Exome sequencing identifies ACAD9 mutations as a cause of complex I deficiency.
Haack TB., Danhauser K., Haberberger B., Hoser J., Strecker V., Boehm D., Uziel G., Lamantea E., Invernizzi F., Poulton J., Rolinski B., Iuso A., Biskup S., Schmidt T., Mewes H-W., Wittig I., Meitinger T., Zeviani M., Prokisch H.
An isolated defect of respiratory chain complex I activity is a frequent biochemical abnormality in mitochondrial disorders. Despite intensive investigation in recent years, in most instances, the molecular basis underpinning complex I defects remains unknown. We report whole-exome sequencing of a single individual with severe, isolated complex I deficiency. This analysis, followed by filtering with a prioritization of mitochondrial proteins, led us to identify compound heterozygous mutations in ACAD9, which encodes a poorly understood member of the mitochondrial acyl-CoA dehydrogenase protein family. We demonstrated the pathogenic role of the ACAD9 variants by the correction of the complex I defect on expression of the wildtype ACAD9 protein in fibroblasts derived from affected individuals. ACAD9 screening of 120 additional complex I-defective index cases led us to identify two additional unrelated cases and a total of five pathogenic ACAD9 alleles.