A genome-wide scan for preeclampsia in the Netherlands

STOX2 but not STOX1 is differentially expressed in decidua from pre-eclamptic women: data from the Second Nord-Trondelag Health Study

Variation in the Storkhead box-1 (STOX1) gene has previously been associated with pre-eclampsia. In this study, we assess candidate single nucleotide polymorphisms (SNPs) in STOX1 in an independent population cohort of pre-eclamptic (n = 1.139) and non-pre-eclamptic (n = 2.269) women (the HUNT2 study). We also compare gene expression levels of STOX1 and its paralogue, Storkhead box-2 (STOX2) in decidual tissue from pregnancies complicated by pre-eclampsia and/or fetal growth restriction (FGR) (n = 40) to expression levels in decidual tissue from uncomplicated pregnancies (n = 59). We cannot confirm association of the candidate SNPs to pre-eclampsia (P > 0.05). For STOX1, no differential gene expression was observed in any of the case groups, whereas STOX2 showed significantly lower expression in deciduas from pregnancies complicated by both pre-eclampsia and FGR as compared with controls (P = 0.01). We further report a strong correlation between transcriptional alterations reported previously in choriocarcinoma cells over expressing STOX1A and alterations observed in decidual tissue of pre-eclamptic women with FGR.

Genetic and molecular functional characterization of variants within TNFSF13B, a positional candidate preeclampsia susceptibility gene on 13q

BACKGROUND

Preeclampsia is a serious pregnancy complication, demonstrating a complex pattern of inheritance. The elucidation of genetic liability to preeclampsia remains a major challenge in obstetric medicine. We have adopted a positional cloning approach to identify maternal genetic components, with linkages previously demonstrated to chromosomes 2q, 5q and 13q in an Australian/New Zealand familial cohort. The current study aimed to identify potential functional and structural variants in the positional candidate gene TNFSF13B under the 13q linkage peak and assess their association status with maternal preeclampsia genetic susceptibility.

METHODOLOGY/PRINCIPAL FINDINGS

The proximal promoter and coding regions of the positional candidate gene TNFSF13B residing within the 13q linkage region was sequenced using 48 proband or founder individuals from Australian/New Zealand families. Ten sequence variants (nine SNPs and one single base insertion) were identified and seven SNPs were successfully genotyped in the total Australian/New Zealand family cohort (74 families/480 individuals). Borderline association to preeclampsia (p = 0.0153) was observed for three rare SNPs (rs16972194, rs16972197 and rs56124946) in strong linkage disequilibrium with each other. Functional evaluation by electrophoretic mobility shift assays showed differential nuclear factor binding to the minor allele of the rs16972194 SNP, residing upstream of the translation start site, making this a putative functional variant. The observed genetic associations were not replicated in a Norwegian case/control cohort (The Nord-Trøndelag Health Study (HUNT2), 851 preeclamptic and 1,440 non-preeclamptic women).

CONCLUSION/SIGNIFICANCE

TNFSF13B has previously been suggested to contribute to the normal immunological adaption crucial for a successful pregnancy. Our observations support TNFSF13B as a potential novel preeclampsia susceptibility gene. We discuss a possible role for TNFSF13B in preeclampsia pathogenesis, and propose the rs16972194 variant as a candidate for further functional evaluation.

Exon deletions of the EP300 and CREBBP genes in two children with Rubinstein-Taybi syndrome detected by aCGH

We demonstrate the utility of an exon coverage microarray platform in detecting intragenic deletions: one in exons 24-27 of the EP300 gene and another in exons 27 and 28 of the CREBBP gene in two patients with Rubinstein-Taybi syndrome (RSTS). RSTS is a heterogeneous disorder in which approximately 45-55% of cases result from deletion or mutations in the CREBBP gene and an unknown portion of cases result from gene changes in EP300. The first case is a 3-year-old female with an exonic deletion of the EP300 gene who has classic facial features of RSTS without the thumb and great toe anomalies, consistent with the milder skeletal phenotype that has been described in other RSTS cases with EP300 mutations. In addition, the mother of this patient also had preeclampsia during pregnancy, which has been infrequently reported. The second case is a newborn male who has the classical features of RSTS. Our results illustrate that exon-targeted array comparative genomic hybridization (aCGH) is a powerful tool for detecting clinically significant intragenic rearrangements that would be otherwise missed by aCGH platforms lacking sufficient exonic coverage or sequencing of the gene of interest.

The ERAP2 gene is associated with preeclampsia in Australian and Norwegian populations

Preeclampsia is a heritable pregnancy disorder that presents new onset hypertension and proteinuria. We have previously reported genetic linkage to preeclampsia on chromosomes 2q, 5q and 13q in an Australian/New Zealand (Aust/NZ) familial cohort. This current study centered on identifying the susceptibility gene(s) at the 5q locus. We first prioritized candidate genes using a bioinformatic tool designed for this purpose. We then selected a panel of known SNPs within ten prioritized genes and genotyped them in an extended set of the Aust/NZ families and in a very large, independent Norwegian case/control cohort (1,139 cases, 2,269 controls). In the Aust/NZ cohort we identified evidence of a genetic association for the endoplasmic reticulum aminopeptidase 1 (ERAP1) gene (rs3734016, P (uncorr) = 0.009) and for the endoplasmic reticulum aminopeptidase 2 (ERAP2) gene (rs2549782, P (uncorr) = 0.004). In the Norwegian cohort we identified evidence of a genetic association for ERAP1 (rs34750, P (uncorr) = 0.011) and for ERAP2 (rs17408150, P (uncorr) = 0.009). The ERAP2 SNPs in both cohorts remained statistically significant (rs2549782, P (corr) = 0.018; rs17408150, P (corr) = 0.039) after corrections at an experiment-wide level. The ERAP1 and ERAP2 genes encode enzymes that are reported to play a role in blood pressure regulation and essential hypertension in addition to innate immune and inflammatory responses. Perturbations within vascular, immunological and inflammatory pathways constitute important physiological mechanisms in preeclampsia pathogenesis. We herein report a novel preeclampsia risk locus, ERAP2, in a region of known genetic linkage to this pregnancy-specific disorder.

