Bestrophinopathies

Excerpt

Clinical characteristics: Bestrophinopathies, the spectrum of ophthalmic disorders caused by pathogenic variants in BEST1, are typically characterized by retinal degeneration. The four recognized phenotypes are the three autosomal dominant disorders: Best vitelliform macular dystrophy (BVMD), BEST1 adult-onset vitelliform macular dystrophy (AVMD), and autosomal dominant vitreoretinochoroidopathy (ADVIRC); and autosomal recessive bestrophinopathy (ARB). Onset is usually in the first decade (except AVMD in which onset is age 30 to 50 years). Slow visual deterioration is the usual course. Choroidal neovascularization can occur in rare cases. ADVIRC is also associated with panophthalmic involvement including nanophthalmos, microcornea, hyperopia, and narrow anterior chamber angle with angle closure glaucoma.

Diagnosis/testing: The diagnosis of autosomal dominant bestrophinopathy is established in a proband with suggestive findings and a heterozygous BEST1 pathogenic (or likely pathogenic) variant identified by molecular genetic testing. The diagnosis of autosomal recessive bestrophinopathy is established in a proband with suggestive findings and biallelic BEST1 pathogenic variants.

Management: Treatment of manifestations: For individuals with significant visual impairment, referral to a low vision clinic; attention to special education needs for children with visual impairment; and occupational counseling. Regarding advanced BVMD fundus lesions, no clinical trials have compared conservative treatment vs laser photocoagulation for choroidal neovascularization (CNV) and hemorrhage. Also, there are no ongoing clinical trials regarding the effectiveness of treatment with anti-VEGF (vascular endothelial growth factor) agents.

Surveillance: Annual ophthalmologic examination (including best corrected visual acuity, visual fields, and spectral domain optical coherence tomography) to monitor progression of fundus lesions and to evaluate for coincidental development of CNV; in childhood, perform annual ophthalmologic examinations to help prevent the development of amblyopia.

Agents/circumstances to avoid: Cessation of smoking to help prevent neovascularization of the retina.

Evaluation of relatives at risk: It is appropriate to clarify the genetic status of apparently asymptomatic older and younger at-risk relatives of an affected individual in order to identify as early as possible those who would benefit from prompt ophthalmologic evaluation and routine follow up.

Genetic counseling: BVMD, AVMD, and ADVIRC are inherited in an autosomal dominant (AD) manner. By definition, autosomal recessive bestrophinopathy (ARB) is inherited in an autosomal recessive (AR) manner.

1. AD bestrophinopathy. Each child of an affected individual has a 50% chance of inheriting the BEST1 pathogenic variant.

2. AR bestrophinopathy. If both parents are known to be heterozygous for a BEST1 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.

Once the BEST1 pathogenic variant(s) have been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing for a bestrophinopathy are possible.