Involved in the interaction of plaque proteins and intermediate filaments mediating cell-cell adhesion. Defects in ACTA2 are the cause of aortic aneurysm familial thoracic type 6 (AAT6) [MIM:611788]. They are primarily associated with a characteristic histologic appearance known as medial necrosis or Erdheim cystic medial necrosis in which there is degeneration and fragmentation of elastic fibers, loss of smooth muscle cells, and an accumulation of basophilic ground substance.