A study of the average effect of the 3'APOB-VNTR polymorphism on lipidemic parameters could explain why the short alleles (<35 repeats) are rare in centenarians.

BACKGROUND

In studies on the genetics of human aging, we observed an age-related variation of the 3'APOB-VNTR genotypic pool (alleles: Short, S, <35 repeats; Medium, M, 35-39 repeats; Long, L, >39 repeats) with the homozygous SS genotype showing a convex frequency trajectory in a healthy aging population. This genotype was rare in centenarians, thus indicating that the S alleles are unfavorable to longevity, while common in adults, thus indicating a protective role at middle age. This apparent paradox could be due to possible effects exerted by the above polymorphism on lipidemic parameters. Aim of the work was to get insights into these puzzling findings

METHODS

We followed a double strategy. Firstly, we analyzed the average effects of S (alphaS), M (alphaM), and L (alphaL) alleles on lipidemic parameters in a sample of healthy people (409 subjects aged 20-102 years) recruited in Calabria (southern Italy). The (alphaS), (alphaM), and (alphaL) values were estimated by relating 3'APOB-VNTR genotypes to lipidemic parameters, after adjustment for age, sex and body mass index (multiple regression). Then, we analyzed the S alleles as susceptibility factors of Cardiovascular Atherosclerotic Disease (CD) in CD patients characterized either by low serum HDL-Cholesterol or by high serum LDL-Cholesterol (CD-H and CD-L patients, 40 and 40 subjects respectively). The Odds Ratios (OR) were computed for carriers of S alleles in CD-H and CD-L patients matched for origin, sex and age with controls extracted from the sample of healthy subjects.

RESULTS

By the analysis of the healthy sample group we found that the S alleles lower the average values of serum Total Cholesterol (alphaS = -5.98 mg/dL with [-11.62/-0.74] 95% confidence interval) and LDL-Cholesterol (alphaS = -4.41 mg/dL with [-8.93/-0.20] 95% confidence interval) while the alleles M and L have no significant effect on the lipidemic phenotype. In line with these findings, the analysis of CD patients showed that the S alleles are protective as for CD-L (O.R. = 0.55 with [0.21/0.98] 95% confidence interval) while neutral as for CD-H (O.R. = 0.75 with [0.32/1.60] 95% confidence interval).

CONCLUSION

On the whole, the S alleles would be advantageous in adults (by protecting from CD-L) while dangerous in the elderly, probably by lowering serum cholesterol below a critical threshold. This could explain the convex frequency trajectory of SS genotypes previously observed in a healthy aging population.