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Association of Angiotensin-Converting Enzyme Insertion/Deletion Polymorphism with Recurrent Pregnancy Loss: a Meta-Analysis of 26 Case-Control Studies

Abstract

Objective

Previous studies investigating the association between angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism and recurrent pregnancy loss (RPL) risk has provided inconsistent results. The aim of our study was to assess the association between the ACE I/D polymorphism and risk of RPL.

Methods

All studies published up to January 30, 2018 on the association of ACE I/D polymorphism with RPL were identified by searching the PubMed, Web of Knowledge, and Google scholar databases.

Results

A total of 26 case-control studies with 3,140 RPL cases and 3,370 controls were included in themeta-analysis. Overall, there was a significant association between ACE I/D polymorphism and RPL risk under the allele model (I versus D: odds ratio [OR] = 0.538, 95% confidence interval [CI] = 0.451-0.643, p 0.001), the homozygote model (II versus DD: OR = 0.766, 95% CI = 0.598-0.981, p = 0.035) and the recessive model (II versus ID + DD: OR = 0.809, 95% CI = 0.658-0.994, p = 0.044). Subgroup analysis by ethnicity showed that there was a significant association between ACE I/D polymorphism and increased risk of RPL in Caucasian and West-Asian populations, but not in East-Asians. When stratified by number of recurrent miscarriages (RMs), a significant association between ACE I/D polymorphism and increased risk of RPL was detected in the group of studies with ≥ 2 RMs, but not in studies with ≥ 3 RMs.

Conclusion

Themeta-analysis suggests that ACE I/D polymorphism is associated with increased risk of RPL. The ACE I/D polymorphism may be a risk factor for RPL in Caucasian and West-Asian populations, but not in East-Asians.

Keywords:
miscarriage; pregnancy loss; angiotensinconverting enzyme; polymorphism; meta-analysis

Introduction

Recurrent pregnancy loss (RPL) is a surprisingly common occurrence, which traditionally is defined as 3 or more (≥ 3) consecutive miscarriages before 20 weeks of pregnancy.11 Ford HB, Schust DJ. Recurrent pregnancy loss: etiology, diagnosis, and therapy. Rev Obstet Gynecol 2009;2(02):76-83 22 Neamatzadeh H, Ramazani V, Kalantar SM, Ebrahimi M, Sheikhha MH. Serum immune reactivity against ß2-Glycoprotein-I and anti-neutrophil cytoplasmic auto-antibodies by ELI-P-Complex Screening Technology in recurrent miscarriage. Minerva Ginecol 2016;68(03):243-249 However, this definition is not used consistently, and pregnancy losses at higher gestational ages are also, in some literatures, classified as miscarriage instead of stillbirth or preterm neonatal death.33 Oliver-Williams C, Fleming M, Wood AM, Smith G. Previous miscarriage and the subsequent risk of pretermbirth in Scotland, 1980-2008: a historical cohort study. BJOG 2015;122(11):1525- -1534. Doi: 10.1111/1471-0528.13276
https://doi.org/10.1111/1471-0528.13276...
It has been estimated that 1 to 3% of couples suffer from recurrent miscarriages.44 Rull K, Nagirnaja L, Laan M. Genetics of recurrent miscarriage: challenges, current knowledge, future directions. Front Genet 2012;3:34. Doi: 10.3389/fgene.2012.00034
https://doi.org/10.3389/fgene.2012.00034...

The etiology of RPL is still unclear and there is a lot of controversy regarding its diagnosis and treatment.55 Sherkat R, Meidani M, Zarabian H, Rezaei A, Gholamrezaei A. Seropositivity of cytomegalovirus in patients with recurrent pregnancy loss. J Res Med Sci 2014;19(Suppl 1):S22-S25 It is well documented that RPL is a multifactorial disorder involving the interaction of genetic, maternal and environmental factors.66 Christiansen OB, Steffensen R, Nielsen HS, Varming K.Multifactorial etiology of recurrent miscarriage and its scientific and clinical implications. Gynecol Obstet Invest 2008;66(04):257-267. Doi: 10.1159/ 000149575 77 Dahm AEA, Tiscia G, Holmgren A, et al. Genetic variations in the annexin A5 gene and the risk of pregnancy-related venous thrombosis. J ThrombHaemost 2015;13(03):409-413.Doi: 10.1111/jth.12817
https://doi.org/10.1111/jth.12817...
An increasing number of genetic association studies are performed to determine the genetic background of RPL.88 Kamali M, Hantoushzadeh S, Borna S, et al. Association between thrombophilic genes polymorphisms and recurrent pregnancy loss susceptibility in the Iranian population: a systematic review and meta-analysis. Iran Biomed J 2018;22(02):78-89. Doi: 10.22034/ibj.22.2.78
https://doi.org/10.22034/ibj.22.2.78...
To date, more than 30 putative major genes involved in immunity (PP14, Annexin II, PIBF, and HLA-DRB1) and angiogenesis (TGF-β, VEGF, TIMP-1, MMP-2, MMP-9, ACE) genes for RPL have been identified.99 Prigoshin N, Tambutti M, Larriba J, Gogorza S, Testa R. Cytokine gene polymorphisms in recurrent pregnancy loss of unknown cause. Am J Reprod Immunol 2004;52(01):36-41. Doi: 10.1111/ j.1600-0897.2004.00179.x 1010 Skrzypczak J, Wirstlein P, Mikolajczyk M, LudwikowskiG, Zak T. TGF superfamily and MMP2, MMP9, TIMP1 genes expression in the endometrium of women with impaired reproduction. Folia Histochem Cytobiol 2007;45(Suppl 1):S143-S148. Doi: 10.5603/4474 1111 Anumba DO, El Gelany S, Elliott SL, Li TC. Circulating levels of matrix proteases and their inhibitors in pregnant women with and without a history of recurrent pregnancy loss. Reprod Biol Endocrinol 2010;8:62. Doi: 10.1186/1477-7827-8-62
https://doi.org/10.1186/1477-7827-8-62...

