Our findings of thrombocytopenia and an increase in platelet volume in Cdc42-deficient mice are in agreement with a recent report of thrombocytopenia and an increase in the size of platelets in mice constitutively lacking Cdc42 in megakaryocytes and platelets [13], and confirm that Cdc42 is involved in platelet production. The gene discussed is CDC42; the disease is Thrombocytopenia.