Huntington disease (HD) is an autosomal dominant progressive neurodegenerative disorder characterized by involuntary movements, especially chorea; frank dementia; behavioral and psychiatric disturbances; and functional disability. It is caused by an unstable expanded CAG trinucleotide repeat in exon 1 on the huntingtin gene (
HD [OMIM 143100) on the tip of the short arm of chromosome 4.
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