Abstract
We reported a 2-year-old boy with mosaic Down's syndrome who had megakaryoblastic leukemia (MKBL) 2 years after recovering from transient abnormal myelopoiesis (TAM). At birth, the peripheral white blood cell count was 101, 000/μl with 59.5% blast cells. However, bone marrow examination revealed the presence of only 30% blast cells. From these findings, he was diagnosed as having TAM. The abnormal findings gradually subsided without any medical treatment and he returned to a healthy state within a few months. At the age of 2 years and 5 moths, he developed petechiae due to thrombocytopenia. Bone marrow examination revealed 65% blast cells. They were positive for platelet peroxidase (PPO) on analysis with electron microscopy. Fresh blast cells did not react to monoclonal antibodies recognizing platelet-associated antigens (pl-gp Ib and pl-gp IIb/ IIIa), but blast cells cultured. for 4 days in vitro turned positive. He was diagnosed as having MKBL and treated with low-dose cytosine arabinoside. He has presently remained in complete remission for 1 year.
