If you would live long, choose your parents well

Protective Effects of Familial Longevity Decrease With Age and Become Negligible for Centenarians

It is known that biological relatives of long-lived individuals demonstrate lower mortality and longer life span compared to relatives of shorter-lived individuals, and at least part of this advantage is likely to be genetic. Less information, however, is available about effects of familial longevity on age-specific mortality trajectories. We compared mortality patterns after age 50 years for 10 045 siblings of US centenarians and 12 308 siblings of shorter-lived individuals (died at age 65 years). Similar comparisons were made for sons and daughters of longer-lived parents (both parents lived 80 years and more) and shorter-lived parents (both parents lived less than 80 years) within each group of siblings. Although relatives of longer-lived individuals have lower mortality at younger ages compared to relatives of shorter-lived individuals, this mortality advantage practically disappears by age 100 years. To validate this observation further, we analyzed the survival of 3 408 US centenarians born in 1890-1897 with known information on maternal and paternal life span. We found using the Cox proportional hazards model that both maternal and paternal longevity (life span 80+ years) is not significantly associated with survival after age 100 years. The results are compatible with the predictions of reliability theory of aging suggesting higher initial levels of system redundancy (reserves) in individuals with protective familial/genetic background and hence lower initial mortality. Heterogeneity hypothesis is another possible explanation for the observed phenomena.

A Mechanistic Theory of Development-Aging Continuity in Humans and Other Mammals

There is consensus among biogerontologists that aging occurs either as the result of a purposeful genome-based, evolved program or due to spontaneous, randomly occurring, maladaptive events. Neither concept has yet identified a specific mechanism to explain aging’s emergence and acceleration during mid-life and beyond. Presented herein is a novel, unifying mechanism with empirical evidence that describes how aging becomes continuous with development. It assumes that aging emerges from deterioration of a regulatory process that directs morphogenesis and morphostasis. The regulatory system consists of a genome-wide “backbone” within which its specific genes are differentially expressed by the local epigenetic landscapes of cells and tissues within which they reside, thereby explaining its holistic nature. Morphostasis evolved in humans to ensure the nurturing of dependent offspring during the first decade of young adulthood when peak parental vitality prevails in the absence of aging. The strict redundancy of each morphostasis regulatory cycle requires sensitive dependence upon initial conditions to avoid initiating deterministic chaos behavior. However, when natural selection declines as midlife approaches, persistent, progressive, and specific DNA damage and misrepair changes the initial conditions of the regulatory process, thereby compromising morphostasis regulatory redundancy, instigating chaos, initiating senescence, and accelerating aging thereafter.

Genomic instability in the naturally and prematurely aged myocardium

Genomic instability, the unresolved accumulation of DNA variants, is hypothesized as one of the contributors to the natural aging process. We assessed the frequency of unresolved DNA damage reaching the transcriptome of the murine myocardium during the course of natural aging and in hearts from four distinct mouse models of premature aging with established aging-related cardiac dysfunctions. RNA sequencing and variant calling based on total RNA sequencing was compared between hearts from naturally aging mice, mice with cardiomyocyte-specific deficiency of Ercc1, a component of the DNA repair machinery, mice with reduced mitochondrial antioxidant capacity, Tert-deficient mice with reduced telomere length, and a mouse model of human Hutchinson-Gilford progeria syndrome (HGPS). Our results demonstrate that no enrichment in variants is evident in the naturally aging murine hearts until 2 y of age from the HGPS mouse model or mice with reduced telomere lengths. In contrast, a dramatic accumulation of variants was evident in Ercc1 cardiomyocyte-specific knockout mice with deficient DNA repair machinery, in mice with reduced mitochondrial antioxidant capacity, and in the intestine, liver, and lung of naturally aging mice. Our data demonstrate that genomic instability does not evidently contribute to naturally aging of the mouse heart in contrast to other organs and support the contention that the endogenous DNA repair machinery is remarkably active to maintain genomic integrity in cardiac cells throughout life.

Not Seeing Double: Discordance in Disease, Function, and Their Longitudinal Associations in Monozygotic Twins

OBJECTIVE

Prior research on the causality and directionality between disease and functional limitations is ambiguous. The current study used longitudinal monozygotic twin data to test both directions linking disease burden and functional limitations in middle-aged and older adults, controlling for genetic and familial factors. We also examined potential moderation by psychological well-being.

METHODS

The twin subsample from the first two waves of the longitudinal Midlife in the United States (MIDUS) study was used (wave 1, 1995-1996; wave 2, 2004-2006). Only monozygotic twins (n = 713) were included in analyses. In separate multilevel models, we examined disease burden at MIDUS 2 predicted by functional limitations at MIDUS 1 and MIDUS 2 functional limitations predicted by disease burden at MIDUS 1.

RESULTS

Disease burden and functional limitations at MIDUS 2 varied substantially within families. There was no within-family association of earlier functional limitations with change in later disease burden (b = 0.40, p = .39), but there was a within-family association such that the twin with higher baseline disease burden had a greater increase in functional limitations than his/her co-twin (b = 0.06, p = .02). Well-being was not a moderator in either model.

CONCLUSIONS

We found support for a potentially causal association between earlier disease burden and later increases in functional limitations, consistent with the Disablement Process Model. Sensitivity analyses confirm the detected within-family effect. Possible mechanisms linking disease burden and functional limitations are discussed as potential targets for future research.

Circulating fatty acids and endocannabinoidome-related mediator profiles associated to human longevity

