Although we have not found specific SNPs of ALDH1A1 associated with respiratory diseases in the GWAS Catalog (https://www.ebi.ac.uk/gwas/home), we found the ALDH1A1 gene tended to be downregulated in ciliated cells from patients with systemic respiratory diseases, including cystic fibrosis and COPD (Supplemental Figure 6A). This evidence concerns the gene ALDH1A1 and chronic obstructive pulmonary disease.