Association Between Hashimoto's Thyroiditis and Rheumatoid Arthritis: A Bidirectional Mendelian Randomization Study

Area of Science:

• Immunology
• Genetics
• Epidemiology

Background:

• Hashimoto's thyroiditis (HT) and rheumatoid arthritis (RA) are common autoimmune diseases.
• The etiological relationship between HT and RA remains unclear.

Purpose of the Study:

• To investigate the potential bidirectional causal association between HT and RA using Mendelian randomization (MR).

Main Methods:

• A bidirectional MR analysis was performed using summary statistics from large genome-wide association studies (GWAS).
• Data included 15,654 HT cases and 14,361 RA cases.
• Inverse-variance weighted (IVW) method was primary; MR-Egger, weighted median, and MR-PRESSO were used for sensitivity analyses.

Main Results:

• Significant evidence of a bidirectional causal relationship between HT and RA was observed.
• HT as exposure increased RA risk (IVW OR=2.45, p=0.0207).
• RA as exposure increased HT risk (IVW OR=1.21, p=3.95×10⁻⁷).

Conclusions:

• There is a bidirectional positive causal relationship between HT and RA in European populations.
• Individuals with HT have an increased risk of RA, and vice versa.
• Findings suggest shared genetic or environmental factors contributing to both conditions.