Pre-eclampsia--still a disease of theories?

Historical evolution of ideas on eclampsia/preeclampsia: A proposed optimistic view of preeclampsia

Eclampsia (together with epilepsy) being the first disease ever written down since the beginning of writings in mankind 5000 years ago, we will make a brief presentation of the different major steps in comprehension of Pre-eclampsia. 1) 1840. Rayer, description of proteinuria in eclampsia, 2) 1897 Vaquez, discovery of gestational hypertension in eclamptic women, 3) In the 1970's, description of the "double" trophoblastic invasion existing only in humans (Brosens & Pijnenborg,), 4) between the 1970's and the 1990's, description of preeclampsia being a couple disease. The "paternity problem" (and therefore irruption of immunology), 5) at the end of the 1980's, a major step forward: Preeclampsia being a global endothelial cell disease (glomeruloendotheliosis, hepatic or cerebral endotheliosis, HELLP, eclampsia), inflammation (J.Roberts.C Redman, R Taylor), 6) End of the 1990's: Consensus for a distinction between early onset preeclampsia EOP and late onset LOP (34 weeks gestation), EOP being rather a problem of implantation of the trophoblast (and the placenta), LOP being rather a pre-existing maternal problem (obesity, diabetes, coagulopathies etc…). LOP is predominant everywhere on this planet, but enormously predominant in developed countries: 90% of cases. This feature is very different in countries where women have their first child very young (88% of world births), where the fatal EOP (early onset) occurs in more than 30% of cases. 7) What could be the common factor which could explain the maternal global endotheliosis in EOP and LOP? Discussion about the inositol phospho glycans P type.

The role of glutathione peroxidase maternal serum level in late onset of severe preeclampsia

OBJECTIVE

This study was done to investigate the association between maternal serum glutathione peroxidase (GP) and late onset of severe preeclampsia.

METHODS

Cross-sectional study was undertaken comparing normal pregnancy and severe preeclampsia at 37-42 weeks of gestational age. Maternal venous blood was taken to assess the level of GP.

RESULT

Twenty normal pregnancy and 20 severe preeclampsia patients were investigated. The median (max-min) of GP level for preeclampsia was 4.31 (0.03-327.41) mU/mL significantly lower than in normal pregnancy 318.90 (6.46-694.11) mU/mL (p < 0.001). A receiver operating characteristics (ROC) analysis showed that the cutoff point for GP to differentiate between normal pregnancy and severe preeclampsia was 41.74 mU/mL. Multivariate analysis was done to investigate the impact of BMI and parity showed that a low level of GP will increase the risk of severe preeclampsia.

CONCLUSION

Low level of GP was associated with the diagnosis of severe preeclampsia.

Biomarker development for presymptomatic molecular diagnosis of preeclampsia: feasible, useful or even unnecessary?

The past decade saw the advent of a number of promising biomarkers to detect pregnancies at risk for preeclampsia (PE), the foremost being those associated with an imbalance of angiogenic factors. In late pregnancy, these are useful for the detection of imminent cases of PE, while earlier they were more predictive for early- than late-onset PE. This suggests that there may be fundamental differences between the underlying pathology of these two PE forms. Therefore, it is possible that such a biological premise may limit the development of biomarkers that will permit the efficacious detection of both early- and late-onset PE via an analysis of first-trimester maternal blood samples. Consequently, a significant increase in our understanding of the underlying pathology of PE, using a variety of approaches ranging from systems biology to animal models, will be necessary in order to overcome this obstacle.

A mass spectrometric multicenter study supports classification of preeclampsia as heterogeneous disorder

OBJECTIVE

The diagnostic value of affinity-based matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis to distinguish preeclampsia (PE) from matched controls was tested in a multicenter setting.

METHODS

Serum samples of preeclamptic (n = 60) and healthy pregnant women (n = 66) from four centers were prospectively analyzed with predefined rule sets.

