A morphometric analysis of the retinal arterioles with adaptive optics imaging in RPE65-associated retinal dystrophy after treatment with voretigene neparvovec

PURPOSE

To investigate the changes in retinal arterial architecture after treatment with voretigene neparvovec in patients with retinal dystrophy caused by bi-allelic mutations in the RPE65 gene.

METHODS

Sixteen eyes treated with voretigene neparvovec at the University Eye Clinic in Tuebingen, Germany, underwent adaptive optics ophthalmoscopy (AO) imaging at baseline and 2 weeks, 1, 3, 6 and 12 months after treatment. Follow-up was performed in six eyes of four patients. For each eye, five different positions at arterial vessels were selected and the wall-to-lumen ratio (WLR), the lumen diameter (LD) and the wall cross-sectional area (WCSA) were measured by the manufacturer's software over the observational period.

RESULTS

Vast retinal atrophy dominated all gained AO images. WLR fluctuated in the observation period without statistically significant change. LD and WCSA changed significantly after 2 weeks from the baseline examination and returned to values similar to baseline thereafter. There were no signs of inflammation such as macrophages or perivascular accumulated fluid visible.

CONCLUSION

AO imaging of the retinal vessels in RPE65-associated retinal dystrophies (IRD) is challenging. There was no change in the retinal arterial vasculature over the observation period of 12 months that would indicate inflammatory changes. Decrease of the LD and WCSA shortly after treatment might be caused by the perioperative prednisolone intake. AO of retinal vessels can be used as a diagnostic module to complement monitoring the disease and effects of genetic treatments if the acquisition is possible in selected cases.

Phenotyping and genotyping inherited retinal diseases: Molecular genetics, clinical and imaging features, and therapeutics of macular dystrophies, cone and cone-rod dystrophies, rod-cone dystrophies, Leber congenital amaurosis, and cone dysfunction syndromes

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population and in children. The scope of this review is to familiarise clinicians and scientists with the current landscape of molecular genetics, clinical phenotype, retinal imaging and therapeutic prospects/completed trials in IRD. Herein we present in a comprehensive and concise manner: (i) macular dystrophies (Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), PRPH2-associated pattern dystrophy, Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)), (ii) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4, KCNV2 and RPGR), (iii) predominant rod or rod-cone dystrophies (retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)), (iv) Leber congenital amaurosis/early-onset severe retinal dystrophy (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (v) cone dysfunction syndromes (achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6), X-linked cone dysfunction with myopia and dichromacy (Bornholm Eye disease; OPN1LW/OPN1MW array), oligocone trichromacy, and blue-cone monochromatism (OPN1LW/OPN1MW array)). Whilst we use the aforementioned classical phenotypic groupings, a key feature of IRD is that it is characterised by tremendous heterogeneity and variable expressivity, with several of the above genes associated with a range of phenotypes.

Unlocking therapeutic potential: dual gene therapy for ameliorating the disease phenotypes in a mouse model of RPE65 Leber congenital amaurosis

Leber congenital amaurosis (LCA) is the most common genetic cause of congenital visual impairment in infants and children. Patients with LCA who harbor RPE65 mutations exhibit a deficiency in photoreceptor rhodopsin, leading to severe night blindness and visual impairment following birth. Since either gene replacement therapy or anti-apoptosis therapy alone cannot maintain both functional and morphological normality for a long time in the animal model, we propose a robust treatment strategy, that is, gene replacement therapy combined with anti-apoptotic therapy to protect photoreceptors from further degeneration while compensating for lost RPE65 function. Here, rd12 mice were injected subretinally at postnatal day 14 with four vector administrations, respectively. At 6 months after treatment, it was discovered that injection of three vectors, AAV8 (Y733F)-CBA-hRPE65, AAV8(Y733F)-CBA-hRPE65-BCL-2-L10 and mixture of half-dose AAV8(Y733F)-CBA-hRPE65 and half-dose AAV8 (Y733F)-CBA-BCL-2-L10, could partially restore the visual function of rd12 mice. Meanwhile, these treated eyes also exhibited a thicker outer nuclear layer (ONL) structure. However, despite the fact that the eyes of rd12 mice injected with the AAV8 (Y733F)-CBA-BCL-2-L10 vector displayed a slightly thicker ONL structure compared to untreated eyes, the visual function of the treated eyes did not recover. Continuing the observation period to 12 months after treatment, we found that compared to rd12 mice at 6-month post-treatment, rd12 mice injected with AAV8 (Y733F)-CBA-hRPE65 or mixture of half-dose AAV8(Y733F)-CBA-hRPE65 and half-dose AAV8 (Y733F)-CBA-BCL-2-L10 exhibited varying degrees of decline in both visual function and ONL thickness. However, in the case of rd12 mice injected with the AAV8(Y733F)-CBA-hRPE65-BCL-2-L10 vector, the ONL thickness remains consistent at both 6 and 12 months after treatment. These mice continued to maintain a relatively strong visual function and showed restoration in the levels of RPE65 and Rhodopsin protein expression. Our findings illustrate that early postnatal treatment with AAV vectors containing both the hRPE65 gene and the Bcl-2L10 anti-apoptotic gene provide enhanced and sustained retinal protection.

[Inherited retinal diseases in Germany-Challenges in health care supply structure and diagnostics]

BACKGROUND

Inherited retinal diseases (IRD) are rare eye diseases and pose high diagnostic challenges. A care structure with few highly specialized centers in Germany, misdiagnosis due to the lack of molecular genetic testing, and a lack of a central registry lead to a lack of reliable information on the prevalence and distribution of IRDs in Germany.

METHODS

Based on clinical data from an ophthalmological center and molecular data from a genetic center as well as a nationwide health insurance data query, we estimated the prevalence of IRDs in Germany in addition to collecting information on their phenotypic and genotypic distribution.

RESULTS

The median travelling distance to the ophthalmological center was 60 km. The most frequent diagnoses were retinitis pigmentosa, macular dystrophy and general retinal dystrophy. Molecular genetic testing was performed in 87% of patients with clinical suspicion of IRD, with marked differences in frequencies among age cohorts. The molecular genetic detection rate in the genetic center was 51%. The prevalence of inherited retinal dystrophy in Germany determined by health insurance data retrieval was approximately 1:1150.

CONCLUSION

Many patients must travel long distances to visit specialized clinics for IRDs with access to genetic testing. To obtain more reliable numbers on the prevalence in Germany, routine molecular genetic testing, and a national registry for IRD detection are needed.

An in silico toolbox for the prediction of the potential pathogenic effects of missense mutations in the dimeric region of hRPE65

hRPE65 is a fundamental enzyme of the retinoid visual cycle, and many missense mutations affecting its expression or function are associated with a wide range of diseases. Many hRPE65 missense mutations lack a clear pathogenicity classification or are labelled as VUS. In this context, we recently developed a protocol based on µs-long molecular dynamics simulations to study the potential pathogenic effect of hRPE65 missense mutations. In the present work, the structure-based protocol was integrated with a hRPE65-tailored consensus bioinformatics strategy, named ConPath, that showed high performance in predicting known pathogenic/benign hRPE65 missense mutations. The combined strategy was used to perform a multi-level evaluation of the potential pathogenicity of 13 different hRPE65 VUS, which were classified based on their likelihood of pathogenic effect. The obtained results provide information that may support the reclassification of these VUS and help clinicians evaluate the eligibility for gene therapy of patients diagnosed with such variants.

A Molecular Genetic Analysis of RPE65-Associated Forms of Inherited Retinal Degenerations in the Russian Federation

Pathogenic variants in the RPE65 gene cause the only known form of inherited retinal degenerations (IRDs) that are prone to gene therapy. The current study is aimed at the evaluation of the prevalence of RPE65-associated retinopathy in the Russian Federation, the characterization of known variants in the RPE65 gene, and the establishment of the specificities of the mutation spectrum in Russian patients.

