1. From the Division of Hematology/Oncology and the Department of Laboratory Medicine, Children's Hospital, Boston, MA; the Department of Pediatric Oncology, Dana Farber Cancer Institute, Boston, MA; the Departments of Pediatrics and Pathology, Harvard Medical School, Boston, MA; the Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine, University of Washington, Seattle, WA; and the Department of Biochemistry, North Carolina State University, Raleigh, NC.