[1] Univ Zurich, Childrens Hosp, Div Clin Chem & Biochem, CH-8032 Zurich, Switzerland
[2] Childrens Hosp Konigsborn, Unna, Germany
[3] Childrens Hosp Augsburg, Augsburg, Germany
[4] Baylor Univ, Med Ctr, Inst Metab Dis, Dallas, TX USA
[5] Univ Texas, SW Med Ctr, Dept Neurol, Dallas, TX 75235 USA
[6] Univ Marburg, Childrens Hosp, Marburg, Germany