To evaluate whether a peculiar plasma profile of fatty acids and endocannabinoidome (eCBome)-related mediators may be associated to longevity, we assessed them in octogenarians (Old; n=42) living in the east-central mountain area of Sardinia, a High-Longevity Zone (HLZ), compared to sexagenarian (Young; n=21) subjects from the same area, and to Olds (n=22) from the Northern Sardinia indicated as Lower-Longevity Zone (LLZ). We found significant increases in conjugated linoleic acid (CLA) and heptadecanoic acid (17:0) levels in Old-HLZ with respect to younger subjects and Old-LLZ subjects. Young-HLZ subjects exhibited higher circulating levels of pentadecanoic acid (15:0) and retinol. Palmitoleic acid (POA) was elevated in both Young and Old subjects from the HLZ. eCBome profile showed a significantly increased plasma level of the two endocannabinoids, N-arachidonoyl-ethanolamine (AEA) and 2-arachidonoyl-glycerol (2-AG) in Old-HLZ subjects compared to Young-HLZ and Old-LLZ respectively. In addition, we found increased N-oleoyl-ethanolamine (OEA), 2-linoleoyl-glycerol (2-LG) and 2-oleoyl-glycerol (2-OG) levels in Old-HLZ group with respect to Young-HLZ (as for OEA an d 2-LG) and both the Old-LLZ and Young-HLZ for 2-OG. The endogenous metabolite of docosahexaenoic acid (DHA), N-docosahexaenoyl-ethanolamine (DHEA) was significantly increased in Old-HLZ subjects. In conclusion, our results suggest that in the HLZ area, Young and Old subjects exhibited a favourable, albeit distinctive, fatty acids and eCBome profile that may be indicative of a metabolic pattern potentially protective from adverse chronic conditions. These factors could point to a suitable physiological metabolic pattern that may counteract the adverse stimuli leading to age-related disorders such as neurodegenerative and metabolic diseases.

DNA Damage and the Aging Epigenome

In mammals, genome instability and aging are intimately linked as illustrated by the growing list of patients with progeroid and animal models with inborn DNA repair defects. Until recently, DNA damage was thought to drive aging by compromising transcription or DNA replication, thereby leading to age-related cellular malfunction and somatic mutations triggering cancer. However, recent evidence suggests that DNA lesions also elicit widespread epigenetic alterations that threaten cell homeostasis as a function of age. In this review, we discuss the functional links of persistent DNA damage with the epigenome in the context of aging and age-related diseases.

[Longevity clocks: The promoting role of telomeres?]

Aging is an alteration of our physiological capacities that is accompanied by an increased susceptibility to develop a wide range of diseases and which determines in large part our longevity. Despite intensive research on the origin of aging, its etiology is still poorly understood. We discuss here the hypothesis that the telomere shortening, programmed to start at the end of embryogenesis in numerous tissues, couples development with aging by a time-dependent regulation of a set of interconnected processes essential for the somatic maintenance of genome, epigenome, metabolism, circadian clock and immunity.

Inequality of opportunities in health and death: an investigation from birth to middle age in Great Britain

Objective

We assess the existence of unfair inequalities in health and death using the normative framework of inequality of opportunities, from birth to middle age in Great Britain.

Methods

We use data from the 1958 National Child Development Study, which provides a unique opportunity to observe individual health from birth to the age of 54, including the occurrence of mortality. We measure health status combining self-assessed health and mortality. We compare and statistically test the differences between the cumulative distribution functions of health status at each age according to one childhood circumstance beyond people’s control: the father’s occupation.

Results

At all ages, individuals born to a ‘professional’, ‘senior manager or technician’ father report a better health status and have a lower mortality rate than individuals born to ‘skilled’, ‘partly skilled’ or ‘unskilled’ manual workers and individuals without a father at birth. The gap in the probability to report good health between individuals born into high social backgrounds compared with low, increases from 12 percentage points at age 23 to 26 at age 54. Health gaps are even more marked in health states at the bottom of the health distribution when mortality is combined with self-assessed health.

Conclusions

There is increasing inequality of opportunities in health over the lifespan in Great Britain. The tag of social background intensifies as individuals get older. Finally, there is added analytical value to combining mortality with self-assessed health when measuring health inequalities.

Prescribing medicines to older people-How to consider the impact of ageing on human organ and body functions

Ageing is associated with several changes in human organs, which result in altered medication pharmacokinetics and pharmacodynamics. Ageing is also associated with changes in human body functions, such as impaired vision, hearing, swallowing, motor and cognitive functions, which can affect the adequate intake and administration of drugs. As a consequence, older people, and especially patients older than 75 years, are the main users of many drugs and they frequently use 5 drugs or more long-term (i.e. polypharmacy). All this increases the complexity of adequate drug intake, administration and adherence. However, there is a lack of evidence on the considerations that should be taken into account to ensure appropriate drug prescribing to older people. This review article summarizes the most clinically relevant changes in human organ and body functions and the consequential changes in pharmacokinetics and pharmacodynamics in older people, along with possible dosing consequences or alternatives for drugs frequently prescribed to this patient population. Recommendations are given on how ageing could be considered in clinical drug development, drug authorization and appropriate prescribing.

Dichotomy between the transcriptomic landscape of naturally versus accelerated aged murine hearts

We investigated the transcriptomic landscape of the murine myocardium along the course of natural aging and in three distinct mouse models of premature aging with established aging-related cardiac dysfunction. Genome-wide total RNA-seq was performed and the expression patterns of protein-coding genes and non-coding RNAs were compared between hearts from naturally aging mice, mice with cardiac-specific deficiency of a component of the DNA repair machinery, mice with reduced mitochondrial antioxidant capacity and mice with reduced telomere length. Our results demonstrate that no dramatic changes are evident in the transcriptomes of naturally senescent murine hearts until two years of age, in contrast to the transcriptome of accelerated aged mice. Additionally, these mice displayed model-specific alterations of the expression levels of protein-coding and non-coding genes with hardly any overlap with age-related signatures. Our data demonstrate very limited similarities between the transcriptomes of all our murine aging models and question their reliability to study human cardiovascular senescence.

Adult Cardiac Stem Cell Aging: A Reversible Stochastic Phenomenon?

Aging is by far the dominant risk factor for the development of cardiovascular diseases, whose prevalence dramatically increases with increasing age reaching epidemic proportions. In the elderly, pathologic cellular and molecular changes in cardiac tissue homeostasis and response to injury result in progressive deteriorations in the structure and function of the heart. Although the phenotypes of cardiac aging have been the subject of intense study, the recent discovery that cardiac homeostasis during mammalian lifespan is maintained and regulated by regenerative events associated with endogenous cardiac stem cell (CSC) activation has produced a crucial reconsideration of the biology of the adult and aged mammalian myocardium. The classical notion of the adult heart as a static organ, in terms of cell turnover and renewal, has now been replaced by a dynamic model in which cardiac cells continuously die and are then replaced by CSC progeny differentiation. However, CSCs are not immortal. They undergo cellular senescence characterized by increased ROS production and oxidative stress and loss of telomere/telomerase integrity in response to a variety of physiological and pathological demands with aging. Nevertheless, the old myocardium preserves an endogenous functionally competent CSC cohort which appears to be resistant to the senescent phenotype occurring with aging. The latter envisions the phenomenon of CSC ageing as a result of a stochastic and therefore reversible cell autonomous process. However, CSC aging could be a programmed cell cycle-dependent process, which affects all or most of the endogenous CSC population. The latter would infer that the loss of CSC regenerative capacity with aging is an inevitable phenomenon that cannot be rescued by stimulating their growth, which would only speed their progressive exhaustion. The resolution of these two biological views will be crucial to design and develop effective CSC-based interventions to counteract cardiac aging not only improving health span of the elderly but also extending lifespan by delaying cardiovascular disease-related deaths.

