COL3A1 and thoracic aortic aneurysm: These patients have mutations in genes of the structural proteins of the connective tissues, that is, fibrillin I (FBN1) in the Marfan syndrome, in theSMAD3,TGFB2, and TGFB-receptor genes (TGFBR1andTGFBR2) in the syndromic forms of thoracic aortic aneurysms, and in Type III collagen gene (COL3A1) in the case of Ehlers–Danlos syndrome Type IV, also known as the vascular type of the Ehlers–Danlos syndrome.