FXN and Friedreich ataxia: The underlying cause of FRDA is frataxin (FXN) deficiencies resulting from either a biallelic GAA trinucleotide repetition (ranging from 200 to 1700 GAA), which constitutes 95% of patients (homozygous) or a point mutation in one FXN allele, which is paired with an expanded allele and represents 5% of patients (heterozygous) [260].