血清叶酸、维生素B12浓度及MTHFR、MS基因多态性与乳腺癌风险相关性研究

目的:分析血清中叶酸和维生素B12的含量以及甲硫氨酸合成酶(Methionine synthase,MS)及亚甲基四氢叶酸还原酶(Methylene tetrahydrofolate reduetase,MTHFR)各基因型在云南籍乳腺癌人群和正常人群中的分布差异,探索MTHFR,MS多态性与乳腺癌易感性之间的关系。方法:应用普通PCR-RFLP技术对95例云南籍乳腺癌患者和90例正常人群MS2756位点、MTHFR677位点和1298位点基因多态与乳腺癌风险关联分析筛查。同时应用全自动免疫分析仪测定血清中叶酸和维生素B12的含量。结果:乳腺癌患者血清维生素B12含量高于正常对照组,而血清叶酸低于正常对照组。云南籍乳腺癌人群和对照人群MS,MTHFR各基因型与分布频率比较无明显差异。结论:血清叶酸和维生素B12含量与乳腺癌发生风险有关,而MS,MTHFR基因多态性与乳腺癌发生风险无明显统计学意义。     

云南人亚甲基四氢叶酸还原酶基因型多态性与乳腺癌易感性的关联

 目的亚甲基四氢叶酸还原酶(MTHFR)是叶酸代谢的关键性酶,其催化作用决定了DNA甲基化与DNA合成之间的平衡。MTHFR基因多态性可能会影响叶酸代谢结局,从而构成肿瘤风险因子。研究分析了MTHFR各基因型在云南籍乳腺癌人群和正常人群中的分布差异,初步探索了MTH-FR多态性与乳腺癌易感性之间的关系。方法以多重PCR-RFLP技术,对125例云南籍乳腺癌患者和103例正常人群MTHFR677位点1298位点多态性进行筛查。结果未发现MTHFRC677T和A1298C基因型频率在乳腺癌和对照样本之间存在显著差异。结论在目前样本条件下,上述两个MTHFR位点基因型多态性与云南籍人群的乳腺癌易感性之间无明显相关性。     

东北地区亚甲基四氢叶酸还原酶基因C677T单核苷酸多态性与乳腺癌易感性的相关性研究

目的::研究亚甲基四氢叶酸还原酶(MTHFR)基因单核苷酸多态性与乳腺癌易感性的关系.方法:采用以人群为基础的病例对照研究方法,聚合酶链反应-限制性片段长度多态性法检测MTHFR基因型在东北地区乳腺癌患者和正常人群中的分布.结果:MTHFR基因677位点在乳腺癌组和对照组中等位基因频率及基因型分布有显著差异性(P<0.05).进一步分析表明,纯合突变G/G基因型、杂合突变C/G基因型与野生C/C基因型相比,患乳腺癌的危险度分别提高了2.23倍和2.00倍.结论:MTHFR基因C677T突变基因型与乳腺癌的易感性有关.     

亚甲基四氢叶酸还原酶基因单核苷酸多态与乳腺癌风险

目的 内研究亚甲基四氢叶酸还原酶(MTHFR)基因单核苷酸多态与女性乳腺癌风险的关系。方法 以聚合酶链反应(PCR)和限制性片段长度多态性(RFLF)分析方法,检测了217例乳腺癌患者和218例配对的正常对照者MTHFR因C677T和A1298C基因型,并比较不同基因型与乳腺癌风险的关系。结果 677TT基因型频率在乳腺癌患者和正常对照中的分布差异有显著性(32．7％比24．8％,P=0．02)。携带MTHFR 677TT基因犁者与携带MTHFR 677CC基因型者比较,前者罹患乳腺癌的风险增加1,84倍(95％ C：1．09～3．14)。MTHFR 677CT基因型以及MTHFR A1298C多态与乳腺癌风险不相关。结论 MTHFR基因677C→T突变是女性乳腺癌的遗传易感因素。     

