Sexual Differences in Closure of the Human Palatal Shelves

Abstract

Clinical data have shown that sexual differences in the incidence and severity of cleft palate types may stem from a sexual dimorphism in the timing of human palatal shelf closure (7). These data generally indicated that female embryos show a greater incidence and severity of palatal clefting than do male embryos of the same age. Based on a hypo— thetical model of human palatal closure, such sexual differences in the clinical data were explained on the assumption that the secondary palate of the female embryo closes at a slower rate than that of the male embryo of the same age. The suggested female time lag further indicates that since the female secondary palate is open for a longer period of time than is that of the male, the female embryo may be susceptible to teratogenic disruption of normal palatal closure for a greater period of time. This stimulating developmental model suggests differential rates of palatal closure for the two sexes, and it correlates well with the cleft palate incidence studies of Knox and Braithwaite (5), Fogh—Andersen (2), and Mazaheri (6). The pooled 619 clinical cases of these investi— gators shows a 1.5/1 female to male ratio for palatal clefts of all types, i.e., complete, partial. More specifically, these collective data indicated a 2.0/1 female to male ratio for complete clefting of the secondary palate and a 1.2/1 ratio for clefts of the soft palate. The present study is a follow—up to the report by Meskin, Pruzansky, and Gullen (7), and is based on two primary questions: (1) Is there an identifiable sex indicator for human embryos during the times of palatal closure? (2) Are there any discernible trends in the relationship between the sex of the human embryo and early stages of its palatal development?