Heterozygous frame-shift or nonsense mutations of ASXL1, usually in exons 11 or 12, before the PHD domain (Figure 1), have been the most frequently found in myeloid malignancies, 10–25% in patients with myelodysplastic syndrome (MDS), 40–50% of chronic myelomonocytic leukemia (CMML) patients, 5–11% of patients with primary Acute myeloid leukemia (AML). The gene discussed is PDC; the disease is chronic myelomonocytic leukemia.