Elsevier

Experimental Gerontology

Volume 41, Issue 8, August 2006, Pages 727-736
Experimental Gerontology

Family clustering in Sardinian longevity: A genealogical approach

https://doi.org/10.1016/j.exger.2006.05.009Get rights and content

Abstract

This paper aims to discuss the validation and family determinants affecting the longevity of Sardinian centenarians, using a genealogical approach. This preliminary study presents the first results of a genealogical tree reconstruction of selected centenarians aged 105 and over, from certain areas. These are mostly situated in the province of Nuoro, an area with the highest rate of centenarians and where the female-to-male sex ratio tends to be male-biased. An accurate centenarian age validation was performed that required a meticulous examination of numerous civil status records and parish registers. An important finding was that longevity occurs among the ascendants of a particular branch of the family. The data used are still provisional but, should it apply to other validated cases, it would provide empirical evidence of a genetic component in longevity. A more thorough examination of the data available may yield deeper insights into the role played by endogamy and consanguinity.

Introduction

The oldest old have recently enjoyed steady growth in life expectancy. The number of centenarians has approximately been doubling every 10 years since 1960 as a result of the growing numbers of over 80-year-olds in the population (Vaupel and Jeune, 1995, Wilmoth et al., 2000, Robine and Caselli, 2005). Centenarians appear to be a unique model to investigate the biological and non-biological determinants of aging and longevity as well as how these intertwine (Baggio et al., 1998).

This paper is part of the multidisciplinary and multipurpose research project, “A demographic analysis of Sardinian Longevity-AKEa2”.1 It aims to document and verify the remarkable pattern of low mortality among 80 and over year-old Sardinian males and to explore the underlying reasons (Caselli and Lipsi, 2005). A large number of exceptionally old men (aged 100 and over or 105 and over) live in Sardinia and the sex ratio among centenarians is unexpectedly low, particularly in the inland municipalities of Nuoro province (Poulain et al., 2004).

The Sardinian population of the 2001 census (October 21) was roughly 1,631,880, including 187 centenarians (53 men and 134 women), with a ratio of 1.2 centenarians per 10,000 inhabitants (compared to 1.0 for Italy) and a centenarian female-to-male sex ratio of 2.5:1. Elsewhere in Italy, the centenarian sex ratio is slightly over 5. In other low mortality countries, it ranges from 5 to 7 (Robine and Caselli, 2005). In certain pockets of Sardinia, the female sex ratio is even lower, in some areas it hovers only slightly above 1 (Poulain et al., 2004).

The demographic history of Sardinia is striking. The cohorts born at the turn of the 20th century, i.e., the cohorts subject to this study, experienced a particularly interesting life-course.

They saw the lowest infant (and especially neonatal) mortality rates recorded in Italy at that time and stillbirth rates lower than the national average (Pozzi, 2000) even though the maternal mean age at birth was particularly high. However, after age 2, the risk of dying during childhood and youth was substantially higher for Sardinian cohorts compared to the corresponding cohorts from other Italian regions. Exposure to malaria, which was still endemic on the island at that time, cannot be ignored and deserves further attention.

Genetic selection has occurred over the centuries owing to malaria. This selection can provoke glucose-6-phosphate deidrogenase (G6PD) deficiency, which is double as high for Sardinian centenarians as it is for the rest of the population. Recent research claims that the lack of this enzyme contributes to longevity in Sardinia and to the exceptionally high number of male centenarians (Deiana et al., in press). Preliminary results seem to indicate that this mutation is present in 11.2% female and 25% male centenarians.2

Hence, generations of centenarians have been able to tap into a great vital potential. Struck down by malaria at young ages, the usual selection process was triggered with the elimination of the relatively fragile and the emergence of individuals more robust due to these genetic mutations.

Sardinia has often been the focus of genetic studies as the population exhibits a number of unique features due to their isolation over the centuries and because they stem from a single familial stock (Cavalli Sforza et al., 2004).

It is also interesting that the men from these cohorts were engaged in the First World War, thus experiencing higher probabilities of death (compared to neighboring cohorts not directly involved in the war). Higher male mortality persisted for many years after the conflict ended, as recent research has pointed out. Having undergone further selection due to high mortality at young-adult ages, these cohorts may contain a large number of individuals at the threshold of old age who are particularly robust (Barbi and Caselli, 2003).

Sardinian centenarians are an exceptionally homogeneous group in terms of socio-occupational status, with the men usually having been either peasants or shepherds, and the women housewives, following an age-old tradition handed down from parent to child. In view of the role the socio-occupational variable plays in mortality studies, this is not a discriminatory factor in the study of Sardinian centenarians.

The centenarians exhibited low mobility between their place of birth and current residence. Besides, a relatively high number of centenarians, particularly those aged 105 and over, lived in certain inland areas where environmental risk factors are lower than along the coast. The Italian Ministry of the Environment has listed 691 polluted sites in Sardinia located around the Gulfs of Cagliari and Oristano, in the extreme north-west of Sassari, in the area known as Porto Torres and along the north-east coast of Nuoro.

