Just Accepted by International Journal of Neuroscience
Association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and ischemic stroke in the Chinese population: a meta-analysis Xiao-Yan Zhu, Rong-Yao Hou, Xu-Dong Pan, Yu-Chun Wang, Zheng-Shou Zhang, Rui-You Guo
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
doi:10.3109/00207454.2014.984295 Purpose: The association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and ischemic stroke (IS) has been extensively studied; however, the results from genetic association studies have been inconsistent even in the Chinese population. As far as we know, there was no previous meta-analysis concerning this association in the Chinese population. Therefore, the aim of our meta-analysis was to further evaluate the association in the Chinese population. Methods: We collected all of the relevant studies from Pubmed, OVID, Embase, Chinese Wan Fang database, CNKI, Chongqing VIP database and CBM up to August 2014. The available data was analyzed by Stata (version 12.0). We used odds ratios (ORs) and corresponding 95% confidence intervals (CIs) to present the strength of the association. Heterogeneity was evaluated by the Q-test and I2 statistic. Different genetic models, subgroup analysis, publication bias and sensitivity analysis were used to improve the comprehensive understanding. Results: The results showed a significant association between the MTHFR gene C677T polymorphism and IS in six genetic models(additive model: OR D 1.34, 95%CI: 1.17∼1.54, p < 0.001; dominant model: OR D 1.44, 95% CI:1.26∼1.64, p < 0.001; recessive model: OR D 1.45, 95% CI: 1.15∼1.83, p D 0.001; heterozygote model: OR D 1.35, 95% CI: 1.18∼1.55, p < 0.001; homozygote model: OR D 1.80, 95% CI: 1.34∼2.41, p < 0.001; and allelic model: OR D 1.34, 95% CI: 1.17∼1.53, p < 0.001) based on the overall population, as well as subgroup analysis. In addition, the similar results were obtained in the sensitivity analysis based on studies with the high quality. Conclusions: This meta-analysis presented a significant association between the MTHFR gene C677T polymorphism and IS, the T allele might be a risk factor for IS in the Chinese population.
© 2014 Informa Healthcare USA, Inc. This provisional PDF corresponds to the article as it appeared upon acceptance. Fully formatted PDF and full text (HTML) versions will be made available soon. DISCLAIMER: The ideas and opinions expressed in the journal’s Just Accepted articles do not necessarily reflect those of Informa Healthcare (the Publisher), the Editors or the journal. The Publisher does not assume any responsibility for any injury and/or damage to persons or property arising from or related to any use of the material contained in these articles. The reader is advised to check the appropriate medical literature and the product information currently provided by the manufacturer of each drug to be administered to verify the dosages, the method and duration of administration, and contraindications. It is the responsibility of the treating physician or other health care professional, relying on his or her independent experience and knowledge of the patient, to determine drug dosages and the best treatment for the patient. Just Accepted have undergone full scientific review but none of the additional editorial preparation, such as copyediting, typesetting, and proofreading, as have articles published in the traditional manner. There may, therefore, be errors in Just Accepted articles that will be corrected in the final print and final online version of the article. Any use of the Just Accepted articles is subject to the express understanding that the papers have not yet gone through the full quality control process prior to publication.
