In addition to their critical role in normal development, oncogenic roles for MLL are well-established, especially in leukemia where MLL1 gene rearrangements and fusion proteins cooperate with the wild-type MLL1 allele to induce malignant transformation of hematopoietic progenitors via deregulation of HOXA and other oncogenic genes [9]. Here, KMT2A is linked to leukemia.