RESULTS

Overall sample classification reached sensitivity of 0.88 and specificity of 0.73. Separate calculations for early-onset PEs only (before 34 weeks of gestation) revealed sensitivity of 0.88 and specificity of 0.89.

CONCLUSION

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry serum-profiling with center-wise standardization offers a fast and robust method to classify PE and contributes to the theory of PE being a heterogeneous disorder that ought to be subclassified.

Calreticulin has opposing effects on the migration of human trophoblast and myometrial endothelial cells

Calreticulin is a calcium binding, endoplasmic reticulum resident protein best known for its roles in intracellular calcium homeostasis and the quality control processes of the endoplasmic reticulum. There is evidence for a range of activities for calreticulin outside the endoplasmic reticulum, including in the cytosol, on the surface of different cells types and in the extracellular matrix. Recent evidence indicates that human pregnancy is a condition of elevated circulating calreticulin. Calreticulin was increased in the plasma of women throughout pregnancy compared to the non-pregnant state. Calreticulin was also further increased during the hypertensive disorder of human pregnancy, pre-eclampsia. To clarify the roles of circulating calreticulin in pregnancy and pre-eclampsia, the aim of this study was to determine the effects of exogenous calreticulin on two cell types that are relevant to normal human pregnancy and to pre-eclampsia. Human primary myometrial microvascular endothelial cells (UtMVEC-Myo) and the human trophoblast cell line, HTR8/SVneo, were cultured with exogenous calreticulin at concentrations (2 μg/ml and 5 μg/ml) comparable to that measured in maternal blood. The higher concentration of calreticulin significantly increased the migration of the UtMVEC-Myo cells, but significantly reduced the migration of the HTR8/SVneo cells. In the presence of only FGF, FBS and antibiotics calreticulin at 5 μg/ml significantly reduced the number of UtMVEC-Myo cells during in vitro culture for 120 h. These results demonstrate that exogenous calreticulin can alter both HTR8/SVneo and UtMVEC-Myo cell functions in vitro at a (patho-) physiologically relevant concentration. Increased calreticulin may also contribute to altered functions of both cell types during pre-eclampsia.

The role of proteoglycans in contributing to placental thrombosis and fetal growth restriction

Fetal growth restriction is an important pregnancy complication that has major consequences for the fetus and neonate as well as an increased risk of long-term morbidity extending into adulthood. The precise aetiology of most cases of fetal growth restriction is unknown although placental thrombosis is a common feature in many of these cases. This paper will outline the potential role of proteoglycans in contributing to placental thrombosis and fetal growth restriction.

Calreticulin in human pregnancy and pre-eclampsia

Pre-eclampsia is a disorder of human pregnancy that involves pregnancy-induced maternal hypertension and proteinuria. Evidence indicates that pre-eclampsia involves widespread activation of maternal endothelial cells. Calreticulin is a ubiquitously expressed, multi-functional protein that has been shown to have both pro- and anti-inflammatory effects on cultured endothelial cells in vitro and in whole animals. In order to clarify the role of this protein in normal human pregnancy and in pre-eclampsia, this study has measured expression of calreticulin in maternal blood and in placenta in patients with pre-eclampsia and in control pregnancies. There was a significant increase (approximately 5-fold) in calreticulin in plasma in term pregnant women compared with women who were not pregnant. There was no difference, however, in calreticulin in plasma from women who were sampled at first trimester, second trimester and at term. In addition, there was a significant increase (approximately 50%) in calreticulin in plasma from pre-eclamptic women compared to controls. Calreticulin mRNA and protein expression in placenta were not changed between pre-eclampsia and control pregnancies. These novel results indicate that calreticulin is increased in peripheral maternal blood early in pregnancy and remains elevated throughout normal gestation and that there is a further increase in calreticulin in pre-eclampsia.