Association between the methylenetetrahydrofolate reductase (MTHFR) gene
meta-analysis 1
2
3
1
TE D
C677T polymorphism and ischemic stroke in the Chinese population: a
1
2
Xiao-Yan Zhu , Rong-Yao Hou , Xu-Dong Pan , Yu-Chun Wang , Zheng-Shou Zhang , Rui-You Guo
Department of Critical Care Medicine, the Affiliated Hiser Hospital of Qingdao University, Qingdao,
EP
China; 2 Department of Neurology, the Affiliated Hiser Hospital of Qingdao University, Qingdao, China; 3
Department of Neurology, the Affiliated Hospital of Qingdao University, Qingdao, China Corresponding Author：Xu-Dong Pan, E-mail：[email protected] Address for corresponding author: Xu-Dong Pan, Department of Neurology, the Affiliated Hospital of
C
Qingdao University, 59 Haier Road, Qingdao 266000, Shandong Province, China Tel: +86 532 82913033 Fax: +86 532 82913018
Guo)
AC
Author’s key words: Xiao-Yan Zhu(XY Zhu ), Rong-Yao Hou (RY Hou ), Xu-Dong Pan(XD Pan ), Yu-Chun Wang(YC Wang), Zheng-Shou Zhang(ZS Zhang), Rui-You Guo (RY
ST
Purpose: The association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and ischemic stroke (IS) has been extensively studied; however, the results from genetic association studies have been inconsistent even in the Chinese population. As far as we know, there was no previous meta-analysis concerning this association in the Chinese population. Therefore, the aim of our
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
1
meta-analysis was to further evaluate the association in the Chinese population. Methods: We collected all of the relevant studies from Pubmed, OVID, Embase, Chinese Wan Fang database, CNKI, Chongqing VIP database and CBM up to August 2014. The available data was analyzed by Stata (version 12.0). We used odds ratios (ORs) and corresponding 95% confidence intervals (CIs) to present the strength of the association. Heterogeneity was evaluated by the Q-test and I2 statistic. Different genetic models, subgroup
1
analysis, publication bias and sensitivity analysis were used to improve the comprehensive understanding. Results: The results showed a significant association between the MTHFR gene C677T polymorphism
TE D
and IS in six genetic models(additive model: OR =1.34, 95%CI: 1.171.54, p 0.001; dominant model: OR =1.44, 95% CI:1.261.64, p 0.001; recessive model: OR = 1.45, 95% CI: 1.151.83, p = 0.001;
heterozygote model: OR = 1.35, 95% CI: 1.181.55, p 0.001; homozygote model: OR = 1.80, 95% CI:
EP
population, as well as subgroup analysis. In addition, the similar results were obtained in the sensitivity
analysis based on studies with the high quality. Conclusions: This meta-analysis presented a significant association between the MTHFR gene C677T polymorphism and IS, the T allele might be a risk factor for
C
IS in the Chinese population.
AC
KEYWORDS: methylenetetrahydrofolate reductase (MTHFR), gene polymorphism, Chinese population, ischemic stroke, meta-analysis
Introduction
[1]
ST
Stroke poses a serious harm to one’s health and is an important cause of disability and death worldwide . Ischemic stroke (IS) is the main subtype of stroke. It has been reported by the World Health
Organization (WHO) that every year approximately 15 million people have an ischemic stroke, of whom
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
1.342.41, p 0.001; and allelic model: OR = 1.34, 95% CI: 1.171.53, p 0.001) based on the overall
approximately 10 million die or become permanently disabled [2]. In China, approximately 2.5 million new cases of stroke are diagnosed each year, of which ischemic stroke accounts for 70% [3]. Multiple factors are included in the incidence of IS, such as environmental and genetic factors [4]. In recent years, extensive studies have shown that an elevated homocysteine (HCY) level is a new and unique risk factor for stroke [5]. Hyperhomocysteinemia can lead to vascular endothelial dysfunction, which is an early stage in the development of atherosclerosis [6]. An elevated homocysteine level can stimulate superoxide anion 2
increase, platelet aggregation, and decrease nitric oxide bioavailability, thus an elevated homocysteine level is a risk factor for venous and arterial thrombosis [7]. The product encoded by the MTHFR gene is
TE D
5,10-methylenetetrahydrofolate reductase, which catalyzes the rate-limiting step in the remethylation of homocysteine to methionine[8].The MTHFR gene is located at 1p36.3, and includes 11 exons with the
mutation mainly occurring at exon 4 [9] . An elevated homocysteine level can be caused by a MTHFR gene
EP
candidate polymorphisms. The C677T polymorphism of MTHFR can result in the conversion of alanine to valine at amino acid 222 (A→V), which could increase homocysteine levels [10]. Brattström et al. [8] reported homocysteine levels elevated over 25% in the TT genotype compared to the CC genotype. It was
C
also shown that individuals with the TT genotype had higher total plasma homocysteine concentrations
AC
than individuals with CT and CC genotypes [11]. Thus, the MTHFR gene C677T polymorphism has been suggested to be a genetic risk factor for cerebrovascular disease [6]. The association between the C677T (A222V) of MTHFR and the risk for IS has been studied in different populations. Many studies have
ST
shown that the MTHFR gene C677T polymorphism is a risk factor for IS; however, the results are inconsistent.
