Fig. 2

Correlation matrix including all analyzed CpGs of MGMT. The correlation plot reveals that several CpG sites within the analyzed area, ranging from CpG 23 (bp -300) to CpG 101 (bp + 309), are strongly correlated. Two clusters (highlighted in yellow) with increased correlation are seen; (CpGs 28–48) in the promoter region and (CpGs 75–96) encompassing exon1, enhancer and the intron1 region. In the latter, a cluster with very strong correlation (CpGs 82–92) emerged (highlighted in pink). In turn, CpGs of exon 1, after the minimal promoter (CpGs 66–74) with highest percentage of missing values (Additional file 2: Fig. S1) and lowest level of methylation (see Fig. 1), demonstrated less correlation (highlighted in green)