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.