Neural crest and normal development: a new perspective.

Several clinical syndromes, including the DiGeorge syndrome, are characterized by clusters of developmental defects of the heart and great vessels with structures derived from the embryonic pharyngeal apparatus including thymus and parathyroids. The connective tissue derivatives of neural crest are necessary for the normal development of these structures, and there is new experimental evidence that depletion of neural crest causes defects similar to these clinical syndromes. Therefore it is proposed that many of these syndromes are due to inappropriate development of neural crest. The implications of this hypothesis include the predictions 1) that asplenia and certain other anomalies have the same etiology, and 2) that it is possible to observe the effects of teratogenic agents upon a cellular population (neural crest) at the time when it is being altered, rather than waiting until definitive organs may be examined.