Retinitis Pigmentosa 3, X-Linked
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. More than 400 mutant genes have been identified as responsible as causative 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 disease elsewhere in the body.
Clinical Correlations
The first symptoms consist of difficulty seeing at night followed by constriction of side vision and these typically appear in the first and second decades of life in this X-linked form. Later, sensitivity to light together with color vision difficulties appear. About this time sharp central vision is lost as well and some patients are legally blind by the 5th decade. Eye examinations usually show clumps of black pigment in the retina and the optic nerve that connects the retina to the brain shows damage as well. Cataracts occur in up to 50% of adult patients.
The X-linked disease is far more common in males, of course, but some females show evidence of RP as well.
Genetics
Inheritance
The X-linked form of RP is caused by a mutation on the X chromosome. Males with the mutation on their single X chromosome will usually have the complete syndrome since they have no normal gene to counterbalance the mutation. They will have no affected sons but their daughters are carriers like their paternal grandmother and have few or no symptoms. Half of the sons of carrier mothers will be affected on average. A considerable number of individuals with RP have no family history of this disease.
Pedigree
X-linked recessive, carrier mother
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
X-linked recessive, father affected
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
Diagnosis and Prognosis
The disease is usually diagnosed by an ophthalmologist based on the symptoms and the appearance of the retina. An electrical test called an ERG is often used to confirm the diagnosis. There are no signs of disease outside of the eye in most cases. Lifespan is not impacted.
Low vision aids and mobility training can be of great benefit. High doses of vitamin A palmitate have been shown to slow the progress of the disease but this requires careful monitoring to avoid complications of liver damage. Several new therapies are under investigation but these are not yet clinically useful.
Cataract surgery is indicated when the lens opacities interfere with vision.
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