A 6-year-old child has recurrent fractures after trivial trauma, short stature, and macrocephaly. X-rays show diffusely dense bones with failure of modeling of the metaphyses producing an Erlenmeyer flask deformity. Optic atrophy and facial nerve palsy are noted. Deficiency of which cell function underlies this disorder?

• A Osteoclast-mediated bone resorption ✓
• B Chondrocyte proliferation at the growth plate
• C Osteoblast-mediated bone formation
• D Mineral deposition by matrix vesicles

Explanation

Osteopetrosis, or marble bone disease, results from failed osteoclast resorption, so bone forms but is never remodeled. Unremodeled primary spongiosa fills the medulla causing dense but brittle bones, narrowed cranial foramina with nerve compression, and Erlenmeyer flask metaphyses. Many cases involve mutations affecting the osteoclast proton pump or carbonic anhydrase II.

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.