign. Antibodies inhibit the activity of these substances.
anticodon - A sequence on the tRNA that is complementary to a codon on the mRNA.
anticipation - A genetic phenomenon where a disease increases in severity in successive generations, and children can have a more severe form of a disease than their parents. A pattern of anticipation is often observed in trinucleotide repeat disorders. For example, in HD children often have earlier an age of onset and experience a more rapid development of the disease.
anticonvulsant - Preventing or relieving convulsions. Anticonvulsant drugs are sometimes prescribed to control or prevent seizures occurring in individuals with juvenile (and sometimes adult-onset) HD.
antioxidant - A molecule that is capable of reacting with free radicals and neutralizing them.
atomoxetine - The first non-stimulant drug approved for the treatment of ADHD
AP-1 - A transcription factor that enhances the production of inflammatory mediators. Association of this transcription factor with the GR complex results in decreased transcription of COX-2 genes.
applied research - Engineering-type research that puts the discoveries of basic research into practice.
apoptosis - Programmed cell death.
AR - Abbreviation for androgen receptor.
arachidonic acid - An omega-6 fatty acid. Arachidonic acid is the compound from which inflammatory mediators such as leukotrienes, thromboxanes, and prostaglandins are produced.
arginine - A non-essential amino acid believed to play a part in the neurodegeneration of HD.
arteriosclerosis - Any of a group of diseases leading to the thickening and loss of elasticity in arterial walls.
arthritis - A disease characterized by joint inflammation. Joint injury can be caused by trauma or by the wear and tear of aging. The general term arthritis includes over 100 kinds of diseases, most of which last for life. In many forms of arthritis, injury is caused by the uncontrolled inflammation of autoimmune disease, in which the immune system attacks the body's own tissues. Common kinds of arthritis include osteoarthritis and rheumatoid arthritis.
ascorbate - A negatively charged form of ascorbic acid, or vitamin C. Inside the human body, ascorbic acid exists as ascorbate and may protect nerve cells against free radical damage.
ascorbic acid - Another name for vitamin C, a compound with antioxidant properties that may help protect nerve cells from free radical damage and glutamate toxicity.
aspiration pneumonia - occurs when a person inhales food into their respiratory tract
aspirin (acetylsalicylic acid) - A compound that is part of a group of drugs called salicylates. Aspirin is widely used for relieving pain and reducing fever in adults. It also relieves mild itching and reduces swelling and inflammation. Use of aspirin by children has been linked to the occurrence of a disorder known as Reye’s Syndrome.
assay - A chemical analysis of a substance to determine its components.
asthma - A chronic inflammatory lung disorder characterized by obstruction of airways.
astrocyte - Another term for a spider cell.
asymptomatic - A term used to describe an individual who does not currently show symptoms of the disease being discussed. Asymptomatic individuals may develop symptoms of the disease at a later point in time.
ataxia - Loss of motor coordination.
atherosclerosis - The clogging, narrowing, and hardening of the blood vessels that can lead to stroke, heart attack, and kidney problems.
atom - The smallest existing particle of a pure element that can exist and still maintain the properties (or chemical characteristics) of that element. It is made up of protons, neutrons, and electrons. Example: Nitrogen is an element. Nitrogen molecules (N2) are made up of two nitrogen atoms (N). Many elements exist in nature as molecules of one or more atom.
ATP - See adenosine triphosphate.
ATP synthase - A large, complex protein that converts the energy stored in the proton gradient to ATP.
atrophin 1 protein - A protein identified in mice as the cause of an adult-onset disorder similar to HD.
atrophin 2 protein - A protein identified in mice as necessary for the proper development of the nervous system in the embryo.
atrophy - Degeneration or shrinking of cells, tissues, or organs. Muscle atrophy ultimately causes muscle weakness.
autooxidation - when oxidation occurs spontaneously
autophagosome - A membrane-enclosed bubble that surrounds cell components destined for degradation and transports them to the lysosome to be broken down in the process called autophagy.
autophagy - The capture and disposal of certain cellular contents like huntingtin protein aggregates.
autosomal - Pertaining to an autosome. An autosomal chromosome is not a sex chromosome, and an autosomal gene is a gene that is on an autosome.
autosome - A chromosome that is not a sex chromosome.
axon - Fiber of a neuron which carries impulses away from the cell body of the neuron; releases neurotransmitters as a means to communicate with other neurons.

B

backup - The optimized drug that is selected as the next most likely to be successfully developed as a therapy in further experiments and trials, and will be used if the lead compound is not successful.
bacteria - A small, single-celled living organism that has DNA and can replicate its own DNA without the help of a host cell. Some bacteria are helpful to humans, such as those that live in our stomach and help with digestion, while some are harmful, releasing toxins or poisonous waste products.
ballismus - uncontrolled, violent movements
basal ganglia - A group of nerve cells located at the base of the brain. It is composed of the putamen, caudate, globus pallidus, and substantia nigra. (The putamen and caudate together make up the striatum.) The basal ganglia participate in the regulation of motor performance, among other things. (Singular form: basal ganglion.)
basal ganglion - Singular form of basal ganglia.
base - A general term referring to the subunits of DNA or RNA. The four DNA bases are A, C, G, and T.
baseline firing rate - cells release neurotransmitters at a constant rate under normal conditions
basic - Adjective used to describe a substance or solution that contains a relatively low amount of positive hydrogen ions.
Batten disease - A fatal, inherited disorder of the nervous system that begins in childhood; the most common form of a group of disorders called neuronal ceroid lipofuscinoses (NCLs). Early symptoms usually appear between the ages of 5 and 10 in the form of vision problems, seizures, personality and behavior changes, slow learning, clumsiness, or stumbling. Eventually, affected children suffer mental impairment, worsening seizures, and progressive loss of sight and motor skills. Batten disease is often fatal by the late teens or twenties.
battenin - The key protein involved in Batten disease.
Bax - A molecule that usually exists in a cell's cytosol. It plays a role in initiating the apoptosis pathway by aggravating the mitochondria's membrane.
benign tumor - An abnormal mass of tissue that replicates uncontrollably, but will not spread to other tissues.
basic research - Research driven by scientists’ interest in questions pertaining to the biology behind a process or disease.
beta-amyloid - A compound that tends to accumulate in the brains of people with Alzheimer's disease. It consists primarily of proteins that are in sheet or ribbon-like formations called beta-amyloid fibrils, which are responsible for the beta-amyloid plaques seen in Alzheimer's. Beta-amyloid is also known as simply amyloid.
beta-amyloid fibrils - A group primarily composed of proteins that lay flatly upon one another like sheets of paper. These are responsible for the amyloid plaques seen in Alzheimer's disease. Also known as simply amyloid fibrils.
beta-amyloid plaques - Thick deposits of proteins in the brain that are believed to play a role in nerve cell degeneration in Alzheimer's disease. Also known as simply amyloid plaques.
beta blocker - Drugs that block the action of certain hormones on the heart. Beta blockers reduce the heart rate and the force of muscle contraction, thereby reducing the oxygen demand of heart muscles.
beta oxidation - The process by which fats, in the form of Acyl-CoA molecules, are broken down in the mitochondria to generate Acetyl-CoA, the entry molecule for the Krebs Cycle.
beta sheet - A three-dimensional structure of a protein that takes on a flat, pleated appearance.
beta wave - A type of brain wave; occurs during times of active thinking.
bile - A fluid produced by the liver and stored in the gall bladder. It plays an important role in digestion by helping to break down fats and absorb vitamins.
bile salts - A product produced in the liver from cholesterol. Bile salts aid in the breakdown of dietary fats.
bilobalide - A component of the terpenoids that has been shown to have neuroprotective properties though its role in motor nerve cell regeneration.
biological target - An enzyme, receptor or other protein that can be modified by an external stimulus, such as a drug, a hormone, molecule, or another protein.
biomarker - A specific biological trait, such as the level of a certain molecule in the body, that can be measured to indicate the progression of a disease or condition.
biophysiological - Referring to the internal biological processes that occur in the body.
biopsy - a medical test to remove cells or tissue from a body to test them for a disease condition. The tissue can either be looked at under a microscope or analyzed using chemical tests. Biopsies are usually taken when the cause or extent of a disease is uncertain.
biosynthesis - The production of chemical compounds by living organisms.
bipolar disorder - also known as manic-depression, this disorder is characterized by alternating periods of extreme moods. For example, a period of mania may be characterized by excessive energy, restlessness and/or irritability. This period of mania may be followed by a period of depression characterized by feelings of hopelessness and a lack of energy.
biotechnology - Biotechnology is technology based on biology, especially when used in agriculture, food science, research, and medicine. When used in research and medicine, some examples are the designing of organisms to produce antibiotics, and the methods to look at the function of naturally occurring proteins.
bivalent - A physical connection between homologous chromosomes that forms during meiosis. Crossing over takes place when the chromosomes are in this orientation.
blastocyst - An early stage of embryo development made up of a hollow sphere and an inner cell mass.
blood-brain barrier - A group of cells that form a special, impermeable lining in the blood vessels of the brain. The blood-brain barrier is made up of astrocytes and prevents toxic substances in the blood from entering the brain.
blood vessels - A tube through which the blood circulates in the body. Blood vessels include a network of arteries, arterioles, capillaries, venules, and veins.
bovine spongiform encephalopathy (BSE) - A form of transmissible spongiform encephalopathy (TSE) that affects cattle.
bradykinesia - difficulty initiating and continuing movements; literally means slow moving
brain stem - The portion of the brain closest to the spinal cord. It consists of the medulla, pons, and midbrain and controls many of the involuntary functions that keep us alive.
brain-derived neurotrophic factor (BDNF) - A protein that causes certain types of nerve cells to survive and grow. BDNF is primarily located in the central nervous system, where it acts on cells in the brain and the eye. In the peripheral nervous system, BDNF promotes the growth of sensory and motor neurons.
bulbar region - An area of the brain composed of the cerebellum, medulla and pons. (Basically, the bulbar region is made up of the brain stem minus the midbrain and plus the cerebellum). The bulbar region is responsible for many involuntary functions that keep us alive.

