Phenome-wide Mendelian randomization analysis reveals multiple health comorbidities of coeliac disease

Coeliac disease (CeD) has been associated with a broad range of diseases in observational data; however, whether these associations are causal remains undetermined. We conducted a phenome-wide Mendelian randomization analysis (MR-PheWAS) to investigate the comorbidities of CeD.Single nucleotide polymorphisms (SNPs) associated with CeD at the genome-wide significance threshold and without linkage disequilibrium (R2 <0.001) were selected from a genome-wide association study including 12,041 CeD cases as the instrumental variables. We first constructed a polygenic risk score for CeD and estimated its associations with 1060 unique clinical outcomes in the UK Biobank study (N = 385,917). We then used two-sample MR analysis to replicate the identified associations using data from the FinnGen study (N = 377,277). We performed a secondary analysis using a genetic instrument without extended MHC gene SNPs.Genetic liability to CeD was associated with 68 clinical outcomes in the UK Biobank, and 38 of the associations were replicated in the FinnGen study. Genetic liability to CeD was associated with a higher risk of several autoimmune diseases (type 1 diabetes and its complications, Graves' disease, Sjögren syndrome, chronic hepatitis, systemic and cutaneous lupus erythematosus, and sarcoidosis), non-Hodgkin's lymphoma, and osteoporosis and a lower risk of prostate diseases. The associations for type 1 diabetes and non-Hodgkin's lymphoma attenuated when excluding SNPs in the MHC region, indicating shared genetic aetiology.This study uncovers multiple clinical outcomes associated with genetic liability to CeD, which suggests the necessity of comorbidity monitoring among this population.This project was funded by Karolinska Institutet and the Swedish Research Council.