Below is an instruction from Human. Write a response.
    ### Instruction:
    How many people are affected by familial thoracic aortic aneurysm and dissection ?
    ### Response:
    Familial TAAD is believed to account for at least 20 percent of thoracic aortic aneurysms and dissections. In the remainder of cases, the abnormalities are thought to be caused by factors that are not inherited, such as damage to the walls of the aorta from aging, tobacco use, injury, or disease.
    