University of Copenhagen - Department of Paediatrics and Adolescent Medicine, University of Copenhagen - Department of Paediatrics and Adolescent Medicine, University College London - Great Ormond Street Institute of Child Health, University of Oslo - Oslo University Hospital, University of Copenhagen - Department of Paediatrics and Adolescent Medicine, Karolinska Institutet - Karolinska University Hospital, Karolinska Institutet - Karolinska University Hospital, Alder Hey Children's NHS Foundation Trust - Department of Paediatric Neurosurgery, Great Ormond Street Hospital, Great Ormond Street Hospital, St. Olavs University Hospital, University of Helsinki - Helsinki University Hospital, Lithuanian University of Health Sciences - Kaunas Clinical Hospital, Semmelweis University, Semmelweis University - 2nd Department of Pediatrics, Princess Máxima Center for Pediatric Oncology, Princess Maxima Center for Pediatric Oncology, University of Tübingen - University Hospitals Tübingen, University of Copenhagen - Department of Paediatrics and Adolescent Medicine, University of Copenhagen - Department of Pediatrics and Adolescent Medicine, University of Copenhagen - Department of Paediatrics and Adolescent Medicine, University of Copenhagen - Institute of Clinical Medicine, University Hospital Rigshospitalet - Department of Paediatrics and Adolescent Medicine and Independent