Prospects for the genetics of human longevity

SuperAgers and centenarians, dynamics of healthy ageing with cognitive resilience

Graceful healthy ageing and extended longevity is the most desired goal for human race. The process of ageing is inevitable and has a profound impact on the gradual deterioration of our physiology and health since it triggers the onset of many chronic conditions like dementia, osteoporosis, diabetes, arthritis, cancer, and cardiovascular disease. However, some people who lived/live more than 100 years called 'Centenarians" and how do they achieve their extended lifespans are not completely understood. Studying these unknown factors of longevity is important not only to establish a longer human lifespan but also to manage and treat people with shortened lifespans suffering from age-related morbidities. Furthermore, older adults who maintain strong cognitive function are referred to as "SuperAgers" and may be resistant to risk factors linked to cognitive decline. Investigating the mechanisms underlying their cognitive resilience may contribute to the development of therapeutic strategies that support the preservation of cognitive function as people age. The key to a long, physically, and cognitively healthy life has been a mystery to scientists for ages. Developments in the medical sciences helps us to a better understanding of human physiological function and greater access to medical care has led us to an increase in life expectancy. Moreover, inheriting favorable genetic traits and adopting a healthy lifestyle play pivotal roles in promoting longer and healthier lives. Engaging in regular physical activity, maintaining a balanced diet, and avoiding harmful habits such as smoking contribute to overall well-being. The synergy between positive lifestyle choices, access to education, socio-economic factors, environmental determinants and genetic supremacy enhances the potential for a longer and healthier life. Our article aims to examine the factors associated with healthy ageing, particularly focusing on cognitive health in centenarians. We will also be discussing different aspects of ageing including genomic instability, metabolic burden, oxidative stress and inflammation, mitochondrial dysfunction, cellular senescence, immunosenescence, and sarcopenia.

Genetic cartography of longevity in humans and mice: Current landscape and horizons

Aging is a complex and highly variable process. Heritability of longevity among humans and other species is low, and this finding has given rise to the idea that it may be futile to search for DNA variants that modulate aging. We argue that the problem in mapping longevity genes is mainly one of low power and the genetic and environmental complexity of aging. In this review we highlight progress made in mapping genes and molecular networks associated with longevity, paying special attention to work in mice and humans. We summarize 40 years of linkage studies using murine cohorts and 15 years of studies in human populations that have exploited candidate gene and genome-wide association methods. A small but growing number of gene variants contribute to known longevity mechanisms, but a much larger set have unknown functions. We outline these and other challenges and suggest some possible solutions, including more intense collaboration between research communities that use model organisms and human cohorts. Once hundreds of gene variants have been linked to differences in longevity in mammals, it will become feasible to systematically explore gene-by-environmental interactions, dissect mechanisms with more assurance, and evaluate the roles of epistasis and epigenetics in aging. A deeper understanding of complex networks-genetic, cellular, physiological, and social-should position us well to improve healthspan.

Metabolic Slowing and Reduced Oxidative Damage with Sustained Caloric Restriction Support the Rate of Living and Oxidative Damage Theories of Aging

Calorie restriction (CR) is a dietary intervention with potential benefits for healthspan improvement and lifespan extension. In 53 (34 CR and 19 control) non-obese adults, we tested the hypothesis that energy expenditure (EE) and its endocrine mediators are reduced with a CR diet over 2 years. Approximately 15% CR was achieved over 2 years, resulting in an average 8.7 kg weight loss, whereas controls gained 1.8 kg. In the CR group, EE measured over 24 hr or during sleep was approximately 80-120 kcal/day lower than expected on the basis of weight loss, indicating sustained metabolic adaptation over 2 years. This metabolic adaptation was accompanied by significantly reduced thyroid axis activity and reactive oxygen species (F2-isoprostane) production. Findings from this 2-year CR trial in healthy, non-obese humans provide new evidence of persistent metabolic slowing accompanied by reduced oxidative stress, which supports the rate of living and oxidative damage theories of mammalian aging.

A Genetic Network Associated With Stress Resistance, Longevity, and Cancer in Humans

Human longevity and diseases are likely influenced by multiple interacting genes within a few biologically conserved pathways. Using long-lived smokers as a phenotype (n = 90)-a group whose survival may signify innate resilience-we conducted a genome-wide association study comparing them to smokers at ages 52-69 (n = 730). These results were used to conduct a functional interaction network and pathway analysis, to identify single nucleotide polymorphisms that collectively related to smokers' longevity. We identified a set of 215 single nucleotide polymorphisms (all of which had p <5×10(-3) in the genome-wide association study) that were located within genes making-up a functional interaction network. These single nucleotide polymorphisms were then used to create a weighted polygenic risk score that, using an independent validation sample of nonsmokers (N = 6,447), was found to be significantly associated with a 22% increase in the likelihood of being aged 90-99 (n = 253) and an over threefold increase in the likelihood of being a centenarian (n = 4), compared with being at ages 52-79 (n = 4,900). Additionally, the polygenic risk score was also associated with an 11% reduction in cancer prevalence over up to 18 years (odds ratio: 0.89, p = .011). Overall, using a unique phenotype and incorporating prior knowledge of biological networks, this study identified a set of single nucleotide polymorphisms that together appear to be important for human aging, stress resistance, cancer, and longevity.

