LEP and obesity due to melanocortin 4 receptor deficiency: Monogenic obesity is caused by variants of only one gene [9], and several genes have been associated with this type of obesity, such as leptin (LEP), leptin receptor (LEPR), pro-opiomelanocortin (POMC), and melanocortin 4 receptor gene (MC4R), which is the most common form of monogenic obesity [10].