1 Division of Endocrinology, Diabetology, Vascular Medicine, Nephrology and Clinical Chemistry Department of Internal Medicine, University of Tübingen, Tübingen, Germany.
2 Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany.
3 German Center for Diabetes Research (DZD), München-Neuherberg, Germany.