Associations between two common variants C677T and A1298C in the methylenetetrahydrofolate reductase gene and measures of folate metabolism and DNA stability (strand breaks, misincorporated uracil, and DNA methylation status) in human lymphocytes in vivo.

OBJECTIVE: Homozygosity for variants of the methylenetetrahydrofolate reductase (MTHFR) gene is associated with decreased risk for colorectal cancer. We have investigated the relationships between two variants of the MTHFR gene (C677T and A1298C) and blood folate, homocysteine, and genomic stability (strand breakage, misincorporated uracil, and global cytosine methylation in lymphocytes) in a study of 199 subjects. RESULTS: The frequencies of homozygosity for the C677T and A1298C variants of the MTHFR gene were 12.6% and 14.6%, respectively. Plasma homocysteine, folate, vitamin B12, 5-methyltetrahydrofolate, and RBC folate were determined in the C677T genotypes. Plasma folate was significantly lower (P < 0.001) in the homozygous variants (6.7 +/- 0.6 ng/mL) compared with wild-types (8.8 +/- 0.4 ng/mL) and heterozygotes (9.1 +/- 0.5 ng/mL). Homocysteine was significantly higher (P < 0.05) in homozygous variants (13.2 +/- 1.1 micromol/L) compared with homozygous subjects (10.9 +/- 0.4 micromol/L). Homozygous variants had significantly lower (P < 0.05) RBC folate (84.7 +/- 6.3 ng/mL) compared with wild-types (112.2 +/- 5.2 ng/mL) and heterozygous individuals (125.1 +/- 6.6 ng/mL). No significant difference in RBC folate was observed between wild-types and heterozygotes. The A1298C variant did not influence plasma homocysteine, folate, 5-methyltetrahydrofolate, vitamin B12, or RBC folate. Lymphocyte DNA stability biomarkers (strand breaks, misincorporated uracil, and global DNA methylation) were similar for all MTHFR C677T or A1298C variants. CONCLUSION: Data from this study do not support the hypothesis that polymorphisms in the MTHFR gene increase DNA stability by sequestering 5,10-methylenetetrahydrofolate for thymidine synthesis and reducing uracil misincorporation into DNA.     

The Common 677C>T Gene Polymorphism of Methylenetetrahydrofolate Reductase Gene is not Associated with Breast Cancer Risk

Methylenetetrahydrofolate reductase (MTHFR) is involved in folate metabolism and plays a role in DNA biosynthesis, methylation, and repair in actively dividing cells. A common 677C>T polymorphism in the gene for MTHFR, leading to a thermolabile enzyme with decreased activity, has been associated with reduced plasma folate levels and elevated homocysteine levels and could be a risk factor for breast cancer. In the present case-control study, MTHFR genotype was determined in 500 women with clinically verified breast cancer and 500 female age-matched healthy control subjects. The homozygous TT genotype was found in 13.0% patients and 13.1% controls (P = n.s.). The odds ratio of TT homozygotes for breast cancer was 0.99 (95% confidence interval 0.68–1.43). The MTHFR genotype was furthermore not associated with tumor size, histological grading, estrogen or progesterone receptor status and age at diagnosis. In a subgroup of 116 premenopausal patients, no increased frequency of the homozygous 677T genotype was found (13.8%). Therefore, we conclude that the MTHFR 677C>T polymorphism is not associated with individual susceptibility to breast cancer.     

Genomic DNA hypomethylation, a characteristic of most cancers, is present in peripheral leukocytes of individuals who are homozygous for the C677T polymorphism in the methylenetetrahydrofolate reductase gene.

