The association of endometriosis risk and genetic polymorphisms involving dioxin detoxification enzymes: A systematic review

Dioxin exposure associated with fecundability and infertility in mothers and daughters of Seveso, Italy

STUDY QUESTION

Is there an association between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure and fecundability and infertility among Seveso women and their daughters?

SUMMARY ANSWER

TCDD exposure is associated with a decrease in fecundability and increased risk of infertility in women, as well as their daughters.

WHAT IS KNOWN ALREADY

In animal studies, maternal exposure to TCDD is associated with decreased fertility in offspring. Effects of TCDD are mediated by activation of the aryl hydrocarbon receptor (AHR) pathway.

STUDY DESIGN, SIZE, DURATION

The Seveso Women's Health Study (SWHS) has followed 981 women exposed to TCDD in a 1976 accident since 1996. In 2014, we initiated the Seveso Second Generation Study to follow-up their children.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We obtained information on pregnancy history including time of trying to conceive from SWHS women and their daughters who were 18 years or older. We considered TCDD exposure as initial 1976 serum TCDD concentration and estimated TCDD at pregnancy. We examined relationships of TCDD exposure with time to pregnancy (TTP, the monthly probability of conception within the first 12 months of trying) and infertility (≥12 months of trying to conceive). We also assessed contributions of polymorphisms in the AHR pathway via genetic risk score.

MAIN RESULTS AND THE ROLE OF CHANCE

Among SWHS women (n = 446), median TTP was 3 months and 18% reported taking ≥12 months to conceive. Initial 1976 TCDD (log10) was associated with longer TTP (adjusted fecundability odds ratio = 0.82; 95% CI 0.68-0.98) and increased risk of infertility (adjusted relative risk = 1.35; 95% CI 1.01-1.79). TCDD at pregnancy yielded similar associations. Among SWHS daughters (n = 66), median TTP was 2 months and 11% reported taking ≥12 months to conceive. Daughters showed similar, but non-significant, associations with maternal TCDD exposure.

LIMITATIONS, REASONS FOR CAUTION

A limitation of this study is time to pregnancy was reported retrospectively, although previous studies have found women are able to recall time to conception with a high degree of accuracy many years after the fact. The number of SWHS daughters who had a live birth was small and we were unable to examine fecundability of SWHS sons.

WIDER IMPLICATIONS OF THE FINDINGS

Consistent with previous findings in animal studies, our study found that TCDD exposure may be associated with decreased fertility in Seveso mothers and potentially in their daughters exposed in utero. There may be susceptible genetic subgroups. The literature has largely considered the genetics of the AHR pathway in the context of male fertility but not female fertility, despite strong biological plausibility. These findings should be replicated in larger populations and of different ancestry. Future studies in Seveso should examine the sons and the grandchildren of exposed mothers given the animal literature suggesting potential heritable epigenetic effects.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grant numbers F06 TW02075-01 from the National Institutes of Health, R01 ES07171 and 2P30-ESO01896-17 from the National Institute of Environmental Health Sciences, R82471 from the U.S. Environmental Protection Agency and #2896 from Regione Lombardia and Fondazione Lombardia Ambiente, Milan, Italy. J.A. was supported by F31ES026488 from the National Institutes of Health. The authors declare they have no actual or potential competing financial interests.

TRIAL REGISTRATION NUMBER

N/A.

Polymorphisms and endometriosis: a systematic review and meta-analyses

BACKGROUND

Endometriosis is an estrogen-dependent gynecological disorder that affects at least 10% of women of reproductive age. It may lead to infertility and non-specific symptoms such as chronic pelvic pain. Endometriosis screening and diagnosis are difficult and time-consuming. Late diagnosis (with a delay ranging from 3.3 to 10.7 years) is a major problem and may contribute to disease progression and a worse response to treatment once initiated. Efficient screening tests might reduce this diagnostic delay. As endometriosis is presumed to be a complex disease with several genetic and non-genetic pathogenic factors, many researchers have sought to identify polymorphisms that predispose to this condition.

OBJECTIVE AND RATIONALE

We performed a systematic review and meta-analysis of the most regularly reported polymorphisms in order to identify those that might predispose to endometriosis and might thus be of value in screening.

SEARCH METHODS

The MEDLINE database was searched for English-language publications on DNA polymorphisms in endometriosis, with no date restriction. The PubTator text mining tool was used to extract gene names from the selected publications' abstracts. We only selected polymorphisms reported by at least three studies, having applied strict inclusion and exclusion criteria to their control populations. No stratification based on ethnicity was performed. All steps were carried out according to PRISMA guidelines.

