Early diagnosis and treatment of Alzheimer’s disease require reliable and cost-effective screening methods. Researchers at Karolinska Institutet in Sweden have now discovered that a type of sugar molecule in the blood is associated with the level of tau—a protein that plays a critical role in the development of severe dementia. The study, published recently in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, may pave the way for a simple screening procedure able to predict onset ten years in advance.
“The role of glycans, structures made up of sugar molecules, is a relatively unexplored field in dementia research,” says the study’s first author Robin Zhou, a medical student and affiliated researcher at the Department of Neurobiology, Care Sciences and Society (NVS), Karolinska Institutet. “We demonstrate in our study that blood levels of glycans are altered early during the development of the disease. This could mean that we’ll be able to predict the risk of Alzheimer’s disease with only a blood test and a memory test.”
In Alzheimer’s disease, the neurons of the brain die, which is thought to be a result of the abnormal accumulation of the proteins, amyloid-beta and -tau. Clinical trials for Alzheimer’s drugs show that treatment should commence early in the pathological process, before too many neurons have died, to reverse the process before it is too late.
More blood biomarkers needed
There is both a practical and financial need for noninvasive screening methods for Alzheimer’s. Blood-based markers are preferable, as taking samples of the cerebrospinal fluid (CSF) is more difficult and brain imaging is expensive.
Researchers at Karolinska Institutet have now shown that the level of a certain glycan structure in blood, known as bisected N-acetylglucosamine, can be used to predict the risk of developing Alzheimer’s disease.
The research group has previously demonstrated a link between tau protein and glycan levels in people with Alzheimer’s disease, but these analyses were done on CSF. Glycans are sugar molecules found on the surface of cells and also attached to proteins—the building blocks of life—and determine the location and function of these proteins in the body.
By measuring blood glycan levels the researchers found that individuals with matching levels of glycans and tau were over twice as likely to develop Alzheimer’s-type dementia.
“We also show that a simple statistical model that takes into account blood glycan and tau levels, the risk gene APOE4, and a memory test, can be used to predict Alzheimer’s disease to a reliability of 80 percent, almost a decade before symptoms such as memory loss appear,” says corresponding author Sophia Schedin-Weiss, assistant professor at NVS, Karolinska Institutet.
A 17-year follow-up
The results are based on 233 participants of the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). The samples were collected between 2001 and 2004, and the participants were monitored regularly with respect to factors such as memory loss and the presence of dementia. The follow-ups were carried out every three to six years and continued for 17 years.
The researchers will now be analyzing blood samples from the remaining participants of the SNAC-K study as well as from participants of other aging studies in and outside Sweden.
“We’re collaborating with researchers in primary care in Sweden to evaluate different biomarkers for dementia at primary healthcare centers,” says Schedin-Weiss. “We hope that glycans in the blood will prove to be a valuable complement to current methods of screening people for Alzheimer’s disease that will enable the disease to be detected early.”
- This press release was originally published on the Karolinska Institutet website