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November 02, 2003

Huntington's Disease Glossary

akinesia-decreased body movements.

at-risk -a description of a person whose mother or father has HD or has inherited the HD gene and who therefore has a 50-50 chance of inheriting the disorder.

autosomal dominant disorder -a non-sex-linked disorder that can be inherited even if only one parent passes on the defective gene.

basal ganglia -a region located at the base of the brain composed of four clusters of neurons, or nerve cells. This area is responsible for body movement and coordination. The neuron groups most prominently and consistently affected by HD—the pallidum and striatum—are located here. See neuron, pallidum, striatum.

caudate nuclei -part of the striatum in the basal ganglia. See basal ganglia, striatum.

chorea -uncontrolled body movements. Chorea is derived from the Greek word for dance.

chromosomes -the structures in cells that contain genes. They are composed of deoxyribonucleic acid (DNA) and proteins and, under a microscope, appear as rod-like structures. See deoxyribonucleic acid (DNA), gene.

computed tomography (CT)- a technique used for diagnosing brain disorders. CT uses a computer to produce a high-quality image of brain structures. These images are called CT scans.

cortex -part of the brain responsible for thought, perception, and memory. HD affects the basal ganglia and cortex. See basal ganglia.

deoxyribonucleic acid (DNA)- the substance of heredity containing the genetic information necessary for cells to divide and produce proteins. DNA carries the code for every inherited characteristic of an organism. See gene.

dominant -a trait that is apparent even when the gene for that disorder is inherited from only one parent. See autosomal dominant disorder, recessive, gene.

gene -the basic unit of heredity, composed of a segment of DNA containing the code for a specific trait. See deoxyribonucleic acid (DNA).

huntingtin -the protein encoded by the gene that carries the HD defect. The repeated CAG sequence in the gene causes an abnormal form of huntingtin to be formed. The function of the normal form of huntingtin is not yet known.

kindred -a group of related persons, such as a family or clan.

magnetic resonance imaging (MRI) -an imaging technique that uses radiowaves, magnetic fields, and computer analysis to create a picture of body tissues and structures.

marker -a piece of DNA that lies on the chromosome so close to a gene that the two are inherited together. Like a signpost, markers are used during genetic testing and research to locate the nearby presence of a gene. See chromosome, deoxyribonucleic acid (DNA).

mitochondria -microscopic, energy-producing bodies within cells that are the cells' "power plants."

mutation -in genetics, any defect in a gene. See gene.

myoclonus -a condition in which muscles or portions of muscles contract involuntarily in a jerky fashion.

neuron -Greek word for a nerve cell, the basic impulse-conducting unit of the nervous system. Nerve cells communicate with other cells through an electrochemical process called neurotransmission.

neurotransmitters -special chemicals that transmit nerve impulses from one cell to another.

pallidum -part of the basal ganglia of the brain. The pallidum is composed of the globus pallidus and the ventral pallidum. See basal ganglia.

positron emission tomography (PET)- a tool used to diagnose brain functions and disorders. PET produces three-dimensional, colored images of chemicals or substances functioning within the body. These images are called PET scans. PET shows brain function, in contrast to CT or MRI, which show brain structure.

prevalence -the number of cases of a disease that are present in a particular population at a given time.

putamen -an area of the brain that decreases in size as a result of the damage produced by HD.

receptor -proteins that serve as recognition sites on cells and cause a response in the body when stimulated by chemicals called neurotransmitters. They act as on-and-off switches for the next nerve cell. See neuron, neurotransmitters.

recessive -a trait that is apparent only when the gene or genes for it are inherited from both parents. See dominant, gene.

senile chorea -a relatively mild and rare disorder found in elderly adults and characterized by choreic movements. It is believed by some scientists to be caused by a different gene mutation than that causing HD.

striatum -part of the basal ganglia of the brain. The striatum is composed of the caudate nucleus, putamen, and ventral striatum. See basal ganglia, caudate nuclei.

trait -any genetically determined characteristic. See dominant, gene, recessive.

transgenic mice-mice that receive injections of foreign genes during the embryonic stage of development. Their cells then follow the "instructions" of the foreign genes, resulting in the development of a certain trait or characteristic. Transgenic mice can serve as an animal model of a certain disease, telling researchers how genes work in specific cells.

ventricles -cavities within the brain that are filled with cerebrospinal fluid. In HD, tissue loss causes enlargement of the ventricles.

Posted by Dave at November 2, 2003 10:48 AM

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