DNA methylation is an epigenetic feature of DNA that influences cellular development and function, and aberrations of DNA methylation are a candidate mechanism for the development of cancer. Methylenetetrahydrofolate reductase (MTHFR) catalyzes the synthesis of 5-methyltetrahydrofolate, the methyl donor for methionine synthesis and the precursor of S-adenosylmethionine. S-adenosylmethionine is the universal methyl donor for methylation reactions, including that of DNA methylation. In the present study, we investigated whether a common C677T mutation in the MTHFR gene, which results in reduced enzyme activity in vitro, affects genomic DNA methylation. We selected 9 subjects homozygous for the wild-type MTHFR and 10 subjects homozygous for the mutation (T/T). Genomic DNA methylation was determined by an established enzymatic assay that measures the capacity of DNA to accept methyl groups in vitro, which is inversely related to endogenous methylation. DNA from subjects with the T/T MTHFR genotype had a significantly higher methyl group acceptance capacity (12,615 +/- 1836 dpm/2 microg of DNA) compared with wild-type MTHFR (7843 +/- 1043 dpm/2 microg of DNA; P < 0.05), indicating DNA hypomethylation in the T/T genotype. Furthermore, DNA methylation was directly and significantly related to RBC folate concentrations in persons with the T/T genotype, but not in those with wild-type MTHFR. These data are consistent with prior observations, which suggest that the T/T genotype is associated with impaired MTHFR activity in vivo and that the cellular impact of this impairment is determined, in part, by folate status. The relationship of genomic DNA hypomethylation in persons with the T/T MTHFR genotype to the development of cancer remains to be defined.     

Genetic polymorphisms of the methylenetetrahydrofolate reductase gene, plasma folate levels and breast cancer susceptibility: a case-control study in Taiwan

Methylenetetrahydrofolate reductase (MTHFR) balances the pool of folate coenzymes in one-carbon metabolism for DNA synthesis and methylation, both are implicated in carcinogenesis. Two common variants in the MTHFR gene (C677T and A1298C) have been associated with reduced enzyme activity, thereby making MTHFR polymorphisms a potential candidate cancer-predisposing factor. To evaluate the C677T and A1298C functional polymorphisms in the MTHFR gene and their associations with breast cancer risk, as well as the potential modifying effect by plasma folate status on the MTHFR-associated risk, a hospital-based case-control study was conducted on a Taiwanese population consisting of 146 histologically confirmed incident breast cancer cases and their 285 age-matched controls without a history of cancer. A PCR-RFLP method was used for MTHFR polymorphism genotyping and RIA was used to measure the plasma folate. Statistical evaluations were performed using logistic regression analysis. The plasma folate level was inversely associated with breast cancer risk with an adjusted odds ratio (OR) of 0.52 [95% confidence interval (CI): 0.26-1.05] observed among women who were in the highest plasma folate tertile. The MTHFR 677T and 1298C variant alleles were associated with decreased risk for breast cancer [adjusted ORs were 0.81 (95% CI: 0.54-1.21) and 0.57 (95% CI: 0.36-0.89) for 677CT + TT genotypes and 1298AC + CC genotypes, respectively]. Furthermore, compound heterozygote and homozygote variants (677CT + TT and 1298AC + CC) had greater reduced risk (adjusted OR: 0.11, 95% CI: 0.03-0.43) among women with lower plasma folate levels. These results provide support for the important role of folate metabolism in breast tumorigenesis. Further mechanistic studies are warranted to investigate how MTHFR combined genotypes exert their effect on cancer susceptibility.     

The MTHFR 1298A>C polymorphism and genomic DNA methylation in human lymphocytes.

