A comprehensive clinical and biochemical functional study of a novel RPE65 hypomorphic mutation

Hypomorphic variants in inherited retinal and ocular diseases: A review of the literature with clinical cases

Hypomorphic variants decrease, but do not eliminate, gene function via a reduction in the amount of mRNA or protein product produced by a gene or by production of a gene product with reduced function. Many hypomorphic variants have been implicated in inherited retinal diseases (IRDs) and other genetic ocular conditions; however, there is heterogeneity in the use of the term "hypomorphic" in the scientific literature. We searched for all hypomorphic variants reported to cause IRDs and ocular disorders. We also discuss the presence of hypomorphic variants in the patient population of our ocular genetics department over the past decade. We propose that standardized criteria should be adopted for use of the term "hypomorphic" to describe gene variants to improve genetic counseling and patient care outcomes.

RPE65-Associated Retinal Dystrophies: Phenotypes and Treatment Effects with Voretigene Neparvovec

Retinal dystrophies linked to the RPE65 gene are mostly fast-progressing retinal diseases, with childhood onset of night blindness and progressive visual loss up to the middle adult age. Rare phenotypes linked to this gene are known with congenital stationary night blindness or slowly progressing retinitis pigmentosa, as well as an autosomal dominant c.1430A>G (p.Asp477Gly) variant. This review gives an overview of the current knowledge of the clinical phenotypes, as well as experience with the efficacy and safety of the approved gene augmentation therapy voretigene neparvovec.

Single Center Experience with Voretigene Neparvovec Gene Augmentation Therapy in RPE65 Mutation-Associated Inherited Retinal Degeneration in a Clinical Setting

PURPOSE

To assess the impact of baseline data on psychophysical and morphological outcomes of subretinal voretigene neparvovec (VN) (Luxturna, Spark Therapeutics, Inc.) treatment.

DESIGN

Single-center, retrospective, longitudinal, consecutive case series.

PARTICIPANTS

Patients with RPE65-biallelic mutation-associated inherited retinal degeneration (RPE65-IRD) treated between February 2020 and March 2022 with VN and oral immunosuppression according to the manufacturer's recommendation by one surgeon (F.G.H.).

METHODS

Retrospective analysis of surgical and clinical records, ancillary testing, and retinal imaging after VN therapy for RPE65-IRD. Descriptive statistics compared data at baseline up to 32 months post-treatment.

MAIN OUTCOME MEASURES

Best-corrected visual acuity (BCVA), low-luminance VA (LLVA), Goldmann visual fields (GVFs), chromatic full-field stimulus threshold (FST) testing (FST), scotopic and photopic 2-color threshold perimetry (2CTP), and multimodal retinal imaging.

RESULTS

Thirty eyes of 19 patients were analyzed (10 pediatric patients < 20 years; 20 adult patients > 20 years of age; overall range: 8-40 years) with a median follow-up of 15 months (range, 1-32). The fovea was completely or partially detached in 16 eyes, attached in 12 eyes, and not assessable in 2 eyes on intraoperative imaging. Median BCVA at baseline was better in the pediatric group (P < 0.05) and did not change significantly independent of age. Meaningful loss of BCVA (≥ 0.3 logarithm of the minimal angle of resolution [logMAR]) occurred in 5 of 18 adult eyes, and a meaningful gain (≥-0.3 logMAR) occurred in 2 of 18 adult and 2 of 8 pediatric eyes. The LLVA and scotopic 2CTP improved considerably in pediatric patients. Scotopic blue FST improved at all ages but more in pediatric patients (8/8 eyes gained ≥ 10 decibels [dB]; P < 0.05). In pediatric patients, median GVF improved by 20% for target V4e and by 50% for target III4e (target I4e not detected). Novel atrophy developed in 13 of 26 eyes at the site of the bleb or peripheral of vascular arcades. Improvements in FST did not correlate with development of chorioretinal atrophy at 12 months. Mean central retinal thickness was 165.87 μm (± 26.26) at baseline (30 eyes) and 157.69 μm (± 30.3) at 12 months (26 eyes). Eight adult patients were treated unilaterally. The untreated eyes did not show meaningful changes during follow-up.

CONCLUSIONS

These data in a clinical setting show the effectiveness of VN therapy with stable median BCVA and mean retinal thickness and improvements of LLVA, FST, and 2CTP up to 32 months. Treatment effects were superior in the pediatric group. We observed new chorioretinal atrophy in 50% of the treated eyes.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Development of a novel prediction model based on protein structure for identifying RPE65-associated inherited retinal disease (IRDs) of missense variants

Purpose

This study aimed to develop a prediction model to classify RPE65-mediated inherited retinal disease (IRDs) based on protein secondary structure and to analyze phenotype-protein structure correlations of RPE65 missense variants in a Chinese cohort.

Methods

Pathogenic or likely pathogenic missense variants of RPE65 were obtained from UniProt, ClinVar, and HGMD databases. The three-dimensional structure of RPE65 was retrieved from the Protein Data Bank (PDB) and modified with Pymol software. A novel prediction model was developed using LASSO regression and multivariate logistic regression to identify RPE65-associated IRDs. A total of 21 Chinese probands with RPE65 variants were collected to analyze phenotype-protein structure correlations of RPE65 missense variants.

Results

The study found that both pathogenic and population missense variants were associated with structural features of RPE65. Pathogenic variants were linked to sheet, β-sheet, strands, β-hairpins, Fe2+ (iron center), and active site cavity, while population variants were related to helix, loop, helices, and helix-helix interactions. The novel prediction model showed accuracy and confidence in predicting the disease type of RPE65 variants (AUC = 0.7531). The study identified 25 missense variants in Chinese patients, accounting for 72.4% of total mutations. A significant correlation was observed between clinical characteristics of RPE65-associated IRDs and changes in amino acid type, specifically for missense variants of F8 (H68Y, P419S).

Conclusion

The study developed a novel prediction model based on the protein structure of RPE65 and investigated phenotype-protein structure correlations of RPE65 missense variants in a Chinese cohort. The findings provide insights into the precise diagnosis of RPE65-mutated IRDs.

Current Management of Patients with RPE65 Mutation Associated Inherited Retinal Degenerations in Europe: Results of a 2-Year Follow-Up Multinational Survey

INTRODUCTION

The aim of this study was to evaluate the current management of RPE65 biallelic mutation-associated inherited retinal degeneration (RPE65-IRD) in Europe since market authorization of voretigene neparvovec (VN, LuxturnaTM) in 2018. By July 2022, over 200 patients have been treated outside the USA, of whom about 90% in Europe. We conducted among all centers of the European Vision Institute Clinical Research Network (EVICR.net) and health care providers (HCPs) of the European Reference Network dedicated to Rare Eye Diseases (ERN-EYE) the second multinational survey on management of IRDs in Europe elaborated by EVICR.net with a special focus on RPE65-IRD.

METHODS

An electronic survey questionnaire with 48 questions specifically addressing RPE65-IRD (2019 survey 35) was developed and sent by June 2021 to 95 EVICR.net centers and 40 ERN-EYE HCPs and affiliated members. Of note, 11 centers are members of both networks. Statistical analysis was performed with Excel and R.

RESULTS

The overall response rate was 44% (55/124); 26 centers follow RPE65 biallelic mutation-associated IRD patients. By June 2021, 8/26 centers have treated 57 RPE65-IRD cases (1-19/center, median 6) and 43 planned for treatment (range 0-10/center, median 6). The overall age range was 3-52 years, and on average 22% of the patients did not (yet) qualify for treatment (range 2-60%/center, median 15%). Main reasons were too advanced (range 0-100, median 75%) or mild disease (range 0-100, median 0). Eighty-three percent of centers (10/12) that follow RPE65 mutation-associated IRD patients treated with VN participate in the PERCEIVE registry (EUPAS31153, http://www.encepp.eu/encepp/viewResource.htm?id=37005). Quality of life and full-field stimulus test improvements had the highest scores of the survey-reported outcome parameters in VN treatment follow-up.

CONCLUSION

This second multinational survey on management of RPE65-IRD by EVICR.net centers and ERN-EYE HCPs in Europe indicates that RPE65-IRD might be diagnosed more reliably in 2021 compared to 2019. By June 2021, 8/26 centers reported detailed results including VN treatment. Main reasons for non-treatment were too advanced or mild disease, followed by absence of 2 class 4 or 5 mutations on both alleles or because of a too young age. Patient satisfaction with treatment was estimated to be high by 50% of the centers.

Therapy with voretigene neparvovec. How to measure success?

