Histology USMLE Step 1 Practice Question
A 31-year-old man with achondroplasia presenting with severe growth retardation is evaluated further. Vital signs show BP 118/76, HR 82, RR 16, temp 37°C, SpO2 98%. He denies joint pain. Long bone biopsy reveals disorganized chondrocyte columns with markedly reduced proliferation zone thickness. X-rays show narrowed growth plates. Serum calcium and alkaline phosphatase are normal. Histologic examination demonstrates loss of normal columnar architecture in the growth plate. Which molecular mechanism best explains these findings?
Answer choices
- ADeficiency of Type II collagen in the cartilage matrix
- BInadequate calcification of the hypertrophic zone
- CIncreased apoptosis of resting zone chondrocytes
- DOveractive fibroblast growth factor receptor signalingCorrect answer
- ELoss of perichondrial ossification
- FDefective Indian hedgehog signaling in the growth plate
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.