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Gene Variants Predict Risk of Vision Loss in AMD |
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Written by Theresa Maher
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Thursday, 26 April 2007 |
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Age-Related Macular Degeneration or AMD is the leading cause of blindness in people aged over 55 in the United States. Although the condition is diagnosed quite early, there is no clue if it will progress to vision loss. A new study by researchers at the Tufts-New England Medical Center and New England Eye Center finds two gene variants supplemented by smoking and obesity determine if AMD will in fact lead to blindness.
Age-related macular degeneration usually affects elderly people. The disease is painless and is linked to loss of central vision because of damage to a part of the eye called macula. The macula is important in distinguishing finer details of vision. While blindness is the final stage of the disease, not everyone who has it loses eyesight.
Researchers have now discovered the role played by two gene variants in predicting progression of AMD to possible vision loss. The study involved 1,500 macular degeneration patients and lasted for six years. All patients were aged from 55 to 80 years and had their macular degeneration diagnosed by fundus photography.
Reporting in the April 25 issue of Journal of the American Medical Association, researchers said they tracked patients' genes from blood samples and took into consideration environmental factors as well. Variations in genes CFH and LOC387715 were linked to progression of age-related macular degeneration, researchers said.
Volunteers who had defects in one or both genes were at 2 1/2 to 7 times increased risk of going blind as compared to those whose genes were normal. Additionally if people smoked and were obese, these chances of vision loss soared by 19 times, researchers said.
"The two genetic variants are related and predict to a certain extent which individuals who have earlier-intermediate forms of macular degeneration progress to the advanced form and visual loss," lead researcher Dr. Johanna M. Seddon, director of the Ophthalmic, Epidemiology and Genetics Service in the department of ophthalmology at Tufts-New England Medical Center revealed.
Earlier studies by the same research tem had suggested variations in CFH, which is located on chromosome 1 and in LOC387715 gene on chromosome 10 determine if AMD would progress to vision loss. The current study examined if the presence of these genetic variations could predict later progression in AMD.
"These results and other similar reports on genes yet to be discovered may in the future affect the management of this disease," Dr. Seddon and colleagues wrote. They added identification of risk factors may compel patients to follow a healthy lifestyle in order to limit the damage caused by AMD.
According to the National Eye Institute, age-related macular degeneration is of two types, wet AMD and dry AMD. The dry form is more common and can progress to wet AMD later on. In dry AMD light-sensitive cells in the macula break down in a slow manner eventually leading to complete loss of central vision.
In wet AMD abnormal blood vessels behind the retina penetrate the macula and sometimes leak blood and other fluid damaging the macula. Women appear to be at an increased risk for AMD. Additional risk factors include family history, smoking and obesity.
Wet AMD is treated by Photodynamic therapy, laser surgery and injections of anti-VEGF into the eye. However there is no treatment for dry AMD. Lifestyle modifications may delay the progression of the disease.
The above study has found genetic variations that lead to progression of the disease. Identification of these risk factors as well as giving up on smoking and reducing weight may lead to slowing down of the process of vision loss.
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