Although doctors can use brain scans or spinal cranes to detect Alzheimer's in patients with symptoms, there is no way to test for the disease in seemingly healthy individuals. However, Alzheimer's can break down the brain for years – even decades – before a person recognizes everything that is wrong. The inability to detect Alzheimer's early is a major reason why pharmaceutical companies have not been able to develop a drug to control the disease, which is the most common form of dementia.
Researchers from Washington University in St. Louis and the German Center for Neurodegenerative Diseases in Tubingen have developed a simple blood test showing signs of brain damage due to Alzheimer's almost seven years before any cognitive changes occur. Theoretically, this test can be used to find patients who will continue to develop the disease so that in the near future they can be enrolled in drug trials and in the long term be rescued from developing dementia. Their work was released (paywall) on Monday 21
The study involved a group of people in the predominantly hereditary Alzheimer's network. This network consists of people with one of three genetic mutations that guarantee they will develop Alzheimer's early and some of their family members who have none of these mutations. In total, only about 1% of Alzheimer's cases are caused by one of these three single mutations.
Scientists sampled blood from 243 people who had one of the mutations and 162 who did not, all in their 40's or 50's, every three years or more, in Six to nine years. They looked at levels of a protein called "neurofilament light chain" that provides structural support for neurons. Although scientists do not know much about these proteins, high levels of those in the blood typically show brain damage. They have appeared in the blood of college football players after a season to play (paywall) and in the blood of people with Alzheimer's and other forms of dementia (paywall).
Everyone in the study had a certain amount of neurofilament light chain in their blood and tended to develop over time. However, people who had the dominant hereditary Alzheimer's gene began to accumulate more of the protein in their blood faster than those without the gene.
Overall hereditary Alzheimer's develops predictably, so scientists have a good idea of when patients begin to show symptoms. The research team found that people with one of the preacher mutations tend to have higher levels of neurofilamentary chains in their blood, which start around six years and nine months before dementia symptoms should have appeared based on predictions. Their family members without mutations had lower levels of neurofilament light chain at that time. (Ultimately, researchers can identify the exact amount of neurofilament-light chains in the blood that predict Alzheimer's, but this was not a large enough study to establish this level.)
The team also conducted brain scans and cognitive tests on 39 subjects. In the study with dominant hereditary Alzheimer's, every two years after the study began. Sure, higher levels of neurofilament light chains in the blood correlate with poorer memory and executive function and degradation in part of the brain associated with memory.
This blood test has not yet been approved by the US Food and Drug Administration. Brian Gordon, a radiologist and psychologist at Washington University, who co-authored the paper, said in a statement that he imagined that it would only be a few years before doctors could give it to their patients or use it in clinical trials.