In 2005, Yang et al. used DNA arrays and found that the expression of RBP4 is elevated in the adipose tissue of adipose-Glut4(−/−) mice; for the first time, they reported that RBP4 is a new adipokine in animal experiments and proved that RBP4 is closely related to insulin resistance and T2DM [21]. This evidence concerns the gene RBP4 and type 2 diabetes mellitus.