Coding regions of INHBA, SFRP4 and HOXA10 are not implicated in familial endometriosis linked to chromosome 7p13-15

Endometriosis

Pelvic endometriosis is a complex syndrome characterized by an estrogen-dependent chronic inflammatory process that affects primarily pelvic tissues, including the ovaries. It is caused when shed endometrial tissue travels retrograde into the lower abdominal cavity. Endometriosis is the most common cause of chronic pelvic pain in women and is associated with infertility. The underlying pathologic mechanisms in the intracavitary endometrium and extrauterine endometriotic tissue involve defectively programmed endometrial mesenchymal progenitor/stem cells. Although endometriotic stromal cells, which compose the bulk of endometriotic lesions, do not carry somatic mutations, they demonstrate specific epigenetic abnormalities that alter expression of key transcription factors. For example, GATA-binding factor-6 overexpression transforms an endometrial stromal cell to an endometriotic phenotype, and steroidogenic factor-1 overexpression causes excessive production of estrogen, which drives inflammation via pathologically high levels of estrogen receptor-β. Progesterone receptor deficiency causes progesterone resistance. Populations of endometrial and endometriotic epithelial cells also harbor multiple cancer driver mutations, such as KRAS, which may be associated with the establishment of pelvic endometriosis or ovarian cancer. It is not known how interactions between epigenomically defective stromal cells and the mutated genes in epithelial cells contribute to the pathogenesis of endometriosis. Endometriosis-associated pelvic pain is managed by suppression of ovulatory menses and estrogen production, cyclooxygenase inhibitors, and surgical removal of pelvic lesions, and in vitro fertilization is frequently used to overcome infertility. Although novel targeted treatments are becoming available, as endometriosis pathophysiology is better understood, preventive approaches such as long-term ovulation suppression may play a critical role in the future.

Epithelial Mutations in Endometriosis: Link to Ovarian Cancer

Epidemiologic and histopathologic associations between endometriosis and epithelial ovarian cancer have been reported; however, the underlying molecular and cellular mechanisms are not well understood. A possible genetic link has been suggested in recent publications. Driver mutations in PIK3CA, KRAS, ARID1A, and other genes have been found in the epithelium of intrauterine endometrial tissue, ovarian and extraovarian pelvic endometriosis tissue, ovarian cancers associated with endometriosis (i.e., clear cell and endometrioid type), and other epithelial ovarian cancers. This makes sense because pelvic endometriosis occurs primarily as a result of retrograde menstruation and implantation of endometrial tissue fragments in ovarian inclusion cysts or extraovarian peritoneal or subperitoneal sites. Unlike epithelial cells, endometriotic stromal cells are mutation free but contain widespread epigenetic defects that alter gene expression and induce a progesterone-resistant and intensely inflammatory environment, driven by estrogen via estrogen receptor-β. The resulting increased estrogenic action in the stroma drives inflammation and sends paracrine signals to neighboring epithelial cells to enhance proliferation. In addition, massively high concentrations of estrogen in the ovary may exert an additional and direct genotoxic effect on DNA and cause accumulation of additional mutations and malignant transformation in initially mutated endometriotic epithelial cells in an ovarian endometrioma, which may initiate epithelial ovarian cancer. The same epithelial mutations and inflammatory processes in stroma are seen in extraovarian deep-infiltrating endometriosis, but carcinogenesis does not occur. We provide a focused review of the literature and discuss the implications of recent genetic breakthroughs linking endometriosis and ovarian cancer.

Genetics of endometriosis

Endometriosis is a heritable complex disorder that is influenced by multiple genetic and environmental factors. Identification of these genetic factors will aid a better understanding of the underlying biology of the disease. In this article, we describe different methods of studying genetic variation of endometriosis, summarize results from genetic studies performed to date and provide recommendations for future studies to uncover additional factors contributing to the heritable component of endometriosis.

Genetic variants underlying risk of endometriosis: insights from meta-analysis of eight genome-wide association and replication datasets

BACKGROUND

Endometriosis is a heritable common gynaecological condition influenced by multiple genetic and environmental factors. Genome-wide association studies (GWASs) have proved successful in identifying common genetic variants of moderate effects for various complex diseases. To date, eight GWAS and replication studies from multiple populations have been published on endometriosis. In this review, we investigate the consistency and heterogeneity of the results across all the studies and their implications for an improved understanding of the aetiology of the condition.

