In 2009, a new family of DNA modifying enzymes, the Tet-eleven translocation family was identified as 2-oxoglutarate (2-OG) and Fe(II)-dependent dioxygenases. This family of enzymes comprises three proteins TET1, TET2 and TET3 that share a carboxyl-terminal core catalytic domain consisting of a conserved cysteine-rich domain, a double stranded β-helix domain and binding sites for the cofactors Fe(II) and 2-oxoglutarate. At their amino-terminal region, TET1 and TET3 have a CXXC DNA-binding domain. Interestingly, during evolution, the segment encoding the CXXC domain of TET2 was separated from the region encoding the catalytic domain and is now encoded separately by a neighboring gene, IDAX (also called CXXC4).