Retinal gene supplementation therapy such as the first approved one, voretigene neparvovec, delivers a functioning copy of the missing gene enabling the protein transcription in retinal cells and restore visual functions. After gene supplementation for the genetic defect, a complex network of functional regeneration is the consequence, whereas the extent is very individualized. Diagnostic and functional testings that have been used routinely by ophthalmologists so far to define the correct diagnosis, cannot be applied in the new context of defining small, sometimes subtle changes in visual functions. New view on retinal diagnostics is needed to understand this processes that define safety and efficacy of the treatment. Not only does vision have many aspects that must be addressed by specific evaluations and imaging techniques, but objective readouts of local retinal function for rods and cones separately have been an unmet need until recently. A reliable test-retest variability is necessary in rare diseases such as inherited retinal dystrophies, because statistics are often not applicable due to a low number of participants. Methods for a reliable individual evaluation of the therapy success are needed. In this manuscript we present an elaboration on retinal diagnostics combining psychophysics (eg. full-field stimulus threshold or dark adapted perimetry) as well as objective measures for local retinal function (eg. photopic and scotopic chromatic pupil campimetry) and retinal imaging for a meaningful workflow to apply in evaluation of the individual success in patients receiving gene therapy for photoreceptor diseases.

Gene Therapy with Voretigene Neparvovec Improves Vision and Partially Restores Electrophysiological Function in Pre-School Children with Leber Congenital Amaurosis

Leber congenital amaurosis caused by mutations in the RPE65 gene belongs to the most severe early-onset hereditary childhood retinopathies naturally progressing to legal blindness. The novel gene therapy voretigene neparvovec is the first approved causative treatment option for this devastating eye disease and is specifically designed to treat RPE65-mediated retinal dystrophies. Herein, we present a follow-up of the youngest treated patients in Germany so far, including four pre-school children who received treatment with voretigene neparvovec at a single treatment center between January 2020 and May 2022. All patients underwent pars plana vitrectomy with circumferential peeling of the internal limiting membrane at the injection site and subretinal injection of voretigene neparvovec. Pre- and postoperative diagnostics included imaging (spectral domain optical coherence tomography, fundus autofluorescence, fundus wide-angle imaging), electrophysiologic examination (ERG), retinal light sensitivity measurements (FST) and visual acuity testing. Behavioral changes were assessed using a questionnaire and by observing the children's vision-guided behavior in different levels of illumination. All children showed marked increase in vision-guided behavior shortly after therapy, as well as marked increase in visual acuity in the postoperative course up to full visual acuity in one child. Two eyes showed partial electrophysiological recovery of an ERG that was undetectable before treatment-a finding that has not been described in humans before.

Frequency of <i>RPE65</i> Gene Mutation in Patients with Hereditary Retinal Dystrophy

Objectives:

Materials and Methods:

Results:

Conclusion:

VITAMIN A DEFICIENCY MONITORED BY QUANTITATIVE SHORT WAVELENGTH FUNDUS AUTOFLUORESCENCE IN A CASE OF BARIATRIC SURGERY

BACKGROUND/PURPOSE

Bariatric surgery is recognized as a treatment option for obesity. However, the cost-efficiency of screening for serum vitamin A and the effectiveness of its oral supplementation in these patients remain unclear. Here, we report a case in which vitamin A and carotenoid deficiency after bariatric surgery were monitored by noninvasive quantitative fundus autofluorescence imaging.

METHODS

Case report.

RESULTS

A 62-year-old man presented with a history of progressive night blindness. He had duodenal switch surgery 13 years earlier. One year before the initial visit, he had begun oral supplements of vitamins A. Short wavelength fundus autofluorescence images acquired for quantitative fundus autofluorescence revealed an intensity that was lower than the healthy-eye range. Scotopic rod-specific full-field electroretinograms were extinguished. These findings were consistent with vitamin A deficiency. The patient was given intramuscular vitamin A injections. At follow-up, quantitative fundus autofluorescence improved, ERG increased to normal, but macular pigment was unchanged.

CONCLUSION

Oral vitamin A supplementation may not be sufficient after mal-absorptive surgery and a quantitative and noninvasive short wavelength fundus autofluorescence imaging technique may be useful to monitor the status of vitamin A and the carotenoids comprising macular pigment in the retina.

RPE65-Associated Retinopathies in the Italian Population: A Longitudinal Natural History Study

Purpose

To investigate the course of inherited retinal degenerations (IRD) due to mutations in the RPE65 gene.

Methods

This longitudinal multicentric retrospective chart-review study was designed to collect best corrected visual acuity (BCVA), Goldman visual field, optical coherence tomography (OCT), and electroretinography (ERG) measurements. The data, including imaging, were collected using an electronic clinical research form and were reviewed at a single center to improve consistency.

Results

From an overall cohort of 60 Italian patients with RPE65-associated IRD, 43 patients (mean age, 27.8 ± 19.7 years) were included and showed a mean BCVA of 2.0 ± 1.0 logMAR. Time-to-event analysis revealed a median age of 33.8 years and 41.4 years to reach low vision and blindness based on BCVA, respectively. ERG (available for 34 patients) showed undetectable responses in most patients (26; 76.5%). OCT (available for 31 patients) revealed epiretinal membranes in five patients (16.1%). Central foveal thickness significantly decreased with age at a mean annual rate of −0.6%/y (P = 0.044). We identified 43 different variants in the RPE65 gene in the entire cohort. Nine variants were novel. Finally, to assess genotype-phenotype correlations, patients were stratified according to the number of RPE65 loss-of-function (LoF) alleles. Patients without LoF variants showed significantly (P < 0.05) better BCVA compared to patients with one or two LoF alleles.

Conclusions

We described the natural course of RPE65-associated IRD in an Italian cohort showing for the first time a specific genotype-phenotype association. Our findings can contribute to a better management of RPE65-associated IRD patients.

Clinical Features and Natural History in a Cohort of Chinese Patients with RPE65-Associated Inherited Retinal Dystrophy

RPE65-associated inherited retinal dystrophy (RPE65-IRD) is an early-onset retinal degeneration. The aim of this study was to describe the clinical features and natural course of this disease in a Chinese patient cohort with RPE65 biallelic variants. Thirty patients from 29 unrelated families with biallelic disease-causing RPE65 variants underwent full ophthalmic examinations. Thirteen were followed up over time. An additional 57 Chinese cases from 49 families were retrieved from the literature to analyze the relationship between best-corrected visual acuity (BCVA) and age. Our 30 patients presented age-dependent phenotypic characteristics. Multiple white dots were a clinical feature of young patients, while maculopathy, epiretinal membrane, and bone spicules were common in adult patients. Among the 84 patients, BCVA declined with age in a nonlinear, positive-acceleration relationship (p < 0.001). All patients older than 40 years met the WHO standard for low vision. Longitudinal observation revealed a slower visual acuity loss in patients younger than 20 years than those in their third or fourth decade of life. Our study detailed the clinical features and natural course of disease in Chinese patients with RPE65-IRD. Our results indicated that these patients have a relatively stable BCVA in childhood and adolescence, but eyesight deteriorates rapidly in the third decade of life. These findings may facilitate the implementation of gene therapy in China.

Inherited Retinal Diseases Due to RPE65 Variants: From Genetic Diagnostic Management to Therapy

Inherited retinal diseases (IRDs) are a heterogeneous group of conditions that include retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) and early-onset severe retinal dystrophy (EO[S]RD), which differ in severity and age of onset. IRDs are caused by mutations in >250 genes. Variants in the RPE65 gene account for 0.6-6% of RP and 3-16% of LCA/EORD cases. Voretigene neparvovec is a gene therapy approved for the treatment of patients with an autosomal recessive retinal dystrophy due to confirmed biallelic RPE65 variants (RPE65-IRDs). Therefore, the accurate molecular diagnosis of RPE65-IRDs is crucial to identify 'actionable' genotypes-i.e., genotypes that may benefit from the treatment-and is an integral part of patient management. To date, hundreds of RPE65 variants have been identified, some of which are classified as pathogenic or likely pathogenic, while the significance of others is yet to be established. In this review, we provide an overview of the genetic diagnostic workup needed to select patients that could be eligible for voretigene neparvovec treatment. Careful clinical characterization of patients by multidisciplinary teams of experts, combined with the availability of next-generation sequencing approaches, can accelerate patients' access to available therapeutic options.

