LEP and obesity due to melanocortin 4 receptor deficiency: Mutations in several genes implicated in the leptin–melanocortin pathway have been shown to lead to autosomal recessive forms of obesity such as leptin (LEP), leptin receptor (LEPR), melanocortin 4 receptor (MC4R), pro-opiomelanocortin (POMC), prohormone convertase subtilisin/kexin type 1 (PCSK1), single-minded 1 (SIM1), neurotrophic tyrosine kinase receptor type 2 (NTRK2), dedicator of cytokinesis 5 (DOCK5), kinase suppressor of Ras2 (KSR2), or tubby-like protein (TUB) [7].