Clinical and Mutation Analysis of Patients with Best Vitelliform Macular Dystrophy or Autosomal Recessive Bestrophinopathy in Chinese Population

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.

Clinical and visual electrophysiological characteristics of vitelliform macular dystrophies in the first decade of life

Purpose:

To evaluate patterns of pediatric vitelliform macular dystrophy (PVMD).

Methods:

This is a retrospective analysis of Indian children with vitelliform macular dystrophy (VMD) presenting within the first decade of life. Records were evaluated for clinical findings, family screening, and investigative findings including optical coherence tomography (OCT), fundus autofluorescence (FAF), full-field electroretinogram (ERG) and electrooculogram (EOG). Electrophysiology was scrutinized and audited for acquisition and interpretation errors. Findings on follow-up were also recorded.

Results:

46 eyes of 24 patients were included. Mean age at presentation was 7.17 ± 2.17 years. Mean follow-up duration was 1.55 ± 1.69 years. Best disease was the commonest type of VMD detected (21 patients), while autosomal recessive bestrophinopathy was seen in three cases. Mean logMAR BCVA was 0.364 which decreased to 0.402 on follow-up. Hyperopia was noted in 29 out of 46 eyes (mean being +3.87 D, range ebing +0.75 to +8.75 D). Four eyes of four children had choroidal neovascular membrane at presentation, while another child developed while in follow-up. Solid type subretinal deposit was the commonest OCT finding (n = 29/38) and central hyper FAF was the commonest pattern (n = 18/32). EOG was available for review in 32 eyes, but was unreliable in 11 eyes. Seven eyes demonstrated complete absence of light rise on EOG.

Conclusion:

PVMD can present in advanced forms. Progression to complications with loss of visual acuity can happen within the first decade of life. EOG shows grossly suppressed waveforms in the light phase in a large number of such children.

Clinical findings in eyes with BEST1-related retinopathy complicated by choroidal neovascularization

PURPOSE

To determine the characteristics of eyes diagnosed with Best vitelliform macular dystrophy (BVMD) and autosomal recessive bestrophinopathy (ARB) complicated by choroidal neovascularization (CNV).

METHODS

This was a retrospective, multicenter observational case series. Fourteen genetically confirmed BVMD patients and 9 ARB patients who had been examined in 2 ophthalmological institutions in Japan were studied. The findings in a series of ophthalmic examinations including B-scan optical coherence tomography (OCT) and OCT angiography (OCTA) were reviewed.

RESULTS

CNV was identified in 5 eyes (17.9%) of BVMD patients and in 2 eyes (11.1%) of ARB patients. Three of 5 eyes with BVMD were classified as being at the vitelliruptive stage and 2 eyes at the atrophic stage. The CNV in 2 BVMD eyes were diagnosed as exudative because of acute visual acuity reduction, retinal hemorrhage, and intraretinal fluid, while the CNV in 3 BVMD eyes and 2 ARB eyes were diagnosed as non-exudative. The visual acuity of the two eyes with exudative CNV did not improve despite anti-VEGF treatments. None of the eyes with non-exudative CNV had a reduction of their visual acuity for at least 4 years. All of the CNV were located within hyperreflective materials which were detected in 16 eyes (57.1%) of the BVMD eyes and in 7 eyes (38.9%) of the ARB eyes.

CONCLUSIONS

CNV is a relatively common complication in BEST1-related retinopathy in Asian population as well. The prognosis of eyes with exudative CNV is not always good, and OCTA can detect CNV in eyes possessing hyperreflective materials.

Autosomal Recessive Bestrophinopathy: Clinical and Genetic Characteristics of Twenty-Four Cases

Background

To describe ocular manifestations, imaging characteristics, and genetic test results of autosomal recessive bestrophinopathy (ARB). The study design is an observational case series.

Methods

Forty-eight eyes of 24 patients diagnosed with ARB underwent complete ophthalmic examinations including refraction, anterior and posterior segment examination, enhanced depth imaging optical coherence tomography (EDI-OCT), fluorescein angiography (FA), electroretinography (ERG), and electrooculography (EOG). Optical coherence tomography angiography (OCTA) and BEST1 gene sequencing were performed in selected patients.

Results

The age at onset was 4–35 years (mean: 18.6 years). The male-to-female ratio was 0.45. All patients were hyperopic, except one with less than one diopter myopia. EOG was abnormal in 18 cases with near-normal ERGs. Six patients did not undergo EOG due to their young age. Eighteen patients (75%) had a thick choroid on EDI-OCT, of which three had advanced angle-closure glaucoma, 15 patients were hyperopic, and eight of them had more than four diopters hyperopia in both eyes. Macular retinoschisis was observed in 46 eyes of 23 patients (95%) with cysts mostly located in the inner nuclear layer (INL) to the outer nuclear layer (ONL). Of the 18 patients who underwent FA, mild peripheral leakage was seen in eight eyes of four patients (22%). Subfoveal choroidal neovascularization (CNV) was seen in three eyes of two patients (6%) that responded well to intravitreal bevacizumab (IVB). Seven mutations of the bestrophin-1 (BEST1) gene were found in this study; however, only two of them (p.Gly34 = and p.Leu319Pro) had been previously reported as the cause of ARB based on ClinVar and other literature studies.

