This proof of concept study will enrol type 1 diabetic patients to avoid confounding factors related to endogen insulin secretion and frequent polymedication of type 2 diabetic patients. The response will be evaluated for each patient by the relative difference between pre-and post-glucagon concentrations following a test meal, measured in the absence and presence of treatment with DPP4 inhibitor. Expected results: the DPP-4 inhibitor should lead to a reduction of about 20 to 30% of the glucagon level in patients without NA and a smaller or no decrease in patients with NA.