【作者】 张艳玲；

【导师】 梁后杰；

【作者基本信息】 第三军医大学 ， 肿瘤学， 2008， 博士

【摘要】 目的结直肠癌是一种常见消化道恶性肿瘤之一。无论是世界范围内还是在我国,结直肠癌发病率和死亡率都居常见恶性肿瘤前列。我国虽属结直肠癌的低发区,但近年来,随着居民饮食结构、生活方式的改变,人均期望寿命明显延长,我国结直肠癌的发生率和死亡率均呈逐年上升趋势。结直肠癌的发生是一个多因素、多步骤的过程,主要受环境暴露因素的影响。流行病学研究表明与结直肠癌易感性有关的环境暴露因素主要包括高脂肪低纤维素饮食,煎炸熏烤食品,少食蔬菜及水果,吸烟、饮酒、饮用不洁水、体力活动较少或静坐时间过长等。此外,肿瘤遗传易感性在结直肠癌发生发展中也起着十分重要的作用,体内参与癌变的基因序列的改变,赋予个体不同的遗传背景。有关结直肠癌机体遗传易感性,与致癌物活化/失活代谢密切相关的代谢酶及与DNA损伤修复密切相关的DNA修复酶基因多态性己得到广泛的研究。近十多年来,叶酸代谢与恶性肿瘤的关系日益受到关注。叶酸代谢过程包括两个主要分支:核苷酸生物合成和甲基化反应,其代谢障碍可引起异常的DNA合成和DNA甲基化。叶酸、蛋氨酸、VitB2、VitB6和VitB12是叶酸代谢过程中的主要营养素,而亚甲基四氢叶酸还原酶(methylenetetrahydrofolate,MTHFR)、蛋氨酸合成酶(methionine synthase, MTR)、蛋氨酸合成酶还原酶(methionine synthase reductase,MTRR)和胸苷酸合成酶(thymidylate synthase, TS)是叶酸代谢过程中的关键酶。这些营养素水平或代谢酶活性发生变化,都可能影响叶酸代谢过程,破坏核苷酸生物合成和甲基化反应之间的平衡,参与结直肠癌的发生发展。目前,结直肠癌病因学研究中存在的主要问题是:一.大多数研究独立、分散进行,结果缺乏可比性;二.遗传易感性对不同人群结直肠癌危险影响的相关研究较少,许多基因的多态性对发病的影响亟待研究;三.缺乏全面考虑环境-膳食-基因间相互作用对发病综合影响的研究,仅考虑单一因素时很难作出明确的病因学结论。因此,将基因分析、营养研究和流行病学调查相结合,按统一的方法和标准,进行多地区、多种族的人群研究,将为得出结直肠癌明确的病因结论提供依据。为此,中、日、韩三国共同协作开展了大规模的人群结直肠癌膳食危险因素和保护因素与遗传易感性关系的系统研究。本课题作为该国际合作研究的组成部分,进行了本溪地区人群的环境膳食因素及遗传易感性对结直肠癌发病影响的研究。本研究应用以非配对的病例-对照研究,了解叶酸代谢酶基因多态性在人群中的分布频率及其在群体水平上与结直肠癌易感性的关系,并在此基础上,分析叶酸代谢酶基因-基因交互作用,以及基因多态性与相关环境暴露因素以及叶酸代谢相关营养素之间的交互作用与结直肠癌易感性的关系。材料与方法1.关联研究中,研究对象包括300例结直肠癌患者和300例非癌症对照,病例采病例来源于2003年1月至2005年6月期间在本溪地区钢铁集团公司总医院住院治疗的结直肠癌患者,对照来源于总医院的同期住院病人(无肿瘤史),对病例与对照组人群的性别、年龄等因素进行频数匹配。2.通过流行学问卷调查获得现场资料。调查内容包括:一般状况,生活方式与习惯,饮食习惯与种类以及既往疾病史等。通过询问各类食物的单次摄入量和摄入频率获得常见食物摄入量信息。3.每位研究对象同时抽取5ml外周血。采用Promage Winzard Genomic DNA Extract提取外周血有核细胞DNA;采用聚合酶链-限制性片断长度多态性(PCR-RFLP)方法检测MTHFRC677T、A1298C、MTRA2756G、MTRRA66G和TS3’-UTR、TS5’-UTR多态位点。CBS844ins68多态位点检测采用PCR方法扩增目的片段后直接经琼脂糖凝胶电泳分析。4.统计分析。分类变量在病例组和对照组的分布特征采用χ2检验;采用SPSS13.0统计软件的非条件Logistic回归模型计算各基因型与结直肠癌风险的相关性,分析时对性别、年龄、吸烟、饮酒等混杂因素进行分层,结果经性别、年龄、文化程度、肿瘤家族史、吸烟和饮酒等因素校正。采用卡方趋势检验判断是否存在剂量一反映关系,采用相乘模型来判断基因一基因和基因一环境之间是否存在交互,同时采用似然比检验来分析总的交互模型是否有意义。全部统计分析均在SPSS13.0 for Windows和Microsoft Excel 2007软件中进行。结果1.相关环境暴露因素与结直肠癌1.1大学及以上文化程度、家族肿瘤史是结直肠癌的危险因素(P<0.05)。1.2饮酒年限与结直肠癌发病风险有关(OR=1.54,95%CI,0.83-2.86);吸烟程度与结直肠癌发病风险有关(OR=1.76,95%CI,1.12-2.76)。被动吸烟者结直肠癌风险有统计学意义的升高(OR=1.87,95%CI,1.09-3.19)。无吸烟史,但有饮酒史者,个体患结直肠癌的风险显著升高,OR值为1.69(95%CI,1.03-2.78)。1.3膳食因素中:视黄醇、维生素C、总膳食纤维等营养素,水果、豆制品和绿叶蔬菜类食物包括花菜、白菜类和大蒜类食物,钾摄入对结直肠癌均表现出较强的保护效应;中等MUFA摄入组个体患结直肠癌的风险显著升高(OR=2.65,95%CI,1.47-4.57)2.叶酸代谢酶基因多态与结直肠癌2.1 MTHFR-677CT/1298AC组合基因型发生结直肠癌的风险增加(OR = 2.32,95%CI,1.10-4.92)。2.2 MTRR-66AG、MTRR-66GG和MTRR-66 G等位基因型发生结直肠癌的风险增加(OR=1.49,95%CI,1.02-2.18;OR=2.49,95%CI,1.35-4.60和1.62(95%CI,1.13-2.32)。2.3 TS5’-UTR 2R/2R基因型发生结直肠癌的风险下降, OR值为0.35(95%CI,0.12-0.98)。3.基因-基因交互作用与结直肠癌3.1 MTHFRC677T与MTRR A66G基因之间存在负交互作用,交互作用产生的ORint=0.46,似然比检验P=0.046。