Candidate-gene association study of mothers with pre-eclampsia, and their infants, analyzing 775 SNPs in 190 genes

Pre-eclampsia (PE) affects 5-7% of pregnancies in the US, and is a leading cause of maternal death and perinatal morbidity and mortality worldwide. To identify genes with a role in PE, we conducted a large-scale association study evaluating 775 SNPs in 190 candidate genes selected for a potential role in obstetrical complications. SNP discovery was performed by DNA sequencing, and genotyping was carried out in a high-throughput facility using the MassARRAY(TM) System. Women with PE (n = 394) and their offspring (n = 324) were compared with control women (n = 602) and their offspring (n = 631) from the same hospital-based population. Haplotypes were estimated for each gene using the EM algorithm, and empirical p values were obtained for a logistic regression-based score test, adjusted for significant covariates. An interaction model between maternal and offspring genotypes was also evaluated. The most significant findings for association with PE were COL1A1 (p = 0.0011) and IL1A (p = 0.0014) for the maternal genotype, and PLAUR (p = 0.0008) for the offspring genotype. Common candidate genes for PE, including MTHFR and NOS3, were not significantly associated with PE. For the interaction model, SNPs within IGF1 (p = 0.0035) and IL4R (p = 0.0036) gave the most significant results. This study is one of the most comprehensive genetic association studies of PE to date, including an evaluation of offspring genotypes that have rarely been considered in previous studies. Although we did not identify statistically significant evidence of association for any of the candidate loci evaluated here after adjusting for multiple testing using the false discovery rate, additional compelling evidence exists, including multiple SNPs with nominally significant p values in COL1A1 and the IL1A region, and previous reports of association for IL1A, to support continued interest in these genes as candidates for PE. Identification of the genetic regulators of PE may have broader implications, since women with PE are at increased risk of death from cardiovascular diseases later in life.

Lack of Association Between Periodontal Parameters and Preeclampsia

BACKGROUND

It was hypothesized that periodontal diseases may increase the risk of preeclampsia. To test this hypothesis, this study was conducted to determine the association between periodontal parameters and preeclampsia among women in the north of Jordan.

METHODS

A case-control study was conducted among women who gave birth at Princes Badea Teaching Hospital between September 2004 and May 2005. A total of 115 preeclamptic women and 230 randomly selected controls were analyzed. The number of teeth, restorations, decayed tooth surfaces, and clinical periodontal parameters were determined within 24 hours after delivery. Information regarding participants' demographics, antenatal history, and family history were collected through personal interviews.

RESULTS

After adjustment for potential confounding factors, there were no statistical differences between preeclamptic cases and normotensive controls with regard to mean periodontal probing depth, mean clinical attachment loss, mean gingival recession, mean plaque index, and mean gingival index. In addition, there were no significant differences in the percentages of sites with periodontal probing depth >/=3 or >/=4 mm, percentages of sites with clinical attachment loss >/=3 mm, number of filled surfaces, and number of missing teeth. Only the number of decayed surfaces was found to be associated with increased odds of preeclampsia (adjusted odds ratio of 1.13; 95% confidence interval of 1.02 and 1.25).

CONCLUSION

This study did not support the hypothesis of an association between periodontal parameters and preeclampsia.

Placental expression of nitric oxide synthase during HELLP syndrome: the correlation with maternal-fetal Doppler velocimetry

BACKGROUND

To correlate Doppler waveform of the uterine and umbilical vessels to placental nitric oxide synthase (NOS) expression in pregnant women with HELLP (hemolysis, elevated liver enzymes, low platelets count) syndrome.

METHODS

mRNA expression of inducible NOS (iNOS) and endothelial NOS (eNOS) was assessed, after cesarean section, in placental samples from 10 women affected by HELLP syndrome and 10 controls. Pulsatility indices on Doppler waveform analysis from uterine and umbilical arteries were measured.

RESULTS

iNOS expression was significantly lower in placenta from women with HELLP syndrome than controls. When comparing the results with Doppler flow measurements, we found a negative correlation between umbilical pulsatility index and eNOS expression (r = -0.91) and a positive correlation with iNOS expression (r = 0.86).

