Risk factors in the prevalence of anencephalus and spina bifida in New Zealand

This paper presents results from an epidemiological study on the 51 anencephalus and 53 spina bifida cases in the 1978 New Zealand birth cohort. Multiple sources were used in the ascertainment, and the prevalence rates were 0.98 and 1.02 per 1,000 total births, respectively. No association was found with the traditional indicators of the effect of environmental factors: maternal age, social class, nuptiality, month of birth, or estimated month of conception. Males comprised 41% of anencephalus and 36% of spina bifida cases; the prevalence was higher in the non-Maori than in the Maori population. New Zealand-born mothers appear to have a much lower risk of spina bifida, but not anencephaly, than those born in England/Scotland. The rate for the latter population was within the range of a number of UK-based studies. As the bloodstock of New Zealand whites has been predominantly derived from the UK population, and as New Zealand is a low prevalence area, this suggests that the higher risk for these women is likely to be attributable to factors present in their birthplace but absent in New Zealand. These findings provide further evidence that the epidemiologic patterns of anencephalus and spina bifida in low-prevalence areas are at variance with those in high-prevalence areas, such as the United Kingdom. They also support the hypothesis that the contrast in rates between high- and low-prevalence areas is a reflection of the impact of environmental factors in high-prevalence areas on the "background" or baseline frequency of anencephalus and spina bifida found in low-prevalence areas.     

Incidence of occult lumbro-sacral spina bifida in parents of children with spina bifida (concerning 80 pairs of parents with affected children)

Authors examined 80 pairs of parents with affected children with spina-bifida. They compared the incidence of spina-bifida occulta in parents and in 211 controls. The conclusion is: there is no increased incidence of spina-bifida occulta in parents of spina-bifida.     

Sex ratio in spina bifida and anencephaly

Timson's (1969, 1970) three locus model for the determination of anencephaly and spina bifida is examined, and it is concluded that observed population incidences of these conditions do not fit the model. A consideration is presented of the relevance of such models to the aetiology of multifactorial disease.     

The sex ratio in spina bifida

It is shown that the well known excess of females in spina bifida children is statistically significant when they are compared with (a) the general population and (b) their sibs.Although there is a small excess of males amongst the sibs this is not statistically significant when compared with the general population and when all the children in these families are considered they appear to have a sex ratio very similar to that general population. The sibs of the parents of spina bifida children show a statistically significant excess of females.These findings are discussed with particular reference to the genetics of spina bifida.