[1] UCL Inst Neurol, Natl Hosp Neurol & Neurosurg, London, England
[2] Leeds Inst Biomed & Clin Sci, Leeds, W Yorkshire, England
[3] UCL, Dept Cell & Dev Biol, London, England
[4] Leeds Gen Infirm, Dept Paediat Neurol, Leeds, W Yorkshire, England
[5] Birmingham Heartlands Hosp, Dept Paediat, Birmingham, W Midlands, England
[6] Leiden Univ, Med Ctr, Leiden, Netherlands
[7] UCL Inst Child Hlth, Dubowitz Neuromuscular Ctr, London, England