[1] Univ London Imperial Coll Sci Technol & Med, Dept Neuromuscular Dis, Div Neurosci & Psychol Med, Fac Med, London W6 8RP, England
[2] Univ London Kings Coll, Randall Ctr Mol Mechanisms Cell Funct, London SE1 1UL, England
[3] Univ London Imperial Coll Sci Technol & Med, Hammersmith Hosp, Sch Med, Dubowitz Neuromuscular Ctr, London W12 0NN, England