Two different laboratory measurements of biological aging rate — not how long someone lives, which /conditions/human-lifespan covers separately. The gene that ties them together, TERT, makes telomerase itself, and shows up as the single strongest hit in the epigenetic-clock study.
Solid lines are connections this site curates. Dashed lines mean the two ends share a research paper — worth knowing, and not a claim that one explains the other.
How long someone lives and how "biologically old" their cells measure as, right now, are two different questions. This site's human lifespan page covers the first — genetic variants linked to actual survival, and its own well-supported conclusion that most of that is disease genetics, not an aging process as such. This page covers the second: two laboratory measurements that claim to capture biological aging rate directly, independent of whether or when anyone dies.
Telomeres are the repetitive DNA caps on the ends of chromosomes that shorten with each cell division; when they get too short, a cell stops dividing. Average telomere length, measured across white blood cells, is a heritable trait and has been genetically mapped several times.
The first genome-wide hit, found in 2,917 people and replicated in 9,492 more, was rs12696304 near TERC — the gene for the RNA component of telomerase, the enzyme that rebuilds telomeres. Each copy of the risk allele was associated with roughly 75 fewer base pairs of telomere, described by the study's own authors as equivalent to about 3.6 years of ordinary age-related telomere loss.
A larger follow-up meta-analysis (9,190 people, validated in 2,226 more) confirmed TERC at a second position (rs1317082) and identified two further genes, CTC1 and ZNF676, both directly involved in telomere maintenance biology rather than being a general-purpose finding. A separate study in a Punjabi Sikh cohort — the first telomere-length GWAS done in a South Asian population — added CSNK2A2 and found that shorter telomeres were independently associated with type 2 diabetes and heart disease in that group.
A different approach measures the pattern of chemical tags (DNA methylation) at specific positions across the genome and compares it to population averages for each chronological age — an "epigenetic clock." When someone's methylation pattern looks older than their actual age, that gap is called epigenetic age acceleration, and it has been shown to predict illness and mortality better than chronological age alone in several studies.
The largest genetic study of this measure, in 9,907 people, found its single strongest signal at TERT — the gene for telomerase's own catalytic subunit, the enzyme partner to TERC above. That same paper reports that telomere-length-associated variants relate to this measure too, a direct, stated mechanistic link between the two halves of this page rather than a coincidence of both involving "telomere" genes. Four further genes came out of that same study: KIF13A (two positions), STXBP4, and ZNF248.
A separate, larger meta-analysis (13,493 people) used a different, more widely-used version of the epigenetic clock and reported ten associated positions, including TPMT — the variant this page draws from that study. That paper also found a real methodological split worth stating plainly: one clock variant (Horvath-based) behaved like a stable cellular process, while the other (Hannum-based) correlated with lifestyle factors like smoking, suggesting the two widely-used "epigenetic clocks" are not measuring exactly the same thing.
Neither telomere length nor an epigenetic clock is a clinical test. No guideline uses either to diagnose a condition, predict remaining lifespan, or guide treatment. Commercial "biological age" tests built on these same principles are not validated for individual prediction, whatever they market.
Both measurements are population-level research tools. Telomere length varies enormously between people of the same chronological age for reasons that include cell type, measurement method and simple biological noise; a single genotype shifts the population average by a small, real amount, not an individual reading. Epigenetic age acceleration is younger as a research field, and the 2019 meta-analysis above found that its two most common versions do not fully agree with each other — a sign the underlying biology is still being worked out, not a settled clinical measure.
Conflating "a biomarker that correlates with aging" and "how long someone actually lived" would misstate what each line of research has actually shown. Keeping them on separate pages, and stating why, follows the same discipline the lifespan page already applies to FOXO3 — say plainly what the evidence does and does not support, rather than letting two related ideas blur into one.
What a 23andMe/AncestryDNA export or raw VCF can and can't tell you about Telomere Length and Epigenetic Age Acceleration comes down to these specific, well-studied positions — not a diagnosis.
The studies behind these variants recruited participants from different ancestries — a result found in one population doesn't always transfer to another. Based on 11 of 11 linked studies with a resolved discovery ancestry.
Databases, guidelines and references
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Telomere Length and Epigenetic Age Acceleration. MyGeneLog™. https://www.mygenelog.com/conditions/telomere-length-and-epigenetic-aging
Telomere length is the size of the protective DNA caps on chromosome ends, which shorten with cell division. Epigenetic age acceleration compares a DNA methylation "clock" to someone's actual age. Both are laboratory measurements proposed as biomarkers of biological aging rate, not diagnoses.
No. This site covers actual survival separately, on the human lifespan page, where the genetics turns out to be mostly about specific diseases. This page covers two different lab measurements of aging rate, which are related to but distinct from lifespan itself.
TERT and TERC, the two core components of telomerase -- the enzyme that rebuilds telomeres. TERC anchors the strongest telomere-length signal; TERT is the single strongest epigenetic-age-acceleration signal in the largest study of it, and that same study reports telomere-length variants relate to the epigenetic measure too.
Commercial tests exist, but neither measurement on this page is validated for individual prediction. Both come from population-level research, and no guideline uses either clinically.
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