Isolated complex I deficiency is the most common enzymatic defect of the oxidative phosphorylation disorders. 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. MC1DN17 is caused by homozygous or compound heterozygous mutation in the NDUFAF6 gene. [From OMIM]