Figure 2.

Genomic characteristics and temporal stability of inter-individual DMRs (iiDMRs). (A) This plot shows the distribution of iiDMRs across different genomic features (promoters, regulatory regions (that is, Regulatory Features from Ensembl), exons, introns and all other regions (that is, other). iiDMRs were defined as differences >5% in DNA methylation between individuals present in two adjacent probes of the Illumina 450K array. The feint line shows the expected level if iiDMRs were found equally in all regions of the genome. (B) A comparison of technical vs. biological variation for iiDMRs. Shown is the number of iiDMR calls between Illumina 450K array for technical replicates, twin pairs and unrelated individuals. This analysis was done with CD14+ DNA from two MZ twin pairs in triplicate. The biological variation significantly exceeded the technical variation (P <10^-7, permutation test). (C) Temporal stability of iiDMRs. The inter-individual DNA methylation differences found in this study were compared with the DNA methylation differences present in the same individuals 2 years prior. The previous DNA methylation differences were obtained from CD14+ DNA methylation profiles from the same individuals using Illumina 27K data as part of a separate study [17]. Shown are all current and historic inter-individual methylation differences from all the common probes present on Illumina 27K and Illumina 450K arrays.