In the Chinese population, the results of the MTHFR gene C677T polymorphism and the risk for IS are also controversial. To the best of our knowledge, there was no previous meta-analysis concerning
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
missense mutation, in which the C677T base mutation is one of the most extensively investigated
this association between the MTHFR gene C677T polymorphism and IS in the Chinese population. Thus, we collected the data from relevant published literature to evaluate the association in the Chinese population.
Materials and methods
3
Data sources The published papers were retrieved by searching electronic databases in English or Chinese (up to
TE D
August 2014) , including Pubmed, OVID, Embase, Chinese Wan Fang database, China National Knowledge Infrastructure (CNKI), Chongqing VIP database, and China Biological Medicine Database (CBM). The following search terms or combinations were used: “stroke” OR “ischemic stroke” OR
EP
OR “variant” OR “gene”. The subjects in each study were limited to humans. We sent e-mail to authors for accurate data if necessary.
C
Selection criteria
AC
The included studies met the following criteria (1) case-control studies of the association between the MTHFR gene C677T polymorphism and IS in the Chinese population;(2) a clear diagnosis for IS by neurologic examination and magnetic resonance imaging (MRI) or computed tomography (CT) or both, according to the revision of the diagnostic criteria in the Chinese cerebrovascular disease conference; (3)
ST
healthy individuals as control group and the sources of controls clearly;(4) studies with full text articles; and(5) sufficient data for estimating an OR with 95% CI. Studies were excluded if one of the following criteria existed:(1) studies without original genotype frequencies; (2) did not conform to the Hardy-
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
“cerebral infarction” AND“MTHFR” OR “methylenetetrahydrofolate reductase” AND “polymorphism”
Weinberg equilibrium (HWE) in the control group;(3) the subjects younger than 18 years; (4) reviews, animal studies, non-case-control studies or case reports; and (5) in the repeated studies, the largest sample size or the most recent one was selected.
Data extraction
4
Each study was carefully and independently extracted from all eligible publications by two authors (XY Zhu and RY Hou), according to the inclusion and exclusion criteria listed above. The following
TE D
information was extracted from the eligible studies: the first author’s name; the year of publication; the ethnicity of the studied population; the region of the population recruited; the numbers of cases and
controls; the diagnostic and matching criteria; the p value of the HWE; the genotyping methods; the
EP
Statistical analysis
The available data of the included studies was analyzed by Stata version 12.0 (StataCorp, Colleage
C
Station, Texas, USA). Heterogeneity was evaluated by the Q-test and I2 statistic. If there was no statistically significant difference between the results (p > 0.05 and I2 < 50%), the fixed-effect model was
AC
selected; otherwise, the random-effect model was used for data processing. We applied the OR with a 95% CI to evaluate the strength of the association. We used a χ2 test to check the HWE for the genotype distribution in controls. The six genetic models were selected as follows: the additive model (TT vs. CT
ST
vs. CC), the dominant model (TT + CT vs. CC); the recessive model (TT vs. CT+CC); the homozygote model (TT vs. CC); the heterozygote model (CT vs. CC) and the allelic model (T vs. C). Sensitivity analysis was adopted to evaluate the stability of the results. We used the funnel plots, Begg’s and Egger’s
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
genotype numbers in cases and controls; and the allele frequencies.
tests to evaluate the publication bias. A p value less than 0.05 was considered statistically significant.
Results
Results of the paper selection We identified 20 relevant studies for our meta-analysis that met the strict criteria. The flow diagram of the article selection process is shown in Figure 1. The meta-analysis included 2317 patients with IS and 5
2123 controls. Of these 20 studies, 12 studies focused on the Han population, and another 8 studies focused on the Chinese population which might include the non-Han population. According to the region of study population, 12 studies focused on the northern region population, and another 8 studies focused
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on the southern region population. The detailed characteristics and the distributions of genotypes are shown in Table 1.
