569 EPIDEMIOLOGIC EVIDENCE THAT VENTRICULAR SEPTAL DEFECTS OCCUR PARTLY AT RANDOM

Abstract

To investigate possible reasons for the recent increase in the reported incidence of ventricular septal defects (VSDs) in the U.S., the epidemiology of VSDs was examined. The known risk factors explain few cases. Incidence rates are similar in different countries, races and seasons, and are unrelated to maternal age, birth order, sex and socioeconomic status. Despite identical genes and similar prenatal environments, the concordance rate in identical twins is only about 10%. The reported increase probably reflects more complete case finding rather than a true increase in the occurrence of VSD. The consistency of incidence in differing environments and the frequency of discordance in identical twins call into question the widely accepted multifactorial inheritance hypothesis. Instead, these findings suggest that, in addition to genes and environment, chance plays a major role in the etiology of VSDs. This hypothesis has two major implications for clinical practice: many VSDs are not preventable, and parents need not feel responsible for VSDs in their children.