In this study, the authors focused on the MPNs, ET and PV, where the same JAK2 mutations are almost universal in both conditions despite very different clinical phenotypes, and sought to determine whether the order of TET2 and JAK2 mutations along the hematopoietic lineage and within malignant clones drove differences in the clinical phenotype of the MPN. The gene discussed is JAK2; the disease is acquired polycythemia vera.