MC4R and obesity due to melanocortin 4 receptor deficiency: Although monogenic forms of obesity—including mutations in the LEP and LEPR genes—are rare in humans, genome-wide association studies of polygenic (common) obesity largely revealed genes in the leptin–melanocortin 4 receptor (MC4R) hypothalamic appetite control axis or other nodes in central control of body weight by the brain (Loos & Yeo, 2022).