DNA methylation of CpG islands. (A) Relative differential MES of subgrouped CGIs. (B) Correlation between differential CGI methylation and distance to the transcription start site. (C) Correlation between gene expression level and the hypermethylation of CGIs. (D) Methylation-specific PCR of histone genes showing the highest differential MES values. M1 and U1 correspond to HIST3H2A, while M2 and U2 correspond to HIST3H2B.