The findings, described in a thesis from the Sahlgrenska Academy at the University of Gothenburg, Sweden, will also be useful in research into new medications.
The researchers conducted two independent studies, and found that Alzheimer's patients have higher levels of the protein in their spinal fluid than do healthy individuals.
"The discovery of the new protein could be used to diagnose patients with Alzheimer's and also help determine which medications are most effective for the disease," said biochemist Erik Portelius, the author of the thesis.
Alzheimer's disease includes the formation of plaque on the brain. Neurons and other cell types form around 20 different beta-amyloid proteins, and these are excreted into the spinal fluid around the brain.
"These types of beta-amyloid proteins can be analysed with great precision, and our research team has also shown that the analyses can be used to distinguish between Alzheimer's patients and healthy individuals with a high degree of accuracy," said Portelius.
The beta-amyloid protein Abeta42, which is particularly prevalent in the plaque, is created when a larger protein is cut into pieces by certain enzymes.
The new Alzheimer's drugs, which are currently being tested, aim to reduce the production of Abeta42 by blocking these enzymes.
The researchers found that these drugs increase the level of the newly discovered Abeta16.
"Abeta42 and Abeta16 are formed from the same precursor molecule, but the enzymatic process is different and Abeta16 is not harmful. The finding that Abeta16 is a very sensitive biomarker for the effect of these drugs may become very useful in future treatment studies," said Portelius.