NDUFS4

Function

Complex I, or NADH:ubiquinone oxidoreductase, the first multisubunit enzyme complex of the mitochondrial respiratory chain, plays a vital role in cellular ATP production, the primary source of energy for many crucial processes in living cells. It removes electrons from NADH and passes them by a series of different protein-coupled redox centers to the electron acceptor ubiquinone. In well-coupled mitochondria, the electron flux leads to ATP generation via the building of a proton gradient across the inner membrane. Complex I is composed of at least 41 subunits, of which 7 are encoded by the mitochondrial genome (ND1-6, ND4L) and the remainder by nuclear genes.

Clinical significance

Mutations in the ACAD9 gene are associated with Mitochondrial Complex I Deficiency, which is autosomal recessive. This deficiency is the most common enzymatic defect of the oxidative phosphorylation disorders. Mitochondrial complex I deficiency shows extreme genetic heterogeneity and can be caused by mutation in nuclear-encoded genes or in mitochondrial-encoded genes. There are no obvious genotype-phenotype correlations, and inference of the underlying basis from the clinical or biochemical presentation is difficult, if not impossible. However, the majority of cases are caused by mutations in nuclear-encoded genes. It causes a wide range of clinical disorders, ranging from lethal neonatal disease to adult-onset neurodegenerative disorders. Phenotypes include macrocephaly with progressive leukodystrophy, nonspecific encephalopathy, hypertrophic cardiomyopathy, myopathy, liver disease, Leigh syndrome, Leber hereditary optic neuropathy, and some forms of Parkinson disease. Complex I deficiency with autosomal recessive inheritance results from mutation in nuclear-encoded subunit genes, including NDUFV1, NDUFV2, NDUFS1, NDUFS2, NDUFS3, NDUFS6, NDUFS7, NDUFS8, NDUFA2, NDUFA11, NDUFAF3, NDUFAF10, NDUFB3, NDUFB9, ACAD9, FOXRED1, and MTFMT.