PRPH2

Macular Dystrophy, Vitelliform 3

Clinical Characteristics
Ocular Features: 

Patients generally become symptomatic (reduced vision and metamorphopsia) in the fourth and fifth decades.  Vision loss is mild as in vitelliform 1 disease and only slowly progressive in most patients.  One or sometimes more small, oval, and slightly elevated yellow lesions resembling an egg yolk may be seen in the fovea along with paracentral drusen and mild RPE changes.  The fundus changes can appear any time in adult life but little is known about their nature history.  The EOG light/dark ratio may be normal or slightly decreased and the ERG likewise can be normal or, in some cases, reveals rod and cone system abnormalities.  Optical coherence tomography shows yellowish deposits between the neurosensory retina and the RPE with foveal thinning.  Color vision has been described as normal. The visual field may show peripheral constriction or central scotomas.  Choroidal neovascularization occurs rarely.

Variability in the clinical features often leads to misdiagnosis in individual patients who are sometimes considered to have age-related macular degeneration, retinitis pigmentosa, fundus flavimaculatus, dominant drusen, butterfly macular dystrophy, and pattern dystrophy.

Systemic Features: 

No systemic abnormalities have been reported.

Genetics

This is an autosomal dominant condition resulting from heterozygous mutations in the RDS (PRPH2) gene (6p21.1). 

The gene product of PRPH2 is active in the retina. It 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.

Genotyping has identified at least 5 forms of vitelliform macular dystrophy.  In addition to the iconic Best disease (VMD2, 153700) apparently first described by Friedreich Best in 1905 and now attributed to mutations in the Best1 gene, we know of at least 4 more and specific mutations have been identified in three.  No mutation or locus has yet been identified in VMD1 (153840) but it is likely a unique condition since mutations in other genes known to cause vitelliform dystrophy have been ruled out.  Other forms are VMD3 described here, VMD4 (616151) resulting from mutations in the IMPG1 gene, and VMD5 (616152) caused by mutations in the IMPG2 gene.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No treatment is known for this disorder.  Anti-VEGF and ablation therapy may be helpful in selected individuals with choroidal neovascularization.  Low vision aids may also be beneficial.

References
Article Title: 

Fundus Albipunctatus

Clinical Characteristics
Ocular Features: 

This disorder is often considered to belong to the category of retinal disease known as flecked retina syndrome.  Further, the nomenclature is not standardized and varying names have been attached to the more or less characteristic fundus picture consisting of uniformly distributed small yellow-white dots in the retina.  These tend to be concentrated in the midperiphery.  The macula usually is not involved in young people although ERG evidence suggests some worsening of cone dysfunction with age and central acuity may be decreased in midlife.  Frank macular degeneration has been seen clinically .  Delayed dark adaptation can be demonstrated with delays in recovery of rod and cone function.  Patients complain of night blindness beginning in childhood with little evidence of progression.

The disease known as retinitis punctata albescens (136880) may or may not be a unique disorder.  It is sometimes grouped with fundus albipunctatus while others consider it to be a separate entity.  Evidence for its uniqueness is based on the progressive nature of field loss and the presence of pigmentary changes and retinal vascular attenuation which are not found in fundus albipunctatus.  Further, the scotopic ERG waveforms usually do not regenerate.  More discriminating studies, especially genotyping, will likely provide additional information.  It would also be useful to have additional follow-up information on families. 

Systemic Features: 

No systemic disease is associated.

Genetics

Fundus albipunctatus is a genetically heterogeneous disorder.  Mutations in two genes, PRPH2 (6p21.1) and RDH5 (12q13.2) have been found among families.  The inheritance pattern for families with mutations in PRPH2 is consistent with autosomal dominant inheritance while mutations in RDH5 result in an autosomal recessive pattern.  Mutations in RLBP1 have also been found in some families.

Gene studies so far have not been helpful in discriminating between fundus albipunctatus and retinitis punctata albescens (136880).  For example, RLBP1 mutations have been identified among members of the same kindred having the clinical diagnosis of retinitis punctata albescens (136880) among older individuals while younger patients had features of fundus albipunctatus.  Further, the latter disorder has also been described among families with mutations in PRPH2 and RHO hinting at further genetic heterogeneity.

A similar clinical picture may be seen in Bietti crystalline corneoretinopathy (210370), Bardet-Biedl syndrome (209900), and hyperoxaluria (259900).  More information on flecked retina syndromes may be found at Flecked Retina Syndromes.

