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November 02, 2003
The HD Gene and Its Product
Although scientists know that certain brain cells die in HD, the cause of their death is still unknown. Recessive diseases are usually thought to result from a gene that fails to produce adequate amounts of a substance essential to normal function. This is known as a loss-of-function gene. Some dominantly inherited disorders, such as HD, are thought to involve a gene that actively interferes with the normal function of the cell. This is known as a gain-of-function gene.
How does the defective HD gene cause harm? The HD gene encodes a protein—which has been named huntingtin—the function of which is as yet unknown. The repeated CAG sequence in the gene causes an abnormal form of huntingtin to be made, in which the amino acid glutamine is repeated. It is the presence of this abnormal form, and not the absence of the normal form, that causes harm in HD. This explains why the disease is dominant and why two copies of the defective gene—one from both the mother and the father—do not cause a more serious case than inheritance from only one parent. With the HD gene isolated, NINDS-supported investigators are now turning their attention toward discovering the normal function of huntingtin and how the altered form causes harm. Scientists hope to reproduce, study, and correct these changes in animal models of the disease.
Huntingtin is found everywhere in the body but only outside the cell's nucleus. Mice called "knockout mice" are bred in the laboratory to produce no huntingtin; they fail to develop past a very early embryo stage and quickly die. Huntingtin, scientists now know, is necessary for life. Investigators hope to learn why the abnormal version of the protein damages only certain parts of the brain. One theory is that cells in these parts of the brain may be supersensitive to this abnormal protein.
Prepared by:
Office of Communications and Public Liaison
National Institute of Neurological Disorders and Stroke
National Institutes of Health
Bethesda, MD 20892
NINDS health-related material is provided for information purposes only and does not necessarily represent endorsement by or an official position of the National Institute of Neurological Disorders and Stroke or any other Federal agency. Advice on the treatment or care of an individual patient should be obtained through consultation with a physician who has examined that patient or is familiar with that patient's medical history.
All NINDS-prepared information is in the public domain and may be freely copied. Credit to the NINDS or the NIH is appreciated.
Reviewed July 1, 2001
Posted by Dave at November 2, 2003 10:59 AM
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