Subsequently, several studies analyzed feNO in pediatric asthma, demonstrating its role as a marker of eosinophilic airway inflammation, since it is correlated with eosinophil counts in blood and induced sputum or bronchoalveolar lavage fluid, with serum eosinophil cationic protein and with IgE levels [9,65,66,67]. This evidence concerns the gene IGHE and asthma.