[Hereditary occurrence of the mesotelesystolic click syndrome: a study of 9 families (author's transl)].

Nine families affected by the mid-systolic click syndrome were studied. Of the one hundred and forty-four first-degree relatives, 117 of whom were living, eighty-four were examined. Thirty-five were found to be affected by the syndrome. Twenty-six were females and nine were males. Auscultatory and phonocardiographic findings consisted either of isolated mis-systolic clicks or systolic murmurs or a combination of the two. Electrocardiograms revealed changes of various types, most commonly of the ST-T segment. About seventy per cent of the patients were symptomatic. Nine members, not examined by the authors, had died suddenly; all had a previous history of "cardiopathy". Progressivity of mitral valve disease with age is not confirmed by the present study. It is suggested that the mode of inheritance of the defect might be that of an autosomal dominant form of Mendelian type with delayed expression of the defect. An alternatove hypothesis of a multifactorial inheritance mechanism, which is more stimulating for future studies on the cause of the syndrome, is also taken into consideration.