As expected, the vessel wall from AAA tissues showed severe medial degeneration with extensive leukocyte infiltration and fibrosis (Fig. 5C, Supplemental Fig. S5): ACTA2 expression was high in vasa vasorum but low or absent in spindle shaped cells in the media of the vessel wall (Fig. 5C), a finding consistent with large AAA. This evidence concerns the gene ACTA2 and triple-A syndrome.