Epigenetics in psychiatry: Beyond DNA methylation

Figure 1 (De)methylation cycle of cytosine. Cytosines can be modified as a result of specific enzyme activity. DNA methyltransferases produce 5-methyl cytosine, which can be further oxidized to 5-hydroxymethyl cytosine by ten-eleven translocation enzymes. Further, two oxidative derivates, 5-formylcytosine and 5-carboxylcytosine, can also be generated and converted back to a cytosine form. BER: Base excision repair; DNMTs: DNA methyltransferases; SAH: S-adenosylhomocysteine; SAM: S-adenosyl methionine TET1: Ten-eleven translocation 1; TET2: Ten-eleven translocation 2; TET3: Ten-eleven translocation 3; TDG: Thymine-DNA-glycosylase.