1. Division of Intramural Research, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA
2. Department of Pediatrics, Johns Hopkins University, Baltimore, Maryland, USA
3. Department of Medicine, University of Virginia, Charlottesville, Virginia, USA
4. Department of Pediatrics, West Virginia University, Morgantown, West Virginia, USA
5. Department of Clinical Chemistry, University of Marburg, Marburg, Germany
6. Department of Pediatrics, University of North Carolina, Chapel Hill, North Carolina, USA