Syndromic TAAs occur in the context of Loeys-Dietz syndrome (LDS) or Marfan syndrome (MFS), which arise from mutations in genes encoding transforming growth factor beta (TGFB, hereafter referred to as TGFβ)-signaling components or the extracellular matrix (ECM) protein fibrillin-1 (FBN1), respectively. The gene discussed is PROS1; the disease is Marfan syndrome.