Mutations in C12orf65 have been previously described in children with Leigh syndrome, optic atrophy and ophthalmoplegia,17 as well as in patients with SPG55,18 also characterised by neuropathy and optic atrophy, but as opposed to the cases presented here they had no cognitive impairment and a less severe phenotype. Here, MTRFR is linked to hereditary optic atrophy.