British Journal of Obstetrics zyxwvutsrq and Gynaecology zyxwvut September zyxwvutsrq 1990, Vol. 97, pp. 762-769 Genetic and familial predisposition to eclampsia and pre-eclampsia in a defined population REYNIR ARNGRTMSSON, STEINGRIMUR BJORNSSON, REYNIR T. GEIRSSON, H6LMGEIR BJORNSSON, JAMES J. WALKER, GUNNLAUGUR SNAEDAL Summary. Familial predisposition and patterns of genetic inheritance of eclampsia and pre-eclampsia were investigated through three or four generations in 94 families from the homogenous island population of Iceland. The families descended from index women delivered in the years 1931-47 and who had either eclampsia (n zyxw = 38) or severe pre- eclampsia (n = 69). Inheritance was followed both through sons and daughters. The prevalence of pre-eclampsia and eclampsia in daughters was significantly higher (23%) than that in daughters-in-law (loyo). No difference was noted in the prevalence of these diseases by whether the daughter was born of an eclamptic or pre-eclamptic mother or whether she was a first or later born daughter. There was a non-significantly higher occurrence of pre-eclampsia among grand-daughters than in grand-daughters-in-law. No difference was seen by whether grand- daughters descended through sons or daughters. With increasing numbers of affected daughters or grand-daughters the probability rose of finding more affected women in a family. Hypotheses of single reces- sive and dominant gene inheritance were compared and maximum like- lihood estimates for gene frequency obtained. For a single recessive gene model this was 0.31 reflecting a population prevalence of 9.6%, whereas a dominant model with incomplete penetrance gave 0.14 at 48% gene penetrance, corresponding to a population prevalence of 0.9% homozygous expression of severe disease and 11 zyx YO heterozygous expression of milder disease. Either genetic model could fit the data. Severe pre-eclampsia and eclampsia have a familial tendency (Humphries 1960; Adams & Finlayson 1961; Chesley et al. 1961, 1968) and appear to involve a genetically determined sus- ceptibility possibly based on single gene inher- itance (Cooper & Liston 1979; Sutherland zy ef al. Department of Obstetrics and Gynecology, National University Hospital, 101 Reykjavik, Iceland STEINGRIMUR BJORNSSON JAMES J. WALKER REYNIR ARNGRIMSSON " REYNIR zyxwvuts T. GEIRSSON GUNNLAUGUR SNAED AL Agricultural Research Institute, Statistical Division, Keldnaholt, 112 Reykjavik, Iceland H6LMGEIR BJORNSSON University Department of Obstetrics and Gynaecology, Royal Infirmary, Glasgow 631 ZER, Scotland Hospital, 101 Kcykjavik, Iceland 762 Correspondence: R. Arngrimsson, Dcpartmcnt of Obstetrics and Gynecology, National University