Identifying the Genetic Association Between Sjogren's Syndrome and Autoimmune Thyroid Disease: A Bidirectional Two‐Sample Mendelian Randomization Study

ABSTRACT Background Although observational studies have suggested a correlation between Sjogren's syndrome (SS) and autoimmune thyroid disease (AITD), a conclusive evidence supporting a causal relationship is still lacking. This study aims to explore the potential causal relationship between SS and AITD. Methods Using genome‐wide association studies, we performed a bidirectional two‐sample Mendelian randomization (MR) analysis. In our analysis, the random‐effects inverse variance weighted (IVW) method was predominantly employed, followed by several sensitivity analyses, which include heterogeneity, horizontal pleiotropy, outliers, and “leave‐one‐out” analyses. Results In the study of the effect of SS on AITD, SS was associated with an increased risk of Hashimoto's thyroiditis (OR = 1.09, 95%CI 1.02–1.16, p = 0.01). The causal associations were supported by sensitivity analyses. In reverse MR analyses, Hashimoto's thyroiditis (OR = 1.24, 95% CI 1.08–1.42, p < 0.01) and Graves' disease (OR = 1.11, 95% CI 1.03–1.21, p < 0.01) were found to be risk factors for SS. Conclusion Our results support a bidirectional causal relationship between SS and Hashimoto's thyroiditis and a positive correlation of genetically predicted Graves' disease on the risk of SS.