Inter-probe Correlations in DNA Methylation Levels by Cell and Tissue Type

Stepan Grinek1, Aurélie Labbe2, Kathleen Klein1, Greg Voisin1, Celia Greenwood1,2,3

1. Lady Davis Institute, Jewish General Hospital, Montreal, QC; 2. Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, QC; 3. Departments of Oncology, and Human Genetics, McGill University, Montreal, QC

DNA methylation levels can be strongly correlated at CpG sites that are very close, but the correlation decays rapidly with distance, decreasing much faster than correlations between genetic variants. However, there are some locations where longer-distance correlations have been seen, possibly due to methylation-SNP associations, and there some genomic features (e.g. CpG islands) where correlations are more persistent. Using the Illumina Infinium 450K array to measure methylation, we examine patterns of correlation in different cell types and tissues, looking for regions where the patterns are different from one another and hence where cell-type-specific methylation patterns may be important.