Stargardt disease

Definition

Stargardt disease (STGD) is an inherited vision disorder with macular degeneration that typically affects younger people.

Description

STGD is the most common form of inherited macular degeneration (or dystrophy), a disorder of the retina, that affects younger people. The condition is also known as Stargardt macular dystrophy, juvenile macular degeneration, macular dystrophy with flecks, and fundus flavimaculatus.

Common symptoms of STGD include progressive loss of central vision, problems identifying and differentiating colors, and difficulty seeing fine details clearly.

Genetic profile

There are different types of STGD. The most common form is Type 1, which is associated with autosomal recessive inheritance . In this type, there may be no family history of the condition, and it usually affects only one generation. A couple has a 25% chance of having another affected son or daughter once a child is diagnosed with STGD Type 1. This type of STGD is associated with mutations in the ABCA4 (or ABCR) gene , which is located on chromosome 1. This gene is involved in moving vitamin A compounds naturally to and from cells in the retina; these cells are often impaired in STGD.

Other rarer forms of macular dystrophy with symptoms nearly identical to STGD have been called Stargardt-like macular dystrophy types 2, 3, and 4. These are associated with autosomal dominant inheritance. In these types, a family history of the condition is quite common and STGD may be present in several generations of a family tree. A parent with these macular dystrophies has a 50% chance of having an affected son or daughter. Some of these individuals have been found to have mutations in the ELOVL4 gene on chromosome 6.

Demographics

STGD is found worldwide, affecting males and females equally. The incidence for Type 1 is estimated to be between one in 1,600 and one in 15,000 individuals. In all, it accounts for 7% of all retinal dystrophies.

STGD Type 1 is usually diagnosed in individuals under the age of 20 when decreased central vision is the first problem noticed. In contrast, Stargardt-like macular dystrophies and age-related macular degeneration typically first show up in adulthood.

Signs and symptoms

Each person with STGD experiences their symptoms differently. STGD affects the macula, a specialized portion of the retina that is highly responsible for the ability to see straight in front, notice colors, and see fine details. The macula is normally full of photoreceptors called cone cells. Cone cells help process the light rays that naturally hit the retina. In STGD, these cone cells slowly begin to die and lose function. In addition, the macula's appearance may begin showing abnormal yellow-white flecks that are shaped irregularly in people who have STGD.

Problems with central vision may be an early sign of STGD. The progression of this varies from person to person, and is impossible to predict. In addition, one's ability to see clearly (visual acuity) becomes progressively worse over time. This can progress from near-normal visual acuity to legal blindness. By the age of 50 years, about half of people with STGD have visual acuity equal to or worse than that of legal blindness. Unfortunately, the reduced visual acuity in STGD cannot usually be corrected with prescription eyeglasses or contact lenses.

In later stages of STGD, color vision can be impacted. People may have trouble identifying colors or distinguishing them from one another. Rarely, people may experience difficulty with brightly lit conditions, blind spots in their vision, and problems with adjusting to dark environments.

Diagnosis

A diagnosis is most commonly made based on a person's symptoms. However, genetic testing is available to those suspected to have the condition. A few laboratories offer molecular testing of the ABCA4 and ELOVL4 genes on a clinical basis. Still others offer testing of these genes as part of a research study.

A young person who complains of problems with their central vision or has poor visual acuity that cannot be corrected should be tested for STGD. A combination of various visual investigations can help rule out other diagnoses and identify visual problems that are consistent with STGD.

A detailed eye examination with an ophthalmologist can help determine one's visual acuity and general eye health. The physician may want to track the visual acuity over time to determine whether it can be corrected with prescription eyeglasses or contact lenses. The ophthalmologist may also order visual tests to get more information about a diagnosis.

Testing of the visual fields can determine how much is being seen from left to right, and up and down. The full field of vision is studied to identify any blind spots or clarify whether the central vision is affected.

