Background: We performed the present study to better elucidate the correlations of methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR) gene polymorphisms with the risk of congenital heart diseases (CHD).

Methods: Eligible articles were searched in PubMed, Medline, Embase and CNKI. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to detect any potential associations of MTHFR and MTRR gene polymorphisms with CHD.

Results: A total of 47 eligible studies were finally included in our meta-analysis. Our overall analyses suggested that MTRR rs1801394, MTRR rs1532268, MTHFR rs1801131 and MTHFR rs1801133 polymorphisms were all significantly associated with the risk of CHD in certain genetic models. Further subgroup analyses according to ethnicity of study participants demonstrated that the MTRR rs1801394 polymorphism was significantly correlated with the risk of CHD only in Asians, whereas MTRR rs1532268, MTHFR rs1801133 and MTHFR rs1801131 polymorphisms were significantly correlated with the risk of CHD in both Asians and Caucasians.

Conclusions: Our findings indicated that MTRR rs1532268, MTHFR rs1801131 and MTHFR rs1801133 polymorphisms may affect the risk of CHD in Asians and Caucasians, while the MTRR rs1801394 polymorphism may only affect in risk of CHD in Asians.

Introduction

Congenital heart diseases (CHD) refer to a group of structural heart defects that are resulted from abnormal cardiac development. The incidence of CHD is estimated to be approximately 1% in newborns, and despite rapid advances in surgical treatments and interventional therapies over the past few decades, CHD is still the primary non-infectious cause of infant mortality worldwide [1]. Moreover, its associated complications such as heart failure, arrhythmia and sudden cardiac death may occur even after effective correction of cardiac abnormalities [2,3]. Until now, the exact cause of CHD is still largely unclear despite extensive investigations. Nevertheless, mounting evidence supports that genetic factors play a crucial part in its development. First, family clustering of CHD with variable phenotypes is not uncommon, and descendants of CHD patients suffer a higher risk of developing cardiac malformations compared with the general population [4,5]. Second, multiple genetic variants have been found to be associated with an increased risk of CHD [6–9]. Overall, these findings jointly indicate that genetic predisposition to CHD is vital for its occurrence and development.

Methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR) play central roles in the regulation of folate metabolism and homocysteine synthesis [10]. Previous studies have shown that taking folate supplements during pregnancy could significantly reduce the risk of cardiovascular congenital malformations in newborns [11,12]. Consequently, functional MTHFR and MTRR polymorphisms, which were known to affect plasma folate levels, were considered to be ideal candidate genetic biomarkers of CHD.

So far, numerous studies have been conducted to assess the roles of MTHFR and MTRR gene polymorphisms in CHD, but the results of these studies were controversial [13–16]. Therefore, we conducted the present meta-analysis to better evaluate potential associations of MTHFR and MTRR gene polymorphisms with the risk of CHD.

Materials and methods

Literature search and inclusion criteria

The current meta-analysis was adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement [17]. A systematic literature search of PubMed, Medline, Embase and China National Knowledge Infrastructure (CNKI) was performed to retrieve all relevant articles. The key words used in this literature search included: ‘5-methyltetrahydrofolate-homocysteine methyltransferase reductase’, ‘methionine synthase reductase’, ‘MTRR’, ‘MSR’, ‘methylenetetrahydrofolate reductase’, ‘MTHFR’, ‘polymorphism’, ‘variant’, ‘mutation’, ‘genotype’, ‘allele’, ‘congenital heart disease‘, ‘congenital heart defect’ and ‘congenital cardiovascular malformation’ (see Supplementary File S1). To identify other potentially relevant publications, we also reviewed the reference lists of all retrieved articles.

Eligible studies of the current meta-analysis must met all the following criteria: (1) evaluate potential associations of MTRR and/or MTHFR gene polymorphisms with the risk of CHD; (2) provide sufficient data to calculate odds ratios (ORs) and 95% confidence intervals (CIs); (3) full text in Chinese or English available. For duplicate reports, only the study with the largest sample size was included. Reviews, comments, letters and family-based association studies were excluded.

Data extraction and quality assessment

The following information was extracted from each included study: name of the first author, year of publication, country and ethnicity of study subjects, type of CHD, genotypic frequencies of MTRR and/or MTHFR gene polymorphisms in cases and controls, and whether the distributions of investigated gene polymorphisms in the control group violated Hardy–Weinberg equilibrium (HWE).

The Newcastle–Ottawa scale (NOS), a classical assessment tool of observational studies that evaluates the quality of articles from three dimensions: selection, comparability and exposure, was adopted to assess the quality of included studies [18]. The NOS has a score range of 0 to 9, and studies with a score of more than 7 were considered to be of high quality.

Two reviewers (Aiping Xu and Weiping Wang) conducted data extraction and quality assessment independently. When necessary, the reviewers wrote to the corresponding authors for extra information or raw data. Disagreements between two reviewers were solved by discussion with the third reviewer (Xiaolei Jiang) until a consensus was reached.

Statistical analysis

All data analyses in the present study were carried out using Review Manager Version 5.3.3 (The Cochrane Collaboration, Software Update, Oxford, United Kingdom). The probability value (P value) of HWE in the control group was calculated with the chi-square test. ORs and 95% CIs were used to estimate potential associations of MTRR and/or MTHFR gene polymorphisms with the risk of CHD in the dominant, recessive, additive and allele models, and a P value of 0.05 or less was considered as statistically significant. The Q test and I2 statistic were adopted to assess between-study heterogeneity. If P value of Q test was less than 0.1 or I2 was greater than 50%, random-effect models would be applied for analyses due to the existence of obvious heterogeneity. Otherwise, fixed-effect models would be employed for analyses. Subgroup analyses were subsequently performed according to ethnicity of study participants and type of disease. Sensitivity analyses were conducted to test the stability of the results. Publication bias was evaluated with funnel plots.

