INS and obesity due to melanocortin 4 receptor deficiency: Although Dnmt3a-Tg mice had normal body weight, glucose tolerance, insulin sensitivity, and comparable sensitivity to high-fat-diet-induced obesity with wild-type (WT) mice (Figures 1C and S1A–S1C), their gastrocnemius, quadriceps, and TA muscle (fast-twitch muscle) mass were smaller (similar to that in patients with sarcopenia); conversely, soleus muscle mass was larger in Dnmt3a-Tg mice (Figure 1D).