World survey of the common cardiac malformations: developmental error or genetic variant?

The common cardiac malformations are prevalent throughout the world, in countries of high technology and among the primitive races. These same malformations were described 200 years ago, ectopia cordis 5,000 years ago. Their recent increase is directly related to the advent of cardiac treatment. Most cardiac malformations known to man occur in the dog. The prevalence rate of these malformations is the same in the dog and in man (5-8/1,000). Several of the malformations are heritable in specific breeds of dogs, one in rabbits, another in rats. These malformations occur in various animals that cannot interbreed. Hence the deoxyribonucleic acid (DNA) that codes these malformations must lie in that portion of the DNA common to all mammals. This suggests that these malformations occurred during the evolution of the Mammalia. Mammals evolved from reptiles, animals with hearts of various structures for the separation of arterial and venous blood. Although the "normal" heart is the most compatible with mammalian life and hence the most common, some mammals may have evolved with a heart with different structures for the separation of arterial and venous blood. Some of these hearts have persisted. These primeval hearts we call cardiac malformations of the cyanotic group. Malformations that apparently are arrests in the development of the normal heart (patent ductus arteriosus, atrioventricular canal) may represent stages in the evolution of the "normal" heart. Although teratogens and mutagens do exist, the author conceives of congenital cardiac malformations not as arrests or errors in the development of a "normal" heart but as genetic variants.