Symptom flares in women with chronic pelvic pain: Questionnaire study within a cohort study (translational research in pelvic pain (TRiPP)).

OBJECTIVE: To quantify the variation, triggers and impact on quality of life of symptom flares in women with chronic pelvic pain (CPP). DESIGN: Cross-sectional questionnaire within the Translational Research in Pelvic Pain clinical cohort study. SETTING: Women with CPP, with subgroups of women with endometriosis (EAP), interstitial cystitis/bladder pain syndrome (BPS), comorbid endometriosis and interstitial cystitis/bladder pain syndrome (EABP), and those with pelvic pain without endometriosis or interstitial cystitis/bladder pain syndrome (PP). POPULATION OR SAMPLE: A total of 100 participants. METHODS: Descriptive and comparative analysis from flares questionnaire. MAIN OUTCOME MEASURES: The prevalence, characteristics and triggers of short, medium and long symptom flares in CPP. RESULTS: We received 100 responses of 104 questionnaires sent. Seventy-six per cent of women with CPP have ever experienced symptom flares of at least one length (short, medium and/or long). Flares are associated with painful and non-painful symptoms. There is large variation for the frequency, duration, symptoms and triggers for flares. Over 60% of participants reported flares as stopping them from doing things they would usually do, >80% reported thinking about symptoms of flares and >80% reported flares being bothersome. CONCLUSIONS: Flares are prevalent and clinically very important in CPP. More research is needed to elucidate the mechanisms and characteristics underlying flares. Clinical practice should include an enquiry into flares with the aim of finding strategies to lessen their burden.

Prevalence, diagnostic delay and economic burden of endometriosis and its impact on quality of life: results from an Eastern Mediterranean population.

BACKGROUND: There are limited data on endometriosis from the Eastern Mediterranean region. This study for the first time estimates the prevalence and impact of endometriosis on women in Northern Cyprus, an under-represented region in Europe. METHODS: Cyprus Women's Health Research Initiative, a cross-sectional study recruited 7646 women aged 18-55 in Northern Cyprus between January 2018 and February 2020. Cases were identified using self-reported and ultrasound data and two control groups were defined, with (n = 2922) and without (n = 4314) pain. Standardized tools, including the 11-point Numerical Rating Scale and the Short Form 36 Health Survey version 2, were used to assess pain and quality of life, respectively. RESULTS: Prevalence and median diagnostic delay of endometriosis were 5.4% [95% confidence interval (CI): 4.9-5.9%, n = 410] and 7 (interquartile range 15.5) years. Endometriosis cases experienced a higher prevalence of bladder pain compared with asymptomatic pain controls (6.3% vs. 1.0%, P < 0.001) and irritable bowel syndrome relating to pelvic pain compared with symptomatic (4.6% vs. 2.6%, P = 0.027) and asymptomatic (0.3%, P < 0.001) controls. The odds of endometriosis cases reporting an anxiety diagnosis was 1.56 (95% CI: 1.03-2.38) higher than the symptomatic and 1.95 (95% CI: 1.30-2.92) times higher than the asymptomatic controls. The physical component score of the health-related quality-of-life instrument suggested a significant difference between the endometriosis cases and the symptomatic controls (46.8 vs. 48.5, P = 0.034). Average annual economic cost of endometriosis cases was Int$9864 (95% CI: $8811-$10 917) including healthcare, costs relating to absence and loss of productivity at work. CONCLUSION: Prevalence was lower than the global 10% estimate, and substantial proportion of women without endometriosis reported moderate/severe pelvic pain hinting at many undiagnosed cases within this population. Coupled with lower quality of life, significant economic burden and underutilized pain management options, the study highlights multiple opportunities to improve care for endometriosis patients and women with pelvic pain.

Utilization of healthcare prior to endometriosis diagnosis: a Danish case-control study.

