Small repeat interruptions, such as the A•T>G•C base changes introduced by our GAA-ABE strategy, are commonly found in FXN alleles in the general population and are associated with greater stability of GAA repeat alleles21,106, higher expression of FXN genes, milder disease or later disease onset in patients with FRDA compared with those with uninterrupted repeats of a similar length16,21,23,49,106,107. This evidence concerns the gene FXN and Friedreich ataxia.