Chromatin and Metabolism

Chromatin is a mighty consumer of cellular energy generated by metabolism. Metabolic status is efficiently coordinated with transcription and translation, which also feed back to regulate metabolism. Conversely, suppression of energy utilization by chromatin processes may serve to preserve energy resources for cell survival. Most of the reactions involved in chromatin modification require metabolites as their cofactors or coenzymes. Therefore, the metabolic status of the cell can influence the spectra of posttranslational histone modifications and the structure, density and location of nucleosomes, impacting epigenetic processes. Thus, transcription, translation, and DNA/RNA biogenesis adapt to cellular metabolism. In addition to dysfunctions of metabolic enzymes, imbalances between metabolism and chromatin activities trigger metabolic disease and life span alteration. Here, we review the synthesis of the metabolites and the relationships between metabolism and chromatin function. Furthermore, we discuss how the chromatin response feeds back to metabolic regulation in biological processes.

Assessment of the contribution of APOE gene variants to metabolic phenotypes associated with familial longevity at middle age

Offspring of long-lived families are characterized by beneficial metabolic phenotypes in glucose and lipid metabolism and low 25-hydroxyvitamin D. Although the genetic basis for human longevity remains largely unclear, the contribution of variation at the APOE locus has been repeatedly demonstrated. We aimed to assess whether ApoE isoforms mark the familial longevity status in middle age and subsequently to test to what extend this association is mediated by the metabolic characteristics marking this status. From the Leiden Longevity Study (LLS), we included offspring from nonagenarian siblings and partners as controls. Using the metabolic phenotypes of familial longevity as mediators, we investigated how APOE gene variants associated with LLS offspring/control status (in 1,515 LLS offspring and 715 controls). Within the LLS (mean age = 59.2 years), ApoE ε4 was not associated with a lower likelihood of being an LLS offspring, whereas ApoE ɛ2 was significantly associated with a higher likelihood of being an LLS offspring (odds ratio = 1.43), but this difference was not mediated (p-values>0.05) by any of the investigated metabolic phenotypes (e.g., diabetes and glucose). Therefore, variation at the APOE locus may not influence familial longevity status in middle age significantly through any of the metabolic mechanisms investigated.

Forward and reverse genetics approaches to uncover metabolic aging pathways in Caenorhabditis elegans

The biological mechanisms of aging have been studied in depth and prominent findings in this field promote the development of new therapies for age-associated disorders. Various model organisms are used for research on aging; among these, the nematode Caenorhabditis elegans has been widely used and has provided valuable knowledge in determining the regulatory mechanisms driving the aging process. Many genes involved in lifespan regulation are associated with metabolic pathways and are influenced by genetic and environmental factors. In line with this, C. elegans provides a promising platform to study such gene by environment interactions, in either a reverse or forward genetics approach. In this review, we discuss longevity mechanisms related to metabolic networks that have been discovered in C. elegans. We also highlight the use of wild populations to study the complex genetic basis of natural variation for quantitative traits that mediate longevity.

Epigenetic mechanisms during ageing and neurogenesis as novel therapeutic avenues in human brain disorders

Ageing is the main risk factor for human neurological disorders. Among the diverse molecular pathways that govern ageing, epigenetics can guide age-associated decline in part by regulating gene expression and also through the modulation of genomic instability and high-order chromatin architecture. Epigenetic mechanisms are involved in the regulation of neural differentiation as well as in functional processes related to memory consolidation, learning or cognition during healthy lifespan. On the other side of the coin, many neurodegenerative diseases are associated with epigenetic dysregulation. The reversible nature of epigenetic factors and, especially, their role as mediators between the genome and the environment make them exciting candidates as therapeutic targets. Rather than providing a broad description of the pathways epigenetically deregulated in human neurological disorders, in this review, we have focused on the potential use of epigenetic enzymes as druggable targets to ameliorate neural decline during normal ageing and especially in neurological disorders. We will firstly discuss recent progress that supports a key role of epigenetic regulation during healthy ageing with an emphasis on the role of epigenetic regulation in adult neurogenesis. Then, we will focus on epigenetic alterations associated with ageing-related human disorders of the central nervous system. We will discuss examples in the context of psychiatric disorders, including schizophrenia and posttraumatic stress disorders, and also dementia or Alzheimer's disease as the most frequent neurodegenerative disease. Finally, methodological limitations and future perspectives are discussed.

Circulating MicroRNAs and Life Expectancy Among Identical Twins

Human life expectancy is influenced not only by longevity assurance mechanisms and disease susceptibility loci but also by the environment, gene-environment interactions, and chance. MicroRNAs (miRNAs) are a class of small noncoding RNAs closely related to genes. Circulating miRNAs have been shown as promising noninvasive biomarkers in the development of many pathophysiological conditions. However, the concentration of miRNA in the circulation may also be affected by environmental factors. We used a next-generation sequencing platform to assess the association of circulating miRNA with life expectancy, for which deaths are due to all causes independent of genes. In addition, we showed that miRNAs are present in 41-year archived plasma samples, which may be useful for both life expectancy and all-cause mortality risk assessment. Plasma miRNAs from nine identical male twins were profiled using next-generation sequencing. The average absolute difference in the minimum life expectancy was 9.68 years. Intraclass correlation coefficients were above 0.4 for 50% of miRNAs. Comparing deceased twins with their alive co-twin brothers, the concentrations were increased for 34 but decreased for 30 miRNAs. Identical twins discordant in life expectancy were dissimilar in the majority of miRNAs, suggesting that environmental factors are pivotal in miRNAs related to life expectancy.

