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.

 

 

N
  • NAD - Nicotinamide adenosine dinucleotide; an electron carrier involved in cellular metabolism. It accepts and donates electrons to various enzymes involved in metabolism, ultimately providing the cell with energy.
  • N-terminus - The end of the amino acid chain that makes up a protein that is terminated by an amino group (-NH2).
  • negative feedback - A mechanism in the body for maintaining a state of internal constancy, or homeostasis; effectors are activated by changes in the internal environment, and the actions of the effectors serve to counteract these changes and maintain a state of balance.
  • negative regulator - One molecule that controls the effects of another (or itself) by repressing or inactivating it.
  • neocortex - Part of the cerebral cortex; constitutes about 85% of the human brain’s total mass. The neocortex is thought to be responsible for higher level cognitive functions, such as language, learning, memory, and complex thought. Also referred to as the isocortex.
  • nerve cell - One of the major classes of cells in the nervous system. They are the fundamental signaling units of the nervous system. They are unique from other cells in that they have the ability to communicate rapidly with one another over great distances and with great precision. Also referred to as a neuron.
  • nerve cell body - The largest part of a cell, the cell body holds all of the general parts of a cell as well as the nucleus, which is the control center. The nucleus contains the cell's genetic material (DNA, located in the chromosomes). The cell body also contains many other unique structures responsible for making energy and getting rid of cellular wastes. Also referred to as the soma.
  • nervous system - A regulatory system of the body that consists of neurons and neuroglial cells. The nervous system is divided into two parts, the central nervous system (CNS) and the peripheral nervous system (PNS).
  • neural connections - Connections between neurons. Neurons send information via neurotransmitters.
  • neurochemicals - Chemicals in the brain.
  • neuroD (ND) - A transcription factor important in neuronal development.
  • neurodegenerative - Characterized by neurodegeneration. Neurodegenerative diseases include HD, Alzheimer’s, Parkinson’s and many more.
  • neurodegeneration - The deterioration or loss of function of nerve cells.
  • neurogenesis - Formation of the nervous system; neurons are produced.
  • neuroglia - The supporting tissue of the nervous system; made up of neuroglial cells. Astrocytes (spider cells) are a type of neuroglial cell. Also referred to as glia.
  • neurological - Having to do with the nervous system and/or nerve cells.
  • neurologist - A specialist in the diagnosis and treatment of disorders of the nervous system.
  • neuron - Another term for nerve cell.
  • neuronal - Of or pertaining to the neurons.
  • neuronal ceroid lipofuscinoses (NCLs) - A group of rare, inherited degenerative disorders of the nervous system; associated with the accumulation of an abnormal pigment in the brain called lipofuscin. These disorders can have severe diseases including blindness, mental retardation, and early death.
  • neuronal inclusions (NI) - Clumps of protein formed by aggregation of mutant proteins. These mutant proteins have abnormally expanded polyglutamine tracts in hereditary tri-nucleotide repeat disorders. Also referred to as neuronal intranuclear inclusions, nuclear inclusions, or inclusion bodies.
  • neuronal intranuclear inclusions - Another term for neuronal inclusions.
  • neuropathy [A group of symptoms caused by abnormalities in motor or sensory nerve cells. Symptoms include tingling or numbness in hands or feet followed by gradual, progressive muscular weakness. oxidative damage - Another term for oxidative stress.
  • neuroplasticity - The brain's natural ability to form new connections in order to compensate for injury or changes in the environment. The ability of the brain to reorganize pathways between neurons as a result of new experiences.
  • neuroprogenitor cells - Undifferentiated cells capable of giving rise to nerve cells and glia in the central nervous system.
  • neuroprotectant drugs - Drugs that prevent harmful calcium ions from destroying the m\itochondria of the nerve cells, which leads to cell death. An example of a neuroprotectant drug is Cyclosporin A.
  • neuroprotection - A process that involves protecting the nerve cells from deterioration due to neurodegenerative disease.
  • neuroprotective - The property of preventing damage and degeneration to nerve cells.
  • neuropsychiatrist - A physician who treats people with psychiatric symptoms that are caused by a brain disorder. For more information, click here.
  • neurotoxic - A substance that damages or destroys nerve tissue.
  • neurotransmitter - A chemical messenger produced in and released by one neuron. A neurotransmitter can excite or inhibit another neuron.
  • neurotrophic factor - A protein in the nervous system that promotes the growth of nerve cells.
