has not been proved in a recent population-based study (31). However, other recent data (32) are discrepant, suggesting a positive association.

As previously has been stated, we have enrolled only healthy persons in the aged group. Our task was to see the e4 allele frequency specifically in aged healthy and active (physically and mentally) individuals. The fact that some aged e4-homozygous individuals ‘‘escape’’ the ‘‘e4 effect’’ (30) raises the possibility that other factors (genetic and environmental) may modify the ApoE-related risk. More- over, e4 allele as a risk factor seems to express its dele- terious effects on the cardiovascular system in early middle age, and significantly loses its importance in Caucasians after the age of 80 years (33). Similarly, the e4 effect in AD is age-specific, with its peak effect observed at around 70 years of age (30).

The e2 and e3 allele frequencies were comparable to those previously reported in one group of 216 Greek blood donors (14), but not in another study of 240 Greek adults with a mean age of 23 years (18). However, the e4 allele frequency was different in our study, being in between the frequencies presented by the other studies.

This discrepancy may be attributed to difference in age, bias in the sample selection, or genotyping. The authors of the earlier studies did not report if the distribution of ApoE genotypes was consistent with the HWE.

In the healthy individuals older than 80 years, we found that e4 allele frequency was significantly lower compared to e4 allele frequency in healthy individuals younger than 60 years (3.1% vs 8.58%, respectively; p ¼ .020). The decrease of e4 allele frequency in the healthy aged individuals was reflected by an increase (though not a significant one) of e3 allele. The appreciably lower prevalence of e4 allele in the healthy aged participants may be attributed to better survival of individuals carrying the other alleles (e2 and e3). APOE e4 allele is associated with increased total cholesterol levels (2). It has been estimated that ApoE polymorphism may account for 2%–11% of the total variation in serum or plasma cholesterol levels in apparently healthy white per- sons (2). In contrast to e4 allele, it was found that e2 allele is associated with decreased total cholesterol levels (34), thereby exerting a protective effect on the cardiovascular system. The comparable frequencies of e2 allele in both groups of our study do not prove the above notion. More- over, in a recent meta-analysis (11), it was found that e2 allele has no effect on CHD development.

The frequencies of e2, e3, and e4 alleles vary among individuals and are indicators for metabolic effects (19). The e3 allele is considered to be the normal allele, and its variation provided little information about traditional risk factors (20). Low total serum cholesterol is attributed to e2 allele (2) and is associated with a low risk of stroke in aged adults (10). Conversely, the increased frequency of e4 allele is a significant risk factor for CHD and Alzheimer’s disease (AD) and has also been associated with adverse effects in the lipid profile (18,21–23). Moreover, the allele e4 isoforms promote deposition of amyloid b-protein, which is known to damage cells by producing superoxide radicals (24). The deposition of amyloid in the brain is considered to be responsible for the brain damage in AD. The frequency of e4 allele in the population appeared to be affected by multiple factors, including those of age, ethnicity, and the region from which the sample was selected. Several studies have shown no evidence indicating that the predictive power of ApoE polymorphism is sex-related (8,25).

The lower prevalence of e4 allele in healthy longer living individuals does not indicate that this allele is unique in determining individual life expectancy. Such factors as hypertension, obesity, and diabetes mellitus are additional determinants that may modulate the CHD risk. It has been suggested that a healthy lifestyle could decrease the un- desirable effects of e4 allele on the lipid profile (35) and hence alleviate its risk. Therefore, the APOE allele fre- quency analysis in different populations cannot be regarded as an accurate indicator of the exact relationship with the serious health risk without taking into account more regional characteristics. ‘‘Regional’’ studies seem to be of impor- tance in obtaining a clearer image of the relationship of apoE polymorphism with a patient’s diet and lifestyle as well as with other local environmental factors.

Growing evidence indicates that ApoE is a strong in- dependent risk factor for macrovascular disease. A recent meta-analysis of 48 relevant studies has shown that the e4 allele is a significant risk factor for CHD (11), and the same was found in a recent large longitudinal study (26). ApoE4 carriers had an increased risk for cerebrovascular disease and stroke as compared to carriers of the e3 allele (27). Variation in the e4 allele frequency predicted approximately 75% of the interpopulation variation in CHD mortality rate and 40% of CHD mortality rate after adjustment for low- density lipoprotein cholesterol levels (20). Moreover, e4 allele has been associated with other pathologic conditions, including AD (23), carcinoma of the proximal colon (28), and breast cancer (29). Therefore, e4 allele seems to play an important role in successful aging due to its inverse association with decreased longevity.

Conclusion

The existence of a biologic link between CHD and AD has been suggested because both diseases share common risk factors, including genetic ones (30). CHD-induced low cardiac output, cerebral hypoperfusion, and microemboliza- tion may accelerate neurodegenerative disorders, which characterize AD. The clinical relevance of this plausible link