Results

Characteristics of included studies

The literature search identified 311 citations. After exclusion of irrelevant and duplicate articles by reading titles and abstracts, 72 articles were selected for further evaluation. Another 25 articles were subsequently excluded after reading full texts, and a total of 47 studies that met the inclusion criteria were finally included in our meta-analysis (see Figure 1). Characteristics of included studies were summarized in Table 1.

Flowchart of study selection for the present study

Figure 1
Flowchart of study selection for the present study
Figure 1
Flowchart of study selection for the present study
Table 1
The characteristics of included studies
First author, year Country Ethnicity Sex, male (%) Case/ Control Age (years) Case/ Control Type of disease Sample size Genotype distribution P-value for HWE NOS score 
       Cases Controls   
rs1801394           
Benke, 2015 Hungry Caucasian 59.2/61.5 2.42/3.08 CHD 72/117 64/7/1 110/6/1 0.016 
Christensen, 2013 Canada Mixed NA NA CHD 245/65 68/123/54 22/32/11 0.912 
Gong, 2010 China Asian NA NA CHD 60/60 38/21/1 52/6/2 0.007 
Guo, 2017 China Asian NA 2.31/2.48 CHD 99/114 44/46/9 67/44/3 0.174 
Guo, 2017 China Asian NA 2.33/2.47 VSD 21/114 7/11/3 67/44/3 0.174 
Hassan, 2017 Egypt Caucasian 36.0/32.0 1.30/1.28 CHD 100/100 26/32/42 48/36/16 0.048 
Liu, 2007 China Asian 48.5/NA 6.50/NA CHD 132/107 33/84/15 52/45/10 0.953 
Locke, 2010 U.S.A. Mixed NA NA CHD 92/94 27/50/15 31/46/17 0.993 
Noori, 2017 Iran Caucasian NA NA CHD 153/147 46/74/33 61/63/23 0.323 
Noori, 2017 Iran Caucasian NA NA VSD 74/147 24/32/18 61/63/23 0.323 
Noori, 2017 Iran Caucasian NA NA TOF 79/147 22/42/15 61/63/23 0.323 
Pishva, 2013 Iran Caucasian 46.3/44.8 4.51/5.43 VSD 123/125 41/54/28 62/53/10 0.776 
Su, 2017 China Asian NA NA VSD 183/201 68/97/18 107/85/9 0.120 
van Beynum, 2006 Netherlands Caucasian NA NA CHD 159/245 51/83/25 74/124/47 0.699 
Verkleij-Hagoort, 2008 Netherlands Caucasian NA 1.40/1.39 CHD 229/251 79/112/38 77/122/52 0.774 
Wang, 2013 China Asian NA NA CHD 160/188 90/59/11 105/71/12 0.999 
Wang, 2018 China Asian NA 2.18/1.81 CHD 102/100 51/39/12 75/21/4 0.126 
Weine, 2012 Russia Caucasian NA 2.15/2.11 CHD 51/390 19/23/9 128/191/71 0.986 
Zeng, 2011 China Asian 43.4/47.2 NA CHD 599/672 309/234/56 375/253/44 0.880 
Zhao, 2012 China Asian 52.4/54.4 6.59/6.59 CHD 2340/2270 1308/860/172 1294/818/158 0.067 
rs1532268           
Hassan, 2017 Egypt Caucasian 36.0/32.0 1.30/1.28 CHD 100/100 14/40/46 38/36/26 0.007 
Pishva, 2013 Iran Caucasian 46.3/44.8 4.51/5.43 VSD 123/125 53/50/20 66/54/5 0.134 
Su, 2017 China Asian NA NA VSD 183/201 66/96/21 105/80/16 0.889 
Zeng, 2011 China Asian 43.4/47.2 NA CHD 599/672 383/201/15 476/176/20 0.450 
rs1801131           
Božović, 2011 Croatia Caucasian 49.1/49.3 1.03/2.78 CHD 54/221 30/22/2 101/98/22 0.803 
Brandalize, 2009 Brazil African NA NA CHD 239/197 143/84/12 113/76/8 0.275 
Chao, 2014 Taiwan Asian 11.8/38.2 46.7/50.9 PDA 17/34 13/2/2 15/19/0 0.024 
Christensen, 2013 Canada Mixed NA NA CHD 246/65 133/93/20 36/22/7 0.212 
Feng, 2016 China Asian 46.3/63.2 1.3/1.9 CHD 257/49 194/51/12 35/14/0 0.243 
Galdieri, 2007 Brazil African NA NA CHD 57/38 35/21/1 19/16/3 0.884 
Guo, 2017 China Asian NA 2.31/2.48 CHD 99/114 71/28/0 89/24/1 0.655 
Guo, 2017 China Asian NA 2.33/2.48 VSD 21/114 14/7/0 89/24/1 0.655 
Huang, 2014 China Asian 56.1/57.5 2.54/2.70 TOF 170/206 111/56/3 146/54/6 0.712 
Koshy, 2015 India Caucasian NA NA CHD 96/100 27/32/37 58/20/22 <0.001 
Locke, 2010 U.S.A. Mixed NA NA CHD 87/88 42/39/6 30/49/9 0.090 
Obermann-Borst, 2011 Netherlands Caucasian 60.8/55.9 17.0/17.3 CHD 139/183 69/57/13 75/90/18 0.227 
Sahiner, 2014 Turkey Caucasian 57.1/NA 7.63/NA CHD 137/93 45/68/24 31/54/8 0.022 