METHODS

The analysis was carried out on blood samples obtained from 1053 non-related IRDs patients. The analysis, which consisted of 211 genes, was carried out based on the method of massive parallel sequencing (MPS) for all probands. Variant validation, as well as biallelic status verification, were carried out using direct automated Sanger sequencing. The number of copies of RPE65 exons 1-14 was analyzed with quantitative MLPA using an MRC-Holland SALSA MLPA probemix.

RESULTS

Out of 1053 non-related patients, a molecular genetic diagnosis of IRDs has been confirmed in 474 cases, including 25 (5.3%) patients with RPE65-associated retinopathy. We detected 26 variants in the RPE65 gene, nine of which have not been previously described in the literature. The most common mutations in the Russian population were c.304G>T/p.(Glu102*), c.370C>T/p.(Arg124*), and c.272G>A/p.(Arg91Gln), which comprised 41.8% of all affected chromosomes.

CONCLUSIONS

The current study shows that pathogenic variants in the RPE65 gene contribute significantly to the pathogenesis of IRDs and comprise 5.3% of all patients with a confirmed molecular genetic diagnosis. This study allowed for the formation of a cohort for target therapy of the disorder; such therapy has already been carried out for some patients.

Leukemia Inhibitory Factor Protects against Degeneration of Cone Photoreceptors Caused by RPE65 Deficiency

BACKGROUND

Retinal pigment epithelium (RPE) 65 is a key enzyme in the visual cycle involved in the regeneration of 11-cis-retinal. Mutations in the human RPE65 gene cause Leber's congenital amaurosis (LCA), a severe form of an inherited retinal disorder. Animal models carrying Rpe65 mutations develop early-onset retinal degeneration. In particular, the cones degenerate faster than the rods. To date, gene therapy has been used successfully to treat RPE65-associated retinal disorders. However, gene therapy does not completely prevent progressive retinal degeneration in patients, possibly due to the vulnerability of cones in these patients. In the present study, we tested whether leukemia inhibitory factor (LIF), a trophic factor, protects cones in rd12 mice harboring a nonsense mutation in Rpe65.

METHODS

LIF was administrated to rd12 mice by intravitreal microinjection. Apoptosis of retinal cells was analyzed by TUNEL assay. The degeneration of cone cells was evaluated by immunostaining of retinal sections and retinal flat-mounts. Signaling proteins regulated by LIF in the retinal and cultured cells were determined by immunoblotting.

RESULTS

Intravitreal administration of LIF activated the STAT3 signaling pathway, thereby inhibiting photoreceptor apoptosis and preserving cones in rd12 mice. Niclosamide (NCL), an inhibitor of STAT3 signaling, effectively blocked STAT3 signaling and autophagy in cultured 661W cells treated with LIF. Co-administration of LIF with NCL to rd12 mice abolished the protective effect of LIF, suggesting that STAT3 signaling and autophagy mediate the protection.

CONCLUSION

LIF is a potent factor that protects cones in rd12 mice. This finding implies that LIF can be used in combination with gene therapy to achieve better therapeutic outcomes for patients with RPE65-associated LCA.

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.

[Gene therapy in ophthalmology]

In 2017 the gene therapy medication voretigene neparvovec-rzyl was approved by the U.S. Food and Drug Administration (FDA) for retinal gene therapy of hereditary retinal dystrophies caused by mutations in the RPE65 gene. Voretigene neparvovec-rzyl is a gene augmentation therapy using an  adeno-associated virus-based vector to express a healthy copy of the human RPE65 gene in the patient's retinal pigment epithelial (RPE) cells. The success of gene augmentation therapy in RPE65-linked retinal dystrophy encouraged research activities on the concept of gene supplementation to be extended to nongenetic diseases, such as age-related macular degeneration; however, it also showed that the principle of success cannot be easily extended to other retinal dystrophies. This review article presents the most commonly used principles and technologies of gene therapy and provides an overview of the current challenges and limitations. Furthermore, practice-relevant aspects of the indications and the treatment procedure are discussed. Particular attention is paid to the consideration of disease stages, especially with respect to patient's expectations and the evaluation of treatment success.

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.

The Amphipathic Helix in Visual Cycle Proteins: A Review

The visual cycle is a complex biological process that involves the sequential action of proteins in the retinal pigment epithelial (RPE) cells and photoreceptors to modify and shuttle visual retinoids. A majority of the visual cycle proteins are membrane proteins, either integral or peripheral membrane proteins. Despite significant progress in understanding their physiological function, very limited structural information is available for the visual cycle proteins. Moreover, the mechanism of membrane interaction is not yet clear in all cases. Here, we demonstrate the presence of an amphipathic helix in selected RPE visual cycle proteins, using in silico tools, and highlight their role in membrane association and function.

Environmental Light Has an Essential Effect on the Disease Expression in a Dominant RPE65 Mutation

The retina pigmented epithelium 65 kDa protein (RPE65) is an essential enzyme in the visual cycle that regenerates the 11-cis-retinal chromophore obligatory for vision. Mutations in RPE65 are associated with blinding diseases. D477G (C.1430G > A) is the only known RPE65 variant to cause autosomal dominant retinitis pigmentosa (adRP). Previously, we reported that the heterozygous D477G knock-in (WT/KI) mice exposed to dim light intensity demonstrated delayed chromophore regeneration rates and slowed recovery of photoreceptor sensitivity following photobleaching. However, visual function and retinal architecture were indistinguishable from the wild-type (WT) mice. In this study, when maintained under the physiological day-light intensity (2 K lux), the WT/KI heterozygous mice displayed retina degeneration and reduced electroretinography (ERG) amplitude, recapitulating that observed in human patients. Our findings indicated the importance of the light environment in the mechanism of RPE65 D477G pathogenicity.

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.

Visual function restoration in a mouse model of Leber congenital amaurosis via therapeutic base editing

Leber congenital amaurosis (LCA), an inherited retinal degeneration, causes severe visual dysfunction in children and adolescents. In patients with LCA, pathogenic variants, such as RPE65, are evident in specific genes, related to the functions of retinal pigment epithelium and photoreceptors. In contrast to the original Cas9, base editing tools can correct pathogenic substitutions without generation of DNA double-stranded breaks (DSBs). In this study, dual adeno-associated virus (AAV) vectors containing split adenine base editors (ABEs) with trans-splicing intein were prepared for in vivo base editing in retinal degeneration of 12 (rd12) mice, an animal model of LCA, possessing a nonsense mutation of C to T transition in the Rpe65 gene (p.R44X). Subretinal injection of AAV-ABE in retinal pigment epithelial cells of rd12 mice resulted in an A to G transition. The on-target editing was sufficient for recovery of wild-type mRNA, RPE65 protein, and light-induced electrical responses from the retina. Compared with our previous therapeutic editing strategies using Cas9 and prime editing, or with the gene transfer strategy shown in the current study, our results suggest that, considering the editing efficacy and functional recovery, ABEs could be a strong, reliable method for correction of pathogenic variants in the treatment of LCA.

Predicting potentially pathogenic effects of hRPE65 missense mutations: a computational strategy based on molecular dynamics simulations

The human retinal pigment epithelium-specific 65-kDa protein (hRPE65) plays a crucial role within the retinoid visual cycle and several mutations affecting either its expression level or its enzymatic function are associated with inherited retinal diseases such as Retinitis Pigmentosa. The gene therapy product voretigene neparvovec (Luxturna) has been recently approved for treating hereditary retinal dystrophies; however, the treatment is currently accessible only to patients presenting confirmed biallelic mutations that severely impair hRPE65 function, and many reported hRPE65 missense mutations lack sufficient evidences for proving their pathogenicity. In this context, we developed a computational approach aimed at evaluating the potential pathogenic effect of hRPE65 missense variants located on the dimerisation domain of the protein. The protocol evaluates how mutations may affect folding and conformation stability of this protein region, potentially helping clinicians to evaluate the eligibility for gene therapy of patients diagnosed with this type of hRPE65 variant of uncertain significance.