Methylenetetrahydrofolate reductase (MTHFR) balances the pool of folate coenzymes in one-carbon metabolism for DNA synthesis and methylation, both implicated in carcinogenesis. Epidemiologic studies have shown that two functional polymorphisms in MTHFR gene, 677C>T and 1298A>C, are related to increased cancer risk. We aimed to analyze lymphocyte DNA from 198 subjects to evaluate the MTHFR 1298A>C polymorphism and folate status affecting genomic DNA methylation as a possible mechanism underlying the relationship between MTHFR polymorphisms and cancer susceptibility. Carriers of the 1298AA wild-type genotype showed lower genomic DNA methylation compared with 1298AC or 1298CC genotypes [3.72 versus 8.59 or 6.79 ng 5-methyl-2'-deoxycytidine (5-mCyt)/microg DNA, P < 0.0001 and P = 0.007, respectively]. When DNA methylation was evaluated according to plasma folate status, only 1298AA with low folate levels revealed diminished DNA methylation (P < 0.0001). Moreover, when the two MTHFR polymorphisms were concomitantly evaluated at the low folate status, DNA methylation was reduced only in 1298AA/677TT compared with 1298AA/677CC (3.11 versus 7.29 ng 5-mCyt/microg DNA, P = 0.001) and 1298CC/677CC genotypes (3.11 versus 7.14 ng 5-mCyt/microg DNA, P = 0.004). However, the high prevalence of 677TT mutants within the 1298AA group (79%) and the similar biochemical features of 1298AA/677CC and 1298CC/677CC combined genotypes suggest that the gene-nutrient interaction affecting DNA methylation in 1298AA is mainly due to the coexistence of the 677TT genotype and that the 1298A>C polymorphism may convey its protective effect not through this interaction but through another pathway in one-carbon metabolism. Further mechanistic studies are warranted to investigate how single polymorphisms as well as MTHFR combined genotypes exert their effect on cancer susceptibility.     

Methylenetetrahydrofolate reductase 677C/T gene polymorphism, gastric cancer susceptibility and genomic DNA hypomethylation in an at-risk Italian population

We performed a case-control study to examine the relationship between MTHFR C677T gene polymorphism (MTHFR677C/T) and gastric cancer susceptibility in at-risk populations in central Italy. To explore genomic DNA hypomethylation as a potential etiologic mechanism, this phenomenon was evaluated in carriers of the MTHFR677T/T genotype and carriers of the wild-type MTHFR677C/C genotype. Lymphocyte genomic DNA from 162 gastric cancer patients and 164 controls was used for MTHFR677C/T genotyping. Unconditional regression analysis with ORs and 95% CIs was used to investigate the association of the polymorphism with disease. Genomic DNA methylation status by an established enzymatic assay that measures the DNA accepting capacity of methyl groups (inversely related to endogenous methylation) was assessed in a random sample of 40 carriers of the wild-type MTHFR677C/C genotype and 40 carriers of the MTHFR677T/T genotype. The global allelic distribution was in Hardy-Weinberg equilibrium. The MTHFR677T allele was significantly associated with gastric cancer risk with an OR of 2.49 (95% CI 1.48-4.20) in heterozygous MTHFR677C/T carriers and an OR of 2.85 (95% CI 1.52-5.35) in homozygous MTHFR677T/T carriers. This risk association was retained in subgroup analyses by tumor histotype and location. Genomic DNA hypomethylation status in MTHFR677T/T carriers was significantly higher than in subjects with wild-type MTHF677C/C genotype (p = 0.012). In the studied population, MTHFR677T played the role of a moderate-penetrance gastric cancer susceptibility allele. Possession of the MTHFR677T/T genotype was significantly associated with genomic DNA hypomethylation. These findings deserve further investigation in the context of novel strategies for gastric cancer prevention.     

Polymorphisms of methylenetetrahydrofolate reductase and the risk of prostate cancer: a nested case-control study.

