A 4-year-old boy has a broad head, delayed tooth eruption, recurrent visual impairment from optic nerve compression, and short stature. Radiographs show diffusely thickened, dense bones with failure of the medullary cavity to form. The defect lies in which cell type?

• A Osteoblasts
• B Chondrocytes of the growth plate
• C Osteocytes
• D Osteoclasts ✓

Explanation

Osteopetrosis, or marble bone disease, arises from defective osteoclast-mediated bone resorption, so modeling and remodeling fail and unresorbed primary spongiosa fills the marrow space. Thickened brittle bones narrow cranial nerve foramina, explaining optic compression. Growth plate chondrocytes and osteoblasts function normally, and osteocytes are mechanosensory cells not responsible for resorption. Carbonic anhydrase II deficiency is one recognized cause of the osteoclast dysfunction.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.