The next analysis was limited to the CpG methylation and mRNA datasets of those probes where an Illumina detection p-value of less than or equal to 0.01 was observed in 95% of samples analyzed in each of the four tissue region. This provided data on a total of 27,277 unique CpG methylation sites and 8,076 probes against individual mRNA transcripts that were present in all four brain regions (Figure S2). The distribution of observed CpG methylation levels and transcript abundance was plotted as a histogram for each tissue (Figure 1C and 1D). A high proportion of CpG sites interrogated within this assay were infrequently methylated, whereas a smaller proportion were highly methylated, a trend that was apparent across tissues. This distribution of DNA methylation (Figure 1C) closely matches distributions of DNA methylation reported previously by sequencing in multiple human cell types [12], [13]. CpG sites that are within CpG Islands [14], [15] were predominately unmethylated. Grouping of mRNAs into high through low expression groups revealed abundance profiles similar to those previously reported (Figure 1D). We next compared CpG methylation and