C

C. elegans - Known as Caenorhabditis elegans. It is a kind of roundworm known as a nematode. About 1 mm in length, C. elegans is often used as a model organism in molecular biology, developmental biology, and genetics.
c [jun - a transcription factor that leads to cell death, or apoptosis
C-terminus - The end of the amino acid chain that makes up a protein that is terminated by a free carboxyl group (-COOH).
CAG codon - The codon (particular sequence of letters) in the DNA code that is repeated 40 or more times along part of the Huntington gene in people who have Huntington's disease.
calcium - An essential element that is obtained through food. A proper balance of this element is critical to cell survival.
calcium channel - A channel in the membrane of a neuron that allows calcium to pass through; essential in sending information through and between neurons.
calcium ions (Ca2+) - Calcium ions are important mediators of a great variety of cellular activities, including the passing of information between neurons and down a neuron. In HD nerve cells, the threshold amount of glutamate necessary for NMDA receptors to allow calcium ions to enter the cell is decreased. This leads to an excess amount of Ca2+ in the cell, which ultimately leads to nerve cell death through the activation of molecules that destroy the cell membranes and essential proteins.
calpains - a family of calcium dependent proteases
cancer - Any malignant growth or tumor caused by abnormal and uncontrolled cell division.
carbohydrates - One of the three main classes of food and a source of energy. Carbohydrates are the sugars and starches found in breads, cereals, fruits, and vegetables, which, during digestion, are changed into a simple sugar called glucose. Glucose is stored in the liver until cells need it for energy.
carcinogen - Something in the environment that causes cancer.
carcinogenic - A substance that causes cancer
cardiovascular - Relating to or involving the heart and blood vessels.
carnitine - A vital component of mitochondrial function that shuttles molecules derived from fatty acids into the mitochondria for conversion into ATP.
cascade - the order of events that are hypthothsized to occur in a disease process, each step involving a certain set of molecules that regulate the molecules in the next step.
caspase - A type of protein that is involved in apoptosis. Caspases are characterized by their unusual ability to cleave proteins at specific sites. Active caspases can often activate other caspases, leading to a cascade of protein degradation.
caspase-3 - A specific type of caspase that is involved in causing cells to undergo apoptosis. Researchers found that it can be inhibited by cystamine.
caspase [6 - A member of the caspase family, a groups of enzymes, involved in apoptosis.
catabolic - Used to describe a destructive process that breaks down larger molecules into smaller molecules.
cataract - A clouding of the eye, making it difficult to see.
caudate - A tail-shaped mass of neuron cell bodies. One of the components of the basal ganglia, it is involved in regulating voluntary movements. (Shortened form of caudate nucleus.)
caudate nucleus - A brain structure within the basal ganglia; responsible for regulating and organizing information being sent to the frontal lobes from other areas of the brain.
causality - A cause and effect relationship. The causality of two events describes to what extent one event is caused by the other. When there is causality, there is a measure of predictability between the two events.
caveolin-1 (cav1) - A protein involved in endocytosis.
Ca2+ - See "calcium ions".
CBP - Abbreviation for CREB-binding protein.
CCI-779 - A more water-soluble and possibly more effective form of the drug rapamycin. It is thought to help cells break down huntingtin aggregates by inducing autophagy.
celastrol - A natural molecule derived from the celastracaeae plant. Used in Chinese medicine, celastrol was found to trigger the production of heat shock proteins in a variety of cell types, including nerve cells. It also was found to be protective, inhibiting apoptosis under conditions of severe stress.
celecoxib - A drug that selectively inhibits COX-2 enzymes.
cell - The smallest structural unit of an organism that is capable of independent functioning, consisting of one or more nuclei, cytoplasm and various organelles, all surrounded by a membrane.
cell body - The portion of a nerve cell that contains the nucleus but does not incorporate the dendrites or axon.
cell cycle - The series of stages of a cell between one cell division and the next.
cell cycle arrest - The halt of the cell cycle.
cell division - A brief time interval during which a cell reproduces by dividing into two; during this period, the DNA in chromosomes becomes highly condensed, making the chromosomes easily visible.
cell lines - Cells grown in tissue culture, representing generations of a primary or original culture. These cells are “immortalized” biochemically so that they continue to reproduce themselves.
cellular - Pertaining to cells. Typically used when referring to objects or events within a cell.
cellular respiration - The process whereby carbon-containing compounds are broken down through a series of reactions that result in the gradual release of energy stored as ATP. Usually, this process uses oxygen and releases carbon dioxide and water as by-products.
central dogma of molecular biology - A term coined by Francis Crick that states that the flow of genetic information is DNA to RNA to protein.
central nervous system (CNS) - The part of the nervous system that consists of the brain and spinal cord.
centrosomes - The major microtubule organizing centers of an animal cell.
cerebellar cortex - The outermost portion of the cerebellum.
cerebellum - Major region of the brain concerned with coordinating movements. The cerebellum is where learned movements are stored.
cerebral blood flow (CBF) - A measure of blood flow to the brain.
cerebral cortex - The part of the brain that is visible from the outside. The cerebral cortex is the outermost layer and consists of a collection of nerve cell bodies.
cerebral lupus - A chronic autoimmune disease characterized by inflammation in the brain.
cerebral spinal tap - A medical procedure to insert a needle into the spinal cord and collect spinal fluid. Cerebral spinal fluid can be used as a diagnostic test for many neurologic disorders, particularly infections and brain/spinal cord damage.
CFTR - see cystic fibrosis transmembrane conductance regulator.
chemotherapy - The treatment of cancer using specific chemicals or drugs that are selectively destructive to malignant (cancerous) cells and tissues.
chemical compound libraries - These are collections of thousands of different molecular compounds each of which has the potential to interact with biological targets.
cholesterol - A soft, waxy substance found among the fats in the bloodstream and in all the body's cells. Cholesterol can undergo various pathways that result in the synthesis of various steroids. It is also an important determinant of membrane fluidity, and an improper amount in the body can lead to membrane instability, which leads to cell death.
cholinergic - Related to the neurotransmitter acetylcholine. If a substance produces, interacts with, or mimicks the behavior of acetylcholine then it can be referred to as cholinergic. Cholinergic nerve cells (or neurons) produce acetylcholine.
chorea - Greek word for "dance." Chorea refers to an uncontrollable dance-like motion of twisting and turning that affects many persons with HD.
chorionic villus sampling (CVS) - A medical procedure that extracts a portion of the outermost membrane surrounding the fetus to enable genetic and biochemical analysis.
chromatography - A process used for separating mixtures by virtue of different affinities of substances for various media, such as paper, gas, or gelatin.
chromosome 4 - The chromosome on which the Huntington gene is located.
chromosomes - The DNA in every cell of every organism is divided into chromosomes. Each chromosome carries a number of genes within its DNA sequence. Chromosomes are usually found in the nucleus of cells as a large, diffuse mass of DNA. However, during cell division chromosomes condense into thick, rod-like structures that can be easily seen under a microscope. See Figure B-9.
chromosomal mutation - A mutation involving a long segment of DNA. These mutations can involve deletions, insertions, or inversions of sections of DNA. In some cases, deleted sections may attach to other chromosomes, disrupting both the chromosomes that loses the DNA and the one that gains it. Also referred to as a chromosomal rearrangement.
chromosomal rearrangement - Another term for a chromosomal mutation.
chronic - Long term or frequently recurring. A chronic disease is either always present or comes back again and again.
C.I. - See confidence interval.
citalopram - A drug used to treat depression associated with mood disorders. It is also used on occasion to treat body dysmorphic disorder (such as in the case of HD) and anxiety.
citric acid cycle - Another term for the Krebs Cycle.
clathrin - A protein involved in endocytosis.
cleave - Chop up.
clinical research - Research that involves administering drugs to patients in government-approved clinical trials.
clinical trials - A type of research study that is used to evaluate the effects of new drugs, medical devices, or other treatments on participants in scientifically controlled settings. They are required for government approval of new drugs or devices. Trials can assess the safety and efficacy of an experimental therapy to determine whether the new intervention is better than standard therapy, or to compare the efficacy of two standard or marketed therapies.
clone - A cell, group of cells, or organism that is descended from and genetically identical to a single common ancestor.
clotting - The process of forming lumps in a liquid.
CNS - Abbreviation for central nervous system.
co-factor - A type of molecule that helps enzymes carry out chemical reactions.
coactivators - Molecules that help the transcription factors bind to the DNA in order for gene transcription to occur.
co-chaperone - The role that one molecular chaperone plays in assisting another; for example, heat-shock protein 40 is a co-chaperone for heat-shock protein 70 because it assists in making direct links between heat-shock protein 70 and its target protein.
codon - A sequence of three DNA or RNA bases that codes for a specific amino acid; a “chemical blueprint” for building proteins from DNA.
codon repeat - A three letter sequence of bases (codon) that is repeated consecutively in a section of DNA. In HD, the repeated codon is C-A-G. Also referred to as a triplet repeat or trinucleotide repeat.
coenzyme - A molecule required for the activity of another enzyme.
coenzyme Q10 - Also called ubiquinone, or CoQ10. CoQ10 is a nutritional supplement that acts as an antioxidant and is an important molecule involved in the respiratory chain.
cognitive - related to the mental processes of knowing, thinking, learning, and judging.
collagen - A protein that is a major component of bones, tendons, cartilage, and other connective tissues in the body.
combinatorial chemistry - The use of chemistry to generate large numbers of molecules that are different but are structurally related. These molecules have the potential to be used as therapeutic drugs or for other purposes.
competitive inhibitor - A substance, similar in structure to an enzyme's substrate, that binds to the active site and inhibits (prevents) a reaction.
complementary - A property of DNA whereby each nitrogenous base pairs with another particular base (A with T and G with C); two complementary single strands have nucleotide sequences that enable their bases to pair up; see Figure B-8.
complement - A large group of proteins activated in sequence when cells are exposed to a foreign substance. Once activated, they form the membrane attack complex, resulting in the death of cells.
Complex I - The largest of the electron transport chain proteins. Complex I accepts electrons from NADH and passes them to the next electron carrier, coenzyme Q. Also reffered to as the NADH dehydrogenase complex.
Complex II - One of the electron transport chain proteins. Complex II transfers electrons from FADH2 onto coenzyme Q. Also referred to as the succinate-Q reductase complex.
Complex III - One of the electron transport chain proteins. Complex III accepts electrons from ubiquinone and passes them on to cytochrome c. Also referred to as the cytochrome b-c1 complex.
Complex IV - One of the electron transport chain proteins. Complex IV accepts electrons from cytochrome c and passes them to oxygen to form water (H2O). Also referred to as the cytochrome oxidase complex.
confidence interval (C.I.) - A statistical range with a given probability associated with it. The probability represents the chance that a certain value falls within the range. For example, for a certain number of CAG repeats, a 95% confidence interval for age of onset means that we can be 95% sure an individual with that number of CAG repeats will begin having symptoms within the given age range. See Table C-2.
confocal microscope - A high-powered microscope used for visualizing extremely small cellular components with beams of fluorescent light.
confound - An extraneous variable that may influence the results of an experiment.
congenital - Existing from birth.
Congo Red - A compound that is believed to both decrease the presence of beta-amyloid fibrils and decrease huntingtin protein aggregation.
conjugate - A related substance, differing only slightly.
conserved sequence - A base sequence in a DNA molecule (or an amino acid sequence in a protein) that has remained essentially unchanged throughout evolution.
constitutive - Used to describe compounds or molecules whose concentration in the body remains stable. Constitutive compounds are often always present in the body.
contractile ring - Temporary structure made of actin filaments that divides a cell during mitosis or meiosis.
contraction - A mutation in which the child has fewer copies of a certain codon in a gene than either of the parents. In Huntington’s disease, a contraction occurs when the child has fewer copies of the CAG codon in the Huntington gene than either of the parents. Contractions are the opposite of expansions.
control - Describes the measures taken in a scientific experiment to account for unsuspected effects of anything other than the thing being tested. For instance, when testing a medical treatment, scientists will have a treatment group as well as a “control” group that is not treated for comparison.
corpus striatum - Another term for striatum.
correlation [Used to describe the observed relationship between instances of two events. A systematic pattern can be seen in the occurrences of events that are correlated. When the events involve numbers, a positive correlation means that as one increases, the other increases as well. A negative correlation means that as one increases, the other decreases. Correlation does NOT imply causation in any way. In other words, just because two events are correlated does not mean that one causes another, or has anything to do with the other - correlations deal only with observed instances of events, and any further conclusions cannot be inferred from correlation alone. Strong correlation, however, does often warrant further investigation to determine causation.
cortex - One of the major components of the brain. The cortex is divided into four lobes (frontal, parietal, temporal, occipital). It also contains the sensory and motor areas.
cortical neurons - Nerve cells that make up the cortex of the brain.
corticosteroids - Steroids released from the adrenal cortex. Corticosteroids include both mineralocorticoids and glucocorticoids. Mineralocorticoids maintain salt and fluid balance in the body, while glucocorticoids have metabolic and anti-inflammatory effects and are important mediators of the stress response.
corticosterone - A corticosteroid secreted by the adrenal cortex; a glucocorticoid.
cortisol - A glucocorticoid that has various metabolic and anti-inflammatory effects in the body.
cortisone - A glucocorticoid that has various metabolic and anti-inflammatory effects in the body.
cover slip - A small, thin piece of glass used to cover a specimen on a microscope slide.
COX - Abbreviation for cyclooxygenase.
COX-1 - One form of the cyclooxygenase enzyme. COX-1 enzymes are always present in the body and are responsible for the synthesis of prostaglandins that maintain the gut lining, among other things.
COX-2 - One form of the cyclooxygenase enzyme. COX-2 enzymes are often produced during inflammatory responses and are responsible for the synthesis of prostaglandins that mediate inflammation.
COX-2 inhibitors - Drugs that selectively inhibit the COX-2 enzymes and have minimal or no effects on the activities of the COX-1 enzymes.
Cr - Abbreviation for creatine.
creatine (Cr) - An amino acid derivative that has been known to enhance strength and build muscle. Often used by athletes for its effects on muscular endurance and strength. Cr is capable of becoming transformed into PCr and used as a source of energy. Because people with HD often suffer from energy deficits, supplementation with Cr can possibly benefit PHD’s by increasing energy availability.
CREB-binding protein (CBP) - An acetyltransferase enzyme which regulates genes by activating transcription.
Creutzfeldt-Jakob disease (CJD) - An infectious neurological disease that is a very rare form of encephalopathy thought to be caused by a virus called a prions. The disease occurs primarily in adults, with peak incidence in the late 50s.
crossing over - An event that occurs during meiosis. During crossing over, alleles on homologous chromosomes can switch places. This switching of alleles increases the number of possible combinations of alleles, and hence increases the variability of a genome. In other words, crossing over contributes to the ability of two parents to produce offspring that are all very different. Also referred to as "recombination."
culture dish - The plastic dishes used in laboratories on which animal and human cell lines are allowed to grow.
culture medium - A liquid or gel-like substance containing nutrients in which tissues are cultivated for scientific purposes; used in tissue culture.
Cushing´s syndrome - A glandular disorder caused by excessive cortisol (glucocorticoids).
cyclocreatine - An analog of creatine. Current research reports that cyclocreatine is toxic to nerve cells.
cyclooxygenase (COX) - An enzyme that plays a pivotal role in the synthesis of prostaglandins.
cystamine - A TGase inhibitor shown to be a potential treatment for HD.
cysteine - A semi-essential amino acid.
Cystic Fibrosis - a common genetic disorder that involves a mutation in a protein called the cystic fibrosis transmembrane conductance regulator, or CFTR for short. It affects the entire body, causing disability and early death. Difficult breathing is the most common symptom and is caused by lung infections that can be treated, but not cured by antibiotics. There are other symptoms, including sinus infections, poor growth, diarrhea, and infertility.
cystic fibrosis transmembrane conductance regulator - the protein that is associated with causing Cystic Fibrosis when it is mutated. Normally, it creates sweat, digestive juices, and mucus in the lungs, pancreas, and liver. When the CFTR protein has a mutation, it misfolds and becomes unable to perform its regular function.
cytochrome b-c1 complex - Another term for Complex III.
cytochrome C - A molecule released by the mitochondria in response to membrane aggravation. It plays a role in initiating a cascade of events leading to apoptosis. Within the mitochondria, it transfers electrons from Complex III to Complex IV in the electron transport chain.
cytochrome oxidase complex - Another term for Complex IV.
cytokines - A vast array of relatively low mass, biologically active proteins that are secreted by immune cells. Cytokines are signaling chemicals involved in various pathways that contribute to the inflammatory response.
cytoplasm - The part of the cell that surrounds the nucleus. Often used interchangeably with cytosol.
cytoplasmic - An adjective describing something that is located in the cytoplasm. For example, a cytoplasmic protein resides in the cytoplasm.
cytosine - One of the four nitrogenous bases found in DNA; pairs with the base guanine; often abbreviated as the letter "C"; see Figure B-3.
cytoskeleton - The structural support of the cell.
cytosol - The fluid portion of the cell, excluding organelles and other solids. Often used interchangeably with cytoplasm.

D

daf-2 - A gene found in roundworms that allows this organism’s cells to respond to a hormone similar to human insulin. Daf-2 controls at least 100 other genes, some of which ward off disease; others act as antioxidants, protecting the worms against damage over time from free radicals in the environment.
daughter cells - The cells that result from the reproductive division of one cell during mitosis or meiosis.
degenerative / degeneration - The deterioration of a tissue or an organ in which its function is diminished or its structure is impaired.
degrade - to break something down. Usually to break a protein down into the original amino acids that were used to build it.
delta-5 desaturase - An enzyme necessary for the production of either eicosapentaenoic acid (EPA) or arachidonic acid (AA).
delta wave - The slowest type of brain wave; occurs during sleep.
dementia - A progressive decline in mental function.
dendrites - Short projections on the neuron that receive signals from other neurons. Neurotransmitters bind to receptors located on the surface of dendrites, causing changes within the nerve cell. See Figure D-2.
dentate nucleus - A group of nerve cell bodies deep inside the cerebellum; plays a role in the control of skilled, rapid movement.
dentate gyrus - A part of the hippocampal formation.
Dentatorubro-pallidoluysian atrophy (DRPLA) - A CAG trinucleotide repeat disorder that is characterized by abrupt muscle jerking, involuntary movements, and eventual dementia. For more information, click here.
deoxyribonucleic acid - For definition, see DNA.
deoxyribose - The particular sugar molecule that is found in DNA.
dexamethasone - A glucocorticoid drug with high glucocorticoid activity and low mineralocorticoid activity that is therefore relatively safe to use in high doses.
DGLA - Abbreviation for Dihommogamma-Linoleic Acid.
DHA - Abbreviation for docosahexaenoic acid.
diabetes mellitus - A chronic disease that renders the body unable to use carbohydrates (sugars) properly. This condition affects many organs and body functions, especially those involved in metabolism. Diabetes is characterized by increased levels of glucose (sugars) in the blood.
diagnose - To determine the nature of a pathological condition; to recognize a disease.
differentiate - The process that cells undergo as they mature to have distinct characteristics and functions.
digestive system - The organs that take in food and turn it into products that the body can use to stay healthy. Waste products the body cannot use leave the body through bowel movements. The digestive system includes the salivary glands, mouth, esophagus, stomach, liver, pancreas, gallbladder, small and large intestines, and rectum.
dihommogamma-linoleic acid (DGLA) - An omega-6 fatty acid that can be converted into arachidonic acid (AA).
dilution - The process of making something weaker or less concentrated.
dimer - A molecule that is made of two monomers bound together.
diploid - Containing two of each type of chromosome and therefore two alleles for each gene.
disaccharide - A molecule made out of two simple sugars. Examples include sucrose and lactose.
diuretic - A drug used to increase urine formation and output. Diuretics are prescribed for the treatment of edema (the accumulation of excess fluids in the tissues of the body), which often occurs as the result of disease of the kidneys, liver, lungs, or heart. Diuretics are also used to treat hypertension (high blood pressure).
divided attention - the ability to split one’s attention between more than one task. Many HD patients often have trouble with divided attention.
DNA - Abbreviation for deoxyribonucleic acid. The molecule of heredity; composed of many nucleotide subunits arranged in a long chain.
DNA Polymerase - An enzyme used to make new copies of DNA during replication.
docosahexaenoic acid (DHA) - A member of the omega-3 family of fatty acids. It is one of the breakdown products of alpha-linolenic acid (ALA) and is essential to nervous system development and maintenance.
domain - A region of a polypeptide chain that independently folds into a structural unit within a protein.
dominance - Used to describe a pattern of inheritance in which the dominant allele will be always be expressed, even in the presence of a recessive allele.
dominant - An allele whose effect is visible in the heterozygote (mixed) state
dopamine - An important neurotransmitter in the nervous system. Nerve cells that release dopamine are most affected in people with Parkinson’s Disease, and are becoming increasingly implicated in HD.
dorsal root ganglion - A group of sensory nerve cell bodies. They pass sensory information to neurons in the spinal cord so it can be analyzed by the brain.
dose [response relationship - The relationship between the dose of the drug and the changes of symptoms and responses of the body. The response could increase exponentially or linearly as the dose of the drug is increased.
dose-dependent - Refers to findings in which the effects of a drug change when people consume a higher or lower amount of the drug.
dose response - A relationship in which a change in the amount, intensity, or duration of an exposure is associated with either an increase or decrease in risk of a specified health outcome.
double blind - A study in which neither the investigator nor the participant are aware of which treatment a participant is receiving (ie experimental or control). Independent monitors keep track of who gets each type of treatment, and only inform the investigators and participants after all subjects have completed treatment and all measurements have been made. Double-blind trials are thought to produce objective results.
double helix - The form in which DNA is most often found in living cells; consists of two complementary single strands of DNA, spiraling around one another; see Figures B-7 and B-1.
Drosophila - The common fruit-fly, whose full name is Drosophila Melanogaster, is often used as an animal model in scientific experiments.
drugable - For a biological target to be drugable, it must be able to be modified (usually changing the shape, function, or the active site of the protein) by some other molecule that might serve as a therapeutic drug.
drug candidates - Chemical compounds that have potential to be developed into a therapeutic drug. Not all drug candidates become products.
drug target - A molecule that can be expected to enhance or inhibit a disease.
drug therapy - The use of a chemical compound or molecule to treat a disease
dry lab - Refers to experiments not performed at the lab bench.
dyskinesia - An impairment in voluntary movement ability.
dysmorphology - Altered development.
dystonia - Prolonged muscle contractions.

