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.



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