The aorta is the largest artery in the human body, carrying blood from the heart to all other organs in the body, with the exception of the lungs. The thoracic aorta is the portion of the aorta in the chest cavity. The walls of the aorta are composed of three layers of tissue; elastic fibers in the walls allow the aorta to stretch and contract as it fills with blood when the heart beats. If an area of the aortic wall becomes weak, a localized swelling may occur, which is known as an aneurysm. An aortic dissection occurs when the inner lining of the aortic wall tears, allowing blood to seep between the layers. Both aortic aneurysms and dissections may lead to aortic rupture, which is associated with a high mortality rate. Thoracic aortic aneurysms and dissections (TAAD) account for approximately 8000 deaths annually in the United States. TAAD is associated with genetic syndromes such as Marfan syndrome and Loeys-Dietz syndrome, but may also occur in isolation. Approximately 20% of patients with isolated TAAD report other family members with the condition.
Five genes and three genetic loci have been identified in patients with familial TAAD. The five genes (TGFBR1, TGFBR2, FBN1, MYH11, and ACTA2) are responsible for approximately 20% of cases of inherited TAAD. In most families with TAAD, the disorder segregates as an autosomal dominant trait with variable expressivity and reduced penetrance, especially in women. Current treatment for TAAD includes drug therapy to reduce blood pressure, and surgery to repair aneurysms and dissections in an attempt to prevent aortic rupture.