OUTCOMES

The initial selection of 395 publications cited 242 different genes. Sixty-two genes (corresponding to 265 different polymorphisms) were cited at least in three publications. After the application of our other selection criteria (an original case-control study of endometriosis, a reported association between endometriosis and at least one polymorphism, data on women of reproductive age and a diagnosis of endometriosis in the cases established by surgery and/or MRI and confirmed by histology), 28 polymorphisms were eligible for meta-analysis. Only five of the 28 polymorphisms were found to be significantly associated with endometriosis: interferon gamma (IFNG) (CA) repeat, glutathione S-transferase mu 1 (GSTM1) null genotype, glutathione S-transferase pi 1 (GSTP1) rs1695 and wingless-type MMTV integration site family member 4 (WNT4) rs16826658 and rs2235529. Six others showed a significant trend towards an association: progesterone receptor (PGR) PROGINS, interCellular adhesion molecule 1 (ICAM1) rs1799969, aryl-hydrocarbon receptor repressor (AHRR) rs2292596, cytochrome family 17 subfamily A polypeptide 1 (CYP17A1) rs743572, CYP2C19 rs4244285 and peroxisome proliferator-activated receptor gamma (PPARG) rs1801282), and 12 showed a significant trend towards the lack of an association: tumor necrosis factor (TNF) rs1799964, interleukin 6 (IL6) rs1800796, transforming growth factor beta 1 (TGFB1) rs1800469, estrogen receptor 1 (ESR1) rs2234693, PGR rs10895068, FSH receptor (FSHR) rs6166, ICAM1 rs5498, CYP1A1 rs4646903, CYP19A1 rs10046, tumor protein 53 (TP53) rs1042522, X-ray repair complementing defective repair in Chinese hamster cells 1 (XRCC1) rs25487 and serpin peptidase inhibitor clade E member 1 (SERPINE1) rs1799889; however, for the 18 polymorphisms identified in the latter two groups, further studies of the potential association with the endometriosis risk are needed. The remaining five of the 28 polymorphisms were not associated with endometriosis: glutathione S-transferase theta 1 (GSTT1) null genotype, vascular endothelial growth factor alpha (VEGFA) rs699947, rs833061, rs2010963 and rs3025039.

WIDER IMPLICATIONS

By carefully taking account of how the control populations were defined, we identified polymorphisms that might be candidates for use in endometriosis screening and polymorphisms not associated with endometriosis. This might constitute the first step towards identifying polymorphism combinations that predispose to endometriosis (IFNG (CA) repeat, GSTM1 null genotype, GSTP1 rs1695, WNT4 rs16826658 and WNT4 rs2235529) in a large cohort of patients with well-defined inclusion criteria. In turn, these results might improve the diagnosis of endometriosis in primary care. Lastly, our present findings may enable a better understanding of endometriosis and improve the management of patients with this disease.

NAT2 gene polymorphisms and endometriosis risk: A PRISMA-compliant meta-analysis

OBJECTIVE

Endometriosis is a common chronic, gynecological disease. Despite many studies on the role of N-acetyltransferase 2 (NAT2) in endometriosis, its clinical significance is unclear. In this study, associations between NAT2 phenotypes as well as single nucleotide polymorphisms (SNPs) within NAT2 (i.e. rs1799929, rs1799930, rs1208, and rs1799931) and endometriosis risk were evaluated using a meta-analysis approach.

METHODS

Embase, PubMed, ClinicalTrials.gov, CNKI (China National Knowledge Infrastructure), Wanfang databases, Cochrane Library for clinical trials, and Web of Science were searched to identify relevant articles. ORs (odds ratios) and 95% CIs (95% confidence intervals) were used to estimate the associations between NAT2 polymorphisms and endometriosis risk. Heterogeneity among included studies was also assessed. In addition, a subgroup analysis of NAT2 phenotypes and endometriosis risk based on ethnicity was performed.

RESULTS

Nine case-control studies met the inclusion criteria. The odds ratio was 2.30 (95% CI: 1.61-3.28) for the NAT2 slow acetylation phenotype versus the intermediate + fast acetylation phenotype in the Asian population. These results suggest that Asian individuals with the NAT2 slow acetylation phenotype have a 130% increased risk of endometriosis. A significant association was also found for rs1799930 (OR = 0.74; 95% CI, 0.59-0.92), suggesting that individuals with this mutant genotype have a 26% decreased risk of endometriosis.

CONCLUSIONS

The rs1799930 mutant genotypes are associated with a decreased risk of endometriosis. No statistically significant associations were found between rs1799931, rs1208, or rs1799929 and endometriosis. Based on a subgroup analysis based on ethnicity, the NAT2 slow acetylation phenotype was found to increase the risk of endometriosis in Asians. No statistically significant associations were found between the NAT2 slow acetylation phenotype and endometriosis risk in Caucasians. Accordingly, NAT2 phenotypes and SNPs are potential biomarkers for the diagnosis and treatment of endometriosis.

The Pathogenesis of Endometriosis: Molecular and Cell Biology Insights

The etiopathogenesis of endometriosis is a multifactorial process resulting in a heterogeneous disease. Considering that endometriosis etiology and pathogenesis are still far from being fully elucidated, the current review aims to offer a comprehensive summary of the available evidence. We performed a narrative review synthesizing the findings of the English literature retrieved from computerized databases from inception to June 2019, using the Medical Subject Headings (MeSH) unique ID term "Endometriosis" (ID:D004715) with "Etiology" (ID:Q000209), "Immunology" (ID:Q000276), "Genetics" (ID:D005823) and "Epigenesis, Genetic" (ID:D044127). Endometriosis may origin from Müllerian or non-Müllerian stem cells including those from the endometrial basal layer, Müllerian remnants, bone marrow, or the peritoneum. The innate ability of endometrial stem cells to regenerate cyclically seems to play a key role, as well as the dysregulated hormonal pathways. The presence of such cells in the peritoneal cavity and what leads to the development of endometriosis is a complex process with a large number of interconnected factors, potentially both inherited and acquired. Genetic predisposition is complex and related to the combined action of several genes with limited influence. The epigenetic mechanisms control many of the processes involved in the immunologic, immunohistochemical, histological, and biological aberrations that characterize the eutopic and ectopic endometrium in affected patients. However, what triggers such alterations is not clear and may be both genetically and epigenetically inherited, or it may be acquired by the particular combination of several elements such as the persistent peritoneal menstrual reflux as well as exogenous factors. The heterogeneity of endometriosis and the different contexts in which it develops suggest that a single etiopathogenetic model is not sufficient to explain its complex pathobiology.