CONCLUSIONS

The reduced iNOS expression in women with HELLP syndrome may indicate the extreme placental dysfunction that is unable to compensate for the endothelial derangement and related hypertension in spite of trying to improve fetoplacental perfusion and the delivery of nutrients to the fetus.

Detection of CAG repeats in pre-eclampsia/eclampsia using the repeat expansion detection method

Pre-eclampsia/eclampsia is a serious disorder of human pregnancy that has a worldwide incidence of 2-10% and carries a severe morbidity and mortality risk for both mother and child. Its precise cause remains unknown. However, there is increasing evidence of an underlying complex maternal genetic susceptibility. Its high population incidence in the face of strong negative selection pressure suggests that the gene(s) involved have a selective advantage and/or a high mutation rate. One class of genetic diseases that involve a high mutation rate are the trinucleotide repeat expansion diseases. Thus, the aim of this study was to determine whether there is an association between a trinucleotide (CAG) repeat expansion and pre-eclampsia/eclampsia. We have used the repeat expansion detection (RED) method, which was developed to directly identify clinically significant repeat expansions, to analyse genomic DNA from an Australian and New Zealand population. The maximal CAG repeat length for each individual was recorded and the Mann-Whitney U and Wilcoxon rank sum test for independent samples were used to compare distributions for CAG/CTG repeats between two populations. There were no statistically significant differences between the distribution of CAG repeats in normotensive (n = 59) and severe pre-eclampsia (n = 69) (Mann-Whitney U = 1732; P = 0.14), and normotensive (n = 59) and eclamptic (n = 15) populations (Mann-Whitney U = 417, P = 0.726). Therefore, these RED results do not support a role for a large CAG expansion in pre-eclampsia/eclampsia. However, these data do not preclude the possibility that a small CAG expansion is associated with the disorder nor do they negate the hypothesis that a highly mutable gene contributes to the genetic component of pre-eclampsia/eclampsia.

Proteinuria in pre-eclampsia: how much matters?

OBJECTIVE

To determine, in women with proteinuric pre-eclampsia, whether a discriminant value of proteinuria at the time of diagnosis predicts the presence or absence of subsequent adverse maternal and fetal outcomes.

DESIGN

Retrospective cohort study.

SETTING

One teaching hospital and two primary referral hospitals in Sydney, Australia.

SAMPLE

Three hundred and twenty-one pregnant women with proteinuric pre-eclampsia, managed according to a uniform management protocol.

METHODS

All women with the diagnosis of proteinuric pre-eclampsia in the years 1998-2001 were studied. After exclusion of women with pre-eclampsia superimposed on pre-existing hypertension, a twin pair, unavailable spot urine results, 353 women were analysed using logistic regression to determine separately the predictors of any adverse maternal or fetal outcomes at the time of delivery. Receiver operating characteristic (ROC) curves, sensitivity and specificity were then calculated from the data.

MAIN OUTCOME MEASURES

Adverse maternal outcomes: severe maternal hypertension (BP > or = 170/110 mmHg), renal insufficiency, liver disease, cerebral irritation, haematological disturbances. Adverse fetal outcomes: small for gestational age, perinatal mortality.

RESULTS

There were 108 (34%) adverse maternal outcomes and 60 (19%) adverse fetal outcomes including two stillbirths. In multivariate analysis, an adverse maternal outcome was significantly associated with higher spot urine protein/creatinine ratio at diagnosis (P < 0.0001) with an odds ratio (OR) of 1.003 per mg/mmol (95% confidence interval [CI] 1.002-1.004) and with older maternal age (P= 0.014) with OR 1.06 per year (95% CI 1.01-1.11). An increased risk of adverse fetal outcome was associated with higher spot urine protein/creatinine (P= 0.013; OR 1.44 per log [mg/mmol], 95% CI 1.08-1.92), gestation at diagnosis <34 weeks (P < 0.0001; OR 3.60, 95% CI 1.90-6.82) and early pregnancy systolic blood pressure < or =115 mmHg (P= 0.0002; OR 3.41, 95% CI 1.77-6.57). The area under the receiver operating characteristic (ROC) curve was 0.67 for adverse maternal outcomes and 0.72 for adverse fetal outcomes.

