Coagulation Disorders USMLE Step 1 Practice Question
A 6-year-old boy presents to the emergency department with spontaneous hemarthrosis of the left knee and ecchymoses on his arms and legs following minor trauma 2 days ago. His mother reports similar bleeding episodes in her brother during childhood that resolved by adolescence. Physical examination reveals joint swelling and warmth. Laboratory studies show: Platelet count: 245,000/μL
PT: 12 seconds (normal)
aPTT: 68 seconds (normal: 25-35 seconds)
Thrombin time: 14 seconds (normal)
Factor VIII activity: 6% (normal: 80-100%)
Factor IX activity: 95% (normal) Which of the following best explains the inheritance pattern of this patient's underlying coagulation disorder?
Answer choices
- AAutosomal dominant with variable expressivity
- BAutosomal recessive requiring two mutant alleles for disease manifestation
- CX-linked recessive affecting males who inherit a single mutant allele from carrier mothersCorrect answer
- DMitochondrial inheritance passed exclusively from the maternal lineage
- EX-linked dominant typically lethal in hemizygous males
- FY-linked inheritance explaining male-to-male transmission
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.