An Endothelial Nitric Oxide Synthase Gene Polymorphism is Associated with Preeclampsia

Association of endothelial nitric oxide synthase gene variants in pre-eclampsia: an updated systematic review and meta-analysis

INTRODUCTION

Three common endothelial nitric oxide synthase (eNOS) gene variants are existed such as; G-894T, T-786C, and variable number tandem repeats in intron-4 (VNTR intron-4) which has been proposed to be linked with PE. However, there is still debate regarding the findings. To address this, a review was conducted to assess the potential association of eNOS gene variants at these positions with the risk of PE.

METHODS

PubMed, Scopus, Science Direct, Hinari, and African Journal Online databases and Google Scholar search engines were utilized to search studies published in English-language until 30 January 2023. The Joanna Briggs Institute Meta-Analysis instrument was used for data extraction process and the Newcastle-Ottawa Scale was used to appraise the quality of the included studies. Meta-regression analysis was conducted using Stata 14 statistical software. The pooled odds ratios (ORs) of fixed and random effect models were utilized to evaluate the association of eNOS gene polymorphism with the risk of PE at 95% CI. Publication bias was assessed using Egger's test and a funnel plot.

RESULTS

The study included 47 observational studies involving 13,795 pregnant women (6216 cases and 7579 controls). Pregnant women carrying TT and CC genotypes of eNOS gene at 894 and 786 positions were found to have a greater probability of developing PE as compared to GG and TT genotypes (OR = 1.54 vs. 1.43 and CI: 1.12 - 2.14 vs.1.02 - 2.00 at 95% CI), respectively. However, a significant association was not observed between aa genotype of eNOS gene in VNTR intron-4 region and risk of PE as compared to bb genotype (OR =1.26, 95% CI: 0.83 - 1.89). The allelic model of eNOS gene at all positions showed nonsignificant association with the risk of PE.

CONCLUSIONS

The women having eNOS gene variants at 894 and 786 positions showed a significant association with the risk of PE. Yet, the women having eNOS gene variant at intron-4 region showed nonsignificant association with the risk of PE. Thus, this study suggests that eNOS gene variants may play a role in the development of PE, but large-scale studies are required to inaugurate concrete evidence on the roles of eNOS gene variants in PE pathogenesis.

Association Between Endothelial Nitric Oxide Synthase (eNOS) -786 T/C and 27-bp VNTR 4b/a Polymorphisms and Preeclampsia Development

The aim of the present study was to analyze the distribution of genotypes and haplotypes of functional eNOS gene polymorphisms in the promoter (-786 T/C), intron 4 (VNTR4b/a) and exon 7 (894 G/T), in Serbian population of pregnant women, and establish a possible association between these polymorphisms and preeclampsia development. DNA was isolated from venous blood samples of 50 heathy pregnant women and 50 preeclampsia patients. Polymerase Chain Reaction/Restriction Fragment Length Polymorphism (PCR/RFLP) technique, with appropriate sets of primers and specific restriction enzymes, was used to determine polymorphisms in eNOS gene. Statistical analysis was done using the SPSS and HAPLOVIEW software packages. eNOS -786 T/C polymorphism was significantly associated with preeclampsia (P = 0.006). Homozygotes for the VNTR polymorphism had also an elevated risk of developing preeclampsia (OR=7.68, 95%CI (0.89-65.98)), especially the mild (OR=9.33, 95%CI (0.98-88.57)) and late form (OR=8.52, 95%CI (0.90-80.58)). The 894 G/T polymorphism was not associated with preeclampsia. "G-C-b" and "T-4a-T" haplotypes were more frequent in preeclampsia, though without reaching statistical significance. -786 T/C and VNTR 4b/a eNOS gene polymorphisms were associated with preeclampsia risk in Serbian patients.

The VNTR polymorphism of the endothelial nitric oxide synthase gene and blood pressure in women at the end of pregnancy

OBJECTIVE

Examine the association of the 4a/4b polymorphism of endothelial nitric oxide synthase (eNOS) with blood pressure in women at late pregnancy.

MATERIALS AND METHODS

Blood pressure before pregnancy and at the end of gestation (37-40-week term) was measured in 588 women of the Russian ancestry. The women were divided into groups according to the body mass index and the presence of preeclampsia at late pregnancy. The 4a/4b polymorphism of the eNOS gene was genotyped using PCR with subsequent screening of amplified fragment length polymorphisms.

