Although GSTP1 is the GST enzyme most expressed in the lung (Fryer et al. 1986), deficiency of two other GST genes, GSTM1 and GSTT1, has also been shown to influence the effect of passive smoking on the risk of childhood asthma and wheezing (Gilliland et al. 2002b; Kabesch et al. 2004). Here, GSTP1 is linked to asthma.