Genetic Factors and Orofacial Clefting.

Cleft lip with or without cleft palate is the most common facial birth defect and it is caused by a complex interaction between genetic and environmental factors. The purpose of this review is to provide an overview of the spectrum of the genetic causes for cleft lip and cleft palate using both syndromic and nonsyndromic forms of clefting as examples. Although the gene identification process for orofacial clefting in humans is in the early stages, the pace is rapidly accelerating. Recently, several genes have been identified that have a combined role in up to 20% of all clefts. While this is a significant step forward, it is apparent that additional cleft causing genes have yet to be identified. Ongoing human genome-wide linkage studies have identified regions in the genome that likely contain genes that when mutated cause orofacial clefting, including a major gene on chromosome 9 that is positive in multiple racial groups. Currently, efforts are focused to identify which genes are mutated in these regions. In addition, parallel studies are also evaluating genes involved in environmental pathways. Furthermore, statistical geneticists are developing new methods to characterize both gene-gene and gene-environment interactions to build better models for pathogenesis of this common birth defect. The ultimate goal of these studies is to provide knowledge for more accurate risk counseling and the development of preventive therapies.