1. Department I of Internal Medicine, University of Freiburg, 79106 Freiburg, Germany
2. Section of Pediatric Hematology/Oncology, Herman B. Wells Center for Pediatric Research, Riley Hospital for Children, Indianapolis, IN 46202 and Howard Hughes Medical Institute, Indiana University School of Medicine, Indianapolis, IN 46202
3. Institute of Genetics, University of Hohenheim, 70599 Stuttgart, Germany