E

early-onset HD - Another term for juvenile HD.
E. coli - A small, simple bacteria used in many biology laboratories.
EGb 761 - A particular extract of Gingko biloba used in Europe to alleviate symptoms associated with several cognitive disorders.
eicosanoids - Any product derived from arachidonic acid. Eicosanoids include prostaglandins, thromboxanes, and leukotrienes. The eicosanoids can collectively mediate almost every aspect of the inflammatory response.
eicosapentaenoic acid (EPA) - An omega-3 fatty acid found in fish oil and fatty fish that is the precursor of beneficial prostaglandins known as Series 3 prostaglandins.
electroencephalograph (EEG) testing - A technique for recording electrical activity in the brain.
electrochemical - Having to do with the interchanges between electrical and chemical energy, especially those taking place in the body.
electron carrier - A molecule that can accept electrons from and donate electrons to various enzymes.
electron - A negatively charged particle; one of the three basic kinds of particles that make up an atom. Electrons can either be free or orbit the nucleus of an atom.
electron transport chain - Also known as the respiratory chain. It is composed of the mitochondrial enzymes (also known as complexes I, II, III and IV) that transfer electrons from one complex to another, eventually resulting in the formation of ATP. Also referred to as the respiratory chain.
embryo - An organism in the early stages of development. In humans, this stage lasts until about 8 weeks after fertilization.
embryonic - Pertaining to the embryo.
embryonic germ (EG) cells - Pluripotent stem cells taken from the primordial germ cells of the growing embryo.
embryonic stem (ES) cells - Pluripotent stem cells taken from the inner cell mass of the growing blastocyst.
encephalomyopathy lactic acidosis - Another term for MELAS.
encephalopathy - Any of various diseases of the brain.
endocrine system - The system of glands that secrete hormones.
endocytosis - A process in which a substance enters a cell inside a vesicle that was created by the invagination of the cell membrane.
endogenous - naturally occurring or made in the body
endorphins - The brain's natural chemicals that are thought to elevate mood and/or kill pain.
energy metabolism - See metabolism.
enkephalin - a kind of neurotransmitter, known as a neuropeptide, which serves in particular regions of the brain
enzyme - A protein that speeds up a chemical reaction. Enzymes do their work without being changed or used up in the process.
EPA - Abbreviation for eicosapentaenoic acid.
epidemiologist - Someone who studies epidemiology.
epidemiology - The study of the spread of diseases within and between populations.
epididymis - Part of the male reproductive system. Sperm undergo their final maturation in the epididymis.
epiglottis - A thin piece of flexible tissue in front of the opening of the trachea that folds back over and protects the wind pipe during swallowing.
epinephrine - Another term for adrenaline.
epitope - A region on the surface of an antigen to which an antibody binds.
equal crossing over - During meiosis, when the crossing over of alleles is equal. Whole alleles switch places, rather than only parts of alleles.
esophagus - A muscular tube that is about nine inches long and carries food from the mouth to the stomach. Also known as the windpipe.
essential - A substance that cannot be produced from the body, and therefore must be obtained from the diet.
essential fatty acids (EFAs) - A fatty acid is a compound derived from the breakdown of fats. Essential fatty acids are those that cannot be produced by the body, and therefore must be obtained from the diet.
estrogen - Any of several female hormones produced primarily by the ovaries.
ethanol - A particular type of alcohol found in alcoholic beverages.
etiology - The study of causes or origins of a disease.
excitation - One of the responses caused by specific neurotransmitters binding to receptors on a neuron. Excitation increases the probability that neurotransmitters will be released by the neuron.
excitatory - Referring to the effect that a substance has on a nerve cell. An excitatory substance excites the nerve cell and makes it able to receive critical information.
excitotoxicity - Excessive stimulation of a nerve cell by a neurotransmitter, which poisons the nerve cell and degrades it.
excitotoxins - Variants of common proteins that are found in most living things. Excitotoxins can cause cell damage and include variants of the amino acids, glutamine, glutamate, and aspartic acid.
exogenous - Originating outside of the organism.
exon - A stretch of DNA that codes for part of a protein.
expanded polyglutamine chain - when a normal protein that has a certain number of glutamines in a chain is mutated, so that the number of glutamines in the chain increases, it is an expanded chain. For example in Huntington’s Disease, a normal polyglutamine chain in the huntingtin protein would have from 10 to 35 glutamines, but an expanded polyglutamine chain would have more than 40 glutamines in a row.
expansion - A mutation involving the increase from one generation to the next (parent to child) in the number of copies of a certain codon. In Huntington’s disease expansions, the codon is CAG.
extracellular fluid - The space outside and between cells.
extraneural - Outside of the nervous system.

F

FAD - Abbreviation for Flavin-adenine dinucleotide.
FALS - Familial Amyotrophic Lateral Sclerosis. This is the form of Amyotrophic Lateral Sclerosis that is linked to a genetic mutation on chromosome 21. A protein called superoxide dismutase (SOD) that normally functions as an antioxidant acquires a mutation that makes the it nonfunctional.
false positives - Also known as Type 1 errors, occur when we observe a difference that in truth is not actually there. In the R&D pipeline, this could occur when experimental results suggest that a drug interacts with a biological target, where in fact it does not.
familial dysautonomia (FD) - An inherited disorder that primarily causes dysfunction of the autonomic and sensory nervous systems as a result of an incomplete development of the nerve cells of these systems. The autonomic nervous system regulates involuntary bodily functions, such as regulation of blood pressure and body temperature and normal swallowing and digestion. The sensory nervous system regulates protective reactions to pain, perceptions of hot and cold, and taste.
family systems theory - A recent theory that attributes the weakening of a couple and/or family relationship to the mounting tension during the waiting period before receiving predictive testing results.
fast track product - A potential drug in development that is believed to meet an unfulfilled medical need and is required urgently, so that the process of testing in clinical trials and FDA evaluation of the results is sped up.
fat-soluble - Capable of being dissolved in fat.
fats - One of the three main classes of foods and a source of energy in the body. Fats help the body use some vitamins and keep the skin healthy. They also serve as energy stores for the body. In food, there are two types of fats: saturated and unsaturated.
fatty acid - A class of compounds that contain a long chain composed of hydrogen and carbon atoms. In general, fatty acids refer to any compound derived from the breakdown of fats.
FDA - Food and Drug Administration. A federal United States agency that, among other responsibilities, makes sure that foods, medicines, cosmetics, and medical devices are safe and/or effective.
feedback loop - a feedback loop is where two or more molecules mutually act upon one another in a cycle. It usually is meant to allow a biological process to efficiently slow down or speed up, depending on the type of feedback loop
fermentation - One process by which carbon-containing compounds are broken down in an energy yielding process. Fermentation occurs during times of low oxygen supply and is therefore known as a type of anaerobic respiration.
fertility - The number of live births per parent; the capacity to conceive and generate live offspring.
fetal neurons - Cells in a fetus that will eventually develop into neurons.
fetus - In human beings, the unborn young from the eighth week of pregnancy to birth; an organism in the stage of development that follows the embryonic stage.
fibril - A small filament or fiber.
fibrinogen - A protein present in blood plasma that causes blood clots when the stress response is activated.
fitness (reproductive fitness) - Measure of the relative survival and reproductive success of a given individual or characteristic compared to others.
fixation - The chemical preservation of cells or tissues.
Flavin-adenine dinucleotide (FAD) - Coenzyme sythesized from riboflavin. FAD acts as an electron carrier in energy metabolism.
Flavin-mononucleotide (FMN) - A coenzyme synthesized from riboflavin. FMN acts as a component of Complex I of the electron transport chain.
flavins - A group of molecules with a unique ring structure. FMN and FAD are part of the flavin group of molecules.
flavonoids - A constituent of Ginkgo biloba extract that has been found to reduce the level of free radicals by decreasing cell membrane lipid peroxidation.
flax oil - A type of oil derived from flax plant that contains a great amount of omega-3 fatty acids.
fluoxetine - A member of the class of drugs known as selective serotonin reuptake inhibitors (SSRIs) . It is normally used to treat depression and obsessive-compulsive disorder, but may also be helpful in improving motor impairment and cognitive functioning in people with HD.
FMN - Abbreviation for Flavin-mononucleotide.
fMRI - Stands for "functional magnetic resonance imaging." This technique uses magnetic fields to measure oxygen use by nerve cells in the brain. It allows researchers to determine which specific areas of the brain are most active during a task.
folate - The naturally occurring version of folic acid.
folding - The process by which a chain of amino acids is modified to reach the final shape of the protein.
folic acid - A B vitamin essential for production of new cells and important for the metabolism of homocysteine.
formulation - When a drug is made up of multiple compounds, the formulation describes the specific recipe for the drug, including which compounds are included and in what proportions.
free radicals - Atoms or molecules that are highly reactive with other cellular structures because they contain unpaired electrons; free radicals can be very harmful to cells.
French paradox - The finding that the rate of heart disease in France is lower than observed in other industrialized countries, despite the fact that the country’s diet is rich in saturated fats.
frequency - The proportion of a population falling into a particular category.
frontal cortex - Part of the brain generally thought to be where higher level thinking, planning, and goal formulation take place.
frontal lobes - One of the four lobes of the brain. It is divided into motor, pre-motor and pre-frontal areas. The pre-frontal area is responsible for many cognitive functions.

G

GA - See geldanamycin.
GABA - Also known as Gamma-aminobutyric acid. It is the major inhibitory neurotransmitter of the nervous system.
gamete - Cell from an organism that has only one set of chromosomes; also called a "germ cell." Sperm and eggs are both examples.
gamma-carbolines - A type of small molecule whose derivatives have recently been associated with antipsychotic, antibiotic and antitumor activity.
gamma linoleic acid (GLA) - A breakdown product of linoleic acid (LA) which leads to the production of prostaglandins.
gamma wave - The highest frequency and most important type of brain wave; involved in higher mental acuity such as perception and consciousness.
ganglia - Plural form of ganglion.
ganglion - A group of nerve cell bodies in the Central Nervous System (CNS) or Peripheral Nervous System (PNS). (Plural form: ganglia.)
GAPDH - Glyceraldehydephosphate dehydrogenase. A multifunctional protein crucial to cellular glycolysis; interacts with the expanded glutamine region of proteins in neurodegenerative disorders like HD.
gastrointestinal - Relating to the stomach and intestines.
geldanamycin - a naturally-occurring drug produced by microorganisms. It acts by binding to hsp90, which then allows heat-shock-factor 1 to activate the heat-shock response.
gel electrophoresis - A research technique used to separate molecules (or fragments of a molecule) according to size. Upon electrical stimulation, smaller fragments of a molecule will move faster through the gel than larger fragments. The process is typically done to separate DNA fragments after the DNA has been cut with restriction enzymes.
gene - A section of DNA that codes for a specific functional product, such as a protein. For example, the Huntington gene codes for the huntingtin protein.
gene expression - The process in which a gene is read and its protein is produced. Hence, the gene is "expressed."
gene locus - Place on a chromosome where a gene is located. A particular gene is located at the same place on the same chromosome in everyone. Plural: loci.
gene silencing - Targeting or interfering with a specific gene and preventing its expression (in other words, preventing it from leading to a protein.)
gene splicing - Joining together or inserting segments of DNA or RNA so as to form new genetic combinations or change a genetic structure.
gene therapy - The insertion of normal or genetically altered genes into cells usually to replace defective genes. Sometimes used in the treatment of genetic disorders.
gene transcription - Another term for transcription.
genotyping - Determining the genetic makeup of an organism.
generalized seizure - A seizure that involves the entire brain. Generalized seizures are caused by electrical discharges originating from both hemispheres of the brain.
generalized tonic-clonic - Tonic-clonic seizures that are generalized, meaning they are caused by discharges from both sides of the brain. Also referred to as grand mal seizures.
genetic - Pertaining to genes. Typically used when referring to the study of genes or when the cause of a disease is somehow traced to genes.
genetic disorder - any disease that is caused by a mutation in a gene. These diseases are usually heritable, passed from parent to child, although mutations can occur sporadically and begin in a new generation.
genetic research cycle - The process of learning about and developing treatments for genetic diseases. The cycle, which begins and ends with patients and their families, includes basic research, applied research, and clinical research.
genetic screen - An experiment to look at an organism’s genome to look for which genes cause a certain desired phenotype to appear.
geneticist - Someone who studies the relationship between genes and the traits that are observed in living things.
genetics - The study of heredity and how traits are passed on through generations.
genome - An organism’s complete set of DNA.
genotype - The genetic makeup of an organism, distinct from its phenotype.
germ cell - A kind of cell that gives rise to the reproductive cells. See also germ line.
germ line - A group of cells that contain the organism's genome and give rise to the reproductive cells.
Ginkgo biloba - A plant that has been shown to have certain antioxidant, anti-inflammatory, and neuroprotective properties. Currently being studied as a potential treatment for HD.
ginkgolide - A component of the terpenoids that have been shown to have anti-inflammatory effects. They also cause a reduction in blood clotting.
gland - An organ that produces and releases one or more substances for use in the body.
glia - Another term for neuroglia.
glial cells - Cells that serve as supporting elements to the brain and act as scavengers, removing debris after injury or neuronal death. They are also responsible for maintaining ionic balance and producing the fatty coating in nerve cells.
gliosis - The excess growth of astrocytes in the brain or spinal cord, usually occurring after injury to one of these parts.
globus pallidus - One of the components of the basal ganglia. It relays information from the caudate and putamen to the thalamus. It is sometimes called the pallidum.
glucocorticoid degenerative cascade - The process that occurs when excess glucocorticoids cause hippocampal nerve cells to die, which then leads to the release of even more glucocorticoids, which then leads to further death of hippocampal nerve cells.
glucocorticoid-glucocorticoid receptor complex - Another term for the glucocorticoid-GR complex.
glucocorticoid-GR complex - Formed when glucocorticoid hormones bind to glucocorticoid receptors in the cell. Also referred to as glucocorticoid-glucocorticoid receptor complex.
glucocorticoid receptors - Receptors found in the cell that contain binding sites for glucocorticoids.
glucocorticoids - A group of steroids that have metabolic and anti-inflammatory effects. Glucocorticoid drugs are compounds with effects similar to those of the natural glucocorticoids produced in the body.
glucose - The major sugar in the body and a key molecule in energy metabolism.
glutamate - An amino acid precursor. Glutamate is the most common excitatory neurotransmitter in the brain and spinal cord.
glutamine - The key amino acid in Huntington’s disease. In most people, there are between 10 and 35 sequential glutamines in the huntingtin protein. In people with HD, there are 40 or more copies. Some people with 36-39 copies develop symptoms of HD while others do not. See Table A-1.
glutathione - A water-soluble antioxidant, antitoxin, and enzyme co-factor found in animals, plants, and microorganisms. Protects mitochondria against oxidative damage.
glutathione peroxidase (GPx) - An enzyme known for its antioxidant effects against peroxides. Its central element is selenium.
glycogen - A substance made up of sugars. It is stored in the liver and muscles and releases glucose (sugar) into the blood when needed by cells. Glycogen is the chief source of stored fuel in the body.
glycolysis - This process occurs in all organisms, and is responsible for converting glucose to pyruvate and generating ATP in the process. Glycolysis does not require oxygen to function.
gonadal ridge - An elevated portion of the developing embryo that contains the primordial germ cells.
gossypol - A compound that is believed to decrease the presence of beta-amyloid fibrils, but has little or no success in inhibiting huntingtin protein aggregation.
graft-versus-host disease (GVHD) - A condition that results when a donated organ reacts against the recipient’s own tissue; symptoms include skin rash, fever, diarrhea, liver dysfunction, abdominal pain, and loss of appetite.
grafting - Transplanting of a portion of cells or tissues.
grand mal - Another term for generalized tonic-clonic seizures.
granule cells - A specific type of nerve cell that projects information to the cerebellum. This information includes the position and movement of the limbs, as well as the regions of the skin that are being stimulated at any given time.
gray matter - Term used to describe an area of the brain that is rich in nerve cell bodies.
green fluorescent protein (GFP) - A protein produced by jellyfish that glows when viewed under a specific wavelength of light. Used by researchers as a tool to tag and visualize specific proteins within a cell.
GRIK2 (GluR6) - A gene whose functional region codes for a subunit of the glutamate receptor; implicated in age of onset of Huntington’s disease symptoms.
growth factors - Proteins that are being tested to see if they prompt nerve growth and brain reorganization.
GRP-78 - A protein chaperone that, along with HSP-70, can help regulate protein folding and degradation, as well as help balance calcium levels in cells.
guanine - One of the four nitrogenous bases found in DNA; pairs with the base cytosine; often abbreviated as the letter "G"; see Figure B-3.