Fluorescein angiography (FA) can be helpful to determine whether blood flow is normal throughout the back of the eye. These detailed photographs of the eye's blood vessels can help identify any circulatory problems at the back of the eye, as well as changes in the retina's structure.

Fundus photographs can be taken to document changes in the eye structure, shape, and color. In STGD, this can sometimes show the yellowish-white flecks on the retina, which may actually fade with time. Sometimes there are other color changes in the retina of people with STGD as well.

An electroretinogram (ERG) tests how well the photoreceptors in the retina are functioning. Specifically for STGD, this test is very good at identifying how well the cone cells are working. It can also show how a person with STGD progressively loses their working cone cells.

An electro-oculogram is similar to an ERG in that it studies retinal function and health. However, it is also meant to study the natural connection that exists between the eye and brain. This pathway must function normally in order for people to recognize an image that their eye sees. For STGD, this type of test can further document the cone cell abnormalities or loss.

STGD should not be confused with age-related macular degeneration (AMD), a relatively common condition in individuals often past the age of 50 years. Though the symptoms may be very similar, AMD has not been found to be associated with mutations in the ABCA4 or ELOVL4 genes.

Treatment and management

There is no cure for STGD, or known way to stop the disease progression altogether. However, some things can help maintain good retinal function and health.

It is felt that a diet rich in leafy green vegetables and fish may be good for the retina. In addition, certain fish contain omega-3 fatty acids, such as docosahexanoic acid (DHA) that is naturally found in the retina in very high concentrations. Eating a diet of fish like salmon, tuna, mackerel, or whitefish twice a week should naturally provide good DHA levels. Otherwise, good fish oil capsules containing DHA and other omega fatty acids can be obtained with a prescription or purchased at specialty health stores.

Multivitamins containing vitamins A, E, and C may be useful. These have antioxidant properties, which may be protective for the eyes. However, large doses of certain vitamins may be toxic, and affected individuals should speak to their doctors before taking supplements.

Protecting the eyes from harmful ultraviolet rays is essential to cone cell health. People with STGD should wear good sunglasses outdoors and especially when over water or near snow on a bright, sunny day.

Smoking has been associated with deteriorating retinal health. Even quitting smoking late in life can make a positive impact on eye health.

Low vision aids can be helpful for those in school or at work. Binocular lens and magnifying screens, large-print reading materials, closed-circuit television, and other tools can be helpful and are often available from organizations supporting those with vision loss.

Living with a chronic vision problem makes a significant impact on a person's life and family. It is often helpful for families to have a social worker connect them to helpful resources. Others may find genetic counseling , psychotherapy, or meeting other individuals with STGD through support groups helpful.

Prognosis

Life expectancy is normal in STGD. A person's vision loss is progressive, but the rate of this is unpredictable. Research and future treatments continue to offer hope for those with this type of macular dystrophy.

Resources

WEBSITES

Genetic Alliance. 2005 (March 16, 2005). <http://www.geneticalliance.org>.

Online Mendelian Inheritance in Man. (March 16, 2005.) <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM>.

ORGANIZATIONS

The Canadian National Institute for the Blind. National Office, 1929 Bayview Avenue, Toronto, ON M4G 3E8. Phone: (416) 486-2500. Fax: (416) 480-7677. <http://cnib.ca/>.

The Foundation Fighting Blindness. 11435 Cronhill Drive, Owings Mills, MD 21117-2220. Local phone: (410) 568-0150. Local TDD: (410) 363-7139. Toll-free phone: (888) 394-3937. Toll-free TDD: (800) 683-5555. Email: [email protected]. <http://www.blindness.org/>.

The Foundation Fighting Blindness–Canada. 60 St. Clair Ave., East Suite 703, Toronto, ON, Canada M4T 1N5. Phone: (416) 360-4200. Toll-free phone: (800) 461-3331. Fax: (416) 360-0060. Email: [email protected]. <http://www.ffb.ca/>.

Deepti Babu, MS, CGC