meta分析教程

Leukemia Research 34 (2010) 1596–1600Contents lists available at ScienceDirectLeukemiaResearchj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /l e u k r esMTHFR C677T polymorphisms and childhood acute lymphoblastic leukemia:A meta-analysisJing Wang a ,Ping Zhan b ,Bing Chen a ,Rongfu Zhou a ,Yonggong Yang a ,Jian Ouyang a ,∗a Department of Hematology,the Affiliated DrumTower Hospital of Nanjing University Medical School,321Zhongshan Road,Nanjing 210008,Jiangsu PR China bDepartment of Respiratory Medicine,Nanjing Chest Hospital,Nanjing,PR Chinaa r t i c l e i n f o Article history:Received 4January 2010Received in revised form 19March 2010Accepted 20March 2010Available online 20 April 2010Keywords:MTHFR polymorphismsAcute lymphoblastic leukemia Meta-analysisa b s t r a c tTo date,case–control studies on the association between methylenetetrahydrofolate reductase (MTHFR)C677T and childhood acute lymphoblastic leukemia have provided either controversial or inconclusive results.To clarify the effect of MTHFR C677T on the risk of childhood acute lymphoblastic leukemia,a meta-analysis of all case–control observational studies was performed.Heterogeneity (I 2=65%,P <0.0001)for C677T among the studies was extreme.The random effects (RE)model showed that the 677T allele was not associated with a decreased susceptibility risk of childhood acute lymphoblastic leukemia compared with the C allele [OR =0.96,95%confidence interval (CI)(0.88–1.04),P =0.34].The contrast of homozygotes,recessive model and dominant model produced the same pattern of results as the allele contrast.Although MTHFR C677T was associated with increased risks of colorectal cancer,leukemia,and gastric cancer,our pooled data suggest no evidence for a major role of MTHFR C677T in the carcinogenesis of childhood acute lymphoblastic leukemia.© 2010 Elsevier Ltd. All rights reserved.1.IntroductionAcute lymphoblastic leukemia (ALL)is the most common malig-nancy affecting children,constituting about 30%of all cancers among children [1,2].Although significant improvements in both ALL diagnosis and treatment have been made over the past decades,the etiology of most cases of ALL remains unknown due to proba-ble multifactorial mechanisms of pathogenesis [3].Pediatric acute leukemias are likely influenced by both the genetic background and the environment of the patient [4,5].Methylenetetrahydrofolate reductase (MTHFR)plays an important role in folate metabolism by catalyzing the irre-versible conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate [4].A common polymorphism at the nucleotide 677,C677T (Ala →Val),in the gene for the enzyme MTHFR,results in a less stable version of the enzyme [6].MTHFR C677T has been associated with an increased risk of colorectal cancer,leukemia,and gastric cancer [7].The role of MTHFR polymorphisms in the development of childhood ALL has been investigated in the past decade,with conflicting results.Sev-eral studies have previously suggested an association between the MTHFR C677T polymorphism and a decreased risk of acute lymphoblastic leukemia (ALL)[8,9].However,other studies have∗Corresponding author.Tel.:+862583105211;fax:+862583105211.E-mail address:ouyang211@ (J.Ouyang).failed to confirm such an association [10,11].Moreover,two meta-analyses [12,13]investigating the same hypothesis,quite similar in methods and performed almost at the same time,yielded different conclusions.The exact relationship between genetic polymorphisms of MTHFR C677T and susceptibility to childhood ALL has not been entirely established.To clarify the effect of MTHFR C677T on the risk of childhood ALL,our study undertakes a meta-analysis of all published case–control observational studies.2.Methods2.1.Publication searchThe electronic databases PubMed,Embase,Web of Science,and CNKI (China National Knowledge Infrastructure)were searched for studies to include in the present meta-analysis,using the terms:“Methylenetetrahydrofolate