MC4R and obesity due to melanocortin 4 receptor deficiency: Several syndromic and monogenic disorders of obesity that have been identified include Prader–Willi syndrome, Bardet–Biedl syndrome, and loss-of-function mutations in the genes encoding for pro-opiomelanocortin (POMC), leptin, leptin receptor (LEPR) or the melanocortin-4 receptor (MC4R) (17).