Predicting onset of Alzheimer’s with a simple blood test

In recent years we are seeing the development of an increasing number of tests that rely on a simple blood sample to predict the onset of disease

Predicting the onset of Alzheimer’s with a simple blood test

In recent years we are seeing the development of an increasing number of tests that rely on a simple blood sample to predict the onset of disease before it has shown any symptoms. Previously we have reported on how blood tests can screen for cancer. Now we will see how they can help predict the onset of Alzheimer's.

ALZHEIMERS

Over 50 million people live with dementia globally, and this is likely to double in just 10 years' time. About 70% of this is caused by Alzheimer's, a chronic neurodegenerative disease with devastating outcomes that is actually quite poorly understood. Though the symptoms of Alzheimer's can be quite noticeable, in particular short term memory loss, behavioural changes, mood swings and the loss of a persons ability to care for themselves, it is difficult to definitively diagnose without samples of brain tissue. When examined under a microscope it is possible to see the presence of amyloid deposits. These misfolded proteins form plaques that are near impossible for the body to destroy, resulting in loss of neuronal function and a slow decline in the person’s cognitive ability.

Unfortunately, this has not led us to any concrete knowledge of how the disease actually progresses, nor the risk factors involved. Current research has suggested a wide range of risk factors, from age, genetic heritability, mutations in the APOE4 gene, head trauma, even general inflammatory states. However, this is not of much clinical use, since the diagnosis is made primarily from the patients clinical history, behavioural observation and supporting evidence from relatives. CT and MRI scans can be useful in looking at cerebral changes, but cannot pick up on the amyloid deposition often found in post mortems.

BIOMARKERS

In the early stages preceding Alzheimer's – Mild Cognitive Impairment – it is possible to detect key pathological hallmarks in a patient's Cerebrospinal Fluid. This fluid surrounds the brain and spinal cord and can be detected through a lumbar puncture to tap this fluid, or by PET-CT scans. Both of these tests are based on the knowledge of amyloid plaques, and the AB and tau proteins responsible for creating these plaques, but both tests also have their limitations. Lumbar punctures are quite invasive, requiring the insertion of a needle very close to a person’s spinal cord, and PET-CT scans are quite costly and not easily available.

This is where blood-based biomarker tests come in. Using a simple blood test, it may be possible to detect the presence of AB, Tau and Neurodegeneration markers in the plasma of Alzheimer's patients. A recent study published in Nature Ageing by researchers at the Lund University of Sweden looked at 573 patients with Mild Cognitive Impairment. They found that certain biomarkers could predict the decline of a person’s cognitive ability up to years in advance and whether they were at risk of developing Alzheimer's Dementia in that interval.

So what does this mean for clinical practice? As with all things related to Alzheimer's, the news is not always pleasant. There is currently no cure for Alzheimer's, nor are the medications particularly effective in the long term. But what this test could provide is time. Time can be precious, particularly in the face of inevitability. Granting a patient an extra four years to sort out affairs, prioritize time with family, and make the most of living before the effects of Alzheimer's set in, to that patient it may be the most important four years they gain.