Genetic monitoring of human polymorphic cancer susceptibility genes by polymerase chain reaction: Application to glutathione transferase μ

Several genes involved in the metabolism of carcinogens have been found to be polymorphic in human populations and are associated with increased risk of cancer at some sites. This study focuses on the polymorphic enzyme glutathione transferase μ (GT μ). Smokers with low lymphocyte GT μ activity are at an approximately 2- fold higher risk for lung cancer and an approximately 3-fold higher risk for stomach and colon adenocarcinomas. Recent cloning and sequencing of the GST1 gene has allowed the development of convenient genotyping methods based on restriction fragment length polymorphisms (RFLP) or the polymerase chain reaction (PCR). The GST1 polymorphism has been shown to be a deletion of the gene locus. To detect the presence or absence of the gene we amplified exons 4-5 and/or exons 6-7 of the GST1 gene by PCR. PCR amplification produced bands of 215-bp or 273-bp from individuals with one or two copies of the GST1 allele and no band if the individual was homozygously deleted (0/0). In the exon 6-7 PCR, we co-amplified a 268-bp portion of the β-globin gene as an internal reference standard for quantitative analysis of product yield. This allowed homozygote individuals (+/+) to be distinguished from heterozygotes (+/0). We have compared the GST1 genotype to lymphocyte GT μ activity measured on trans-stilbene oxide (TSO) in the lymphocytes of 45 individuals. Low GT μ activity (< 67 pmole/min/10⁷ cells) was strongly associated (24/24) with the GST1 0/0 genotype. With the exception of one individual, activities greater than 67 pmole/ min/10⁷ were associated with the presence of the GST1 allele (20/21). Individuals with the highest GT-TSO activity were found to be homozygous for GST1 (+/+), while heterozygotes (+/0) generally had lower activity suggesting a gene dosage effect in lymphocytes. The allele distribution among four sampled populations varied considerably. In a North Carolina population, 51% (65/127) were GST1 0/0, and this finding is consistent with those of other studies based on phenotypic analysis. In three smaller cohorts, the GST1 0/0 genotype was observed to occur in: 30% (14/47) of Finnish foundry workers, 33% (18/54) of Georgia dye workers, and 62% (74/120) of Taiwanese placental samples. In the future, we shall investigate the mechanistic link between polymorphisms in carcinogen metabolism genes and interindividual variation in measures of DNA damage, such as DNA adducts and hprt mutation frequency.