New best1 mutations in autosomal recessive bestrophinopathy

Non-vasogenic cystoid maculopathy in autosomal recessive bestrophinopathy: novel insights from NIR-FAF and OCTA imaging

BACKGROUND

Autosomal Recessive Bestrophinopathy (ARB) is an inherited retinal disease caused by biallelic mutations in the BEST1 gene. Herein, we report the multimodal imaging findings of ARB presenting with cystoid maculopathy and investigate the short-term response to combined systemic and topical carbonic anhydrase inhibitors (CAIs).

MATERIAL AND METHODS

An observational, prospective, case series on two siblings affected by ARB is presented. Patients underwent genetic testing and optical coherence tomography (OCT), blue-light fundus autofluorescence (BL-FAF), near-infrared fundus autofluorescence (NIR-FAF), fluorescein angiography (FA), MultiColor imaging, and OCT angiography (OCTA).

RESULTS

Two male siblings, aged 22 and 16, affected by ARB resulting from c.598C>T, p.(Arg200*) and c.728C>A, p.(Ala243Glu) BEST1 compound heterozygous variants, presented with bilateral multifocal yellowish pigment deposits scattered through the posterior pole that corresponded to hyperautofluorescent deposits on BL-FAF. Vice versa, NIR-FAF mainly disclosed wide hypoautofluorescent areas in the macula. A cystoid maculopathy and shallow subretinal fluid were evident on structural OCT, albeit without evidence of dye leakage or pooling on FA. OCTA demonstrated disruption of the choriocapillaris throughout the posterior pole and sparing of intraretinal capillary plexuses. Six months of combined therapy with oral acetazolamide and topical brinzolamide resulted in limited clinical benefit.

CONCLUSIONS

We reported two siblings affected by ARB, presenting as non-vasogenic cystoid maculopathy. Prominent alteration of NIR-FAF signal and concomitant choriocapillaris rarefaction on OCTA were noted in the macula. The limited short-term response to combined systemic and topical CAIs might be explained by the impairment of the RPE-CC complex.

Photoreceptor function and structure in retinal degenerations caused by biallelic BEST1 mutations

The only approved retinal gene therapy is for biallelic RPE65 mutations which cause a recessive retinopathy with a primary molecular defect located at the retinal pigment epithelium (RPE). For a distinct recessive RPE disease caused by biallelic BEST1 mutations, a pre-clinical proof-of-concept for gene therapy has been demonstrated in canine eyes. The current study was undertaken to consider potential outcome measures for a BEST1 clinical trial in patients demonstrating a classic autosomal recessive bestrophinopathy (ARB) phenotype. Spatial distribution of retinal structure showed a wide expanse of abnormalities including large intraretinal cysts, shallow serous retinal detachments, abnormalities of inner and outer segments, and an unusual prominence of the external limiting membrane. Surrounding the central macula extending from 7 to 30 deg eccentricity, outer nuclear layer was thicker than expected from a cone only retina and implied survival of many rod photoreceptors. Co-localized however, were large losses of rod sensitivity despite preserved cone sensitivities. The dissociation of rod function from rod structure observed, supports a large treatment potential in the paramacular region for biallelic bestrophinopathies.

Distinct expression requirements and rescue strategies for BEST1 loss- and gain-of-function mutations

Genetic mutation of the human BEST1 gene, which encodes a Ca²⁺-activated Cl^- channel (BEST1) predominantly expressed in retinal pigment epithelium (RPE), causes a spectrum of retinal degenerative disorders commonly known as bestrophinopathies. Previously, we showed that BEST1 plays an indispensable role in generating Ca²⁺-dependent Cl^- currents in human RPE cells, and the deficiency of BEST1 function in patient-derived RPE is rescuable by gene augmentation (Li et al., 2017). Here, we report that BEST1 patient-derived loss-of-function and gain-of-function mutations require different mutant to wild-type (WT) molecule ratios for phenotypic manifestation, underlying their distinct epigenetic requirements in bestrophinopathy development, and suggesting that some of the previously classified autosomal dominant mutations actually behave in a dominant-negative manner. Importantly, the strong dominant effect of BEST1 gain-of-function mutations prohibits the restoration of BEST1-dependent Cl^- currents in RPE cells by gene augmentation, in contrast to the efficient rescue of loss-of-function mutations via the same approach. Moreover, we demonstrate that gain-of-function mutations are rescuable by a combination of gene augmentation with CRISPR/Cas9-mediated knockdown of endogenous BEST1 expression, providing a universal treatment strategy for all bestrophinopathy patients regardless of their mutation types.