STUDY QUESTION: Do women with endometriosis have higher utilization of primary and secondary healthcare prior to diagnosis compared to women without endometriosis? SUMMARY ANSWER: Women with a hospital-based diagnosis of endometriosis had an overall higher utilization of both primary and secondary healthcare in all 10 years prior to diagnosis. WHAT IS KNOWN ALREADY: Endometriosis is associated with a diagnostic delay, but only a few studies have investigated the potential consequences of this delay with regard to the utilization of healthcare. To the best of our knowledge, no study has investigated it in a period corresponding to the estimated diagnostic delay. STUDY DESIGN, SIZE, DURATION: This national Danish registry-based case-control study included 129 696 women. Cases were women with a first-time hospital-based diagnosis of endometriosis between 1 January 2000 and 31 December 2017. PARTICIPANTS/MATERIALS, SETTING, METHODS: We identified 21 616 cases using density sampling. Each case was matched on age at the date of diagnosis (index date) to five women without diagnosed endometriosis (n = 108 080). The utilization of healthcare was assessed for the 10 years before the index. MAIN RESULTS AND THE ROLE OF CHANCE: Cases had significantly higher use of healthcare in all 10 years preceding the index. The mean number of yearly contacts with the GP was 9.99 for cases and 7.85 for controls, with an adjusted incidence rate ratio of 1.28 (1.27; 1.29). For hospital contacts, the association increased slightly in the first 9 years and was most profound in the last year preceding index when the adjusted incidence rate ratio was 2.26 (95% CI 2.28; 2.31). LIMITATIONS, REASONS FOR CAUTION: We were not able to include women with an endometriosis diagnosis from the general practitioner or private gynaecologist. Therefore, our results are only applicable to hospital-based diagnoses of endometriosis. We do not have information on the specific reasons for contacting the healthcare providers and we can therefore only speculate that the higher utilization of healthcare among cases was related to endometriosis. WIDER IMPLICATIONS OF THE FINDINGS: This study is in agreement with the other known studies on the subject. Future studies should include specific reasons for contacting the healthcare system and thereby identify any specific contact patterns for women with endometriosis. With this knowledge, healthcare professionals could be better at relating certain healthcare seeking behaviour to endometriosis earlier and thereby reduce the time from onset of symptoms to diagnosis. STUDY FUNDING/COMPETING INTEREST(S): This study is supported by grants from the project 'Finding Endometriosis using Machine Learning' (FEMaLe/101017562), which has received funding from The European Union's Horizon 2020 research and innovation program and Helsefonden (21-B-0141). K.Z. report grants from Bayer AG, Roche Inc. and Volition, royalties from Oxford-Bayer scientific collaboration in gynaecological therapies, non-financial collaboration with the World Endometriosis Society and World Endometriosis Research Foundation and is a Wellbeing of Women research advisory committee member. All this is outside the submitted work. The other authors have no conflict of interest to declare. TRIAL REGISTRATION NUMBER: N/A.

Obesity and risk of female reproductive conditions: A Mendelian randomisation study.

BACKGROUND: Obesity is observationally associated with altered risk of many female reproductive conditions. These include polycystic ovary syndrome (PCOS), abnormal uterine bleeding, endometriosis, infertility, and pregnancy-related disorders. However, the roles and mechanisms of obesity in the aetiology of reproductive disorders remain unclear. Thus, we aimed to estimate observational and genetically predicted causal associations between obesity, metabolic hormones, and female reproductive disorders. METHODS AND FINDINGS: Logistic regression, generalised additive models, and Mendelian randomisation (MR) (2-sample, non-linear, and multivariable) were applied to obesity and reproductive disease data on up to 257,193 women of European ancestry in UK Biobank and publicly available genome-wide association studies (GWASs). Body mass index (BMI), waist-to-hip ratio (WHR), and WHR adjusted for BMI were observationally (odds ratios [ORs] = 1.02-1.87 per 1-SD increase in obesity trait) and genetically (ORs = 1.06-2.09) associated with uterine fibroids (UF), PCOS, heavy menstrual bleeding (HMB), and pre-eclampsia. Genetically predicted visceral adipose tissue (VAT) mass was associated with the development of HMB (OR [95% CI] per 1-kg increase in predicted VAT mass = 1.32 [1.06-1.64], P = 0.0130), PCOS (OR [95% CI] = 1.15 [1.08-1.23], P = 3.24 × 10-05), and pre-eclampsia (OR [95% CI] = 3.08 [1.98-4.79], P = 6.65 × 10-07). Increased waist circumference posed a higher genetic risk (ORs = 1.16-1.93) for the development of these disorders and UF than did increased hip circumference (ORs = 1.06-1.10). Leptin, fasting insulin, and insulin resistance each mediated between 20% and 50% of the total genetically predicted association of obesity with pre-eclampsia. Reproductive conditions clustered based on shared genetic components of their aetiological relationships with obesity. This study was limited in power by the low prevalence of female reproductive conditions among women in the UK Biobank, with little information on pre-diagnostic anthropometric traits, and by the susceptibility of MR estimates to genetic pleiotropy. CONCLUSIONS: We found that common indices of overall and central obesity were associated with increased risks of reproductive disorders to heterogenous extents in a systematic, large-scale genetics-based analysis of the aetiological relationships between obesity and female reproductive conditions. Our results suggest the utility of exploring the mechanisms mediating the causal associations of overweight and obesity with gynaecological health to identify targets for disease prevention and treatment.

