Histological changes in AAA mainly involve 1) inflammatory cell invasion of the aorta, medial thinning, and adventitial thickening of the aneurysm; 2) decreased elastin level (from 15-33% to 5-8%) and imbalanced elastin/collagen ratio, resulting in aorta elasticity loss and vessel dilation; 3) vascular smooth muscle cell (VSMC) apoptosis in the tunica media that diminishes vessel repair capacity; and 4) inflammation of the aortic adventitia and perivascular tissues, which are accompanied by angiogenesis. The gene discussed is ELN; the disease is triple-A syndrome.