IRS1 and obesity due to melanocortin 4 receptor deficiency: Notable ones included insulin receptor substrate 1 (Irs1) gene and monoacylglycerol O-acyltrasferase 1 (Mogat1) gene located within the Chr 1 obesity QTL interval near D1Mit215. Within the Chr 1 QTL interval, insulin-like growth factor binding protein 2 (Igfbp2) gene expression levels in liver were also negatively correlated with mesenteric fat pad weights.