Epigenetic Mechanisms of Longevity and Aging

Aging is an inevitable outcome of life, characterized by progressive decline in tissue and organ function and increased risk of mortality. Accumulating evidence links aging to genetic and epigenetic alterations. Given the reversible nature of epigenetic mechanisms, these pathways provide promising avenues for therapeutics against age-related decline and disease. In this review, we provide a comprehensive overview of epigenetic studies from invertebrate organisms, vertebrate models, tissues, and in vitro systems. We establish links between common operative aging pathways and hallmark chromatin signatures that can be used to identify "druggable" targets to counter human aging and age-related disease.

Contemporary views on human aging and longevity

Aging is currently stimulating intense interest of both researchers and the general public. In developed countries, the average life expectancy has increased by roughly 30 years within the last century, and human senescence has been delayed by around a decade. Although aging is arguably the most familiar aspect of human biology, its proximate and ultimate causes have not been elucidated fully and understood yet. Nowadays there are two main approaches to the ultimate causes of aging. These are deterministic and stochastic models. The proximate theories constitute a distinct group of explanations. They focus on mechanistic causes of aging. In this view, there is no reason to believe that there is only one biological mechanism responsible for aging. The aging process is highly complex and results from an accumulation of random molecular damage. Currently, the disposable soma theory (DST), proposed by Thomas Kirkwood, is the most influential and coherent line of reasoning in biogerontology. This model does not postulate any particular mechanism underpinning somatic defense. Therefore, it is compatible with various models, including mechanistic and evolutionary explanations. Recently, however, an interesting theory of hyper-function of mTOR as a more direct cause of aging has been formulated by Mikhail Blagosklonny, offering an entirely different approach to numerous problems and paradoxes in current biogerontology. In this view, aging is quasi-programmed, which means that it is an aimless continuation of developmental growth. This mTOR-centric model allows the prediction of completely new relationships. The aim of this article is to present and compare the views of both parties in the dispute, based on the results of some recent experimental studies, and the contemporary knowledge of selected major aspects of human aging and longevity

Heritability of Health and Aging Limitations on Personally Desired Activities

The aim of this study is to estimate heritability of incident limitations on personally desired activities within the eighth decade of life. We measured self-rated ability to perform ten personally desired activities in 1606 male veteran twin pairs at baseline and four years later. At follow-up, 33% of the cohort reported more limitations in desired activities. Among twins who completed both assessments, there were no statistically significant differences in incidence rates of limitations as a function of zygosity. Sensitivity tests showed the same for change scores; and that, if cognitive impairment or death are deemed to belong among limitations of desired activities, zygosity contributed 10% to new limitations at follow-up. Maintaining personally desired activities over four years in the eighth decade is not subject to substantial genetic influence. However, if death and cognitive impairment are added to incident limitations, then genetics plays a modest role. In all cases, unique environment is the predominant influence.

Epigenetic regulation of ageing: linking environmental inputs to genomic stability

Ageing is affected by both genetic and non-genetic factors. Here, we review the chromatin-based epigenetic changes that occur during ageing, the role of chromatin modifiers in modulating lifespan and the importance of epigenetic signatures as biomarkers of ageing. We also discuss how epigenome remodelling by environmental stimuli affects several aspects of transcription and genomic stability, with important consequences for longevity, and outline epigenetic differences between the 'mortal soma' and the 'immortal germ line'. Finally, we discuss the inheritance of characteristics of ageing and potential chromatin-based strategies to delay or reverse hallmarks of ageing or age-related diseases.

Intergenerational and Genealogical Approaches for the Study of Longevity in the Saguenay-Lac-St-Jean Population

The mechanisms of longevity have been the subject of investigations for a number of years. Although the role of genetic factors is generally acknowledged, important questions persist regarding the relative impact of environmental exposures, lifestyle characteristics, and genes. The BALSAC population register offers a unique opportunity to study longevity from an intergenerational and genealogical point of view. Individuals from the Saguenay-Lac-St-Jean population who died at age 90 or older between 1950 and 1974 were selected from this database (n = 576), along with a control group of individuals born in the same period who died between 50 and 75 years of age. For these subjects and controls, spouses' ages at death and parental ages at death and at their birth were investigated using regression analysis. Genealogical reconstructions were carried out for each individual, and various analyses were performed on both groups. Both fathers' and mothers' mean ages at death were significantly higher among the longer-lived cases than among controls whereas spouses' ages at death and parental ages at birth had no effect. Regression analysis confirmed the positive effect of both fathers' and mothers' age at death. Mean kinship coefficients for the parents' generations displayed significant differences, indicating that kinship was higher among subjects than controls (this effect was stronger among the oldest 10% of the subjects). Frequencies and genetic contributions of ancestors were very similar for the two groups, and none of these ancestors appeared more likely to have introduced genetic variants involved in longevity patterns in this French Canadian population.

Unraveling genetic origin of aging-related traits: evolving concepts

Discovering the genetic origin of aging-related traits could greatly advance strategies aiming to extend health span. The results of genome-wide association studies (GWAS) addressing this problem are controversial, and new genetic concepts have been fostered to advance the progress in the field. A limitation of GWAS and new genetic concepts is that they do not thoroughly address specifics of aging-related traits. Integration of theoretical concepts in genetics and aging research with empirical evidence from different disciplines highlights the conceptual problems in studies of genetic origin of aging-related traits. To address these problems, novel approaches of systemic nature are required. These approaches should adopt the non-deterministic nature of linkage of genes with aging-related traits and, consequently, reinforce research strategies for improving our understanding of mechanisms shaping genetic effects on these traits. Investigation of mechanisms will help determine conditions that activate specific genetic variants or profiles and explore to what extent these conditions that shape genetic effects are conserved across human lives and generations.

Genome wide association and linkage analyses identified three loci-4q25, 17q23.2, and 10q11.21-associated with variation in leukocyte telomere length: the Long Life Family Study

Leukocyte telomere length is believed to measure cellular aging in humans, and short leukocyte telomere length is associated with increased risks of late onset diseases, including cardiovascular disease, dementia, etc. Many studies have shown that leukocyte telomere length is a heritable trait, and several candidate genes have been identified, including TERT, TERC, OBFC1, and CTC1. Unlike most studies that have focused on genetic causes of chronic diseases such as heart disease and diabetes in relation to leukocyte telomere length, the present study examined the genome to identify variants that may contribute to variation in leukocyte telomere length among families with exceptional longevity. From the genome wide association analysis in 4,289 LLFS participants, we identified a novel intergenic SNP rs7680468 located near PAPSS1 and DKK2 on 4q25 (p = 4.7E-8). From our linkage analysis, we identified two additional novel loci with HLOD scores exceeding three, including 4.77 for 17q23.2, and 4.36 for 10q11.21. These two loci harbor a number of novel candidate genes with SNPs, and our gene-wise association analysis identified multiple genes, including DCAF7, POLG2, CEP95, and SMURF2 at 17q23.2; and RASGEF1A, HNRNPF, ANF487, CSTF2T, and PRKG1 at 10q11.21. Among these genes, multiple SNPs were associated with leukocyte telomere length, but the strongest association was observed with one contiguous haplotype in CEP95 and SMURF2. We also show that three previously reported genes-TERC, MYNN, and OBFC1-were significantly associated with leukocyte telomere length at p empirical < 0.05.

