C677T methylenetetrahydrofolate reductase polymorphism is not a risk factor for pre-eclampsia/eclampsia among Australian women

Folate metabolism gene polymorphisms MTHFR C677T and A1298C and risk for preeclampsia: a meta-analysis

OBJECTIVES

MTHFR C677T and A1298C have been associated with the risk of preeclampsia (PE), but with conflicting results. We performed this meta-analysis to derive a more precise estimation of the association between MTHFR polymorphisms and PE.

STUDY DESIGN

An electronic search of PubMed and Chinese Biomedicine database was conducted to select studies for meta-analysis. 54 case controlled studies containing MTHFR C677T and A1298C gene polymorphisms were chosen, and odds ratio (OR) with confidence interval (CI) was used to assess the strength of this association.

RESULT

These studies evaluated 7398 cases and 11230 controls for MTHFR C677T. The overall results suggested that MTHFR C677T was associated with the risk of PE. (T vs. C: OR = 1.157, 95% CI: 1.057-1.266, p = 0.002; TT + CT vs. CC: OR = 1.165, 95% CI : 1.049-1.293, P = 0.004; TT vs. CT + CC: OR = 1.371, 95% CI: 1.153-1.63, p < 0.001). We also evaluated 1103 cases and 988 controls for MTHFR A1298C but could not demonstrate an increased risk of PE for this polymorphism (p = 0.667). A symmetric funnel plot, the Egger's test (p = 0.819) suggested a lack of publication bias.

CONCLUSION

This meta-analysis supports the idea that MTHFR C677T genotype is associated with increased risk for PE, especially in the case of Asians and Caucasians.

Hypertension in pregnancy is associated with elevated homocysteine levels later in life

OBJECTIVE

Hyperhomocysteinemia is associated with an elevated cardiovascular disease risk. We examined whether women with a history of hypertension in pregnancy are more likely to have a high level of serum homocysteine decades after pregnancy.

STUDY DESIGN

Serum homocysteine was measured at a mean age of 60 years in nulliparous women (n = 216), and women with a history of normotensive (n = 1825) or hypertensive (n = 401) pregnancies who participated in the Genetic Epidemiology Network of Arteriopathy (GENOA) study. Relationships between homocysteine and pregnancy history were examined by linear and logistic regression, controlling for multiple covariates including personal and family history of hypertension, diabetes, obesity, tobacco use, and demographics.

RESULTS

A history of hypertension in pregnancy, when compared with normotensive pregnancy, was associated with a 4.5% higher serum homocysteine level (P = .015) and 1.60-fold increased odds of having an elevated homocysteine (95% confidence interval, 1.15-2.21; P = .005) after adjusting for potentially confounding covariates. In contrast, a history of normotensive pregnancy, as compared with nulliparity, was associated with a 6.1% lower serum homocysteine level (P = .005) and a 0.49-fold reduced odds of elevated homocysteine levels (95% confidence interval, 0.32-0.74; P < .001).

CONCLUSION

Homocysteine levels decades after pregnancy are higher in women with a history of pregnancy hypertension, even after controlling for potential confounders. Thus, pregnancy history may prompt homocysteine assessment and risk modification in an attempt at primary prevention of cardiovascular disease.

Methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and risk of preeclampsia: an updated meta-analysis based on 51 studies

BACKGROUND AND AIMS

The methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism has been considered to be associated with preeclampsia (PE), but the results from previous studies were conflicting. The present study aimed at investigating the frequency of preeclampsia according to the distribution polymorphism using a meta-analysis on the published studies.

METHODS

The English and Chinese databases were searched to identify eligible studies published in English before August 2012. Data were extracted using standardized methods. The association was assessed by odds ratio (OR) with 95% confidence intervals (CI). Begg's test was used to measure publication bias.

RESULTS

A total of 51 case-control studies containing 6,403 patients and 11,346 controls were involved in this meta-analysis. Significant associations were detected between MTHFR C677T polymorphism and risk of PE in the overall population for TT vs. CC (OR = 1.280, 95% CI: 1.074-1.525), recessive model (OR = 1.264, 95% CI: 1.067-1.303), and dominant genetic model (OR = 1.174, 95% CI: 1.057-1.303); in Caucasian population for dominant model (OR = 1.136, 95% CI: 1.022-1.263), and in East Asia population for TT vs. CC (OR = 2.199, 95% CI: 1.366-3.924) CT vs. CC (OR = 1.453, 95% CI: 1.001-2.109), recessive model (OR = 1.742, 95% CI: 1.202-2.525), and dominant model (OR = 1.783, 95% CI: 1.271-2.501). Conversely, no associations were detected in Latin America, South Asia, and Africa populations.

