International conference on biomedical aspects of aging research

Aging Clin. Exp. Res. 10: 141-177, 1998

SYMPOSIUM REPORT American Federation for AGING Research (AFAR)

International conference on biomedical aspects of aging research December 10-13, 1997 Fondazione Cini, San Giorgio, Venezia, Italy Organized by AFAR in partnership with: The Center for the Study of AGING of the National Research Council at the University of Padova, Italy; The National Institute on Aging and National Institutes of Health, United States; and The United Nations, Division of Social Policies and Development, United States.

INTRODUCTION The idea for the First International AFAR meeting in Venice, Italy, grew from discussions in New York at the Board meeting of AFAR in December of 1995. The discussions began informally between the two of us, and then formally with the entire board. There were two compelling reasons to have such a meeting; first, AFAR is an American group supporting research on aging and especially dedicated to funding of “start-up” research for young investigators who are new to the field of aging. AFAR receives its support from the private sector. We realized that this model was virtually unknown in Europe. Yet it is an enormously successful model. AFAR has launched the careers of over 1000 young scientists and student investigators over the 15 years of its existence. The second reason was to bring scientists together from around the world to discuss current research on aging. We organized a major scientific meeting that would be international in scope and would include a broad diversity of subject matters ranging from basic cell and molecular research to more clinically based investigations on age-associated diseases. Our hope is that this tradition of meetings will continue every several years to bring investigators from around the world together to focus on problems of aging and age-associated diseases and to attract young investigators into this enormously important field. We also hope that innovative ways will be identified to fund these young investigators so that the next generation of researchers is assured. We wish to thank all who participated in the meeting. We also wish to thank the staff of AFAR, particularly Staci Zeil, and the representative of CNR in

Padova, Dr. Stefania Maggi, for their important contributions. Vincent J. Cristofalo, Ph.D. Gaetano Crepaldi, M.D. International Conference Co-Chairs

KEYNOTE ADDRESSES

Economic, political and ethical implications of aging J. Grimley Evans Nuffield Department of Clinical Medicine, University of Oxford, England

The aging of populations is a permanent change to which our social systems and structures need to adapt. There are four things to be done: 1) Funding: A new element in debates about future funding of health care is that of inter-generational equity. Inter-generational equity can have an important impact on social well-being in determining whether older people are seen as parasitic on the working population or merely receiving their agreed deserts. One manifestation of the view of older people as parasitic has been the growth of support for the doctrine of age-based rationing of health care. We must recognize that some elements in society will be glad for inter-gen-

Aging Clin. Exp. Res., Vol. 10, No. 2 141

Venice AFAR Meeting

erational conflict to divert attention from an underlying problem of inadequate funding for health and social services. 2) We must agree on the aims of health care for an aging population. This is primarily an ethical issue. The output of clinical health services comprises the changes induced in the well-being of individuals, but there is a long-running ethical debate about how such health transitions should be valued. The collectivist view is that outputs of health care should be valued on behalf of the state. This valuation will usually be in terms of some derivative of extra life-years obtained, for example in quality-adjusted life-years (QALYs). The individualist view is that a health transition can only be valued by the person seeking or receiving it. For the individualist, all lives must be seen as of equal value because they cannot be compared under the scrutiny of a single observer. Surely in North America and Europe our national ideologies are based on the individualist ideal. This ideal sets a research agenda in requiring that we measure health service outcomes in terms of the realization of individually specified goals. These issues are of particular relevance to older people who are more diverse, physiologically and psychologically than younger. There is some common ground for collectivists and individualists in seeking to prevent disability in old age which the individualist does not want people to have to endure and the collectivist does not want to have to pay for. Disability is most usefully conceptualized as arising from an ecological gap between what an environment demands and what an individual is capable of doing. At a clinical level this gap can be closed by therapeutic intervention to improve patients’ capabilities and by prosthetic measures to reduce the demands of their environments. At a political level we should seek to make our environment less disabling for an aging population. Apart from issues of safer cities and more rigorous traffic control, we can enhance the ease of visual perception and cognitive mapping of outdoor and indoor environments. As it has repeatedly been said, and repeatedly ignored by architects and planners, environments that are safer and pleasanter for older people are also safer and pleasanter for us all. 3) We must maximize the efficiency of services; this is to link economics with research using the multidisciplinary approaches of Health Services Research (HSR). A problem for HSR is the impossibility of carrying out randomized controlled trials of different systems and structures of health care. We have not, however, explored sufficiently the potential of systematic comparisons of health and social services between nations as a means of exploring cost-utilities

