IRX3 and obesity due to melanocortin 4 receptor deficiency: In a detailed study by Claussnitzer et al., it has been described that single-nucleotide polymorphism (SNP) rs1421085 underlies the genetic association between fat mass and obesity-associated (FTO) locus; obesity and the presence of the C risk-allele of the FTO locus results in a cell-autonomous, IRX3- and IRX5-dependent shift in the gene expression programs, generating white adipocytes instead of brown with lipid-storage and decreased thermogenesis.