population had the opportunity to age into middle and older ages. If nearly one fifth of the population had an increased genetic predisposition to survive to 100 years, it is understandable why the number of centenarians is growing at such a relatively high rate.

Although sensitivity and specificity of our classification rule may improve with a more comprehensive knowledge of human genomic variation, its limitations could also suggest that environmental factors (e.g., lifestyle) contribute in important ways to the ability of people to survive to very old ages. Replications of these results in independent cohorts will help to answer these

Materials and Methods

Ethics statement

NECS and Elixir subjects were enrolled under similar protocols approved by Boston Medical Center’s Institutional Review Board and the Western Institutional Review Board, respectively. Written informed consent was obtained for all NECS and ELIXIR subjects.

Study populations

The New England Centenarian Study (NECS) began in 1994 as a population-based study of all centenarians living within 8 towns in the Boston area [81]. Since ,2000, the NECS expanded enrollment to include centenarians from throughout the USA (www.bumc.bu.edu/centenarian). Potential subjects are ascer- tained via voting records and media alerts. Subjects are sent a demographic data, life style choices, medical history and functional status questionnaire, family pedigree form and blood kit. A dementia scale test is administered over the telephone. The study is still actively recruiting centenarians, with an average of 50 subjects enrolled per year.

on the liability scale. In the ELIXIR replication set, the AUC of our genetic risk model is 0.58 and this would represent 1–2% of explained genetic variance. Since the ELIXIR set includes more nonagenarians than centenarians, and their prevalence in the population is 0.5% and the sibling relative risk of this trait is approximately 2.5, we repeated the calculations in this scenario and the 0.58 AUC translated into approximately 4% of the genetic variance in the liability scale. These results show that although we explained a good amount of genetic variability on the liability scale to live to very old ages, there is still more than 80% missing heritability that remained to be explained, and more comprehensive genetic studies have the real potential to decipher the genetic base of this complex phenotype.

2001–2003, Elixir Pharmaceuticals (co-founded by Leonard Guarante and Cynthia Kenyon) conducted a U.S. nation-wide centenarian recruitment effort. Since 2006, Elixir’s centenarian research effort has ceased (and DNA and data are stored and have also been shared with the NECS, where genotyping of all the samples was performed in 2008). Recruitment and data collection were modeled after the NECS protocol.

Some centenarians in our study however lack a genetic signature conducive to exceptional longevity. The strong clustering of exceptional longevity in some of their families suggests that these individuals harbor rare or private alleles associated with exceptional longevity. This in turn would suggest that sequencing these individuals could be particularly fruitful.

NECS controls. The NECS has recruited approximately 450 referent subjects comprised of spouses of centenarian offspring and children of parents who died at the mean age of 73 years, with an age at enrollment ranging between 53 and 90 years.

The specificity of our classification rule is 60–61% in the independent sets and is comparable to other genetic studies of complex traits [76,77,78]. Although the specificity is better than random, it would not be useful as a diagnostic test. The decreased specificity in this study could be explained by the fact that the control subjects from the Illumina database are primarily made up of healthy controls used for other genome-wide association studies and therefore the control data set may be enriched for healthy aging subjects.

Illumina controls. We identified 3,613 Caucasian healthy controls from the Illumina control database (iControlDB, http:// www.illumina.com/downloads/PurposeDocument.pdf). No pheno- typic information is available for subjects selected from the Illumina repository, except for gender (,60% females) and age at blood draw for some subjects (age range 0—75 years).

The Coriell NINDS control sample in the Parkinson’s disease (PD) set is described elsewhere [21].

Subjects from these studies were combined to generate a discovery and replication set using genetic matching (see below) and an additional replication set in which subjects were not genetically matched.

Our finding that about 17% of Illumina controls have signatures with .70% chance of exceptional longevity (Figure S14) suggests that a substantial proportion of this group have a genetic predisposition to exceptional longevity. If this observation is replicated in more representative samples of the population, it could in part explain why centenarians are the fastest growing age group in developed countries [79,80]. At the turn of the last century, infant mortality was approximately 25%. As public health measures markedly reduced infant mortality rates in the first quarter of the 20th century, a greater and greater proportion of the

Discovery set (NECS). This consisted of 801 cases and 914 controls. Cases are long lived individuals from the NECS who were born between 1880 and 1910 and reached an age at death between 95 and 119 (mean 10463, median 104). Controls were comprised of 673 healthy controls from the Illumina database (Illumina I), and 241 referent subjects from the NECS. Controls were selected to match the genetic background of cases.

heterozygosity of the X chromosome and gender recorded in the database.