Furthermore, an Italian study demonstrated that the combination of mtDNA mutations in genes m.12033A>G/MT-ND4 and m.14258G>A/MT-ND6 affects proton pumping in the ETC and causes LHON (Caporali et al., 2018[3]). The gene discussed is MT-ND4; the disease is Leber hereditary optic neuropathy.