FXN and Friedreich ataxia: FXN was first identified for its connection to Friedreich's ataxia (Campuzano et al., 1996), a progressive neurodegenerative disease caused by an expansion of a GAA trinucleotide repeat within the first intron of the FXN gene, which results in reduced levels of FXN (Campuzano et al., 1996, 1997).