LEP and obesity due to melanocortin 4 receptor deficiency: Pathogenic variants in several genes have been found to be responsible for monogenic obesity, including the leptin gene (LEP), the leptin receptor gene (LEPR), the melanocortin-4 receptor gene (MC4R), proopiomelanocortin gene (POMC), the proprotein convertase subtilisin/kexin type 1 gene (PCSK1), the single-minded homolog 1 gene (SIM1), the SH2B adaptor protein 1 gene (SH2B1), the melanocortin receptor accessory protein 2 gene (MRAP2) and others [2].