- What is retinitis pigmentosa?
- What are the symptoms?
- How is RP inherited?
- What treatments are available?
- What testing is available?
- Are there any related diseases?
Retinitis pigmentosa (RP) refers to a group of inherited diseases causing retinal degeneration. The cell-rich retina lines the back inside wall of the eye. It is responsible for capturing images from the visual field. People with RP experience a gradual decline in their vision because photoreceptor cells (rods and cones) die. Forms of RP and related diseases include Usher syndrome, Leber’s congenital amaurosis, rod-cone disease, Bardet-Biedl syndrome, and Refsum disease, among others.
As seen by a person with retinitis pigmentosa
Symptoms depend on whether rods or cones are initially involved. In most forms of RP, rods are affected first. Because rods are concentrated in the outer portions of the retina and are triggered by dim light, their degeneration affects peripheral and night vision. When the more centrally located cones - responsible for color and sharp central vision - become involved, the loss is in color perception and central vision.
Night blindness is one of the earliest and most frequent symptoms of RP. People with mainly cone degeneration, however, first experience decreased central vision and ability to discriminate color.
RP is typically diagnosed in adolescents and young adults. It is a progressive disorder. The rate of progression and degree of visual loss varies from person to person. Most people with RP are legally blind by age 40, with a central visual field of less than 20 degrees in diameter. In families with X-linked RP, males are more often and more severely affected; females carry the genetic trait and experience vision loss less frequently.
An estimated 100,000 people in the U.S. have RP, mainly caused by gene mutations (variations) inherited from one or both parents. Mutated genes give the wrong instructions to photoreceptor cells, telling them to make an incorrect protein, or too little or too much protein. (Cells need the proper amount of particular proteins in order to function properly.) Many different gene mutations exist in RP. In Usher syndrome, for example, at least 14 disease-causing genes have been identified.
Genetic mutations can be passed from parent to offspring through one of three genetic inheritance patterns — autosomal recessive, autosomal dominant, or X-linked.
In autosomal recessive RP, both parents carry one copy of the mutated gene but have no symptoms themselves. Children have a 25 percent chance of being affected by inheriting a mutated copy from each parent.
In autosomal dominant RP, usually one parent is affected and is the only parent with a mutated gene. A child has a 50 percent chance of being affected by inheriting the mutated gene from that parent.
In families with X-linked RP, the mother carries the mutated gene, and her sons have a 50 percent chance of being affected. Daughters are carriers and aren’t usually affected. However, some daughters are affected, but with milder symptoms.
If a family member is diagnosed with RP, it is strongly advised that other members of the family also have an eye exam by a physician who is specially trained to detect and treat retinal degenerative disorders. Discussing inheritance patterns and family planning with a genetic counselor can also be useful.
Foundation-funded researchers are currently working towards treatments for RP. For the latest information on the work that is being done, please click here.
Genetic testing is available for RP. It helps assess the risk of passing the disorder from parent to offspring. It also helps with attaining an accurate diagnosis. A patient with an accurate diagnosis is in a better position to keep track of new findings, research developments, and treatment approaches.
Other inherited diseases share some of the clinical symptoms of RP. The most common is Usher syndrome, where hearing and vision are both affected. Other related syndromes being studied through FFB funding include Best disease, choroideremia, gyrate-atrophy, and Stargardt disease.
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*Images courtesy of the National Eye Institute, NIH