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Alpha 1-antitrypsin deficiency
Autism and Aspergers Syndrome
Benign Infantile Epilepsy
Cri du chat
Duchenne Muscular Dystrophy
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by Dallas and Kyle
Nature of the Genetic Difficulty
HD is a familial disease, passed from parent to child through a mutation in the normal gene. Each child of an HD parent has a 50-50 chance of inheriting the HD gene. If a child does not inherit the HD gene, he or she will not develop the disease and cannot pass it onto coming generations.
A genetic test, coupled with a complete medical history and neurological and laboratory tests, helps physicians diagnose HD. Presymptomic testing is available for individuals who are at risk for carrying the HD gene. In 1 to 3 percent of individuals with HD, no family history of HD can be found.
Huntington's disease is autosomal dominant, this means the gene involved is on an autosomal chromosome (not one of the sex chromosomes) and recently has been localized on the fourth autosomal chromosome pair (the #4 chromosome). In affected individuals, one gene of this gene pair (the HD gene) is not functioning correctly and expresses itself more strongly, or 'dominates', the other working gene. Since it is not on one of the sex chromosomes, it can affect both males and females. Males and females have the same chance of having affected children.
Each gene has its own unique sequence of base pairs. In Huntington's disease, the DNA segment, CAG (cytosine-adenine-guanine), is part of this sequence. This sequence may be duplicated many times in individuals; up to 26 times in the general population. The duplication of this segment is called a "trinucleotide repeat" in which these three nucleotides (CAG) are repeated over and over again. Individuals with Huntington's disease may have anywhere from 40 to over 100 repeated CAG segments.
It is not known how this repeated sequence causes Huntington's disease, but research to develop therapies to treat Huntington's disease is ongoing.
Basic Facts of Disease
Huntington's disease (HD) results from the genetically programmed degeneration of neurons in certain areas of the brain. This progressive degeneration causes lack of motor control, loss of memory and mental capacity, and personality changes in addition to emotional disturbance (i.e. depression and hyperactivity).
Some early symptoms of HD are mood swings, depression, irritability or trouble driving, inefficiency in learning new things, ability in remembering random facts with no memory or relevance to their importance, or indecisiveness. As the disease progresses, concentration on intellectual tasks becomes increasingly difficult. Finally, the most important and habitual tasks become difficult, first memory, then eating, then bowel control, and lastly, breathing.
But perhaps the most interesting thing about Huntington's Disease is the fact that it is a developing genetic disorder rather than one that can be pointed out at birth. Huntington's disease is a genetic disorder that reveals itself during middle age - there is no way to detect it before it hits. The only clues towards the development of HD is if the parents had it (as stated earlier) and if so, there is a 50/50 chance that you will have it, and again a 50/50 chance that you will pass it on.
Is there any treatment? Physicians prescribe a number of medications to help control emotional and movement problems associated with HD. In August 2008, the U.S. Food and Drug Administration approved tetrabenazine to treat Huntington’s involuntary muscle spasms, making it the first drug approved for use in the United States to treat the disease. Most drugs used to treat the symptoms of HD have side effects such as fatigue, restlessness, or hyperexcitability. It is extremely important for people with HD to maintain physical fitness as much as possible, as individuals who exercise and keep active tend to do better than those who do not.
At this time, there is no way to stop or reverse the course of HD. Now that the HD gene has been located, investigators are continuing to study the HD gene with an eye toward understanding how it causes disease in the human body.
Huntington's Disease Info
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