The three most important physiopathologic reasons of thrombocytosis are clonal, including essential thrombocythemia (ET) and other chronic myeloproliferative disorders, familial, including hereditary cases of nonclonal myeloproliferation resulting from thrombopoietin and thrombopoietin receptor mutations, and reactive, where thrombocytosis occurs secondary to various acute and chronic clinical conditions [2]. The gene discussed is MPL; the disease is essential thrombocythemia.