Methylated Genes in Sputum Among Older Smokers With Asthma

RUHRC Authors: Blanchette, C
Publication Date: 02/16/2012
Full Publication: Methylated Genes in Sputum Among Older Smokers With Asthma


Objective: The epigenetic basis for human asthma is not well studied, particularly among older adults. This study investigated the methylation profiles in sputum DNA among older adults with asthma, using a population of smokers.

Methods: This was a cross-sectional study using the Lovelace Smokers Cohort, a population of former and current smokers aged ≥ 40 years in New Mexico. One hundred eighty-four smokers with asthma were compared with 511 smoker control subjects with a similar smoking history, after carefully excluding those with COPD. Environmental exposures were assessed by a standard questionnaire. Postbronchodilator spirometry was performed. Induced sputum was analyzed for the methylation prevalence of 12 selected asthma-related genes using nested methylation-specific polymerase chain reaction assay.

Results: Asthma was associated with a greater number of methylated genes and, specifically, with methylated protocadherin-20 gene in sputum DNA compared with control subjects with a similar smoking history. These associations remained significant after adjustment for covariates as well as Bonferroni correction. A synergistic interaction was noted between two methylated genes (protocadherin-20 and paired box protein transcription factor-5α) in sputum DNA on the odds for asthma (P = .009). Interestingly, the epigenetic-asthma associations were not explained by the environmental factors studied. Further, methylated genes in sputum DNA, including the protocadherin-20 gene, identified a symptomatically more severe asthma phenotype in a subgroup analysis.

Conclusions: Asthma is associated with methylation of selected genes, such as protocadherin-20 gene, in sputum DNA. If future studies establish causality, novel demethylating interventions to prevent and treat asthma among older smokers may be possible.

Suggested Citation

Sood A, Petersen H, Blanchette CM, et al. Methylated Genes in Sputum Among Older Smokers With Asthma. Chest. 2012;142(2):425-431.