Clinical diagnosis of T2DM.Age ≥30 and ≤80 years.Currently treated with one or two classes of oral glucose-lowering therapy (given either as separate or combined medications), that do not include a DPP4 inhibitor, a SGLT2 inhibitor or a thiazolidinedione.Diabetes duration ≥12 months.No change in diabetes treatment (new treatments or dose change) within previous 3 months.HbA1c > 58 mmol/mol (>7.5%) and ≤110 mmol/mol (≤12.2%).eGFR ≥60 mL/min/1.73 m2.Able and willing to give informed consent. The gene discussed is DPP4; the disease is type 2 diabetes mellitus.