Phenotype and genotype of patients with autosomal recessive bestrophinopathy

A pathogenic in-frame deletion-insertion variant in BEST1 phenocopies Stargardt disease

Here, we describe affected members of a 2-generation family with a Stargardt disease-like phenotype caused by a 2-base pair deletion insertion, c.1014_1015delGAinsCT;p.(Trp338_Asn339delinsCysTyr), in BEST1. The variant was identified by whole-exome sequencing, and its pathogenicity was verified through chloride channel recording using WT and transfected mutant HEK293 cells. Clinical examination of both patients revealed similar phenotypes at 2 different disease stages that were attributable to differences in their age at presentation. Hyperautofluorescent flecks along the arcades were observed in the proband, while the affected mother exhibited more advanced retinal pigment epithelium (RPE) loss in the central macula. Full-field electroretinogram testing was unremarkable in the daughter; however, moderate attenuation of generalized cone function was detected in the mother. Results from electrooculogram testing in the daughter were consistent with widespread dysfunction of the RPE characteristic of Best disease. Whole-cell patch-clamp recordings revealed a statistically significant decrease in chloride conductance of the mutant compared with WT cells. This report on a mother and daughter with a BEST1 genotype that phenocopies Stargardt disease broadens the clinical spectrum of BEST1-associated retinopathy.

Case report: Autosomal recessive bestrophinopathy with macular cysts and MNV over 13-year follow-up

Purpose: To describe the phenotype and genotype of a patient with autosomal recessive bestrophinopathy (ARB) over a 13-year follow-up period.

Methods: The phenotype of the subject was described after a complete ophthalmological examination, which included fundus photography, optical coherence tomography (OCT), fundus autofluorescence, fluorescein angiography (FA), indocyanine green angiography (ICGA), electroretinogram (EOG), electroretinography (ERG), and multifocal electroretinogram (mfERG). Genetic analyses were carried out by screening the variations via whole-exome sequencing.

Results: This patient presented with retinoschisis and cystic changes when he was 7 years old and was diagnosed with X-linked retinoschisis. In the 13th year after the first presentation, enlarged macular cysts with retinoschisis, macular neovascularization (MNV), and subretinal fluid were displayed on OCT. Autofluorescence showed hyperfluorescence corresponding to the area of retinal pigment epithelium (RPE) change. EOG showed no light peak, and the Arden ratio was less than 2.0. Whole-exome sequencing revealed compound heterozygous sequence variations (p. [Arg47Leu; Trp287*]) in the coding sequence of the BEST1 allele inherited from his parents. Thus, a diagnosis of ARB combined with secondary MNV was made.

Conclusion: Patients with compound heterozygous BEST1 mutations developed ARB, which could show significant retinoschisis at a young age. Genetic analyses, autofluorescence, and EOG are essential to diagnose ARB correctly in consequence of considerable phenotypic variations.

BEST1 novel mutation causes Bestrophinopathies in six families with distinct phenotypic diversity

PURPOSE

To report novel BEST1 variants in six Chinese families with bestrophinopathies of two different inheritance modes and analyze the intrafamilial phenotypic diversity.

METHOD

A total of 25 participants including 13 patients and 12 healthy family members from 6 Chinese families with bestrophinopathies were available for genetic and clinical analysis. All of the patients were subjected to comprehensive ophthalmic evaluations and exome sequencing was performed on the probands to detect the causative variants. The pathogenicity of gene variants was predicted using silico analysis and evaluated according to ACMG guidelines. All (likely) pathogenic variants were determined by Sanger sequencing and co-segregation analyses were performed on available family members. The relevant original literature previously reported was retrieved to explore the relationship between BEST1-related gene variants and clinical features.

RESULTS

In the 6 families, 3 families (10 patients) were assigned as autosomal dominant bestrophinopathies (VMD) and 3 families (3 patients) were assigned as Autosomal recessive Bestrophinopathies (ARB). A total of 9 variants on the BEST1 gene were identified, containing 7 missense variants, 1 nonsense variant, and 1 frameshift variant, respectively, of which 3 variants c.88A > G (p.Lys30Glu), c.764G > A (p.Arg255Gln) and c.233dupT (p.Ser79Phefs*153) were novel variants. Three families with ARB were detected with heterozygous variants on the BEST1 gene.2 families (8 patients) with BVMD showed markedly irregular dominant inheritance, and the severity of macular lesions varies greatly among individuals of the same family. Among them, the probands showed typical vitelliform lesions in the macula, while the other six patients had no visible signs of the disease by fundus photography (ophthalmoscopy) and minor lesions could be detected on OCT in two patients, the continuity of the ellipsoidal band was interrupted with the chimeric band. The phenotypes of the patients in the three ARB families ranged from typical/atypical vitelliform lesions to extensive extramacular deposits (peripheral spots).

