Erasmus MC, University Medical Centre Rotterdam, Department of Public Health, Rotterdam, The Netherlands. Erasmus MC - Sophia Children's Hospital, University Medical Centre Rotterdam, Department of Paediatric Haematology, Rotterdam, The Netherlands. Erasmus MC, Erasmus University Medical Centre Rotterdam, Department of Haematology, Rotterdam, The Netherlands. Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, Department of Paediatric Haematology, Amsterdam, The Netherlands. Van Creveldkliniek, University Medical Centre Utrecht, Utrecht University, Utrecht, The Netherlands. Radboud University Medical Centre, Department of Haematology, Nijmegen, The Netherlands.