Retinitis Pigmentosa 20

Alternative Names

  • RP20
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WHO-ICD-10 version:2010

Diseases of the eye and adnexa

Disorders of choroid and retina

OMIM Number

613794

Mode of Inheritance

Autosomal Recessive

Gene Map Locus

1p31.3-p31.2

Description

Retinitis pigmentosa (RP) is a group of genetic disorders with extremely high heterogeneity, characterized by pigment deposits predominant in the peripheral retina and by a relative sparing of the central retina, which leads to blindness. RP patients show a wide variation in severity, mode of inheritance, age of onset, progression, and clinical manifestation. RP is usually non-syndromic (isolated), but also it can be associated with systemic disease, such as Usher syndrome and other conditions. The prevalence of non-syndromic forms of retinitis pigmentosa is approximately 1/4,000. There are autosomal dominant, autosomal recessive, X-linked, and rare mitochondrial and digenic forms of retinitis pigmentosa. The autosomal dominant and the autosomal recessive forms each account for 20% of the cases, the X-linked is about 10%, while the rest (50%) are still unidentified types of retinitis pigmentosa.

Diagnosis of retinitis pigmentosa 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 performed, but it is difficult because of the genetic heterogeneity of the disease. Therapies of retinitis pigmentosa are limited and there is no therapy to stop the progression of the disease or restores the vision; it is only restricted to slowing down the degenerative process by sunlight protection and vitamin therapy.

Retinitis pigmentosa 20 (RP20) is inherited as an autosomal recessive pattern caused by mutations in the RPE65 gene.

Molecular Genetics

More than 45 genes/loci have been identified causing the non syndromic autosomal dominant, autosomal recessive, X-linked, and digenic forms of retinitis pigmentosa. Homozygous and compound heterozygous mutations have been identified in the RPE65 gene, resulting in a complete or partial loss of protein function, causing retinitis pigmentosa.

Epidemiology in the Arab World

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Other Reports

Tunisia

El Matri et al. (2006) conducted genome-wide linkage analysis in three consanguineous Tunisian families presenting with early-onset retinal degeneration (EORD). Of 53 examined members, 11 were clinically affected with an EORD. Mutational screening of the RPE65 gene identified a homozygous p.R91W mutation co-segregating with the disease in all affected individuals. Eleven homozygotes had nystagmus and acuities ranging from CF to NLP. Two retinal patterns were identified: pattern 1 presented mid-peripheral deep white dot deposits and virtually no clumped pigmentation, whereas pattern 2 showed mid-peripheral pigmented clumps without any white deposits. Homozygotes had no detectable full-field ERG and an abnormal pupillary light reflex. Eleven heterozygotes had normal visual function.

United Arab Emirates

Al-Gazali et al. (2010) reported six Emirati children from the same family with retinitis pigmentosa. A homozygous deletion of exons one to seven of the RPE65 gene was identified in the affected patients.

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