SAG

Retinitis Pigmentosa 47

Clinical Characteristics
Ocular Features: 

Onset of night blindness and field constriction symptoms occur during the 4th and 5th decades of life.  Pigmentary abnormalities of the retina are the hallmark of this condition.  Retinal thinning, bone spicule pigmentation, vascular attenuation, optic disc pallor, and pigmentary atrophy have all been noted.

In patients with the autosomal dominant form of this disease, rod function is severely impaired or absent as evidenced by ERG studies.  Cone responses are often reduced on an age-related basis and in the range of 85-95% below normal.  As expected, dark-adapted visual thresholds are elevated and visual fields are restricted peripherally.  Loss of vision is age-related but some individuals can retain acuities of 20/35 to 20/40 into their sixth decade.  It is more common for acuities to be in the range of 20/200 to 20/400 later in life.

Systemic Features: 

No systemic disease is associated with this disorder.

Genetics

Mutations in the SAG gene (2q37) are responsible for this form of RP.  Both autosomal recessive and autosomal dominant modes of inheritance have been reported.

In one family with homozygous mutations a sib had features of Oguchi disease which also results from homozygous mutations in SAG.

Among Hispanic families in the southwestern US, heterozygous mutations in SAG are a common cause of autosomal dominant retinitis pigmentosa.

Pedigree: 
Autosomal dominant
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been reported for this disorder.

References
Article Title: 

A Novel Dominant Mutation in SAG, the Arrestin-1 Gene, Is a Common Cause of Retinitis Pigmentosa in Hispanic Families in the Southwestern United States

Sullivan LS, Bowne SJ, Koboldt DC, Cadena EL, Heckenlively JR, Branham KE, Wheaton DH, Jones KD, Ruiz RS, Pennesi ME, Yang P, Davis-Boozer D, Northrup H, Gurevich VV, Chen R, Xu M, Li Y, Birch DG, Daiger SP. A Novel Dominant Mutation in SAG, the Arrestin-1 Gene, Is a Common Cause of Retinitis Pigmentosa in Hispanic Families in the Southwestern United States. Invest Ophthalmol Vis Sci. 2017 May 1;58(5):2774-2784.

PubMed ID: 
28549094

Oguchi Disease, Type 1

Clinical Characteristics
Ocular Features: 

The distinctive feature of Oguchi disease is the peculiar and distinctive discoloration of the fundus under various light conditions, known as the Mizuo phenomenon.  Typically, the fundus assumes a golden or gray-white coloration under light adapted conditions but this disappears during acute dark adaptation and only reappears after prolonged time spent in darkness.  Rod dark adaptation is markedly delayed while that of cones is normal.  Visual acuity, visual fields and color vision are all normal.   A- and b-waves on single flash ERG are decreased or absent under lighted conditions but increase after prolonged dark adaptation.  Night blindness is present from birth without progression.

Systemic Features: 

No systemic abnormalities are associated with Oguchi disease.

Genetics

Oguchi type 1 disease is an autosomal recessive condition caused by mutations in the arrestin (SAG) gene (2q37.1) whose product is an intrinsic photoreceptor protein that participates in the recovery phase of light transduction.

Oguchi disease type 2 (613411), a similar form of congenital stationary night blindness, is caused by mutations in the GRK1 gene.  Genotyping is required to distinguish between the two types.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available.

References
Article Title: 
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