Two family studies of children with ventricular septal defect.

All first-degree relatives of 81 index patients with isolated ventricular septal defects were examined cardiologically in sample one. The congenital abnormalities in first-degree relatives of 296 index patients affected ventricular septal defects were studied by questionnaire in sample two. (The relatives reported as having congenital cardiovascular malformations were checked). Ventricular septal defects were found in 3.3% and 1.45% of sibs in samples one and two, respectively. The heritability of isolated VSD was 0.57 +/- 0.22. The familial clustering fitted the multifactorial threshold model well. Other congenital cardiovascular malformations were somewhat higher in first-degree relatives of index patients (1.6% in sample one and 1.2% in sample two) than their expected rates. The occurrence of other congenital abnormalities, however, does not exceed the prevalence at birth in the population.