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Oguchi disease is an autosomal recessive retinal disorder characterized by congenital stationary night blindness (see this term) and the Mizuo-Nakamura phenomenon.
ORPHA:75382Classification level: Disorder
Oguchi disease is a very rare condition with approximately 50 cases described in the literature to date. It was originally discovered in Japan where the prevalence is the highest but has been found occasionally in European, American, Pakistani and Indian patients.
The disease is characterized by congenital stationary night blindness and the Mizuo-Nakamura phenomenon which is a unique morphological and functional abnormality of the retina that presents with a typical golden-yellow or silver-gray discoloration of the fundus in the presence of light that disappears after dark-adaptation and appears again after the onset of light. Patients have non progressive night blindness since young childhood with normal day vision, but they often claim improvement of light sensitivities when they remain a long time in a dark environment. Eye fundus shows the Mizuo-Nakamura phenomenon as the only fundus feature. A prolonged dark adaptation of 3 hours or more leads to disappearance of the Mizuo-Nakamura phenomenon fundus changes. No evidence of spicules, macular changes or chorioretinal atrophy is observed. Normal visual acuity, normal caliber of retinal blood vessels and usually normal cone response on electroretinogram (ERG) recording suggest retinal dysfunction rather than degeneration.
Oguchi disease is caused by mutations in the SAG gene coding for arrestin located on chromosome 2q37(Oguchi type 1) or by mutations in the GRK1 gene that codes for the rhodopsin kinase located on the chromosome 13q34 (Oguchi type 2). Remarkably, some mutations in the SAG gene are associated with Oguchi disease and retinitis pigmentosa (RP) in the same family. Some mutations in SAG lead to RP.
The diagnosis is clinical and is based on the presence of night blindness and the observation of the Mizuo-Nakamura phenomenon by funduscopy and electroretinography (ERG). The clinical diagnosis is confirmed by genetic testing.
The differential diagnosis includes Stargardt disease, RP in female carriers, juvenile retinoschisis, and progressive cone dystrophy (see these terms). All these conditions may have fundus changes but without the classical Mizuo-Nakamura phenomenon.
Oguchi disease is an autosomal recessive condition. Brothers and sisters of an affected case have a 25% risk to be also affected.
Management and treatment
To date, there is not a specific treatment for Oguchi disease.
In Oguchi disease the visual prognosis is good in absence of progression of symptoms. Although Oguchi disease is categorized as a stationary condition it can lead to reduced visual acuity or constricted visual fields, especially in older patients.