photoreceptor dystrophy

Choroidal Dystrophy, Central Areolar 2

Clinical Characteristics
Ocular Features: 

Slowly progressive loss of vision is noted in the 4th and 6th decades with a mean age of onset at 46 years. ERG recordings suggest that the cone dysfunction is more severe and occurs earlier than rod deterioration.  Night blindness is usually not a major complaint.  A central scotoma is usually present but peripheral fields may be relatively intact.  Dyschromatopsia is often present.  Early in the disease the RPE may have a granular appearance but in later stages there is usually a sharply demarcated area of central RPE atrophy (sometimes called geographic atrophy).

Autoflourescence, pattern ERGs, and fine matrix mapping can reveal abnormalities before patients become symptomatic.

Systemic Features: 

No systemic features are known.

Genetics

This is a clinically and genetically heterozygous disorder.  Multiple mutations in the PRPH2 gene (6p21.1) have been identified in this condition.  Some of the clinical variation may be mutation-specific.

For a somewhat similar disorder see choroidal dystrophy, central areolar 1 (215500).

CACD is a genetically heterogeneous disorder with mutations in several genes responsible.  The majority of patients have one of several mutations in the PRPH2 gene (6p21.1-cen) and the inheritance pattern seems to be autosomal recessive (CACD2).  Other family trees in which mutations in PRPH2 were excluded suggest autosomal dominant inheritance (CACD3; 613144).   

The gene product of PRPH2 is important to the integrity and stability of the structures that contain light-sensitive pigments (e.g., photoreceptors). More than 100 mutations have been identified. The resultant phenotype can be highly variable, even within members of the same family but most affected individuals have some degree of pigmentary retinopathy within the macula or throughout the posterior pole.

The altered gene product resulting from mutations in PRPH2 often leads to symptoms beginning in midlife as a result of the slow degeneration of photoreceptors. This database contains at least 11 disorders in which PRPH2 mutations have been found.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No effective treatment is known.

References
Article Title: 

Central areolar choroidal dystrophy

Boon CJ, Klevering BJ, Cremers FP, Zonneveld-Vrieling MN, Theelen T, Den Hollander AI, Hoyng CB. Central areolar choroidal dystrophy. Ophthalmology. 2009 Apr;116(4):771-82, 782.e1.

PubMed ID: 
19243827

Cone-Rod Dystrophy with Hearing Loss

Clinical Characteristics
Ocular Features: 

Patients note reduced vision in brightly-lit environments with onset in early adulthood and progressive central vision loss thereafter.   Nystagmus, photophobia, and dyschromatopsia may be present.  Younger individuals may complain of night blindness.  Visual fields show diffuse progressive suppression with relative sparing of selected areas such as the peripapillary region.  The ERG documents primary cone dystrophy but less involvement of the rods.  EOG testing in 4 patients showed reduced light-dark ratios.  Macular degeneration, attenuated vessels, subtle salt-and-pepper pigmentation, and spicular pigmentary deposits in the mid-periphery may be seen.

Systemic Features: 

The hearing loss is sensorineural in nature and can be progressive from its onset in childhood.

Genetics

This autosomal recessive disorder results from homozygous or compound heterozygous mutations in the CEPL78 (9q21.2) gene.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment for the basic condition has been reported.  Assistive hearing devices and tinted lenses could be helpful.

References
Article Title: 

Mutations in CEP78 Cause Cone-Rod Dystrophy and Hearing Loss Associated with Primary-Cilia Defects

Nikopoulos K, Farinelli P, Giangreco B, Tsika C, Royer-Bertrand B, Mbefo MK, Bedoni N, Kjellstrom U, El Zaoui I, Di Gioia SA, Balzano S, Cisarova K, Messina A, Decembrini S, Plainis S, Blazaki SV, Khan MI, Micheal S, Boldt K, Ueffing M, Moulin AP, Cremers FP, Roepman R, Arsenijevic Y, Tsilimbaris MK, Andreasson S, Rivolta C. Mutations in CEP78 Cause Cone-Rod Dystrophy and Hearing Loss Associated with Primary-Cilia Defects. Am J Hum Genet. 2016 Sep 1;99(3):770-6.

PubMed ID: 
27588451

CEP78 is mutated in a distinct type of Usher syndrome

Fu Q, Xu M, Chen X, Sheng X, Yuan Z, Liu Y, Li H, Sun Z, Li H, Yang L, Wang K, Zhang F, Li Y, Zhao C, Sui R, Chen R. CEP78 is mutated in a distinct type of Usher syndrome. J Med Genet. 2016 Sep 14. pii: jmedgenet-2016-104166. doi: 10.1136/jmedgenet-2016-104166.

PubMed ID: 
27627988
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