SF3B1 and myeloproliferative disorder: Moreover, a colony assay targeting a patient with myelodysplastic syndrome (MDS)/MPN-RS-T harboring both JAK2 exon 12 (p.H538_K539delinsL) and SF3B1E622D mutations demonstrated that SF3B1-mutated clones existed in isolation but all clones with JAK2 exon 12 mutations had accompanying SF3B1 mutations.