METHODS

Meta-analyses were conducted on four GWASs and four replication studies including a total of 11 506 cases and 32 678 controls, and on the subset of studies that investigated associations for revised American Fertility Society (rAFS) Stage III/IV including 2859 cases. The datasets included 9039 cases and 27 343 controls of European (Australia, Belgium, Italy, UK, USA) and 2467 cases and 5335 controls of Japanese ancestry. Fixed and Han and Elkin random-effects models, and heterogeneity statistics (Cochran's Q test), were used to investigate the evidence of the nine reported genome-wide significant loci across datasets and populations.

RESULTS

Meta-analysis showed that seven out of nine loci had consistent directions of effect across studies and populations, and six out of nine remained genome-wide significant (P < 5 × 10⁻⁸), including rs12700667 on 7p15.2 (P = 1.6 × 10⁻⁹), rs7521902 near WNT4 (P = 1.8 × 10⁻¹⁵), rs10859871 near VEZT (P = 4.7 × 10⁻¹⁵), rs1537377 near CDKN2B-AS1 (P = 1.5 × 10⁻⁸), rs7739264 near ID4 (P = 6.2 × 10⁻¹⁰) and rs13394619 in GREB1 (P = 4.5 × 10⁻⁸). In addition to the six loci, two showed borderline genome-wide significant associations with Stage III/IV endometriosis, including rs1250248 in FN1 (P = 8 × 10⁻⁸) and rs4141819 on 2p14 (P = 9.2 × 10⁻⁸). Two independent inter-genic loci, rs4141819 and rs6734792 on chromosome 2, showed significant evidence of heterogeneity across datasets (P < 0.005). Eight of the nine loci had stronger effect sizes among Stage III/IV cases, implying that they are likely to be implicated in the development of moderate to severe, or ovarian, disease. While three out of nine loci were inter-genic, the remaining were in or near genes with known functions of biological relevance to endometriosis, varying from roles in developmental pathways to cellular growth/carcinogenesis.

CONCLUSIONS

Our meta-analysis shows remarkable consistency in endometriosis GWAS results across studies, with little evidence of population-based heterogeneity. They also show that the phenotypic classifications used in GWAS to date have been limited. Stronger associations with Stage III/IV disease observed for most loci emphasize the importance for future studies to include detailed sub-phenotype information. Functional studies in relevant tissues are needed to understand the effect of the variants on downstream biological pathways.

Interplay between Misplaced Müllerian-Derived Stem Cells and Peritoneal Immune Dysregulation in the Pathogenesis of Endometriosis

In the genetic regulation of Müllerian structures development, a key role is played by Hoxa and Wnt clusters, because they lead the transcription of different genes according to the different phases of the organogenesis, addressing correctly cell-to-cell interactions, allowing, finally, the physiologic morphogenesis. Accumulating evidence is suggesting that dysregulation of Wnt and/or Hox genes may affect cell migration during organogenesis and differentiation of Müllerian structures of the female reproductive tract, with possible dislocation and dissemination of primordial endometrial stem cells in ectopic regions, which have high plasticity to differentiation. We hypothesize that during postpubertal age, under the influence of different stimuli, these misplaced and quiescent ectopic endometrial cells could acquire new phenotype, biological functions, and immunogenicity. So, these kinds of cells may differentiate, specializing in epithelium, glands, and stroma to form a functional ectopic endometrial tissue. This may provoke a breakdown in the peritoneal cavity homeostasis, with the consequent processes of immune alteration, documented by peripheral mononuclear cells recruitment and secretion of inflammatory cytokines in early phases and of angiogenic and fibrogenic cytokines in the late stages of the disease.

Insights into Assessing the Genetics of Endometriosis

Endometriosis is a complex disease arising from the interplay between multiple genetic and environmental factors. The genetic variants potentially underlying the hereditary component of endometriosis have been widely investigated through hypothesis-driven candidate gene studies, an approach that generally has proven to be inherently difficult and problematic for a number of reasons. Recently, through major collaborative efforts in the endometriosis research field, hypothesis-free genome-wide approaches have started to provide new insights into potential pathways leading to development of endometriosis, as well as highlighting the phenotypic heterogeneity of the condition. This review summarizes the most recent studies investigating the genetic variation contributing to endometriosis, with a particular focus on genome-wide approaches, and discusses promising future directions of genetic research.