The review highlights the etiopathogenesis of prothrombotic states - particularly myeloproliferative neoplasms (predominantly JAK2 V617F), hereditary thrombophilias, and acquired conditions, such as antiphospholipid syndrome and paroxysmal nocturnal hemoglobinuria - as well as the contributory role of pregnancy, the puerperium, and systemic diseases. The gene discussed is JAK2; the disease is myeloproliferative neoplasm.