Proportions of acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML) cases are more similar among infants (47 vs 37%, respectively; Linabery and Ross, 2008) and most cases (ALLs: ∼75%, AMLs: ∼60%) have mixed lineage leukaemia (MLL) gene rearrangements in their leukaemia cells (Pui et al, 1995; Greaves, 1996). The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.