What you carry at this position in your DNA and what research says about it.
Telomere and Cancer Risk: 8/10 evidence, 80 publications.
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Sample genotype (not yours): C/C
Higher Cancer Risk but Lower Fibrosis Risk
This genotype is associated with longer telomeres, which promotes cellular longevity but increases the risk of brain and lung cancers. However, it offers significant protection against progressive lung scarring.
What this genotype means: Increased risk of glioma; Increased risk of lung adenocarcinoma; Lower risk of pulmonary fibrosis.
Sample genotype (not yours): A/A
Higher Fibrosis Risk but Lower Cancer Risk
This genotype is associated with shorter telomeres, which accelerates cellular aging and increases the risk of lung scarring and testicular cancer. However, it provides strong protection against brain and lung cancers.
What this genotype means: Increased risk of pulmonary fibrosis; Increased risk of testicular cancer; Lower risk of glioma.
Sample genotype (not yours): C/A
Higher Risk for Both Cancer and Fibrosis
Carrying one C allele and one A allele gives intermediate telomere length, but because each allele raises the risk of a different condition, you carry a modestly elevated risk of both certain cancers and lung scarring rather than a protective balance.
What this genotype means: Moderate risk of glioma; Moderate risk of pulmonary fibrosis; Not protected against either cancer or fibrosis.
Gene function and biological role
Gene Function: The TERT gene encodes the catalytic subunit of telomerase, an enzyme essential for maintaining telomere length [1]. Telomeres act as protective caps on the ends of chromosomes, preventing genomic instability during cell division [1]. While telomerase activity is typically low in adult tissues, its reactivation can lead to cellular immortality and tumor growth [2]. Conversely, insufficient telomerase activity leads to accelerated telomere shortening and tissue degeneration [3]. This creates a fundamental biological trade-off between cancer risk and cellular aging [2].
Variant Impact: The rs2736100 variant is an intronic change in the TERT gene that modulates telomerase expression and telomere length [1]. Carrying the C allele is associated with longer telomeres, which supports cell longevity but increases the risk of various cancers [2]. In contrast, the A allele is linked to shorter telomeres, which protects against certain cancers but increases susceptibility to degenerative diseases [3]. This variant is one of the most prominent examples of genetic pleiotropy, where a single change has opposing health effects [4].
Key Insight: This variant represents a direct evolutionary trade-off where alleles that protect against cellular aging and lung scarring simultaneously increase the risk of brain and lung cancers.
Location: TERT. Chromosome 5 · 5p15.33 · 1.3 Mb
Estimated prevalence by population
Global 23.4%; European 25.4%; African 21.3%; East Asian 16.9%; South Asian 34.7%; Americas 16.2%; Ashkenazi 30.6%; Finnish 23.1%; Middle Eastern 46.6%; Amish 28.2%.
Estimated CC genotype frequency.
Global 49.6%; European 50.0%; African 49.7%; East Asian 48.4%; South Asian 48.4%; Americas 48.1%; Ashkenazi 49.4%; Finnish 49.9%; Middle Eastern 43.3%; Amish 49.8%.
Estimated CA genotype frequency.
Global 27.1%; European 24.7%; African 29.0%; East Asian 34.6%; South Asian 16.9%; Americas 35.7%; Ashkenazi 20.0%; Finnish 27.0%; Middle Eastern 10.1%; Amish 22.0%.
Estimated AA genotype frequency.
Showing effects for C/C genotype
Cancer & Oncology
Brain & Nervous System Cancers
Glioma. Evidence: 8/10. Source: PMID 19578367. ~1.6x Higher Risk.
Lung Cancer
Lung Cancer. Evidence: 8/10. Source: PMID 27501781. ~1.34x Higher Risk.
Urologic Cancers
Testicular Cancer. Evidence: 7/10. Source: PMID 20543847. Typical Risk.
Organ Systems
Respiratory Health
Pulmonary Fibrosis. Evidence: 6/10. Source: PMID 18835860. Typical Risk.
Showing effects for A/A genotype
Glioma. Evidence: 8/10. Source: PMID 19578367. Typical Risk.
Lung Cancer. Evidence: 8/10. Source: PMID 27501781. Typical Risk.
Testicular Cancer. Evidence: 7/10. Source: PMID 20543847. ~1.33x Higher Risk.
Pulmonary Fibrosis. Evidence: 6/10. Source: PMID 18835860. ~2.1x Higher Risk.
Showing effects for C/A genotype
Glioma. Evidence: 8/10. Source: PMID 19578367. ~1.3x Higher Risk.
Lung Cancer. Evidence: 8/10. Source: PMID 27501781. Slightly Increased.
Testicular Cancer. Evidence: 7/10. Source: PMID 20543847. Slightly Increased.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Having two copies of the C allele leads to higher telomerase activity and longer telomeres [1]. While longer telomeres prevent premature cellular aging, they also allow cells to divide indefinitely, increasing the risk of cancers like glioma [2] and lung adenocarcinoma [3]. Conversely, this genotype is highly protective against degenerative conditions like idiopathic pulmonary fibrosis [4]. It is also associated with a lower risk of testicular cancer [5].
Increased risk of glioma; Increased risk of lung adenocarcinoma; Lower risk of pulmonary fibrosis.
Sample genotype: AA (Homozygous)
Having two copies of the A allele is linked to lower telomerase activity and shorter telomeres [1]. Shorter telomeres accelerate cellular aging and tissue degeneration, significantly increasing the risk of idiopathic pulmonary fibrosis [2] and interstitial lung disease [3]. This genotype is also associated with an increased risk of testicular germ cell tumors [4]. However, the rapid aging of these cells makes them less likely to become cancerous, resulting in a lower risk of glioma [5] and lung adenocarcinoma [6].
Increased risk of pulmonary fibrosis; Increased risk of testicular cancer; Lower risk of glioma.
Sample genotype: CA (Heterozygous)
Carrying one C allele and one A allele produces intermediate telomerase activity and roughly average telomere length [1]. Because the C allele raises cancer risk while the A allele raises fibrosis risk, this heterozygote carries a risk allele for each condition and is therefore modestly elevated for both glioma [3] and idiopathic pulmonary fibrosis [4], with protection on neither axis. This differs from the two homozygotes, each of which trades a higher risk on one axis for a lower risk on the other; the heterozygote instead sits at a moderate but elevated risk for both.
Moderate risk of glioma; Moderate risk of pulmonary fibrosis; Not protected against either cancer or fibrosis.
Variants with shared genetic architecture
rs2242652 · TERT Gene · Chr 5 · Cancer Risk Trade-offs
rs2735940 · TERT Gene · Chr 5 · Colorectal Cancer Risk
rs2853677 · TERT Gene · Chr 5 · Cancer Susceptibility
hTERT cancer risk genotypes are associated with telomere length.
Variants near TERT and TERC influencing telomere length are associated with high-grade glioma risk.
Variants near DMRT1, TERT and ATF7IP are associated with testicular germ cell cancer.
Genome-wide association study identifies five susceptibility loci for glioma.
Genome-wide association study identifies multiple susceptibility loci for pulmonary fibrosis.
Content updated August 2026.
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