DNA methylation

DNA methylation is an epigenetic mechanism (i.e., a change in gene activity or function that is not associated with any change of the DNA sequence itself) involving the transfer of a methyl group to the C5 position of the cytosine ring of DNA.^[1] It is essential for normal development and plays an important role in many key processes, such as repressing the expression of potentially harmful genetic elements.

Aging brings an increase in DNA methylation variability (i.e., an increase in DNA methylation in some tissues and a decrease in others) due to concurrent genetic and environmental influences.^[2]