Present results suggest that increased superoxide production and subsequent NO inactivation is associated to IR rather than to obesity itself, since elevated vascular superoxide generation and improving vasodilation in response to SOD are not detected in obese subjects without IR, who do not present altered endothelial vasodilation although they have a BMI similar to those with IR. The gene discussed is SOD1; the disease is obesity due to melanocortin 4 receptor deficiency.