LEP and obesity due to melanocortin 4 receptor deficiency: Factors that are raised in obesity, such as blood insulin levels, insulin-like growth factor (IGF) 1, leptin, interleukin 6, and tumor necrosis factor-alpha (TNF-α) are associated with activation of intracellular signaling pathways, such as the PI3kinase or mitogen-activated protein kinases (MAPK) pathway 7,8.