Eye and smell tests may detect Alzheimer’s onset
Alzheimer’s disease, the most common form of dementia, is a progressive brain condition that damages and destroys brain cells. It is the sixth leading cause of death in the United States. One of the main issues is that current clinical diagnostic tests can only be detected in its late stages. However, 4 new studies suggest that eye and smell tests could be used for early detection of Alzheimer’s.
The studies presented during the week of July 12-17, 2014 at the Alzheimer’s Association International Conference 2014 in Copenhagen, Denmark, strengthen earlier evidence that the earliest signs of Alzheimer’s disease may start in the eyes or nose, not in the brain.
In two of the studies, the decreased ability to identify odors was significantly associated with loss of brain cell function and progression to Alzheimer’s disease. In two other studies, the level of beta-amyloid, a protein associated with Alzheimer’s, detected in the eye was significantly correlated with the burden of beta-amyloid in the brain and allowed researchers to accurately identify the people with Alzheimer’s in the studies.
Beta-amyloid protein is the primary material found in the sticky brain “plaques” characteristic of Alzheimer’s disease. It is known to build up in the brain many years before typical Alzheimer’s symptoms of memory loss and other cognitive problems.
Researchers at the Harvard Aging Brain Study used the University of Pennsylvania Smell Identification Test (UPSIT) to study the ability of 215 healthy participants with no memory loss to recognize familiar smells. UPSIT consists of 40 scratch-and-sniff panels with different odors.
The PET scans used an injected substance to determine the level of beta-amyloid protein deposits inside each participant’s brain. Clumps of beta-amyloid fragments, which are a distinguishing characteristic of Alzheimer’s, form plaques between brain cells and are thought to kill them. The MRI scans measured each subject’s entorhinal cortex, which is located in the brain’s medial temporal lobe near the hippocampus and plays a role in processing smell and forming short-term memories. It is also one of the first regions of the brain affected by Alzheimer’s.
The study showed that patients who scored lower on the odor recognition test also had higher levels of beta-amyloid in the brain. The researcher team intends to follow the patients over an extended time to continue the study.
In a similar study, Davangere Devanand, a professor of psychiatry at Columbia University Medical Center, and colleagues administered the same University of Pennsylvania odor-detection test on 1,037 non-demented elderly people in New York City. From 2004 to 2010, they assessed participants in a variety of ways during three cycles.
His team also found some correlation between declining sense of smell and the transition from mild cognitive impairment to dementia: Of those who took part, 757 people who scored lower on tests of their sense of smell also showed a decline from mild cognitive impairment to dementia and Alzheimer’s.
“If further large-scale studies reproduce these results, a relatively inexpensive test such as odor identification may be able to identify subjects at increased risk of dementia and Alzheimer’s disease at a very early stage, and may be useful in identifying people at increased risk of cognitive decline more broadly,” Devanand said.
On a separate track, two groups of researchers also studied how deposits of beta-amyloid in the eye can help predict the onset of Alzheimer’s.
Paul D. Hartung, M.S, President and CEO of Cognoptix, Inc. and colleagues concentrated on the lens of the eye Shaun Frost of the CSIRO (Commonwealth Scientific and Industrial Research Organization, Australia) and colleagues studied the eye’s retina.
Both groups developed ways to measure beta-amyloid deposits in the eye and both found correlations between the amount of beta-amyloid in the eye and deposits in the brain revealed by PET scans.
We envision this technology potentially as an initial screen that could complement what is currently used: brain PET imaging, MRI imaging, and clinical tests,“ Frost said.
“If further research shows that our initial findings are correct, it could potentially be delivered as part of an individual’s regular eye check-up. The high resolution level of our images could also allow accurate monitoring of individual retinal plaques as a possible method to follow progression and response to therapy.”
Although these studies resulted in similar findings, the authors suggest that studies with larger sample sizes and longer follow-up times are needed to validate the outcomes.