Rearrangements of the lysine methyltransferase 2A gene (KMT2Ar) and mutations in nucleophosmin 1 (NPM1m) are among the most common genetic aberrations in acute leukaemia, with KMT2Ar seen in both acute myeloid leukaemia (AML) and acute lymphoblastic leukaemia (ALL) and NPM1m present in ~30% of AML cases.1 The gene discussed is KMT2A; the disease is acute myeloid leukemia.