142 Aging Clin. Exp. Res., Vol. 10, No. 2

of systems of care. Advocates of age-based rationing of health services are too ready to assert that depriving old people of health care will necessarily save money. 4) We must minimize the need for care by reducing the incidence of age-associated disease and disability. The disabilities of later life come about because of an interaction between intrinsic (genetic) factors and extrinsic factors in environment and life-style. However, demonstrating that life-style changes could be beneficial in improving the pattern of aging is less difficult than persuading people to adopt them. Health education improves knowledge but has little effect in changing behavior. There is a research agenda for the social sciences in identifying the opportunities and incentives for optimal life-styles that could inform a public health approach to an aging society. The loss of adaptability that characterizes aging means that the older one is at the onset of a potentially disabling condition, such as stroke, the shorter the period of disability one can expect to have to endure. This is the rationale for a policy of postponement as prevention. Whether this policy will also lead to lower costs of care depends partly on the substitute morbidity that may appear as people survive one hazard only to encounter another at a later age. Perhaps our biggest challenge is to persuade politicians to address these issues seriously and responsibly. We have to plan for 30 years ahead in a political system with a horizon no further away than the next election.

Successful aging J.W. Rowe1 and R.L. Kahn2 1Mount Sinai School of Medicine and The Mount Sinai Hospital, New York City, New York, 2University of Michigan, Institute for Social Research, Ann Arbor, Michigan, U.S.A. Defining successful aging Recent and projected substantial increases in the relative and absolute number of older persons in our society pose a significant challenge for biology, social and behavioral science, and medicine. Gerontology is broadening its perspective from a prior preoccupation with disease and disability to a more robust view that includes successful aging. As conceptual and empiric research in this area accelerates, successful aging is seen as multidimensional, encompassing three distinct

Biomedical aspects of aging research

domains: avoidance of disease and disability; maintenance of high physical and cognitive function; and sustained engagement in social and productive activities. All three terms are relative and the relationship among them is to some extent hierarchical. Successful aging is more than absence of disease, important thought that is, and more than the maintenance of functional capacities, important as it is. While both are important components of successful aging, it is their combination with active engagement with life that represents the concept of successful aging most fully. Each of the three components of successful aging includes subparts. Low probability of disease refers not only to absence or presence of disease itself, but also to absence, presence, or severity of risk factors for disease. High functional level includes both physical and cognitive components. Physical and cognitive capacities are potentials for activity; they tell us what a person can do, not what he or she does do. Successful aging goes beyond potential; it involves activity. While active engagement with life takes many forms, we are most concerned with two - interpersonal relations and productive activity. Interpersonal relations involve contacts and transactions with others, exchange of information, emotional support, and direct assistance. An activity is productive if it creates societal value, whether or not it is reimbursed. Thus, a person who cares for a disabled family member or works as a volunteer in a local church or hospital is being productive, although unpaid. Reducing risk factors for disease and disability in late life The previously held view that increased risk of diseases and disability with advancing age results from inevitable, intrinsic aging processes, for the most part genetically determined, is inconsistent with a rapidly developing body of information that many usual aging characteristics are due to life-style and other factors that may be age-related (i.e., they increase with age) but are not age-dependent (not caused by aging itself). Substantial and growing evidence supports the contention that established risk factors for the emergence of diseases in older population, such as cardiovascular and cerebrovascular disease, can be substantially reduced and perhaps reversed. Research on risk factors for disease with advancing age reveals three consistent findings. First, intrinsic factors alone, while highly significant, do not dominate the determination of risk in advancing age. Extrinsic environmental factors, including elements of life-style, play a very important role in determining risk for disease. Second, with advancing age the relative contribution of