Phenotypic and Genetic Spectrum of Autosomal Recessive Bestrophinopathy and Best Vitelliform Macular Dystrophy

Purpose

Autosomal recessive bestrophinopathy (ARB) and vitelliform macular dystrophy (VMD) are distinct phenotypes, typically inherited through recessive and dominant patterns, respectively. Recessively inherited VMD (arVMD) has been reported, suggesting that dominant and recessive BEST1-related retinopathies represent a single disease spectrum. This study compares adVMD, arVMD, and ARB to determine whether a continuum exists and to define clinical and genetic features to aid diagnosis and management.

Methods

One arVMD patient and nine ARB patients underwent standard ophthalmic examination, imaging, electrophysiology, and genetic assessments. A meta-analysis of reported BEST1 variants was compiled, and clinical parameters were analyzed with regard to inheritance and phenotype.

Results

Among 10 patients with biallelic BEST1 variants, three novel ARB variants (p.Asp118Ala, p.Leu224Gln, p.Val273del) were discovered. A patient with homozygous p.Glu35Lys was clinically unique, presenting with VMD, including hyperautofluorescence extending beyond the macula, peripheral punctate lesions, and shortened axial-length. A tritan-axis color vision deficit was seen in three of six (50%) of ARB patients. Attempts to distinguish recessively-inherited ARB and dominantly-inherited VMD genotypically, by variant frequency and residue location, did not yield significant differences. Literature meta-analysis with principle component analysis of clinical features demonstrated a spectrum of disease with arVMD falling between adVMD and ARB.

Conclusions

This study suggests that arVMD is part of a continuum of autosomal recessive and dominant BEST1-related retinopathies. Detailed clinical and molecular assessments of this cohort and the literature are corroborated by unsupervised analysis, highlighting the overlapping heterogeneity among BEST1-associated clinical diagnoses. Tritan-axis color vision deficit is a previously unreported finding associated with ARB.

Evaluating BEST1 mutations in pluripotent stem cell-derived retinal pigment epithelial cells

Bestrophin-1 (BEST1) is a calcium-activated chloride channel (CaCC) predominantly expressed at the basolateral membrane of the retinal pigment epithelium (RPE). Over 250 mutations in the BEST1 gene have been documented to cause at least five retinal degenerative disorders, commonly termed bestrophinopathies, to which no treatment is currently available. Therefore, understanding the influences of BEST1 disease-causing mutations on the physiological function of BEST1 in RPE is critical for deciphering the pathology of bestrophinopathies and developing therapeutic strategies for patients. However, this task has been impeded by the rarity of BEST1 mutations and limited accessibility to native human RPE cells. Here, we describe a pluripotent stem cell (PSC)-based pipeline for reproducibly generating RPE cells expressing endogenous or exogenous mutant BEST1, which provides us with a powerful "disease-in-a-dish" approach for studying BEST1 mutations in physiological environments.

The Clinical Features and Genetic Spectrum of a Large Cohort of Chinese Patients With Vitelliform Macular Dystrophies

PURPOSE

To provide the clinical and genetic characteristics of a large cohort of Chinese patients with vitelliform macular dystrophies.

DESIGN

Cross-sectional study.

METHODS

One hundred and thirty-four unrelated Chinese patients diagnosed with Best vitelliform macular dystrophy (BVMD), autosomal recessive bestrophinopathy (ARB), or adult vitelliform macular dystrophy (AVMD) were enrolled. Detailed ophthalmic examinations and genetic testing on vitelliform macular dystrophy-related genes were performed. Genotype and phenotype association were analyzed among different diagnostic groups.

