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Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis
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Review
Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis Yi-Le Wu a,1, Hui-Yun Yang a,1, Xiu-Xiu Ding b, Xue Zhao a, Jian Chen a, Peng Bi c, Ye-Huan Sun a,* a b c
Department of Epidemiology and Statistics, School of Public Health, Anhui Medical University, No. 81 Meishan Road, Hefei, Anhui 230032, China Department of Maternal, Child and Adolescent Health, School of Public Health, Anhui Medical University, No. 81 Meishan Road, Hefei, Anhui 230032, China Discipline of Public Health, The University of Adelaide, Australia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 November 2013 Received in revised form 21 January 2014 Accepted 23 January 2014
Purpose: Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism has been implicated as a potential risk factor for epilepsy. To date, many case–control studies have investigated the association between MTHFR C677T polymorphism and epilepsy susceptibility. However, those findings were inconsistent. The objective of this study is to evaluate the precise association between MTHFR C677T polymorphism and epilepsy. Methods: An electronic search of PubMed, EMBASE for papers on the MTHFR C677T polymorphism and epilepsy susceptibility was performed. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the association. Results: Ten case–control studies containing 1713 cases and 1867 controls regarding MTHFR C677T polymorphism were selected. A significant association between the MTHFR C677T polymorphism and epilepsy susceptibility was revealed in this meta-analysis (for T vs. C: OR = 1.19, 95% CI = 1.08–1.32; for TT + CT vs. CC: OR = 1.20, 95% CI = 1.05–1.38; for TT vs. CC: OR = 1.48, 95% CI = 1.20–1.83; for TT vs. CT + CC: OR = 1.35, 95% CI = 1.12–1.64). In subgroup analysis by ethnicity, the results also indicated the association between the MTHFR C677T polymorphism and epilepsy susceptibility within the Asian populations (for T vs. C: OR = 1.55, 95% CI = 1.15-2.07; for TT + CT vs. CC: OR = 1.67, 95% CI = 1.08-2.59; for TT vs. CC: OR = 2.33, 95% CI = 1.30-4.20; for TT vs. CT + CC: OR = 1.89, 95% CI = 1.12-3.18). Conclusion: The results indicated that MTHFR C677T polymorphism was associated with an increased risk of epilepsy. However, further studies in various regions are needed to confirm the findings from this meta-analysis. ß 2014 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Epilepsy Homocysteine Meta-analysis Polymorphism
1. Introduction Epilepsy is one of the most common neurologic conditions and a cause of substantial morbidity and mortality. Around 50 million people around the world are likely to suffer from epilepsy1 and its etiologies include genetic, structural, and metabolic factors.2 Genetic factors may play a role in most cases, as either the underlying cause is primarily genetic, or there are genes that modulate the susceptibility to this disease.3 Studies of the
* Corresponding author. Tel.: +86 551 65143334; fax: +86 551 65143334. E-mail address: [email protected] (Y.-H. Sun). 1 Both authors contributed equally to this work.
neurophysiologic and neurodevelopmental effects of mutations in related genes can elucidate the underlying epileptogenic mechanisms and obtained such information may help to promote the development of new treatments targeted and ways of preventing epileptogenesis.4 Genome-wide scans and other previous studies which aimed at finding susceptibility genes for epilepsy have implicated mostly ion channel and ligand receptor genes.5,6 Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism as another candidate risk gene for epilepsy has been investigated for many years. MTHFR plays an important role in folate metabolism, which catalyzes the reduction of 5,10-methylenetetrahydrofolate to produce 5-methyltetrahydrofolate. The product is the dominant form of circulating folate, and provides a methyl group for the
1059-1311/$ – see front matter ß 2014 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.seizure.2014.01.018
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018
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remethylation of homocysteine (Hcy) back to methionine. A common MTHFR polymorphism, 677C-T transition results in decreased enzyme activity and elevated plasma Hcy levels.7,8 The latter is known to cause vascular endothelial damage,9 enhanced apoptosis,10 DNA hypomethylation11 and may be associated with a direct effect on neurodevelopment.12 MTHFR C677T polymorphism has been associated with vascular disease,13 congenital heart defects,14 and some neurological diseases including Alzheimer’s disease,15 Parkinson’s disease16 and schizophrenia.17 Previous studies also showed an association between the MTHFR C677T polymorphism and epilepsy.5,18,19 Several lines of evidence suggest a role for the MTHFR C677T polymorphism as a predisposing factor for epilepsy. Lipton et al. founded that Hcy may have excitotoxicity to neurons as an agonist at the glutamate site of the N-methyl-D-aspartate (NMDA) receptors.20 In an animal model, it was demonstrated that the NMDA receptor antagonist was protective against seizures induced by Hcy.21 Furthermore, other studies have suggested that Hcy lowered seizure thresholds and has been exploited as a pro-convulsant in models of experimental epilepsy.22,23 In addition, the 677TT genotype has been identified as a risk factor for migraines with aura,24 a condition that may share pathophysiological mechanisms with epilepsy. Hence, it is possible that the MTHFR C677T variant may be a predisposing factor for epilepsy.18 Many previous studies have been performed to investigate the association between MTHFR C677T gene polymorphism and epilepsy susceptibility. However, the findings were inconsistent, which may be due to the limitation of individual study sample sizes. Therefore, we performed this meta-analysis including all available case–control studies to clarify the effect of MTHFR C677T polymorphism on the risk of epilepsy.
source of controls, number of cases and controls for each genotype. 2.4. Statistical analysis The strength of association between MTHFR C677T polymorphism and epilepsy susceptibility was assessed by ORs with 95% CIs. The pooled ORs were performed for the allele model (T vs. C), the dominant model (TT + CT vs. CC), the homozygote model (TT vs. CC) and the recessive model (TT vs. CT + CC). Moreover, a Chisquare test was used to determine whether the observed frequencies of the genotypes in the controls conformed to Hardy–Weinberg Equilibrium (HWE) expectations. Heterogeneity among the studies was quantized by the I2 statistics. I2 > 50% indicated an obvious of the between-study heterogeneity,26 the pooled OR was calculated by the random effects model;27 otherwise, the fixed effects model was used.28 Additionally, sensitivity analyses were performed to assess the stability of the meta-analysis results by sequential removal of each study. Finally, the Begg’s tests and Egger’s tests were used to analyze the publication bias.29 All statistical analyses were conducted using Stata 9.0 (StataCrop, College Station, TX). A P value less than 0.05 was considered statistically significant.
3. Results 3.1. Characteristics of eligible studies
The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement was consulted to report this review.25
A detailed process for selecting eligible studies was shown in Fig. 1. Based on the search criteria, a total of 81 potentially relevant publications were identified, and three of them were selected from the reference lists of the identified articles. After careful selection, 10 eligible studies5,18,19,30–36 were finally included in this metaanalysis. All control samples from included studies were in HWE. Detailed characteristics of included studies were summarized in Table 1.
2.1. Search strategy and selection criteria
3.2. Quantitative synthesis
Potentially relevant articles were selected by searching PubMed, EMBASE databases using the search terms ‘‘MTHFR’’, ‘‘methylenetetrahydrofolate reductase’’ ‘‘C677T’’, ‘‘MTHFR C677T’’, and ‘‘epilepsy’’, ‘‘epileptic’’. Related reference articles were also searched to identify other relevant publications. All researches were limited to English literatures published up to October 2013.
The eligible publications must meet the following inclusion criteria: (1) examining the association between MTHFR C677T polymorphism and epilepsy; (2) the study was using a case– control study design; (3) providing enough data on genotype frequencies of the MTHFR C677T polymorphism for calculating an odd ratio (OR) with 95% confidence interval (95% CI). The exclusion criteria included: (1) a review or case report; (2) a duplicated study. If studies contained overlapping cases and/or controls, the largest study was preferred.