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Our meta-analysis showed a significant association between the MTHFR gene C677T polymorphism and IS among total population in the additive model (OR =1.34, 95%CI: 1.171.54, p 0.001; p heterogeneity =0.003, I2=53.1%; Figure 2), in the dominant model (OR =1.44 ,95% CI:1.261.64 ,p 0.001; p heterogeneity
C
= 0.175, I2=22.7%; Figure 3), in the recessive model (OR = 1.45,95% CI: 1.151.83, p=0.001; p heterogeneity
AC
=0.02, I2=43.5%; Figure 4), in the heterozygote model (OR = 1.35,95% CI: 1.181.55, p 0.001; p heterogeneity
= 0.858, I2=0.0%) , in the homozygote model (OR = 1.80,95% CI: 1.342.41, p 0.001; p
heterogeneity
=0.004, I2=51.8%), and in the allelic model (OR = 1.34,95% CI: 1.171.53, p 0.001; p I2=54.1 %; Figure 5).To better clarify the heterogeneity among our studies, we used
ST
heterogeneity=0.002,
subgroup analysis in the ethnicity and study region. In the Han population, northern region and southern region population, significant association was in all genetic models between the MTHFR gene C677T polymorphism and IS. The main results of this meta-analysis are detailed in Table 2.
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
Quantitative synthesis
Sensitivity analysis Sensitivity analysis was performed to assess the stability of the results. In the sensitivity analysis, we removed each single study in turn, and did a meta-analysis using the left studies. We also observed a significant association between MTHFR C677T polymorphism and IS in different genetic models, which
6
indicated that the pooled estimate was stable and not influenced by a single study. The pooled OR and 95%CI values ranged from 1.30(1.141.48) to 1.38(1.201.58) in the additive model, 1.40 (1.221.60) to
TE D
1.51(1.301.74) in the dominant models, 1.36(1.111.67) to 1.52 (1.211.90) in the recessive models, 1.33(1.151.53) to 1.41(1.211.65) in the heterozygote models, 1.68(1.272.21) to 1.90 (1.422.55) in
EP
Publication bias
Funnel plots, Begg’s and Egger’s regression tests were used to assess potential publication bias (Table 2). In the additive model (p Begg’s =0.48, p Egger’s =0.39), in the dominant model (p Begg’s =0.14, p Egger’s
0.16), in the homozygote model (p Begg’s =0.60, p Egger’s =0.62) and in the allelic model (p Begg’s
AC
Egger’s =
C
=0.30), in the recessive model (p Begg’s =0.36, p Egger’s =0.47), in the heterozygote model (p Begg’s =0.14, p
=0.85, p Egger’s =0.58), all suggested no publication bias in total population. There was no publication bias
ST
in the subgroup analysis.
Discussion
Extensive evidence highlights the role of MTHFR gene polymorphisms in stroke, especially in IS. Epidemiologic studies have reported the association between MTHFR gene C677T polymorphism and
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
the homozygote model and 1.30(1.141.48) to 1.37(1.201.57) in the allelic models.
stroke with inconsistent results. Some studies involving the MTHFR gene C677T polymorphism and IS have shown that the TT gene can increase the risk of IS [32, 33]. Another studies have shown that the TT gene can increase the risk of hemorrhagic stroke [34, 35].On the contrary, Sabino et al. [36] reported the incidence of IS risk was not increased with the MTHFR gene C677T polymorphism .
