Mutations in three polypeptides are responsible for 90-95% of all cases of LHON: MT-ND1 (m.3460G>A), MT-ND4 (m.11778G>A) and MT-ND6 (m.14484T>C) [15, 16]. The gene discussed is MT-ND4; the disease is Leber hereditary optic neuropathy.