TSH receptor antibodies (TRAb) – A potential new biomarker for endometriosis

Objectives: The prevalence of several autoimmune diseases, including thyroid dysfunction, has been reported to be increased in patients with endometriosis. Upregulated thyroid stimulation hormone (TSH) receptors in ectopic endometrium and elevated serum titers of TSH receptor antibodies (TRAb) IgG in endometriosis patients indicates an overlap in pathophysiology. However, cross-reactivity with other antibodies must be excluded. The objective of this study was to compare the expression of autoantibodies in women with endometriosis and two control groups to evaluate the potential of TRAb IgG as a diagnostic marker for endometriosis. Study design: This cross-sectional study was carried out in 172 women with surgically confirmed endometriosis and two control groups consisting of 50 healthy blood donors and 114 women from Malmö Offspring Study consisting of people from the general population. Serum levels of thyroid hormones, TSH and TRAb autoantibodies, AXIN1, and autoantibodies against follicle stimulating hormone (FSH), human chorionic gonadotropin (hCG), luteinizing hormone (LH), and their receptors, were analyzed. The patients answered a questionnaire and estimated their gastrointestinal symptoms using the Visual Analogue Scale for Irritable Bowel Syndrome. Results: Of the endometriosis patients, 29.1 % had TRAb IgG above the present detection limit of ≥ 1.0 IE/L compared to 2.6 % of the controls from MOS (p < 0.001) and 94.5 % had levels of TRAb over the previous detection limit ≥ 0.3 IE/L compared to 7.9 % of the controls (p < 0.001). Titers of both TRAb IgG and IgM were increased in patients compared to controls from MOS and blood donors, respectively (p < 0.001). There was no increase of autoantibodies against FSH, FSH receptor (FSHR), hCG, LH, LH receptor (LHR) or TSH compared to the blood donor controls. TRAb titers did not correlate with age, disease duration, AXIN1, TSH, thyroid hormones or gastrointestinal symptoms. Conclusion: TRAb IgG and IgM are slightly elevated in patients with endometriosis with no cross-reactivity with other autoantibodies. The results indicate that TRAb is truly elevated and thereby has the potential to be used to support the diagnosing of endometriosis.