Correction: Obesity and risk of female reproductive conditions: A Mendelian randomisation study.

[This corrects the article DOI: 10.1371/journal.pmed.1003679.].

Genome-wide associations for birth weight and correlations with adult disease.

Birth weight (BW) has been shown to be influenced by both fetal and maternal factors and in observational studies is reproducibly associated with future risk of adult metabolic diseases including type 2 diabetes (T2D) and cardiovascular disease. These life-course associations have often been attributed to the impact of an adverse early life environment. Here, we performed a multi-ancestry genome-wide association study (GWAS) meta-analysis of BW in 153,781 individuals, identifying 60 loci where fetal genotype was associated with BW (P < 5 × 10-8). Overall, approximately 15% of variance in BW was captured by assays of fetal genetic variation. Using genetic association alone, we found strong inverse genetic correlations between BW and systolic blood pressure (Rg = -0.22, P = 5.5 × 10-13), T2D (Rg = -0.27, P = 1.1 × 10-6) and coronary artery disease (Rg = -0.30, P = 6.5 × 10-9). In addition, using large -cohort datasets, we demonstrated that genetic factors were the major contributor to the negative covariance between BW and future cardiometabolic risk. Pathway analyses indicated that the protein products of genes within BW-associated regions were enriched for diverse processes including insulin signalling, glucose homeostasis, glycogen biosynthesis and chromatin remodelling. There was also enrichment of associations with BW in known imprinted regions (P = 1.9 × 10-4). We demonstrate that life-course associations between early growth phenotypes and adult cardiometabolic disease are in part the result of shared genetic effects and identify some of the pathways through which these causal genetic effects are mediated.

Endometriosis Classification Systems: An International Survey to Map Current Knowledge and Uptake.

OBJECTIVE: In the field of endometriosis, several classification, staging and reporting systems have been developed, but do clinicians routinely use these classification systems, which system do they use and what are the clinicians' motivations? DATA SOURCES: A cross-sectional study was performed to gather data on the current use of endometriosis classification systems, problems encountered and interest in a new simple surgical descriptive system for endometriosis. Of particular focus were three systems most commonly used: the Revised American Society for Reproductive Medicine (rASRM) classification, the Endometriosis Fertility Index (EFI), and the ENZIAN classification. Data were analysed by SPSS. A survey was designed using the online SurveyMonkey tool consisting of 11 questions concerning three domains-participants background, existing classification systems and intentions with regards to a new classification system for endometriosis. Replies were collected between 15 May and 1 July 2020. METHODS OF STUDY SELECTION: na TABULATION, INTEGRATION AND RESULTS: The final dataset included the replies of 1178 clinicians, including surgeons, gynecologists, reproductive endocrinologists, fertility specialists and sonographers, all managing women with endometriosis in their clinical practice. Overall, 75.5% of the professionals indicate that they currently use a classification system for endometriosis. The rASRM classification system was the best known and used system, the EFI system and ENZIAN system were known by a majority of the professionals but used by only a minority. The lack of clinical relevance was most often selected as a problem with using any system. The findings of the survey suggest that clinicians worldwide are open to using a new classification system for endometriosis that can achieve standardized reporting, and is clinically relevant and simple. The findings therefore support future initiatives for the development of a new descriptive system for endometriosis and provide information on user expectations and conditions for universal uptake of such a system. CONCLUSION: Even with a high uptake of the existing endometriosis classification systems (rASRM, ENZIAN and EFI), most clinicians managing endometriosis would like a new simple surgical descriptive system for endometriosis.

Machine Learning based histology phenotyping to investigate the epidemiologic and genetic basis of adipocyte morphology and cardiometabolic traits.