Role of C825T Polymorphism of GNβ3 Gene in Preeclampsia

OBJECTIVE

The main objective of the study was to understand the role of C825T polymorphism that generates a splice variant in the beta3 subunit of heterotrimeric G-protein in preeclampsia.

RESULTS

We analyzed genomic DNA of 151 women with preeclampsia (72 Caucasians and 79 African-Americans) and 198 women with normal delivery (102 Caucasians and 96 African-Americans) for C825T polymorphism of GNbeta3 gene. The T-allele frequency in Caucasian women with preeclampsia was 0.42 as compared to 0.25 in normal pregnant women (p = 0.0004) and in African-American women with preeclampsia was 0.82 as compared to 0.68 in normal pregnant women (p = 0.0028).

CONCLUSIONS

Results of these experiments show that the allele frequency of C825T polymorphism is significantly different in women with preeclampsia compared with women with normal delivery in Caucasian as well as African-American population.

Alpha-T-catenin (CTNNA3) gene was identified as a risk variant for toluene diisocyanate-induced asthma by genome-wide association analysis

BACKGROUND

Toluene diisocyanate (TDI) is the most important cause of occupational asthma, but the genetic mechanism of TDI-induced asthma is still unknown.

OBJECTIVE

The objective of the study was to identify susceptibility alleles associated with the TDI-induced asthma phenotype.

METHODS

We conducted a genome-wide association study in 84 patients with TDI-induced asthma and 263 unexposed healthy normal controls using Affymetrix 500K SNPchip. We also investigated the relationships between genetic polymorphisms and transcript levels in Epstein-Barr virus-transformed lymphoblastoid cell lines from patients with TDI-induced asthma enrolled in this study.

RESULTS

Genetic polymorphisms of CTNNA3 (catenin alpha 3, alpha-T catenin) were significantly associated with the TDI-induced asthma phenotype (5.84 x 10(-6) for rs10762058, 1.41 x 10(-5) for rs7088181, 2.03 x 10(-5) for rs4378283). Carriers with the minor haplotype, HT2 [GG], of two genetic polymorphisms (rs10762058 and rs7088181) showed significantly lower PC(20) methacholine level (P=0.041) and lower mRNA expression of CTNNA3 than non-carriers (P=0.040). A genetic polymorphism in the 3' downstream region of CTNNA3 (rs1786929), as identified by DNA direct sequencing, was significantly associated with the TDI-induced asthma phenotype (P=0.015 in recessive analysis model) and the prevalence of serum-specific IgG to cytokeratin 19 (P=0.031).

CONCLUSION

These findings suggested that multiple genetic polymorphisms of CTNNA3 may be determinants of susceptibility to TDI-induced asthma.

Association between the candidate susceptibility gene ACVR2A on chromosome 2q22 and pre-eclampsia in a large Norwegian population-based study (the HUNT study)

Genome-wide scans in Icelandic, Australian/New Zealand and Finnish pedigrees have provided evidence for maternal susceptibility loci for pre-eclampsia on chromosome 2, although at different positions (Iceland: 2p13 and 2q23, Australia/New Zealand: 2p11-12 and 2q22, Finland: 2p25). In this project, a large population-based (n=65 000) nested case-control study was performed in Norway to further explore the association between positional candidate genes on chromosome 2q and pre-eclampsia, using single-nucleotide polymorphisms (SNPs). DNA samples from 1139 cases (women with one or more pre-eclamptic pregnancies) and 2269 controls (women with normal pregnancies) were genotyped using the Applied Biosystems SNPlex high-throughput genotyping assay. In total, 71 SNPs within positional candidate genes at 2q22-23 locus on chromosome 2 were genotyped in each individual. Genotype data were statistically analysed with the sequential oligogenic linkage analysis routines (SOLAR) computer package. Nominal evidence of association was found for six SNPs (rs1014064, rs17742134, rs1424941, rs2161983, rs3768687 and rs3764955) within the activin receptor type 2 gene (ACVR2A) (all P-values <0.05). The non-independence of statistical tests due to linkage disequilibrium between SNPs at a false discovery rate of 5% identifies our four best SNPs (rs1424941, rs1014064, rs2161983 and rs3768687) to remain statistically significant. The fact that populations with different ancestors (Iceland/Norway-Australia/New Zealand) demonstrate a common maternal pre-eclampsia susceptibility locus on chromosome 2q22-23, may suggest a general role of this locus, and possibly the ACVR2A gene, in pre-eclampsia pathogenesis.

Genetic association of the activin A receptor gene (ACVR2A) and pre-eclampsia

Pre-eclampsia is a common serious disorder of human pregnancy, which is associated with significant maternal and perinatal morbidity and mortality. The suspected aetiology of pre-eclampsia is complex, with susceptibility being attributable to multiple environmental factors and a large genetic component. Recently, we reported significant linkage to chromosome 2q22 in 34 Australian/New Zealand (Aust/NZ) pre-eclampsia/eclampsia families, and activin A receptor type IIA (ACVR2A) was identified as a strong positional candidate gene at this locus. In an attempt to identify the putative risk variants, we have now comprehensively re-sequenced the entire coding region of the ACVR2A gene and the conserved non-coding sequences in a subset of 16 individuals from these families. We identified 45 single nucleotide polymorphisms (SNPs), with 9 being novel. These SNPs were genotyped in our total family sample of 480 individuals from 74 Aust/NZ pre-eclampsia families (including the original 34 genome-scanned families). Our best associations between ACVR2A polymorphisms and pre-eclampsia were for rs10497025 (P = 0.025), rs13430086 (P = 0.010) and three novel SNPs: LF004, LF013 and LF020 (all with P = 0.018). After correction for multiple hypothesis testing, none of these associations reached significance (P > 0.05). Based on these data, it remains unclear what role, if any, ACVR2A polymorphisms play in pre-eclampsia risk, at least in these Australian families. However, it would be premature to rule out this gene as significant associations between ACVR2A SNPs and pre-eclampsia have recently been reported in a large Norwegian (HUNT) population sample.