Sayin Kocakap, 2015 Turkey Caucasian NA NA CHD 69/99 20/36/13 51/37/11 0.288 
Shi, 2015 China Asian 38.85/57.41 2.18/2.12 CHD 153/216 95/39/19 157/53/6 0.555 
Storti, 2003 Italy Caucasian NA 2.50/2.58 CHD 100/100 43/46/11 50/43/7 0.582 
van Driel, 2008 Netherlands Caucasian 58.0/57.0 1.40/1.39 CHD 230/251 104/102/24 116/104/31 0.311 
Wang, 2018 China Asian NA 2.18/1.81 CHD 102/100 57/40/5 60/36/4 0.624 
Xu, 2010 China Asian 53.7/53.0 6.50/6.69 CHD 502/527 316/168/18 326/185/16 0.091 
Xu, 2010 China Asian NA NA VSD 257/527 169/86/2 326/185/16 0.091 
Xu, 2010 China Asian NA NA ASD 41/527 21/16/4 326/185/16 0.091 
Zidan, 2013 Egypt Caucasian NA NA CHD 80/80 16/27/37 30/26/24 0.002 
rs1801133           
Božović, 2011 Croatia Caucasian 49.1/49.3 1.03/2.78 CHD 54/221 20/28/6 101/97/23 0.968 
Brandalize, 2009 Brazil African NA NA CHD 239/197 94/113/32 86/93/18 0.313 
Chao, 2014 Taiwan Asian 11.8/38.2 46.7/50.9 PDA 17/34 10/5/2 19/12/3 0.586 
Christensen, 2013 Canada Mixed NA NA CHD 246/65 94/117/35 27/29/9 0.787 
Feng, 2016 China Asian 46.3/63.2 1.3/1.9 CHD 257/49 122/114/21 21/22/6 0.949 
Galdieri, 2007 Brazil African NA NA CHD 58/38 30/21/7 18/14/6 0.263 
Gong, 2012 China Asian 65.5/61.8 1.91/1.58 CHD 244/136 45/123/76 43/72/21 0.309 
Gong, 2012 China Asian 61.6/61.8 1.55/1.58 TOF 120/136 21/59/40 43/72/21 0.309 
Gong, 2012 China Asian 69.4/61.8 2.27/1.58 TGA 124/136 24/64/36 43/72/21 0.309 
Guo, 2017 China Asian NA 2.31/2.48 CHD 99/114 20/41/38 36/48/30 0.097 
Guo, 2017 China Asian NA 2.33/2.48 VSD 21/114 8/8/5 36/48/30 0.097 
Huang, 2014 China Asian 56.1/57.5 2.54/2.70 TOF 168/204 63/45/60 84/72/48 <0.001 
Jiang, 2015 China Asian NA 2.34/2.35 CHD 100/100 38/46/16 41/48/11 0.523 
Jing, 2013 China Asian NA NA CHD 104/208 16/42/46 55/114/39 0.139 
Junker, 2001 Germany Caucasian 53.0/NA 16.0/NA CHD 114/228 51/42/21 129/78/21 0.075 
Koshy, 2015 India Caucasian 63.5/49.0 6.51/7.61 CHD 96/90 95/1/0 83/7/0 0.701 
Kuehl, 2010 U.S.A. Mixed 50.4/56.0 NA CHD 55/300 12/33/10 134/134/32 0.861 
Lee, 2005 Taiwan Asian NA NA CHD 213/195 110/89/14 114/68/13 0.513 
Li, 2005 China Asian 48.4/57.2 NA CHD 183/103 30/95/58 22/57/24 0.277 
Li, 2013 China Asian 54.2/57.1 2.68/2.79 CHD 144/168 26/52/66 49/84/35 0.928 
Liu, 2007 China Asian 48.5/NA 6.5/NA CHD 132/107 30/68/34 46/48/13 0.930 
Locke, 2010 U.S.A. Mixed NA NA CHD 91/94 38/39/14 49/37/8 0.787 
Noori, 2017 Iran Caucasian NA NA CHD 153/147 95/51/7 100/46/1 0.078 
Noori, 2017 Iran Caucasian NA NA VSD 74/147 24/32/18 100/46/1 0.078 
Noori, 2017 Iran Caucasian NA NA TOF 79/147 22/42/15 100/46/1 0.078 
Obermann-Borst, 2011 Netherlands Caucasian 60.8/55.9 1.41/1.44 CHD 139/183 64/66/9 92/76/15 0.900 
Sahiner, 2014 Turkey Caucasian 57.1/NA 7.63/NA CHD 136/93 69/53/14 47/39/7 0.779 
Sayin Kocakap, 2015 Turkey Caucasian NA NA CHD 75/95 40/33/2 43/44/8 0.484 
Shaw, 2005 China Asian NA NA CHD 153/434 69/68/16 202/180/52 0.227 
Shi, 2015 China Asian 38.85/57.41 2.18/2.12 CHD 153/216 55/68/30 70/101/45 0.444 
Storti, 2003 Italy Caucasian NA 2.50/2.58 CHD 100/100 27/53/20 26/54/20 0.401 
van Beynum, 2006 Netherlands Caucasian 55.0/49.0 3.4/9.4 CHD 158/261 72/68/18 131/107/23 0.863 
van Driel, 2008 Netherlands Caucasian 58.0/57.0 1.40/1.39 CHD 229/251 99/103/27 119/107/25 0.895 
Wang, 2013 China Asian NA NA CHD 160/188 59/76/25 53/100/35 0.312 
Wang, 2016 China Asian NA NA CHD 147/168 14/73/60 49/84/35 0.928 
Wang, 2018 China Asian NA 2.18/1.83 CHD 102/100 31/58/13 55/42/3 0.130 
Xu, 2010 China Asian 53.7/53.0 6.50/6.69 CHD 502/527 162/244/96 151/261/115 0.911 
Xu, 2010 China Asian NA NA VSD 257/527 83/130/44 151/261/115 0.911 
Xu, 2010 China Asian NA NA ASD 41/527 12/17/12 151/261/115 0.911 
Xu, 2013 China Asian 64.8/52.4 NA CHD 228/230 73/106/49 124/74/32 <0.001 
Yan, 2003 China Asian NA NA CHD 187/103 32/97/58 22/57/24 0.277 