Genetic studies have recently highlighted the importance of fat distribution, as well as overall adiposity, in the pathogenesis of obesity-associated diseases. Using a large study (n = 1,288) from 4 independent cohorts, we aimed to investigate the relationship between mean adipocyte area and obesity-related traits, and identify genetic factors associated with adipocyte cell size. To perform the first large-scale study of automatic adipocyte phenotyping using both histological and genetic data, we developed a deep learning-based method, the Adipocyte U-Net, to rapidly derive mean adipocyte area estimates from histology images. We validate our method using three state-of-the-art approaches; CellProfiler, Adiposoft and floating adipocytes fractions, all run blindly on two external cohorts. We observe high concordance between our method and the state-of-the-art approaches (Adipocyte U-net vs. CellProfiler: R2visceral = 0.94, P < 2.2 × 10-16, R2subcutaneous = 0.91, P < 2.2 × 10-16), and faster run times (10,000 images: 6mins vs 3.5hrs). We applied the Adipocyte U-Net to 4 cohorts with histology, genetic, and phenotypic data (total N = 820). After meta-analysis, we found that mean adipocyte area positively correlated with body mass index (BMI) (Psubq = 8.13 × 10-69, ßsubq = 0.45; Pvisc = 2.5 × 10-55, ßvisc = 0.49; average R2 across cohorts = 0.49) and that adipocytes in subcutaneous depots are larger than their visceral counterparts (Pmeta = 9.8 × 10-7). Lastly, we performed the largest GWAS and subsequent meta-analysis of mean adipocyte area and intra-individual adipocyte variation (N = 820). Despite having twice the number of samples than any similar study, we found no genome-wide significant associations, suggesting that larger sample sizes and a homogenous collection of adipose tissue are likely needed to identify robust genetic associations.

An International Terminology for Endometriosis, 2021.

OBJECTIVE: Different classification systems have been developed for endometriosis, using different definitions for the disease, the different subtypes, symptoms and treatments. In addition, an International Glossary on Infertility and Fertility Care has been published in 2017 by the International Committee for Monitoring Assisted Reproductive Technologies (ICMART) in collaboration with other organisations. An international working group convened over the development of a classification or descriptive system for endometriosis. As a basis for such system, a terminology for endometriosis was considered a condition sine qua non. The aim of the current study was to develop a set of terms and definitions be prepared on endometriosis that would be the basis for standardization in disease description, classification and research. DATA SOURCES: The working group listed a number of terms relevant to be included in the terminology, documented currently used and published definitions, and discussed and adapted them until consensus was reached within the working group. Following stakeholder review, further terms were added, and definitions further clarified. Although definitions were collected through published literature, the final set of terms and definitions is to be considered consensus-based. After finalization of the first draft, the members of the international societies and other stakeholders were consulted for feedback and comments, which lead to further adaptations. METHODS OF STUDY SELECTION: na TABULATION, INTEGRATION, AND RESULTS: A list of 49 terms and definitions in the field of endometriosis is presented, including a definition for endometriosis and its subtypes, different locations, interventions, symptoms and outcomes. Endometriosis is defined as a disease characterized by the presence of endometrium-like epithelium and/or stroma outside the endometrium and myometrium, usually with an associated inflammatory process. CONCLUSION: The current paper outlines a list of 49 terms and definitions in the field of endometriosis. The application of the defined terms aims to facilitate harmonization in endometriosis research and clinical practice. Future research may require further refinement of the presented definitions.

Endometriosis Classification, Staging and Reporting Systems: A Review on the Road to a Universally Accepted Endometriosis Classification.

OBJECTIVE: In the field of endometriosis, several classification, staging and reporting systems have been developed. Which endometriosis classification, staging and reporting systems have been published and validated for use in clinical practice? DATA SOURCES: A systematic PUBMED literature search was performed. Data were extracted and summarized. METHODS OF STUDY SELECTION: na TABULATION, INTEGRATION AND RESULTS: Twenty-two endometriosis classification, staging and reporting systems have been published between 1973 and 2021, each developed for specific, and different, purposes. There still is no international agreement on how to describe the disease. Studies evaluating the different systems are summarized showing a discrepancy between the intended and the evaluated purpose, and a general lack of validation data confirming a correlation with pain symptoms or quality of life for any of the current systems. A few studies confirm the value of the ENZIAN system for surgical description of deep endometriosis. With regards to infertility, the endometriosis fertility index has been confirmed valid for its intended purpose. CONCLUSION: Of the 22 endometriosis classification, staging and reporting systems identified in this historical overview, only a few have been evaluated for the purpose for which they were developed. The literature search was limited to PUBMED. Unpublished classification, staging or reporting systems, or those published in books were not considered. It can be concluded that there is no international agreement on how to describe endometriosis or how to classify it, and that most classification/staging systems show no or very little correlation with patient outcomes. This overview of existing systems is a first step in working towards a universally accepted endometriosis classification.

