Loss of function (LoF) mutations in the MC4R pathway, including mutations in the pro-opiomelanocortin (POMC), prohormone convertase 1 (PCSK1), leptin receptor (LEPR), or MC4R genes, have been shown to cause early-onset severe obesity.
Furthermore, both mutations PCSK1-p.Asn180Ser and POMC-p.Phe144Leu, which had previously been reported to be associated with severe obesity, were also identified in this study, but did not co-segregate with obesity.
Proprotein convertase 1/3 (PC1/3) deficiency, an autosomal-recessive disorder caused by rare mutations in the proprotein convertase subtilisin/kexin type 1 (PCSK1) gene, has been associated with obesity, severe malabsorptive diarrhea, and certain endocrine abnormalities.
In humans, mutations in leptin, leptin receptor, proopiomelanocortin (POMC), melanocortin-4 receptor (MC4R) and prohormone convertase 1 (PC1) have been described in patients with severe obesity.