1. Department of Pediatrics and Adolescent Medicine; The University Hospital Rigshospitalet; Copenhagen; Denmark
2. Division of Hematology-Oncology, Department of Pediatrics; University of Tampere; Tampere; Finland
3. Department of Pediatrics; Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg; Gothenburg; Sweden
4. Department of Pediatrics; Oslo University Hospital/Medical Faculty, University of Oslo; Oslo; Norway