The heterogeneity was not significant in all the genetic models (I2 < 50%) and the fixed effects model was therefore used in this meta-analysis. The association was detected between the MTHFR C677T polymorphism and epilepsy susceptibility in all the genetic models (Table 2, for T vs. C: OR = 1.19, 95% CI = 1.08–1.32; for TT + CT vs. CC: OR = 1.20, 95% CI = 1.05–1.38; for TT vs. CC: OR = 1.48, 95% CI = 1.20–1.83; for TT vs. CT + CC: OR = 1.35, 95% CI = 1.12–1.64, forest plots were shown in Fig. 2). The sensitivity analyses did not alter the results. Consequently, it demonstrated the results of this study were robust. In subgroup analysis by ethnicity, results indicated that the MTHFR C677T polymorphism was associated with an increased risk of epilepsy in Asian populations (for T vs. C: OR = 1.55, 95% CI = 1.15-2.07; for TT + CT vs. CC: OR = 1.67, 95% CI = 1.08-2.59; for TT vs. CC: OR = 2.33, 95% CI = 1.30-4.20; for TT vs. CT + CC: OR = 1.89, 95% CI = 1.12-3.18).However, we were unable to detect any association between the MTHFR C677T polymorphism and epilepsy susceptibility in white populations.
2.3. Data extraction
3.3. Publication bias
According to the inclusion and exclusion criteria, data were extracted independently from each study by two authors (Wu and Yang) and the consensus was achieved for all data. The following information was extracted from each study included: the first author’s name, year of publication, ethnicity of study population,
The funnel plot was basically symmetric, indicating that no obvious evidence of publication bias in this meta-analysis (Supplemental Fig. S1). Furthermore, neither the Begg’s test nor the Egger’s test detected any obvious evidence of publication bias in all the genetic models (Table 2).
2. Methods
2.2. Inclusion and exclusion criteria
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018
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Addional records idenfied through other sources (n = 3)
PubMed, EMBASE databases (n =78)
Records aer duplicates removed (n = 52)
Records underwent tle and abstract screen (n = 52)
Records excluded (n = 18)
Eligibility
Full-text arcles assessed for eligibility (n = 34)
24 arcles excluded aer full text review: – Review arcles (n=3) – Case reports (n= 1) – No target outcomes (n=15) – No comparison group (n= 5)
Included
Screening
Idenficaon
Records idenfied from
3
Studies included in the meta-analysis (n = 10)
Fig. 1. PRISMA flow diagram for inclusion of the studies examining the association between MTHFR C677T polymorphism and epilepsy susceptibility. PRISMA, Preferred Reporting Items for Systematic Review and Meta-Analyses.
Table 1 Characteristics of 10 case–control studies included in this meta-analysis. First author
Year
Country
Ethnicity
Definition of epilepsy
Yoo Vilaseca Ono Caccamo Kini Dean Gorgone Belcastro Sniezawska Scher
1999 2000 2000 2004 2007 2008 2009 2010 2011 2011
Korea Spain Japan Italy UK UK Italy Italy Poland USA
Asian White Asian White White White White White White Mixed
Clinical records ILAE ILAE ILAE Clinical records ILAE ILAE Clinical records ILAE ICD-9-CM
Case
Control
CC
CT
TT
CC
CT
TT
25 19 24 26 50 64 14 68 36 350
54 30 29 50 75 80 30 119 22 262
24 10 19 19 16 26 16 72 7 77
37 7 43 33 85 146 18 60 24 366
53 17 37 47 115 128 26 110 29 249
13 4 17 18 26 29 14 61 2 53
PHWE
SOC
0.37 0.23 0.08 0.86 0.17 0.90 0.45 0.47 0.06 0.25
PB HB NA PB PB PB PB PB NA PB
Abbreviations: ILAE, International League Against Epilepsy; ICD-9-CM, The International Classification of Diseases, Ninth Revision, Clinical Modification; PHWE, P-value for Hardy–Weinberg Equilibrium in control group; SOC, source of controls; PB, population-based; HB, hospital-based; Mixed, including white, black and other population; NA, not available.
Table 2 Meta-analysis of the MTHFR gene polymorphism on epilepsy risk. Studies
Comparison model
Test of association
M*
OR(95%CI)
POR
I2(%)
P (publication bias test) Begg’s test
Egger’s test
0.86 0.47 0.72 0.28
0.93 0.89 0.62 0.86
0.0 15.6 0.0 0.0
– – – –
– – – –
0.0 0.0 0.0 0.0
– – – –
– – – –
All studies
T vs. C TT + CT vs. CC TT vs. CC TT vs. CT + CC
1.19(1.08–1.32) 1.20(1.05–1.38) 1.48(1.20–1.83) 1.35(1.12–1.64)
<0.001 0.009 <0.001 0.002
F F F F
0.0 6.3 0.0 0.0
Caucasian
T vs. C TT + CT vs. CC TT vs. CC TT vs. CT + CC
1.13(0.99–1.29) 1.15(0.94–1.40) 1.31(0.98–1.74) 1.21(0.95–1.55)
0.080 0.175 0.065 0.130
F F F F
Asian
T vs. C TT + CT vs. CC TT vs. CC TT vs. CT + CC
1.55(1.15–2.07) 1.67(1.08–2.59) 2.33(1.30–4.20) 1.89(1.12–3.18)
0.003 0.021 0.005 0.017
F F F F
M*, model of meta-analysis; F, fixed effect model.
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018
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T vs. C
TT vs. CC
Study ID
OR (95% CI)
%
Study
Weight
ID
OR (95% CI)
% Weight
Sniezawska (2011)
0.89 (0.51, 1.56) 3.58
Sniezawska (2011)
2.33 (0.45, 12.20) 1.48
Dean (2008)
1.43 (1.09, 1.89) 11.33
Dean (2008)
2.05 (1.12, 3.75)
9.95
Vilaseca (2000)
0.91 (0.48, 1.73) 2.71
Vilaseca (2000)
0.92 (0.22, 3.92)
2.70
Kini (2007)
1.04 (0.77, 1.42) 11.03
Kini (2007)
1.05 (0.51, 2.14)
10.43
Yoo (1999)
1.58 (1.07, 2.33) 5.53
Yoo (1999)
2.73 (1.17, 6.36)
4.66
Gorgone (2009)
1.23 (0.74, 2.05) 3.68
Gorgone (2009)
1.47 (0.54, 4.00)
4.49
Belcastro (2010)
1.02 (0.80, 1.31) 16.73
Belcastro (2010)
1.04 (0.64, 1.69)
22.58
Ono (2000)
1.51 (0.97, 2.34) 4.48
Ono (2000)
2.00 (0.88, 4.56)
5.63
Scher (2011)
1.19 (1.01, 1.41) 34.86
Scher (2011)
1.52 (1.04, 2.22)
31.15
Caccamo (2004)
1.17 (0.79, 1.76) 6.08
Caccamo (2004)
1.34 (0.59, 3.06)
6.93
Overall (I-squared = 0.0%, p = 0.475)
1.19 (1.08, 1.32) 100.00
Overall (I-squared = 0.0%, p = 0.603)
1.48 (1.20, 1.83)
100.00
.428
1
2.34 .082
12.2
TT vs. CT+CC
TT+CT vs. CC Study ID
1
OR (95% CI)
%
%
Study
Weight
ID
OR (95% CI)
Weight
Sniezawska (2011)
0.62 (0.30, 1.29) 5.02
Sniezawska (2011)
3.20 (0.64, 16.08) 1.07
Dean (2008)
1.54 (1.05, 2.26) 11.47
Dean (2008)
1.71 (0.97, 3.01)
9.73
Vilaseca (2000)
0.70 (0.25, 1.94) 2.48
Vilaseca (2000)
1.22 (0.35, 4.31)
2.48
Kini (2007)
1.10 (0.71, 1.70) 10.38
Kini (2007)
0.98 (0.51, 1.91)
9.76
Yoo (1999)
1.75 (0.96, 3.20) 4.33
Yoo (1999)
2.10 (1.00, 4.41)
5.50
Gorgone (2009)
1.48 (0.65, 3.35) 2.56
Gorgone (2009)
1.14 (0.50, 2.62)
5.75
Belcastro (2010)
0.99 (0.66, 1.48) 12.82
Belcastro (2010)
1.07 (0.72, 1.60)
25.66
Ono (2000)
1.59 (0.85, 3.00) 4.14
Ono (2000)
1.69 (0.80, 3.54)
5.88
Scher (2011)
1.17 (0.95, 1.45) 42.07
Scher (2011)
1.46 (1.01, 2.11)
26.35
Caccamo (2004)
1.35 (0.73, 2.49) 4.73
Caccamo (2004)
1.11 (0.54, 2.28)
7.81
Overall (I-squared = 6.3%, p = 0.383)
1.20 (1.05, 1.38) 100.00
Overall (I-squared = 0.0%, p = 0.714)
1.35 (1.12, 1.64)
100.00
.254
1
3.93
.0622
1
16.1
Fig. 2. Forest plots for the association between MTHFR C677T polymorphism and epilepsy for four genotype models.
