Epidemiology and etiology of clefts.

Epidemiologic and etiologic studies based on the international literature and Danish observations of 4500 patients show a steadily increasing incidence of human cleft deformities at birth. The incidence at present is nearly 2 per 1000. Heredity is the most important etiologic factor and is probably responsible for 25 to 50% of the cases depending on the type of cleft, whereas the influence of exogenous factors is still of unknown nature. Empiric risk figures and some examples of cleft syndromes are presented.