1 Department of Haematology and Oncology, Children's Hospital of Michigan and Wayne State University, 3901 Beaubien Blvd, Detroit MI 48201-2196, USAHaruard Medical School, and Brigham and Women's Hospital, 75 Francis Street, Boston MA 02115, USAUCSF Medical Centre, 1466 Fourth Avenue, San Francisco, CA 94143, USARiley Hospital, 702 Bamhitt Drive, Indianapolis, IN 46202, USAUniversity of Minnesota Hospital and Clinic, Box 713, 420 Delaware Street, S.E., Minneapolis, MN 55455, USANew York Hospital, Cornell Medical Centre, 525 E. 68th Street, New York, NY 10021, USALos Angeles Children's Hospital, 4650 Sunset Blvd, Los Angeles, CA 90027, USARoyal Free Hospital, Pond Street, London NW3 20G, UKHospital Ste.-Justine, 3175 Clre-Sainte-Catherine, Montreal, Quebec, CanadaMayo Clinic/Foundation, Rochester, MN 55905, USADepartment of Pediatrics, Hannover Medical School, Hanover, Germany.