Transforming growth factor beta(TGF-beta) mediates disease pathogenesis in MFS and contributes to aortic stiffness. Cross-talk between TGF-beta system and renin-angiotensin system (RAS) has been demonstrated. The angiotensin receptor blocker (ARB), losartan, inhibits TGF-beta activity and reverses aortic wall pathology in a Marfan mouse model. In a small cohort study, the use of ARB therapy (losartan or irbesartan) significantly slowed the rate of progressive aortic dilatation in patients with MFS, after BB therapy had failed to prevent aortic root dilatation. In another study, angiotensin converting enzyme inhibitor, perindopril, reduced both aortic stiffness and aortic root diameter in patients with MFS taking standard BB therapy. Renin inhibitor, aliskiren, has not been studied to reduce aortic stiffness and attenuate aortic dilatation in patients with MFS.