Placental protein 13 (galectin-13) has decreased placental expression but increased shedding and maternal serum concentrations in patients presenting with preterm pre-eclampsia and HELLP syndrome

Placental protein 13 (PP13) is a galectin expressed by the syncytiotrophoblast. Women who subsequently develop preterm pre-eclampsia have low first trimester maternal serum PP13 concentrations. This study revealed that third trimester maternal serum PP13 concentration increased with gestational age in normal pregnancies (p < 0.0001), and it was significantly higher in women presenting with preterm pre-eclampsia (p = 0.02) and hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome (p = 0.01) than in preterm controls. Conversely, placental PP13 mRNA (p = 0.03) and protein, as well as cytoplasmic PP13 staining of the syncytiotrophoblast (p < 0.05) was decreased in these pathological pregnancies compared to controls. No differences in placental expression and serum concentrations of PP13 were found at term between patients with pre-eclampsia and control women. In contrast, the immunoreactivity of the syncytiotrophoblast microvillous membrane was stronger in both term and preterm pre-eclampsia and HELLP syndrome than in controls. Moreover, large syncytial cytoplasm protrusions, membrane blebs and shed microparticles strongly stained for PP13 in pre-eclampsia and HELLP syndrome. In conclusion, parallel to its decreased placental expression, an augmented membrane shedding of PP13 contributes to the increased third trimester maternal serum PP13 concentrations in women with preterm pre-eclampsia and HELLP syndrome.

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.

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.

Genetic and epigenetic factors contribute to the onset of preeclampsia

Preeclampsia (PE) is a major cause of perinatal materno-foetal morbidity and pregnancy-associated-mortality in industrialized countries. Clinically, PE associates maternal pregnancy-induced hypertension with proteinuria. PE is often considered as a two-stage disease. The first stage is a shallow cytotrophoblastic invasion which induces cycles of hypoxia-reoxygenation at the placental level. Subsequently an abnormal expression pattern occurs and is followed by the release of soluble factors and trophoblastic debris in the maternal blood flow. These stimuli trigger the second phase of the disease, the maternal syndrome. Although some molecular actors have been recently identified, mechanisms of the disease onset remains poorly understood. It seems that combinations of genetic, epigenetic and environmental factors are involved. Here, we suggest that epigenetic marks have to be considered to decipher the physiopathological process of PE. Since these marks must be established early and are traceable in the maternal blood flow, they could constitute a diagnosis tool.

Amplification and specific expression of T-bet gene in nasal NK/T-cell lymphoma

To define the specific genetic alterations in nasal natural killer/T-cell lymphoma (N-NK/T-L), the assay of restriction landmark genomic scanning (RLGS), a genome-wide method, was used to investigate a pair of genomic DNA from N-NK/T-L cells and peripheral blood leukocytes of the same patient. The intensified spots in displayed N-NK/T-L gel of RLGS were subjected to bioinformatic analysis by virtual genome scan (VGS) and one of candidate spots proved to be T-bet gene (T-box expressed in T-cell). The pair of samples was consequently analysed by Southern hybridization, revealing genomic amplification of T-bet but not different status of DNA methylation. The amplification of T-bet was also discovered in other cases of N-NK/T-L by dot blotting. The expression of T-bet was investigated by in situ hybridization (ISH) and immunohistochemistry (IHC). The results showed that T-bet predominantly expressed in N-NK/T-L (ISH: 90.0%, 18/20; IHC: 80%, 16/20), while few cases of B-cell lymphoma (ISH: 11.8%, 2/17; IHC: 17.6%, 3/17) or T-cell lymphoma (ISH: 33.3%, 2/6; IHC: 16.7%, 1/6) were positive. The difference of T-bet expression in either ISH or IHC between N-NK/T-L and B-cell lymphoma or T-cell lymphoma was statistically significant (P < 0.05). Moreover, the expression of T-bet was not detected in normal spleen tissue and chronic inflammatory nasal mucosa. The results suggested that the amplification of T-bet gene or resulting its over-expression of T-bet gene might be involved in the development of N-NK/T-L and thus it should be worth confirming whether the over-expression of T-bet be helpful to the diagnosis of N-NK/T-L in further study.

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.

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.

Extremely skewed X-chromosome inactivation is increased in pre-eclampsia

Pre-eclampsia is a disorder that affects approximately 5% of pregnancies. We tested the hypothesis that skewed X-chromosome inactivation (XCI) could be involved in the pathogenesis of pre-eclampsia. Peripheral blood DNA was obtained from 67 pre-eclampsia patients and 130 control women. Androgen receptor (AR) was analyzed by the HpaII/polymerase chain reaction assay to assess XCI patterns in DNA extracted from peripheral-blood cells. In addition, buccal cells were obtained from seven patients, and the analysis repeated. Extremely skewed XCI was observed in 10 of 46 informative patients (21.74%), and in 2 of 86 informative controls (2.33%, P = 0.0005; chi(2) test). Our findings support a role for the X-chromosome in the pathogenesis of pre-eclampsia in a subgroup of patients.

