Teratogenic effects of alcohol and isotretinoin on craniofacial development: an analysis of animal models.

The teratogens alcohol and isotretinoin cause different patterns of facial dysmorphogenesis in the human. For isotretinoin the pattern is consistent with interference with the normal development of the cranial neural crest, particularly that destined for the second visceral arch. In vitro studies in the rat indicate that, at threshold levels of exposure to isotretinoin, the development of the second arch crest represents the most sensitive process of organogenic development. For alcohol, the facial abnormalities result from exposure very early in development, during the gastrulation process. There is no evidence that this is a peculiarly sensitive stage of development with respect to alcohol; animal studies indicate that other processes in the organogenic period are equally or more vulnerable. The emphasis given to the abnormal facial features in the fetal alcohol syndrome is considered a phenomenon associated with the exclusivity of syndromes.