4. Discussion Many case–control studies have been performed to investigate the association between MTHFR C677T polymorphism and epilepsy, but the available evidence is still weak due to inconsistent findings among those studies. The contradictory results obtained from those studies may partly be due to a small sample size in individual studies or differences in various ethnic groups. Meta-analysis has been recognized as a useful statistical method that combines findings from independent studies to precisely evaluate the effect of selected genetic polymorphism on the risk of disease.37 To the best of our knowledge, no meta-analysis has been conducted to assess the association between MTHFR C677T polymorphism and epilepsy. Therefore, there is a need to perform a meta-analysis using published data to clarify inconsistent findings. Based on 10 case–control studies, this meta-analysis revealed that MTHFR C677T polymorphism was associated with an increased risk of epilepsy in all genetic models. The sensitivity analyses did not substantively alter the results, indicating that results of this study were robust and reliable. T variant of the MTHFR C677T gene results in reduced MTHFR enzyme activity and elevated plasma Hcy levels. With a significant reduction in MTHFR activity, Hcy cannot be remethylated to methionine, hence accumulates within the nervous system.38 Hcy is directly toxic to neurons and endothelial cells and can induce DNA strand breakage, oxidative stress, and apoptosis.41 Study have shown that
Hcy substantially increased the vulnerability of hippocampal neurons to excitotoxic and oxidative injury in cell cultures and in vivo, suggesting Hcy may contribute to the pathogenesis of neurodegenerative disorders.42 Patients with severe hyperhomocysteinemia exhibit a wide range of clinical manifestations including neurological abnormalities such as mental retardation and cerebral atrophy.43 Consequently, it is biologically plausible that the elevated plasma Hcy may be an intermediary factor involved in the mechanism of MTHFR C677T polymorphism that results in epilepsy. The other common functional variants in this enzyme, MTHFR A1298C, as another candidate risk gene for epilepsy have also been investigated in previous studies,5,18,32 but findings were inconsistent. An earlier study with 95 cases and 98 controls conducted by Caccamo et al. suggested that the frequency of C1298 polymorphic allele was significantly higher in patients with epilepsy as compared to controls (30.5% vs. 19.4%, P < 0.05).32 Nevertheless, no significant association between MTHFR A1298C polymorphism and epilepsy was detected in the subsequent studies with relatively large samples.5,18 However, MTHFR A1298C polymorphism is believed to have a marginal or no effect on plasma Hcy concentration.39,40 Consequently, this less interference with Hcy levels caused by MTHFR A1298C polymorphism might account for the lack of significant association. It would be useful to study the MTHFR A1298C polymorphism and look at polymorphisms in other genes involved in the folate metabolic pathway, but that would have increased the sample size further.
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018
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In subgroup analysis stratified by ethnicity, the results revealed that the MTHFR C677T polymorphism was associated with significantly increased epilepsy susceptibility in Asian populations in all genetic models. However, this association cannot be detected in white populations in any genetic model. Hence, some potential factors may contribute to the results that the same gene polymorphism affects different ethnic populations. Firstly, the differences in genetic backgrounds may play a role. Secondly, epilepsy is a multi-factorial chronic disease with socioeconomic status, access to health care and environmental exposure such as neurocysticercosis involved in its pathophysiology.44 It is possible that individual susceptibility in different ethnic populations may be modified by those factors. In addition, the significant association between MTHFR C677T polymorphism and epilepsy within the Asian populations may be false positive due to a small sample size. Thus, further studies with larger samples are needed to confirm the association found within this ethnic group. Several potential limitations of this meta-analysis should be acknowledged. (1) The overall outcomes were based on individual unadjusted ORs due to unavailable data, whereas a more precise estimation should be adjusted by potentially influential factors including age, gender, and environmental factors. (2) The wrong diagnosis of epilepsy occurring worldwide may contribute to the ethnic group variations in subgroup analysis. For instance, among patients diagnosed with epilepsy, 20–30% are found to have been misdiagnosed.45,46 Consequently, the observed effect of MTHFR C677T polymorphism may be alleviated by the incorrect diagnosis of epilepsy. (3) Although neither the funnel plots nor the Begg’s test or Egger’s test detected any obvious evidence of publication bias, selection bias may have occurred attributed to the fact that only English and published articles were included in this meta-analysis. In conclusion, the present meta-analysis revealed that MTHFR C677T polymorphism was a risk factor for epilepsy in overall populations and Asian populations. However, the association between MTHFR C677T polymorphism and epilepsy could not be detected within white populations. Future studies with larger sample sizes are warranted to further confirm these findings. Conflict of interest None of the authors have any conflict of interest to disclose. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.seizure.2014.01.018. References 1. Ngugi AK, Bottomley C, Kleinschmidt I, Sander JW, Newton CR. Estimation of the burden of active and life-time epilepsy: a meta-analytic approach. Epilepsia 2010;51:883–90. 2. Bhalla D, Godet B, Druet-Cabanac M, Preux PM. Etiologies of epilepsy: a comprehensive review. Expert Rev Neurother 2011;11:861–76. 3. Pandolfo M. Genetics of epilepsy. Semin Neurol 2011;31:506–18. 4. Ottman R, Hirose S, Jain S, Lerche H, Lopes-Cendes I, Noebels JL, et al. Genetic testing in the epilepsies—report of the ILAE Genetics Commission. Epilepsia 2010;51:655–70. 5. Dean JC, Robertson Z, Reid V, Wang Q, Hailey H, Moore S, et al. A high frequency of the MTHFR 677C>T polymorphism in Scottish women with epilepsy: possible role in pathogenesis. Seizure 2008;17:269–75. 6. Scheffer IE, Berkovic SF. The genetics of human epilepsy. Trends Pharmacol Sci 2003;24:428–33. 7. Jacques PF, Bostom AG, Williams RR, Ellison RC, Eckfeldt JH, Rosenberg IH, et al. Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations. Circulation 1996;93:7–9. 8. Yuan RY, Sheu JJ, Yu JM, Hu CJ, Tseng IJ, Ho CS, et al. Methylenetetrahydrofolate reductase polymorphisms and plasma homocysteine in levodopa-treated and non-treated Parkinson’s disease patients. J Neurol Sci 2009;287:64–8.
