Mitochondrial DNA haplogroups and APOE4 allele are non-independent variables in sporadic Alzheimer's disease.

Allele epsilon4 of the nuclear APOE gene is a leading genetic risk factor for sporadic Alzheimer's disease (AD). Moreover, an allele-specific effect of APOE isoforms on neuronal cell oxidative death is known. Because of the role of the mitochondrial genome (mtDNA) in oxidative phosphorylation and oxidative stress, an interaction between APOE polymorphism and mtDNA inherited variability in the genetic susceptibility to sporadic AD can be hypothesized. We have explored this hypothesis by analyzing mtDNA germline variants (mtDNA haplogroups) in a sample of AD patients (213 subjects) genotyped for APOE and classified as APOE epsilon4 carriers and non-carriers. We found that the frequency distribution of mtDNA haplogroups is different between epsilon4 carriers and non-carriers (P=0.018), thus showing non-random association between APOE and mtDNA polymorphisms. The same analysis, carried out in two samples of healthy subjects (179 age-matched and 210 individuals aged more than 100 years), showed independence between epsilon4 allele and mtDNA haplogroups. Therefore, the APOE/mtDNA interaction is restricted to AD and may affect susceptibility to the disease. In particular, some mtDNA haplogroups (K and U) seem to neutralize the harmful effect of the APOE epsilon4 allele, lowering the epsilon4 odds ratio from statistically significant to non-significant values.

Genes and longevity: lessons from studies of centenarians.

In population studies of aging, the data on genetic markers are often collected for individuals from different age groups. The idea of such studies is to identify "longevity" or "frailty" genes by comparing the frequencies of genotypes in the oldest and in the younger groups of individuals. In this paper we discuss a new approach to the analysis of such data. This approach, based on the maximum likelihood method, combines data on genetic markers with survival information obtained from standard demographic life tables. This method allows us to evaluate survival characteristics for individuals carrying respective candidate genes. It can also be used in the estimation of the effects of allele-area and allele-allele interaction, either in the presence or absence of hidden heterogeneity. We apply this method to the analysis of Italian data on genetic markers for five autosomal loci and mitochondrial genomes. Then we discuss basic assumptions used in this analysis and directions of further research.

Genes, demography, and life span: the contribution of demographic data in genetic studies on aging and longevity.

In population studies on aging, the data on genetic markers are often collected for individuals from different age groups. The purpose of such studies is to identify, by comparison of the frequencies of selected genotypes, "longevity" or "frailty" genes in the oldest and in younger groups of individuals. To address questions about more-complicated aspects of genetic influence on longevity, additional information must be used. In this article, we show that the use of demographic information, together with data on genetic markers, allows us to calculate hazard rates, relative risks, and survival functions for respective genes or genotypes. New methods of combining genetic and demographic information are discussed. These methods are tested on simulated data and then are applied to the analysis of data on genetic markers for two haplogroups of human mtDNA. The approaches suggested in this article provide a powerful tool for analyzing the influence of candidate genes on longevity and survival. We also show how factors such as changes in the initial frequencies of candidate genes in subsequent cohorts, or secular trends in cohort mortality, may influence the results of an analysis.