在MTHFR-677CC基因型的个体中,MTRR-66 AG或GG基因型发生结直肠癌风险增加,OR为2.84(95%CI,1.43-5.66),在MTHFR-677 CT或TT等位基因型的个体中,MTRR-66AA基因型发生结直肠癌风险增加,OR为1.93(95%CI,1.01-3.68),MTRR-66AG或GG等位基因型发生结直肠癌风险增加,OR为2.34(95%CI,1.33-4.14)。3.2在MTR-2756AA基因型的个体中,携带MTRR-66 AG或GG基因型者发生结直肠癌风险增加,OR为1.62(95%CI,1.05-2.51)。3.3在MTRR-66AG或GG基因型的个体中,携带TS5’-UTR 3Rg/3Rg基因型者发生结直肠癌风险增加,OR为3.24(95%CI,1.22-8.58)。3.4 TS5’-UTR 3Rg/3Rc+3Rg/2R+3Rc/2R+2R/2R+3Rc/3Rc组合基因型合并TS3’-UTR ins6等位基因携带者患结直肠癌的风险有一定程度下降,OR值为0.47(95%CI,0.22-1.19)。4.基因-环境交互作用与结直肠癌4.1吸烟-基因与结直肠癌:MTRR A66G基因多态与吸烟对结直肠癌发生的风险表现出明显的协同作用。在不吸烟者中,66G等位基因携带者发生结直肠癌的风险增加,OR为1.72(95%CI, 1.10-2.69);而在吸烟者中,66G等位基因携带者发生结直肠癌的风险增加,OR为2.08(95%CI, 1.16-3.71)。MTRR A66G基因型与吸烟之间存在负交互作用(ORint=0.78,似然比检验P=0.04)。吸烟程度与MTHFR C677T、A1298C,MTR A2756G,MTRRA66G,TS5’-UTR和TS3’-UTR基因之间均存在交互作用(P< 0.05)。以不吸烟者为参照组,吸烟<16包年者中,MTHFR-677 T等位基因型患结直肠癌的风险增加2.09(95%CI,1.07-4.04),MTRR-66 G等位基因型患结直肠癌的风险增加,OR为2.91(95%CI,1.51-5.62);而在吸烟≥16包年者中,MTHFR-1298AA基因和TS3’-UTR del6/del6基因型者患结直肠癌的风险明显下降,OR值分别为0.37(95%CI,0.17-0.80)和0.17(95%CI,0.05-0.56)。MTRR A66G基因型与吸烟年限之间存在负交互作用(ORint=0.70,似然比检验P=0.002),在吸烟年限小于26年者中,MTRR-66G等位基因型者患结直肠癌的风险增加,OR为4.55(95%CI,1.98-10.43)。4.2饮酒-基因与结直肠癌: MTRR A66G多态与饮酒之间存在正交互作用(ORint=1.07,似然比检验P=0.001)。MTHFR C677T、MTR A2756G、MTRR A66G与饮酒年限之间存在负交互作用,而MTHFR A1298C和TS5’-UTR与饮酒年限之间存在正交互作用。饮酒年限<20年者,MTRR-66G等位基因型发生结直肠癌的风险增加,OR为3.98(95%CI,1.54-10.24);而饮酒年限≥20年者,MTHFR-677AA、1298AA基因型发生结直肠癌的风险下降,OR值分别为0.24(95%CI,0.10-0.58)和0.58(95%CI,0.34-0.98)。4.3饮酒-吸烟-基因与结直肠癌:在饮酒的人群中,吸烟者并MTHFR -677T等位基因发生结直肠癌的风险增加,OR为4.61(95%CI,1.57-13.46),吸烟者并MTRR-66 G等位基因型发生结直肠癌的风险增加,OR为4.06(95%CI,1.53-10.79)。5.基因-膳食交互作用与结直肠癌5.1 MTHFRC677T与VitB12、蛋氨酸之间存在交互作用(P<0.05),ORint分别为1.07和1.12。在高VitB 12和蛋氨酸中、高摄入组中,677CC和677T等位基因携带者患直肠癌的风险显著下降。在VitB2中等摄入和叶酸高摄入组中,MTHFR-677T等位基因型发生结直肠癌的风险显著下降。5.2 MTHFR A1298C与VB12、叶酸摄入之间分别存在交互作用(P<0.05),在VB12高摄入组中,1298AA、AC或CC基因型者结直肠癌的风险均显著下降。5.3 MTRA2756G在高VitB12摄入水平组中,AA、G等位基因发生结肠癌的风险显著下降。5.4 MTRRA66G与VitB2、烟酸、VitB6、叶酸和蛋氨酸之间分别存在正交互作用(P<0.05),ORint分别为1.46、1.29、1.19、1.10和1.07,与VitB12摄入之间存在负交互作用(P<0.05),ORint为0.79。低和高VitB12摄入组,叶酸、蛋氨酸高摄入组中,66G等位基因携带者患直肠癌的风险显著下降,在高VitB12摄入组中,66AA基因型患结直肠癌的风险显著下降。5.5 TS3’-UTR多态和VitB12摄入之间存在交互作用(P<0.05),ORint为0.70,在高VitB12摄入组中,TS3’-UTR del6/del6和ins6等位基因发生结直肠癌的风险显著下降。5.6 TS5’-UTR多态和与VB2、叶酸和蛋氨酸摄入之间亦存在交互作用(P<0.05),ORint分别为1.35、1.41和1.47。在烟酸中等摄入组中,TS5’-UTR 3Rg/3Rc+3Rg/2R +3Rc/2R+2R/2R +3Rc/3Rc组合基因型发生结直肠癌的风险是3Rg/3Rg的2.65倍。结论本次以非配对人群为基础的病例对照研究揭示:1.结直肠癌的危险因素有大学以上文化程度、家族肿瘤史和被动吸烟、MTHFR-677CT/1298AC组合型基因、MTRR -66G等位基因;2.结直肠癌的保护因素有常吃蔬菜、水果,视黄醇、维生素C、总膳食纤维等营养素的摄入较高、TS5’-UTR 2R/2R基因型。