Epigenome-Wide Association Studies of COPD and Lung Function: A Systematic Review.

BACKGROUND:Chronic Obstructive Pulmonary Disease (COPD) results from gene-environment interactions over the lifetime. These interactions are captured by epigenetic changes, such as DNA methylation. This systematic review synthesizes evidence from epigenome-wide association studies (EWAS) related to COPD and lung function. METHODS:Systematic literature search on PubMed, Embase and CINAHL databases, identified 1947 articles that investigated epigenetic changes associated with COPD/lung function; 17 of them met our eligibility criteria from which data was manually extracted. Differentially methylated positions (DMPs) and/or annotated genes, were considered replicated if identified by ≥2 studies with a p<1 x 10-4. RESULTS:Ten studies profiled DNA methylation changes in blood and 7 in respiratory samples, including surgically resected lung tissue (n=3), small airways epithelial brushings (n=2), bronchoalveolar lavage (n=1) and sputum (n=1). Main results showed: (1) high variability in study design, covariates and effect sizes, which prevented a formal meta-analysis; (2) in blood samples, 51 DMPs were replicated in relation to lung function and 12 related to COPD; (3) in respiratory samples, 42 DMPs were replicated in relation to COPD but none in relation to lung function; and, (4) in COPD vs. control studies, 123 genes (2.6% of total) were shared between ≥1 blood and ≥1 respiratory sample and associated with chronic inflammation, ion transport and coagulation. CONCLUSIONS:There is high heterogeneity across published COPD/lung function EWAS studies. A few genes (n=123; 2.6%) were replicated in blood and respiratory samples, suggesting that blood can recapitulate some changes in respiratory tissues. These findings have implications for future research.