Friederike Flachsbart

Association of FOXO3A variation with human longevity confirmed in German centenarians

The human forkhead box O3A gene (FOXO3A) encodes an evolutionarily conserved key regulator of the insulin–IGF1 signaling pathway that is known to influence metabolism and lifespan in model organisms. A recent study described 3 SNPs in the FOXO3A gene that were statistically significantly associated with longevity in a discovery sample of long-lived men of Japanese ancestry [Willcox et al. (2008) Proc Natl Acad Sci USA 105:13987–13992]. However, this finding required replication in an independent population. Here, we have investigated 16 known FOXO3A SNPs in an extensive collection of 1,762 German centenarians/nonagenarians and younger controls and provide evidence that polymorphisms in this gene were indeed associated with the ability to attain exceptional old age. The FOXO3A association was considerably stronger in centenarians than in nonagenarians, highlighting the importance of centenarians for genetic longevity research. Our study extended the initial finding observed in Japanese men to women and indicates that both genders were likely to be equally affected by variation in FOXO3A. Replication in a French centenarian sample generated a trend that supported the previous results. Our findings confirmed the initial discovery in the Japanese sample and indicate FOXO3A as a susceptibility gene for prolonged survival in humans.

A genome-wide association study confirms APOE as the major gene influencing survival in long-lived individuals

We conducted a case-control genome-wide association study (GWAS) of human longevity, comparing 664,472 autosomal SNPs in 763 long-lived individuals (LLI; mean age: 99.7 years) and 1085 controls (mean age: 60.2 years) from Germany. Only one association, namely that of SNP rs4420638 near the APOC1 gene, achieved genome-wide significance (allele-based P=1.8×10(-10)). However, logistic regression analysis revealed that this association, which was replicated in an independent German sample, is fully explicable by linkage disequilibrium with the APOE allele ɛ4, the only variant hitherto established as a major genetic determinant of survival into old age. Our GWAS failed to identify any additional autosomal susceptibility genes. One explanation for this lack of success in our study would be that GWAS provide only limited statistical power for a polygenic phenotype with loci of small effect such as human longevity. A recent GWAS in Dutch LLI independently confirmed the APOE-longevity association, thus strengthening the conclusion that this locus is a very, if not the most, important genetic factor influencing longevity.

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

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

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

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

Genome-wide miRNA signatures of human longevity

Little is known about the functions of miRNAs in human longevity. Here, we present the first genome‐wide miRNA study in long‐lived individuals (LLI) who are considered a model for healthy aging. Using a microarray with 863 miRNAs, we compared the expression profiles obtained from blood samples of 15 centenarians and nonagenarians (mean age 96.4 years) with those of 55 younger individuals (mean age 45.9 years). Eighty miRNAs showed aging‐associated expression changes, with 16 miRNAs being up‐regulated and 64 down‐regulated in the LLI relative to the younger probands. Seven of the eight selected aging‐related biomarkers were technically validated using quantitative RT‐PCR, confirming the microarray data. Three of the eight miRNAs were further investigated in independent samples of 15 LLI and 17 younger participants (mean age 101.5 and 36.9 years, respectively). Our screening confirmed previously published miRNAs of human aging, thus reflecting the utility of the applied approach. The hierarchical clustering analysis of the miRNA microarray expression data revealed a distinct separation between the LLI and the younger controls (P‐value < 10−5). The down‐regulated miRNAs appeared as a cluster and were more often reported in the context of diseases than the up‐regulated miRNAs. Moreover, many of the differentially regulated miRNAs are known to exhibit contrasting expression patterns in major age‐related diseases. Further in silico analyses showed enrichment of potential targets of the down‐regulated miRNAs in p53 and other cancer pathways. Altogether, synchronized miRNA–p53 activities could be involved in the prevention of tumorigenesis and the maintenance of genomic integrity during aging.

