GSTP1 and asthma: Recent studies support the presence of gene–environment interaction, or effect modification, between exposure to air pollutants and glutathione S-transferase P1 (GSTP1) variants, especially the isoleucine (Ile)/valine (Val) polymorphism at amino acid position 105 with respect to childhood asthma and nasal allergic responses (Gilliland et al. 2004; Lee et al. 2004).