Genome-wide association meta-analysis of human longevity identifies a novel locus conferring survival beyond 90 years of age

The genetic contribution to the variation in human lifespan is ∼25%. Despite the large number of identified disease-susceptibility loci, it is not known which loci influence population mortality. We performed a genome-wide association meta-analysis of 7729 long-lived individuals of European descent (≥85 years) and 16 121 younger controls (<65 years) followed by replication in an additional set of 13 060 long-lived individuals and 61 156 controls. In addition, we performed a subset analysis in cases aged ≥90 years. We observed genome-wide significant association with longevity, as reflected by survival to ages beyond 90 years, at a novel locus, rs2149954, on chromosome 5q33.3 (OR = 1.10, P = 1.74 × 10⁻⁸). We also confirmed association of rs4420638 on chromosome 19q13.32 (OR = 0.72, P = 3.40 × 10⁻³⁶), representing the TOMM40/APOE/APOC1 locus. In a prospective meta-analysis (n = 34 103), the minor allele of rs2149954 (T) on chromosome 5q33.3 associates with increased survival (HR = 0.95, P = 0.003). This allele has previously been reported to associate with low blood pressure in middle age. Interestingly, the minor allele (T) associates with decreased cardiovascular mortality risk, independent of blood pressure. We report on the first GWAS-identified longevity locus on chromosome 5q33.3 influencing survival in the general European population. The minor allele of this locus associates with low blood pressure in middle age, although the contribution of this allele to survival may be less dependent on blood pressure. Hence, the pleiotropic mechanisms by which this intragenic variation contributes to lifespan regulation have to be elucidated.

Genome-wide linkage analysis for human longevity: Genetics of Healthy Aging Study

Clear evidence exists for heritability of human longevity, and much interest is focused on identifying genes associated with longer lives. To identify such longevity alleles, we performed the largest genome-wide linkage scan thus far reported. Linkage analyses included 2118 nonagenarian Caucasian sibling pairs that have been enrolled in 15 study centers of 11 European countries as part of the Genetics of Healthy Aging (GEHA) project. In the joint linkage analyses, we observed four regions that show linkage with longevity; chromosome 14q11.2 (LOD = 3.47), chromosome 17q12-q22 (LOD = 2.95), chromosome 19p13.3-p13.11 (LOD = 3.76), and chromosome 19q13.11-q13.32 (LOD = 3.57). To fine map these regions linked to longevity, we performed association analysis using GWAS data in a subgroup of 1228 unrelated nonagenarian and 1907 geographically matched controls. Using a fixed-effect meta-analysis approach, rs4420638 at the TOMM40/APOE/APOC1 gene locus showed significant association with longevity (P-value = 9.6 × 10(-8) ). By combined modeling of linkage and association, we showed that association of longevity with APOEε4 and APOEε2 alleles explain the linkage at 19q13.11-q13.32 with P-value = 0.02 and P-value = 1.0 × 10(-5) , respectively. In the largest linkage scan thus far performed for human familial longevity, we confirm that the APOE locus is a longevity gene and that additional longevity loci may be identified at 14q11.2, 17q12-q22, and 19p13.3-p13.11. As the latter linkage results are not explained by common variants, we suggest that rare variants play an important role in human familial longevity.

Design, recruitment, logistics, and data management of the GEHA (Genetics of Healthy Ageing) project

In 2004, the integrated European project GEHA (Genetics of Healthy Ageing) was initiated with the aim of identifying genes involved in healthy ageing and longevity. The first step in the project was the recruitment of more than 2500 pairs of siblings aged 90 years or more together with one younger control person from 15 areas in 11 European countries through a coordinated and standardised effort. A biological sample, preferably a blood sample, was collected from each participant, and basic physical and cognitive measures were obtained together with information about health, life style, and family composition. From 2004 to 2008 a total of 2535 families comprising 5319 nonagenarian siblings were identified and included in the project. In addition, 2548 younger control persons aged 50-75 years were recruited. A total of 2249 complete trios with blood samples from at least two old siblings and the younger control were formed and are available for genetic analyses (e.g. linkage studies and genome-wide association studies). Mortality follow-up improves the possibility of identifying families with the most extreme longevity phenotypes. With a mean follow-up time of 3.7 years the number of families with all participating siblings aged 95 years or more has increased by a factor of 5 to 750 families compared to when interviews were conducted. Thus, the GEHA project represents a unique source in the search for genes related to healthy ageing and longevity.

