The earlier we detect Alzheimer's disease, the better, but we don't have an easy and reliable method for doing that yet. Thanks to new research, though, the disease could eventually show up in a simple blood test 10 years before symptoms appear, if the new models prove correct.
Researchers have linked a sugar molecule in the blood with the abnormal build-up of the amyloid beta and tau proteins that characterize Alzheimer's. These proteins clump up in the brain, killing off neurons.
Spotting this particular molecule – bisected N-acetylglucosamine – could give doctors a way of recognizing a higher Alzheimer's risk level. It's a molecule called a glycan, and these glycans sit on the surface of proteins, influencing how they work.
"The role of glycans, structures made up of sugar molecules, is a relatively unexplored field in dementia research," says Robin Ziyue Zhou, a neurologist at the Karolinska Institute in Sweden.
"We demonstrate in our study that blood levels of glycans are altered early during the development of the disease."
The researchers studied the data of 233 people who were part of the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). The original data were collected in 2001-2004, with follow-ups continuing for 17 years at set intervals based on the participants' ages.
Those individuals with matching levels of glycans and tau in their blood were over twice as likely to develop Alzheimer's-type dementia, the data showed. This link has been seen before in cerebrospinal fluid in the spine, but blood tests are much easier to carry out.
If these findings develop into an Alzheimer's screening test, the researchers want to add other criteria, such as looking for the APOE4 gene, which is also associated with an increased risk of developing Alzheimer's.
"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 medical biochemist Sophia Schedin Weiss, from the Karolinska Institute.
Quite why the glycan molecules show signs of Alzheimer's before damage starts happening in the brain isn't clear, though it's absolutely something that future studies are going to be able to dig deeper into.
While we don't have a cure for Alzheimer's yet or a way to reverse its effects, there are ways in which the symptoms can be managed – and discoveries like this can get us closer to understanding why Alzheimer's starts and how it can be prevented.
Ultimately, it means that Alzheimer's risk could eventually be very accurately predicted with a small series of tests, none of which are complicated or take long to do. The researchers are now partnering with primary care experts to explore this further.
"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," says Schedin Weiss
The research has been published in Alzheimer's & Dementia.