Zhou, 2012 China Asian 48.5/57.8 NA TOF 136/277 23/60/53 88/126/63 0.168 
Zhu, 2006 China Asian 35.1/57.7 6.2/8.4 CHD 56/103 7/22/27 22/57/24 0.277 
Zhu, 2006 China Asian NA NA ASD 22/103 3/7/12 22/57/24 0.277 
Zhu, 2006 China Asian NA NA PDA 34/103 4/15/15 22/57/24 0.277 
Zidan, 2013 Egypt Caucasian NA NA CHD 80/80 18/21/41 32/21/27 <0.001 
First author, year Country Ethnicity Sex, male (%) Case/ Control Age (years) Case/ Control Type of disease Sample size Genotype distribution P-value for HWE NOS score 
       Cases Controls   
rs1801394           
Benke, 2015 Hungry Caucasian 59.2/61.5 2.42/3.08 CHD 72/117 64/7/1 110/6/1 0.016 
Christensen, 2013 Canada Mixed NA NA CHD 245/65 68/123/54 22/32/11 0.912 
Gong, 2010 China Asian NA NA CHD 60/60 38/21/1 52/6/2 0.007 
Guo, 2017 China Asian NA 2.31/2.48 CHD 99/114 44/46/9 67/44/3 0.174 
Guo, 2017 China Asian NA 2.33/2.47 VSD 21/114 7/11/3 67/44/3 0.174 
Hassan, 2017 Egypt Caucasian 36.0/32.0 1.30/1.28 CHD 100/100 26/32/42 48/36/16 0.048 
Liu, 2007 China Asian 48.5/NA 6.50/NA CHD 132/107 33/84/15 52/45/10 0.953 
Locke, 2010 U.S.A. Mixed NA NA CHD 92/94 27/50/15 31/46/17 0.993 
Noori, 2017 Iran Caucasian NA NA CHD 153/147 46/74/33 61/63/23 0.323 
Noori, 2017 Iran Caucasian NA NA VSD 74/147 24/32/18 61/63/23 0.323 
Noori, 2017 Iran Caucasian NA NA TOF 79/147 22/42/15 61/63/23 0.323 
Pishva, 2013 Iran Caucasian 46.3/44.8 4.51/5.43 VSD 123/125 41/54/28 62/53/10 0.776 
Su, 2017 China Asian NA NA VSD 183/201 68/97/18 107/85/9 0.120 
van Beynum, 2006 Netherlands Caucasian NA NA CHD 159/245 51/83/25 74/124/47 0.699 
Verkleij-Hagoort, 2008 Netherlands Caucasian NA 1.40/1.39 CHD 229/251 79/112/38 77/122/52 0.774 
Wang, 2013 China Asian NA NA CHD 160/188 90/59/11 105/71/12 0.999 
Wang, 2018 China Asian NA 2.18/1.81 CHD 102/100 51/39/12 75/21/4 0.126 
Weine, 2012 Russia Caucasian NA 2.15/2.11 CHD 51/390 19/23/9 128/191/71 0.986 
Zeng, 2011 China Asian 43.4/47.2 NA CHD 599/672 309/234/56 375/253/44 0.880 
Zhao, 2012 China Asian 52.4/54.4 6.59/6.59 CHD 2340/2270 1308/860/172 1294/818/158 0.067 
rs1532268           
Hassan, 2017 Egypt Caucasian 36.0/32.0 1.30/1.28 CHD 100/100 14/40/46 38/36/26 0.007 
Pishva, 2013 Iran Caucasian 46.3/44.8 4.51/5.43 VSD 123/125 53/50/20 66/54/5 0.134 
Su, 2017 China Asian NA NA VSD 183/201 66/96/21 105/80/16 0.889 
Zeng, 2011 China Asian 43.4/47.2 NA CHD 599/672 383/201/15 476/176/20 0.450 
rs1801131           
Božović, 2011 Croatia Caucasian 49.1/49.3 1.03/2.78 CHD 54/221 30/22/2 101/98/22 0.803 
Brandalize, 2009 Brazil African NA NA CHD 239/197 143/84/12 113/76/8 0.275 
Chao, 2014 Taiwan Asian 11.8/38.2 46.7/50.9 PDA 17/34 13/2/2 15/19/0 0.024 
Christensen, 2013 Canada Mixed NA NA CHD 246/65 133/93/20 36/22/7 0.212 
Feng, 2016 China Asian 46.3/63.2 1.3/1.9 CHD 257/49 194/51/12 35/14/0 0.243 
Galdieri, 2007 Brazil African NA NA CHD 57/38 35/21/1 19/16/3 0.884 
Guo, 2017 China Asian NA 2.31/2.48 CHD 99/114 71/28/0 89/24/1 0.655 
Guo, 2017 China Asian NA 2.33/2.48 VSD 21/114 14/7/0 89/24/1 0.655 
Huang, 2014 China Asian 56.1/57.5 2.54/2.70 TOF 170/206 111/56/3 146/54/6 0.712 
Koshy, 2015 India Caucasian NA NA CHD 96/100 27/32/37 58/20/22 <0.001 
Locke, 2010 U.S.A. Mixed NA NA CHD 87/88 42/39/6 30/49/9 0.090 
Obermann-Borst, 2011 Netherlands Caucasian 60.8/55.9 17.0/17.3 CHD 139/183 69/57/13 75/90/18 0.227 
Sahiner, 2014 Turkey Caucasian 57.1/NA 7.63/NA CHD 137/93 45/68/24 31/54/8 0.022 
Sayin Kocakap, 2015 Turkey Caucasian NA NA CHD 69/99 20/36/13 51/37/11 0.288 
Shi, 2015 China Asian 38.85/57.41 2.18/2.12 CHD 153/216 95/39/19 157/53/6 0.555 
Storti, 2003 Italy Caucasian NA 2.50/2.58 CHD 100/100 43/46/11 50/43/7 0.582 
van Driel, 2008 Netherlands Caucasian 58.0/57.0 1.40/1.39 CHD 230/251 104/102/24 116/104/31 0.311 
Wang, 2018 China Asian NA 2.18/1.81 CHD 102/100 57/40/5 60/36/4 0.624 