Epigenetic memory of longevity in Caenorhabditis elegans

A recent study by Greer et al. in the nematode C. elegans has shown transgenerational epigenetic inheritance of longevity in the descendants of worms deficient for subunits of a complex responsible for histone H3 lysine 4 trimethylation (H3K4me3). In this commentary, we discuss the implications of this epigenetic memory of longevity and the potential mechanisms underlying this phenomenon. The transgenerational inheritance of longevity could result from heritable depletion of H3K4me3 at particular aging-regulating gene loci that would only be progressively replenished. The epigenetic memory of longevity could also be explained by the transgenerational transmission of other molecules, for example other proteins or non-coding RNAs. The discovery of an epigenetic memory of longevity in worms raises the intriguing possibility that environmental cues modulating longevity in ancestors might affect subsequent generations in a non-Mendelian manner. Another remaining intriguing question is whether transgenerational inheritance of longevity also exists in other species, including mammals.

Genetics of healthy aging and longevity

Longevity and healthy aging are among the most complex phenotypes studied to date. The heritability of age at death in adulthood is approximately 25 %. Studies of exceptionally long-lived individuals show that heritability is greatest at the oldest ages. Linkage studies of exceptionally long-lived families now support a longevity locus on chromosome 3; other putative longevity loci differ between studies. Candidate gene studies have identified variants at APOE and FOXO3A associated with longevity; other genes show inconsistent results. Genome-wide association scans (GWAS) of centenarians vs. younger controls reveal only APOE as achieving genome-wide significance (GWS); however, analyses of combinations of SNPs or genes represented among associations that do not reach GWS have identified pathways and signatures that converge upon genes and biological processes related to aging. The impact of these SNPs, which may exert joint effects, may be obscured by gene-environment interactions or inter-ethnic differences. GWAS and whole genome sequencing data both show that the risk alleles defined by GWAS of common complex diseases are, perhaps surprisingly, found in long-lived individuals, who may tolerate them by means of protective genetic factors. Such protective factors may ‘buffer’ the effects of specific risk alleles. Rare alleles are also likely to contribute to healthy aging and longevity. Epigenetics is quickly emerging as a critical aspect of aging and longevity. Centenarians delay age-related methylation changes, and they can pass this methylation preservation ability on to their offspring. Non-genetic factors, particularly lifestyle, clearly affect the development of age-related diseases and affect health and lifespan in the general population. To fully understand the desirable phenotypes of healthy aging and longevity, it will be necessary to examine whole genome data from large numbers of healthy long-lived individuals to look simultaneously at both common and rare alleles, with impeccable control for population stratification and consideration of non-genetic factors such as environment.

MAP3K7 and GSTZ1 are associated with human longevity: a two-stage case-control study using a multilocus genotyping

The pathways that regulate energy homeostasis, the mechanisms of damage repair, and the signaling response to internal environmental changes or external signals have been shown to be critical in modulating lifespan of model organisms and humans. In order to investigate whether genetic variation of genes involved in these pathways contribute to longevity, a two-stage case-control study in two independent sets of long-lived individuals from Calabria (Italy) was performed. In stage 1, 317 SNPs in 104 genes were analyzed in 78 cases (median age 98 years) and 71 controls (median age 67 years). In stage 2, 31 candidate SNPs identified in stage 1 (π markers = 0.1) were analyzed in an independent sample composed by 288 cases (median age 92 years) and 554 controls (median age 67 years). Two SNPs, rs282070 located in intron 1 of the MAP3K7 gene, and rs2111699 located in intron 1 of the GSTZ1 gene, were significantly associated (after adjustment for multiple testing) with longevity in stage 2 (p = 1.1 × 10(-3) and p = 1.4 × 10(-3), respectively). Interestingly, both genes are implicated in the cellular response to internal and external environmental changes, playing a crucial role in the inflammation processes that accompany aging. Our data confirm that long-lived subjects are endowed with genetic variants that allow them to optimize these cellular responses and to better deal with environmental and internal stresses.

Personality profile of the children of long-lived parents

OBJECTIVES

Past research has shown that parental longevity is related to offspring physical health and longevity. Preliminary studies suggest that parental longevity may be linked to the offspring's personality traits. A comprehensive 5-factor personality model has been related to physical health, but the association with parental longevity has not yet been investigated. We used a 5-factor personality model to investigate the relationship between parental longevity and offspring personality.

METHOD

Data from the longitudinal Health and Retirement Study (HRS) was used in the analyses. Using the Midlife Development Inventory and the Life Orientation test, the relationship between parental attained age and offspring personality was assessed using regression models for both men and women.

RESULTS

Male offspring of long-lived fathers and mothers were more likely to be open to new experiences (p < .01) and be more extroverted (p = .03) compared with male offspring of short-lived fathers or mothers. Maternal or paternal attained age had no effect on the female offspring personality traits.

DISCUSSION

Personality is an important phenotype to consider when investigating genetic and environmental determinants of longevity. Further research is needed to investigate the potential of gender-specific mechanisms.

Biogenetic mechanisms predisposing to complex phenotypes in parents may function differently in their children

This study focuses on the participants of the Long Life Family Study to elucidate whether biogenetic mechanisms underlying relationships among heritable complex phenotypes in parents function in the same way for the same phenotypes in their children. Our results reveal 3 characteristic groups of relationships among phenotypes in parents and children. One group composed of 3 pairs of phenotypes confirms that associations among some phenotypes can be explained by the same biogenetic mechanisms working in parents and children. Two other groups including 9 phenotype pairs show that this is not a common rule. Our findings suggest that biogenetic mechanisms underlying relationships among different phenotypes, even if they are causally related, can function differently in successive generations or in different age groups of biologically related individuals. The results suggest that the role of aging-related processes in changing environment may be conceptually underestimated in current genetic association studies using genome wide resources.

