IRX3 and obesity due to melanocortin 4 receptor deficiency: These data corroborate the suggestion that the FTO gene does not exert its effects on BMI and obesity through functional mutations, and that this effect is more likely to be exerted by the intron 1 of the FTO gene regulating the expression of the IRX3 and IRX5 loci, vital for adipocyte maturation [6, 7].