KMT2A and leukemia: The mixed lineage leukemia gene MLL, the human homolog of the Drosophila trithorax gene, encodes a histone H3 lysine 4 (H3K4) methyltransferase that positively regulates multiple homeobox transcription factors, including Hoxa9 and MEIS1, which are pivotal for leukemogenesis [1].