CONCLUSIONS

With increasing proteinuria, there is increased risk of adverse maternal and fetal outcomes. Although we did not identify a specific spot protein/creatinine ratio that could be used as a definitive screening value for adverse outcomes, it is possible to utilise data from this study to predict the likelihood of adverse maternal and fetal outcomes. A high spot urine protein/creatinine ratio in pre-eclamptic women of greater than 900 mg/mmol ( approximately 9 g/day), or greater than 500 mg/mmol (approximately 5 g/day) in women over 35 years, is associated with a greatly increased likelihood of adverse maternal outcomes.

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.

Increased breath markers of oxidative stress in normal pregnancy and in preeclampsia

OBJECTIVES

The purpose of this study was to compare the intensity of oxidative stress in normal pregnancy, preeclampsia, and nonpregnant women using a breath test.

STUDY DESIGN

We studied primiparous women in third trimester pregnancy (38 uncomplicated, 26 with preeclampsia) and 60 nonpregnant control subjects. Volatile organic compounds (VOCs) in alveolar breath were analyzed by gas chromatography/mass spectroscopy to construct the breath methylated alkane contour (BMAC), a 3-dimensional display of abundance of C4-C20 alkanes and monomethylated alkanes.

RESULTS

The mean volume under curve (VUC) of the BMAC was significantly higher in preeclampsia patients than in normal pregnant women (P < .003) and nonpregnant control subjects (P < .005). A predictive model employing 5 VOCs distinguished preeclampsia from uncomplicated pregnancy (sensitivity = 92.3%, specificity = 89.7%; cross-validated sensitivity = 88.5%, specificity = 79.3%).

CONCLUSION

A breath test significantly demonstrated greater oxidative stress in women with preeclampsia than in uncomplicated pregnancy and nonpregnant control subjects. The breath test accurately identified women with established preeclampsia, but further studies are required to determine if this test can predict the onset of disease.

Pre-eclampsia and thrombophilia

Pre-eclampsia is a major cause of perinatal and maternal morbidity and mortality worldwide. Although knowledge of the precise aetiology remains uncertain a number of risk factors have been described. Thrombophilias have been associated with pre-eclampsia in a number of studies and it is biologically plausible that they may contribute to the uteroplacental thrombosis that is frequently seen in pre-eclampsia. If this association is confirmed, there is the potential to investigate preventive treatments, including low-molecular-weight heparins, aspirin and folate.

Androgen levels of preeclamptic patients in the third trimester of pregnancy and six weeks after delivery

BACKGROUND

The aim of this study was to measure the circulating levels of androgens in the third trimester of pregnancy and six weeks after delivery and to discuss androgen contribution in the pathogenesis of preeclampsia.

METHODS

Twenty-two preeclamptic and 20 normotensive women completed this prospective study. Blood samples were drawn in the third trimester (28-32 gestational weeks) and six weeks after delivery. Serum total testosterone (T), free testosterone (fT) dehydroepiandrosterone sulfate (DHEAS), androstenodione (A), sex hormone binding globulin (SHBG) and estradiol (E2) levels were measured. The statistical analyses of the data were performed by using Wilcoxon Rank test within the groups, Student unpaired t test and Chi-square test between the groups with the SPSS program.

RESULTS

T and fT levels were found to be significantly higher (p<0.05) in preeclamptic women in the third trimester compared to the values of normotensive controls. However, there were significant decreases (p<0.05) in T and fT levels six weeks after delivery, reaching values not significantly different from normotensive subjects (p>0.05). Furthermore, SHBG, DHEAS, A and E2 levels were not significantly different (p>0.05) between the groups in the third trimester or six weeks after delivery.

