What is a biomarker?
Biomarkers (short for ‘biological markers’) are characteristics of the body that can be objectively measured1 – like body temperature or blood pressure.
They play a crucial role in medical research, diagnosis of disease and treatment by:2
- Helping scientists evaluate the efficacy and safety of medicines and understand how diseases affect the body.
- Providing clinicians with vital information to diagnose and manage health conditions more effectively.
Why are biomarkers important in Alzheimer’s disease?
Alzheimer’s disease (AD) is a highly complex disease. However, the more we learn about biomarkers of AD, the more our understanding of the disease – and how to accurately diagnose and manage it – improves.
While biomarkers to confirm AD are not yet widely used by doctors in caring for their patients,3 they already play an important role in research.4 Doctors and scientists are excited about the potential impact AD biomarkers could have on improving care for people with AD.
It is hoped biomarkers could help to:
Support earlier, more accurate diagnosis
Today, the diagnosis of AD is largely based on symptoms that individuals and their families describe to their doctor and measure through memory tests, as well as tests to exclude other illnesses.5 However, because symptoms are less noticeable in the early stages or are attributed to normal aging, an accurate early diagnosis can be challenging.6
Biomarker testing could help overcome this challenge, as changes in AD biomarkers occur decades before symptoms are noticed.7,8
Monitor the progression of the disease
Measuring changes in biomarkers can help us to understand how quickly a person’s disease is advancing – and, potentially, predict how it may develop in the future.9,10
Biomarkers are already used for this purpose in clinical trials.9 Broader use of biomarker monitoring could help doctors to build personalized care plans for people living with AD.11
Measure response to treatment
Measuring changes in AD biomarkers may also allow doctors to detect early signs that a person is – or is not – responding to a medicine10 and adjust their treatment as needed.
This plays an important role in clinical trials today and will become more important for doctors and people with AD as disease-modifying treatments become available.2,11
Which biomarkers can be used to diagnose AD?
There are several biomarkers in AD, with the list growing along with our knowledge of the disease. Two of the main hallmarks and earliest signs of AD are amyloid ‘plaques’ and tau ‘tangles.’12
Hallmarks of AD
Two of the main hallmarks and earliest signs of AD are the beta-amyloid ‘plaques’ and tau ‘tangles’ that develop in the brain.12
Beta-amyloid and tau are proteins produced as a normal part of the brain’s functioning.13,14,15 However, in people with AD:
- There is an excessive production of beta-amyloid proteins or their clearance decreases; these lead to the build-up of clusters or ‘plaques’ around brain cells11, preventing the cells from functioning normally and causing them to eventually die.
- Tau proteins become misfolded and eventually form ‘tangles’ within the brain cells, causing them to die.11
The established biomarkers used today accurately measure those proteins and help diagnose AD.12
How are these biomarkers currently tested?
Brain Scanning
There are different types of brain scans. Some inform us about the shape or size of the brain/brain areas like CT and certain MRIs. Other brain scans inform us about how the brain works including functional MRIs and certain PET scans. In AD, PET scans allow us to look at the brain to see if beta-amyloid plaques and/or tau tangles have formed, how much of them are present in the brain and how they increase over time (i.e., since a previous scan).2
This form of testing may not be the most practical tool for widespread use due to its cost, limited machinery, testing time and small risk associated with exposure to radiation.16,17
Cerebrospinal Fluid Testing
The cerebrospinal fluid is a clear, watery fluid that surrounds the brain and spinal cord.
It is thought that the build-up of beta-amyloid plaques and tau tangles in the brain changes the amount of these proteins in the spinal fluid.18 By testing the level of beta-amyloid and tau proteins in the spinal fluid, we can understand if AD is developing in brain14 and potentially detect the disease earlier.
A spinal tap (or lumbar puncture) is a minimally invasive medical procedure used to collect spinal fluid performed by healthcare professionals. Associated risks are minimal; the most common side effects are headache and back soreness.18
How can biomarkers support earlier diagnosis in the future?
One of the priorities for scientists working in AD is to develop faster, less invasive and widely accessible blood tests to measure AD biomarkers.
With a simple blood test, there is potential to conduct AD testing on a much broader scale. Initially, it could enable doctors to determine if AD could be the cause of a person’s symptoms – and transfer them to specialist care for further tests to confirm a diagnosis. In the future, it may even support screening for AD before symptoms appear.
Advancing the Scientific Understanding of AD
Thanks to the collaborative efforts of patients and caregivers, healthcare professionals, academics, research institutions and industry partners around the world, significant progress is already being made towards this goal.
Together with the community, we will continue to advance the scientific understanding of AD and find better ways to diagnose, monitor and treat the condition. By bringing these pieces together, our hope for the future is to create a tomorrow where neurological disorders no longer limit human potential – to help preserve what makes people who they are.