MMP9 and abdominal aortic aneurysm: Other studies have shown that MMP-9 is the most expressed gelatinase in abdominal aortic aneurysm, especially when compared to the essential role of MMP-2 and MMP-9 in aneurysm production having been highlighted by an experimental study, which showed that deficiency of both MMPs in mice will protect against the production of abdominal aortic aneurysm [28].