亚甲基四氢叶酸还原酶基因多态性与肺癌易感性的关系

目的研究亚甲基四氢叶酸还原酶(MTHFR)基因多态性与肺癌易感性的关系。方法采用PCRRFLP方法检测MTHFR基因型在广东地区肺癌患者和正常人群中的分布。结果肺癌组和对照组中MTHFR各基因型的分布有显著性差异(P=0.030),在男女两种性别之间,非小细胞肺癌和小细胞肺癌之间,非小细胞肺癌各个病理类型之间,肺癌病例各个临床分期之间MTHFRC677T多态性的分布没有显著性差异。结论MTHFR基因C677T突变在肺癌病例中的分布与正常人群中的分布有明显的差异。     

MTHFR基因C667T位点多态性与亚洲人群乳腺癌易感性的Meta分析

目的:采用Meta分析的方法定量评价亚甲基四氢叶酸还原酶（MTHFR）基因C667T位点的多态性与亚洲人群乳腺癌易感性的关系。方法:计算机检索PubMed、Web of Science、中国生物医学文献数据库、CNKI、重庆维普和万方数据库,搜索有关MTHFR基因C667T位点的多态性与亚洲人群乳腺癌易感性的研究,检索时间截止2017年2月。采用Stata 12.0软件进行统计分析。结果:共纳入24篇病例对照研究,共计7 268例乳腺癌患者,9 223例健康对照。Meta分析结果显示:MTHFR基因C667T位点的多态性均与亚洲人群乳腺癌易感性有相关性［CC vs CT:OR=0.70,95%CI（0.60,0.83）,P=0.001;CT vs TT:OR=0.87,95%CI（0.79,0.96）,P=0.05;CC vs TT:OR=0.79,95%CI（0.72,0.88）,P=0.002;CT+TT vs CC:OR=0.81,95%CI（0.76,0.87）,P=0.001;CC+CT vs TT:OR=0.85,95%CI（0.77,0.93）,P=0.003］。结论:MTHFR基因C667T位点的多态性增加了亚洲人群乳腺癌的易感性。     

砷及MTHFR和MTR基因多态性与乳腺癌发生风险的关系

[目的]探讨尿砷与乳腺癌的关联,并分析5,10-亚甲基四氢叶酸还原酶(MTHFR)rs1801133和甲硫氨酸合成酶(MTR) rs 1805087多态性位点对其关联的影响.[方法]2009年10月至2010年7月对新诊断的240例乳腺癌患者及同时期同医院体检的246例年龄频数匹配对照进行问卷调查、尿样和血样收集.尿砷浓度采用电感耦合等离子体质谱(ICP-MS)检测;MTHFR rs1801133和MTR rs1805087基因型采用基质辅助激光解吸/电离飞行时间质谱(MALDI-TOF-MS)方法,在Sequenom平台检测.[结果]病例组和对照组尿碑含量差异无统计学意义(P=0.32).rs1801133和rs1805087在病例组和对照组中基因型分布差异无统计学意义(P＞0.05).rs1801133和rs 1805087与砷对乳腺癌发生风险不存在交互作用(P＞0.05).[结论]在本研究人群中,未发现尿砷与乳腺癌风险有关联,MTHFR rs1801133和MTR rs1805087位点对该关联的影响也无统计学意义.     

雌激素受体基因ESR1多态性与乳腺癌易感性的关系

目的：研究雌激素受体α（ESR1）基因单核苷酸多态性（SNPs）与乳腺癌易感性的关系。方法：运用聚合酶链反应（PCR）和限制性片段长度多态性（RFLP）分析的方法检测193例中国汉族女性乳腺癌患者和71名正常女性对照者ESR1基因上rs11155816位点的基因型,以SPSS 11.0软件卡方检验处理数据。结果：rs11155816位点等位基因频率符合Hardy-Weinberg遗传平衡定律。rs11155816位点的等位基因及基因型与患者肿瘤位置及是否存在远处转移相关,差异有显著性（P〈0.05）;与年龄、大小、组织学类型、受体表达无关。rs11155816位点等位基因及基因型频率在乳腺癌人群与正常对照者间分布差异有显著性,乳腺癌人群中等位基因A频率高于正常人群（23.8%比15.5%,P〈0.05）。结论：rs11155816位点基因的多态性与乳腺癌患者的肿瘤位置和远处转移相关,等位基因A携带者乳腺癌发病风险较高。     

活性氧代谢通路相关基因多态性对放射性肺炎的预测价值分析?

