Review Question - QID 213663

An 11-year-old boy presents to the emergency department with knee pain after being hit in the leg during gym. On presentation, he is found to have a swollen, warm right knee with significant bruising in his right lower extremity. He says that he has always bruised easily throughout his childhood but has never had a joint injury like this before. Aspiration of the joint reveals blood in the right knee. Coagulation labs are obtained with the following results:

Bleeding time: 2.5 minutes
Prothrombin time (PT): 12 seconds
Partial thromboplastin time (PTT): 56 seconds

If this boy has a younger brother, what is the chance that his brother will have this disease assuming that neither parent is affected?