In humans, TET2 loss-of-function mutations are frequent in clonal hematopoiesis (a premalignant syndrome)13–15 and a variety of haematopoietic malignancies, including diffuse large B cell lymphoma (DLBCL)16–18, peripheral T cell lymphoma (PTCL) and angioimmunoblastic T cell lymphoma (AITL)19–23, and myeloid malignancies including myelodysplastic syndrome (MDS), myeloproliferative neoplasms (MPN), chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML)24–30. The gene discussed is TET2; the disease is myelodysplastic syndrome.