Retinitis pigmentosa

Retinitis pigmentosa, or RP, is a genetic eye condition. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some sight all their life. Others go completely blind from RP, in some cases as early as childhood. Progression of RP is different in each case.

RP is a group of inherited disorders in which abnormalities of the photoreceptors (rods and cones) or the retinal pigment epithelium (RPE) of the retina lead to progressive visual loss. Affected individuals first experience defective dark adaptation or nyctalopia (night blindness), followed by constriction of the peripheral visual field and, eventually, loss of central vision late in the course of the disease.

Signs

Mottling of the retinal pigment epithelium with bone-spicule pigmentation is typically pathognomonic for retinis pigmentosa. Other ocular features include waxy pallor of the optic nerve head, attenuated retinal vessels, cellophane maculopathy, cystic macular edema, and posterior subcapsular cataract.

Diagnosis

The diagnosis of RP relies upon documentation of progressive loss in photoreceptor function by electroretinography (ERG) and visual field testing. The mode of inheritance of RP is determined by family history. At least 35 different genes or loci are known to cause nonsyndromic RP. DNA testing is available on a clinical basis for RLBP1 (autosomal recessive, Bothnia type RP), RP1 (autosomal dominant, RP1), RHO (autosomal dominant, RP4), RDS (autosomal dominant, RP7), PRPF8 (autosomal dominant, RP13), PRPF3 (autosomal dominant, RP18), CRB1 (autosomal recessive, RP12), ABCA4 (autosomal recessive, RP19), and RPE65 (autosomal recessive, RP20). For all other genes, molecular genetic testing is available on a research basis only.

RP can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. X-linked RP can be either recessive, affecting primarily only males, or dominant, affecting both males and females, although females are always more mildly affected. Some digenic and mitochondrial forms have also been described. Genetic counseling depends on an accurate diagnosis, determination of the mode of inheritance in each family, and results of molecular genetic testing. RP combined with progressive deafness is called Usher syndrome.

Genetics

In 1989, a mutation of Rhodopsin, gene that plays an essential part in the visual transduction cascade, has been identified. Until now, more than 100 mutations have been found in this gene, accounting for 15% of all types of retinal degeneration. Most of those mutations are missense mutation and inherited mostly in a dominant manner.

Treatment

There is currently no medical treatment for retinitis pigmentosa, although scientists continue to investigate possible treatments. Future treatments may involve retinal transplants, artificial retinal implants ^*, gene therapy, stem cells, nutritional supplements, and/or drug therapies.

Bibliography

Jones BW, CB Watt, JM Frederick, W Baehr, CK Chen, EM Levine, AH Milam, MM LaVail, RE Marc 2003 Retinal remodeling triggered by photoreceptor degenerations. The Journal of Comparative Neurology 464: 1-16.

Marc RE, BW Jones 2003 Retinal remodeling in inherited photoreceptor degenerations. Molecular Neurobiology 28: 139-148.

Marc RE, BW Jones, CB Watt and E Strettoi 2003 Review: Neural Remodeling in Retinal Degeneration. Progress in Retinal and Eye Research 22: 607-655.

Jones BW and RE Marc. 2005 Review: Retinal remodeling during retinal degeneration. Experimental Eye Research, 81: 121-244

Marc RE, BW Jones and CB Watt. 2005 Review: Retinal remodeling: Circuitry revisions triggered by photoreceptor degeneration. In Plasticity in the Visual system: from Genes to Circuits. Springer, pp. 33-54.

Jones BW, CB Watt and RE Marc. 2005 Review: Retinal remodeling in retinal degenerations. Clinical and Experimental Optometry, 88: 282-291.

External links

The British Retinitis Pigmentosa Society
Retina New Zealand
Retinitis Pigmentosa (Medline Plus).
More about Retinitis Pigmentosa
Not Fade Away — one man's journey into blindness (Exploratorium)
Retinal implants may soon restore lost vision
The Boston Retinal Implant Project

genetic disorders | Ophthalmology