Large-scale meta-analysis highlights the hypothalamic-pituitary-gonadal axis in the genetic regulation of menstrual cycle length.

The normal menstrual cycle requires a delicate interplay between the hypothalamus, pituitary and ovary. Therefore, its length is an important indicator of female reproductive health. Menstrual cycle length has been shown to be partially controlled by genetic factors, especially in the follicle-stimulating hormone beta-subunit (FSHB) locus. A genome-wide association study meta-analysis of menstrual cycle length in 44 871 women of European ancestry confirmed the previously observed association with the FSHB locus and identified four additional novel signals in, or near, the GNRH1, PGR, NR5A2 and INS-IGF2 genes. These findings not only confirm the role of the hypothalamic-pituitary-gonadal axis in the genetic regulation of menstrual cycle length but also highlight potential novel local regulatory mechanisms, such as those mediated by IGF2.

Mass cytometry analysis reveals a distinct immune environment in peritoneal fluid in endometriosis: a characterisation study.

BACKGROUND: Endometriosis is a gynaecological condition characterised by immune cell infiltration and distinct inflammatory signatures found in the peritoneal cavity. In this study, we aim to characterise the immune microenvironment in samples isolated from the peritoneal cavity in patients with endometriosis. METHODS: We applied mass cytometry (CyTOF), a recently developed multiparameter single-cell technique, in order to characterise and quantify the immune cells found in peritoneal fluid and peripheral blood from endometriosis and control patients. RESULTS: Our results demonstrate the presence of more than 40 different distinct immune cell types within the peritoneal cavity. This suggests that there is a complex and highly heterogeneous inflammatory microenvironment underpinning the pathology of endometriosis. Stratification by clinical disease stages reveals a dynamic spectrum of cell signatures suggesting that adaptations in the inflammatory system occur due to the severity of the disease. Notably, among the inflammatory microenvironment in peritoneal fluid (PF), the presence of CD69+ T cell subsets is increased in endometriosis when compared to control patient samples. On these CD69+ cells, the expression of markers associated with T cell function are reduced in PF samples compared to blood. Comparisons between CD69+ and CD69- populations reveal distinct phenotypes across peritoneal T cell lineages. Taken together, our results suggest that both the innate and the adaptive immune system play roles in endometriosis. CONCLUSIONS: This study provides a systematic characterisation of the specific immune environment in the peritoneal cavity and identifies cell immune signatures associated with endometriosis. Overall, our results provide novel insights into the specific cell phenotypes governing inflammation in patients with endometriosis. This prospective study offers a useful resource for understanding disease pathology and opportunities for identifying therapeutic targets.

DNA methylation alterations-potential cause of endometriosis pathogenesis or a reflection of tissue heterogeneity?

Alterations in the DNA methylation pattern of endometriotic lesions and endometrium of endometriosis patients have been proposed as one potential factor accompanying the endometriosis development. Although many differentially methylated genes have been associated with the pathogenesis of this disease, the overlap between the results of different studies has remained small. Among other potential confounders, the impact of tissue heterogeneity on the outcome of DNA methylation studies should be considered, as tissues are mixtures of different cell types with their own specific DNA methylation signatures. This review focuses on the results of DNA methylation studies in endometriosis from the cellular heterogeneity perspective. We consider both the studies using highly heterogeneous whole-lesion biopsies and endometrial tissue, as well as pure cell fractions isolated from lesions and endometrium to understand the potential impact of the cellular composition to the results of endometriosis DNA methylation studies. Also, future perspectives on how to diminish the impact of tissue heterogeneity in similar studies are provided.

The miRNA Mirage: How Close Are We to Finding a Non-Invasive Diagnostic Biomarker in Endometriosis? A Systematic Review.

