1. Laboratory of Metabolism and Pathological Biochemistry, Istituto Superiore di Sanita, 00161 Roma, Italy
2. Division of Gastroenterology, Department of Medicine, University of California-San Diego, La Jolla, CA 92093
3. Department of Developmental Biochemistry, New York State Office of Mental Retardation and Developmental Disabilities, Institute for Basic Research in Developmental Disabilities, Staten Island, NY 10314