No difference was found between the metformin taking and non-taking patients in the T2D group in the serum DPP-4 activity (Metformin non-taking: 25.98 U/L (95%CI: 21.39–30.58) Metformin taking: 23.67 U/L (95%CI: 21.82–25.51). This evidence concerns the gene DPP4 and type 2 diabetes mellitus.