U2AF1 and myeloproliferative disorder: Mutations in SF3B1 gene were initially identified by whole exome sequencing in 6 cases of 9 MDS, 8 of them being refractory anemia with ring sideroblasts, and a large scale mutational analysis confirmed the high frequency of SF3B1 mutations in MDS (20%) compared to other myeloid neoplasms (AML 5%; MPN 3%).[3] Yoshida and colleagues analyzed 29 MDS cases and identified multiple mutations of the RNA splicing machinery including SF3B1, U2AF35, SRSF2, ZRSR2, SF3A1 and PRPF40B in 16 cases [1].