A patient with a bleeding tendency has a prolonged activated partial thromboplastin time (aPTT) with a normal prothrombin time. In what phase of the clotting process is the disturbance located? What...

A patient with a bleeding tendency has a prolonged activated partial thromboplastin time (aPTT) with a normal prothrombin time. In what phase of the clotting process is the disturbance located? What is one possible disease that could produce these findings?