To date, GSTP1 polymorphisms have been reported to modify the association between traffic-related air pollution and allergic sensitization (Melén et al. 2008), persistent wheeze (Schroer et al. 2009), and asthma (Carlsten et al. 2011a) in individual birth cohorts; and in one study these strata-specific findings were further attenuated by TNF (tumor necrosis factor) polymorphisms (Melén et al. 2008). This evidence concerns the gene TNF and asthma.