Monthly Archives: January 2018

Macular Degeneration: Alzheimer’s Disease of the Eye?

Macular degeneration affects more than 10 million Americans, making it the leading cause of vision loss. It occurs when, for reasons that aren’t entirely understood, the central region of the retina (known as the “macula”) begins to deteriorate. The disease is considered incurable and usually occurs in people over the age of 55. Smokers and individuals of Caucasian decent are at an increased risk, as well as anyone with a family history of the disease.

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This animation from the American Macular Degeneration Foundation shows the loss of central vision that occurs with this disease.

Surprisingly, there are many parallels between macular degeneration and Alzheimer’s disease. Though the two conditions may seem unrelated, both are believed to be caused by the buildup of a toxic protein called amyloid-beta. In Alzheimer’s disease, amyloid-beta plaques accumulate in the brain, while in macular degeneration, amyloid-beta forms fatty deposits behind the retina called “drusen.” Plaques and drusen appear to have similar composition of proteins and fats, and utilize the same mechanisms to damage surrounding tissue.

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Diagram of a normal eye and an eye with macular degeneration. Image Source

The similarities between these two diseases don’t end there. Older people with macular degeneration are three times as likely to have cognitive impairment, suggesting that the same processes leading to amyloid-beta accumulation in the retina could also be occurring in the brain. This makes sense, since the retina and the brain are both part of the central nervous system. Additionally, several mouse models of Alzheimer’s disease exhibit amyloid-beta buildup in both the brain and the retina, further cementing the link between the two conditions.

The emerging connection between Alzheimer’s and macular degeneration has several important consequences. If amyloid-beta buildup in the retina could be a sign of a similar process happening in the brain, it raises the possibility that eye exams could serve as a non-invasive method to screen people for Alzheimer’s disease. Clinical trials for this idea are still ongoing, but the early results seem encouraging. These eye exams could potentially allow for earlier Alzheimer’s diagnosis or a lower risk of misdiagnosis.

This relationship also suggests that people with Alzheimer’s disease could be at a greater risk of macular degeneration, or vice versa. If you or a loved one is experiencing dementia, it’s recommended to minimize the risk of macular degeneration by receiving regular eye exams, protecting the eyes from sunlight, and maintaining a healthy diet.

 

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Anxiety and Depression May Be Early Signs of Alzheimer’s Disease

Though most people with Alzheimer’s disease aren’t diagnosed until after age 65, the disease can begin in their brains years or even decades before that. For this reason, scientists have been trying to identifying biomarkers that will allow us to diagnose Alzheimer’s at an earlier stage, prior to the onset of cognitive symptoms.

In a study published last week in The American Journal of Psychiatry, researchers from Harvard University examined 270 subjects aged 62 to 90, all of whom lived in a retirement community and initially showed no signs of cognitive impairment or mental illness. The subjects were given a test for geriatric depression and a PET scan of their brains annually for five years.

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Researchers used a PET scanner like this one to examine amyloid-beta levels in the subjects’ brains.

At the beginning of the study, participants who had depression had higher levels of amyloid-beta, a toxic protein linked to Alzheimer’s disease, in their brains. Furthermore, participants with higher amyloid-beta levels at baseline had steeper increases in their geriatric depression scores after five years. These results suggest that a sudden development or worsening of depressive symptoms could be a sign of early Alzheimer’s disease.

Next, the researchers looked at the participants’ subscores for different sections of the depression test. They found that only the anxiety subscore was correlated with amyloid-beta levels. The other two subscores, which relate to apathy and unhappiness, had no relationship to amyloid-beta. This suggests that anxious-depressive symptoms are the strongest predictor of early Alzheimer’s disease.

It’s difficult to determine from this study whether anxiety or depression could lead to Alzheimer’s disease, or if instead preclinical Alzheimer’s causes anxiety/depression. It’s likely that there are many other factors at play, such as social interaction, diet, and exercise levels. Additionally, the small sample size prevents us from drawing broad conclusions. However, the authors of the study are currently working on a follow-up analysis of these subjects, which should illuminate whether the people with higher amyloid-beta levels went on to be diagnosed with Alzheimer’s disease.

In the meantime, if you or a loved one notices a sudden increase in anxious-depressive symptoms, this should be taken seriously and brought up with a doctor. An earlier Alzheimer’s disease diagnosis, prior to the development of dementia, may allow our drugs to act more effectively and slow the rate of cognitive decline.

 

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