Are apolipoprotein E alleles correlated with semen quality?

Apolipoproteins have a unique role in lipoprotein metabolism regulation, aiding lipid transport and acting as a cofactor of the enzymes involved in metabolism. There are three co-dominant alleles, APOE*2, APOE*3 and APOE*4, which encode three protein isoforms, apoE2, apoE3 and apoE4. APOE*3 is the most frequent in all populations thus far investigated, ranging from 50 to 90%. Some studies have tried to resolve a genetic 'dilemma' by evaluating the cause of the frequency and survival of the three alleles. Genetic drift, migration or natural selection could explain the current distribution of APOE gene frequencies worldwide. If APOE*4 is the ancestral allele, APOE*3 must have offered a considerable selective advantage, perhaps consisting of a positive effect during the reproductive period. Given this, there is a need to understand if APOE gene polymorphism might affect reproductive capacity. Few studies have been conducted in this area, and they generally correlate APOE polymorphism with reproductive efficiency in terms of number of children. The aim of our study was to look for correlations between APOE polymorphism in humans and semen quality, to establish if APOE genotypes have any demonstrable effect on spermatogenesis. In conclusion, our data show that APOE polymorphism is not associated with semen quality, as it is present to a similar extent in both normal and impaired or absent spermatogenesis. This demonstrates once again that the use of number of children as an index of fertility is not indicative of real male reproductive capacity.