1. Department of Biology/Genetic Counseling, Brandeis University, Waltham, MA 02454.
2. Division of Medical Genetics, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107.
3. Division of Medical Genetics, Shriver Center for Mental Retardation, Waltham, MA 02254.
4. Harvard Medical School and Departments of Neurology, Pathology and Pediatrics, Massachusetts General Hospital, Boston, MA 02114.