[Embryonic mechanisms of human holoprosencephaly development].

12 human embryos (stages 14-18) with different form of holoprosencephaly were studied. Spatial organization of the brain was reproduced with graphic reconstructions. It is demonstrated that the cause of different forms of holoprosencephaly is disturbed or delayed movement of the neurulation wave coming through the hemispheres of the forebrain. The cause of the defect may be an unspecific teratogenic factor or some cytogenetic damage. Severity and type of holoprosencephaly are associated not with the etiological factor but with the time of the action on the neurulation wave. Alobar holoprosencephaly results from the impact on neuralation for 22 days, semilobar--for 23 days and lobar--for 24 days.