Chromosomal rearrangements involving the histone lysine [K]-MethylTransferase 2A (KMT2A) gene on chromosome 11q23, formerly known as the mixed-lineage leukemia (MLL) gene, are found in 10% of ALL and 2.8% of AML patients, with the highest incidence in infants [97]. The gene discussed is KMT2A; the disease is acute myeloid leukemia.