Tell Me More about Telomeres

June 9, 2011 by Marta Gwinn, Consultant, McKing Consulting Corp, Office of Public Health Genomics, Centers for Disease Control and Prevention

Researchers, journalists, and inquiring minds want to know more about telomeres, which seem to hold clues to human aging and age-related diseases. Could telomeres provide an answer to questions like “How long will I live?” or “Will I get cancer?”

What are telomeres?

Telomeres are structures at the ends of chromosomes that contain repetitive stretches of DNA. They “seal” chromosomes at the tips, preventing them from unraveling or sticking together. Telomeres also protect a chromosome’s DNA sequence as it is being copied during cell division. Because the enzymes that copy DNA aren’t able to continue to the very end of the sequence, a bit of DNA is lost each time the chromosome is copied. Telomeres provide a buffer that grows shorter every time a cell divides.

Over time, telomeres become so short that cell division stops and the cell dies. This mechanism is thought to restrict the lifespan of cells to a limited number of divisions, making telomere length a measure of aging at the cellular level.

Telomeres and stress

Environmental stress can accelerate telomere shortening. Studies have implicated cigarette smoking, radiation, poor diet, and even psychological stress as causes. A newly published study reported that children who spent a large proportion of their early lives in institutions had shorter telomeres on average than children who received high-quality foster care as part of an intervention study. Previous studies have found telomere shortening in adults who were maltreated as children.

Telomeres and disease

Chromosomes that have lost their telomeres can rearrange or fuse together; these abnormal chromosomes are often observed in cancer cells. In some families, inheritance of exceptionally short telomeres is linked to specific diseases, such as pulmonary fibrosis or bone marrow failure.

Several epidemiologic studies have found that shorter telomeres tend to be associated with diseases that become more frequent with age, including heart disease and cancer. Telomere shortening and chronic diseases could be caused by the same cell-damaging processes, such as oxidative stress and inflammation.

Telomeres and aging

Is telomere length a biomarker for aging? According to a systematic review published last year, the evidence is equivocal. On average, older people have shorter telomeres; however, there is a great deal of variation among individuals. It isn’t clear whether shorter telomeres are just a sign of aging, or whether they contribute to it.

Studies of telomere length and mortality have found mixed results. Very few studies have actually followed people over time to see how changes in telomere length correlated with survival. Several such studies now underway should shed more light on this question.

Telomeres and immortality

Germ cells (eggs and sperm) and stem cells contain an enzyme, telomerase, that restores telomere length. Although it is normally inactive in most other cells in the body, telomerase is activated in cancer cells, making them “immortal.” Although activating telomerase to immortalize normal cells is a theoretical possibility, its feasibility isn’t known.

Testing for telomeres

Research on telomeres is still at an early stage but some entrepreneurs see human curiosity as an untapped market. Last week, a company in the UK announced that it would soon be offering a test of “biological age” based on telomere length to the public for approximately $700 (US). Given the state of the science, it doesn’t sound like a good deal.

Most of the 2,000 or so genetic tests currently available for clinical use are for diagnosing rare disorders, like cystic fibrosis. Many other tests are being developed and marketed directly to the public via the Internet and other media. Tests that are based on very limited scientific information may not be valid or useful. Let the buyer beware!