RBP4 and obesity due to melanocortin 4 receptor deficiency: Increased white-adipose-tissue (WAT) content, which constitutes the hallmark of obesity, leads to enhanced secretion of adipokines, including leptin, resistin, interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), visfatin, vaspin, and retinol-binding protein 4 (RBP-4).