Reactive oxygen species regulate DNA copy number in isolated yeast mitochondria by triggering recombination-mediated replication

Mitochondrial DNA (mtDNA) encodes proteins that are essential for cellular ATP production. Reactive oxygen species (ROS) are respiratory byproducts that damage mtDNA and other cellular components. In Saccharomyces cerevisiae, the oxidized base excision-repair enzyme Ntg1 introduces a double-stranded break (DSB) at the mtDNA replication origin ori5; this DSB initiates the rolling-circle mtDNA replication mediated by the homologous DNA pairing protein Mhr1. Thus, ROS may play a role in the regulation of mtDNA copy number. Here, we show that the treatment of isolated mitochondria with low concentrations of hydrogen peroxide increased mtDNA copy number in an Ntg1- and Mhr1-dependent manner. This treatment elevated the DSB levels at ori5 of hypersuppressive [rho^–] mtDNA only if Ntg1 was active. In vitro Ntg1-treatment of hypersuppressive [rho^–] mtDNA extracted from hydrogen peroxide-treated mitochondria revealed increased oxidative modifications at ori5 loci. We also observed that purified Ntg1 created breaks in single-stranded DNA harboring oxidized bases, and that ori5 loci have single-stranded character. Furthermore, chronic low levels of hydrogen peroxide increased in vivo mtDNA copy number. We therefore propose that ROS act as a regulator of mtDNA copy number, acting through the Mhr1-dependent initiation of rolling-circle replication promoted by Ntg1-induced DSB in the single-stranded regions at ori5.

Lipoprotein particle profiles mark familial and sporadic human longevity

BACKGROUND

Genetic and biochemical studies have indicated an important role for lipid metabolism in human longevity. Ashkenazi Jewish centenarians and their offspring have large low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles as compared with control individuals. This profile also coincided with a lower prevalence of disease. Here, we investigate whether this observation can be confirmed for familial longevity in an outbred European population and whether it can be extended to sporadic longevity in the general population.

METHODS AND FINDINGS

NMR-measured lipoprotein profiles were analyzed in 165 families from the Leiden Longevity Study, consisting of 340 long-lived siblings (females >91 y, males >89 y), 511 of their offspring, and 243 partners of the offspring. Offspring had larger (21.3 versus 21.1 nm; p = 0.020) and fewer (1,470 versus 1,561 nmol/l; p = 0.011) LDL particles than their same-aged partners. This effect was even more prominent in the long-lived siblings (p < 10(-3)) and could be pinpointed to a reduction specifically in the concentration of small LDL particles. No differences were observed for HDL particle phenotypes. The mean LDL particle sizes in 259 90-y-old singletons from a population-based study were similar to those in the long-lived siblings and thus significantly larger than in partners of the offspring, suggesting that the relevance of this phenotype extends beyond familial longevity. A low concentration of small LDL particles was associated with better overall health among both long-lived siblings (p = 0.003) and 90-y-old singletons (p = 0.007).

CONCLUSIONS

Our study indicates that LDL particle profiles mark both familial and sporadic human longevity already in middle age.

The voyage to healthy longevity: from experimental models to the ultimate goal

Understanding mechanisms underlying longevity, and endeavor towards the specific goals of alleviating frailty in old age, require a comprehensive approach that considers the various theoretical and experimental approaches, as well as compiling the data on humans. This logistic has underlined the program of the conference, and is reflected in the present special issue. Considerable volume of data now point to distinct genes that are associated with exceptional longevity in humans, as reflected from the articles in this volume. However, this symposium also highlighted non-genetic effects, including physical, mental and social activities, and elucidate the relevant underlying mechanisms. The symposium focused on understanding the basis of human longevity coupled to extended health-span and function into old age.

Exceptional survival in human populations: National Institute on Aging perspectives and programs

Identifying the factors that contribute to long and healthy life can lead to improved interventions that can help delay or prevent the onset of major aging-related diseases and disabilities and increase the time that older persons spend in good health. Studies on longevity and other exceptional survival outcomes can contribute to this knowledge. The National Institute on Aging (NIA) supports a considerable amount of basic, behavioral, demographic, epidemiologic, and clinical research on these topics, including a large research program on longevity assurance genes, primarily in laboratory animals, and in biodemographic aspects of longevity in humans and other species. This article describes NIA's activities regarding one important aspect of research on longevity and related phenotypes: exceptional survival phenotypes in humans, including exceptional longevity, health span, and active life expectancy.

Association between the HLA-DR alleles and longevity: a study in Sardinian population

Human longevity may be correlated with optimal functioning of the immune system, suggesting that genetic determinants of longevity also resides in those polymorphisms for the immune system genes that regulate immune responses as histocompatibility (HLA) antigens. However, conflicting results have been obtained. Some well planned and designed association studies performed in Caucasians suggest that longevity is associated with positive selection of alleles (i.e. HLA-DR11) or haplotypes (i.e. HLA-B8,DR3) that confer resistance to infectious diseases, respectively, via peptide presentation or via antigen non-specific control of immune response. Association studies are subjected to a number of possible confounding factors, the homogeneity of the population in term of geographical origin among others. Because of the lack of large-scale heterogeneity, the Sardinians represent a suitable population for association studies addressed to dissect the complex traits as longevity. Thus, we have evaluated, by the amplification refractory mutation system/polymerase chain reaction, HLA-DR frequencies in 120 centenarians (79 women and 41 men) and 86 controls (53 women and 33 men) from Sardinia, to validate, in this very homogeneous population, the associations between HLA alleles or haplotypes and longevity observed in other Caucasoid populations. No significant differences were obtained by analysing the differences between Centenarians and controls except for HLA-DRB1*15 that was increased in centenarians. However, the significance was not maintained by multiplying P values for the number of alleles under study. Thus, in Sardinian centenarians, we were not able to confirm the findings observed in the well planned and designed studies performed in other Caucasoid populations. Besides, HLA HFE gene polymorphisms have been recently demonstrated to be associated with longevity in the Sicilian population but not in Danish one. On the whole these findings clearly show that HLA/longevity associations are population-specific, being heavily affected by the population-specific genetic and environmental history. So, in our opinion, HLA genes might be considered survival genes not longevity genes.

