Chromosomal rearrangements involving the MLL gene are found in 5–10% of pediatric and adult AML (Antony-Debre and Steidl, 2014), and in 80% or greater in cases of infant ALL (Van Der Linden et al., 2014); these translocations are usually associated with a poor prognosis. The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.