POMC and obesity due to melanocortin 4 receptor deficiency: By contrast, Pomc knockout mice [10,30,31] exhibit a phenotype that is more dramatic than ablation of Pomc neurons, with obesity starting at 4–8 wk of age and an eventual ∼50% increase in body weight, whereas Pomc-ablation mice develop obesity starting at 4 mo of age with an eventual 15%–30% increase in body weight (Figure 5).