A 28-year-old woman presents with joint hypermobility, skin hyperextensibility, and easy bruising. Genetic testing reveals a mutation in COL5A1. Which feature best distinguishes Ehlers–Danlos syndrome (EDS) classical type from osteogenesis imperfecta (OI)?

## Distinguishing EDS Classical Type from Osteogenesis Imperfecta ### Key Pathophysiology **Key Point:** EDS classical type (caused by COL5A1 or COL1A2 mutations affecting type V collagen) presents with **skin and joint manifestations**, while OI (caused by COL1A1/COL1A2 mutations affecting type I collagen) presents with **bone fragility and ocular findings**. ### Comparative Table | Feature | EDS Classical | OI Type I | |---------|---------------|----------| | **Primary defect** | Type V collagen (COL5A1) | Type I collagen (COL1A1/A2) | | **Skin findings** | Hyperextensible, velvety; atrophic scars | Normal skin elasticity | | **Joint involvement** | Hypermobility (major feature) | Normal or stiff joints | | **Bone fragility** | Mild/absent | Severe, recurrent fractures | | **Blue sclerae** | Absent | Present (classic sign) | | **Teeth** | Normal | Dentinogenesis imperfecta (opalescent) | | **Cardiac involvement** | Mitral valve prolapse | Aortic root dilatation | ### Clinical Pearl **Clinical Pearl:** The **combination of skin hyperextensibility + atrophic scarring + joint hypermobility** is pathognomonic for EDS classical type. In contrast, OI patients have **normal or tight skin but fragile bones and blue sclerae**—a completely different phenotype despite both being collagen disorders. ### High-Yield Mnemonic **Mnemonic:** **SKIN for EDS, BONE for OI** - **EDS**: Skin hyperextensibility, joint hypermobility, atrophic scars - **OI**: Osteoporosis (fractures), blue sclerae, Imperfect dentition ### Why the Correct Answer Option B (skin fragility with atrophic scarring and joint hypermobility) is the **discriminating feature** because: 1. It is **present in EDS classical** (type V collagen defect → poor skin tensile strength and wound healing → atrophic scars) 2. It is **absent in OI** (type I collagen defect → bone is primarily affected; skin is normal) This combination of skin + joint findings is unique to EDS and absent in OI. [cite:Robbins 10e Ch 7]