Fig. 1

(a) Graphical representation of the MGMT 5′-CpG island methylation patterns detected by Sanger sequencing in 113 MSP-positive (left side) and 102 MSP-negative (right side) glioblastoma patients. The ordinate represents the case numbers, while the top abscissa represents the numbering of the MGMT promoter CpG residues investigated. The 25 CpG sites map between nucleotides 46,922 and 47,124 according to GenBank accession number AL355531. CpG sites were classified as ‘strongly methylated’ (ratio of C/T-peak > 1.00; green rectangles) and ‘partially methylated’ (ratio of C/T-peak 0.50–1.00; yellow rectangles), while unmethylated CpG sites were subdivided in ‘weakly methylated’ (ratio of C/T-peak 0.10–0.49; orange rectangles) and ‘non-methylated’ (ratio of C/T-peak < 0.10; red rectangles). (b) Hierarchical clustering of the 25 analyzed CpG sites of the MGMT promoter gene (CpG sites 74–98) using the Jaccard distance and the maximum linkage criterion. Three distinct clusters (red, green and blue colour) can be found. (c) Graphical representation of methylation correlations between the different CpG sites (abscissa and ordinate). Dark blue squares display high positive and dark red squares high negative intercorrelations, while white squares display no intercorrelations