MC4R and obesity due to melanocortin 4 receptor deficiency: Genes in the leptin–melanocortin pathway, such as leptin (LEP), leptin receptor (LEPR), melanocortin-4 receptor (MC4R), adenylyl cyclase 3 (ADCY3), and brain-derived neurotrophic factor (BDNF) genes, are established contributors to obesity and insulin resistance [13].