1. Department of Endocrinology and Metabolism, Ajou University School of Medicine, Suwon, Korea.
2. Department of Gastroenterology, Ajou University School of Medicine, Suwon, Korea.
3. Department of Nuclear Medicine, Ajou University School of Medicine, Suwon, Korea.
4. Division of Endocrinology, Metabolism and Nutrition, Department of Internal Medicine, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA.