MT-ND1 is the core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) that is believed to belong to the minimal assembly required for catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone. Defects in MT-ND1 are a cause of Leber hereditary optic neuropathy (LHON) [MIM:535000]; also known as Leber optic atrophy. LHON is a maternally inherited disease resulting in acute bilateral blindness due to retinal degeneration predominantly in young men. Cardiac conduction defects and neurological defects have also been described, resulting in optic nerve degeneration and cardiac dysrhythmia. Defects in MT-ND1 may also be associated with mitochondrial susceptibility to Alzheimer disease (AD) and non insulin dependent diabetes mellitus (NIDDM).