Further studies revealed that hematopoietic progenitor cells from MPN patients exhibit hypersensitivity to cytokines such as erythropoietin (EPO), insulin-like growth factor-1 (IGF-1), IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF), and were able to form erythroid and megakaryocyte colonies despite reduced or even absent cytokine levels (Figure 2) [26]. The gene discussed is EPO; the disease is myeloproliferative disorder.