Study Supports a Bidirectional Causal Link Between Psoriasis, Psoriatic Arthritis, Crohn’s Disease

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The results suggest a basis for clinicians to detect the earlier potential development of psoriasis, psoriatic arthritis, and Crohn’s disease.

A bidirectional causal relationship exists between psoriasis, psoriatic arthritis (PsA) and Crohn’s disease, but not between psoriasis, PsA and ulcerative colitis, according to a study published in Scientific Reports.1

“The results suggest a compelling rationale for the clinician to detect the earlier potential development of these diseases,” Yang Sun, department of orthopedics at The First Hospital of Jilin University in Changchun, Jilin, China, and colleagues, stated.

While there is a link between PsA and inflammatory bowel disease (IBD), consisting of ulcerative colitis and Crohn’s disease, it is difficult to determine whether PsA and IBD are causally related. Moreover, anti-tumor necrosis factor-alpha used to treat patients with IBD is a risk factor for psoriasis.

In this study, investigators evaluated the potential causal relationship between psoriasis, PsA, and IBD using the summary statistics from the public available genome-wide association (GWAS) studies’ data. The largest GWAS of psoriasis included 4510 cases, and PsA included 1637 cases, with 212,242 controls each. The largest GWAS for ulcerative colitis included 2251 cases and Crohn’s disease included 657 cases, with 210,300 controls each. All cases were European individuals from the FinnGen biobank.

Genetically predicted psoriasis and PsA were associated with a 35% and a 31.9% increased risk of Crohn’s disease, respectively. Similarly, genetically predicted Crohn’s disease was associated with a 42.5% increased risk of psoriasis and a 44.8% increased risk of PsA, respectively. No correlations were found between ulcerative colitis and psoriasis or PsA.

The results align with previous studies and could be explained by the fact that psoriasis, PsA and Crohn’s disease have a similar pathogenesis. Seven non-human leukocyte antigens (HLA) susceptibility loci shared by Crohn’s disease and psoriasis were found, and 4 previously identified common risk loci were affirmed, according to the study. While Crohn’s disease and ulcerative colitis have similar clinical signs, genetic risk loci and immune pathways, they have distinctive properties that may explain the discrepancy in their link with psoriasis and PsA, investigators explained.

A limitation of the study was that the population only included individuals of European ancestry. “More studies should be conducted to verify the applicability of these results to other ethnicities,” investigators concluded.


Sun Y, Li Y, Zhang J. The causal relationship between psoriasis, psoriatic arthritis, and inflammatory bowel diseasesSci Rep. 2022;12(1):20526. Published 2022 Nov 28. doi:10.1038/s41598-022-24872-5