THEORIES OF CAUSATION OF CONGENITAL DEFECTS IN HUMAN BEINGS
WHAT CAUSES congenital defects? Interest in this problem increases as the control of bacteriological and nutritional sources of ill-health continues to improve and as the congenitally defective group makes a proportionately greater contribution to the infant mortality and morbidity rates.1 Yet there is probably no pediatric field in which more widely divergent views are held. This paper will discuss some of these opinions and review briefly the rapidly growing body of literature on experimentally produced congenital defects in mammals.1. Defects with Genetic Causation.—"Hereditary" defects are defined as "those determined by factors transmitted through the germ cells," while "congenital" defects are defined as "those present at birth." Obviously, congenital defects are not necessarily hereditary, and hereditary abnormalities are not necessarily congenital. The terms "hereditary" and "genetic" are used synonymously.It is well established that in some families some congenital