Best vitelliform macular dystrophy is an autosomal dominant genetic form of macular degeneration that usually begins in childhood or adolescence and slowly progresses to affect central vision. The age of onset and severity of vision loss are highly variable. Best vitelliform macular dystrophy is associated with an abnormality in the VMD2 gene.
Affected individuals initially have normal vision and then experience blurred vision, reduced sharpness or clarity of vision or the appearance objects that have a distorted shape (metamorphosia). Best vitelliform macular dystrophy affects central vision but usually not peripheral vision and varies in severity, even among members of the same family. Some people with the disorder do not notice a decline in vision, whereas others experience significant loss of vision, especially after 40 years of age. The degree of visual loss can be different in each eye.
The macula is the region of the retina that contains the light-sensing cells necessary for central vision. Individuals with Best vitelliform macular dystrophy develop a mass on the macula that resembles an egg yolk. (Vitelliform means yolk-like). This mass eventually breaks up and spreads throughout the macula, leading to a reduction in central vision.
Best vitelliform macular dystrophy is inherited as an autosomal dominant genetic condition. The VMD2 gene is the only gene that has been associated with this condition and has been mapped to chromosome 11q13. Some affected individuals do not have an abnormality in the VMD2 gene. Therefore, other genes may also be associated with this condition.
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 11q13” refers to band 13 on the long arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. Most individuals affected with Best vitelliform macular dystrophy have an affected parent. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Best vitelliform macular dystrophy is a rare disease and the prevalence is unknown. This condition has been diagnosed in individuals of European, African and Hispanic ancestry.
Best vitelliform macular dystrophy is diagnosed by the appearance of a yellow mass on the macula during an eye exam, specialized testing of the eye called an electro-oculogram (EOG) and family history. Molecular genetic testing for the VMD2 gene is available to confirm the diagnosis.
Affected individuals should have regular ophthalmologic examinations to monitor the progression of the disease. Low vision aids are beneficial for those who experience significant vision loss.
Genetic counseling is beneficial for affected individuals and their families.
Direct laser photocoagulation may be useful in the treatment of Best vitelliform macular dystrophy, but clinical trials have not been conducted to evaluate this approach.
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FROM THE INTERNET
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