SMAD3 and thoracic aortic aneurysm: Recent studies show that mutations in Smad3 cause AOS, a new syndromic form of thoracic aortic aneurysms and dissections characterized by arterial aneurysms, early-onset osteoarthritis and mild craniofacial features (van de Laar et al., 2011; van de Laar et al., 2012).