PCSK1 and obesity due to melanocortin 4 receptor deficiency: The presence of mutations in different genes have been reported to be pathogenic for obesity with alterations of the leptin–melanocortin pathway, including leptin (LEP), leptin receptor (LEPR), proopiomelanocortin (POMC), prohormone convertase 1 (PCSK1), and the melanocortin 4 receptor (MC4R), [4] as reported in Figure 1.