Xu, 2010 China Asian 53.7/53.0 6.50/6.69 CHD 502/527 316/168/18 326/185/16 0.091 
Xu, 2010 China Asian NA NA VSD 257/527 169/86/2 326/185/16 0.091 
Xu, 2010 China Asian NA NA ASD 41/527 21/16/4 326/185/16 0.091 
Zidan, 2013 Egypt Caucasian NA NA CHD 80/80 16/27/37 30/26/24 0.002 
rs1801133           
Božović, 2011 Croatia Caucasian 49.1/49.3 1.03/2.78 CHD 54/221 20/28/6 101/97/23 0.968 
Brandalize, 2009 Brazil African NA NA CHD 239/197 94/113/32 86/93/18 0.313 
Chao, 2014 Taiwan Asian 11.8/38.2 46.7/50.9 PDA 17/34 10/5/2 19/12/3 0.586 
Christensen, 2013 Canada Mixed NA NA CHD 246/65 94/117/35 27/29/9 0.787 
Feng, 2016 China Asian 46.3/63.2 1.3/1.9 CHD 257/49 122/114/21 21/22/6 0.949 
Galdieri, 2007 Brazil African NA NA CHD 58/38 30/21/7 18/14/6 0.263 
Gong, 2012 China Asian 65.5/61.8 1.91/1.58 CHD 244/136 45/123/76 43/72/21 0.309 
Gong, 2012 China Asian 61.6/61.8 1.55/1.58 TOF 120/136 21/59/40 43/72/21 0.309 
Gong, 2012 China Asian 69.4/61.8 2.27/1.58 TGA 124/136 24/64/36 43/72/21 0.309 
Guo, 2017 China Asian NA 2.31/2.48 CHD 99/114 20/41/38 36/48/30 0.097 
Guo, 2017 China Asian NA 2.33/2.48 VSD 21/114 8/8/5 36/48/30 0.097 
Huang, 2014 China Asian 56.1/57.5 2.54/2.70 TOF 168/204 63/45/60 84/72/48 <0.001 
Jiang, 2015 China Asian NA 2.34/2.35 CHD 100/100 38/46/16 41/48/11 0.523 
Jing, 2013 China Asian NA NA CHD 104/208 16/42/46 55/114/39 0.139 
Junker, 2001 Germany Caucasian 53.0/NA 16.0/NA CHD 114/228 51/42/21 129/78/21 0.075 
Koshy, 2015 India Caucasian 63.5/49.0 6.51/7.61 CHD 96/90 95/1/0 83/7/0 0.701 
Kuehl, 2010 U.S.A. Mixed 50.4/56.0 NA CHD 55/300 12/33/10 134/134/32 0.861 
Lee, 2005 Taiwan Asian NA NA CHD 213/195 110/89/14 114/68/13 0.513 
Li, 2005 China Asian 48.4/57.2 NA CHD 183/103 30/95/58 22/57/24 0.277 
Li, 2013 China Asian 54.2/57.1 2.68/2.79 CHD 144/168 26/52/66 49/84/35 0.928 
Liu, 2007 China Asian 48.5/NA 6.5/NA CHD 132/107 30/68/34 46/48/13 0.930 
Locke, 2010 U.S.A. Mixed NA NA CHD 91/94 38/39/14 49/37/8 0.787 
Noori, 2017 Iran Caucasian NA NA CHD 153/147 95/51/7 100/46/1 0.078 
Noori, 2017 Iran Caucasian NA NA VSD 74/147 24/32/18 100/46/1 0.078 
Noori, 2017 Iran Caucasian NA NA TOF 79/147 22/42/15 100/46/1 0.078 
Obermann-Borst, 2011 Netherlands Caucasian 60.8/55.9 1.41/1.44 CHD 139/183 64/66/9 92/76/15 0.900 
Sahiner, 2014 Turkey Caucasian 57.1/NA 7.63/NA CHD 136/93 69/53/14 47/39/7 0.779 
Sayin Kocakap, 2015 Turkey Caucasian NA NA CHD 75/95 40/33/2 43/44/8 0.484 
Shaw, 2005 China Asian NA NA CHD 153/434 69/68/16 202/180/52 0.227 
Shi, 2015 China Asian 38.85/57.41 2.18/2.12 CHD 153/216 55/68/30 70/101/45 0.444 
Storti, 2003 Italy Caucasian NA 2.50/2.58 CHD 100/100 27/53/20 26/54/20 0.401 
van Beynum, 2006 Netherlands Caucasian 55.0/49.0 3.4/9.4 CHD 158/261 72/68/18 131/107/23 0.863 
van Driel, 2008 Netherlands Caucasian 58.0/57.0 1.40/1.39 CHD 229/251 99/103/27 119/107/25 0.895 
Wang, 2013 China Asian NA NA CHD 160/188 59/76/25 53/100/35 0.312 
Wang, 2016 China Asian NA NA CHD 147/168 14/73/60 49/84/35 0.928 
Wang, 2018 China Asian NA 2.18/1.83 CHD 102/100 31/58/13 55/42/3 0.130 
Xu, 2010 China Asian 53.7/53.0 6.50/6.69 CHD 502/527 162/244/96 151/261/115 0.911 
Xu, 2010 China Asian NA NA VSD 257/527 83/130/44 151/261/115 0.911 
Xu, 2010 China Asian NA NA ASD 41/527 12/17/12 151/261/115 0.911 
Xu, 2013 China Asian 64.8/52.4 NA CHD 228/230 73/106/49 124/74/32 <0.001 
Yan, 2003 China Asian NA NA CHD 187/103 32/97/58 22/57/24 0.277 
Zhou, 2012 China Asian 48.5/57.8 NA TOF 136/277 23/60/53 88/126/63 0.168 
Zhu, 2006 China Asian 35.1/57.7 6.2/8.4 CHD 56/103 7/22/27 22/57/24 0.277 
Zhu, 2006 China Asian NA NA ASD 22/103 3/7/12 22/57/24 0.277 
Zhu, 2006 China Asian NA NA PDA 34/103 4/15/15 22/57/24 0.277 
Zidan, 2013 Egypt Caucasian NA NA CHD 80/80 18/21/41 32/21/27 <0.001 

