While there is a high degree of cellular heterogeneity within the cells of an individual leukaemia [8], there is striking redundancy of mutated genes in distinct diseases like AML [9], T-lymphoblastic leukemia (T-ALL) [10], and primary myelofibrosis [11], including mutations in DNMT3A and several other genes. The gene discussed is DNMT3A; the disease is acute lymphoblastic leukemia.