目的探讨活性氧代谢通路相关基因亚甲基四氢叶酸还原酶(MTHFR)rs1801131、rs1801133位点和超氧化物歧化酶2(SOD2)rs4880位点多态性与放射性肺炎的关系。方法通过聚合酶链反应(PCR)-荧光探针方法检测317例接受胸部放射治疗的肺癌患者MTHFR基因rs1801131、rs1801133位点和SOD2基因rs4880位点单核苷酸多态性(SNP)的基因型,采用Logistic回归模型分析基因多态性与≥2级放射性肺炎的相关性。结果317例患者均完成放疗计划。中位随访时间为16.7个月(3.6~43.0个月),其中67例患者发生≥2级放射性肺炎。Logistic回归模型分析结果显示,MTHFR基因rs1801131位点SNP与放射性肺炎的发生密切相关(P<0.05)。结论MTHFR基因rs1801131位点多态性与肺癌患者放射性肺炎的发生风险密切相关。     

叶酸缺乏与MTHFR C677 T 多态性对乳腺癌 患者淋巴细胞遗传损伤的影响

 目的　探讨叶酸缺乏与MTHFR C677 T 基因型多态性对乳腺癌患者淋巴细胞遗传损伤的影响 及其与对照的差异。方法　采用9 天淋巴细胞长期培养辅以胞质阻断微核细胞组分析(CBMN cyt) ,分 析不同浓度的叶酸对三种MTHFR C677 T 基因型乳腺癌人群和健康人群双核细胞微核率的影响与差 异。结果　MTHFR C677 T 三种基因型(CC ,CT , TT) 的乳腺癌个体与对照组淋巴细胞在叶酸浓度为 30 nmol/ L 时双核细胞微核率(MNBN) 均显著高于60 、120 、240 和2 260 nmol/ L 测试组( P < 0. 001～ 0. 05) ,60 和120 nmol/ L 两个测试组之间以及120 、240 和2 260 nmol/ L 三个测试组之间都未发现显著 性差异。乳腺癌个体和对照组淋巴细胞中,MTHFR677 TT 在任何培养条件下,MNBN 频率均显著高于 相应样本组同类培养的野生纯合型(CC) ( P < 0. 01～0. 05) ;消减样本自身遗传损伤背景后,相同基因型 的乳腺癌个体和正常个体淋巴细胞在MNBN 频率上无显著性差异。结论　在离体情况下,低于120 nmol/ L 的叶酸浓度可增加人类淋巴细胞遗传损伤,无论是健康人群还是癌症患者,MTHFR 677 TT 型 纯合个体,对叶酸缺乏都更加敏感。     

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.     

Folate status,metabolic genotype,and biomarkers of genotoxicity in healthy subjects

