MT-ND4 and optic nerve disorder: The LHON susceptibility allele (m.14502T > C, p. 58I > V) in the ND6 gene modulated the phenotypic expression of primary LHON-associated m.11778G > A mutation in the ND4 gene, which was demonstrated by 22 Han Chinese pedigrees carrying m.14502T > C and m.11778G > A mutations exhibiting significantly higher penetrance of optic neuropathy than those carrying only m.11778G > A mutation (Jiang et al. 2016).