Vitelliform Macular Dystrophy

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What is vitelliform macular dystrophy?

Vitelliform macular dystrophy is a genetic eye disorder that can cause progressive vision loss. This disorder affects the retina, which is a specialized light-sensitive tissue that lines the back of the eye. Specifically, vitelliform macular dystrophy disrupts cells in a small area near the center of the retina called the macula. The macula is responsible for sharp central vision, which is needed for detailed tasks such as reading, driving, and recognizing faces.

Vitelliform macular dystrophy causes a fatty yellow pigment (lipofuscin) to build up in cells underlying the macula. Over time, the abnormal accumulation of this substance can damage cells that are critical for clear central vision. As a result, people with this disorder often lose their central vision and may experience blurry or distorted vision. Vitelliform macular dystrophy does not affect side (peripheral) vision or the ability to see at night.

Researchers have described two forms of vitelliform macular dystrophy with similar features. The early-onset form (known as Best disease) usually appears in childhood; however, the onset of symptoms and the severity of vision loss vary widely. The adult-onset form begins later, usually in middle age, and tends to cause relatively mild vision loss. The two forms of vitelliform macular dystrophy each have characteristic changes in the macula that can be detected during an eye examination.

How common is vitelliform macular dystrophy?

Vitelliform macular dystrophy is a rare disorder; its incidence is unknown.

What genes are related to vitelliform macular dystrophy?

Mutations in the BEST1 and RDS genes cause vitelliform macular dystrophy.

Mutations in the BEST1 gene are responsible for Best disease. Changes in either the BEST1 or RDS gene can cause the adult-onset form of vitelliform macular dystrophy; however, less than a quarter of cases result from mutations in these two genes. In most cases, the cause of the adult-onset form is unknown.

The BEST1 gene provides instructions for making a protein called bestrophin. Although its exact function is uncertain, this protein likely acts as a channel that controls the movement of negatively charged chlorine atoms (chloride ions) into or out of cells in the retina. Mutations in the BEST1 gene probably lead to the production of an abnormally shaped channel that cannot regulate the flow of chloride. Researchers have not determined how these malfunctioning channels are related to the buildup of lipofuscin in the macula and progressive vision loss.

The RDS gene provides instructions for making a protein called peripherin. This protein is essential for the normal function of light-sensing (photoreceptor) cells in the retina. Mutations in the RDS gene disrupt the structures in these cells that contain light-sensing pigments, leading to vision loss. It is unclear why RDS mutations affect only central vision in people with adult-onset vitelliform macular dystrophy.

How do people inherit vitelliform macular dystrophy?

Best disease is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one parent with the condition.

The inheritance pattern of adult-onset vitelliform macular dystrophy is uncertain. Some studies have suggested that it may be inherited in an autosomal dominant pattern. Many affected people, however, have no history of the disorder in their family and only a small number of affected families have been reported.

Source: National Institutes of Health

New ophthalmology study findings have been reported by researchers at University of Nijmegen, Department of Ophthalmology

"Patients who did not have a mutation in the VMD2 gene were screened for mutations in the peripherin/RDS gene. Patient age at onset of the disease was highly variable, ranging from 5 to 59 years. The peripheral lesions varied in number, size, and overall appearance but showed similar characteristics at autofluorescence imaging and optical coherence tomography compared with the central vitelliform lesion. Mutations in the VMD2 gene were identified in 9 of 15 patients. One patient without a VMD2 mutation carried a sequence variant in the 5' untranslated region of the peripherin/RDS gene. Multifocal vitelliform dystrophy is a clinically and genetically heterogeneous retinal disease that can be caused by mutations in the VMD2 gene. Other genes associated with this phenotype remain to be identified," wrote C.J. Boon and colleagues, University of Nijmegen, Department of Ophthalmology.

The researchers concluded: "Clinical Relevance Clinical and molecular genetic characterization of multifocal vitelliform dystrophy may lead to better understanding of the pathophysiological mechanisms underlying this phenotype and may enable a more accurate prognosis in individual patients."

Boon and colleagues published their study in Archives of Ophthalmology (Clinical and genetic heterogeneity in multifocal vitelliform dystrophy. Archives of Ophthalmology, 2007;125(8):1100-6).

For additional information, contact C.J. Boon, Radboud University Nijmegen Medical Centre, Dept. of Ophthalmology, PO Box 9101, 6500 HB Nijmegen, Netherlands.

Publisher contact information for the journal Archives of Ophthalmology is: American Medical Association, 515 N State St., Chicago, IL 60610, USA.

Keywords: Netherlands, Genetics, Ophthalmology.

This article was prepared by Life Science Weekly editors from staff and other reports. Copyright 2007, Life Science Weekly via NewsRx.com.