Huntington’s disease (HD) is an inherited brain disorder named for Dr. George Huntington, who first described this disorder in 1872. HD is now recognized as one of the more common genetic disorders. HD currently affects 30,000 Americans, and nearly 250,000 more are at risk for this disease. At present, there is no known cure.
This disorder was traditionally known as Huntington’s chorea (after the Greek word for dance) because of the involuntary movements associated with HD. The gene that causes HD is known to code for a specific protein called huntingtin. Mutant huntingtin is thought to be more resistant to destruction than normal huntingtin, which leads to toxic buildup and cell death. The HD gene is located on the tip of the short arm of chromosome 4 and was isolated in 1993 by the Huntington’s Disease Collaborative Research Group. The discovery of this gene led to the development of a genetic test that can accurately determine whether a person will develop HD. However, there is as yet no test that can predict when symptoms will begin.
The gene causing HD is dominant, meaning that only one copy of the Huntington’s gene is necessary to develop the disease. Each parent who possesses one HD gene has a 50% risk for passing on the gene to each of their children. Everyone who carries the gene will develop the disease eventually, and it appears most frequently after age 30. These symptoms rarely appear in infants, but children who do develop the juvenile form of the disease rarely live to adulthood. Death usually occurs 15 to 20 years after onset of the disease.
Early symptoms appear as slight physical, cognitive, and emotional changes. Physical changes can include nervous behavior, clumsiness, alterations of handwriting, and difficulty with normal skills such as driving. Cognitive changes can involve problems with organization and dealing with novel situations, short-term memory loss, and impairments in decision making and attention to detail. Emotional changes can include periods of depression, apathy, irritability, and impulsiveness and changes in personality. In some cases, a person may become delusional or paranoid. At-risk individuals should not worry about the occasional appearance of some of these symptoms because these incidents happen to everyone and do not necessarily indicate the onset of the disease. The person dies, not from the disease itself, but from complications such as pneumonia, heart failure, choking, or infections developing from the weakened condition of the body.
The symptoms of HD are associated with atrophy of the caudate nucleus, particularly the head of the caudate. Reduced metabolism and blood flow have been observed in the caudate nuclei of HD patients using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) as well as other methods. This reduction has been found to precede caudate nucleus atrophy. There is no known cure for HD, but a number of treatments have been proposed. Drugs antagonistic to dopamine D2 receptors reduce the chorea of early HD, and some experimental treatments may help to decrease the aggregation of the huntingtin protein.
In summary, HD is a fatal genetic disorder due to mutation of a specific gene and currently has no cure.
Research is progressing to identify the exact mechanism of cell death and methods to stop it, with the hope that one day this disease may be conquered.
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