RESULTS

In total, 87 BVMD, 30 AVMD, and 17 ARB patients were enrolled in this study. Genetic analysis identified 37 BEST1 mutations in 53 patients with BVMD and ARB. Of these, 5 variants (c.254A>C, c.291C>G, c.722C>G, c.848_850del, c.1740-2A>C) were novel. The variant c.898G>A was a hotspot mutation, which was identified in 13 patients with BVMD and 1 patient with ARB. There were significant differences of ocular biometric parameters among patients with homozygous or compound heterozygous mutations, heterozygous mutations, and those without mutations of BEST1. Homozygous or compound heterozygous patients had shortest axial length (AL), shallowest anterior chamber depth (ACD), and highest intraocular pressure (IOP); patients without mutations had longest AL, deepest ACD, and lowest IOP; and heterozygous patients were in between. Moreover, 7 patients harboring heterozygous mutations in BEST1 and 3 patients without BEST1 mutations showed similar clinical appearance to ARB in our cohort.

CONCLUSIONS

This is the largest sample size study of Chinese vitelliform macular dystrophy patients. Our results indicated that assessment of angle-closure risk is a necessary consideration for all types of BEST1-related vitelliform macular dystrophies. The study expanded both the clinical and genetic findings of 3 common types of vitelliform macular dystrophies in a Chinese population.

Peripapillary Sparing in Autosomal Recessive Bestrophinopathy

PURPOSE

To demonstrate that peripapillary sparing on autofluorescence images is a characteristic feature of autosomal recessive bestrophinopathy (ARB).

DESIGN

Retrospective, cross-sectional case series and review of previous published cases.

PARTICIPANTS

Twelve patients with ARB.

METHODS

Ophthalmic assessment included best-corrected visual acuity testing, electrophysiologic examinations, and multimodal retinal imaging. Retinal imaging included OCT, blue-light autofluorescence imaging, fundus photography, and widefield pseudocolor and autofluorescence fundus imaging.

MAIN OUTCOME MEASURES

Presence of peripapillary sparing on fundus autofluorescence images.

RESULTS

Relatively normal-appearing peripapillary autofluorescence was identified in all patients, independent of the disease stage or presence of widespread changes on autofluorescence widefield images. OCT images of the peripapillary region revealed mild structural abnormalities, including a thinned outer nuclear layer and intraretinal or subretinal fluid. A review of previously published cases confirmed peripapillary sparing as consistent feature on fundus autofluorescence images. Genetic analysis revealed 10 previously reported mutations, 1 novel missense (c.83T>A; p.Ile28Asn) and 2 novel truncating (c.658C>T; p.Gln220* and c.1370C>G; p.Ser457*) variants in BEST1.

CONCLUSIONS

In ARB patients, peripapillary sparing is a consistent feature on fundus autofluorescence images, whereas the same region is less preserved on OCT images.

Novel BEST1 mutations and special clinical characteristics of autosomal recessive bestrophinopathy in Chinese patients

PURPOSE

The aim of this study was to describe the genetic and clinical characteristics of Chinese patients with autosomal recessive bestrophinopathy (ARB).

METHODS

This study presents a retrospective observational case series. Twenty-one ARB patients and 25 clinically healthy family members were recruited. The coding regions and adjacent intronic regions of BEST1 were analysed via Sanger sequencing. Clinical examinations, including ultrasound biomicroscopy, A-scan, optical coherence tomography, fundus autofluorescence, fundus fluorescein angiography (FFA), indocyanine green angiography (ICGA) and visual electrophysiology, were reviewed.

RESULTS

Six novel mutations (c.380C>T, p.T127M; c.397A>G, p.N133D; c.500A>G, p.E167G; c.817G>A, p.V273M; c.174_176del, p.Q58del; and c.950_955del, p.S318_L319) and 8 previously reported mutations were identified. The p.R255W mutation had the highest frequency in our cohort. Twenty patients had serous retinal detachment with multifocal subretinal vitelliform deposits in the posterior poles. One patient exhibited chorioretinal atrophy. FFA revealed peripheral vascular leakage in 10 patients, and ICGA revealed hyperfluorescent spots in 8 patients. Visual electrophysiology was abnormal in all patients. Fifteen patients with angle closure (AC) or angle-closure glaucoma (ACG) had shallower anterior chambers and shorter axial lengths than the patients with open angle, contributing to their risk of developing AC/ACG. One patient developed AC during the 7-year follow-up period. The misdiagnosis and missed rates were 35.3% and 58.8%, respectively.

CONCLUSION

The six novel mutations and high frequency of p.R255W suggest ethnical differences in the BEST1 mutation spectrum among Chinese patients. BEST1 gene screening and detailed clinical examinations help establishing a diagnosis of ARB. Clinical evaluations of the risk of developing AC/ACG are recommended for ARB patients.

