The familial occurrence of the syndrome of mid-late systolic click and late systolic murmur.

Patients with late systolic murmurs, with and without mid-late systolic extra sounds, have recently been shown to have mitral regurgitation. This syndrome has been found to be familial in each of the four families we have studied. These families were found to have a high prevalence of mid-late systolic extra sounds, late systolic murmurs, pansystolic murmurs, abnormal electrocardiograms, and unexplained premature sudden death. The prognosis for these patients is unknown but is generally considered good. Periodic medical observation of these patients and their families seems warranted, however, in view of the current lack of knowledge concerning the cause of the chest pain, the rate of progression of the mitral regurgitation, the significance of the electrocardiographic abnormalities, the frequency of important arrhythmias, and the mechanism of sudden death. In addition, antibiotic prophylaxis to attempt to prevent bacterial endocarditis seems clearly indicated.