Gene-environment interactions play an important role in folate metabolism, with a potential impact on human health. Deficiencies in the uptake of key micronutrients and variant genotypes can affect the folic acid cycle, modulating methyl group transfer in key processes and leading to increased cancer risk and Down syndrome incidence. So far, the significance of folate status and metabolic genotypes on baseline levels of DNA damage in normal individuals has not been fully elucidated. In this study, the possible modulation of SCE, micronuclei and tail moment values in peripheral lymphocytes by plasma levels of folic acid, homocysteine and vitamin B12, and by the methylenetetrahydrofolate reductase (MTHFR) C677T and methionine synthase reductase (MTRR) A66G polymorphisms was investigated in 191 healthy subjects. The results obtained show a highly significant (P = 0.001) positive association between plasma levels of vitamin B12 and frequencies of both SCE and high frequency cells (HFC, above 90 degrees percentile) in smokers. No significant effect was observed in non-smokers. Moreover, after correction for age, gender and GSTM1 genotype, a significant association (P = 0.026) between the MTRR 66GG variant genotype and higher micronucleus rates was observed. Tail moment values were not affected by any of the independent variables considered. Overall, the results obtained suggest that both folate status and relevant metabolic genotype can influence background levels of DNA damage in normal subjects. The significant association observed in smokers between plasma vitamin B12 and SCE frequencies may highlight the effect of methylation status on DNA damage and repair, although the role of other, unidentified dietary factors cannot be ruled out. At the same time, micronucleus data indicate that the MTRR 66GG variant may represent another individual trait of relative genomic instability, thus supporting epidemiological data on increased risk of Down syndrome conception in MTRR 66GG subjects.     

Methylenetetrahydrofolate reductase, diet, and risk of colon cancer.

Individuals with different forms of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, carriers of the C677T mutation versus wild type, show differences in enzyme levels; these differences have been hypothesized to be related to DNA methylation and, perhaps, to the nucleotide pool size. Using data from an incident case-control study, we evaluated the combined effect of dietary intake of folate, methionine, vitamin B6, vitamin B12, and alcohol and various forms of the MTHFR gene on risk of colon cancer. Individuals homozygous for the variant form of the MTHFR gene (TT) had a slightly lower risk of colon cancer than did individuals who were wild type [CC, odds ratio (OR) = 0.8, 95% confidence interval (CI) = 0.6-1.1 for men; and OR = 0.9, 95% CI = 0.6-1.2 for women]. High levels of intake of folate, vitamin B6, and vitamin B12 were associated with a 30-40% reduction in risk of colon cancer among those with the TT relative to those with low levels of intake who were CC genotype. Associations were stronger for proximal tumors, in which high levels of intake of these nutrients were associated with a halving of risk among those with the TT genotype. The inverse association with high levels of these nutrients in those with the TT genotype was stronger among those diagnosed at an older age. Although imprecise, the inverse association with the low-risk diet that was high in folate and methionine and without alcohol was observed for both the TT genotype (OR = 0.4 95% CI = 0.1-0.9) and the CC/CT genotype (OR = 0.6, 95% CI = 0.4-1.0), but this association was not seen with the high-risk diet for either the TT or CC/CT genotype. Although associations were generally weak, these findings suggest that those with differing MTHFR genotypes may have different susceptibilities to colon cancer, based on dietary consumption of folate, vitamin B6, and vitamin B12.     

Effect of the methylenetetrahydrofolate reductase C677T polymorphism on patients with cisplatin/gemcitabine-treated stage IV non-small-cell lung cancer

Single nucleotide polymorphisms (SNPs) in the metabolic pathways of S-adenosylmethionine have been related to global hypomethylation and a lower number of hypermethylated CpG islands of tumor suppressor genes. Hypermethylation of checkpoint and DNA repair genes has been shown to be indicative of chemosensitivity. In the present study, we have examined the SNP of methylenetetrahydrofolate reductase (MTHFR) C677T, which affects DNA methylation patterns and is linked to elevated plasma homocysteine levels in 208 patients with gemcitabine/cisplatin-treated stage IV non-small-cell lung cancer (NSCLC). No differences in response rate were observed according to the MTHFR genotype. However, time to progression was 7.4 months for 68 patients with CC genotype, 5.5 months for 108 patients with heterozygous CT genotype, and 5.2 months for 28 patients with TT genotype. These findings can lead us to distinguish different outcome patterns among patients with stage IV NSCLC whose similar clinical prognostic factors would otherwise indicate similar outcomes. Carriers of the MTHFR 677T allele could benefit from supplementation with folic acid and vitamin B12. The Spanish Lung Cancer Group has undertaken a phase III randomized trial to elucidate this concept.     

