On the basis of these and other data, several active clinical trials arenow investigating the efficacy of losartan in treating aortic aneurysms in humans.The central hypothesis underlying these trials is that losartan antagonizes TGF-betasignaling,26,27likely by inhibition of the AT1 receptor or other pathways independent of a TGF-betareceptor itself.16 However, less is known about the influence of AT1 on theopposing BMP signaling pathway (the pathway directly influenced by mutations inalk1). The gene discussed is AGTR1; the disease is aortic aneurysm.