It has been proposed that folate and polymorphisms of the enzyme methylenetetrahydrofolate reductase (MTHFR), which regulates influx of folate from DNA synthesis and repair to methylation reactions, are involved in the aetiology of cancer. To relate the MTHFR 677C-->T and 1298A-->C polymorphisms to the risk of prostate cancer, taking into consideration prospective plasma levels of folate, vitamin B12 and homocysteine. The design was a case-control study of 223 prostate cancer cases and 435 matched controls nested within the population-based Northern Sweden Health and Disease Cohort. Neither the MTHFR 677C-->T nor the MTHFR 1298A-->C polymorphism was statistically significantly associated with the risk of prostate cancer in univariate analysis by conditional logistic regression. After adjustment for MTHFR 1298A-->C, plasma folate, vitamin B12, homocysteine, body mass index and smoking, the odds ratios were, for the 677 CT genotype, 1.52 [95% confidence interval (CI) 1.02-2.26], and for TT, 0.91 (95% CI 0.41-2.04). Our previously reported observation of a possible increase in the risk of prostate cancer at high plasma folate levels was attributable in this study to subjects having the MTHFR 677C-->T polymorphism. We found that the MTHFR 677C-->T polymorphism is not likely to have a major role in the development of prostate cancer, although it may possibly increase the risk in combination with high plasma folate levels. Further investigation in larger studies is warranted.     

Methylenetetrahydrofolate reductase polymorphisms and risk of sporadic and hereditary colorectal cancer with or without microsatellite instability

Methylenetetrahydrofolate reductase (MTHFR) is an essential enzyme in the folate metabolism, which affects DNA synthesis and methylation. Low enzyme activity may reduce the capacity of DNA methylation, and possibly reduce uracil misincorporation into DNA, which can result in double strand breaks. Both processes may be critical for the oncogenic transformation of human cells. Two common amino acid-changing and enzyme activity-reducing nucleotide polymorphisms (677C --> T/Ala222Val and 1298A --> C/Glu428Ala) have been described in MTHFR. We performed estimations of the relative risk associated with these two polymorphisms in samples from 287 colorectal cancer patients, compared to 346 healthy controls. Relative risk were further determined for subpopulations of cancer patients having sporadic (n = 227) or suspected/verified hereditary disease (n = 60) and tumours exhibiting high-level microsatellite instability (n = 41) or not (n = 246). No significant differences for the relative risk of colorectal cancer were observed for the MTHFR genotypes either alone or in combination in the analysed cohorts, although the frequency of the 1298AA + AC genotypes was increased among the 60 cases with hereditary disease. Whereas our results do not support an association of high enzyme activity and increased risk of colorectal cancer in general, we can not exclude an association of patients with hereditary disease and the MTHFR 1298A --> C variant.     

Diet Folate,DNA Methylation and Polymorphisms in Methylenetetrahydrofolate Reductase in Association with the Susceptibility to Gastric Cancer

Methylenetetrahydrofolate reductase (MTHFR) has been reported to be associated with DNA methylation, anepigenetic feature frequently found in gastric cancer. We conducted a case-control study to explore the associationof MTHFR C677T polymorphisms with gastric cancer risk and its relation with the DNA methylation of COX-2,MGMT, and hMLH1 genes. Genotyping of P16, MGMT and HMLH1 was determined by methylation-specificPCR after sodium bisulfate modification of DNA, and genotyping of MTHFR C677T was conducted by TaqManassays using the ABI Prism 7911HT Sequence Detection System. Folate intake was calculated with the aid ofa questionnaire. Compared with the MTHFR 677CC genotype, the TT genotype was significantly associatedwith 2.08 fold risk of gastric cancer when adjusting for potential risk factors. Individuals who had an intakeof folate above 310 μg/day showed protective effects against gastric cancer risk. The effect of MTHFR C677Tpolymorphisms on the risk of gastric cancer was modified by folate intake and methylation status of MGMT (Pfor interaction <0.05).     