Carrier frequency and incidence estimation of RPE65-associated inherited retinal diseases in East Asian population by population database-based analysis

BACKGROUND

Inherited retinal diseases (IRDs) are clinically and genetically heterogenous disorders leading to visual impairment and blindness. Because gene therapy for RPE65-associated IRDs was recently approved, it is necessary to predict the carrier frequency and prevalence for RPE65-associated IRDs. This study aimed to analyze the carrier frequency and expected incidence of RPE65-associated IRDs in East Asians and Koreans using exome data from the Genome Aggregation Database (gnomAD) and the Korean Reference Genome Database (KRGDB).

METHODS

We analyzed 9,197 exomes for East Asian populations from gnomAD comprising 1,909 Korean and 1,722 Korean genomes from KRGDB. All identified RPE65 variants were classified according to the 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines.

RESULTS

The total carrier frequencies of East Asians and Koreans from both gnomAD and KRGDB were 0.10% (11/10,919) and 0.06% (2/3,631), respectively. The estimated incidence of RPE65-associated IRDs was 1/3,941,308 in East Asians and 1/13,184,161 in Koreans.

CONCLUSION

This study identified carrier frequencies of RPE65-associated IRDs in East Asians and Koreans using gnomAD and KRGDB. We confirmed that the carrier frequency of RPE65-associated IRDs patients was low in Koreans among all East Asian populations, and the incidence was also predicted to be lower than in other East Asian populations. The variant spectrum of RPE65 gene in East Asian and Korean populations differed greatly from those of other ethnic groups.

Gene Therapy for Inherited Retinal Disease: Long-Term Durability of Effect

The recent approval of voretigene neparvovec (Luxturna®) for patients with biallelic RPE65 mutation-associated inherited retinal dystrophy with viable retinal cells represents an important step in the development of ocular gene therapies. Herein, we review studies investigating the episomal persistence of different recombinant adeno-associated virus (rAAV) vector genomes and the preclinical and clinical evidence of long-term effects of different RPE65 gene replacement therapies. A targeted review of articles published between 1974 and January 2021 in Medline®, Embase®, and other databases was conducted, followed by a descriptive longitudinal analysis of the clinical trial outcomes of voretigene neparvovec. Following an initial screening, 14 publications examining the episomal persistence of different rAAV genomes and 71 publications evaluating gene therapies in animal models were included. Viral genomes were found to persist for at least 22 months (longest study follow-up) as transcriptionally active episomes. Treatment effects lasting almost a decade were reported in canine disease models, with more pronounced effects the earlier the intervention. The clinical trial outcomes of voretigene neparvovec are consistent with preclinical findings and reveal sustained results for up to 7.5 years for the full-field light sensitivity threshold test and 5 years for the multi-luminance mobility test in the Phase I and Phase III trials, respectively. In conclusion, the therapeutic effect of voretigene neparvovec lasts for at least a decade in animal models and 7.5 years in human subjects. Since retinal cells can retain functionality over their lifetime after transduction, these effects may be expected to last even longer in patients with a sufficient number of outer retinal cells at the time of intervention.

PacMAGI: A pipeline including accurate indel detection for the analysis of PacBio sequencing data applied to RPE65

Third generation sequencing methods, like PacBio, provide information about structural variants, introns, enhancers and promoters. We developed an automated pipeline, called PacMAGI, including quality control, alignment, SNV, INDELs, structural variant calling, phasing, annotation and variant interpretation, for the analysis of PacBio data for any target region. Bi-allelic mutations in the RPE65 gene are associated with different inherited retinal dystrophies, such as Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP). Diagnostic panel-based NGS analysis is performed on coding regions and intron/exon junctions of genes. To obtain a more conclusive diagnosis, we applied PacMAGI to obtain a second hit on RPE65 in LCA or RP patients who showed a single heterozygous variant by NGS. We used PacBio to sequence the full gene and identify putative second-hits in intronic, problematic and promoter regions. All variants identified in the diagnostic setting with NGS were correctly detected by the pipeline, and thanks to our custom algorithm for INDELs, a previously undetected 'Pathogenic' frameshift variant was found in a RP patient already identified to carry a 'Likely Pathogenic' variant.

Quantitative and qualitative characterization of retinal dystrophies in canine models of inherited retinal diseases using spectral domain optical coherence tomography (SD-OCT)

The purpose of this study was to establish spectral domain optical coherence tomography (SD-OCT) assessment data in well-established canine models of inherited retinal dystrophies: PDE6B-rod-cone dysplasia 1 (RCD1: early onset retinitis pigmentosa), PRCD-progressive rod-cone degeneration (PRCD: late onset retinitis pigmentosa), CNGB3-achromatopsia, and RPE65-Leber congenital amaurosis (LCA). High resolution SD-OCT images of the retina were acquired from both eyes in 5 planes: temporal; superotemporal; superior; nasal; and inferior in adult dogs with: RCD1 (n = 4 dogs, median age: 1.5 yrs); PRCD (n = 2, 4.3 yrs); LCA (n = 3, 5.2 yrs); achromatopsia (n = 3, 4.2 yrs); and wild types (wt, n = 6, 5.5 yrs). Total, inner and outer retinal thicknesses and ellipsoid zone were analyzed. In selected animals, histomorphometric evaluations were performed. In dogs with RCD1, PRCD, and LCA, the thickness of the outer retina was, compared to wt, significantly decreased (p ≤ 0.02) in all OCT imaging planes, and in superotemporal and inferior imaging planes in dogs with achromatopsia. No significant thinning was observed in inner retina thickness in any disease model except in the inferior imaging plane in dogs with RCD1. Dogs with RCD1, PRCD, and LCA had significantly more areas with disrupted ellipsoid zone in the presumed area centralis than wt (p ≤ 0.001). OCT findings provide baseline information for research of retinal dystrophies using these canine models.

Cost-effectiveness of voretigene neparvovec in the treatment of patients with inherited retinal disease with RPE65 mutation in Switzerland

Objective

We aimed to evaluate the cost-effectiveness of voretigene neparvovec (VN) compared with standard of care (SoC) for patients with inherited retinal disease (IRD) caused by a biallelic RPE65-mutation. VN is a live, non-replicating adeno-associated virus serotype 2 (AAV2). SoC is best supportive care provided to patients with visual impairment. Patients under SoC may experience progressive vision loss leading to complete blindness.

Methods

We adapted a previously published Markov cohort model for IRD. An annual cycle length, life-long time horizon, discount rate of 3% for cost and health outcomes, and Swiss health system perspective were used. Data from a randomised controlled phase III trial of VN versus SoC (ClinicalTrials.gov: NCT00999609) were used to estimate transitions between health states in the first year, after which VN patients were assumed to remain for 39 subsequent years in the health state they were in at the end of the first year. After the 40^th year for VN patients and 1^st year for SoC patients, visual decline was modelled based on observational data on the natural progression of the disease. Quality-adjusted life years (QALYs) were calculated based on an external study which elicited clinicians’ EQ-5D-5L-based utility estimates for IRD patients with a RPE65-mutation. Costs (Swiss Francs (CHF), year 2018-2019) included drug acquisition/ administration, adverse events, testing for sufficient viable retinal cells, and healthcare-related costs of blindness. Societal costs of blindness were added in a complementary analysis. Robustness of the model results were tested in sensitivity and scenario analyses.

