Recent studies have revealed that DOT1L is involved in the initiation and maintenance of mixed lineage leukemia (MLL)-rearranged leukemia, by associating with MLL fusion partner proteins, e.g., AF4, AF9, AF10, or ENL, resulting in abnormal H3K79 methylation and overexpression of a number of MLL target genes (e.g., HoxA9 and Meis1) [8–10]. Here, KMT2A is linked to leukemia.