GSTM1, GSTT1 Null Variants, and GPX1 Single Nucleotide Polymorphism Are Not Associated with Bladder Cancer Risk in Egypt

Bladder cancer is the most common male malignancy in Egypt, and disparities in incidence exist between men and women regardless of geographic region, with a worldwide age-standardized incidence rate of 10.1 per 100,000 persons-years for men and 2.5 per 100,000 persons-years for women (1). Tobacco smoke exposure and Schistosoma haematobium (SH) infection are established risk factors for bladder cancer. In Egypt, smoking is much more prevalent (2) among adult males (22%–47%) than among females (2%–7%), but smoking has not been shown to fully account for the observed gender differences in bladder cancer incidence (1). A common pathway of bladder carcinogenesis for both tobacco smoke and SH infection may be that the cellular response to oxidative stress and inflammation, and several genes including glutathione-S-transferase (GST) and glutathione peroxidase (GPX) are thought to be involved in the mediation of the toxicity of reactive oxygen species. A number of studies have investigated the association between GSTM1, GSTT1, and GPX1 variant genotypes and increased bladder cancer risk, including interactions with smoking, SH infection, and gender, however, with conflicting results. In the present study, polymorphisms in GSTM1, GSTT1, and GPX1 genes were hypothesized to modify bladder cancer risk and possibly explain these gender differences.

Adult urinary bladder cancer cases (n = 625) were recruited within 1 year of diagnosis and noncancer controls (n = 626) were recruited as previously described (3). Cases were confirmed by pathologic examination and defined as urothelial (transitional) cell carcinoma (UCC) and squamous cell carcinoma (SCC), adenocarcinoma, or other types of carcinoma of the bladder. We included only those with UCC and SCC (95% of the cases) in this analysis. After informed consent, cases and controls were administered a detailed questionnaire that included questions on sociodemographic characteristics, smoking history, and medical history, including a history of schistosomiasis.

GSTM1 null, GSTT1 null, and GPX1 rs1050450 genotypes were determined using TaqMan allelic discrimination assays (Applied Biosystems), with a successful genotyping rate of 99.0% or more and genotype concordance (among 10% blind quality control duplicates) of 99.0% or more.

ORs and 95% CIs were used to estimate associations between each genotype and bladder cancer risk. The estimates were obtained from unconditional logistic regression analysis, adjusting for sex, age, region of residence, tobacco smoking, and schistosomiasis. After the initial analysis of all cases combined, separate models were created for UCC and SCC, and stratified by gender, tobacco smoking in men (ever vs. never), and self-reported history (yes/no) of schistosomiasis. For instances wherein the number of exposed subjects was fewer than 10 for any of the aforementioned comparisons, we used exact methods to estimate the OR and 95% CI. All statistical analyses were done using SAS (version 9.2; SAS Institute Inc.). The genotype distributions of all 3 polymorphisms were in Hardy–Weinberg equilibrium in control subjects, calculated using Pearson's goodness-of-fit test.

Table 1 shows the frequency distribution of the demographic variables and putative risk factors of bladder cancer. We found no statistically significant association between bladder cancer risk for developing both UCC and SCC (in men and women combined) and the GSTM1 null variant (OR = 0.94, 95% CI = 0.74–1.18), GSTT1 null variant (OR = 1.09, 95% CI = 0.83–1.42), and GPX1 T/T genotype (OR = 1.02, 95% CI = 0.64–1.64; ref. Table 2). In addition, no statistically significant associations were observed for UCC or SCC separately. Similarly, we found no significant interactions between genotypes and smoking, SH infection, or gender (data not shown).

We found no statistically significant association between bladder cancer risk and functional polymorphisms in the GSTM1, GSTT1, and GPX1 genes, and no significant interactions between genotypes and smoking, SH infection, or gender.

Previous studies have found that the GSTM1 null genotype is associated with an increased risk of developing bladder cancer overall, among SH-infected individuals (4), and among male smokers (5). Other studies have reported increased risk in women but not in men, among women, and only among smokers (6), as well as no overall association with increased risk (7). Associations between the GSTT1 null variant and overall increased risk were reported by some investigators (7) but not others (6) and among women but not among men (7). Similarly, studies of the association of the variant GPX1 genotype with bladder cancer reported inconsistent findings (8, 9).

One possible explanation for the inconsistencies in findings of prior and current studies is that they could reflect differences in gene–environment interactions in different populations. Another possibility is differences in laboratory methods (e.g., RFLP may have a higher rate of false positives vs. TaqMan).

In conclusion, our results suggest that common genetic variations in GSTM1, GSTT1, and GPX1 are not associated with overall bladder cancer risk.

No potential conflicts of interest were disclosed.

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