KMT2A and leukemia: An epigenetic block of normal differentiation appears to be a key driver of pediatric leukemia harboring chromosomal rearrangements that lead to fusion proteins, notably MLL fusions and NUP98-NSD1 (Deshpande et al., 2012; Hatlen et al., 2012; Popovic and Licht, 2012; Vu et al., 2013).