7
In the Chinese population, extensive research regarding the association between the MTHFR gene C677T polymorphism and IS has been conducted, but the results are inconsistent. Some studies in our
TE D
meta-analysis presented the MTHFR gene C677T polymorphism was significantly associated with increased risk of IS in the Chinese population [12,15-17,20-25,29,31]; however, another studies showed that there was not a significant association between them[13,14,18,19,26-28,30] .Therefore, our meta-analysis was very
EP
association only in the Han Chinese population, the literature in this study was collected 8 years ago and the sample size was
Association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and ischemic stroke in the Chinese population: a meta-analysis Xiao-Yan Zhu, Rong-Yao Hou, Xu-Dong Pan, Yu-Chun Wang, Zheng-Shou Zhang, Rui-You Guo
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
doi:10.3109/00207454.2014.984295 Purpose: The association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and ischemic stroke (IS) has been extensively studied; however, the results from genetic association studies have been inconsistent even in the Chinese population. As far as we know, there was no previous meta-analysis concerning this association in the Chinese population. Therefore, the aim of our meta-analysis was to further evaluate the association in the Chinese population. Methods: We collected all of the relevant studies from Pubmed, OVID, Embase, Chinese Wan Fang database, CNKI, Chongqing VIP database and CBM up to August 2014. The available data was analyzed by Stata (version 12.0). We used odds ratios (ORs) and corresponding 95% confidence intervals (CIs) to present the strength of the association. Heterogeneity was evaluated by the Q-test and I2 statistic. Different genetic models, subgroup analysis, publication bias and sensitivity analysis were used to improve the comprehensive understanding. Results: The results showed a significant association between the MTHFR gene C677T polymorphism and IS in six genetic models(additive model: OR D 1.34, 95%CI: 1.17∼1.54, p < 0.001; dominant model: OR D 1.44, 95% CI:1.26∼1.64, p < 0.001; recessive model: OR D 1.45, 95% CI: 1.15∼1.83, p D 0.001; heterozygote model: OR D 1.35, 95% CI: 1.18∼1.55, p < 0.001; homozygote model: OR D 1.80, 95% CI: 1.34∼2.41, p < 0.001; and allelic model: OR D 1.34, 95% CI: 1.17∼1.53, p < 0.001) based on the overall population, as well as subgroup analysis. In addition, the similar results were obtained in the sensitivity analysis based on studies with the high quality. Conclusions: This meta-analysis presented a significant association between the MTHFR gene C677T polymorphism and IS, the T allele might be a risk factor for IS in the Chinese population.
© 2014 Informa Healthcare USA, Inc. This provisional PDF corresponds to the article as it appeared upon acceptance. Fully formatted PDF and full text (HTML) versions will be made available soon. DISCLAIMER: The ideas and opinions expressed in the journal’s Just Accepted articles do not necessarily reflect those of Informa Healthcare (the Publisher), the Editors or the journal. The Publisher does not assume any responsibility for any injury and/or damage to persons or property arising from or related to any use of the material contained in these articles. The reader is advised to check the appropriate medical literature and the product information currently provided by the manufacturer of each drug to be administered to verify the dosages, the method and duration of administration, and contraindications. It is the responsibility of the treating physician or other health care professional, relying on his or her independent experience and knowledge of the patient, to determine drug dosages and the best treatment for the patient. Just Accepted have undergone full scientific review but none of the additional editorial preparation, such as copyediting, typesetting, and proofreading, as have articles published in the traditional manner. There may, therefore, be errors in Just Accepted articles that will be corrected in the final print and final online version of the article. Any use of the Just Accepted articles is subject to the express understanding that the papers have not yet gone through the full quality control process prior to publication.
