Since the launch of the first DPP-4 inhibitor, severe hypoglycemia has been reported in Japan, including 32 cases of serious hypoglycemia in patients receiving sitagliptin reported within six months after the approval [18], the majority of which (28/32) used an SU concomitantly in spite of cautions of hypoglycemia in concomitant use with SU in the sitagliptin labeling. The gene discussed is DPP4; the disease is Hypoglycemia.