LONGITUDINAL STUDY OF RPE65-ASSOCIATED INHERITED RETINAL DEGENERATIONS

PURPOSE

To study the disease course of RPE65-associated inherited retinal degenerations (IRDs) as a function of the genotype, define a critical age for blindness, and identify potential modifiers.

METHODS

Forty-five patients with IRD from 33 families with biallelic RPE65 mutations, 28 stemming from a genetic isolate. We collected retrospective data from medical charts. Coexisting variants in 108 IRD-associated genes were identified with Molecular Inversion Probe analysis.

RESULTS

Most patients were diagnosed within the first years of life. Daytime visual function ranged from near-normal to blindness in the first four decades and met WHO criteria for blindness for visual acuity and visual field in the fifth decade. p.(Thr368His) was the most common variant (54%). Intrafamilial variability and interfamilial variability in disease severity and progression were observed. Molecular Inversion Probe analysis confirmed all RPE65 variants and identified one additional variant in LRAT and one in EYS in two separate patients.

CONCLUSION

All patients with RPE65-associated IRDs developed symptoms within the first year of life. Visual function in childhood and adolescence varied but deteriorated inevitably toward blindness after age 40. In this study, genotype was not predictive of clinical course. The variance in severity of disease could not be explained by double hits in other IRD genes.

RPE65-associated inherited retinal diseases: consensus recommendations for eligibility to gene therapy

Background

This research aimed to establish recommendations on the clinical and genetic characteristics necessary to confirm patient eligibility for gene supplementation with voretigene neparvovec.

Methods

An expert steering committee comprising an interdisciplinary panel of Italian experts in the three fields of medical specialisation involved in the management of RPE65-associated inherited retinal disease (IRD) (medical retina, genetics, vitreoretinal surgery) proposed clinical questions necessary to determine the correct identification of patients with the disease, determine the fundamental clinical and genetics tests to reach the correct diagnosis and to evaluate the urgency to treat patients eligible to receive treatment with voretigene neparvovec. Supported by an extensive review of the literature, a series of statements were developed and refined to prepare precisely constructed questionnaires that were circulated among an external panel of experts comprising ophthalmologists (retina specialists, vitreoretinal surgeons) and geneticists with extensive experience in IRDs in Italy in a two-round Delphi process.

Results

The categories addressed in the questionnaires included clinical manifestations of RPE65-related IRD, IRD screening and diagnosis, gene testing and genotyping, ocular gene therapy for IRDs, patient eligibility and prioritisation and surgical issues. Response rates by the survey participants were over 90% for the majority of items in both Delphi rounds. The steering committee developed the key consensus recommendations on each category that came from the two Delphi rounds into a simple and linear diagnostic algorithm designed to illustrate the patient pathway leading from the patient’s referral centre to the retinal specialist centre.

Conclusions

Consensus guidelines were developed to guide paediatricians and general ophthalmologists to arrive at the correct diagnosis of RPE65-associated IRD and make informed clinical decisions regarding eligibility for a gene therapy approach to RPE65-associated IRD. The guidelines aim to ensure the best outcome for the patient, based on expert opinion, the published literature, and practical experience in the field of IRDs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01868-4.

Clinical Perspective: Treating RPE65-Associated Retinal Dystrophy

Until recently, there was no approved treatment for a retinal degenerative disease. Subretinal injection of a recombinant adeno-associated virus (AAV) delivering the normal copy of the human RPE65 cDNA led to reversal of blindness first in animal models and then in humans. This led to the first US Food and Drug Administration (FDA)-approved gene therapy product for a genetic disease, voretigene neparvovec-rzyl (Luxturna). Luxturna was then approved by the European Medicines Association and is now available in the US through Spark Therapeutics and worldwide through Novartis. Not only has treatment with Luxturna changed the lives of people previously destined to live a life of blindness, but it has fueled interest in developing additional gene therapy reagents targeting numerous other genetic forms of inherited retinal disease. This review describes many of the considerations for administration of Luxturna and describes how lessons from experience with Luxturna could lead to additional gene-based treatments of blindness.

Inverse correlation between fatty acid transport protein 4 and vision in Leber congenital amaurosis associated with RPE65 mutation

Fatty acid transport protein 4 (FATP4), a transmembrane protein in the endoplasmic reticulum (ER), is a recently identified negative regulator of the ER-associated retinal pigment epithelium (RPE)65 isomerase necessary for recycling 11-cis-retinal, the light-sensitive chromophore of both rod and cone opsin visual pigments. The role of FATP4 in the disease progression of retinal dystrophies associated with RPE65 mutations is completely unknown. Here we show that FATP4-deficiency in the RPE results in 2.8-fold and 1.7-fold increase of 11-cis- and 9-cis-retinals, respectively, improving dark-adaptation rates as well as survival and function of rods in the Rpe65 R91W knockin (KI) mouse model of Leber congenital amaurosis (LCA). Degradation of S-opsin in the proteasomes, but not in the lysosomes, was remarkably reduced in the KI mouse retinas lacking FATP4. FATP4-deficiency also significantly rescued S-opsin trafficking and M-opsin solubility in the KI retinas. The number of S-cones in the inferior retinas of 4- or 6-mo-old KI;Fatp4 ^-/- mice was 7.6- or 13.5-fold greater than those in age-matched KI mice. Degeneration rates of S- and M-cones are negatively correlated with expression levels of FATP4 in the RPE of the KI, KI;Fatp4 ^+/- , and KI;Fatp4 ^-/- mice. Moreover, the visual function of S- and M-cones is markedly preserved in the KI;Fatp4 ^-/- mice, displaying an inverse correlation with the FATP4 expression levels in the RPE of the three mutant lines. These findings establish FATP4 as a promising therapeutic target to improve the visual cycle, as well as survival and function of cones and rods in patients with RPE65 mutations.

Cost Effectiveness of Voretigene Neparvovec for RPE65-Mediated Inherited Retinal Degeneration in Germany

Purpose

Voretigene Neparvovec-rzyl (VN) is the first available treatment for biallelic RPE65 mutation-associated inherited retinal degeneration, which is usually associated with infancy-onset severe visual impairment and complete blindness during the third life decade. We aim to estimate the cost effectiveness of VN in Germany considering medication costs of €410,550 per eye and potential indirect cost offsets by higher labor force participation.

Methods

We developed an individual patient sampling model to simulate patients over their lifetime. In a Monte Carlo analysis, 1000 simulations are performed. Cycle length of the two-state Markov model is 1 year. For each cycle, visual field and best-corrected visual acuity are tracked, compared with natural progression and converted to quality of life. Direct and indirect costs are recorded and the incremental cost-utility ratio is calculated.

Results

In the base case scenario, VN provides 4.82 additional quality-adjusted life-years over a patient's lifetime at an incremental cost-utility ratio of €156,853 per additional quality-adjusted life-year gained. Sensitivity analyses show the robustness of the results when altering treatment effect duration, discounting of quality-adjusted life-years and costs, direct costs, and natural progression.

Conclusions

Under a lifetime perspective, VN proves to be cost effective for the German statutory health insurance system despite high initial treatment costs. Because VN has important implications for future gene therapies, cost-utility analyses have high economic relevance from a societal perspective.

Translational Relevance

Our research analyzes the value of a gene augmentation therapy in clinical care in terms of quality of life gains for patients with blindness from retinal degeneration.

RPE65 mutation frequency and phenotypic variation according to exome sequencing in a tertiary centre for genetic eye diseases in China

PURPOSE

Retinoid isomerohydrolase RPE65 has received a tremendous amount of attention due to successful clinical gene therapy for Leber congenital amaurosis (LCA) cases caused by RPE65 mutations. This study aimed to evaluate the frequency of RPE65 mutations and the associated phenotypes based on exome sequencing.

METHODS

RPE65 variants were collected from exome sequencing data obtained from 2133 probands with different forms of hereditary retinal degeneration (HRD). Clinical data were collected from probands with homozygous or compound heterozygous variants in RPE65. Associated phenotypes were characterized based on clinical data.

RESULTS

Biallelic RPE65 mutations were detected in 18 families, including eight with LCA, five with early-onset retinal degeneration, four with fundus albipunctatus-like (FA-like) changes and one with high hyperopia. These cases accounted for approximately 3.0% (8/269) of LCA and 0.8% (18/2133) of HRD cases. An almost identical FA-like change was identified in seven patients from four unrelated families with RPE65 mutations. Classification of mutations suggested that FA-like changes may be associated with biallelic missense mutations in RPE65.

CONCLUSION

Fundus albipunctatus-like (FA-like) change, a common characteristic fundus sign in RPE65 biallelic mutations, was unexpected but was confirmed by the finding that affected siblings from different families exhibited similar phenotypes. These results enrich our understanding of RPE65 mutation frequencies and their associated phenotypic variants.

