Orofacial clefts in Czechoslovakia. Incidence, genetics and prevention of cleft lip and palate over a 19-year period.

The precise value of incidence was calculated based on the sample of 3,660 probands with orofacial clefts born in Bohemia between 1964-1982, as all cases born in this region and time were registered. For non-syndromic cases, the incidence of cleft lip was 0.4396 per 1,000 live birth, 0.7684 for cleft lip and palate and 0.6024 for isolated cleft palate. The sample of 4,950 of our older probands born between 1886-1963 was added and the whole sample of 8,250 individuals was evaluated with respect to sex-ratio, laterality, clinical severity, seasonal incidence and age of parents. The risk of recurrence and value of heritability were calculated as well. Based on these evaluations, a four-threshold multifactorial model for cleft lip and palate was suggested and also confirmed by our results of primary prevention of orofacial clefts using periconceptional supplementation with vitamins and folic acid.