MT-ND5 and Leber hereditary optic neuropathy: The amino acid at position 393 of ND5 subunit encoded by m.13513 is located at an evolutionarily conserved part of a putative quinone-reactive site of the enzyme, and the D393N amino acid change caused by m.13513 G>A mutation may lead to loss of the quinine reactive site and a subsequent negative effect on the activity of the oxidative phosphorylation system, followed by significant mitochondrial impairment, as well as an increased reactive oxygen species generation and reduced ATP production, which finally resulting in the development of LHON (24, 25, 27).