Association between thyroid diseases and autoimmune hepatitis: A bidirectional Mendelian randomization study

Previous studies on the relationship between thyroid diseases (TDs) and autoimmune hepatitis (AIH) are inconclusive. As a result, the aim of this study is to elucidate the potential causality between TDs and AIH. A bidirectional 2-sample Mendelian randomization (MR) analysis was performed to explore the causal associations between TDs and AIH. The primary approach utilized was the inverse variance weighted method, with sensitivity analyses conducted using the weighted median, MR-Egger, Cochran Q, and MR-PRESSO methods. The MR analysis showed that the odds ratio (OR) of hypothyroidism or myxedema on AIH was 1.23 (95% confidence intervals [CI] = 1.10 to 1.38, P = .0004), the OR of thyrotoxicosis with diffuse goiter on AIH was 1.27 (95% CI = 1.13-1.44, P = .0001), and the OR of Hashimoto thyroiditis on AIH was 1.41 (95% CI = 1.10-1.80, P = .0062) with inverse variance weighted method. No evidence for the effects of malignant neoplasm of the thyroid gland and goiter on AIH was found via 5 MR methods. The reverse MR analysis did not reveal any causal relationship between AIH and TDs. This is the first study to employ MR analysis to elucidate the causal relationships between TDs and AIH. The findings indicate that individuals with hypothyroidism, hyperthyroidism, or Hashimoto thyroiditis exhibit an elevated risk of AIH.