CRB1

Pigmented Paravenous Chorioretinal Atrophy

Clinical Characteristics
Ocular Features: 

This is a rare type of pigmentary retinopathy with few symptoms in many patients.  Pigment clumps in the form of bone spicules in a paravenous distribution appear as young as 1 year of age and may be present congenitally.  The pigment may begin peripherally and is often segmental but eventually progresses centrally along with chorioretinal atrophy involving the majority of the fundus.  For unknown reasons, males are more severely affected than females.  In one family the retinal changes were associated with hyperopia, esotropia and vitreous degeneration (cells and liquefaction).  There is considerable variation in expressivity among patients and the vision and fundus pigmentation can be highly asymmetrical in the two eyes.  ERG abnormalities likewise vary widely with decreased photopic responses in some individuals and complete lack of both scotopic and photopic responses in severely affected eyes.  Decreased night vision is not a symptom.

This is generally considered to be a stationary condition but long term follow up reveals progression of pigmentary changes, chorioretinal atrophy and increasing constriction of the peripheral visual field.  Symptoms of decreased vision may be noted as early as 3 months of age.  Some patients retain vision of 20/20 or 20/30 into midlife whereas others in the first decade already have count fingers vision.  Likewise the size of the visual field varies widely and is not correlated with age.

Systemic Features: 

No systemic abnormalities have been reported.

Genetics

This is an autosomal dominant disorder caused by heterozygous mutations in the crumbs homolog 1 (CRB1) gene (1q31.3).

CRB1 mutations have been identified in other retinal disorders including nanophthalmos with retinitis pigmentosa, pigmented paravenous chorioretinal atrophy (172870), retinitis pigmentosa-12 (600105), and Leber congenital amaurosis 8 (613835).  No consistent retinal phenotype has been found, however.  There is often marked asymmetry between the two eyes and the rate of visual loss varies widely.  Most individuals have some patchy areas of hypoautofluorescence in the posterior pole with variable amounts of pigmentary anomalies from mild speckling to frank bone spicule formation.

   

 

   

 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No effective treatment is available although low vision aids are likely to be helpful in selected patients.

References
Article Title: 

Nanophthalmos with Retinitis Pigmentosa

Clinical Characteristics
Ocular Features: 

Poor vision is present beginning in childhood and may progress to hand motion or even loss of light perception when retinal detachments occur.  Nystagmus has been seen in one patient.  Corneal diameters were 11 mm, the angles were open, and axial lengths were shortened to about 17 mm.  Alternating areas of hypo- and hyperfluorescence are seen with fluorescein angiography corresponding to areas with pigment clumping seen throughout the fundi.  The fundus pigmentation is atypical for retinitis pigmentosa, however, in spite of the title given by the authors.  No scotopic or photopic responses are seen on the ERG.  Drusen were present in the optic nerves. 

Systemic Features: 

No systemic disease is associated. 

Genetics

A single family with affected male and female sibs has been reported and a homozygous nonsense mutation in exon 5 of the CRB1 gene (1q31-32.1) was present in both. 

Another recessive form of microphthalmia with retinitis pigmentosa plus has been reported (611040) without nanophthalmos features and having a mutation in the MFRP gene. True nanophthalmos with retinopathy (267760) has some features similar to the disorder described here but with macular cysts.  No responsible mutation has been identified in this disorder however. 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Low vision aids might be helpful in early stages of the disease. 

References
Article Title: 
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