FGF21 may also improve pancreatic β-cells function and survival [49], stimulate skeletal muscle glucose uptake [50], stimulate thermogenesis of brown fat by increasing the expression of thermogenic genes and enhancing the total and uncoupled respiration and glucose oxidation [32], and stimulate the hypothalamus or central nervous system for energy expenditure and reduction of obesity in rat DIO model [51]. The gene discussed is FGF21; the disease is obesity due to melanocortin 4 receptor deficiency.