In transgenic animal models, such as leptin-deficient (ob/ob) mice and LepRb-deficient (db/db) mice, exhibit the development of marked obesity, insulin resistance, hyperinsulinemia, impaired glucose homeostasis, and diabetes (Schwartz et al., 1996; Cohen et al., 2001; McMinn et al., 2005). Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.