STRs database » FXN locus
Overview of repeats
Friedreich ataxia (FRDA) is an autosomal recessive disorder caused by GAA repeat expansions in intron 1 of the FXN gene. Expanded alleles can contain more than 1000 repeats, most often between 600-900 (Pandolfo (2001)). Normal alleles generally contain 5-33 GAA repeats, intermediate alleles 34-65, and pathogenic expansions 66 or more. However, disease has been reported with a 56-repeat allele, so the lower pathogenic boundary remains uncertain. Interpretation of borderline alleles also depends on the other FXN allele (Bidichandani et al. (2025)).
In a series of 112 unrelated patients, Devore et al. (2026) found expanded composite GAA/GGA alleles in approximately 20% and other minor sequence interruptions in a further 10%. The authors reported that these composite expanded alleles were pathogenic and that many were not detected by standard PCR-based testing.