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Vitreoretinal Degeneration, Snowflake Type

Vitreoretinal Degeneration, Snowflake Type

Patient Information

Characteristics

Background and History

This is a rare and recently described disorder that has only ocular manifestations.  It has some clinical similarities to other degenerative disorders of the retina and vitreous (jelly-like material that fills the posterior part of the eye) but is considered unique.

Clinical Correlations

The age of onset is unknown but changes in the eye have been seen as early as the second decade of life.  These include the appearance of yellow –white crystalline-like (hence the name) spots in the retina and thickening of the peripheral part of the vitreous.  Vision remains excellent throughout life unless the retina detaches (a relatively small risk), or unless cataracts develop.  The latter are frequently present and may occur as early as the 4th or 5th decades.  Many patients experience ‘floaters” which are shadows cast by debris in the vitreous.  There is some progressive deterioration of the vitreous with the appearance of fibers which cause few symptoms.  There is a lifelong risk of developing a retinal detachment.

 

Genetics

Inheritance

This disorder is caused by a mutant gene in single dose and hence is passed from parent to child in an autosomal dominant pattern.  Affected parents can expect that there is a 50% chance of the disease appearing in each of their children.

Pedigree

Autosomal dominant

Autosomal dominant disorders require only one mutation for the disease to be expressed.  Since an affected parent has two chromosomes, only one of which has the mutant gene, parents can expect that half (50%) of their children will receive that one and inherit the disease.  It is common for individuals that inherit the mutation, however, to not have evidence of the disease (nonpenetrance).

Sample pedigree of autosomal dominant inheritance

Autosomal dominant inheritance leads to a vertical pattern of transmission

Diagnosis and Prognosis

The diagnosis can only be made by an ophthalmologist based on a complete eye examination.  All children and parents of individuals with snowflake degeneration should be examined for on average half will be affected.  The prognosis is excellent although those with the disease must be monitored throughout life because of the small but significant risk of developing a retinal detachment.  The prognosis is usually good when detachments are repaired promptly.

When visually significant opacities of the lens (cataracts) develop as they do in midlife in about 80% of individuals they can be safely removed.

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