Mutations in genes encoding epigenetic modifiers, such as DNMT3A (DNA Methyltransferase 3α), ASXL1 (Additional Sex Comb-like 1), TET2 (Ten-Eleven Translocation 2) and IDH1,2 (Isocitrate Dehydrogenase 1,2) are commonly acquired early during the leukaemogenesis process and are known to be present in the initial leukaemia clone. The gene discussed is TET2; the disease is leukemia.