Association between schizophrenia and psoriasis: A two-sample bidirectional Mendelian randomization study

Background: Observational studies have showed an association between schizophrenia and risk of psoriasis and vice versa. However, whether schizophrenia is causally associated with psoriasis is unclear.

Methods: A two-sample bidirectional Mendelian randomization (MR) analysis was performed with publicly available genome-wide association study data including schizophrenia (n = 77 096) and psoriasis (n = 462 933). The inverse-variance weighted method was performed as the main analysis, with a complementary with the other two analyses: MR-Egger and weighted median method. A series of sensitivity analyses were also conducted to evaluate the robustness of the results.

Results: MR analyses indicated that genetically predicted schizophrenia was significantly associated with an increased risk of psoriasis [OR: 1.001, 95% confidence interval (CI): 1.000-1.002, p = 0.012]. However, no causal effect of genetically predicted psoriasis on schizophrenia (OR: 0.221, 95% CI: 0.029-1.682, p = 0.145) was detected. No pleiotropy or heterogeneity was detected in sensitivity analysis (all p > 0.05).

Conclusions: Our study provides genetic evidence for the causal association between schizophrenia and psoriasis.