MT-ND4 and Leber hereditary optic neuropathy: LHON is caused by point mutations in mitochondrial DNA (mtDNA) genes encoding subunits of oxidative phosphorylation complex I. Most people with vision loss from LHON harbor one of three primary LHON mutations in MT-ND4 (m.11778G>A [p.Arg340His]),2 MT-ND6 (m.14484T>C [p.Met64Val]),3,4 or MT-ND1 (m.3460G>A [p.Ala52Thr]).5