MLL1 (also known as lysine methyltransferase 2A [KMT2A]) is located on chromosome 11q23, but chromosomal translocation (MLL1-rearrangement [MLL1-r]) occurs in 5%–10% of acute leukemia cases (AML and ALL) in adults and children [14, 15]. The gene discussed is KMT2A; the disease is acute myeloid leukemia.