Best Disease

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Best disease is an inherited retinal disease, which causes macular degeneration and loss of central vision, visual acuity, and color perception.

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What is Best Disease?

Best disease, also known as vitelliform macular dystrophy, is an inherited retinal disease causing macular degeneration. The retina is a thin piece of tissue lining the back of the eye. Rod and cone photoreceptors in the retina convert light into electrical signals that the brain interprets as vision. Best disease affects the macula, the central part of the retina, and is characterized by loss of central vision, as well as the ability to perceive colors and details.

Symptoms

Although the age of onset for those with Best disease can vary, it is usually diagnosed during childhood or adolescence. In the initial stages, a bright yellow cyst (fluid-filled sac) forms under the retinal pigment epithelium (RPE) beneath the macula. The RPE is a layer of cells that provides support for photoreceptors.

Upon examination by an eye doctor, the cyst looks like a sunny-side-up egg. Despite the presence of the cyst, visual acuity may remain normal or near normal for many years. Peripheral (side) vision usually remains unaffected.

In many individuals with Best disease, the cyst eventually ruptures. Fluid and yellow deposits from the ruptured cyst spread throughout the macula. At this point the macula has a scrambled egg appearance. Once the cyst ruptures, the macula and the RPE begin to atrophy (degenerate) causing further vision loss.

What someone with Best Disease may see: Loss of central vision; Reduced ability to perceive colors; Reduced ability to perceive details

Retinas affected by Best disease also have the accumulation of yellow flecks called lipofuscin, which can also cause vision loss.

In many people with Best disease, central vision deteriorates to about 20/100 later in life. However, the condition does not always affect both eyes equally. Many individuals retain useful central vision in one eye with a visual acuity of about 20/40 in the less-affected eye.

In some cases, Best disease does not progress far enough to cause significant central vision loss. However, retinal specialists can still detect the disease using sophisticated diagnostic tests that measure the function of the RPE and the retina.

How the Disease is Inherited

Mutations in the BEST1 (VMD2) gene cause Best disease. The condition is genetically passed through families by the autosomal dominant pattern of inheritance. In this pattern of inheritance, an affected person has one Best disease gene paired with one normal gene. When the affected person has children with an unaffected partner, there is a 50 percent chance that the affected parent will pass the disease-causing gene to each child.

The unaffected partner will only pass normal genes. A child who does not have the Best disease gene will not have the disease and cannot then pass the disease to his or her children.

Genetic counselors are excellent resources for discussing inheritability, family planning, genetic testing, and other related issues.

HOW IS BEST DISEASE INHERITED? Best disease is usually autosomal dominant. That means it is genetically passed when one parent has one disease causing gene, BEST1 (VMD2), paired with one normal gene. There is a 50% chance that the affected parent will pass the disease-causing gene to their child. The unaffected partner will only pass normal genes. Genetic testing helps confirm the diagnosis and the risk of passing the condition to offspring. A patient with an accurate diagnosis is in a better position to understand which emerging treatment approaches and clinical trials are most appropriate for them.

Living with Best Disease

There are many services and accommodative and assistive resources available to people and families with Best disease. Visit the Foundation’s Low Vision Resources page to learn about many of these resources. A low vision specialist can help recommend the resources that are right for you.

Genetic Testing

Genetic testing is available for Best disease. It helps confirm the diagnosis and the risk of passing the condition from parent to offspring. It also helps with attaining an accurate diagnosis. A patient with an accurate diagnosis is in a better position to understand which emerging treatment approaches and clinical trials are most appropriate for them.

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