Expressional and epigenetic alterations of placental serine protease inhibitors: SERPINA3 is a potential marker of preeclampsia

Preeclampsia is the major pregnancy-induced hypertensive disorder. It modifies the expression profile of placental genes, including several serine protease inhibitors (SERPINs). The objective of this study was to perform a systematic expression analysis of these genes in normal and pathological placentas and to pinpoint epigenetic alterations inside their promoter regions. Expression of 18 placental SERPINs was analyzed by quantitative RT-PCR on placentas from pregnancies complicated by preeclampsia, intrauterine growth restriction, or both and was compared with normal controls. SERPINA3, A5, A8, B2, B5, and B7 presented significant differences in expression in >or=1 pathological situation. In parallel, the methylation status of the CpG islands located in their promoter regions was studied on a sample of control and preeclamptic placentas. Ten SERPIN promoters were either totally methylated or totally unmethylated, whereas SERPINA3, A5, and A8 presented complex methylation profiles. For SERPINA3, the analysis was extended to 81 samples and performed by pyrosequencing. For the SERPINA3 CpG island, the average methylation level was significantly diminished in preeclampsia and growth restriction. The hypomethylated CpGs were situated at putative binding sites for developmental and stress response (hypoxia and inflammation) factors. Our results provide one of the first observations of a specific epigenetic alteration in human placental diseases and provide new potential markers for an early diagnosis.

Identification of two novel quantitative trait loci for pre-eclampsia susceptibility on chromosomes 5q and 13q using a variance components-based linkage approach

Pre-eclampsia/eclampsia (PE/E) is a common and serious disorder of human pregnancy that is associated with substantial maternal and perinatal morbidity and mortality. The suspected aetiology of PE/E is complex, with susceptibility being attributable to multiple environmental factors and a large genetic component. By assuming that the underlying liability towards PE/E susceptibility is inherently quantitative, any PE/E susceptibility gene would represent a quantitative trait locus (QTL). This assumption enables a more refined and powerful variance components procedure using a threshold model for our PE/E statistical analysis. Using this more efficient linkage approach, we have now re-analysed our previously completed Australian/New Zealand genome scan data to identify two novel PE/E susceptibility QTLs on chromosomes 5q and 13q. We have obtained strong evidence of linkage on 5q with a peak logarithm-of-odds (LOD) score of 3.12 between D5S644 and D5S433 [at approximately 121 centimorgan (cM)] and strong evidence of linkage on 13q with a peak LOD score of 3.10 between D13S1265 and D13S173 (at approximately 123 cM). Objective identification and prioritization of positional candidate genes using the quantitative bioinformatics program GeneSniffer revealed highly plausible PE/E candidate genes encoding aminopeptidase enzymes and a placental peptide hormone on the 5q QTL and two type IV collagens on the 13q QTL regions, respectively.

Genetics of preeclampsia: paradigm shifts

Segregation of preeclampsia into early-onset, placental and late-onset, maternal subtypes along with the acknowledgement of the contribution of epigenetics in placentally expressed genes proved to be a key first step in the identification of essential gene variants associated with preeclampsia. Application of this insight to other populations and related pregnancy-induced syndromes, such as HELLP, and acknowledgment of the features shared between chromosomal loci associated with preeclampsia in different populations provide the rationale for new strategies for the identification of susceptibility genes and for new and more effective diagnostic strategies.

Heterogeneity-based genome search meta-analysis for preeclampsia

Preeclampsia is a pregnancy-related disorder that causes maternal and fetal morbidity and mortality. Its exact inheritance pattern is still unknown, and genome searches for identifying susceptibility loci for preeclampsia have thus far produced inconclusive or inconsistent results. We performed a heterogeneity-based genome search meta-analysis (HEGESMA) that synthesized the available genome scan data on preeclampsia. HEGESMA identifies genetic regions (bins) that rank highly on average in terms of linkage statistics across genome scans (searches). The significance of each bin's average rank and heterogeneity across scans was calculated using Monte Carlo tests. The meta-analysis involved four genome-scans on general preeclampsia and five scans on severe preeclampsia. In general preeclampsia, 13 bins had significantly high average rank (Prank< 0.05) by either unweighted or weighted analyses, while four of them (2p11.2-2q21.1, 9q21.32-9q31.2, 2p15-2p11.2, 2q32.1-2q35) were formally significant by both analyses. Heterogeneity of bin 2.8 (2q32.1-2q35) was significantly low in both unweighted and weighted analysis (PQ< 0.01). In severe preeclampsia, 10 bins had significantly high average rank by either unweighted or weighted analyses and five of them (3q11.1-3q21.2, 2q37.1-2q37.3, 18p11.32-18p11.22, 2p15-2p11.2, 7q34-7q36.3) were significant by both analyses. Bin 2q37.1-2q37.3 showed marginal low heterogeneity in unweighted and weighted analysis (PQ= 0.06). Results should be interpreted with caution as the p values were modest. Further investigation of these regions by genotyping with additional markers and families may help to direct the identification of candidate genes for preeclampsia.

Prolylcarboxypeptidase gene, chronic hypertension, and risk of preeclampsia

OBJECTIVE

Renin-angiotensin System is essential for the homeostasis of blood pressure in humans. The roles of renin-angiotensin system gene polymorphisms including angiotensinogen, angiotensin-converting enzyme, renin and angiotensin II receptor, type 1 genes in the pathogenesis of preeclampsia have been extensively studied, but most association studies produced either negative or inconsistent results. Prolylcarboxypeptidase encodes a lysosomal enzyme and is a regulator for both renin-angiotensin system and the kallikrein-kinin system. There is no published study on prolylcarboxypeptidase gene and preeclampsia.

STUDY DESIGN

We investigated the independent and joint association of five polymorphisms in angiotensinogen, angiotensin-converting enzyme, and prolylcarboxypeptidase gene and chronic hypertension with the risk of preeclampsia in 125 preeclamptic and 1040 non-preeclamptic black women enrolled at the Boston Medical Center. We used logistic regression models to estimate the odds ratios of risk for preeclampsia associated with each gene polymorphism and its joint association with chronic hypertension.

