Background. Human genetic polymorphisms in metabolic activation and detoxification pathways are a major source of inter-individual variation in susceptibility to environmentally induced disease. The group has developed genotyping assays for the """"""""at-risk"""""""" variants of enzymes that protect against carcinogens in cigarette smoke, diet, industrial processes and environmental pollution. Population studies indicate that for these candidate susceptibility genes, the frequency of the at-risk genotypes for glutathione transferase M1 (GSTM1), theta 1 (GSTT1), Pi (GSTP1) and N-acetyltransferase (NAT1 and NAT2), XRCC1, XPD, vary significantly between ethnic groups. Some differences in cancer incidence among groups may be due to genetic metabolic differences as well as exposure differences. Mission: Our long-term goal is to understanding how genes and environment interact to influence risk of environmentally induced disease. To this end we are engaged in """"""""Environmental Genomics."""""""" This encompasses: 1) identification of candidate environmental response genes, 2) discovery and functional characterization of genetic and phenotypic variation in these genes, and; 3) the analysis in population studies of environmental disease susceptibility associated with functional polymorphisms, acquired susceptibility factors and exposures; and the interactions between these factors. Eventually we hope these genomic approaches will help us to develop assays using genotype, gene expression, and other biomarkers of exposure and effect, that will be predictive of future risk. This information will allow us to more carefully determine the bounds of human variability in risk assessment and will be useful in developing prevention strategies to reduce disease incidence. The Genetic Susceptibility Project takes the candidate susceptibility factors from the laboratory genotype/phenotype studies and tests them in population studies. We are collaborating with numerous NIH, and university-based epidemiology groups to design and carryout appropriate tests of these factors in population-based epidemiology studies. ? Progress/accomplishments:? 1) Genetically determined factors that alter the metabolism of tobacco carcinogens can influence an individuals susceptibility to bladder cancer. The associations between the genotypes of glutathione S-transferase (GST) M1, GSTP1, GSTT1 and N-acetyl-transferase (NAT) 1, and the phenotypes of NAT2 and cytochrome P450 (CYP) 1A2 and bladder cancer risk were examined in a case-control study involving 731 bladder cancer patients and 740 control subjects in Los Angeles County, California. Individual null/low-activity genotypes of GSTM1, GSTT1 and GSTP1 were associated with a 19-48% increase in odds ratio (OR) of bladder cancer. The strongest association was noted for GSTM1 (OR for the null genotype=1.48, 95% confidence interval CI=1.19-1.83). When the three GST genes were examined together, there was a monotonic, statistically significant association between increasing number of null/low-activity genotypes and risk (P for trend=0.002). OR (95% CI) for one and 2 or more null/low-activity GST genotypes was 1.42 (1.12-1.81) and 1.71 (1.25-2.34), respectively, relative to the absence of null/low-activity GST genotype. NAT2 slow acetylation was associated with increased bladder cancer risk (OR=1.26, 95% CI=1.00-1.57, P=0.048). The joint effect of NAT2 slow acetylator and null/low-activity GST genotypes on bladder cancer risk became stronger (OR=2.27, 95% CI=1.32-3.91), especially among individuals with known high exposures to carcinogenic arylamines. Among subjects with known low exposures to carcinogenic arylamines, the NAT2 slow acetylation-bladder cancer association was apparent only in the presence of 2 or more null/low-activity GST genotypes. There were no associations between bladder cancer risk and NAT1 genotype or CYP1A2 phenotype. ? 2) In collaboration with Columbia University, we have begun a new study examining how genotype may modify exposure effects on CpG methylation in newborn infants. We have started a pilot examining CpG island methylation levels in the umbilical cord blood DNA of 12 infants and if successful will expand this to the full group of 505 infants.
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