Information on the following diseases can be found in the Related Disorders section of this report:

• adult vitelliform macular dystrophy
• age-related macular degeneration

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.

Adult vitelliform macular dystrophy is an autosomal dominant form of macular dystrophy that usually begins in middle age. A yolk-like mass is often present on the macula but the EOG testing that is used to evaluate the function of the layer of cells between the retina and eye wall (retinal pigment epithelium) is usually normal. Some affected individuals have an abnormality in the RDS gene or the VMD2 gene.

Age-related macular degeneration is a common type of macular degeneration that usually occurs in people over 60 years of age. (For more information on this condition, choose “macular degeneration” as your search term in the Rare Disease Database).

Diagnosis
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.

Treatment
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.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

MacDonald IM, Lee T, and Mah DY, (Updated 10/27/03). Best Vitelliform Macular Dystrophy. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2005. Available at http://www.genetests.org. Accessed 5/05.

Altaweel M. Best Disease. EMedicine. Last Updated: 10/4/04.

McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore, MD: The Johns Hopkins University; Entry No. 153700; Last Update: 3/9/04.

Blodi CF and Stone EM. Best’s vitelliform dystrophy. Opthalmic Paediatr Genet 1990;11:49-59.

Eksandh L, Bakall B, Bauer B, et al. Best’s vitelliform macular dystrophy caused by a new mutation (Val89Ala) in the VMD2 gene. Opthalmic Genet 2001; 22:107-15.

Fishman GA, Baca W, Alexander KR, et al. Visual acuity in patients with best vitelliform macular dystrophy. Opthalmology 1993;100:1165-70.

Loewenstein A, Godel V, Godel L, et al. Variable phenotypic expressivity of Best’s vitelliform dystrophy. Opthalmic Paediatr Genet 1993;14:131-6.

Marano F, Deutman AF, Leys A, et al. Hereditary retinal dystrophies and choroidal neovascularization. Graefes Arch Clin Exp Opthalmol 2000;238:760-4.

Palmowski AM Allagayer R, Heinemann-Vernaleken B, et al. Detection of retinal dysfunction in vitelliform macular dystrophy using the multifocal ERG (MF-ERG). Doc Opthalmol 2003;106:145-52.

Petrukhin K, Koisti MJ, Bakall B, et al. Identification of the gene responsible for Best Macular dystrophy. Nat Genet 1998;19:241-7.