We read with interest the recent description by Bidichandani and colleagues1 describing a case of very late-onset Friedreich ataxia with a large GAA repeat expansion. This report suggests that clinical diagnostic criteria for Friedreich ataxia (FRDA), useful in the majority of patients, cannot comprise the whole broadened phenotype of the disease in terms of age of onset. According to the Harding criteria,2 FRDA is characterized by progressive gait and limb ataxia with onset before 25 years, as well as lower limb areflexia, dysarthria, extensor plantar response, pyramidal weakness, decreased vibratory sensation, pes cavus, and scoliosis. In addition, accessory findings such as cardiomyopathy and diabetes are often present. Friedreich ataxia is associated with an unstable expansion of a GAA trinucleotide repeat in the first intron of the X25 gene on chromosome 9, resulting in a decreased expression of this gene. The majority of patients are homozygous for an unstable GAA trinucleotide expansion in the first X25 intron. Normal individuals have a repeat size varying from 7 to 25, whereas FRDA patients carry expanded alleles with 120 to 1700 repeats.3
Sorbi S, Forleo P, Cellini E, et al. Atypical Friedreich Ataxia With a Very Late Onset and an Unusual Limited GAA Repeat. Arch Neurol. 2000;57(9):1380–1383. doi:
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