General Pathology USMLE Step 1 Practice Question
A 7-year-old boy with a restrictive diet avoiding fruits and vegetables presents with gum bleeding, perifollicular hemorrhages, and delayed wound healing. Vital signs: BP 95/60, HR 102, RR 20, Temp 37°C, SpO2 98%. Laboratory studies show serum ascorbic acid 0.1 mg/dL (normal 0.6-2.0). Gingival examination reveals petechiae without loose teeth. Deficiency of which of the following most directly impairs collagen cross-linking required for normal scar formation?
Answer choices
- AVitamin K dependent gamma carboxylation of clotting factors
- BVitamin C dependent hydroxylation of proline and lysine residuesCorrect answer
- CBiotin dependent carboxylation of pyruvate
- DFolate dependent thymidylate synthesis
- ECopper dependent lysyl oxidase activity
- FVitamin B12 dependent methylation of collagen precursor molecules
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.