CONCLUSION

This study provided evidence that the phenotype of BVMD manifested irregular dominant inheritance, with patients carrying a pathogenic heterozygous variant of BEST1 to develop obvious intrafamilial phenotypic diversity, and the patients who harbor two pathogenic alleles showed recessive inheritance bestrophinopathies with distinct phenotypic diversity. Our study also emphasized the importance of comprehensive genetic analysis in patients with bestrophinopathies, and in such challenging families with distinct intrafamilial phenotypic diversity, it shall provide novel insights into phenotypic assessments of bestrophinopathies, and contribute to better diagnosis, prognosis, and treatment for these patients.

Autosomal Recessive Bestrophinopathy Presenting With a Macular Hole Retinal Detachment

Purpose: To report a case of autosomal recessive bestrophinopathy (ARB) that presented with macular hole retinal detachment (MHRD). Methods: A case report. Results: A 31-year-old male patient presented with rapid deterioration of vision in the left eye. On fundus examination, bilateral retinal deposits in both eyes, which were brightly hyperautofluorescent, and an MHRD in the left eye could be detected. An electrooculogram demonstrated absent light rise with abnormal Arden’s ratio in both eyes. The patient was offered surgery for the MHRD but refused due to the guarded visual prognosis. Follow up of the patient after one year revealed progression of the retinal detachment. Genetic testing revealed a novel, homozygous missense mutation in the BEST1 gene, confirming the diagnosis of ARB. Conclusion: ARB can present with an MHRD. Counseling patients with inherited retinal dystrophies about the visual prognosis following surgical intervention is important.

Twelve-year follow up of a case of autosomal recessive bestrophinopathy with transient resolution of retinal edema in one eye

PURPOSE

To report 12-year follow-up of a patient with ARB.

CASE REPORT

A 25-year-old man presented with blurred vision in his both eyes (OU). Best-corrected visual acuity (BCVA) was 20/63 Snellen equivalent in the right eye (OD) and 20/32 Snellen equivalent in the left eye. The intraocular pressures and anterior segment examination were unrevealing in OU. Posterior segment examination revealed multiple yellowish flecks and dots in the posterior pole in OU. Optical coherence tomography (OCT) showed subretinal fluid (SRF), intraretinal hyporeflective spaces, elongated and shaggy photoreceptors and outer retinal defects. Fundus autofluorescence demonstrated mottling hyperautofluorescence and hypoautofluorescence in the posterior pole in OU. Fluorescein angiography illustrated hyperfluorescence in the posterior pole and surrounding the arcades in OU. Multifocal electroretinography objectified mild to markedly abnormal responses in all ring areas in OU. Molecular genetic testing confirmed two heterozygous sequence variations in the BEST1 gene. At 4 years of follow-up, OCT revealed a complete resolution of SRF and a partial resolution of intraretinal hyporeflective spaces in the OD with corresponding improvement in the BCVA to 20/23 Snellen equivalent in the OD, even though outer retinal defects persisted. Our patient denied recent changes in his alimentary habits and medical history at that time. Posteriorly, SRF and intraretinal hyporeflective spaces reappeared in the OD.

CONCLUSION

To the best of our knowledge, this is the first case report of ARB with a transient resolution of retinal edema in one eye without medical treatment and dietary therapy.

Clinical reassessments and whole-exome sequencing uncover novel BEST1 mutation associated with bestrophinopathy phenotype

BACKGROUND

The diagnosis of retinal dystrophies can be challenging due to the spectrum of protean phenotypic manifestations. This study employed trio-whole-exome sequencing (trio-WES) to unveil the genetic cause of an inherited retinal disorder in a south Indian family.

MATERIALS AND METHODS

Proband's initial ophthalmic examinations was performed in the year 2016. WES was performed on a proband-parent trio to identify causative mutation followed by Sanger validation, segregation analysis, sequence and structure-based computational analysis to assess its pathogenicity. Based on the genetic findings, detailed clinical reassessments were performed in year 2020 for the proband and available family members.

