1. Divisions of Medical Genetics and Biomedical Sciences, E.K. Shriver Center for Mental Retardation, Waltham, Massachusetts, Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts, Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts, Department of Pediatrics, Massachusetts General Hospital, Boston, Massachusetts
2. Department of Pediatrics, Massachusetts General Hospital, Boston, Massachusetts
3. Divisions of Medical Genetics and Biomedical Sciences, E.K. Shriver Center for Mental Retardation, Waltham, Massachusetts, Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts
4. Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts