MIEF2 and Leber hereditary optic neuropathy: 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.