Lifespan in captive baboons is heritable

The effects of aging are evident in multiple organ systems, tissues, cell types, and molecules; all complex phenotypes affected by multiple shared and unique environmental factors and genes, which makes identifying the role of genetics in human aging difficult. Researchers have used yeast, nematodes, fruit flies, and mice to search for genes that influence the aging process. Given the phylogenetic distance and anatomic and physiologic dissimilarities of these organisms from humans, directly extrapolating these results to our species is problematic. However, nonhuman primates have a high degree of genetic, anatomic and physiologic similarity with humans and, thus, they may assist in the detection, characterization, and identification of genetic and environmental influences on human aging. Our goal is to demonstrate that effects of genes on variation in lifespan, a surrogate measure of aging, can be detected in a nonhuman primate species. Using variance component analysis, heritability of age at death was estimated to be 0.23+/-0.08 (P=0.0003) in 674 baboons from the Southwest Foundation for Biomedical Research (SFBR). This research demonstrates that lifespan is under partial genetic control. Given these findings, we believe that the baboon has potential as a model of human aging.

Genetic determination of biological age in the Mennonites of the Midwestern United States

Numerous studies have shown that longevity is moderately heritable in human populations. Longevity, however, contains limited information on functional status, since individuals may exhibit differential survival patterns. In this study, we employed a stepwise multiple regression approach to estimate biological aging in a Mennonite population, using chronological age as a dependent variable and various predictors of chronological age including subphenotypes related to diabetes, coronary heart disease, hypertension, renal function, and markers of functional ability. The residual (the difference between chronological and predicted ages) is considered a marker of biological age. In fact, two different data sets were used to obtain residuals due to the availability of data. In each analysis, chronological age was regressed on predictor variables in a stepwise manner, retaining the variables significant at the 5% level. The first analysis (N=729) included 6 significant predictors (R(2)=44.3%): glucose, blood urea nitrogen (BUN), cholesterol, albumin, systolic blood pressure (SBP), and ln potassium, and the second analysis (N=232) included 9 significant predictors (R(2)=71.5%): BUN, albumin, SBP, low-density lipoprotein cholesterol, forced expiratory volume in 1 sec (FEV1), grip strength, trunk flexibility, reaction time, and FEV1xsex. Using a variance components approach, we found that the data set-specific residuals were significantly heritable (h(2)+/-SE): first analysis=0.265+/-0.106, and second analysis=0.469+/-0.180. The residuals from the second data set appear to be more informative for biological aging, perhaps due to the inclusion of functional ability-related phenotypes in addition to the blood chemistry variables. In summary, we have shown that markers of biological aging in Mennonites are under substantial additive genetic influences.

Beneficial influences of systemic cooperation and sociological behavior on longevity

During his long research career in the field of aging, Dr Bernard Strehler developed a series of theories concerning the identity of genes that can promote longevity and their role in natural selection. As a tribute to Dr Strehler, we have taken this opportunity to summarize a selection of these theories and to illustrate how these insights have influenced our search for longevity genes within the immune system. The identification of longevity genes has proven difficult. We believe that, at least in part, this reflects the emphasis on the concept of survival of the 'physically' fittest. We have used the immune system as a model to demonstrate that, over and above the self-evident advantage of those genes that contribute the attributes commonly associated with survival of the 'physically' fittest, those genes that lead to a predisposition to cooperate also confer a competitive survival advantage. As the acquisition of cooperativity in a society is linked to support mechanisms provided by older individuals, the search for longevity genes should not be limited to those genes that are associated with extended expression of a youthful phenotype. Rather these studies should be expanded to include identification of those genes that regulate physiologic parameters that affect individual longevity, even if they do not correspond with the traditional view of reproductive competitiveness. At the societal level, longevity genes may encode attributes that regulate sociologic or psychological parameters that may contribute to a tendency to non-aggressive or cooperative behavior that leads to achievement of common goals necessary for the survival of the species. This view of the selection for longevity impacts the analysis of longevity genes and aging at the organismal level. Dr Strehler viewed organismal aging as an integrated functional state, in which he conceived the outcome as reflecting the net balance of functional decrementers and evolved compensatory features. We propose that, in more evolved species, the longevity genes will be those genes, or sets of genes, that counterbalance of age-related functional decrementers with the age-related manifestation of evolved compensatory features. Thus, as illustrated here through analysis of the immune system, the longevity genes may well be those genes that promote overall systemic cooperation and compensation within the immune system and associated systems, rather than the genes that prevent age-related alterations in only one or a limited number of pathways.

