Environmental modification of the expression of neural tube defects in SELH/Bc mice

The objective of this work was to explore the environmental modification of the expression of neural tube defects (NTDs) in SELH/Bc mice. One approach was to examine the potential of SELH/Bc mice as an animal model for the reduction in recurrence and occurrence rates of NTDs in women given periconceptional folic acid supplementation. Neither folic acid nor methionine supplementation produced a detectable reduction of the exencephaly frequency in SELH/Bc mice. However, the frequency of exencephaly was consistently higher in SELH/Bc dams fed a chemically-defined Harlan Teklad diet than in SELH/Bc dams fed the standard ration of Purina Lab Chow. This observation was directly tested. The exencephaly frequency was 7-fold higher on Harlan Teklad diet than on the Purina Lab Chow diet (21% versus 3%). This finding represents the first demonstration of the nutritional modification of the expression of NTDs in SELH/Bc mice, and it affords a unique opportunity to study the mechanism of prevention of exencephaly in the SELH/Bc mouse model, something that is not possible to examine directly in human studies of NTDs. Another approach tested for the presence of a genotype-teratogen interaction of SELH/Bc mice with valproic acid as an animal model of the effect of genetic liability to NTDs on the liability to anticonvulsant induced birth defects. The SELH/Bc response to valproic acid treatment was compared to the response of two inbred strains of mice that rarely have spontaneous exencephaly. When the data were transformed according to the developmental threshold model with an underlying normally distributed scale of liability, the response to valproic acid treatment was found to be additive with the genetic liability. The genetic liability to exencephaly in SELHBc mice greatly increased the absolute risk after valproic acid treatment. At the peak response time, the frequency of exencephaly in SELH/Bc mice was 69% compared to 35% and 40% respectively in SWV/Bc and ICR/Be mice. This observation may have clinical significance for women with a positive family history of NTDs taking valproic acid during the first trimester of pregnancy.Medicine, Faculty ofMedical Genetics, Department ofGraduat