Background: Dilated cardiomyopathy is characterized by an increase in ventricular size and impairment of ventricular function. Most cases are believed to be sporadic, and familial dilated cardiomyopathy is usually considered to be a rare and distinct disorder.Methods: We studied the proportion of cases of idiopathic dilated cardiomyopathy that were familial in a large sequential series of patients whose first-degree relatives were investigated regardless of whether these relatives had cardiac symptoms. We studied the relatives of 59 index patients with idiopathic dilated cardiomyopathy by obtaining a family history and performing a physical examination, electrocardiography, and two-dimensional, M-mode, and Doppler echocardiography. A total of 315 relatives were examined.Results: Eighteen relatives from 12 families were shown to have dilated cardiomyopathy. Thus, 12 of the 59 index patients (20.3 percent) had familial disease. There was no difference in age, sex, severity of disease, exposure to selected environmental factors, or electrocardiographic or echocardiographic features between the index patients with familial disease and those with nonfamilial disease. A noteworthy finding was that 22 of 240 healthy relatives (9.2 percent) with normal ejection fractions had increased left ventricular diameters during systole or diastole (or both), as compared with 2 of 112 healthy control subjects (1.8 percent) who were studied separately.Conclusions: Dilated cardiomyopathy was found to be familial in at least one in five of the patients in this study, a considerably higher percentage than in previous reports. This finding has important implications for family screening and provides direction for further investigation into the causes and natural history of dilated cardiomyopathy. (N Engl J Med 1992;326:77–82.).
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