It is widely recognized that one of three common mutations, m.11778G>A, m.3460G>A and m.14484T>C respectively affecting the MT-ND4, MT-ND1 and MT-ND6 subunit genes of complex I, are present in over 90% of LHON patients. The gene discussed is MT-ND1; the disease is Leber hereditary optic neuropathy.