So far, only biallelic nonsense MFF mutations (MIM#614785) have been identified in individuals with a severe encephalopathy associated with optic atrophy and peripheral neuropathy [21], while no mutation has been reported for optic atrophy in MIEF1 or MIEF2, which encode for MID51 and MID49, respectively. This evidence concerns the gene MIEF1 and Leber hereditary optic neuropathy.