3. MTHFRC677T和MTRR A66G基因多态,吸烟史与MTRR A66G,吸烟年限与MTRR A66G多态,吸烟程度与MTHFRC677T,吸烟程度与MTHFRA1298C,吸烟程度与MTRA2756G,吸烟程度与MTRRA66G,吸烟程度与TS3’-UTRHE,吸烟程度与TS5’-UTR基因,饮酒史与MTRR A66G多态,饮酒年限与MTHFRC677T,饮酒年限与MTHFRA1298C,饮酒年限与MTRA2756G,饮酒年限与MTRRA66G,饮酒年限与TS5’-UTR多态,饮食VitB2摄入和MTRRA66G,饮食VitB2摄入和TS5’-UTR多态,饮食烟酸摄入和MTRRA66G,饮食VitB6摄入和MTRR A66G,饮食VitB12摄入和MTHFRC677T、A1298C,饮食VitB12摄入和MTRR A66G,饮食VitB12摄入和TS3’-UTR多态,饮食叶酸摄入和MTHFRA 1298C,饮食叶酸摄入和MTRR A66G,饮食叶酸摄入和TS5’-UTR多态、饮食蛋氨酸摄入和MTHFRC677T,饮食蛋氨酸摄入和MTRR A66G,饮食蛋氨酸摄入和TS 5’-UTR多态之间存在交互作用,共同改变个体结直肠癌风险。更多还原

【Abstract】 Background and ObjectiveColorectal cancer is one of the most common malignant tumors of human alimentary tract. lts incidence rate and mortality rate rank the forefront among all common cancers both domestic and worldwide. Although China is a low-incidence area, its incidence rate and mortality rate in China show a yearly increasing trend with changes in dietary structures and life styles of residents and prolongation of per capita expectancy in recent years.The accumulated evidence suggest the occurrence of colorectal cancer is a multi-factor involved and multi-stage process, which is mainly influenced by environmental exposures. Epidemiological studies indicated common environmental exposures related to the susceptibility of colorectal cancer are high-fat and/or low-fiber diet, fried, fumed, or baked food, low intakes of vegetables and fruits, smoking, drinking, low physical activity or long sedentary time.Associations between folate metabolism and cancers development showed more and more importance in last decade. Folate metabolic process includes two main branches, biological synthesis of nucleic acid and methylation process. Disturbances of folate metabolism can cause abnormal DNA synthesis and DNA methylation. Folate, methionine, VitB2, VitB6, and VitB12 are primary nutrients taking part in folic acid metabolism, and methylenetetrahydrofolate(MTHFR), methionine(MTR), methionine synthase reductase (MTRR), and thymidylate synthase (TS) are primary enzymes enrolling in folic acid metabolism. The level or activity changes of the above-mentioned nutrients or metabolic enzymes might influence folate metabolism, cause inbalance between biological synthesis of nucleic acid and methylation reaction, and take part in colorectal carcinogenesis.Major defects in past etiology study may be: first, most study was carried out independently and separately which lack of comparability among mass of results; second, little was known about the linkage between cancer development and some special polymorphism in different ethnics demanding the necessity to get more evidence about it; third, it was hard to get absolute conclusion with single aspect taken into consideration, above all, study on the role