KMT2A and acute lymphoblastic leukemia: Rearrangements of the mixed-lineage leukemia (also known as MLL, KMT2A, HRX, or ALL1) gene are found in de novo and therapy-related myeloid and lymphoblastic leukemias, accounting for 9% of adult cases, 3–5% of children [1,2,3,4] and 61–80% of infants in acute lymphoblastic leukemia (ALL) [5,6,7], as well as 5–11% of adult cases, ~15% of children [8,9,10,11] and 33–75% of infant cases in acute myeloid leukemia (AML) [12,13].