RESULTS

WES revealed a novel homozygous BEST1 mutation c.G310A (p.D104N) in the proband and heterozygous for the parents, indicating autosomal recessive inheritance. Segregation analysis showed heterozygous mutation in maternal grandfather and normal genotype for younger brother and maternal grandmother. Moreover, the structure-based analysis revealed the mutation p.D104N in the cytoplasmic domain, causing structural hindrance by altering hydrogen bonds and destabilizing the BEST1 protein structure. Proband's clinical assessments were consistent with autosomal recessive bestrophinopathy (ARB) phenotype. Additionally, characteristic absent light rise and decreased light peak-to-dark trough ratio (LP:DT) was observed bilaterally in EOG.

CONCLUSIONS

Our study demonstrates the utility of WES and clinical re-evaluations in establishing the precise diagnosis of autosomal recessive bestrophinopathy associated with a novel mutation, thus expanding the BEST1-related mutation spectrum.

Deciphering the genetic architecture and ethnographic distribution of IRD in three ethnic populations by whole genome sequence analysis

Patients with inherited retinal dystrophies (IRDs) were recruited from two understudied populations: Mexico and Pakistan as well as a third well-studied population of European Americans to define the genetic architecture of IRD by performing whole-genome sequencing (WGS). Whole-genome analysis was performed on 409 individuals from 108 unrelated pedigrees with IRDs. All patients underwent an ophthalmic evaluation to establish the retinal phenotype. Although the 108 pedigrees in this study had previously been examined for mutations in known IRD genes using a wide range of methodologies including targeted gene(s) or mutation(s) screening, linkage analysis and exome sequencing, the gene mutations responsible for IRD in these 108 pedigrees were not determined. WGS was performed on these pedigrees using Illumina X10 at a minimum of 30X depth. The sequence reads were mapped against hg19 followed by variant calling using GATK. The genome variants were annotated using SnpEff, PolyPhen2, and CADD score; the structural variants (SVs) were called using GenomeSTRiP and LUMPY. We identified potential causative sequence alterations in 61 pedigrees (57%), including 39 novel and 54 reported variants in IRD genes. For 57 of these pedigrees the observed genotype was consistent with the initial clinical diagnosis, the remaining 4 had the clinical diagnosis reclassified based on our findings. In seven pedigrees (12%) we observed atypical causal variants, i.e. unexpected genotype(s), including 4 pedigrees with causal variants in more than one IRD gene within all affected family members, one pedigree with intrafamilial genetic heterogeneity (different affected family members carrying causal variants in different IRD genes), one pedigree carrying a dominant causative variant present in pseudo-recessive form due to consanguinity and one pedigree with a de-novo variant in the affected family member. Combined atypical and large structural variants contributed to about 20% of cases. Among the novel mutations, 75% were detected in Mexican and 50% found in European American pedigrees and have not been reported in any other population while only 20% were detected in Pakistani pedigrees and were not previously reported. The remaining novel IRD causative variants were listed in gnomAD but were found to be very rare and population specific. Mutations in known IRD associated genes contributed to pathology in 63% Mexican, 60% Pakistani and 45% European American pedigrees analyzed. Overall, contribution of known IRD gene variants to disease pathology in these three populations was similar to that observed in other populations worldwide. This study revealed a spectrum of mutations contributing to IRD in three populations, identified a large proportion of novel potentially causative variants that are specific to the corresponding population or not reported in gnomAD and shed light on the genetic architecture of IRD in these diverse global populations.

The study was performed to identify the underlying cause of inherited retinal degeneration (IRD) in 409 individuals from 108 families. Primarily, these families were recruited from three different geographic regions: Mexico, Pakistan and European Americans from the United States. Blood samples were collected from all individuals for genome analysis. This analysis detected causative variants in 61 out of the 108 pedigrees. A total of 93 gene variants were found in the 61 families. Among these, 54 were previously reported as causative variants and the remaining 39 have not been reported in IRD pedigrees. Interestingly, 54% of these novel variants were not listed in gnomAD. In addition to these findings, complex causative genotypes were observed in 20% of pedigrees. Overall, causative variants were detected in 63% Mexican, 60% Pakistani and 45% European American pedigrees. This study revealed the distribution of IRD causative variants in pedigrees with diverse ethnic and geographic backgrounds.

