Causes
A person's risk of developing an aneurysm may be inherited. Ascending aortic aneurysms and berry aneurysms are especially likely to run in families. The men of an affected family are more likely to develop aneurysms than are the women. Scientists haven't yet identified the responsible genes in humans, though they have identified some in mice.
About half of all people with ascending aortic aneurysms are born with deformations known as Marfan's syndrome. Such people are unusually tall with long extremities. Abraham Lincoln is thought to have had Marfan's syndrome. They also have a weakness in the aortic wall, just where the aorta leaves the top of the heart.
Two other types of aneurysms are mycotic and atherosclerotic aneurysms. Mycotic aneurysms are caused by bacterial or fungal infection. Almost any such organism can damage the arteries, but the infection must be very deep and severe. Salmonella and syphilis both seem to have a special liking for arterial walls.
Atherosclerotic aneurysms are linked to the process that causes coronary artery disease - the buildup of fatty deposits on the inner wall of the arteries. In reality, the picture's not so clear. Even someone with severe atherosclerosis may not develop an aneurysm if they are not already genetically predisposed.
High blood pressure, high cholesterol, inactivity, smoking, and obesity, which are risk factors for heart disease, are also risk factors for aneurysms. Severe aneurysms are probably due to a combination of genes and poor cardiovascular health. Occasionally, aneurysms develop where stab or gunshot wounds have perforated an artery.