Reductase,”“genotype,”“Leuk(a)emia,”“Acute lymphocytic,”“Acute lymphoblastic,”“Child-hood,”“P(a)ediatric,”“polymorphism,”“MTHFR,”“C677T,”“folate,”and “mutation.”An upper date limit of August 30,2009was applied;we used no lower date limit.The search was conducted without any restrictions on language but focused on stud-ies that had been conducted on human subjects.We also reviewed the Cochrane Library for relevant articles.The reference lists of reviews and retrieved articles were hand-searched simultaneously.Only published studies with full text articles were included.When more than one instance of the same patient population was included in several publications,only the most recent or complete study was used in this meta-analysis.2.2.Data extractionThe following information was extracted from each study:first author,year of publication,ethnicity of study population,genotyping method,and the num-ber of cases and controls for the C677T genotype.We did not define any0145-2126/$–see front matter © 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.leukres.2010.03.034J.Wang et al./Leukemia Research34 (2010) 1596–16001597Table1Study characteristics.Studyfirst author Country Source of controls No.of cases/controls Leukemia characteristicsFranco et al.[8]Brazil Population71/7177%B-ALL and23%T-ALLWiemels et al.[10]United Kingdom Population216/20036%were TEL-AML1and64%were hyperdiploid leukemiasBalta et al.[11]Turkey Population142/18552%B-ALL,28%non-B-ALL,and20%undeterminedKarjinovic et al.[14]Canada Hospital270/30085%pre B-ALL,11%T-ALL,and4%undeterminedJiang et al.[9]China Population29/67Immunophenotype not describedChatzidakis et al.[18]Greece Population52/8887%B-ALL and13%T-ALLOliveira et al.[16]Portugal Population103/111Immunophenotype not describedSchnakenberg et al.[17]Germany Population443/37977.7%B-ALL,18.3%T-ALL,0.9%biphenotype,and3.2%undetermined Thirumaran et al.[15]Germany Population453/1448Immunophenotype not describedZanrosso et al.[19]Brazil Population165/19894.9%B-ALL and5.1%T-ALLKim et al.[22]Korea Population66/100Immunophenotype not describedReddy et al.[21]India Population135/142Immunophenotype not describedYu et al.[20]China Population51/5372.5%B-ALL and27.5%T-ALLPetra et al.[24]Slovenia Hospital68/25875%B-ALL,11.8%T-ALL,13.2%biphenotype,and3.2%undetermined Kamel et al.[23]Egypt Population88/311B-ALLGiovannetti et al.[25]Indonesia Population71/44Immunophenotype not describedAlcasabas et al.[26]Philippines Population189/394Immunophenotype not describedLiu et al.[27]China Population83/83Immunophenotype not describedde Jonge et al.[28]Netherlands Population243/49675%B-ALL and25%T-ALLKim et al.[29]Korea Population107/1700Immunophenotype not describedYeoh et al.[30]Singapore Population318/34589.4%B-ALL,7.8%T-ALL and2.8%infant ALLThree studies[9–11]were excluded from this meta-analysisminimum number of patients as a criterion for a study’s inclusion in our meta-analysis.2.3.Statistical analysisThe meta-analysis examined the overall association for the allele contrasts,the contrast of homozygotes,and the recessive and dominant models.The effect of the association was indicated as an odds ratio(OR)with its corresponding95%confi-dence interval(CI).Pooled OR was estimated usingfixed effects and random effects models.Heterogeneity between studies was tested using the Q statistic.Such het-erogeneity was considered statistically significant if P<0.10.Heterogeneity was quantified using the I2metric,which is independent of the number of studies in the meta-analysis(I2<25%no heterogeneity;I2=25–50%moderate heterogene-ity;I2>50%large or extreme heterogeneity).An estimate of potential publication bias was carried out by the funnel plot,in which the standard error of log(OR) of each study was plotted against its log(OR).An asymmetric plot suggests a possible publication bias.Funnel plot asymmetry was assessed by the method of Egger’s linear regression test,a linear regression approach for measuring fun-nel plot asymmetry on the natural