RPE65 and retinal dystrophy: Report of new and recurrent mutations

BACHGROUND

Leber congenital amaurosis (LCA) is a severe and congenital or early onset form of inherited retinitis pigmentosa (RP). To date, approximately 25 genes have been introduced in relation to LCA. In this regard, retinal pigment epithelium-specific 65 kDa (RPE65) is a well-known gene mutation that plays a role in the pathogenesis of 5-10% of LCA cases.

METHOS

Two individuals fromseparate families were subjected to ehole exome sequencing (WES). Causativevariants were searched further assessed using Sanger sequencing.

RESULTS

Here, two families with mutations in the RPE65 gene show severe and early onset LCA, as expected. In addition to the characterization of the phenotype, by reporting a new mutation (c.1451-1G>A), we further expand the mutation spectrum of RPE65. Likewise, as an interesting aspect of our study, we report on a previously reported RP-linked mutation associated with severe early onset LCA (c.T200G:p.L67R).

CONCLUSIONS

Considering this variant in different populations, it is likely that it represents a hotspot and affects the function of the coded protein. The variable expressivity of the phenotype can be assumed by the presence of the modifier allele(s) as a result of a different genetic background or the effect of different environments on phenotype expression.

Pathogenicity Reclasssification of RPE65 Missense Variants Related to Leber Congenital Amaurosis and Early-Onset Retinal Dystrophy

A challenge in molecular diagnosis and genetic counseling is the interpretation of variants of uncertain significance. Proper pathogenicity classification of new variants is important for the conclusion of molecular diagnosis and the medical management of patient treatments. The purpose of this study was to reclassify two RPE65 missense variants, c.247T>C (p.Phe83Leu) and c.560G>A (p.Gly187Glu), found in Brazilian families. To achieve this aim, we reviewed the sequencing data of a 224-gene retinopathy panel from 556 patients (513 families) with inherited retinal dystrophies. Five patients with p.Phe83Leu and seven with p.Gly187Glu were selected and their families investigated. To comprehend the pathogenicity of these variants, we evaluated them based on the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) classification guidelines. Initially, these RPE65 variants met only three pathogenic criteria: (i) absence or low frequency in the population, (ii) several missense pathogenic RPE65 variants, and (iii) 15 out of 16 lines of computational evidence supporting them as damaging, which together allowed the variants to be classified as uncertain significance. Two other pieces of evidence were accepted after further analysis of these Brazilian families: (i) p.Phe83Leu and p.Gly187Glu segregate with childhood retinal dystrophy within families, and (ii) their prevalence in Leber congenital amaurosis (LCA)/early-onset retinal dystrophy (EORD) patients can be considered higher than in other inherited retinal dystrophy patients. Therefore, these variants can now be classified as likely pathogenic according to ACMG/AMP classification guidelines.

Safety of Same-Eye Subretinal Sequential Readministration of AAV2-hRPE65v2 in Non-human Primates

We have demonstrated safe and effective subretinal readministration of recombinant adeno-associated virus serotype (rAAV) to the contralateral eye in large animals and humans even in the setting of preexisting neutralizing antibodies (NAbs). Readministration of AAV to the same retina may be desirable in order to treat additional areas of the retina not targeted initially or to boost transgene expression levels at a later time point. To better understand the immune and structural consequences of subretinal rAAV readministration to the same eye, we administered bilateral subretinal injections of rAAV2-hRPE65v2 to three unaffected non-human primates (NHPs) and repeated the injections in those same eyes 2 months later. Ophthalmic exams and retinal imaging were performed after the first and second injections. Peripheral blood monocytes, serum, and intraocular fluids were collected at baseline and post-injection time points to characterize the cellular and humoral immune responses. Histopathologic and immunohistochemical studies were carried out on the treated retinas. Ipsilateral readministration of AAV2-hRPE65v2 in NHPs did not threaten the ocular or systemic health through the time span of the study. The repeat injections were immunologically and structurally well tolerated, even in the setting of preexisting serum NAbs. Localized structural abnormalities confined to the outer retina and retinal pigmented epithelium (RPE) after readministration of the treatment do not differ from those observed after single or contralateral administration of an AAV carrying a non-therapeutic transgene in NHPs and were not observed in a patient treated with the nearly identical, FDA-approved, AAV2-hRPE65v2 vector (voretigene neparvovec-rzyl), suggesting NHP-specific abnormalities.

Long-Term Follow-Up of Retinal Degenerations Associated With LRAT Mutations and Their Comparability to Phenotypes Associated With RPE65 Mutations

Purpose

To investigate the natural history in patients with LRAT-associated retinal degenerations (RDs), in the advent of clinical trials testing treatment options.

Methods

A retrospective cohort of 13 patients with LRAT-RDs.

Results

Twelve patients from a genetic isolate carried a homozygous c.12del mutation. One unrelated patient carried a homozygous c.326G>T mutation. The mean follow-up time was 25.3 years (SD 15.2; range 4.8–53.5). The first symptom was nyctalopia (n = 11), central vision loss (n = 1), or light-gazing (n = 1), and was noticed in the first decade of life. Seven patients (54%) reached low vision (visual acuity < 20/67), four of whom reaching blindness (visual acuity < 20/400), respectively, at mean ages of 49.9 (SE 5.4) and 59.9 (SE 3.1) years. The fundus appearance was variable. Retinal white dots were seen in six patients (46%). Full-field electroretinograms (n = 11) were nondetectable (n = 2; ages 31–60), reduced in a nonspecified pattern (n = 2; ages 11–54), or showed rod–cone (n = 6; ages 38–48) or cone–rod (n = 1; age 29) dysfunction. Optical coherence tomography (n = 4) showed retinal thinning but relative preservation of the (para-)foveal outer retinal layers in the second (n = 1) and sixth decade of life (n = 2), and profound chorioretinal degeneration from the eighth decade of life (n = 1).

Conclusions

LRAT-associated phenotypes in this cohort were variable and unusual, but generally milder than those seen in RPE65-associated disease, and may be particularly amenable to treatment. The window of therapeutic opportunity can be extended in patients with a mild phenotype.

Translational Relevance

Knowledge of the natural history of LRAT-RDs is essential in determining the window of opportunity in ongoing and future clinical trials for novel therapeutic options.

A high prevalence of biallelic RPE65 mutations in Costa Rican children with Leber congenital amaurosis and early-onset retinal dystrophy

BACKGROUND

Leber congenital amaurosis (LCA) and early-onset retinal dystrophy (EORD), are primary causes of inherited childhood blindness. Both are autosomal recessive diseases, with mutations in more than 25 genes explaining approximately ~70% of cases. However, the genetic cause for many cases remains unclear. Sequencing studies from genetically isolated populations with increased prevalence of a disorder has proven useful for rare variant studies, making Costa Rica an ideal place to study LCA/EORD genetics.

MATERIALS AND METHODS

Twenty-eight affected children (25 LCA, three EORD) and their immediate family members, totaling 52 individuals (30 affected) from 22 families, were sequenced. Whole exome sequencing was performed on all affected individuals. Available parents were analyzed either by whole exome sequencing (WES) or Sanger sequencing to determine transmission.

RESULTS

All affected individuals demonstrated compound heterozygous or homozygous mutations in known Inherited Retinal Disease (IRD) associated genes. Twelve variants were identified in at least one individual in three genes, RDH12, RPE65, and USH2A. Four recurrent RPE65 mutations were observed in 97% of individuals and 95% of families. All patients with LCA and two of the three individuals with EORD had biallelic mutations in RPE65; one child with EORD had a homozygous RDH12 mutation.

CONCLUSIONS

These data suggest that the majority of LCA/EORD in Costa Rica is due to four founder mutations in RPE65 which have been maintained in this genetically isolated population. This finding is of great clinical significance due to the availability of gene therapy recently approved in the US and European Union for patients with biallelic RPE65 defects.

The Natural History of Inherited Retinal Dystrophy Due to Biallelic Mutations in the RPE65 Gene

PURPOSE

To delineate the natural history of visual parameters over time in individuals with biallelic RPE65 mutation-associated inherited retinal dystrophy (IRD); describe the range of causative mutations; determine potential genotype/phenotype relationships; and describe the variety of clinical diagnoses.

DESIGN

Global, multicenter, retrospective chart review.

METHODS

Study Population: Seventy individuals with biallelic RPE65 mutation-associated IRD.

