drusen

Macular Dystrophy, Vitelliform 4

Clinical Characteristics
Ocular Features: 

This is a late onset form of vitelliform dystrophy in which symptoms are usually noted between the ages of 20 to 45 years.  The vitelliform lesions usually occur singly and are often small.  Some individuals have small drusen-like macular lesions adjacent to the vitelliform lesions, at the periphery of the macula, or even outside the macula.  The lesions contain lipofuscin which can be seen on autofluorescence photographs.  Visual acuity can remain near normal for many years.  The EOG ratio and ERG responses are usually normal or near normal.  Choroidal neovascularization has not been described. 

Systemic Features: 

There are no systemic manifestations.

Genetics

This form of vitelliform dystrophy (VMD4) is caused by heterozygous mutations in the IMPG1 gene (6q14.1).  However, rare families have been reported in which compound heterozygous or homozygous mutations have been found.  Some of the heterozygous parents of children with two mutations were found to have minor fundus changes such as tiny extramacular vitelliform spots in spite of being asymptomatic. This suggests that the transmission pattern of fundus changes may be both autosomal recessive and autosomal dominant. 

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 (608161) due to mutations in the PRPH2 gene, VMD4 described here, and VMD5 (616152) caused by mutations in the IMPG2 gene.

Pedigree: 
Autosomal dominant
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available for the vitelliform disease but low vision devices can be helpful in some patients for selected tasks.

References
Article Title: 

Mutations in IMPG1 cause vitelliform macular dystrophies

Manes G, Meunier I, Avila-Fernandez A, Banfi S, Le Meur G, Zanlonghi X, Corton M, Simonelli F, Brabet P, Labesse G, Audo I, Mohand-Said S, Zeitz C, Sahel JA, Weber M, Dollfus H, Dhaenens CM, Allorge D, De Baere E, Koenekoop RK, Kohl S, Cremers FP, Hollyfield JG, Senechal A, Hebrard M, Bocquet B, Ayuso Garcia C, Hamel CP. Mutations in IMPG1 cause vitelliform macular dystrophies. Am J Hum Genet. 2013 Sep 5;93(3):571-8.

PubMed ID: 
23993198

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: 

Doyne Honeycomb Macular Dystrophy

Clinical Characteristics
Ocular Features: 

Beginning usually in midlife, the retina has radially localized white, large drusen in the posterior pole.  These may begin as small drusen that later enlarge and become confluent creating a honeycomb pattern.  The disease begins as an accumulation of material between the Bruch membrane and the RPE.  Eventually drusen occupy the entire thickness of the Bruch membrane and are continuous with or internal to the RPE basement membrane.  Vision early is normal and a slow loss of vision occurs sometime after the drusen appear in most individuals.  In some patients geographic atrophy, pigmentary changes, and a subfoveal neovascular net develops with macular scarring, vitreous hemorrhage, and severe reduction of vision.

Systemic Features: 

No systemic disease is associated.

Genetics

Doyne honeycomb macular disease, or dominant drusen, is the result of mutations in the EFEMP1 gene at 2p16 in the majority of cases.  It is an autosomal dominant disorder. The mutant protein product (a member of the fibulin famiy) is folded abnormally and secreted inefficiently.  It is also resistant to degradation which may lead to receptor damage by limiting access to nutrients from the choriocapillaris.  Some genetic heterogeneity may exist since a few cases seem to be linked to a locus at 6q14.    Some have considered Malattia Leventinese and Doyne honeycomb retinal dystrophy as separate entities but mutations in the same gene seem to be responsible for both conditions suggesting they are clinical variations of the same disorder.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

The subfoveal net responds to photodynamic therapy.

References
Article Title: 
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