Association between the methylenetetrahydrofolate reductase (MTHFR) gene
meta-analysis 1
2
3
1
TE D
C677T polymorphism and ischemic stroke in the Chinese population: a
1
2
Xiao-Yan Zhu , Rong-Yao Hou , Xu-Dong Pan , Yu-Chun Wang , Zheng-Shou Zhang , Rui-You Guo
Department of Critical Care Medicine, the Affiliated Hiser Hospital of Qingdao University, Qingdao,
EP
China; 2 Department of Neurology, the Affiliated Hiser Hospital of Qingdao University, Qingdao, China; 3
Department of Neurology, the Affiliated Hospital of Qingdao University, Qingdao, China Corresponding Author：Xu-Dong Pan, E-mail：[email protected] Address for corresponding author: Xu-Dong Pan, Department of Neurology, the Affiliated Hospital of
C
Qingdao University, 59 Haier Road, Qingdao 266000, Shandong Province, China Tel: +86 532 82913033 Fax: +86 532 82913018
Guo)
AC
Author’s key words: Xiao-Yan Zhu(XY Zhu ), Rong-Yao Hou (RY Hou ), Xu-Dong Pan(XD Pan ), Yu-Chun Wang(YC Wang), Zheng-Shou Zhang(ZS Zhang), Rui-You Guo (RY
ST
Purpose: The association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and ischemic stroke (IS) has been extensively studied; however, the results from genetic association studies have been inconsistent even in the Chinese population. As far as we know, there was no previous meta-analysis concerning this association in the Chinese population. Therefore, the aim of our
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
1
meta-analysis was to further evaluate the association in the Chinese population. Methods: We collected all of the relevant studies from Pubmed, OVID, Embase, Chinese Wan Fang database, CNKI, Chongqing VIP database and CBM up to August 2014. The available data was analyzed by Stata (version 12.0). We used odds ratios (ORs) and corresponding 95% confidence intervals (CIs) to present the strength of the association. Heterogeneity was evaluated by the Q-test and I2 statistic. Different genetic models, subgroup
1
analysis, publication bias and sensitivity analysis were used to improve the comprehensive understanding. Results: The results showed a significant association between the MTHFR gene C677T polymorphism
TE D
and IS in six genetic models(additive model: OR =1.34, 95%CI: 1.171.54, p 0.001; dominant model: OR =1.44, 95% CI:1.261.64, p 0.001; recessive model: OR = 1.45, 95% CI: 1.151.83, p = 0.001;
heterozygote model: OR = 1.35, 95% CI: 1.181.55, p 0.001; homozygote model: OR = 1.80, 95% CI:
EP
population, as well as subgroup analysis. In addition, the similar results were obtained in the sensitivity
analysis based on studies with the high quality. Conclusions: This meta-analysis presented a significant association between the MTHFR gene C677T polymorphism and IS, the T allele might be a risk factor for
C
IS in the Chinese population.
AC
KEYWORDS: methylenetetrahydrofolate reductase (MTHFR), gene polymorphism, Chinese population, ischemic stroke, meta-analysis
Introduction
[1]
ST
Stroke poses a serious harm to one’s health and is an important cause of disability and death worldwide . Ischemic stroke (IS) is the main subtype of stroke. It has been reported by the World Health
Organization (WHO) that every year approximately 15 million people have an ischemic stroke, of whom
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
1.342.41, p 0.001; and allelic model: OR = 1.34, 95% CI: 1.171.53, p 0.001) based on the overall
approximately 10 million die or become permanently disabled [2]. In China, approximately 2.5 million new cases of stroke are diagnosed each year, of which ischemic stroke accounts for 70% [3]. Multiple factors are included in the incidence of IS, such as environmental and genetic factors [4]. In recent years, extensive studies have shown that an elevated homocysteine (HCY) level is a new and unique risk factor for stroke [5]. Hyperhomocysteinemia can lead to vascular endothelial dysfunction, which is an early stage in the development of atherosclerosis [6]. An elevated homocysteine level can stimulate superoxide anion 2
increase, platelet aggregation, and decrease nitric oxide bioavailability, thus an elevated homocysteine level is a risk factor for venous and arterial thrombosis [7]. The product encoded by the MTHFR gene is
TE D
5,10-methylenetetrahydrofolate reductase, which catalyzes the rate-limiting step in the remethylation of homocysteine to methionine[8].The MTHFR gene is located at 1p36.3, and includes 11 exons with the
mutation mainly occurring at exon 4 [9] . An elevated homocysteine level can be caused by a MTHFR gene
EP
candidate polymorphisms. The C677T polymorphism of MTHFR can result in the conversion of alanine to valine at amino acid 222 (A→V), which could increase homocysteine levels [10]. Brattström et al. [8] reported homocysteine levels elevated over 25% in the TT genotype compared to the CC genotype. It was
C
also shown that individuals with the TT genotype had higher total plasma homocysteine concentrations
AC
than individuals with CT and CC genotypes [11]. Thus, the MTHFR gene C677T polymorphism has been suggested to be a genetic risk factor for cerebrovascular disease [6]. The association between the C677T (A222V) of MTHFR and the risk for IS has been studied in different populations. Many studies have
ST
shown that the MTHFR gene C677T polymorphism is a risk factor for IS; however, the results are inconsistent.