CONCLUSIONS

Results of the meta-analysis suggest that the MTHFR C677T polymorphism was associated with risk of PE in overall, Caucasian, and East Asia populations. Nevertheless, the results for Latino, East Asians, South Asians and Africans should be interpreted with caution due to the small sample size.

FOLATE METABOLISM AND PREECLAMPSIA

Preeclampsia (PE) is a multisystem disorder of human pregnancy, affecting about 6% of all pregnancies worldwide, and is one of the leading causes of maternal and infant morbidity and mortality. Despite decades of research into the pathogenesis of this complex disease, the underlying mechanisms remain unclear. As a result, the options for prevention and management of PE are limited. In recent years, there has been a growing body of evidence suggesting that folate deficiency is associated with PE, and folic acid supplementation may reduce the risk of developing PE in certain populations. Folate contributes to cell division and growth, and folate metabolism is involved in a large number of physiological and pathophysiological processes in human development. Sufficient supply of folate is therefore particularly important during pregnancy. Nevertheless, the exact mechanisms of folic acid deficiency increasing the risk of developing PE are still unclear. This article reviews what is understood about the aetiology of PE and the relationship between folate metabolism and PE so as to enhance further discussions on the subject.

Preeclampsia and angiotensin converting enzyme (ACE) I/D and angiotensin II type-1 receptor (AT1R) A1166C polymorphisms: association with ACE I/D polymorphism

BACKGROUND

The aim of the present study was to investigate the association between angiotensin converting enzyme (ACE) insertion/deletion (I/D) and angiotensin II type-1 receptor (AT1R) A1166C polymorphisms with the risk of preeclampsia and lipid peroxidation in preeclamptic women from Western Iran.

METHODS

One hundred and ninety-eight preeclamptic women (128 women with mild and 70 with severe forms) and 100 age- and parity-matched controls were enrolled in this case-control study.

RESULTS

The presence of D allele of ACE was associated with a 1.8-fold increased risk of preeclampsia (p=0.002) in total preeclamptic patients. The frequency of AT1R AC+CC genotypes was higher in mild preeclamptic women (32%) compared to controls (27.2%) (p>0.05). In mild preeclamptic women with ID genotype, the level of total antioxidant capacity (TAC) was significantly decreased compared to those with II genotype. Also, there was a trend toward increasing malondialdehyde (MDA) and decreasing TAC levels in mild and severe preeclamptic women with AT1R AA through CC genotypes.

CONCLUSIONS

Our study indicates that lipid peroxidation and oxidative stress are involved in the development of preeclampsia that might be influenced by polymorphism in the renin-angiotensin-aldosterone system genes.

One-carbon metabolism enzyme polymorphisms and uteroplacental insufficiency

OBJECTIVES

This study was undertaken to test novel genetic polymorphisms involved in 1-carbon metabolism for a potential association with increased risk of developing pregnancy complications associated with uteroplacental insufficiency.

STUDY DESIGN

This was a prospective cohort study consisting of 50 women at low risk and 93 women at high risk for having a pregnancy complication develop. Maternal and fetal DNA samples were genotyped for methionine synthase (MTR) A2756G, methionine synthase reductase (MTRR) A66G and methylenetetrahydrofolate dehydrogenase (MTHFD1) G1958A. A chi squared or chi(2) analysis was used to compare genotypes and pregnancy outcome, 1-way analysis of variance and linear regression were used to compare genotype with continuous variables.

RESULTS

The fetal MTR 2756 G allele was associated with uteroplacental insufficiency (P = .022, likelihood ratio = 10.4) and maternal homocysteine (P = .017). The maternal MTR A2756G polymorphism was associated with uteroplacental insufficiency (P = .049, likelihood ratio = 6.0), but only in mothers not supplementing with high-dose B-vitamins. The maternal MTHFD1 AA genotype was associated with intrauterine growth restriction (P = .047, likelihood ratio = 5.8).

CONCLUSION

This study suggests the maternal and fetal MTR 2756 G allele is an important risk factor in the development of uteroplacental insufficiency. In addition, the maternal MTHFD1 1958 AA genotype may be associated with intrauterine growth restriction.