Association between the MHC class I gene HFE polymorphisms and longevity: a study in Sicilian population

Classes I and II human leukocyte antigens (HLA) genes encode highly polymorphic heterodimeric glycoproteins involved in the control of immune responses. The HLA class I gene HFE seemingly no longer participates in immunity because it has lost its ability to bind peptides and it has acquired the ability to form complex with the receptor for iron-binding transferrin by regulating iron uptake by intestinal cells. Thus, it indirectly regulates immune responses too, because iron availability plays a role in specific and non-specific immune responses. The distribution of HFE polymorphisms in Sicilian centenarians and nonagenarians was studied to evaluate if HFE alleles might be represented differently in people selected for longevity. DNA samples were obtained from 106 young controls (age range from 22 to 55 years; 40 men and 66 women) and 35 elderly subjects (age range from 91 to 105 years; seven men and 28 women). Samples were typed for C282Y, H63D and S65C alleles using polymerase chain reaction and sequence specific primers. Among the young individuals, none was heterozygous for the C282Y or for S65C mutation. Twenty-six were heterozygous for H63D mutation. Among the elderly subjects, 11 were heterozygous for the C282Y mutation or for H63D mutation. None was heterozygous for the S65C mutation. No compound heterozygous individuals (C282Y/H63D) were found. A highly significant difference was observed in frequencies of C282Y alleles between the young and the elderly subjects on the whole. By analysing polymorphisms according to gender, heterozygous subjects for C282Y were found both in old men and in old women, but by comparing the allele frequencies to those of young people significance was attained only in women. Concerning H63D polymorphisms, no significant differences were observed, between old and young people, both in men and in women. Possession of C282Y allele, known to be associated with an increase of iron uptake, significantly increases women possibility to reach longevity. Thus, present data adds another piece of evidence to the complex puzzle of genetic and environmental factors involved in control of lifespan expectancy in humans.

Complex adaptive systems, aging and longevity

Mortality and reproduction are intimately entwined in the study of aging and longevity. I apply the modern theory of complex adaptive systems (nonlinear, stochastic, dynamic methods) to questions of aging and longevity. I begin by highlighting major questions that must be answered in order to obtain a deeper understanding of aging. These are: (i) What should (in an evolutionary sense) mortality trajectories look like? (ii) Why does caloric restriction slow aging? (iii) Why does reproduction cause delayed mortality? (iv) Why does compensatory growth cause delayed mortality? I show how dynamic state variable models based on stochastic dynamic programming (Clark & Mangel, 2000) can be used to embed genetic theories of senescence (either mutation accumulation or antagonistic pleiotropy) in the somatic environment, as George Williams called for in 1957, and how they make the disposable soma theory of aging operational. Such models will allow unification of genetic and phenotypic theories of aging.

Genetic dissection of age-related changes of immune function in mice

Understanding of the genetic basis of normal and abnormal development of the immune response is an enormous undertaking. The immune response, at the most minimal level, involves interactions of antigen presenting cells (APCs), T and B cells. Each of these cells produce cell surface and soluble factors (cytokines) that affect both autocrine and paracrine functions. A second level of complexity needs to consider the development of the macrophage/monocyte lineage as well as the production of the common lymphoid precursor which undergoes distinct maturation steps in the thymus and periphery to form mature T cells as well as in BM (BM) and lymphoid organs to form mature B cells. A third level of complexity involves the immune response to infectious agents including viruses and also the response to tumour antigens. In addition, there are imbalances that predispose to decreased responses (immunodeficiencies) or increased responses (autoimmunity). A fourth level of complexity involves attempts to understand the differences in the immune response that occurs at a very young age, in adults, and at a very old age. This review will focus on the use of C57BL/6 J X DBA/2 J (BXD) recombinant inbred (RI) strains of mice to map genetic loci associated with the production of lymphoid precursors in the BM, development of T cells in the thymus, and T-cell responses to stimulation in the peripheral lymphoid organs in adult and in aged mice. Strategies to improve the power and precision in which complex traits such as the age-related immune response can be mapped is limited with the current set of 35 strains of BXD mice. Strategies to increase these strains by generating recombinant intercross (RIX) strains of mice are being developed to enable this large set of lines to detect quantitative trait loci (QTLs) with a much higher consistency and statistical power. More importantly, the resolution with which these QTLs can be mapped would be greatly improved and, in many cases, adequate to carry out direct identification of candidate genes. It is likely that, given the complexity of the immune system development, the number of cells involved in an immune response, and especially the changes in the immune system with ageing, mapping hundreds of genes will be required to fully understand age-related changes in the immune response. This review outlines ongoing and future strategies that will enable the mapping and identification of these genes.

Self-reported exercise before age 40: influence on quantitative skeletal ultrasound and fall risk in the elderly

OBJECTIVES

To compare musculoskeletal factors with bone structure, as measured by quantitative ultrasound (QUS) at the calcaneus, and their potential to predict fall risk in geriatric inpatients.

