Administration of exogenous FGF21, FGF21 analogs, or FGFR1-KLB agonists promotes an array of metabolic benefits in mice that intercept obesity, type 2 diabetes, fatty liver disease, and hyperlipidemia [137,138,139,140,141]. The gene discussed is FGF21; the disease is obesity due to melanocortin 4 receptor deficiency.