FBN1 and Marfan syndrome: The insights gained from study of Marfan syndrome–related fibrillin 1 highlight the potential role of transforming growth factor β (TGF-β) signaling in AA.10,11,24 The use of TGF-β neutralizing antibodies in fibrillin 1–deficient mice prevented AA in Marfan syndrome.25 Mice treated with losartan, an angiotensin II type 1 receptor (AT1R) blocker that antagonizes TGF-β signaling, exhibited no further aortic dilatation, thus suggesting the therapeutic efficacy of losartan against aneurysms.26