A search for environmental and genetic background for neural tube defects: twenty-five years of experience

The present paper illustrates the author's 25-year experience in a step by step approach to the definition of environmental and genetic background of neural tube defects. Based on the birth defects registry, a complete ascertainment of all deliveries was performed in Southern Poland during two periods: 1970-1972, and 1979-1981. The birth prevalence of neural tube defects (NTD), as well as other CNS malformations was determined. The empiric recurrence risk was calculated as 3.2% +/- 1.6. Based on this figure, the relative risk (RR = 37.6 p < 0.001) and heritability (h2 = 74.7 +/- 6.7) were estimated. Our own modification of Morton's complex segregation analysis was applied. Three Mendelian (dominant, additive and recessive) and one multifactorial model were tested. The results did not provide a clear cut discrimination between different models; however the lowest x2 value was obtained for additive inheritance with 61% of penetrance and the frequency of sporadic cases equaled 55%. A search for genetic markers did not support the hypothesis that HLA-A,B,C loci are equivalents of T/t like locus in mice. The results of the study on transcobalamine levels in amniotic fluid may suggests that different transcobalamine metabolism reflects phenotypic expression of genetic susceptibility to NTD development. Current research status and future perspectives on genetic and environmental background of NTD are also presented.