LEP and obesity due to melanocortin 4 receptor deficiency: Leptin deficient (ob/ob) and LepR deficient (db/db) mice, carrying mutations in leptin (ob) and LepR (db) genes, respectively, exhibit excessive eating, develop obesity and diabetes, and are widely used as animal models of T2DM (Chen et al., 1996; Ninomiya et al., 2002; Gautron and Elmquist, 2011).