genetic factors decreases and the force of nongenetic factors increases. Third, usual aging characteristics are modifiable. These findings underline the importance of environmental and behavioral factors in determining the risk of disease late in life. Maximizing cognitive and physical function in late life A second essential component of successful aging is maximization of functional status. The MacArthur Foundation Research Network on Successful Aging conducted a longitudinal study of older persons to identify those physical, psychological, social and biomedical characteristics predictive of the maintenance of high function in late life. The 1189 subjects in this three-site longitudinal study were 70-79 years old at initial evaluation, and were functionally in the upper one third of the general aging population. Cognitive ability was assessed with neuropsychological tests of language, nonverbal memory, verbal memory, conceptualization, and visual spatial ability. In the initially high functioning group, four variables education, strenuous activity in and around the home, peak pulmonary flow rate, and self-efficacy - were found to be direct predictors of change or maintenance of cognitive function, together explaining 40% of the variance in cognitive test performance. Maintenance of high physical performance, including hand, trunk, and lower extremity movements and integrated movements of balance and gait, was predicted by both socio-demographic and health status characteristics. Being older and having an income of less than $10,000 a year increased the likelihood of a decline in physical performance, as did higher body mass index (greater fat), high blood pressure, and lower initial cognitive performance. Behavioral predictors of maintenance of physical function included moderate and/or strenuous leisure activity and emotional support from family and friends. Moderate levels of exercise activity (e.g., walking leisurely) appeared in these studies to convey similar advantages to more strenuous exercise (e.g., brisk walking). Continuing engagement with life The third component of successful aging, engagement with life, has two major elements: maintenance of interpersonal relations and of productive activities. Research on social relations and their effects reveals that: 1) isolation (lack of social ties) is a risk factor for health; 2) social support, both emotional and instrumental, can have positive health-relevant effects; and 3) no single type of support is uniformly effective; effectiveness depends on the appropriateness of the supportive acts to the requirements of the situation and the person.


Venice AFAR Meeting

Productive activities Older people are not considered “old” by their families and friends, nor do they think of themselves as “old”, so long as they remain active and productive in some meaningful sense. The America’s Changing Lives Study of the University of Michigan and the MacArthur studies addressed the question of what factors enable sustained productivity in old age. Three factors emerged as predictors of productive activity: functional capacity, education, and self-efficacy. Conclusion For each of the domains of successful aging, an interdisciplinary database is coalescing that relates to both reducing the risk of adverse events and enhancing resilience in their presence. Many of the predictors of disease risk and of both functional capacity and engagement with life appear to be modifiable, either by individuals or by changes in their immediate environments. The stage is thus set for intervention studies to identify effective strategies that enhance the proportion of our older population that ages successfully. ACKNOWLEDGEMENT

9.Rowe J.W., Kahn R.L.: Human aging: Usual and successful. Science 237: 143-149, 1987. 10.Schaie K.W., Willis S.L.: Can adult intellectual decline be reversed? Developmental Psychology 22: 223-232, 1986. 11.Seeman T.E., Berkman L.F., Blazer D., Rowe J.W.: Social ties and support and neuroendocrine function: The MacArthur Studies of Successful Aging. Annals of Behavioral Medicine 16: 95106, 1994. 12.Seeman T.E., Berkman L.F., Charpentier P.A., Blazer D.G., Albert M.S., Tinetti M.E.: Behavioral and psychosocial predictors of physical performance: MacArthur Studies of Successful Aging. J. Gerontol.: Med. Sci. 50A: M177-M183, 1995.

LECTURES: BIOLOGY OF AGING

Biological theories of aging: An overview T.B.L. Kirkwood Biological Gerontology Group, Department of Geriatric Medicine and School of Biological Sciences, University of Manchester, Manchester, United Kingdom

Supported by the John D. and Catherine T. MacArthur Foundation, Chicago, IL, U.S.A.

REFERENCES 1.Albert M.S., Savage C.R., Jones K., Berkman L., Seeman T., Blazer D., Rowe J.W.: Predictors of cognitive change in older persons: MacArthur Studies of Successful Aging. Psychol. Aging 10: 578-589, 1995. 2.Hazzard W.R.: Weight control and exercise: Cardinal features of successful preventive gerontology (Editorial). JAMA 274: 19641965, 1995. 3.Hazzard W.R., Bierman E.L.: Preventative gerontology: Strategies for attenuation of the chronic disease of aging. In: Hazzard W., Andres R., Bierman E., Blass J. (Eds.), Principles of geriatric medicine and gerontology, ed. 2. McGraw Hill, New York, 1990, pp.167-171. 4.Heller D., deFaire U., Pedersen N., Dahlén G., McClearn G.: Genetic and environmental influences on serum lipid levels in twins. N. Engl. J. Med. 328: 1150-1156, 1993. 5.Herzog A.R., Kahn R.L., Morgan J.N., Jackson J.S., Antonucci T.C.: Age differences in productive activities. J. Gerontol.: Soc. Sci. 44: S129-S138, 1989. 6.Katzel L.I., Bleecker E.R., Colman E.G., Rogus E.M., Sorkin J.D.: Effects of weight loss vs aerobic exercise training on risk factors for coronary disease in healthy, obese, middle-aged and older men: A randomized controlled trial. JAMA 274: 19151921, 1995. 7.Lachman M.E., Leff R.: Perceived control and intellectual functioning in the elderly. Psychol. Aging 2: 266-271, 1989. 8.Marenberg M., Risch N., Berkman L., Floderus B., deFaire U.: Genetic susceptibility to death from coronary heart disease in a study of twins. N. Engl. J. Med. 330: 1041-1046, 1994.