5
9. Karabiber H, Sonmezgoz E, Ozerol E, Yakinci C, Otlu B, Yologlu S. Effects of valproate and carbamazepine on serum levels of homocysteine, vitamin B12, and folic acid. Brain Dev 2003;25:113–5. 10. Suhara T, Fukuo K, Yasuda O, Tsubakimoto M, Takemura Y, Kawamoto H, et al. Homocysteine enhances endothelial apoptosis via upregulation of Fas-mediated pathways. Hypertension 2004;43:1208–13. 11. Yi P, Melnyk S, Pogribna M, Pogribny IP, Hine RJ, James SJ. Increase in plasma homocysteine associated with parallel increases in plasma S-adenosylhomocysteine and lymphocyte DNA hypomethylation. J Biol Chem 2000;275:29318–23. 12. Dean JC, Moore SJ, Osborne A, Howe J, Turnpenny PD. Fetal anticonvulsant syndrome and mutation in the maternal MTHFR gene. Clin Genet 1999;56:216–20. 13. Gouveia LO, Canha˜o P. MTHFR and the risk for cerebral venous thrombosis—a meta-analysis. Thromb Res 2010;125:e153–8. 14. Brandalize AP, Bandinelli E, dos Santos PA, Roisenberg I, Schu¨ler-Faccini L. Evaluation of C677T and A1298C polymorphisms of the MTHFR gene as maternal risk factors for Down syndrome and congenital heart defects. Am J Med Genet A 2009;149A:2080–7. 15. Mansoori N, Tripathi M, Luthra K, Alam R, Lakshmy R, Sharma S, et al. MTHFR (677 and 1298) and IL-6-174 G/C genes in pathogenesis of Alzheimer’s and vascular dementia and their epistatic interaction. Neurobiol Aging 2012;33:1003.e1–e8. 16. Gorgone G, Curro` M, Ferlazzo N, Parisi G, Parnetti L, Belcastro V, et al. Coenzyme Q10, hyperhomocysteinemia and MTHFR C677T polymorphism in levodopatreated Parkinson’s disease patients. Neuromol Med 2012;14:84–90. 17. Allen NC, Bagade S, McQueen MB, Ioannidis JP, Kavvoura FK, Khoury MJ, et al. Systematic meta-analyses and field synopsis of genetic association studies in schizophrenia: the SzGene database. Nat Genet 2008;40:827–34. 18. Scher AI, Wu H, Tsao JW, Blom HJ, Feit P, Nevin RL, et al. MTHFR C677T genotype as a risk factor for epilepsy including post-traumatic epilepsy in a representative military cohort. J Neurotrauma 2011;28:1739–45. 19. Ono H, Sakamoto A, Mizoguchi N, Sakura N. Methylenetetrahydrofolate reductase 677C>T mutation and epilepsy. J Inherit Metab Dis 2000;23:525–6. 20. Lipton SA, Kim WK, Choi YB, Kumar S, D’Emilia DM, Rayudu PV, et al. Neurotoxicity associated with dual actions of homocysteine at the N-methyl-Daspartate receptor. Proc Natl Acad Sci U S A 1997;94(11):5923–8. 21. Folbergrova´ J. Anticonvulsant action of both NMDA and non-NMDA receptor antagonists against seizures induced by homocysteine in immature rats. Exp Neurol 1997;145:442–50. 22. Diaz-Arrastia R. Homocysteine and neurologic disease. Arch Neurol 2000;57:1422–7. 23. Mares P, Haugvicova´ R, Kubova´ H. Interaction of excitatory amino acid agonists with cortical after discharges in developing rats. Epilepsia 2002;43:61–7. 24. Schurks M, Rist PM, Kurth T. MTHFR 677C>T and ACE D/I polymorphisms in migraine: a systematic review and meta-analysis. Headache 2010;50:588–99. 25. Moher D, Liberati A, Tetzlaff J, Altman DG, PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med 2009;151:264–9. 26. Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. BMJ 2003;327:557–60. 27. DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trial 1986;7:177–88. 28. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959;22:719–48. 29. Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997;315:629–34. 30. Yoo JH, Hong SB. A common mutation in the methylenetetrahydrofolate reductase gene is a determinant of hyperhomocysteinemia in epileptic patients receiving anticonvulsants. Metabolism 1999;48:1047–51. 31. Vilaseca MA, Monro´s E, Artuch R, Colome´ C, Farre´ C, Valls C, et al. Anti-epileptic drug treatment in children: hyperhomocysteinaemia, B-vitamins and the 677C!T mutation of the methylenetetrahydrofolate reductase gene. Eur J Paediatr Neurol 2000;4:269–77. 32. Caccamo D, Condello S, Gorgone G, Crisafulli G, Belcastro V, Gennaro S, et al. Screening for C677T and A1298C MTHFR polymorphisms in patients with epilepsy and risk of hyperhomocysteinemia. Neuromol Med 2004;6: 117–26. 33. Kini U, Lee R, Jones A, Smith S, Ramsden S, Fryer A, et al. Influence of the MTHFR genotype on the rate of malformations following exposure to antiepileptic drugs in utero. Eur J Med Genet 2007;50:411–20. 34. Gorgone G, Caccamo D, Pisani LR, Curro` M, Parisi G, Oteri G, et al. Hyperhomocysteinemia in patients with epilepsy: does it play a role in the pathogenesis of brain atrophy? A preliminary report. Epilepsia 2009;50(Suppl. 1):33–6. 35. Belcastro V, Striano P, Gorgone G, Costa C, Ciampa C, Caccamo D, et al. Hyperhomocysteinemia in epileptic patients on new antiepileptic drugs. Epilepsia 2010;51:274–9. 36. Sniezawska A, Dorszewska J, Rozycka A, Przedpelska-Ober E, Lianeri M, Jagodzinski PP, et al. MTHFR, MTR, and MTHFD1 gene polymorphisms compared to homocysteine and asymmetric dimethylarginine concentrations and their metabolites in epileptic patients treated with antiepileptic drugs. Seizure 2011;20:533–40. 37. Yang Z, Zhang XF, Liu HX, Hao YS, Zhao CL. MTHFR C677T polymorphism and colorectal cancer risk in Asians, a meta-analysis of 21 studies. Asian Pac J Cancer Prev 2012;13:1203–8. 38. Prasad AN, Rupar CA, Prasad C. Methylenetetrahydrofolate reductase (MTHFR) deficiency and infantile epilepsy. Brain Dev 2011;33:758–69.
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018
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39. Lievers KJ, Kluijtmans LA, Blom HJ. Genetics of hyperhomocysteinaemia in cardiovascular disease. Ann Clin Biochem 2003;40:46–59. 40. Meisel C, Cascorbi I, Gerloff T, Stangl V, Laule M, Mu¨ller JM, et al. Identification of six methylenetetrahydrofolate reductase (MTHFR) genotypes resulting from common polymorphisms: impact on plasma homocysteine levels and development of coronary artery disease. Atherosclerosis 2001;154:651–8. 41. Folstein M, Liu T, Peter I, Buell J, Arsenault L, Scott T, et al. The homocysteine hypothesis of depression. Am J Psychiatry 2007;164:861–7. 42. Kruman II, Culmsee C, Chan SL, Kruman Y, Guo Z, Penix L, et al. Homocysteine elicits a DNA damage response in neurons that promotes apoptosis and hypersensitivity to excitotoxicity. J Neurosci 2000;20:6920–6.
43. van den Berg M, van der Knaap MS, Boers GH, Stehouwer CD, Rauwerda JA, Valk J. Hyperhomocysteinaemia; with reference to its neuroradiological aspects. Neuroradiology 1995;37:403–11. 44. Banerjee PN, Filippi D, Allen Hauser W. The descriptive epidemiology of epilepsy—a review. Epilepsy Res 2009;85:31–45. 45. Smith D, Defalla BA, Chadwick DW. The misdiagnosis of epilepsy and the management of refractory epilepsy in a specialist clinic. Quart J Med 1999;92:15–23. 46. Benbadis S. The differential diagnosis of epilepsy: a critical review. Epilepsy Behav 2009;15:15–21.