logarithm scale of the OR.The significance of the intercept was determined by the t-test suggested by Egger(P<0.05indicated a statistically significant publication bias).All calculations were performed using ReviewManage5.0.3.Results3.1.Study characteristicsWe found21published articles addressing the relation-ship between MTHFR C677T and childhood acute lymphoblastic leukemia(Table1).The studies were published between1999and 2009.In all studies,the cases were histologically confirmed,and the control groups were free of ALL and were matched for age and gender.Studies were conducted in various populations of dif-ferent ethnicities:nine were conducted in populations of Asian regions[9,20–22,25–27,29,30],and eight studies looked at Euro-peans[10,11,15–18,24,28].Table2Distribution of methylenetetrahydrofolate reductase(MTHFR)C677T genotypes and allelic frequency.Studyfirst author(year)Distribution of C677T MTHFR genotype Frequency of C677T MTHFR alleles Hardy–Weinbergequilibrium(HWE)PvalueCC CT TT C TCases,n Controls,n Cases,n Controls,n Cases,n Controls,n Cases,n Controls,n Cases,n Controls,nFranco et al.(2001)[8]362228366131008040620.796Wiemels et al.(2001)[10]9889917927322872571451430.047Balta et al.(2004)[11]71906087118202267821030.020Karjinovic et al.(2004)[14]11212612712831463513801892200.159Jiang et al.(2004)[9]1518144108447714570.039Chatzidakis et al.(2005)[18]31321847398011124650.169Oliveira et al.(2005)[16]484550575914114760750.120 Schnakenberg et al.(2005)[17]19518420115247435915203042380.179Thirumaran et al.(2005)[15]19960019568159167593188131310150.210Yu et al.(2006)[20]30201423710746328430.466Zanrosso et al.(2006)(W)[19]4359355081012116851700.896Zanrosso et al.(2006)(nW)[19]5337213251012710631520.462Kim et al.(2006)[22]1724385511217210360970.313Reddy et al.(2006)[21]517977587517921691680.148Petra et al.(2007)[24]301123311053693334431820.287Kamel et al.(2007)[23]3915642135720120447561750.195Liu et al.(2008)[27]343823362699111275540.914Giovannetti et al.(2008)[25]512611630113581760.558Alcasabas et al.(2008)[26]14532241663633171047780.227de Jonge et al.(2009)[28]1302199322322543536611373310.805Kim et al.(2009)[29]295405186327297109194310514570.132Yeoh et al.(2009)[30]18416311115023324794761572140.7651598J.Wang et al./Leukemia Research34 (2010) 1596–1600Fig.1.Forest plot of the OR of T allele vs.C allele.The size of the squares reflects each study’s relative weight and the diamond (♦)represents the aggregate OR and 95%CI.The studies provided 3358cases and 6961controls for C677T.The variant genotype and allele frequencies of C677T in the indi-vidual studies are shown in Table 2.For case groups,the frequency of C677T polymorphism among CC-homozygous individuals was 48.9%;while 40.9%of CT-heterozygous individuals and 10.2%of TT-homozygous individuals displayed C677T polymorphism.In control groups,the frequencies of C677T polymorphism among CC-homozygous individuals,CT-heterozygous individuals,and TT-homozygous individuals were 43.1%,45.0%,and 12.1%,respectively.The 677T allelic frequencies in the case and control groups were 30.8%and 34.5%,respectively.In three studies [9–11]of the C677T polymorphism,the distribution of genotypes in the control group was not in HWE (P <0.05),indicating genotyping errors and/or pop-ulation stratification (Table 2).These three studies were excluded from this meta-analysis to clarify the effect of MTHFR C677T on the risk of childhood ALL.3.2.Meta-analysis resultsTable 3lists the main results of this meta-analysis.Overall,the 677T allele was not associated with the risk of childhood ALL compared with the C allele (OR =0.93;95%CI =0.82–1.07,Fig.1).Contrasting homozygotes (TT ),the recessive model,and the dominant model produced the same pattern of results as the allele contrast.In the analysis stratified by ethnicity and region,no sig-nificant associations were found between childhood ALL and the various genetic models.There was extreme heterogeneity (I 2=65%,P <0.0001)among the 