[Role and significance of DNA methylation]

DNA methylation is covalent addition of a methyl group to cytosine within the CpG dinucleotide. It has profound effects on the mammalian genome. These effects include transcriptional repression via inhibition of transcription factor binding, X chromosome inactivation, and imprinting. DNA methylation is important for both DNA repair and genome stability. Normal methylation patterns are frequently disrupted in tumour cells with global hypomethylation accompanying region-specific hypermethylation. When this hypermethylation occurs within the promoter of a tumour suppressor gene it could silence the gene and provide the cell with a growth advantage in a way similar to deletions or mutations. There is considerable evidence suggesting that alterations in DNA methylation play an important role in tumorigenesis and tumour progression.