Researchers examined the influence of OCT1, OCT2, MATE1 and MATE2 promoter variations on metformin sensitivity, and they found that SLC47A1 rs2289669 and SLC47A2 rs12943590 variants could predict resistance to insulin in T2DM subjects under metformin therapy [18]. The gene discussed is SLC22A2; the disease is type 2 diabetes mellitus.