On Sardinia and particularly inland there is a considerable variation in the frequency of given surnames in different areas of the region (Zei et al., 1986) and in the prevalence of specific territorial surnames, assuming the practice of endogamy in the past. The literature has reported higher infant and child mortality among births from consanguineous marriage (Cavalli Sforza et al., 2004). Thus, we should be surprised to find so many Sardinian centenarians in highly endogamic communities? Does consanguinity generate a selection effect? Do individuals born to an endogamically selected couple have a longer life potential?

These and other considerations led us to believe that Sardinian centenarians are an ideal population group to test the impact of different determinants on survivorship to exceptionally old ages.

Longevity is, broadly speaking, the outcome of various factors of a genetic or environmental nature (early life factors, life style, education, occupation, place of residence, dietary habits, environment, etc.).3 The number of centenarians in developed societies is a fast growing segment of the population and has inspired research into the role played by genetics in longevity. The wide debate on many of the most relevant issues regarding familial longevity continues to date (Bouquet-Appel and Jakobi, 1991). Some authors are playing down the role of genetics in familial longevity and find that familial resemblance plays a minor role to the benefit of social explanations. An impressive and coherent series of epidemiological data in different populations (New England Americans, Mormons, Askenazi Jewsh, Islandic, Okinawan Japanese) indicate the presence of a strong familial and genetic component of longevity (Gudmundsson et al., 2000, Kerber et al., 2001, Perls et al., 2002, Terry et al., 2003, Terry et al., 2004, Atzmon et al., 2006, Schoenmaker et al., 2006, Willcox et al., 2006). These studies demonstrate that parents, siblings and the offspring of long-lived subjects, but not the spouses of the long-lived subjects who shared with them most part of their adult life, have a significant survival advantage, a higher probability to have been or to become long-living and a lower risk regarding the most important age-related diseases, such as cardio- and cerebro-vascular diseases, diabetes and cancer, when compared to the appropriate controls. Thus, longevity is present in many generations of the same families in spite of the great variations in life style and life expectancy of the last century. Moreover, the most recent studies on twins strongly support that genetic effects are important for survival at older ages, and that genetic influences on lifespan are minimal prior to age 60 (Hjelmborg et al., 2006).

Extreme longevity in a centenarian’s family history supports the inheritability of oldest old longevity (Perls et al., 2000). This would imply increased homogeneity among the oldest old and could depend on shared genetic factors. Indeed, recent findings indicate that increased homozygosity at loci involved in human longevity occurs, suggesting two copies of the same allele may favor survival at later ages (Bonafe et al., 2001, Cardelli et al., 2006), this phenomenon likely being more frequent in consanguineous subjects, assuming that such alleles are recessive.

Demography could help to provide deeper insights into the role inheritability plays in longevity, even in the absence of genetic variables. To this end, data are needed to reconstruct the family histories of the oldest old and, in this instance, of centenarians from a distinct geographical area. Next, an analysis of genealogies and family life histories can be performed, using features from individual trajectories to reconstruct the life history of each sibling.

The paper first aims to illustrate the various steps taken to reconstruct the genealogies of centenarians aged 105 and over, using a thorough validation procedure, combining civil and parish data. Individuals aged 105–109 and 110 and over are named “semi-supercentenarians” and “supercentenarians”, respectively. The second aim is to look into the family relationships and the family clustering of Sardinian longevity, using the genealogical trees of the study subjects. To date, 11 genealogical trees have been built. This paper presents the initial results of an ongoing research that should be extended in the future.

Section snippets

Materials

Our sample consists of 207 centenarians (100 men and 107 women) and certainly is representative of a population that only some years previously numbered 310 centenarians (January 1, 1997 to September 15, 2003). The centenarians participating in the AKeA2 project were selected on the basis of their place of birth. Only a small proportion of the centenarian data collected will be used in our study, however. Selected genealogies are examined that typify certain traits of Sardinian centenarians and

Results

As mentioned above, 11 genealogies are complete from the end of the 18th century: six for men and five for women. Of the 11 centenarians, three were born in the province of Cagliari, six in the province of Nuoro, and two in the province of Sassari. The priority selection criteria was age. Naturally, we began with the two individuals aged 110 and over, both males and both born in the Nuoro Province: Antono Todde in Tiana and Giovanni Efisio Emanuele Frau in Orroli. We applied the same criteria

Discussion

The clustering of exceptional survival within families suggests a familial component affecting mortality differences, especially at extreme old ages, as in other centenarian genealogical studies (Robine and Allard, 1997). But of course not all familial effects are genetic. That an exceptional number of persons in the same family reach extreme old ages does not necessarily imply that genetic factors play a role in human longevity. Shared characteristics, such as life style and the environment,

Acknowledgments

The Records and Document Assets Editorial and Information Service of the Sardinian Region has produced microfilms and digitalized images of the parish registers of almost all Sardinian parishes. We thank Maurizio Pirisi, Director of the Sassari office, who placed at our disposal the documentation collected and Susann Backer, editor of the Max Planck Institute for Demographic Research, for her kind help in the language editing.

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