A 3-year-old boy presents with recurrent fractures after minor trauma, blue sclerae, and hearing loss. His father had similar features. Which protein is most likely defective?

• A Type I collagen ✓
• B Type II collagen
• C Type III collagen
• D Type IV collagen

Explanation

This describes osteogenesis imperfecta, most commonly caused by mutations in COL1A1 or COL1A2 genes encoding type I collagen. The triad of recurrent fractures, blue sclerae, and hearing loss is classic for type I OI. The autosomal dominant inheritance pattern (affected father) is consistent. Type II collagen defects cause spondyloepiphyseal dysplasia. Type III collagen defects cause vascular Ehlers-Danlos. Type IV collagen defects cause Alport syndrome.

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.