LEP and obesity due to melanocortin 4 receptor deficiency: Leptin was identified as the product of the obesity (ob) gene [10], which is secreted into the circulation by large adipocytes, and has been shown to cross the blood–brain barrier and bind to specific receptors in the hypothalamus to alter the expression of several neuropeptides that regulate neuroendocrine function, energy intake and expenditure leading to a decrease in appetite, reduction of body fat and body weight [11, 12].