cDNA Sequencing of Nuclear NADH Dehydrogenase Subunit Genes in Complex I Deficient Myopathic Patients

Twenty-one nuclear genes for subunits of complex I of the electron transport chain were screened for mutations by cDNA sequencing in eight myopathic patients that exhibited complex I deficiency but lacked the common MERRF and MELAS mitochondrial DNA mutations. Seven common sequence variants were discovered in the tested complex I genes, including two non-synonymous and five synonymous single base changes. In addition, a rare polymorphism causing the substitution of an evolutionarily conserved glycine to arginine at amino acid position 32 in the NDUFA1 gene (encoding the MWFE subunit) was found in one patient who suffered a form of fatal infantile cardiomyopathy. This variation was found to be present in the patients father but not in an unselected series of 168 Scottish, 17 Swedish, and 18 French controls, nor in 80 Italian myopathy patients. Sequencing of the mtDNA from the bearer of the G32R variation revealed no tRNA mutations. This sequencing approach, while not exhaustive, suggests that complex I mutations may be very rare in patients suffering from various forms of myopathy and that complex I enzymatic deficiency may in many cases be an epiphenomenon in these disorders.