MT-ND4 and Leber hereditary optic neuropathy: Other well-studied mtDNA diseases affecting ATP synthesis include LHON (Leber’s hereditary optic neuropathy, due to mutations in ND1, ND4, ND4L, or ND6 genes) [30,31,32,33,34], Leigh’s syndrome (with mutations in ND3, ATP6, and ATP8) [35,36,37], and NARP (neuropathy, ataxia, and retinitis pigmentosa, with mutations in the ATP6 gene) [22,38,39,40].