Department of Neurology, Neuromuscular Unit, 12 de Octubre University Hospital, Madrid, Spain. Electronic address: doctoregr@gmail.com. Department of Neurology, Sagrado Corazón Clinic, Seville, Spain. La Fe University and Polytechnic Hospital, Valencia, Spain. Neuromuscular Pathology Unit, Department of Neurology, Santa Creu i Sant Pau Hospital, Barcelona, Spain. Neuropathology Institute IDIBELL, Bellvitge Hospital, Barcelona, Spain. Department of Neurology, La Paz University Hospital, Madrid, Spain. Department of Neurology, Donostia University Hospital, San Sebastián, Spain. Clínical Biochemistry Section, Virgen del Rocío University Hospital, Seville, Spain. Molecular Oncogenetic Unit, Institute of Medical and Molecular Genetics, La Paz University Hospital, Madrid, Spain. Institute of Clinical Chemistry, Department of Pediatrics, Hamburg University Medical Center, Hamburg, Germany.