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Contents lists available at ScienceDirect
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Review
Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis Yi-Le Wu a,1, Hui-Yun Yang a,1, Xiu-Xiu Ding b, Xue Zhao a, Jian Chen a, Peng Bi c, Ye-Huan Sun a,* a b c
Department of Epidemiology and Statistics, School of Public Health, Anhui Medical University, No. 81 Meishan Road, Hefei, Anhui 230032, China Department of Maternal, Child and Adolescent Health, School of Public Health, Anhui Medical University, No. 81 Meishan Road, Hefei, Anhui 230032, China Discipline of Public Health, The University of Adelaide, Australia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 November 2013 Received in revised form 21 January 2014 Accepted 23 January 2014
Purpose: Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism has been implicated as a potential risk factor for epilepsy. To date, many case–control studies have investigated the association between MTHFR C677T polymorphism and epilepsy susceptibility. However, those findings were inconsistent. The objective of this study is to evaluate the precise association between MTHFR C677T polymorphism and epilepsy. Methods: An electronic search of PubMed, EMBASE for papers on the MTHFR C677T polymorphism and epilepsy susceptibility was performed. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the association. Results: Ten case–control studies containing 1713 cases and 1867 controls regarding MTHFR C677T polymorphism were selected. A significant association between the MTHFR C677T polymorphism and epilepsy susceptibility was revealed in this meta-analysis (for T vs. C: OR = 1.19, 95% CI = 1.08–1.32; for TT + CT vs. CC: OR = 1.20, 95% CI = 1.05–1.38; for TT vs. CC: OR = 1.48, 95% CI = 1.20–1.83; for TT vs. CT + CC: OR = 1.35, 95% CI = 1.12–1.64). In subgroup analysis by ethnicity, the results also indicated the association between the MTHFR C677T polymorphism and epilepsy susceptibility within the Asian populations (for T vs. C: OR = 1.55, 95% CI = 1.15-2.07; for TT + CT vs. CC: OR = 1.67, 95% CI = 1.08-2.59; for TT vs. CC: OR = 2.33, 95% CI = 1.30-4.20; for TT vs. CT + CC: OR = 1.89, 95% CI = 1.12-3.18). Conclusion: The results indicated that MTHFR C677T polymorphism was associated with an increased risk of epilepsy. However, further studies in various regions are needed to confirm the findings from this meta-analysis. ß 2014 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Epilepsy Homocysteine Meta-analysis Polymorphism
1. Introduction Epilepsy is one of the most common neurologic conditions and a cause of substantial morbidity and mortality. Around 50 million people around the world are likely to suffer from epilepsy1 and its etiologies include genetic, structural, and metabolic factors.2 Genetic factors may play a role in most cases, as either the underlying cause is primarily genetic, or there are genes that modulate the susceptibility to this disease.3 Studies of the
* Corresponding author. Tel.: +86 551 65143334; fax: +86 551 65143334. E-mail address: [email protected] (Y.-H. Sun). 1 Both authors contributed equally to this work.
neurophysiologic and neurodevelopmental effects of mutations in related genes can elucidate the underlying epileptogenic mechanisms and obtained such information may help to promote the development of new treatments targeted and ways of preventing epileptogenesis.4 Genome-wide scans and other previous studies which aimed at finding susceptibility genes for epilepsy have implicated mostly ion channel and ligand receptor genes.5,6 Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism as another candidate risk gene for epilepsy has been investigated for many years. MTHFR plays an important role in folate metabolism, which catalyzes the reduction of 5,10-methylenetetrahydrofolate to produce 5-methyltetrahydrofolate. The product is the dominant form of circulating folate, and provides a methyl group for the
1059-1311/$ – see front matter ß 2014 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.seizure.2014.01.018
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018
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remethylation of homocysteine (Hcy) back to methionine. A common MTHFR polymorphism, 677C-T transition results in decreased enzyme activity and elevated plasma Hcy levels.7,8 The latter is known to cause vascular endothelial damage,9 enhanced apoptosis,10 DNA hypomethylation11 and may be associated with a direct effect on neurodevelopment.12 MTHFR C677T polymorphism has been associated with vascular disease,13 congenital heart defects,14 and some neurological diseases including Alzheimer’s disease,15 Parkinson’s disease16 and schizophrenia.17 Previous studies also showed an association between the MTHFR C677T polymorphism and epilepsy.5,18,19 Several lines of evidence suggest a role for the MTHFR C677T polymorphism as a predisposing factor for epilepsy. Lipton et al. founded that Hcy may have excitotoxicity to neurons as an agonist at the glutamate site of the N-methyl-D-aspartate (NMDA) receptors.20 In an animal model, it was demonstrated that the NMDA receptor antagonist was protective against seizures induced by Hcy.21 Furthermore, other studies have suggested that Hcy lowered seizure thresholds and has been exploited as a pro-convulsant in models of experimental epilepsy.22,23 In addition, the 677TT genotype has been identified as a risk factor for migraines with aura,24 a condition that may share pathophysiological mechanisms with epilepsy. Hence, it is possible that the MTHFR C677T variant may be a predisposing factor for epilepsy.18 Many previous studies have been performed to investigate the association between MTHFR C677T gene polymorphism and epilepsy susceptibility. However, the findings were inconsistent, which may be due to the limitation of individual study sample sizes. Therefore, we performed this meta-analysis including all available case–control studies to clarify the effect of MTHFR C677T polymorphism on the risk of epilepsy.
source of controls, number of cases and controls for each genotype. 2.4. Statistical analysis The strength of association between MTHFR C677T polymorphism and epilepsy susceptibility was assessed by ORs with 95% CIs. The pooled ORs were performed for the allele model (T vs. C), the dominant model (TT + CT vs. CC), the homozygote model (TT vs. CC) and the recessive model (TT vs. CT + CC). Moreover, a Chisquare test was used to determine whether the observed frequencies of the genotypes in the controls conformed to Hardy–Weinberg Equilibrium (HWE) expectations. Heterogeneity among the studies was quantized by the I2 statistics. I2 > 50% indicated an obvious of the between-study heterogeneity,26 the pooled OR was calculated by the random effects model;27 otherwise, the fixed effects model was used.28 Additionally, sensitivity analyses were performed to assess the stability of the meta-analysis results by sequential removal of each study. Finally, the Begg’s tests and Egger’s tests were used to analyze the publication bias.29 All statistical analyses were conducted using Stata 9.0 (StataCrop, College Station, TX). A P value less than 0.05 was considered statistically significant.
3. Results 3.1. Characteristics of eligible studies
The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement was consulted to report this review.25
A detailed process for selecting eligible studies was shown in Fig. 1. Based on the search criteria, a total of 81 potentially relevant publications were identified, and three of them were selected from the reference lists of the identified articles. After careful selection, 10 eligible studies5,18,19,30–36 were finally included in this metaanalysis. All control samples from included studies were in HWE. Detailed characteristics of included studies were summarized in Table 1.
2.1. Search strategy and selection criteria
3.2. Quantitative synthesis
Potentially relevant articles were selected by searching PubMed, EMBASE databases using the search terms ‘‘MTHFR’’, ‘‘methylenetetrahydrofolate reductase’’ ‘‘C677T’’, ‘‘MTHFR C677T’’, and ‘‘epilepsy’’, ‘‘epileptic’’. Related reference articles were also searched to identify other relevant publications. All researches were limited to English literatures published up to October 2013.
The eligible publications must meet the following inclusion criteria: (1) examining the association between MTHFR C677T polymorphism and epilepsy; (2) the study was using a case– control study design; (3) providing enough data on genotype frequencies of the MTHFR C677T polymorphism for calculating an odd ratio (OR) with 95% confidence interval (95% CI). The exclusion criteria included: (1) a review or case report; (2) a duplicated study. If studies contained overlapping cases and/or controls, the largest study was preferred.
