Relationship Between Polymorphism Of MTHFR Gene And Susceptibility Of Colorectal Carcinoma

Objective:Colorectal carcinoma (CRC) is one of the most common malignanttumors of human. Recently the incidence of CRC has an increased trend. Theage of onset is becoming younger and younger. CRC was thought to be theresults of a complicated multistep process undergone the impact ofenvironment and genes. However, not all the subjects came to new CRC,when the total people exposured to the same high-risk environment. Itindicated that there was some difference about susceptibility of subjects. Theefficacy of the chemotherapy is not satisfied. It brings a lot of suffering andeconomic burden to patients with CRC. Presently reported Folic acid intakewas too low or reduced synthesis was a risk factor for CRC. Folate intakeexerts their biological functions after metabolic conversion, andmethylenetetrahydrofolate reductase (MTHFR) is the rate-limiting enzyme inthe folate metabolic pathway. In addition, presently reported severalmethylenetetrahydrofolate reductase gene (MTHFR) single nucleotidepolymorphism (SNP), two of those reside in codon677C�'T (677C�'T SNP)and1298A�'C (1298A�'C SNP), have a close relationship with CRC. We tryto investigate the possible relationship between the methylenetetrahydrofolatereductase (MTHFR) C677T and A1298C polymorphism and susceptibility ofCRC, and investigate its correlation to clinical pathological features (such astumor size, location, histological type, differentiation, metastasis of lymphnode and Duke’s stage), in order to further reveal the etiology mechanism ofCRC, and contribute to early diagnosis of CRC and prognosis, and as aspecific biological indicators for screening and protection of susceptiblepopulation. Methods:This case-control study included120cases of CRC,202cases of controls.In the same period, we collected the patient’s age, gender, susceptive factorssuch as smoking and drinking. Two milliliters of the peripheral anticoagulantblood was harvested from the patients and controls before chemotherapy andstored at-80℃. Genemic DNA was extracted from peripheral blood byTIANamp Genomic DNA. The MTHFR gene C677T and A1298Cpolymorphism of the120patients and202controls were analyzed by thePCR-based restriction fragment length polymorphism (PCR-RFLP) method.Hardy-Weinberg analysis was performed by comparing the observed andexpected genotype frequencies in study groups using Chi-square test.Comparison of the MTHFR C677T and A1298C genotype and allelotypedistribution in the study groups was performed by means of two-sidedcontingency tables using Chi-square test. The associations of different factorswith CRC risk were estimated by calculating the odds ratios (ORs) and their95%confidence intervals (95%CIs) with unconditional logistic regressionmodel adjusted by age, gender and so on.Results:1MTHFR gene C677T polymorphism and CRC1.1The frequencies of the MTHFR C677T C/C、C/T and T/T genotypeswere45.0%、46.7%and8.3%in CRC cases, and32.7%、47.5%and19.8%incontrols, the genetype frequency distribution of two groups have significantvariance (x~2=9.46，P＜0.01)；The frequencies of the MTHFR C677T C and Tallelotype were68.3%and31.7%in CRC cases, and56.4%and43.6%incontrols, the allelotype frequency distribution of two groups have significantvariance (x~2=8.95，P＜0.01).1.2The C677T T allele showed a significantly decreased risk for CRC(aOR=0.57,95％CI=0.40-0.81, P＜0.01) when compared with the C677T Callele; Compared with C/C homozygotes, T/T homozygotes had a0.28-folddecreased risk (95％CI=0.12-0.63, P＜0.01).1.3The C677T T allele also showed a significantly decreased risk forCRC (aOR=0.44,95％CI=0.25-0.80, P＜0.01) when compared with the C677T C allele among non-drinkers; And a significant reduction of theMTHFR genotypes with CRC risk was observed, with an aOR of0.41(95％CI=0.17-1.95, P＜0.05) for C/T heterozygotes and0.26(95％CI=0.09-0.78,P＜0.05) for T/T homozygotes when compared with C/C homozygotes.Among drinkers compared with C/C homozygotes, C/T heterozygotes and T/Thomozygotes were not significantly different with CRC risk (C/T: aOR=0.86,95％CI=0.43-1.72, P＞0.05; T/T: aOR=0.29,95％CI=0.08-1.00, P＞0.05).1.4No correlation was found between MTHFR C677T polymorphismand tumor size, location, differentiation, histological grade, lymph nodemetastases, or Duke’s stage (P＞0.05).2MTHFR gene A1298C polymorphism and CRC2.1The frequencies of the MTHFR A1298C A/A、 A/C and C/Cgenotypes were64.2%、32.5%and3.3%in CRC cases, and62.9%、31.2%and5.9%in controls, the genetype frequency distribution of two groups have notsignificant variance (x~2=1.09，P＞0.05)；The frequencies of the MTHFRA1298C A and C allelotype were80.4%and19.6%in CRC cases, and78.5%and21.5%in controls, the allelotype frequency distribution of two groupshave not significant variance (x~2=0.35，P＞0.05).2.2The A1298C C allele showed a significantly decreased risk for CRC(aOR=0.91,95％CI=0.60-1.39, P＞0.05) when compared with the A1298C Aallele. Compared with A1298C A/A homozygotes, A1298C C/C homozygoteshad a0.63-fold decreased risk (95％CI=0.19-2.09, P＞0.05), whereas A1298CA/C heterozygotes had a1.03-fold increased risk (95％CI=0.61-1.73, P＞0.05)of CRC.2.3The A1298C C allele showed a significantly increased risk for CRC(aOR=1.01,95％CI=0.25-0.76, P＞0.05) when compared with the A1298C Aallele among non-drinkers; compared with A/A homozygotes, A/Cheterozygotes and C/C homozygotes were not significantly different withCRC risk (P＞0.05). Among drinkers compared with AA homozygotes, A/Cheterozygotes was not significantly different with CRC risk (P＞0.05).2.4No correlation was found between MTHFR A1298C polymorphism and tumor size, location, differentiation, lymph node metastases, or Duke’sstage (P＞0.05).3. MTHFR gene C677T and A1298C polymorphism and CRC3.1Combined MTHFR C677T and A1298C genotypes, The frequenciesof MTHFR CC/AA (677CC+1298AA) genotype is31.7％for the cases and19.8％for the controls, the frequencies of MTHFR TT/AA (677TT+1298AA)genotype is6.7％for the cases and18.3％for the controls, the differencebetween the cases and controls was statistically significant (P＜0.01).3.2Compared with MTHFR C677T C/C homozygotes and A1298C A/Ahomozygotes, MTHFR C677T T/T homozygotes and A1298C A/Ahomozygotes had a0.22-fold decreased risk (95％CI=0.09-0.57, P＜0.01).Conclusions:1The MTHFR C677T T/T homozygotes is associated with a decreasedrisk of CRC; Alcohol drinking negates the protective effect of C677T T/Thomozygotes. The C677T polymorphism has no relations with clinicalpathological features of CRC.2The MTHFR A1298C polymorphism has no relations withsusceptibility of CRC; The A1298C polymorphism has no relations withclinical pathological features of CRC.3There is a synergic effect between MTHFR C677T T/T and A1298CA/A genotypes with CRC risk.