BACKGROUND: Endometriosis is a common disorder of the reproductive age group, characterised by the presence of ectopic endometrial tissue. The disease not only causes enormous suffering to the affected women, but also brings a tremendous medical and economic burden to bear on society. There is a long lag phase between the onset and diagnosis of the disease, mainly due to its non-specific symptoms and the lack of a non-invasive test. Endometriosis can only be diagnosed invasively by laparoscopy. A specific, non-invasive test to diagnose endometriosis is an unmet clinical need. The recent discovery of microRNAs (miRNAs) as modulators of gene expression, and their stability and specificity, make them an attractive candidate biomarker. Various studies on miRNAs in endometriosis have identified their cardinal role in the pathogenesis of the disease, and have proposed them as potential biomarkers in endometriosis. Rationale/Objectives: The aims of this review were to study the role of circulatory miRNAs in endometriosis, and bring to light whether circulatory miRNAs could be potential non-invasive biomarkers to diagnose the disease. SEARCH METHODS: Three databases, PubMed, EMBASE, and BIOSIS were searched, using a combination of Mesh or Emtree headings and free-text terms, to identify literature relating to circulating miRNAs in endometriosis published from 1996 to 31 December 2017. Only peer-reviewed, full-text original research articles in English were included in the current review. The studies meeting the inclusion criteria were critically assessed and checked using the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies) tool. The dysregulated miRNAs were assessed regarding the concordance between the various studies and their role in the disease. OUTCOMES: Nine studies were critically analysed, and 42 different miRNAs were found to be dysregulated in them, with only one common miRNA (miR-20a) differentially expressed in more than one study. miR-17-5p/20a, miR-200, miR-199a, miR-143, and miR-145 were explored for their pivotal role in the aetiopathogenesis of endometriosis. Wider implications: It is emerging that miRNAs play a central role in the pathogenesis of endometriosis and have the potential of being promising biomarkers. Circulating miRNAs as a non-invasive diagnostic tool may shorten the delay in the diagnosis of the disease, thus alleviating the suffering of women and reducing the burden on health care systems. However, despite numerous studies on circulating miRNAs in endometriosis, no single miRNA or any panel of them seems to meet the criteria of a diagnostic biomarker. The disagreement between the various studies upholds the demand of larger, well-controlled systematic validation studies with uniformity in the research approaches and involving diverse populations.

Genome-wide enrichment analysis between endometriosis and obesity-related traits reveals novel susceptibility loci.

Endometriosis is a chronic inflammatory condition in women that results in pelvic pain and subfertility, and has been associated with decreased body mass index (BMI). Genetic variants contributing to the heritable component have started to emerge from genome-wide association studies (GWAS), although the majority remain unknown. Unexpectedly, we observed an intergenic locus on 7p15.2 that was genome-wide significantly associated with both endometriosis and fat distribution (waist-to-hip ratio adjusted for BMI; WHRadjBMI) in an independent meta-GWAS of European ancestry individuals. This led us to investigate the potential overlap in genetic variants underlying the aetiology of endometriosis, WHRadjBMI and BMI using GWAS data. Our analyses demonstrated significant enrichment of common variants between fat distribution and endometriosis (P = 3.7 × 10(-3)), which was stronger when we restricted the investigation to more severe (Stage B) cases (P = 4.5 × 10(-4)). However, no genetic enrichment was observed between endometriosis and BMI (P = 0.79). In addition to 7p15.2, we identify four more variants with statistically significant evidence of involvement in both endometriosis and WHRadjBMI (in/near KIFAP3, CAB39L, WNT4, GRB14); two of these, KIFAP3 and CAB39L, are novel associations for both traits. KIFAP3, WNT4 and 7p15.2 are associated with the WNT signalling pathway; formal pathway analysis confirmed a statistically significant (P = 6.41 × 10(-4)) overrepresentation of shared associations in developmental processes/WNT signalling between the two traits. Our results demonstrate an example of potential biological pleiotropy that was hitherto unknown, and represent an opportunity for functional follow-up of loci and further cross-phenotype comparisons to assess how fat distribution and endometriosis pathogenesis research fields can inform each other.

Challenges in endometriosis miRNA studies - From tissue heterogeneity to disease specific miRNAs.

In order to uncover miRNA changes in endometriosis pathogenesis, both endometriotic lesions and endometrial biopsies, as well as stromal and epithelial cells isolated from these tissues have been investigated and a large number of dysregulated miRNAs have been reported. However, the concordance between the result of different studies has remained small. One potential explanation for limited overlap between the proposed disease-related miRNAs could be the heterogeneity in tissue composition, as some studies have compared highly heterogeneous whole-lesion biopsies with endometrial tissue, some have compared the endometrium from patients and controls, and some have used pure cell fractions isolated from lesions and endometrium. This review focuses on the results of published miRNA studies in endometriosis to reveal the potential impact of tissue heterogeneity on the discovery of disease-specific miRNA alterations in endometriosis. Additionally, functional studies that explore the roles of endometriosis-involved miRNAs are discussed.