Angiotensin I-converting enzyme (ACE) is a zinc metallopeptidase that converts angiotensin I to angiotensin II.1212 Zhang K, Cheng D, Yi L, Shi H, Zhen G. Association between angiotensin I-converting enzyme gene polymorphism and susceptibility to cancer: a meta analysis. Int J Clin Exp Pathol 2014;7 (09):6291-6300 The ACE plays an important role in the modulation of vascular homeostasis, inflammation and angiogenesis.1313 Guimarães PB, Alvarenga EC, Siqueira PD, et al. Angiotensin II binding to angiotensin I-converting enzyme triggers calcium signaling. Hypertension 2011;57(05):965-972. Doi: 10.1161/HYPERTENSIONAHA.110.167171
https://doi.org/10.1161/HYPERTENSIONAHA....
Based on its biological functions, the insertion/deletion (I/D) polymorphism of the ACE gene can be seen as a candidate locus for RPL.1414 Zhang S, Wang J, Wang B, Ping Y, Ma X. Strong association between angiotensin I-convertingenzyme I/Dpolymorphismand unexplained recurrent miscarriage of Chinese women-a case-control study. Reprod Sci 2011;18(08):743-746. Doi: 10.1177/1933719111415865
https://doi.org/10.1177/1933719111415865...
Angiotensin I-converting enzyme is related with plasminogen activator inhibitor-1 (PAI-1) activity, which is a key regulator in embryo implantation.1515 Shakarami F, AkbariMT, Zare Karizi S. Association of plasminogen activator inhibitor-1 and angiotensin converting enzyme polymorphismswith recurrent pregnancy loss in Iranianwomen. Iran J Reprod Med 2015;13(10):627-632 The human ACE gene is located on chromosome 17q23, and it consists of 26 exons and 25 introns.1616 SuMT, Lin SH, Chen YC, Kuo PL. Genetic association studies of ACE and PAI-1 genes in women with recurrent pregnancy loss: a systematic review and meta-analysis. Thromb Haemost 2013; 109(01):8-15. Doi: 10.1160/TH12-08-0584
https://doi.org/10.1160/TH12-08-0584...
1717 Yang C, Fangfang W, Jie L, et al. Angiotensin-converting enzyme insertion/deletion (I/D) polymorphisms and recurrent pregnancy loss: ameta-analysis. JAssistReprodGenet2012;29(11):1167-1173. Doi: 10.1007/s10815-012-9870-3
https://doi.org/10.1007/s10815-012-9870-...
One of the well-known polymorphisms in the ACE gene is the 287-bp insertion/deletion (or named repetitive element) in intron 16 (ACE I/D).1515 Shakarami F, AkbariMT, Zare Karizi S. Association of plasminogen activator inhibitor-1 and angiotensin converting enzyme polymorphismswith recurrent pregnancy loss in Iranianwomen. Iran J Reprod Med 2015;13(10):627-632 1616 SuMT, Lin SH, Chen YC, Kuo PL. Genetic association studies of ACE and PAI-1 genes in women with recurrent pregnancy loss: a systematic review and meta-analysis. Thromb Haemost 2013; 109(01):8-15. Doi: 10.1160/TH12-08-0584
https://doi.org/10.1160/TH12-08-0584...
Angiotensin converting enzyme I/D polymorphism (dbSNP rs4646994) is actually not a single nucleotide polymorphism (SNP) at all; instead, it is an I/D of an Alu repeat sequence in an intron of the ACE gene. The ACE I/D polymorphism is associated with ACE activity and levels in plasma and tissues.1717 Yang C, Fangfang W, Jie L, et al. Angiotensin-converting enzyme insertion/deletion (I/D) polymorphisms and recurrent pregnancy loss: ameta-analysis. JAssistReprodGenet2012;29(11):1167-1173. Doi: 10.1007/s10815-012-9870-3
https://doi.org/10.1007/s10815-012-9870-...
1818 Merlo S, Novák J, Tkácová N, et al. Association of the ACE rs4646994 and rs4341 polymorphisms with the progression of carotid atherosclerosis in slovenian patients with type 2 diabetes mellitus. Balkan J Med Genet 2016;18(02):37-42. Doi: 10.1515/ bjmg-2015-0084 It has been shown that individuals with the D allele have higher serum ACE activity than those with the I allele. Therefore, ACE enzyme activity is increased in homozygotes for the DD genotype, intermediate in heterozygotes (ID) and decreased in homozygotes for I (II).1919 Rigat B, Hubert C, Alhenc-Gelas F, Cambien F, Corvol P, Soubrier F. An insertion/deletion polymorphism in the angiotensin I-converting enzyme gene accounting for half the variance of serum enzyme levels. JClinInvest1990;86(04):1343-1346.Doi: 10.1172/JCI114844
https://doi.org/10.1172/JCI114844...
Emerging evidence has shown that the ACE D allele leads to increased expression of PAI-1, which can increase the risk of thrombotic events and enhances the production of angiotensin II from angiotensin I.1616 SuMT, Lin SH, Chen YC, Kuo PL. Genetic association studies of ACE and PAI-1 genes in women with recurrent pregnancy loss: a systematic review and meta-analysis. Thromb Haemost 2013; 109(01):8-15. Doi: 10.1160/TH12-08-0584
https://doi.org/10.1160/TH12-08-0584...
1717 Yang C, Fangfang W, Jie L, et al. Angiotensin-converting enzyme insertion/deletion (I/D) polymorphisms and recurrent pregnancy loss: ameta-analysis. JAssistReprodGenet2012;29(11):1167-1173. Doi: 10.1007/s10815-012-9870-3
https://doi.org/10.1007/s10815-012-9870-...

Accumulating studies have assessed the association between this polymorphism and RPL, but the results are unconvincing and unreliable, which may be partly due to the relatively small samples and different ethnic subgroups. The most recent meta-analysis was conducted in 2013, and it aimed at investigating the association of ACE I/D polymorphism with the risk of RPL.1616 SuMT, Lin SH, Chen YC, Kuo PL. Genetic association studies of ACE and PAI-1 genes in women with recurrent pregnancy loss: a systematic review and meta-analysis. Thromb Haemost 2013; 109(01):8-15. Doi: 10.1160/TH12-08-0584
https://doi.org/10.1160/TH12-08-0584...
When taking into account the 11 eligible case-control studies, the results indicate that ACE I/D polymorphism is significantly associated with the risk of RPL in the overall population, but not in Caucasian and non-Caucasian populations. In the past 2 years, several other case-control studies conducted to evaluate the effect of ACE polymorphism on RPL provided some new data and diverse conclusions.1515 Shakarami F, AkbariMT, Zare Karizi S. Association of plasminogen activator inhibitor-1 and angiotensin converting enzyme polymorphismswith recurrent pregnancy loss in Iranianwomen. Iran J Reprod Med 2015;13(10):627-632 1919 Rigat B, Hubert C, Alhenc-Gelas F, Cambien F, Corvol P, Soubrier F. An insertion/deletion polymorphism in the angiotensin I-converting enzyme gene accounting for half the variance of serum enzyme levels. JClinInvest1990;86(04):1343-1346.Doi: 10.1172/JCI114844
https://doi.org/10.1172/JCI114844...
2020 Namazi A, Forat-YazdiM, JafariM, et al. Association of interleukin-10 -1082 a/G (Rs1800896) polymorphism with susceptibility to gastric cancer: meta-analysis of 6,101 cases and 8,557 controls. Arq Gastroenterol2018; 55(01):33-40.Doi:10.1590/s0004-2803.201800000-18
https://doi.org/10.1590/s0004-2803.20180...
2121 Sobhan MR, Mehdinejad M, Jamaladini MH, Mazaheri M, Zare- Shehneh M, Neamatzadeh H. Association between aspartic acid repeat polymorphismof the asporin gene and risk of knee osteoarthritis: A systematic review and meta-analysis. Acta Orthop Traumatol Turc 2017;51(05):409-415. Doi: 10.1016/j.aott.2017.08.001
https://doi.org/10.1016/j.aott.2017.08.0...
2222 DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials 1986;7(03):177-188. Doi: 10.1016/0197-2456(86)90046-2
https://doi.org/10.1016/0197-2456(86)900...
2323 Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959;22 (04):719-748. Doi: 10.1093/jnci/22.4.719
https://doi.org/10.1093/jnci/22.4.719...
2424 Begg CB, Mazumdar M. Operating characteristics of a rank correlation test for publication bias. Biometrics 1994;50(04): 1088-1101. Doi: 10.2307/2533446
https://doi.org/10.2307/2533446...
Accordingly, we performed the present systematic review and meta-analysis with more eligible studies to investigate the association between ACE I/D polymorphism and the risk of RPL.