In the Chinese population, the results of the MTHFR gene C677T polymorphism and the risk for IS are also controversial. To the best of our knowledge, there was no previous meta-analysis concerning
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
missense mutation, in which the C677T base mutation is one of the most extensively investigated
this association between the MTHFR gene C677T polymorphism and IS in the Chinese population. Thus, we collected the data from relevant published literature to evaluate the association in the Chinese population.
Materials and methods
3
Data sources The published papers were retrieved by searching electronic databases in English or Chinese (up to
TE D
August 2014) , including Pubmed, OVID, Embase, Chinese Wan Fang database, China National Knowledge Infrastructure (CNKI), Chongqing VIP database, and China Biological Medicine Database (CBM). The following search terms or combinations were used: “stroke” OR “ischemic stroke” OR
EP
OR “variant” OR “gene”. The subjects in each study were limited to humans. We sent e-mail to authors for accurate data if necessary.
C
Selection criteria
AC
The included studies met the following criteria (1) case-control studies of the association between the MTHFR gene C677T polymorphism and IS in the Chinese population;(2) a clear diagnosis for IS by neurologic examination and magnetic resonance imaging (MRI) or computed tomography (CT) or both, according to the revision of the diagnostic criteria in the Chinese cerebrovascular disease conference; (3)
ST
healthy individuals as control group and the sources of controls clearly;(4) studies with full text articles; and(5) sufficient data for estimating an OR with 95% CI. Studies were excluded if one of the following criteria existed:(1) studies without original genotype frequencies; (2) did not conform to the Hardy-
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
“cerebral infarction” AND“MTHFR” OR “methylenetetrahydrofolate reductase” AND “polymorphism”
Weinberg equilibrium (HWE) in the control group;(3) the subjects younger than 18 years; (4) reviews, animal studies, non-case-control studies or case reports; and (5) in the repeated studies, the largest sample size or the most recent one was selected.
Data extraction
4
Each study was carefully and independently extracted from all eligible publications by two authors (XY Zhu and RY Hou), according to the inclusion and exclusion criteria listed above. The following
TE D
information was extracted from the eligible studies: the first author’s name; the year of publication; the ethnicity of the studied population; the region of the population recruited; the numbers of cases and
controls; the diagnostic and matching criteria; the p value of the HWE; the genotyping methods; the
EP
Statistical analysis
The available data of the included studies was analyzed by Stata version 12.0 (StataCorp, Colleage
C
Station, Texas, USA). Heterogeneity was evaluated by the Q-test and I2 statistic. If there was no statistically significant difference between the results (p > 0.05 and I2 < 50%), the fixed-effect model was
AC
selected; otherwise, the random-effect model was used for data processing. We applied the OR with a 95% CI to evaluate the strength of the association. We used a χ2 test to check the HWE for the genotype distribution in controls. The six genetic models were selected as follows: the additive model (TT vs. CT
ST
vs. CC), the dominant model (TT + CT vs. CC); the recessive model (TT vs. CT+CC); the homozygote model (TT vs. CC); the heterozygote model (CT vs. CC) and the allelic model (T vs. C). Sensitivity analysis was adopted to evaluate the stability of the results. We used the funnel plots, Begg’s and Egger’s
JU
Int J Neurosci Downloaded from informahealthcare.com by Dicle Univ. on 11/16/14 For personal use only.
genotype numbers in cases and controls; and the allele frequencies.
tests to evaluate the publication bias. A p value less than 0.05 was considered statistically significant.
Results
Results of the paper selection We identified 20 relevant studies for our meta-analysis that met the strict criteria. The flow diagram of the article selection process is shown in Figure 1. The meta-analysis included 2317 patients with IS and 5
2123 controls. Of these 20 studies, 12 studies focused on the Han population, and another 8 studies focused on the Chinese population which might include the non-Han population. According to the region of study population, 12 studies focused on the northern region population, and another 8 studies focused
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on the southern region population. The detailed characteristics and the distributions of genotypes are shown in Table 1.