Sirtuin 1 (SIRT1) sequence variation is not associated with exceptional human longevity

The SIR2/Sirt1 gene has been demonstrated as regulating lifespan in many model organisms, including yeast, Caenorhabditis elegans and rodents. These findings render the human homologue, SIRT1, a very plausible candidate as a modifier of human life expectancy. We therefore sought to investigate whether common allelic variation in the SIRT1 gene was associated with human longevity. Five single nucleotide polymorphisms (SNPs), distributed across the entire gene, including the promoter region, were genotyped in our extensive DNA collections of 1573 long-lived individuals (centenarians and nonagenarians) and matched younger controls. Four of the markers were haplotype-tagging SNPs (htSNPs) that defined five common haplotypes. No evidence for an association was detected between any of the tested SNPs and the longevity phenotype at the allele, genotype or haplotype levels. These findings, based on an htSNP approach, suggest that there is no noteworthy influence of SIRT1 sequence variation on exceptional human longevity in the German population. However, this does not rule out the possibility that allelic variants in direct regulators or downstream substrates of SIRT1 could play critical roles in extending lifespan in humans.

Human longevity and 11p15.5: a study in 1321 centenarians

The 11p15.5 chromosomal region (2.8 Mb) is of particular interest as it encloses five genes (HRAS1, SIRT3, TH, INS and IGF2), the variability of which was found to be associated with life extension by association studies. Mostly important, the above genes are homologous of genes that modulate lifespan in model organisms. We scanned the area in four European sample groups for a total of 1321 centenarians and 1140 younger subjects, who shared with centenarians ethnicity and geographical origin, with a set of 239 SNPs. No significant results (P<0.05) have been found on the earlier associated loci (ie, TH, IGF2, INS and HRAS1), and this study could not confirm the earlier findings on each of those genes. A meta-analysis was carried out on the SIRT3 SNP data; a total number of 2461 samples were included, but no positive association was found except for one SNP having a significant effect (rs939915). The same meta-analysis approach has been applied to the other 229 markers, and six SNPs have been found significant for the frequent genotype (rs4073591, DEAF1-rs4073590, KRTAP5-6-rs11040489, rs4930001, TSPAN32-rs800140 and rs16928120). This experience, although unable to confirm the earlier findings of the literature, highlights all the common difficulties of such studies in human longevity. Despite the rather negative findings presented here, the results derived from unprecedented studies involving such a large number of centenarians should be disseminated, thus contributing to set up adequate strategies to disentangle complex and likely heterogeneous phenotypes.

A functional EXO1 promoter variant is associated with prolonged life expectancy in centenarians

Human longevity is heritable with a genetic component of 25-32%. Variation in genes regulating the levels of somatic maintenance and DNA repair functions is thought to modulate the aging process and to contribute to survival at advanced age. We tested 92 non-synonymous SNPs in 49 DNA repair genes for a possible association with longevity in a sample of 395 German centenarians and 411 controls. The obtained association signal in exonuclease 1 (EXO1) was further investigated by fine mapping and mutation detection, leading to the identification of the functionally relevant SNP rs1776180. Our detailed analyses revealed that the C allele of this promoter SNP is significantly enriched in female centenarians. This finding replicated in 455 female French centenarians and 109 controls. The C allele leads to the loss of a binding site for the basic helix-loop-helix transcription factor E47, resulting in higher EXO1 expression. Thus, we have detected a hitherto undescribed role for E47 as a negative regulator of EXO1 transcription and a genetic variant in the EXO1 promoter that counteracts the E47-mediated repression of the gene. Given the survival advantage that is associated with the C allele of rs1776180, EXO1 can be considered a candidate for a novel longevity-enabling gene.

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

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

Role of the toll-like receptor 4 polymorphism Asp299Gly in longevity and myocardial infarction in German men.

In a previous study on Sicilian men, an association of the functional polymorphism Asp299Gly in the TLR4 gene was reported with longevity and a reduced risk of myocardial infarction (MI). Here, we sought to confirm the findings in our extensive collection of 273 long-lived men (95-107 years), 606 male early-onset MI patients and 594 appropriate controls from Germany. Despite sufficient statistical power to replicate the findings observed in the South Italians, our results rule out a noteworthy influence of the TLR4 polymorphism upon human longevity or MI in German men. Therefore, the previously described associations in Sicilians might reflect either population-specific or potentially false-positive results.