Alterations in SF3B1 were initially discovered in myelodysplastic syndromes (MDSs) and chronic lymphocytic leukemia (CLL), together with other mutations of splicing factors, such as U2AF1, SRSF2 and ZRSR2 (refs 1, 2, 3). This evidence concerns the gene U2AF1 and B-cell chronic lymphocytic leukemia.