[1] Univ London Imperial Coll Sci Technol & Med, MRC, Hammersmith Hosp, Ctr Clin Sci, London W12 0NN, England
[2] Inst Neurol, Neurogenet Unit, London WC1N 3BG, England
[3] Royal Free Hosp & Univ Coll, Sch Med, Reta Lila Weston Inst Neurol Studies, London, England