IYSC13 - Dermal Extracellular Matrix Abnormalities Reflect Genotype-Associated Substrate Vulnerability in Vascular Ehlers–Danlos Syndrome

Objectives: Vascular Ehlers–Danlos syndrome (VEDS), caused by pathogenic COL3A1 variants, is characterized by arterial fragility. However, the extracellular matrix (ECM) mechanisms underlying its variable clinical presentation remain poorly understood. This study investigates whether genotype-specific differences in dermal collagen fibril architecture and elastic fiber integrity, used as a window into arterial wall biology, can identify distinct patterns of arterial tissue vulnerability.

Methods: Transmission electron microscopy (TEM) was performed on dermal skin biopsies from 23 individuals with genetically confirmed VEDS and 19 controls. Collagen fibril diameters and fibril diameter heterogeneity were quantified in the reticular dermis using a validated, semi-automated Fiji/ImageJ macro, enabling high throughput and standardized measurement. Elastic fiber architecture was graded semi-qualitatively based on fragmentation patterns. COL3A1 variants were grouped by predicted structural mechanisms (null, small side-chain, large-chain/charged substitutions, and splice site variants). Clinical phenotypes of dissection, rupture, and multi-territory arteriopathy were extracted from longitudinal clinical records.

Results: Collagen fibril architecture differed by COL3A1 variant class. Patients with small glycine substitutions (n = 8) demonstrated significantly larger reticular dermal collagen fibril diameters than controls (median 0.092 vs 0.079 µm; Welch’s t = 3.20, p=0.008). Large or charged substitutions (n = 9) exhibited fibril diameters comparable to controls but trended smaller (median 0.076 µm; p=0.23), producing an ordered pattern of fibril caliber (small substitutions > controls > large substitutions). Absolute fibril diameter heterogeneity (IQR width; Figure 1) showed a graded trend (large > small substitutions > controls). However, only small amino-acid substitutions differed significantly from controls (p=0.044). Elastic fiber architecture (Figure 2) demonstrated greater discriminatory power by both variant class and clinical phenotype than collagen fibril metrics. Large/charged glycine substitutions were associated with marked elastic fiber fragmentation, whereas null variants and small substitutions exhibited milder elastic fiber fragmentation. Moderate-to-severe elastic fiber degradation was significantly associated with arteriopathy involving ≥3 vascular territories (80.0% vs 30.8% with no or mild degradation; Fisher’s exact p=0.036). Notably, elastic fiber fragmentation was present in young VEDS patients, resembling age-related ECM changes typically seen later in life, suggesting a phenotype of premature vascular aging.

Conclusions: VEDS reflects genotype-specific patterns of ECM failure, with collagenopathy linked to arterial fragility and elastinopathy associated with broader arterial involvement and features of premature ECM aging. Dermal ultrastructure may offer a clinically relevant window into arterial vulnerability, capturing tissue-level risk beyond arterial diameter alone.