The embryology, classification, epidemiology, and genetics of facial clefting.

Facial clefting results from a variety of genetic and environmental causes. It occurs when developing facial processes fail to fuse, merge, or interact; the clefts range from mild to severe. The embryology and classification of these clefts have been characterized. Moreover, the epidemiology has been determined from population data. Unfortunately, complete understanding of the genetics of facial clefting has not been completely uncovered. Facial clefts exist within more than 300 syndromes with only a few being commented on in this article. As the human genome project continues, the understanding of facial clefting and its syndromes may continue to improve. Such knowledge could advance diagnosis and treatment of the patient and counseling of the affected family. Other articles within this issue address the management of these clefts.