1. Division of Gastroenterology and Hepatology, Graduate School of Medical and Dental Sciences, Niigata University, 1-757, Aasahimachi-Dori, Chuo-Ku, Niigata 951-8510, Japan
2. Department of General Medicine, Niigata University School of Medicine, 1-757, Aasahimachi-Dori, Chuo-Ku, Niigata 951-8510, Japan