Alzheimer's disease, the most common form of dementia, affects more than five million Americans and is the sixth leading cause of death in the U.S. Current clinical applications can diagnose the disease only when it is in its later stages, past the point of significant brain damage.

Researchers are beginning to find evidence of ways they may be able to detect the development of the disease earlier. Early diagnoses could be the key to helping those with the disease maintain a high quality of life and, possibly, respond to potential cures.

The Alzheimer's Association International Conference 2014 in Copenhagen revealed two research trials that reported significant links between a decreased ability to smell and the development of Alzheimer's disease. Another two trials reported significant associations between the levels of a specific protein in the eyes and the onset of Alzheimer's.

Researchers at Harvard Medical School and Harvard School of Public Health conducted studies to understand links between ability to detect and correctly identify odors and the development of cognitive impairments leading to Alzheimer's.

They hypothesized that when the disease kills brain cells, many of the dying cells are necessary for functional olfaction, or sense of smell. They found that elderly participants with a decreased ability to smell had a smaller hippocampus and a thinner entorhinal cortex. These two regions of the brain are crucial for memory formation and recall. The findings suggest that cells important for smell and olfactory memories are destroyed in the very early stages of the disease. If so, this offers potential for doctors to detect the development of the disease before it becomes too serious.

"It may prove useful to identify proper candidates for more expensive or invasive tests," said Matthew Growdon, an author of the study. "These results reflect a snapshot in time; research conducted over time will give us a better idea of the utility of olfactory testing for early detection of Alzheimer's."

Researchers at Columbia University Medical Center tested 1,037 non-demented elderly people in New York City-109 participants developed dementia during the follow-up study; 270 died. They found similar results to those found by the Harvard research team: lower odor identification scores on the same test used in the Harvard study was significantly linked to the progress of dementia and Alzheimer's.

Future studies using large sample sizes will help to confirm or deny these findings. If they confirm the results, simple tests can be designed to test for odor identification abilities.

Another two studies reported results that also hold promise for future non-invasive, simple preliminary tests for Alzheimer's. The Commonwealth Scientific and Industrial Research Organization (CSIRO) from Australia, as well as researchers from Cognoptix, Inc., found a significant correlation between levels of beta-amyloid protein in the eyes and the development of Alzheimer's. CSIRO reported that the test for the protein separated Alzheimer's patients from non-Alzheimer's patients with 100% sensitivity and high specificity.

High levels of beta-amyloid in the eyes, researchers believe, may indicate buildup of the protein in the brain. This protein is strongly associated with Alzheimer's as the disease produces sticky plaques in the brain, of which beta-amyloid is the primary material. Past studies confirm that the protein builds up in the brain in the very early stages of the disease, before memory loss and other symptoms appear.

If future studies confirm these results, tests could be conducted at routine eye exams to distinguish healthy individuals from those who may need to undergo further tests for possible early diagnoses. These tests could make all the difference for Alzheimer's patients. Catching the disease early might even mean life over death.

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