Typically, DNMT1 almost certainly maintains DNA methylation during DNA replication,48 whereas DNMT3A and DNMT3B are prone to de novo DNA methylation by catalysing the methylation of unmethylated DNA, with the assistance of the catalytically inactive DNMT3 L.49, 50It is noteworthy that hypermethylated CpG islands are observed in or near promoter regions, whereas gene bodies become hypomethylated in tumours with abnormal methylation.51 This evidence concerns the gene DNMT1 and neoplasm.