H

half-life - The half-life of a substance is the amount of times it takes for half of the original molecule to be chemically degraded or eliminated in some other way (for example, in the urine). For example; if the half life of a compound is 5 hours, there will be 50% left at 5 hours, 25% of the original amount left at 10 hours, and 12.5% left after 15 hours.
hairpin - A section of single-stranded DNA that curls back onto itself, creating a partial double helix that resembles a hairpin.
hairpin-mediated polymerase slippage model - A possible explanation for why expansions occur. This model expands on the polymerase slippage model and shows how hairpins make long-range polymerase slippage energetically feasible.
HAP-1 - huntingtin-associated protein-1. A cytoplasmic protein (associated with the membrane cytoskeleton) that is expressed predominantly in the brain. HAP-1 is expressed in many neurons. Expanded CAG repeats in the huntingtin protein show increased binding to HAP-1.
haploid - Containing one set of chromosomes. Gametes are haploid cells.
haplotype - The genetic makeup of an individual with respect to a specific pair of alleles or genes.
HD allele - A version of the Huntington gene that contains a higher than normal number of repeats. Individuals with the HD allele will develop Huntington’s disease (Note that although there are many different alleles that can cause HD, for simplicity, this site refers to any allele that causes HD as "the HD allele.") This allele may be called the “mutant Huntington allele” in other places. See Table A-1.
HDAC - Abbreviation for histone deacetylase.
HDAC inhibitors - Abbreviation for histone deacetylase inhibitors.
HDBP1 - Abbreviation for Huntington’s Disease Binding Protein 1, a protein that binds to the promoter region of the Huntington gene, leading to transcription of the HD allele. The allele, in turn, gives rise to the huntingtin protein.
HDBP2 - Abbreviation for Huntington’s Disease Binding Protein 2, a protein that binds to the promoter region of the Huntington gene, leading to transcription of the HD allele. The allele, in turn, gives rise to the huntingtin protein.
HDJ1 - A human protein that is known to exert protective effects against polyglutamine toxicity.
HD Motor Rating Scale (HDMRS) - A rating system designed to measure the motor capacity of people with HD. It consists of 14 items that are specific to the motor symptoms that are typically exhibited by people with HD.
HDSA Center of Excellence - Clinics recognized by HDSA for providing high quality, comprehensive care for HD patients and their families and for offering clinical trial opportunities and running outreach and educational programs.
heart attack - Heart attacks occur when a coronary artery is completely blocked and a portion of the heart muscle is left without a supply of oxygenated blood. If the portion is large enough, the heart attack may be deadly.
heart disease - A general term for high blood pressure and/or the narrowing of arteries supplying blood to the heart; the most common cause of death in the United States.
HEAT repeat sequences - A series of three to four amino acids repeated along the length of a protein; acronym HEAT comes from four proteins in which these repeated sequences have been found. The normal huntingtin protein contains 36 HEAT-like repeats, which fold up into a spiral structure and may serve as docking sites for other proteins. Also referred to as HEAT domains.
heat shock - stress upon the cell resulting from temperatures outside its tolerable range. Overheating the cell usually causes proteins to misfold because of the harsh environment, and will trigger the heat shock response.
heat shock factor 1 (HSF-1) - A protein that performs various cellular activities while associated with heat shock protein 90 (Hsp 90). HSF-1 initiates the production of heat shock proteins 40 and 70 when disassociated from Hsp 90.
heat shock protein (Hsp) - Proteins that are synthesized in organisms in response to various environmental stressors (such as extremes in temperature). There are various kinds of heat shock proteins, each of them performing different functions.
heat shock response - A mechanism cells use to maintain stability when subjected to stress. Heat shock response often involves the production of heat shock proteins.
helicase - An enzyme that unwinds the double helix of DNA to allow for replication.
heme - A compound made mostly of iron.
heme oxygenase - An enzyme that breaks down heme and plays various roles in the processes of oxidative stress and inflammation.
hemisphere - Half of the cerebral cortex (the brain has a left and right hemisphere).
hemoglobin - A substance found within red blood cells that binds to oxygen and carries it from the lungs to the tissues.
hemorrhage - A copious discharge of blood from the blood vessels.
hereditary - Something that is passed on through generations genetically. The inheritance of a hereditary disease is dependent upon the genes received from one’s parents.
heredity - The passing of traits from one generation to the next.
high-density lipoprotein (HDL) cholesterol - A complex of lipids and proteins in approximately equal amounts that functions as a transporter of cholesterol in the blood. High levels are associated with a decreased risk of atherosclerosis and coronary heart disease.
high pressure liquid chromatography (HPLC) - A piece of equipment used in labs to facilitate the separation of molecules under high pressure in a stainless steel column filled with a special chemical substance called a matrix.
high throughput machines - A system which enables researchers can rapidly and efficiently search through chemical compound libraries, each with thousands of different samples, testing each of them for positive interactions with the biological target
highly unsaturated fatty acids - Fatty acids that contain more than one double bond. These double bonds affect the chemical characteristics of the fatty acids, making them less solid and more fluid.
HIP-1 - huntingtin-interacting protein-1. It is a membrane-associated protein that interacts with the cytoskeleton. Huntingtin proteins with an expanded number of glutamines show decreased binding to HIP-1.
hippocampal - Of or relating to the hippocampus.
hippocampal region - Relating to the hippocampus, a complex structure involved with certain types of memory functions.
hippocampus - A part of the brain that plays a role in the establishment of new memories.
histones - Proteins that play a part in the regulation of gene transcription by helping to condense DNA into its compact form as chromosomes.
histone acetyltransferases - These enzymes add an acetyl group to histones, thus releasing the restricted access to DNA imposed by histones. Transcription factors can then bind to the DNA, allowing gene transcription to occur. Patients with HD tend to have decreased histone acetyltransferase activity.
histone deacetylase (HDAC) - These enzymes remove an acetyl group from histones, which allows histones to bind DNA and inhibit gene transcription.
histone deacetylase inhibitors (HDAC inhibitors) - Histone deacetylase inhibitors block the activity of histone deacetylases (HDACs). This leads to an increase in the overall level of transcriptional activity. This is thought to be therapeutic in a patient with HD because HDAC inhibitors help to combat the effects of HD by allowing essential genes to be transcribed, thus decreasing the rate of nerve cell death.
histone methyltransferase (HMT) - This enzyme adds a methyl group to histones, causing the DNA to coil up into chromosomes and preventing further transcription.
homeostatic - Of or relating to homeostasis.
homeostasis - A state of balance in the body maintained by several complex biological mechanisms that operate to offset disruptive changes.
homing - A process in which transplanted cells are attracted to and travel to an injured site.
homocysteine - A sulfur containing amino acid. Considered a risk factor for cardiovascular disease and possibly neurodegeneration.
homolog(ue) - 1. One member of a chromosome pair. 2. A gene similar in structure and evolutionary origin to a gene in another species.
homologous - Homologous chromosomes have corresponding DNA sequences and come from separate parents.
homologous chromosomes - A pair of chromosomes made up of two homologs. Homologous chromosomes have corresponding DNA sequences and come from separate parents; one homolog comes from the mother and the other comes from the father. Homologous chromosomes line up during meiosis.
homozygote - An individual with two identical alleles of a specific gene; matching genes at the same location on both homologous chromosomes.
hormone - A substance produced and released by certain parts of the body that can travel through the bloodstream and exert significant effects on other parts of the body (such as growth or changes in metabolism) over extended periods of time.
HPA axis - The hypothalamic-pituitary-adrenal axis (HPA axis) is a major part of the neuroendocrine system that controls reactions to stress. Species from humans to the most ancient organisms share components of the HPA axis. It is the mechanism for a set of interactions among glands, hormones and parts of the mid-brain that mediate a stress reaction.
HSF-1 - Abbreviation for heat shock factor 1.
Hsp - Abbreviation for heat shock protein.
Hsp 40 - The mouse analog of HDJ1.
HSP 70 and HSP 40 - Heat shock proteins that bind and associate with the misfolded huntingtin protein and prevent its aggregation. Production of Hsp 70 and Hsp 40 is stimulated by free HSF-1.
HSP 90 - A heat-shock protein that acts as a molecular chaperone to proteins involved in the progression of cancer. It also binds and associates with HSF-1. Geldenamycin binds to and inhibits Hsp 90, leading to both the misfolding of cancer-associated proteins and the freeing-up of HSF-1, which can then prevent misfolded huntingtin protein aggregation through the effects of Hsp 70 and Hsp 40.
Htt - Abbreviation sometimes used by researchers for the altered huntingtin protein.
human development - Continuous changes that occur during an individual’s life, starting at fertilization.
huntingtin aggregates - Rigid clumps of protein that form when a cell produces the altered form of huntingtin that causes HD. Huntingtin aggregates can also “kidnap” other proteins, and nerve cells with build-ups of huntingtin aggregates often die.
huntingtin protein - A key protein in Huntington’s disease. It exists in all humans but has a chemically different form in people with HD. Please note that although "Huntington's disease" is spelled with an "o", the correct spelling of the protein involved is "huntingtin" with an "i."
Huntington Study Group - "A non-profit group of physicians and other health care providers from medical centers in the U.S., Canada, Europe and Australia, experienced in the care of Huntington patients and dedicated to clinical research of Huntington's disease."
http://huntington-study-group.org/] - http://huntington-study-group.org/]
Huntington's disease - A hereditary neurological disorder characterized by movement, cognitive, and psychiatric symptoms.
Huntington’s Disease Society of America - A national health organization dedicated to finding a cure for Huntington’s Disease and to providing support for everyone affected with HD.
Huntington gene - The section of DNA that codes for the huntingtin protein. The scientific literature on HD refers to the gene as both the "Huntington gene" and the "huntingtin gene." For the purposes of this website, we will refer to the gene as the "Huntington gene" or, when it is in the altered form that results in HD, the "HD allele."
hydrocortisone - A drug that has much more mineralocorticoid activity than common glucocorticoid drugs and is therefore not suitable for long-term use. Hydocortisone is used extensively as a cream or lotion to treat skin irritations such as rashes or itches.
hydrogen bond - A weak bond between hydrogen and another atom (usually oxygen, fluorine, or nitrogen). Hydrogen bonds are critical in the formation of many biological molecules, including DNA and proteins.
hydrogen peroxide - A waste product of the cell that is a dangerous free radical.
hydrogenation - A process that alters the chemical structure of unsaturated fat and makes it more solid and long-lasting.
hydrolysis - Hydrolysis is the process by which a molecule is split in two by the addition of a water molecule, which has the chemical formula H2O. One of the parts gets an OH from the water molecule and the other part gets an H from the water.
hydrophilic - A property meaning “water loving,” describing molecules that are attracted to water.
hydrophobic - A property meaning "water fearing," describing molecules that are repelled by water.
hydroxyl radical - A free radical.
hyperglycemia - High glucose levels in the blood.
hypertension - High blood pressure.
hypothalamus - Small structure at the base of the brain that regulates many body functions, including appetite and body temperature.
hypothesis - A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation.
hypoxia - Oxygen starvation at the cellular level.

I

I5-lipoxygenase - An enzyme that leads to the production of leukotrienes, which are chemicals that contribute significantly to inflammation.
ibuprofen - A compound that is effective for relief of pain, fever and inflammation. Ibuprofen inhibits prostaglandin synthesis and acts as a PPAR-gamma activator. Common brand names include Motrin® and Advil®.
IL-1 - Abbreviation for interleukin-1.
IL-1 beta - A cytokine that is overexpressed in various inflammatory diseases. IL-1 beta activates glial cells and is responsible for other activities involved in the inflammatory response.
immune system - The cells and tissues involved in recognizing and attacking foreign substances in the body.
immunocytochemistry (IC) - A method of staining cells with antibodies to pinpoint the location of the huntingtin protein under a microscope.
immunohistochemistry (IH) - A method of staining tissue slices with antibodies to pinpoint the location of the huntingtin protein under a microscope.
immunosuppressant - A drug that suppresses the action of the immune system and is often used after organ transplant surgery to prevent the body from rejecting the organ.
immunostaining - Any use of an antibody and some coloring agent to detect a specific protein in a cell or tissue sample.
implant - See implantation.
implantation - The process by which an embryo attaches to the wall of the uterus.
implicit memory - Motor memories or memories that deal with procedures (i.e. riding a bicycle). Often considered "unconscious" memories.
impulse (nerve impulse) - The signal that travels along the length of a nerve fiber and ends in the release of neurotransmitters. Nerve impulses are the means by which information is transmitted along the neuron and throughout the nervous system.
in vitro - Latin phrase for "in glass"; in a test tube or other artificial environment, as opposed to inside a living organism.
in vivo - Latin phrase for "in the living"; in the living body of a plant or animal.
inclusion bodies - Another term for neuronal inclusions.
independent assortment - Process by which each chromosome is shuffled into a daughter cell during meiosis. Chromosomes do not remain associated with their homologues.
inducible nitric oxide synthetase (iNOS) - An enzyme responsible for the production of the free radical nitric oxide.
inferior olive - Part of the brain that sends sensory information to the cerebellum.
inflammation - The reaction that occurs in the affected cells and adjacent tissues in response to an injury or abnormal stimulation caused by a physical, chemical, or biological substance.
inflammatory bowel disease - A chronic inflammatory disease that can affect any part of the gastrointestinal tract but most commonly affects a part of the small intestine.
inflammatory mediators - Molecules that are released by immune cells when harmful agents invade the body.
inflammatory response - See inflammation.
incidence - The number of new events (such as being born with HD) in a population during a specified period.
inhibition - One of the responses caused by specific neurotransmitters binding to receptors on a neuron. Inhibition decreases the probability that neurotransmitters will be released by the neuron.
inner cell mass - A group of cells found in the blastocyst that give rise to all the tissues of the embryo.
iNOS - Abbreviation for inducible nitric oxide synthetase.
inosital hexaniacinate - A variation of niacin. Inosital hexaniacinate is recommended by some doctors for individuals who need large amounts of niacin because it has not been linked with any of the usual niacin toxicity found by some studies.
Institutional Review Board (IRB) - An IRB is an independent ethics committee for an institution that serves to approve, monitor, and review biomedical and behavioral research involving humans with the aim to protect the rights and welfare of the subjects.
insulin - A hormone involved in the storage of glucose (sugar) in tissues. Insulin helps regulate glucose concentration in the blood.
interleukin-1 (IL-1) - A cytokine that mediates various inflammatory activities. Production of mature IL-1 requires caspase activity.
interleukin-beta - A cytokine that mediates various activities of the inflammatory response.
interphase - Stage of the cell cycle that occurs between divisions. DNA is replicated during this phase.
intestines - The part of the gastrointestinal tract through which food passes after passing through the stomach. The intestines finish the process of digestion and carry out nutrient absorption.
intracellular - Inside a cell.
intracellular receptor - Receptor located inside of a cell.
in-vitro fertilization (IVF) - The process by which eggs and sperm are combined in a laboratory setting outside of the body.
ion - An atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons (negatively-charged particles). An example of an ion is Na+ (a sodium atom that has become positively charged by losing an electron).
ion channels - Passageways in the cell membrane through which charged molecules can pass.
iron - An element that plays a role in the transport of oxygen by the blood.
isocortex - Another term for neocortex.

