The interaction of the FTO gene SNPs with the Iroquois homeobox 3 (IRX3) and Iroquois homeobox 5 (IRX5), genes also associated with the development of obesity and an effector of the FTO variants (48), may jointly regulate adipogenesis and cause white adipose tissue browning in mice (49). This evidence concerns the gene IRX5 and obesity due to melanocortin 4 receptor deficiency.