Next generation sequencing identifies novel disease-associated BEST1 mutations in Bestrophinopathy patients

Bestinopathies are a spectrum of retinal disorders associated with mutations in BEST1 including autosomal recessive bestrophinopathy (ARB) and autosomal dominant Best vitelliform macular dystrophy (BVMD). We applied whole-exome sequencing on four unrelated Indian families comprising eight affected and twelve unaffected individuals. We identified five mutations in BEST1, including p.Tyr131Cys in family A, p.Arg150Pro in family B, p.Arg47His and p.Val216Ile in family C and p.Thr91Ile in family D. Among these, p.Tyr131Cys, p.Arg150Pro and p.Val216Ile have not been previously reported. Further, the inheritance pattern of BEST1 mutations in the families confirmed the diagnosis of ARB in probands in families A, B and C, while the inheritance of heterozygous BEST1 mutation in family D (p.Thr91Ile) was suggestive of BVMD. Interestingly, the ARB families A and B carry homozygous mutations while family C was a compound heterozygote with a mutation in an alternate BEST1 transcript isoform, highlighting a role for alternate BEST1 transcripts in bestrophinopathy. In the BVMD family D, the heterozygous BEST1 mutation found in the proband was also found in the asymptomatic parent, suggesting an incomplete penetrance and/or the presence of additional genetic modifiers. Our report expands the list of pathogenic BEST1 genotypes and the associated clinical diagnosis.

Patient-specific mutations impair BESTROPHIN1's essential role in mediating Ca2+-dependent Cl- currents in human RPE

Mutations in the human BEST1 gene lead to retinal degenerative diseases displaying progressive vision loss and even blindness. BESTROPHIN1, encoded by BEST1, is predominantly expressed in retinal pigment epithelium (RPE), but its physiological role has been a mystery for the last two decades. Using a patient-specific iPSC-based disease model and interdisciplinary approaches, we comprehensively analyzed two distinct BEST1 patient mutations, and discovered mechanistic correlations between patient clinical phenotypes, electrophysiology in their RPEs, and the structure and function of BESTROPHIN1 mutant channels. Our results revealed that the disease-causing mechanism of BEST1 mutations is centered on the indispensable role of BESTROPHIN1 in mediating the long speculated Ca²⁺-dependent Cl^- current in RPE, and demonstrate that the pathological potential of BEST1 mutations can be evaluated and predicted with our iPSC-based 'disease-in-a-dish' approach. Moreover, we demonstrated that patient RPE is rescuable with viral gene supplementation, providing a proof-of-concept for curing BEST1-associated diseases.

Idiopathic Acute Exudative Polymorphous Vitelliform Maculopathy: Clinical Spectrum and Multimodal Imaging Characteristics

PURPOSE

To describe clinical findings in patients with acute exudative polymorphous vitelliform maculopathy (AEPVM).

DESIGN

Retrospective, observational, multicenter case series review.

PARTICIPANTS

Consecutive patients diagnosed with idiopathic AEPVM.

METHODS

Review of clinical charts, multimodal imaging, electrophysiologic findings, and genetic findings in previously unpublished patients and review of the literature.

MAIN OUTCOME MEASURES

Clinical features of idiopathic AEPVM and differential diagnosis.

RESULTS

Eighteen patients (age range, 21-74 years) with typical features of AEPVM, including initial localized, serous detachments followed by the development of characteristic yellow-white deposits in the vitelliform space. Over time, this hyperautofluorescent material gravitated within the larger lesions, resulting in typical curvilinear deposits characteristic of later stages. Symptoms and clinical findings lasted from weeks to several years. Some patients showed previously undescribed features such as fluorescein-negative intraretinal cystic changes, choroidal neovascularization, serous retinal elevations mimicking retinal folds, increased choroidal thickness, lack of rapid visual recovery, and recurrence years after complete resolution of initial manifestations.

CONCLUSIONS

Acute exudative polymorphous vitelliform maculopathy can present with a more variable natural course than previously described. Paraneoplastic retinopathy and autosomal recessive bestrophinopathy closely resemble AEPVM, necessitating medical and hereditary evaluation to exclude these clinical possibilities. This series of patients with AEPVM expands the clinical spectrum of the disorder, including demographics, clinical manifestations, imaging features, natural course, and visual prognosis.

