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.

 

 

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