FXN and mitochondrial DNA depletion syndrome, encephalomyopathic form with methylmalonic aciduria: These include Friedreich’s ataxia (FRDA), a neurodegenerative disease caused by mutations in frataxin (FXN), myopathies caused by mutations in ISCU2 and FDX2, a rare form of sideroblastic anemia caused by mutation in the GLRX5 gene, a form of encephalomyopathy caused by dysfunction of the respiratory chain complex I as a consequence of mutation in the gene encoding for IND1, and multiple mitochondrial dysfunction syndromes (MMDSs) caused by mutations in the genes encoding for the proteins acting in the last step of the ISC machinery (see later).