Division of Neurology (M.P., A.M.C., J.F., D.L.), Children's Hospital of Philadelphia; Department of Neurology (M.P., A.M.C., D.L.), Perelman School of Medicine at the University of Pennsylvania; Division of Endocrinology and Diabetes (J.T., J.D., S.E.M.), Children's Hospital of Philadelphia; Department of Pediatrics (J.A.M, K.Y.L., S.E.M.), Perelman School of Medicine at the University of Pennsylvania; Division of Gastroenterology (J.A.M.), Hepatology and Nutrition, Children's Hospital of Philadelphia; Division of Cardiology (K.Y.L), Children's Hospital of Philadelphia; Friedreich's Ataxia Research Alliance (J.F.); Clinical Data Science GmbH (C.R.), Basel, Switzerland; Department of Neurology (S.L.P), University of California Los Angeles; Murdoch Children's Research Institute (M.B.D.), Victoria, Australia; Department of Neurology (G.R.W), Emory University School of Medicine, Atlanta, Georgia; Department of Pediatrics (K.D.M.), University of Iowa Carver College of Medicine, Iowa; Divisions of Neurology (G.Y.) and Clinical and Metabolic Genetics, Department of Paediatrics, the Hospital for Sick Children, University of Toronto, Ontario, Canada; Department of Neurology (J.H.), Ohio State University College of Medicine, Columbus, Ohio; Department of Neurology (M.C., S.H.S.), University of Florida, College of Medicine, Gainesville, Florida; Department of Neurology (T.Z.), University of South Florida, Tampa, Florida.