RESULTS

No association was found in four polymorphisms in angiotensinogen and angiotensin-converting enzyme. Prolylcarboxypeptidase E112D (rs2298668) D allele along and jointly with chronic hypertension were associated with a significantly increased risk of preeclampsia. Compared to women with homozygous EE genotype and without chronic hypertension, higher risks of preeclampsia were observed in DD women without chronic hypertension (OR = 3.7, 95% CI, 1.2 - 12.4) and EE women with chronic hypertension (OR = 9.1, 95% CI: 4.7 - 17.6). Women with both D allele and chronic hypertension had the highest risk (OR = 158, 95% CI, 25-infinite). This finding was validated in an independent sample of 1,015 non-black women. We further compared the prolylcarboxypeptidase transcript levels in peripheral blood cells of 23 preeclamptic (30% with chronic hypertension) and 51 non-preeclamptic (6% with chronic hypertension) women 2 - 3 days after delivery. The PRCP transcript levels were lower in ED/DD women than in EE woman (P = .03) and lower in preeclamptic women than in non-preeclamptic women (P = .007).

CONCLUSION

Our data showed that prolylcarboxypeptidase D allele coupled with chronic hypertension was associated with a significantly increased risk of preeclampsia in both black and non-black women. Gene expression assays lent further support for the functional significance of prolylcarboxypeptidase in the etiology of preeclampsia.

Searching for genetic clues to the causes of pre-eclampsia

Pre-eclampsia and its related syndromes are significant causes of maternal and fetal death, but much remains unclear about the underlying disease mechanisms. Epidemiological research has consistently demonstrated a familial predisposition to pre-eclampsia, which has encouraged genetic research in this area. The goal is the discovery of susceptibility genes which will inform understanding of the pathophysiology of pre-eclampsia, and may prove to be targets for therapeutic or preventative strategies. This review examines the application of molecular technologies to the search for genetic clues in pre-eclampsia and emphasizes the importance of integrative approaches. The results of recent genome-wide linkage studies have been particularly encouraging, identifying a number of loci which merit closer examination. Candidate gene studies have proved less fruitful, generating conflicting and inconclusive results. Possible explanations and remedies for this deficiency are discussed with a view to stimulating closer collaboration between researchers in this field.

Gene expression profiling of human placentas from preeclamptic and normotensive pregnancies

The aim of this study was to investigate patterns of gene expression in placental samples from patients with preeclampsia (PE), persistent bilateral uterine artery notching (without PE), and normal controls. This study included placental tissue from nine women with PE, seven with uncomplicated pregnancies and five with bilateral uterine artery notching in Doppler velocimetry tracings. Human cDNA microarrays with 6500 transcripts/genes were used and the results verified with real-time PCR and in-situ hybridization. Multidimensional scaling method and random permutation technique demonstrated significant differences among the three groups examined. Within the 6.5K arrays, 6198 elements were unique cDNA clones representing 5952 unique UniGenes and 5695 unique LocusLinks. Multidimensional scaling plots showed 5000 genes that met our quality criteria; among these, 366 genes were significantly different in at least one comparison. Differences in three genes of interest were confirmed with real-time PCR and in-situ hybridization; acid phosphatase 5 was shown to be overexpressed in PE samples and calmodulin 2 and v-rel reticuloendotheliosis viral oncogene homolog A (RELA) were downregulated in PE and uterine artery notch placentas. In conclusion downregulation of RELA and calmodulin 2 might represent an attempt by the placenta to compensate for elevations in intracellular calcium, possibly caused by hypoxia and/or apoptosis, in both pregnancies with uterine artery notching and preeclampsia.

Circulating angiogenic proteins in trisomy 13

OBJECTIVE

Women who are carrying a trisomy 13 fetus are more prone to develop preeclampsia. Excess circulating soluble fms-like tyrosine kinase-1 has been implicated recently in the pathogenesis of preeclampsia. Since the fms-like tyrosine kinase-1/soluble fms-like tyrosine kinase-1 gene is located on chromosome 13q12, we hypothesized that the extra copy of this gene in trisomy 13 may lead to excess circulating soluble fms-like tyrosine kinase-1, reduced free placental growth factor level, and increased soluble fms-like tyrosine kinase-1/placental growth factor ratio. This may then contribute to the increased risk of preeclampsia that has been observed in these patients. Our objective was to characterize the maternal circulating angiogenic proteins in trisomy 13 pregnancies.

STUDY DESIGN

Maternal serum samples of trisomy 13, 18, 21 and normal karyotype pregnancies were obtained from first and second trimester screening programs. We chose 17 cases of trisomy 13 that were matched for maternal age, freezer storage time, and parity with 85 normal karyotype control samples. Additionally, 20 cases of trisomy 18 and 17 cases of trisomy 21 were included. Cases and control samples were assayed for levels of soluble fms-like tyrosine kinase-1 and placental growth factor by enzyme-linked immunosorbent assay in a blinded fashion. Because of the skewed distributions of soluble fms-like tyrosine kinase-1 and placental growth factor, nonparametric analytic techniques were used, and the results are reported as median and ranges.

RESULTS

In early pregnancy trisomy 13 cases and control samples, the median circulating soluble fms-like tyrosine kinase-1/placental growth factor ratios were 17.0 (range, 1.2-61.3) and 6.7 (range, 0.8-62.9), respectively (P = .003). The median soluble fms-like tyrosine kinase-1/placental growth factor ratios in trisomy 18 and 21 were 4.8 (range, 0.9-53.9) and 5.1 (range, 1.0-18.1), which were not significantly different than the control samples. Furthermore, the differences between trisomy 13 and control samples were more pronounced in the second trimester specimens than in the specimens from the first trimester.

CONCLUSION

These data suggest that alterations in circulating angiogenic factors may be involved intimately in the pathogenesis of preeclampsia in trisomy 13. A larger clinical study that measures these factors longitudinally and correlates them with pregnancy outcomes is needed to further establish the link between trisomy 13, altered angiogenic factors, and preeclampsia.