Results

For the base-case, VN resulted in incremental costs per patient of CHF 764’402 (VN: CHF 901’654, SoC: CHF 137’252), incremental blindness-free years of 7.67 (VN: 28.32, SoC: 20.65) and incremental QALYs of 6.73 (VN: 18.35, SoC: 11.62), leading to an incremental cost-effectiveness ratio of CHF 113’526 per QALY gained. In probabilistic sensitivity analysis, the cost-effectiveness of VN was better than CHF 100,000 per QALY gained in 41% of iterations. For the scenario analysis in which a societal perspective was adopted and for which a 50% work-related productivity loss from blindness was assumed, incremental costs of CHF 423,837 and an ICER of CHF 62’947 per QALY gained were produced. The scenario assuming VN treatment effect lasts for 20 years produced an ICER of CHF 156’171 per QALY gained, whereas assuming a life-long VN treatment effect resulted in an ICER of CHF 96’384 per QALY gained.

Conclusion

The incremental cost-effectiveness ratio of VN compared to the SoC was estimated to be CHF 113’526 and CHF 62’947 per QALY gained, respectively, from a Swiss healthcare system, and societal perspective assuming a 50% productivity loss.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12913-022-08211-y.

Short term morphological rescue of the fovea after gene therapy with voretigene neparvovec

PURPOSE

Leber congenital amaurosis type 2 (LCA2) and early-onset severe retinal dystrophy (EOSRD) are linked to visual impairment with nyctalopia and visual acuity reduction in early childhood. In 2017, the first gene therapy voretigene neparvovec (Luxturna™) for patients with LCA and EOSRD cause by bi-allelic mutations in the RPE65 gene has been approved. Here we report on an example of short-term change in the foveal morphology after functionally successful gene therapy with voretigene neparvovec in a 15-year old patient.

METHODS

The clinical examinations included best corrected visual acuity (BCVA), spectral domain optical coherence tomography (OCT) and adaptive optics retinal imaging.

RESULTS

During follow-up over a period of 3 months after the treatment, an improvement of the central foveal morphology could be observed in OCT, with a clear demarcation of the external limiting membrane and changes in the photoreceptor mosaic on adaptive optics retinal imaging. These morphological rescue parameters correlated in part with the improvement in foveal-mediated vision after the treatment and adaptive optics imaging. Although the visual acuity improved only slightly at month 3, objective central cone evaluation with chromatic pupil campimetry showed an increase in the central sensitivity. In daily life, the patient reported her visional experience after the treatment as 'brighter'.

CONCLUSION

Rapid changes in the correlates of photoreceptor morphology after successful gene therapy in patients with LCA/EORD can be quantifiable on individual level.

The interplay of environmental luminance and genetics in the retinal dystrophy induced by the dominant RPE65 mutation

SignificanceIn humans, genetic mutations in the retinal pigment epithelium (RPE) 65 are associated with blinding diseases, for which there is no effective therapy alleviating progressive retinal degeneration in affected patients. Our findings uncovered that the increased free opsin caused by enhancing the ambient light intensity increased retinal activation, and when compounded with the RPE visual cycle dysfunction caused by the heterozygous D477G mutation and aggregation, led to the onset of retinal degeneration.

Visual Acuity, Retinal Morphology, and Patients' Perceptions after Voretigene Neparvovec-rzyl for RPE65-Associated Retinal Disease

OBJECTIVE

To explore the effect of patient's age, baseline visual acuity, and intraoperative foveal detachment on outcomes of subretinal voretigene neparvovec-rzyl (VN, Luxturna®) therapy and to assess patients' perceptions of the treatment effect.

DESIGN

Multicenter, retrospective, consecutive case series and cross-sectional prospective survey.

SUBJECTS

All 41 consecutive patients treated with VN after FDA approval at three institutions between January 2018 and May 2020.

METHODS

Retrospective chart review of operative reports, clinical notes, ancillary testing and complications, comparing data at baseline and 1, 2-3, 6-9, and 10-15 months after subretinal surgery. A survey was administered to adult patients and parents of pediatric patients.

MAIN OUTCOME MEASURES

Changes in BCVA and retinal morphology, and patients' perceptions.

RESULTS

77 eyes of 41 patients (16 adults and 25 children, range 2-44 years, mean follow-up 10 months, range 1 week to 18.5 months) were analyzed. There was no statistically significant vision change for the adults, whereas there was a trend of improvement for children that reached statistical significance for some time points but not all. At the last follow-up, 14/48 (29%) pediatric and 3/26 (12%) adult eyes improved ≥2 lines (p=0.15). Baseline VA did not have an effect on post-therapy VA (p=0.23). Central foveal thickness decreased mildly in both children and adults, without significant difference between the populations. The fovea was detached by VN in 62 eyes (81%). Inner segment-outer segment junction remained unchanged in 91% of 54 eyes with gradable OCTs, with or without foveal detachment. Thirty-two patients (78%) were reached for the survey an average of 1.15±0.50 years (range 0.31 to 2.31) after surgery in the first eye. Improvement in night, day, and/or color vision was reported by 23 (72%), 22 (69%), and 18 (56%) patients respectively.

CONCLUSIONS

This study is limited by large variability in follow-up time. There were no persistent statistical significant vision changes. A decrease in foveal thickness was noted in most eyes. The long-term significance of this remains to be determined.

A reinterpretation of critical flicker-frequency (CFF) data reveals key details about light adaptation and normal and abnormal visual processing

Our ability to see flicker has an upper frequency limit above which flicker is invisible, known as the "critical flicker frequency" (CFF), that typically grows with light intensity (I). The relation between CFF and I, the focus of nearly 200 years of research, is roughly logarithmic, i.e., CFF ∝ log(I)-a relation called the Ferry-Porter law. However, why this law should occur, and how it relates to the underlying physiology, have never been adequately explained. Over the past two decades we have measured CFF in normal observers and in patients with retinal gene defects. Here, we reanalyse and model our data and historical CFF data. Remarkably, CFF-versus-I functions measured under a wide range of conditions in patients and in normal observers all have broadly similar shapes when plotted in double-logarithmic coordinates, i.e., log (CFF)-versus-log(I). Thus, the entire dataset can be characterised by horizontal and vertical logarithmic shifts of a fixed-shape template. Shape invariance can be predicted by a simple model of visual processing built from a sequence of low-pass filters, subtractive feedforward stages and gain adjustment (Rider, Henning & Stockman, 2019). It depends primarily on the numbers of visual processing stages that approach their power-law region at a given intensity and a frequency-independent gain reduction at higher light levels. Counter-intuitively, the CFF-versus-I relation depends primarily on the gain of the visual response rather than its speed-a conclusion that changes our understanding and interpretation of human flicker perception. The Ferry-Porter "law" is merely an approximation of the shape-invariant template.

RPE65-related retinal dystrophy: Mutational and phenotypic spectrum in 45 affected patients

INTRODUCTION

Biallelic pathogenic RPE65 variants are related to a spectrum of clinically overlapping inherited retinal dystrophies (IRD). Most affected individuals progress to severe disease, with 50% of patients becoming legally blind by 20 years of age. Deeper knowledge of the mutational spectrum and the phenotype-genotype correlation in RPE65-related IRD is needed.

PATIENTS AND METHODS

Forty-five affected subjects from 27 unrelated families with a clinical diagnosis of RPE65-related IRD were included. Clinical evaluation consisted of self-reported ophthalmological history and objective ophthalmological examination. Patients' genotype was classified according to variant class (truncating or missense) or to variant location at different protein domains. The main phenotypic outcome measure was age at onset (AAO) of symptomatic disease and a Kaplan-Meier analysis of disease symptom event-free survival was performed.

RESULTS

Twenty-nine different RPE65 variants were identified in our cohort, 7 of them novel. Patients carrying two missense alleles showed a later disease onset than those with 1 or 2 truncating variants (log-rank test p <0.05). While 60% of patients carrying a missense/missense genotype presented symptoms before or during the first year of life, almost all patients with at least 1 truncating allele (91%) had an AAO ≤1 year (p <0.05).

CONCLUSION

Our findings suggest an association between the type of RPE65 variant carried and AAO. These findings provide useful data on RPE65-associated IRD phenotypes and may help improve clinical and therapeutic management of these patients.

