[1] Childrens Natl Hosp, Div Hosp Med, 111 Michigan Ave NW, Washington, DC 20010 USA
[2] George Washington Univ, Sch Med & Hlth Sci, Dept Pediat, Washington, DC USA
[3] NIH, Div Populat Human Dev, Epidemiol Branch, Bethesda, MD USA
[4] Univ Albany, Sch Publ Hlth, Dept Environm Hlth Sci, Albany, NY USA
[5] Uniformed Serv Univ Hlth Sci, Murtha Canc Ctr Res Program, Bethesda, MD USA
[6] Glotech Inc, Bethesda, MD USA