Methylenetetrahydrofolate reductase C677T and A1298C polymorphisms and colorectal cancer: the Fukuoka Colorectal Cancer Study

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme regulating folate metabolism, which affects DNA synthesis and methylation. This study investigated the relation of MTHFR C677T and A1298C polymorphisms to colorectal cancer in a case-control study in Fukuoka, Japan. The subjects comprised 685 incident cases of histologically confirmed colorectal adenocarcinomas and 778 community controls selected randomly in the study area. The genotype was determined by the PCR-RFLP method using genomic DNA extracted from buffy coat. Alcohol use was ascertained by in-person interview. Statistical adjustment was made for gender, age class, area, and alcohol use. The MTHFR 677TT genotype was associated with a statistically significant decrease in the risk with an adjusted odds ratio of 0.69 (95% confidence interval 0.51-0.93) compared with the 677CC and 677CT combined, and the decrease was most evident in individuals with no alcohol consumption. While the A1298C polymorphism showed no measurable association with the overall risk of colorectal cancer, the 1298CC genotype was associated with a statistically significant increase in the risk when alcohol consumption was high, and was also associated with an approximately 2-fold increase in the risk of each of proximal and distal colon cancer. The findings add to evidence that individuals with the MTHFR 677TT genotype have a decreased risk of colorectal cancer in the absence of folate depletion, suggesting a protective role of folate by ensuring a sufficient thymidylate pool for DNA synthesis. Because very few individuals had the 1298CC genotype, the findings regarding the A1298C polymorphism need careful interpretation and confirmation in larger studies.     

MTHFR polymorphisms, dietary folate intake, and breast cancer risk: results from the Shanghai Breast Cancer Study.

Folate plays an important role in DNA methylation, synthesis, and repair; intake has been associated with breast cancer. The folate-metabolizing enzyme, methylenetetrahydrofolate reductase (MTHFR) is polymorphic at nucleotides 677 (C-->T) and 1298 (A-->C), resulting in allozymes with decreased activity. We evaluated these two common polymorphisms and their effects on the folate intake and breast cancer risk association in a population-based case-control study of 1144 breast cancer cases and 1236 controls using a PCR-RFLP-based assay. All subjects completed in-person interviews, which included a food frequency questionnaire. Unconditional logistic regression models were used to calculate odds ratios and their 95% confidence intervals, after adjusting for potential confounding factors. Cases and controls were similar in the distribution of MTHFR polymorphisms at codons 677 (41.4% cases and 41.8% controls carried the T allele) and 1298 (17.6% cases and 17.5% controls carried the C allele). An inverse association of breast cancer risk with folate intake was observed in all genotype groups, particularly among subjects with the 677TT genotype. Compared with those with the 677CC genotype and high folate, the adjusted odds ratios (95% confidence intervals) associated with low folate intake were 1.94 (1.15-3.26), 2.17 (1.34-3.51), and 2.51 (1.37-4.60) for subjects who had CC, CT, and TT genotypes (p for interaction, 0.05). No modifying effect of A1298C genotypes on the association of folate intake with breast cancer risk was observed. Results of this study suggest that the MTHFR C677T polymorphisms may modify the association between dietary folate intake and breast cancer risk.     

Polymorphisms in the MTHFR gene are associated with breast cancer.

The methylenetetrahydrofolate reductase (MTHFR) gene is a polymorphic gene involved in folate metabolism, DNA biosynthesis, methylation and genomic integrity in actively dividing cells. The MTHFR C677T and A1298C polymorphisms are likely to play an important role in the susceptibility to breast cancer. In this case-control study, we examined the role of MTHFR C677T and A1298C polymorphisms in breast cancer patients. We genotyped 118 premenopausal women with sporadic breast cancer and 193 controls, using a PCR-RFLP method. The allele frequencies of the MTHFR 677T were 31.36% in the breast cancer cases and 28.76% in the controls. The allele frequencies of the MTHFR 1298C were 37.29% in the breast cancer subjects and 31.35% in the controls. Frequencies of MTHFR C677C, C677T and T677T were 50.8, 33.9 and 14.4% in the breast cancer patients and 48.7, 45.1 and 6.2% in the controls, respectively. The results of a chi(2) analysis indicated that the MTHFR 677T allele was significantly distributed (chi(2) = 7.234; p = 0.027). Likewise, the MTHFR T677T genotype showed a 2.5-fold increased risk for breast cancer and the C1298C genotype showed a 1.9-fold increased risk for breast cancer. In the compound genotypes, T677T/A1298A and C677C/C1298C showed a 4.472- and a 2.301-fold increased risk for breast cancer (OR = 4.472, p = 0.001, and OR = 2.301, p = 0.024), respectively. In conclusion, our data suggest that the MTHFR 677T, 1298C alleles, T677T, C1298C genotypes, and C677C/C1298C and T677T/A1298A compound genotypes are genetic risk factors for premenopausal women with sporadic breast cancer.     

