MLL1-rearrangements (MLL-r) account for ~10% of all leukemia cases and are especially prominent in infants (70–80%) and, lacking an effective standard of care, bear a very poor prognosis (Marks et al., 2013; Jabbour et al., 2015; Mann et al., 2010; Pieters et al., 2007; Winters and Bernt, 2017). The gene discussed is KMT2A; the disease is leukemia.