A guanine-adenine-adenine (GAA) trinucleotide repeat expansion within the first intron of the frataxin (Fxn) gene in the chromosome 9 is the major cause of Friedreich's ataxia (FRDA), the most commonly inherited ataxia (Chamberlain et al., 1988; Campuzano et al., 1996). The gene discussed is FXN; the disease is Friedreich ataxia.