DESIGN

Longitudinal.

SETTING

Two geriatric hospitals in Switzerland.

PARTICIPANTS

A total of 134 of 207 long-stay geriatric patients (96 women, 38 men) who were able to perform the timed up and go (TUG) test.

INTERVENTIONS

Five musculoskeletal tests: 2 functional tests (TUG, for mobility; functional reach test, for balance), and 3 muscle strength tests (knee flexor, knee extensor, grip). Falls were monitored prospectively in a subgroup of 94 mobile subjects of 1 geriatric hospital throughout each individual length of stay (median, 31.4wk: interquartile range, 16-56.4wk).

MAIN OUTCOME MEASUREMENTS

Functional and strength tests, mobility status, and self-reported exercise before age 40 were musculoskeletal factors to be compared with QUS.

RESULTS

QUS was higher in mobile subjects without walking aid (p < .0001) and correlated significantly with muscle strength (knee flexor: r = .36; knee extensor: r = .30) and functional tests (TUG: r = -.25; functional reach: r = .16). Women who reported regular exercise before age 40 had higher QUS (p = .01) and fewer falls (p = .01). Falls were less frequent in subjects with walking aid (p = .03). No single musculoskeletal test, but rather a combination of demographic variables, musculoskeletal factors, and QUS could predict 76% of total variation of fall risk.

CONCLUSION

This study showed the important impact of current mobility and muscle strength status on bone structure, as measured by QUS at the calcaneus. In addition, a beneficial effect of former exercise on QUS and fall risk at advanced age could be documented in women. Both findings support life-long engagement in exercise, which might be particularly meaningful for women.

If you would live long, choose your parents well

Human longevity appears to have a modest but significant heritable component. A recent study in Iceland has added to this evidence by making a unique assessment based on records for an entire population. Although the evidence for inheritance of human lifespans appears robust, there remains considerable uncertainty about the extent of the genetic versus the nongenetic contribution and about the importance of gene-environment interactions. Sex-specific patterns of transmission of lifespan between parents and offspring might provide clues to the basis of lifespan heritability, but the reported patterns are neither conclusive nor consistent.

Zinc, infections and immunosenescence

Infections may cause mortality in old age due to damaged immune responses. As zinc is required as a catalyst, structural (zinc fingers) and regulatory ion, it is involved in many biological functions, including immune responses. Low zinc ion bioavailability and impaired cell-mediated immunity are common in ageing and may be restored by physiological supplementation with zinc for 1-2 months, impacting upon morbidity and survival. This article reviews the role of zinc in immune efficacy during ageing, and also describes the main biochemical pathways involved in the role of zinc in resistance to infections in ageing in order to better understand the possible causes of immunosenescence.

Evidence of sex-linked effects on the inheritance of human longevity: a population-based study in the Valserine valley (French Jura), 18-20th centuries

A long-standing puzzle in gerontology is the sex dependence of human longevity and its inheritance. We have analysed the sex-linked pattern of inheritance of longevity from 643 nuclear families on the historical population register of a French valley. We have focused on mean conditional life expectancy at a minimum age of 50 years, thus, in the present study, longevity refers to late or post-reproductive survival. A comparison of parents' and offspring's longevity has shown the existence of a heritable component of late survival in this population. We have found that the heritable component was substantially larger for daughters compared to sons. Moreover, this result appeared to be specific to late survival, that is, when only post-reproductive mortality for parental and offspring generations is taken into account. The stronger resemblance of parents to their daughters was no longer observed when considering younger ages at death for the offspring. This observation explains the hitherto unaccountable diversity of data in previous studies.

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.

Age at death and rectangularisation of the survival curve: trends in Switzerland, 1969-1994

OBJECTIVE

To check if signs of rectangularisation of the survival curve appeared during recent decades in Switzerland--that is, if life expectancy is approaching a maximum with a clustering of age at death around an average value (the so called "compression of mortality").

METHODS

Descriptive analysis of age of death and its trends over 26 years, as characterised by the modal value, median, and various percentiles beyond the median.

POPULATION

All deaths occurring after the 50th birthday in Switzerland between 1969 and 1994 (n = 1,390,362).

MAIN RESULTS

Age at death is increasing at a sustained rate at all percentiles equal or greater than 50, without any slow down in the trend during this period. The increase is more marked among women. Rates of increase are diminishing as the percentiles of age at death are higher, suggesting some clustering of deaths beyond the median value. However, the maximum age at death, if any, seems to be far from the current median values, even for women who enjoy a relatively high median age at death.

