E2F1 and acute myeloid leukemia: Interestingly, two of the most infant-specific miRNAs, miR20b and miR363 are part of an X chromosome miR cluster that is upregulated in T cell leukemias [12], and represses the E2F1 transcription factor [13, 14], a cell-cycle regulator that is highly expressed in normal bone marrow and down-regulated in KMT2E-deleted AML [15].