Pathogenesis of endometriosis: the genetic/epigenetic theory

OBJECTIVE

To study the pathophysiology of endometriosis.

DESIGN

Overview of observations on endometriosis.

SETTING

Not applicable.

PATIENT(S)

None.

INTERVENTIONS(S)

None.

MAIN OUTCOME MEASURE(S)

The hypothesis is compatible with all observations.

RESULT(S)

Endometriosis, endometrium-like tissue outside the uterus, has a variable macroscopic appearance and a poorly understood natural history. It is a hereditary and heterogeneous disease with many biochemical changes in the lesions, which are clonal in origin. It is associated with pain, infertility, adenomyosis, and changes in the junctional zone, placentation, immunology, plasma, peritoneal fluid, and chronic inflammation of the peritoneal cavity. The Sampson hypothesis of implanted endometrial cells following retrograde menstruation, angiogenic spread, lymphogenic spread, or the metaplasia theory cannot explain all observations if metaplasia is defined as cells with reversible changes and an abnormal behavior/morphology due to the abnormal environment. We propose a polygenetic/polyepigenetic mechanism. The set of genetic and epigenetic incidents transmitted at birth could explain the hereditary aspects, the predisposition, and the endometriosis-associated changes in the endometrium, immunology, and placentation. To develop typical, cystic ovarian or deep endometriosis lesions, a variable series of additional transmissible genetic and epigenetic incidents are required to occur in a cell which may vary from endometrial to stem cells. Subtle lesions are viewed as endometrium in a different environment until additional incidents occur. Typical cystic ovarian or deep endometriosis lesions are heterogeneous and represent three different diseases.

CONCLUSION(S)

The genetic epigenetic theory is compatible with all observations on endometriosis. Implications for treatment and prevention are discussed.

The AhRR-c.565C>G transversion may increase total antioxidant capacity levels of the seminal plasma in infertile men

The Aryl hydrocarbon receptor (AhR)-repressor (AhRR) is a regulator of the AhR pathway, which plays an important role in xenobiotic and reactive oxygen species (ROS) metabolism. Total antioxidant capacity (TAC) is a major factor in semen quality that protects sperm against ROS stress. Malondialdehyde (MDA) is the indicator of lipid peroxidation damage that is occurred due to ROSs. In this study, we determined and compared the MDA and TAC levels of infertile men's semen and blood plasma regarding genotype groups of AhRR-c.565C>G transversion. Semen and blood samples of 123 infertile males were collected from the Fatemeh Zahra IVF Centre, Babol, Iran. TAC and MDA levels of seminal and blood plasma were measured by TBARS and FRAP methods, respectively. Cases were genotyped by the PCR-RFLP method. The frequency of c.565C>G genotypes was determined as CC (34.14%), CG (55.28%) and GG (10.58%). Mean levels of TAC μm/L and MDA nmol/mL in semen plasma of CC, CG and GG groups were (1365.7, 1.28), (1542.8, 1.51) and (1860.2, 0.82), respectively. Also, mean levels of TAC μm/L and MDA nmol/mL in blood plasma samples in CC, CG and GG genotypes were (806.14, 1.168), (727.1, 1.006) and (635.7, 0.83), respectively. Comparison of marker levels between genotypes revealed that the TAC level of semen plasma in the GG genotype was significantly higher than its level in the CC group (p < 0.05). Our findings showed that in seminal plasma of infertile men with the GG genotype of AhRR-c.565C>G transversion, the level of total antioxidant capacity is significantly higher in comparison with the CC genotype. Then, the G allele of AhRR-c.565C>G transversion may have a role in the increase in antioxidant capacity of seminal plasma.

The cytochrome P4501A1 gene polymorphisms and endometriosis: a meta-analysis

PURPOSE

Cytochrome P450 1A1 (CYP1A1) polymorphisms were implicated in endometriosis risk, but individual published studies showed inconclusive results. Thus, a meta-analysis was performed to clarify the effect of CYP1A1 polymorphisms on endometriosis risk.

METHODS

PubMed, Embase, and CNKI databases were searched to identify the eligible studies focusing on the associations between CYP1A1 MspI and Ile462Val polymorphisms and susceptibility to endometriosis. Summary odds ratios (ORs) and 95 % confidence intervals (95 % CIs) for CYP1A1 polymorphisms and endometriosis were calculated.