18studies.To eliminate heterogeneity,we divided the 18studies into subgroups as far as possible;subse-quently,heterogeneity only decreased for subgroups of white and European subjects,which revealed that most of the studies could not be grouped helpfully according to ethnicity and region.3.3.Publication biasBegg’s funnel plot and Egger’s test were performed to assess the publication bias of literatures.Evaluation of publication bias for 677T allele versus C allele showed that the Egger test was not significant (P =0.346).These results did not indicate a potential forpublication bias.For TT versus CC,the publication bias was also not found (P =0.356).4.DiscussionIt is well recognized that individual susceptibility to the same kind of cancer can vary,even with identical environmental expo-sures.Host factors,including polymorphism in the genes involved in carcinogenesis may account for this difference.Therefore,genetic susceptibility to cancer has been the focus of research in the scientific community.Recently,genetic variants of the MTHFR gene have been subject to increasing attention in the etiology of leukemia.This meta-analysis summarized all the available data on the association between MTHFR C677T and childhood acute lymphoblastic leukemia,including a total of 3358cases and 6961controls.Our results indicated no evidence for a major protective role of MTHFR C677T in the carcinogenesis of childhood acute lym-phoblastic leukemia.Additionally,white ethnicity and European region were not found to be significantly associated with any of the genetic models.Although in Caucasians,no significant associa-tions were found for the genetic models examined,heterogeneity disappeared when that population was viewed as a separate group,which suggested that the effect of T allele on the risk of pediatric ALL may differ by ethnicity.Population stratification is an area of concern,and it can lead to spurious evidence for the association between the genetic marker and the disease,suggesting a possible role of ethnic differences in genetic backgrounds and environments [31].In an effort to shed some light on the impact of MTHFR C677T on pediatric ALL,data was pooled from available published trials for meta-analysis.However,two previous meta-analyses [12,13]per-formed almost at the same time came to different conclusions from one another.One of these previously published meta-analyses [12]drew on four fewer publications than the other [13].Of these four missed/excluded publications,two examined adult ALL [32,33]and two evaluated childhood ALL [15,19].In fact,electronic searches by Zintzaras et al.were carried out solely using Medline [12].The use of this database alone is not sufficient for literature searches [34].Previous research assessing different electronic databases hasJ.Wang et al./Leukemia Research34 (2010) 1596–16001599Table3Odds ratios(ORs)and heterogeneity results for the genetic contrasts of MTHFR gene C677T polymorphisms for childhood acute lymphoblastic leukemia.Population OR I2(%)P value Q testFixed effects(95%CI)Random effects(95%CI)Alleles(T vs.C)All0.95(0.89–1.02)0.93(0.82–1.07)65<0.0001 Non-White 1.02(0.91–1.15) 1.03(0.80–1.31)730.0001 White0.91(0.84–1.00)0.87(0.76–1.01)510.04 European0.93(0.84–1.03)0.89(0.75–1.05)540.05 Asian 1.05(0.92–1.20) 1.09(0.83–1.43)720.0007 East Asian a0.96(0.82–1.11)0.97(0.68–1.39)790.0007TT to CC All0.91(0.78–1.07)0.87(0.68–1.11)440.02 Non-White 1.08(0.82–1.42) 1.05(0.67–1.67)550.02 White0.84(0.68–1.02)0.80(0.62–1.02)210.25 European0.88(0.70–1.10)0.85(0.65–1.12)170.30 Asian 1.18(0.88–1.58) 1.20(0.72–2.01)570.02 East Asian 1.11(0.81–1.52) 1.07(0.56–2.06)720.006TT to(CT+CC)All0.98(0.84–1.14)0.95(0.76–1.18)380.05 Non-White 1.19(0.93–1.54) 1.16(0.78–1.72)480.04 White0.87(0.72–1.06)0.87(0.72–1.07)30.41 European0.93(0.75–1.15)0.94(0.76–1.17)00.43 Asian 1.26(0.96–1.65) 1.25(0.80–1.96)520.04 East Asian 1.24(0.93–1.64) 1.20(0.68–2.14)710.009TT+CT to CC All0.93(0.84–1.02)0.91(0.76–1.08)65<0.0001 Non-White 