J

Japanese knotweed - A plant that contains resveratrol, an antioxidant compound in red wine.
juvenile form - Another term for juvenile HD.
juvenile HD - Juvenile Huntington’s disease (juvenile HD) is a form of Huntington’s disease with an onset before age 20. Juvenile HD is caused by the same gene as the adult form of the disease, but its symptoms are different. Common symptoms include rigidity, seizures, and dementia. Also referred to as the juvenile form of HD, or early-onset HD. See Table E-1.

K

kidney - An organ that plays a critical role in the excretory system; it is responsible for generating urine.
kinase - A molecule that phosphorylates, or adds a phosphate group onto, other molecules in the cell in order to turn them on or off. Often used in signaling cascades that tell the cell to carry out certain functions.
kinetics - The rate at which a compound reacts. More specifically, the kinetics of a particular drug is the rate at which the drug completes its function.
Kearns-Sayre syndrome - A rare mitochondrial disorder that usually has an onset before the age of 20. Kearns-Sayre syndrome is characterized by progressive paralysis of the eye muscles and mild skeletal muscle weakness.
knock-in - Refers to an organism that has a particular gene or trait purposely inserted by selective breeding or laboratory techniques (e.g., a huntingtin knock-in mouse).
knock out - The process of purposely removing a particular gene or trait from an organism.
knockout - Refers to an organism that has a particular gene or trait purposely removed by selective breeding or laboratory techniques (e.g., a huntingtin knockout mouse).
Krebs cycle - A series of chemical reactions involved in aerobic respiration that occur naturally in animals. Also referred to as the citric acid cycle.

L

LA - Abbreviation for linoleic acid.
lactate / lactic acid - A chemical that is formed when sugars are broken down for energy in the absence of adequate oxygen. Lactate causes the muscle pain athletes experience after engaging in strenuous physical activity for long periods of time. In people with mitochondrial disorders, too much lactate forms because the ability to burn foods using aerobic respiration is impaired.
lactose - The major sugar in milk.
lateral geniculate body - The “visual middleman,” the lateral geniculate body receives information from the eyes via the optic tract, does a preliminary analysis of the information, and then sends it onto the visual cortex.
lamotrigine - An anticonvulsant drug normally used to control seizures or stabilize mood. It inhibits the release of glutamate but conflicting evidence exists about its effect on physical symptoms associated with HD.
LAX-101 - A purified form of eicopentaenoic acid (EPA) that has shown some efficacy in slowing the progression of HD in a phase III clinical trial.
lead compound - A chemical compound that is considered the most likely to become an effective therapeutic treatment.
lesion - A piece of tissue that is either missing or so damaged that it cannot perform its normal function.
lethargy - A state of tiredness or inactivity.
leukotriene - A powerful inflammatory mediator. Leukotriene is important in inflammation and allergic reactions because of its ability to constrict blood vessels and attract various types of immune cells.
LI 1379 - A Ginkgo biloba extract.
limbic system - A group of brain structures and their connections with each other as well as their connections with the hypothalamus and other areas. This system is largely associated with emotions.
linoleic acid - An essential fatty acid. Linoleic acid is an omega-6 fatty acid that serves as the parent compound in the synthesis of other omega-6 fatty acids such as arachidonic acid.
lipid - A family of compounds that cannot be dissolved or mixed in water. These compounds are a structural component of cell membranes, are used for energy storage, and constitute certain signaling molecules. Examples of lipids include fats, phospholipids, and steroids.
lipid peroxidation - The process by which free radicals “steal” electrons from the lipids in our cell membranes, resulting in cell damage and increased production of free radicals.
lipid-soluble - Capable of dissolving in substances made of compounds known as lipids. Lipids include fats, phospholipids, and steroids. The term fat-soluble is also commonly used to describe such substances.
lipocortin - An enzyme that inhibits the activity of phospholipase A2. Lipocortins are activated by glucocorticoids.
lipoic acid - A coenzyme that aids in energy production in the mitochondria. Known for its antioxidant properties, it may be able to combat oxidative stress and slow the progression of HD.
lipoxygenase - An enzyme that plays a pivotal role in the synthesis of inflammatory mediators known as leukotrienes.
lithium chloride - A chemical that is injected below the skin and works with quinolinic acid to reduce the loss of nerve cells and promote neurogenesis in the striatum of the brain.
liver - An organ responsible for many critical functions in the body; highly important in protein and sugar metabolism.
locus - A particular location in the DNA, but not necessarily a gene (plural: loci).
low-density lipoproteins (LDL) - Molecules made of lipids and proteins that carry cholesterol and fat through the bloodstream.
low-density lipoprotein (LDL) cholesterol - A complex of lipids and proteins, with greater amounts of lipid than protein, that transports cholesterol in the blood. High levels are associated with an increased risk of atherosclerosis and coronary heart disease.
lymphocyte - A type of white blood cell that is a crucial part of the immune system.
lysosome - An organelle that acts as the “garbage disposal” of the cell by breaking down cell components that are no longer needed as well as molecules or even bacteria that are ingested by the cell.

M

MAC - Abbreviation for membrane attack complex.
macrophage - An immune cell found throughout the body. Macrophages act as scavengers that engulf dead cells, foreign substances, and other debris.
mad cow disease - Another term for bovine spongiform encephalopathy (BSE).
magnesium ion (Mg2+) - A single magnesium ion blocks the opening of the NMDA receptor, preventing the influx of calcium ions into the cell. This magnesium ion is removed only when the electrical charge inside the cell rises above a certain value. This increase in charge is mediated by the binding of glutamate to non-NMDA receptors.
mammal - Any of various warm-blooded vertebrate animals, including humans, characterized by a covering of hair on the skin and, in the female, milk-producing mammary glands for nourishing the young.
malonate - An inhibitor of complex II of the electron transport chain.
marker - A variable segment of DNA, often located near a gene. An allele at the marker is typically inherited along with the corresponding allele at the nearby disease gene.
mass - The amount of matter in an object; often used interchangeably with weight. (Weight is actually the force with which an object is attracted toward the center of the earth.)
maximum tolerated dose (MTD) - The highest daily dose of a drug that the average human body can tolerate before passing a threshold level of excessive toxicity
median - The middle value in a set of numbers arranged in increasing order. If there is an even number of values, then the median is the average of the middle two values. For example, the median of the set {10, 12, 14, 19, 20} is 14. The median of the set {2, 3, 4, 6, 8, 9} is 5, which is the average of 4 and 6.
medium - A nutrient-rich liquid used in tissue cultures.
medulla - Also known as the medulla oblongata, this region of the brain is concerned with vital functions like breathing, blood circulation, vomiting, and swallowing.
meiosis - A reproductive process involving two successive divisions of a cell, resulting in four daughter cells. Unlike what occurs in mitosis, the daughter cells produced in meiosis are not identical to each other. Meiosis is the process by which sperm and egg cells are made.
MELAS - Mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes; a common type of mitochondrial myopathy (MM). MELAS is one of a group of rare muscular disorders called mitochondrial myopathies. It is caused by a defect in the gene encoding for certain proteins/components of the mitochondria and results in disorders in the brain and muscles. Characteristics of MELAS include stroke-like episodes, seizures, vomiting, hearing loss, and elevated lactate levels. Also referred to as mitochondrial myopathy, encephalomyopathy lactic acidosis, and stroke-like episodes.
melatonin - A compound that is believed to decrease the presence of beta-amyloid fibrils, but has little or no success in inhibiting huntingtin protein aggregation.
memantine - A well-tolerated drug that acts as an NMDA receptor antagonist, preventing glutamate toxicity. It may slow the progression of HD.
membrane - A flexible layer surrounding a cell, organelle (such as the nucleus), or other bodily structure. The movement of molecules across a membrane is strictly regulated in both directions.
membrane attack complex (MAC) - A complex of complement proteins that assemble together to form a pore across the membrane of the cell. The MAC allows the entrance and exit of various ions and substances, resulting in the death of the cell.
membrane fluidity - The motion of the phospholipids within the cell membrane, dependent on the membrane´s fatty acid composition and cholesterol content.
menstruation - The discharging of blood, secretions, and tissue debris from the uterus that occurs in non-pregnant females of childbearing age at approximately monthly intervals.
MERRF - Myoclonus epilepsy with ragged-red fibers; a common type of mitochondrial myopathy (MM).
messenger cascade - A process in which an initial message is greatly amplified in a cascade of ensuing messages, resulting in cellular change.
messenger RNA (mRNA) - The mediating molecule between DNA and protein synthesis.
metabolic - Pertaining to metabolism, the process of breaking down food and producing energy.
metabolism - The process of cells burning food to produce energy. This is similar to a car's engine burning gasoline to produce the energy that is used to rotate the car's wheels. The cell’s mitochondria acts as the car’s engine, the food we eat acts as the gasoline, and the energy we need to move and think is similar to the energy used to move the car. Also referred to as energy metabolism.
methionine - An amino acid that must be obtained through the diet because it cannot be produced by humans.
methionine cycle - The cycling of methionine to SAM, homocysteine, and back to methionine.
methionine synthase (MS) - Along with methyltetrahydrofolate, methionoine synthase is an enzyme responsible for the addition of a methyl group to the sulfur atom of homocysteine to form methionine.
methyl group - A chemical group made up of one carbon atom and three hydrogen atoms that is added to histones to silence genes by causing the DNA to coil up. Methylation of histones prevents further transcription.
methylation - A way to silence genes by adding a methyl group to a histone, causing the DNA to coil up into chromosomes and preventing further transcription.
methyltetrahydrofolate (methylTHF) - Along with methionoine synthase, methyltetrahydrofolate is an enzyme responsible for the addition of a methyl group to the sulfur atom of homocysteine to form methionine.
Mg2+ - See Magnesium ion.
MHC II - Proteins that bind to and “present” proteins of foreign substances on the surface of cells for recognition by other immune cells.
microglia - A type of glial cell that is activated in the inflammatory response. Sometimes called “brain macrophages.”
microgram (mcg) - A measurement of mass; commonly used in measuring dietary supplements (1 mcg= 10^-6 grams).
microRNA (miRNA) - A group of small RNA molecules, distinct from but related to small interference RNA (siRNA), that can prevent the expression of certain genes.
microtubule - An intracellular component of the cytoskeleton which aids in cell support, intracellular transport, and cell proliferation.
midbrain - A part of the brain that is mainly concerned with the control of eye movement. Also relays signals for auditory and visual reflexes.
mineralcorticoids - Steroids released from the adrenal cortex that maintain salt and fluid balance in the body.
mini mental state examination (MMSE) - A screening test designed to measure the cognitive (thinking) abilities in adults. It can be used to test if a person is cognitively impaired, to track the deterioration or improvement in cognitive functioning over time, or to rate the degree of cognitive impairment. It is scored on a scale of 30, with 0 being profoundly impaired and 24-30 normal for most adults. As a screening test, the MMSE is designed to yield falsely positive results (i.e. cognitive problems when there are none) as opposed to falsely negative results (i.e. no problems when problems do, in fact, exist). Because of this, low MMSE scores are usually followed up with more in-depth cognitive assessments for clinical diagnosis purposes.
minocycline - An antibiotic commonly used to treat arthritis and acne. Studies indicate that minocycline may have beneficial effects on people with HD due to the decreased caspase activity that results from minocycline treatment.
Miraxion - A novel compound that may function as a neuroprotectant by inhibiting harmful enzymes known as phospholipases and stabilizing the phospholipid components of cell membranes and mitochondria.
misfolded protein - proteins have a certain shape, or structure that they should have in the cell, and this structure is often very important to a protein’s correct function. Under various conditions, a protein can misfold or take the wrong shape, which can impair the function of the protein, render it useless or even harmful.
mismatch repair enzyme - An enzyme that recognizes and repairs incorrect pairings of nitrogenous bases in DNA. For instance, a mismatch repair enzyme would recognize when Cytosine (C) is mistakenly paired with Thymine (T). The enzyme would then replace Thymine with Guanine (G), resulting in a correct pair between Cytosine (C) and Guanine (G).
mithramycin - An antibiotic that binds to specific regions of DNA rich in guanine and cytosine to regulate transcription. While it is currently prescribed to treat certain types of cancer and a few other conditions, recent research shows that it is also helpful in treating motor symptoms and prolonging life in a mouse model of HD. Also known as MIT and plicamycin.
mitochondria - Plural form of mitochondrion.
mitochondrial creatine kinase (mtCK) - A protein found in the mitochondria that exists in two forms. The first form prevents the mitochondrial membrane from destabilizing. When mtCK is inactivated by free radicals, it transforms to the second form, making the membrane less stable.
mitochondrial myopathies (mm) - A group of neuromuscular diseases caused by damage to the mitochondria in cells.
mitochondrion - A part of the cell (organelle) that is responsible for energy production. The mitochondria take care of many specialized tasks, including converting nutrients into energy. (Plural form: mitochondria.)
mitogen-activated protein (MAP) kinase - An enzyme that is involved in numerous aspects of signal transduction.
mitosis - A reproductive process in cells that ultimately results in one cell dividing into two new cells, both identical to the original. The two new cells are called daughter cells.
mitotic spindle - Array of microtubules that forms during mitosis and physically separates duplicated chromosomes.
MLK2 - Abbreviation for mixed-lineage kinase 2, a protein that interacts with the normal huntingtin protein.
models - There are many parallels between biological systems in many types of creatures, so this has led to the establishment of a number of "model organisms". Scientists reproduce features of a disease of interest in an organism and then study it. For example, inserting the gene for HD into a mouse means that it will produce the altered HD protein in the brain. This creates an HD mouse model. To do the same experiments with people would be very time-consuming, not to mention unethical, but the consistent use of these models allows us to test ideas about biology in a reproducible way.
modifier - A gene that alters the effect of another.
molecular chaperones - Substances inside the cell that bind and stabilize proteins at intermediate stages of folding, assembly, movement across membranes, and degradation.
molecular pathways - A system where one molecule affects another, either by activating it or deactivating it. This molecule, in turn, affects another molecule, and so on. Any mutation or change in one part of the pathway has a cascading effect, changing everything that happens after the mutation.
molecule - The smallest unit of matter of a substance that retains all the physical and chemical properties of that substance, consisting of a single atom or a group of atoms bonded together. Example: A single water molecule (H2O) consists of just one single oxygen atom bonded to just two hydrogen atoms. There are thousands of water molecules in a single droplet of water. Molecules are too small to be seen without the assistance of powerful microscopes.
molecular compounds - A substance formed when two or more non-metal molecules combine
molecular structure - The size and shape of a molecule, determined by the atoms that make up the molecule. The structure of a molecule usually determines its function, which other molecules it interacts with, and how it affects those molecules.
monoamine oxidase (MAO) - An enzyme found primarily in the liver and nervous system that generates free radicals.
monomer - A single molecule or molecular unit that has the potential to be chemically bound to more molecules or units.
monounsaturated fat - A type of unsaturated fat in which there is only one double bond.
motor cortex - A region of the cortex that carries out the initial processing of motor information in the brain; involved in the control of movement.
motor neuron - A neuron that has the specific job of controlling muscle movement.
MPTP - A toxic molecule that causes damage to the nervous system, resulting in Parkinson’s Disease.
mRNA - Abbreviation for messenger RNA.
MSH2 - A mismatch repair enzyme that also repairs unpaired regions of DNA (such as bubbles resulting from polymerase slippage) and stops hairpins from forming. It is possible that this enzyme becomes altered and unable to function in the cells of people with Huntington’s disease.
mtCK - See mitochondrial creatine kinase.
mTOR - Stands for “target of rapamycin”; a protein that inhibits the process of autophagy.
multipotent - The ability to give rise to a number of limited cell types.
muscular system - The muscular system is the biological system of animals that allows them to move internally and externally.
mutagen - Something in the environment that causes mutations.
mutagenic - See mutation
mutant huntingtin - The altered form of the huntingtin protein caused by having the HD gene.
mutation - Any heritable change in DNA. There are many types of mutations, such as chromosomal mutations, point mutations, contractions, and expansions.
myelin - The fatty sheath coating the axons of the nerves; it allows for the efficient conduction of nerve impulses.
myoclonic seizure - A seizure characterized by myoclonus (sudden, brief muscle contractions).
myoclonus - Twitching or contraction of a muscle or group of muscles.
myorelaxation - Relaxation of the muscle.
myotonia - Frequent spasms of the muscles.