Methods

Search Strategy

A systematic search of eligible studies on the association of ACE I/D polymorphism with RPL susceptibility was conducted in PubMed, Web of Science, the Chinese Biomedical Literature database (CBM), and the Chinese National Knowledge Infrastructure database (CNKI) up to the January 30, 2018. The following terms were included in the search: (Recurrent pregnancy loss OR recurrent miscarriage OR habitual abortion OR miscarriage OR fetal loss OR RPL) AND (Angiotensin-converting enzyme OR ACE OR SERPINE1) AND (insertion/deletion polymorphism OR I/D polymorphism OR rs4646994) AND (single nucleotide polymorphisms OR SNPs OR polymorphism OR mutation OR variant OR genotype). To minimize potential publication bias, the extracted publications were not limited to English. Additionally, the references list of the retrieved case-control studies, previous meta-analysis, review articles and clinical trials were manually searched for more additional original articles. If there were multiple reports of the same study or overlapping data, only the study with the largest sample sizes or the most recent one was included to the current meta-analysis.

Inclusion and Exclusion Criteria

Studies were included based on the following criteria: (1) only full-text and published studies; (2) studies with case-control or cohort design; (3) a study evaluated the association of ACE I/D polymorphism with RPL risk; (4) available genotypes frequencies of ACE I/D polymorphism were provided to estimate the odds ratios (ORs) with 95% confidence intervals (CIs). The exclusion criteria were as follows: (1) the study was not conducted on RPL; (2) studies on secondary causes for RPL; (3) family-based linkage studies; (4) abstracts, case reports, and review articles; (5) studies with only RPL cases (not including healthy individuals); (6) studies on the other polymorphisms of the ACE gene; (7) studies without detail genotype frequencies, which were unable to calculate ORs; and (8) duplicate publications of data from the same study.

Data Extraction

Two authors independently extracted the following data from each eligible study according to the inclusion criteria: first author, year of publication, country of origin, ethnicity, total number of cases and controls, the frequencies of genotypes, minor allele frequencies (MAFs), and Hardy-Weinberg Equilibrium (HWE) test in control subjects. Any discrepancy between these two authors was resolved by reaching a consensus through discussion or the involvement of a third author who made the final decision through discussions.

Quality Assessment

Two authors performed the quality assessment of the included studies, which was adjusted from the Newcastle-Ottawa scale (NOS) for case-control studies (Table 1), and solved disagreement through discussion. In this scale, six items, including the selection of patients with unexplained recurrent pregnancy loss, source of controls, comparability of cases and controls on the basis of the design or analysis, sample size, quality control of genotyping methods, and HWE, were carefully checked. The quality assessment values ranged from 0 to 10, with higher scores indicating a better quality of the study.

Table 1
Scale for methodological quality assessment

Statistical Analysis

The association between ACE I/D polymorphism and RPL was assessed using crude odds ratio (OR) with 95% confidence interval (CI). Five different genetic models were constructed to determine pooled ORs in accordance with the assumed genetic effect of the D allele including: allele model (I versus D), homozygous model (II versus DD), heterozygous model (ID versus DD), dominant model (II + ID versus DD) and recessive model (II versus ID + DD). The Z-test was used to assess the pooled OR with the significance set at p< 0.05. Between-studies heterogeneity was evaluated by the Cochran C2-based Q test (heterogeneity was considered statistically significant if p< 0.10) and I2 statistics.2020 Namazi A, Forat-YazdiM, JafariM, et al. Association of interleukin-10 -1082 a/G (Rs1800896) polymorphism with susceptibility to gastric cancer: meta-analysis of 6,101 cases and 8,557 controls. Arq Gastroenterol2018; 55(01):33-40.Doi:10.1590/s0004-2803.201800000-18
https://doi.org/10.1590/s0004-2803.20180...
An I2 value of 0% represents no heterogeneity; values of 25%, 50%, 75%, or more represent low, moderate, high, and extreme heterogeneity, respectively.2121 Sobhan MR, Mehdinejad M, Jamaladini MH, Mazaheri M, Zare- Shehneh M, Neamatzadeh H. Association between aspartic acid repeat polymorphismof the asporin gene and risk of knee osteoarthritis: A systematic review and meta-analysis. Acta Orthop Traumatol Turc 2017;51(05):409-415. Doi: 10.1016/j.aott.2017.08.001
https://doi.org/10.1016/j.aott.2017.08.0...
The random-effects model (based on the DerSimonian and Laird method)2222 DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials 1986;7(03):177-188. Doi: 10.1016/0197-2456(86)90046-2
https://doi.org/10.1016/0197-2456(86)900...
was used when heterogeneity existed among studies; otherwise the fixed-effects model (based on the Mantel-Haenszel method)2323 Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959;22 (04):719-748. Doi: 10.1093/jnci/22.4.719
https://doi.org/10.1093/jnci/22.4.719...
was applied. Departure from Hardy-Weinberg equilibrium (HWE) in healthy subjects was examined using the Chi-square test, and a p-value < 0.05 was considered significant. Furthermore, to explore the source of between-study heterogeneity, subgroup analyses by number of recurrent miscarriages (RMs) (≥ 2 or ≥ 3), ethnicity, and HWE status were performed. The one-way sensitivity analyses were performed to assess the stability and liability of the meta-analysis, namely, a single study in the meta-analysis was omitted each time to reflect the influence of the individual dataset to the pooled OR. Publication bias was examined by using a funnel plot and Egger's linear regression, and a p< 0.05 was considered significant.2424 Begg CB, Mazumdar M. Operating characteristics of a rank correlation test for publication bias. Biometrics 1994;50(04): 1088-1101. Doi: 10.2307/2533446
https://doi.org/10.2307/2533446...
2525 Egger M, Davey Smith G, Schneider M, Minder C. Bias in metaanalysis detected by a simple, graphical test. BMJ 1997;315 (7109):629-634. Doi: 10.1136/bmj.315.7109.629
https://doi.org/10.1136/bmj.315.7109.629...
All the statistical analyses were performed using the Comprehensive Meta-Analysis (CMA) software version 2.2 (Biostat, USA). All p-values were two-tailed with a significant level set at 0.05.

