The causal relationship between psoriasis and chronic obstructive pulmonary disease: A bidirectional mendelian randomization study

Purpose: Although many studies have investigated the association between psoriasis and chronic obstructive pulmonary disease (COPD), the causal relationship between psoriasis and COPD is still unknown. Methods: We employed bidirectional Mendelian randomization to investigate the causal relationship between psoriasis and COPD. Genetic instruments for exposure were selected from two distinct genome-wide association study databases. Single nucleotide polymorphisms associated with exposures at the genome-wide significance level (p < 5 × 10^⁻⁸) and exhibiting low linkage disequilibrium (r^{^2}< 0.001) were chosen as instrumental variables. Causality was assessed using multiple MR methods, including Inverse-Variance Weighted (IVW), MR-Egger, Weighted Median, Simple Mode, and Weighted Mode. A significance level of p < 0.05 was considered statistically significant. Heterogeneity was examined using Cochran's Q test, and MR-Egger regression was employed to detect pleiotropy. The robustness and reliability of the results were further evaluated through leave-one-out analysis. Results: We found a positive causal association between psoriasis and COPD [IVW: odds ratio (OR): 1.0006; p = 0.0056]. Heterogeneity and pleiotropy have not been discovered, so the results of the study are reliable. In the reverse analysis, no causal association between CPOD and psoriasis was found. Conclusion: Our findings revealed that psoriasis was associated with an elevated risk of COPD. However, no causal association between COPD and psoriasis was identified in our study.