Familial mitral valve prolapse and myotonic dystrophy.

When a patient with mitral valve prolapse was found to have myotonic dystrophy, his family was studied to ascertain the occurrence of these abnormalities. Of 25 relatives screened, 8 had evidence of both myotonic dystrophy and mitral valve prolapse and 2 had evidence of myotonic dystrophy alone. Thirteen patients had evidence of neither condition and 1 had mitral valve prolapse alone. The association of these two conditions within a family has not previously been observed and valvular heart disease has not been recognized in myotonic dystrophy. This association should be looked for in other patients.