-OGTT: For ethical reasons, the OGTT cannot performed in patients presenting with fasting plasma glucose higher than 15 mmol/l. During the entire test patients are sitting in a comfortable cardiac chair. One teflon (21 g) venous catheter is inserted into an antecubital vein for blood sampling and kept patent with heparinized normal saline solution. After a 30' rest to establish baseline and after collecting a 20 cc blood sample for leukocyte DNA extraction, at time = 0' subjects ingest 75 g of glucose in 300 ml of water over 5 min. Blood samples to measure glucose, C-peptide and insulin concentrations are collected at times -10', 0', +15', +30', +45', +60', +90', +120', +150', +180', +210' and +240', +270' and +300'. Urines are collected to measure glycosuria.