IRX3 and obesity due to melanocortin 4 receptor deficiency: A striking finding is that obesity-associated noncoding sequences within the FTO locus are associated with expression of the homeobox gene IRX3 at megabase distances, but not with expression of FTO itself; (91) this association seems to be driven by a topologically associated domain (TAD) structure encompassing the FTO and IRXB genes cluster (92).