Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
Address for correspondence: Joon Chang, M.D. Department of Internal Medicine, Yonsei University, College of Medicine, 134, Shinchon, Seodaemun, Seoul 120-752 Korea. Phone: 02-2228-1952, Fax: 02-393-6884, chang@yumc.yonsei.ac.kr