Aortopathy in Marfan syndrome, Loeys-Dietz syndrome, Turner syndrome, and nsHTAD is associated with increased aortic stiffness.63,64 Ex vivo biomechanical testing of dilated aortas demonstrates that increased stiffness appears to be attributable to higher collagen and lower elastin content, making aortic stiffness a proxy marker of wall remodeling, which may be apparent well before aortic diameters begin to increase.14 Consistently, the aortic stiffness increases with age, and a steep rise in stiffness is seen after 55 years of age, coinciding with the natural decreases in elastin. This evidence concerns the gene ELN and familial thoracic aortic aneurysm and aortic dissection.