Folate restriction and methylenetetrahydrofolate reductase 677T polymorphism decreases adoMet synthesis via folate-dependent remethylation in human-transformed lymphoblasts.

The homozygous mutation (677TT) in the methylenetetrahydrofolate reductase (MTHFR) gene reduces enzyme activity and alters cellular folate composition. Previous epidemiological studies reported a potential protective effect of MTHFR677C --> T against acute lymphocytic leukemia and malignant lymphoma, but the mechanism remains to be determined. We investigated the biochemical impacts of MTHFR677C --> T on cellular S-adenosyl methionine (adoMet) synthesis, global DNA methylation, and de novo purine synthesis, all of which are potential regulatory pathways involved in tumorigenesis. Metabolic fluxes of homocysteine remethylation and de novo purine synthesis were compared between Epstein-Barr virus-transformed lymphoblasts expressing MTHFR 677C and MTHFR 677T using stable isotopic tracers and GCMS. MTHFR TT genotype significantly reduced folate-dependent remethylation under folate restriction, reflecting limited methylated folates under folate restriction. Data also suggested increased formylated folate pool and increased purine synthesis when folate is adequate. The impacts of MTHFR 677T polymorphism appeared closely related to folate status, and such alterations may modulate metabolic pathways involved in cancer onset/progression. The advantage of de novo purine synthesis found in the MTHFR TT genotype may account for the protective effect of MTHFR in hematological malignancies. These transformed cells are potential models for studying the consequences of human genetic variation and cancer pathogenesis.     

Polymorphisms in genes involved in folate metabolism and plasma DNA methylation in colorectal cancer patients

Aberrant methylation of promoter regions associated with gene silencing is one of the major mechanisms underlying the inactivation of tumor suppressor genes in carcinogenesis. Previous studies have proposed that methylated DNA from tumor cells is released into the circulation and might be widely used as a marker for non-invasive tumor detection. Catalytic activities of folate metabolism-related enzymes and adequate synthesis of methyl donors are important elements for the cellular methylation reaction. In the present study, we sought to determine the following: i) genotype frequencies of MTHFR and MTR involved in folate metabolism in cases and cancer-free controls; and ii) the methylation status of three candidate genes (p16INK4A, p73 and hMLH1) in plasma related to the folate and homocysteine levels. From genotype frequency analysis, individuals homozygous for the MTHFR 677TT genotype had a significantly reduced risk of developing colorectal cancer compared with those harboring the MTHFR 677CC genotype (OR, 0.206; 95% CI, 0.070-0.604; P=0.005), and had a lower plasma folate concentration than those with the MTHFR 677CC+CT genotype (P<0.05). Using methylation-specific PCR, p73 was shown to be more frequently methylated in the high folate group [50% (8 of 16)] than in the medium [16.7% (3 of 18)] or low folate subgroups [11.1% (2 of 18)]. In conclusion, subjects with the variant MTHFR 677TT genotype appeared to have a significantly lower risk for colorectal cancer than those with the MTHFR 677CC genotype, and the methylation status of circulating p73 genomic DNA was substantially altered by the plasma folate level.     