RESULTS

The 4a4a eNOS genotype was associated with higher levels of diastolic blood pressure in pregnant women and with more pronounced dynamics of the diastolic and mean arterial pressure in the development of pregnancy (p = 0.02-0.03). Pregnant women with the 4a4a genotype and increased body mass index had higher systolic, diastolic, and mean arterial pressure (p = 0.001-0.009). In pregnant women with preeclampsia, the 4a4a genotype was associated with higher level of diastolic blood pressure at the end of pregnancy (p = 0.04), whereas in the women without preeclampsia this genotype was associated with more pronounced changes of blood pressure at pregnancy (p = 0.02).

CONCLUSION

The results of our study suggest that the genotype 4a4a of the eNOS gene is associated with higher levels of blood pressure in women at the end of pregnancy.

Endothelial nitric oxide synthase polymorphisms affect the changes in blood pressure and nitric oxide bioavailability induced by propofol

Propofol anesthesia is usually accompanied by hypotension, which is at least in part related to enhanced endothelial nitric oxide synthase (NOS3)-derived NO bioavailability. We examined here whether NOS3 polymorphisms (rs2070744, 4b/4a VNTR, rs3918226 and rs1799983) and haplotypes affect the changes in blood pressure and NO bioavailability induced by propofol. Venous blood samples were collected from 168 patients at baseline and after 10 min of anesthesia with propofol 2 mg/kg administered intravenously by bolus injection. Genotypes were determined by polymerase chain reaction and haplotype frequencies were estimated. Nitrite concentrations were measured by using an ozone-based chemiluminescence assay, while NOx (nitrites + nitrates) levels were determined by using the Griess reaction. We found that CT + TT genotypes for the rs3918226 polymorphism, the ba + aa genotypes for the 4b/4a VNTR and the CTbT haplotype were associated with lower decreases in blood pressure and lower increases in nitrite levels after propofol anesthesia. On the other hand, the TCbT and CCbT haplotypes were associated with more intense decreases in blood pressure and higher increases in nitrite levels in response to propofol. Our results suggest that NOS3 polymorphisms and haplotypes influence the hypotensive responses to propofol, possibly by affecting NO bioavailability.

Polymorphisms of Thrombophilic and Vasoactive Genes and Severe Preeclampsia: A Pilot Study

OBJECTIVE

Carriage of thrombophilic and vasoactive polymorphic alleles has been associated with various pregnancy complications. The effect of carrying multiple polymorphisms is not known. We conducted a case-control study to determine the association between eight polymorphisms of thrombophilic and vasoactive genes and the risk of severe preeclampsia.

METHODS

The following polymorphisms were analyzed by sequencing-on-chip-technology using solid-phase polymerase chain reaction on oligonucleotide microarrays: factor 5 (F5) Leiden, factor 2 (F2)-prothrombin G20210A, plasminogen activator inhibitor (PAI)-1 4G/5G, nitric oxide synthase (NOS) 3 T768C, NOS 3 Glu298Asp, angiotensinogen (AGT) Met235Thr, estrogen receptor (ER) alpha Pvu II, and mineralcorticoid receptor (MLR) Ser810Leu. The study comprised 24 patients with severe preeclampsia and 24 controls from a cohort of consecutive white women treated at the Obstetrics Department of the University of Vienna Medical School. Genotypes were correlated with clinical data.

RESULTS

The investigated polymorphisms did not influence the risk of severe preeclampsia independently. When separately considering the simultaneous carriage of multiple thrombophilic or vasoactive polymorphisms, neither the combined carriage of thrombophilic polymorphisms (F5 Leiden, F2 G20210A, PAI-1 4G/5G), nor the combined carriage of vasoactive polymorphisms (NOS 3 T768C, NOS 3 Glu298Asp, AGT Met235Thr) conferred an increased risk of severe preeclampsia. Cumulative genotype frequencies for at least two homozygous mutant genotypes, however, were nine of 24 (38%) and two of 24 (8%) for the study and control groups, respectively (P <.05). All of these nine women with severe preeclampsia had at least two homozygous mutant genotypes of four polymorphisms, ie, F5 Leiden, NOS 3 T768C, NOS 3 Glu298Asp, or ER alpha Pvu II.