of diet-environment-gene interaction in colorectal cancer is still rare.To carry out lagre scale cooperative population studies in different ethnics with standard methodology which integrated epidemiology, nutriology, molecularbiology and bioinformatics will help overcoming the problems remaining in CRC ,concluding clearer etiological evidence. So, a collaborative study was carried out in China, Japan and Korea for the purpose of revealing dietary protective / risk factors and relationship between genetic susceptibility and colorectal cancer in eastern Asian populations. The present study is part of the study with the aim to examine the effects of environmental and dietary factors, genetic susceptibility and their interactions on colorectal cancer in Benxi population.The purpose of the case-control study is to explore distributions of gene polymorphisms of folate metabolic enzymes in a natural population and associations between these polymorphisms and susceptibility to colorectal cancer at a population level, and further to analyze the role of gene-gene and gene-environment interactions in the development of colorectal cancer.Materials and MethodsThe cases were 300 patients who were histologically diagnosed as having CRCs between January 2003 and June 2005 at Benxi country steel group center hospital and not having any earlier history of cancer. Controls were inpatient who visited Benxi country steel group Center Hospital during the same period as cases and were confirmed to have no cancers and no prior history of cancers. Controls were randomly selected and matched for age and sex strata to cases .Field data were obtained by an epidemiological questionnaire investigation. The investigation contents mainly included common state , life styles and habits, dietary habits and categories,and past disease histories. Intake quantities of all common kinds of foods were obtained by asking subjects single time intake and intake frequencies of foods.A sample of venous blood (5m1) was taken from every subject. Genomic DNA was extracted from karyocyte by Promage Winzard Genomic DNA Extract . Genotypes of MTHFRC677T,A1298C,MTR A2756G,MTRR A66G ,TS3’-UTR and TS5’-UTR polymorphisms were determined by PCR-restriction fragment lengthen polymorphism method.Genotype of CBS844ins68 polymorphism was determined by directly electrophoreses of PCR products on agarose gels.Distributional characteristics of cases and controls were analyzed by X2 test, and the non-conditional Logistic model was applied to estimate the ORs delaminated by age, sex, smoking and drinking for colorectal cancer of related study