Auricular septal defect in one of monozygotic twins.

In the cardiac clinic of the Hospital for Sick Children, Toronto, a 6-year-old girl with an auricular septal defect was found to have a monozygotic twin in whom the heart was normal. Instances of congenital heart disease in both of monozygotic twins have been reported by several authors. Smith (1929) observed a patent ductus arteriosus in both of twin boys of similar general appearance, size, and weight. Ullrich (1938) described a case of congenital hypertrophy of the heart muscle in two members of a set of triplets that developed from two ova. The monozygotic pair were the affected ones, the third member being normal. Cor biloculare and persistent truncus arteriosus in both of twin brothers was found by Giustra and Tosti (1939). Pezzi and Carugati's cases (1924) of concordant dextrocardia with situs inversus in twin soldiers have been quoted by various authors as an instance of congenital heart disease in monozygotic twins, but the original article makes no reference to the zygosity of the twins. On the other hand, congenital cardiac abnormalities in one member of a monozygotic twin pair have also been reported. Dubreuil-Chambardel (1927) observed monozygotic twins in France, only one of whom had dextrocardia and transposition of the viscera. In Germany Weitz (1936) noted patent ductus arteriosus also occurring in only one of a monozygotic pair. Rabl and Schulz (1940) erroneously report Dissmann's (1932) description of congenital aortic stenosis as appearing in one of uniovular twins. The original paper, however, describes these children as binovular twins. In the English literature we have been able to locate one case of discordance. A patent ductus arteriosus in one of twin girls is described by McClintock (1945). In her article there is an interesting history of identical twins on both the maternal and paternal sides of the family. However, the only evidence of monozygosity mentioned in her paper is that of a 58= single placenta which is now known to be insufficient proof. To these instances of congenital heart disease