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.

Bestrophinopathies: perspectives on clinical disease, Bestrophin-1 function and developing therapies

Bestrophinopathies are a group of clinically distinct inherited retinal dystrophies that typically affect the macular region, an area synonymous with central high acuity vision. This spectrum of disorders is caused by mutations in bestrophin1 (BEST1), a protein thought to act as a Ca²⁺-activated Cl^- channel in the retinal pigment epithelium (RPE) of the eye. Although bestrophinopathies are rare, over 250 individual pathological mutations have been identified in the BEST1 gene, with many reported to have various clinical expressivity and incomplete penetrance. With no current clinical treatments available for patients with bestrophinopathies, understanding the role of BEST1 in cells and the pathological pathways underlying disease has become a priority. Induced pluripotent stem cell (iPSC) technology is helping to uncover disease mechanisms and develop treatments for RPE diseases, like bestrophinopathies. Here, we provide a comprehensive review of the pathophysiology of bestrophinopathies and highlight how patient-derived iPSC-RPE are being used to test new genomic therapies in vitro.

The best course of action

An 11-year-old girl noted gradual visual loss in the right eye for 1 year with subfoveal yellow deposits in both eyes. Optical coherence tomography, electro-oculogram and electroretinogram was in-keeping with Best Disease. This disorder is discussed.

Association of Clinical and Genetic Heterogeneity With BEST1 Sequence Variations

Importance

Detailed phenotypic information on the spectrum of fundus abnormalities and clinical variability of all phenotypes associated with sequence variations in BEST1 is limited.

Objective

To report a detailed phenotypic and genetic analysis of a patient cohort with sequence variations in BEST1.

Design, Setting, and Participants

This retrospective case series took place at the Oxford Eye Hospital in Oxford, UK. Thirty-six patients from a single center with disease-causing sequence variations in BEST1 from 25 different families were analyzed. Data were collected from November 2017 to June 2018, and analysis began April 2018.

Main Outcomes and Measures

Results of ocular phenotyping and genetic testing using targeted next-generation sequencing to identify BEST1 sequence variations.

Results

Thirty-six patients from 25 families with disease-causing sequence variations in BEST1 were included. Of 36 patients, 20 (55.6%) were female. Three distinct clinical phenotypes were identified: autosomal recessive bestrophinopathy (ARB), best vitelliform macular dystrophy (BVMD), and adult-onset vitelliform macular dystrophy. The ARB phenotype group comprised 18 patients from 9 families with age in years at symptom onset ranging from less than 10 to 40s. All patients showed a common phenotype of fundus autofluorescence abnormalities, and spectral-domain optical coherence tomography features were similar in all patients with schitic and cystoid changes. A phenotype of a beaten metallic retinal appearance extending from the mid periphery to the far periphery was identified in 8 patients. Four patients from 1 family with ARB were previously reported to have autosomal recessive retinitis pigmentosa but were reclassified as having ARB as part of this study. The BVMD phenotype group comprised 16 patients from 14 families with age at symptom onset ranging from less than 10 to 70s. Fundus features were localized to the macula and consistent with the stage of BVMD. In the adult-onset vitelliform macular dystrophy phenotype group, the age in years at symptom onset varied from 50s to 70s in 2 patients from 2 families. Fundus features included small vitelliform lesions. Where available, electro-oculogram results demonstrated a reduced or absent light rise in all patients with ARB and BVMD. Genetic testing identified 22 variants in BEST1.

Conclusions and Relevance

These findings support the notion that ARB, BVMD, and adult-onset vitelliform macular dystrophy are clinically distinct and recognizable phenotypes and suggest that the association of autosomal recessive retinitis pigmentosa with sequence variations in BEST1 should be rereviewed.

IMAGING OF VITELLIFORM MACULAR LESIONS USING POLARIZATION-SENSITIVE OPTICAL COHERENCE TOMOGRAPHY

PURPOSE

To examine the involvement of the retinal pigment epithelium (RPE) in the presence of vitelliform macular lesions (VML) in Best vitelliform macular dystrophy (BVMD), autosomal recessive bestrophinopathy, and adult-onset vitelliform macular degeneration using polarization-sensitive optical coherence tomography (PS-OCT).

