Rheumatoid arthritis and inflammatory bowel disease: A bidirectional two-sample Mendelian randomization study

Area of Science:

• Genetics
• Immunology
• Gastroenterology

Background:

• Observational studies suggest an association between rheumatoid arthritis (RA) and inflammatory bowel disease (IBD).
• The causal relationship and directionality between RA and IBD remain unclear.

Purpose of the Study:

• To investigate the causal relationship between rheumatoid arthritis and inflammatory bowel disease using a two-sample Mendelian randomization study.
• To determine if RA causally influences IBD or vice versa.

Main Methods:

• Utilized a two-sample Mendelian randomization approach with genetic instruments from large genome-wide association studies (GWAS).
• Analyzed RA's effect on IBD (including Crohn's disease and ulcerative colitis) and the reverse association.
• Employed inverse-variance weighted (IVW) method and conducted sensitivity analyses for robustness.

Main Results:

• Genetically predicted rheumatoid arthritis showed a significant positive causal effect on inflammatory bowel disease (OR 1.214, P = 3x10^-8).
• Rheumatoid arthritis was suggestively associated with Crohn's disease (OR 1.108, P = 0.011) and ulcerative colitis (OR 1.082, P = 0.044).
• No significant causal effect of IBD (overall or subtypes) on rheumatoid arthritis was detected.

Conclusions:

• This study provides genetic evidence supporting a causal link where rheumatoid arthritis increases the risk of inflammatory bowel disease.
• Findings suggest a unidirectional causal relationship from RA to IBD.
• Supports the clinical recommendation for screening IBD in patients diagnosed with rheumatoid arthritis.