Results

Characteristics of Eligible Studies

The study selection and inclusion processes are shown in Fig. 1. After a comprehensive literature search, a total of 216 publications were identified. Of these studies, x 97 were excluded in the first screening as duplicates or not relevant, leaving 119 studies for further selection. Among the remaining studies, 93 articles were excluded because they were review articles, letters to editors, previous meta-analyses, not relevant to ACE I/D polymorphism, not case-control studies, evaluated other diseases instead of RPL, and case reports. Finally, a total of 26 case-control studies with 3,140 RPL cases and 3,370 controls were included in the present meta-analysis.1414 Zhang S, Wang J, Wang B, Ping Y, Ma X. Strong association between angiotensin I-convertingenzyme I/Dpolymorphismand unexplained recurrent miscarriage of Chinese women-a case-control study. Reprod Sci 2011;18(08):743-746. Doi: 10.1177/1933719111415865
https://doi.org/10.1177/1933719111415865...
1515 Shakarami F, AkbariMT, Zare Karizi S. Association of plasminogen activator inhibitor-1 and angiotensin converting enzyme polymorphismswith recurrent pregnancy loss in Iranianwomen. Iran J Reprod Med 2015;13(10):627-632 2525 Egger M, Davey Smith G, Schneider M, Minder C. Bias in metaanalysis detected by a simple, graphical test. BMJ 1997;315 (7109):629-634. Doi: 10.1136/bmj.315.7109.629
https://doi.org/10.1136/bmj.315.7109.629...
2626 Fatini C, Gensini F, Battaglini B, et al. Angiotensin-converting enzyme DD genotype, angiotensin type 1 receptor CC genotype, and hyperhomocysteinemia increase first-trimester fetal-loss susceptibility. Blood Coagul Fibrinolysis 2000;11(07):657-662 2727 Buchholz T, Lohse P, Rogenhofer N, Kosian E, Pihusch R, Thaler CJ. Polymorphisms in the ACE and PAI-1 genes are associated with recurrent spontaneous miscarriages. Hum Reprod 2003;18(11): 2473-2477. Doi: 10.1093/humrep/deg474
https://doi.org/10.1093/humrep/deg474...
2828 Soltan Ghoraei H,Memariani T, AarabiM, et al. Association of ACE, PAI-1 and coagulation factor XIII gene polymorphisms with recurrent spontaneous abortion in Iranian patients. J Reprod Infertil 2007;7:324-330 2929 Goodman C, Hur J, Goodman CS, Jeyendran RS, Coulam C. Are polymorphisms in the ACE and PAI-1 genes associated with recurrent spontaneous miscarriages? Am J Reprod Immunol 2009;62(06):365-370. Doi: 10.1111/j.1600-0897.2009.00744.x
https://doi.org/10.1111/j.1600-0897.2009...
3030 Vettriselvi V, Vijayalakshmi K, Paul SFD, Venkatachalam P. ACE and MTHFR gene polymorphisms in unexplained recurrent pregnancy loss. J Obstet Gynaecol Res 2008;34(03):301-306. Doi: 10.1111/j.1447-0756.2008.00792.x
https://doi.org/10.1111/j.1447-0756.2008...
3131 Pan L. Association of the PAI-1 and ACE Gene Polymorphismwith the Recurrent Spontaneous Abortion [master's thesis]. Yinchuan, China: Ningxia Medical University; 2009 3232 Bukreeva L, Grigorov A, Kiesewetter H, Hoppe B. Association of angiotensin-converting enzyme intron 16 insertion/deletion polymorphism with history of foetal loss. J Renin Angiotensin Aldosterone Syst 2009;10(04):237-240. Doi: 10.1177/1470320309343813
https://doi.org/10.1177/1470320309343813...
3333 Al Sallout RJ, Sharif FA. Polymorphisms in NOS3, ACE and PAI-1 genes and risk of spontaneous recurrent miscarriage in the Gaza Strip. Med Princ Pract 2010;19(02):99-104. Doi: 10.1159/000273067
https://doi.org/10.1159/000273067...
3434 Bagheri M, Abdi Rad I, Omrani MD, Nanbaksh F. Polymorphisms of the angiotensin converting enzyme gene in Iranian Azeri Turkish women with unexplained recurrent pregnancy loss. Hum Fertil (Camb) 2010;13(02):79-82. Doi: 10.3109/14647273.2010.484844
https://doi.org/10.3109/14647273.2010.48...
3535 Choi YS, Kwon H, Kim JH, et al. Haplotype-based association of ACE I/D, AT1R 1166A>C, and AGT M235T polymorphisms in renin-angiotensin-aldosterone system genes in Korean women with idiopathic recurrent spontaneous abortions. Eur J Obstet Gynecol Reprod Biol 2011;158(02):225-228. Doi: 10.1016/j.ejogrb.2011.04.028
https://doi.org/10.1016/j.ejogrb.2011.04...
3636 Aarabi M, Memariani T, Arefi S, et al. Polymorphisms of plasminogen activator inhibitor-1, angiotensin converting enzyme and coagulation factor XIII genes in patients with recurrent spontaneous abortion. J Matern Fetal Neonatal Med 2011;24(03): 545-548. Doi: 10.3109/14767058.2010.511331
https://doi.org/10.3109/14767058.2010.51...
3737 Corbo RM, Ulizzi L, Piombo L, Scacchi R. Association of ACE I/D polymorphism and recurrent miscarriages in an Italian population with a pre-modern reproductive pattern. Ann Hum Biol 2011;38(01):102-105. Doi: 10.3109/03014460.2010.481265
https://doi.org/10.3109/03014460.2010.48...
3838 Ozdemir O, Yenicesu GI, Silan F, et al. Recurrent pregnancy loss and its relation to combined parental thrombophilic gene mutations. Genet Test Mol Biomarkers 2012;16(04):279-286. Doi: 10.1089/gtmb.2011.0191
https://doi.org/10.1089/gtmb.2011.0191...
3939 Poursadegh Zonouzi A, Farajzadeh D, Bargahi N, Farajzadeh M. Apolipoprotein E genotyping inwomenwith recurrent pregnancy loss: an in silico and experimental hybrid study. Gene 2014;549 (02):209-213. Doi: 10.1016/j.gene.2014.07.055
https://doi.org/10.1016/j.gene.2014.07.0...
4040 Kim JJ, Choi YM, Lee SK, et al. The PAI-1 4G/5G and ACE I/D polymorphisms and risk of recurrent pregnancy loss: a casecontrol study. Am J Reprod Immunol 2014;72(06):571-576. Doi: 10.1111/aji.12302
https://doi.org/10.1111/aji.12302...
