Background

Little is known on shared origins between inflammatory bowel diseases (IBD) and asthma and allergic disease. 

Aims

To expand current knowledge on the etiological sources of comorbidities between IBD, asthma and allergic diseases, using a range of genetically informed methods.

Methods

Within-individual and familial co-aggregation analysis was applied to 2,873,445 individuals born in Sweden 1987-2014 and their relatives. Quantitative genetic modelling was used to decompose the genetic and environmental sources for comorbidity in 38,723 twin pairs. Polygenic risk score (PRS) analysis between IBD and allergic diseases was conducted in 48,186 genotyped twins, and linkage disequilibrium score regression (LDSC) was applied using public available data to explore the genetic overlap.

Results

IBD was associated with asthma (aOR 1.35, 95%CI 1.30-1.40), allergic rhinitis (aOR 1.27, 95%CI 1.20-1.34) and eczema (aOR 1.47, 95%CI 1.38-1.56), with similar estimates for ulcerative colitis and Crohn?s disease. The ORs for familial co-aggregation decreased with decreasing genetic relatedness. Quantitative genetic modelling revealed little evidence of common genetic factors explaining IBD and allergic diseases comorbidity, but some evidence of a unique environmental factor between IBD and eczema, re=0.16, (95%CI 0.00-0.32). PRS and LDSC results were null for IBD and allergic diseases except for a weak association between Crohn?s disease-PRS and eczema (OR 1.09, 95%CI 1.06-1.12).

Conclusions

We found little evidence to support a shared origin between IBD and allergic diseases and weak evidence for shared genetic and unique environmental components for IBD and eczema comorbidity.