DNA methylating enzyme DNA methyl transferases 1 (DNMT1) is necessary in maintaining global methylation and aberrant CpG island methylation in human cancer cells [42], whereas the de novo DNA methyltransferase 3a (DNMT3a) is responsible for the establishment of de novo genomic DNA methylation patterns, involving in normal development and in many diseases including cancer [43]. The gene discussed is DNMT3A; the disease is cancer.