Multiplex PCR for simultaneous detection of 677 C-->T and 1298 A-->C polymorphisms in methylenetetrahydrofolate reductase gene for population studies of cancer risk

Methylenetetrahydrofolate reductase (MTHFR) plays a pivotal role in folate metabolism by regulating the diversion of folate metabolites toward DNA methylation or toward DNA synthesis. Because aberrations in both of these pathways can be tumor promoting, the two common polymorphisms in the MTHFR gene, 677 C-->T and 1298 A-->C, have been implicated as risk factors for several cancers. Homozygosity for the 677 C-->T polymorphism and compound heterozygosity for 677 C-->T and 1298 A-->C polymorphisms both reduce enzyme activity by more than 50% and can promote oncogenic alterations in DNA methylation especially when folate status is low. Thus, rapid identification of both polymorphisms in MTHFR gene would be of importance in understanding the genetics of abnormal folate metabolism as related to human cancer risk. Here we describe a multiplex polymerse chain reaction/restriction fragment length polymorphism procedure in which two sets of primers are used to amplify simultaneously the DNA regions spanning 677 and 1298 loci in one PCR reaction. The amplified products are digested by HinfI or MboII followed by agarose gel electrophoresis for simultaneous detection of the 677 C-->T and 1298 A-->C polymorphisms in the same gel.     

Localized depletion: the key to colorectal cancer risk mediated by MTHFR genotype and folate?

Dietary folate has been consistently associated with reduced risk of colorectal cancer (CRC). One of the known biochemical roles of folate is donation of methyl moieties. DNA hypomethylation is an early and almost ubiquitous occurrence in tumor tissue. Therefore, it was originally suggested that adequate folate intake contributed to reduced risk of CRC by facilitating methyl-mediated silencing of oncogenes. Methylene tetrahydrofolate reductase (MTHFR) metabolizes 5,10-MTHF (important in DNA synthesis) to 5-MTHF (contributes to downstream methylation reactions by regeneration of methionine from homocysteine). A common polymorphism in the MTHFR gene (C677T) results in a thermolabile phenotype associated with increased homocysteine levels and DNA hypomethylation. Consistent with the folate/methylation hypothesis, it was originally proposed that C677T may increase risk of CRC due to hypomethylation of oncogenes. However, most subsequent studies have reported a reduced risk associated with this polymorphism. This is inconsistent with methylation as the mechanism by which folate and MTHFR genotype mediate CRC risk. The hypothesis presented here proposes that localized folate depletion combined with the effect of the C677T polymorphism on enzyme stability, impacts on the DNA synthesis pathway and accounts for the observed variation in risk associated with genotype and folate status.     

Sensitivity of markers of DNA stability and DNA repair activity to folate supplementation in healthy volunteers

We have previously reported that supplementation with folic acid (1.2 mg day(-1) for 12 week) elicited a significant improvement in the folate status of 61 healthy volunteers. We have examined effects of this supplement on markers of genomic stability. Little is known about the effect of folate supplementation on DNA stability in a cohort, which is not folate deficient. Preintervention, there was a significant inverse association between uracil misincorporation in lymphocyte DNA and red cell folate (P < 0.05). In contrast, there were no associations between folate status and DNA strand breakage, global DNA methylation or DNA base excision repair (measured as the capacity of the lymphocyte extract to repair 8-oxoGua ex vivo). Folate supplementation elicited a significant reduction in uracil misincorporation (P < 0.05), while DNA strand breakage and global DNA methylation remained unchanged. Increasing folate status significantly decreased the base excision repair capacity in those volunteers with the lowest preintervention folate status (P < 0.05). Uracil misincorporation was more sensitive to changes in folate status than other measures of DNA stability and therefore could be considered a specific and functional marker of folate status, which may also be relevant to cancer risk in healthy people.     

