A 28-year-old woman presents to the rheumatology clinic with a 3-year history of progressive joint pain, skin fragility, and easy bruising. On examination, she has hyperextensible skin, joint hypermobility, and multiple scars with abnormal healing. Serum procollagen III N-terminal peptide levels are elevated. A skin biopsy shows abnormal collagen fibril architecture with irregular diameter and spacing. Which of the following collagen types is primarily defective in this patient?

Explanation

## Clinical Diagnosis: Ehlers-Danlos Syndrome (EDS) — Vascular Type ### Key Clinical Features This patient presents with the classic triad of **vascular EDS**: - Skin hyperextensibility and fragility - Joint hypermobility - Abnormal wound healing with thin, atrophic scars ### Collagen Defect in Vascular EDS **Key Point:** Vascular EDS (type IV) is caused by mutations in **COL3A1 gene**, encoding **Type III collagen**. **High-Yield:** Type III collagen comprises ~10% of total collagen but is critical in: - Blood vessel walls (tunica media) - Hollow organs (GI tract, uterus) - Skin dermis (provides elasticity) - Tendons and ligaments ### Pathophysiology Type III collagen defects lead to: 1. **Structural instability** of collagen triple helix (abnormal fibril diameter and spacing on electron microscopy) 2. **Vascular fragility** → spontaneous arterial rupture, GI perforation 3. **Skin fragility** → easy bruising, poor wound healing 4. **Joint laxity** → hypermobility ### Laboratory Findings | Finding | Significance | |---------|-------------| | ↑ Procollagen III N-terminal peptide (P3NP) | Increased Type III collagen turnover; marker of disease activity | | Abnormal fibril architecture on EM | Irregular diameter and spacing = defective collagen assembly | | Skin biopsy | Thin, fragmented collagen fibrils | ### EDS Classification by Collagen Type ```mermaid flowchart TD A[Ehlers-Danlos Syndrome]:::outcome --> B{Clinical Phenotype?}:::decision B -->|Skin hyperextensibility + hypermobility| C[Classical EDS]:::outcome C --> C1[Type I/III collagen defect]:::outcome B -->|Vascular fragility + skin fragility| D[Vascular EDS]:::outcome D --> D1[Type III collagen defect<br/>COL3A1 mutation]:::urgent B -->|Periodontal disease + hypermobility| E[Periodontal EDS]:::outcome E --> E1[Type I collagen defect]:::outcome B -->|Ocular involvement| F[Kyphoscoliotic EDS]:::outcome F --> F1[Type VI collagen defect<br/>PLOD1 mutation]:::outcome ``` **Clinical Pearl:** Vascular EDS carries the **highest mortality risk** due to spontaneous arterial rupture (aorta, carotid, mesenteric arteries). Patients require strict activity restriction and prophylactic beta-blockers. **Warning:** Do NOT confuse vascular EDS with classical EDS — vascular EDS has **minimal skin hyperextensibility** but **severe vascular complications**; classical EDS has marked skin changes but normal vascular integrity.