Mutations in MFN2 and OPA1 cause MDDS, presenting as optic atrophy, myopathy, axonal neuropathy and Charcot–Marie–Tooth disease in the case of MFN2 [31] and optic atrophy and Behr syndrome in the case of OPA1 [30]. Here, OPA1 is linked to Leber hereditary optic neuropathy.