4141 Yalcintepe S, Ozdemir O, Hacivelioglu SO, et al. Multiple inherited thrombophilic gene polymorphisms in spontaneous abortions in Turkish population. Int J Mol Cell Med 2015;4(02):120-127 4242 Kurzawinska G, Barlik M, Drews K, et al. Coexistence of ACE (I/D) and PAI-1 (4G/5G) gene variants in recurrentmiscarriage in Polish population. Ginekol Pol 2016;87(04):271-276. Doi: 10.17772/gp/62203
https://doi.org/10.17772/gp/62203...
4343 Al-Mukaynizi FB, AlKhuriji A, Babay Z, et al. Lack of association between angiotensin converting enzyme I/D polymorphism and unexplained recurrent miscarriage in Saudi Arabia. J Med Biochem 2016;35(02):166-173. Doi: 10.1515/jomb-2015-0020
https://doi.org/10.1515/jomb-2015-0020...
4444 Hussian AMF, Mohammed NEA, Ahmed MAM, Ali EW. Angiotensin converting enzyme Insertion/Deletion (I/D) polymorphism and riskof recurrent pregnancy loss among Sudanesewomen. Rev Obstet Gynecol 2016;4:7-10. Doi: 10.5923/j.rog.20160401.02
https://doi.org/10.5923/j.rog.20160401.0...
4545 Pereza N, Ostojic S, Zdravcevic M, Volk M, Kapovic M, Peterlin B. Insertion/deletion polymorphism in intron 16 of ACE gene in idiopathic recurrent spontaneous abortion: case-control study, systematic review and meta-analysis. Reprod Biomed Online 2016;32(02):237-246. Doi: 10.1016/j.rbmo.2015.11.003
https://doi.org/10.1016/j.rbmo.2015.11.0...
4646 Fazelnia S, Farazmandfar T, Hashemi-Soteh SMB. Significant correlation of angiotensin converting enzyme and glycoprotein IIIa genes polymorphisms with unexplained recurrent pregnancy loss in north of Iran. Int J Reprod Biomed (Yazd) 2016;14(05): 323-328 4747 López-Jiménez JJ, Porras-Dorantes Á, Juárez-Vázquez CI, et al. Molecular thrombophilic profile in Mexican patients with idiopathic recurrent pregnancy loss. Genet Mol Res 2016;15(04):. Doi: 10.4238/gmr.15048728
https://doi.org/10.4238/gmr.15048728...
4848 Heidari MM, Sheikholeslami M, Yavari M, Khatami M, Seyedhassani SM. The association of renin-angiotensinogen system genes polymorphisms and idiopathic recurrent pregnancy loss. Hum Fertil (Camb) 2017;•••:1-7. Doi: 10.1080/14647273.2017.1388545
https://doi.org/10.1080/14647273.2017.13...
The characteristics of the selected studies are summarized in Table 1. Of these, 10 case-control studies involving 1,391 cases and 1,292 controls were conducted in Caucasians,2525 Egger M, Davey Smith G, Schneider M, Minder C. Bias in metaanalysis detected by a simple, graphical test. BMJ 1997;315 (7109):629-634. Doi: 10.1136/bmj.315.7109.629
https://doi.org/10.1136/bmj.315.7109.629...
2626 Fatini C, Gensini F, Battaglini B, et al. Angiotensin-converting enzyme DD genotype, angiotensin type 1 receptor CC genotype, and hyperhomocysteinemia increase first-trimester fetal-loss susceptibility. Blood Coagul Fibrinolysis 2000;11(07):657-662 2828 Soltan Ghoraei H,Memariani T, AarabiM, et al. Association of ACE, PAI-1 and coagulation factor XIII gene polymorphisms with recurrent spontaneous abortion in Iranian patients. J Reprod Infertil 2007;7:324-330 3131 Pan L. Association of the PAI-1 and ACE Gene Polymorphismwith the Recurrent Spontaneous Abortion [master's thesis]. Yinchuan, China: Ningxia Medical University; 2009 3636 Aarabi M, Memariani T, Arefi S, et al. Polymorphisms of plasminogen activator inhibitor-1, angiotensin converting enzyme and coagulation factor XIII genes in patients with recurrent spontaneous abortion. J Matern Fetal Neonatal Med 2011;24(03): 545-548. Doi: 10.3109/14767058.2010.511331
https://doi.org/10.3109/14767058.2010.51...
3737 Corbo RM, Ulizzi L, Piombo L, Scacchi R. Association of ACE I/D polymorphism and recurrent miscarriages in an Italian population with a pre-modern reproductive pattern. Ann Hum Biol 2011;38(01):102-105. Doi: 10.3109/03014460.2010.481265
https://doi.org/10.3109/03014460.2010.48...
4040 Kim JJ, Choi YM, Lee SK, et al. The PAI-1 4G/5G and ACE I/D polymorphisms and risk of recurrent pregnancy loss: a casecontrol study. Am J Reprod Immunol 2014;72(06):571-576. Doi: 10.1111/aji.12302
https://doi.org/10.1111/aji.12302...
4141 Yalcintepe S, Ozdemir O, Hacivelioglu SO, et al. Multiple inherited thrombophilic gene polymorphisms in spontaneous abortions in Turkish population. Int J Mol Cell Med 2015;4(02):120-127 4444 Hussian AMF, Mohammed NEA, Ahmed MAM, Ali EW. Angiotensin converting enzyme Insertion/Deletion (I/D) polymorphism and riskof recurrent pregnancy loss among Sudanesewomen. Rev Obstet Gynecol 2016;4:7-10. Doi: 10.5923/j.rog.20160401.02
https://doi.org/10.5923/j.rog.20160401.0...
4848 Heidari MM, Sheikholeslami M, Yavari M, Khatami M, Seyedhassani SM. The association of renin-angiotensinogen system genes polymorphisms and idiopathic recurrent pregnancy loss. Hum Fertil (Camb) 2017;•••:1-7. Doi: 10.1080/14647273.2017.1388545
https://doi.org/10.1080/14647273.2017.13...
10 case-control studies in the west-Asians,1515 Shakarami F, AkbariMT, Zare Karizi S. Association of plasminogen activator inhibitor-1 and angiotensin converting enzyme polymorphismswith recurrent pregnancy loss in Iranianwomen. Iran J Reprod Med 2015;13(10):627-632 2727 Buchholz T, Lohse P, Rogenhofer N, Kosian E, Pihusch R, Thaler CJ. Polymorphisms in the ACE and PAI-1 genes are associated with recurrent spontaneous miscarriages. Hum Reprod 2003;18(11): 2473-2477. Doi: 10.1093/humrep/deg474
https://doi.org/10.1093/humrep/deg474...
2929 Goodman C, Hur J, Goodman CS, Jeyendran RS, Coulam C. Are polymorphisms in the ACE and PAI-1 genes associated with recurrent spontaneous miscarriages? Am J Reprod Immunol 2009;62(06):365-370. Doi: 10.1111/j.1600-0897.2009.00744.x