Theory of a type which begets no experimental work has been validly criticized as not helping, and even obscuring, research on aging (1). However, theory is a key part of the process of scientific discovery and it is particularly essential to the study of a process like aging, whose phenomenology is so diverse that without a coherent theoretical framework, to which new experimental data can be referred, progress will be slow and inefficient (2). Significant progress has come from the application of evolution theory in asking why aging occurs, why species have the life spans they do, and what kinds of genes are likely to influence the aging process (3, 4). A wide array of mechanistic theories exists (5), due to the fact that during aging almost every character of the body undergoes some form of change. However, many of these changes are secondary rather than primary events, and a major problem is to devise ways of disentangling causes from effects. Evolution theory has been helpful in prioritizing the candidates for research. An important contribution of evolution theory has been the dismissal of the idea that aging is a programmed process under active genetic control. There is no plausible basis for this hypothesis in view of the fact that in the wild environment, individuals rarely live long enough to show clear signs of senescence (6). Instead, the evolution of aging needs to be understood in


terms of the indirect action of natural selection. A key observation is that the force of natural selection progressively weakens with advancing age (7). What happens early in the life span impacts more directly on Darwinian fitness than what happens late. The upshot is that there is only loose genetic control over the later stages of the life span, potentially allowing accumulation of lateacting deleterious mutations. Furthermore, any physiological or genetic trade-off which favors the reproductive potential of the young organism at the expense of its long-term survival, is expected to be favored through natural selection (3). A trade-off of considerable significance for aging affects the investment of metabolic resources in mechanisms for somatic maintenance and repair vs the investment in reproductive effort. Somatic maintenance requires significant energy investments, and there is no advantage to be gained from better maintenance than is needed to keep the soma in good condition through its natural expectation of life in the wild environment, where extrinsic mortality (caused by predators, accidents, etc.) is the prevailing cause of death. This “disposable soma” theory predicts an evolved limitation in the levels of key maintenance systems and supports a central role for the action of extrinsic and intrinsic stressors in causing a lifelong accumulation of somatic damage leading eventually to aging and death (8). Many mechanisms cause damage to somatic cells and tissues. Individual theories have focused, in particular, on the roles of free radicals and oxidative damage (9), aberrant proteins (10), defective mitochondria (11, 12), and somatic mutations (13, 14). This list is by no means exhaustive. A corollary of the evolutionary theories is that multiple genes are likely to influence aging rates. We therefore need to consider integrated approaches to the study of multiple factors in the determination of longevity. In the context of somatic cell damage and protection, this means multiple elements of the cell maintenance and stress response network (8). The concept of a network of somatic maintenance functions brings a coherence to the study of mechanisms of aging, but it also highlights a major complexity, namely understanding how different processes synergize and interact. The experimental study of multiply interacting processes is challenging. Theory can play a significant role in the design and interpretation of these studies. An example of applying the network concept to the intracellular mechanisms of aging is found in a recent series of theoretical models by Kowald and Kirkwood, the most recent of which (15) incorporates the following features: accumulation of defective mitochondria, effects of aberrant proteins in protein synthesis, damaging actions of oxygen free radicals, the protective role of an-

