RUNX1 mutations and ASXL1 mutations frequently co-occurred with mutations in spliceosome genes (SF3B1, SRSF2, U2AF1, ZRSR2) with 49/62 (79%) RUNX1mut MDS and 97/153 (63%) ASXL1mut MDS harboring also spliceosome mutations. The gene discussed is U2AF1; the disease is myelodysplastic syndrome.