CONCLUSION

We conclude that higher blood androgen levels measured in preeclamptic patients may be implicated in the pathogenesis of preeclampsia.

Serum nitric oxide and glutathione levels in preeclamptic and normotensive women during labor

This study was performed on 38 preeclamptic women, including 26 severely preeclamptic and eclamptic cases, as well as 50 normotensive pregnant controls. Twenty cases in the preeclamptic group and 34 cases in the control group were in labor. Serum nitric oxide levels were measured as total nitrites after reduction of nitrates to nitrites. Among the control subjects, nitric oxide levels were significantly lower in the cases in labor when compared to those not in labor (p < 0.05), but glutathione levels were not significantly different (p >0.05). Among the preeclamptic patients, although nitric oxide levels were not significantly different between the cases in and not in labor (p > 0.05), glutathione levels were significantly higher in the latter group (p < 0.05). Thus, in preeclamptic patients there might be a compensatory increase in nitric oxide production during labor in order to maintain the systemic circulation. Glutathione levels might also be increased to compensate for the marked oxidative stress.

A regulatory role for neurokinin B in placental physiology and pre-eclampsia

Tachykinin dogma has assumed, so far, that neurokinin B (NKB) is a neuropeptide that is not produced in any peripheral tissue even though its endogenous receptor, NK3, has been found in a number of locations throughout the human body. We have found an abundant source of peripheral NKB in the human and rat placenta. In this review we describe the discovery of NKB in the placenta and examine its possible role in placental physiology and pre-eclampsia (PE). Excessive secretion of placental NKB into the maternal circulation during the third trimester of pregnancy has been found in women suffering from PE. This may provide the key to the cause of the multiple and complex symptoms associated with this potentially life-threatening illness. We also reveal the structural organisation of the human NKB gene for the first time as well as discussing putative mechanisms for its control.

Methylenetetrahydrofolate reductase polymorphisms in preeclampsia and the HELLP syndrome

OBJECTIVE

To investigate the prevalence of the 677 (C --> T) and 1298 (A --> C) polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene in our preeclamptic population. For a summary estimation of the risk of the 677 (C --> T) polymorphism for preeclampsia, we also performed a meta-analysis on four previously published case-control studies to which our results were added.

METHODS

Genotypes were analyzed by polymerase chain reaction followed by restriction enzyme analysis. The results of 176 nonpregnant women, previously hospitalized for preeclampsia in a tertiary care center, were compared with 403 Dutch population-based controls. Results were statistically analyzed with a chi-square test.

MEAN OUTCOME MEASURES

The incidence of the 677 (C --> T) and 1298 (A --> C) polymorphisms in the MTHFR gene.

RESULTS

The incidence of both MTHFR missense polymorphisms was not significantly different between cases and controls. We found an odds ratio (OR) of 1.5 [95% confidence interval (CI) 0.8-2.6, p = 0.17] and an OR of 1.0 (95% CI 0.6-1.9, p = 0.23) for the 677 (C --> T) and the 1298 (A --> C) polymorphism, respectively, in cases comparing the prevalence of the homozygous genotype versus the other two genotypes. The meta-analysis resulted in a significant OR of 2.0 (95% CI 1.4-2.9).

CONCLUSIONS

In contrast to four previous studies, we were neither able to confirm an increased risk for preeclampsia to the 677 (C --> T) polymorphism nor did we find an increased risk for preeclampsia to the 1298 (A --> C) polymorphism. From the meta-analysis, however, we conclude that it cannot be ruled out that the homozygous 677TT genotype is a modest but significant risk factor for preeclampsia.

An Australian twin study of the genetic basis of preeclampsia and eclampsia

OBJECTIVE

We investigated maternal versus fetal genetic causes of preeclampsia and eclampsia by assessing concordance between monozygotic and dizygotic female co-twins, between female partners of male monozygotic and dizygotic twin pairs, and between female twins and partners of their male co-twins in dizygotic opposite-sex pairs.

