[1] Univ Oxford, John Radcliffe Hosp, Womens Ctr, Nuffield Dept Obstet & Gynaecol, Oxford OX3 9DU, England
[2] Kings Coll Hosp London, Dept Clin Neurosci, London, England
[3] St Thomas Hosp, Evelina Childrens Hosp, Dept Paediat Neurol Neuromuscular Serv, London, England
[4] Churchill Hosp, Oxford Med Genet Lab, Oxford OX3 7LJ, England
[5] Hosp Univ Miguel Servet, Zaragoza, Spain
[6] Univ Cagliari, Serv Puericultura, I-09124 Cagliari, Italy
[7] UCL Inst Child Hlth, Dubowitz Neuromuscular Ctr, London, England
[8] IRCCS Fdn, C Besta Neurol Inst, Unit Mol Neurogenet, Milan, Italy
[9] Manchester Childrens Hosp, Dept Paediat Neurol, Manchester, Lancs, England
[10] Childrens Univ Hosp, Natl Ctr Inherited Metab Dis, Dublin, Ireland
[11] Univ Oxford, Ctr Stat Med, Oxford OX1 2JD, England
[12] Univ Oxford, Dept Biochem, Oxford OX1 3QU, England