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Retinal Dystrophy, Newfoundland Type

Clinical Characteristics
Ocular Features: 

There is considerable clinical heterogeneity, mostly age-dependent.  Night blindness can occur in early childhood but usually later even though scotopic responses can be undetectable in the first decade of life while photopic responses are reduced on the ERG at all ages.  Both rod and cone responses may be extinguished in later life.  Visual acuity can be decreased beginning in early childhood and legal blindness usually occurs by the second or third decade of life.  However, the loss of vision continues to progress and severe vision loss to finger-counting may be present in older individuals.  A scallop-bordered lacunar atrophy may be seen in the midperiphery.  The macula is only mildly involved by clinical examination although central retinal thinning is seen in all cases.  Dyschromatopsia is mild early and usually becomes more severe.  The visual fields are moderately to severely constricted although in younger individuals a typical ring scotoma is present.  The peripheral retina contains ‘white dots’ and often resembles the retinal changes seen in retinitis punctate albescens.

Systemic Features: 

None reported.

Genetics

Homozygous mutations in the RLBP1 gene (15q26.1) are responsible for this disorder.  Homozygous mutations in RLBP1 have also been found among patients with fundus albipunctatus (136880), retinitis punctata albescens, and in Bothnia type retinal dystrophy (607475),

NFRCD clinically resembles Bothnia type retinal dystrophy (607475) which likewise results from mutations in the RLBP1 gene but the maculae appear normal or have only a mild ‘beaten-bronze’ atrophy.

See Flecked Retina entry for somewhat similar conditions.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is known.

References
Article Title: 

Vitreoretinal Degeneration, Snowflake Type

Clinical Characteristics
Ocular Features: 

The retina and vitreous are primarily affected in this disorder.  The age of onset is unknown but characteristic signs can be seen early in the second decade of life.   Early changes include thickening of the cortical vitreous and white dots in the superficial layers of the retina.  The latter are minute yellow-white crystalline deposits more common in the peripheral retina.  Many (83%) patients have early onset cataracts.  Corneal guttae are common (80% of patients).  The vitreous undergoes fibrillar degeneration with liquefaction and eventually appears optically empty.  Many patients experience symptoms of floaters.  The vitreous changes most closely resemble that seen in Wagner syndrome (143200) but with important differences.  In the latter disorder the vitreous changes are membranous, the retinal changes are deeper in location, RPE changes are evident, the choroid and RPE are involved, and the risk of retinal detachment is much higher.  Only 21% of patients with snowflake vitreoretinal degeneration have retinal detachments compared with about 50% in Wagner syndrome.  Retinal vasculature change such as perivascular sheathing and attenuation of arterioles may be seen in both disorders but occur far less commonly in snowflake degeneration.

Based on lack of visual symptoms, the photoreceptors are minimally involved.  Electrophysiologic studies reveal an elevated dark adaptation and reduced scotopic B waves.  Most patients retain excellent vision.  However, the optic nerve may have a waxy pallor and frequently appears flat and lacks a visible cup. 

Systemic Features: 

None.

Genetics

Snowflake vitreoretinal degeneration is an autosomal dominant disorder.   Heterozygous missense mutations have been found in KCNJ13 (2q37) in a single family.  Mutations in the same gene have been identified in rare cases of Leber congenital amaurosis.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Visually significant cataracts may be removed.  Patients need to be observed throughout life to enable prompt intervention when retinal detachments occur.

References
Article Title: 
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