[Huntington's disease--advances in gene mapping].

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor disturbance, cognitive loss, and psychiatric manifestations. It is inherited in an autosomal dominant fashion. The genetic defect causing HD was assigned to chromosome 4 in 1983 using polymorphic DNA markers in humans. Thereafter, a location cloning approach was pursued to isolate and characterize the HD gene. Recently, the Huntington's disease collaborative research group has isolated a new gene, IT 15, in 4p 16.3. IT 15 contains a polymorphic trinucleotide repeat that is expanded and unstable on HD chromosomes. A (CAG)n repeat longer than the normal range was observed on HD chromosomes from disease families. The (CAG)n repeat appears to be located within the coding sequence of a predicted 348 kd protein that is unrelated to any known gene.