Abstract MP32: Epigenome-Wide DNA Methylation Profiling in a CVD Cohort: The ARIC Study

Abstract

DNA methylation is mitotically heritable modification in chromatin structure that impacts transcriptional control of genes and cellular function. Recent technological advances provide opportunities to systematically interrogate variation in DNA methylation across the genome in large epidemiologic studies. However, unlike inherited changes to the genetic sequence, variation in site-specific methylation varies by tissue, stage of development, disease state, and may be affected by gender, aging and exposure to environmental factors. As a result, there is likely a greater threat of confounding in epigenome-wide methylation studies compared to genome-wide association studies of SNPs. The Illumina Infinium HumanMethylation450 BeadChip was used to measure DNA methylation in peripheral blood obtained from African American participants from the Jackson, Mississippi and Forsyth County, North Carolina field centers of the Atherosclerosis Risk in Communities (ARIC) Study, a population-based cohort of middle-aged men and women. After excluding outlier samples and CpG sites using quality control filters, we analyzed 473,687 sites in 2873 subjects who were between 47-71 years of age at the time of DNA collection. We used linear regression with robust standard errors to examine cross-sectional associations of demographic factors with the beta value, an estimate of the average methylation level at each locus, and applied a Bonferroni correction to account for multiple testing. In univariate analysis, 91% of sites on the X chromosome and 10% of sites on the autosomes exhibited statistically significant gender differences in methylation level (p<1x10-7). Average methylation was higher in women than men for most of the significant sites (63% and 89% on the X chromosome and autosomes, respectively). Percent European ancestry estimated from ancestry informative markers was significantly associated with methylation level at 4% of sites. Age was also significantly associated with methylation at 4% of sites; average methylation was lower in older subjects compared to younger subjects for the majority (58%) of these sites. As we begin to implement epigenome-wide studies of DNA methylation and CVD outcomes, these results indicate that such studies will require careful consideration of adjustment techniques to avoid confounding by gender, age, and other covariates.