Genes and the preeclampsia syndrome

Preeclampsia is specific to pregnancy and is still a leading cause of maternal and perinatal mortality and morbidity, affecting about 3% of women, but the underlying pathogenetic mechanisms still remain unclear. Immune maladaptation, placental ischemia and increased oxidative stress represent the main components discussed to be of etiologic importance, and they all may have genetic implications. Since the familial nature of preeclampsia is known for many years, extensive research on the genetic contribution to the pathogenesis of this severe pregnancy disorder has been performed. In this review, we will overview the linkage and candidate gene studies carried out so far as well as summarize important historical notes on the genetic hypotheses generated in preeclampsia research. Moreover, the influence of maternal and fetal genes and their interaction as well as the role of genomic imprinting in preeclampsia will be discussed.

Changes in haemostasis during normal pregnancy: does homocysteine play a role in maintaining homeostasis?

Homocysteine, derived from the demethylation of the ammo acid methionine, is either further catabolised by trans-sulfuration to cysteine or remethylated to methionine. Remethylation to methionine requires the cofactors, folate and vitamin B12. Folate is an effective homocysteine-lowering agent and, thus, homocysteine and folate status are inversely related. Hyperhomocysteinaemia is a strong independent risk factor for venous thromboembolism (VTE) and is associated with adverse pregnancy outcomes such as pre-eclampsia, placental abruption, early pregnancy loss and neural-tube defects. Pregnancy is a risk factor for VTE as a result of prothrombotic changes in levels of haemostatic factors. However, despite this hypercoagulable state, the incidence of pregnancy-associated VTE is relatively low. Hyperhomocysteinaemia is associated with abnormalities in markers of coagulation activation, and recent research suggests that folic acid supplementation, as well as lowering homocysteine, lowers markers of coagulation activation and increases levels of coagulation inhibitors. Tissue factor (TF) is the initiator of blood coagulationin vivo, and homocysteine induces TF expressionin vitro. During pregnancy, monocyte TF expression is lower than that in the non-pregnant state, and this lowering of TF may act to counterbalance increases in coagulation activation. Furthermore, despite a high folate requirement, several studies have reported that homocysteine is lower in normal pregnancy than in the non-pregnant state. Although the exact mechanism of homocysteine lowering during pregnancy is unclear, one possible outcome of lower homocysteine may be the protection of women from pregnancy complications and VTE, and thus lower homocysteine may contribute to maintaining homeostasis in haemostasis.

Evaluation of Factor V Leiden, Prothrombin and Methylenetetrahydrofolate Reductase Gene Mutations in Patients with Severe Pregnancy Complications in Northern Finland

BACKGROUND

Thrombosis in placenta may lead to severe pregnancy complications. Most important inherited thrombophilias are factor V Leiden mutation, prothrombin mutation, and methylenetetrahydrofolate reductase mutation. The aim of our research was to evaluate the prevalence of inherited thrombophilias in severe pregnancy complications and in normal pregnancies.

MATERIAL AND METHODS

The study subjects with severe preeclampsia, intrauterine growth restriction, placental abruption or fetal death were collected during the period 1999-2004 from Oulu University Hospital. We also collected during the same period voluntary parturients with normal pregnancy outcome as the control group. FVL, FII, and MTHFR gene mutations of the patients and controls were analyzed.

RESULTS

We found a significant difference in the prevalence of FVL mutation between the groups. There were 9.5% FVL mutations in the study group compared to 1.8% in the control group; the observed difference between prevalences was 7.7% (95% CI 2.0-13.4). No statistical difference was found in the FII or MTHFR mutations between the groups. All FV and FII mutations were heterozygous and all the MTHFR mutations homozygous.

CONCLUSION

Women with thrombophilia have a risk for severe pregnancy complications. Randomized controlled trials are needed to assess the influence of low-molecular-weight heparin in pregnant women with thrombophilia.

Methylenetetrahydrofolate Reductase Polymorphisms and the Risk of Gestational Hypertension

BACKGROUND

Evidence on the association of 5,10 methylentetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms in women with gestational hypertension is inconsistent. It is also unknown whether the fetal genotype is relevant, or whether folic acid supplementation modifies this association.

