A 23-year-old man presents with prolonged nose bleeds. He has always noted easy bruising, and ongoing bleeding after minor cuts. There is no prior history of surgery or dental procedures. His hemoglobin is 14.5 g/dL, platelets 200,000/mL, and PT/PPT is normal. Further testing reveals that the bleeding time is elevated; the factor VIII level is reduced, as is the ristocetin cofactor assay.For the above patient with a bleeding disorder, select the most likely diagnosis.