  • new indication studies - New phase II and III trials required when a drug seems promising as a new treatment for a different condition than it was originally approved for.
  • NF-kappa B (NF-KB) - A transcription factor that enhances the production of inflammatory mediators. Association with the GR complex inhibits the transcription of COX-2 genes.
  • NF-kB - Abbreviation for NF-kappa B.
  • NI - Abbreviation for neuronal inclusions.
  • niacin - A precursor of nicotinamide. Nicotinamide is the biologically active form of nicotinic acid. Also known as nicotinic acid.
  • nicotinamide - A drug that may help improve cellular energy production by acting as a precursor of NAD. Also known as Vitamin B3.
  • nicotinic acid - Also known as niacin.
  • nitric acid - A chemical that increases blood flow; also used to make organic compounds in the body.
  • nitric oxide (NO) - A gas where each molecule is made of one nitrogen atom and one oxygen atom; it is found in many brain and body tissues, and plays a part in many bodily functions.
  • nitric oxide synthase - a family of enzymes responsible for the synthesis of nitric oxide (NO). NO can become mutated in some neurodegenerative disorders like Alzheimer’s, causing oxidative stress and neurodegeneration.
  • nitrogenous base - One of the molecular components of a nucleotide; a class of ringed molecules with carbon, oxygen, hydrogen, and nitrogen.
  • NMDA receptor - One type of receptor that binds glutamate. It is selectively activated by the drug NMDA (N-methyl-D-aspartate).
  • non-coding region - A segment of DNA that does not comprise a gene and thus does not code for a protein. Non-coding regions are interspersed throughout DNA.
  • non-competitive inhibitor - An antagonist that inhibits the binding of a neurotransmitter (or hormone) by changing the shape of its receptor. In this way, the receptor will no longer "recognize" the neurotransmitter (or hormone).
  • nondisjunction - An event that can occur during meiosis in which chromosomes fail to separate properly, resulting in daughter cells with too many or too few chromosomes.
  • non-hd allele - A version of the Huntington gene that contains a normal number of CAG repeats and codes for the normally functioning form of the huntingtin protein. Individuals with the non-HD allele will not develop Huntington’s Disease, and they will not pass the disease on to their children. This allele is sometimes called the "normal Huntington allele." See Table A-1.
  • nonpolar - a nonpolar molecule does not have a separation of positive and negative electric charges within the molecule. Nonpolar molecules are pushed towards one another by polar molecules. For example, nonpolar compounds, like oil, can’t dissolve in water because of the water's polarity.
  • non-refined - refers to breads and cereals in which the whole grain (including its bran and germ) are included in the food product. Non-refined breads and cereals (such as whole wheat bread and oatmeal) are healthier than refined products because the fiber is beneficial.
  • non-specific - A type of response that is not specific to any particular body organ or location. Rather, the response occurs throughout the body.
  • nonsteroidal anti-inflammatory drugs (NSAIDs) - Compounds that significantly reduce the inflammatory response by interfering with the cyclooxygenase pathway, reducing the level of compounds that mediate inflammation.
  • normal huntingtin - See huntingtin protein
  • noradrenaline - A molecule that acts both as a neurotransmitter and hormone and works to increase heart rate, blood pressure, and blood sugar levels in times of physical or mental stress. Also known as norepinephrine.
  • norepinephrine - A molecule that acts as a neurotransmitter and as a hormone to increase heart rate, blood pressure, and blood sugar levels in times of physical or mental stress. Also known as noradrenaline.
  • NSAIDs - Abbreviation for nonsteroidal anti-inflammatory drugs.
  • NRSE (nerve cell restrictive silencer element) - A molecule that silences the BDNF promoter and thus leads to decreased levels of BDNF in the brain.
  • nuclear envelope - The double layered membrane in the cell that surrounds and contains the nucleus, which holds the cell’s DNA.
  • nuclear inclusions - Another term for neuronal inclusions.
  • nuclear membrane - Separates the nucleus from the cytoplasm of the cell. It is similar to the cell membrane in that it is selectively permeable.
  • nuclei - Plural form of nucleus.
  • nucleosome - A structure composed of histones that aids in the coiling up of DNA into compact chromosomes. It can be thought of as a spool that winds up the DNA "thread."
  • nucleotide - The molecular subunit that makes up DNA; consists of a sugar, phosphate group, and nitrogenous base; see Figure B-2. A molecule of DNA is made up of a long chain of nucleotides.
  • nucleus - 1. A spherical body within the cell that is enclosed by a double membrane. The nucleus contains the chromosomes and is the information center of the cell. 2. A collection of nerve cells in the brain that are anatomically discrete and which typically serve a particular function. (Plural form: nuclei.)