A 32-year-old woman presents with a 10-year history of progressive joint pain, skin hyperextensibility, and easy bruising. Physical examination reveals hyperextensible skin, hypermobile joints, and several atrophic scars. Serum prothrombin time and activated partial thromboplastin time are normal. Which investigation is most appropriate to confirm the diagnosis of Ehlers–Danlos syndrome (vascular type)?

Explanation

## Diagnostic Approach to Ehlers–Danlos Syndrome ### Clinical Context The patient presents with classic features of EDS: skin hyperextensibility, joint hypermobility, easy bruising, and atrophic scars. Normal coagulation studies help exclude bleeding disorders but do not rule out EDS. ### Investigation of Choice: Genetic Sequencing **Key Point:** Genetic sequencing for COL3A1 mutations is the gold standard confirmatory test for vascular EDS (type IV), which is the most clinically severe form with high mortality risk from vascular rupture. **High-Yield:** COL3A1 encodes type III collagen (α1 chain), which is the primary collagen in blood vessel walls, skin, and hollow organs. Mutations cause defective type III collagen synthesis or structure, leading to vascular fragility. ### Why Genetic Sequencing is Superior | Investigation | Sensitivity | Specificity | Clinical Use | |---|---|---|---| | **Genetic sequencing (COL3A1)** | ~95% in vascular EDS | Definitive | Gold standard; enables risk stratification and family screening | | Skin biopsy with TEM | ~80% | Moderate | Supportive; shows abnormal collagen fibrils but not specific | | P3NP levels | Variable | Low | Reflects collagen turnover, not diagnostic | | Urine hydroxyproline | Non-specific | Low | Marker of collagen metabolism, not diagnostic | ### Clinical Pearl **Warning:** Vascular EDS (type IV) has a median life expectancy of ~50 years due to spontaneous arterial rupture, bowel perforation, and uterine rupture. Early genetic diagnosis allows for prophylactic management (beta-blockers, ARBs, avoidance of contact sports, planned cesarean delivery). ### Mnemonic: EDS Types and Key Genes **CHOP** = **C**lassical (COL5A1/COL5A2), **H**ypermobility (TNXB), **O**steogenesis imperfecta–like (FKBP14), **P**eriodontitis (C1R/C1S) — but **vascular = COL3A1** (remember: **V**ascular = **V**essels = type **III** collagen). ## Why Other Options Are Incorrect **Skin biopsy with TEM:** While it may show abnormal collagen fibril morphology (e.g., irregular diameter, abnormal packing), it is not diagnostic. It is supportive and often used when genetic testing is unavailable or inconclusive, but it cannot definitively identify the molecular defect. **Serum P3NP levels:** This reflects collagen type I turnover and is non-specific. It may be elevated in various collagen disorders and connective tissue diseases but does not confirm EDS or identify the specific genetic mutation. **Urine hydroxyproline:** This is a marker of overall collagen metabolism and degradation. It is neither sensitive nor specific for EDS and does not provide diagnostic confirmation.