Bitter taste receptor polymorphisms and human aging

Several studies have shown that genetic factors account for 25% of the variation in human life span. On the basis of published molecular, genetic and epidemiological data, we hypothesized that genetic polymorphisms of taste receptors, which modulate food preferences but are also expressed in a number of organs and regulate food absorption processing and metabolism, could modulate the aging process. Using a tagging approach, we investigated the possible associations between longevity and the common genetic variation at the three bitter taste receptor gene clusters on chromosomes 5, 7 and 12 in a population of 941 individuals ranging in age from 20 to 106 years from the South of Italy. We found that one polymorphism, rs978739, situated 212 bp upstream of the TAS2R16 gene, shows a statistically significant association (p = 0.001) with longevity. In particular, the frequency of A/A homozygotes increases gradually from 35% in subjects aged 20 to 70 up to 55% in centenarians. These data provide suggestive evidence on the possible correlation between human longevity and taste genetics.

Parental longevity correlates with offspring's optimism in two cohorts of community-dwelling older subjects

Dispositional optimism and other positive personality traits have been associated with longevity. Using a familial approach, we investigated the relationship between parental longevity and offspring's dispositional optimism among community-dwelling older subjects. Parental age of death was assessed using structured questionnaires in two different population-based samples: the Leiden Longevity Study (n = 1,252, 52.2% female, mean age 66 years, SD = 4) and the Alpha Omega Trial (n = 769, 22.8% female, mean age 69 years, SD = 6). Adult offspring's dispositional optimism was assessed with the Life Orientation Test-Revised (LOT-R). The association between parental age of death and levels of optimism in the offspring was analysed using linear regression analysis within each sample and a meta-analysis for the overall effect. In both samples, the parental mean age of death was positively associated with optimism scores of the offspring. The association remained significant after adjustment for age, gender, living arrangement, body mass index, smoking status, education and self-rated health of the offspring. The pooled B coefficient (increase in LOT-R score per 10-year increase in parental mean age of death) was 0.30 (SE = 0.08, p < 0.001). In conclusion, parental longevity was positively associated with optimism in adult offspring, suggesting a partial linked heritability of longevity and optimism.

Contemporary human genetic strategies in aging research

Human aging is a complex, multifactorial process influenced by a number of genetic and non-genetic factors. This article first reviews genetic strategies for human aging research and considers the advantages and disadvantages of each. We then discuss the issue of phenotypic definition for genetic studies of aging, including longevity/life span, as well as disease-free survival and other endophenotypes. Finally, we argue that extensions of this area of research, including incorporation of gene×environment interactions, multivariate phenotypes, integration of functional genomic annotations, and exploitation of orthology - many of which are already initiated and ongoing - are critical to advancing this field.

Genomics for disease treatment and prevention

The enormous advances in genetics and genomics of the past decade have the potential to revolutionize health care, including mental health care, and bring about a system predominantly characterized by the practice of genomic and personalized medicine. This article briefly reviews the history of genetics and genomics and assesses the extent to which the results of genetic and genomic studies are currently being leveraged clinically for disease treatment and prevention. Relevant social, economic, and policy issues relevant to genomic medicine are also reviewed, and priority research areas in which further work is needed are identified.

Heritability analysis of life span in a semi-isolated population followed across four centuries reveals the presence of pleiotropy between life span and reproduction

Although genetic factors are known to influence the human aging process, the proportion of life span and longevity variation explained by them is still controversial. We evaluated the genetic contribution to life span using historical data from three Alpine communities in South Tyrol, Italy. We estimated the heritability of life span and survival to old age (longevity), and we assessed the hypothesis of a common genetic background between life span and reproduction. The heritability of life span was 0.15 (SE = 0.02), whereas the heritability of longevity increased from 0.20 to 0.35 as the longevity threshold increased. Heritability estimates were little influenced by shared environment, most likely due to the homogeneity of lifestyle and environmental factors in our study population. Life span showed both positive association and genetic correlation with reproductive history factors. Our study demonstrates a general low inheritance of human life span, but which increases substantially when considering long-living individuals, and a common genetic background of life span and reproduction, in agreement with evolutionary theories of aging.

High-density genomewide linkage analysis of exceptional human longevity identifies multiple novel loci

BACKGROUND

Human lifespan is approximately 25% heritable, and genetic factors may be particularly important for achieving exceptional longevity. Accordingly, siblings of centenarians have a dramatically higher probability of reaching extreme old age than the general population.

METHODOLOGY/PRINCIPAL FINDINGS

To map the loci conferring a survival advantage, we performed the second genomewide linkage scan on human longevity and the first using a high-density marker panel of single nucleotide polymorphisms. By systematically testing a range of minimum age cutoffs in 279 families with multiple long-lived siblings, we identified a locus on chromosome 3p24-22 with a genomewide significant allele-sharing LOD score of 4.02 (empirical P = 0.037) and a locus on chromosome 9q31-34 with a highly suggestive LOD score of 3.89 (empirical P = 0.054). The empirical P value for the combined result was 0.002. A third novel locus with a LOD score of 4.05 on chromosome 12q24 was detected in a subset of the data, and we also obtained modest evidence for a previously reported interval on chromosome 4q22-25.

CONCLUSIONS/SIGNIFICANCE

Our linkage data should facilitate the discovery of both common and rare variants that determine genetic variability in lifespan.

HLA and KIR frequencies in Sicilian Centenarians

Several studies suggest that human longevity appears to be linked inextricably with optimal functioning of the immune system, suggesting that specific genetic determinants may reside in loci that regulate the immune response, as human leukocyte antigen (HLA) and killer cell immunoglobulin-like receptor (KIR) genes. It has been suggested 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 disease(s). On the other hand, the cytolytic activity of natural killer (NK) cells is controlled by activating and inhibitory cell-surface receptors, including KIR. The genetic diversity of the KIR loci with respect to successful aging has been analyzed only in one study performed in the Irish population. Although two KIR genes (2DS3, 2DL5) displayed an initial increased frequency in the aged group, the significance of this association was lost when repeated in a second cohort. We have evaluated by polymerase chain reaction-sequence-specific primers (PCR-SSP) HLA-DRB1 and KIR receptors/HLA ligands frequencies in centenarians and controls from Sicily. Our results demonstrate an increase of the HLA DRB1*18 allele in male centenarians (p = 0.0266, after Bonferroni correction). Concerning KIR, no significant difference was observed after Bonferroni correction. However, our findings suggest that HLA/KIR/longevity associations are population specific, being heavily affected by the population-specific genetic and environmental history. This kind of study is important to better understand aging and longevity, hence enhancing the planning of antiaging strategies.

