1. Department of Pediatric Metabolic Diseases, University Medical Centre Utrecht, KC 03.063.0, P.O. Box 85090, 3508 AB Utrecht, The Netherlands
2. Institute of Cancer Research, London SW7 3RP, U.K.
3. Laboratory for Genetic Metabolic Diseases, Academic Medical Centre, 1105AZ Amsterdam, The Netherlands
4. Department of Child Neurology, Emma Children's Hospital, Academic Medical Centre, 1105AZ Amsterdam, The Netherlands
5. Neurosciences Unit, Institute of Child Health, University College London, London WC1N 1EH, U.K.