Candidate pathway polymorphisms in one-carbon metabolism and risk of rectal tumor mutations.

We examined candidate polymorphisms in genes involved in the folate-mediated, one-carbon metabolism pathway, DNMT1 1311V, MTHFD1 R134K and R653Q, MTHFR R594Q, MTR D919G, MTRR H595Y and I22M, SHMT1 L474F, SLC19A1 H27R, and TDG G199S, and associations with rectal tumor characteristics. We hypothesized that these candidate genes would influence CpG Island Methylator Phenotype and potentially KRAS2 or TP53 tumors. Data from a population-based study of 747 rectal cases (593 with tumor markers) and 956 controls were evaluated using generalized estimating equations. We observed an increased risk of TP53 tumor mutations in homozygous carriers of the MTHFD1 134K allele (0R=2.0, 95%CI 1.2-3.1, P- trend=0.02). In the presence of low folate intake, the R134K variant was associated with increased risk of CIMP+ tumors (OR=2.8, 95%CI 1.04-7.7). The MTRR I22M variant genotype was associated with a modest increased risk of TP53 mutations (OR=1.7, 95%CI 1.2-2.5, P-trend=0.001). Our findings offer limited support that polymorphisms in one-carbon metabolism genes influence rectal tumor phenotype, and that folate may interact with MTHFD1 to alter CIMP+ risk.