1. Institute for Clinical Diabetology, German Diabetes Center at Heinrich Heine University; Leibniz Center for Diabetes Research; Düsseldorf Germany
2. Department of Endocrinology and Diabetology, Medical Faculty; Heinrich Heine University; Düsseldorf Germany
3. German Center for Diabetes Research (DZD); München-Neuherberg; Germany
4. Department of Internal Medicine IV, Division of Endocrinology, Diabetology, Vascular Medicine, Nephrology and Clinical Chemistry; University Hospital Tübingen; Germany
5. Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University of Tübingen; Tübingen Germany
6. Institute for Clinical Biochemistry and Pathobiochemistry, German Diabetes Center at Heinrich Heine University; Leibniz Center for Diabetes Research; Düsseldorf Germany
7. Department of Endocrinology and Clinical Chemistry; University of Heidelberg; Heidelberg Germany
8. Second Department of Internal Medicine; Democritus University of Thrace; Alexandroupolis Greece