At the time of this review five DPP-4 inhibitors are approved by the European Medicines Agency (EMA) (vildagliptin, alogliptin, sitagliptin, linagliptin, and saxagliptin) for treatment of type 2 diabetes mellitus, also reflected by the Global Guideline for Type 2 Diabetes [191]. The gene discussed is DPP4; the disease is type 2 diabetes mellitus.