Apolipoprotein E polymorphism and fertility: a study in pre-industrial populations

Human apolipoprotein E is the most important supplier of the cholesterol precursor for steroid hormone production in steroidogenic tissues and therefore could play a role in the regulation of steroid hormone function and influence human reproduction. This hypothesis has been confirmed by studies describing a differential fertility associated with common apolipoprotein (APOE) genotypes in two European populations. In the present investigation the impact of APOE genetic variation on fertility was studied in two Ecuadorian populations, African-Ecuadorians (57 women) and Cayapa Indians (27 women). In addition some biodemographic variables concerning women's fertility were investigated (124 African-Ecuadorian women; 40 Cayapa women) to better understand the APOE-fertility relationships in these pre-industrial populations. General fertility rates in both populations were very high (6.5 and 6.2 for the African-Ecuadorians and for the Cayapa respectively). When considering only women near the end of reproductive life (>/=40 years), a more marked difference was observed between the two groups (9.1 versus 7.7, P=0.09). In both communities, the highest number of children was found to be associated with the e*4/e*3 genotype; the e*4/e*3 genotype frequency (0.50) in the African-Ecuadorian women with 9-17 children was about three times that of the women with 0-8 children (0.14) (P=0.02). The present findings are at variance with those observed in European populations, where e*3/e*3 was the genotype associated with the highest reproductive efficiency. A possible explanation for this inconsistency could be due to the different functional properties associated with the e*3 and e*4 alleles and to genotype interactions with environmental factors including reproductive strategies.