The World Health Organization has revised the criteria for diagnosis and classification of myeloproliferative neoplasms, including PMF, which now include the detection of driver mutations such as CALR and MPL, the increased importance of assessing morphologic findings in bone marrow biopsy to help with differential diagnosis of PMF, and the addition of a pre-PMF category [1]. The gene discussed is MPL; the disease is myeloproliferative neoplasm.