Lack of replication of genetic associations with human longevity

Prospects for life span extension

Life expectancy has increased dramatically in the United States and in much of the world in recent years and decades. The factors underlying this increase are incompletely understood and are undoubtedly complex. A question that drives current research is whether life expectancy can be further extended using current knowledge of modifiable risk factors. A still more challenging research focus is on the possibility that life expectancy might be further increased through knowledge gained from studies of the basic biology of aging and its genetic and environmental modifiers.

Association of the FOXO3A locus with extreme longevity in a southern Italian centenarian study

A number of potential candidate genes in a variety of biological pathways have been associated with longevity in model organisms. Many of these genes have human homologs and thus have the potential to provide insights into human longevity. Recently, several studies suggested that FOXO3A functions as a key bridge for various signaling pathways that influence aging and longevity. Interestingly, Willcox and colleagues identified several variants that displayed significant genotype-gender interaction in male human longevity. In particular, a nested case-control study was performed in an ethnic Japanese population in Hawaii, and five candidate longevity genes were chosen based on links to the insulin-insulin-like growth factor-1 (IGF-1) signaling pathway. In the Willcox study, the investigated genetic variations (rs2802292, rs2764264, and rs13217795) within the FOXO3A gene were significantly associated with longevity in male centenarians. We validated the association of FOXO3A polymorphisms with extreme longevity in males from the Southern Italian Centenarian Study. Particularly, rs2802288, a proxy of rs2802292, showed the best allelic association--minor allele frequency (MAF) = 0.49; p = 0.003; odds ratio (OR) = 1.51; 95% confidence interval (CI), 1.15-1.98). Furthermore, we undertook a meta-analysis to explore the significance of rs2802292 association with longevity by combining the association results of the current study and the findings coming from the Willcox et al. investigation. Our data point to a key role of FOXO3A in human longevity and confirm the feasibility of the identification of such genes with centenarian-controls studies. Moreover, we hypothesize the susceptibility to the longevity phenotype may well be the result of complex interactions involving genes and environmental factors but also gender.

Human genetic variations: Beacons on the pathways to successful ageing

Avoiding age-related disease until late in life is key to 'successful' ageing. Over 300 genome-wide association study papers have been published. Over 50 variants have already been identified as associated with four key age-related diseases, namely cardiovascular disease, type 2 diabetes, osteoporosis and prostate cancer. We review these findings with reference to pathways linked to ageing, including cell cycle control or cell senescence, oxidative stress, insulin, IGF1 and other endocrine signalling, and inflammation. Many variants are disease specific or of unknown function. Of the remainder, those with functions likely to be relevant to ageing are predominantly in cell cycle control and therefore tissue repair. Three loci associated with two or more age-related diseases have been identified, two apparently related to cell cycle control. The third shared locus (near TERT), may be involved in telomerase activity and is associated with several environmentally caused age-related cancers. These findings challenge current ideas, suggesting large numbers of cell type specific effects, often driven by regulatory rather than coding changes. They also confirm the central role of cell cycle and re-growth as a key pathway underlying the human variation in successful ageing.

Genetic polymorphism in long-lived people: cues for the presence of an insulin/IGF-pathway-dependent network affecting human longevity

Longevity in yeast, nematodes, fruit flies and mice is affected by mutations in the insulin/IGF-1 or homologous pathways. Studies on long-living people revealed some associations between genetic variants of the insulin/IGF-1 pathway and longevity. Here, we review such investigations, and we will report human longevity association studies regarding the variability of genes which modulate lifespan in model organisms by interacting with the insulin/IGF-1 pathway. These studies will be presented in three groups: (1) insulin/IGF-1 pathway transcriptional target, superoxide dismutase 2, heat shock protein, cytochrome p450 isoenzymes, glutathione transferases; (2) insulin/IGF-1 pathway accessory transduction proteins H-Ras, p66Shc; and (3) longevity pathways that converge on the insulin/IGF-1 pathway (Klotho, p53, Sirtuins, TGF-beta). The data reported support the notion that the insulin/IGF-1 pathway drives an evolutionarily conserved network that regulates lifespan and affects longevity across species.

Genetic epidemiology in aging research

Over the last two decades, aging research has expanded to include not only age-related disease models, and conversely, longevity and disease-free models, but also focuses on biological mechanisms related to the aging process. By viewing aging on multiple research frontiers, we are rapidly expanding knowledge as a whole and mapping connections between biological processes and particular age-related diseases that emerge. This is perhaps most true in the field of genetics, where variation across individuals has improved our understanding of aging mechanisms, etiology of age-related disease, and prediction of therapeutic responses. A close partnership between gerontologists, epidemiologists, and geneticists is needed to take full advantage of emerging genome information and technology and bring about a new age for biological aging research. Here we review current genetic findings for aging across both disease-specific and aging process domains. We then highlight the limitations of most work to date in terms of study design, genomic information, and trait modeling and focus on emerging technology and future directions that can partner genetic epidemiology and aging research fields to best take advantage of the rapid discoveries in each.

Progress & prospects: gene therapy in aging

Studies performed on various experimental model systems indicate that genetic interventions can increase longevity, even if in a highly protected laboratory condition. Generally, such interventions required partial or complete switching off of the gene and inhibiting the activity of its gene products, which normally have other well-defined roles in metabolic processes. Overexpression of some genes, such as stress response and antioxidant genes, in some model systems also extends their longevity. Such genetic interventions may not be easily applicable to humans without knowing their effects on human growth, development, maturation, reproduction and other characteristics. Studies on the association of single nucleotide polymorphisms and multiple polymorphisms (haplotype) in genes with human longevity have identified several genes whose frequencies increase or decrease with age. Whether genetic redesigning can be achieved in the wake of numerous and complex epigenetic factors that effectively determine the life course and the life span of an individual still appears to be a 'mission impossible'.