MC4R and obesity due to melanocortin 4 receptor deficiency: Although obesity is most commonly polygenic, rare monogenic forms do exist, and the affected genes described thus far include leptin, the leptin receptor, pro‐opiomelanocortin (POMC), single‐minded 1 (SIM1), neurotrophic tyrosine kinase receptor type‐2 (NTRK2), and the melanocortin 4 receptor (Dubern and Clement 2012).