1Division of Endocrinology and Metabolism, Department of Internal Medicine, Yonsei University College of Medicine, Seoul 120-752, Korea
2Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul 120-752, Korea
3Division of Nephrology, Department of Internal Medicine, Yonsei University College of Medicine, Seoul 120-752, Korea
4Institute of Endocrine Research, Yonsei University College of Medicine, Seoul 120-752, Korea
5Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02215, USA
6Department of Environmental Health, Harvard School of Public Health, Boston, MA 02215, USA