Most of the patients with LHON (95%) are affected by either one of three primary mtDNA missense variants encoding for the respiratory chain subunits of the nicotinamide adenine dinucleotide ubiquinone- oxidoreductase (complex I) genes: 3460 G > A ND1, 11778 G > A ND4, and 14484 T > C ND6 [15]. The gene discussed is MT-ND4; the disease is Leber hereditary optic neuropathy.