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Stargardt Disease
Stargardt disease is an inherited retinal degeneration (IRD) which causes damage to the central region of the retina, known as the macula.
The cone photoreceptor cells are concentrated in the macula and degenerate, resulting in a progressive decline in central vision, colour vision and fine detailed visual acuity, with tasks such as recognising faces and driving become increasingly challenging.
Peripheral vision is largely preserved in people living with Stargardt disease because the rod cells are not severely affected.
What are the symptoms of Stargardt disease?
Stargardt disease has similar symptoms to Age-related Macular Degeneration (AMD) but arises earlier in life around 20 years of age, and is often referred to as Juvenile Macular Degeneration. People living with Stargardt disease generally experience problems with central vision and may have difficulty seeing the board at school. Affected individuals may also struggle with recognising faces and identifying colours. Blind spots in central vision are also common and may enlarge as the condition progresses.
The rate of progression and degree of visual loss can vary from person to person and even among affected members of the same family. It is, therefore, very difficult to predict what an individual’s vision will be like at a specific time in the future, although it is rare that someone living with Stargardt disease will become totally blind.
What Causes Stargardt Disease?
Mutations in the ABCA4 gene and ELOVL4 gene are responsible for Stargardt disease. The ABCA4 gene is the most common gene implicated in stargardt disease and when functioning normally, it produces the ABCA4 protein which removes vitamin A by-products, such as A2E and other toxic substances from the photoreceptors. When the ABCA4 gene is mutated, toxic substances which form lipofuscin accumulate in the photoreceptor cells and supporting retinal pigment epithelium (RPE) cells. This causes the RPE and subsequently the photoreceptor cells to die, particularly the cone cells which are most concentrated around the macula and is why central vision is so commonly affected.
Stargardt disease caused by mutations in the ABCA4 gene is inherited in an autosomal recessive pattern of inheritance, meaning that two faulty copies of the faulty gene copy are required to cause the disease. Therefore, an affected individual received one faulty gene copy from each parent and people with one faulty gene copy are “carriers” of the disease, meaning they are not affected.
People living with Stargardt disease caused by a mutated ELOVL4 gene have an autosomal dominant form of the disease, meaning only one faulty gene copy is required for a person to be affected. People who have the faulty ELOVL4 gene develop protein clumps which interfere with their photoreceptors, resulting in gradual cell-death and progressive loss of central vision. However, this autosomal dominant form of Stargardt disease is much less common than the recessive form, which is caused by the ABCA4 gene.
More information on genetic inheritance patterns can be found at our Genetics and Inheritance section.
There are a number of tests which can help to correctly diagnose Stargardt disease. Electroretinograms assess the integrity of the rod and cone photoreceptor cells and measure their electrical impulses in response to light are frequently used, while optical coherence tomography (OCT) tests examine the different layers of the retina for abnormalities. Fundus photos, which take images of the retina and reveal the presence of lipofuscin is another common diagnostic test for stargardt disease. Genetic testing is also a crucial part of the screening process which can reveal the specific mutation causing stargardt disease and can help identify who else may be at risk in your family.
What treatments are available?
Currently, there are no treatments available for Stargardt disease, although there have been many advances in clinical research, with many studies reaching clinical trial. You can read about the various clinical trials for stargardt disease on the clinicaltrials.gov website.
There is research to suggest that UV light can cause toxicity of the waste products accumulating in the retina. Therefore, it is recommended that people living with Stargardt disease wear UV screening sunglasses when out in direct sunlight. Recent evidence also suggests that taking more than the recommended amount of vitamin A, such as in a vitamin supplement, may have a negative effect on the condition and should be avoided. Low vision aids can support people living with stargardt disease, with magnification tools and electronic reading devices proving very useful for people when reading.
Gene therapy is a very promising field of clinical research for stargardt disease, particularly to replace mutations in the ABCA4 gene with normal functioning copies. Gene therapy uses a harmless virus called an adeno-associated virus to deliver the normal gene copy. Originally, the ABCA4 gene was too large to fit into the standard viral vector and another delivery method had to be engineered, which was successful in mouse models with stargardt disease.
Stem-cell therapy investigates how certain cells (stem-cells) can generate into many of the body’s cell-types, including the photoreceptor cells and is a promising treatment strategy which is also being investigated in other retinal conditions, including Age-related Macular Degeneration.
Although there is no treatment currently available for Stargardt disease, it is still very important that people with the condition have regular eye exams as they may develop other retinal conditions, some of which can be treated.