IRS1 and obesity due to melanocortin 4 receptor deficiency: Out of 9436 genes differentially expressed by CC strain, 1516 genes were found to be associated with obesity traits in humans according to the GWAS database, including Hmga1 and Irs1; 431 of these 1516 genes were also significantly correlated with body fat % in the CC (Fig. 4B; see Supplementary Table 8, Additional file 2).