MT-ND4 and Leber hereditary optic neuropathy: Almost all LHON maternal lineages present with homoplasmic mutation (100% mtDNA copies are mutant in all tissues), having one of three frequent mtDNA mutations found in over 90% of patients worldwide (m.11778G>A/MT-ND4, m.3460G>A/MT-ND1, m.14484T>C/MT-ND6), but only some individuals develop the disease.