Retinitis Pigmentosa 77
Patient Information
Characteristics
Background and History
Retinitis pigmentosa (RP) consists of a large group of disorders resulting from a progressive loss of the rods and cones in the retina. These are the cells that respond to light and send signals to the brain that enable us to see. Hundreds of mutant genes have been identified as responsible for these hereditary disorders and there is considerable variation in onset and progression of symptoms. The disease usually is present as an isolated eye disease but syndromal forms also occur in which there is a similar disease of the retina in association with other problems elsewhere in the body.
Clinical Correlations
The first symptom is unusual difficulty seeing in dim light which may be reported in early childhood but sometimes later in the second decade of life. There is some loss of sharp vision about the same time and this is progressive. However, the loss of vision is only roughly correlated with age. Older individuals may be legally blind. The electroretinogram (ERG) reveals severe loss of retinal function. Side vision becomes progressively constricted to between 10 and 30 degrees.
Examination of the retina often shows disturbances with clumping of retinal pigment while the retinal vessels are narrowed. Some patients develop cataracts.
There are no abnormalities outside of the eye.
Genetics
Inheritance
This condition is inherited in an autosomal recessive pattern. Parents, who are clinically normal, carry one copy of the mutation while affected individuals have two mutated copies. If both parents carry a single copy, each of their children have a 25% risk of inheriting this disorder because they may receive both copies.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
The diagnosis is made by a medical eye doctor (ophthalmologist) based on the symptoms, the appearance of the retina, and the findings of an ERG (electroretinogram).
Patients are otherwise healthy. No treatment is available for the retinal disease but they may benefit from low vision aids. If cataracts are sufficiently dense to interfere with vision they may be surgically removed.
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