A unique case series of autosomal recessive bestrophinopathy exhibiting multigenerational inheritance

INTRODUCTION

Autosomal recessive bestrophinopathy (ARB) is a retinal disease caused by biallelic mutations of the BEST1 gene. It has a variable phenotype with white flecks in the retina, multifocal yellow subretinal deposits, macular edema, choroidal neovascularization, hyperopia, and electrophysiological abnormalities. We describe a family with ARB and multigenerational inheritance.

METHODS

Three generations of a Middle Eastern family (a woman, one son, and two grandchildren) were evaluated by our ocular genetics team. Eye examinations, fundus photography, and optical coherence tomography (OCT) were performed. Genetic testing was obtained on examined patients and available relatives.

RESULTS

The proband demonstrated counting fingers vision and white flecks in the retinal periphery, with macular subretinal fluid (SRF), loss of outer photoreceptor segments, and epiretinal membrane (ERM) on OCT. Two grandchildren demonstrated decreased vision, multifocal yellow subretinal deposits, and SRF on OCT. Two grandchildren examined elsewhere were reported to be similarly affected. A son's examination was normal except for extra-macular scars (from prior toxoplasmosis) and ERM. Genetic history revealed consanguinity and testing showed homozygosity for BEST1 mutations in the proband and two grandchildren c.473G>A/c.473G>A (R218H /R218H) and heterozygosity in two unaffected sons and two unaffected daughters-in-law c.473G>A/WT (p.R218H/WT).

DISCUSSION

We present a consanguineous family of five affected individuals with ARB and four confirmed carriers. Their pedigree was consistent with dominant inheritance and incomplete penetrance. Genetic testing clarified the diagnosis and mode of inheritance. We describe the genetic findings, phenotypic variability, and recessive inheritance of an often dominantly inherited mutation as notable elements in their case.

Bestrophinopathy: An RPE-photoreceptor interface disease

Bestrophinopathies, one of the most common forms of inherited macular degenerations, are caused by mutations in the BEST1 gene expressed in the retinal pigment epithelium (RPE). Both human and canine BEST1-linked maculopathies are characterized by abnormal accumulation of autofluorescent material within RPE cells and bilateral macular or multifocal lesions; however, the specific mechanism leading to the formation of these lesions remains unclear. We now provide an overview of the current state of knowledge on the molecular pathology of bestrophinopathies, and explore factors promoting formation of RPE-neuroretinal separations, using the first spontaneous animal model of BEST1-associated retinopathies, canine Best (cBest). Here, we characterize the nature of the autofluorescent RPE cell inclusions and report matching spectral signatures of RPE-associated fluorophores between human and canine retinae, indicating an analogous composition of endogenous RPE deposits in Best Vitelliform Macular Dystrophy (BVMD) patients and its canine disease model. This study also exposes a range of biochemical and structural abnormalities at the RPE-photoreceptor interface related to the impaired cone-associated microvillar ensheathment and compromised insoluble interphotoreceptor matrix (IPM), the major pathological culprits responsible for weakening of the RPE-neuroretina interactions, and consequently, formation of vitelliform lesions. These salient alterations detected at the RPE apical domain in cBest as well as in BVMD- and ARB-hiPSC-RPE model systems provide novel insights into the pathological mechanism of BEST1-linked disorders that will allow for development of critical outcome measures guiding therapeutic strategies for bestrophinopathies.

Flat Anterior Chamber after Trabeculectomy in Secondary Angle-Closure Glaucoma with BEST1 Gene Mutation: Case Series

Purpose

Trabeculectomy has been regarded as a mainstay of initial treatment in eyes of angle closure glaucoma (ACG) with peripheral anterior synechia > 180° in the Chinese population while its efficacy in secondary ACG with BEST1 gene mutation remains unclear. We set out to investigate the treatment outcome of trabeculectomy for secondary ACG in a group of patients with autosomal recessive bestrophinopathy (ARB).

