RISKOF ANENCEPHALYINMIGRANT AND NON-MIGRANT WOMEN INTHE OXFORD AREA

Geographical variation intheincidence ofneural tubeabnormalities, particularly anencephalus, is welldocumented. Penrose(1957) reviewed the available European dataandfoundthatthehighest ratesforanencephalus werefoundinIreland, Wales, andwestemregions ofEngland andScotland, andthattheydecreased progressively towardsEasternEurope.Stevenson, Johnston, Stewart, andGolding (1966), intheir comparative studyofcongenital malformations, confirmed a widevariation intheincidence ofneural tube defects inthe24centres studied. Fromnational statistics (Fig. 1)itisapparent thatthehighest stillbirth ratesintheBritish Isles duetoneural tubeabnormalities intheyears 19611965occurred inNorthern Ireland, Scotland, and Walesanddecreased progressively towards the south andeastofEngland. Animportant question arising fromthese observations iswhether thegeographical variations in neural abnormalities notedabovearerelated to environmental factors operating during pregnancy, orwhether theymaybeduetootherlong-term influences, including thegenetic structure ofthe population. A possible methodofresolving this problem inpolytypic populations, asshownby Carter andWoolf(1961) ina study ofphenyl ketonuria, istoexamine theparental birthplaces of casestodetermine whether migrant groups share theexperience ofthehostpopulation orthepopulation fromwhichtheyoriginated. ThusCarter andWoolf, byexamining thebirthplaces ofparents andgrandparents ofchildren withphenyl ketonuria borninsouth-east England, wereable todemonstrate thatthegenefrequency forthis disorder isapproximately fourtimesgreater inthepopulation of Ireland andwestScotland thaninsouth-east England. Inthispapera studyismadeoftheriskof neural tubedefects occurring inbabies borninthe OxfordRecordLinkage StudyAreainthefive