METHODS

The study population was composed of U.S. and Canadian white women with nonmalformed infants participating in the Slone Epidemiology Center Birth Defects Study between 1993 and 2000. Women were interviewed within 6 months after delivery regarding multivitamin use in pregnancy and the occurrence of gestational hypertension, among other factors. DNA was extracted from cheek swabs and gene alleles determined by restriction fragment length polymorphism analysis. We compared the prevalence of the 677TT/CT and 1298CC/AC genotypes between cases with gestational hypertension (54 mothers and their 51 offspring) and controls (100 mothers and their 99 offspring). We also estimated odds ratios (ORs) and 95% confidence intervals (CIs) using conditional logistic regression to control for geographic region and calendar year.

RESULTS

The T allele was present in 69% of women with gestational hypertension versus 57% of control women (compared with 677CC, OR = 1.9; 95% CI = 0.9-4.0). The offspring of case and control women had a 677TT/CT genotype prevalence of 68% and 47%, respectively (2.4; 1.1-5.0). Among women supplemented with folic acid during the first 5 months of pregnancy, the ORs for maternal and fetal 677TT/CT genotypes were 0.9 (0.3-2.5) and 2.1 (0.7-6.0), respectively. Neither maternal nor fetal 1298CC/AC genotypes were associated with an increased risk of gestational hypertension.

CONCLUSION

Maternal and fetal MTHFR C677T polymorphism may be associated with a moderately increased risk of gestational hypertension, and there is a suggestion that this association may be diminished among women receiving folate supplementation during pregnancy.

Polymorphisms of genes involved in homocysteine metabolism in preeclampsia and in uncomplicated pregnancies

OBJECTIVE

To evaluate the possible relationship between preeclampsia and polymorphisms in the main genes involved in folate-homocysteine metabolism.

STUDY DESIGN

Case-control study: 43 patients with preeclampsia and 122 controls without pregnancy complications. Laboratory studies: tHcy and other amino acids, folate and vitamin B(12) and polymorphisms: 677C > T and 1298A > C (MTHFR); 699C > T, 844ins68 and 1080C > T (CBS); 2756A > G (MTR); and 66G > A, IVS1+766G > A and IVS1+754A > C (MTRR).

RESULTS

Plasma tHcy and folate values were significantly higher (P = 0.004 and P = 0.019), while Met/tHcy ratios were lower (P < 0.001) in the patients compared with controls. No association was observed between polymorphisms tested and preeclampsia. In the control group, four such associations were found: the 1298A > C polymorphism (MTHFR) with the ratio Met/tHcy (P = 0.014); the 699C > T polymorphism (CBS) with the ratio tHcy/SigmaAA (P = 0.013); the 2756A > G polymorphism (MTR) with tHcy (P = 0.034); and the IVS1+766G > A polymorphism (MTRR) with hyperhomocysteinemia (P = 0.012).

CONCLUSION

An association between the polymorphisms analysed and preeclampsia could not be demonstrated.

Association of C677T polymorphism in the methylenetetrahydrofolate reductase gene with hypertension in pregnancy and pre-eclampsia: a meta-analysis

OBJECTIVE

To evaluate whether the C677T polymorphism of the methylenetetrahydofolate reductase (MTHFR) gene is consistently associated with hypertension in pregnancy.

DESIGN

Meta-analysis of studies comparing women with and without hypertension in pregnancy for the C677T MTHFR polymorphism.

METHODS

Studies were identified with MEDLINE and EMBASE searches complemented with perusal of bibliographies of retrieved articles and communication with investigators. Between-study heterogeneity was estimated and data were combined with random effects models. Sensitivity analyses examined the effect of population and disease characteristics. Bias diagnostics evaluated the evolution of the postulated genetic effect over time and the potential for publication bias.

RESULTS

Across 23 comparisons (3169 hypertensive women, 3044 controls), having the T allele (TT or CT) increased the odds of hypertensive disease of pregnancy by 1.21-fold (95% confidence interval, 1.01-1.44), but there was large between-study heterogeneity (P = 0.003). The results were similar and heterogeneity persisted when sensitivity analyses were limited to studies of Caucasian populations, or those of patients with significant proteinuria. While patients with diastolic hypertension > or = 110 mmHg showed an odds ratio of 1.41 (95% confidence interval, 1.03-1.73), no association was seen in patients with less severe diastolic hypertension (odds ratio, 1.00; 95% confidence interval, 0.61-1.65). Early published studies tended to show stronger associations than the subsequent studies.

