Based on an analysis of 299 AML patients, mutations in spliceosome genes such as SRSF2, SF3B1, ZRSF2 and U2AF1, EZH2, BCOR and STAG2 are >95% specific for AML-MRC and can distinguish AML-MRC from de novo AML, even in the absence of an antecedent MDS diagnosis [8]. The gene discussed is U2AF1; the disease is acute myeloid leukemia.