A catalytic defect in mitochondrial respiratory chain complex I due to a mutation in NDUFS2 in a patient with Leigh syndrome

In this study, we investigated the pathogenicity of a homozygous Asp446Asn mutation in the NDUFS2 gene of a patient with a mitochondrial respiratory chain complex I deficiency. The clinical, biochemical, and genetic features of the NDUFS2 patient were compared with those of 4 patients with previously identified NDUFS2 mutations. All 5 patients presented with Leigh syndrome. In addition, 3 out of 5 showed hypertrophic cardiomyopathy. Complex I amounts in the patient carrying the Asp446Asn mutation were normal, while the complex I activity was strongly reduced, showing that the NDUFS2 mutation affects complex I enzymatic function. By contrast, the 4 other NDUFS2 patients showed both a reduced amount and activity of complex I. The enzymatic defect in fibroblasts of the patient carrying the Asp446Asn mutation was rescued by transduction of wild type NDUFS2. A 3-D model of the catalytic core of complex I showed that the mutated amino acid residue resides near the coenzyme Q binding pocket. However, the KM of complex I for coenzyme Q analogs of the Asp446Asn mutated complex I was similar to the KM observed in other complex I defects and in controls. We propose that the mutation interferes with the reduction of coenzyme Q or with the coupling of coenzyme Q reduction with the conformational changes involved in proton pumping of complex I.

► The clinical features of 5 mitochondrial complex I deficient NDUFS2 patients were compared. ► The pathogenicity of a homozygous Asp446Asn mutation in the NDUFS2 gene was studied in detail. ► The Asp446Asn mutation leads to a catalytic defect in complex I. ► Modeling shows that the Asp446Asn mutation resides near the CoQ binding site in complex I. ► The KM of complex I for CoQ is similar in all NDUFS2 patients and controls.