## Clinical Diagnosis: Ehlers-Danlos Syndrome (EDS) — Lysyl Oxidase Deficiency Type ### Pathophysiology of Lysyl Oxidase Deficiency **Key Point:** Lysyl oxidase catalyzes the oxidation of lysine and hydroxylysine residues to aldehydes (allysine and hydroxyallysine), which are essential for cross-linking collagen molecules. Without cross-linking, collagen fibrils lack tensile strength despite normal synthesis. ### Why Type I Collagen? Type I collagen is the predominant structural collagen in: - Skin (70% of dry weight) - Bone - Tendons - Ligaments Defective cross-linking of Type I collagen explains the clinical triad: | Feature | Mechanism | |---------|----------| | Joint hypermobility | Weak ligament support due to poor collagen cross-linking | | Hyperextensible skin | Reduced tensile strength of dermal collagen | | Easy bruising | Fragile blood vessel walls (Type IV collagen also affected but Type I is primary) | | Translucent skin | Thin, loosely organized collagen fibrils | ### Biochemical Basis **High-Yield:** The lysyl oxidase pathway: 1. Lysine/hydroxylysine residues in collagen → oxidized to allysine/hydroxyallysine 2. Aldol condensation → Schiff base formation 3. Cross-links stabilize collagen triple helix 4. **Without this:** collagen is synthesized normally but mechanically weak **Clinical Pearl:** This is distinct from other EDS types where the collagen molecule itself is abnormal (e.g., Type III EDS has defective Type III collagen synthesis). ### Diagnostic Confirmation - Serum lysyl oxidase activity: **markedly reduced** - Collagen synthesis: normal - Collagen cross-links: absent or severely reduced - Copper status: often abnormal (lysyl oxidase is copper-dependent) [cite:Robbins 10e Ch 3]
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