In response to vascular injury or alterations in local environmental cues, VSMCs switch to a dedifferentiated phenotype, characterized by extracellular matrix synthesis along with decreased expression of contractile markers, such as SM22 and α-SMA, and the loss of VSMC in the medial layer of the aortic wall because of apoptosis is an early hallmark of AAA development (13, 14). Here, ACTA1 is linked to triple-A syndrome.