Clinical and Genetic Findings of Autosomal Recessive Bestrophinopathy (ARB)

Multimodal imaging and genetic characteristics of autosomal recessive bestrophinopathy

PURPOSE

To report the ocular manifestations, multimodal imaging characteristics and genetic testing results of six patients with autosomal recessive bestrophinopathy (ARB).

METHODS

This was an observational case series including 12 eyes of 6 patients who were diagnosed with ARB. All patients underwent a complete ophthalmic examination including refraction, slit-lamp biomicroscopy, dilated fundus examination, fundus autofluorescence, optical coherence tomography and electrooculography. BEST1 gene sequencing was also performed for all patients.

RESULTS

The mean age was 22.8years and the male-female ratio was 0.50. All ARB patients had a hyperopic refractive error. A spectrum of fundus abnormalities, including multifocal yellowish subretinal deposits in the posterior pole, subfoveal accumulation of vitelliform material and cystoid macular edema, was observed. Fundus autofluorescence imaging demonstrated marked hyperautofluorescence corresponding to the yellowish subretinal deposits. Optical coherence tomography revealed serous retinal detachment, intraretinal cysts, brush border appearance caused by elongation of the outer segments of photoreceptors, and hyperreflective dome-shaped deposits at the level of the retinal pigment epithelium. Fundus fluorescein angiography showed hyperfluorescence with staining of the yellowish subretinal deposits. Electrooculography showed reduced Arden ratio in all patients. In addition, biallelic pathogenic variants in the BEST1 gene were detected in all patients.

CONCLUSION

ARB is a rare autosomal recessive inherited retinal disorder with biallelic pathogenic variants in the BEST1 gene and may present with a wide range of ocular abnormalities that may not be easily diagnosed. Multimodal retinal imaging in conjunction with EOG is helpful to establish the correct diagnosis.

Detection of Novel BEST1 Variations in Autosomal Recessive Bestrophinopathy Using Third-generation Sequencing

OBJECTIVE

Autosomal recessive bestrophinopathy (ARB), a retinal degenerative disease, is characterized by central visual loss, yellowish multifocal diffuse subretinal deposits, and a dramatic decrease in the light peak on electrooculogram. The potential pathogenic mechanism involves mutations in the BEST1 gene, which encodes Ca2+-activated Cl- channels in the retinal pigment epithelium (RPE), resulting in degeneration of RPE and photoreceptor. In this study, the complete clinical characteristics of two Chinese ARB families were summarized.

METHODS

Pacific Biosciences (PacBio) single-molecule real-time (SMRT) sequencing was performed on the probands to screen for disease-causing gene mutations, and Sanger sequencing was applied to validate variants in the patients and their family members.

RESULTS

Two novel mutations, c.202T>C (chr11:61722628, p.Y68H) and c.867+97G>A, in the BEST1 gene were identified in the two Chinese ARB families. The novel missense mutation BEST1 c.202T>C (p.Y68H) resulted in the substitution of tyrosine with histidine in the N-terminal region of transmembrane domain 2 of bestrophin-1. Another novel variant, BEST1 c.867+97G>A (chr11:61725867), located in intron 7, might be considered a regulatory variant that changes allele-specific binding affinity based on motifs of important transcriptional regulators.

CONCLUSION

Our findings represent the first use of third-generation sequencing (TGS) to identify novel BEST1 mutations in patients with ARB, indicating that TGS can be a more accurate and efficient tool for identifying mutations in specific genes. The novel variants identified further broaden the mutation spectrum of BEST1 in the Chinese population.

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.

A novel compound heterozygous BEST1 gene mutation in two siblings causing autosomal recessive bestrophinopathy

PURPOSE

To describe the clinical features, imaging characteristics, and genetic test results associated with a novel compound heterozygous mutation of the BEST1 gene in two siblings with autosomal recessive bestrophinopathy.

METHODS

Two siblings underwent a complete ophthalmic examination, including dilated fundus examination, fundus photography, fundus autofluorescence imaging, spectral-domain optical coherence tomography, fluorescein angiography, electroretinography, and electrooculography. A clinical diagnosis of autosomal recessive bestrophinopathy was established based on ocular examination and multimodal retinal imaging. Subsequently, clinical exome sequencing consisting of a panel of 6670 genes was carried out to confirm the diagnosis and assess genetic alterations in the protein-coding region of the genome of the patients. The identified mutations were tested in the two affected siblings and one of their parents.

RESULTS

Two siblings (a 17-year-old female and a 15-year-old male) presented with reduced visual acuity and bilaterally symmetrical subretinal deposits of hyperautofluorescent materials in the posterior pole, which showed staining in the late phase of fluorescein angiogram. Spectral-domain optical coherence tomography demonstrated hyperreflective subretinal deposits and subretinal fluid accumulation. Both patients shared two mutations in the protein-coding region of the BEST1 gene, c.103G > A, p.(Glu35Lys) and c.313C > A, p.(Arg105Ser) (a novel disease-causing mutation). Sanger sequencing confirmed that the unaffected mother of the proband was carrying p.(Glu35Lys) variant in a heterozygous state.

