Huntington's Disease Society of America

HD Glossary

Note: Some words can have differing definitions depending on the context in which they are used. The definitions presented here are the ones that best apply to the words as they are used. HDSA is grateful to the Stanford Hopes website for their contribution and maintenance of this glossary.

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.

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.

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. 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.

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.

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.

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.

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.

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.