We demonstrated that the asymptomatic sister had a compound heterozygote for an expanded GAA allele and an uncommon (GAAGGA) 66–67 repeat expansion; of note, expression studies showed that both sisters displayed a similar significant reduction in frataxin levels in leukocytes and fibroblasts, but only one sister developed clinical disease manifestation of FRDA. Here, FXN is linked to Friedreich ataxia.