TET1 is an MLL fusion partner and thus a likely oncogene: t(10;11)(q22;q23) translocations which fuse the N-terminal region of the histone-3 lysine-4 (H3K4) methyltransferase MLL with the catalytic domain of TET1 have been found in several cases of acute myeloid and lymphocytic leukemias (AML, ALL) [18]–[21]. The gene discussed is KMT2A; the disease is acute myeloid leukemia.