factors ,adjusted for age sex status of smoking and drinking where appropriate.Chi-square trend test was applied to analyze dose-reaction relationship, subjugation model to ananlyze gene-gene and gene-environment interactions,likelihood test for calculating P values . All statistical analysis was processed by SPSS 13.0 for windows and Microsoft Excel 2007.Results1. Related environmental exposures and colorectal cancer1.1 For demographic factors, Subjects with education degrees of college and above, Family cancer history are significant risk factors of CRC .1.2 For smoking and drinking, long period drinkers had a statistically significant increased risk of CRC with OR value of 1.54 (95%Cl, 0.83-2.86). Smoking was associated with CRC at the OR of 1.76(95%CI,1.12-2.76).Passive smokers were at statistically significant increased risks of CRC with OR values of 1.87 (95%CI,1.09-3.19) .The drinkers without smoking history showed significantly increased risk to CRC with the OR value of 1.69(95%CI,1.03-2.78).1.3 For dietary factors,retinol,VitC,dietary total fibre,fruit,bean and its derivates,leafy vegetables including Cauliflover,cabbage and garlic are strong protective factors to CRC,as also potassium intake .Middle level of MUFA intake increased the risk of CRC significantly(OR=2.65, 95%CI,1.47-4.57)2. Gene polymorphisms of folate metabolic enzymes and colorectal cancer2.1 MTHFR-677CT/1298AC genes were associated with significantly increased risk of CRC(OR=2.32,95%CI, 1.10-4.92)2.2 MTRR-66AG,66GG and 66G allele are associated with increased risk of CRC(OR=1.49,95%CI, 1.02-2.18; OR=2.49,95%CI, 1.35-4.60 and OR=1.62,95%CI, 1.13-2.32, respectively).2.3 TS5’-UTR 2R/2R showed decreaed risk to CRC with the OR value of 0.35(95%CI, 0.12-0.98)3. Gene-gene interactions and colorectal cancer3.1 The interaction between MTHFR C677T and MTRR A66G showed a decreased risk of CRC with the ORint value of 0.46,and its likelihood test P is 0.046.Individuals carrying MTHFR-677CC showed increased risk of CRC eith the OR value of 2.84(95% CI,1.43-5.66), when also carrying MTRR-66AG or GG;Individuals carrying MTHFR-677CT or TT allele ,showed increased risk of CRC with the OR value of 1.93(95%CI,1.01-3.68)when also carrying MTRR-66AA,and 2.34(95%CI,1.33-4.14)when also carrying MTRR-66AG or GG allele..3.2 Individuals with MTR-2756AA,showed increased risk of CRC with the OR value of 1.62(95%CI,1.43-5.66), when also carrying MTRR-66AG or GG.3.3 Individuals with MTRR-66AG or GG allele showed increased risk of CRC with the OR value of 3.24(95%CI,1.22-8.58), when also carrying TS5’-UTR 3Rg/3Rg3.4 TS5’-UTR 3Rg/3Rc+3Rg/2R +3Rc/2R+2R/2R +3Rc/3Rc combined gene with TS3’-UTR ins6 allele was associated with decreased the risk of CRC with the OR of 0.47(95%CI,0.22-1.19)4. Gene-environment interactions and colorectal cancer4.1 Smoking-gene and CRC : MTRR A66G polymorphism and smoking showed synergistic effect on CRC. In non-smokers,the risk of CRC in 66G allele carrier was 1.72-fold to that in 66AA gene carrier ;While in smokers ,this increased to 2.08-fold,which means negative interaction between MTRR A66G and smoking (ORint=0.78, likelihood test P=0.04).Interactions were found between the extent of smoking and MTHFR C677T、A1298C,MTR A2756G,MTRRA66G,TS5’-UTR and TS3’-UTR.Refered to non-smokers,the risk of CRC increased by 2.09(95%CI,1.07-4.04) in smokers lower than 16 pack year with MTHFR-677T allele ,while MTRR-66G allele 2.91(95% CI,151-5.62). In MTHFR-1298AA gene and TS3’-UTR del6/del6 significantly decreased the risk CRC by 0.37 (95%CI,0.17-0.80) and 0.17(95%CI, 0.05-0.56), respectively .Negative interation between smoking years and MTRR A66G was found (ORint=0.70, likelihood test P=0.002).In smokers ,smoking less than 26years,MTRR-66G increased risk of CRC by 4.55(95%CI,1.98-10.43).4.2 Drinking-gene and CRC: Interation between drinking and MTRR A66G was found (ORint=1.07, likelihood test P=0.001). Negative interation between drinking extent and MTHFR A1298C or was found ,while interation between drinking extent and MTHFR C677T、MTR A2756G or TS5’-UTR was also found ;The risk of CRC increased by 3.98(95%CI,1.54-10.24) in drinkers lower than 20 years with MTRR-66G allele ,while In drinkers lower than 20 years with MTHFR-677AA and 1298AA gene significantly decreased the risk CRC by 0.24(95%CI,0.10-0.58)and 0.58(95%CI,0.34-0.98 ),respectively.4.3 Drinking-smoking-gene and CRC: In drinkers,the risk of CRC in smokers and MTHFR-677T allele increased by 4.61(95%CI,1.57-13.46) ,when also carrying MTRR-66G 4.06(95%CI,1.53-10.79).5. gene-meal interactions and colorectal cancer5.1 The interaction between MTHFR C677T and VitB12 or Methionine was showed , the ORint value of 1.07 and 1.12 ,respectively. In high VitB12 and middle、high Methionine intake groups, the risk of CRC in MTHFR-677CC and 677T allele significantly decreased . In middle VitB2 and high folate intake groups, the risk of CRC in MTHFR-677T allele significantly decreased .5.2 The interaction between MTHFR A1298C and VitB12 or folate was showed. In high VitB12 intake groups, the risk of CRC in MTHFR-1298AA and 1298C allele significantly decreased .5.3 In high VitB12 intake groups, the risk of CRC in MTR-2756AA and 2756G allele significantly decreased .5.4 The interaction between MTRR A66G and VitB2 or nicacid or VitB6 or folate or Methionine were showed, the ORint value of 1.46、1.19、1.10 and 1.07,respectively. In high VitB12 intake groups, the risk of CRC in MTHFR-1298AA and 1298C allele significantly decreased. while negative interation and VitB12 intake, the ORint value of 0.79. In lower、high VitB12 intake groups and in high folate、methionine intake groups, the risk of CRC in MTRR-66G allele significantly decreased . the risk of CRC in MTR-2756AA and 2756G allele significantly decreased . In high VitB12 intake groups, the risk of CRC in MTRR-66AA significantly decreased .5.5 The interaction between TS3’-UTR and VitB12 was showed, the ORint value of 0.70. In high VitB12 intake groups, the risk of CRC in TS3’-UTR del6/del6 and ins6 allele significantly decreased .5.6 The interaction between TS5’-UTR and VitB2、folate and methionine was showed, the ORint value of 1.35、1.41 and 1.47,respectively. In middle nicacid intake group, the risk of CRC in TS5’-UTR 3Rg/3Rc+3Rg/2R +3Rc/2R+2R/2R +3Rc/3Rc combine genes was 2.65-fold to than 3Rg/3Rg gene carrier .Conclusions1. The risk factors of CRC are education degrees of college and above, individual histories of cancer, passive smoking, MTHFR-677CT/1298AC combine genotype and MTRR -66G allele .2. The protective factors of CRC are often eating vegetable、fruit and higher retinol or VitC or dietary total fibre intake, TS5’-UTR 2R/2R genotype.3. There are interactions between MTHFR C677T and MTRR A66G polymorphisms, smoking history and MTRR A66G, smoking duration and MTHFRC677T,smoking duration and MTRRA66G, smoking extent and MTHFRC677T , smoking extent and MTHFR A1298C, smoking extent and MTRA2756G, smoking extent and MTRRA66G, smoking extent and TS3’-UTR, smoking extent and TS5’-UTR ,drinking history and MTRR A66G, drinking duration and MTHFRC677T、A1298C, drinking duration and MTRA2756C, drinking duration and MTRRA66C, drinking duration and TS5’-UTR polymorphism, dietary VitB2 intakes and MTRRA66G , dietary VitB2 intakes and TS5’-UTR, dietary nicacid intakes and MTRRA66G, dietary VitB6 intakes and MTRRA66G, dietary VitB12 intakes and MTHFR C677T or A1298C, dietary VitB12 intakes and MTRRA66G , dietary VitB12 intakes and TS3’-UTR polymorphism ,dietary folate intakes and MTHFR A1298C, dietary folate intakes and MTRRA66G, dietary folate intakes and TS5’-UTR, dietary methionine intakes and MTHFRC677T, as welL as dietary methionine intakes and MTRR A66G or TS5’-UTR. Gene-gene and gene-environment interactions in folate metabolic process can jointly influence individual susceptibility of CRC.更多还原