FGF21 and obesity due to melanocortin 4 receptor deficiency: FGF21 is a member of the endocrine FGF subfamily, which is expressed predominantly in the liver and stimulates glucose uptake through the induction of GLUT1 in adipocytes [14]. In vivo treatment with FGF21 results in the amelioration of glucose and regulates lipid metabolism in both murine and nonhuman primate models of diabetes and obesity [15].