ULTRASTRUCTURAL STUDIES OF THE MEGAKARYOBLASTIC LEUKEMIAS OF DOWN-SYNDROME

The ultrastnucture of the leukemic cells in transient leukemia (six ca ses), myelodysplasia (five cases) and acute megakaryoblastic leukemia (one case) in patients with Down syndrome were studied. The cells were identified to be of megakaryocytic lineage by virtue of the expressio n of platelet glycoprotein GpIIIa, detected by immunogold labelling. I n all patients, some of the leukemic cells had ultrastructural feature s of megakaryocytes, including ectoplasmic protrusions, demarcation me mbranes, and alpha granules. Differentiation was greatest in the cells of patients with transient leukemia. These studies provide a detailed assessment of the ultrastructural features of the leukemic cells in t he megakaryoblastic leukemias of Down syndrome.