MT-ND4 and type 2 diabetes mellitus: We found several significant variants positively correlated with T2D located in the nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit genes (ND4, ND4L, and ND6) of respiratory complex I. NADH dehydrogenase is essential for energy generation; thus, variants within its encoding genes could result in metabolic disorders (65).