Isolated complex I deficiency is the most common enzymatic defect of the oxidative phosphorylation disorders (McFarland et al., 2004; Kirby et al., 2004). 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 (see 256000), Leber hereditary optic neuropathy (535000), and some forms of Parkinson disease (see 556500) (Loeffen et al., 2000; Pitkanen et al., 1996; Robinson, 1998).
Genetic Heterogeneity of Complex I Deficiency
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 (summary by Haack et al., 2012). However, the majority of cases are caused by mutations in nuclear-encoded genes (Loeffen et al., 2000; Triepels et al., 2001).
Complex I deficiency resulting from mutation in nuclear-encoded genes include MC1DN1, caused by mutation in the NDUFS4 gene (602694); MC1DN2 (618222), caused by mutation in the NDUFS8 gene (602141); MC1DN3 (618224), caused by mutation in the NDUFS7 gene (601825); MC1DN4 (618225), caused by mutation in the NDUFV1 gene (161015); MC1DN5 (618226), caused by mutation in the NDUFS1 gene (157655); MC1DN6 (618228), caused by mutation in the NDUFS2 gene (602985); MC1DN7 (618229), caused by mutation in the NDUFV2 gene (600532); MC1DN8 (618230), caused by mutation in the NDUFS3 gene (603846); MC1DN9 (618232), caused by mutation in the NDUFS6 gene (603848); MC1DN10 (618233), caused by mutation in the NDUFAF2 gene (609653); MC1DN11 (618234), caused by mutation in the NDUFAF1 gene (606934); MC1DN12 (301020), caused by mutation in the NDUFA1 gene (300078); MC1DN13 (618235), caused by mutation in the NDUFA2 gene (602137); MC1DN14 (618236), caused by mutation in the NDUFA11 gene (612638); MC1DN15 (618237), caused by mutation in the NDUFAF4 gene (611776); MC1DN16 (618238), caused by mutation in the NDUFAF5 gene (612360); MC1DN17 (618239), caused by mutation in the NDUFAF6 gene (612392); MC1DN18 (618240), caused by mutation in the NDUFAF3 gene (612911); MC1DN19 (618241), caused by mutation in the FOXRED1 gene (613622); MC1DN20 (611126), caused by mutation in the ACAD9 gene (611103); MC1DN21 (618242), caused by mutation in the NUBPL gene (613621); MC1DN22 (618243), caused by mutation in the NDUFA10 gene (603835); MC1DN23 (618244), caused by mutation in the NDUFA12 gene (614530); MC1DN24 (618245), caused by mutation in the NDUFB9 gene (601445); MC1DN25 (618246), caused by mutation in the NDUFB3 gene (603839); MC1DN26 (618247), caused by mutation in the NDUFA9 gene (603834); MC1DN27 (618248), caused by mutation in the MTFMT gene (611766); MC1DN28 (618249), caused by mutation in the NDUFA13 gene (609435); MC1DN29 (618250), caused by mutation in the TMEM126B gene (615533); MC1DN30 (301021), caused by mutation in the NDUFB11 gene (300403); MC1DN31 (618251), caused by mutation in the TIMMDC1 gene (615534); MC1DN32 (618252), caused by mutation in the NDUFB8 gene (602140); MC1DN33 (618253), caused by mutation in the NDUFA6 gene (602138); MC1DN34 (618776), caused by mutation in the NDUFAF8 gene (618461); MC1DN35 (619003), caused by mutation in the NDUFB10 gene (603843); MC1DN36 (619170), caused by mutation in the NDUFC2 gene (603845); MC1DN37 (619272), caused by mutation in the NDUFA8 gene (603359); MC1DN38 (619382), caused by mutation in the DNAJC30 gene (618202); and MC1DN39 (620135), caused by mutation in the NDUFB7 gene (603842).
Complex I deficiency with mitochondrial inheritance has been associated with mutation in 6 mitochondrial-encoded components of complex I: MTND1 (516000), MTND2 (516001), MTND3 (516002), MTND4 (516003), MTND5 (516005), MTND6 (516006). Most of these patients have a phenotype of Leber hereditary optic neuropathy (LHON; 535000) or Leigh syndrome. Features of complex I deficiency may also be caused by mutation in other mitochondrial genes, including MTTS2 (590085). [from OMIM]
