The investigators designed a clinical trial in which a new generation Beta-Blocker Nebivolol with expected effects on shear stress, heart rate and potential anti-stiffness benefits is compared to Losartan, and Angiotensin receptor blocker anti TGF-beta effects, and to the association of both molecules in patients with Marfan Syndrome. Nebivolol is a patented drug that differs chemically, pharmacologically and therapeutically from all other BBs. Nebivolol shows the highest selectivity for ß1 receptors among the currently available BBs, influences the arterial stiffness through an agonistic effect on ß2-receptors and preserves the arterial compliance. We expect a significantly lower progression of the Aortic Root Dilation in the arm of Nebivolol plus Losartan vs. single drug (primary end-point).The investigators further expect: decrease of arterial stiffness higher in the arm treated with both drugs than in solely Nebivolol or Losartan; a decrease of serum levels of active TGFb in both Losartan arms, a drug & age-dependant variation of the expression of the mutated FBN1 gene. As for other end-points, the potential results are the improvement of valve function, hard events & delay of surgical timing for the aortic root. The enrolment period will last 12 months, while the overall follow-up period will be of 4 years. An interim analysis for the primary outcome is programmed at month 24.