Methods

In this retrospective case series study, 8 secondary ACG patients with ARB and their 4 recruited family members underwent a thorough ophthalmic examination including best-corrected visual acuity, Goldmann applanation tonometry, gonioscopy, and fundus examinations. Ultrasound biomicroscopy, optical coherence tomography (OCT), ultrasound A-scan, B-scan, electro-oculography (EOG), Humphrey perimetry, fundus photography, fundus fluorescein angiography (FFA) and indocyanine green angiography (ICGA) were also performed. Blood samples were obtained in the patients and their available family members to analyze the variants of the BEST1 gene. Trabeculectomy was performed in the 8 patients (15 eyes).

Results

The age of onset varied from 13 to 38 years. The average axial length (AL) of the affected eyes was 21.82 ± 0.92 mm and the average anterior chamber depth (ACD) was 2.19 ± 0.29 mm. There was marked axial shallowing of the anterior chamber in all 15 eyes after trabeculectomy, and was not improved with potent mydriatics. The IOP was elevated in 3 eyes. Variable degree of yellowish subretinal deposits was observed in the posterior retina. The FFA showed punctuate or patched hyperfluorescence suggesting retinal pigment epithelium impairment. The ICGA demonstrated dilatation of choroidal vessels. The OCT revealed diffused neuroretinal detachment in the posterior and midperipheral retina, with intraretinal fluid collections, and hyperreflective subretinal accumulations. The average subfoveal choroidal thickness of the patients was 382.36 ± 80.09 μm. All the patients and enrolled family members carried mutation in BEST1 gene.

Conclusions

ARB is a rare condition with fundus manifestations mimicking various diseases. Careful discrimination should be taken to exclude any secondary causes for ACG before treatment. Concerning the high incidence of postoperative shallow anterior chamber, selection of filtering surgery should be very careful in these patients.

A Report on Molecular Diagnostic Testing for Inherited Retinal Dystrophies by Targeted Genetic Analyses

AIM

To test the utility of targeted sequencing as a method of clinical molecular testing in patients diagnosed with inherited retinal degeneration (IRD).

METHODS

After genetic counseling, peripheral blood was drawn from 188 probands and 36 carriers of IRD. Single gene testing was performed on each patient in a Clinical Laboratory Improvement Amendment (CLIA) certified laboratory. DNA was isolated, and all exons in the gene of interest were analyzed along with 20 base pairs of flanking intronic sequence. Genetic testing was most often performed on ABCA4, CTRP5, ELOV4, BEST1, CRB1, and PRPH2. Pathogenicity of novel sequence changes was predicted by PolyPhen2 and sorting intolerant from tolerant (SIFT).

RESULTS

Of the 225 genetic tests performed, 150 were for recessive IRD, and 75 were for dominant IRD. A positive molecular diagnosis was made in 70 (59%) of probands with recessive IRD and 19 (26%) probands with dominant IRD. Analysis confirmed 12 (34%) of individuals as carriers of familial mutations associated with IRD. Thirty-two novel variants were identified; among these, 17 sequence changes in four genes were predicted to be possibly or probably damaging including: ABCA4 (14), BEST1 (2), PRPH2 (1), and TIMP3 (1).

CONCLUSIONS

Targeted analysis of clinically suspected genes in 225 subjects resulted in a positive molecular diagnosis in 26% of patients with dominant IRD and 59% of patients with recessive IRD. Novel damaging mutations were identified in four genes. Single gene screening is not an ideal method for diagnostic testing given the phenotypic and genetic heterogeneity among IRD cases. High-throughput sequencing of all genes associated with retinal degeneration may be more efficient for molecular diagnosis.

Unilateral BEST1-Associated Retinopathy

Purpose

To describe a series of patients with molecularly confirmed mutation in BEST1 causing Best disease but with unilateral clinical manifestation.

Design

Retrospective observational case series.

Methods

Setting: Moorfields Eye Hospital and Great Ormond Street Hospital, London (United Kingdom). Patients: Five patients (10 eyes) with uniocular manifestation of BEST1 mutation causing Best disease were ascertained retrospectively from the clinical and genetic databases. Main Outcome Measures: Patients had full ophthalmologic examination, color fundus photography, fundus autofluorescence imaging, spectral-domain optical coherence tomography, and detailed electrophysiological assessment. Genetic testing was performed.

Results

All cases had a clinical appearance typical of and consistent with Best disease at various stages, except that the presentation was unilateral. The reduced electrooculogram light rise was bilateral and in the context of normal electroretinograms therefore indicates generalized dysfunction at the level of the retinal pigment epithelium.

