1. From Tufts-New England Medical Center and Tufts University School of Medicine, Boston, Massachusetts; Bloomberg School of Public Health, Welch Center for Prevention, Epidemiology and Clinical Research, and the Johns Hopkins University, Baltimore, Maryland; University of British Columbia, Vancouver, British Columbia, Canada; University of Minnesota, Minneapolis, Minnesota; North Texas Hospital for Children, Dallas, Texas; and Baylor College of Medicine, Houston, Texas.