In Friedreich ataxia the deficiency of frataxin protein leads to progressive mitochondrial dysfunction, oxidative stress, and cell death, with the main affected sites being the large sensory neurons of the dorsal root ganglia and the dentate nucleus of the cerebellum. The GAA repeat expansions may be pure (GAA)n in sequence or may be interrupted with regions of non-GAA sequence. This is the first large-scale study of FRDA patient DNA samples to determine the frequency of large interruptions in GAA repeat expansions. The group investigated a panel of 245 Friedreich ataxia patient and carrier DNA samples and showed that the vast majority (97.8%) of Friedreich ataxia GAA repeat expansion samples do not contain significant sequence changes, indicating that they are primarily pure GAA repeats. These results show for the first time that large interruptions in the GAA repeats are very rare.

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