Cytogenetic findings and clinical features in acute leukemia and transient myeloproliferative disorder in Down's syndrome.

Cytogenetic, immunologic, and electron microscopic studies were performed on the blast cells of 28 pediatric patients with Down's syndrome, 13 with acute leukemia (DS-AL) and 15 with transient myeloproliferative disorders (DS-TMD). Clonal chromosome abnormalities were found in the cells of all patients with DS-AL but not those with DS-TMD. The younger ages and higher hemoglobin concentrations, platelet counts, and WBC counts of DS-TMD patients provided a clinical contrast with the frankly leukemic cases. Myelodysplastic syndrome, characterized by a small percentage of leukemic blast cells, was observed in 11 of the 13 patients with DS-AL compared with none in the DS-TMD group. Electron microscopy disclosed a positive platelet peroxidase reaction in each of the 11 DS-TMD patients and in nine of the 13 DS-AL patients. Immunologic studies revealed antiplatelet-megakaryocyte antigens on the blast cells of the majority of patients in both study groups. Our findings suggest that the blast cells in cases of DS-AL and DS-TMD arise from cells of the megakaryocytic lineage or from a myeloid progenitor with the capacity for megakaryocytic differentiation. The high risk of the development of AL in patients with DS who are less than 3 years old may be related to increased megakaryocyte proliferation in this age group.