FXN and neurodegenerative disease: Friedreich ataxia (FRDA) is a rare neurodegenerative disease that is characterized by spinocerebellar and sensory ataxia and is associated with hypertrophic cardiomyopathy and diabetes [117] FRDA is mainly caused by a homozygous n(GAA) expansion within the first intron of the frataxin gene (FXN), an essential mitochondrial protein involved in the biosynthesis of iron–sulfur (Fe-S) clusters.