Bidirectional Mendelian Randomization Study Identifies No Genetic Link Between Psoriasis and Diabetes

Epidemiological studies proposed a bidirectional link between psoriasis (Ps) and diabetes mellitus (DM); their causal relationship remains inadequately explored. We obtained summary statistics of genome-wide association analyses for Type 1 diabetes mellitus (T1DM), Type 2 diabetes mellitus (T2DM), and Ps from individuals of European ancestry by accessing the UK Biobank and FinnGen datasets. Inverse-variance weighted (IVW) method was utilized as the primary method. Additional analyses included debiased IVW (dIVW), constrained maximum likelihood with model averaging, robust adjusted profile score, Mendelian randomization (MR)-Egger, weighted median, and weighted mode. Moreover, sensitivity tests were conducted, including Cochran's Q, MR pleiotropy residual sum, and outlier analyses. Eventually, bidirectional MR was conducted to examine the possibility of a causal link between Ps and DM. No significant causal associations were indicated between DM and Ps. Moreover, there was no causal link between Ps and T1DM. Although certain positive correlations were identified between Ps and T2DM, aggregate evidence remains insufficient to establish a causal relationship. The results demonstrated no evidence of horizontal pleiotropy between genetic variants. Furthermore, a leave-one-out test validated the stability and robustness of this correlation. Our study identifies no genetic causal effect of Ps on DM and of DM on Ps in European ancestry. Additional research is warranted to verify the presence of an association between Ps and DM in diverse populations.