[1] Leyenburg Hosp, Dept Haematol, The Hague, Netherlands
[2] Univ Nijmegen St Radboud Hosp, Dept Paediat, NL-6500 HB Nijmegen, Netherlands
[3] Dr Daniel den Hoed Hosp, Dept Haematol, Rotterdam, Netherlands
[4] Univ Leiden Hosp, Dept Epidemiol, Dept Immunohaematol, NL-2300 RC Leiden, Netherlands