NRXN1 and asthma: A logistic regression model including an interaction term between genotype and ETS exposure in relation to the asthma–eczema comorbidity confirmed a significant gene–environment interaction for both TNS1 rs918949 (p for interaction < 0.001) and NRXN1 rs10194978 (p for interaction = 0.037), consistent with their synergistic effect on the risk of developing the combined asthma–eczema phenotype.