[1] Childrens Mercy Hosp, Kansas City, MO 64108 USA
[2] CDC, Div Blood Disorders, Ctr Dis Control & Prevent, Atlanta, GA 30333 USA
[3] Childrens Natl Med Ctr, Washington, DC 20010 USA
[4] Ctr Dis Control & Prevent, Div Hereditary Blood Disorders, Natl Ctr Birth Defects & Dev Disabil, Atlanta, GA USA