In addition, it has been also reported that other two well-recognized standard genetic models of obesity, including mouse mammary tumor virus (MMTV)-TGF-α/Lep(ob)/(ob) (leptin-deficient) and MMTV-TGF-α/Lepr(db)/(db) (leptin receptor-deficient) mice, did not develop mammary tumors compared to wild-type mice [182,183]. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.