CONCLUSIONS

We have identified and described the phenotype of a novel disease-causing mutation NM_004183.4:c.313C > A, p.(Arg105Ser) in a heterozygous state along with a previously reported mutation NM_004183.4:c.103G > A, p.(Glu35Lys) of the BEST1 gene in two related patients with autosomal recessive bestrophinopathy.

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.

Clinical Features and Genetic Findings of Autosomal Recessive Bestrophinopathy

Autosomal recessive bestrophinopathy (ARB) is a rare subtype of bestrophinopathy caused by biallelic mutations of the BEST1 gene. ARB is characterized by multifocal subretinal deposits accompanied by macular edema or subretinal fluid, hyperopia, co-existing narrow angle, and a marked decrease in electrooculogram. However, little is known about the genetic variants and specific clinical features of ARB. This is an observational case series of patients with a clinical and genetic diagnosis of ARB who underwent multimodal imaging. We describe ten patients from nine unrelated families with six known variants and three novel missense variants: c.236C→T, p.(Ser79Phe); C.452C→T, p.(Leu151Pro); and c.650C→T, p.(Trp217Met). The most common variant was c.584C→T, p.(Ala195Val), observed in six patients, without correlation to the severity of the phenotype. All patients manifested bilateral multifocal subretinal deposits and subretinal fluid throughout the follow-up period, while intraretinal fluid was found in approximately half of the eyes. The extent or chronicity of the fluid collection did not correlate with visual acuity. Angle-closure glaucoma was present in five eyes. Three patients had a genetically confirmed family history of ARB, and one patient had a clinically suspected family history. This study reveals novel mutations in the BEST1 gene and adds to the spectrum of clinical presentations of ARB.

Impaired Bestrophin Channel Activity in an iPSC-RPE Model of Best Vitelliform Macular Dystrophy (BVMD) from an Early Onset Patient Carrying the P77S Dominant Mutation

Best Vitelliform Macular dystrophy (BVMD) is the most prevalent of the distinctive retinal dystrophies caused by mutations in the BEST1 gene. This gene, which encodes for a homopentameric calcium-activated ion channel, is crucial for the homeostasis and function of the retinal pigment epithelia (RPE), the cell type responsible for recycling the visual pigments generated by photoreceptor cells. In BVMD patients, mutations in this gene induce functional problems in the RPE cell layer with an accumulation of lipofucsin that evolves into cell death and loss of sight. In this work, we employ iPSC-RPE cells derived from a patient with the p.Pro77Ser dominant mutation to determine the correlation between this variant and the ocular phenotype. To this purpose, gene and protein expression and localization are evaluated in iPSC-RPE cells along with functional assays like phagocytosis and anion channel activity. Our cell model shows no differences in gene expression, protein expression/localization, or phagocytosis capacity, but presents an increased chloride entrance, indicating that the p.Pro77Ser variant might be a gain-of-function mutation. We hypothesize that this variant disturbs the neck region of the BEST1 channel, affecting channel function but maintaining cell homeostasis in the short term. This data shed new light on the different phenotypes of dominant mutations in BEST1, and emphasize the importance of understanding its molecular mechanisms. Furthermore, the data widen the knowledge of this pathology and open the door for a better diagnosis and prognosis of the disease.

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.

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.

Automatic Detection of Genetics and Genomics of Eye Disease Using Deep Assimilation Learning Algorithm

Diabetic retinopathy (DR) is one of the most prevalent genetic diseases in human and it is caused by damage to the blood vessels in the eye retina. If it is undetected and untreated at right time, it can lead to vision loss. There are many medical imaging and processing technologies to improve the diagnostic process of DR to overcome the lack of human experts. In the existing image processing methods, there are issues such as lack of noise removal, improper clustering segmentation and less classification accuracy. This can be accomplished by automatic diagnosis of DR using advanced image processing method. The cotton wool spot (CWS), hard exudates (HE) contains a common manifestation of many diseases in retina including DR and acquired immunodeficiency syndrome. In the present work, super iterative clustering algorithm (SICA) is proposed to identify the CWS, HE on retinal image. Feature-based medical image retrieval (FBMIR) datasets are utilized for this purpose. Noises present on the images and histogram-filtering technique is used to convert red, green, and blue (RGB) images into a perfect greyscale image without noise. After pre-processing, SICA is used to identify the CWS, HE detection on retinal images and eliminates unnecessary areas of interest. In the third stage, after detecting CWS and HE, various statistical features are extracted for further classification using deep assimilation learning algorithm (DALA). The performance of DALA technique is examined with various classification parameters like recall, precision, and F-measure. Finally, the false classification ratios are computed to compare the performance of the trained networks. The proposed method produces accurate detection of affected regions with an accuracy ratio of 98.5% and it is higher than the other conventional methods. This method may improve the accuracy of automatic detection and classification of eye diseases.