Interference between rheumatoid arthritis and autoimmune thyroid diseases: A bidirectional Mendelian randomization

The relationship between rheumatoid arthritis (RA) and autoimmune thyroid disease (AITD) remains controversial. This study aimed to analyze the causal relationship between RA and AITD by bidirectional Mendelian randomization (MR). Single nucleotide polymorphisms for RA, autoimmune thyroiditis (AIT), and Graves' disease (GD) were obtained from the FinnGen database. Inverse variance weighted was chose to assess the causal relationships between RA and AITD. MR-Egger, Cochran Q, and sensitivity analyses were used to assess horizontal pleiotropy, heterogeneity, and robustness of the MR results, respectively. MR analysis showed that RA was associated with increased risk of AIT (odds ratio [OR] 1.552, 95% confidence interval [CI] 1.266 to 1.903, P < .001) and GD (OR 1.177, 95% CI 1.076-1.286, P < .001). Furthermore, GD was associated with an increased risk of RA (OR 1.030, 95% CI 1.007-1.053, P = .010), whereas AIT was not associated with the risk of RA (OR 0.994, 95% CI 0.979-1.009, P = .420). These results lacked horizontal pleiotropy and heterogeneity, and were considered robust. This MR analysis indicates that RA may act as a potential risk factor for AIT and GD, while GD also appears to pose a potential risk for RA. We recommend proactive screening for AIT and GD in patients diagnosed with RA, as well as screening for RA in patients with GD. Early and active screening, coupled with appropriate care and management, will help mitigate the risk of complications and improve patient outcomes.