The other two major criteria are the same for both forms: (2) presence of a clonal marker such as JAK2, CALR, or MPL mutation, or another clonal abnormality, and (3) exclusion of other myeloid neoplasms, including BCR::ABL1-positive chronic myeloid leukemia, PV, ET, myelodysplastic syndromes, or other myeloid disorders. This evidence concerns the gene JAK2 and myelodysplastic syndrome.