Lysine methyltransferase 2A (KMT2A, previously called Mixed lineage leukaemia, MLL) gene rearrangements (KMT2Ar, previously called MLLr) are generally associated with ALL-L1/ALL-L2 pB-ALL and are present in 6% of paediatric ALL cases [2, 3]. The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.