Leber's Congenital Amaurosis: Current Concepts of Genotype-Phenotype Correlations

Leber’s congenital amaurosis (LCA), one of the most severe inherited retinal dystrophies, is typically associated with extremely early onset of visual loss, nystagmus, and amaurotic pupils, and is responsible for 20% of childhood blindness. With advances in molecular diagnostic technology, the knowledge about the genetic background of LCA has expanded widely, while disease-causing variants have been identified in 38 genes. Different pathogenetic mechanisms have been found among these varieties of genetic mutations, all of which result in the dysfunction or absence of their encoded proteins participating in the visual cycle. Hence, the clinical phenotypes also exhibit extensive heterogenicity, including the course of visual impairment, involvement of the macular area, alteration in retinal structure, and residual function of the diseased photoreceptor. By reviewing the clinical course, fundoscopic images, optical coherent tomography examination, and electroretinogram, genotype-phenotype correlations could be established for common genetic mutations in LCA, which would benefit the timing of the diagnosis and thus promote early intervention. Gene therapy is promising in the management of LCA, while several clinical trials are ongoing and preliminary success has been announced, focusing on RPE65 and other common disease-causing genes. This review provides an update on the genetics, clinical examination findings, and genotype-phenotype correlations in the most well-established causative genetic mutations of LCA.

Characterizing temporal and spatial recruitment of systemically administered RPE65-programmed bone marrow-derived cells to the retina in a mouse model of age-related macular degeneration

PURPOSE

Previously, we reported that the intravenous injection of bone marrow-derived cells (BMDC) infected with lentivirus expressing the human RPE65 gene resulted in the programming of BMDC to promote visual recovery in a mouse model of age-related macular degeneration (AMD). The aim of this study was to characterize the spatial and temporal recruitment of these programmed BMDC to the retinal pigment epithelial (RPE) layer.

METHODS

C57BL/6J female mice received a subretinal injection of AAV1-SOD2 ribozyme to knock down (KD) superoxide dismutase 2 (SOD2) and induce AMD-like pathology. BMDC were isolated from GFP⁺ mice and infected with a lentivirus expressing RPE65. One month after SOD2 KD, fifty thousand GFP⁺ RPE65-BMDC were injected in the mouse tail vein. Animals were terminated at different time points up to 60 min following cell administration, and localization of GFP⁺ cells was determined by fluorescence microscopy of neural retina and RPE flat mounts and tissue sections.

RESULTS

GFP⁺ RPE65- BMDC were observed in SOD2 KD neural retina and RPE as early as 1 min following administration. With increasing time, the number of cells in the neural retina decreased, while those in the RPE increased. While the number of cells in peripheral and central retina remained similar at each time point, the number of BMDC recruited to the central RPE increased in a time-dependent manner up to a maximum by 60 min post administration. Immunohistochemistry of cross-sections of the RPE layer confirmed the incorporation of donor GFP⁺ BMDC into the RPE layer and that these GFP⁺ human RPE65 expressing cells co-localized with murine RPE65. No GFP⁺ cells were observed in the neural retina or RPE layer of normal uninjured control eyes.

CONCLUSIONS

Our study shows that systemically administered GFP⁺ RPE65-BMDC can reach the retina within minutes and that the majority of these BMDC are recruited to the injured RPE layer by 60 min post injection.

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.

Effect of Long-term Anti-VEGF Treatment on Viability and Function of RPE Cells

Purpose/Aim of the study: Vascular endothelial growth factor (VEGF)-antagonists are given over long time periods in the clinic, but the long-term effects on retinal pigment epithelium (RPE) cells are not fully investigated. This study aims to investigate these effects with two clinical relevant VEGF antagonists, bevacizumab and aflibercept, on the function of primary RPE cells.Materials and Methods: All tests were conducted with primary porcine RPE. Cells were stimulated with bevacizumab or aflibercept (both 250 µg/ml) for 1 day, 7 days or 4 weeks. Cell viability was tested in MTT Assay. Secretion of TGF-ß was tested in ELISA, phagocytosis in a microscopic assay, migration in a scratch assay, and expression of RPE65 in Western blot. Barrier function was tested for bevacizumab in transwell-cultured cells by measuring transepithelial electrical resistance for up to 3 days.Results: Viability was reduced by both antagonists at all time points tested. TGF-ß secretion was not altered by any treatment. Phagocytosis was not significantly reduced by any treatment. Wound healing ability was not significantly altered by any treatment. The expression of RPE65 was reduced by bevacizumab but not aflibercept after 4 weeks. Transepithelial electrical resistance was not altered.Conclusions: Long-term treatment with anti VEGF may affect viability of RPE cells, and treatment with bevacizumab may have effects on RPE function in long-term treatment.

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.

Durability of Voretigene Neparvovec for Biallelic RPE65-Mediated Inherited Retinal Disease: Phase 3 Results at 3 and 4 Years

PURPOSE

To determine whether functional vision and visual function improvements after voretigene neparvovec (VN; Luxturna [Spark Therapeutics, Inc]) administration in patients with biallelic RPE65 mutation-associated inherited retinal disease are maintained at 3 to 4 years and to review safety outcomes.

DESIGN

Open-label, randomized, controlled phase 3 trial.

PARTICIPANTS

Thirty-one individuals were enrolled and randomized 2:1 to intervention (n = 21) or control (n = 10). One participant from each group withdrew before, or at, randomization.

METHODS

Patients in the original intervention (OI) group received bilateral subretinal VN injections. Delayed intervention (DI) patients served as control participants for 1 year then received VN.

MAIN OUTCOME MEASURES

Change from injection baseline in bilateral performance on the multiluminance mobility test (MLMT), a measure of ambulatory navigation, and change from injection baseline in full-field light sensitivity threshold white light, visual field (VF), and visual acuity (VA).

RESULTS

Mean bilateral MLMT change scores at year 4 for OI patients and year 3 for DI patients were 1.7 and 2.4, respectively, with 71% of patients with a year 3 visit able to pass MLMT at the lowest light level. Mean change in full-field light sensitivity threshold white light, averaged over both eyes at year 4 for OI patients and year 3 for DI patients, was -1.90 log₁₀(cd.s/m²) and -2.91 log₁₀(cd.s/m²), respectively. Mean change in Goldmann kinetic VF III4e sum total degrees, averaged across both eyes, was 197.7 at year 4 for OI patients and 157.9 at year 3 for DI patients. Mean change in VA (Holladay scale), averaged across both eyes, was -0.003 logarithm of the minimum angle of resolution (logMAR) at year 4 for OI patients and -0.06 logMAR at year 3 for DI patients. One OI patient experienced retinal detachment at approximately year 4 that impacted VA for the OI group. No product-related serious adverse events (AEs) occurred, nor did any deleterious immune responses.

CONCLUSIONS

Improvements in ambulatory navigation, light sensitivity, and VF were consistent in both intervention groups. Overall, improvements were maintained up to 3 to 4 years, with ongoing observation. The safety profile of VN was consistent with vitrectomy and the subretinal injection procedure and was similar between intervention groups, with no product-related serious AEs reported.

A Virtual Reality Orientation and Mobility Test for Inherited Retinal Degenerations: Testing a Proof-of-Concept After Gene Therapy

Purpose

To test the ability of a virtual reality (VR) orientation and mobility (O&M) protocol to serve a measure of functional vision for patients with inherited retinal degenerations (IRDs).

Methods

A VR-O&M protocol designed using a commercially available VR hardware was tested in normally sighted control subjects (n=7; ages 10–35yo; Average 22.5yo) and patients with RPE65-associated Leber Congenital Amaurosis (n=3; ages 7–18yo; Average 12.7yo), in two of them before and after gene therapy. Patients underwent perimetry and full-field sensitivity testing. VR-O&M parameters correlated with the visual dysfunction.

