Recent advances in understanding the pathogenesis of Huntington's disease.

Huntington's disease (HD) is an autosomal, dominantly inherited neurodegenerative disorder that is characterized by abnormal involuntary movements (chorea), intellectual impairment and selective neuronal loss. The expansion of a polymorphic trinucleotide repeat (the sequence CAG that codes for glutamine) to a length that exceeds 40 repeat units in exon 1 of the gene, HD, correlates with the onset and progression of the disease. The protein encoded by HD, huntingtin, is normally localized in the cytoplasm, whereas the mutant protein is also found in the nucleus, suggesting that its translocation to this site is important for the pathogenesis of HD. Although several proteins that interact with huntingtin have been identified in vitro, the significance of these interactions with the mutant protein in the pathogenesis of HD has yet to be determined. Recent progress in the development of cellular and animal models for the disease have provided invaluable insights and resources for studying the disease mechanisms underlying HD, and will be useful for screening and evaluating possible therapeutic strategies.