In contrast, mutation of Mpl-Y565 resulted in thrombocytosis, excess megakaryopoiesis and increased HSC production and activity, as well as augmented platelet recovery from 5-FU treatment, observations consistent with the identification of TPO-hypersensitive mutations at this tyrosine residue in human MPN [40, 41]. The gene discussed is MPL; the disease is myeloproliferative disorder.