A Genetic Study on Palatolabial Defects

Abstract

(1) Incidence. Through the analysis of 35,868 children born to white couples (W), in urban and rural zones of the States of Minas Gerais, Parana and Santa Catarina, the incidence of cleft lip with or without cleft palate (CL ± CP) was found to be 0.84 ± 0.15°/00. Among 33,263 non-whites (mulattoes and negroes: NW) surveyed in the same regions, this frequency was 0.69 ± 0.14°/00. These data show a general agreement to those obtained in other W and NW populations. The frequency of isolate cleft palate (CP) was found to be 0.06 ± 0.04°/00 both among W and NW. (2) Etiology. Our data on CL ± CP agree with the hypothesis of a multifactorial inheritance but they do not support the view of a sex modified inheritance. The fact that the incidence and the recurrence risks have the same order of magnitude in Brazilian populations characterized by low socio-economic level as those verified in developed countries may be accepted as an indication that exogeneous factors (such as those prevalent in our underdeveloped populations) are not important as etiologic factors.(3) Recurrence. The risk of recurrence of CL ± CP for sibs with normal parents is 3–4% in the Caucasian fraction. Among 79 NW sibs, no CL ± CP cases were verified. In 5 sibships (3 W and 2 NW) with 1 affected parent, no recurrence was verified in a total of 20 children. In two W families, with a total of 5 sibships, where CL ± CP had a familial character, the recurrence among sibs was 7%. This value however does not differ statistically from the general risk (around 4%).(4) Inbreeding. The incidence of consanguineous marriages is larger among the parents of CL ± CP children than in the general population, although the difference is not statistically significant. No recurrence has been verified among inbred individuals. (5) Genetic load. An estimate of the mean number of abnormal (CL ± CP) equivalents per gamete (B) among Caucasians revealed 0.01 ± 0.01 and among NW 0.01 ± 0.02. These values are not significantly different from zero; B/A∼16. (6) Maternal age and parity. Our data do not show any effect in relation to these parameters. (7) Sex-ratio. Our data show a statistically non-significant excess of affected (CL ± CP) females.