Intrinsic Platelet Defects in Hereditary Thrombocytopenia*

SUMMARY Nine families with hereditary thrombocytopenia have been described. They have been discussed and classified according to mode of inheritance, the presence or absence of clinical features of the Wiskott‐Aldrich Syndrome, platelet size, and platelet lifespan studies. These features and an assay for serum Antiplatelet Factor help to distinguish hereditary disease from acquired thrombocytopenias such as idiopathic thrombocytopenic purpura. This distinction is important, since response to therapy, particularly splenectomy, is clearly different for hereditary and acquired disease.