The JAK2 c.1849G>T (V617F) mutation was detected in all PV (17 of 17), 4 of 10 ET, 7 out of 10 PMF, 1 out of 1 post-ET-MF, and in 8 out of 8 post-PV-MF patients. The gene discussed is JAK2; the disease is essential thrombocythemia.