ACTA2 and familial thoracic aortic aneurysm and aortic dissection: In familial nonsyndromic thoracic aortic aneurysms and dissections (FTAAD), while most causative genes remain unidentified, around 20% of cases are associated with mutations in genes that support the contractile apparatus of smooth muscle cells, including smooth muscle actin and myosin (ACTA2 and MYH11, respectively).