Cleft lip and palate due to deficiency of mesencephalic neural crest cells.

The mesencephalic crest was partially eliminated in chick embryos by means of tangential microlaser. The heads of the surviving embryos were serially sectioned and microscopically studied. A deficiency of mesenshyme in the anlage of the maxillary process was observed in 4 of the 42 embryos sacrificed after 24 hours, on the side of irradiation. Among the 99 surviving embryos sacrificed at the ages of 7 or 12 days, 26 showed a unilateral cleft lip, a wide palatal cleft or a combination of these anomalies. It is concluded that cleft lip and palate can result from insufficient growth of the mesenchyme in the maxillary process caused by partial deficiency of mesencephalic neural crest cells.