Inheritance of mitral valve prolapse: effect of age and sex on gene expression.

To ascertain if mitral valve prolapse is inherited we studied 45 probands and 179 first-degree relatives. Echocardiographic mitral prolapse was present in 54 of 179 first-degree relatives (30%); at least one first-degree relative was affected in 29 families, including members of two generations in 23 families. The number of affected persons in the 54 sibships fell within the range predicted for autosomal dominant inheritance. The familial prevalence of prolapse was similar whether or not the proband had characteristic symptoms, auscultatory abnormalities, electrocardiographic findings, thoracic bony abnormalities, or coexistent heart disease. Mitral prolapse occurred in 37 of 90 women (41%) but 17 of 89 men (19%; p less than 0.005), and in 51 of 143 adults (35%) but only 3 of 36 children aged 1 to 15 (p less than 0.005). Mitral valve prolapse is an inherited autosomal dominant condition irrespective of clinical findings, and the mitral prolapse gene shows age and sex dependent expression. Mitral valve prolapse appears to be the commonest mendelian cardiovascular abnormality in humans.