Association of Dietary Intake of Folate,Vitamin B6 and B12 and MTHFR Genotype with Breast Cancer Risk

Aim: We aimed to investigate the associations of dietary intake of folate, vitamin B6 and B12 and MTHFRgenotype with breast cancer in a Chinese population. Methods: A matched case-control study was conducted, and435 patients with newly diagnosed and histologically confirmed breast cancer and 435 controls were collected. Thefolate intake, vitamin B6 and vitamin B12 were calculated, and MTHFR C665T, C677T and A1298C were analyzedby PCR-RFLP. Results: We found vitamin B12 was likely to reduce the risk of breast cancer, and MTHFR 665TTwas associated with increased risk of breast cancer. Folate intake, vitamin B12 intake and variants of MTHFRC677T and MTHFR A1298C demonstrated no association with risk of breast cancer. However, we found patientswith low intake of vitamin B6 and MTHFR 665TT genotype had a higher risk of breast cancer (OR=1.87, 95%CI=1.29-2.77), the association being less pronounced among subjects with a moderate intake of vitamin B6 andMTHFR 665TT genotype (OR=1.58, 95% CI=1.03-2.49, P=0.03). Conclusion: Our study indicated that theMTHFR C665T polymorphism and vitamin B6 are associated with risk of breast cancer, which indicated rolesfor nutrients in developing breast cancer.     

Genetic polymorphisms of methylenetetrahydrofolate reductase and colorectal cancer and adenoma

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme regulating folate metabolism, which affects DNA methylation and synthesis. Two functional, common polymorphisms (C677T and A1298C) are known in the MTHFR gene. MTHFR activity is lowered in individuals with the 677TT genotype and is somewhat reduced in those with the 1298CC genotype. We reviewed the consistency of reported associations of these polymorphisms with colorectal cancer and adenoma with consideration of the effects of nutritional status. A total of 16 studies have addressed the association between MTHFR C677T polymorphism and colorectal cancer in 10 countries. Decreased risk of colorectal cancer associated with the 677TT genotype has fairly consistently been observed, with few exceptions. This decrease was observable in people with either high or low folate status. Alteration in the thymidylate pool associated with MTHFR activity is postulated as an underlying mechanism. Studies on the A1298C polymorphism are limited, and their results are variable. Almost all of seven studies of colorectal adenoma have found no association between C677T polymorphism and adenoma, but the 677TT genotype seems to be related to increased risk when folate status is poor. Reduced availability of methyl groups for DNA methylation might be more relevant to adenoma formation. Although the underlying mechanisms still remain to be clarified, epidemiological findings regarding MTHFR C677T polymorphism provide strong evidence that adequate folate status confers protection from colorectal cancer.     

The MTHFR C677T and ΔDNMT3B C‐149T polymorphisms confer different risks for right‐ and left‐sided colorectal cancer

Etiological risk factors for proximal (right‐sided) colon cancers may be different to those of distal colon and rectal (left‐sided) cancers if these tumors develop along distinct pathways. The CpG Island Methylator Phenotype (CIMP+) occurs in approximately 15% of colorectal cancers (CRC) and predominantly in the proximal colon. CIMP+ tumors have frequent methylation of gene promoter regions and increased tissue folate levels. The aim here was to determine whether polymorphisms in 2 genes involved in cellular methyl group metabolism were associated with different risks for right‐ and left‐sided CRC. This population‐based case–control study involved 859 incident cases of CRC and 973 sex and age‐matched controls. Information on dietary folate and alcohol intake was obtained from food frequency questionnaires and information on the anatomical site of tumors from pathology reports. DNA was collected using FTA cards and genotyping performed for the MTHFR C677T and ΔDNMT3B C‐149T polymorphisms. The MTHFR 677 T allele was associated with increased risk for proximal colon cancer (adjusted odds ratio, AOR = 1.29) but decreased risk for distal cancers (AOR = 0.87). The increased risk for proximal cancers was especially pronounced in older individuals (AOR = 1.49) and those with a low folate diet (AOR = 1.67) or high alcohol consumption (AOR = 1.90). The ΔDNMT3B‐149 TT genotype was protective against proximal colon cancers (AOR = 0.65), but showed no association with the risk of distal colon and rectal cancers (AOR = 1.02). Epidemiological studies on dietary and genetic risk factors for CRC should take into account these may confer different risks for right‐ and left‐sided tumors. © 2009 UICC