METHODS

A total of 35 eyes of 18 patients were imaged using a PS-OCT system and blue light fundus autofluorescence imaging. Pathogenic mutations in the BEST1 gene, 3 of which were new, were detected in all patients with BVMD and autosomal recessive bestrophinopathy.

RESULTS

Polarization-sensitive optical coherence tomography showed a characteristic pattern in all three diseases with nondepolarizing material in the subretinal space consistent with the yellowish VML seen on funduscopy with a visible RPE line below it. A focal RPE thickening was seen in 26 eyes under or at the edge of the VML. Retinal pigment epithelium thickness outside the VML was normal or mildly thinned in patients with BVMD and adult-onset vitelliform macular degeneration but was diffusely thinned or atrophic in patients with autosomal recessive bestrophinopathy. Patients with autosomal recessive bestrophinopathy showed sub-RPE fibrosis alongside the subretinal VML. Polarization-sensitive optical coherence tomography was more reliable in assessing the localization and the integrity of the RPE than spectral domain OCT alone. On spectral domain OCT, identification of the RPE was not possible in 19.4% of eyes. Polarization-sensitive optical coherence tomography allowed for definite identification of the location of VML in respect to the RPE in all eyes, since it provides a tissue-specific contrast.

CONCLUSION

Polarization-sensitive optical coherence tomography confirms in vivo the subretinal location of VML and is useful in the assessment of RPE integrity.

Novel BEST1 gene mutations associated with two different forms of macular dystrophy in Tunisian families

BACKGROUND

Epidemiological studies of hereditary eye diseases allowed us to identify two Tunisian families suffering from macular dystrophies: Best vitelliform macular dystrophy (BVMD) and autosomal recessive bestrophinopathy (ARB). The purpose of the current study was to investigate the clinical characteristics and the underlying genetics of these two forms of macular dystrophy.

METHODS

Complete ophthalmic examination was performed including optical coherence tomography, electroretinography, electrooculography and autofluoresence imaging in all patients. Genomic DNA was extracted from peripheral blood collected from patients and family members.

RESULTS

Sanger sequencing of all exons of the BEST1 gene in both families identified two new mutations: a missense mutation c.C91A [p.L31 M] at the N-terminal transmembrane domain within the ARB family and a nonsense mutation C1550G (p.S517X) in the C-terminal domain segregating in the BVMD family.

CONCLUSIONS

Several mutations of the BEST1 gene have been reported which are responsible for numerous ocular pathologies. To the best of our knowledge, it is the first time we report mutations in this gene in Tunisian families presenting different forms of macular dystrophy. Our report also expands the list of pathogenic BEST1 genotypes and the associated clinical diagnosis.

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.

AUTOSOMAL RECESSIVE BESTROPHINOPATHY: MULTIMODAL IMAGING UPDATE

BACKGROUND

Autosomal recessive bestrophinopathy is part of the diverse spectrum of retinal diseases caused by mutations in the BEST1 gene.

METHODS

A case report.

RESULTS

We present a case that highlights the classic retinal findings of autosomal recessive bestrophinopathy with an emphasis on modern multimodal imaging.

CONCLUSION

We describe modern multimodal imaging in an individual with a BEST1 gene mutation and clinical findings consistent with an autosomal recessive bestrophinopathy.

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.

BESTROPHINOPATHY: A Spectrum of Ocular Abnormalities Caused by the c.614T>C Mutation in the BEST1 Gene

PURPOSE

To describe the variable ocular phenotype associated with a heterozygous mutation in the BEST1 gene.

METHODS

Clinical and genetic assessment was performed in five members of the same family. Molecular genetic analysis of the BEST1 gene was performed by direct sequencing. Extensive ophthalmic examination included color fundus imaging, spectral domain optical coherence tomography, fundus autofluorescence, electro-oculography (EOG), and full-field electroretinography (ERG). The main outcome measures were BEST1 mutations, imaging, and electroretinography findings.