CONCLUSION

Our data fail to document an independent significant influence of the investigated polymorphisms on the risk of severe preeclampsia. In an attempt to build a multigenetic model of severe preeclampsia, the combination of F5 Leiden, NOS 3 T768C, NOS 3 Glu298Asp, and ER alpha Pvu II was the most effective combination to predict the presence of severe preeclampsia in this small series of white women.

Endothelial nitric oxide synthase: From biochemistry and gene structure to clinical implications of NOS3 polymorphisms

Nitric oxide (NO) is an important vasodilator with a well-established role in cardiovascular homeostasis. While mediator is synthesized from L-arginine by neuronal, endothelial, and inducible nitric oxide synthases (NOS1,NOS3 and NOS2 respectively), NOS3 is the most important isoform for NO formation in the cardiovascular system. NOS3 is a dimeric enzyme whose expression and activity are regulated at transcriptional, posttranscriptional,and posttranslational levels. The NOS3 gene, which encodes NOS3, exhibits a number of polymorphic sites including single nucleotide polymorphisms (SNPs), variable number of tandem repeats (VNTRs), microsatellites, and insertions/deletions. Some NOS3 polymorphisms show functional effects on NOS3 expression or activity, thereby affecting NO formation. Interestingly, many studies have evaluated the effects of functional NOS3 polymorphisms on disease susceptibility and drug responses. Moreover, some studies have investigated how NOS3 haplotypes may impact endogenous NO formation and disease susceptibility. In this article,we carried out a comprehensive review to provide a basic understanding of biochemical mechanisms involved in NOS3 regulation and how genetic variations in NOS3 may translate into relevant clinical and pharmacogenetic implications.

Polymorphisms in oxidative stress-related genes are associated with nasopharyngeal carcinoma susceptibility

Nasopharyngeal carcinoma (NPC) is a complex multifactorial disorder involving both genetic and environmental factors. Polymorphisms of genes encoding nitric oxide synthase (NOS) and antioxidant glutathione-S transferases (GSTs) have been associated with various tumors. We examined the combined role of NOS3, NOS2 and GST polymorphisms in NPC risk in Tunisians. We found that NOS3−786C allele and −786 CC genotype, NOS3+894T allele and +894 GT+TT genotypes, NOS2−277 G allele and −277 GG genotype, and GSTT1 del/del genotype, are more prevalent in NPC patients as compared to healthy controls. Our results suggest that genetically driven dysfunction in red–ox stress pathway could augment the risk in NPC-susceptible individuals.

Polymorphisms in endothelial nitric oxide synthase gene in early and late severe preeclampsia

Preeclampsia (PE) is characterized by hypertension and proteinuria, occurring after the 20th week of pregnancy in women who have had no previous symptoms. The disease progresses with generalized vasoconstriction and endothelial dysfunction. Clinically, it is important to diagnose the severe form of the disease (sPE), in which blood pressure and proteinuria are much higher. Recently, the gestational age (GA) of the onset of PE has led to the classification of this disease as early (GA <34 weeks) and late (GA ≥34 weeks). Several genetic polymorphisms affecting endothelial nitric oxide synthase (eNOS) levels or function were described, including G894T (Glu298Asp), VNTR b/a (variable-number 27-bp tandem repeat) and T-786C (promoter) polymorphisms. Thus, the aim of this study was to compare the distribution of G894T, VNTR b/a and T-786C polymorphisms and their haplotypes in Brazilian early and late sPE, as well as in normotensive pregnant. A total of 201 women were evaluated, 53 with early sPE, 45 with late sPE and 103 as normotensive pregnant women. The frequency of 894T allele was higher in late sPE vs normotensive pregnant, and 894TT genotype was higher in late sPE vs early sPE and normotensive pregnant. For VNTR b/a polymorphism, higher frequencies of aa genotype and a allele were observed in early sPE vs late sPE and normotensive pregnant. Besides, the frequency of haplotype T-b-C was higher in late sPE vs early sPE and normotensive pregnant. Considering the results found for eNOS polymorphisms, it is possible to suggest that the functional alterations induced by these two polymorphisms may influence the time of severe PE onset, although both alterations are putatively associated with low NO bioavailability. However, other studies are necessary to validate these findings and clarify this issue.

eNOSI4 and EPHX1 polymorphisms affect maternal susceptibility to preeclampsia: analysis of five polymorphisms predisposing to cardiovascular disease in 279 Caucasian and 241 African women

PURPOSE

The aim of this study was to evaluate possible associations of genetic polymorphisms predisposing to cardiovascular disease with the development and/or the severity of preeclampsia.

