Alzheimer’s is an insidious disease that many people fear, so it’s super exciting to hear that a blood test could detect the disease as many as 16 years before onset. This would give doctors and sufferers time to make lifestyle changes and try treatments that could slow the onset of the disease earlier rather than later.
The test is simple. It is designed to measure changes in the levels of neurofilament light chain (NfL), a certain protein found in blood. Researchers wrote in the journal Nature Medicine that when levels of NfL rise, it may be an early sign of Alzheimer’s disease.
Lead researcher Mathias Jucker, professor of cell biology of neurological diseases at the German Center for Neurodegenerative Diseases, explained that NfL is a “marker in the blood which gives an indication of nerve cell loss in the brain. The more neurofilament you have in the blood, the more brain damage you have.”
Alzheimer’s remains an ‘incurable disease,’ unfortunately. But Jucker said the test will be “very important for clinical studies.” Being able to spot the disease years before the manifestation of symptoms could allow researchers to monitor the effectiveness of new treatments before symptoms arise, simply by measuring NfL levels.
“Alzheimer’s disease starts at least a decade, maybe even 20 years, before we have any symptoms.”
It is not clear what causes Alzheimer’s to develop, which has made it difficult to predict its onset. It is believed that the disease is driven by the production and proliferation of amyloid-beta plaques in the brain.
As many as 5 million Americans are currently living with Alzheimer’s disease, according to the U.S. Centers for Disease Control and Prevention (CDC). That number is expected to rise to almost 14 million by the year 2050, the Alzheimer’s Association says.  
Hunting for Signs of Alzheimer’s
For the study, the researchers recruited more than 400 people, including about 250 who had a genetic mutation that made them more susceptible to Alzheimer’s disease. This version of Alzheimer’s is quite rare and represents only 1% of all cases of the disease.  
The researchers took blood samples from the participants and conducted brain scans and cognitive tests every 2-3 years. 
The team used a blood test kit similar to others already on the market that are not yet approved by the U.S. Food and Drug Administration (FDA) to diagnose or predict brain damage.
People with the genetic mutation had higher baseline levels of NfL that rose throughout the duration of the study. By comparison, participants without the mutation had low baseline NfL levels that remained steady. The researchers spotted a noticeable difference in levels of the protein between both groups, even 16 years before the onset of symptoms.
Stephanie Schultz, a graduate student at Washington University, said:
“Sixteen years before symptoms arise is really quite early in the disease process, but we were able to see differences even then. This could be a good preclinical biomarker to identify those who will go on to develop clinical symptoms.”
The researchers then conducted brain scans and cognitive tests on 40 of the participants who had the gene mutation 2 years after the study began. They found that those individuals had fewer neurons in brain tissue and performed worse and cognitive tests, compared to those without the gene variant.
The team further observed that there was an increase in NfL proteins at the same time the precuneus of the brain – which plays a role in memory – thinned and shrank.
Study co-author Brian Gordon, an assistant professor of radiology at Washington University’s Mallinckrodt Institute of Radiology, said:
“This is something that would be easy to incorporate into a screening test in a neurology clinic.
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.”
For example, higher NfL protein levels are seen in people with progressive brain disorders like Lewy body dementia and Huntington’s disease. Spikes in protein levels can also be seen in people with multiple sclerosis (MS) who experience a sudden episode of symptoms, and in football players who have received a blow to the head.
For those reasons, researchers are working to determine 2 hallmarks before the test is used to predict Alzheimer’s: How much protein in the blood is too much, and how quickly protein levels spike before doctors become concerned.
It will take several years, but the team hopes the blood test can be adapted as an early warning sign of Alzheimer’s disease.
“I could see this being used in the clinic in a few years to identify signs of brain damage in individual patients. We’re not at the point we can tell people: ‘In 5 years you’ll have dementia.’ We are all working towards that.”
In 2015, researchers announced that another type of blood test, this one measuring the “vitality” of certain genes that are indicative of a person’s biological age versus their chronological age, allowed them to predict who would develop Alzheimer’s disease years before symptoms emerged.
That particular test measured RNA, an acid associated with genes in different body tissues. People who had been diagnosed with Alzheimer’s disease had an altered RNA signature in their blood and a lower healthy aging score.
 Daily Mail