Nico Wulffraat1, Annet van Royen1, Marc Bierings1, Jaak Vossen2, Wietse Kuis1
1Department of Pediatric Immunology and Haematology, University Hospital for Children “Het Wilhelmina kinderziekenhuis”, PO Box 18009, 3501CA Utrecht, Netherlands
2Department of Pediatrics, Leiden University Medical Centre, Leiden, Netherlands