A myeloid proliferation occurring in newborns with Down syndrome. It is clinically and morphologically indistinguishable from acute myeloid leukemia and is associated with GATA1 mutations. The blasts display morphologic and immunophenotypic features of megakaryocytic lineage. In the majority of patients the myeloid proliferation undergoes spontaneous remission. The disease is transient myeloproliferative syndrome (MONDO_0008040, a Monarch Disease Ontology identifier). Also known as: MST, TAM, TMD, Transient abnormal myelopoiesis associated with Down syndrome, leukemia, transient, of Down syndrome, transient abnormal myelopoiesis, transient leukaemia, transient leukemia.