In contrast to the association of SF3B1 mutations with ringed sideroblast-containing subtypes of MDS, SRSF2 and U2AF1 mutations appear to be enriched in more aggressive subtypes of MDS, including the WHO subtypes refractory anemia with excess blasts I (RAEB I) and RAEB II. Here, SF3B1 is linked to myelodysplastic syndrome with single lineage dysplasia.