LEP and obesity due to melanocortin 4 receptor deficiency: In mice leptin has been shown to enhance airway responsiveness, suggesting an immunomodulatory role,48 and the effect has also been reported in human subjects, although results are inconsistent.49-51 If this potential underlying mechanism is a factor in the association between growth and asthma, we suggest that not only obesity but also weight gain in normal and overweight children leads to increased leptin levels.