RESULTS

Pooled analysis of 12 studies involved a total of 1555 cases and 2868 controls showed that in all genetic models, no significant association between CYP1A1 MspI polymorphism and endometriosis risk was observed in the overall, Asians and Caucasians population, respectively. Interestingly, increased endometriosis risk was associated with carrying the C allele of CYP1A1 combined with GSTM1 null genotypes. For CYP1A1 Ile462Val polymorphism, eight studies were available (878 cases and 1991 controls). In the overall analysis, CYP1A1 Ile462Val polymorphism had a statistically significant association with increased endometriosis risk in allele contrast and all genetic models except the model of Val/Ile vs. Ile/Ile. In the subgroup analysis by ethnicity, significant elevated endometriosis risk was associated with CYP1A1 Ile462Val polymorphism in Asians but not in Caucasians under all genetic models. No publication bias was found in the present studies.

CONCLUSIONS

This meta-analysis suggested that CYP1A1 Ile462Val polymorphism was associated with an increased risk of endometriosis, particularly in Asians. CYP1A1 MspI polymorphism may not be associated with endometriosis risk, but GSTM1 and CYP1A1 MspI polymorphism may have a joint effect on endometriosis risk.

Exposure to the environmental endocrine disruptor TCDD and human reproductive dysfunction: Translating lessons from murine models

Humans and other animals are exposed to a wide array of man-made toxicants, many of which act as endocrine disruptors that exhibit differential effects across the lifespan. In humans, while the impact of adult exposure is known for some compounds, the potential consequences of developmental exposure to endocrine disrupting chemicals (EDCs) is more difficult to ascertain. Animal studies have revealed that exposure to EDCs prior to puberty can lead to adult reproductive disease and dysfunction. Specifically, in adult female mice with an early life exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we demonstrated a transgenerational occurrence of several reproductive diseases that have been linked to endometriosis in women. Herein, we review the evidence for TCDD-associated development of adult reproductive disease as well as known epigenetic alterations associated with TCDD and/or endometriosis. We will also introduce new "Organ-on-Chip" models which, combined with our established murine model, are expected to further enhance our ability to examine alterations in gene-environment interactions that lead to heritable disease.

Association between glutathione S-transferase M1/T1 gene polymorphisms and susceptibility to endometriosis: A systematic review and meta-analysis

Endometriosis is a polygenic/multifactorial disease caused by interactions between multiple genes and the environment. Findings from studies evaluating the association between the glutathione S-transferase (GST) M1/T1 null genotype and susceptibility to endometriosis are inconsistent. This meta-analysis updated and reevaluated the possible associations between GSTM1, GSTT1 and combined GSTM1/GSTT1 (null genotype versus wild-type) gene polymorphisms and susceptibility to endometriosis. The PubMed, Embase and Chinese BioMedical Literature databases and Google Scholar were searched for case-control genetic association studies on GSTM1/GSTT1 (null genotype versus wild-type) gene polymorphisms and endometriosis in comparison with non-endometriosis or healthy controls. Fixed-effect and random-effect meta-analytical techniques were conducted for the outcome measure and subgroup analyses. The meta-analysis demonstrated significant associations between the GSTM1 [odds ratio (OR)=1.56; 95% confidence interval (CI): 1.25–1.95; P<0.0001), GSTT1 (OR=1.31; 95% CI: 1.02–1.68; P=0.037) and GSTM1/GSTT1 (OR=1.68; 95% CI: 1.29–2.17; P<0.0001) null genotypes and increased risk for endometriosis. The results suggest that the GSTM1, GSTT1, and combined GSTM1/GSTT1 null genotypes increase susceptibility to endometriosis. Additional well-designed studies and precise analyses are warranted to confirm these findings.

A current view of the role of epigenetic changes in the aetiopathogenesis of endometriosis

The purpose of the study was to examine the role of epigenetic changes in the aetiopathogenesis of endometriosis. The analysis and review of the relevant current literature in English language related to the role of epigenetic changes in the aetiopathogenesis of endometriosis. Epigenetic changes are common denominators for hormonal, immunological and inflammatory aberrations which play a key role in the aetiopathogenesis of endometriosis. Many internal and external factors may cause the different running of the epigenetic mechanism. As yet fully unknown genetic factors may increase the sensitivity of the epigenetic mechanism to various internal and external factors. The breakdown of epigenetic regulation is the main factor initiating the pathogenetic mechanisms for endometriosis formation.

Meta-analysis of the association of AhR Arg554Lys, AhRR Pro185Ala, and ARNT Val189Val polymorphisms and endometriosis risk in Asians

PURPOSE

Several studies have suggested an association between the polymorphisms AhR Arg554Lys, AhRR Pro185Ala, and ARNT Val189Val and endometriosis, but results have been inconclusive. The aim of the present study was to assess these associations by meta-analysis.

METHODS

Eligible literatures were retrieved from PubMed, ISI Web of Science, Elsevier Science Direct, and several Chinese databases. The pooled odds ratios (ORs) and the corresponding 95 % confidence intervals (CIs) were calculated with a random or fixed-effect model.

RESULTS

A total of six eligible studies were included. Regarding the AhR Arg554Lys and ARNT Val189Val polymorphisms, no obvious associations were found in either overall analysis or subgroup analysis based on the country, source of control, sample size, and genotyping method. For the AhRR Pro185Ala polymorphism, overall results suggested a marginal association with endometriosis susceptibility under the dominant model (OR = 1.65, 95 % CI = 1.00-2.72). Furthermore, a significantly increased risk for endometriosis was found in the subgroups which used the TaqMan method for genotype analysis or had a sample size ≥200.

