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.

 

 

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.