RESULTS

All affected family members carried a single heterozygous c.614T>C (p.I205T) mutation in exon 5 of the BEST1 gene. The 46-year-old proband showed nanophthalmos with chorioretinal atrophy in the macula, extensive coarse hyperpigmentation in the (mid) peripheral retina with tractional vitreous strands. Full-field ERG revealed nonrecordable cone and rod responses, and EOG showed an absent light rise. The daughter and son of the proband showed a phenotype resembling autosomal recessive bestrophinopathy, including short axial lengths, cystoid fluid collections, and shallow serous subretinal fluid accumulation on spectral domain optical coherence tomography throughout the macula in combination with mild retinal pigment epithelium changes. The son of the proband also showed subretinal yellowish deposits inferiorly in the macula as well as outside the temporal vascular arcade, that were hyperfluorescent on fundus autofluorescence, similar to those seen in autosomal recessive bestrophinopathy. Full-field ERG revealed a reduced rod and cone response and a markedly reduced or absent EOG light peak in both brother and sister of the proband.

CONCLUSION

The clinical spectrum of bestrophinopathy may encompass severe ocular phenotypes that affect the development and function of the entire eye. A clinical picture similar to autosomal recessive bestrophinopathy can also be caused by a single heterozygous mutation in the BEST1 gene, such as the c.614T>C (p.I205T) variant in this family.

Genetic analysis of 10 pedigrees with inherited retinal degeneration by exome sequencing and phenotype-genotype association

Our purpose was to identify causative mutations and characterize the phenotype associated with the genotype in 10 unrelated families with autosomal recessive retinal degeneration. Ophthalmic evaluation and DNA isolation were carried out in 10 pedigrees with inherited retinal degenerations (IRD). Exomes of probands from eight pedigrees were captured using Nimblegen V2/V3 or Agilent V5+UTR kits, and sequencing was performed on Illumina HiSeq. The DHDDS gene was screened for mutations in the remaining two pedigrees with Ashkenazi Jewish ancestry. Exome variants were filtered to detect candidate causal variants using exomeSuite software. Segregation and ethnicity-matched control sample analysis were performed by dideoxy sequencing. Retinal histology of a patient with DHDDS mutation was studied by microscopy. Genetic analysis identified six known mutations in ABCA4 (p.Gly1961Glu, p.Ala1773Val, c.5461-10T>C), RPE65 (p.Tyr249Cys, p.Gly484Asp), PDE6B (p.Lys706Ter) and DHDDS (p.Lys42Glu) and ten novel potentially pathogenic variants in CERKL (p.Met323Val fsX20), RPE65 (p.Phe252Ser, Thr454Leu fsX31), ARL6 (p.Arg121His), USH2A (p.Gly3142Ter, p.Cys3294Trp), PDE6B (p.Gln652Ter), and DHDDS (p.Thr206Ala) genes. Among these, variants/mutations in two separate genes were observed to segregate with IRD in two pedigrees. Retinal histopathology of a patient with a DHDDS mutation showed severe degeneration of retinal layers with relative preservation of the retinal pigment epithelium. Analysis of exome variants in ten pedigrees revealed nine novel potential disease-causing variants and nine previously reported homozygous or compound heterozygous mutations in the CERKL, ABCA4, RPE65, ARL6, USH2A, PDE6B, and DHDDS genes. Mutations that could be sufficient to cause pathology were observed in more than one gene in one pedigree.

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.

Identification of Novel and Recurrent Disease-Causing Mutations in Retinal Dystrophies Using Whole Exome Sequencing (WES): Benefits and Limitations

Inherited retinal dystrophies (IRDs) are Mendelian diseases with tremendous genetic and phenotypic heterogeneity. Identification of the underlying genetic basis of these dystrophies is therefore challenging. In this study we employed whole exome sequencing (WES) in 11 families with IRDs and identified disease-causing variants in 8 of them. Sequence analysis of about 250 IRD-associated genes revealed 3 previously reported disease-associated variants in RHO, BEST1 and RP1. We further identified 5 novel pathogenic variants in RPGRIP1 (p.Ser964Profs*37), PRPF8 (p.Tyr2334Leufs*51), CDHR1 (p.Pro133Arg and c.439-17G>A) and PRPF31 (p.Glu183_Met193dup). In addition to confirming the power of WES in genetic diagnosis of IRDs, we document challenges in data analysis and show cases where the underlying genetic causes of IRDs were missed by WES and required additional techniques. For example, the mutation c.439-17G>A in CDHR1 would be rated unlikely applying the standard WES analysis. Only transcript analysis in patient fibroblasts confirmed the pathogenic nature of this variant that affected splicing of CDHR1 by activating a cryptic splice-acceptor site. In another example, a 33-base pair duplication in PRPF31 missed by WES could be identified only via targeted analysis by Sanger sequencing. We discuss the advantages and challenges of using WES to identify mutations in heterogeneous diseases like IRDs.