https://doi.org/10.1111/j.1600-0897.2009...
3232 Bukreeva L, Grigorov A, Kiesewetter H, Hoppe B. Association of angiotensin-converting enzyme intron 16 insertion/deletion polymorphism with history of foetal loss. J Renin Angiotensin Aldosterone Syst 2009;10(04):237-240. Doi: 10.1177/1470320309343813
https://doi.org/10.1177/1470320309343813...
3333 Al Sallout RJ, Sharif FA. Polymorphisms in NOS3, ACE and PAI-1 genes and risk of spontaneous recurrent miscarriage in the Gaza Strip. Med Princ Pract 2010;19(02):99-104. Doi: 10.1159/000273067
https://doi.org/10.1159/000273067...
3939 Poursadegh Zonouzi A, Farajzadeh D, Bargahi N, Farajzadeh M. Apolipoprotein E genotyping inwomenwith recurrent pregnancy loss: an in silico and experimental hybrid study. Gene 2014;549 (02):209-213. Doi: 10.1016/j.gene.2014.07.055
https://doi.org/10.1016/j.gene.2014.07.0...
4242 Kurzawinska G, Barlik M, Drews K, et al. Coexistence of ACE (I/D) and PAI-1 (4G/5G) gene variants in recurrentmiscarriage in Polish population. Ginekol Pol 2016;87(04):271-276. Doi: 10.17772/gp/62203
https://doi.org/10.17772/gp/62203...
4545 Pereza N, Ostojic S, Zdravcevic M, Volk M, Kapovic M, Peterlin B. Insertion/deletion polymorphism in intron 16 of ACE gene in idiopathic recurrent spontaneous abortion: case-control study, systematic review and meta-analysis. Reprod Biomed Online 2016;32(02):237-246. Doi: 10.1016/j.rbmo.2015.11.003
https://doi.org/10.1016/j.rbmo.2015.11.0...
4747 López-Jiménez JJ, Porras-Dorantes Á, Juárez-Vázquez CI, et al. Molecular thrombophilic profile in Mexican patients with idiopathic recurrent pregnancy loss. Genet Mol Res 2016;15(04):. Doi: 10.4238/gmr.15048728
https://doi.org/10.4238/gmr.15048728...
with 984 cases and 1,108 cases, 4 case-control studies in the East-Asians,1414 Zhang S, Wang J, Wang B, Ping Y, Ma X. Strong association between angiotensin I-convertingenzyme I/Dpolymorphismand unexplained recurrent miscarriage of Chinese women-a case-control study. Reprod Sci 2011;18(08):743-746. Doi: 10.1177/1933719111415865
https://doi.org/10.1177/1933719111415865...
3030 Vettriselvi V, Vijayalakshmi K, Paul SFD, Venkatachalam P. ACE and MTHFR gene polymorphisms in unexplained recurrent pregnancy loss. J Obstet Gynaecol Res 2008;34(03):301-306. Doi: 10.1111/j.1447-0756.2008.00792.x
https://doi.org/10.1111/j.1447-0756.2008...
3434 Bagheri M, Abdi Rad I, Omrani MD, Nanbaksh F. Polymorphisms of the angiotensin converting enzyme gene in Iranian Azeri Turkish women with unexplained recurrent pregnancy loss. Hum Fertil (Camb) 2010;13(02):79-82. Doi: 10.3109/14647273.2010.484844
https://doi.org/10.3109/14647273.2010.48...
with 670 cases and 880 controls, 1 study involving 55 cases and 50 controls in Latinos,4343 Al-Mukaynizi FB, AlKhuriji A, Babay Z, et al. Lack of association between angiotensin converting enzyme I/D polymorphism and unexplained recurrent miscarriage in Saudi Arabia. J Med Biochem 2016;35(02):166-173. Doi: 10.1515/jomb-2015-0020
https://doi.org/10.1515/jomb-2015-0020...
and 1 study with 40 cases and 40 controls in Africans.4646 Fazelnia S, Farazmandfar T, Hashemi-Soteh SMB. Significant correlation of angiotensin converting enzyme and glycoprotein IIIa genes polymorphisms with unexplained recurrent pregnancy loss in north of Iran. Int J Reprod Biomed (Yazd) 2016;14(05): 323-328 The countries of these studies included Italy, Germany, Iran, USA, India, China, Gaza, Korea, Turkey, Poland, Saudi Arabia, Sudan, Slovenia, Mexico, and Greece. All the genotype distributions of controls were in agreement with HWE for ACE I/D polymorphism except for six studies.1515 Shakarami F, AkbariMT, Zare Karizi S. Association of plasminogen activator inhibitor-1 and angiotensin converting enzyme polymorphismswith recurrent pregnancy loss in Iranianwomen. Iran J Reprod Med 2015;13(10):627-632 2828 Soltan Ghoraei H,Memariani T, AarabiM, et al. Association of ACE, PAI-1 and coagulation factor XIII gene polymorphisms with recurrent spontaneous abortion in Iranian patients. J Reprod Infertil 2007;7:324-330 2929 Goodman C, Hur J, Goodman CS, Jeyendran RS, Coulam C. Are polymorphisms in the ACE and PAI-1 genes associated with recurrent spontaneous miscarriages? Am J Reprod Immunol 2009;62(06):365-370. Doi: 10.1111/j.1600-0897.2009.00744.x
https://doi.org/10.1111/j.1600-0897.2009...
3232 Bukreeva L, Grigorov A, Kiesewetter H, Hoppe B. Association of angiotensin-converting enzyme intron 16 insertion/deletion polymorphism with history of foetal loss. J Renin Angiotensin Aldosterone Syst 2009;10(04):237-240. Doi: 10.1177/1470320309343813
https://doi.org/10.1177/1470320309343813...
3636 Aarabi M, Memariani T, Arefi S, et al. Polymorphisms of plasminogen activator inhibitor-1, angiotensin converting enzyme and coagulation factor XIII genes in patients with recurrent spontaneous abortion. J Matern Fetal Neonatal Med 2011;24(03): 545-548. Doi: 10.3109/14767058.2010.511331
https://doi.org/10.3109/14767058.2010.51...
4545 Pereza N, Ostojic S, Zdravcevic M, Volk M, Kapovic M, Peterlin B. Insertion/deletion polymorphism in intron 16 of ACE gene in idiopathic recurrent spontaneous abortion: case-control study, systematic review and meta-analysis. Reprod Biomed Online 2016;32(02):237-246. Doi: 10.1016/j.rbmo.2015.11.003
https://doi.org/10.1016/j.rbmo.2015.11.0...
Therefore, 20 of 26 case-control studies were defined as high-quality studies (Tables 1, 2 and 3).