N

NAD - Nicotinamide adenosine dinucleotide; an electron carrier involved in cellular metabolism. It accepts and donates electrons to various enzymes involved in metabolism, ultimately providing the cell with energy.
N-terminus - The end of the amino acid chain that makes up a protein that is terminated by an amino group (-NH2).
negative feedback - A mechanism in the body for maintaining a state of internal constancy, or homeostasis; effectors are activated by changes in the internal environment, and the actions of the effectors serve to counteract these changes and maintain a state of balance.
negative regulator - One molecule that controls the effects of another (or itself) by repressing or inactivating it.
neocortex - Part of the cerebral cortex; constitutes about 85% of the human brain’s total mass. The neocortex is thought to be responsible for higher level cognitive functions, such as language, learning, memory, and complex thought. Also referred to as the isocortex.
nerve cell - One of the major classes of cells in the nervous system. They are the fundamental signaling units of the nervous system. They are unique from other cells in that they have the ability to communicate rapidly with one another over great distances and with great precision. Also referred to as a neuron.
nerve cell body - The largest part of a cell, the cell body holds all of the general parts of a cell as well as the nucleus, which is the control center. The nucleus contains the cell's genetic material (DNA, located in the chromosomes). The cell body also contains many other unique structures responsible for making energy and getting rid of cellular wastes. Also referred to as the soma.
nervous system - A regulatory system of the body that consists of neurons and neuroglial cells. The nervous system is divided into two parts, the central nervous system (CNS) and the peripheral nervous system (PNS).
neural connections - Connections between neurons. Neurons send information via neurotransmitters.
neurochemicals - Chemicals in the brain.
neuroD (ND) - A transcription factor important in neuronal development.
neurodegenerative - Characterized by neurodegeneration. Neurodegenerative diseases include HD, Alzheimer’s, Parkinson’s and many more.
neurodegeneration - The deterioration or loss of function of nerve cells.
neurogenesis - Formation of the nervous system; neurons are produced.
neuroglia - The supporting tissue of the nervous system; made up of neuroglial cells. Astrocytes (spider cells) are a type of neuroglial cell. Also referred to as glia.
neurological - Having to do with the nervous system and/or nerve cells.
neurologist - A specialist in the diagnosis and treatment of disorders of the nervous system.
neuron - Another term for nerve cell.
neuronal - Of or pertaining to the neurons.
neuronal ceroid lipofuscinoses (NCLs) - A group of rare, inherited degenerative disorders of the nervous system; associated with the accumulation of an abnormal pigment in the brain called lipofuscin. These disorders can have severe diseases including blindness, mental retardation, and early death.
neuronal inclusions (NI) - Clumps of protein formed by aggregation of mutant proteins. These mutant proteins have abnormally expanded polyglutamine tracts in hereditary tri-nucleotide repeat disorders. Also referred to as neuronal intranuclear inclusions, nuclear inclusions, or inclusion bodies.
neuronal intranuclear inclusions - Another term for neuronal inclusions.
neuropathy [A group of symptoms caused by abnormalities in motor or sensory nerve cells. Symptoms include tingling or numbness in hands or feet followed by gradual, progressive muscular weakness. oxidative damage - Another term for oxidative stress.
neuroplasticity - The brain's natural ability to form new connections in order to compensate for injury or changes in the environment. The ability of the brain to reorganize pathways between neurons as a result of new experiences.
neuroprogenitor cells - Undifferentiated cells capable of giving rise to nerve cells and glia in the central nervous system.
neuroprotectant drugs - Drugs that prevent harmful calcium ions from destroying the m\itochondria of the nerve cells, which leads to cell death. An example of a neuroprotectant drug is Cyclosporin A.
neuroprotection - A process that involves protecting the nerve cells from deterioration due to neurodegenerative disease.
neuroprotective - The property of preventing damage and degeneration to nerve cells.
neuropsychiatrist - A physician who treats people with psychiatric symptoms that are caused by a brain disorder. For more information, click here.
neurotoxic - A substance that damages or destroys nerve tissue.
neurotransmitter - A chemical messenger produced in and released by one neuron. A neurotransmitter can excite or inhibit another neuron.
neurotrophic factor - A protein in the nervous system that promotes the growth of nerve cells.
new indication studies - New phase II and III trials required when a drug seems promising as a new treatment for a different condition than it was originally approved for.
NF-kappa B (NF-KB) - A transcription factor that enhances the production of inflammatory mediators. Association with the GR complex inhibits the transcription of COX-2 genes.
NF-kB - Abbreviation for NF-kappa B.
NI - Abbreviation for neuronal inclusions.
niacin - A precursor of nicotinamide. Nicotinamide is the biologically active form of nicotinic acid. Also known as nicotinic acid.
nicotinamide - A drug that may help improve cellular energy production by acting as a precursor of NAD. Also known as Vitamin B3.
nicotinic acid - Also known as niacin.
nitric acid - A chemical that increases blood flow; also used to make organic compounds in the body.
nitric oxide (NO) - A gas where each molecule is made of one nitrogen atom and one oxygen atom; it is found in many brain and body tissues, and plays a part in many bodily functions.
nitric oxide synthase - a family of enzymes responsible for the synthesis of nitric oxide (NO). NO can become mutated in some neurodegenerative disorders like Alzheimer’s, causing oxidative stress and neurodegeneration.
nitrogenous base - One of the molecular components of a nucleotide; a class of ringed molecules with carbon, oxygen, hydrogen, and nitrogen.
NMDA receptor - One type of receptor that binds glutamate. It is selectively activated by the drug NMDA (N-methyl-D-aspartate).
non-coding region - A segment of DNA that does not comprise a gene and thus does not code for a protein. Non-coding regions are interspersed throughout DNA.
non-competitive inhibitor - An antagonist that inhibits the binding of a neurotransmitter (or hormone) by changing the shape of its receptor. In this way, the receptor will no longer "recognize" the neurotransmitter (or hormone).
nondisjunction - An event that can occur during meiosis in which chromosomes fail to separate properly, resulting in daughter cells with too many or too few chromosomes.
non-hd allele - A version of the Huntington gene that contains a normal number of CAG repeats and codes for the normally functioning form of the huntingtin protein. Individuals with the non-HD allele will not develop Huntington’s Disease, and they will not pass the disease on to their children. This allele is sometimes called the "normal Huntington allele." See Table A-1.
nonpolar - a nonpolar molecule does not have a separation of positive and negative electric charges within the molecule. Nonpolar molecules are pushed towards one another by polar molecules. For example, nonpolar compounds, like oil, can’t dissolve in water because of the water's polarity.
non-refined - refers to breads and cereals in which the whole grain (including its bran and germ) are included in the food product. Non-refined breads and cereals (such as whole wheat bread and oatmeal) are healthier than refined products because the fiber is beneficial.
non-specific - A type of response that is not specific to any particular body organ or location. Rather, the response occurs throughout the body.
nonsteroidal anti-inflammatory drugs (NSAIDs) - Compounds that significantly reduce the inflammatory response by interfering with the cyclooxygenase pathway, reducing the level of compounds that mediate inflammation.
normal huntingtin - See huntingtin protein
noradrenaline - A molecule that acts both as a neurotransmitter and hormone and works to increase heart rate, blood pressure, and blood sugar levels in times of physical or mental stress. Also known as norepinephrine.
norepinephrine - A molecule that acts as a neurotransmitter and as a hormone to increase heart rate, blood pressure, and blood sugar levels in times of physical or mental stress. Also known as noradrenaline.
NSAIDs - Abbreviation for nonsteroidal anti-inflammatory drugs.
NRSE (nerve cell restrictive silencer element) - A molecule that silences the BDNF promoter and thus leads to decreased levels of BDNF in the brain.
nuclear envelope - The double layered membrane in the cell that surrounds and contains the nucleus, which holds the cell’s DNA.
nuclear inclusions - Another term for neuronal inclusions.
nuclear membrane - Separates the nucleus from the cytoplasm of the cell. It is similar to the cell membrane in that it is selectively permeable.
nuclei - Plural form of nucleus.
nucleosome - A structure composed of histones that aids in the coiling up of DNA into compact chromosomes. It can be thought of as a spool that winds up the DNA "thread."
nucleotide - The molecular subunit that makes up DNA; consists of a sugar, phosphate group, and nitrogenous base; see Figure B-2. A molecule of DNA is made up of a long chain of nucleotides.
nucleus - 1. A spherical body within the cell that is enclosed by a double membrane. The nucleus contains the chromosomes and is the information center of the cell. 2. A collection of nerve cells in the brain that are anatomically discrete and which typically serve a particular function. (Plural form: nuclei.)

O

Obsessive-Compulsive Disorder - A disorder characterized by recurrent thoughts or behaviors (e.g., excessive hand washing or repeated doubt about having locked a door) that are severe enough to be time consuming or cause significant impairment in social functioning.
occupational therapy - a type of therapy that teaches (or re-teaches) individuals the skills they would need to lead balanced lives and perform necessary functions for everyday living, and may either be skills that pertain to the home or to work.
oligomenorrhea - Infrequent or very light menstruation; risk factor for osteoporosis.
oligopeptide - Several amino acids linked together.
omega-3 fatty acid - A type of fatty acid that our body derives from food. Omega-3 fatty acids have anti-inflammatory properties due to their ability to convert into anti-inflammatory prostaglandins.
omega-6 fatty acid - Essential fatty acids that use the same enzymes as omega-3 fatty acids to produce their final products.
operationalize - The process of converting concepts into specific observable behaviors that a researcher can measure.
optic nerve - A collection of nerve cells that project visual information from the eyes to the lateral geniculate nucleus.
optic tract - Fibers of the optic nerve which project visual information mainly to the lateral geniculate body.
optimization - The process by which a chemical compound is modified by chemical or biological means to make it interact more effectively with the biological target.
optimal dosage - The dosage that would be best for the patient population at large. It confers the most benefit with the least amount of side effects.
organelle - A membrane-bound compartment in a cell with a specialized function.
organism - Any living thing.
osteoporosis - A disease in which the bones are weakened by reduced calcium absorption. Long-term use of glucocorticoids can result in this condition.
oxidation - The process by which a molecule or atom loses an electron. Oxidation of cell components by free radicals can accelerate cell death and plays a role in the HD disease process.
oxidative damage - The harmful condition that occurs when there is an excess of free radicals, a decrease in antioxidant levels, or both.
oxidative phosphorylation - Refers to the coupling of the electron transport chain to ATP synthesis via the proton gradient and ATP synthase. This occurs primarily in the presence of oxygen.
oxidative stress - See oxidative damage.
oxygen - An element active in physiological processes and crucial to brain functioning.

