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What is Stargardt disease?
Stargardt disease is an inherited disorder of the retina – the tissue at the back of the eye that senses light. The disease typically causes vision loss during childhood or adolescence, although in some forms, vision loss may not be noticed until later in adulthood. It is rare for people with the disease to become completely blind. For most people, vision loss progresses slowly over time to 20/200 or worse. (Normal vision is 20/20).
Stargardt disease is also called Stargardt macular dystrophy, juvenile macular degeneration, or fundus flavimaculatus. The disease causes progressive damage or degeneration of the macula, which is a small area in the center of the retina that is responsible for sharp, straight-ahead vision. Stargardt disease is one of several genetic disorders that cause macular degeneration. Experts estimate that 1 in 8-10 thousand people have Stargardt disease.
What causes Stargardt’s Disease?
Stargardt’s is an inherited disease passed along to children when both parents carry mutations of a gene associated with vitamin A processing in the eye. Parents can carry recessive genetic traits responsible for Stargardt’s, even though they themselves may not have the disease.
Researchers have found that about 5 percent of people carry gene mutations that cause inherited retinal diseases such as Stargardt’s disease and retinitis pigmentosa. However, the inheritance pattern of Stargardt’s is variable, and it’s possible for up to half of the children of a single affected parent to develop the condition. Also, the degree of vision loss caused by Stargardt’s disease can be more severe or less severe in children, compared with that experienced by an affected parent.
What are the symptoms of Stargardt’s Disease?
The symptom that brings most people to an eye doctor is a change in central vision. A doctor looking at the retina of a person with Stargardt disease will see characteristic yellowish flecks in and under the macula. The flecks might extend outward in a ring-like fashion.
The flecks are deposits of lipofuscin, a fatty byproduct of normal cell activity. In Stargardt disease, lipofuscin accumulates abnormally. The Foundation Fighting Blindness supports research studying lipofuscin build up and ways to prevent it.
A decrease in color perception also occurs in Stargardt disease. This is because photoreceptor cells involved in color perception are concentrated in the macula.
Who is at risk for Stargardt disease?
Stargardt disease is almost always the result of a genetic defect. The gene that causes the disease is recessive, meaning it has to be inherited by both parents in order for the disease to appear. Someone who inherits the gene from only one parent will be a carrier for Stargardt disease but will not have any symptoms of it. However, if that person has a child with someone else who is a carrier, there is a 25 percent chance the child will have Stargardt disease.
How is Stargardt disease inherited?
Genes are bundled together on structures called chromosomes. One copy of each chromosome is passed by a parent at conception through egg and sperm cells. The X and Y chromosomes, known as sex chromosomes, determine whether a person is born female (XX) or male (XY) and also carry other non-sex traits.
In autosomal recessive inheritance, it takes two copies of the mutant gene to give rise to the disease. An individual who has one copy of a recessive gene mutation is known as a carrier. When two carriers have a child, there is a:
- 1 in 4 chance of having a child with the disease,
- 1 in 2 chance of having a child who is a carrier,
- 1 in 4 chance of having a child who neither has the disease nor is a carrier.
In autosomal dominant inheritance, it takes just one copy of the mutant gene to bring about the disease. When an affected parent with one dominant gene mutation has a child, there is a 1 in 2 chance that a child will inherit the disease.
Autosomal recessive mutations in the ABCA4 gene account for about 95 percent of Stargardt disease. The other five percent of cases are caused by rarer mutations in different genes that play a role in lipofuscin function. Some of these mutations are autosomal dominant.
Are there any treatments for Stargardt disease?
Unfortunately, at the moment there are no treatments for Stargardt disease. Research and developments into gene therapy and stem cells is very active and it is hoped that this may lead to treatments becoming available at some stage in the future.
Researchers have reported that exposure to ultraviolet (UV) light may theoretically cause further retinal damage. Therefore it may be sensible to wear sunglasses with UV protection, that conform to European Standard, and a hat with a wide brim to protect you from the sun’s damaging ultraviolet rays.
Stargardt disease is also known as Stargardt macular dystrophy or fundus flavimaculatus. In addition to recessive Stargardt disease, there are other rarer forms inherited as dominant rather than recessive traits.