Insights Gained from Genomic Studies on the Role of Sex Steroids in the Aetiology of Endometriosis

Abstract

Endometriosis is a chronic neuro-inflammatory disorder the defining feature of which is the growth of tissue (lesions) that resembles the endometrium in sites outside the uterus. Estimates of prevalence typically quote rates of ~10% of women of reproductive age, equating to ~190 million women world-wide. Three subtypes of endometriosis are usually considered when discussing the aetiology of the disorder - superficial peritoneal, ovarian (endometrioma cysts), and deep (infiltrating). Genetic, hormonal and immunological factors have all been proposed as contributing to risk factors associated with the development of lesions. Twin studies report the heritable component of endometriosis as ~50%. Genome wide association studies (GWAS) have been conducted allowing unbiased scanning of the genome for single nucleotide polymorphisms (SNPs) in many thousands of individuals. These studies have identified SNPs that appear over-represented in patients with endometriosis, particularly those with more extensive disease (stage III/IV). Amongst the larger scale GWAS there has been replication of SNPs near genes involved in oestrogen and other signalling pathways including ESR1 (oestrogen receptor alpha), GREB1, HOXA10, WNT4 and MAPK kinase signalling. The results from patients with endometriosis have also provided an opportunity to make comparisons with GWAS conducted on other patient cohorts including those with reproductive traits (age at menarche) and disorders (fibroids, endometrial and ovarian cancer) and conditions that are reported by women with endometriosis (migraine, depression). These comparative studies have highlighted some shared genetically-controlled biological mechanisms, including hormone-regulated pathways which might explain the co-occurrence of endometriosis with these disorders. In summary, unbiased genetic analysis has provided new insights into the genetic factors that may contribute to increased risk of developing endometriosis. New studies are needed to broaden the range of patients contributing to these datasets and to improve integration with non-genomic and tissue expression data before their full potential for diagnosis and improvements in patient care can be fully realised.