Causal associations between both psoriasis and psoriatic arthritis and multiple autoimmune diseases: a bidirectional...

Numerous observational studies have identified associations between both psoriasis (PsO) and psoriatic arthritis (PsA), and autoimmune diseases (AIDs); however, the causality of these associations remains undetermined.

We conducted a bidirectional two-sample Mendelian Randomization study to identify causal associations and directions between both PsO and PsA and AIDs, such as systemic lupus erythematosus (SLE), Crohn's disease (CD), ulcerative colitis (UC), multiple sclerosis (MS), uveitis, bullous pemphigoid (BP), Hashimoto's thyroiditis (HT), rheumatoid arthritis (RA), vitiligo, and ankylosing spondylitis (AS). The causal inferences were drawn by integrating results from four regression models: Inverse Variance Weighting (IVW), MR-Egger, Weighted Median, and Maximum Likelihood. Furthermore, we performed sensitivity analyses to confirm the reliability of our findings.

The results showed that CD [IVW odds ratio (OR_IVW), 1.11; 95% confidence interval (CI), 1.06-1.17; P = 8.40E-06], vitiligo (OR_IVW, 1.16; 95% CI, 1.05-1.28; P = 2.45E-03) were risk factors for PsO, while BP may reduce the incidence of PsO (OR_IVW, 0.91; 95% CI, 0.87-0.96; P = 1.26E-04). CD (OR_IVW, 1.07; 95% CI, 1.02-1.12; P = 0.01), HT (OR_IVW, 1.23; 95% CI, 1.08-1.40; P = 1.43E-03), RA (OR_IVW, 1.11; 95% CI, 1.02-1.21, P = 2.05E-02), AS (OR_IVW, 2.18; 95% CI, 1.46-3.27; P = 1.55E-04), SLE (OR_IVW, 1.04; 95% CI, 1.01-1.08; P = 1.07E-02) and vitiligo (OR_IVW, 1.27; 95% CI, 1.14-1.42; P = 2.67E-05) were risk factors for PsA. Sensitivity analyses had validated the reliability of the results.

Our study provides evidence for potential causal relationships between certain AIDs and both PsO and PsA. Specifically, CD and vitiligo may increase the risk of developing PsO, while CD, HT, SLE, RA, AS, and vitiligo may elevate the risk for PsA. Additionally, it is crucial to closely monitor the condition of PsO patients with specific AIDs, as they have a higher likelihood of developing PsA than those without AIDs. Moving forward, greater attention should be paid to PsA and further exploration of other PsO subtypes is warranted.