What are telomeres and how do they function?

Here we’ll run through a brief 101 of telomeres: what they are, how they function and what can happen when they don’t work as they should…

What are telomeres?

Our chromosomes have protective structures located at their ends called telomeres. These protect our chromosomes by preventing them from damage or fusion with other chromosomes.

Telomeres are made up of thousands of repeats of the same DNA sequence, bound by a special set of proteins called shelterin. They are often described using the helpful analogy of an aglet of a shoelace, which prevents the end of the lace from fraying.

It is normal for telomeres to shorten as we age. In some individuals the length is abnormally short or the shortening process is accelerated (in some cases both issues can occur).

What happens to telomeres during cell division?

Every time a cell divides, each chromosome needs to be duplicated to provide a copy of genetic information for the new cell. However, the very end of each chromosome cannot be copied. Therefore, every time a chromosome is duplicated the telomeres become shorter.

Telomeres therefore act as a buffer to ensure that the important genetic information coded on the chromosome is protected and doesn’t get lost during replication.

To protect the genetic information, critically short telomeres act as a signal for the cell to stop dividing or die.

How is telomere length regulated?

So that telomeres don’t shorten too quickly, resulting in early cell death (or premature biological aging), an enzyme called telomerase acts to replenish the telomere repeat DNA sequences at the ends of the chromosomes. This maintenance of the telomeres ensures the genetic information is continually protected and the cell can continue to divide normally.

What happens when something goes wrong?

In some individuals this process doesn’t work as smoothly. It may be that the telomeres are inherently shorter. Or it could be that the telomere shortening process is accelerated. In fact, it could be a combination of these factors. Perhaps the telomerase enzyme is not working correctly to maintain a healthy telomere length or the telomere protective structure is defective.

In Telomere Biology Disorders (or TBDs) the extension, replication or maintenance of telomere length or structure is affected.

The range of symptoms of TBDs is varied, as cells with short telomeres can affect any of the organs in the body. For instance, in the case of pulmonary fibrosis it is the lungs that are primarily affected. Individuals with dyskeratosis congenita can experience many different symptoms, but bone marrow failure is one of the most common.

There are an increasing number of known genetic mutations that result in short telomeres and TBDs, however in a significant number of cases we still don’t know the root cause of the TBD. For these cases in particular, telomere length testing can play a vital role in diagnosis and treatment management.

You can find out more about telomere biology disorders and why telomere testing can be an important diagnostic and treatment guidance tool here.