The authors thank Lena Pawella, Elisabeth Specht-Delius, Eva Eiteneuer, Marion Hahne, Zlata Antoni, Lena Protzmann, and Sabine Schäfer for excellent technical assistance. Human control tissues were provided by the Tissue Bank of the National Center for Tumor Diseases (NCT, Heidelberg, Germany) in accordance with the ethics committee of the University of Heidelberg. We thank Dr. Ronald J.A. Wanders, Department of Medical Biochemistry, Academic Medical Centre, University of Amsterdam, the Netherlands, who excluded fatty acid oxidation disorders in individuals from families 1, 2, 3, 5, and 7. This study was supported by the German Bundesministerium für Bildung und Forschung (BMBF) through the German Network for mitochondrial disorders (mitoNET, 01GM1113C to T.M. and H.P.) and through the E-Rare project GENOMIT (01GM1207 for T.M. and H.P.). T.B.H. and J.G. were supported by the BMBF through the Juniorverbund in der Systemmedizin “mitOmics” (FKZ 01ZX1405C and 01ZX1405A). R.W.T was supported by a Wellcome Trust Strategic Award (096919/Z/11/Z) and the UK NHS Highly Specialised “Rare Mitochondrial Disorders of Adults and Children” Service. B.K.S. was supported by grants of the DFG (STR 1160/1-1 and 1-2). D.M.B. was supported by a DFG Fellowship through the Graduate School of Quantitative Biosciences Munich (QBM).