Neuromuscular Diseases Unit, Department of Neurology, Hospital de la Santa Creu i Sant Pau; Department of Medicine, Universitat Autònoma de Barcelona; and Biomedical Research Institute Sant Pau (IIB Sant Pau), Barcelona, SpainCentro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain