IRX3 and obesity due to melanocortin 4 receptor deficiency: SNPs located in intron1 of FTO have also been shown to affect the expression of neighboring genes such as Iroquois homeobox 3 (IRX3), Iroquois homeobox 5 (IRX5), and RPGR-Interacting Protein 1-Like (RPGRIP1L); another possible role of FTO in obesity is the regulation of macronutrient intake, as the FTO gene is expressed in the hypothalamus during starvation.