Multiple or single congenital anomalies may be produced experimentally by certain maternal dietary deficiencies. The similarity of the anomalies resulting from all acute dietary deficiencies and other acute teratogenic procedures is striking. When the dietary deficiency is controlled by the use of anti-metabolites, it can easily be demonstrated that the teratogenic effects vary with the time of instituting the deficiency and with its duration or severity. It can also be demonstrated that the period of sensitivity to the teratogenic dietary deficiencies is usually limited to the critical period of differentiation and organogenesis, as it is in irradiation. However, fetal vitamin deficiencies similar to those observed in the adult can probably be produced by the deficiency later in pregnancy. The severe fetal damage is in marked contrast to the relatively slight effects on the maternal organism. Presumably, although this point has not been proven, the effect of the deficiency is directly on the fetus and indicates that certain vitamins play a highly significant role in embryonic differentiation and organogenesis. We already have considerable knowledge concerning the biochemical reactions with which the B vitamins are concerned in adult tissues. It is possible that, by use of these specific vitamin deficiencies as tools, we may succeed in identifying certain key reactions in embryonic differentiation and organogenesis and thus advance our knowledge of chemical embryology.The teratogenic dietary deficiencies can provide abundant material for the pathologist to study the early stages of specific anomalies. For the physiologist, studies of anomalous conditions before and after birth are possible for some organs and systems. Studies of the interrelations of nutritional and genetic factors should lead to increasing knowledge concerning individual susceptibility to such teratogenic conditions and the application of these findings to man. The briefness of the period necessary to affect fetal development and the irreversibility of fetal damage by dietary supplementation later in pregnancy must be emphasized.
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