1.00(0.85–1.16) 1.00(0.73–1.38)720.0002 White0.89(0.79–1.00)0.84(0.69–1.03)550.02 European0.89(0.78–1.02)0.85(0.67–1.07)590.03 Asian 1.03(0.86–1.22) 1.07(0.75–1.53)720.0008 East Asian0.82(0.67–1.01)0.85(0.58–1.23)600.04a East Asian is composed of Chinese and Korean.demonstrated that a single search engine does not provide all of the pertinent articles,and combining more databases yields greater coverage of possible articles[35].Conference proceedings and jour-nal supplements should also be searched to ensure that relevant remaining reports are identified.However,additional assessments of databases other than PubMed and EMBASE should be analyzed with caution,due to a potential lack of quality in study design. Although the other meta-analysis included more publications in its analysis,one study may not suitable for the subgroup analysis according to age[36].In this study,cases and controls were not matched for age and gender(P<0.05).Krajinovic et al.found a protective effect of MTHFR polymor-phisms in children born before1996(about the time that Health Canada recommended folate supplementation during pregnancy) but not in children born later[14].More conceivable would be the relation between folate status and genotype in adult ALL,where folate status might be more conditional on the subject’s own geno-type and folate intake.In studies of breast cancer risk,high folate intake may be more protective in women with the polymorphism than in those with the wild type[37,38].Thesefindings demon-strate that the risks associated with the MTHFR677TT genotype vary depending on folate status.Genetic and/or environmental exposures are required for cancer to develop.None of the studies to date has assessed dietary folate intake to evaluate whether overall folate status may have modified the relation between having the MTHFR genotype and one’s risk of developing leukemia.We cannot rule out the possibility that the C677T variant plays a major role in risk modulation in pediatric ALL for populations with inadequate folate intake.Considering some limitations of this meta-analysis,our results should be interpreted with caution.Firstly,heterogeneity is a potential problem when interpreting the results from any meta-analysis.We minimized the likelihood of encountering het-erogeneity problems by performing a careful search for published studies and using explicit criteria for study inclusion,precise data extraction,and strict data analysis.Significant between-study heterogeneity existed in almost each comparison.Heterogene-ity can result from study differences in the selection of controls, age distribution,lifestyle factors,and so on.There are major differences of genetic background within the Asian population studied,and it should be stratified to add moreflavor to the subject.Secondly,only published studies were included in this meta-analysis.The presence of publication bias indicates that non-significant or negativefindings may be stly,our results were based on unadjusted estimates,while a more pre-cise analysis should be conducted using individual data if they were available,which would allow researchers to adjust covari-ates including age,ethnicity,family history,environmental factors, and lifestyle.In conclusion,although studies investigating the association between MTHFR C667T polymorphism and the risk of childhood ALL arrive at different conclusions,this meta-analysis suggests that MTHFR C667T polymorphism is not associated with childhood ALL.Conflict of interestWe declare that we have nofinancial and personal relationships with other people or organizations that can inappropriately influ-ence our work,there is no professional or other personal interest of any nature or kind in any product,service and company that could be construed as influencing the position presented in,or the review of,the manuscript.AcknowledgementsContributions.JW,PZ and JO conceived and designed the study. 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