Methylenetetrahydrofolate reductase C677T polymorphism does not alter folic acid deficiency-induced uracil incorporation into primary human lymphocyte DNA in vitro.

Methylenetetrahydrofolate reductase (MTHFR) is an enzyme which converts 5,10-methylene tetrahydrofolate (5,10-MnTHF) to 5-methyl tetrahydrofolate. A common C to T transition (C677T) in the MTHFR gene is reported to reduce the risk for colorectal cancer and acute lymphocytic leukemia in homozygotes (TTs). It is hypothesized that because TTs have reduced MTHFR activity, more 5,10-MnTHF is available to provide methyl groups for the conversion of uracil to thymidine. Folic acid deficiency causes the intracellular accumulation of dUMP and the subsequent incorporation of uracil into DNA. The removal of uracil from DNA may result in double-stranded DNA breaks, the accumulation of which is a putative risk factor for cancer. We tested whether human lymphocytes taken from TTs (n = 10) were more able to resist uracil incorporation into DNA than controls (n = 14 CCs and 6 CTs) when cultured in medium containing 12-120 nM folic acid for 9 days. DNA uracil content of these lymphocytes was measured by CG-MS. TTs and controls showed a dose-dependent increase in DNA uracil content during folic acid deficiency (P < 0.0001, R2 = 0.23 for TTs and P < 0.0001, R2 = 0.19 for controls). DNA uracil content was not different between the two groups at any of the folic acid concentrations (two-way ANOVA: media [folic acid], P < 0.0001; genotype, P = 0.4). The results show that, in this in vitro system, the MTHFR C677T polymorphism does not affect the cell's ability to resist uracil incorporation into DNA. Chromosome breakage, as measured by micronuclei, was also shown to correlate with folic acid concentration in a preliminary experiment (P < 0.0001). Although the results appear not to support the hypothesis that a reduced risk for certain cancers in TTs is due to diversion of folic acid to thymidine synthesis, differences between the in vivo and in vitro situation make this conclusion not definitive.     

Folate, vitamin B12, homocysteine status and chromosome damage rate in lymphocytes of older men

Deficient levels of folic acid and vitamin B12 are associated with elevated chromosome damage rate and high concentrations of homocysteine in the blood. We have therefore performed a study to determine the prevalence of folate deficiency, vitamin B12 deficiency and hyperhomocysteinemia in 64 healthy men aged between 50 and 70 years, and evaluate the relationship of these micronutrient levels in the blood with the micronucleus frequency in peripheral blood lymphocytes. We also performed a placebo-controlled, double-blind intervention study to determine whether supplementation of the diet with a daily dose of 0.7 mg (as a supplement in cereal) or 2.0 mg (in a tablet) over a period of 4 months resulted in a significant alteration of folate status, homocysteine status and the micronucleus index. Twenty-three per cent of the men were serum folate deficient (<6.8 nmol/l), 16% were red blood cell folate deficient (<317 nmol/l), 4.7% were vitamin B12 deficient (<150 pmol/l) and 37% has plasma homocysteine levels >10 micromol/l. In total, 56% of the men had one or more abnormal blood values for folate, vitamin B12 or homocysteine. The micronucleus index of these men (n = 34) in cytokinesis-blocked binucleated cells (19.2 +/- 1.1) was significantly elevated (P = 0.02) when compared to the micronucleus index of the rest of the men who had normal levels of folate, vitamin B12 and homocysteine (16.3 +/- 1.3, n = 30). Interestingly, the micronucleus index in men with normal folate and vitamin B12, but homocysteine levels >10 micromol/l (19.4 +/- 1.7, n = 15) was also significantly higher (P = 0.05) when compared to those with normal folate, vitamin B12 and homocysteine. This novel result was also supported by the observation that the micronucleus index and plasma homocysteine were significantly (P = 0.0086) and positively correlated (r2 = 0.172) in those subjects who were not deficient in folate or vitamin B12. The micronucleus index was not significantly correlated with folate indices, but there was a significant (P = 0.013) negative correlation with serum vitamin B12 (r2 = 0.099). Daily supplementation of the diet with 0.7 mg free folic acid in cereal for 2 months followed by 2.0 mg free folic acid via a tablet produced a 4- fold increase in plasma folate, a 2.6-fold increase in red blood cell folate and a 11% reduction in plasma homocysteine; however, these changes were not accompanied by a reduction in the micronucleus index. In conclusion, it is apparent that elevated homocysteine status, in the absence of vitamin deficiency and low, but not deficient, vitamin B12 status are important risk factors for increased chromosome damage in lymphocytes.      

