Single Hit Aetiology of Human Minor Congenital Malformations unassociated with Major Congenital Malformations

Abstract

MINOR birth defects can be defined as anatomical variants which occur at low frequency in the normal population and, as distinguished from major malformations, have no clinical or cosmetic effects per se. Many syndromes associated with major defects such as the trisomies and rubella embryopathy also have a high incidence of minor malformations. Conversely, almost all minor defects which have been studied clinically are known to be more frequent in individuals with major malformations. The latter types of malformations have been shown to cluster in the sense that an individual with a major defect in one organ or system is more likely than an individual chosen at random to have a significant defect elsewhere¹. But we have found that minor malformations in individuals without major malformations do not show such a tendency to cluster but rather are independent. Furthermore, our subsequent analysis of published data of other workers which bear on this problem supports this conclusion.