Abbreviations: ASD, atrial septal defect; CHD, congenital heart disease; HWE, Hardy–Weinberg equilibrium; NA, not available; NOS, Newcastle–Ottawa scale; PDA, patent ductus arteriosus; TGA, transposition of the great arteries; TOF, tetralogy of fallot; VSD, ventricular septal defect.

Overall and subgroup analyses for MTRR polymorphisms

To investigate potential associations between MTRR gene polymorphisms and the risk of CHD, 17 studies about rs1801394 polymorphism and 4 studies about rs1532268 polymorphism were enrolled for overall analyses. Significant associations with the risk of CHD were detected for rs1801394 (dominant model: P=0.0001, OR = 0.68, 95%CI 0.56–0.83; recessive model: P=0.009, OR = 1.40, 95%CI 1.09–1.79; additive model: P=0.008, OR = 1.12, 95%CI 1.03-1.21; allele model: P=0.0001, OR = 0.73, 95%CI 0.63–0.86) and rs1532268 (dominant model: P=0.001, OR = 0.56, 95%CI 0.39–0.80; additive model: P=0.0009, OR = 1.36, 95%CI 1.13–1.63; allele model: P=0.0006, OR = 0.61, 95%CI 0.47–0.81) polymorphisms in overall analyses. Further subgroup analyses according to ethnicity of study participants demonstrated that the rs1801394 polymorphism was significantly correlated with the risk of CHD only in Asians, whereas the rs1532268 polymorphism was significantly correlated with the risk of CHD in both Asians and Caucasians. When we stratified data based on type of disease, we found that both rs1801394 and rs1532268 polymorphisms were significantly associated with the risk of VSD (see Table 2 and Supplementary Figure S1).

