However, several proteases may need to be simultaneously inhibited to halt disease progression,4 and although absence of matrix metalloproteinase (MMP)9 inhibits aneurysm development in animal models,5, 6, 7 administration of the MMP inhibitor, doxycycline, to patients with small aneurysms failed to decrease aneurysm growth.8 This evidence concerns the gene MMP9 and aneurysm.