Familial syndrome of midsystolic click and late systolic murmur.

Evidence has recently been produced to show that patients with a midsystolic click and late systolic murmur have a peculiar abnormality of the mitral valve: the systolic ballooning of the leaflets, particularly the posterior one, usually associated with mild mitral insufficiency. Occurrence of similar clinical, phonocardio- graphic, and electrocardiographic findings in more than one member of each of eight families studied strongly supports the hypothesis of a genetic basis. The frequent association with findings indicating myocardial involvement is pointed out. Its potential aetiological implications are discussed. The possible links with the forme fruste of the Marfan syndrome are also considered. Some distinctive clinical, phonocardiographic, and electrocardiographic features are described.