The heterogeneity was not significant in all the genetic models (I2 < 50%) and the fixed effects model was therefore used in this meta-analysis. The association was detected between the MTHFR C677T polymorphism and epilepsy susceptibility in all the genetic models (Table 2, for T vs. C: OR = 1.19, 95% CI = 1.08–1.32; for TT + CT vs. CC: OR = 1.20, 95% CI = 1.05–1.38; for TT vs. CC: OR = 1.48, 95% CI = 1.20–1.83; for TT vs. CT + CC: OR = 1.35, 95% CI = 1.12–1.64, forest plots were shown in Fig. 2). The sensitivity analyses did not alter the results. Consequently, it demonstrated the results of this study were robust. In subgroup analysis by ethnicity, results indicated that the MTHFR C677T polymorphism was associated with an increased risk of epilepsy in Asian populations (for T vs. C: OR = 1.55, 95% CI = 1.15-2.07; for TT + CT vs. CC: OR = 1.67, 95% CI = 1.08-2.59; for TT vs. CC: OR = 2.33, 95% CI = 1.30-4.20; for TT vs. CT + CC: OR = 1.89, 95% CI = 1.12-3.18).However, we were unable to detect any association between the MTHFR C677T polymorphism and epilepsy susceptibility in white populations.
2.3. Data extraction
3.3. Publication bias
According to the inclusion and exclusion criteria, data were extracted independently from each study by two authors (Wu and Yang) and the consensus was achieved for all data. The following information was extracted from each study included: the first author’s name, year of publication, ethnicity of study population,
The funnel plot was basically symmetric, indicating that no obvious evidence of publication bias in this meta-analysis (Supplemental Fig. S1). Furthermore, neither the Begg’s test nor the Egger’s test detected any obvious evidence of publication bias in all the genetic models (Table 2).
2. Methods
2.2. Inclusion and exclusion criteria
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Addional records idenfied through other sources (n = 3)
PubMed, EMBASE databases (n =78)
Records aer duplicates removed (n = 52)
Records underwent tle and abstract screen (n = 52)
Records excluded (n = 18)
Eligibility
Full-text arcles assessed for eligibility (n = 34)
24 arcles excluded aer full text review: – Review arcles (n=3) – Case reports (n= 1) – No target outcomes (n=15) – No comparison group (n= 5)
Included
Screening
Idenficaon
Records idenfied from
3
Studies included in the meta-analysis (n = 10)
Fig. 1. PRISMA flow diagram for inclusion of the studies examining the association between MTHFR C677T polymorphism and epilepsy susceptibility. PRISMA, Preferred Reporting Items for Systematic Review and Meta-Analyses.
Table 1 Characteristics of 10 case–control studies included in this meta-analysis. First author
Year
Country
Ethnicity
Definition of epilepsy
Yoo Vilaseca Ono Caccamo Kini Dean Gorgone Belcastro Sniezawska Scher
1999 2000 2000 2004 2007 2008 2009 2010 2011 2011
Korea Spain Japan Italy UK UK Italy Italy Poland USA
Asian White Asian White White White White White White Mixed
Clinical records ILAE ILAE ILAE Clinical records ILAE ILAE Clinical records ILAE ICD-9-CM
Case
Control
CC
CT
TT
CC
CT
TT
25 19 24 26 50 64 14 68 36 350
54 30 29 50 75 80 30 119 22 262
24 10 19 19 16 26 16 72 7 77
37 7 43 33 85 146 18 60 24 366
53 17 37 47 115 128 26 110 29 249
13 4 17 18 26 29 14 61 2 53
PHWE
SOC
0.37 0.23 0.08 0.86 0.17 0.90 0.45 0.47 0.06 0.25
PB HB NA PB PB PB PB PB NA PB
Abbreviations: ILAE, International League Against Epilepsy; ICD-9-CM, The International Classification of Diseases, Ninth Revision, Clinical Modification; PHWE, P-value for Hardy–Weinberg Equilibrium in control group; SOC, source of controls; PB, population-based; HB, hospital-based; Mixed, including white, black and other population; NA, not available.
Table 2 Meta-analysis of the MTHFR gene polymorphism on epilepsy risk. Studies
Comparison model
Test of association
M*
OR(95%CI)
POR
I2(%)
P (publication bias test) Begg’s test
Egger’s test
0.86 0.47 0.72 0.28
0.93 0.89 0.62 0.86
0.0 15.6 0.0 0.0
– – – –
– – – –
0.0 0.0 0.0 0.0
– – – –
– – – –
All studies
T vs. C TT + CT vs. CC TT vs. CC TT vs. CT + CC
1.19(1.08–1.32) 1.20(1.05–1.38) 1.48(1.20–1.83) 1.35(1.12–1.64)
<0.001 0.009 <0.001 0.002
F F F F
0.0 6.3 0.0 0.0
Caucasian
T vs. C TT + CT vs. CC TT vs. CC TT vs. CT + CC
1.13(0.99–1.29) 1.15(0.94–1.40) 1.31(0.98–1.74) 1.21(0.95–1.55)
0.080 0.175 0.065 0.130
F F F F
Asian
T vs. C TT + CT vs. CC TT vs. CC TT vs. CT + CC
1.55(1.15–2.07) 1.67(1.08–2.59) 2.33(1.30–4.20) 1.89(1.12–3.18)
0.003 0.021 0.005 0.017
F F F F
M*, model of meta-analysis; F, fixed effect model.
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4
T vs. C
TT vs. CC
Study ID
OR (95% CI)
%
Study
Weight
ID
OR (95% CI)
% Weight
Sniezawska (2011)
0.89 (0.51, 1.56) 3.58
Sniezawska (2011)
2.33 (0.45, 12.20) 1.48
Dean (2008)
1.43 (1.09, 1.89) 11.33
Dean (2008)
2.05 (1.12, 3.75)
9.95
Vilaseca (2000)
0.91 (0.48, 1.73) 2.71
Vilaseca (2000)
0.92 (0.22, 3.92)
2.70
Kini (2007)
1.04 (0.77, 1.42) 11.03
Kini (2007)
1.05 (0.51, 2.14)
10.43
Yoo (1999)
1.58 (1.07, 2.33) 5.53
Yoo (1999)
2.73 (1.17, 6.36)
4.66
Gorgone (2009)
1.23 (0.74, 2.05) 3.68
Gorgone (2009)
1.47 (0.54, 4.00)
4.49
Belcastro (2010)
1.02 (0.80, 1.31) 16.73
Belcastro (2010)
1.04 (0.64, 1.69)
22.58
Ono (2000)
1.51 (0.97, 2.34) 4.48
Ono (2000)
2.00 (0.88, 4.56)
5.63
Scher (2011)
1.19 (1.01, 1.41) 34.86
Scher (2011)
1.52 (1.04, 2.22)
31.15
Caccamo (2004)
1.17 (0.79, 1.76) 6.08
Caccamo (2004)
1.34 (0.59, 3.06)
6.93
Overall (I-squared = 0.0%, p = 0.475)
1.19 (1.08, 1.32) 100.00
Overall (I-squared = 0.0%, p = 0.603)
1.48 (1.20, 1.83)
100.00
.428
1
2.34 .082
12.2
TT vs. CT+CC
TT+CT vs. CC Study ID
1
OR (95% CI)
%
%
Study
Weight
ID
OR (95% CI)
Weight
Sniezawska (2011)
0.62 (0.30, 1.29) 5.02
Sniezawska (2011)
3.20 (0.64, 16.08) 1.07
Dean (2008)
1.54 (1.05, 2.26) 11.47
Dean (2008)
1.71 (0.97, 3.01)
9.73
Vilaseca (2000)
0.70 (0.25, 1.94) 2.48
Vilaseca (2000)
1.22 (0.35, 4.31)
2.48
Kini (2007)
1.10 (0.71, 1.70) 10.38
Kini (2007)
0.98 (0.51, 1.91)
9.76
Yoo (1999)
1.75 (0.96, 3.20) 4.33
Yoo (1999)
2.10 (1.00, 4.41)
5.50
Gorgone (2009)
1.48 (0.65, 3.35) 2.56
Gorgone (2009)
1.14 (0.50, 2.62)
5.75
Belcastro (2010)
0.99 (0.66, 1.48) 12.82
Belcastro (2010)
1.07 (0.72, 1.60)
25.66
Ono (2000)
1.59 (0.85, 3.00) 4.14
Ono (2000)
1.69 (0.80, 3.54)
5.88
Scher (2011)
1.17 (0.95, 1.45) 42.07
Scher (2011)
1.46 (1.01, 2.11)
26.35
Caccamo (2004)
1.35 (0.73, 2.49) 4.73
Caccamo (2004)
1.11 (0.54, 2.28)
7.81
Overall (I-squared = 6.3%, p = 0.383)
1.20 (1.05, 1.38) 100.00
Overall (I-squared = 0.0%, p = 0.714)
1.35 (1.12, 1.64)
100.00
.254
1
3.93
.0622
1
16.1
Fig. 2. Forest plots for the association between MTHFR C677T polymorphism and epilepsy for four genotype models.