Results

Visual acuities in RPE65 patients were on average worse than 20/200, dark-adapted sensitivity losses >5 log units, and fields constricted between 20° and 40°. Before treatment, patients required ~1000-fold brighter environment to navigate, had at least x4 more collisions, and were slower both to orient and navigate compared to control subjects. Improvements in cone- (by 1–2 L.u.) and rod-mediated (by >4 L.u.) sensitivities post-treatment led to fewer collisions (at least by half) at ~100-fold dimmer luminances, and to x4 times faster navigation times.

Conclusion

This study provides proof-of-concept data in support for the use of VR-O&M systems to quantify the impact that the visual dysfunction and improvement of vision following treatments has on functional vision in IRDs. The VR-O&M was useful in potentially challenging scenarios such as in pediatric patients with severe IRDs.

Translational Relevance

A VR-O&M test will provide much needed flexibility, both in its deployment as well as in the possibility to test various attributes of vision that may be impacted by gene therapy in the setting of translational studies.

Precis

This study provides proof-of-concept data in support for the use of a virtual reality orientation and mobility test to quantify the impact of the disease and of treatments thereof on functional vision in inherited retinal degenerations.

BBS Proteins Affect Ciliogenesis and Are Essential for Hedgehog Signaling, but Not for Formation of iPSC-Derived RPE-65 Expressing RPE-Like Cells

Bardet-Biedl syndrome (BBS) is a ciliopathy characterized by retinal dystrophy, renal cysts, obesity and polydactyly. BBS genes have been implicated in ciliogenesis, hedgehog signaling and retinal pigment epithelium maturation. BBS1 and BBS5 are members of the BBSome, implicated in cilia transport of proteins, and BBS10 is a member of the chaperonin-complex, mediating BBSome assembly. In this study, involvement of BBS1, BBS5 and BBS10 in ciliogenesis and hedgehog signaling were investigated in BBS-defective patient fibroblasts as well as in RPE-hTERT cells following siRNA-mediated knockdown of the BBS genes. Furthermore, the ability of BBS1-defective induced pluripotent stem-cells (iPSCs) to differentiate into RPE cells was assessed. We report that cells lacking functional BBS5 or BBS10 have a reduced number of primary cilia, whereas cells lacking functional BBS1 display shorter primary cilia compared to wild-type cells. Hedgehog signaling was substantially impaired and Smoothened, a component of hedgehog signaling, was trapped inside the cilia of the BBS-defective cells, even in the absence of Smoothened agonist. Preliminary results demonstrated the ability of BBS1-defective iPSC to differentiate into RPE-65 expressing RPE-like cells. The BBS1^-/--defective RPE-like cells were less pigmented, compared to RPE-like cells differentiated from control iPSCs, indicating an impact of BBS1 on RPE maturation.

Pathways and disease-causing alterations in visual chromophore production for vertebrate vision

All that we view of the world begins with an ultrafast cis to trans photoisomerization of the retinylidene chromophore associated with the visual pigments of rod and cone photoreceptors. The continual responsiveness of these photoreceptors is then sustained by regeneration processes that convert the trans-retinoid back to an 11-cis configuration. Recent biochemical and electrophysiological analyses of the retinal G-protein-coupled receptor (RGR) suggest that it could sustain the responsiveness of photoreceptor cells, particularly cones, even under bright light conditions. Thus, two mechanisms have evolved to accomplish the reisomerization: one involving the well-studied retinoid isomerase (RPE65) and a second photoisomerase reaction mediated by the RGR. Impairments to the pathways that transform all-trans-retinal back to 11-cis-retinal are associated with mild to severe forms of retinal dystrophy. Moreover, with age there also is a decline in the rate of chromophore regeneration. Both pharmacological and genetic approaches are being used to bypass visual cycle defects and consequently mitigate blinding diseases. Rapid progress in the use of genome editing also is paving the way for the treatment of disparate retinal diseases. In this review, we provide an update on visual cycle biochemistry and then discuss visual-cycle-related diseases and emerging therapeutics for these disorders. There is hope that these advances will be helpful in treating more complex diseases of the eye, including age-related macular degeneration (AMD).

Clinical vision and molecular loss: Integrating visual psychophysics with molecular genetics reveals key details of normal and abnormal visual processing

Over the past two decades we have developed techniques and models to investigate the ways in which known molecular defects affect visual performance. Because molecular defects in retinal signalling invariably alter the speed of visual processing, our strategy has been to measure the resulting changes in flicker sensitivity. Flicker measurements provide not only straightforward clinical assessments of visual performance but also reveal fundamental details about the functioning of both abnormal and normal visual systems. Here, we bring together our past measurements of patients with pathogenic variants in the GNAT2, RGS9, GUCA1A, RPE65, OPA1, KCNV2 and NR2E3 genes and analyse the results using a standard model of visual processing. The model treats flicker sensitivity as the result of the actions of a sequence of simple processing steps, one or more of which is altered by the genetic defect. Our analyses show that most defects slow down the visual response directly, but some speed it up. Crucially, however, other steps in the processing sequence can make compensatory adjustments to offset the abnormality. For example, if the abnormal step slows down the visual response, another step is likely to speed up or attenuate the response to rebalance system performance. Such compensatory adjustments are probably made by steps in the sequence that usually adapt to changing light levels. Our techniques and modelling also allow us to tease apart stationary and progressive effects, and the localised molecular losses help us to unravel and characterise individual steps in the normal and abnormal processing sequences.

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.

Properties and Therapeutic Implications of an Enigmatic D477G RPE65 Variant Associated with Autosomal Dominant Retinitis Pigmentosa

RPE65 isomerase, expressed in the retinal pigmented epithelium (RPE), is an enzymatic component of the retinoid cycle, converting all-trans retinyl ester into 11-cis retinol, and it is essential for vision, because it replenishes the photon capturing 11-cis retinal. To date, almost 200 loss-of-function mutations have been identified within the RPE65 gene causing inherited retinal dystrophies, most notably Leber congenital amaurosis (LCA) and autosomal recessive retinitis pigmentosa (arRP), which are both severe and early onset disease entities. We previously reported a mutation, D477G, co-segregating with the disease in a late-onset form of autosomal dominant RP (adRP) with choroidal involvement; uniquely, it is the only RPE65 variant to be described with a dominant component. Families or individuals with this variant have been encountered in five countries, and a number of subsequent studies have been reported in which the molecular biological and physiological properties of the variant have been studied in further detail, including observations of possible novel functions in addition to reduced RPE65 enzymatic activity. With regard to the latter, a human phase 1b proof-of-concept study has recently been reported in which aspects of remaining vision were improved for up to one year in four of five patients with advanced disease receiving a single one-week oral dose of 9-cis retinaldehyde, which is the first report showing efficacy and safety of an oral therapy for a dominant form of RP. Here, we review data accrued from published studies investigating molecular mechanisms of this unique variant and include hitherto unpublished material on the clinical spectrum of disease encountered in patients with the D477G variant, which, in many cases bears striking similarities to choroideremia.

Voretigene Neparvovec in Retinal Diseases: A Review of the Current Clinical Evidence

Subretinal gene therapy trials began with the discovery of RPE65 variants and their association with Leber congenital amaurosis. The RPE65 protein is critical for the normal functioning of the visual phototransduction cascade. RPE65 gene knockout animal models were developed and showed similar diseased phenotypes to their human counterparts. Proof of concept studies were carried out in these animal models using subretinal RPE65 gene replacement therapy, resulting in improvements in various visual function markers including electroretinograms, pupillary light responses, and object avoidance behaviors. Positive results in animal models led to Phase 1 human studies using adeno-associated viral vectors. Results in these initial human studies also showed positive impact on visual function and acceptable safety. A landmark Phase 3 study was then conducted by Spark Therapeutics using a dose of 1.5 x10¹¹ vector genomes after dose-escalation studies confirmed its efficacy and safety. Multi-luminance mobility testing was used to measure the primary efficacy endpoint due to its excellent reliability in detecting the progression of inherited retinal diseases. After the study met its primary endpoint, the Food and Drug Administration approved voretigene neparvovec (Luxturna^®) for use in RPE65-associated inherited retinal diseases.