Pedigree: 
Autosomal dominant
Autosomal recessive
Treatment
Treatment Options: 

No effective treatment is available to restore full receptor cell function.  However, high oral doses of beta-carotene may lead to an improvement in night blindness. Low vision aids could be beneficial when central acuity is damaged.

References
Article Title: 

Choroidal Dystrophy, Central Areolar

Clinical Characteristics
Ocular Features: 

The primary feature of this form of macular dystrophy is atrophy of the RPE and choriocapillaris in the central macula.  In early stages among young patients in the second decade of life, some pigment changes are seen in the parafoveal area.  Later, the central macula develops hypopigmentation followed by atrophy of the choriocapillaris.  The area is usually sharply defined but fluorescein angiography often shows multiple window defects beyond the edges.  The same region often has speckled autofluorescence.  Secondary dysfunction of the photoreceptors in this area leads to some mild degree of vision loss in adults between the ages of 30 and 60 years but this progressive disease may eventually result in legal blindness.  The ERG demonstrates a cone dystrophy. The rate of disease progression is highly variable.  Visual acuity varies considerably as does the appearance of the macula.  Older individuals may be misdiagnosed as having age-related macular degeneration. 

Systemic Features: 

There is no associated systemic disease. 

Genetics

This 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).  CACD1 is caused by an unknown mutation localized to 17p13. 

The gene product of PRPH2 is active in the retina. It 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
Autosomal recessive
Treatment
Treatment Options: 

There is no treatment of the macular disease.  However, some patients can benefit from low vision aids. 

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

Macular Dystrophy, Patterned 1

Clinical Characteristics
Ocular Features: 

Patterned dystrophies of the macula are clinically heterogeneous.  It is common for different patterns to be seen among multiple members of a single family.  They can also be different in the two eyes of the same individual.  RPE changes can often be seen in the second decade of life but visual disturbances may not be noted until a decade or two later.  The process is progressive and eventually macular function is severely depressed with vision in the range of 20/200.  The pigmentary retinopathy occurs at the level of the RPE with the typical appearance of pigment but sometimes an accumulation of white or yellowish deposits is present.  The pattern of changes may appear in a configuration resembling the wings of a butterfly, hence the name.  However, vitelliform-like lesions have also been reported.  Paracentral tritan color defects have been described.

Subfoveal choroidal neovascularization can occur.

While the ERG may show some diffuse photoreceptor dysfunction in the presence of normal vision, there is little to suggest a primary rod or cone abnormality. Dark adaptation is normal.  Visual fields can reveal a small central scotoma and fluorescein angiography often shows window defects in the posterior pole. 

Systemic Features: 

Simple patterned macular dystrophy is not associated with systemic disease. 

Genetics

Pattern macular dystrophies are usually inherited as autosomal dominant conditions.  Several mutations in separate genes have been linked to these disorders suggesting that this group is genetically as well as clinically heterogeneous. 

Some families have mutations in the photoreceptor peripherin gene (PRPH2) at 6p21.1-cen (169150) whose gene product is active in the retina. It 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 coded by 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.

A locus at 5q21.2-q33.2 containing heterozygous CTNNA1 mutations has been linked to a pattern dystrophy (Macular Dystrophy, Patterned 2) (608970). 

As many as 25% of patients with myotonic dystrophy 1 (160900) and myotonic dystrophy 2 (602668) have a patterned pigmentary maculopathy.

 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No treatment is available for the macular disease but low vision aids should be considered for appropriate individuals. 

Surveillance is useful for the detection of choroidal neovascularization and prompt treatment with ranibizumab injections can be useful in the elimination of this complication.

References
Article Title: 

Pattern dystrophy with high intrafamilial variability associated with Y141C mutation in the peripherin/RDS gene and successful treatment of subfoveal CNV related to multifocal pattern type with anti-VEGF (ranibizumab) intravitreal injections

Vaclavik V, Tran HV, Gaillard MC, Schorderet DF, Munier FL. Pattern dystrophy with high intrafamilial variability associated with Y141C mutation in the peripherin/RDS gene and successful treatment of subfoveal CNV related to multifocal pattern type with anti-VEGF (ranibizumab) intravitreal injections. Retina. 2012 Oct;32(9):1942-9.

PubMed ID: 
22466463
Subscribe to RSS - PRPH2