[1] George Washington Univ, Sch Med & Hlth Sci, Childrens Natl Med Ctr, Washington, DC 20052 USA
[2] Univ Mississippi, Med Ctr, Dept Pediat, Jackson, MS 39216 USA
[3] Ctr Dis Control & Prevent, Div Blood Disorders, Natl Ctr Birth Defects & Dev Disabil, Atlanta, GA USA
[4] Childrens Hosp Los Angeles, Div Hematol, Los Angeles, CA 90027 USA
[5] Univ Michigan, Dept Pediat, Ann Arbor, MI 48109 USA
[6] Northwestern Univ, Feinberg Sch Med, Chicago, IL 60611 USA