Bacterium, Gene Play Roles in Elderly Vision Loss

Discovery gives new clues to age-related macular degeneration

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THURSDAY, Nov. 10, 2005 (HealthDay News) -- The diseased eye tissue of some patients with "wet" age-related macular degeneration (AMD) contains a bacterium called Chlamydia pneumoniae, which can cause chronic inflammation and has been linked to heart disease, researchers report.

The finding may confirm links between AMD and an immune-system gene long suspected of playing a role in the sight-robbing disease.

Researchers at the Massachusetts Eye and Ear Infirmary found C. pneumoniae in the diseased eye tissue of five of nine people with wet AMD but not in the eyes of 20 people without AMD. The findings offer more evidence that AMD may be caused by inflammation, the researchers said.

The study appears in the November issue of the journal Graefe's Archive for Clinical and Experimental Ophthalmology.

"The paper showed that C. pneumoniae is capable of modifying the function of important cell types involved in regulating normal eye function," study lead author Dr. Murat Kalayoglu said in a prepared statement.

"We found that C. pneumoniae infection led to increased production of vascular endothelial growth factor (VEGF), the key protein involved in wet AMD. That C. pneumoniae infection of human eye cell types increases VEGF production is therefore significant and could explain in part why VEGF levels are increased in many people with wet AMD," Kalayoglu said.

Recent research has found that nearly half of AMD cases can be explained by variations in a gene called Complement Factor H (CFH), which makes a protein that regulates the body's immune and inflammatory responses.

"Our hypothesis is that C. pneumoniae may be the key link between CFH and AMD. That is, patients with CFH variations may be particularly susceptible to the damaging effects of chronic infection, and an infectious organism like C. pneumoniae may be particularly effective in accelerating inflammation and driving progression of AMD in these patients," Kalayoglu said.

More information

The U.S. National Eye Institute has more about age-related macular degeneration.

SOURCE: Massachusetts Eye and Ear Infirmary, news release, Nov. 7, 2005

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