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.

 

 

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