MT-ND5 and Leber hereditary optic neuropathy: Taken together, this could explain why a mutation in MTND5 subunits at lower mutant load could result in severe cases of LS and other complex I related disorders such as MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes) or LHON (Leber’s hereditary optic neuropathy).