Review Question - QID 213817

A 13-year-old boy presents to the emergency department with severe pain and knee swelling after rock climbing. The patient was rock climbing when he bumped his knee on the wall. Shortly thereafter, the patient developed a large painful swelling of his knee. The patient is otherwise healthy, and his parents are concerned as this is the first time they have let their son participate in a sport. The child is otherwise healthy, up to date on his vaccinations, and both of his parents are healthy and not taking any medications currently. He has no history of bleeding gums or epistaxis but has bruised easily in the past. His temperature is 97.6°F (36.4°C), blood pressure is 100/64 mmHg, pulse is 89/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for the finding in Figure A. If the mother were to have another son, what is the probability that he would have a similar condition?