transient myeloproliferative disorder, usually transient leukocytosis associated with Down syndrome and generally diagnosed in the first few weeks of life. It is often accompanied by hepatosplenomegaly, pericardial and pleural effusions, hepatic disease, and a pustular rash. Although spontaneous remission occurs in most cases, some affected infants develop a myelodysplastic syndrome or acute leukemia. Also called congenital leukemoid reaction, transient leukemia of infancy.
