LEP and obesity due to melanocortin 4 receptor deficiency: Leptin, which belongs to a family of adipokines released from white adipose tissue and is upregulated in obesity, has been shown to play an important role in the mechanism of initiation and progression of IBD exerting the proinflammatory intestinal activity due to promoting the expression of cytokines such as TNF-α and IL-6 [42,46].