CONCLUSIONS

While bias cannot be excluded, the meta-analysis suggests that the T allele may increase the risk of severe diastolic hypertension during pregnancy.

Genetic thrombophilias and preeclampsia: a meta-analysis

OBJECTIVE

To assess the relationship between the factor V Leiden (1691 G-A) single nucleotide polymorphism (SNP), the methylene tetrahydrofolate reductase (MTHFR) 677 C-T SNP, and the prothrombin 20210 G-A SNP and the risk of preeclampsia, by conducting a meta-analysis of all case-control studies with data on these polymorphisms and the risk of preeclampsia.

DATA SOURCES

MEDLINE (1966 to November 2002), EMBASE (1980 to November 2002). Search terms included "preeclampsia," "thrombophilia," "factor V Leiden," "protein C," "MTHFR," "methylenetetrahydrofolate reductase," "homocysteine," and "prothrombin gene 20210."

METHODS OF STUDY SELECTION

Case-control studies of genetic thrombophilias and preeclampsia were included.

TABULATION, INTEGRATION, AND RESULTS

We identified 349 titles and reviewed 47 articles for inclusion and exclusion criteria. Thirty-one studies with 7,522 patients were included in the meta-analysis. Data from patients characterized as having severe preeclampsia were extracted and analyzed separately. The pooled odds ratio (OR) for the association of factor V Leiden and all cases of preeclampsia was 1.81 (95% confidence interval [CI] 1.14-2.87) and 2.24 (95% CI 1.28-3.94) for cases of severe preeclampsia. The pooled OR for the MTHFR 677 TT genotype and all preeclampsia was 1.01 (95% CI 0.79-1.29) and 1.38 (95% CI 0.93-2.06) for severe preeclampsia. The OR for the prothrombin 20210 polymorphism and all preeclampsia was 1.37 (95% CI 0.72-2.57) and 1.98 (.94-4.17) for severe preeclampsia.

CONCLUSION

This meta-analysis suggests that the factor V Leiden SNP is associated with an increased risk of preeclampsia. Further studies are warranted to determine whether subgroups of high-risk women should be screened for this mutation.

Genetic thrombophilia has pleiotropic effects in pregnancy

Genetic thrombophilia has been established as a risk factor for pregnancy-associated disorders, such as thrombosis, early and late miscarriage, and pre-eclampsia. Associations between the factor V (F5) Leiden G1691A and the prothrombin/factor II (F2) G20210A SNPs and pre-eclampsia have been evaluated in over 50 association studies. A pooled analysis of 23 and 11 studies demonstrates that carriage of the F5 Leiden G1691A (p < 0.001; odds ratio [OR] 2.0; 95% confidence interval [CI] 1.6-2.5) and the F2 G20210A (p < 0.001; OR 1.8; 95% CI 1.1-2.9) SNPs is significantly associated with pre-eclampsia. Besides pre-eclampsia, genotyping for the F5 Leiden G1691A and the F2 G20210A SNPs is also useful for individual risk assessment regarding pregnancy-associated thrombosis. Carriers of the F5 Leiden G1691A SNP will develop this condition in 6.4% of heterozygotes and in 8.9-16.7% of homozygotes. A total of 6.2% of women with the F2 G20210A SNP and 17.8% of women with simultaneous carriage of the F5 Leiden G1691A and F2 G20210A SNPs will develop pregnancy-associated thrombosis. Both the F5 Leiden G1691A and F2 G20210A SNPs are also risk factors of early recurrent, late recurrent and late spontaneous miscarriage based on a published meta-analysis of 31 studies. These women may benefit from prophylactic heparinization. Six case-control and cohort studies of 687 women with genetic thrombophilia document live birth rates of 82% (181/221) using low-molecular-weight heparin or fractionated heparin compared with 20% (95/466) without therapy (p < 0.001, OR 17.7; 95% CI 12.2-25.5). Based on the data in the literature, including association studies and meta-analyses of these association studies, it can be concluded that genetic thrombophilia due to carriage of the F5 Leiden G1691A and F2 G20210A SNPs is a significant and clinically relevant risk factor for pre-eclampsia, pregnancy-associated thrombosis, and early and late miscarriages.

