The Aetiology of Congenital Abnormalities

GROSS abnormalities are fortunately not common. Murphy (1940) in.Philadelphia found that approximately 47 individuals possessing congenital malformations were born alive or dead per 10,000 live births. About one-quarter of these were reported as stillbirthls. His data was collected mainly from death certificates and included only the grosser defects. Malpas (1937) recorded 294 cases in 13,964 consecutive births in Liverpool. The occurrence of any congenital abnormality is especially painful to all concerned, and the parents will wish to know the cause of the condition, and whether it is likely to recur in subsequent pregnancies. It is not possible to give a satisfactory answer to-these questions, but it may be useful to survey some recent contributions to the problem, to indicate in what directions progress may be expected, and to acknowledge the valuable contributions made in allied fields of biological science. As an individual, developed from the fusion of the sex cells or gametes of his parents, grows through intra-uterine and extra-uterine life his whole being expresses the result of the interaction of his genetic pattern or constitution with the environment. The environment is at first the seemingly constant one of the uterus, and here the internal environment is determined primarily by such substances as can pass across the placenta. The genetic pattern is a mosaic inherited from his parents and more remote ancestors. It is composed of unit characteristics, or traits, all of which the geneticist hopes some day to recognise individually, and to trace as they are transmitted as physical entities, or genes, from generation to generation on the chromosomes of the sex cells. In accordance with the modern knowledge of Mendelian inheritance some of these characters or traits may not have been expressed for generations; either because they are recessive and have not been present as homozygotes, or because other genes or environmental factors have modified their expression. The present enquiry is concerned with the relative importance of genetic influences and the intra-uterine environment on the development of such variations from the normal as can be usefully recognised. These