Genetic variants in key genes, such as TCF7L2, IRS1, solute carrier family 30 member 8 (SLC30A8), cyclin-dependent kinase 5 regulatory subunit associated protein 1-like 1 (CDKAL1), MTNR1B, and glucokinase (GCK), have been linked to susceptibility to GDM through effects on β-cell function and insulin action. The gene discussed is TCF7L2; the disease is gestational diabetes.