tioxidant enzymes like superoxide dismutase, and the turnover of proteins by proteolytic scavengers. A clear demonstration of the importance of this kind of integrative approach to modelling mechanisms of cell senescence was given by the fact that in the network model the predicted effects on measurable properties of the system, e.g., the levels of defective mitochondria, were in some cases qualitatively and quantitatively different from predictions in earlier models that considered only single systems. An area of great importance for understanding the biological basis of aging in multicellular organisms is the analysis of how age changes at the cell level affect the organism as a whole. The Hayflick model of cell replicative senescence has been a powerful stimulus in this field, but even now, after nearly forty years of investigation, the relationship between in vitro and in vivo cell senescence remains unclear. Theory can help us to define the questions that still need to be addressed (16). Cell death (apoptosis) has some relationship with aging (17), but again this relationship needs to be clarified. Far from being an agent of programmed organismal destruction, apoptosis is often a part of the repertoire of defenses against accumulation of somatic damage, with key roles to play in tissue homeostasis and suppression of autoimmunity and malignancy. Failure of programmed cell death may be a factor in the pathogenesis of certain age-associated diseases. Even where apoptosis directly contributes to certain degenerative conditions, its role may only be secondary. In tissues which are maintained by stem cells there is growing interest in the extent to which functional changes arise in stem cells which affect the functional homeostasis of these tissues (18). There is a role for theoretical studies of how altered stem cell properties affect tissue homeostasis during aging. In conclusion, theory cannot substitute for experimental investigation, but it can significantly assist in the planning and interpretation of experimental studies and in building a coherent understanding of the complex biological basis of aging. Theory points strongly to a polygenic basis for longevity, and there is significant potential to extend this work by combining theoretical and experimental approaches to the analysis of gene-gene and gene-environment interactions. Theory is also contributing to our understanding of the molecular and cellular mechanisms that underlie the aging process. The major challenge for theories of aging today is to address the need for further integration in our studies of the most fascinating and complicated process. REFERENCES 1.Comfort A.: The Biology of Senescence. Churchill Livingstone, Edinburgh, 1979, pp. 17-18.


Venice AFAR Meeting

2.Kirkwood T.B.L.: Towards a unified theory of cellular aging. Monogr. Dev. Biol. 17: 9-20, 1984. 3.Kirkwood T.B.L., Rose M.R.: Evolution of senescence: late survival sacrificed for reproduction. Philos. Trans. R. Soc. Lond. B332: 15-24, 1991. 4.Partridge L., Barton N.H.: Optimality, mutation and the evolution of aging. Nature 362: 305-311, 1993. 5.Medvedev Z.A.: An attempt at a rational classification of theories of aging. Biol. Rev. 65: 375-398, 1990. 6.Medawar P.B.: An unsolved problem of biology. H.K. Lewis, London, 1952. 7.Charlesworth B.: Evolution of Age-Structured Populations, ed. 2. Cambridge University Press, Cambridge, 1994. 8.Kirkwood T.B.L., Franceschi C.: Is aging as complex as it would appear ? Ann. N. Y. Acad. Sci. 663: 412-417, 1992. 9.Sohal R.S., Weindruch R.: Oxidative stress, caloric restriction and aging. Science 273: 59-63, 1996. 10.Rosenberger R.F.: Senescence and the accumulation of abnormal proteins. Mutat. Res. 256: 255-262, 1991. 11.Linnane A.W., Marzuki S., Ozawa T., Tanaka M.: Mitochondrial DNA mutations as an important contributor to aging and degenerative diseases. Lancet 25: 642-645, 1989. 12.Wallace D.C.: Mitochondrial genetics: a paradigm for aging and degenerative diseases? Science 256: 628-632, 1992. 13.Kirkwood T.B.L.: DNA, mutations and aging. Mutat. Res. 219: 1-7, 1989. 14.Vijg J.: DNA sequence changes in aging: how frequent ?, how important? Aging Clin. Exp. Res. 2: 105-123, 1990. 15.Kowald A., Kirkwood T.B.L.: A network theory of aging: the interactions of defective mitochondria, aberrant proteins, free radicals and scavengers in the aging process. Mutat. Res. 316: 209-236, 1996. 16.Kirkwood T.B.L.: Genetic basis of limited cell proliferation. Mutat. Res. 256: 323- 328, 1991. 17.Holbrook N.J., Martin G.R., Lockshin R.A. (Eds.): Cellular aging and cell death. Wiley, Liss, New York, 1996. 18.Martin K., Kirkwood T.B.L., Potten C.S.: Age changes in stem cells of murine small intestinal crypts. Exp. Cell. Res., 1998 (in press).

Aging is not a disease L. Hayflick University of California, San Francisco, California, U.S.A.

