Socioeconomic status and asthma: A bidirectional Mendelian randomization study.

Background: Asthma is closely associated with lower socioeconomic status (SES), while the causal relationship between asthma and SES is undetermined. We aim to examine bidirectional relationships between asthma and SES using two-sample bidirectional Mendelian randomization (MR) for assessing potential causal inference.

Methods: Education attainment (years of schooling), household income, and Townsend deprivation index (TDI) were 3 indicators of SES considered in our study. The genetic summary data for SES and asthma were retrieved from publicly available genome-wide association studies (GWASs) conducted in participants of European ancestry. The MR estimates from each genetic instrument were combined using random effects inverse variance weighted (IVW) meta-analysis, with alternate methods (eg, MR-Egger, weighted median). Horizontal pleiotropy was assessed by sensitivity analyses. Analyses were performed using the package TwoSampleMR in R.

Results: The genetically instrumented years of schooling, household income, and TDI were not associated with the risk of asthma. However, according to the IVW method, 1.72 times increase in the odds ratio (OR) for asthma will lead to 0.024 standard deviation (SD) decrease in the years of schooling, 0.026 SD decrease in the household income, and 0.016 SD increase in the TDI. Although the substantial heterogeneity may undermine the reliability of results to some extent, sensitivity analyses further supported the causation of low household income by asthma.

Conclusion: Our study indicated that genetically predicted asthma may play a causal role in lowering the household income. However, the causal role of lower SES in asthma development was not supported by our MR analyses. Considering the heterogeneity in the current study, additional MR studies are needed to validate the results in the future.