MLL1, located on chromosome 11q23 in humans, is a frequent chromosome translocation partner present in over 70% of infant B-cell acute lymphoblastic leukemia (B-ALL) and 5%–10% of acute myeloid leukemia (AML) (Gu et al., 1992; Tkachuk et al., 1992). Here, KMT2A is linked to acute myeloid leukemia.