Smoking, overnutrition and a high red meat and low folate and calcium diet have been associated with colorectal cancer (CRC) and adenoma. The epidemiologic features of CRC among migrants and native populations in Hawaii suggest the modifying effects of genetic susceptibility factors on most of these associations. Taking advantage of the genetic and dietary diversity of our population, we have made good progress in investigating specific gene variants that affect one's capacity to bioactivate dietary carcinogens or utilize one-carbon groups for DNA synthesis or methylation. We also showed that a genetic variant associated with lower circulating IGF-I hormones may protect against colorectal neoplasia. We seek to renew grant 1 -R01-CA72520 to extend a case-control study of colorectal adenoma in order to test these gene-diet interactions in a large series of adenoma cases and controls, as well as to examine several new variants in these pathways in relation to adenoma, as well as CRC using existing samples/data from a companion study.
New aims also include discovering new SNPs and mapping haplotypes in major genes related to the activation of heterocyclic amines and assessing population stratification in our subjects using random genetic markers. A diet and lifestyle questionnaire will be administered in person to another 904 new adenoma cases and 904 endoscopically normal controls (for a total study sample of 1,204 adenoma cases and 1,404 controls) frequency-matched on age, sex, race/ethnicity, date and mode of endoscopy. Usual consumption of meat and fish items prepared by high-temperature methods and doneness of meats will be assessed, in addition to estimating the total intake of energy, nutrients, and other dietary components. Subjects will be phenotyped for several P450 enzymes by caffeine challenge. A blood sample will also be collected to genotype subjects for variants in a number of genes related to growth hormones, carcinogen activation and folate metabolism. Sequencing of genes related to heterocyclic amine activation in colorectal cancer patients of Japanese, Caucasian, African American, Latino or Native Hawaiian origin will allow for the construction of haplotypes. Correlations with CYP1A2 phenotype will help to select functional haplotypes which will then be tested for associations with adenoma and colorectal cancer. Genotyping for random markers will permit to exclude residual confounding by ethnicity.
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