A model for antagonistic pleiotropic gene action for mortality and advanced age

Association or linkage studies involving control and long-lived populations provide information on genes that influence longevity. However, the relationship between allele-specific differences in survival and the genetic structure of aging cohorts remains unclear. We model a heterogeneous cohort comprising several genotypes differing in age-specific mortality. In its most general form, without any specific assumption regarding the shape of mortality curves, the model permits derivation of a fundamental property underlying abrupt age-related changes in the composition of a cohort. The model is applied to sex-specific survival curves taken from period life tables, and Gompertz-Makeham mortality coefficients are calculated for the French population. Then, adjustments are performed under Gompertz-Makeham mortality functions for three genotypes composing a heterogeneous cohort, under the constraint of fitting the resultant mortality to the real French population mortality obtained from life tables. Multimodal curves and divergence after the 8th decade appear as recurrent features of the frequency trajectories. Finally, a fit to data previously obtained at the angiotensin-converting-enzyme locus is realized, explaining what had seemed to be paradoxical results-namely, that the frequency of a genotype known as a cardiovascular risk factor was increased in centenarians. Our results help explain the well-documented departure from Gompertz-Makeham mortality kinetics at older ages. The implications of our model are discussed in the context of known genetic effects on human longevity and age-related pathologies. Since antagonistic pleiotropy between early and late survival emerges as a general rule, extrapolating the effects measured for a gene in a particular age class to other ages could be misleading.

Cloning and identification of genes that associate with mammalian replicative senescence

Cellular senescence and limited proliferative capacity of normal diploid cells has a dominant phenotype over immortality of cancerous cells, suggesting its regulation by the expression of a set of genes. In order to isolate the genes that associate with senescence, we have employed a clonal system of conditional SV40 T antigen rat embryo fibroblast cell lines which undergo senescence upon T antigen inactivation. Construction of cDNA libraries from two conditional cell lines and application of differential screening and subtractive hybridization techniques have resulted in the cloning of eight senescence-induced genes (SGP-2/Apo J, alpha 1-procollagen, osteonectin, fibronectin, SM22, cytochrome C oxidase, GTP-alpha, and a novel gene) and a senescence-repressed gene (FRS-2). Three of these genes encode for extracellular matrix proteins, others are involved in the calcium-dependent signal transduction pathways, while the SGP-2/Apo J gene may have a cellular protective function. RNA analysis has shown that the senescence-associated genes are overexpressed in both normal rat embryonic fibroblasts and human osteoblasts cell cultures undergoing aging in vitro. In comparison, the expression of these genes in a rat fibroblast immortalized cell line (208F cells) was down-regulated after both its partial and its full transformation by ras oncogenes. Thus, cloning of senescence-associated genes opens up new ways to elucidate and/or to modulate aging and cancer.

The origins of human ageing

The origins of human ageing are to be found in the origins and evolution of senescence as a general feature in the life histories of higher animals. Ageing is an intriguing problem in evolutionary biology because a trait that limits the duration of life, including the fertile period, has a negative impact on Darwinian fitness. Current theory suggests that senescence occurs because the force of natural selection declines with age and because longevity is only acquired at some metabolic cost. In effect, organisms may trade late survival for enhanced reproductive investments in earlier life. The comparative study of ageing supports the general evolutionary theory and reveals that human senescence, while broadly similar to senescence in other mammalian species, has distinct features, such as menopause, that may derive from the interplay of biological and social evolution.

Genetics of aging

The role of genetics in determining life-span is complex and paradoxical. Although the heritability of life-span is relatively minor, some genetic variants significantly modify senescence of mammals and invertebrates, with both positive and negative impacts on age-related disorders and life-spans. In certain examples, the gene variants alter metabolic pathways, which could thereby mediate interactions with nutritional and other environmental factors that influence life-span. Given the relatively minor effect and variable penetrance of genetic risk factors that appear to affect survival and health at advanced ages, life-style and other environmental influences may profoundly modify outcomes of aging.

Interactions between genetic predisposition and environmental toxicants for development of lung cancer

Significant interindividual variations in health outcome may be caused by the inheritance of variant polymorphic genes, such as CYP2D6 and CYP2E1 for activation, and GSTM1 and GSTT1 for detoxification of chemicals. However, mechanistic studies linking the inheritance of predisposing genes with genotoxic effects towards cancer have yet to be systematically conducted. We have studied 54 lung cancer patients and 50 matched normal controls, who have been cigarette smokers, to elucidate the role of polymorphic genes in cancer. Our data indicates that the inheritance of unfavorable CYP2D6, CYP2E1, and GSTT1 genes in strongly correlated with the smoking-related lung cancer. For heavy cigarette smokers (> 30 pack-years), the smoking habit is the strongest predictor of lung cancer risk irrespective of the inheritance of unfavorable metabolizing genes. For moderate to light smokers (< 30 pack-years), the genetic predisposition plays an important role for the risk (odds ratio = 3.46; 95% Cl = 0.46-40.2). Using a subgroup of the study population, we observed that cigarette smokers having the defective GST genes have significantly more chromosome aberrations as determined by the fluorescence-in-situ-hybridization (FISH) technique than smokers with the normal GST genes (P < 0.001). In conclusion, our study provides data to indicate that individuals who have inherited unfavorable metabolizing genes have increased body burden of toxicants to cause increased genetic damage and to have increased risk for cancer. Studies like ours can be used to understand the basis for interindividual variations in cancer outcome, to identify high risk individuals and to assess health risk.