Effect of long-term inflammation on viability and function of RPE cells

PURPOSE

Degenerative ocular disorders like age-related macular degeneration (AMD) are associated with long-term pro-inflammatory signals on retinal pigment epithelial (RPE) cells. In this study, we investigated the effect of long term treatment of RPE cells with agonists of toll-like receptor (TLR) -3 (Polyinosinic:polycytidylic acid, Poly I:C), TLR-4 (lipopolysaccharide, LPS) and the pro-inflammatory cytokine TNFα.

METHODS

All tests were conducted with primary porcine RPE. Cells were stimulated with Poly I:C (1, 10, 100 μg/ml), LPS (0.1, 1, 10 μg/ml) or TNFα (12.5, 25 or 50 ng/ml) for 1 day, 7 days or 4 weeks. Cell viability tests (MTT) were additionally tested in ARPE-19 cells. Cytokine secretion (IL-6, IL-1β, IL-8, TNFα, TGF-β) was tested in ELISA, phagocytosis in a microscopic assay, and expression of RPE65 in Western blot. Barrier function was tested in transwell-cultured cells by measuring transepithelial resistance for up to 3 days.

RESULTS

LPS and TNFα significantly reduce cell viability after 1 day and 7 days, Poly I:C after 7 days and 4 weeks. LPS, Poly I:C and TNFα significantly induce the secretion of IL-6 and IL-8 at all tested time points. IL-1β is increased by LPS and Poly I:C after 1 day, but not by TNFα. TNFα secretion is increased by Poly I:C and LPS after 1 day but not at later time points. TGF-β secretion is not influenced by any stimulus. Concerning RPE function, LPS decreased phagocytosis after 7 days, while Poly I:C and TNFα showed no effect. RPE65 expression was strongly reduced by TNFα and LPS after 4 weeks. Wound healing capacity was reduced by Poly I:C but induced by LPS after 7 d and 4 w. Barrier function was not affected by Poly I:C or LPS, while TNFα reduced barrier function after 1 h, 4 h and 3 days.

CONCLUSION

Long term pro-inflammatory stimuli reduce RPE viability, barrier properties and cellular function and induce pro-inflammatory cytokines and therefore may contribute directly to atrophic changes in AMD.

Validation of a Vision-Guided Mobility Assessment for RPE65-Associated Retinal Dystrophy

Purpose

To validate a vision-guided mobility assessment for individuals affected by RPE65-associated retinal dystrophy (RPE65-RD).

Methods

In this comparative cross-sectional study, 29 subjects, comprising 19 subjects with RPE65-RD and 10 normally-sighted subjects undertook three assessments of mobility: following a straight line, navigating a simple maze, and stepping over a sidewalk "kerb." Performance was quantified as the time taken to complete each assessment, number of errors made, walking speed, and percent preferred walking speed, for each assessment. Subjects also undertook assessments of visual acuity, contrast sensitivity, full-field static perimetry, and age-appropriate quality of life questionnaires. To identify the most relevant metric to quantify vision-guided mobility, we investigated repeatability, as well as convergent, discriminant, and criterion validity. We also measured the effect of illumination on mobility.

Results

Walking speed through the maze assessment best discriminated between RPE65-RD and normally-sighted subjects, with both convergent and discriminant validity. Walking speed also approached statistical significance when assessed for criterion validity (P = 0.052). Subjects with RPE65-RD had quantifiably poorer mobility at lower illumination levels. A relatively small mean difference (-0.09 m/s) was identified in comparison to a relatively large repeatability coefficient (1.10 m/s).

Conclusions

We describe a novel, quantifiable, repeatable, and valid assessment of mobility designed specifically for subjects with RPE65-RD. The assessment is sensitive to the visual impairment of individuals with RPE65-RD in low illumination, identifies the known phenotypic heterogeneity and will furthermore provide an important outcome measure for RPE65-RD.

Translational Relevance

This assessment of vision-guided mobility, validated in a dedicated cohort of subjects with RPE65-RD, is a relevant and quantifiable outcome measure for RPE65-RD.

Structural basis for carotenoid cleavage by an archaeal carotenoid dioxygenase

Apocarotenoids are important signaling molecules generated from carotenoids through the action of carotenoid cleavage dioxygenases (CCDs). These enzymes have a remarkable ability to cleave carotenoids at specific alkene bonds while leaving chemically similar sites within the polyene intact. Although several bacterial and eukaryotic CCDs have been characterized, the long-standing goal of experimentally visualizing a CCD-carotenoid complex at high resolution to explain this exquisite regioselectivity remains unfulfilled. CCD genes are also present in some archaeal genomes, but the encoded enzymes remain uninvestigated. Here, we address this knowledge gap through analysis of a metazoan-like archaeal CCD from Candidatus Nitrosotalea devanaterra (NdCCD). NdCCD was active toward β-apocarotenoids but did not cleave bicyclic carotenoids. It exhibited an unusual regiospecificity, cleaving apocarotenoids solely at the C14'-C13' alkene bond to produce β-apo-14'-carotenals. The structure of NdCCD revealed a tapered active site cavity markedly different from the broad active site observed for the retinal-forming Synechocystis apocarotenoid oxygenase (SynACO) but similar to the vertebrate retinoid isomerase RPE65. The structure of NdCCD in complex with its apocarotenoid product demonstrated that the site of cleavage is defined by interactions along the substrate binding cleft as well as selective stabilization of reaction intermediates at the scissile alkene. These data on the molecular basis of CCD catalysis shed light on the origins of the varied catalytic activities found in metazoan CCDs, opening the possibility of modifying their activity through rational chemical or genetic approaches.

Progress in treating inherited retinal diseases: Early subretinal gene therapy clinical trials and candidates for future initiatives

Due to improved phenotyping and genetic characterization, the field of 'incurable' and 'blinding' inherited retinal diseases (IRDs) has moved substantially forward. Decades of ascertainment of IRD patient data from Philadelphia and Toronto centers illustrate the progress from Mendelian genetic types to molecular diagnoses. Molecular genetics have been used not only to clarify diagnoses and to direct counseling but also to enable the first clinical trials of gene-based treatment in these diseases. An overview of the recent reports of gene augmentation clinical trials by subretinal injections is used to reflect on the reasons why there has been limited success in this early venture into therapy. These first-in human experiences have taught that there is a need for advancing the techniques of delivery of the gene products - not only for refining further subretinal trials, but also for evaluating intravitreal delivery. Candidate IRDs for intravitreal gene delivery are then suggested to illustrate some of the disorders that may be amenable to improvement of remaining central vision with the least photoreceptor trauma. A more detailed understanding of the human IRDs to be considered for therapy and the calculated potential for efficacy should be among the routine prerequisites for initiating a clinical trial.

Compound heterozygous RPE65 mutations associated with an early onset autosomal recessive retinitis pigmentosa

BACKGROUND

Retinitis pigmentosa (RP) is one of the most common form of inherited retinal dystrophies. Identification of disease-causing mutations is a prerequisite for applying targeted therapeutic approaches. The present study aimed to identify disease-associated mutations in a large Serbian family, in which two brothers have suffered from RP starting in the first decade of their lives.

METHODS

The index patient and 12 additional members of a four-generation family were analyzed. All participants underwent detailed ophthalmic examinations. Genomic DNA was isolated from family members to perform whole exome sequencing (WES) and Sanger sequencing of candidate genes.

