MC4R and obesity due to melanocortin 4 receptor deficiency: Other loci which have been implicated in severe childhood monogenic obesity include genes of the proopiomelanocortin (POMC), the melanocortin receptor 4 (MC4R), the protein convertase 1/3 (PC 1/3), the single-minded homolog 1 (SIM1), and the brain-derived neurotrophic factor (BDNF) (31).