PRKAA2 and obesity due to melanocortin 4 receptor deficiency: Beginning at 29 weeks of age, the chow-fed AKO mice gained more weight than their counterparts, and the HFD challenge exacerbated the weight gain caused by the deletion of adipocyte AMPK, as evidenced by the earlier appearance (at 25 weeks of age) of more severe obesity in HFD-fed AKO mice (Figure 2A).