A 2-year-old child has multiple fractures from minimal trauma, blue sclerae, and hearing loss. Genetic testing shows a heterozygous mutation in COL1A1. Which statement about the pathophysiology is correct?

• A The mutation causes complete absence of type I collagen
• B The condition is inherited in an X-linked recessive pattern
• C Blue sclerae result from iron deposition in the sclera
• D Mutations in COL1A1 or COL1A2 account for approximately 90% of osteogenesis imperfecta cases ✓

Explanation

Osteogenesis imperfecta (OI) types I through IV are caused by autosomal dominant mutations in COL1A1 or COL1A2, accounting for about 90% of cases. Most are heterozygous null alleles producing half the normal amount of type I collagen (quantitative defect), not complete absence. Blue sclerae result from thin sclera allowing visualization of the underlying choroid, not iron deposition. The inheritance is autosomal dominant, not X-linked recessive.

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.