[1] Childrens Natl Med Ctr, Ctr Canc & Blood Disorders, Washington, DC 20111 USA
[2] SCUSF Med Ctr, Sch Nursing, San Francisco, CA 94143 USA
[3] Lucile Packard Childrens Hosp Stanford, Palo Alto, CA 94304 USA
[4] Hosp Sick Children, Toronto, ON M5G 1X8, Canada
[5] Hosp Sick Children, Div Haematol Oncol, Toronto, ON M5G 1X8, Canada
[6] Univ Toronto, Dept Paediat, Toronto, ON M5S 1A1, Canada
[7] Hosp Sick Children, Dept Dent, Toronto, ON M5G 1X8, Canada
[8] McMaster Univ, Dept Clin Epidemiol & Biostat, Populat Genom Program, Hamilton, ON L8S 4L8, Canada