PROCEDURES

Data were extracted from patient charts.

MEASUREMENTS

Visual acuity (VA), Goldmann visual field (GVF), optical coherence tomography, color vision testing, light sensitivity testing, and electroretinograms (retinal imaging and fundus photography were collected and analyzed when available).

RESULTS

VA decreased with age in a nonlinear, positive-acceleration relationship (P < .001). GVF decreased with age (P < .0001 for both V4e and III4e), with faster GVF decrease for III4e stimulus vs V4e (P = .0114, left eye; P = .0076, right eye). On average, a 1-year increase in age decreased III4e GVF by ∼25 sum total degrees in each eye while V4e GVF decreased by ∼37 sum total degrees in each eye, although individual variability was observed. A total of 78 clinical diagnoses and 56 unique RPE65 mutations were recorded, without discernible RPE65 mutation genotype/phenotype relationships.

CONCLUSIONS

The number of clinical diagnoses and lack of a consistent RPE65 mutation-to-phenotype correlation underscore the need for genetic testing. Significant relationships between age and worsening VA and GVF highlight the progressive loss of functional retina over time. These data may have implications for optimal timing of treatment for IRD attributable to biallelic RPE65 mutations.

Aberrant RNA splicing is the major pathogenic effect in a knock-in mouse model of the dominantly inherited c.1430A>G human RPE65 mutation

Human RPE65 mutations cause a spectrum of retinal dystrophies that result in blindness. While RPE65 mutations have been almost invariably recessively inherited, a c.1430A>G (p.(D477G)) mutation has been reported to cause autosomal dominant retinitis pigmentosa (adRP). To study the pathogenesis of this human mutation, we have replicated the mutation in a knock-in (KI) mouse model using CRISPR/Cas9-mediated genome editing. Significantly, in contrast to human patients, heterozygous KI mice do not exhibit any phenotypes in visual function tests. When raised in regular vivarium conditions, homozygous KI mice display relatively undisturbed visual functions with minimal retinal structural changes. However, KI/KI mouse retinae are more sensitive to light exposure and exhibit signs of degenerative features when subjected to light stress. We find that instead of merely producing a missense mutant protein, the A>G nucleotide substitution greatly affects appropriate splicing of Rpe65 mRNA by generating an ectopic splice site in comparable context to the canonical one, thereby disrupting RPE65 protein expression. Similar splicing defects were also confirmed for the human RPE65 c.1430G mutant in an in vitro Exontrap assay. Our data demonstrate that a splicing defect is associated with c.1430G pathogenesis, and therefore provide insights in the therapeutic strategy for human patients.

Severe Loss of Tritan Color Discrimination in RPE65 Associated Leber Congenital Amaurosis

Purpose

RPE65-associated Leber congenital amaurosis (RPE65-LCA) is a progressive severe retinal dystrophy with early profound dysfunction of rod photoreceptors followed by progressive cone photoreceptor degeneration. We aim to provide detailed information about how cone dysfunction affects color discrimination.

Methods

Seven adults (aged 16-21) with RPE65-LCA underwent monocular color discrimination assessment using the Trivector and Ellipse versions of three computerized tests: Cambridge Colour Test (CCT), low vision version of the Cambridge Colour Test (lvvCCT), and the Universal Colour Discrimination Test (UCDT). For comparison, subjects were also tested using the American Optical Hardy Rand Rittler (AO-HRR) plates. Each assessment was repeated three times.

Results

The Trivector version of the tests demonstrated that color discrimination along the tritan axis was undetectable in four subjects, and severely reduced in three subjects. These findings were confirmed by the Ellipse version of the tests. Color discrimination along the protan and deutan axes was evident but reduced in six of seven subjects. Four of seven subjects were unable to read any of the HRR plates.

Conclusions

The computerized color vision tests adopted in this study provide detailed information about color discrimination in adult RPE65-LCA patients. The condition is associated with severe impairment of color discrimination, particularly along the tritan axis indicating possible early involvement of S-cones, with additional protan and deutan loss to a lesser extent. This psychophysical assessment strategy is likely to be valuable in measuring the impact of therapeutic intervention on cone function.

Early onset flecked retinal dystrophy associated with new compound heterozygous RPE65 variants

Purpose

To report genetic and clinical features of two unrelated Japanese patients with early onset flecked retinal dystrophy.

Methods

Patients underwent comprehensive ophthalmic examinations that included electroretinography (ERG) after 30 min and 24 h of dark adaptation (DA). Disease-causing gene variants were identified with whole exome sequencing (WES), with identified candidates confirmed with direct sequencing.

Results

WES identified compound heterozygous RPE65 variants in both patients. Variants in patient 1 included c.1543C>T (p.R515W) and c.683A>C (p.Q228P), while patient 2 exhibited c.1028T>A (p.L343*) and c.683A>C (p.Q228P). Although variants p.R515W and p.L343* have been previously reported as pathogenic, variant p.Q228P was reported as uncertain significance. Each unaffected parent carried the variant heterozygously. Both patients had similar ophthalmic findings, including decreased visual acuity with early onset night blindness, numerous dense white dots/flecks occurring mainly outside the vascular arcades, a diffuse and/or disrupted ellipsoid line as shown with optical coherence tomography, and non-recordable rod and combined responses along with decreased cone responses after 30 min of DA. After 24 h of DA, both patients exhibited marked or partial recovery of the combined responses.

Conclusions

The results indicate that the recovery of combined or residual cone responses might be associated with a mild form of RPE65-related early onset flecked retinal dystrophy with new compound heterozygous variants.

Pharmacological Amelioration of Cone Survival and Vision in a Mouse Model for Leber Congenital Amaurosis

RPE65, an abundant membrane-associate protein in the retinal pigment epithelium (RPE), is a key retinoid isomerase of the visual cycle necessary for generating 11-cis-retinal that functions not only as a molecular switch for activating cone and rod visual pigments in response to light stimulation, but also as a chaperone for normal trafficking of cone opsins to the outer segments. Many mutations in RPE65 are associated with Leber congenital amaurosis (LCA). A R91W substitution, the most frequent LCA-associated mutation, results in a severe decrease in protein level and enzymatic activity of RPE65, causing cone opsin mislocalization and early cone degeneration in the mutation knock-in mouse model of LCA. Here we show that R91W RPE65 undergoes ubiquitination-dependent proteasomal degradation in the knock-in mouse RPE due to misfolding. The 26S proteasome non-ATPase regulatory subunit 13 mediated degradation specifically of misfolded R91W RPE65. The mutation disrupted membrane-association and colocalization of RPE65 with lecithin:retinol acyltransferase (LRAT) that provides the hydrophobic substrate for RPE65. Systemic administration of sodium 4-phenylbutyrate (PBA), a chemical chaperone, increased protein stability, enzymatic activity, membrane-association, and colocalization of R91W RPE65 with LRAT. This rescue effect increased synthesis of 11-cis-retinal and 9-cis-retinal, a functional iso-chromophore of the visual pigments, led to alleviation of S-opsin mislocalization and cone degeneration in the knock-in mice. Importantly, PBA-treatment also improved cone-mediated vision in the mutant mice. These results indicate that PBA, a U.S. Food and Drug Administration-approved safe oral medication, may provide a noninvasive therapeutic intervention that delays daylight vision loss in patients with RPE65 mutations.

SIGNIFICANCE STATEMENT

LCA is a severe early onset retinal dystrophy. Recent clinical trials of gene therapy have implicated the need of an alternative or combination therapy to improve cone survival and function in patients with LCA caused by RPE65 mutations. Using a mouse model carrying the most frequent LCA-associated mutation (R91W), we found that the mutant RPE65 underwent ubiquitination-dependent proteasomal degradation due to misfolding. Treatment of the mice with a chemical chaperone partially corrected stability, enzymatic activity, and subcellular localization of R91W RPE65, which was also accompanied by improvement of cone survival and vision. These findings identify an in vivo molecular pathogenic mechanism for R91W mutation and provide a feasible pharmacological approach that can delay vision loss in patients with RPE65 mutations.