Association of pre-eclampsia with hyperhomocysteinaemia and methylenetetrahydrofolate reductase gene C677T polymorphism in a Turkish population

BACKGROUND

Hyperhomocysteinaemia is a common finding in a wide variety of pathological conditions that exhibit endothelial disturbances. In the pathogenesis of pre-eclampsia, endothelial cell activation or dysfunction has been proposed as a central feature, and the presence of hyperhomocysteinaemia in varying degrees has been detected. One of the known causes of hyperhomocysteinaemia is polymorphism in the methylenetetrahydrofolate reductase gene that lowers the activity of the enzyme.

AIMS

In the current study, we measured plasma homocysteine concentrations in pre-eclamptic pregnants, and searched for the altered methylenetetrahydrofolate reductase (MTHFR) gene in which the cytosine 677 was replaced by the thymine (C677T polymorphism).

METHODS

The study groups consisted of 64 pre-eclamptic and 47 normotensive healthy pregnant women in their third trimester. The C677T transition in the MTHFR gene was detected by HinfI restriction enzyme analysis and subsequent electrophoresis in a 3% agarose gel. Total homocysteine concentrations were measured by high performance liquid chromatography.

RESULTS

The prevalence of the homozygous mutant thymine-thymine genotype was non-significant in the pre-eclamptic group. Total homocysteine in the plasma of pre-eclamptic women was found to be increased in comparison with healthy pregnant women (P < 0.001). Any influence of the allelic distribution on plasma homocysteine concentrations was not detected in either group. However, pre-eclamptic patients bearing the non-mutated cytosine-cytosine genotype had significantly higher homocysteine levels than those with an uncomplicated pregnancy (P = 0.009), ruling out the possibility that the presence of a mutated allele is associated with the hyperhomocysteinaemia seen in pre-eclamptic women.

CONCLUSION

In our pre-eclamptic study population, a mild hyperhomocysteinaemia was observed. This finding seems to be a consequence of hypertension and vascular injury rather than an independent factor with a genetic origin.

Thrombophilia and pregnancy complications

OBJECTIVE

This systematic review examines the strength of the association between thrombophilia and recurrent pregnancy loss and other serious obstetric complications. Study design Electronic databases and manual bibliography searches were used to identify studies evaluating the association between thrombophilia and pregnancy loss, preeclampsia, fetal growth retardation, and placental abruption.

RESULTS

Thrombophilic disorders are associated with an increased risk of fetal loss in the majority of case control and cohort studies. The risk is increased throughout pregnancy, but may be higher in the second and third trimester. The common pathologic finding of placental infarction suggests unexplained fetal loss may result from uteroplacental insufficiency and thrombosis. Thrombophilic disorders are not consistently associated with preeclampsia, fetal growth retardation, or placental abruption. Preliminary data suggest prophylactic anticoagulation may improve outcome in thrombophilic women with unexplained recurrent fetal loss.

CONCLUSION

Women with thrombophilia have an increased risk of pregnancy loss and possibly other serious obstetric complications, although definition of the magnitude of risk will require prospective longitudinal studies. Preliminary data suggesting prophylactic anticoagulation may improve gestational outcome provide a rationale for prospective randomized trials in thrombophilic women with unexplained recurrent fetal loss.

Association of the TNF2 Allele with Eclampsia

The genetic background predisposing pregnant women to the disorder pre-eclampsia/eclampsia (PE/E) is still unknown. There is compelling evidence to suspect involvement of the immune system in the development of PE/E. The aim of this current study was to investigate whether there is an association between the tumor necrosis factor (TNF)-alpha -307 polymorphism and PE or eclampsia. In this study, 51 cases of eclampsia, 122 cases of PE and 100 normotensive control cases were genotyped for the TNF-alpha -307 polymorphism. We found a significant difference between the TNF2 allele frequencies of eclamptic and normotensive controls (chi(2) = 6.3 and p = 0.025), but not of pre-eclamptic and normotensive controls (chi(2) = 0.5 and p = 1.0). We conclude from this study that the TNF2 allele contributes to the occurrence of eclampsia in our population.

A mutation in the 5,10-methylenetetrahydrofolate reductase gene is not associated with preeclampsia in women of southeast mexico

BACKGROUND

We investigated the possible association between C677T-5,10-methylenetetrahydrofolate (MTHFR) polymorphism and preeclampsia in women from the Yucatan Peninsula in Mexico.

