MT-ND6 and hyperinsulinemic hypoglycemia, familial, 4: ND6 gene encodes ND6 subunit, which is 1 of the 40 subunits of the NADH dehydrogenase (also known as complex I), in mammalian cells.[19] NADH dehydrogenase activity was associated with polymorphism or mutations of ND6 gene.[20] NADH dehydrogenase deficiency may cause maternally inherited diseases such as Leber hereditary optic neuropathy and mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes.