In this blog, we will give a general introduction to biomarkers, including what they are and how they can be used. Then, in the next blog, we will explore biomarkers being studied for MND.
What is a biomarker?
Biomarkers are biological markers in the body, such as molecules or processes, that can be measured or observed. They are used to help to find out if there are changes happening in the body and why this may be. There are many different types of biomarkers, and they are used for lots of different things, some of which we will explore in this blog.
Body fluids, such as the blood, urine and cerebrospinal fluid (CSF), are a really good source of biomarkers in the body. They contain lots of molecules that can be measured to show changes in the body, such as proteins (find out more about proteins in our previous blog).
Here are some common examples of biomarkers found in the blood:
As well as fluid-based biomarkers, there are lots of other types of biomarkers in the body, some of which you might be familiar with:
Body temperature can be a biomarker for having a fever, indicating an infection.
Blood pressure is a biomarker for how hard the heart is working.
Amyloid plaques are a biomarker for Alzheimer’s disease, and these can be detected on brain scans.
What are biomarkers used for?
Biomarkers are really useful in healthcare because they help to explain what’s happening in the body. Click on the drop-down menu to find out more about some of the potential uses of biomarkers.
Diagnosis
Biomarkers can be used to help find out what is wrong with you. If a specific marker, or group of markers, can be used to tell the difference between someone with and someone without a particular disease, it can speed up the diagnostic process. One biomarker by itself might not be enough to tell the difference between similar diseases and in these cases, a biomarker signature might be needed. This is when a group of biomarkers are all used together to determine whether someone has a particular disease. Only when all of the biomarkers are changed in a specific way, can the diagnosis be made.
Monitoring disease over time
Tracking a disease over time is very important. Biomarkers can be used to show if a disease is getting worse, staying the same or getting better. As the levels of the biomarker change over time, it can show how the disease is progressing over time.
Monitoring treatment response
Similarly to monitoring disease progression over time, changes in the levels of biomarkers can be used to tell how effective a treatment is at helping a particular disease. For example, if a patient is prescribed a medication to lower their blood pressure and the blood pressure is taken before and after treatment, if the blood pressure has gone down it indicates that the treatment has worked.
Predicting disease risk
Some biomarkers can be used to determine if you are at a higher risk of developing a particular disease before you develop it. For example, if cholesterol levels are found to be too high in a blood test, it shows that the patient has a higher risk of heart disease.
Predicting disease prognosis
Prognosis is a prediction of how a disease might develop in the future. Sometimes, a disease can progress very quickly in one person but slowly in another. Biomarkers can be used to help to predict how the disease will develop in an individual.
Early detection
The symptoms of a particular disease might not show until the disease has progressed, at which point treatment might be less effective. By screening for a disease using biomarkers, it can help to identify disease in the early stages so that treatment can start sooner. An example of this is bowel cancer screening by the NHS, which tests for blood in the stool. This is a biomarker that could be a sign of bowel cancer and it prompts further investigation to hopefully diagnose and treat it earlier.
What makes a good biomarker?
Key features of a good biomarker are specificity, practicality, stability and reliability. This essentially means that the biomarker can identify a specific condition, be easy to obtain, remain present until it can be measured, and be consistent across different people with the same disease. Click on the drop-down menu to find out more about things that make a good biomarker.
Specificity
Biomarker specificity is all about how good a biomarker is at correctly identifying one specific disease or condition, and not getting it confused with others. A very specific biomarker can only be detected if specific disease is present, and it won’t be found in people who don’t have the disease. A good example of a specific biomarker is the genetic material from the SARS-CoV-2 virus that is detected by polymerase chain reaction (PCR) as a test for COVID-19. The test detects genetic material from the virus itself, so a positive test is very unlikely to be anything else, making it highly specific to COVID-19.
Some biomarkers can still be useful even if they are not specific for just one disease. For example, to confirm whether someone has muscle wasting, a blood test showing higher than average amounts of a molecule called miR-206 would confirm this. However, elevated miR-206 expression is seen in lots of muscular conditions, including MND, Duchenne muscular dystrophy and spinal muscular atrophy. Therefore, higher levels of miR-206 are not a specific biomarker for MND.
Practicality
Some fluid biomarkers are a lot easier to collect and less invasive for the person being tested. For example, urine and saliva are very easy to collect, at any time or place, without the need for a medical practitioner. Blood samples are a little harder to obtain because they need a healthcare professional to collect the sample, but they are still relatively easy to obtain and non-invasive. CSF, which is the fluid that surrounds the brain and spinal cord, is a lot harder to collect. It is usually collected by lumbar puncture, where a needle is inserted into the spine. This requires highly skilled medical professionals to perform the procedure, and the process comes with some risks of damaging the spinal cord. The easier a biomarker is to obtain, the more likely it is that it will be able to be used in standard medical practice.
Stability
When a sample is collected to measure biomarkers, it needs to be able to be stored and transported to a laboratory for testing. Sometimes, it is not possible to process a sample straight away and it will need to be stored at room temperature or in a fridge or freezer. There is no use looking at a biomarker that will break down as soon as it is removed from the body, as there will be nothing to measure when the sample gets to the lab. Some types of biomarkers, called RNAs, are really stable in the blood and CSF, so they can be measured in the laboratory.
Reliability
Before a biomarker can be used routinely in people, it has to first undergo extensive testing in a laboratory. This gathers as much evidence as possible to show that the biomarker is likely to show the same thing when used in humans. A reliable biomarker is one that is able to accurately detect disease time and time again in samples from people. If a biomarker is unreliable, then it may show disease in one person but not in another, even though they both have the disease.
How are new biomarkers found?
Biomarkers offer a lot of potential for managing different conditions, including speeding up diagnosis, improving prognosis predictions and helping drug development. To identify new biomarkers, researchers need to collect lots of biological samples from people with the condition or disease, people with similar conditions (sometimes called disease mimics) and healthy people. This enables them to look for differences between the samples and find unique signatures, or ‘fingerprints’, that are changed only in the disease.
Biomarkers can be an incredibly useful tool for diagnosing disease and monitoring disease progression. You can find out more about biomarkers for MND in the next blog.
The MND Association’s vision is a world free from MND. Realising this vision means investing more in research, further developing partnerships with the research community, funding bodies and industry, while ensuring that advances in understanding and treating MND are communicated as quickly and effectively as possible.
