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: 



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.

Treatment Options: 

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

Article Title: 


Pattnaik BR, Tokarz S, Asuma MP, Schroeder T, Sharma A, Mitchell JC, Edwards AO, Pillers DA. Snowflake Vitreoretinal Degeneration (SVD) Mutation R162W Provides New Insights into Kir7.1 Ion Channel Structure and Function. PLoS One. 2013 Aug 19. PubMed PMID: 23977131.

PubMedID: 23977131

Jiao X, Ritter R 3rd, Hejtmancik JF, Edwards AO. Genetic linkage of snowflake vitreoretinal degeneration to chromosome 2q36. Invest Ophthalmol Vis Sci. 2004 Dec;45(12):4498-503.

PubMedID: 15557460

Lee MM, Ritter R 3rd, Hirose T, Vu CD, Edwards AO. Snowflake vitreoretinal degeneration: follow-up of the original family. Ophthalmology. 2003 Dec;110(12):2418-26.

PubMedID: 14644728