Retinitis pigmentosa, also known as RP, refers to a group of inherited diseases causing retinal degeneration. The retina is a thin piece of tissue lining the back of the eye. Rod and cone photoreceptors in the retina convert light into electrical signals that the brain interprets as vision. People with RP experience a gradual decline in their vision, because photoreceptors degenerate.
Forms of RP and related diseases include Usher syndrome, Leber congenital amaurosis, and Bardet-Biedl syndrome, among others.
Living 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 activated by dim light, their degeneration affects peripheral and night vision. Vision becomes more constricted over time. If and when the disease progresses and cones become affected, visual acuity, color perception, and central vision are diminished.
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 reduced ability to discriminate colors and perceive details.
RP is typically diagnosed in children, adolescents and young adults. It is a progressive disorder. The rate of progression and degree of visual loss varies from person to person. Many people with RP are legally blind by age 40, with a central visual field of less than 20 degrees in diameter.
An estimated 100,000 people in the U.S. have RP, mainly caused by mutations (variations) in a single gene inherited from one or both parents. The mutated gene gives 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.) Mutations in dozens of genes have been linked to RP.
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 and one normal copy, but have no symptoms themselves. They are therefore referred to as unaffected carriers. Each of their children has a 25 percent chance of being affected by inheriting a mutated copy from each parent. If the child inherits one mutated copy from one parent, they will be an unaffected carrier.
Genetic testing is available for retinitis pigmentosa. It helps with attaining an accurate diagnosis and assessing the risk of passing the disorder from parent to offspring. A patient with an accurate diagnosis is in a better position to understand which emerging treatment approaches and clinical trials are most appropriate for them.