A new blood test can determine whether someone is likely to develop Alzheimer’s disease an impressive 16 years before noticeable symptoms start to appear. Reporting their findings in the journal Nature Medicine, an international team of researchers found that they could predict whether someone was likely to develop Alzheimer’s based on the level of a specific protein in their blood.
The protein is called neurofilament light change (NLC) and forms part of the internal structure of nerve cells. If nerve cells get damaged, the protein leaks out into the cerebrospinal fluid – the watery fluid that surrounds the brain and spinal cord – and then into the blood. We know that detecting high levels of the protein in cerebrospinal fluid is a good indicator of brain cell damage, but obtaining this fluid requires a spinal tap, which involves inserting a needle into the lower spine and is unpleasant for patients to endure.
So, the researchers decided to see whether raised levels of neurofilament light change were detectable in blood samples.
To conduct their experiment, the team enlisted people from families with rare genetic variants that cause Alzheimer’s to develop at a young age (between their 30s and 50s). Those unlucky enough to inherit one of these variants will most likely go on to develop Alzheimer’s. This gives researchers the chance to look for physical changes that might occur long before any symptoms arise.
The team studied 247 people carrying a genetic variant for early-onset Alzheimer’s and 162 of their relatives who were not. Those carrying an early-onset variant had higher levels of NLC protein in their blood, with this concentration rising over time. In contrast, protein levels remained low and stable in people with healthy genetic variants.
The team also looked at brain scans of their participants, finding that as NLC levels increased, a part of the brain related to memory (the precuneus) started to shrink.
Rising levels of NLC were detectable up to 16 years before symptoms were likely to develop. The people with rapidly rising protein levels in their blood were more likely to show signs of cognitive decline and brain cell degeneration two years later.
"Sixteen years before symptoms arise is really quite early in the disease process, but we were able to see differences even then," said co-first author Stephanie Schultz. "This could be a good preclinical biomarker to identify those who will go on to develop clinical symptoms."
The researchers focused on Alzheimer’s disease for their study but note that the blood test could actually be used to spot signs of various conditions relating to the brain, allowing earlier treatment.
"We validated it in people with Alzheimer's disease because we know their brains undergo lots of neurodegeneration, but this marker isn't specific for Alzheimer's. High levels could be a sign of many different neurological diseases and injuries," said study co-author Brian Gordon.
However, the study has its limitations and the blood test still needs to be refined before it can be used clinically. For example, the researchers only looked at people genetically predisposed to Alzheimer's, a group that makes up just 1 percent of sufferers.
"We're not at the point we can tell people, 'In five years you'll have dementia,'" added Gordon. "We are all working towards that."