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The Value of Genetic Testing for Age-Related Macular Degeneration Detection

November 18, 2014

Age-related macular degeneration is the leading cause of irreversible blindness in people over age 55 throughout the developed world. The potential for blindness or vision loss from all types of AMD increases if the disease is undetected, untreated or incorrectly treated. Of the more than 9 million people currently diagnosed with AMD in the United States, about 1.75 million of them have late-stage disease, meaning that their risk for vision loss is now extremely high. As with many diseases, early detection is key, so a new development that uses genetic testing to determine a risk level for each patient may be a breakthrough in reducing the number of those affected by the disease.

Forms of Macular Degeneration

There are two forms of macular degeneration, each with their own set of symptoms.  The two derive from the term “neovascular”, referring to the growth of new blood cells in an area where they are not recognized as normal.  The two forms are described by the terms “dry” and “wet”.

Non neovascular: Also known as “dry” macular degeneration, this form of macular degeneration accounts for about 85-90% of macular degeneration diagnoses.  This form is diagnosed when deterioated tissue appears in the macula and takes the form of yellowish spots known as drusen.  Resulting effects will include gradual vision loss in the eyes of the patient.

Neovascular: Also known as “wet” macular degeneration, this form accounts for only 10% of diagnoses, however the effects and results are much more severe than its counterpart.  In “wet” macular degeneration, new blood vessels grow beneath the retina and ultimately leak blood and fluid.  In the end, this can cause permanent damage to light sensitive retina cells, which can eventually impair vision extensively.

Causes of Macular Degeneration

Age and genetics have proven to be the two major causes of macular degeneration and scientists have concluded that that there is a strong association between development of AMD and a variant gene.  The variant gene, known as complement factor H (CFH), has been found in virtually half of of all potentially blinding cases of AMD, and doctors have also noticed that the variants of another gene, complement factor B may also be associated.  In addition, evidence points to smoking, high blood pressure, and obesity raising the risk of being afflicted by the condition.  It has also been noted that the condition is most common in whites, females in particular.  However, the most common factor in macular degeneration cases remains to be age.

An overview of genetic testing

Similar to other genetic tests, the one for AMD begins with swabbing the inside of each cheek with a brush. The sample is enclosed and mailed to a testing site, where it is analyzed within a few weeks to determine if a patient has high-risk properties in their DNA. These genetic properties, paired with behavioral risk factors, such as smoking, help to determine a risk category and frequency of follow-up.

The risk categories range from one to five. A risk category of one, which represents 50% of the U.S. population, or a two, which represents 30% of the population, means that a patient is at no greater risk to develop AMD than the rest of the general populace. In contrast, however, a risk category of a three, four or five means that the patient is at a higher risk that the general population, consequently requiring more frequent evaluations, typically every three to four months. By increasing the evaluation schedule, doctors and patients are given the opportunity to detect the disease at an earlier stage, thus reducing the risk that it will advance to the point of irreversible blindness.

The importance of early detection

Since early detection can be the key to saving a person’s vision from descending to blindness, genetic testing may play a crucial role for those high-risk patients. The progression of age-related macular degeneration is difficult to predict in any specific patient because there are a number of factors that contribute to the progression of the disease. Some of these factors include diet, smoking habits, body mass index and cholesterol levels. Although these factors can make it more difficult to predict the progression of AMD, fixed factors such as age, gender, and genetic makeup are the keys to determining at-risk patients.

Approximately 20% of the U.S. population is estimated to have a risk category of three or higher, representing millions and millions of Americans. With the development of genetic testing, these people are given hope that they can delay the onset of the disease or catch it at an earlier stage, thus dramatically increasing their chances of maintaining their vision well into old age.

Currently, the practice of genetic testing a decision left up to individual practitioners, as it has not been widely accepted in the field. If you feel that you may be at risk for developing AMD, make an appointment to come in to speak with one of OCLI’s physicians today!

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