The science and practice of testing for Huntington's disease
How is genetic testing for HD possible?
In 1983, a team of scientists located the first genetic marker for Huntington’s disease, indicating the approximate location of the Huntington gene on chromosome 4. This discovery led to the development of the first pre-symptomatic genetic test for HD, which traced the inheritance of markers linked to the Huntington gene. This original test procedure required blood samples from several family members and was not widely available or informative in all cases.
In 1993, the Huntington’s Disease Collaborative Research Group isolated the Huntington gene and identified the hereditary version of this gene that causes HD. They discovered that in all people, the three-letter codon sequence C-A-G is repeated several times at one end of the Huntington gene. In people with HD, the Huntington gene contains an increased number of CAG repeats. Thus, there are different versions, or alleles, of the Huntington gene. (Within this website, any allele within the normal range of CAG repeats is referred to as a “non-HD allele,” and any allele with extra CAG repeats is described as an “HD allele.”) The HD allele produces a longer than usual huntingtin protein, which in turn leads to HD. (For more information about the Huntington gene and altered huntingtin protein, click here.)
The discovery of the genetic variant that is responsible for HD allowed for the development of a highly accurate direct gene test for HD that is the subject of this chapter.
Last Modified: 9-16-02
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