Mechanisms of Disease: pre-eclampsia

Pre-eclampsia, a syndrome of pregnant women, is one of the leading causes of maternal and fetal morbidity and mortality. Despite active research, the etiology of this disorder remains an enigma. Recent work has, however, provided promising explanations for the causation of the disorder and some of its phenotypes. Evidence indicates that the symptoms of hypertension and proteinuria, upon which the diagnosis of pre-eclampsia is based, have several underlying causes. Nevertheless, the treatment of pre-eclampsia has not changed significantly in over 50 years. This review describes the most recent insights into the pathophysiology of pre-eclampsia from both basic and clinical research, and attempts to provide a unifying hypothesis to reconcile the abnormalities at the feto-placental level and the clinical features of the maternal syndrome. The novel findings outlined in this review provide a rationale for potential future prophylactic and therapeutic interventions for pre-eclampsia.

Preeclampsia

Preeclampsia is a pregnancy complication with serious consequences for mother and infant. The disorder is diagnosed by gestational hypertension and proteinuria but is far more than pregnancy induced hypertension. Preeclampsia is proposed to occur in 2 stages. Stage 1 reduced placental perfusion is postulated as the root cause and to lead to the maternal syndrome, Stage 2. Why perfusion is reduced, how this translates to a maternal disease in some but not all women and what is the linkage of the 2 stages are topics of intense study. In the last decade such studies have provided valuable insights into pathophysiology that now guide ongoing clinical trials.

Novel biomarkers in preeclampsia

Preeclampsia is a pregnancy-associated disease with maternal symptoms, but placental origin. Although clinical symptoms are late, systemic and maternal, the origin of preeclampsia is early, local and placental. Despite that various protein biomarkers display changed levels in maternal serum at presymptomatic stages, they lack discriminative and predictive power in individual patients. In contrast to protein markers, placental RNA analyzed in maternal plasma permits rapid screening of novel biomarkers including markers not accessible by antibody based assays. This includes transcription factors, non-coding RNA, epigenetic features, as well as genes functionally or genetically linked with preeclampsia. By reviewing genes with placental expression in the Human SymAtlas and comparison with proven qualifiers, a large set of RNA biomarkers was targeted for use in maternal plasma. These biomarkers qualify as novel RNA biomarkers for the presymptomatic detection in first trimester of pregnancy-associated diseases with placental origin and/or dysfunction such as pregnancy-induced hypertension without or with proteinuria (preeclampsia), the HELLP syndrome, and intrauterine growth restriction.

Preeclampsia: a renal perspective

Preeclampsia is a syndrome that affects 5% of all pregnancies, producing substantial maternal and perinatal morbidity and mortality. The aim of this review is to summarize our current understanding of the pathogenesis of preeclampsia with special emphasis on the recent discovery that circulating anti-angiogenic proteins of placental origin may play an important role in the pathogenesis of proteinuria and hypertension of preeclampsia.

Maternal segregation of the Dutch preeclampsia locus at 10q22 with a new member of the winged helix gene family

Preeclampsia is a pregnancy-associated disease with maternal symptoms but placental origin. Epigenetic inheritance is involved in some populations. By sequence analysis of 17 genes in the 10q22 region with maternal effects, we narrowed the minimal critical region linked with preeclampsia in the Netherlands to 444 kb. All but one gene in this region, which lies within a female-specific recombination hotspot, encode DNA- or RNA-binding proteins. One gene, STOX1 (also called C10orf24), contained five different missense mutations, identical between affected sisters, cosegregating with the preeclamptic phenotype and following matrilineal inheritance. Four STOX1 transcripts are expressed in early placenta, including invasive extravillus trophoblast, generating three different isoforms. All contain a winged helix domain related to the forkhead (FOX) family. The largest STOX1 isoform has exclusive nuclear or cytoplasmic expression, indicating activation and inactivation, respectively, of the PI3K-Akt-FOX pathway. Because all 38 FOX proteins and all 8 STOX1 homologs have either tyrosine or phenylalanine at position 153, the predominant Y153H variation is highly mutagenic by conservation criteria but subject to incomplete penetrance. STOX1 is a candidate for preeclampsia controlling polyploidization of extravillus trophoblast.

Emerging technologies for the identification of therapeutic targets for the management of pre-eclampsia

Pre-eclampsia is a common and serious complication of pregnancy characterised by hypertension and proteinuria. Genetic and environmental factors influence the occurrence and progression of the disease. Emerging experimental systems and increasingly specific analytical methods for the study of differences between normal and pre-eclamptic placentae are close to identifying specific indicators of disease, which may allow early diagnosis and intervention and reveal targets against which therapeutic agents can be developed.

Differential downregulation of αT-catenin expression in placenta: trophoblast cell type-dependent imprinting of the CTNNA3 gene

The alphaE-catenin is a well-known invasion suppressor. A recently described novel alpha-catenin, i.e. alphaT-catenin (CTNNA3), shows related functions being necessary for the formation of cell-cell adhesion complexes. We recently demonstrated that the 10q21.3 region containing the CTNNA3 gene shows a parent-of-origin effect and that transcription of the CTNNA3 gene is downregulated in placental tissues of complete androgenetic origin. As this suggests that the CTNNA3 gene is subject to imprinting, we performed allele-specific RT-PCR on early placenta tissues using informative heterozygous samples. This was supplemented by immunostaining for alphaT-catenin, p57KIP2 and low molecular weight cytokeratin in tissues of a partial hydatidiform mole. As shown here we demonstrate that the CTNNA3 gene is subject to imprinting with preferential expression of the maternal allele in first trimester placental tissues. Imprinting, however, is trophoblast cell type-dependent: expression in extravillus trophoblast is biallelic; expression in villus cytotrophoblast is from the maternal allele only. Expression of alphaT-catenin is lost in villus syncytiotrophoblast as well as in extravillus trophoblast following epithelial-mesenchymal transition. The trophoblast cell type-dependent imprinting of CTNNA3 is identical to p57KIP2 imprinting with respect to trophoblast cell type (villus) and parental origin of the expressed allele (maternal). This suggests that gene dosage compensation of CTNNA3 and p57KIP2 in the placenta shares a conserved regulatory mechanism that correlates with an early step in trophoblast determination, i.e. differentiation into villus or extravillus trophoblast.

