They are closely associated with the MPN driver oncogenes, such as BCR-ABL in chronic myeloid leukemia (CML) [2], JAK2V617F in polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis (MF) [3,4], and calreticulin (CALR) frameshift mutations in ET and MF [5,6]. The gene discussed is CALR; the disease is acquired polycythemia vera.