Twins and Congenital Heart Disease

Abstract

Summary and Conclusions The number of twins in 942 families where the propositus had a congenital malformation of the heart has been studied. The 38 pairs were not significantly more than could be expected by chance: nor were the 21 pairs where one member had a malformation of the heart. In 16 pairs, one was affected and the other normal; and in 5 pairs, one was affected and the other unknown. In 2 pairs, both were unknown because of early deaths; and in 15, both members of the pair were normal. In no pair were both members known to be affected. There is clear evidence from this series and from the series of Uchida and Rowe (1957) and of Lamy et al. (1957) that where one member of a pair of monozygotic twins has a congenital malformation of the heart, the other is generally normal. It is the exception rather than the rule for both members to be affected, though several examples of such pairs have been reported. There is some evidence from these three series that monozygotic twins are more liable to have a malformation of the heart than dizygotic twins and their sibs. It follows from these two findings, that the immediate cause of the malformation of the heart must be environmental, though probably there is some genetic predisposition. A disturbance of the foetal circulation to the affected twin because of a single placenta and chorion seems to be the most likely environmental cause. I should like to thank Professor Gedda of Rome and Professor Polani for their helpful suggestions and Dr. I. E. Evans for letting me see his unpublished paper on the evidence for monozygosity in some of the pairs of twins included in this paper.