Several case control studies have found a higher prevalence of both GSTM1 null genotypes and GSTT1 null genotypes in asthma cases, compared with controls (Vavilin et al., 2002; Mostafa et al., 2004; Zhang et al., 2004; Hanene et al., 2007; Karam et al., 2012; Iorio et al., 2015). This evidence concerns the gene GSTM1 and asthma.