IRX5 and obesity due to melanocortin 4 receptor deficiency: In another elegant study, Claussnitzer et al. [133] demonstrated that rs1421085, an obesity-associated SNP present in the first intron of the fat mass and obesity-associated (FTO) gene, was actually not affecting FTO expression, but instead of Iroquois homeobox 3 (IRX3) and Iroquois homeobox 5 (IRX5) through long-range interactions [133,134].