Often an enlarged arota can be due to a congenital anomaly (bicuspid, two leaflets) and that conditon can relate to a vessel, valve's root tissue abnormality.... the aorta may be less resilient and respond detrimentily to high blood pressure. Also, valve stenosis (narrow opening) can enlarge the aorta, or valve regurgitition (some back flow of blood into the left ventricle) can be the underlying cause.
Thanks for the question, and if you have any further questions or comments you are welcome to respond.
Ken