JAK2 and myeloproliferative disorder: In another study where paired MPN specimens from the chronic and blast phases were compared, mutations in SRSF2, U2AF1, and IDH1/2 in combination with mutations in driver genes (JAK2 V617F in the vast majority of cases) at the time of diagnosis were associated with rapid leukemic transformation; the mean time to disease progression was 1.5 years in patients harboring mutated SRSF2 and U2AF1 [38].