[1] Vrije Univ Amsterdam, Med Ctr, Amsterdam, Netherlands
[2] Royal Hosp Sick Children, Dept Paediat Haematol, Glasgow G3 8SJ, Lanark, Scotland
[3] Guys Hosp, Dept Med & Mol Genet, London SE1 9RT, England
[4] Pediat Clin, Bologna, Italy
[5] Our Ladys Hosp Sick Children, Dept Paediat Haematol, Dublin, Ireland
[6] Univ Roma La Sapienza, Dipartimento Biotecnol Cellulari & Ematol, Rome, Italy