The general approach to treat a patient with type 2 diabetes mellitus is the following: metformin is the first-line treatment; when a patient is not adequately controlled with metformin, a second noninsulin medication may be added; this second medication may be a sulphonylurea, a dipeptidyl peptidase-4 (DPP-4) inhibitor or a glitazone and, in the more recent guidelines, a glucagon-like peptide-1 (GLP-1) analog or a sodium-glucose cotransporter 2 (SGLT2) inhibitor. This evidence concerns the gene SLC5A2 and diabetes mellitus.