An epidemiological study of facial clefting in Manitoba.

The results of an epidemiological survey of facial clefting in the province of Manitoba which covered the years 1964 to 1977, inclusive, are reported. The mean annual incidence of total facial clefts was 2 in 1000 births; the incidence of cleft lip +/- cleft palate (CLP), and of cleft palate (CP), unassociated with a syndrome or two or more major malformations, was 1.05 in 1000 and 0.46 in 1000, respectively. Mennonite infants were over-represented in the CLP group and Amerindian infants in both the CLP and CP groups. These ethnic groups also had more familial cases and showed higher average coefficients of inbreeding. Recurrence rates among sibs were found to be influenced by the presence or absence of additional affected relatives and by the presence of malformations in the proband. It is possible that these latter two variables may not be independent.