Scientists may have found a way to screen for Alzheimer’s disease years before patients develop severe signs of neurological deficits.
Alzheimer’s disease affects a staggering 44 million people worldwide. This number might actually be even greater, as some people with the condition go undetected.
Currently, diagnosing Alzheimer’s disease is limited and time-consuming. Doctors and experts have to conduct a battery of cognitive tests to look for impairments in cognition, memory, social functioning, and behaviors. These tests are highly subjective, but can be supported with neuroimaging data, such as magnetic resonance imaging (MRI) and positron emission tomography (PET) scans. Unfortunately, these methods are expensive and have limited accuracy. True Alzheimer’s diagnoses are confirmed when post-mortem autopsies reveal presence of beta-amyloid plaques and neurofibrillary tangles – neurological hallmark features of the disease.
A team from the Washington University School of Medicine in St. Louis, Missouri, thought there may be a better way to screen for this disease. Their cohort consisted of 23 people who had presence of amyloid plaques in their brain and cognitive impairment, and 18 people who were controls.
They observed that ratios of two proteins, amyloid beta 42 and amyloid beta 40, were different in people with amyloid plaques compared to those who don’t. In particular, the ratio of the two proteins were consistently 10 to 15 percent lower in people who had amyloid plaques.
"Amyloid plaques are composed primarily of amyloid beta 42, so this probably means that it is being deposited in the brain before moving into the bloodstream," explains Dr. Randall Bateman, the study’s senior author. "The differences are not big, but they are highly consistent. Our method is very sensitive, and particularly when you have many repeated samples as in this study - more than 500 samples overall - we can be highly confident that the difference is real. Even a single sample can distinguish who has amyloid plaques."
Based on the proportions of the proteins, the team correctly identified presence of amyloid plaques with 89 percent accuracy.
“Our results demonstrate that this amyloid beta blood test can detect if amyloid has begun accumulating in the brain. This is exciting because it could be the basis for a rapid and inexpensive blood screening test to identify people at high risk of developing Alzheimer's disease,” said Dr. Bateman.
Among the follow-up investigations, the team is planning on developing a similar test for tau, the other protein characteristic of Alzheimer’s disease. “If we had a blood test for tau as well, we could combine them to get an even better idea of who is most at risk of developing Alzheimer's disease. That would be a huge step forward in our ability to predict, and maybe even prevent, Alzheimer's disease," he said.