A missense mutation in ASRGL1 is involved in causing autosomal recessive retinal degeneration

Inherited retinal dystrophies are a group of genetically heterogeneous conditions with broad phenotypic heterogeneity. We analyzed a large five-generation pedigree with early-onset recessive retinal degeneration to identify the causative mutation. Linkage analysis and homozygosity mapping combined with exome sequencing were carried out to map the disease locus and identify the p.G178R mutation in the asparaginase like-1 gene (ASRGL1), segregating with the retinal dystrophy phenotype in the study pedigree. ASRGL1 encodes an enzyme that catalyzes the hydrolysis of L-asparagine and isoaspartyl-peptides. Studies on the ASRGL1 expressed in Escherichia coli and transiently transfected mammalian cells indicated that the p.G178R mutation impairs the autocatalytic processing of this enzyme resulting in the loss of functional ASRGL1 and leaving the inactive precursor protein as a destabilized and aggregation-prone protein. A zebrafish model overexpressing the mutant hASRGL1 developed retinal abnormalities and loss of cone photoreceptors. Our studies suggest that the p.G178R mutation in ASRGL1 leads to photoreceptor degeneration resulting in progressive vision loss.

Biallelic Mutations in the BEST1 Gene: Additional Families with Autosomal Recessive Bestrophinopathy

PURPOSE

To describe the genotype and phenotype of patients with autosomal recessive bestrophinopathy (ARB), and heterozygous carriers.

METHODS

The members of three unrelated ARB families were investigated. Molecular genetic analysis was performed on 11 members of these families. Ten members were examined clinically; including visual acuity, slit-lamp examination, biomicroscopy, fundus photography, and Goldmann applanation tonometry. Measurements were also made of the anterior chamber depth and axial length, and optical coherence tomography (OCT), electrooculography (EOG), and full-field electroretinography (full-field ERG) were performed. Multifocal electroretinography (mfERG) was performed on eight members of these families.

RESULTS

Two novel combinations of missense mutations in the BEST1 gene were identified: p.R141H/p.M325T in three patients with ARB in two unrelated Norwegian families, and p.R141H/p.I201T was found in an ARB patient in a Swedish family. All four patients with ARB had clinical and electrophysiological features of ARB. All the heterozygous carriers of the p.R141H mutation were clinically normal, and showed normal OCT, EOG and full-field ERG findings, but had mildly abnormal mfERG results. Only one heterozygous carrier of the p.M325T mutation was studied and he was clinically normal, showing normal OCT and full-field ERG results, but subnormal EOG and mfERG findings. The heterozygous carrier of the p.I201T mutation was clinically normal, showing normal OCT, EOG and full-field ERG results, but subnormal mfERG results.

CONCLUSIONS

We have shown that the two novel combinations of compound heterozygous mutations p.R141H/p.M325T and p.R141H/p.I201T in the BEST1 gene can also lead to the ARB phenotype.

Two novel mutations in the bestrophin-1 gene and associated clinical observations in patients with best vitelliform macular dystrophy

The purpose of the current study was to investigate the 11 bestrophin-1 (BEST1) exons in patients with best vitelliform macular dystrophy (BVMD), and to characterize the associated clinical features. Complete ophthalmic examinations were conducted on two families, and two family members were diagnosed with BVMD. Genomic DNA was extracted from the leukocytes of peripheral blood collected from the patients and their family members, in addition to 100 unrelated control subjects recruited from the same population. The polymerase chain reaction was used to amplify a total of 11 exons of the BEST1 gene, which were directly sequenced. Ophthalmic examinations, including best-corrected visual acuity, slit-lamp examination, fundus examination, fundus photography and fluorescein angiography imaging, as well as anterior segment analysis with Pentacam and optical coherence tomography, were conducted. The patients exhibited yellowish lesions in the macular area. A heterozygous mutation c.910_912delGAT (p.304del Asp) in exon 7 was identified in Case 1. A heterozygous BEST1 missense mutation c.685T>G (p.Trp229Gly) in exon 5 was identified in Case 2, but not in any of the unaffected family members or normal controls. Although BEST1 gene mutations and polymorphisms have previously been reported in various ethnic groups, the current study identified, for the first time to the best of our knowledge, two novel BEST1 gene mutations in patients with BVMD.

