Transient abnormal myelopoiesis (TAM) is a unique disorder of Down syndrome newborns that presents with clinical and morphologic findings indistinguishable from AML. The blasts have morphologic and immunologic features of megakaryocytic lineage. This is part of the myeloid
proliferations with Down syndrome WHO group, which also includes myeloid leukemia
associated with Down syndrome (see 9898/3).