KMT2A and acute lymphoblastic leukemia: Assuming that the typical cancer requires 2–8 mutation in genes regulating cell fate, cell survival and/or genome maintenance,22 neither of these mechanisms appears sufficient to account for the incidence of IL, and genome-sequencing results from MLL+ infant ALL reported exceptionally few somatic mutations in these three classes of genes.12 One category of genetic variation that has not been deeply explored in these patients is rare germline variants.