Correlations between lichen planus and autoimmune diseases: a Mendelian randomization study.

Previous observational studies have found that lichen planus (LP) is associated with autoimmune diseases. To determine the association between LP and 15 autoimmune diseases, we applied the Mendelian randomization (MR) approach, which uses genetic variants as a tool to improve causal inference. We performed a two-sample MR with the genetic instruments identified for 15 autoimmune diseases. Genome-wide association study (GWAS) data was sourced from the IEU Open GWAS database. The instrumental variables (IVs) for LP (1865 cases and 212,242 non-cases) were genetic variations highly associated (P < 5 × 10) with LP in the European population. To calculate causal effects, odds ratios (ORs) with 95% confidence intervals (CIs) are employed. MR showed that the genetic risk of psoriasis was positively associated with atopic dermatitis (OR [95%CI] = 0.964[0.936, 0.992], P = 0.013), ankylosing spondylitis (OR [95%CI] = 0.879[0.774, 0.999], P = 0.047) and Type 1 diabetes (OR [95%CI] = 1.074[1.008, 1.145], P = 0.027). These results didn't exhibit horizontal pleiotropy, and "leave-one-out" analysis demonstrated result stability. The MR study indicates a causal relationship between atopic dermatitis, ankylosing spondylitis and Type 1 diabetes in Europe. Further research is necessary to clarify the biological mechanisms that underlie these associations.