[1] UCL Inst Neurol, Dept Mol Neurosci, Queen Sq, London, England
[2] UCL Great Ormond St Inst Child Hlth, Dubowitz Neuromuscular Ctr, London, England
[3] UCL Inst Neurol, MRC Ctr Neuromuscular Dis, Queen Sq, London, England
[4] Hosp Britanico, Serv Neurol, Buenos Aires, DF, Argentina
[5] UCL Inst Neurol, Dept Clin Neurosci, London, England