Learning Objective: By the end of this lesson, medical students should be able to recognize the genetic, clinical, and diagnostic features of Osteogenesis Imperfecta, differentiate it from child abuse, and understand the molecular basis of type I collagen defects relevant to USMLE Step 1.
Overview
Osteogenesis Imperfecta (OI) is a genetic connective tissue disorder characterized by defective synthesis of type I collagen, leading to brittle bones and multiple fractures. It primarily affects the bones, teeth, sclerae, and hearing apparatus.
Genetic Basis
| Feature |
Description |
| Genes involved |
COL1A1 and COL1A2 |
| Inheritance pattern |
Most commonly autosomal dominant |
| Molecular defect |
↓ production of normal type I collagen due to abnormal triple-helix formation |
| Type I collagen locations |
Bone, dentin, sclera, tendons |
Clinical Manifestations
| System |
Key Findings |
| Skeletal |
Multiple fractures and bone deformities after minimal trauma (e.g., during birth) |
| Eyes |
Blue sclerae due to thin scleral collagen, revealing underlying choroidal veins |
| Teeth |
Dentinogenesis imperfecta → opalescent, fragile teeth with defective dentin |
| Ears |
Hearing loss due to abnormal ossicle formation |
Diagnosis and Differential
| Feature |
Osteogenesis Imperfecta |
Child Abuse |
| Fracture pattern |
Multiple, with minimal trauma |
Various stages of healing |
| Associated findings |
Blue sclerae, dentin defects, and hearing loss |
Bruising, inconsistent history |
| Family history |
Often positive |
Typically negative |
Management
- Bisphosphonates → reduce fracture risk and improve bone density.
- Supportive therapy: physical therapy, orthopedic interventions, and hearing aids.
Key Points for USMLE Step 1
- The most common mutation involves COL1A1 or COL1A2.
- Defective collagen synthesis affects bone and connective tissue strength.
- Blue sclerae are a hallmark finding.
- It may be mistaken for child abuse in infants with multiple fractures.
- Treatment focuses on reducing bone fragility and improving quality of life.
🧩 Activity