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Our meta-analysis showed a significant association between the MTHFR gene C677T polymorphism and IS among total population in the additive model (OR =1.34, 95%CI: 1.171.54, p 0.001; p heterogeneity =0.003, I2=53.1%; Figure 2), in the dominant model (OR =1.44 ,95% CI:1.261.64 ,p 0.001; p heterogeneity
C
= 0.175, I2=22.7%; Figure 3), in the recessive model (OR = 1.45,95% CI: 1.151.83, p=0.001; p heterogeneity
AC
=0.02, I2=43.5%; Figure 4), in the heterozygote model (OR = 1.35,95% CI: 1.181.55, p 0.001; p heterogeneity
= 0.858, I2=0.0%) , in the homozygote model (OR = 1.80,95% CI: 1.342.41, p 0.001; p
heterogeneity
=0.004, I2=51.8%), and in the allelic model (OR = 1.34,95% CI: 1.171.53, p 0.001; p I2=54.1 %; Figure 5).To better clarify the heterogeneity among our studies, we used
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heterogeneity=0.002,
subgroup analysis in the ethnicity and study region. In the Han population, northern region and southern region population, significant association was in all genetic models between the MTHFR gene C677T polymorphism and IS. The main results of this meta-analysis are detailed in Table 2.
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Quantitative synthesis
Sensitivity analysis Sensitivity analysis was performed to assess the stability of the results. In the sensitivity analysis, we removed each single study in turn, and did a meta-analysis using the left studies. We also observed a significant association between MTHFR C677T polymorphism and IS in different genetic models, which
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indicated that the pooled estimate was stable and not influenced by a single study. The pooled OR and 95%CI values ranged from 1.30(1.141.48) to 1.38(1.201.58) in the additive model, 1.40 (1.221.60) to
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1.51(1.301.74) in the dominant models, 1.36(1.111.67) to 1.52 (1.211.90) in the recessive models, 1.33(1.151.53) to 1.41(1.211.65) in the heterozygote models, 1.68(1.272.21) to 1.90 (1.422.55) in
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Publication bias
Funnel plots, Begg’s and Egger’s regression tests were used to assess potential publication bias (Table 2). In the additive model (p Begg’s =0.48, p Egger’s =0.39), in the dominant model (p Begg’s =0.14, p Egger’s
0.16), in the homozygote model (p Begg’s =0.60, p Egger’s =0.62) and in the allelic model (p Begg’s
AC
Egger’s =
C
=0.30), in the recessive model (p Begg’s =0.36, p Egger’s =0.47), in the heterozygote model (p Begg’s =0.14, p
=0.85, p Egger’s =0.58), all suggested no publication bias in total population. There was no publication bias
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in the subgroup analysis.
Discussion
Extensive evidence highlights the role of MTHFR gene polymorphisms in stroke, especially in IS. Epidemiologic studies have reported the association between MTHFR gene C677T polymorphism and
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the homozygote model and 1.30(1.141.48) to 1.37(1.201.57) in the allelic models.
stroke with inconsistent results. Some studies involving the MTHFR gene C677T polymorphism and IS have shown that the TT gene can increase the risk of IS [32, 33]. Another studies have shown that the TT gene can increase the risk of hemorrhagic stroke [34, 35].On the contrary, Sabino et al. [36] reported the incidence of IS risk was not increased with the MTHFR gene C677T polymorphism .
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In the Chinese population, extensive research regarding the association between the MTHFR gene C677T polymorphism and IS has been conducted, but the results are inconsistent. Some studies in our
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meta-analysis presented the MTHFR gene C677T polymorphism was significantly associated with increased risk of IS in the Chinese population [12,15-17,20-25,29,31]; however, another studies showed that there was not a significant association between them[13,14,18,19,26-28,30] .Therefore, our meta-analysis was very
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association only in the Han Chinese population, the literature in this study was collected 8 years ago and the sample size was
