U2AF1 and myelodysplastic syndrome with ring sideroblasts: For instance, mutations in SF3B1 are strongly associated with refractory anemia with ring sideroblasts (RARS) and a good prognosis [2, 3], whereas SRSF2 and U2AF1 (U2AF35) mutations are mainly observed in refractory cytopenia with multi lineage dysplasia (RCMD) and refractory anemia with excess blasts (RAEB), and associated with high risk of leukemic transformation [4].