Table 2
Main characteristics of studies included in this meta-analysis
Table 3
Results of meta-analysis for angiotensin-converting enzyme deletion/instertion polymorphism and recurrent pregnancy loss

Fig. 1
The study selection and inclusion process.

Quantitative Synthesis

Table 2 listed the main results of the meta-analysis of ACE I/D polymorphism and RPL risk. When all the eligible studies were pooled into the meta-analysis of ACE I/D polymorphism, a significant association was found between ACE I/D polymorphism and RPL under the allele model (I versus D: OR = 0.538, 95% CI = 0.451–0.643, p ≤ 0.001), the homozygote model (II versus DD: OR = 0.766, 95% CI = 0.598–0.981, p= 0.035) (Fig. 2A) and recessive model (II versus ID + DD: OR = 0.809, 95% CI = 0.658–0.994, p= 0.044) (Fig. 2B).

Fig. 2
Forest plot of the association between ACE I/D polymorphism and RPL. (A) represents the homozygote model (II versus DD); (B) represents the recessive model (II versus ID + DD).

The studies were further stratified on the basis of number of RM, ethnicity and studies HWE status. When stratified by number of RM, a significant association between ACE I/D polymorphism and increased risk of RPL was detected in the group of studies with ≥ 2 pregnancy loss under the allele model (I versus D: OR = 0.479, 95% CI = 0.383–0.600, p ≤0 .001), the homozygote model (II versus DD: OR = 0.709, 95% CI = 0.520–0.966, p= 0.029) and the recessive model (II versus ID + DD: OR = 0.754, 95% CI = 0.574–0.990, p= 0.042), but not in studies with ≥ 3 RM. When stratified by ethnicity, a significant association was established between ACE I/D polymorphism and increased risk of RPL among Caucasians (allele model: I versus D: OR = 0.753, 95% CI = 0.574–0.988, p= 0.040; homozygote model: OR = 0.640, 95% CI = 0.440–0.930, p= 0.019; dominant model: II + ID versus DD: OR = 0.643, 95% CI = 0.439–0.943, p= 0.024; and recessive model II versus ID + DD: OR = 0.661, 95% CI = 0.492–0.888, p= 0.006) and West-Asians (dominant model: II versus ID + DD: OR = 1.361, 95% CI = 1.122–1.650, p= 0.002). In contrast, no significant association was observed in the East-Asian subgroup under any of the genetic models (Table 3). Subgroup analysis of studies by HWE status showed that there was a significant association between ACE I/D polymorphism and increased risk of RPL under the homozygote model (II versus DD: OR = 0.693, 95% CI = 0.545–0.881, p= 0.003) and the recessive model (II versus ID + DD: OR = 0.787, 95% CI = 0.643–0.964, p= 0.021) in studies in accordance with HWE.

Sensitivity Analyses

Sensitivity analysis was conducted to confirm the stability and liability of the meta-analysis by sequential omission of each eligible study. The results showed that the significance of the OR was not materially changed by any single study (data not showed), indicating the stability of our results. In addition, after the removal of studies with low quality (departure from the HWE), the corresponding pooled ORs were not significantly changed.

Test of Heterogeneity

As shown in Table 3, there was a significant moderate to high heterogeneity among these studies for ACE I/D polymorphism in overall comparisons under all five genetic models, that is, allele (I2= 80.49%, PH ≤ 0.001), homozygote (I2= 55.47%, PH ≤ 0.001), heterozygote (I2= 60.21%, PH ≤ 0.001), dominant (I2= 73.79%, PH ≤ 0.001) and recessive model (I2= 57.96%, PH ≤ 0.001). Then, we assessed the source of heterogeneity by subgroup analyses. The I2 decreased obviously and the p value exceeded 0.05 among West-Asian studies under four genetic models, namely, homozygote (I2= 14.57%, PH= 0.0309), heterozygote (I2= 46.75%, PH= 0.051), dominant (I2= 41.65%, PH= 0.080) and recessive model (I2= 0.00, PH= 0.569), indicating that these studies were the major source of heterogeneity. However, we found that studies conducted in Caucasians and East-Asians, number of RM, and studies' quality did not contribute to heterogeneity (Table 3).

Publication Bias

Publication bias of the selected articles was assessed by the funnel plot and Egger's linear regression. The shape of the funnel plot did not reveal any evidence of obvious asymmetry (Fig. 3A and B). Similarly, no evidence of publication bias was observed by the Egger's test (Table 3).

Fig. 3
Funnel plot for publication bias in the meta-analysis of the ACE I/D polymorphism and RPL. (A) represents the allele model (I versus D); and (B) represents the dominant model (II + ID versus DD).

Minor Allele Frequency (MAF)

The minor allele frequencies (MAFs) of the ACE I/D polymorphism by ethnicity are presented in Tables 1 and 2. The allele and genotype distributions of ACE I/D polymorphism exhibited ethnic variations. The ACE I allele frequency in the Caucasian, West-Asian and East-Asian populations were 51.50% (42.20–60.80%), 42.80% (24.0–61.60%), and 68.75% (56.50–81.0%), respectively. Therefore, the ACE I allele frequency in East-Asian populations was higher than in the other populations (Fig. 3).

Discussion

The present meta-analysis was conducted to systematically identify the association between ACE I/D polymorphism with risk of RPL. In the present meta-analysis, a significant association of the ACE I/D polymorphism with risk of RPL was found under the homozygote and recessive genetic models, and in subgroup analysis, among the Caucasian and West-Asian populations. However, for East-Asians, the results indicated that the ACE I/D polymorphism was not associated with increased risk of RPL. The inconsistent results between East-Asians on subgroup analysis and pooled estimates may be caused by genetic diversity and environmental factors among different ethnicities. Furthermore, as RPL is a multifactorial condition, beside genetic factors, internal and external factors play a major role in RPL etiology. Therefore, this discrepancy might be due to other factors, such as untreated hypothyroidism, uncontrolled diabetes mellitus, certain uterine anatomic abnormalities, and antiphospholipid antibody syndrome (APS). Moreover, stratified analysis according to number of RM revealed a significantly increased risk of RPL with the ACE I/D polymorphism in those studies with ≥ 2 RM, but not in studies with ≥ 3 RM. This finding is possible because the number of studies with ≥ 2 RM included to the meta-analysis was higher than the number of studies with ≥ 3 RM. Two previous meta-analyses by Su et al1616 SuMT, Lin SH, Chen YC, Kuo PL. Genetic association studies of ACE and PAI-1 genes in women with recurrent pregnancy loss: a systematic review and meta-analysis. Thromb Haemost 2013; 109(01):8-15. Doi: 10.1160/TH12-08-0584
https://doi.org/10.1160/TH12-08-0584...
and Yang et al1717 Yang C, Fangfang W, Jie L, et al. Angiotensin-converting enzyme insertion/deletion (I/D) polymorphisms and recurrent pregnancy loss: ameta-analysis. JAssistReprodGenet2012;29(11):1167-1173. Doi: 10.1007/s10815-012-9870-3
https://doi.org/10.1007/s10815-012-9870-...
also estimated the association between ACE I/D polymorphism and risk of RPL. Their results have confirmed that ACE I/D polymorphism is associated with the risk of RPL in overall estimates. However, their result was basically inconsistent with the present meta-analysis results, which show that ACE I/D polymorphism may not contribute to the susceptibility of RPL in Caucasians.