Conclusions

ARB can be presented with a wide spectrum of ocular abnormalities that may not be easily diagnosed. Pachychoroid can occur alongside retinal schisis and may be the underlying cause of angle-closure glaucoma in ARB. Our study also expands the pathogenic mutation spectrum of the BEST1 gene associated with ARB.

Novel BEST1 mutations and clinical characteristics of autosomal recessive bestrophinopathy in a Spanish patient

PURPOSE

To describe the clinical and genetic characteristics (novel mutation in BEST1 gene) of a Spanish patient with autosomal recessive bestrophinopathy (ARB).

METHODS

The detailed ophthalmological examination included best corrected visual acuity (BCVA), color and autofluorescence photography, fluorescein angiography, optical coherence tomography, and electrophysiology tests. A next-generation sequencing (NGS) strategy was applied to the index patient, and then sequenced in an Illumina NextSeq500 system.

RESULTS

A 55-year-old male presented with a BCVA of 20/25 in the right eye and 20/20 in the left eye. Fundoscopy revealed perifoveal yellow flecked-like lesions. Fluorescein angiography and fundus autofluorescence results were consistent with pattern dystrophy. A homozygous frameshift mutation in BEST1 (c.341_342del; p.(Leu114Glnfs*57)) was identified as the cause of the disease.

CONCLUSION

ARB is a genetic disease that leads to irreversible visual loss. In this report we found a novel mutation responsible for this disease.

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.

Disease-causing mutations associated with bestrophinopathies promote apoptosis in retinal pigment epithelium cells

PURPOSE

Best vitelliform macular dystrophy (BVMD) and autosomal recessive bestrophinopathy (ARB) are two kinds of bestrophinopathies which are caused by BEST1 mutations and characterized by accumulation of lipofuscin-like materials on the retinal pigment epithelium cell-photoreceptor interface. In the past two decades, research about the pathogenesis of bestrophinopathies was mainly focused on the anion channel and intracellular Ca²⁺ signaling, but seldom concentrated on the function of retinal pigment epithelium (RPE) cells. In this study, we explored the possible effect of the three BEST1 mutations p.V143F, p.S142G, and p.A146T on the apoptosis in human fetal RPE cells.

METHODS

Wild-type plasmid and mutant plasmids BEST1-pcDNA3.1 p.V143F, p.S142G, and p.A146T were transfected to human fetal RPE cells. The molecules caspase-3, phospho-Bcl-2, BAX, PARP, and AIF associated with apoptosis were determined by quantitative PCR and Western blot. Apoptotic rate and active Caspase-3 staining were analyzed by flow cytometry.

RESULTS

Caspase-3 and PARP expression were significantly increased in BEST1-pcDNA3.1 p.S142G and p.A146T group. Flow cytometry showed that the apoptosis rates were significantly increased in the BEST1-pcDNA3.1 p.V143F, p.S142G, and p.A146T group compared with the wild-type group.

CONCLUSIONS

For the first time, we found that the three mutations promoted RPE cell apoptosis. Furthermore, the results indicated that BEST1 mutations p.S142G and p.A146T may contribute apoptosis of RPE cells by targeting Caspase 3. Our observations suggested that the apoptosis of RPE cells may be one of the mechanisms in bestrophinopathies, which may provide a new potential therapeutic target for the treatment of this disease.

Clinical and Genetic Findings of Autosomal Recessive Bestrophinopathy (ARB)

Mutations in BEST1 cause several phenotypes including autosomal dominant (AD) Best vitelliform macular dystrophy type 2 (BVMD), AD vitreo-retino-choroidopathy (ADVIRC), and retinitis pigmentosa-50 (RP50). A rare subtype of Bestrophinopathy exists with biallelic mutations in BEST1. Its frequency is estimated to be 1/1,000,000 individuals. Here we report 6 families and searched for a genotype-phenotype correlation. All patients were referred due to reduced best-corrected visual acuity (BCVA), ranging from 0.1/10 to 3/10. They all showed vitelliform lesions located at the macula, sometimes extending into the midperiphery, along the vessels and the optic disc. Onset of the disease varied from the age of 3 to 25 years. Electrooculogram (EOG) revealed reduction in the EOG light rise in all patients. Molecular analysis revealed previously reported mutations p.(E35K);(E35K), p.(L31M);(L31M), p.(R141H);(A195V), p.(R202W);(R202W), and p.(Q220*);(Q220*) in five families. One family showed a novel mutation: p.(E167G);(E167G). All mutations were heterozygous in the parents. In one family, heterozygous children showed various reductions in the EOG light rise and autofluorescent deposits. Autosomal recessive Bestrophinopathy (ARB), although rare, can be recognized by its phenotype and should be validated by molecular analysis. Genotype-phenotype correlations are difficult to establish and will require the analysis of additional cases.