Human senescence

Human life expectancy has increased dramatically through improvements in public health, housing, nutrition and general living standards. Lifespan is now limited chiefly by intrinsic senescence and its associated frailty and diseases. Understanding the biological basis of the ageing process is a major scientific challenge that will require integration of molecular, cellular, genetic and physiological approaches. This article reviews progress that has been made to date, particularly with regard to the genetic contribution to senescence and longevity, and assesses the scale of the task that remains.

What good is it to get old?

The physiologic basis for aging is still incompletely understood, and most investigators have looked at aging as a process of decay without any clear adaptive advantage to the species. It is proposed that aging has potential evolutionary advantages, and that the aging process may have been the subject of positive selection.

The heritability of human longevity: a population-based study of 2872 Danish twin pairs born 1870-1900

The aim of this study was to explore, in a large and non-censored twin cohort, the nature (i.e., additive versus non-additive) and magnitude (i.e., heritability) of genetic influences on inter-individual differences in human longevity. The sample comprised all identified and traced non-emigrant like-sex twin pairs born in Denmark during the period 1870-1900 with a zygosity diagnosis and both members of the pairs surviving the age of 15 years. A total of 2872 pairs were included. Age at death was obtained from the Danish Central Person Register, the Danish Cause-of-Death Register and various other registers. The sample was almost non-censored on the date of the last follow-up (May 1, 1994), all but 0.6% had died, leaving a total of 2872 pairs for analysis. Proportions of variance attributable to genetic and environmental factors were assessed from variance-covariance matrices using the structural equation model approach. The most parsimonious explanation of the data was provided by a model that included genetic dominance (non-additive genetic effects caused by interaction within gene loci) and non-shared environmental factors (environmental factors that are individual-specific and not shared in a family). The heritability of longevity was estimated to be 0.26 for males and 0.23 for females. The small sex-difference was caused by a greater impact of non-shared environmental factors in the females. Heritability was found to be constant over the three 10-year birth cohorts included. Thus, longevity seems to be only moderately heritable. The nature of genetic influences on longevity is probably non-additive and environmental influences non-shared. There is no evidence for an impact of shared (family) environment.

Genetic Control of the Aging Process: A Review and Interpretation

Le processus de vieillissement est sous contrôle génétique. Le point de vue traditionnel, dérivé de la biologie évolutive, est que le vieillissement est un trait polygénique, contrôlé par un grand nombre de gènes, chacun avec un effet additif. Un autre point de vue est développé ici, en ajoutant qu'il y a un nombre limité de gènes importants dans le contrôle du vieillissement. Ces derniers peuvent inclure les gènes protecteurs qui assurent l'exactitude de la synthèse de protéines et aussi les gènes qui servent à activer ou à retarder le processus de vieillissement. On continue à développer la technologie génétique afin de faire la carte complète du génome humain. Ces percées offrent la possibilité de comprendre les mécanismes génétiques du vieillissement et même d'envisager la thérapie génétique pour les maladies associées au vieillissement.

Human epidermal cells progressively lose their cardiolipins during ageing without change in mitochondrial transmembrane potential

Mitochondria dysfunction is considered to be a major cause of the modifications that occur during cell ageing. For this reason, cardiolipin, a suitable marker of the chondriome, as well as the mitochondrial transmembrane potential were examined in keratinocytes obtained from 9- to 75-year-old women. The study was carried out by flow cytometry using two fluorescent mitochondria probes: nonyl acridine orange, which binds specifically to cardiolipin, and rhodamine 123, which is incorporated mainly in response to transmembrane potential. Cardiolipin levels in cells from elderly donors (75 years old) would be 57% lower (r = 0.540; P = 0.0002) than those in children (9 years old), while the inner transmembrane potential remained unchanged (r = 0.0394; P = 0.8017). The stability of the membrane potential may be explained by either or both of the following hypotheses: (i) the same pool of organelles able to maintain membrane potential is conserved even when cardiolipin levels decrease (ii) mitochondria membrane potential does indeed decrease with age but is compensated by glycolysis energy production. Finally, it may be stated that the fluorescent probes nonyl acridine orange and rhodamine 123 might be of interest in testing the phenotype of senescent cells and would be useful in screening the role of certain specific genes in cell ageing.

Genetic associations with human longevity at the APOE and ACE loci

In an effort to dissect the genetic components of longevity, we have undertaken case-control studies of populations of centenarians (n = 338) and adults aged 20-70 years at several polymorphic candidate gene loci. Here we report results on two genes, chosen for their impact on cardiovascular risk, encoding apolipoprotein E (ApoE), angiotensin-converting enzyme (ACE). We find that the epsilon 4 allele of APOE, which promotes premature atherosclerosis, is significantly less frequent in centenarians than in controls (p < 0.001), while the frequency of the epsilon 2 allele, associated previously with type III and IV hyperlipidemia, is significantly increased (p < 0.01). A variant of ACE which predisposes to coronary heart disease is surprisingly more frequent in centenarians, with a significant increase of the homozygous genotype (p < 0.01). These associations provide examples of genetic influences on differential survival and may point to pleiotropic age-dependent effects on longevity.