Causal relationship between asthma and inflammatory bowel disease : A two-sample bidirectional mendelian...

Area of Science:

• Genetics
• Epidemiology
• Gastroenterology

Background:

• Observational studies suggest an association between asthma and inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC).
• Methodological limitations in previous studies prevent establishing a definitive causal link.
• Investigating the causal relationship between these conditions is crucial for understanding disease mechanisms and developing targeted therapies.

Purpose of the Study:

• To investigate the potential causal relationship between asthma and inflammatory bowel disease (IBD) using a two-sample bidirectional Mendelian randomization (MR) approach.
• To overcome confounding factors inherent in observational studies and explore the directionality of the association.
• To provide robust evidence regarding the etiological link between asthma and IBD subtypes.

Main Methods:

• Utilized two-sample bidirectional Mendelian randomization (MR) analysis with genome-wide association studies (GWAS) data for asthma and IBD.
• Selected single nucleotide polymorphisms (SNPs) associated with asthma and IBD.
• Employed inverse variance weighted (IVW), MR-Egger, maximum likelihood, and weighted median (WM) methods for MR analysis.
• Assessed heterogeneity using Cochran's Q test and horizontal pleiotropy using the MR-Egger intercept.
• Conducted sensitivity analyses with leave-one-out method and funnel plots.

Main Results:

• MR analysis indicated that asthma increases the risk of Crohn's disease (CD) (e.g., IVW: OR=1.17, P=0.0082).
• No significant causal effect of IBD on asthma was detected in the reverse MR analysis.
• No evidence of heterogeneity or horizontal pleiotropy was found, supporting the validity of the MR results.

Conclusions:

• The study suggests a potential causal link between asthma and an increased risk of Crohn's disease.
• No evidence supports a causal effect of IBD on asthma.
• Further research is warranted to confirm these findings and elucidate the underlying biological mechanisms.