Genes functioning in the leptin-melanocortin pathway such as those encoding leptin (LEP), leptin receptor (LEPR), melanocortin 4 receptor (MC4R), pro-opiomelanocortin (POMC) and brain-derived neurotrophic factor (BDNF) have been implicated in the monogenic form of obesity (reviewed in [30]). The gene discussed is MC4R; the disease is obesity due to melanocortin 4 receptor deficiency.