Definition of methylation


A chemical reaction in the body in which a small molecule called a methyl group gets added to DNA, proteins, or other molecules. The addition of methyl groups can affect how some molecules act in the body. For example, methylation of the DNA sequence of a gene may turn the gene off so it does not make a protein. Changes in the methylation patterns of genes or proteins can affect a person’s risk of developing a disease, such as cancer.

Source: NCI Dictionary of Cancer Terms