[1] UCL Inst Child Hlth, Mitochondrial Res Grp, London, England
[2] Natl Hosp Neurol, MRC Ctr Neuromuscular Dis, London, England
[3] Great Ormond St Hosp Sick Children, Metab Unit, London WC1N 3JH, England
[4] Univ Oxford, Nuffield Dept Obstet & Gynaecol, Oxford, England
[5] Great Ormond St Hosp Sick Children, Dubowitz Neuromuscular Ctr, London WC1N 3JH, England