Retinitis pigmentosa

Abstract

Retinis Pigmentosa (RP) is a term that includes a group of progressive hereditary retinal diseases involving degeneration of rod and cone photoreceptors, predominantly the former, and is one of the leading causes of hereditary blindness in the developed world. Ganglion cells are also affected, possibly due to transsynaptic neuronal damage caused by loss of neuronal input from the degenerating photoreceptor cell layer. Clinical symptoms include nyctalopia, progressive visual field loss, and deterioration in visual acuity in adolescence. No effective therapy exists at present. It affects one in 3000-5000 individuals and can be caused by mutations in more than 40 genes. Retinitis Pigmentosa may exist either alone (nonsyndromic) or as part of a neurological or systemic disorder, such as Usher's syndrome and Infantile Refsum's disease. Typical findings on retinal examination include retinal vessel attenuation. Bone spicule formation is also noted around the intraretinal vessels (pigmentary clumping), caused by the hyperplasia and migration of retinal pigment epithelial cells into the inner layers of the neurosensory retina. The disease may be inherited as either autosomal recessive, autosomal dominant or X-linked. Autosomal dominant inheritance is the most common. Several mechanisms to explain the degeneration process have been proposed. These include misfolding of the rod visual pigment Rhodopsin preventing its transportation to the outer segment, dysfunction of cell transport systems that are involved with photoreceptor protein localization, starvation of cones and cyclic GMP-dependent protein kinase activation. Therapies that are currently under investigation include the use of ribozymes for the targeted reduction of mutant-allele mRNA and the use of retinoids to improve protein folding. © 2010 by Nova Science Publishers, Inc. All rights reserved.