ACTA1 and triple-A syndrome: Moreover, IF staining revealed a substantial number of tdT+ cells accumulating in the thickened adventitia of both the suprarenal and infrarenal aneurysmal aortas, with few tdT+ cells in these aortas co‐expressing SMC markers (SM22, αSMA, Calponin, and Myh11; Figure 2D,E; Figure S5A, Supporting Information), suggesting a limited contribution of CD34+ cells to SMCs in AAA.