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The Huntington's disease (HD) gene has been mapped to chromosome 4p16.3. The disease is inherited in an autosomal dominant manner.
A gene, IT15, contains a polymorphic trinucleotide repeat that is expanded and unstable on HD chromosomes.
The (CAG)n repeat is found within the coding sequence of a previously unknown, but widely-expressed, gene.
The larger the number of CAG repeats, the earlier the likely onset of HD:
Early-onset HD is associated with paternal inheritance of the HD gene. It may be that the trinucleotide repeats are more prone to expansion during spermatogenesis than oogenesis.
The trinucleotide expansion which causes Huntington's disease can be detected. This test is used in two main contexts:
In common with other autosomal dominant conditions there is a 50% chance that the child of a patient with Huntington's disease will inherit the gene.