In this study we also investigated the

In this study, we also investigated the role of GST Pefloxacin Mesylate sale in relation to ASD. In univariable analyses, where the role of each GST gene (i.e., GSTM1, GSTT1, GSTP1) was individually assessed, we did not observe any significant associations between the GST genotypes and ASD. In contrast, a previous study that involved 70 ASD cases and 70 TD controls reported an increased ASD risk for individuals with the null polymorphism of GSTM1 of 2.02 (95% CI 1.03–4.04) (Buyske et al., 2006). In multivariable analyses, when we included the interactions between GST genes we found evidence of significant interaction between GSTP1 and GSTT1 in relation to ASD. Specifically, for children who were heterozygous for the GSTP1 Ile105Val polymorphism under the co-dominant genetic model, those with the null genotype (i.e., DD) in GSTT1 have almost three times higher odds of ASD when compared to children with either the GSTT1 I/I or I/D genotype. Though marginally significant, under the recessive model, in children with either the Ile/Ile or Ile/Val genotype, the odds of ASD were 2.14 times higher in those who also had the null GSTT1 genotype than in those with the other two genotypes. To the best of our knowledge, we are the first to report significant interactions between GSTT1 and GSTP1 in relation to ASD. Other studies have reported interactive effects of GST genes with other genes in relation to ASD. For example, James et al. (2006) reported a marginally significant increased risk of ASD for individuals with the GSTM1 null polymorphism alone (OR=1.37; 95% CI, 0.98–1.96), although in combination with a polymorphism in the reduced folate carrier gene, the OR was 3.78 (95% CI, 1.80–7.95) (James et al., 2006). These results, along with our findings, demonstrate the importance of incorporating gene–gene interaction effects in genetic association studies of complex diseases such as ASD, since interaction may be detected even when there are no main effects identified for the individual genes that are tested for association. This should be done whenever the interaction effects are meaningful from a biological perspective and when the sample size is sufficiently large to ensure the desired statistical power (e.g., 0.80) for such analyses. In this study, with 111 matched-pairs (222 children) and at 5% level of significance, we have a power of at least 0.8 to detect odds ratios of 3.0 or higher between each pair of genotypes, assuming that the frequency of the null genotypes is between 0.2 and 0.3, and the correlation between matched ASD cases and TD controls is 0.35. Our results suggest that the GSTP1 and GSTT1genes have an interactive effect in relation to ASD and that the heterozygous genotype of GSTP1 is the most deleterious. In the literature, we did not find a well-established genetic model for GSTP1. In fact, conflicting effects are reported for GSTP1, not only for the genetic models but also for the direction of influence [see http://snpedia.com/index.php/Rs1695]. For example, a study by Williams et al. (2007) indicated that the GSTP1 Ile allele seems to be over-transmitted in mothers who have a child with ASD (Williams et al., 2007). Another study by Aynacioglu, Nacak, Filiz, Ekinci, and Roots (2004) reported that the Val/Val homozygous genotype appeared to be somewhat protective against developing asthma compared to the other two genotypes (Aynacioglu et al., 2004). A recessive model of GSTP1 was used in a study by Wei et al. (2013), where a significant association was found for low-stage prostate cancer in a meta-analysis. A dominant model was considered by Chen et al. (2010) and a significant association of GSTP1 with hepatocellular carcinoma was observed (Chen et al., 2010). Using dominant and co-dominant models, Safarinejad et al. (2011) found an association between GSTP1 and prostate cancer in an Iranian population, and they emphasized that the heterozygous GSTP1 genotype Ile/Val is significantly associated with this disease (Safarinejad et al., 2011). Interestingly, Longo et al. (2013) recently reported an interaction between heterozygosity for the GSTP1 Ile105Val polymorphism and exposure to pesticides in relation to Parkinson's disease (Longo et al., 2013). Our results provide further evidence in support of the role of the GSTP1 Ile/Val genotype in susceptibility to a complex disease. Our findings also suggest that the deletion in the GSTT1gene on a GSTP1 heterozygous genetic background (Ile/Val) may influence the production of GST related enzymes that could contribute to increasing lipid peroxidation and oxidative stress, resulting in neuronal cell death or brain damage (Kern & Jones, 2006) and ASD. Although it is difficult to demonstrate the biological plausibility for our finding of a gene–gene interaction involving the heterozygous GSTP1 Ile/Val genotype, it should be noted that we observed a relatively large effect (i.e., MOR ∼3.0). While the results from our permutation tests are reassuring that our observations are very unlikely to be due to chance, we not only recommend replication in other populations, but also detailed functional analyses of the GST genes in order to confirm the role and significance of the interaction between GSTP1 and GSTT1 in the pathogenesis of ASD. Additionally, future research should investigate differences in GST genotypes in relation to oxidative stress and ASD severity.