Retinitis Pigmentosa 7

Alternative Names

  • RP7
  • Retinitis Pigmentosa 7, Digenic
  • Leber Congenital Amaurosis 18
  • LCA18
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WHO-ICD-10 version:2010

Diseases of the eye and adnexa

Disorders of choroid and retina

OMIM Number

608133

Mode of Inheritance

Autosomal recessive Autosomal dominant

Gene Map Locus

6p21.1

Description

Leber congenital amaurosis 18 (LCA18) is an inherited retinal dystrophy that presents with a severe visual impairment within the first year of life.  LCA is characterized by night blindness, constricted visual fields, narrowed vessels, bone-spicule pigmentation in midperiphery of retina, pigment deposits in macular region, and macular pattern dystrophy in some patients.  Cardinal features of LCA18 include photophilia, high hyperopia, and a normal or near normal fundus examination.  In addition, parents report profound initial visual impairment that improves with time. 

There is no substantial treatment for LCA.  Care is supportive.  Parents should be referred to programs for the visually impaired child within their state or locality.  Correction of refractive error in the affected individuals is beneficial.

Molecular Genetics

The syndrome follows either an autosomal recessive or autosomal dominant pattern of inheritance.  It is caused by homozygous or heterozygous mutations in the PRPH2 gene.  PRPH2 encodes a protein with four transmembrane domains that is important for photoreceptor outer segment function.  Mutations in the PRPH2 gene cause a variety of other retinal disorders that are involved in a slow degeneration of photoreceptor cells, leading to progressive vision loss.

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Khan et al. (2016) studied three families confirmed to have children affected with non-syndromic early childhood-onset retinal dysfunction and found to harbor bi-allelic mutations in PRPH2.  All the three families were first cousin consanguineous marriages.  The first family had a 6-month-old boy, who was referred because of poor fixation and nystagmus noted at 2-months of age.  He seemed completely blind, but improved with time.  He was found to have photophilia, low-amplitude high-frequency variable nystagmus, and no strabismus.  The second family had two affected siblings.  The first child was a 1-year-old boy when he was referred because of poor fixation and nystagmus noted at 4-months age.  Vision was poor initially but improvement had been noted with time.  He had photophilia, low-amplitude high frequency variable nystagmus, and a small angle esotropia.  His younger sister had poor fixation and nystagmus noted at 4-months age as well.  She presented with a similar phenotype.  Both parents had mild myopia.  The third family also had two affected siblings.  The eldest was 35-years old and the younger was 24-years old.  The 24-year-old man had decreased vision since early childhood.  He had left exotropia of less than 20 prism dioptres and pendular nystagmus.  His elder brother had decreased vision since early childhood.  He had moderate left exotropia and pendular nystagmus.  Their mother had noticed loss of vision in her right eye 4-years before and had been diagnosed with subfoveal scarring secondary to choroidal neovascularization.  The authors concluded that bi-allelic PRPH2 mutations caused a distinct Leber congenital amaurosis phenotype in infancy that transformed into prominent maculopathy in adulthood.  The heterozygous parents could be asymptomatic but have clinically obvious macular phenotypes with or without peripheral retinal findings.  

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