Epigenome-Wide Association Study of Asthma Exacerbations in Europeans

Background: Asthma exacerbations (AEs) represent the major contributor to the global asthma burden. Although genetic and environmental factors have been associated with AEs, the role of epigenetics remains uncovered. Objective: This study aimed to identify whole blood DNA methylation (DNAm) markers associated with AEs in Europeans. Methods: DNAm was assessed in 406 blood samples from Spanish individuals using the Infinium MethylationEPIC microarray (Illumina). An epigenome-wide association study was conducted to test the association of DNAm with AEs at differentially methylated positions, regions, and epigenetic modules. CpGs suggestively associated with AEs (false discovery rate [FDR] < 0.1) were followed up for replication in 222 European individuals, and the genome-wide significance (p < 9 × 10⁻⁸) was declared after meta-analyzing the discovery and replication samples. Additional assessment was performed using nasal tissue DNAm data from 155 Spanish individuals. The effects of genetic variation on DNAm were assessed through cis-methylation quantitative trait loci (meQTL) analysis. Enrichment analyses of previous EWAS signals were conducted. Results: Four CpGs were associated with AEs, and two were replicated and reached genomic significance in the meta-analysis (annotated to ZBTB16 and BAIAP2). Of those, CpG cg25345365 (ZBTB16) was cross-tissue validated in nasal epithelium (p= 0.003) and associated with five independent meQTLs (FDR < 0.05). Additionally, four differentially methylated regions and one module were significantly associated with AEs. Enrichment analyses revealed an overrepresentation of prior epigenetic associations with prenatal and environmental exposures, immune-mediated diseases, and mortality. Conclusions: DNAm in whole blood and nasal samples may contribute to AEs in Europeans, capturing genetic and environmental risk factors.