1. From the Department of Medicine, Division of Medical Genetics and the Clayton Laboratories, the Department of Pharmacology and Experimental Therapeutics, Johns Hopkins University School of Medicine and Johns Hopkins Hospital, Baltimore, MD, and the Department of Genetics and the Lt. Joseph P. Kennedy, Jr., Laboratories, Stanford University School of Medicine, Stanford, CA (address reprint requests to Dr. Siggers at Southampton University Child Health Unit, Southampton General Hospital, Southampton,...