Medical School, Sector of Medicine, National and Kapodistrian University of Athens, 15772 Athens, Greece. Department of Clinical Biochemistry, Medical School, National and Kapodistrian University of Athens, 15772 Athens, Greece. Department of Clinical Biochemistry, Medical School, "Attikon" University Hospital, Rimini 1, 12462 Chaidari, Greece. Research Institute and Diabetes Center, 2nd Department of Internal Medicine, "Attikon" University Hospital, 1 Rimini Street, 12542 Haidari, Greece. St. Hilda's College, Cowley, University of Oxford, Oxford OX4 1DY, UK.