Genetic association between asthma and alopecia areata: A two-sample Mendelian randomization study

Background: Many patients with asthma experience alopecia areata (AA) in their lives. However, it is unclear whether asthma causes or results from AA. Our objective was to investigate the genetic causal relationship between asthma and AA. Methods: Two-sample Mendelian randomization (MR) was used to assess the causal relationship between asthma and AA based on the largest publicly available genome-wide association study summary statistics. Androgenetic alopecia (AGA) and cicatricial alopecia (CA) were chosen as the control groups for AA. The main estimates were obtained using inverse variance weighting meta-analysis (IVW), Mendelian randomization-Egger (MR-Egger), maximum likelihood estimation, and the weighted median. Sensitivity analyses were conducted using Cochran's Q test, MR-Egger, and leave-one-out methods. Lastly, we conducted a reverse MR analysis to evaluate the possibility of reverse causation. Results: Genetically, asthma is associated with an increased risk of AA, while the association between genetically predicted AGA or CA and asthma was negative. The risk of AA increased by 1.86 times in patients with asthma under the IVW method (OR = 1.86, 95% CI = 1.31-2.629, p < 0.001). The reverse MR analysis did not find evidence supporting reverse causality from three phenotypes of alopecia to asthma. Sensitivity analyses yielded consistent causal estimates. Conclusion: This study suggests that asthma is causally associated with AA. The findings deepen our understanding of the role of asthma in the pathology of AA, which emphasizes the potential for opening a new vista for the prevention and diagnosis of AA.