METHODS

A two hospital-based prospective case-control study was performed in Germany and Ghana. 470 blood samples of 250 Caucasian and 220 black African have been genotyped by pyrosequencing and fragment length analysis. We evaluated the distribution of the epoxide hydrolase 1 (EPHX1) polymorphism on exon 3, the endothelial nitric oxide synthase (eNOS) polymorphisms on exon 7 and on intron 4, the angiotensinogen polymorphism on exon 2 and the estrogen receptor 1 polymorphism in intron 1.

RESULTS

74 Caucasian and 84 African were classified as preeclampsia with 27 Caucasian developing a hemolysis, elevated liver enzymes and low platelets (HELLP) syndrome and 17 African women experiencing eclampsia. Multivariate logistic regression analysis adjusting for ethnicity, age and parity revealed for carriers of eNOSI4 VNTR4a a 1.7-fold increased (95% CI 1.10-2.711, p = 0.016) risk to develop preeclampsia and a 3.6-fold increase for carriers of the EPHX1 113Tyr (95% CI 1.366-8.750, p = 0.009) to develop severest preeclampsia.

CONCLUSION

Our finding of eNOSI4 polymorphism predisposing to preeclampsia independently of ethnicity, age and parity supports the concept of NO being involved in the endothelial disorder preeclampsia. Since EPHX1 is highly expressed in the liver, can interact with various signaling pathways and is involved in central nervous system disorders, the association of EPHX1 polymorphism with the HELLP syndrome and eclampsia may hint to EPHX being a further key player in the pathogenesis of preeclampsia.

The polymorphism for endothelial nitric oxide synthase gene, the level of nitric oxide and the risk for pre-eclampsia: a meta-analysis

Endothelial NO, which is synthesized by endothelial nitric oxide synthase (eNOS), has been reported to be related with the occurrence of pre-eclampsia (PE). However, the polymorphisms of eNOS (-786 T>C, 4b/a and G894T), the level of nitric oxide and the risk of PE remain unclear. Thus we performed this meta-analysis to determine the associations between them in order to predict the risk for PE and interference with PE development in the early period of antenatal care. All studies investigating the associations between PE risk and polymorphisms of eNOS, or PE risk and serum concentration of NO were reviewed. Finally, 29 studies were included, involving 11 for -786 T>C, 11 for 4b/a, and 22 for G894T polymorphisms and PE risk. In the overall analysis, -786 T>C polymorphism was found to be related with increased PE risk in the dominant model (OR=1.17, 95% CI=1.02-1.35). a allele for 4b/a suffers the high risk of PE (OR=1.46, 95% CI=1.01-2.10). In the subgroup analysis, significantly increased risk was detected among Europeans for -786 T>C polymorphism (OR=1.40, 95%CI=1.14-1.73).However, no significant association was detected for G894T polymorphism in the overall and subgroup analysis. The comprehensive evaluation of 9 available studies indicated that serum NO level was significantly decreased in case group (SMD=-0.96 umol/mL, 95%CI=-1.80, -0.12 umol/mL).Hence, we concluded that eNOS gene -786 T>C and 4b/a except for G894T polymorphisms were contributed significantly to PE risk, especially for Europeans, and a low NO concentration in serum increased the risk for PE.

eNOS tag SNP haplotypes in hypertensive disorders of pregnancy

Haplotypes formed by polymorphisms (T-786C, rs2070744; a variable number of tandem repeats in intron 4, and Glu298Asp, rs1799983) of the eNOS gene were associated previously with gestational hypertension (GH) and preeclampsia (PE). However, no study has explored the Tag SNPs rs743506 and rs7830 in these disorders. The aim of the current study was to compare the distribution of the genotypes and haplotypes formed by the five eNOS polymorphisms mentioned among healthy pregnant (HP, n=122), GH (n=138), and PE (n=157). The haplotype formed by "C b G G C" was more frequent in HP compared to GH and PE (p=0.0071), which is supported by previous findings that demonstrated the association of the combination "C b G" with a higher level of nitrite (NO marker). Our results suggest a protective effect of the haplotype "C b G G C" against the development of hypertensive disorders of pregnancy.

