1. Department of Genetics and Center for Genetics in Medicine, Washington University School of Medicine, St. Louis, MO 63110.
2. Department of Pediatrics, Washington University School of Medicine, St. Louis, MO 63110.
3. Department of Microbiology and Immunology and Center for Genetics in Medicine, Box 8093, Washington University School of Medicine, St. Louis, MO 63110.
4. Department of Medicine and Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110.