GATA1 and Down syndrome: Paradoxically, while structural mutations in GATA1 that are found in almost all megakaryoblastic leukemia in patients with Down syndrome, overexpression of GATA1 has been reported in a subset of AML patients [37, 38] and high levels of GATA1 expression have been suggested to confer resistance to chemotherapy in acute megakaryocytic leukemia [39].