Polymorphisms of the endothelial nitric oxide synthase (NOS3) gene in preeclampsia: a candidate-gene association study

BACKGROUND

The endothelial nitric oxide synthase gene (NOS3) has been proposed as a candidate gene for preeclampsia. However, studies so far have produced conflicting results. This study examines the specific role of variants and haplotypes of the NOS3 gene in a population of Caucasian origin.

METHODS

We examined the association of three common variants of the NOS3 gene (4b/a, T-786C and G894T) and their haplotypes in a case-control sample of 102 patients with preeclampsia and 176 women with a history of uncomplicated pregnancies. Genotyping for the NOS3 variants was performed and odds ratios and 95% confidence intervals were obtained to evaluate the association between NOS3 polymorphisms and preeclampsia.

RESULTS

The single locus analysis for the three variants using various genetic models and a model-free approach revealed no significant association in relation to clinical status. The analysis of haplotypes also showed lack of significant association.

CONCLUSIONS

Given the limitations of the candidate-gene approach in investigating complex traits, the evidence of our study does not support the major contributory role of these common NOS3 variants in preeclampsia. Future larger studies may help in elucidating the genetics of preeclampsia further.

Variable effects of maternal and paternal-fetal contribution to the risk for preeclampsia combining GSTP1, eNOS, and LPL gene polymorphisms

Objective

To evaluate the maternal, paternal, and fetal genotype contribution to preeclampsia.

Study design, materials, and methods

We combined the analysis of polymorphisms of the GSTP1, eNOS, and LPL genes – affecting biotransformation enzymes and endothelial function – in a cohort of 167 preeclamptic and normal control trios (mother, father, and child) comprising a total of 501 samples in the Greek population, never analyzed before by this approach.

Results

For the frequency of the GSTP1 Ile¹⁰⁵/Val¹⁰⁵, the eNOS Glu298Asp and the LPL-93 polymorphisms, statistically significant differences were found between the two groups. However, the transmission rates of the parental alleles to neonates studied by the transmission disequilibrium test, disclosed no increased rate of transmission to preeclampsia children for the variant alleles of Val¹⁰⁵ GSTP1, 298Asp eNOS, and -93G LPL.

Conclusions

These novel data, suggest that interaction of all three types of genotypes (mother, father and neonate), reveals no effects on the development of preeclampsia, but provide the impetus for further studies to decipher the individual contribution of each genetic parameter of preeclampsia.

The significance of -786T > C polymorphism of endothelial NO synthase (eNOS) gene in severe preeclampsia

OBJECTIVE

Preeclampsia (PE) is believed to be induced by endothelial cell dysfunction in placenta. Highly polymorphic endothelial nitric oxide synthase (eNOS) activity belongs to the factors significantly influencing vaso-motor tone in placenta and PE susceptibility. The aim of this study was to evaluate prevalence of -786T/C polymorphism of eNOS gene in the groups of women with mild and severe PE.

STUDY DESIGN

The study was performed in the group of 218 preeclamptic (including 136 with severe PE) and of 400 normotensive healthy women delivered normally after a healthy gestation. The eNOS -786T/C polymorphism was determined using PCR/RFLP assay. Additionally, detailed correlation between eNOS genotypes and clinical/laboratory data in the PE group has been analyzed.

RESULTS

The higher frequency of mutated homozygous CC genotypes (17.4% vs. 11.5% in controls, OR 1.62, n.s.) and of C alleles (allelic frequency 44.1 vs. 36.6%; OR 1.36, p = 0.012) in the group of PE has been determined. Furthermore, in the group of severe PE the overrepresentation of mutated CC genotypes (23.5% vs. 11.5%, OR 2.37, p = 0.0014) and mutated C alleles (47.8 vs. 36.6%, OR 1.58, p = 0.0016) has been found.

CONCLUSIONS

The presence of mutated homozygous CC genotype and C allele of -786T/C polymorphism of eNOS gene influences the higher susceptibility to develop severe PE development.

