• Rate of change in aortic root (sinuses of Valsalva) body-surface-area-adjusted Z-score [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  

• Rate of change in aortic root (sinuses of Valsalva) absolute dimension [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Rate of change in ascending aorta and aortic annulus absolute dimension and body-surface-area-adjusted Z-score [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Rate of change of aortic and mitral regurgitation [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Time to first occurrence of aortic dissection, aortic root surgery, or death [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Rate of change in Z-scores for left ventricular size, wall thickness, and function by two-dimensional and M-mode echocardiography [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Rate of change of aortic root and ascending aortic elastic modulus and stiffness index [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Rate of change in Z-scores for somatic growth, where available [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Rate of change in weight and body mass index with covariate adjustment for age [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: No ]
  
• Incidence of adverse drug reactions reported during routine surveillance [ Time Frame: Measured at Month 36 ] [ Designated as safety issue: Yes ]
  

Marfan syndrome is an inheritable disorder that affects the body's connective tissue. An abnormal protein results in connective tissue that is weaker than normal. Because connective tissue is found throughout the body, Marfan syndrome can affect many body systems, including the skeleton, eyes, nervous system, skin, lungs, heart, and blood vessels. Overall, heart and blood vessel abnormalities are the leading cause of death in individuals with Marfan syndrome. A common blood vessel abnormality associated with this disease involves the aorta, which is the large artery that carries blood away from the heart to the rest of the body. The aortic root, the portion of the aorta that is attached to the heart, may enlarge and tear or even rupture. A tear or rupture is considered a life-threatening emergency. Recent studies have shown that the medication losartan may reduce aortic root growth and improve heart function. The purpose of this study is to compare the effectiveness of losartan versus atenolol at slowing aortic root growth in individuals with Marfan syndrome.

This 3-year study will enroll individuals with Marfan syndrome. Participants will be randomly assigned to receive either losartan or atenolol on a daily basis. All participants will initially receive a low dose of their assigned medication. This dose will be gradually increased every 3 to 4 weeks until the maximum tolerated dose is reached. A continuous electrocardiogram (ECG) that monitors heart rate and activity in 24-hour intervals will be used to determine the proper dose increase for each participant. Participants will then receive the maximum tolerated dose for the remainder of the study. Study visits will occur at baseline and Months 6, 12, 24, and 36. Each study visit will include a physical examination, a medical history review, an ECG, an echocardiogram, and questionnaires. Additionally, at the baseline study visit blood will be collected for laboratory testing.