ETHNIC ORIGIN AND NEURAL TUBE MALFORMATIONS

THE neural tube malformations have a multifactorial origin’. There is an important genetic component, probably polygenic, and also an important environmental component. Nothing is yet known of the mechanisms by which either the environmental or the genetic factors act. On the genetic side it is not even certain whether it is the mother’s or the fetus’s genotype that is important, or both, Similarly, consideration of birth order and maternal age and the secular and seasonal variations in incidence has not clarified the environmental factors. One source of information now being explored is the effect of migration and mixed marriages. Migration will not alter gene frequencies in the migrating population except by selection over a century or more. Some environmental factors, however, for example climatic, will change at once on migration, while others, such as dietary habits, may change more slowly. Studies by LECK~ in Birmingham are already providing some interesting information. With respect to anencephalus and spina bifida, the West Indian immigrants are showing the characteristic low incidence seen among peoples living in, or originating from, West and Central Africa whether in their area of origin or in the United States, or now in Birmingham via the West Indies. The low incidence is the more remarkable, as most are in the lower socio-economic classes where the incidence of neural tube malformations is normally high. As Dr. LECK points out, it is difficult to account for this relative immunity in such different areas and often some hundreds of years after migration in other than genetic terms. The birthplaces of the mothers of infants born in Birmingham were in ascending order of frequency of neural tube malformation: West Indies, England, India and Pakistan (both largely from the Punjab) and Ireland. The high frequency (the world’s highest) in lreland itself is well-established and there have been indications of a high incidence, at least among Sikhs in the Punjab. The situation in Birmingham then as regards frequency of neural tube malformations probably represents little or no change from that in the country of origin of the migrants. In other countries, however, there are indications of a move away from the pattern of frequency of the country of origin towards that of the local population. For example, a decrease among the Irish in Boston6 and an increase among the Japanese in Hawaii4. In the Boston Irish, however, identification was by surname and this may have concealed admixture on the distaff side from other Catholic groups (for example, Italian) with lower racial incidences. In the Japanese there is at least the possibility that the ascertainment of cases was not so complete in Japan itself as by the admirable medical services in Hawaii. There is then a strong indication that migrant populations tend to keep their specific rates of neural tube malformations, and that in particular the low rates for peoples of West and Central African extraction is genetically based. On a more domestic scale, HOBBS~ has recently shown that the mothers of anencephalics in the Oxford region tend to have been born in the high incidence areas in Britain. The second piece of information from migrants comes from reciprocal racial crosses between groups with widely differing incidences of malformation. This will tell us whether only the mother’s race is important or whether, as one would expect if the fetal genotype is important, there were both maternal and paternal effects. The numbers from Birmingham are as yet small, but it is interesting that the few children born to Irish wives of West Indian men have had the high Irish incidence of neural tube malformations. There are, however, few instances of the reciprocal cross to show if West