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[Huntington's chorea: clinical aspects, genetics and current diagnosis].

Huntington's disease is a late manifesting autosomal dominant neurodegenerative disorder. It is characterized by motor disturbance, loss of cognitive functions and psychiatric manifestations. The disease causing mutation, an unstable DNA sequence in the coding region of the Huntington gene on chromosome 2p, has recently been identified. A trinucleotide [CAG] repeat is expanded over the normal range and can be easily detected by standard laboratory methods. Accurate genetic testing can now be offered in clinically questionable cases and to presymptomatic subjects at risk for Huntington's disease. Furthermore, there is a correlation between the size of the expanded CAG repeat and the age of onset in affected individuals. The predictive value of this correlation, however, is limited due to the range of onset ages found at a given repeat length in large series of patients. Expanded triplet repeats exhibit a marked instability especially in male meiosis with a tendency to further increase during transmission over the generations. This is likely to be the molecular mechanism explaining anticipation, as well as the occurrence of juvenile cases and new mutations.