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
rod-cone disease, Bardet-Biedl syndrome, and Refsum disease, among
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
When the more centrally located cones - responsible for color and sharp
central vision - become involved, the loss is in color perception and
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.
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
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.
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.
Are there any other related diseases?
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