[1] Royal Manchester Childrens Hosp, Willink Unit, Manchester M27 1HA, Lancs, England
[2] Royal Liverpool Childrens Hosp, Dept Neurol, Liverpool L7 7DG, Merseyside, England
[3] Royal Liverpool Childrens Hosp, Dept Biochem, Liverpool L7 7DG, Merseyside, England
[4] Royal Liverpool Childrens Hosp, Dept Radiol, Liverpool L7 7DG, Merseyside, England
[5] Univ Newcastle Upon Tyne, Sch Neurol Neurobiol & Psychiat, Mitochondrial Res Grp, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England
[6] Vrije Univ Amsterdam, Med Ctr, Metab Unit, Dept Clin Chem, Amsterdam, Netherlands