Failure to distinguish aging from disease has not only blurred our efforts to understand the fundamental biology of aging, but it has profound political and economic consequences that compromise the field of biogerontology. Changes attributable to disease, or pathological


change, can be distinguished from age changes for at least four important reasons. Unlike any known disease or pathology, age changes occur in every human given sufficient time. Unlike any known disease, age changes cross virtually all species barriers. Unlike age changes, no disease afflicts all members of a species only after the age of reproductive success. Unlike disease, aging occurs in all feral animals subsequently protected by humans, even when the species has probably not experienced aging for thousands or millions of years. Unlike disease or pathology, many, if not most, age changes do not compromise health or increase the likelihood of death. No one has ever died of wrinkled skin, grey hair, or the menopause. The resolution of Alzheimer’s disease, cancer or vascular disease as causes of death in old age will advance our knowledge of the aging process to the same extent as the resolution of pediatric pathologies and infectious diseases such as poliomyelitis, rubella, rubeola, varicella, diphtheria and whooping cough advanced our knowledge of childhood development. That is, no advancement occurred at all. What we have failed to convey is that greater support must be given to a question that is rarely posed. It is a question that is applicable to all diseases and pathologies of the elderly. And, it is a question whose resolution will also advance our fundamental knowledge of aging. It is this: Why are old cells more vulnerable to pathology and disease than are young cells? REFERENCE Hayflick L.: How and why we age. Ballantine Books, New York City, 1996, pp. 1-377.

Theories of aging: An overview S.N. Austad Department of Biological Sciences, University of Idaho, Moscow, Idaho, U.S.A.

The major conceptual advance in aging research over the past several decades has been the general acceptance of evolutionary senescence theory, as developed originally by Medawar and refined and extended by Williams, Hamilton, Kirkwood, and others. Acceptance of this theory has had three major effects: 1) It has provided a coherent framework to an


otherwise chaotic welter of information on the longevity of different species, such that we now know how the ecological history of exposure to environmental hazards is a major key to understanding an organism’s aging rate. 2) It has emphasized how the role of the environment cannot be ignored when attempting to understand the action of longevity-associated alleles. Thus, genes promoting longevity in the laboratory must be understood in the context of the laboratory environment and may require specific conditions such as larval crowding (in Drosophila melanogaster), or lack of an environmental necessity to enter a “waiting stage” (as in the C. elegans dauer larval form), to express their effect. Similarly in humans, we must beware of attempting to understand the action of alleles associated with specific age-associated diseases such as the ε4 allele of apolipoprotein E without considering how the specific environment of modern society may be crucial to gene expression. 3) It has provided stimulus and direction for empirical research both by enforcing a comparative perspective which encourages the development of new animal models of the aging process, and by looking for secondary, possibly deleterious, early life effects of alleles otherwise associated with increased longevity.

LECTURES: GENETICS OF AGING

The genetics of successful aging G. De Benedictis1 and C. Franceschi2 Biology Department, University of Calabria, Cosenza, 2Biomedical Sciences Department, University of Modena, Modena, Italy

1Cell

To explore the role of inherited factors in successful aging it may be useful to take into account the model outlined in Figure 1, where genes affecting aging are considered, and attention is paid to the frequency of the variant in the gene pool. The majority of these genes could carry polymorphisms shaping the homeostatic capability by which the organism is able to respond to age-related environmental blows (for example, somatic mutations). Some alleles will be frail, others robust, thus predisposing to or, alternatively, protecting from late-onset multifactorial diseases. Consequently, frail and robust alleles will form a critical genotypic network for

Aging Affecting Genes Mutations

Polymorphisms

Mutations

Life span shortening

Homeostatic functions

Life span lengthening

Frail alleles Robust alleles Epistatic suppressors 1

Epistatic suppressors 2

Hypostatic genes

Figure 1 - A hypothetical model of aging affecting genes.

unsuccessful or successful aging. However, the genes affecting aging may also carry mutations: one could induce premature aging and life span shortening, another could delay aging and life lengthening. The former would be epistatic over all the others, since they would prevent the phenotypic expression of other genes due to premature death. Werner's disease mutations (1) could be an example. On the contrary, mutations which induce life lengthening would be hypostatic with respect to all the others; indeed, a genotypic network poor in frail alleles and, possibly, rich in robust alleles may be necessary to allow these mutations to manifest themselves. According to this model, polymorphisms would play an important role in successful aging. We are carrying out a widespread research aimed at the identification of frail and robust alleles that form the genotypic network predisposing to or preventing from successful aging. Polymorphic markers located inside candidate loci (Table 1) are compared between healthy centenarians, the best example of successful aging, and younger individuals from the same population. APOB, THO and mtDNA have shown a clear association with successful aging. As for APOB locus, a significant age-related change in the genotypic pool has been observed: the frequency of homozygous SS genotypes [S are 3’APOB VNTR alleles with less than 35 repeats, (2)] tends to increase as the age of the cohort increases, and then decreases starting from 50-60 years (p