Inequality of opportunities in health in France: a first pass

This article analyses the role played by childhood circumstances, especially social and family background in explaining health status among older adults. We explore the hypothesis of an intergenerational transmission of health inequalities using the French part of SHARE. As the impact of both social background and parents' health on health status in adulthood represents circumstances independent of individual responsibility, this study allows us testing the existence in France of inequalities of opportunity in health related to family and social background. Empirically, our study relies on tests of stochastic dominance at first order and multivariate regressions, supplemented by a counterfactual analysis to evaluate the long-lasting impact of childhood conditions on inequality in health. Allocating the best circumstances in both parents' socioeconomic status and parents' health reduces inequality in health by an impressive 57% using the Gini coefficient. The mother's social status has a direct effect on the health of her offspring. By contrast, the effect on descendant's health from their father's social status is indirect only, which goes through the descendant's social status as an adult. There is also a strong effect of the father vital status on health in adulthood, revealing a selection effect.

"Predicting" parental longevity from offspring endophenotypes: data from the Long Life Family Study (LLFS)

While there is evidence that longevity runs in families, the study of long-lived families is complicated by the fact that longevity-related information is available only for the oldest old, many of whom may be deceased and unavailable for testing, and information on other living family members, primarily descendents, is censored. This situation requires a creative approach for analyzing determinants of longevity in families. There are likely biomarkers that predict an individual's longevity, suggesting the possibility that those biomarkers which are heritable may constitute valuable endophenotypes for exceptional survival. These endophenotypes could be studied in families to identify human longevity genes and elucidate possible mechanisms of their influence on longevity. In this paper, we analyze data collected in the Long Life Family Study (LLFS) investigating whether indicators of physiological state, cognitive functioning and health/well-being among offspring predict longevity in parents. Good predictors can be used as endophenotypes for exceptional survival. Our analyses revealed significant associations between cumulative indices describing physiological state, as well as a number of offspring phenotypes, and parental lifespan, supporting both their familial basis and relevance to longevity. We conclude that the study of endophenotypes within families is a valid approach to the genetics of human longevity.

Genetic variation in healthy oldest-old

Individuals who live to 85 and beyond without developing major age-related diseases may achieve this, in part, by lacking disease susceptibility factors, or by possessing resistance factors that enhance their ability to avoid disease and prolong lifespan. Healthy aging is a complex phenotype likely to be affected by both genetic and environmental factors. We sequenced 24 candidate healthy aging genes in DNA samples from 47 healthy individuals aged eighty-five years or older (the 'oldest-old'), to characterize genetic variation that is present in this exceptional group. These healthy seniors were never diagnosed with cancer, cardiovascular disease, pulmonary disease, diabetes, or Alzheimer disease. We re-sequenced all exons, intron-exon boundaries and selected conserved non-coding sequences of candidate genes involved in aging-related processes, including dietary restriction (PPARG, PPARGC1A, SIRT1, SIRT3, UCP2, UCP3), metabolism (IGF1R, APOB, SCD), autophagy (BECN1, FRAP1), stem cell activation (NOTCH1, DLL1), tumor suppression (TP53, CDKN2A, ING1), DNA methylation (TRDMT1, DNMT3A, DNMT3B) Progeria syndromes (LMNA, ZMPSTE24, KL) and stress response (CRYAB, HSPB2). We detected 935 variants, including 848 single nucleotide polymorphisms (SNPs) and 87 insertion or deletions; 41% (385) were not recorded in dbSNP. This study is the first to present a comprehensive analysis of genetic variation in aging-related candidate genes in healthy oldest-old. These variants and especially our novel polymorphisms are valuable resources to test for genetic association in models of disease susceptibility or resistance. In addition, we propose an innovative tagSNP selection strategy that combines variants identified through gene re-sequencing- and HapMap-derived SNPs.

Familial Transmission of Human Longevity Among the Oldest-Old in China

This paper investigates the relationship between longevity of parents and exceptional longevity (survival to age 80 or older) of offspring, using data from the first three waves of the Chinese Longitudinal Healthy Longevity Survey. We apply the Fixed-Attributes Dynamics method and logistic regression models to the data. Results of both methods show that the familial transmission of longevity exists at very old ages, and the transmission is same-sex linked between parents and offspring; that is, there is a strong father-son resemblance of longevity and a strong mother-daughter resemblance of longevity, but a non-significant or weak association of longevity between father and daughter or between mother and son.

Parental effects on offspring longevity—evidence from 17th to 19th century reproductive histories

BACKGROUND

Family studies provide support for a modest genetic influence on offspring life span, although the magnitude of these correlations is small.

AIM

The study aimed to clarify the relative contributions of parental age at birth and overall parental longevity on offspring lifespan, and to identify the biological and cultural mechanisms.

SUBJECTS AND METHODS

Information was derived from two village genealogies (1650-1927) encompassing 9979 births (5315 males, 4664 females). Data selection was guided by the inclusion of information about parental age at birth and lifespan, offspring lifespan and cohort-specific life expectancy.

RESULTS

Parental age at reproduction displayed a negative association with offspring survivability, which was caused by a host of biological as well as environmental factors. In contrast, parental lifespan was positively associated with offspring age at death. These effects differed by parent's and child's sex.

CONCLUSION

The maternal age effect on female progeny is thought to be indicative of a preferential genetic load. From an evolutionary point of view, direct selection for maternal lifespan may be an adaptive strategy to enhance child survival prospects.

