Genetic and Non-Genetic Factors in the Etiology of Facial Clefts

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Abstract
A survey is given of our present knowledge of genetic and non-genetic factors in the etiology of facial clefts, based on the international literature and Danish observations of 4000 patients. The most important factor is heredity, which is responsible for cleft lip with or without associated cleft palate in probably 40–50%, and for cleft palate alone in about 20–25% of the cases. Chromosome anomalies and exogenous influences have been proved causal in very few instances so far. There is a steadily increasing incidence of cleft lip and palate at birth, at the present amounting to nearly 2 per 1000. This increase is most likely genetically as well as environmentally determined. Preventive measures are as yet inconceivable—apart from advice against any kind of drug during the first trimester of pregnancy.