Polymorphisms of 5,10-methylenetetrahydrofolate reductase (MTHFR C677T) and thymidylate synthase enhancer region (TSER) as a risk factor of cholangiocarcinoma in a Korean population

Background: 5, 10-Methylenetetrahydrofolate reductase (MTHFR), a key enzyme in folate metabolism, plays a major role in the provision of methyl groups for DNA methylation; thymidylate synthase (TS) is a rate-limiting enzyme in the synthesis of dTMP and DNA repair. The clinical role of genetic polymorphisms of MTHFR and that of the TS enhancer region (TSER) were demonstrated in several clinical studies with colorectal, esophageal, gastric and breast cancer. However, there have never been any studies on the association between cholangiocarcinoma (CCC) and genetic polymorphisms of MTHFR and TSER. Therefore, the polymorphism of MTHFR and TSER, which share a common substrate, 5,10-methylenetetrahydrofolate, in CCC was examined, concurrently. The influence of these polymorphisms on plasma homocysteine levels was also investigated. Patients and Methods: Blood samples were obtained from 47 patients with CCC and 204 healthy control donors. Using polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP), the C to T transition at position 677 of MTHFR and tandem repeat of 28bp in the enhancer region of TS gene were analyzed. Plasma homocysteine levels were also determined. Results: According to the logistic regression model, a combination of MTHFR 677CC with the TSER 2R(+) genotype had a relative risk of 5.38 (95% CI, 1.23-23.56) of developing CCC compared to MTHFR 677CC with TSER 2R(-) (p=0.0257). The level of homocysteine was lower in CCC patients than healthy controls without statistical significance (8.27 +/- 4.17 vs. 9.40 +/- 2.57, p=0.093). Conclusion: Our data suggest a role of MTHFR 677CC with the TSER 2R(+) genotype in increasing the risk of CCC. This study is the first to suggest an association between CCC and the polymorphisms of MTHFR and TSER.