From the Neuromuscular Research Center (J.P., S.P., B.U.), Tampere University and University Hospital, Neurology; The Finnish Medical Society Duodecim (P.K.), Helsinki; Department of Pediatrics (P.K.), Kuopio University Hospital, and University of Eastern Finland Kuopio; Neurocenter (P.H.H.), Neurology, Kuopio University Hospital; Department of Child Neurology (P.I.), Children's Hospital, Pediatric Research Center, University of Helsinki and Helsinki University Hospital; Research Programs Unit (P.I.), Stem Cells and Metabolism, University of Helsinki; Clinical Neurosciences (M.A.), Neurology, University of Helsinki and Helsinki University Hospital; Department of Pediatric Neurology (K.V.); Department of Genetics (S.L.), Fimlab Laboratories, Tampere University Hospital; Department of Pediatric Neurology (J.K.), Kuopio University Hospital; Department of Neurology (S.H., K.P.), Central Finland Central Hospital, Jyväskylä; Institute for Molecular Medicine Finland FIMM (J.S.), University Helsinki, Finland; Centre for Molecular Medicine Norway (J.S.), University of Oslo, Norway; Folkhälsan Institute of Genetics and the Department of Medical Genetics (B.U.), Haartman Institute, University of Helsinki; and Department of Neurology (B.U.), Vaasa Central Hospital, Finland.