Retinitis Pigmentosa

What is Retinitis Pigmentosa?

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.

Normal vision

As seen by a person with retinitis pigmentosa

What are the symptoms?

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. It is a genetic disorder and, therefore, is almost always inherited.

How is RP inherited?

An estimated 100,000 people in the U.S. have RP, mainly caused by mutated genes 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, parents who carry the gene but have no symptoms themselves could have some children who are affected and others who are not. Similarly, in autosomal dominant RP, an affected parent could have affected and unaffected children. In families with X-linked RP, only males are affected; females carry the genetic trait but do not experience serious vision loss.

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.

What treatments are available?

The Foundation Fighting Blindness (FFB) has funded many important RP research and clinical advances. A nutritional therapy using vitamin A and docosahexaenoic acid (DHA) has emerged as an effective treatment for many patients; gene therapies are progressing through preclinical trials; technologies for delivering therapeutic agents to rod and cone cells are being studied in Phase II/lll clinical studies; an implantable microchip to enhance retinal function is under development. Details are available on FFB’s Web site, www.FightBlindness.org, or by calling 1-800-683-5555.

Although not a treatment for RP, it is also important to know that low vision aids are useful for maintaining independence. Low vision specialists can make personalized recommendations for mechanical, optical, electronic, and computer-based low vision products.

What testing is available?

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.

However, not all RP-causing genes have been discovered. If a person chooses to get genetically tested, there is about a 50 percent chance that their disease-causing gene will be identified.

Retinitis Pigmentosa - Risk Factors

Recent research findings suggest that in some forms of Retinitis Pigmentosa, prolonged, unprotected exposure to sunlight may accelerate vision loss. Therefore, The Foundation recommends that patients wear sunglasses and visors when outdoors.

Some women feel that their vision loss progressed more rapidly during pregnancy. However, the effect of pregnancy on Retinitis Pigmentosa has not been clinically studied.

Retinitis Pigmentosa is an inherited, genetic disease. It is caused by mutations in genes that are active in retinal cells. Gene mutations are programmed into your cells at the time of conception. Retinitis Pigmentosa is not caused by injury, infection or exposure to any toxic substance.

There are three common inheritance patterns: autosomal dominant, autosomal recessive, and X-linked.

In autosomal dominant forms of Retinitis Pigmentosa, an affected person has one gene with a mutation causing the disease paired with one healthy, normal gene. When the affected person has children with an unaffected partner, there is a 50 percent chance that the affected parent will pass the disease-causing gene to each child. The unaffected partner will only pass normal genes. In dominant diseases, a child who does not have the disease gene will not have the disease and cannot pass the disease to his or her children.

In autosomal recessive forms of Retinitis Pigmentosa, unaffected parents, who are carriers, have one gene with a disease-causing mutation paired with one normal gene. Each of their children then has a 25 percent chance (or 1 chance in 4) of inheriting the two diseased genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene.

In X-linked forms of Retinitis Pigmentosa, the gene for the disease is located on the X chromosome. Females have two X chromosomes and can carry the disease gene on one of these X chromosomes. Because they have a healthy version of the gene on their other X chromosome, X-linked diseases typically do not affect females. Sometimes, however, when carrier females are examined, the retina shows minor signs of the disease.

Males have only one X chromosome paired with one Y chromosome and are therefore genetically susceptible to X-linked diseases. Males cannot be carriers of X-linked diseases. Males affected with an X-linked disease always pass the gene on the X chromosome to their daughters, who then become carriers. Affected males never pass an X-linked disease gene to their sons because fathers pass the Y chromosome to their sons.

Female carriers have a 50 percent chance (or 1 chance in 2) of passing the X-linked disease gene to their daughters, who become carriers, and a 50 percent chance of passing the gene to their sons, who are then affected by the disease.

It is important to remember that because Retinitis Pigmentosa is an inherited disorder, it commonly affects other members of a family. If someone in your family is diagnosed with a retinal degeneration, it is strongly advised that all members of the family contact an eye care professional.