Various defects of type III collagen are the cause of the phenotype in all patients with Ehlers-Danlos syndrome. Both skin and joint manifestations are associated with spontaneous rupture of medium and large caliber arteries. The skin is fragile leading to skin abnormalities and the eyes may show a blue coloring of the sclerae, which is also seen with osteogenesis imperfecta.
A rupture of an artery without aneurysm formation or dissection may occur. The abdominal aorta or medium-sized branches of aorta; for example, the subclavian or large arteries of the limbs may rupture, but true aneurysms rarely form. Mitral valve prolapse occurs, but aortic root dilatation is rare.