KMT2A and acute lymphoblastic leukemia: Acute lymphoblastic leukemia (ALL) in children below 1 year of age, that is, infants, accounts for 2.5% to 5% of pediatric ALL.1 Genetic rearrangements of the KMT2A gene (previously MLL) are present in around 80% of infant ALL and correlate with a poor prognosis.1,2 While the overall survival rate of childhood leukemia has improved during recent years, now exceeding 90%,3,4 this success has not been translated to KMT2A-rearranged (KMT2A-r) infant ALL.1 Thus, an increased understanding of its pathogenesis combined with novel therapeutic approaches are needed to improve outcome.