To further interpret the present meta-analysis results, it is necessary to clarify the difference between this meta-analysis and the previous one. More recently, Su et al1616 SuMT, Lin SH, Chen YC, Kuo PL. Genetic association studies of ACE and PAI-1 genes in women with recurrent pregnancy loss: a systematic review and meta-analysis. Thromb Haemost 2013; 109(01):8-15. Doi: 10.1160/TH12-08-0584
https://doi.org/10.1160/TH12-08-0584...
performed a meta-analysis including 11 studies with 1,275 RPL cases and 2,049 controls; the study discussed the association between ACE I/D polymorphism and the risk of RPL.1616 SuMT, Lin SH, Chen YC, Kuo PL. Genetic association studies of ACE and PAI-1 genes in women with recurrent pregnancy loss: a systematic review and meta-analysis. Thromb Haemost 2013; 109(01):8-15. Doi: 10.1160/TH12-08-0584
https://doi.org/10.1160/TH12-08-0584...
Their results showed a significant association between ACE I/D polymorphism and risk of RPL. In addition, their results suggested the ACE I/D polymorphism might not increase the risk of RPL in Caucasian and non-Caucasian populations. However, they only enrolled 11 case-control studies and discussed the RPL risk only under 2 dominant and recessive genetic models. Hence, it may significantly affect their overall results and subgroup results. By contrast, the present meta-analysis included 26 relevant case-control studies with higher numbers of the cases and controls and discussed the RPL risk under all 5 genetic models. In addition, we evaluated the association by quality of studies, while the prior meta-analysis did not conduct any study quality assessment. Besides, the meta-analysis by Yang et al,1717 Yang C, Fangfang W, Jie L, et al. Angiotensin-converting enzyme insertion/deletion (I/D) polymorphisms and recurrent pregnancy loss: ameta-analysis. JAssistReprodGenet2012;29(11):1167-1173. Doi: 10.1007/s10815-012-9870-3
https://doi.org/10.1007/s10815-012-9870-...
in 2012, reported that the ACE I/D polymorphism is associated with an increased risk of RPL in Asians and not in Caucasians, but their meta-analysis only included 9 studies with 1,264 RPL cases and 845 controls. To the best of our knowledge, the present meta-analysis was the most comprehensive meta-analysis on the association of ACE I/D polymorphism and the risk of RPL, which can provide results with greater statistical power. Moreover, with newly added case-control studies, we performed subgroup analyses to further interpret the results.

Between-study heterogeneity is a common and potential problem when interpreting the results of all meta-analyses, which should be explored in the meta-analysis.5050 Forat-Yazdi M, Jafari M, Kargar S, et al. Association between SULT1A1 Arg213His (Rs9282861) polymorphism and risk of breast cancer: a systematic review and meta-analysis. J Res Health Sci 2017;17(04):e00396 5151 JafariNedooshan J, Forat Yazdi M,Neamatzadeh H, Zare ShehnehM, Kargar S, Seddighi N. Genetic association of XRCC1 gene rs1799782, rs25487 and rs25489 polymorphisms with risk of thyroid cancer: a systematic reviewandmeta-analysis. Asian Pac J Cancer Prev 2017; 18(01):263-270. Doi: 10.22034/APJCP.2017.18.1.263
https://doi.org/10.22034/APJCP.2017.18.1...
5252 Jafari Nedooshan J, Kargar S, Neamatzadeh H, Haghighi F, Dehghani Mohammad Abadi R, Seddighi N. Lack of association of the fat mass and obesity associated (FTO) gene rs9939609 polymorphism with breast cancer risk: a systematic review and meta-analysis based on case - control studies. Asian Pac J Cancer Prev 2017;18(04): 1031-1037. Doi: 10.22034/APJCP.2017.18.4.1031
https://doi.org/10.22034/APJCP.2017.18.4...
There are several factors responsible for such heterogeneity, such as the diverse genotype distribution of ACE I/D polymorphism in different ethnicity, sample sizes, genetic backgrounds for cases and controls, diversity in study designs, inclusion criteria, and genotyping methods.5353 Sadeghiyeh T, Hosseini Biouki F, Mazaheri M, Zare-Shehneh M, Neamatzadeh H, Poursharif Z. Association between Catechol-OMethyltransferase Val158Met (158G/A) polymorphism and suicide susceptibility: a meta-analysis. J Res Health Sci 2017;17(02): e00383 In the current study, significant heterogeneity was found in the association of ACE I/D polymorphism with RPL risk under all genetic models. Therefore, we have performed meta-regression and subgroup analyses to explore the sources of between-study heterogeneity. The results suggested that ethnicity was not the source of heterogeneity. Sensitivity analysis revealed that the removing of any single study did not have significant impact on the overall meta-analysis estimate. Moreover, the funnel plot did not reflect considerable asymmetry and the Egger's test also indicated no obvious publication bias. All these made the present meta-analysis results reliable to some extent.

The present meta-analysis had several strengths. Most importantly, it the biggest, most comprehensive and most recent meta-analysis of the association between ACE and the risk of RPL. Therefore, it was more powerful than previous cohort and case-control studies. Even though there were 26 case-control studies in our meta-analysis, its limitations should be pointed out. First, the number of studies was moderate, especially in subgroup analyses, thus limiting the interpretation of results in our analysis. Second, the study population in our meta-analysis focused on Caucasians and Asians. In the present meta-analysis, the sample size and numbers of studies in African groups and mixed groups were not adequate to evaluate any association. Thus, the conclusion may not be suitable for Africans. Second, there was significant between-study heterogeneity in all genetic models. Heterogeneity is a problem that may affect the precision of overall results. Third, the meta-analysis was based on data that had not been adjusted for the main confounding variables, such as age, gestation age at miscarriage, number of previous abortions, environmental factors and so on, which might have caused serious confounding bias. To provide a more reliable estimation of the association, more studies with a better design and a larger sample size are needed. Finally, gene–gene, gene–environment, or even different polymorphism loci of the ACE gene were not fully addressed in the meta-analysis due to lack of relevant data.

Conclusion

In conclusion, although there was significant heterogeneity in the studies included, our meta-analysis suggests that ACE I/D polymorphism is associated with increased risk of RPL, especially in the Caucasian and West-Asian populations. However, more studies, well-designed and with a large sample, are needed to give a more reliable estimation of the association between ACE I/D polymorphism and the risk of RPL.

Acknowledgments

The authors would like to thank Dr. SeyedMahdi Kalantar for her assisting in data collection.

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Publication Dates

  • Publication in this collection
    Oct 2018

History

  • Received
    01 Feb 2018
  • Accepted
    12 June 2018
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