FTO and obesity due to melanocortin 4 receptor deficiency: We also found that higher maternal BMI at the start of pregnancy was associated with lower newborn methylation at a site (cg03221837) near IRX3. More copies of the risk allele at the obesity-associated SNP FTO is associated with higher blood expression of IRX3 in humans, and IRX3-deficient mice have been shown to have a 25-30% reduction in body weight (47).