Transient abnormal myelopoiesis

**Definition:** A myeloid proliferation occurring in newborns with Down syndrome. It is clinically and morphologically indistinguishable from acute myeloid leukaemia 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.