A newborn is noted to have blue sclerae, multiple fractures, and excessive joint laxity. The parents are unaffected. Which type of osteogenesis imperfecta (OI) does this most likely represent, and what is the underlying defect?

• A OI type III — progressively deforming, autosomal recessive, structural defect in type I collagen ✓
• B OI type II — lethal perinatal form, autosomal recessive, due to quantitative or structural defect in type I collagen
• C OI type I — mildest form, autosomal dominant, reduced quantity of structurally normal type I collagen
• D OI type IV — moderate severity, autosomal dominant, normal sclerae

Explanation

OI type III (progressively deforming type) presents at birth or in utero with multiple fractures, blue or grey sclerae, severe deformity, and extreme short stature. It is the most severe non-lethal form (unlike type II which is lethal perinatally). The molecular defect is a structural mutation in COL1A1 or COL1A2 producing abnormal type I collagen chains that disrupt the triple helix. OI type I is the mildest and most common form with blue sclerae and normal stature.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.