CONCLUSIONS

This meta-analysis suggested that the polymorphisms of AhR Arg554Lys and ARNT Val189Val are not associated with endometriosis, while the AhRR Pro185Ala polymorphism may be associated with endometriosis risk. However, further case-control studies with larger sample sizes are needed to confirm our results.

Screening of a panel of steroid-related genes showed polymorphisms of aromatase genes confer susceptibility to advanced stage endometriosis in the Taiwanese Han population

OBJECTIVE

To establish a multilocus model for studying the effect of steroid-related genes on advanced stage endometriosis.

MATERIALS AND METHODS

A total of 121 patients with advanced stage endometriosis and 171 control women were included. Eighteen single-nucleotide polymorphisms (SNPs) from nine genes (HSD17B1, HSD17B2, HSD17B5, HSD17B6, CYP17, CYP19, ERα, ERβ, and PGR) were genotyped using the TaqMan assays. Logistic regression models were used to evaluate the genetic effects, with adjustment for other covariates.

RESULTS

Only the presence of the mutant CYP19 (aromatase gene) was associated with a significantly increased risk of endometriosis after adjusting for age, BMI, and parity (p = 0.002, OR = 2.69; 95% CI = 1.44-5.02). No association was ascertained between the other investigated SNPs and endometriosis.

CONCLUSION

Polymorphisms of the aromatase gene confer susceptibility to advanced stage endometriosis in the Taiwanese Han population.

Null genotypes of GSTM1 and GSTT1 and endometriosis risk: a meta-analysis of 25 case-control studies

Endometriosis is one of the most frequent benign gynecological disorders. Numerous studies have shown an association between GSTM1 and/or GSTT1 polymorphisms and endometriosis susceptibility. However, these associations remain inconclusive. To derive a more precise estimation, we conducted a comprehensive search to identify all existing studies and then performed a meta-analysis. Electronic literature searches of the PubMed, Chinese Biomedical, and China National Knowledge Infrastructure databases were performed up to December 2013. GSTM1-, GSTT1-, and dual-null genotypes were analyzed independently, and pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated by comparing the null genotype with other genotypes using the random-effects or fixed-effects model. Twenty-five and 16 independent studies on GSTM1 and GSTT1 polymorphisms, respectively, and five GSTM1-GSTT1 interaction analyses were identified and included in this meta-analysis. Both GSTM1- and GSTT1-null genotypes increased risk of endometriosis (OR = 1.54, 95% CI: 1.30-1.83, P<0.001; OR = 1.41, 95% CI: 1.10-1.82, P = 0.007; respectively). Moreover, we found a significant positive association between the dual null genotype GSTM1-GSTT1 and endometriosis susceptibility (OR = 1.33, 95% CI: 1.03-1.72, P = 0.027). This meta-analysis provides evidence that null genotypes of GSTM1 and/or GSTT1 contribute to risk of endometriosis. Further investigations are required to confirm these findings.

Guidelines for the design, analysis and interpretation of 'omics' data: focus on human endometrium

BACKGROUND

'Omics' high-throughput analyses, including genomics, epigenomics, transcriptomics, proteomics and metabolomics, are widely applied in human endometrial studies. Analysis of endometrial transcriptome patterns in physiological and pathophysiological conditions has been to date the most commonly applied 'omics' technique in human endometrium. As the technologies improve, proteomics holds the next big promise for this field. The 'omics' technologies have undoubtedly advanced our knowledge of human endometrium in relation to fertility and different diseases. Nevertheless, the challenges arising from the vast amount of data generated and the broad variation of 'omics' profiling according to different environments and stimuli make it difficult to assess the validity, reproducibility and interpretation of such 'omics' data. With the expansion of 'omics' analyses in the study of the endometrium, there is a growing need to develop guidelines for the design of studies, and the analysis and interpretation of 'omics' data.

METHODS

Systematic review of the literature in PubMed, and references from relevant articles were investigated up to March 2013.

RESULTS

The current review aims to provide guidelines for future 'omics' studies on human endometrium, together with a summary of the status and trends, promise and shortcomings in the high-throughput technologies. In addition, the approaches presented here can be adapted to other areas of high-throughput 'omics' studies.

CONCLUSION

A highly rigorous approach to future studies, based on the guidelines provided here, is a prerequisite for obtaining data on biological systems which can be shared among researchers worldwide and will ultimately be of clinical benefit.

Environmental Influences on the Development of Endometriosis

Purpose

Several environmental toxicants (ETs), including dioxins and dioxin-like compounds (DLCs), perfluorochemicals, organochlorine pesticides, phthalates, and heavy metals (especially cadmium with its estrogen-like properties in animal models) have been investigated as possibly being related to endometriosis.

Methods

Systematic review of pertinent literature.

Results

DLCs have been the most investigated ETs. DLCs are persistent organic pollutants with highly toxic potential and include three types of compounds: polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) or furans, and polychlorinated biphenyls (PCBs). The most toxic is 2, 3, 7, 8- tetrachlorodibenzo-p-dioxin (TCDD). The connection mechanism between dioxins and endometriosis is still unclear. However, dioxins and DLCs are endocrine-disrupting compounds that can affect the pathobiology of endometriosis at multiple levels. Part of the dioxin and DLCs toxic effects can be accounted for by their interaction with the aryl hydrocarbon receptor (AhR). It has been proposed that dioxin can initiate or promote endometriosis by means of interaction with estrogen receptors or by suppressing the expression of progesterone receptors. Furthermore, TCDD alters the expression of cytokines and growth factors, remodeling enzymes and cytochrome P450 expression and activity.

