1. UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery and Great Ormond Street; MRC Centre for Neuromuscular Diseases and Dubowitz Neuromuscular Centre; PO Box 114 London UK WC1B 3BN
2. Rigshospitalet, University of Copenhagen; Neuromuscular Research Unit, Department of Neurology; Blegdamsvej 9, DK-2100 Copenhagen Denmark
3. John Radcliffe Hospital; Department of Clinical Neurology; Oxford UK OX3 9DU
4. University of Chester; Department of Clinical Sciences; Parkgate Road Chester UK CH1 4BJ