November 15, 2005.
New York Times.
A bacterium linked to heart disease may also be a factor in age-related macular degeneration, the leading cause of blindness in people over 55 in the United States.
A new study has found the organism, Chlamydia pneumoniae, in the eye tissue of 6 of 9 patients with macular degeneration, but in none of 22 who did not have the disorder.
The paper, based on work carried out at the Massachusetts Eye and Ear Infirmary in Boston, was published in the November issue of Graefe's Archive for Clinical and Experimental Ophthalmology.
Most vision loss in age-related macular degeneration is caused by the growth of abnormal blood vessels under the retina, a form called neovascular. With it, the vessels bleed, and scar tissue is formed, blocking vision.
One phase in the growth of these blood vessels is the production of vascular endothelial growth factor, the body's response to injury and inflammation.
In this study, researchers using human eye tissue demonstrated that C. pneumoniae may, at least in some cases, be the reason for the inflammation.
While recent studies have shown that drug therapy for the vascular endothelial growth factor can be effective, the underlying cause of age-related macular degeneration is poorly understood.
Dr. Joan W. Miller, the senior author on the paper and chairwoman of the department of ophthalmology at Harvard, remains cautious.
"There is growing evidence that chronic inflammation plays a role in the development of macular degeneration," Dr. Miller said, "and our findings suggest that chlamydia may cause some of this inflammation."
But, she warned, "Our data is very preliminary, and really just supports a link between chlamydia and macular degeneration."
C. pneumoniae is ubiquitous, and almost everyone is infected with it at one time or another. Usually, it causes respiratory illnesses of various kinds and severity. It has also been implicated in coronary artery disease, heart attack and cerebrovascular disease.
Many of the risk factors for cardiovascular disease are risk factors for macular degeneration as well, a fact that led the researchers to wonder whether chlamydia might also be involved in macular degeneration.
Dr. Murat V. Kalayoglu, a research fellow at Harvard who directed the study, pointed out that C. pneumoniae is not the same as chlamydia trachomatis, which causes a sexually transmitted disease, but each form causes a low-grade infection that often has no symptoms.
The authors say their findings do not rule out the "innocent bystander" hypothesis - that C. pneumoniae arrives in tissue after the inflammation has begun, and that it is not the cause.
In addition, because C. pneumoniae was not detected in all of the tissue samples, it is clear that its presence alone is not enough to cause the disease. But the scientists point out that the presence of the pathogen at the site of the disease may accelerate the progression of the disorder in some people.
Detecting C. pneumoniae in eye tissue is not easy. It depends on extracting and then amplifying the DNA of the organism from the tissue, a complex process that is not always reliable, especially when working with preserved tissue samples.
The authors point out that the samples they used had been preserved for several years, and that no tests for chlamydia infection had been performed on the patients at the time of surgery to remove the tissue.
Antibiotic treatment for age-related macular degeneration is still a long way off, Dr. Miller said.
"We would not suggest at this point that treatment for chlamydia be undertaken in patients with macular degeneration," she said.
There are, she added, too many unanswered questions.
"Who do you treat?" Dr. Miller asked. "At what point in the disease process would you begin treatment? For how long would it continue? We need more studies before we are close to answering these questions."
But she added that she was hopeful based on recent clinical trials showing that some patients improved after being treated with drugs directed at the vascular endothelial growth factor.
End of article.
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