Mitral valve prolapse in persons with Down syndrome. 
This study was designed to determine the prevalence of mitral valve prolapse and aortic insufficiency in home-reared, young persons with Down syndrome.  Of the 36 individuals (ages 20-32 years) enrolled in this study, 20 had abnormal echocardiographic findings.  Thirteen patients had mitral valve prolapse, 3 had both mitral valve prolapse and aortic insufficiency, 2 had only aortic insufficiency, and 2 had other mitral valve disorders.  In 14 of the 16 patients with mitral valve prolapse, a midsystolic click was heard.  Theories of the pathogenesis and possible complications of mitral valve prolapse and its relationship to exercise and sport activities are discussed.