We genotyped the four common hTERT variants, with a minor allele frequency (MAF) of >5% [IVS1 187T>C, 973G>A (Ala-305 Ala), 3097 C>T (His-1013 His), IVS16+99 C>T], in 73 centenarians and 49 controls. Information on telomere length was available for all these individuals. We did not find an association of the IVS1 187 T>C, 973 G>A (Ala-305 Ala), and IVS16+99 C>T with longevity. However, significant associations were detected with the 3097 C>T (His-1013 His) variant: the T allele is significantly enriched in centenarians (21.8%) compared with controls (8.2%; P = 0.026) (Table 3), and both CT and TT genotypes are significantly enriched in centenarians compared with controls (26.Offspring and controls' lipid profiles are known predictors of age-related diseases. Previously, we demonstrated that centenarians and their offspring have significantly larger HDL and LDL particle sizes, which are heritable phenotypes associated with a lower prevalence of morbidity. Our findings indicate that longer telomeres are associated with a lower prevalence of hypertension, metabolic syndrome, type 2 diabetes, better cognitive function, and healthier lipid profiles. 

Discussion: Several studies have highlighted a close relationship between telomere length and lifespan in humans, including long-lived humans. However, the interpretations of results from these studies are often confounded by a lack of adequate controls. To overcome this shortcoming, we employed a unique study design in a cohort of Ashkenazi Jewish individuals with exceptional longevity (centenarians), their offspring (approximately 70 years old), and age- and gender-matched controls without a family history of unusual longevity. Using the offspring of individuals with exceptional longevity and their matched controls provides a powerful approach to identify genetic factors associated with healthy aging.

Telomere length is a quantitative trait that is fairly well studied, but the genetic factors that influence it are not well understood. Recent studies suggest that heterozygote mutations in hTERC and hTERT genes, which are essential components of telomerase, show defective phenotypes in several diseases, indicating that half the usual dose of telomerase is inadequate for maintaining telomeres with normal length. Because living to 100 years is a rare phenotype in humans, with a prevalence of 1 in 10,000 individuals in the general population, we hypothesized that centenarians may harbor rare gain-of-function mutations in the telomerase genes that may also influence the length of telomeres.

Sequence analysis of hTERT and hTERC genes revealed that rare synonymous or intronic variants are enriched in centenarians compared to controls. In contrast, centenarians are completely devoid of nonsynonymous variants, whereas there are two control individuals who carry heterozygote nonsynonymous variants, 893 G>A (Ala-279 Thr) and 3148 G>A (Ala-1050 Thr). Although these nonsynonymous changes are predicted to be functionally benign, they are also found in idiopathic pulmonary fibrosis (IPF) patients with a minor allele frequency (MAF) of 5%, raising the possibility that these variants may have negative functional effects.

Our study also revealed that common genetic variations in hTERT may influence the telomere length maintenance associated with longer telomeres in families with exceptional longevity. The expression level of hTERT is a major determinant of telomerase activity. Recent studies indicate that telomerase activation can be regulated by environmental interventions such as lifestyle changes or stress management. There are functional hTERT promoter variants known to influence telomerase expression and telomere length. However, because there is very little linkage disequilibrium in the gene, it is unlikely that the centenarian-enriched rare variants are proxies of functional hTERT variants in the promoter. It is tempting to speculate that the rare variants might influence expression of hTERT in response to environmental stresses such as inflammation or oxidative stress, which then promotes better maintenance of telomere length. Indeed, mean telomere length is much greater among the carriers of the rare variant compared with the non-carriers after adjusting for age and gender [telomere repeat copy number to single-copy gene copy number (T/S) ratio of 0.62:0.41, crude difference = 0.21; P = 0.02 by Student t-test, P = 0.037 by Mann-Whitney U test], raising the possibility that these rare variants may have a positive functional impact on telomere maintenance.

Haplotypes of the hTERT gene derived from four common variants showed associations with longevity and/or telomere length. These are two intronic variants, IVS1-187 T>C and IVS16+99 C>T, and two synonymous variants, 973 G>A (Ala-305 Ala) and 3097 C>T (His-1013 His). These common variants may contribute to the regulation of gene expression. A common intronic variant of hTERT shown to be associated with susceptibility to IPF may also affect the expression levels of hTERT. Taken together, our study demonstrates that centenarians may harbor individually rare but collectively more common genetic variations in genes involved in the telomere maintenance pathway, implicating a role of regulatory variants in healthy aging.

Quantitative polymerase chain reaction (qPCR) was used to measure relative telomere length. Two sets of qPCR reactions using 2 L of each DNA dilution were carried out in a 20-L volume using the LightCycler FastStart DNA Master SYBR Green kit (Roche Diagnostics), with MgSample Previously Measured