Spectrum of hypertensive emergencies in pregnancy

Hypertension in pregnancy represents a spectrum of clinical entities, including pregnancy-induced hypertension (PIH), preeclampsia, eclampsia, and hemolysis, elevated liver enzyme levels, low platelet count syndrome. Although hypertension is a common denominator in this group of disorders, the pathogenesis, clinical features, and clinical course of these disorders is variable and somewhat distinct. Therapy must be tailored to the clinical entity and the patient. The incidence and prevalence of preeclampsia and eclampsia is decreasing worldwide. This decrease partly may be caused by the improved treatment of PIH and improved obstetrical services.

Metformin, pre-eclampsia, and pregnancy outcomes in women with polycystic ovary syndrome

AIMS

Was metformin during pregnancy in women with polycystic ovary syndrome (PCOS) associated with pre-eclampsia, and was it safe for mother and neonate?

METHODS

In the current study, pre-eclampsia and other pregnancy outcomes were prospectively studied in 90 women with PCOS who conceived on metformin 1.5-2.55 g/day, and had > or = 1 live birth (97 pregnancies, 100 live births) compared with 252 healthy women (not known to have PCOS) with > or = 1 live birth, consecutively delivered in a community obstetrics practice.

RESULTS

Women with PCOS were older than controls (33 +/- 5 vs. 29 +/- 6 years, P < 0.0001), more likely to be > 35 years old at conception (23 vs. 13%, P = 0.028), much heavier (93 +/- 23 vs. 72 +/- 18 kg, P < 0.0001, BMI 33.8 +/- 7.8 kg/m2 vs. 25.6 +/- 5.9, P < 0.0001), and more likely to be Caucasian (97 vs. 90%, P = 0.05), but there were similar numbers with preconception Type 2 diabetes mellitus [2/90 (2.2%) vs. 1/252 (0.4%), P = 0.17]. Pre-eclampsia in PCOS (5/97 pregnancies, 5.2%), did not differ (P = 0.5) from controls (9/252, 3.6%), nor did it differ (P = 1.0) in PCOS vs. control primigravidas [2/45 (4.4%) vs. 4/91 (4.4%)]. Development of gestational diabetes in PCOS did not differ from controls [9/95 pregnancies (9.5%) vs. 40/251 (15.9%), P = 0.12]. Of the 100 live births to 90 women with PCOS, there were no major birth defects. Mean +/- sd birth weight of the 80 live births > or = 37 weeks gestation in women with PCOS (3414 +/- 486 g) did not differ from controls' 206 live births > or = 37 weeks (3481 +/- 555 g), P = 0.34, nor did the percentage of > or = 37 week gestation neonates > or = 4000 g (12.5 vs. 17.5%, P = 0.3) or > or = 4500 g (1.3 vs. 2.9%, P = 0.7).

CONCLUSIONS

Metformin is not associated with pre-eclampsia in pregnancy in women with PCOS, and appears to be safe for mother and fetus.

The parent-of-origin effect of 10q22 in pre-eclamptic females coincides with two regions clustered for genes with down-regulated expression in androgenetic placentas

By affected sib-pair linkage analysis of 24 families with pre-eclampsia, we confirm a susceptibility locus on chromosome 10q22.1 in Dutch females: a multipoint non-parametric linkage score of 3.6 near marker D10S1432 was obtained. Haplotype analysis showed a parent-of-origin effect: maximal allele sharing in the affected sibs was found for maternally derived alleles in all families, but not for the paternally derived alleles. As matrilineal inheritance suggests the presence of maternally expressed imprinted genes, while imprinting operates predominantly in (extra)embryonic tissues, all genes (n=132) known on 10q22 between GATA121A08 and D10S580 were screened for seven sequence-related features associated with imprinting and subsequently tested for expression in first trimester placenta. Placental expression of genes selected in this way (n=55) was compared with expression in androgenetic placentas of identical gestational age. Two regions on 10q22 were identified with developmentally co-repressed genes with non-random chromosomal distribution. Interestingly, these two clusters, near CTNNA3 and KCNMA1 and each containing five genes with down-regulated expression in androgenetic placentas, coincided with the regions with maximal maternal allele sharing seen in the pre-eclamptic sisters. Our linkage and expression data are compatible with the concept that pre-eclampsia involves maternally expressed imprinted genes that operate in the first trimester placenta.

Implication of an AGT Haplotype in a Multigene Association Study With Pregnancy Hypertension

Several association studies of candidate genes for preeclampsia and essential hypertension have led to discordant results, partly because of small sample sizes. Using a large population-based sample of pregnant women, we conducted an association study of 10 polymorphisms in 9 genes and aimed (1) to validate 10 published associations with preeclampsia or essential hypertension, (2) to investigate candidate polymorphisms previously associated with preeclampsia for association with essential hypertension and similarly with polymorphisms previously associated with essential hypertension. From a prospective sample of 3391 nulliparous French Canadian pregnant women, we identified 180 cases of preeclampsia, 203 cases of essential hypertension that were matched with normotensive control subjects (n=310 and 357, respectively). Polymorphisms were genotyped by allele-specific PCR. Among our candidate polymorphisms, the Met allele of Thr174Met of AGT was associated with preeclampsia ( P =0.0033). Haplotype analysis revealed that the A-Met-Thr (G1035A-Thr174Met-Met235Thr) haplotype was associated with a 2.1-fold increased risk of preeclampsia (95% CI, 1.4 to 3.4; P =0.0008). In conclusion, we observed a strong association between a specific AGT haplotype and preeclampsia in our population, without replicating previous published associations with either preeclampsia or essential hypertension. Our data support a role for AGT in genetic susceptibility to preeclampsia.

