Recurrent mutations in DNA methyltransferases (DNMTs), isocitrate dehydrogenases (IDH1/IDH2), methylcytosine dioxygenases of the ten-eleven-translocated (TET) family, and human homologs of the Drosophila polycomb complex such as Enhancer of Zeste 2 (EZH2) and additional sex-combs like genes (ASXL1/2) have been discovered in AML and myelodysplastic syndromes and myeloproliferative neoplasms (MDS/MPN), and many of these mutations have been causally linked to myeloid transformation in murine models. The gene discussed is ASXL1; the disease is myelodysplastic syndrome.