Genetic polymorphism at GSTM1 and GSTT1 gene loci and susceptibility to oral cancer

Abstract

GSTs are phase II enzymes which are involved in the detoxification of active metabolites of many potential carcinogens from tobacco smoke and therefore may play an important role in modulating susceptibility to tobacco related cancers. This study evaluates the influence of genetic polymorphisms of GSTM1 and GSTT1 gene loci on susceptibility to oral cancer. The genotyping was based on multiplex PCR assay that identified the GSTM1 and GSTT1 null (-/-) genotypes but didn't distinguish homozygous wild type+/+ and heterozygous +/- individuals. Genomic DNA was isolated from cases with oral cancer (n=40) and normal controls (n=87). The prevalence of the GSTM1 null genotypes was 29/87 (33.3%) and 21/40 (52.5%) in controls and oral cancer cases, respectively but the differences were not significant (OR=2.2; 95%CI=0.96-5.1; p=0.06). The frequency of homozygous GSTT1 null genotype in cancer cases was 17/40 (42.5%) as compared to 13/87 (14.94%) in controls and the differences were highly significant (OR=4.2; 95%CI=1.64-10.9; p=0.0002). Oral cancer cases had higher proportion of both GSTM1 and GSTT1 null genotypes as compared to controls but the differences were not statistically significant (OR=2.9; 95%CI=0.71-11.9; p=0.17). When individuals were categorized into two groups, no differences were observed for GSTM1 null genotype frequencies in control and cancer cases (OR=2.9; 95%CI=0.9-9.6; p=0.08) (OR=1.6; 95%CI=0.44-6.1; p=0.58) in <=50 yrs and >50 yrs of age groups. Significant differences between control and cancer cases were observed for GSTT1 null genotypes both in <=50 yrs and >50 yrs of age groups (OR=4.0; 95%CI=1.1-15.0; p=0.03) (OR=4.5; 95%CI=0.97-22.29; p=0.05), respectively. The effect of smoking on GSTM1 null individuals was not found significant (OR=1.0; 95%CI=0.19-4.86; p=0.75) but it was significant in case of GSTT1 null individuals (OR=6.33; 95%CI=1.0-44.1; p=0.02). Our results thus suggest that GSTT1 gene polymorphisms modulate susceptibility to tobacco-related cancer of the oral cavity.