Introduction. There is evidence to suggest that common genetic polymorphisms can modify the effect of environmental risk factors on colorectal neoplasia.

Methods. Data on 1430 individuals were obtained from two chemoprevention trials, the Wheat Bran Fiber Trial (WBF) (1) and the Effects of Ursodeoxycholic Acid on Adenomatous Polyp Recurrence Trial (URSO) (2). Data were analyzed to test for gene-environment interactions between allelic variation in PPAR-γ (Pro12Ala, C1431T), body mass index (BMI) and waist circumference, and the biochemical biomarkers of metabolic syndrome. Simulated data were then used to determine if the sample size required to formally test the relationship between gene-exposure interactions could be reduced by using a genetically enriched study population. For this simulation aspect of the work, an established gene-drug interaction (i.e.: flavin monooxygenase 3 (FMO3) and sulindac) was used as a model system.

Results. There was a borderline significant interaction between BMI and PPAR-γ for the Pro12Ala genotype (p _inter = 0.11) and significant interactions between BMI and the C1431T genotype (p_inter = 0.09). Results from the recursive partition model identified BMI (p = 0.007) and baseline fasting glucose levels (p = 0.033) as significant predictors of colorectal adenoma recurrence for carriers of Ala12 and waist circumference as a significant predictor for the Pro12Pro12 carriers (p = 0.002). Results from the simulated studies indicated that using genetically pre-screened and enriched populations can result in a 50% savings in the number of subjects required to test the candidate gene-drug interaction.

Conclusions. These findings provide evidence that the effect of allelic variation in PPAR-γ on colorectal adenoma recurrence is modified by BMI and that component traits of metabolic syndrome differentially affect the risk of colorectal adenoma recurrence depending on genotype. In addition, using genotype as an inclusion criterion in future studies of adenoma recurrence will result in a smaller sample size required to test gene-environment interactions.