Racial variations in the incidence of congenital malformations.

Racial variation in the incidence of several common congenital malformations has been studied in Atlanta, Georgia. The white-to-black incidence ratios were substantially different from unity for single defects, while approximate equality of rates was noted for multiple defects. Amongst the specific malformations for which familial data were available, affected first- and second-degree relatives were found only in the families of probands with single defects. It is postulated that these findings may indicate a more prominent function of the environment in the genesis of multiple malformations than is the case for single defects, the occurrence of which may be more strongly affected by non-sporadic genetic factors.