1. Endocrinology, Nutrition and Growth Branch, Center for Research for Mothers and Children, National Institute of Child Health and Human Development, 6100 Executive Boulevard, 4B11, Rockville, MD 20852, USA.
2. Department of Pediatrics and Child Health, University of Alberta, Edmonton, AB, Canada.
3. Genetic Epidemiology and Clinical Research Group, Department of Medicine, Institute of Public Health and Clinical Medicine, Umeå University Hospital, Umeå, Sweden; MRC Epidemiology Unit, University of Cambridge, Cambridge, UK.