1. Division of Diabetes, Metabolism, and Endocrinology, Showa University School of Medicine, Shinagawa-ku, Tokyo, Japan
2. Kansai Electric Power Medical Research Institute, Kobe-shi, Hyogo, Japan
3. Department of Endocrinology, Diabetes and Geriatric Medicine, Akita University Graduate School of Medicine, Akita-shi, Akita, Japan