1. Laboratoire des Maladies MétaboliquesDepartment of Neuropediatry, Cliniques Universitaires St. Luc, 10 Avenue Hippocrate, B-1200, Brussels, Belgium
2. Department of Pediatrics, Cliniques Universitaires St. Luc, 10 Avenue Hippocrate, B-1200, Brussels, Belgium
3. Laboratoire de Spectrométrie de Masse, Unversite Catholique de Louvain, Institut de Chimie,B-1348,Louvain-La-Neuve, Belgium
4. Nonstandard abbreviation: FAB-MS, fast atom bombardment mass spectrometry; CAD, collision activated dissociation; GC, gas chromatography; and MS/MS, tandem mass spectrometry