Conclusions

Studies in rhesus models have revealed a correlation between dioxin exposure and endometriosis. However, evidence from epidemiologic studies is inconclusive.

Genetic variation in the sex hormone metabolic pathway and endometriosis risk: an evaluation of candidate genes

OBJECTIVE

To evaluate the relationship between common genetic variation in genes involved in the biosynthesis and signaling of estrogen and progesterone and endometriosis risk.

DESIGN

Genetic polymorphism analysis.

SETTING

Population-based case-control study conducted in Group Health Cooperative enrollees in western Washington.

PATIENT(S)

Women with newly diagnosed, surgically confirmed endometriosis between 1996 and 2001 (n = 256) and age- and reference year-matched female control subjects without a history of endometriosis (n = 567).

INTERVENTIONS(S)

None.

MAIN OUTCOME MEASURE(S)

We evaluated the relationship between common genetic variation and endometriosis risk, using gene-based tests and single-variant analysis of genetic polymorphisms in ESR1, ESR2, PGR, CYP17A1, CYP19A1, HSD17B1, HSD17B2, CYP1A1, CYP1A2, COMT, and GSTM1.

RESULT(S)

The most consistent gene-based association with endometriosis risk was for CYP19A1. We did not find evidence for consistent significant associations between previously reported candidate SNPs in sex hormone-related genes and endometriosis risk.

CONCLUSION(S)

In summary, we report increased endometriosis risk with CYP19A1 gene-based tests; replication of the association between endometriosis and this gene or gene region is necessary in a larger study population.

Single nucleotide polymorphisms in the human aryl hydrocarbon receptor nuclear translocator (ARNT) gene

Species' variation(s) in gene homologues can result in differences among species in their quantitative and qualitative susceptibility and responsiveness to environmental contaminants. In the case of dioxin-like compounds (DLCs), it has been hypothesized that single nucleotide polymorphisms (SNPs) in genes associated with aryl hydrocarbon receptor (AHR)-regulated pathways may result in greater susceptibility to DLC toxicity. A key step in the activation of AHR involves heterodimerization with the AHR nuclear translocator (ARNT) protein before binding to its DNA response element. The objective of this study was to identify SNPs in the human ARNT gene that could potentially affect the sensitivity of AHR-dependent gene transcription. Results from DNA sequencing of 101 human samples demonstrated the presence of five unique SNPs at the ARNT locus, including three non-synonymous SNPs, of which two were novel: V304M and T462A. The genetic frequencies of the non-synonymous SNPs were very low (≤0.02), and the novel SNPs occurred in the Per-ARNT-Sim (PAS) functional domain. In silico analysis indicated that V304M was the only SNP identified in the current population with the potential to significantly alter ARNT protein function. Our findings indicated a very limited occurrence of SNPs with predicted functional consequence in key domains of human ARNT.

Genetics and genomics of endometriosis

Endometriosis is a common cause of morbidity in women with an unknown etiology. Studies have demonstrated the familial nature of endometriosis and suggest that inheritance occurs in a polygenic/multifactorial fashion. Studies have attempted to define the gene or genes responsible for endometriosis through association or linkage studies with candidate genes or DNA mapping technology. A number of genomics studies have demonstrated significant alterations in gene expression in endometriosis. A more thorough understanding of the genetics and genomics of endometriosis will facilitate understanding the basic biology of the disease and open new inroads to diagnosis and treatment of this enigmatic condition.

Role of CYP2C19 polymorphisms in patients with endometriosis

AIM

To investigate the association of CYP2C19 genotypes with endometriosis.

METHODS

The study included 100 women who underwent laparotomy or laparoscopy: 50 patients with endometriosis diagnosed with surgery and histopathology, and 50 control subjects who had no evidence of endometriosis during exploratory laparotomy or laparoscopy. Genomic DNA of subjects was extracted from the whole blood using High Pure PCR template preparation kit. Genotyping of CYP2C19 polymorphisms were detected by using a LightCycler CYP2C19 mutation detection kit in a real-time PCR, and were compared between the two groups.

RESULTS

Logistic regression analyses showed that the CYP2C19*2 heterozygote genotype was associated with a significantly increased risk of endometriosis. The odds ratio of endometriosis for the CYP2C19*2 heterozygote genotype was 3.165 (p = 0.023) compared with the control group. CYP2C19*3 genotype was detected as wild in all subjects in the endometriosis and control groups.

CONCLUSION

Our results suggest that CYP2C19*2 heterozygote genotype has higher risk of developing endometriosis. Therefore, CYP2C19*2 allele gene polymorphisms may be associated with genetic susceptibility of endometriosis.