RESULTS

An early onset RP phenotype was presented in both ocular fundi of the index patient and his brother: arteriolar attenuation, as well as retinal pigmentary changes in peripheral fundus and waxy disc pallor. Both brothers showed foveal thinning. The index patient showed epiretinal membranes in both eyes and a parafoveal cystic lesion in his right eye, whereas the brother of the index patient showed choroid folds and vitreomacular adhesion in his left eye. We identified compound heterozygous mutations in the RPE65 gene (a novel c.1338+1G>A splice donor site mutation in addition to the frame-shifting mutation c.1207_1210dup (p.Glu404Alafs*4)) using an in-house WES pipeline.

CONCLUSIONS

Evaluation of all previously described RPE65 mutations showed that the sequence variants identified in the present study located to rarely altered exons and likely effect a highly conserved region of the RPE65 protein. Gene augmentation therapies might be a promising treatment option for the patients described.

Molecular components affecting ocular carotenoid and retinoid homeostasis

The photochemistry of vision employs opsins and geometric isomerization of their covalently bound retinylidine chromophores. In different animal classes, these light receptors associate with distinct G proteins that either hyperpolarize or depolarize photoreceptor membranes. Vertebrates also use the acidic form of chromophore, retinoic acid, as the ligand of nuclear hormone receptors that orchestrate eye development. To establish and sustain these processes, animals must acquire carotenoids from the diet, transport them, and metabolize them to chromophore and retinoic acid. The understanding of carotenoid metabolism, however, lagged behind our knowledge about the biology of their receptor molecules. In the past decades, much progress has been made in identifying the genes encoding proteins that mediate the transport and enzymatic transformations of carotenoids and their retinoid metabolites. Comparative analysis in different animal classes revealed how evolutionary tinkering with a limited number of genes evolved different biochemical strategies to supply photoreceptors with chromophore. Mutations in these genes impair carotenoid metabolism and induce various ocular pathologies. This review summarizes this advancement and introduces the involved proteins, including the homeostatic regulation of their activities.

Yap1 is required for maintenance of adult RPE differentiation

Nuclear YAP1 plays a critical role in regulation of stem cell proliferation, tissue regeneration, and organ size in many types of epithelia. Due to rapid turnover of most epithelial cell types, the cytoplasmic function of YAP1 in epithelial cells has not been well studied. The retinal pigment epithelium (RPE) is a highly polarized epithelial cell type maintained at a senescence state, and offers an ideal cell model to study the active role of YAP1 in maintenance of the adult epithelial phenotype. Here, we show that the cytoplasmic function of YAP1 is essential to maintain adult RPE differentiation. Knockout of Yap1 in the adult mouse RPE caused cell depolarization and tight junction breakdown, and led to inhibition of RPE65 expression, diminishment of RPE pigments, and retraction of microvilli and basal infoldings. These changes in RPE further prompted the loss of adjacent photoreceptor outer segments and photoreceptor death, which eventually led to decline of visual function in older mice between 6 and 12 months of age. Furthermore, nuclear β-catenin and its activity were significantly increased in mutant RPE. These results suggest that YAP1 plays an important role in active inhibition of Wnt/β-catenin signaling, and is essential for downregulation of β-catenin nuclear activity and prevention of dedifferentiation of adult RPE.

An Economic Evaluation of Voretigene Neparvovec for the Treatment of Biallelic RPE65-Mediated Inherited Retinal Dystrophies in the UK

INTRODUCTION

Voretigene neparvovec (VN) is a gene therapy and the first approved pharmacological treatment for biallelic RPE65-mediated inherited retinal dystrophies (IRD), a rare condition that starts in early life and causes vision to progressively deteriorate towards complete blindness. In a phase III trial, treatment with VN significantly improved functional vision and visual function, and in October 2019 the National Institute for Health and Care Excellence (NICE) Highly Specialised Technologies (HST) process recommended VN for patients in England and Wales. We assessed the cost-effectiveness of VN compared with best supportive care (BSC) in individuals with biallelic RPE65-mediated IRD in the UK.

METHODS

A Markov model was developed to estimate the incremental cost per quality-adjusted life-year (QALY) gained for VN compared with BSC, from the perspective of the UK National Health Service and Personal Social Services. Phase III trial data were used to inform transition probabilities up to year 1, after which the treatment effect was assumed to be maintained for 40 years, followed by a decline in vision. A bespoke elicitation exercise involving clinical experts, patients and carers was conducted to estimate utility values for each model health state.

RESULTS

At list price, VN is associated with incremental costs of £612,404 and incremental QALYs of 6.4, resulting in an incremental cost-effectiveness ratio (ICER) of £95,072 per QALY gained. Voretigene neparvovec is associated with a significant undiscounted QALY gain (20.5) and is therefore eligible for additional QALY weighting under the NICE HST process; an ICER of up to £205,000 per QALY gained could be considered cost-effective under this framework.

CONCLUSION

The results of the model show VN to be a cost-effective use of healthcare resources in the UK at list price. The availability of a commercial discount in the UK (as considered in the NICE appraisal) means that in reality the ICER will be even lower. Plain language summary available for this article.

Evolutionary aspects and enzymology of metazoan carotenoid cleavage oxygenases

The carotenoids are terpenoid fat-soluble pigments produced by plants, algae, and several bacteria and fungi. They are ubiquitous components of animal diets. Carotenoid cleavage oxygenase (CCO) superfamily members are involved in carotenoid metabolism and are present in all kingdoms of life. Throughout the animal kingdom, carotenoid oxygenases are widely distributed and they are completely absent only in two unicellular organisms, Monosiga and Leishmania. Mammals have three paralogs 15,15'-β-carotene oxygenase (BCO1), 9',10'-β-carotene oxygenase (BCO2) and RPE65. The first two enzymes are classical carotenoid oxygenases: they cleave carbon‑carbon double bonds and incorporate two atoms of oxygen in the substrate at the site of cleavage. The third, RPE65, is an unusual family member, it is the retinoid isomerohydrolase in the visual cycle that converts all-trans-retinyl ester into 11-cis-retinol. Here we discuss evolutionary aspects of the carotenoid cleavage oxygenase superfamily and their enzymology to deduce what insight we can obtain from their evolutionary conservation.

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.

Late presentation of RPE65 retinopathy in three siblings

Purpose

Gene therapy for RPE65 retinopathy has been recently approved. The purpose of this study was to assess retinal structure and function in 3 siblings presenting with late-stage RPE65 retinopathy and to assess the unmet need for such therapy in Saudi Arabia.

Methods

Search of the retinal dystrophy registry at King Khaled Eye Specialist Hospital and clinical examination including multimodal retinal imaging, full-field electroretinography (ERG), dark adapted full-field stimulus sensitivity thresholds, and molecular genetic testing in 3 patients.

Results

Nine (9) patients were identified with biallelic RPE65 mutations, corresponding to a prevalence rate of 9/187 = 5% among early onset retinal dystrophies. Of these, 3 siblings (2 male and 1 female) with RPE65 retinopathy were assessed in detail, because of an unusual, late presentation. They were all over 30 years old at the time of their most recent visits and had non-recordable ERGs. The 2 male siblings presented with poor vision and paracentral loss of the inner segment ellipsoid (ISe) and focal attenuation of the outer nuclear layer (ONL) in the macula. On the other hand, the female sibling presented with 20/100 vision with preserved foveal ISe and intact ONL throughout the macula and significantly lower light sensitivity thresholds compared to her male siblings. A homozygous missense p.Arg91Trp mutation in RPE65 was identified in all. All patients were eligible for gene therapy, demonstrating a central retinal thickness of more than 100 microns on repeated examinations.

Conclusions

RPE65 retinopathy seems to be relatively common on the Arabian peninsula, and in addition it may be underdiagnosed. To the best of our knowledge, this is the first detailed presentation, including multimodal retinal imaging and electrophysiological assessment, of such patients from this region. Patients with late presentation of RPE65 retinopathy may be eligible for gene therapy, in terms of remaining retinal function and structural preservation. The therapeutic window of such therapy remains to be determined.

Electronic supplementary material

The online version of this article (10.1007/s10633-019-09745-z) contains supplementary material, which is available to authorized users.