WASHINGTON (dpa-AFX) - A common bacterium that usually infects the respiratory system may be linked to memory loss and Alzheimer's disease when it is found in the retina of the eye, according to recent research.
Chlamydia pneumoniae, which often causes pneumonia and sinus infections, has been detected in the brains of people with Alzheimer's. In a new study, researchers have now found higher levels of this bacterium in the retina, the light-sensitive layer at the back of the eye, of people living with the disease.
The study, led by researchers at Cedars-Sinai Medical Center in the US, examined retinal tissue from 104 people using advanced imaging, genetic analysis, and protein testing. The group included individuals with normal brain function, mild cognitive impairment, and Alzheimer's disease.
Results showed that people with Alzheimer's had much higher levels of Chlamydia pneumoniae in both the retina and the brain compared to those with normal cognition. The study also found that higher bacterial levels were linked to more severe brain damage and greater cognitive decline.
The bacterium was more commonly found at elevated levels in people carrying the APOE4 gene variant, which is known to increase the risk of Alzheimer's disease.
Further tests on human nerve cells and mouse models of Alzheimer's revealed that infection with the bacterium increased inflammation, nerve cell death, and memory problems. It also triggered the production of amyloid-beta, the protein that builds up in the brains of people with Alzheimer's.
Overall, the findings suggest that long-term bacterial infections and the inflammation they cause could play a role in Alzheimer's progression. They also point to the retina as a possible non-invasive way to help detect and track the disease in the future.
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