Best Vitelliform Macular Dystrophy
Also referred to as best macular dystrophy or best disease, best vitelliform macular dystrophy is a gradually advanced type of macular degeneration. It tends to begin during childhood or youth, although the age of onset and the severity of loss of vision can vary from one person to the next. Affected individuals will have normal vision at first, which will then be followed by a decrease in their central visual acuity and partial vision. Their peripheral vision isn’t impacted.
BVMD is categorized by the atrophy of the retinal pigment epithelium and impaired function of the central vision. It is generally inherited in an autosomal dominant manner, although autosomal recessive inheritance has been known to occur. It’s generally caused by changes within the BEST1 gene, and in some instances, the exact cause is not known.
Treatment is symptomatic and consists of using low vision aids as well as photodynamic therapy or laser treatment. Some more modern treatment options include transcorneal electrical retinal stimulation and anti-VEGF agents.
Symptoms of BVMD
With most diseases, the symptoms that people experience will differ from one person to the next. Individuals with the same exact disease will not necessarily have all of the symptoms that are listed below.
Causes of BVMD
This disease is the result of changes in the BEST1 gene, which provides instructions to the body for making bestrophin, a protein. This protein serves as a channel that works to direct the way that chloride ions move in the retina. It’s believed that changes in the BEST1 gene impact the channel’s shape and ability to regulate the proper flow of chloride. Yet, it is not clear how this specifically correlates to the features of this particular disease.
Inheritance of BVMD
Best vitelliform macular dystrophy is generally inherited in an autosomal dominant form, though it is possible for it to be inherited by autosomal recession.
With autosomal dominant inheritance, it is enough to have one changed copy of the accountable gene in every cell to cause BVMD symptoms. When an individual with this condition has children, every child has a 50 percent change to receive the changed gene. The majority of individuals with the disease will have an impacted parent, though some have BVMD due to a new mutation that happened for the very first time.
With autosomal recessive inheritance, an individual needs to have a change in both of the copies of the accountable gene in every cell in order to be impacted. The parents of the impacted individual generally both carry a changed copy of the gene and are known as carriers. Generally, carriers will not show symptoms or signs of the condition. In the event that two carriers have children, each child will have a 25 percent change to develop the condition, a 50 percent change to become a carrier, and a 25 percent chance to not become a carrier or develop the condition.
Diagnosis of BVMD
Best vitelliform macular dystrophy can be diagnosed with an exam of the interior eye surface that is opposite of the lens known as the fundus. An electrooculogram (EOG) and a family history is also necessary. An eye examination could include additional tests. A standard yellow macular lesion similar to that of a yolk may appear in the fundus exam.
The EOG serves as the most common diagnostic test to evaluate vitelliform macular dystrophy. Generally, a significant decrease will occur in response to the light, which is reflected by an Arden ratio of 1.1 to 1.5. A normal ratio is 1.8. Carriers will have an abnormal result on the EOG. There is no correlation between the EOG result and the stage of the disease, patient age, and visual acuity. The EOG results are typically the same for both of the eyes.
The family medical history in individuals affected tend to be consistent with autosomal recessive or autosomal dominant inheritance.
In some cases, genetic testing can be used for diagnosis. The mutation of the BEST1 gene can be detected in roughly 95 percent of individuals who are affected and have a family member who is affected. In individuals with zero family history of the condition, the mutation rate of detection can range anywhere between 50 and 70 percent. A BEST1 gene mutation is more likely when there is a vitelliform lesion and a reduced Arden ratio. The specific form of genetic test that is used to confirm a diagnosis will depend on the individual’s family history, ancestry, and whether additional eye disorders are being taken into consideration.
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