[Friedreich ataxia with GAA repeat expansion: molecular mechanism and clinical feature].

Friedreich ataxia(FRDA) is an autosomal recessive, degenerative disease that involves central and peripheral nervous system and the heart. FRDA mutation has recently been identified as an unstable GAA repeat expansion in the first intron of frataxin gene on chromosome 9q13-21.1. The length of FRDA alleles ranged from 120 to 1,700 repeat units. A few FRDA patients were found to have point mutation in frataxin, but the majority were homozygous for an unstable GAA expansion. The GAA expansion was unstable during transmission, and meiotic instability showed a sex bias(paternally transmitted alleles tend to decrease). Some patients of atypical FRDA can carry the GAA expansion. The clinical spectrum of FRDA is broader than previously recognized.