ACTA1 and aneurysm: Notably, ≈30% (5 out of 16) of ACTA2R179H/+ mice exhibited tears in the middle aortic layer by 24 weeks of age, as evidenced by hematoxylin & eosin and immunofluorescence staining with α-SMA, although no visible aneurysms or bleeding were observed during aorta harvest in some of these mice (Figure 4D).