Table 2
Results of overall and subgroup analyses
Population Sample size Dominant comparison Recessive comparison Additive comparison Allele comparison 
  P value OR (95%CI) I2 statistic P value OR (95%CI) I2 statistic P value OR (95%CI) I2 statistic P value OR (95%CI) I2 statistic 
rs1801394              
Overall 4899/5246 0.0001 0.68 (0.56–0.83) 72% 0.009 1.40 (1.09–1.79) 56% 0.008 1.12 (1.03–1.21) 48% 0.0001 0.73 (0.63–0.86) 77% 
Caucasian 887/1375 0.11 0.75 (0.52–1.07) 68% 0.18 1.45 (0.852.49) 76% 0.62 1.05 (0.871.26) 0% 0.10 0.75 (0.531.06) 84% 
Asian 3675/3712 0.0008 0.60 (0.45–0.81) 82% 0.02 1.24 (1.04–1.48) 34% 0.006 1.43 (1.11–1.85) 74% 0.0007 0.69 (0.55–0.85) 79% 
VSD 558/587 <0.0001 0.55 (0.43–0.69) 0% <0.0001 2.22 (1.51–3.26) 15% 0.02 1.32 (1.04–1.66) 0% <0.0001 0.60 (0.51–0.72) 0% 
rs1532268              
Overall 1005/1098 0.001 0.56 (0.39–0.80) 64% 0.06 1.83 (0.963.48) 68% 0.0009 1.36 (1.13–1.63) 23% 0.0006 0.61 (0.47–0.81) 68% 
Caucasian 223/225 0.08 0.44 (0.18–1.09) 78% <0.0001 2.93 (1.77–4.88) 16% 0.94 1.02 (0.701.48) 0% <0.0001 0.50 (0.38–0.66) 46% 
Asian 782/873 0.008 0.64 (0.46–0.89) 52% 0.65 1.12 (0.691.80) 29% 0.0002 1.48 (1.21–1.83) 0% 0.0007 0.75 (0.63–0.88) 33% 
VSD 306/326 <0.0001 0.58 (0.42–0.79) 0% 0.11 2.48 (0.827.52) 70% 0.47 1.25 (0.682.28) 71% <0.0001 0.62 (0.49–0.79) 0% 
rs1801131              
Overall 2834/2761 0.44 0.93 (0.76–1.13) 63% 0.003 1.36 (1.11–1.67) 42% 0.88 0.99 (0.881.11) 38% 0.23 0.90 (0.751.07) 72% 
Caucasian 905/1127 0.14 0.74 (0.49–1.10) 78% 0.01 1.40 (1.08–1.81) 45% 0.62 1.05 (0.871.26) 43% 0.10 0.77 (0.571.05) 81% 
Asian 1300/1246 0.75 0.97 (0.82–1.15) 23% 0.009 1.78 (1.15–2.75) 47% 0.97 0.99 (0.741.34) 55% 0.42 0.89 (0.681.18) 64% 
VSD 601/641 0.95 0.99 (0.79–1.25) 21% 0.74 1.12 (0.582.18) 0% 0.96 0.99 (0.781.26) 44% 0.88 0.98 (0.811.20) 0% 
rs1801133              
Overall 5508/6207 <0.0001 0.73 (0.63–0.84) 62% <0.0001 1.54 (1.30–1.83) 59% 0.86 1.01 (0.931.09) 86% <0.0001 0.75 (0.67–0.84) 73% 
Caucasian 1334/1749 0.02 0.83 (0.72–0.97) 26% 0.01 1.35 (1.06–1.72) 28% 0.42 1.06 (0.911.24) 0% 0.004 0.84 (0.75–0.95) 50% 
Asian 3485/3764 <0.0001 0.67 (0.55–0.83) 73% <0.0001 1.66 (1.32–2.10) 71% 0.43 0.96 (0.871.06) 48% <0.0001 0.70 (0.60–0.83) 81% 
TOF 701/764 0.0001 0.63 (0.50–0.80) 48% <0.0001 2.17 (1.66–2.84) 0% 0.28 0.89 (0.711.10) 0% <0.0001 0.62 (0.53–0.72) 4% 
VSD 754/788 0.48 0.85 (0.54–1.33) 68% 0.37 1.43 (0.653.14) 75% 0.90 0.99 (0.811.21) 0% 0.36 0.82 (0.541.25) 80% 
Population Sample size Dominant comparison Recessive comparison Additive comparison Allele comparison 
  P value OR (95%CI) I2 statistic P value OR (95%CI) I2 statistic P value OR (95%CI) I2 statistic P value OR (95%CI) I2 statistic 
rs1801394              
Overall 4899/5246 0.0001 0.68 (0.56–0.83) 72% 0.009 1.40 (1.09–1.79) 56% 0.008 1.12 (1.03–1.21) 48% 0.0001 0.73 (0.63–0.86) 77% 
Caucasian 887/1375 0.11 0.75 (0.52–1.07) 68% 0.18 1.45 (0.852.49) 76% 0.62 1.05 (0.871.26) 0% 0.10 0.75 (0.531.06) 84% 
Asian 3675/3712 0.0008 0.60 (0.45–0.81) 82% 0.02 1.24 (1.04–1.48) 34% 0.006 1.43 (1.11–1.85) 74% 0.0007 0.69 (0.55–0.85) 79% 
VSD 558/587 <0.0001 0.55 (0.43–0.69) 0% <0.0001 2.22 (1.51–3.26) 15% 0.02 1.32 (1.04–1.66) 0% <0.0001 0.60 (0.51–0.72) 0% 
rs1532268              
Overall 1005/1098 0.001 0.56 (0.39–0.80) 64% 0.06 1.83 (0.963.48) 68% 0.0009 1.36 (1.13–1.63) 23% 0.0006 0.61 (0.47–0.81) 68% 
Caucasian 223/225 0.08 0.44 (0.18–1.09) 78% <0.0001 2.93 (1.77–4.88) 16% 0.94 1.02 (0.701.48) 0% <0.0001 0.50 (0.38–0.66) 46% 
Asian 782/873 0.008 0.64 (0.46–0.89) 52% 0.65 1.12 (0.691.80) 29% 0.0002 1.48 (1.21–1.83) 0% 0.0007 0.75 (0.63–0.88) 33% 
VSD 306/326 <0.0001 0.58 (0.42–0.79) 0% 0.11 2.48 (0.827.52) 70% 0.47 1.25 (0.682.28) 71% <0.0001 0.62 (0.49–0.79) 0% 
rs1801131              
Overall 2834/2761 0.44 0.93 (0.76–1.13) 63% 0.003 1.36 (1.11–1.67) 42% 0.88 0.99 (0.881.11) 38% 0.23 0.90 (0.751.07) 72% 
Caucasian 905/1127 0.14 0.74 (0.49–1.10) 78% 0.01 1.40 (1.08–1.81) 45% 0.62 1.05 (0.871.26) 43% 0.10 0.77 (0.571.05) 81% 
Asian 1300/1246 0.75 0.97 (0.82–1.15) 23% 0.009 1.78 (1.15–2.75) 47% 0.97 0.99 (0.741.34) 55% 0.42 0.89 (0.681.18) 64% 
VSD 601/641 0.95 0.99 (0.79–1.25) 21% 0.74 1.12 (0.582.18) 0% 0.96 0.99 (0.781.26) 44% 0.88 0.98 (0.811.20) 0% 
rs1801133              
Overall 5508/6207 <0.0001 0.73 (0.63–0.84) 62% <0.0001 1.54 (1.30–1.83) 59% 0.86 1.01 (0.931.09) 86% <0.0001 0.75 (0.67–0.84) 73% 
Caucasian 1334/1749 0.02 0.83 (0.72–0.97) 26% 0.01 1.35 (1.06–1.72) 28% 0.42 1.06 (0.911.24) 0% 0.004 0.84 (0.75–0.95) 50% 
Asian 3485/3764 <0.0001 0.67 (0.55–0.83) 73% <0.0001 1.66 (1.32–2.10) 71% 0.43 0.96 (0.871.06) 48% <0.0001 0.70 (0.60–0.83) 81% 
TOF 701/764 0.0001 0.63 (0.50–0.80) 48% <0.0001 2.17 (1.66–2.84) 0% 0.28 0.89 (0.711.10) 0% <0.0001 0.62 (0.53–0.72) 4% 
VSD 754/788 0.48 0.85 (0.54–1.33) 68% 0.37 1.43 (0.653.14) 75% 0.90 0.99 (0.811.21) 0% 0.36 0.82 (0.541.25) 80% 

Abbreviations: ASD, atrial septal defect; CHD, congenital heart disease; CI, confidence interval; NA, not available; OR, odds ratio; PDA, patent ductus arteriosus; TOF, tetralogy of fallot; VSD, ventricular septal defect.

