No abstract

The incidence of neurovertebral defects in mutant mice of the curly-tail strain was investigated and found to be similar to that observed in the same mice twenty-five years ago. The results of breeding experiments support the hypothesis of Grüneberg that the defects in these mice are probably caused by a recessive gene, the expression of which is markedly affected by the genetic background. Selection against the curly-tail phenotype for six generations did not affect the incidence of abnormalities. A marked excess of females was found among exencephalic mice, as among humans with neural tube defects. Similarly, polyhydramnios, hydrocephaly, high levels of amniotic fluid alphafoetoprotein and distinctive, rapidly adhering cells in the amniotic fluid also occurred in these mice, as in humans. The curly-tail mice thus provide a useful model for the investigation of neural tube defects in man.

Summary An elevation of maternal AFP levels was observed in 11 of 65 cases (17 per cent) after amniocentesis. It is suggested that blood samples in which AFP levels are to be measured should always be collected before and not after amniocentesis.

Vitamin A, a known teratogen of the central nervous system, was administered in various doses, at the time of active neural tube closure, to pregnant curly-tail mice which have a genetic predisposition to neural tube defects (n. t. d. ), and to A Strong mice, which are not so predisposed. The curly-tail mice showed an enhanced susceptibility to the terato­genic effect of vitamin A given on day 8 of gestation, demonstrating a clear gene─environment interaction. There was a differential response by the two sexes. Females seemed to be more affected by the vitamin A than males. When vitamin A was administered on day 9, instead of day 8, of gestation, the incidence of n. t. d. decreased rather than increased. Furthermore, the number of mice affected by n. t. d. was markedly lower even than that found spontaneously in untreated curly-tail mice.