A 5-year-old boy is being evaluated for recurrent epistaxis and other abnormal bleeding episodes, including excessive bleeding from the umbilical cord at bih. Laboratory studies reveal the following: decreased hemoglobin (with microcytic hypochromic red cell indices), normal platelet count, markedly prolonged prothrombin time (PT) and paial thromboplastin time (PTT), and unmeasurable thrombin time (TT). Platelet aggregation studies reveal a normal platelet response to ristocetin, but with other substances (including collagen, ADP, and epinephrine), this patient's platelets exhibit a primary wave defect. Based on these findings, this patient most likely has