Somatic mutations of additional sex comb-like protein 1 (ASXL1) gene have been described in patients with various types of myeloid malignancies, including myelodysplastic syndromes (MDS) (15–25%), myeloproliferative neoplasms (MPN) (10–15%), 40% of chronic myelomonocytic leukemia (CMML), a few patients with chronic myeloid leukemia (CML), and 15–20% of acute myeloid leukemia (AML) [1–5]. The gene discussed is ASXL1; the disease is myeloproliferative neoplasm.