Palatal width growth rates as the genetic determinant of cleft palate induced by vitamin A.

While many studies have demonstrated sexual dimorphism and racial variation (Mongoloid greater than Caucasian greater than Black) in the incidence of palatal clefting, only generalized statements have been made concerning the causal mechanism (eg, "genetic propensity"). The present study tests the hypothesis that the more rapid the growth rate of the width of the facial skeleton, the higher the incidence of palatal clefting, given a uniform environmental insult. Two strains of pregnant rats with differing rates of craniofacial development (Wistar-fast and Sprague-Dawley-slow) were injected prenatally with high doses of vitamin A (300,000 IU/kg) on days 10-13 gestation. Fetuses were examined at 20 d prenatally and the incidence of palatal clefting was recorded. A significantly higher (P less than .05) incidence of palatal clefting was noted in the more rapidly developing strain (66% vs 81%). These results support statements by Fraser and others who suggest that head width and palatal clefting are causally related. The "genetic propensity" in this case, then, is the rate of palatal width development.