GPAA1 and Friedreich ataxia: In typical FRDA patients, the length of the shortest GAA expansion (GAA1) correlates with the severity of the disease and conversely correlates with the age of onset; longer GAA expansions result in earlier onset and a faster progression (Filla et al., 1996; Sacca et al., 2011b), The presence of compound heterozygotes can complicate confirmation of a clinical diagnosis (Anheim et al., 2012) and the phenotype of compound heterozygotes cannot be predicted with certainty (Forrest et al., 1998).