Concordance and discordance of congenital heart disease in 20 families.

It is generally accepted that the frequency of congenital heart disease is higher in relatives of patients than in the general population. Estimates both of population frequencies, and of the extent to which these frequencies are exceeded in relatives of those affected, vary considerably. This is not surprising as some authors have reported series diagnosed at birth, while others have reported such series but with follow-up to detect cases unrecog- nized at birth. Stillbirths were not always included, while cases with congenital heart disease found in association with other malformations, or as part of a syndrome, were sometimes excluded. Finally, a majority of the larger studies had, as their starting points, cases identified at specialist cardiac clinics or in children attending hospital, so that the severe cases determining early death would be under- reported in such series. Other problems involved in arriving at realistic and useful frequency estimates of congenital heart disease in communities have recently been reviewed by Hay (1966).