CMML is another MPN/MDS overlap disorder whose diagnosis requires persistent (≥3 months) peripheral monocytosis >1 × 109/L, absence of BCR-ABL fusion or PDGFRA/B rearrangements, fewer than 20% blasts or promonocytes in blood and bone marrow, and evidence of dysplasia or clonal abnormality (or persistent monocytosis lasting ≥3 months with exclusion of all other causes). The gene discussed is PDGFRA; the disease is myeloproliferative disorder.