Endothelial nitric oxide synthase, angiotensin-converting enzyme and angiotensinogen gene polymorphisms in hypertensive disorders of pregnancy

We investigated the variations in genes encoding endothelial nitric oxide synthase (NOS3), angiotensin-converting enzyme (ACE) and angiotensinogen (AGT) in hypertensive disorders of pregnancy and the relationship between the polymorphisms and circulating nitric oxide (NO) and ACE levels in pregnant north Indian women. Frequencies of NOS3 G894T, 4b/a and T(-786) --> C, AGT T704C and ACE ins/del polymorphisms were studied in 342 subjects: 120 with preeclampsia (PE), 104 with gestational hypertension and 118 normotensive pregnant women. Variations were evaluated by polymerase chain reaction-restriction fragment length polymorphism. NO and ACE levels were determined using ELISA. There was no difference in the distribution of individual NOS3 and ACE polymorphisms in the study groups. Haplotype analysis showed a global difference in the NOS3 haplotype distribution between the PE and non-PE subjects (P=0.03). The presence of AGT 704C allele was associated with a reduced risk of developing PE (odds ratio: 0.33, 95% CI: 0.19-0.59 in recessive mode). Circulating total NO and ACE levels were similar in three groups. No relationship was found between circulating NO levels and any of the NOS3 polymorphisms, but the circulating ACE levels were higher in those with DD genotype (P<0.05). In conclusion, there was no association between individual NOS3 and the ACE gene polymorphisms and hypertensive disorders of pregnancy in north Indian women. The presence of minor alleles at all the three sites in NOS3 seemed to increase the risk of PE, and AGT 704C allele was associated with a reduced PE risk. The complexity of interaction between these genetic abnormalities requires further studies.

The genetic aspects of pre-eclampsia: achievements and limitations

Pre-eclampsia, a life-threatening disease during pregnancy, is a leading cause of global maternal mortality. Although there is substantial evidence of a genetic background, the complexity of the processes involved and nature of the maternal-fetal phenomenon do not make the search for the causative genes easy. Recent retrospective studies on the subject suggest the heritable allelic variations, particularly the utero-placental renin-angiotensin system with defective placental vascular development, could become the cornerstone for the genetics of pre-eclampsia and hence might well be associated with such defective development. Moreover, the role of immune mechanisms (immune maladaptation) deserves not to be ignored. Large-scale studies entailing genomewide scanning, sib-pair linkage analysis, and family-based association studies with appropriate power to detect genes with a lower relative risk are necessary to understand the puzzle of the disease. Moreover, recently, the importance of epigenetic features and the effect of imprinted genes related to trophoblast growth as well as fetal development on hypertension in pregnancy have been highlighted. All these possibilities are intuitively attractive and are supported by some circumstantial evidence. Although the consistent tenor of a series of papers instill some confidence, we need meticulously designed larger-scale investigations including large numbers of affected women and their babies to provide the analytic stringency essential to study the polygenic multifactorial basis of pre-eclampsia.

Endothelial nitric oxide synthase gene influences the risk of pre-eclampsia, the recurrence of negative pregnancy events, and the maternal-fetal flow

OBJECTIVES

Pre-eclampsia is associated with vascular endothelial dysfunction, adverse pregnancy outcome and cardiovascular disease in later life. An inadequate nitric oxide availability related to polymorphisms in the endothelial nitric oxide synthase gene (eNOS) might predispose to the disease.

METHODS

We investigated the role of eNOS T-786C, G894T and 4a4b polymorphisms in predisposing to both pre-eclampsia and the recurrence of negative pregnancy events, per se and in the presence of angiotensin-converting enzyme (ACE) DD genotype, and investigated their influence on maternal-fetal flow in 106 non-thrombophilic women with a history of pre-eclampsia, compared with 106 women with a history of normal pregnancy.

RESULTS

No association between eNOS polymorphisms and predisposition to pre-eclampsia was found; nevertheless, the contemporary presence of eNOS 894TT and -786CC genotypes represented a susceptibility factor to the disease. In 48 out of 106 women, documented complications (pre-eclampsia and fetal growth restriction) were present in the current pregnancy. The eNOS 894TT genotype influenced the risk of recurrence of negative events (odds ratio = 5.45), particularly in contemporary women homozygous for both eNOS 894TT and ACE DD genotypes (odds ratio = 11.4). Throughout the pregnancy, a progressive alteration of maternal-fetal flow indices was found in women carrying the eNOS 894TT genotype, and this effect was strengthened in women with the contemporary presence of the ACE DD genotype.

CONCLUSIONS

An original finding is the increased risk of pre-eclampsia and recurrence of pregnancy negative events, probably by modulating the maternal-fetal flow, in women homozygous for the eNOS 894T allele previously analyzed for the ACE I/D polymorphism.

