GATA1 and Macrothrombocytopenia: Mice with targeted mutations on the Gata1 promoter affecting its expression, such as Gata-1.05/X female mice and ΔneoΔHS mice, display severe macrothrombocytopenia, an increased proliferation of megakaryocytes, and platelets with a defective response to collagen and vWF [2, 24].