METHODS

We performed a comparative study among three groups of subjects: 148 preeclamptic women; 177 women with normal pregnancies, and 313 healthy volunteers as control group. All subjects were genotyped for C677T polymorphism in MTHFR gene by PCR amplification and digestion of the product with Hinf I restriction enzyme. Genotypic and allelic frequencies were compared between affected women (preeclamptic) and nonaffected groups to determine the association using Fisher exact test. Odds ratios (ORs) were also calculated to obtain estimation of relative risk (RR) for developing preeclampsia.

RESULTS

Statistical analysis of intergroup comparisons among preeclamptic women, women with normal pregnancies, and control group showed no statistically significant differences for any genotype or for T allele (p >0.05).

CONCLUSIONS

Our results suggest that C677T-MTHFR polymorphism is not an associated risk factor for developing preeclampsia in southeast Mexico. Results also confirmed high prevalence of C677T mutation in Mexico.

Genetics of preeclampsia: what are the challenges?

Despite recent efforts to identify susceptibility genes of preeclampsia, the genetic determinants of the condition remain ill-defined, as is the situation for most disorders of complex inheritance patterns. The angiotensinogen, factor V, and methylenetetrahydrofolate reductase genes have been investigated in different populations, as have other genes involved in blood pressure, vascular volume control, thrombophilia, lipid metabolism, oxidative stress, and endothelial dysfunction. The study of the genetics of complex traits is faced with both methodological and genetic issues; these include adequate sample size to allow for the identification of modest genetic effects, of gene-gene and gene-environment interactions, the study of adequate quantitative traits and extreme phenotypes, haplotype analyses, statistical genetics, genome-wide (hypothesis-free) versus candidate-gene (hypothesis-driven) approaches, and the validation of positive associations. The use of genetically well-characterized populations showing a founder effect, such as the French-Canadian population of Quebec, in genetic association studies, may help to unravel the susceptibility genes of disorders showing complex inheritance, such as preeclampsia. It is necessary to better evaluate the role of the fetal genome in the resulting predisposition to preeclampsia and its complications. Eventually, we may be able to integrate genetic information to better identify the women at risk of developing preeclampsia, and to improve the management of those suffering from this condition.

Molecular epidemiology of preeclampsia

Numerous articles have been published that address the possible genetic influences on the development of preeclampsia (PE). However, to our knowledge, a complete review of the results has not yet been completed. We undertook a MEDLINE search to identify English-language articles published after January 1, 1990 that examined the possible role of specific genes in the etiology of PE. After a brief introduction and a concise review of the prevailing etiologic hypotheses, we have categorized the candidate genes into six categories, based on their hypothesized role in PE etiology. The purpose of this paper is to review the literature, comment on its quality, and provide a reference for researchers interested in the molecular epidemiology of preeclampsia.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader will be able to list the prevailing etiologic hypotheses of preeclampsia, to outline the published data on possible genetic influence on the development of preeclampsia, and to clearly state the definition of preeclampsia.

Hiperhomocisteinemia durante el embarazo como factor de riesgo de preeclampsia

A revision about the role of hyperhomocysteinemia in the development of preeclampsia is presented, which summarises our experience in different biochemical and genetic points in relation to this possible association. Plasma total homocysteine concentrations (tHcy) during pregnancy were significantly lower than those of non-pregnant women: 2nd trimester (median, 5.3 micromol/l; range, 3.1-10.0 micromol/l); 3rd trimester (median, 6.3 micromol/l; range, 3.2-13.0 micromol/l). Hyperhomocysteinemia (tHcy>P95) was established as values higher than 7.7 micromol/l in the 2nd trimester, and as values higher than 10.5 micromol/l in the 3rd trimester of pregnancy. We found an association between hyperhomocysteinemia and preeclampsia: tHcy values were significantly higher in the preeclamptic group than in uncomplicated pregnancies; the OR for preeclampsia in hyperhomocysteinemic patients was 7.7 (CI 95%, 1.7-34.8). The other amino acid concentrations were also higher in preeclamptic women. The negative correlation observed between homocysteine and folate in the control group, was not present in preeclamptic women. An association between homocysteine concentrations in preeclampsia and glucose intolerance was not observed. The Doppler study of uterine artery flow velocity waveforms seems to be a good screening method to identify pregnancies at high risk of preeclampsia. The addition of homocysteine determination did not usefully improve its predictive value. The polymorphisms in the main genes involved in folate-homocysteine metabolism studied could not be considered as the determinants of the hyperhomocysteinemia observed in preeclamptic pregnants.

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.