It is a medical condition, a subset of Ehlers–Danlos syndrome which especially affects the body's vascular system, including blood vessels and organs, and makes them prone to rupture.

Patients with Sack–Barabas syndrome have thin, fragile skin, especially in the chest and abdomen, that bruises easily; hands and feet may have an aged appearance.

[citation needed] Facial features are often distinctive, including protruding eyes, a thin nose and lips, sunken cheeks, and a small chin.

Other signs of the disorder include hypermobility of joints, tearing of tendons and muscles, painfully swollen veins in the legs, lung collapse, and slow wound healing following injury or surgery.

[citation needed] The protein determined by the COL3A1 gene is used to assemble larger type III collagen molecules, found mostly in skin, blood vessels, and internal organs.