Tyrosinase-Cre-Mediated Deletion of the Autophagy Gene Atg7 Leads to Accumulation of the RPE65 Variant M450 in the Retinal Pigment Epithelium of C57BL/6 Mice

Targeted gene knockout mouse models have helped to identify roles of autophagy in many tissues. Here, we investigated the retinal pigment epithelium (RPE) of Atg7f/f Tyr-Cre mice (on a C57BL/6 background), in which Cre recombinase is expressed under the control of the tyrosinase promoter to delete the autophagy gene Atg7. In line with pigment cell-directed blockade of autophagy, the RPE and the melanocytes of the choroid showed strong accumulation of the autophagy adaptor and substrate, sequestosome 1 (Sqstm1)/p62, relative to the levels in control mice. Immunofluorescence and Western blot analysis demonstrated that the RPE, but not the choroid melanocytes, of Atg7f/f Tyr-Cre mice also had strongly increased levels of retinoid isomerohydrolase RPE65, a pivotal enzyme for the maintenance of visual perception. In contrast to Sqstm1, genes involved in retinal regeneration, i.e. Lrat, Rdh5, Rgr, and Rpe65, were expressed at higher mRNA levels. Sequencing of the Rpe65 gene showed that Atg7f/f and Atg7f/f Tyr-Cre mice carry a point mutation (L450M) that is characteristic for the C57BL/6 mouse strain and reportedly causes enhanced degradation of the RPE65 protein by an as-yet unknown mechanism. These results suggest that the increased abundance of RPE65 M450 in the RPE of Atg7f/f Tyr-Cre mice is, at least partly, mediated by upregulation of Rpe65 transcription; however, our data are also compatible with the hypothesis that the RPE65 M450 protein is degraded by Atg7-dependent autophagy in Atg7f/f mice. Further studies in mice of different genetic backgrounds are necessary to determine the relative contributions of these mechanisms.

Results at 2 Years after Gene Therapy for RPE65-Deficient Leber Congenital Amaurosis and Severe Early-Childhood-Onset Retinal Dystrophy

PURPOSE

To provide an initial assessment of the safety of a recombinant adeno-associated virus vector expressing RPE65 (rAAV2-CB-hRPE65) in adults and children with retinal degeneration caused by RPE65 mutations.

DESIGN

Nonrandomized, multicenter clinical trial.

PARTICIPANTS

Eight adults and 4 children, 6 to 39 years of age, with Leber congenital amaurosis (LCA) or severe early-childhood-onset retinal degeneration (SECORD).

METHODS

Patients received a subretinal injection of rAAV2-CB-hRPE65 in the poorer-seeing eye, at either of 2 dose levels, and were followed up for 2 years after treatment.

MAIN OUTCOME MEASURES

The primary safety measures were ocular and nonocular adverse events. Exploratory efficacy measures included changes in best-corrected visual acuity (BCVA), static perimetry central 30° visual field hill of vision (V30) and total visual field hill of vision (VTOT), kinetic perimetry visual field area, and responses to a quality-of-life questionnaire.

RESULTS

All patients tolerated subretinal injections and there were no treatment-related serious adverse events. Common adverse events were those associated with the surgical procedure and included subconjunctival hemorrhage in 8 patients and ocular hyperemia in 5 patients. In the treated eye, BCVA increased in 5 patients, V30 increased in 6 patients, VTOT increased in 5 patients, and kinetic visual field area improved in 3 patients. One subject showed a decrease in BCVA and 2 patients showed a decrease in kinetic visual field area.

CONCLUSIONS

Treatment with rAAV2-CB-hRPE65 was not associated with serious adverse events, and improvement in 1 or more measures of visual function was observed in 9 of 12 patients. The greatest improvements in visual acuity were observed in younger patients with better baseline visual acuity. Evaluation of more patients and a longer duration of follow-up will be needed to determine the rate of uncommon or rare side effects or safety concerns.

Preserved visual function in retinal dystrophy due to hypomorphic RPE65 mutations

BACKGROUND/AIMS

To present detailed phenotypic and molecular findings in four patients from four families with atypical, mild, recessive RPE65-related retinal dystrophy and discuss potential implications for gene replacement therapy.

METHODS

Four patients from four families with early onset retinal dystrophy underwent clinical examination, retinal imaging and electrophysiological testing. Bidirectional Sanger sequencing of all exons and intron-exon boundaries of RPE65 was performed.

RESULTS

All patients presented with nyctalopia in early childhood but demonstrated a mild phenotype with good visual acuity until at least 19 years of age. All had generalised retinal dysfunction on electroretinography. Central macular thickness on optical coherence tomography was preserved in those patients with good visual acuity. One patient had extensive white dots throughout the retina reminiscent of fundus albipunctatus with electrophysiological evidence of partial recovery of rod function after prolonged dark adaptation. Sanger sequencing identified RPE65 mutations in all patients including three missense variants likely to represent hypomorphic alleles.

CONCLUSIONS

Hypomorphic mutations of RPE65 are associated with mild disease in childhood with preservation of good visual acuity into adulthood; they may in rare cases be associated with a flecked retina appearance similar to fundus albipunctatus. The presence of normal visual acuity in patients with hypomorphic mutations in RPE65 suggests that efficiency of transduction may not be the limiting factor in improving visual acuity in trials of gene replacement therapy. Rather, it suggests that for optimal recovery of visual acuity gene replacement therapy may need to be given much earlier in childhood.

Animal modelling for inherited central vision loss

Disease-causing variants of a large number of genes trigger inherited retinal degeneration leading to photoreceptor loss. Because cones are essential for daylight and central vision such as reading, mobility, and face recognition, this review focuses on a variety of animal models for cone diseases. The pertinence of using these models to reveal genotype/phenotype correlations and to evaluate new therapeutic strategies is discussed. Interestingly, several large animal models recapitulate human diseases and can serve as a strong base from which to study the biology of disease and to assess the scale-up of new therapies. Examples of innovative approaches will be presented such as lentiviral-based transgenesis in pigs and adeno-associated virus (AAV)-gene transfer into the monkey eye to investigate the neural circuitry plasticity of the visual system. The models reported herein permit the exploration of common mechanisms that exist between different species and the identification and highlighting of pathways that may be specific to primates, including humans.

Shared decision-making, control preferences and psychological well-being in patients with RPE65 deficiency awaiting experimental gene therapy

PURPOSE

Retinal gene therapy trials are currently ongoing in a small number of inherited retinal disorders and this number is expected to rise significantly. The aim of this study was to analyze the psychological aspects of patients with RPE65 deficiency awaiting potential enrollment in gene therapy trials.

METHODS

Five patients with genetically proven RPE65 deficiency took part in this study. They were asked to complete the German versions of (i) the Patient Health Questionnaire (PHQ-D), (ii) the National Eye Institute Visual Function Questionnaire (NEI-VFQ), (iii) the Shared Decision Making Questionnaire (PEF-FB-9), and (iv) the Autonomy Preference Index (API-Dm), and in addition they took part in qualitative interviews.

RESULTS

The evaluations of the questionnaires and the interviews showed that the patients have quite high information needs and wish to take part in medical decisions. The perspective to participate in gene therapy trials does not seem to cause pronounced worries. Only the insecurity about if and when enrollment in a trial takes place may be burdensome.

DISCUSSION

This study generated important data about the psychological situation of patients awaiting potential enrollment in clinical trials, which can be used to improve patient care in the increasing number of future gene therapy trials around the world.

Mouse model of human RPE65 P25L hypomorph resembles wild type under normal light rearing but is fully resistant to acute light damage

Human RPE65 mutations cause a spectrum of blinding retinal dystrophies from severe early-onset disease to milder manifestations. The RPE65 P25L missense mutation, though having <10% of wild-type (WT) activity, causes relatively mild retinal degeneration. To better understand these mild forms of RPE65-related retinal degeneration, and their effect on cone photoreceptor survival, we generated an Rpe65/P25L knock-in (KI/KI) mouse model. We found that, when subject to the low-light regime (∼100 lux) of regular mouse housing, homozygous Rpe65/P25L KI/KI mice are morphologically and functionally very similar to WT siblings. While mutant protein expression is decreased by over 80%, KI/KI mice retinae retain comparable 11-cis-retinal levels with WT. Consistently, the scotopic and photopic electroretinographic (ERG) responses to single-flash stimuli also show no difference between KI/KI and WT mice. However, the recovery of a-wave response following moderate visual pigment bleach is delayed in KI/KI mice. Importantly, KI/KI mice show significantly increased resistance to high-intensity (20 000 lux for 30 min) light-induced retinal damage (LIRD) as compared with WT, indicating impaired rhodopsin regeneration in KI/KI. Taken together, the Rpe65/P25L mutant produces sufficient chromophore under normal conditions to keep opsins replete and thus manifests a minimal phenotype. Only when exposed to intensive light is this hypomorphic mutation manifested physiologically, as its reduced expression and catalytic activity protects against the successive cycles of opsin regeneration underlying LIRD. These data also help define minimal requirements of chromophore for photoreceptor survival in vivo and may be useful in assessing a beneficial therapeutic dose for RPE65 gene therapy in humans.

