[1] Univ Texas, SW Med Ctr, Dept Pediat, Div Hematol Oncol, Dallas, TX 75390 USA
[2] Univ Oklahoma, Hlth Sci Ctr, Dept Biostat & Epidemiol, Oklahoma City, OK USA
[3] Univ Oklahoma, Hlth Sci Ctr, Dept Med, Oklahoma City, OK USA
[4] Childrens Hosp Philadelphia, Div Hematol, Philadelphia, PA 19104 USA
[5] Univ Toronto, Hosp Sick Children, Div Hematol, Toronto, ON M5G 1X8, Canada
[6] Univ Basel, Dept Pediat, Basel, Switzerland