FGF21 and obesity due to melanocortin 4 receptor deficiency: FGF21 is supposed to have therapeutic potential for the treatment of metabolic syndrome and obesity, as it increases glucose uptake by the muscles [14] and adipose tissue (AT), induces adiponectin secretion by AT [15] and increases energy expenditure due to induction of browning of white adipose tissue (WAT) [16,17].