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. This evidence concerns the gene LEP and asthma.