Chromosomal rearrangements of the MLL gene are frequently identified in pediatric, adult, and therapy-related leukemia in approximately 10% of all human leukemia, with MLL rearrangements causing over 70% of infant (≤1 year of age) acute lymphoblastic leukemia (ALL) and 35–50% of infant acute myeloid leukemia (AML) cases [41]. This evidence concerns the gene KMT2A and acute lymphoblastic leukemia.