Sjögren's syndrome and psoriasis: a two-sample Mendelian randomization study

Primary Sjögren's Syndrome (PSS) and psoriasis are frequently observed to co-occur in clinical settings. However, the causal associations and underlying mechanisms between PSS and psoriasis remain poorly defined. In this study, we conducted bidirectional MR analysis to explore the causal relationship between PSS and psoriasis using four MR methods: inversevariance weighted, MR-Egger regression, weighted median, and weighted mode. Sensitivity analyses were carried out, employing different models and testing methods for comparison to assess the influence of heterogeneity and pleiotropy on our findings and to confirm the robustness of these results. We primarily employed the Inverse Variance Weighting (IVW) method for our analysis. A p-value of less than 0.05 indicates a significant causal relationship, while a p-value greater than 0.05 suggests the absence of such a relationship. The IVW analysis confirmed a causal relationship between psoriasis and primary Sjögren's syndrome (PSS) (OR: 3.149E-10, 95% CI 1.114E-18-0.089, P = 0.028), with the weighted median yielding similar results. Conversely, there was no causal association found between PSS and the risk of developing psoriasis (OR: 1.000, 95% CI 0.999-1.000, P = 0.328). This study reveals a causal relationship between primary Sjögren's syndrome (PSS) and psoriasis, demonstrating that psoriasis increases the risk of developing PSS, while the reverse is not true. This potential causal link offers new insights into the etiology of both PSS and psoriasis.