Pseudo-fovea formation after gene therapy for RPE65-LCA

PURPOSE

The purpose of this study was to evaluate fixation location and oculomotor characteristics of 15 patients with Leber congenital amaurosis (LCA) caused by RPE65 mutations (RPE65-LCA) who underwent retinal gene therapy.

METHODS

Eye movements were quantified under infrared imaging of the retina while the subject fixated on a stationary target. In a subset of patients, letter recognition under retinal imaging was performed. Cortical responses to visual stimulation were measured using functional magnetic resonance imaging (fMRI) in two patients before and after therapy.

RESULTS

All patients were able to fixate on a 1° diameter visible target in the dark. The preferred retinal locus of fixation was either at the anatomical fovea or at an extrafoveal locus. There were a wide range of oculomotor abnormalities. Natural history showed little change in oculomotor abnormalities if target illuminance was increased to maintain target visibility as the disease progressed. Eleven of 15 study eyes treated with gene therapy showed no differences from baseline fixation locations or instability over an average of follow-up of 3.5 years. Four of 15 eyes developed new pseudo-foveas in the treated retinal regions 9 to 12 months after therapy that persisted for up to 6 years; patients used their pseudo-foveas for letter identification. fMRI studies demonstrated that preservation of light sensitivity was restricted to the cortical projection zone of the pseudo-foveas.

CONCLUSIONS

The slow emergence of pseudo-foveas many months after the initial increases in light sensitivity points to a substantial plasticity of the adult visual system and a complex interaction between it and the progression of underlying retinal disease. The visual significance of pseudo-foveas suggests careful consideration of treatment zones for future gene therapy trials. (ClinicalTrials.gov number, NCT00481546.).

Genetic deletion of S-opsin prevents rapid cone degeneration in a mouse model of Leber congenital amaurosis

Mutations in RPE65 or lecithin-retinol acyltransferase (LRAT) disrupt 11-cis-retinal synthesis and cause Leber congenital amaurosis (LCA), a severe hereditary blindness occurring in early childhood. The pathology is attributed to a combination of 11-cis-retinal deficiency and photoreceptor degeneration. The mistrafficking of cone membrane-associated proteins including cone opsins (M- and S-opsins), cone transducin (Gαt2), G-protein-coupled receptor kinase 1 (GRK1) and guanylate cyclase 1 (GC1) has been suggested to play a role in cone degeneration. However, their precise role in cone degeneration is unclear. Here we investigated the role of S-opsin (Opn1sw) in cone degeneration in Lrat(-) (/-), a murine model for LCA, by genetic ablation of S-opsin. We show that deletion of just one allele of S-opsin from Lrat(-) (/-) mice is sufficient to prevent the rapid cone degeneration for at least 1 month. Deletion of both alleles of S-opsin prevents cone degeneration for an extended period (at least 12 months). This genetic prevention is accompanied by a reduction of endoplasmic reticulum (ER) stress in Lrat(-) (/-) photoreceptors. Despite cone survival in Opn1sw(-/-)Lrat(-) (/-) mice, cone membrane-associated proteins (e.g. Gαt2, GRK1 and GC1) continue to have trafficking problems. Our results suggest that cone opsins are the 'culprit' linking 11-cis-retinal deficiency to cone degeneration in LCA. This result has important implications for the current gene therapy strategy that emphasizes the need for a combinatorial therapy to both improve vision and slow photoreceptor degeneration.

A novel mutation in the RPE65 gene causing Leber congenital amaurosis and its transcriptional expression in vitro

The retinal pigment epithelium-specific 65 kDa protein is an isomerase encoded by the RPE65 gene (MIM 180069) that is responsible for an essential enzymatic step required for the function of the visual cycle. Mutations in the RPE65 gene cause not only subtype II of Leber congenital amaurosis (LCA) but also early-onset severe retinal dystrophy (EOSRD). This study aims to investigate a Chinese case diagnosed as EOSRD and to characterize the polymorphisms of the RPE65 gene. A seven-year-old girl with clinical symptoms of EOSRD and her parents were recruited into this study. Ophthalmologic examinations, including best-corrected visual acuity, slit-lamp, Optical coherence tomography (OCT), and fundus examination with dilated pupils, were performed to determine the clinical characteristics of the whole family. We amplified and sequenced the entire coding region and adjacent intronic sequences of the coding regions of the RPE65 gene for the whole family to explore the possible mutation. Our results demonstrate that the patient exhibited the typical clinically features of EOSRD. Her bilateral decimal visual acuity was 0.3 and 0.4 in the left and right eyes, respectively. Spectral-domain optical coherence tomography (SD-OCT) was used to assess the retinal stratification for the whole family. All together, we identified four mutations within the RPE65 gene (c.1056G>A, c.1243+2T>A, c.1338+20A>C and c.1590C>A) in the patient. Among the four mutations, c.1056G>A and c.1338+20A>C had been reported previously and another two were found for the first time in this study. Her mother also carried the novel mutation (c.1243+2T>A). Either a single or a compound heterozygous or a homozygous one mutation is expected to cause EOSRD because mutations of RPE65 gene usually cause an autosomal recessive disease. Therefore, we speculate that the c.1590C>A mutation together with the c.1243+2T>A mutation may cause the patient’s phenotype.

Immuno-histochemical analysis of rod and cone reaction to RPE65 deficiency in the inferior and superior canine retina

Mutations in the RPE65 gene are associated with autosomal recessive early onset severe retinal dystrophy. Morphological and functional studies indicate early and dramatic loss of rod photoreceptors and early loss of S-cone function, while L and M cones remain initially functional. The Swedish Briard dog is a naturally occurring animal model for this disease. Detailed information about rod and cone reaction to RPE65 deficiency in this model with regard to their location within the retina remains limited. The aim of this study was to analyze morphological parameters of cone and rod viability in young adult RPE65 deficient dogs in different parts of the retina in order to shed light on local disparities in this disease. In retinae of affected dogs, sprouting of rod bipolar cell dendrites and horizontal cell processes was dramatically increased in the inferior peripheral part of affected retinae, while central inferior and both superior parts did not display significantly increased sprouting. This observation was correlated with photoreceptor cell layer thickness. Interestingly, while L/M cone opsin expression was uniformly reduced both in the superior and inferior part of the retina, S-cone opsin expression loss was less severe in the inferior part of the retina. In summary, in retinae of young adult RPE65 deficient dogs, the degree of rod bipolar and horizontal cell sprouting as well as of S-cone opsin expression depends on the location. As the human retinal pigment epithelium (RPE) is pigmented similar to the RPE in the inferior part of the canine retina, and the kinetics of photoreceptor degeneration in humans seems to be similar to what has been observed in the inferior peripheral retina in dogs, this area should be studied in future gene therapy experiments in this model.

Pathophysilogical mechanism and treatment strategies for Leber congenital amaurosis

Mutations in retinoid isomerase, RPE65, or lecithin-retinol acyltransferase (LRAT) disrupt 11-cis-retinal recycling and cause Leber congenital amaurosis (LCA), the most severe retinal dystrophy in early childhood. We used Lrat (-/-), a murine model for LCA, to investigate the mechanism of rapid cone degeneration. We found that mislocalized M-opsin was degraded whereas mislocalized S-opsin accumulated in Lrat (-/-) cones before the onset of massive ventral/central cone degeneration. Since the ventral and central retina expresses higher levels of S-opsin than the dorsal retina in mice, our results may explain why ventral and central cones degenerate more rapidly than dorsal cones in Rpe65 (-/-) and Lrat (-/-) LCA models. In addition, human blue opsin and mouse S-opsin, but not mouse M-opsin or human red/green opsins, aggregated to form cytoplasmic inclusions in transfected cells, which may explain why blue cone function is lost earlier than red/green-cone function in LCA patients. The aggregation of short-wavelength opsins likely caused rapid cone degenerations through an ER stress pathway as demonstrated in both the Lrat (-/-) retina and transfected cells. Based on this mechanism, we designed a new therapy of LCA by reducing ER stress. We found that systemic injection of an ER chemical chaperone, tauroursodeoxycholic acid (TUDCA), is effective in reducing ER stress, preventing apoptosis, and preserving cones in Lrat (-/-) mice.

