Pathogenic COL3A1 gene variants cause vEDS, and in rare cases specific arginine-to-cysteine substitution variants in COL1A1. [2] COL3A1 encodes the α1 chain of (pro)collagen type III (COLIII), an extracellular matrix (ECM) component expressed in the tissues of the dermis, vasculature, and that of multiple major organs. This evidence concerns the gene COL3A1 and Ehlers-Danlos syndrome, vascular type.