The genetics of pre-eclampsia: a feto-placental or maternal problem?

Pre-eclampsia is a potentially life-threatening disease of women during pregnancy leading to hypertension and proteinuria. It affects 1 in 15 pregnancies but, despite intense research efforts, the cause of the disease remains mysterious. Because pre-eclampsia only occurs during pregnancy and its symptoms resolve after delivery, factors from the placenta are thought to be involved. The role of the placenta could be production of 'abnormal' factors that initiate widespread inflammation and vaso-constriction. Alternatively, because the placenta normally contributes to maternal cardiovascular adaptations of pregnancy, it may be that normal placental functions fail in pre-eclampsia or that susceptibilities in the mother to hypertensive, vascular and/or renal disease prevent the appropriate normal responses to them. The potential contributions of both maternal and fetal genes to the onset of the disease have complicated the genetic analysis of the disease in humans. Recent studies have identified strains of transgenic and mutant mice that develop the hallmark features of pre-eclampsia-like disease - gestational hypertension, proteinuria and kidney lesions (glomerulosclerosis). Comparison of three different mouse models suggests that pre-eclampsia can be initiated by at least three independent mechanisms: pre-existing borderline maternal hypertension that is exacerbated by pregnancy (BPH/5 strain of mice), elevated levels of the vasoconstrictor angiotensin II in the maternal circulation by placental over-production of renin (renin/angiotensinogen transgenic mice), and placental pathology (p57Kip2 mutant mice). These findings imply that the pathogenesis of pre-eclampsia cannot be explained by a single mechanism. Therefore, segregation of the human disease into different subtypes may be a key first step in identifying genetic risk factors.

Microsatellite marker association at chromosome region 2p13 in Finnish patients with preeclampsia and obstetric cholestasis suggests a common risk locus

The pathophysiology of preeclampsia is incompletely understood, but the familial nature of the disease has long been recognized. Recent genome-scan studies have indicated linkage at the p23 region of chromosome 2. We have previously reported microsatellite marker association at chromosome region 2p13 in patients with obstetric cholestasis. We conducted population-based association screening with microsatellite markers to find potential preeclampsia-associated loci on chromosome region 2p13-p12 and to test whether preeclampsia and obstetric cholestasis share a single risk locus. The study was carried out among 115 unrelated control women, 133 preeclamptic women and 57 cholestatic women. Screening with microsatellite markers at the 2p13-p12 region revealed that the marker D2S286 was significantly associated with obstetric cholestasis in the overall association analysis (P=0.03), while it revealed only borderline association with preeclampsia (P=0.08). However, single allele association analysis indicated that both preeclampsia and obstetric cholestasis showed a statistically significant association with a common allele (P < 0.05), which was overrepresented in both the obstetric cholestasis (0.42) and preeclamptic (0.37) groups when compared with the control group (0.28). In conclusion, These findings suggest a possible genetic link between chromosome region 2p13-p12, preeclampsia and obstetric cholestasis. More specifically, these data suggest that there may be a common risk locus associated with both obstetric complications located in the vicinity of the 2p13-p12 association region.

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.

Susceptibility loci for preeclampsia on chromosomes 2p25 and 9p13 in Finnish families

Preeclampsia is a common, pregnancy-specific disorder characterized by reduced placental perfusion, endothelial dysfunction, elevated blood pressure, and proteinuria. The pathogenesis of this heterogeneous disorder is incompletely understood, but it has a familial component, which suggests that one or more common alleles may act as susceptibility genes. We hypothesized that, in a founder population, the genetic background of preeclampsia might also show reduced heterogeneity, and we have performed a genomewide scan in 15 multiplex families recruited predominantly in the Kainuu province in central eastern Finland. We found two loci that exceeded the threshold for significant linkage: chromosome 2p25, near marker D2S168 (nonparametric linkage [NPL] score 3.77; P=.000761) at 21.70 cM, and 9p13, near marker D9S169 (NPL score 3.74; P=.000821) at 38.90 cM. In addition, there was a locus showing suggestive linkage at chromosome 4q32 between D4S413 and D4S3046 (NPL score 3.13; P=.003238) at 163.00 cM. In the present study the susceptibility locus on chromosome 2p25 is clearly different (21.70 cM) from the locus at 2p12 found in an Icelandic study (94.05 cM) and the locus at 2q23 (144.7 cM) found in an Australian/New Zealand study. The locus at 9p13 has been shown to be a candidate region for type 2 diabetes in two recently published genomewide scans from Finland and China. The regions on chromosomes 2p25 and 9p13 may harbor susceptibility genes for preeclampsia.

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.

[Pregnancy-related hypertension]

PURPOSE

Hypertension occurs in 10 to 15 p cent of pregnancies. Among them, 10 to 20% also have proteinuria. This situation defines preeclampsia, and involves a serious threat on fetal and even maternal prognosis. Presence of the hepatic (HELLP) syndrome still severely worsens the prognosis.

CURRENT KNOWLEDGE AND KEY POINTS

Pathophysiology of preeclampsia is based on a very early abnormality of placentation, leading to insufficient blood supply to the feto-placental unit. At the maternal level, the main consequence of placental ischemia is generalized endothelial dysfunction, responsible for systemic vasoconstriction and clotting abnormalities. In such a context, lowering blood pressure with drugs is quite inefficient, or even harmful. The prognosis of this disease is mainly related to the pertinence of obstetrical management.

FUTURE PROSPECTS AND PROJECTS

An early preventive strategy is the most logical approach of preeclampsia, its modalities remain under discussion.