Calreticulin (CALR) mutation type 1 frequencies in ET are estimated between 7% and 11% and ET patients carrying <i>CALR</i> type 1 mutation are associated with lower risk of thrombosis but higher risk of myelofibrosis transformation compared to ET patients with <i>JAK2</i> mutation. The gene discussed is JAK2; the disease is essential thrombocythemia.