Abstract
The incidence of cleft lip and cleft palate is influenced by environmental factors, although the mechanism still remains incompletely understood. The aim of this study was to investigate the maternal environmental effect on occurrence of cleft lip with palate (CLP) in mice. A/WySn and C3 H/He strains were used. The F, hybrids from a reciprocal cross between A/WySn and C3 H/He were raised, and the reciprocal F, and A/WySn were used to produce as [A×F1(A×C3H)](A; A/WySn, C3H; C3H/He), [A×F1(C3H×A)3, [F1(A×C3H)×A] and[F1(C3H×A)×A]N2 backcross fetuses. Pregnant mice were injected on days 11 through 14 of gestation with 2.5 mg/mouse/day of cortisone. A laparotomy was performed on the 18th gestational day at which time the implant, resorption and litter size were recorded. Each fetus that attained at least Day 18 of development was checked for the presence of CLP. The frequencies of fetal resorptions that ranged from 36.4% to 45.0% did not differ significantly among the 6 groups. The rate of dams that had CLP fetuses was significantly higher in the A/WySn strain itself (35.5%) than in the A×F1(15.5%)and in the F1×A (22.2%). The mean number of implantations and the mean number of resorptions was higher in the dams that had CLP fetuses than the dams that had normal lip and palate fetuses, although the mean number of litter size did not show a significant difference. The highest incidence of CLP in the progeny was observed in the dams that had litter sizes of 8 not only A/WySn strain itself but also N2strains of mice. These results suggested that a high frequency of fetal resorption was affected by cortisone treatment, and the incidence of CLP might be influenced by litter size.
