Reevaluating the standard: A bidirectional Mendelian randomization study of autoimmune thyroiditis and thyroid function.

Previous studies have yielded inconsistent results regarding the causal relationship between autoimmune thyroiditis (AIT) and thyroid function. This study employs the Mendelian randomization (MR) method to clarify the connection between AIT and thyroid function. We conducted a comprehensive statistical analysis using data from publicly available genome-wide association studies focusing on individuals of European ancestry. A 2-sample MR approach was used to explore the causal relationship between AIT and thyroid function. Single nucleotide polymorphisms served as instrumental variables, with the inverse-variance weighted (IVW) method as the primary analytical technique. Additional analyses included MR-Egger regression, the weighted median estimator, the simple-mode, and the weighted-mode. Cochran Q test assessed SNP heterogeneity, and sensitivity analyses, such as the MR-Egger intercept and leave-one-out tests, ensured the robustness and reliability of our findings. The analysis found no significant association between AIT and conditions like hyperthyroidism, hypothyroidism, free thyroxine (FT4), or thyroid-stimulating hormone (TSH). For hyperthyroidism, the weighted median estimator suggested a potential protective effect of AIT (OR = 0.989, 95% CI = 0.979-0.999, P = .034). However, the IVW method did not yield statistically significant results (OR = 0.992, 95% CI = 0.985-1.000, P = .053), and similar nonsignificant outcomes were observed with MR-Egger regression, the simple-mode, and the weighted-mode. The IVW method found no significant association between hyperthyroidism and the development of AIT (OR = 1.076, 95% CI = 0.904-1.280, P = .408) in reverse causality analysis. Consistent results across various analytical approaches indicated no significant causal relationship between hyperthyroidism, hypothyroidism, FT4, TSH, and the onset of AIT. This research suggests no causal link between autoimmune thyroiditis and thyroid function indicators.