1 Wellcome Centre for Mitochondrial Research (E.W.S., R.L.J., S.A.H., E.L.B., A.M.S., D.M.T., G.S.G., R.W.T.), Institute of Neuroscience, The Medical School, Newcastle University, United Kingdom; Department of Molecular and Human Genetics (E.W.S.), Baylor College of Medicine, Houston, TX; NHS Highly Specialised Mitochondrial Diagnostic Laboratory (R.L.J., S.A.H., E.L.B., R.W.T.), Newcastle upon Tyne Hospitals NHS Foundation Trust, United Kingdom; Wellcome Centre for Mitochondrial Research (A.P.), Institute of Genetic Medicine, Newcastle University, United Kingdom; and Department of Clinical Neurosciences (P.F.C.), School of Clinical Medicine, and MRC Mitochondrial Biology Unit (P.F.C.), University of Cambridge, United Kingdom.