A novel epigenetic marker: 5-hydroxymethylcytosine (5 hmC)

5-methylcytosine (5-mC) is the principal epigenetic marker in mammalian genomic DNA. 5-hydroxymethylcytosine (5-hmC) is a recently discovered modification that results from the enzymatic conversion of 5-mC into 5-hmC by the TET family of oxygenases (1, 2).

There is considerable interest and speculation surrounding the role of what has been called the “sixth DNA base”, although its precise function has not yet been elucidated. Preliminary results indicate that 5-hmC may have important roles distinct from 5-mC. Evidence to-date suggests that 5-hydroxymethylcytosine may represent a new pathway to demethylate DNA involving a repair mechanism that converts hmC to C. This may have significant implications in epigenetics, accelerating epigenetic research (3).