Genetic polymorphisms in vasoactive genes and preeclampsia: a meta-analysis

There are controversies in reports on the association of polymorphisms in endothelial nitric oxide synthase, angiotensinogen, angiotensin receptor type 1 and angiotensin-converting enzyme genes with an increased risk of developing preeclampsia. We performed a systematic search of published case-control studies through the PubMed database up to January 2006, and report the results of a meta-analysis of polymorphisms investigated in more than five studies: Glu298Asp in eNOS gene (9 analyses involving 1055 patients and 1788 controls), Met235Thr in AGT gene (13 analyses involving 1128 patients and 2278 controls), and intron 16 insertion-deletion polymorphism in ACE gene (10 analyses involving 1121 patients and 1361 controls). Statistically significant associations with preeclampsia were identified for the Met235Thr/AGT polymorphism: OR 1.65 (95% CI 1.19, 2.29) if the polymorphism is considered under the dominant genetic model, and OR 1.54 (95% CI 1.12, 2.11) under the recessive model. For insertion-deletion/ACE polymorphism, statistical significance was demonstrated when the polymorphism was considered under the recessive model: OR 1.51 (95% CI 1.17, 1.94). No single polymorphism was identified as having a major effect.

Endothelial nitric oxide synthase gene polymorphisms and cardiovascular disease: a HuGE review

This review examines the association of a subset of endothelial nitric oxide synthase gene (NOS3) polymorphisms (Glu298Asp, intron 4, and -786T>C) with cardiovascular disease. The Glu298Asp polymorphism within exon 7 is the only common nonsynonymous variant. The variants have been associated with low plasma nitric oxide concentrations and reduced vascular reactivity; difficulties in measuring those phenotypes means that their functional role remains unclear. A large meta-analysis of NOS3 polymorphisms in coronary heart disease revealed per-allele odds ratios of 1.17 (95% confidence interval: 1.07, 1.28) for Glu298Asp, 1.17 (95% confidence interval: 1.07, 1.28) for -786T>C, and 1.12 (95% confidence interval: 1.01, 1.24) for intron 4. However, there was evidence that small studies with more striking results could affect the associations of the Glu298Asp and -786T>C polymorphisms with coronary heart disease. Associations of NOS3 polymorphisms with hypertension, preeclampsia, stroke, and diabetes remain uncertain. To date, no reliable gene-gene or gene-environmental interactions have been described. Use of these variants in predictive testing is unlikely to be useful, although the population attributable fraction could be substantial if the modest associations are causal. The need for large-scale genetic association studies using tagging polymorphisms is warranted to confirm or refute a role of the NOS3 gene in coronary heart disease.

Recurrent early pregnancy loss and endothelial nitric oxide synthase gene polymorphisms

OBJECTIVE(S)

Studies on the relation between endothelial nitric oxide synthase (eNOS) activity in implantation and maintenance of pregnancy highlights the importance of eNOS gene polymorphisms in recurrent early pregnancy loss (REPL). We investigated the relationship between idiopathic REPL and polymorphisms in eNOS among South Indian women.

METHODS

A case-control study comprising 145 females with REPL and 99 control females. The polymorphisms studied include a 27 bp intron 4 repeat, Glu298Asp variation of exon 7 and a novel 140 A --> G polymorphism in intron 6. A polymerase chain reaction-based di-deoxy dye terminator sequencing method was used for genotyping.

RESULTS

A novel A --> G polymorphism was identified in intron 6. The more frequent b allele of intron 4 repeat was present at a frequency of 0.84 in cases as compared to 0.86 in controls (O.R 1.17); the G allele of exon 7 coding for the wild-type glutamate containing isoform was present at a frequency of 0.79 in cases and 0.83 in controls (O.R 1.30, CI 0.6-2.8). The intron 6 variant A allele was present at a frequency of 0.58 in cases and 0.45 in controls (O.R 0.59, CI 0.33-1.08). Overall, the polymorphism in intron 6, in homozygous condition, exhibited a significant association to the risk of REPL (O.R 0.43, CI 0.21-0.89), P: 0.021).

CONCLUSIONS

The present study identifies and validates a novel polymorphism in the eNOS gene which was found associated with the risk of REPL.

Polymorphisms of the Nos3 gene and unexplained late intrauterine fetal death

OBJECTIVE

Genetic polymorphisms associated with vascular diseases have been proposed to be involved in the pathogenesis of late unexplained intrauterine fetal death (IUFD). The Nos3 gene is known to regulate vascular tone via the endothelial nitric oxide synthase/nitric oxide pathway.