P

P53 - One of the transcription factors that requires the presence of CBP in order to bind to DNA. An inability of P53 to access and bind to the DNA can lead to abnormal gene transcription and expression, ultimately leading to cell death.
pancreas - A large gland that secretes digestive enzymes and the hormones insulin and glucagon.
parasite - Something that lives in, with, or on another organism and obtains benefits from the host, which it usually injures.
Parkinson's disease - A neurodegenerative disorder that primarily affects one's ability to perform smooth movements. The disease is associated with a loss of dopamine-producing nerve cells in the substantia nigra region of the brain.
parietal lobes - Sections of the brain that are involved with cognition, information processing, spatial orientation, and the perception of stimuli related to touch, pressure, temperature and pain.
paroxetine - A member of the class of drugs known as selective serotonin reuptake inhibitors (SSRIs). It is normally used to treat depression and severe anxiety, but may also be helpful in slowing the progression of HD.
partial seizure - A seizure that usually begins with electrical discharges in one part of the brain. Partial seizures may or may not result in a loss of consciousness.
paternally - From or related to the father of an individual. A disease that is paternally inherited is inherited from an individual’s father.
pathogen - A microorganism (such as a bacterium or virus) that causes disease.
pathogenesis - The origination and development of a disease.
pathology - The branch of medicine concerned with disease, especially the structure of pathogens and their functional effects on the body.
PCr - See phosphocreatine.
PDC - See pyruvate dehydrogenase complex.
PDC Kinases - A group of molecules that add a phosphate onto one of the enzymes in the pyruvate dehydrogenase complex (PDC), effectively turning the entire PDC off. These kinases are usually activated by acetyl-CoA.
pedigree - A family lineage, or a chart of a family lineage that follows the inheritance of a particular trait.
peptide - A description of two linked amino acids.
peptide bond - The actual link between two amino acids. More specifically, the new bond that forms between the carboxylic acid group (COOH) of one amino acid and the amine group (NH2) of another amino acid.
peripheral nervous system (PNS) - The part of the nervous system consisting of everything but the brain and spinal cord. The PNS includes spinal and cranial nerves, ganglia, and plexuses.
peripheral neurons - Neurons that are part of the nervous system but are not in the brain or spinal cord; usually associated with supplying sensation or motor messages to the skin and skeletal muscles.
peripheral neuropathy - Damage to the nerve cells that supply sensation to the arms and legs.
peristriatal - An area of the brain's occipital lobe that is concerned with vision.
permeability - The degree to which cells and other molecules can pass through the walls of a blood vessel.
peroxides - Chemicals capable of causing oxidative damage to cell membranes and other molecules.
petri dish - a shallow glass or plastic cylindrical dish that scientists use to grow cells. These cells can be from many different kinds of organisms, like bacteria, yeast, mouse, or human, and can be from different tissues, like muscle, the liver, or the brain.
PG1 and PG3 - Classes of prostaglandins that are known to have anti-inflammatory effects such as decreasing pain, increasing oxygen flow, dilating airways, and decreasing inflammation.
PG2 - A class of prostaglandins that is known to have pro-inflammatory effects such as increasing pain, decreasing oxygen flow, constricting airways, and increasing inflammation.
pH - A measure of how acidic or basic a solution is. Water has a pH of 7 and is neutral. Solutions with a pH below 7 are acidic, while solutions with a pH above 7 are basic.
pharmacodynamics - explain at what the drug does to the body. This looks at the dose-response relationship, and what effect the drug has on each of the major organs within the animal.
pharmacokinetics - indicate what the body does to the drug. It is characterized by the ADME, or absorption (how it gets into the body), distribution (how it spreads around the body), metabolism (how cells and tissues in the body utilize it, and change its composition), and excretion (how it gets removed from the body) of the compound.
pharmacological - pharmacological research involves studing how chemicals interact with living organisms. It involves looking at the composition and properties of drugs (also called pharmaceuticals), therapy, and medical applications
phase I clinical trial - The first in a series of studies that test the safety and efficacy of a new drug or treatment in human participants. This type of study usually involves a very small number of participants, tests for side effects of the treatment, and attempts to determine safe dosages.
phase II clinical trial - The second in a series of studies that test the safety and efficacy of a new drug or treatment in human participants and is only performed once the drug has successfully passed the phase I clinical trial. This study involves more participants and attempts to determine if the treatment has positive effects on the participants’ conditions. Side effects continue to be noted.
phase III clinical trial - The third in a series of studies that test the safety and efficacy of a new drug or treatment in human participants and is only performed once the drug has successfully passed the phase II clinical trial. This study involves large numbers of participants and may compare the efficacy of the new treatment with a standard treatment. It also assesses the safety of long-term use.
PHD - A person with Huntington’s disease.
phenotype - The physical characteristics displayed by an organism; results from interaction between the genotype and the environment.
phosphate - One of the molecular components of a nucleotide; a small molecule made up of phosphorus and oxygen.
phosphocreatine (PCr) - A phosphorylated form of creatine. Phosphocreatine is a molecule that stores high-energy bonds in the body.
phospholipase A2 (PLA2) - A key enzyme involved in the release of arachidonic acid (AA) from the cell membrane. Inhibition of PLA2 by lipocortins results in a decrease in inflammation.
phospholipid - An important constituent of cell membranes that is composed mainly of fatty acids.
phosphorylation - The process of adding on a phosphate group to a molecule. Often used in cell signaling to turn molecules on or off.
photoreceptor - A cell or group of cells that can sense and receive light.
physical therapy - Treatment of injury or disease by physical therapeutic means instead of by medical, surgical, or radiologic measures. Physical therapy can include massage, patient education, and water therapy. Also referred to as physiotherapy.
physiological - Pertaining to physiology, the science of how living organisms function. A treatment with physiological effects influences the way that the body functions.
physiotherapy - Another term for physical therapy.
phytoalexin - A type of compound produced by some plants in response to fungal infection or injury. Resveratrol is one example of a phytoalexin.
pipetting - Using a pipette (a syringe-like instrument) to measure and transfer liquids from one container to another.
PLA2 - An abbreviation for Phospholipase A2.
placebo - Any intentionally ineffective medical treatment, such as a sugar pill, used to replace medication. In clinical trials, placebos are given to control groups to compare the results of people who receive the placebo with the results of those who receive the experimental drug. The experimental treatment must produce better results than the placebo in order to be considered effective.
plasmid - A small, independently replicating piece of DNA that can be taken from one organism and inserted into another.
plastic - Able to be shaped or changed.
platelet-activating factor (PAF) - A compound that reduces inflammation by increasing permeability of blood vessels and contracting various involuntary muscles such as those in airways.
platelets - Cells that aid in blood clotting.
plexus - A network or interweaving of nerves and blood vessels. (Plural form: plexuses.)
plexuses - Plural form of plexus.
pluripotent - The ability to give rise to most of the cells required to produce an organism, excluding the placenta and other supporting tissues.
pneumonia - An inflammation of the lungs that can be caused by infection or other environmental irritants.
PNS - See peripheral nervous system.
point mutation - A mutation in which a single base pair in the DNA strand is replaced by a different base pair.
poly(ADP-ribose) polymerase (PARP1) - An enzyme involved in a number of cellular processes including DNA repair and apoptosis.
polyglutamine diseases - Diseases that arise from extra copies of the CAG codon in certain segments of the DNA. The CAG codon codes for the amino acid glutamine. Also referred to as polyglutamine expansion disorders.
polyglutamine expansion disorders - Another term for polyglutamine diseases.
polymer - A large molecule made up of repeating subunits, called monomers. Polymers made up of proteins are called polypeptides.
polymerase chain reaction (PCR) - A technique used to produce millions of copies of a particular stretch of DNA.
polymerase slippage - During replication, the slipping of DNA polymerase III from the DNA template strand at the repeat region and the subsequent reattachment at a more distant site. Polymerase slippage can cause the newly created DNA strand to contain an expanded section of DNA.
polymerase slippage model - A possible model for how expansions occur. This model suggests that polymerase slippage is the cause of increased repeat regions.
polymerization - The process of single molecules coming together to bind into a variety of three dimensional shapes, including a chain.
polymorphism - Multiple alleles (versions) of a gene within a population, usually expressing different phenotypes.
polypeptide - A chain of multiple amino acids.
polyunsaturated fat - A type of unsaturated fat in which there are many double bonds.
pons - Region of the brain that acts as a relay station between the cerebellum and the cerebrum. The pons is part of the brain stem, and it also aids the medulla in the control of breathing.
pool therapy - A type of physiotherapy in which the individual does exercises while submerged in warm water. The temperature of the water is soothing for muscles, and the buoyancy of the water makes movement easier.
population genetics - Field of study that investigates the fate of genes within populations.
postmortem - Pertaining to the period after death. The word can also be used in reference to the medical examination of a body after death.
postsynaptic - Literally “after the synapse;” a structure or event that occurs after small gaps between nerve cells. This word is often used to describe the nerve cell that receives the message (i.e. neurotransmitter) sent by a presynaptic cell.
postsynaptic cell - cell that receives a neurotransmitter signal
PPAR-gamma - Proteins that inhibit the expression of genes that code for proteins involved in inflammation.
PPAR-gamma activators - Compounds that activate PPAR-gamma proteins, leading to a decrease in the inflammatory response. NSAIDs are said to be PPAR-gamma activators.
pre-clinical development - The testing of a lead compound before clinical trials start. This includes testing the drug in at least two animal models to determine safe doses, to understand side effects, and know more about long-term toxicity
predictive testing - Predictive testing determines whether the genetic sequence that causes HD is present or absent (also called genetic testing).
Prednisolone - Similar to prednisone in its high glucocorticoid activity. Most commonly used glucocorticoid because of its high glucocorticoid activity. Prednisone is transformed by the liver into prednisolone. Prednisolone may be administered in tablet form or produced by the body from prednisone. These medications are considered to be interchangeable.
Prednisone - Most commonly used glucocorticoid because of its high glucocorticoid activity, which reduces the risk of dangerous side effects caused by mineralocorticoids. Prednisone is transformed by the liver into prednisolone. The two medications are considered to be interchangeable.
pre-implantation genetic diagnosis (PGD) - The procedure by which a single cell is removed from an embryo to test it for genetic disease. It is done in combination with in-vitro fertilization.
pre-symptomatic - The state of health prior to the clinical appearance of the signs and symptoms of a disease.
presynaptic - Literally “before the synapse;” a structure or event that occurs before small gaps between nerve cells. This word is often used to describe the nerve cell that transmits the message (i.e. neurotransmitter) to another receiving cell.
presynaptic cell - cell that releases a neurotransmitter signal
pre-synaptic terminal - The region of the neuron at the end of the axon where neurotransmitters are stored. When an action potential reaches the pre-synaptic terminal, neurotransmitters are released into the synapse.
pretest counseling - Counseling offered to help individuals make informed decisions as to whether or not they should be genetically tested for HD. For more on genetic testing, click here
prevalence - The proportion of individuals in a population having a given disease.
primate - Any member of the order of animals including monkeys, apes, and humans.
primordial germ cells - The most primitive sex cells; will eventually give rise to sperm or eggs.
prion [A protein particle similar to a virus but lacking nucleic acid (any of a group of complex compounds - such as DNA and RNA] that are found in living cells and viruses and control cellular function and heredity). Prions are thought to be the infectious agent responsible for certain degenerative diseases of the nervous system.
pro-inflammatory cytokines - Cytokines produced predominantly by activated immune cells such as microglia and are involved in the amplification of inflammatory reactions. These include IL-1, IL-6, TNF-a, and TGF-ß.
proline - One of 20 amino acids essential for human life.
promoter - See promoter region.
promoter region - A DNA sequence that is recognized and bound by an RNA polymerase (enzyme) during the initiation of transcription.
prostaglandins - Short-lived, hormone-like chemicals that regulate cellular activities on a moment-to-moment basis and are produced in most tissues of the body.
protease - An enzyme that breaks down proteins.
proteasome - An enzyme that destroys abnormal proteins (which are flagged by ubiquitin).
protein - An important kind of molecule in the human body, consisting of a sequence of amino acids. The shape of a protein depends on the number and sequence of amino acids that make it.
protein aggregate - A misfolded, rigid protein grouping. In HD, protein aggregates result from excess glutamines.
protein aggregation - the process of forming protein aggregates.
protein chaperones - Molecules that discriminate between slowly-folding and misfolded proteins and localize with aggregates to inhibit their formation.
protein complex - a group of two or more associated proteins that function together to perform a specific task or make a certain structure.
protofibrils - Intermediate fibrils formed early in the protein aggregation process.
proton gradient - The product of the electron transport chain. A higher concentration of protons outside the inner membrane of the mitochondria than inside the membrane is the driving force behind ATP synthesis.
proximal - Near the center of the body.
psychiatric - related to a set of mental, emotional, or behavioral disorders
psychopathy - A condition characterized by the inability to connect to other people normally. Psychopathic individuals often show lack of empathy or conscience and poor inhibition. Specific psychopathic symptoms can include lack of restraint, touchiness, conflict making, evil mindedness, manipulative behaviors and aggressiveness.
psychosocial - A term used to describe the interaction between psychological and social aspects of one’s life.
psychostimulants - A group of drugs that lead to increased motor activity and decreased fatigue as well as an induced euphoric state.
Purkinje cells - A specific type of nerve cell that carries each and every piece of information sent out by the cerebellum. These cells possess a great deal of control over the refinement of motor activities.
putamen - Part of the basal ganglia in the brain. The putamen acts with the caudate to influence motor activity.
pyramidal nerve cells - Nerve cells projecting from the motor cortex to other parts of the brain and spinal cord. The pyramidal nerve cells play a key role in performing highly skilled movements.
pyruvate - This product of glycolysis is used and synthesized by many metabolic pathways. In energy generation, it can be either converted to lactate under anaerobic conditions, or broken down to water and carbon dioxide in the presence of oxygen, generating large amounts of ATP.
pyruvate dehydrogenase complex - A critical group of enzymes involved in energy metabolism.
pyruvate oxidation - The process in cellular metabolism where pyruvate is turned into acetyl-coA.

Q

quinolinic acid (QUIN or QA) - An excitotoxin used by researchers to induce degeneration of nerve cells and oxidative stress in the brains of animals to simulate diseases such as HD.

R

R&D pipeline - See research and development
randomized - In the context of a clinical trial, randomized refers to how the different treatments (either the potential drug or the standard treatment) are allocated to the trial subjects. This ensures that the different treatment groups are similar in important characterisitics such as how severe their disease might be and what other conditions they may have along with the disease being studied.
range - A set of values that a number can have. A range is usually specified by its maximum and minimum value. Any number that is between these two values is said to be within the range. For example, the range 12-15 has a maximum value of 15 and a minimum value of 12. The numbers 12, 13, 14 and 15 are said to be within the range 12-15.
rapamycin - A drug that has been shown to promote the breakdown of huntingtin aggregates by inhibiting the protein mTOR and inducing autophagy.
re-methylation - See methylation.
reactive oxygen species (ROS) - A highly reactive free radical that can result from excessive levels of iron in the body.
receptor - A specialized protein on a cell’s surface that binds to substances that affect the activities of the cell. Specifically, in a nerve cell, neurotransmitters bind to receptors on the surface of the neuron. The binding of a neurotransmitter can have either excitatory or inhibitory effects on the neuron. Once a neurotransmitter is bound to a receptor, changes occur within the neuron that can result in the neuron sending messages to other neurons.
recessive - A term used to describe the degree of penetrance of an allele relative to other alleles of the same gene. A recessive trait is only expressed when there are two recessive alleles present. If a dominant allele and recessive allele are both present, the dominant trait will be expressed instead.
recombination - An event that occurs during meiosis involving the transfer of segments of DNA from one homologous chromosome to the other.
red blood cells - Cells specialized for oxygen transport, having a high concentration of hemoglobin (oxygen-carrying protein) in the cytoplasm.
red nucleus - A small part of the brain involved in the control of movement.
redox-buffer - Acts to protect against oxidative damage.
refined - refers to breads and cereals in which the fibrous bran and germ are removed from the grain by machinery. Refined cereals and breads (such as white bread and pasta) are, thus, less healthy than non-refined cereals and breads.
refractory period - In a voltage-gated ion channel, the stage between open and closed. During this time the channel is inactivated, no molecules are allowed in or out, and the channel cannot be excited further.
relevant - A protein or molecule is relevant to a disease if it contributes to the disease mechanism or its symptoms in some manner.
remacemide - A drug that acts as an NMDA receptor antagonist. It may be helpful in combating glutamate toxicity in people with HD. For the chapter on remacemide, click here.
renal system - Part of the metabolic system; responsible for the regulation of bodily fluids and the elimination of wastes.
renal dysfunction - Problems with the kidney that detract from the body's ability to adequately retain essential nutrients and clear out toxic substances from the blood.
repeat region - The part of DNA where a certain codon is repeated many times. Expansions sometimes occur during replication of repeat regions. In Huntington’s disease, the repeat region involves the CAG codon.
replication - The process by which DNA copies itself before cell division. Unless mutation occurs, the new copy of DNA is identical to the original DNA. (Verb form: replicate.)
reproductive system - The male and female organs responsible for reproduction.
research and development - The process involves the scientific discovery of a mutation, or a pathway or biological target responsible for the disease all the way through to the creation of a therapeutic treatment, such as a drug. It has many stages, takes several years, and costs millions of dollars.
respiratory chain - The respiratory chain is composed of mitochondrial complexes that transfer electrons from one complex to another, eventually resulting in the formation of ATP. Also referred to as the electron transport chain.
restriction enzymes - Proteins produced by bacteria that break foreign DNA molecules at very specific sites; Enzymes that cut DNA. Different restriction enzymes cut at different sequences of nucleotides. For instance, one restriction enzyme will cut the DNA wherever it sees the sequence ACGGT, while another will cut when it sees CCTAT.
resveratrol - A phytoalexin found mainly in red wine that exhibits both antioxidant and anti-inflammatory abilities.
retina - A layer of receptors at the back of the eye that forwards information to the optic tract and eventually to the brain.
reuptake - The process by which a presynaptic nerve cell takes neurotransmitter out of the synapse and recycles it to prevent too much signaling.
Reye's syndrome - A rare and serious brain and liver disorder that is associated with the use of aspirin in children.
ribonucleic acid - See RNA.
ribose - The particular sugar molecule that is found in RNA.
ribosome - A tiny organelle in the cytoplasm of the cell that directs protein synthesis.
rifampicin - A compound that is believed to decrease the presence of beta-amyloid fibrils, but has little or no success in inhibiting huntingtin protein aggregation.
rigidity - Stiffness or tenseness of muscles; inability to bend or be bent.
riluzole - A drug that has been shown to have energy buffering and anti-glutamate properties
RNA - Abbreviation for ribonucleic acid; composed of many nucleotide subunits arranged in a long chain and associated with the control of cellular chemical activities; carries the information necessary to make proteins.
RNA interference (RNAi) - A technique for gene silencing. RNA is introduced into the cell to disrupt messenger RNA and prevent it from being translated into a protein.
RNA polymerase - An enzyme that catalyzes (speeds up) the synthesis of a complementary strand of RNA from a DNA template, or, in some viruses, from an RNA template.
RNA world - the RNA world hypothesis proposes that RNA was the basis of the first forms of proto-life, and then later developed into the first cell.
rofecoxib - A COX-2 inhibitor.
RRS1 - Regulator of ribosome synthesis; a gene that directs the production of ribosomes that, in turn, direct the synthesis of nuclear proteins (proteins found in the nucleus of the cell).