Relationships between distributions of longevous population and trace elements in the agricultural ecosystem of Rugao County, Jiangsu, China

Soil, plant, and water, as well as trace elements they contain, can influence human health through the food chain. A survey was conducted on distributions of trace elements in soils, plants, and drinking water in Rugao County, Jiangsu Province, China, an agricultural area with a high level of centenarians and nonagenarians. The ratio of people over 90 years old per 100,000 inhabitants (90-rate) based on village (about 4,000 residents in 4 km(2)) was correlated with trace elements in soil, drinking water, and rice by means of correlation analysis and/or principal component analysis. Although the average 90-rate in the whole area was as high as 277, the rates were not uniform across the entire region. The 90-rate in the area of loamy and strongly-developed Anthrosols and Cambosols was about 330, significantly higher than the 255 in the areas of sandy and strongly-developed Cambosols and of clayey and weakly-developed Cambosols. The concentrations of available Se, B, Ni, and Mo in soils of the area with the high 90-rate were markedly greater than those in the area with the low 90-rate. This was demonstrated by highly positive correlations between the 90-rate and available Se (r = 0.33), B (r = 0.21), Ni (r = 0.17) and Mo (r = 0.17) at the p < 0.01 level and high loadings of available Se (0.851), B (0.535), Ni (0.594) and Mo (0.394) in the longevous factor. Similar relationships between the available elements in soils and elements in water and rice were found. These results suggest that: (1) the available forms of elements in soil were more crucial to elemental bio-availability in the ecosystem and human health than total elements in soil; and (2) the element association above might have affected the 90-rate positively and could be an important environmental geochemical factor influencing the longevity of humans.

Aging and animal models of systemic insult: trauma, burn, and sepsis

In the acute-care setting, it is widely accepted that elderly patients have increased morbidity and mortality compared with young healthy patients. The reasons for this, however, are largely unknown. Although animal modeling has helped improve treatment strategies for young patients, there are a scarce number of studies attempting to understand the mechanisms of systemic insults such as trauma, burn, and sepsis in aged individuals. This review aims to highlight the relevance of using animals to study the pathogenesis of these insults in the aged and, despite the deficiency of information, to summarize what is currently known in this field.

Epistatic genetic determinants of blood pressure and mortality in a salt-sensitive hypertension model

Although genetic determinants protecting against the development of elevated blood pressure (BP) are well investigated, less is known regarding their impact on longevity. We concomitantly assessed genomic regions of rat chromosomes 3 and 7 (RNO3 and RNO7) carrying genetic determinants of BP without known epistasis, for their independent and combinatorial effects on BP and the presence of genetic determinants of survival using Dahl salt-sensitive (S) strains carrying congenic segments from Dahl salt-resistant (R) rats. Although congenic and bicongenic S.R strains carried independent BP quantitative trait loci within the RNO3 and RNO7 congenic regions, only the RNO3 allele(s) independently affected survival. The bicongenic S.R strain showed epistasis between R-rat RNO3 and RNO7 alleles for BP under salt-loading conditions, with less-than-additive effects observed on a 2% NaCl diet and greater-than-additive effects observed after prolonged feeding on a 4% NaCl diet. These RNO3 and RNO7 congenic region alleles had more-than-additive effects on survival. Increased survival of bicongenic compared with RNO3 congenic rats was attributable, in part, to maintaining lower BP despite chronic exposure to an increased dietary salt (4% NaCl) intake, with both strains showing delays in reaching highest BP. R-rat RNO3 alleles were also associated with superior systolic function, with the S.R bicongenic strain showing epistasis between R-rat RNO3 and RNO7 alleles leading to compensatory hypertrophy. Whether these alleles affect survival by additional actions within other BP-regulating tissues/organs remains unexplored. This is the first report of simultaneous detection of independent and epistatic loci dictating, in part, longevity in a hypertensive rat strain.

Antagonistic pleiotropy and p53

George Williams' antagonistic pleiotropy theory of aging proposes that cellular damage and organismal aging are caused by pleiotrophic genes, or genes with multiple phenotypic effects [Williams, G.C., 1957. Pleiotropy, natural selection, and the evolution of senescence. Evolution 11, 398-411]. According to this theory, genes that exhibit antagonistic pleiotropy increase the odds of successful reproduction early in life, but have deleterious effects later in life. The tumor suppressor p53 confers protection against cancer (and death) by interrupting the abnormal proliferation of cells. When control of proliferation is applied to normal stem cells, however, it can impair tissue homeostasis and accelerate aging. We use data from recently developed models of accelerated aging in mice to determine if the deleterious effects of p53 on aging reflect antagonistic pleiotropy of the p53 gene or are attributable to genes that can modify p53 activity but are evolving independently.

Age-dependent variability in gene expression in male Fischer 344 rat retina

Recent evidence suggests that older adults may be a sensitive population with regard to environmental exposure to toxic compounds. One source of this sensitivity could be an enhanced variability in response. Studies on phenotypic differences have suggested that variation in response does increase with age. However, few reports address the question of variation in gene expression as an underlying cause for increased variability of phenotypic response in the aged. In this study, we utilized global analysis to compare variation in constitutive gene expression in the retinae of young (4 months), middle-aged (11 months), and aged (23 months) Fischer 344 rats. Three hundred and forty transcripts were identified in which variance in expression increased from 4 to 23 months of age, while only 12 transcripts were found for which it decreased. Functional roles for identified genes were clustered in basic biological categories including cell communication, function, metabolism, and response to stimuli. Our data suggest that population stochastically induced variability should be considered in assessing sensitivity due to old age.

Increased longevity in offspring of mothers with Alzheimer's disease

Life expectancy is a familial trait. However, the effectiveness of using the age at death of a deceased parent to estimate life expectancy in their offspring can vary depending on whether death in the parent was due to extrinsic versus intrinsic causes, as well as demographic characteristics such as sex. While Alzheimer's disease (AD) risk increases with increased age, mortality for individuals with AD is increased in contrast to comparably aged individuals without AD. Yet in most cases it is not the defining neuropathology of AD that directly terminates life but instead conditions and illnesses extrinsic to AD pathology that nevertheless have increased likelihood in its presence. For this reason, we hypothesized that offspring of AD mothers would have greater longevity than offspring of mothers without AD (insufficient numbers prevented a comparable analysis using fathers with AD). The longevity of 345 offspring of 100 deceased 60+ year old AD mothers was compared with 5,465 offspring in 1,312 deceased 60+ year old non-AD mothers. We used a proportional hazards model that accounted for clustered (nonindependent) observations due to the inclusion of several offspring from the same family. In both an unadjusted model and one that adjusted for the age at death in the mother, and the sex and birth year in the offspring we found evidence for increased longevity in the offspring of AD mothers. The results suggest that, in addition to genes that might directly affect pathways leading to AD, there may be familial/genetic factors not connected to specific pathophysiological processes in AD but instead associated with increased longevity that contribute to the familial aggregation observed in AD.