In this blog we examine what short telomeres are and what short telomere syndromes can mean for certain individuals.
What are telomeres for?
Our chromosomes need to be protected to prevent damage, or them fusing with other chromosomes. Telomeres are the protective structures found on the end of chromosomes. They are made up of thousands of repeats of the same DNA sequence, bound by a special set of proteins called shelterin.
During cell division each chromosome is copied, however, the very end of each chromosome cannot be duplicated with a little lost every division. The telomere at the end of the chromosome acts as a buffer to ensure that the important genetic information coded on the chromosome doesn’t get degraded.
What do short telomeres mean?
Telomeres shorten naturally as we age.
In some individuals the average telomere length in cells is abnormally short or the shortening process is accelerated (in some cases both issues can occur). This can have an effect on the fitness of our cells.
There is not a one-size-fits-all for the length of short versus healthy (or even long) telomeres, because what is considered healthy varies with age.
When measuring telomere length, it is therefore very important to compare length to an age matched control group. We report all patient telomere lengths against a telomere reference curve – available for all ages from pediatric to geriatric. Read more here.
Using these reference curves when presenting telomere length results enables us to present the telomere length against a range of percentiles for that age.
Very low telomere length would be in the 1st percentile for that particular age or below, whereas the healthy range of telomere lengths would fall between the 10th and 90th percentiles.
What are short telomere syndromes?
In cases where telomere length measurements are found to be in the lowest percentiles, it may be an indication that the individual has a short telomere syndrome (STS). These syndromes are defined by genetic deficits affecting telomere maintenance and by the presence of very short telomeres.
Short telomeres caused by a genetic defect can affect any organ in the body – so symptoms and disease presentation can vary from individual to individual.
There are 15 known genes which can experience damaging mutations, or other abnormalities, that can cause very short telomeres (for example the telomerase genes TERC and TERT). However, there remain cases when an individual has very short telomeres but no genetic defect can yet be found.
Short telomere syndromes can also be called telomere biology disorders (TBDs). Find out more here.