Nonhuman primate models for translational research in endometriosis

Endometriosis, defined as the ectopic presence of endometrial-like cells, is associated with infertility and pelvic pain in women. Whereas pathogenesis and spontaneous evolution of endometriosis are still poorly understood, recurrences after surgical therapy or after medical treatment are common. Spontaneous endometriosis occurs only in women and in nonhuman primates (NHPs). Inbred rhesus monkeys kept in colonies offer an attractive preclinical model to study the inheritance of spontaneous endometriosis. Baboons with spontaneous or induced endometriosis appear to be the best NHP model to study pathogenesis, pathophysiology, spontaneous evolution and new medical treatment options. In baboons, induction of endometriosis after intrapelvic injection of menstrual endometrium leads to biological changes in peritoneal cavity and in endometrium. This induction process may allows the study of cause-effect relationships which may lead to the discovery of new biomarkers for the development of new non-invasive diagnostic tests and drugs that may prevent or treat endometriosis.

The active form of human aryl hydrocarbon receptor (AHR) repressor lacks exon 8, and its Pro 185 and Ala 185 variants repress both AHR and hypoxia-inducible factor

The aryl hydrocarbon receptor (AHR) repressor (AHRR) inhibits AHR-mediated transcription and has been associated with reproductive dysfunction and tumorigenesis in humans. Previous studies have characterized the repressor function of AHRRs from mice and fish, but the human AHRR ortholog (AHRR(715)) appeared to be nonfunctional in vitro. Here, we report a novel human AHRR cDNA (AHRRDelta8) that lacks exon 8 of AHRR(715). AHRRDelta8 was the predominant AHRR form expressed in human tissues and cell lines. AHRRDelta8 effectively repressed AHR-dependent transactivation, whereas AHRR(715) was much less active. Similarly, AHRRDelta8, but not AHRR(715), formed a complex with AHR nuclear translocator (ARNT). Repression of AHR by AHRRDelta8 was not relieved by overexpression of ARNT or AHR coactivators, suggesting that competition for these cofactors is not the mechanism of repression. AHRRDelta8 interacted weakly with AHR but did not inhibit its nuclear translocation. In a survey of transcription factor specificity, AHRRDelta8 did not repress the nuclear receptor pregnane X receptor or estrogen receptor alpha but did repress hypoxia-inducible factor (HIF)-dependent signaling. AHRRDelta8-Pro(185) and -Ala(185) variants, which have been linked to human reproductive disorders, both were capable of repressing AHR or HIF. Together, these results identify AHRRDelta8 as the active form of human AHRR and reveal novel aspects of its function and specificity as a repressor.

Functional genetic polymorphisms and female reproductive disorders: part II--endometriosis

BACKGROUND

Endometriosis has a strong genetic component, and numerous genetic studies have been reported.

METHODS

We have systematically reviewed these studies and included 114 in our final selection.

RESULTS

We found no consistent evidence linking endometriosis with specific polymorphisms in genes encoding inflammatory mediators, proteins involved in sex steroid metabolism, vascular function and tissue remodelling. Although a number of polymorphisms have been associated with endometriosis in selected populations, the associations have not been independently confirmed, either because only single studies were carried out on these markers/genes or because other studies reported no association. The most solid evidence linking specific polymorphisms to endometriosis came from studies investigating glutathione-S-transferase, a phase II detoxification enzyme. Carriage of the GSTT1 null deletion variant showed consistent association with endometriosis with a 29% increased risk; however, it cannot be excluded that this result was due to publication bias, and this association should be independently confirmed in large-scale, well-designed case–control studies.

CONCLUSIONS

The evidence of an association between genetic polymorphisms and endometriosis is weak. Carriage of the GSTT1 null deletion may moderately increase the risk of this disease. We suggest that the methodology of association studies should be improved in order to identify and validate associations in endometriosis.

The search for genes contributing to endometriosis risk

BACKGROUND

Genetic variation contributes to the risk of developing endometriosis. This review summarizes gene mapping studies in endometriosis and the prospects of finding gene pathways contributing to disease using the latest genome-wide strategies.

METHODS

To identify candidate-gene association studies of endometriosis, a systematic literature search was conducted in PubMed of publications up to 1 April 2008, using the search terms 'endometriosis' plus 'allele' or 'polymorphism' or 'gene'. Papers included were those with information on both case and control selection, showed allelic and/or genotypic results for named germ-line polymorphisms and were published in the English language.

RESULTS

Genetic variants in 76 genes have been examined for association, but none shows convincing evidence of replication in multiple studies. There is evidence for genetic linkage to chromosomes 7 and 10, but the genes (or variants) in these regions contributing to disease risk have yet to be identified. Genome-wide association is a powerful method that has been successful in locating genetic variants contributing to a range of common diseases. Several groups are planning these studies in endometriosis. For this to be successful, the endometriosis research community must work together to genotype sufficient cases, using clearly defined disease classifications, and conduct the necessary replication studies in several thousands of cases and controls.

CONCLUSIONS

Genes with convincing evidence for association with endometriosis are likely to be identified in large genome-wide studies. This will provide a starting point for functional and biological studies to develop better diagnosis and treatment for this debilitating disease.

The contribution of genetic variations of aryl hydrocarbon receptor pathway genes to male factor infertility

OBJECTIVE

To determine whether the polymorphisms in aryl hydrocarbon receptor (AHR), aryl hydrocarbon receptor repressor (AHRR), and aryl hydrocarbon receptor nuclear translocator (ARNT) genes are associated with male factor infertility.

DESIGN

An association study.

SETTING

University research laboratory and andrology clinic.

PATIENT(S)

The subjects were infertile Estonian men (n = 112) with azoospermia or oligozoospermia and controls (n = 212) with normal sperm parameters.