The values in bold represent there is statistically significant differences between cases and controls.

Overall and subgroup analyses for MTHFR polymorphisms

To investigate potential associations between MTHFR gene polymorphisms and the risk of CHD, 19 studies about rs1801131 polymorphism and 37 studies about rs1801133 polymorphism were enrolled for overall analyses. Significant associations with the risk of CHD were detected for rs1801131 (recessive model: P=0.003, OR = 1.36, 95%CI 1.11–1.67) and rs1801133 (dominant model: P<0.0001, OR = 0.73, 95%CI 0.63–0.84; additive model: P<0.0001, OR = 1.54, 95%CI 1.30–1.83; allele model: P<0.0001, OR = 0.75, 95%CI 0.67–0.84) polymorphisms in overall analyses. Further subgroup analyses according to ethnicity of study participants demonstrated that rs1801133 and rs1801131 polymorphisms were significantly correlated with the risk of CHD in both Asians and Caucasians. When we stratified data based on type of disease, we found that the rs1801133 polymorphism was significantly associated with the risk of TOF (see Table 2 and Supplementary Figure S1).

Sensitivity analyses

To examine stabilities of synthetic results, sensitivity analyses were further performed by removing studies that departed from HWE. No changes of results were detected for investigated gene polymorphisms in any comparisons, which indicated that our findings were quite statistically stable.

Publication biases

Funnel plots were used to assess potential publication biases in the present study. No apparent asymmetry of funnel plots was observed in any comparisons, which suggested that our findings were unlikely to be influenced by obvious publication biases (see Supplementary Figure S2).

Discussion

CHD contain various structural cardiovascular malformations that are actually or potentially of functional significances [19]. Historically, few CHD patients reached adulthood, but thanks to enormous advances in interventional therapies and surgical treatments over the past few years, the average life expectancy of CHD patients has been significantly improved [20]. However, despite substantially improved prognosis, CHD remains to be the leading cause of infant deaths all over the world.

MTHFR and MTRR are fundamental regulatory enzymes of folate and homocysteine metabolism. Considering the consistently observed association between folic acid consumption and a reduced risk of cardiac deformity, functional polymorphisms of MTHFR and MTRR, which were known to be associated with altered enzymatic activities, were thought to be correlated with the risk of CHD [11,12]. Recently, several studies have tried to explore the potential associations of functional MTHFR and MTRR gene polymorphisms with the risk of CHD, but the results of these studies were inconsistent. Therefore, we conducted the present meta-analysis to obtain a more conclusive result. Our overall analyses suggested that MTRR rs1801394, MTRR rs1532268, MTHFR rs1801131 and MTHFR rs1801133 polymorphisms were all significantly associated with the risk of CHD in certain genetic models. Further subgroup analyses according to ethnicity of study participants demonstrated that the MTRR rs1801394 polymorphism was significantly correlated with the risk of CHD only in Asians, whereas MTRR rs1532268, MTHFR rs1801133 and MTHFR rs1801131 polymorphisms were significantly correlated with the risk of CHD in both Asians and Caucasians. When we stratified data based on type of disease, we found that both MTRR rs1801394 and MTRR rs1532268 polymorphisms were significantly associated with the risk of VSD, whereas the MTHFR rs1801133 polymorphism was significantly associated with the risk of TOF. The stabilities of synthetic results were subsequently evaluated in sensitivity analyses, and no changes of results were observed in any comparisons, which indicated that our findings were quite stable and reliable. It is noteworthy that obvious between-study heterogeneities were detected in several comparisons. However, a great reduction in heterogeneities was found in further stratified analyses, which suggested that differences in ethnic background and type of disease could partially explain the observed heterogeneities.

Our meta-analysis is certainly not without limitations. First, our results were based on unadjusted estimations, and lack of analyses adjusted for potential confounding factors such as age, sex and co-morbidity conditions may impact the reliability of our findings. Second, heterogeneity remained significant in certain subgroups, which suggested that the conflicting results of eligible studies could not be fully explained by differences in ethnicity of study population or type of CHD, and other unmeasured characteristics of study participants may also attribute to the observed between-study heterogeneities. Third, associations between investigated polymorphisms and the risk of CHD may also be influenced by gene–gene and gene–environmental interactions. However, we failed to analyze the effect of these interactions in our study because only very little relevant data were provided by enrolled literatures. Taken these limitations into consideration, the results obtained by the present study should be interpreted with caution.

In conclusion, the current meta-analysis indicated that MTRR rs1801394, MTRR rs1532268, MTHFR rs1801131 and MTHFR rs1801133 polymorphisms may affect the risk of CHD in Asians and Caucasians, while the MTRR rs1801394 polymorphism may only affect in risk of CHD in Asians. However, it is notable that relevant studies were still at the early stage and further well-designed studies are still warranted to confirm our findings.

None.

Author Contribution

Aiping Xu and Weiping Wang conceived the study and participated in its design. Aiping Xu and Weiping Wang conducted the systematic literature review. Aiping Xu, Weiping Wang and Xiaolei Jiang performed data analyses. Aiping Xu and Weiping Wang drafted the manuscript. All authors have read and approved the final manuscript.

Funding

The authors declare that there are no sources of funding to be acknowledged.

Competing Interests

The authors declare that there are no competing interests associated with the manuscript.

Abbreviations

     
  • CHD

    congenital heart diseases

  •  
  • CI

    confidence interval

  •  
  • HWE

    Hardy–Weinberg equilibrium

  •  
  • MTHFR

    methylenetetrahydrofolate reductase

  •  
  • MTRR

    methionine synthase reductase

  •  
  • NOS

    Newcastle–Ottawa scale

  •  
  • OR

    odds ratio

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