MC3R and obesity due to melanocortin 4 receptor deficiency: To date, several genes have been found to be related to obesity including the leptin (LEP) gene on chromosome 7 q, leptin receptor (LEPR) gene on 1 p, pro-opiomelanocortin (POMC) gene on 2 p, melanocortin 4 receptor (MC4R) gene on 18 q, melanocortin 3 receptor (MC3R) gene on 20 q, prohormone convertase 1 (PC1) gene on 5 q, peroxisome proliferator activated receptor gamma 2 (PPARγ2) gene on chromosome 3 p, obesity-associated FTO gene on chromosome 16 q 12.2 and the Niemann-Pick C1 (NPC1) gene on chromosome 18 q 11.2 (5,6,7).