One-carbon metabolism, MTHFR polymorphisms, and risk of breast cancer

Accumulating evidence from epidemiologic studies suggests that risk of breast cancer is reduced in relation to increased consumption of folate and related B vitamins. We investigated independent and joint effects of B vitamin intake as well as two polymorphisms of a key one-carbon metabolizing gene [i.e., methylenetetrahydrofolate reductase (MTHFR) 677C>T and 1298A>C] on breast cancer risk. The study uses the resources of a population-based case-control study, which includes 1,481 cases and 1,518 controls. Significant inverse associations between B vitamin intake and breast cancer risk were observed among non-supplement users. The greatest reduction in breast cancer risk was observed among non-supplement users in the highest quintile of dietary folate intake [odds ratio (OR), 0.61; 95% confidence interval (95% CI), 0.41-0.93] as compared with non-supplement users in the lowest quintile of dietary folate intake (high-risk individuals). The MTHFR 677T variant allele was associated with increased risk of breast cancer (P, trend = 0.03) with a multivariate-adjusted OR of 1.37 (95% CI, 1.06-1.78) for the 677TT genotype. The 1298C variant allele was inversely associated with breast cancer risk (P, trend = 0.03), and was likely due to the linkage of this allele to the low-risk allele of 677C. The MTHFR-breast cancer associations were more prominent among women who did not use multivitamin supplements. Compared with 677CC individuals with high folate intake, elevation of breast cancer risk was most pronounced among 677TT women who consumed the lowest levels of dietary folate (OR, 1.83; 95% CI, 1.13-2.96) or total folate intake (OR, 1.71; 95% CI, 1.08-2.71). From a public heath perspective, it is important to identify risk factors, such as low B vitamin consumption, that may guide an effective prevention strategy against the disease.     

Sex differences in risk of lung cancer associated with methylene-tetrahydrofolate reductase polymorphisms.

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the metabolism of folate and nucleotides needed for DNA synthesis and repair. Variations in MTHFR functions likely play roles in the etiology of lung cancer. The MTHFR gene has three nonsynonymous single nucleotide polymorphisms (i.e., C677T, A1298C, and G1793A) that have a minor allele frequency of >5%. We investigated the associations between the frequencies of MTHFR variant genotypes and risk of lung cancer in a hospital-based case-control study of 1,051 lung cancer patients and 1,141 cancer-free controls in a non-Hispanic White population. We found that compared with the MTHFR 1298AA genotype, the 1298CC genotype was associated with a significantly increased risk of lung cancer in women [(odds ratio (OR), 2.09; 95% confidence interval (95% CI), 1.32-3.29)] but not in men (OR, 0.95; 95% CI, 0.62-1.45). The MTHFR 677TT genotype was associated with a significantly decreased risk of lung cancer in women (OR, 0.60; 95% CI, 0.40-0.92) but not in men. No association was found between the MTHFR G1793A polymorphism and risk of lung cancer. Further analysis suggested evidence of gene-dietary interactions between the MTHFR C677T polymorphism and dietary intake of vitamin B6, vitamin B12, and methionine in women and evidence of gene-environment interactions between the MTHFR C677T and A1298C polymorphisms and tobacco smoking in men. In conclusion, the polymorphisms of MTHFR may contribute to the risk of lung cancer in non-Hispanic Whites and modify the risk associated with the dietary and environmental exposure in a sex-specific manner.