S

SAHA - Abbreviation for suberoylanilide hydroxamic acid.
salicylates - A group of drugs to which aspirin belongs.
saturated fat - A type of fat found mainly in meats, butter, and dairy products which, due to its chemical structure, tends to pack very tightly and raise levels of unhealthy cholesterol.
schizophrenia - a psychiatric disorder that usually involves problems with perceptions or expressions of reality, significant social or occupational problems, disorganized thinking, and delusions or hallucinations.
scientific method - The principles and empirical processes governing investigation into the truth or falsity of a scientific question.
scrapie - A common transmissible spongiform encephalopathy (TSE) in sheep and goats.
screening assay - A test for potential drugs that are available from biotechnology companies and academic laboratories under contract. Once researchers have figured out the appropriate target for a drug (such as nerve cell machinery clogged by mutated huntingtin protein aggregates), they can test these chemical compounds to see which one of them really goes after the target.
second-generation - The modified form of a naturally occurring protein or molecule that has been biologically or chemically manipulated in order to enhance its function to use for drug development.
seizure - A convulsion caused by electrical activity in the brain. Physical manifestations of a seizure can include shaking, twitching, staring, or a loss of consciousness.
selective serotonin reuptake inhibitors (SSRIs) - A class of drugs that is used to increase the amount of serotonin in the brain. These drugs are commonly used to treat depression.
selenium - A mineral essential to the mammalian diet and the central element in glutathione peroxidase (GPx). It has antioxidant properties and is normally obtained through foods such as yeast, whole grains, and seafood.
self-complementary - A single strand of DNA that curls back onto itself is described as self-complementary.
self-renewal - The ability of a self to divide continuously to produce more copies of itself.
self-replication - See self-renewal.
serotonin - A neurotransmitter that is a powerful vasoconstrictor (constricts the blood vessels) and is found especially in the brain, blood serum, and gastric mucous membrane of mammals; also called 5-HT or 5-hydroxytryptamine.
sex-linked - Used to describe a gene or disease whose inheritance is related to sex in some way.
sex chromosome - Sex chromosomes determine the sex of an individual. In humans, the two sex chromosomes happen to make up the last (23rd) pair of chromosomes. See Figure B-10.
short interference RNA (siRNA) - A small molecule that is used in the gene disabling technique to prevent the translation of genes to protein.
side effects - Problems that occur when treatment causes undesired effects, too much of the desired effect, or other problems occuring in addition to the desired therapeutic effect.
signal - when one protein in a molecular pathway can activate or deactivate another protein, it is a signal to the affected protein.
signal transduction - A basic process in molecular cell biology involving the conversion of a signal from outside the cell to a functional change within the cell.
silent mutation - A point mutation that has no effect on the organism involved.
single nucleotide polymorphism (SNP) - A variation of a gene that differs by one base pair. An example would be substituting an “A” where there is usually a “C” in the genetic code.
sirolimus - Another name for the drug rapamycin, which has been shown to promote breakdown of huntingtin aggregates by inducing autophagy.
sirtuins - A group of enzymes that may play a role in lifespan extension.
sister chromatid - A double helix of DNA, tightly coiled and compacted into a rod-like form. See Figure B-9.
small interfering RNA (siRNA) - See short interference RNA (A small molecule that is used in the gene disabling technique to prevent the translation of genes to protein).
sodium butyrate - An HDAC inhibitor.
sodium (Na+) channels - Gated ion channels that are necessary for glutamate release. Riluzole and lamotrigine interfere with these channels.
sodium selenite - A chemical form of selenium used for its antioxidant effects.
solution - A homogenous mixture of two or more substances.
soma - See nerve cell body.
specialized cells - Cells that are committed to a specific function (e.g., muscles cells, skin cells).
spermatogonia (singular: spermatogonium) - Primitive male germ cells; precursors to sperm cells.
spider cell - A type of neuroglial cell in the central nervous system that helps support other nerve cells. Also referred to as an astrocyte.
spinal cord - The major pathway for information traveling between the brain and the skin, muscles, and joints of the body.
Spinobulbar muscular atrophy (SBMA) - A C-A-G trinucleotide repeat disorder that occurs predominantly in males in which weakness and atrophy of the proximal muscles occurs. For more information, click here.
spinocerebellar ataxias (SCAs) - A family of disorders involving variable degeneration of the cerebellum, spinal cord, and brain stem. Symptoms such as loss of coordination and difficulty articulating speech are common to all SCAs. There are 7 SCAs described on the HOPES site: SCAs 1, 2, 3, 6, 7, 8, and 12.
sporadic - Occurring in a random or isolated manner.
ST14A cell line - Cells that exhibit quite accurately many of the properties of striatal nerve cells and can be engineered to express either normal or mutant huntingtin.
stem cells - Cells that have the ability to divide for an indefinite time and to give rise to specialized cells.
stereotactic lesions - highly specific damage done to a part of the brain
sterol regulatory element-binding proteins (SREBPs) - Sterol regulatory element-binding proteins; proteins involved in regulating cholesterol biosynthesis.
stimulus - Something causing a response; something in the environment detected by a receptor. Ex: a chemical that causes a nerve impulse.
stress - The effects of psychosocial and environmental factors on physical and mental well-being.
stress response - A set of nerve cell and endocrine responses that are elicited in response to a stressor to help restore homeostasis.
stressor - Any agent that causes stress to an organism.
striatal nerve cells - see striatal neurons.
striatal neurons - Nerve cells that make up the striatum. See striatum.
striatonigral pathway - pathway of cell communication from the striatum to the substantia nigra and back
striatum - Term that refers to the part of the brain consisting of both the caudate and the putamen. Also referred to as the corpus striatum.
stroke - Occurs when brain cells die because of inadequate blood flow to the brain.
stromal cells - Bone marrow cells that can be the source of other kinds of tissues.
suberoylanilide hydroxamic acid (SAHA) - An HDAC inhibitor.
substance P - a kind of neurotransmitter, known as a neuropeptide, which serves in particular regions of the brain
substantia nigra - A group of nerve cells at the base of the midbrain that receives input from a number of nerve cells. Some scientists consider the substantia nigra to be a part of the basal ganglia.
substrate - A molecule that an enzyme binds and acts upon.
subthalamic nuclei / subthalamic nucleus - A group of nerve cells that receives input from the caudate and putamen and participates in the modulation of motor control.
sugar - One of the molecular components of a nucleotide; sugars are a class of molecules made up of carbon, oxygen, and hydrogen arranged in a ringed structure.
suicide ideation - Thoughts about fatally harming one's self
SUMO-1 - A protein that is responsible for making the mutated huntingtin protein significantly more toxic to nerve cells in the brain.
superoxide [An unstable molecule that is very reactive and has the potential to do damage to nerve cells; O 2 - is a common one.
superoxide anion - A type of free radical.
sympathetic nervous system - A subdivision of the body's nervous system that is automatic (not consciously controlled) and is involved in preparing the body for physical activity.
symptoms - Changes in the body or its functions, experienced by the patient and indicative of disease.
synapse [The narrow gap between the end of one neuron and the beginning of another where neurotransmitters are passed. Very important for communication between neurons - "subserves the transmission of nerve impulses."

T

target site - A specific sequence of amino acids in a protein that serve as the point at which the protein interacts with other specific proteins.
tau pathologies - neurodegenerative diseases related to problems with the tau protein found in nerve cells. Tau pathologies include Alzheimer's disease and myotonic dystrophy, among others.
tauroursodeoxycholic acid (TUDCA) - An acid found in large quantities in bear bile and small amounts in human bile. It helps in preventing programmed cell death, possibly by protecting mitochondria.
temporal lobe - A part of the brain associated with memory, hearing, and perception.
teratogenic - A substance that disturbs the development of the embryo or fetus
tertile - This term is often used in explaining the distribution of scores on a test. A tertile is one-third of the total number of scores. For instance, the highest tertile is the one-third of scores that have the highest scores on the test.
terpenoids - A constituent of Ginkgo biloba extract that includes the ginkgolides and the bilobalides.
testosterone - A steroid hormone produced primarily in the testes and responsible for the development and maintenance of male secondary sex characteristics. It is also produced synthetically for use in medical treatment.
tetrabenazine (TBZ) - A dopamine depletor used to treat chorea.
Tetracycline - an antibiotic drug that is used for medicine and for research. In some cases it can serve to regulate the production of certain proteins in the cell, by starting or stopping transcription for a certain target gene
TFC - See total functional capacity.
TGase - An abbreviation for transglutaminase.
thalamus - A collection of nerve cells in the brain. Although it performs many functions, the primary role of the thalamus is to relay sensory information from other parts of the brain to the cerebral cortex.
thivoflavine S - A compound that is believed to both decrease the presence of beta-amyloid fibrils, and decrease huntingtin protein aggregation.
thivoflavine T - A compound that is believed to decrease the presence of beta-amyloid fibrils, but has little or no success in inhibiting huntingtin protein aggregation.
thymine - One of the four nitrogenous bases found in DNA; pairs with the base adenine; often abbreviated as the letter "T"; see Figure B-3.
thymus gland - The thymus gland lies at the root of the neck behind the breastbone. It grows from birth to puberty and then starts to diminish in size but remains active. Its main function is the formation of T-lymphocytes which are an essential part of the immune system.
thyroid gland - A small organ located near the neck that produces several hormones.
Tibetan Buddhism - A branch of Buddhism, which traveled to Tibet from India sometime after Buddhism had traveled to eastern China from India. This resulted in some additional sophisticated techniques for understanding ultimate truth.
tissue culture - A technique used to grow body tissue outside the body on a culture medium.
tolerability - The potential of a drug to be endured. A drug with good tolerability produces few side effects in the subject.
tonic-clonic - Seizures that involve both tonic and clonic phases. During the tonic phase the body is rigid, but during the clonic phase the individual often suffers from rhythmic jerking movements. When tonic-clonic seizures are generalized, they are referred to as grand mal seizures.
total functional capacity (TFC) - A standardized scale used to assess capacity to work, handle finances, perform domestic chores and self-care tasks, and live independently. The TFC scale ranges from 13 (normal) to 0 (severe disability).
total homocysteine (tHcy) - The sum of all forms of homocysteine, usually measured from blood plasma.
totipotent - The ability to give rise to all cell types (including the placenta, other supporting tissues, and the body of the organism itself); having unlimited capability.
toxic soluble oligomers - Small, harmful molecules believed to trigger cell damage in HD and related diseases.
trachea - (a.k.a. the "windpipe") the main trunk of the system of tubes by which air passes between the mouth and the lungs.
trait - A physical characteristic brought about by the expression of a gene or many genes. Examples of traits are height, eye color, and the ability to roll your tongue. Variations in these characteristics are dependent upon the particular alleles an individual has for the genes determining the trait.
trans fat - A highly damaging type of fat which is produced when unsaturated fat is subjected to the process of hydrogenation.
trans-sulfuration pathway - A two-reaction pathway which degrades homocysteine.
transcribe - To undergo transcription. In order for the DNA code of a gene to result in the production of a specific protein, the gene must first be transcribed.
transcript - A sequence of RNA produced by transcription from a DNA template.
transcription - One part of the process that uses the DNA code to make a protein.
transcription factor - A protein that aids in transcription.
transcriptional dysregulation - A disease mechanism that disrupts the expression of certain genes, which affects when essential proteins are produced by the cell. Transcriptional dysregulation plays a major role in HD.
transfer RNA (tRNA) - An important player in the translation of mRNA to protein; it binds to a specific mRNA codon on one end and a specific amino acid on the other end.
transgene - A foreign piece of DNA that has been inserted into the germ line of an organism. Since germ cells give rise to the reproductive cells, an organism that contains a transgene will pass it down to all of its descendents. An organism that contains a transgene is known as "transgenic."
transgenic - An organism that has had DNA from another organism introduced into it. For example, if jellyfish DNA is introduced into a mouse, the mouse is then called a transgenic mouse. Transgenic animals are generated by introducing the outside DNA into the developing embryo and then implanting the embryo into a host mother until the animal is born.
transglutaminase - An enzyme that helps produce huntingtin protein aggregates.
translation - The process by which the protein molecule is formed from the mRNA blueprint.
transmissible spongiform encephalopathy (TSE) - A family of human and animal diseases characterized by spongy deterioration of the brain with severe and fatal neurological symptoms.
transposable element - Segment of DNA that can move around within a chromosome or between chromosomes in the same cell. Can also be called a transposon.
trehalose - A disaccharide made out of two glucose molecules that has been shown to stabilize proteins. Trehalose is used as a sweetener and preservative, and can be found in foods such as lobster, shrimp, honey, and mushrooms.
tremor - A quivering, involuntary movement of a part or parts of the body.
triglyceride - A fat-like substance found in the blood.
trimer - A molecule that is made of three monomers bound together.
trinucleotide repeat - Another term for triplet repeat.
trinucleotide repeat disorder - An illness in which there is an abnormally large number of repeats of a specific codon of DNA. In addition to Huntington's disease, other trinucleotide repeat disorders include fragile X syndrome and spinobulbar muscular atrophy. In HD, the repeated codon is C-A-G, which codes for the amino acid glutamine.
triplet repeat - A three letter sequence of bases (codon) that is repeated consecutively in a section of DNA. In HD, the repeated sequence is C-A-G. Also referred to as a trinucleotide repeat or a codon repeat.
tryptophan - One of the amino acids found in our bodies. It can be converted into niacin.
tryptophan hydroxylase (TPH) - The rate-limiting enzyme in the synthesis of serotonin. It is very susceptible to free radical damage.
tumor - An abnormal mass of tissue that is not inflammatory, possesses no real function, and is the result of uncontrolled cell growth.
tumor suppressor - A protein that inhibits the uncontrolled cell growth that leads to formation of tumors.

U

ubiquinone - Another term for coenzyme Q10.
ubiquitin - A small molecule that latches onto damaged or mutated proteins in the cell. Ubiquitin acts as a flag indicating that these proteins can be destroyed by proteasomes.
ubiquitin-proteasome system (UPS) - A cellular quality control system that tags misfolded proteins for refolding or degradation.
UHDRS - The Unified Huntington's Disease Rating Scale, used to provide uniform assessment of the clinical features and progression of HD.
unequal crossing over - During meiosis, when the crossing over that takes place between homologous chromosomes is unequal. Instead of entire alleles switching places, only parts of each allele will switch, and these parts are usually unequal in length.
unequal crossing over model - A possible model for how repeat expansions occur. Since unequal crossing over can result in chromosomes that differ from their original lengths, this model suggests that unequal crossing over is the cause of extended repeat regions.
unsaturated fat - A type of fat found mainly in vegetable oils which, due to its chemical structure, tends to reduce levels of cholesterol and improve cell membrane function.
upregulation - A process that increases the responsiveness of a cell by increasing the number of receptors on the cell membrane.
UPS - Abbreviation for ubiquitin-proteasome system.
uracil - One of the four nitrogenous bases found in RNA; often abbreviated as the letter “U.” It pairs with the base adenine.
uterus - The female reproductive organ where the fertilized egg implants and the growing embryo is nourished.

V

validation [To validate a protein as a biological target it must be proven that the potential target is relevant to the disease and that it is drugable - that is, can it be targeted and that its function can be changed by treatment with a drug
vascular - Pertaining to or made up of blood vessels.
vasodilation - The stretching and shrinking of blood vessels as blood is pumped by the heart.
vector - A method for delivering gene therapy. Modified viruses are common vectors for transmitting genetic material.
ventral horn - Another term for anterior horn.
ventricles - Openings in the brain that are common to all humans. In people with HD, the ventricles may become enlarged due to the decay of neurons in the surrounding area. A picture of some enlarged ventricles can be seen in Figure D-2 (the ventricles are called "openings" in this figure)
vertebrate - An animal whose nerve cord is surrounded by a backbone. The main groups of vertebrate animals are the fishes, amphibians, reptiles, birds, and mammals.
vesicles - Vesicles are created when part of the cell membrane pinches off and surrounds some kind of cellular product in an enclosed compartment. Vesicles store, transport, or digest cellular products and wastes.
virus - An intracellular parasite that depends on the host cell machinery to manufacture copies of itself. Viruses are not living organisms.
visual cortex - The part of the cerebral cortex that processes visual information. The visual cortex is where we actually see the images before our eyes.
vitamin A - A lipid-soluble vitamin with antioxidant properties that may also play an important role in learning and memory.
vitamin B3 - Another term for nicotinamide.
vitamin B11 - Another name for folic acid.
vitamin C - A vitamin with antioxidant properties that may help protect nerve cells from free radical damage and glutamate toxicity. Also known as ascorbic acid.
vitamin D - A hormone, synthesized from cholesterol, which promotes the uptake of calcium.
vitamin E - A lipid-soluble antioxidant that protects cell membranes and other lipid cell components from free radical damage.
voltage - A force caused by a difference in electric charge between two areas.

W

warfarin - A drug taken by mouth to prevent blood clotting. Studies have shown that taking warfarin in combination with aspirin could lead to excessive bleeding.
water-soluble - Capable of being dissolved in water.
wet lab - Refers to experiments performed at the lab bench.
white blood cells - Cells that circulate in the blood and lymphatic system and congregate in the lymph glands and spleen. (The lymphatic system consists of the tissues and organs, including the bone marrow, spleen, thymus, and lymph nodes that produce and store cells that fight infection and the network of vessels that carry a fluid called lymph). White blood cells are part of the immune system and are responsible for both directly and indirectly attacking foreign invaders of the body.
white matter - The matter in the brain underlying the gray matter which contains a large number of nerve fibers.
wild-type - The typical form of an organism or gene as it occurs in nature, as distinguished from mutant forms that may result from selective breeding or disease.

X

X chromosome - One of the two sex chromosomes (the other is the Y chromosome). Males have one X and one Y. Females have two X’s.

Y

Y chromosome - One of the two sex chromosomes (the other is the X chromosome). Males have one X and one Y. Females have two X’s.

Z

ZGE - A Chinese Ginkgo biloba extract.
zygote - The first cell created after an egg is fertilized by a sperm.

Research

HD Glossary