U2AF1 and essential thrombocythemia: The SRSF2 mutation affected transcriptional regulation through predominant splicing of RUNX1 to form the RUNX1a transcript.97 The short isoform RUNX1a overexpression has been reported in MPN.98 The SRSF2 mutation is found in 3% to 20% of MPN, with lower frequencies in PV and ET compared with PMF.99 In PMF, U2AF1 mutations were associated with inferior survival.100 PMF, PV, and ET patients with U2AF1 mutations have a poorer myelofibrosis-free survival compared with wild-type patients.