[1] UCL Inst Neurol, MRC, Ctr Neuromuscular Dis, London, England
[2] UCL Inst Neurol, Acad Neuroradiol Unit, Dept Brain Repair & Rehabil, London, England
[3] Univ Zurich Hosp, Inst Clin Chem, Zurich, Switzerland
[4] Natl Hosp Neurol & Neurosurg, Div Neuropathol, London WC1N 3BG, England
[5] IRCCS Fdn Carlo Besta Neurol Inst, Neurol Unit 3, Milan, Italy
[6] Nuffield Dept Clin Neurosci, Oxford, England
[7] Norfolk & Norwich Hosp, Dept Clin Neurophysiol, Norwich NR1 3SR, Norfolk, England