SIM1 and obesity due to melanocortin 4 receptor deficiency: Therefore, mutations in the leptin (LEP), leptin receptor (LEPR), proopiomelanocortin (POMC), single-minded homolog-1 (SIM1), prohormone convertase subtilisin/kexin type 1 (PCSK1) genes, melanocortin receptor 4 (MC4R) brain-derived neurotrophic factors (BDNFs), and neurotrophic tyrosine kinase receptor type 2 gene (NTRK2) are associated with the occurrence of monogenic obesity.