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Abstract
Alpha-1 antitrypsin (AAT) deficiency and tobacco smoking are confirmed risk factors for Chronic Obstructive Pulmonary Disease. We hypothesized that variable DNA methylation would be associated with smoking and inflammation, as reflected by the level of C-Reactive Protein (CRP) in AAT-deficient subjects. Methylation levels of 1,411 autosomal CpG sites from the Illumina GoldenGate Methylation Cancer Panel I were analyzed in 316 subjects. Associations of five smoking behaviors and CRP levels with individual CpG sites and average methylation levels were assessed using non-parametric testing, linear regression and linear mixed effect models, with and without adjustment for age and gender. Univariate linear regression analysis revealed that methylation levels of 16 CpG sites significantly associated with ever-smoking status. A CpG site in the TGFBI gene was the only site associated with ever-smoking after adjustment for age and gender. No highly significant associations existed between age at smoking initiation, pack-years smoked, duration of smoking, and time since quitting smoking as predictors of individual CpG site methylation levels. However, ever-smoking and younger age at smoking initiation associated with lower methylation level averaged across all sites. DNA methylation at CpG sites in the RUNX3, JAK3 and KRT1 genes associated with CRP levels. The most significantly associated CpG sites with gender and age mapped to the CASP6 and FZD9 genes, respectively. In summary, this study identified multiple potential candidate CpG sites associated with ever-smoking and CRP level in AAT-deficient subjects. Phenotypic variability in Mendelian diseases may be due to epigenetic factors.
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
Acknowledgments
The authors would like to thank all of the participants in the AAT Genetic Modifier Study for their enthusiastic support and participation. We also thank Ms. Toni M. Delorey for technical assistance. We would also like to thank Dr. Robert Crapo for his review and quality assurance of a subset of the spirometry data.
Funding
Alpha-1 Foundation Research Grant (DLD), Doris Duke Clinical Scientist Award (DLD), R01 HL 089438 (DLD), R01 HL68926 and HL105339; M. Siedlinski was supported during this work by a generous postdoctoral fellowship from the Niels Stensen Foundation.