Chromosomal rearrangements of the MLL1 gene usually involve the fusion of the N‐terminal region of MLL1 with a variety of partners to create fusions that account for most cases of the MLL1‐associated leukemia (Li and Ernst, 2014; Marschalek, 2016; Slany, 2009; Winters and Bernt, 2017). The gene discussed is KMT2A; the disease is leukemia.