4. Discussion Many case–control studies have been performed to investigate the association between MTHFR C677T polymorphism and epilepsy, but the available evidence is still weak due to inconsistent findings among those studies. The contradictory results obtained from those studies may partly be due to a small sample size in individual studies or differences in various ethnic groups. Meta-analysis has been recognized as a useful statistical method that combines findings from independent studies to precisely evaluate the effect of selected genetic polymorphism on the risk of disease.37 To the best of our knowledge, no meta-analysis has been conducted to assess the association between MTHFR C677T polymorphism and epilepsy. Therefore, there is a need to perform a meta-analysis using published data to clarify inconsistent findings. Based on 10 case–control studies, this meta-analysis revealed that MTHFR C677T polymorphism was associated with an increased risk of epilepsy in all genetic models. The sensitivity analyses did not substantively alter the results, indicating that results of this study were robust and reliable. T variant of the MTHFR C677T gene results in reduced MTHFR enzyme activity and elevated plasma Hcy levels. With a significant reduction in MTHFR activity, Hcy cannot be remethylated to methionine, hence accumulates within the nervous system.38 Hcy is directly toxic to neurons and endothelial cells and can induce DNA strand breakage, oxidative stress, and apoptosis.41 Study have shown that
Hcy substantially increased the vulnerability of hippocampal neurons to excitotoxic and oxidative injury in cell cultures and in vivo, suggesting Hcy may contribute to the pathogenesis of neurodegenerative disorders.42 Patients with severe hyperhomocysteinemia exhibit a wide range of clinical manifestations including neurological abnormalities such as mental retardation and cerebral atrophy.43 Consequently, it is biologically plausible that the elevated plasma Hcy may be an intermediary factor involved in the mechanism of MTHFR C677T polymorphism that results in epilepsy. The other common functional variants in this enzyme, MTHFR A1298C, as another candidate risk gene for epilepsy have also been investigated in previous studies,5,18,32 but findings were inconsistent. An earlier study with 95 cases and 98 controls conducted by Caccamo et al. suggested that the frequency of C1298 polymorphic allele was significantly higher in patients with epilepsy as compared to controls (30.5% vs. 19.4%, P < 0.05).32 Nevertheless, no significant association between MTHFR A1298C polymorphism and epilepsy was detected in the subsequent studies with relatively large samples.5,18 However, MTHFR A1298C polymorphism is believed to have a marginal or no effect on plasma Hcy concentration.39,40 Consequently, this less interference with Hcy levels caused by MTHFR A1298C polymorphism might account for the lack of significant association. It would be useful to study the MTHFR A1298C polymorphism and look at polymorphisms in other genes involved in the folate metabolic pathway, but that would have increased the sample size further.
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In subgroup analysis stratified by ethnicity, the results revealed that the MTHFR C677T polymorphism was associated with significantly increased epilepsy susceptibility in Asian populations in all genetic models. However, this association cannot be detected in white populations in any genetic model. Hence, some potential factors may contribute to the results that the same gene polymorphism affects different ethnic populations. Firstly, the differences in genetic backgrounds may play a role. Secondly, epilepsy is a multi-factorial chronic disease with socioeconomic status, access to health care and environmental exposure such as neurocysticercosis involved in its pathophysiology.44 It is possible that individual susceptibility in different ethnic populations may be modified by those factors. In addition, the significant association between MTHFR C677T polymorphism and epilepsy within the Asian populations may be false positive due to a small sample size. Thus, further studies with larger samples are needed to confirm the association found within this ethnic group. Several potential limitations of this meta-analysis should be acknowledged. (1) The overall outcomes were based on individual unadjusted ORs due to unavailable data, whereas a more precise estimation should be adjusted by potentially influential factors including age, gender, and environmental factors. (2) The wrong diagnosis of epilepsy occurring worldwide may contribute to the ethnic group variations in subgroup analysis. For instance, among patients diagnosed with epilepsy, 20–30% are found to have been misdiagnosed.45,46 Consequently, the observed effect of MTHFR C677T polymorphism may be alleviated by the incorrect diagnosis of epilepsy. (3) Although neither the funnel plots nor the Begg’s test or Egger’s test detected any obvious evidence of publication bias, selection bias may have occurred attributed to the fact that only English and published articles were included in this meta-analysis. In conclusion, the present meta-analysis revealed that MTHFR C677T polymorphism was a risk factor for epilepsy in overall populations and Asian populations. However, the association between MTHFR C677T polymorphism and epilepsy could not be detected within white populations. Future studies with larger sample sizes are warranted to further confirm these findings. Conflict of interest None of the authors have any conflict of interest to disclose. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.seizure.2014.01.018. References 1. Ngugi AK, Bottomley C, Kleinschmidt I, Sander JW, Newton CR. Estimation of the burden of active and life-time epilepsy: a meta-analytic approach. Epilepsia 2010;51:883–90. 2. Bhalla D, Godet B, Druet-Cabanac M, Preux PM. Etiologies of epilepsy: a comprehensive review. Expert Rev Neurother 2011;11:861–76. 3. Pandolfo M. Genetics of epilepsy. Semin Neurol 2011;31:506–18. 4. Ottman R, Hirose S, Jain S, Lerche H, Lopes-Cendes I, Noebels JL, et al. Genetic testing in the epilepsies—report of the ILAE Genetics Commission. Epilepsia 2010;51:655–70. 5. Dean JC, Robertson Z, Reid V, Wang Q, Hailey H, Moore S, et al. A high frequency of the MTHFR 677C>T polymorphism in Scottish women with epilepsy: possible role in pathogenesis. Seizure 2008;17:269–75. 6. Scheffer IE, Berkovic SF. The genetics of human epilepsy. Trends Pharmacol Sci 2003;24:428–33. 7. Jacques PF, Bostom AG, Williams RR, Ellison RC, Eckfeldt JH, Rosenberg IH, et al. Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations. Circulation 1996;93:7–9. 8. Yuan RY, Sheu JJ, Yu JM, Hu CJ, Tseng IJ, Ho CS, et al. Methylenetetrahydrofolate reductase polymorphisms and plasma homocysteine in levodopa-treated and non-treated Parkinson’s disease patients. J Neurol Sci 2009;287:64–8.