Conclusions

Mutation in BEST1 has variable penetrance and expressivity, and can be uniocular. The clinical and electrophysiological features described assist targeted mutational screening and alert to the potential diagnosis even when there is an atypical unilateral presentation.

Clinical and Genetic Findings of Autosomal Recessive Bestrophinopathy in Japanese Cohort

PURPOSE

To report the clinical and genetic findings of 9 Japanese patients with autosomal recessive bestrophinopathy (ARB).

DESIGN

Retrospective, multicenter observational case series.

METHODS

Nine ARB patients from 7 unrelated Japanese families that were examined in 3 institutions in Japan were studied. A series of ophthalmic examinations including fundus photography, spectral-domain optical coherence tomography, fundus autofluorescence, electrooculography (EOG), electroretinography, and the results of genetic analysis were reviewed.

RESULTS

Genetic analyses identified 7 pathogenic variants in BEST1 including 2 novel variants, c.478G>C (p.A160P) and c.948+1delG. Homozygous variants were found in 4 families and compound heterozygous variants were found in 3 families. Two patients were diagnosed as ARB only after the whole exome sequencing analyses. The Arden ratio of the EOG was less than 1.5 in all 7 patients tested. Vitelliform lesions typical for Best vitelliform macular dystrophy were not seen in any of the patients. Seven patients shared some of the previously described features of ARB: subretinal deposits, extensive subretinal fluid, and cystoid macular edema (CME). However, the other 2 patients with severe retinal degeneration lacked these features. Focal choroidal excavations were present bilaterally in 2 patients. One case had a marked reduction of the CME and expansion of subretinal deposits over an 8-year of follow-up period.

CONCLUSIONS

Japanese ARB patients had some but not all of the previously described features. Genetic analyses are essential to diagnose ARB correctly in consequence of considerable phenotypic variations.

Detailed analysis of family with autosomal recessive bestrophinopathy associated with new BEST1 mutation

Purpose

To describe the clinical and genetic findings in a patient with autosomal recessive bestrophinopathy (ARB) and his healthy parents.

Methods

The patient and his healthy non-consanguineous parents underwent detailed ophthalmic evaluations including electro-oculography (EOG), spectral-domain optical coherence tomography (SD-OCT), and fundus autofluorescence (FAF) imaging. Mutation analysis of the BEST1 gene was performed by Sanger sequencing.

Results

The FAF images showed multiple spots of increased autofluorescence, and the sites of these spots corresponded to the yellowish deposits detected by ophthalmoscopy. SD-OCT showed cystoid macular changes and a shallow serous macular detachment. The Arden ratio of the EOG was markedly reduced to 1.1 in both eyes. Genetic analysis of the proband detected two sequence variants of the BEST1 gene in the heterozygous state: a novel variant c.717delG, p.V239VfsX2 and an already described c.763C>T, p.R255W variant associated with Best vitelliform macular dystrophy and ARB. The proband’s father carried the c.717delG, p.V239VfsX2 variant in the heterozygous state, and the mother carried the c.763C>T, p.R255W variant in the heterozygous state. The parents who were heterozygous for the BEST1 variants had normal visual acuity, EOG, SD-OCT, and FAF images.

Conclusions

In a truncating BEST1 mutation, the phenotype associated with ARB is most likely due to a marked decrease in the expression of BEST1 promoted by the nonsense-mediated decay surveillance mechanism, and it may depend on the position of the premature termination of the codon created.

BEST1: the Best Target for Gene and Cell Therapies

A retinal pigmented epithelial (RPE) disorder, bestrophinopathy has recently been proven to be amenable to gene and cell-based therapies in preclinical models. RPE disorders and allied retinal degenerations exhibit significant genetic heterogeneity, and diverse mutations can result in similar disease phenotypes. Several RPE disorders have recently become targets for gene therapies in humans. The year 2011 brought a new advance in cell-based therapies, with the Food and Drug Administration approving clinical trials using embryonic stem cells for an RPE disorder known as age-related macular degeneration. Recent studies on induced pluripotent stem (iPS)-RPE generation indicate strong potential for developing patient-specific disease models in vitro, which could eventually enable personalized treatment. This mini-review will briefly highlight the suitability of the retina for gene and cell therapies, the pathophysiology of bestrophinopathy, and the research and treatment opportunities afforded by stem cell and genetic therapies.