But research has shown that the seeds of Alzheimer's disease precede symptoms years, even decades, long before signs of cognitive decline appear. The germ is beta amyloid proteins that misalign and clump together, forming small aggregates called oligomers. Over time, through a process that scientists are still trying to understand, these toxic proteins are thought to develop into Alzheimer's disease.

A team led by researchers at the University of Washington has developed a test that can measure amyloid beta levels in blood samples. As they report in a paper published in Proceedings of the National Academy of Sciences, the trial, called SOBA, detected Alzheimer's in 10 people without symptoms of dementia. Years later, these 10 were diagnosed with mild cognitive impairment or brain disease consistent with Alzheimer's disease. This means that the test detected the toxic proteins before symptoms appeared.

"What clinicians and researchers want is a reliable Alzheimer's diagnostic test, not just a diagnostic reconfirmation test," said lead author Valerie Daggett, professor of engineering. biology of the University of Washington, said. "SOBA could be the basis of such a test."

SOBA, short for soluble oligomer binding assay, exploits a unique property of the toxic protein. When misfolded beta amyloid proteins begin to clump together into oligomers, they form a structure known as an alpha plate. Alpha plates are not normally found in nature, and previous research by the Daggett group has shown that they tend to bond with other alpha sheets. SOBA is an artificial alpha sheet that can bind to oligomers in samples of cerebrospinal fluid or blood.

The team tested SOBA on blood samples from 310 study subjects, who had their blood samples and medical records taken for Alzheimer's research. At the time of blood sampling, subjects were noted to have no signs of cognitive impairment, mild cognitive impairment, Alzheimer's disease or any other form of dementia.

SOBA has detected oligomers in the blood of people who later develop mild cognitive impairment and moderate to severe Alzheimer's disease.
Daggett's team is working with scientists at AltPep, a subsidiary of UW, to develop SOBA as a diagnostic test for oligomers. In the study, the team also showed that SOBA can be modified to detect toxic oligomers of another protein, which has been implicated in Parkinson's disease and Lewy body dementia. Daggett believes the test has much more potential.