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9. Karabiber H, Sonmezgoz E, Ozerol E, Yakinci C, Otlu B, Yologlu S. Effects of valproate and carbamazepine on serum levels of homocysteine, vitamin B12, and folic acid. Brain Dev 2003;25:113–5. 10. Suhara T, Fukuo K, Yasuda O, Tsubakimoto M, Takemura Y, Kawamoto H, et al. Homocysteine enhances endothelial apoptosis via upregulation of Fas-mediated pathways. Hypertension 2004;43:1208–13. 11. Yi P, Melnyk S, Pogribna M, Pogribny IP, Hine RJ, James SJ. Increase in plasma homocysteine associated with parallel increases in plasma S-adenosylhomocysteine and lymphocyte DNA hypomethylation. J Biol Chem 2000;275:29318–23. 12. Dean JC, Moore SJ, Osborne A, Howe J, Turnpenny PD. Fetal anticonvulsant syndrome and mutation in the maternal MTHFR gene. Clin Genet 1999;56:216–20. 13. Gouveia LO, Canha˜o P. MTHFR and the risk for cerebral venous thrombosis—a meta-analysis. Thromb Res 2010;125:e153–8. 14. Brandalize AP, Bandinelli E, dos Santos PA, Roisenberg I, Schu¨ler-Faccini L. Evaluation of C677T and A1298C polymorphisms of the MTHFR gene as maternal risk factors for Down syndrome and congenital heart defects. Am J Med Genet A 2009;149A:2080–7. 15. Mansoori N, Tripathi M, Luthra K, Alam R, Lakshmy R, Sharma S, et al. MTHFR (677 and 1298) and IL-6-174 G/C genes in pathogenesis of Alzheimer’s and vascular dementia and their epistatic interaction. Neurobiol Aging 2012;33:1003.e1–e8. 16. Gorgone G, Curro` M, Ferlazzo N, Parisi G, Parnetti L, Belcastro V, et al. Coenzyme Q10, hyperhomocysteinemia and MTHFR C677T polymorphism in levodopatreated Parkinson’s disease patients. Neuromol Med 2012;14:84–90. 17. Allen NC, Bagade S, McQueen MB, Ioannidis JP, Kavvoura FK, Khoury MJ, et al. Systematic meta-analyses and field synopsis of genetic association studies in schizophrenia: the SzGene database. Nat Genet 2008;40:827–34. 18. Scher AI, Wu H, Tsao JW, Blom HJ, Feit P, Nevin RL, et al. MTHFR C677T genotype as a risk factor for epilepsy including post-traumatic epilepsy in a representative military cohort. J Neurotrauma 2011;28:1739–45. 19. Ono H, Sakamoto A, Mizoguchi N, Sakura N. Methylenetetrahydrofolate reductase 677C>T mutation and epilepsy. J Inherit Metab Dis 2000;23:525–6. 20. Lipton SA, Kim WK, Choi YB, Kumar S, D’Emilia DM, Rayudu PV, et al. Neurotoxicity associated with dual actions of homocysteine at the N-methyl-Daspartate receptor. Proc Natl Acad Sci U S A 1997;94(11):5923–8. 21. Folbergrova´ J. Anticonvulsant action of both NMDA and non-NMDA receptor antagonists against seizures induced by homocysteine in immature rats. Exp Neurol 1997;145:442–50. 22. Diaz-Arrastia R. Homocysteine and neurologic disease. Arch Neurol 2000;57:1422–7. 23. Mares P, Haugvicova´ R, Kubova´ H. Interaction of excitatory amino acid agonists with cortical after discharges in developing rats. Epilepsia 2002;43:61–7. 24. Schurks M, Rist PM, Kurth T. MTHFR 677C>T and ACE D/I polymorphisms in migraine: a systematic review and meta-analysis. Headache 2010;50:588–99. 25. Moher D, Liberati A, Tetzlaff J, Altman DG, PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med 2009;151:264–9. 26. Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. BMJ 2003;327:557–60. 27. DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trial 1986;7:177–88. 28. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959;22:719–48. 29. Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997;315:629–34. 30. Yoo JH, Hong SB. A common mutation in the methylenetetrahydrofolate reductase gene is a determinant of hyperhomocysteinemia in epileptic patients receiving anticonvulsants. Metabolism 1999;48:1047–51. 31. Vilaseca MA, Monro´s E, Artuch R, Colome´ C, Farre´ C, Valls C, et al. Anti-epileptic drug treatment in children: hyperhomocysteinaemia, B-vitamins and the 677C!T mutation of the methylenetetrahydrofolate reductase gene. Eur J Paediatr Neurol 2000;4:269–77. 32. Caccamo D, Condello S, Gorgone G, Crisafulli G, Belcastro V, Gennaro S, et al. Screening for C677T and A1298C MTHFR polymorphisms in patients with epilepsy and risk of hyperhomocysteinemia. Neuromol Med 2004;6: 117–26. 33. Kini U, Lee R, Jones A, Smith S, Ramsden S, Fryer A, et al. Influence of the MTHFR genotype on the rate of malformations following exposure to antiepileptic drugs in utero. Eur J Med Genet 2007;50:411–20. 34. Gorgone G, Caccamo D, Pisani LR, Curro` M, Parisi G, Oteri G, et al. Hyperhomocysteinemia in patients with epilepsy: does it play a role in the pathogenesis of brain atrophy? A preliminary report. Epilepsia 2009;50(Suppl. 1):33–6. 35. Belcastro V, Striano P, Gorgone G, Costa C, Ciampa C, Caccamo D, et al. Hyperhomocysteinemia in epileptic patients on new antiepileptic drugs. Epilepsia 2010;51:274–9. 36. Sniezawska A, Dorszewska J, Rozycka A, Przedpelska-Ober E, Lianeri M, Jagodzinski PP, et al. MTHFR, MTR, and MTHFD1 gene polymorphisms compared to homocysteine and asymmetric dimethylarginine concentrations and their metabolites in epileptic patients treated with antiepileptic drugs. Seizure 2011;20:533–40. 37. Yang Z, Zhang XF, Liu HX, Hao YS, Zhao CL. MTHFR C677T polymorphism and colorectal cancer risk in Asians, a meta-analysis of 21 studies. Asian Pac J Cancer Prev 2012;13:1203–8. 38. Prasad AN, Rupar CA, Prasad C. Methylenetetrahydrofolate reductase (MTHFR) deficiency and infantile epilepsy. Brain Dev 2011;33:758–69.
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018
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Y.-L. Wu et al. / Seizure xxx (2014) xxx–xxx
39. Lievers KJ, Kluijtmans LA, Blom HJ. Genetics of hyperhomocysteinaemia in cardiovascular disease. Ann Clin Biochem 2003;40:46–59. 40. Meisel C, Cascorbi I, Gerloff T, Stangl V, Laule M, Mu¨ller JM, et al. Identification of six methylenetetrahydrofolate reductase (MTHFR) genotypes resulting from common polymorphisms: impact on plasma homocysteine levels and development of coronary artery disease. Atherosclerosis 2001;154:651–8. 41. Folstein M, Liu T, Peter I, Buell J, Arsenault L, Scott T, et al. The homocysteine hypothesis of depression. Am J Psychiatry 2007;164:861–7. 42. Kruman II, Culmsee C, Chan SL, Kruman Y, Guo Z, Penix L, et al. Homocysteine elicits a DNA damage response in neurons that promotes apoptosis and hypersensitivity to excitotoxicity. J Neurosci 2000;20:6920–6.
43. van den Berg M, van der Knaap MS, Boers GH, Stehouwer CD, Rauwerda JA, Valk J. Hyperhomocysteinaemia; with reference to its neuroradiological aspects. Neuroradiology 1995;37:403–11. 44. Banerjee PN, Filippi D, Allen Hauser W. The descriptive epidemiology of epilepsy—a review. Epilepsy Res 2009;85:31–45. 45. Smith D, Defalla BA, Chadwick DW. The misdiagnosis of epilepsy and the management of refractory epilepsy in a specialist clinic. Quart J Med 1999;92:15–23. 46. Benbadis S. The differential diagnosis of epilepsy: a critical review. Epilepsy Behav 2009;15:15–21.
Please cite this article in press as: Wu Y-L, et al. Association between methylenetetrahydrofolate reductase C677T polymorphism and epilepsy susceptibility: A meta-analysis. Seizure: Eur J Epilepsy (2014), http://dx.doi.org/10.1016/j.seizure.2014.01.018