KMT2A and leukemia: Leukemia patients with MLL-fusions often have additional mutations that affect growth signaling pathways (Grossmann et al., 2013; Liang et al., 2006; Armstrong et al., 2003) and MLL-fusions in mouse models cause leukemias with longer-than-expected latencies, suggesting that additional mutations are required for full progression (Ono et al., 2005; Corral et al., 1996; Forster et al., 2003).