FXN and Friedreich ataxia: Defects in protein components of the mitochondrial ISC machinery are associated with numerous diseases, including Friedreich ataxia (defects in frataxin), myopathy (defects in ISCU or FDX2), and multiple mitochondrial dysfunction syndromes (defects in NFU1, BOLA3, ISCA2, and IBA57) [24,49,50,51].