A Phe-rich region in short-wavelength sensitive opsins is responsible for their aggregation in the absence of 11-cis-retinal

Human blue and mouse S-opsin are prone to aggregation in the absence of 11-cis-retinal, which underlie the rapid cone degeneration in human patients and animal models of Leber congenital amaurosis (LCA). By in silico analysis and domain swapping experiments, we show that a Phe-rich region in short-wavelength sensitive (SWS) opsins, but not in medium/long-wavelength sensitive opsins, is responsible for SWS opsin aggregation. Mutagenesis studies suggest that Phe residues in this region are critical in mediating protein aggregation. Fusing the Phe-rich region of SWS opsins to GFP causes the latter to aggregate. Our findings suggest that new therapeutics can be designed to disrupt the Phe-rich region in preventing cone degeneration due to S-opsin aggregation in LCA.

Human retinal gene therapy for Leber congenital amaurosis shows advancing retinal degeneration despite enduring visual improvement

Leber congenital amaurosis (LCA) associated with retinal pigment epithelium-specific protein 65 kDa (RPE65) mutations is a severe hereditary blindness resulting from both dysfunction and degeneration of photoreceptors. Clinical trials with gene augmentation therapy have shown partial reversal of the dysfunction, but the effects on the degeneration are not known. We evaluated the consequences of gene therapy on retinal degeneration in patients with RPE65-LCA and its canine model. In untreated RPE65-LCA patients, there was dysfunction and degeneration of photoreceptors, even at the earliest ages. Examined serially over years, the outer photoreceptor nuclear layer showed progressive thinning. Treated RPE65-LCA showed substantial visual improvement in the short term and no detectable decline from this new level over the long term. However, retinal degeneration continued to progress unabated. In RPE65-mutant dogs, the first one-quarter of their lifespan showed only dysfunction, and there was normal outer photoreceptor nuclear layer thickness retina-wide. Dogs treated during the earlier dysfunction-only stage showed improved visual function and dramatic protection of treated photoreceptors from degeneration when measured 5-11 y later. Dogs treated later during the combined dysfunction and degeneration stage also showed visual function improvement, but photoreceptor loss continued unabated, the same as in human RPE65-LCA. The results suggest that, in RPE65 disease treatment, protection from visual function deterioration cannot be assumed to imply protection from degeneration. The effects of gene augmentation therapy are complex and suggest a need for a combinatorial strategy in RPE65-LCA to not only improve function in the short term but also slow retinal degeneration in the long term.

RPE65 gene therapy slows cone loss in Rpe65-deficient dogs

Recent clinical trials of retinal pigment epithelium gene (RPE65) supplementation therapy in Leber congenital amaurosis type 2 patients have demonstrated improvements in rod and cone function, but it may be some years before the effects of therapy on photoreceptor survival become apparent. The Rpe65-deficient dog is a very useful pre-clinical model in which to test efficacy of therapies, because the dog has a retina with a high degree of similarity to that of humans. In this study, we evaluated the effect of RPE65 gene therapy on photoreceptor survival in order to predict the potential benefit and limitations of therapy in patients. We examined the retinas of Rpe65-deficient dogs after RPE65 gene therapy to evaluate the preservation of rods and cone photoreceptor subtypes. We found that gene therapy preserves both rods and cones. While the moderate loss of rods in the Rpe65-deficient dog retina is slowed by gene therapy, S-cones are lost extensively and gene therapy can prevent that loss, although only within the treated area. Although LM-cones are not lost extensively, cone opsin mislocalization indicates that they are stressed, and this can be partially reversed by gene therapy. Our results suggest that gene therapy may be able to slow cone degeneration in patients if intervention is sufficiently early and also that it is probably important to treat the macula in order to preserve central function.

Mutations in RD3 are associated with an extremely rare and severe form of early onset retinal dystrophy

PURPOSE

To identify the underlying mutation and describe the phenotype in a consanguineous Kurdish family with Leber's congenital amaurosis (LCA)/early onset severe retinal dystrophy (EOSRD).

METHODS

Members of the index family were followed up to 22 years by ophthalmological examinations, including best corrected visual acuity (BCVA), Goldmann visual field (GVF), two-color-threshold perimetry (2CTP) and Ganzfeld electroretinogram (ERG), fundus photographs, fundus autofluorescence (FAF), and optical coherence tomography (OCT). After excluding seven of nine known LCA/EOSRD genes in the index patient, linkage analysis was performed in the family using a microarray followed by microsatellite fine mapping and direct sequencing of candidate genes. RD3 was screened by direct sequencing of 85 independent patients with LCA/EOSRD presenting with a BCVA ≥ 1.0 LogMAR before the age of 2 years to assess the prevalence of RD3 mutations in LCA/EOSRD. Since RD3 and RetGC1 have a functional relation, study authors screened for a modifying effect of RD3 mutations in 17 independent patients with mutations in GUCY2D.

RESULTS

BCVA was severely reduced from the earliest examinations (as early as 3 months), never exceeding 1.3 LogMAR. The disease presented as cone-rod dystrophy with dystrophic changes in the macula and bone spicules in the periphery on progression. Linkage analysis narrowed the region of interest towards the LCA12 locus. Direct sequencing of RD3 revealed a homozygous nonsense mutation (c.180C > A) in all affected members tested. Screening of additional unrelated LCA/EOSRD patients revealed only polymorphisms in RD3.

CONCLUSIONS

This is the second family reported so far with mutations in RD3. Mutations in RD3 are a very rare cause of LCA associated with an extremely severe form of retinal dystrophy.

Next-generation genetic testing for retinitis pigmentosa

Molecular diagnostics for patients with retinitis pigmentosa (RP) has been hampered by extreme genetic and clinical heterogeneity, with 52 causative genes known to date. Here, we developed a comprehensive next-generation sequencing (NGS) approach for the clinical molecular diagnostics of RP. All known inherited retinal disease genes (n = 111) were captured and simultaneously analyzed using NGS in 100 RP patients without a molecular diagnosis. A systematic data analysis pipeline was developed and validated to prioritize and predict the pathogenicity of all genetic variants identified in each patient, which enabled us to reduce the number of potential pathogenic variants from approximately 1,200 to zero to nine per patient. Subsequent segregation analysis and in silico predictions of pathogenicity resulted in a molecular diagnosis in 36 RP patients, comprising 27 recessive, six dominant, and three X-linked cases. Intriguingly, De novo mutations were present in at least three out of 28 isolated cases with causative mutations. This study demonstrates the enormous potential and clinical utility of NGS in molecular diagnosis of genetically heterogeneous diseases such as RP. De novo dominant mutations appear to play a significant role in patients with isolated RP, having major implications for genetic counselling.

Structural and functional correlates in color vision deficiency

PURPOSE

The aim of this study is to assess the photoreceptor integrity, using spectral domain optical coherence tomography (SD-OCT), and to measure the retinal sensitivity of patients with congenital red-green color vision deficiency (CVD).

METHODS

In all, 14 eyes from 7 patients with congenital red-green CVD (diagnosed by Farnsworth Munsell 100 hue test), and 14 eyes from 7 control subjects were examined by SD-OCT and microperimetry. Radial scans (7-mm) were taken of the macula. The center of the fovea was defined. The thickness of different retinal layers, at the foveal center, and at multiple defined points along all six radial scans, was measured. The median readings were compared between the two groups using Mann-Whitney U-test.

RESULTS

SD-OCT demonstrated normal total retinal thickness, normal thickness of the photoreceptor layer, normal thickness of the outer nuclear layer, normal vertical thickness of the outer segments (OSs), and normal vertical thickness of the inner segments. OS horizontal diameter was less in left eye in cases with CVD when compared with controls. The mean retinal and foveal sensitivity was similar between cases and controls.

CONCLUSIONS

In subjects with congenital red-green CVD, there are no discernible anatomical abnormalities seen on SD-OCT in various retinal layers, except for a narrower foveal pit. However, further studies with larger sample size are required.

The retinal pigment epithelium in health and disease

Retinal pigment epithelial cells (RPE) constitute a simple layer of cuboidal cells that are strategically situated behind the photoreceptor (PR) cells. The inconspicuousness of this monolayer contrasts sharply with its importance [1]. The relationship between the RPE and PR cells is crucial to sight; this is evident from basic and clinical studies demonstrating that primary dysfunctioning of the RPE can result in visual cell death and blindness. RPE cells carry out many functions including the conversion and storage of retinoid, the phagocytosis of shed PR outer segment membrane, the absorption of scattered light, ion and fluid transport and RPE-PR apposition. The magnitude of the demands imposed on this single layer of cells in order to execute these tasks, will become apparent to the reader of this review as will the number of clinical disorders that take origin from these cells.