A fast automated method for calculating the EOG Arden ratio

BACKGROUND

Recording of the dark trough/light peak of the electrooculogram (EOG) remains a useful electrodiagnostic tool. Manual analysis of the recording is tedious and lengthy, and automated analysis needs to deal with artefacts due to suboptimal patient cooperation.

METHODS

We present a novel method of automating the processing and analysis of raw EOG data using the open-source statistical software R. Rather than attempting saccade detection, we utilize the fact that basic properties of the response (rough waveform timing) are known and simply fit a square wave to each response run-free parameters are amplitude and phase. To assess this analysis method, responses from 54 eyes of 27 patients with a variety of ophthalmic diagnoses were analysed with manual calculation and with a number of automated methods of fitting the response curve. The Arden ratio was the main outcome measure.

RESULTS

Robust regression of a fundamental with a three-harmonic approximation of a square wave was found to be the best method. Classification accuracy with this method compared with the manual calculations as gold standard; using a lower normal threshold of 200%, Arden ratio was found to achieve a sensitivity of 96% and specificity of 81%. Time taken to process and analyse the data for a subject was reduced from 20 min for the manual method to 2 min for the automated method.

CONCLUSIONS

The simple approach yielded a surprisingly effective automatic estimation of the Arden ratio. In one author's laboratory (MB), this procedure has proved to be useful over 5 years for routine analysis.

Ocular phenotype analysis of a family with biallelic mutations in the BEST1 gene

PURPOSE

To investigate the genetic cause and perform a comprehensive clinical analysis of a Danish family with autosomal recessive bestrophinopathy; to investigate whether Bestrophin may be expressed in normal human retina.

DESIGN

Retrospective clinical and molecular genetic analysis and immunohistochemical observational study.

METHODS

setting: National referral center. participants: A family with 5 individuals and biallelic BEST1 mutations, and enucleated eyes from 2 individuals with nonaffected retinas. observation procedures: Molecular genetic analysis included sequencing of BEST1 and co-segregation analysis. Clinical investigations included electro-oculography, full-field electroretinography, multifocal electroretinography, spectral-domain optical coherence tomography, and fundus autofluorescence imaging. Immunohistochemical analysis was performed. main outcome measures: BEST1 mutations, imaging findings, electroretinography amplitudes, and implicit times.

RESULTS

The index case was compound heterozygous for p.A195V and a novel 15 base pair deletion leading to p.Q238L. The index case at age 10 demonstrated multifocal vitelliform changes that were hyperautofluorescent, cystoid macular edema in the inner nuclear layer, no light rise in the electro-oculography, and a reduced central but preserved peripheral retinal function by multifocal electroretinography. Full-field electroretinography demonstrated a reduced rod response and inner retina dysfunction. Retinal structure was normal in all 3 family members who carried a sequence change in BEST1. Electro-oculography light peak was reduced in both the mother and sister (heterozygous for p.Q238L). Immunohistochemistry could not confirm the presence of Bestrophin in normal human retina.

CONCLUSIONS

Because of a relatively well preserved retinal function, autosomal recessive bestrophinopathy may be a suitable first candidate, among the BEST1-related ocular conditions, for gene replacement therapy.

Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities

Retinitis Pigmentosa (RP) is a common form of retinal degeneration characterized by photoreceptor degeneration and retinal pigment epithelium (RPE) atrophy causing loss of visual field and acuities. Exome sequencing identified a novel homozygous splice site variant (c.111+1G>A) in the gene encoding retinol binding protein 4 (RBP4). This change segregated with early onset, progressive, and severe autosomal recessive retinitis pigmentosa (arRP) in an eight member consanguineous pedigree of European ancestry. Additionally, one patient exhibited developmental abnormalities including patent ductus arteriosus and chorioretinal and iris colobomas. The second patient developed acne from young age and extending into the 5^th decade. Both patients had undetectable levels of RBP4 in the serum suggesting that this mutation led to either mRNA or protein instability resulting in a null phenotype. In addition, the patients exhibited severe vitamin A deficiency, and diminished serum retinol levels. Circulating transthyretin levels were normal. This study identifies the RBP4 splice site change as the cause of RP in this pedigree. The presence of developmental abnormalities and severe acne in patients with retinal degeneration may indicate the involvement of genes that regulate vitamin A absorption, transport and metabolism.