STUDY DESIGN

Two large birth cohorts of volunteer Australian female twin pairs (N = 1504 pairs and N = 858 pairs) were screened and interviewed, and available medical and hospital records were obtained and reviewed where indicated, with diagnoses assigned according to predetermined criteria.

RESULTS

With strict diagnostic criteria used for preeclampsia and eclampsia, no concordant female twin pairs were found. Collapsing diagnoses of definite, probable, or possible preeclampsia or eclampsia resulted in very low genetic recurrence risk estimates.

CONCLUSION

Results from these two cohorts of female twin pairs do not support clear, solely maternal genetic influences on preeclampsia and eclampsia. Numbers of parous female partners of male twins were too low for conclusions to be drawn regarding paternal transmission.

A genome scan in families from Australia and New Zealand confirms the presence of a maternal susceptibility locus for pre-eclampsia, on chromosome 2

Epidemiological studies have shown that genetic factors contribute to the etiology of the common and serious pregnancy-specific disorder pre-eclampsia (PE)/eclampsia (E). Candidate-gene studies have provided evidence (albeit controversial) of linkage to several genes, including angiotensinogen on 1q42-43 and eNOS on 7q36. A recent medium-density genome scan in Icelandic families identified significant linkage to D2S286 (at 94.05 cM) on chromosome 2p12 and suggestive linkage to D2S321 (at 157.5 cM) on chromosome 2q23. In the present article, the authors report the results of a medium-density genome scan in 34 families, representing 121 affected women, from Australia and New Zealand. Multipoint nonparametric linkage analysis, using the GENEHUNTER-PLUS program, showed suggestive evidence of linkage to chromosome 2 (LOD=2.58), at 144.7 cM, between D2S112 and D2S151, and to chromosome 11q23-24, between D11S925 and D11S4151 (LOD=2.02 at 121.3 cM). Given the limited precision of estimates of the map location of disease-predisposing loci for complex traits, the present finding on chromosome 2 is consistent with the finding from the Icelandic study, and it may represent evidence of the same locus segregating in the population from Australia and New Zealand. The authors propose that the PE/E-linked locus on chromosome 2p should be designated the "PREG1" (pre-eclampsia, eclampsia gene 1) locus.

The eNOS gene: a candidate for the preeclampsia susceptibility locus?

OBJECTIVE

To investigate the endothelial cell nitric oxide synthase (eNOS) gene as a candidate for susceptibility to preeclampsia.

METHODS

Twenty-six Australian families containing 11 eclamptics, 59 severe preeclamptics, and 27 mild preeclamptics were used to test for linkage between the eNOS gene region and preeclampsia. Two microsatellite markers (D7S483 and D7S505) in the proximity of the eNOS gene were used.

MAIN OUTCOME MEASURES

Logarithm of odds (LOD) scores were used to examine the cosegregation of alleles with the disease under a variety of inheritance models. Model-independent analysis, affected pedigree member method (AFFPED), and pairwise haplotype sharing between affected sibs were also used.

RESULTS

Two-point LOD score analysis gave no evidence of linkage between preeclampsia and two markers in close proximity to the eNOS gene (LOD scores < 1) for any of the inheritance models investigated, with no evidence of heterogeneity between pedigrees. The AFFPED and the pairwise haplotype sharing test on affected sibs also gave no evidence of linkage (p-values > 0.05).

CONCLUSION

This study provides no evidence for linkage between two markers in close proximity to the eNOS gene and preeclampsia in these families. These results do not support the recent suggestion that eNOS could be a familial pregnancy-induced hypertension gene (Arngrimsson R, et al., Am J Hum Genet 1997;61:354-62). Distinguishing preeclampsia from other hypertensive disorders in pregnancy is difficult. Hypertension appears to be a consequence, rather than a primary cause of preeclampsia. Given the vasodilatory role of the eNOS gene product, it is possible that the linkage recently reported for eNOS reflects its relationship with hypertension rather than preeclampsia.