1 Department of Child Neurology and Amsterdam Neuroscience, VU University Medical Center, Amsterdam, The Netherlands.
2 Division of Human Genetics, Medical University Innsbruck, Innsbruck, Austria.
3 Department of Clinical Chemistry, VU Medical Center, Amsterdam, The Netherlands.
4 Pediatric Neurology, University Children's Hospital, Heidelberg, Germany.
5 Pediatric Neurology and Metabolic Medicine, Center for Pediatric and Adolescent Medicine, and Center for Rare Disorders, Heidelberg University Hospital, Heidelberg, Germany.