IRX3 is a member of the Iroquois homeobox gene family and plays a role in an early step of neural development. Members of this family appear to play multiple roles during pattern formation of vertebrate embryos. Specifically, IRX3 contributes to pattern formation in the spinal cord where it tranlates a morphogen gradient into transcriptional events, and is directly regulated by NKX2-2. 
Obesity-associated noncoding sequences within FTO interact with the promoter of IRX3 and FTO in human, mouse, and zebrafish. Obesity-associated single nucleotide polymorphisms are related to the expression of IRX3 (not FTO) in the human brain. A direct connection between the expression of IRX3 and body mass and composition was shown through the decrease in body weight of 25-30% in IRX3-deficient mice. This suggests that IRX3 influences obesity.
^Lewis MT, Ross S, Strickland PA, Snyder CJ, Daniel CW (Jun 1999). "Regulated expression patterns of IRX-2, an Iroquois-class homeobox gene, in the human breast". Cell and Tissue Research296 (3): 549–54. doi:10.1007/s004410051316. PMID10370142.
^Smemo S, Tena JJ, Kim KH, Gamazon ER, Sakabe NJ, Gómez-Marín C et al. (Mar 2014). "Obesity-associated variants within FTO form long-range functional connections with IRX3". Nature507 (7492): 371–5. doi:10.1038/nature13138. PMID24646999.
Trynka G, Zhernakova A, Romanos J, Franke L, Hunt KA, Turner G et al. (Aug 2009). "Coeliac disease-associated risk variants in TNFAIP3 and REL implicate altered NF-kappaB signalling". Gut58 (8): 1078–83. doi:10.1136/gut.2008.169052. PMID19240061.