O-030 Gut microbiome in endometriosis: a cohort study on 1000 individuals
Authors: Pérez-Prieto I , Vargas E , Salas-Espejo E , Canha-Gouveia A , Fontes-Jiménez J , Salumets A , Lüll K , Whiteson K , Org E , Altmäe S 
Published: June 2023

Abstract

Study question
Do gut microbial composition and functionality differ between women with and without endometriosis?

Summary answer
Gut microbiome diversity and composition (species and microbial pathways) were not significantly different between women with and without endometriosis.

What is known already
Endometriosis, defined as the presence of endometrial-like tissue outside of the uterus, is one of the most common female reproductive disorders. Although different theories of the possible causes of endometriosis have been proposed, its pathogenesis is not clear. Novel studies indicate that the gut microbiome may be involved in the etiology of endometriosis, nevertheless, the connection between microbes, its dysbiosis and the development of endometriosis remains unexplored. This study aims to analyze and compare the gut microbiome profile in women with and without endometriosis in a large cohort to identify microbial targets potentially involved in the development of the disease.

Study design, size, duration
This case-control study included a subsample of 1000 women (age = 45.61±10.36 years; BMI = 25.67±5.59) of the Estonian Microbiome (EstMB) cohort, a volunteer-based sub-cohort of the Estonian Biobank created in 2017. 136 women with endometriosis and 864 control women who have not been diagnosed with endometriosis or any of its most prevalent comorbidities (systemic lupus erythematosus, rheumatoid arthritis, autoimmune thyroiditis, celiac disease, multiple sclerosis and irritable bowel syndrome) were included in this study.

Participants/materials, setting, methods
Microbial DNA from fecal samples was extracted and sequenced by paired-end metagenomic shotgun sequencing (Illumina Novaseq 6000 platform). Microbial functional pathways were annotated using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database (https://www.genome.jp/kegg/). Partitioning around medoids (PAM) algorithm was performed to cluster the microbial profile of the Estonian population. The alpha- and beta-diversity and differential abundance analyses were performed to assess the gut microbiome (species and KEGG orthologies [KO]) in both groups.

Main results and the role of chance
After metagenomics analysis, 17180 microbes and 7869 KO were detected. Those bacteria and KO with a relative abundance &gt; 1 % were used for the diversity and differential abundance analyses, resulting in 2442 species and 1974 KO. PAM clustering analysis stratified the study population into two enterotypes: one characterized by a high abundance of Prevotella copri and the second presented a high abundance of Bacteroides genus (PERMANOVA, p = 0.001). However, the enterotypes were not associated with the presence/absence of endometriosis. Microbial alpha-diversity (observed richness and Shannon’s index) was not significantly different between women with and without endometriosis (all p-value &gt; 0.05). Beta-diversity analyses on the microbial and functional profile (species and KO profile) indicated no significant dissimilarity between groups (PERMANOVA, all p &gt; 0.05). No differential species nor KO were detected after multiple testing adjustment (all FDR p &gt; 0.05).

Limitations, reasons for caution
This case-control study did not identify a distinct gut microbial profile in women with endometriosis. A deeper analysis considering potential confounders (specifically hormonal treatment in patients) is needed to further confirm our results.

Wider implications of the findings
Endometriosis is a widespread disorder affecting ∼10% of reproductive-age women. To the best of our knowledge, this is the biggest metagenome study performed in women with endometriosis. Our findings do not find enough evidence to support the existence of a gut microbiome-dependent mechanism implicated in the pathogenesis of endometriosis.

Trial registration number
Not applicable