Immunophenotype of a transient myeloproliferative disorder in a newborn with trisomy 21

Cytologic, immunologic, and cytogenetic studies were performed on the blast cells of a newborn with Down syndrome and transient myeloproliferative dis ease. This hematologic disorder is uncommon, and occurs primarily in infant s with Down syndrome. This boy presented with a high white blood cell count and a high percentage of blast cells, without anemia or thrombocytopenia. Chromosome analysis showed a constitutional trisomy 21 without any other cl onal abnormality. A three-color flow cytometric analysis was performed and revealed two different CD45 dim, CD34(+), CD117(+), CD56(+) immature subpop ulations: the normal immature myeloid precursor and an immature blast cell population that expressed CD41, CD42, CD61, CD36, CD13, CD1a, and CD2. We p ostulate that this population could be the leukemic precursor involved in t he acute megakaryoblastic leukemia frequently observed in children with Dow n syndrome. Cytometry (Comm. Clin. Cytometry) 42:118-122, 2000. (C) 2000 Wi ley-Liss, Inc.