INTERVENTION(S)

Blood samples were obtained for DNA extraction and genotyping.

MAIN OUTCOME MEASURE(S)

AHR (Arg554Lys), AHRR (Pro185Ala), and ARNT (G/C allele) polymorphisms were genotyped using allele-specific polymerase chain reaction. Allele and genotype frequencies were compared between infertile men and controls and separately in the normozoospermia, oligozoospermia, and azoospermia groups.

RESULT(S)

The AHRR Ala185Ala genotype was implicated in susceptibility to male factor infertility. Ala/Ala genotype frequency increased in the following order: normozoospermia (18.0%), oligozoospermia (26.0%), azoospermia (42.1%). Allele and genotype frequencies of AHR and ARNT polymorphisms were similar between cases and controls.

CONCLUSION(S)

We demonstrated that the AHRR Pro185Ala polymorphism contributed to a predisposition to male factor infertility in the Estonian population. A greater prevalence of the Ala/Ala genotype was found among infertile patients.

Endometriosis and Genetic Polymorphisms

Endometriosis is a benign gynecological disease with an unclear pathophysiology characterized by ectopic endometrium causing endometrium-like inflammatory lesions outside the uterine cavity. Recently, a number of studies have investigated genetic polymorphisms as a possible factor contributing to the development of endometriosis. In this review, we have summarized current data regarding genes with nucleotide polymorphisms investigated with regard to endometriosis. We searched PubMed for publications on endometriosis and polymorphism and found 108 publications between January 1979 and September 2005. These were classified according to the type of genetic polymorphism investigated and whether the result favored or did not favor association with endometriosis. We found a strikingly large amount of conflicting results. About 50% of the reviewed studies demonstrated positive correlations between different polymorphisms and endometriosis. This relation is most clearly seen in groups 1 (cytokines and inflammation), 2 (steroid-synthesizing enzymes and detoxifying enzymes and receptors), 4 (estradiol metabolism), 5 (other enzymes and metabolic systems), and 7 (adhesion molecules and matrix enzymes). Group 8 (apoptosis, cellcycle regulation, and oncogenes) seemed to be negatively correlated with the disease, whereas group 3 (hormone receptors), 6 (growth factor systems), and especially 9 (human leukocyte antigen system components) showed a relatively strong correlation. The review indicates that polymorphisms may have a limited value in assessing possible development of endometriosis.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to recall the complexity of attempting to link endometriosis to single nucleotide polymorphisms (SNPs), explain that the literature is varied on results and recommendations and is population specific, and state that there are some SNP relationships that are clinically stronger than others.

Description of a novel polymorphic gene encoding for arylamine N-acetyltransferase in the rhesus macaque (Macaca mulatta), a model animal for endometriosis

OBJECTIVES

Case-control studies have previously associated polymorphisms in the gene encoding the xenobiotic metabolizing enzyme arylamine N-acetyltransferase 2 (NAT2) with endometriosis, a common multifactorial disease in women. These studies, however, have been problematic on methodological grounds and their results are inconclusive. To better understand the possible relationship between the NAT2 gene and endometriosis, we characterized its homologue in the rhesus macaque, an animal model for the disease.

METHODS

Human NAT2-specific primers were used to isolate orthologous gene sequences from four unrelated rhesus macaques of the same colony. Recombinant proteins were expressed in mammalian cells and analysed for their ability to acetylate NAT substrates and bind anti-NAT antibodies.

RESULTS

A polymorphic gene, showing 94% identity to human NAT2, was identified in the rhesus macaque. Its two characterized alleles, designated (MACMU)NAT2*1 and (MACMU)NAT2*2, were differentiated by one synonymous (C(624)T) and one nonsynonymous (G(691)A) polymorphism, the latter causing a Val(231)Ile substitution. The recombinant (MACMU)NAT2 protein was not recognized by anti-(HUMAN)NAT1 antibody, but reacted with antibodies against (HUMAN)NAT2 or the active site of NAT. Rhesus NAT2 provided relatively high acetylation activity with p-anisidine, lower activity with procainamide, sulphamethazine or 5-aminosalicylate and poor activity with p-aminobenzoic acid. Differences in the activities of the two allozymes were evident with most substrates.

CONCLUSIONS

A polymorphic homologue of human NAT2 was characterized in the rhesus macaque, to facilitate investigations of the postulated involvement of this isoenzyme in the toxicogenetics of endometriosis.

The arylhydrocarbon receptor repressor (AhRR): structure, expression, and function

The arylhydrocarbon receptor (AhR) pathway is known to be critical for cellular events, especially for those evoked by several environmental chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Whereas the function of the AhR in TCDD toxicity is well analyzed, the importance of the recently cloned AhRR in the TCDD-stimulated AhR signaling cascade is still unclear. In mammalian tissues, the AhRR gene seems to be ubiquitously expressed and its expression is altered by various AhR ligands. Basal and induced AhRR mRNA levels were found to be highly cell-, tissue- and species-specific. An inhibitory activity of the AhRR on AhR signaling was proposed from overexpression studies. However, there are not sufficient data showing such functional activity of the AhRR in vivo. This short overview summarizes the present knowledge about the AhRR and should stimulate research in the AhRR field to elucidate its physiological function and its toxicological importance in dioxin toxicity.