It has been suggested that the metformin response in type 2 diabetes is associated with variants in, for example, SLC22A1, ATM and SLC2A2; however, the replicability of the SLC22A1 locus associations has been inconsistent, potentially owing to differences between studies in study design, population characteristics or disease stage [46–50]. The gene discussed is SLC22A1; the disease is type 2 diabetes mellitus.