STUDY DESIGN

In a multicenter case-control study, we evaluated two Nos3 polymorphisms (exon 7 Glu298Asp and a 27bp-repeat in intron 4) in 92 women with IUFD and 92 healthy control women.

RESULTS

The investigated Nos3 polymorphisms were not associated with the occurrence of IUFD. In the subgroup of pregnancies affected by IUFD, women with at least one mutant allele of the Nos3 intron 4 polymorphism were diagnosed with IUFD at a significantly earlier gestational age (31.8 [standard deviation (S.D.) = 4.9] weeks versus 34.6 [S.D. = 4.8] weeks, p = 0.02) and showed a significantly reduced birth weight (2113 g [S.D. = 1028] versus 1571 g [S.D. = 568], p = 0.03).

CONCLUSION

We are the first to report on Nos3 polymorphisms and IUFD. While not being associated with the incidence of IUFD overall, the intron 4 Nos3 polymorphism might modulate the timing of IUFD in affected pregnancies.

Endothelial NO synthase genotype and risk of preeclampsia: a multicenter case-control study

Polymorphisms in the endothelial NO synthase (eNOS) gene have been evaluated as risk factors for preeclampsia. However, data from small studies are conflicting. We assessed whether eNOS genotypes alter the risk of preeclampsia in a population in which the incidence of this disorder is high. A total of 844 young pregnant women (322 preeclamptic and 522 controls) were recruited from 5 cities. Genotyping for the Glu298Asp, intron-4 and -786T-->C polymorphisms in the eNOS gene was conducted. Multivariate odds ratios (ORs) were obtained to estimate the association of individual polymorphisms and haplotypes with preeclampsia risk. No increase in the risk of preeclampsia for the intron-4 or -786T-->C polymorphisms was observed under any model of inheritance. In contrast, in women homozygous for the Asp298 allele, the adjusted OR for preeclampsia was 4.60 (95% confidence interval [CI], 1.73 to 12.22) compared with carriers of the Glu298 allele. After a multivariate analysis, carriage of the "Asp298-786C-4b" haplotype was also associated with increased risk of preeclampsia (OR, 2.11 [95% CI, 1.33 to 3.34]) compared with carriers of the "Glu298-786T-4b" haplotype. The eNOS Glu298Asp polymorphism and the Asp298-786C-4b haplotype are risk factors for preeclampsia.

Does endothelial nitric oxide synthase gene variation play a role in the occurrence of hypertension in pregnancy?

OBJECTIVE

Nitric oxide is suggested to play a role in the development of preeclampsia.

METHODS

We studied 61 patients with gestational hypertension (GH), 77 with GH and significant proteinuria (urine protein excretion > or = 300 mg/24 h), 82 with essential hypertension (EH) and 188 normotensive women with at least one normal pregnancy.

MAIN OUTCOME MEASURE(S)

A polymorphism within the constitutive endothelial nitric oxide synthase (ecNOS) gene in various types of hypertension in pregnancy was explored.

RESULTS

Allelic and genotypic frequencies did not differ between controls and case groups. A significant difference was observed between the frequency of the rare allele in GH patients and that in EH group (chi2: 4.47, P <.04). This difference approximated the significance when GH subjects with or without proteinuria were grouped (chi2 square: 3.33; P =.068). Cigarette smoking or gravidity did not interact with the ecNOS polymorphism in identifying different types of hypertension in this setting.

CONCLUSION

Our findings argue against an association between ecNOS polymorphism and preeclampsia and support the hypothesis for a different pathogenesis of GH in respect to EH.

Searching for preeclampsia genes: the current position

Although there is substantial evidence that preeclampsia has a genetic background, the complexity of the processes involved and the fact that preeclampsia is a maternal-fetal phenomenon does not make the search for the molecular basis of preeclampsia genes easy. It is possible that the single phenotype 'preeclampsia' in fact should be divided into different sub-groups on genetic or biochemical level. In the present review, the preeclampsia phenotype and its pathophysiologic features are discussed. Family studies and postulated inheritance models are summarized. A systematic overview is given on the numerous candidate gene studies and gene-expression studies performed so far and on the currently available genome-wide scan data. Despite extensive research the molecular genetic basis of preeclampsia remains unclear. Future studies will hopefully enhance our insights in the molecular pathogenesis of preeclampsia.