Norton J. Greenberger, MD is a Senior Attending Physician and Clinical Professor of Medicine at Harvard Medical School. Dr. Greenberger is a past President of the American Gastroenterological Association, the American College of Physicians, the Central Society for Clinical Research and the Association of Professors of Medicine. He is the author or co-author of more than 230 publications including chapters in major medical texts. Richard S. Blumberg, MD is Professor of Medicine, Harvard Medical School Chief, Division of Gastroenterology, Hepatology and Endoscopy at Brigham and Women's Hospi...