1. Department of Respiratory Medicine, Academic Medical Center, University of Amsterdam, P.O. Box 22700, NL-1100 DE Amsterdam, The Netherlands
2. Department of Paediatrics, Paediatric Pulmonology & Allergology, Erasmus Medical Center-Sophia Children's Hospital, Rotterdam, The Netherlands
3. Department of Paediatric Pulmonology & Paediatric Allergology, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Groningen, The Netherlands
4. Groningen Research Institute for Asthma & COPD (GRIAC), University of Groningen, University Medical Center Groningen, Groningen, The Netherlands