Autosomal recessive bestrophinopathy (ORPHA:139455)
A rare retinal dystrophy, characterized by central visual loss in the first 2 decades of life, associated with an absent electrooculogram (EOG) light rise and a reduced electroretinogram (ERG).
Epidemiology
The prevalence of ARB is still unknown; to date less than 20 cases have been described in the world literature.
Clinical description
ARB generally manifests in the first 2 decades of life, but patients may also first become symptomatic as late as the fifth decade of life. Most affected individuals initially present with central visual loss (visual acuity ranging from 20/200 to 20/25) and are usually mildly to highly hyperopic. Additional ocular findings may include short axial length with angle-closure glaucoma, amblyopia, anterior uveitis, strabismus, and color vision defects. Choroidal neovascularization (CNV) has been described in one case. Leukokoria and esotropia have also been reported.
Etiology
ARB is caused by compound heterozygous or homozygous mutations in the BEST1 gene (11q12) which encodes the chloride ion channel bestrophin-1 (expressed in the retinal pigment epithelium (RPE)). Mutations in BEST1 reduce or abolish the activity of the channel. It has been proposed that ARB may represent the null phenotype of bestrophin-1 in humans.
Diagnostic methods
Diagnosis of ARB relies on ophthalmologic examination, familial history and visual electrophysiology revealing an abnormal full-field ERG (reduced amplitudes and delayed implicit times of the rod and cone ERGs). Absent or severe reduction in EOG light rise (Arden ratio= 1.0) is commonly observed. Irregularity of the RPE throughout the posterior fundus, often with scattered punctate flecks (observed by autofluorescence imaging) is also found. Optical coherence tomography (OCT) imaging shows retinal edema, serous subretinal fluid, subretinal yellowish lesions and scars. Classic vitelliform lesions are not present. Fluorescein angiography reveals widespread patchy areas of hyperfluorescence and signs of mild perivascular leakage in the peripheral retina. Cystoid macular edema may be observed. Diagnosis is confirmed by the genetic screening of BEST1.
Differential diagnosis
Differential diagnosis includes Stargardt disease, familial drusen, Best vitelliform macular dystrophy, age-related macular degeneration (see these terms), central serous chorioretinopathy and chorioretinitis.
Genetic counseling
Transmission is autosomal recessive. Genetic counseling should be offered to at-risk couples (both individuals are carriers of a disease-causing mutation) informing them of the 25% risk of having an affected child.
Management and treatment
Management of ARB is mainly symptomatic and includes treatment of amblyopia, surgical strabismus correction, prophylactic laser (YAG) peripheral iridotomy to prevent angle closure and treat glaucoma, and intravitreal bevacizumab for the treatment for CNV. Cystoid macular edema may be treated with oral administration of acetazolamide. Gene therapy may offer a possible treatment for ARB in the future. Close monitoring of ARB patients is recommended, including repeated gonioscopy to judge the risk of angle closure.
Prognosis
Onset of vision loss in patients has been reported to vary between the ages of 4 to 40, and is coincident with initial presentation.

                            Last update: 
                            March 2014


                            - Expert reviewer(s): 
                             Stephanie CHAN  - Pr Ian MACDONALD