ABSTRACT: Retinitis pigmentosa (RP) is an inherited retinal dystrophy caused by the loss of photoreceptors and characterized by retinal pigment deposits visible on fundus examination. Prevalence of non syndromic RP is approximately 1/4,000. The most common form of RP is a rod-cone dystrophy, in which the first symptom is night blindness, followed by the progressive loss in the peripheral visual field in daylight, and eventually leading to blindness after several decades. Some extreme cases may have a rapid evolution over two decades or a slow progression that never leads to blindness. In some cases, the clinical presentation is a cone-rod dystrophy, in which the decrease in visual acuity predominates over the visual field loss. RP is usually non syndromic but there are also many syndromic forms, the most frequent being Usher syndrome. To date, 45 causative genes/loci have been identified in non syndromic RP (for the autosomal dominant, autosomal recessive, X-linked, and digenic forms). Clinical diagnosis is based on the presence of night blindness and peripheral visual field defects, lesions in the fundus, hypovolted electroretinogram traces, and progressive worsening of these signs. Molecular diagnosis can be made for some genes, but is not usually performed due to the tremendous genetic heterogeneity of the disease. Genetic counseling is always advised. Currently, there is no therapy that stops the evolution of the disease or restores the vision, so the visual prognosis is poor. The therapeutic approach is restricted to slowing down the degenerative process by sunlight protection and vitaminotherapy, treating the complications (cataract and macular edema), and helping patients to cope with the social and psychological impact of blindness. However, new therapeutic strategies are emerging from intensive research (gene therapy, neuroprotection, retinal prosthesis).

Retinitis pigmentosa, pigmentary retinopathies, and neurologic diseases.Curr Neurol Neurosci Rep. 2006 Sep;6(5):403-13

Retinitis pigmentosa (RP) refers to a group of inherited retinal diseases with phenotypic and genetic heterogeneity. The pathophysiologic basis of the progressive visual loss in patients with RP is not completely understood but is felt to be due to a primary retinal photoreceptor cell degenerative process mainly affecting the rods of the peripheral retina. In most cases RP is seen in isolation (nonsyndromic), but in some other cases it may be a part of a genetic, metabolic, or neurologic syndrome or disorder. Nyctalopia, or night blindness, is the most common symptom of RP. The classic fundus appearance of RP includes retinal pigment epithelial cell changes resulting in retinal hypo- or hyperpigmentation ("salt-and-pepper"), retinal granularity, and bone spicule formation. The retinal vessels are often narrowed or attenuated and there is a waxy pallor appearance of the optic nerve head. Electroretinography will demonstrate rod and cone photoreceptor cell dysfunction and is a helpful test in the diagnosis and monitoring of patients with RP. A detailed history with pedigree analysis, a complete ocular examination, and the appropriate paraclinical testing should be performed in patients complaining of visual difficulties at night or in dim light. This review discusses the clinical manifestations of RP as well as describing the various systemic diseases, with a special emphasis on neurologic diseases, associated with a pigmentary retinopathy.

Light in retinitis pigmentosa.Trends Genet. 2005 Feb;21(2):103-10.

Retinitis pigmentosa (RP) is one of the most genetically heterogeneous inherited disorders. Twelve genes have now been identified in the autosomal dominant form of the disease, including some recently characterized genes that show unprecedented and fascinating traits in both their function and in their expression profiles. These include many widely expressed genes encoding components of the spliceosome and a guanine nucleotide synthesis gene. Intriguingly, the most recently identified dominant gene does not appear to be expressed in the neuronal retina but is expressed in the capillaries of the choroid. In attempting to understand the effects of mutations in these genes, investigators are forced to re-evaluate their thinking on the molecular mechanisms of genetic blindness and to undertake an increasingly inter-disciplinary approach in their analysis of this disease. Recently, this has resulted in significant developments in the elucidation of the molecular pathogenesis of RP.

Gene mutations in retinitis pigmentosa and their clinical implications.Clin Chim Acta. 2005 Jan;351(1-2):5-16

Retinitis pigmentosa (RP) is a group of inherited progressive retinal diseases affecting about 1 in 3500 people worldwide. So far, there is no prevention or cure, with permanent visual loss or even blindness the ultimate consequence usually after midlife. The genetics of RP are complex. It can be sporadic, autosomal dominant, autosomal recessive, or X-linked. Thirty-two genes are known to be associated with RP, sometimes the same gene gets involved in different inheritance traits. Some RP cases have a digenic cause. About 60% RP cases still have no known genetic cause. A large number of mutations cause RP, and they can be deletions, insertions, or substitutions that cause missense mutations or truncations. The RHO, RP1, and RPGR genes contribute the greatest number of known mutations causative of RP. But there is no single mutation that alone accounts for more than 10% of unrelated patients. Genetic testing for RP therefore requires screening for a group of genes. High-throughput and automated sequence detection technologies are essential. Due to the complexity in phenotype and genetics, and the fact that RP is untreatable, genetic testing for presymptomatic diagnosis of RP is controversial. Meanwhile, new genes are still to be identified, mostly by family linkage and sib-pair analysis. Research on gene therapy for RP requires information on gene mutations causative of RP.

Histopathologic study of variation in severity of retinitis pigmentosa due to the dominant rhodopsin mutation Pro23His. Am J Ophthalmol. 2002 Aug;134(2):290-3.

PURPOSE: To compare histopathologic findings in an autopsy eye of an 87-year-old woman with retinitis pigmentosa and the rhodopsin mutation Pro23His with findings in an autopsy eye of a 77-year-old female relative (first cousin) with retinitis pigmentosa and the same mutation. DESIGN: Histopathologic study. METHODS: One eye from each patient was prepared for light and electron microscopy within 5 hours after death. Photoreceptor nuclear counts were performed. RESULTS: Photoreceptor degeneration and intraretinal bone spicule pigmentation were evident in both cases. The younger patient had more extensive photoreceptor loss and more intraretinal pigmentation than her older relative. CONCLUSION: A marked variation in the extent of retinal degeneration can be seen in two relatives with retinitis pigmentosa and rhodopsin, Pro23His. This study supports the idea that factors other than the primary gene defect are responsible for the severity of this condition.

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