1 MRC Centre for Neuromuscular Diseases (E.B., A.M.R., J.C.B., M.G.H., J.L.H., M.M.R., E.M.), UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery; Department of Molecular Neuroscience (D.S.L., A.M.P., M.G.H., H.H., J.L.H.), and Division of Neuropathology (J.L.H.), UCL Institute of Neurology, London; Department of Neurology (M.S.), The Royal London Hospital; and Department of Clinical Neurophysiology (J.C.B.), Norfolk and Norwich University Hospital, UK.