Preserved visual function in retinal dystrophy due to hypomorphic RPE65 mutations

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.

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 www.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 www.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 www.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, www.encepp.eu. 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 www.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.

Pathogenicity reclassification of the RPE65 c.1580A>G (p.His527Arg) - a case report

BACKGROUND

It is of utmost importance to define the molecular diagnosis of patients with retinitis pigmentosa (RP) due to existing targeted therapeutic option: voretigene neparvovec.We provide clinical evidence for pathogenicity reclassification of variants of uncertain significance (VUSs) RPE65 c.1580A>G (p.His527Arg).

MATERIALS AND METHODS

A case report of a 10-year-old boy with progressive vision loss. The patient manifested disease highly suggestive of RPE65 retinal dystrophy: nyctalopia, fairly good central vision, severely depressed full-field electroretinography responses and complete loss of peripheral fundus aut ofluorescence.

RESULTS

Invitae Inherited Retinal Disorders Panel identified likely pathogenic mutation RPE65 c.499G>T (p.Asp167Tyr) and RPE65 c.1580A>G (p.His527Arg), variant of uncertain significance. Segregation analysis confirmed that these variants are in trans.

CONCLUSIONS

We conclude that the variant RPE65 c.1580A>G (p.His527Arg) has contributed to the pathologic phenotype, demonstrating its significance clearly in the case presented, and should be reclassified according to the criteria of evidence as pathogenic. Therefore, patients with this specific variant in homozygous or compound heterozygous form would likely benefit from genetic treatment based on recombinant adeno-associated virus vector, providing a working RPE65 gene to act in place of a mutated RPE65 gene.

Short-Term Outcomes of the First in Vivo Gene Therapy for RPE65-Mediated Retinitis Pigmentosa

Here, we report early treatment outcomes of gene therapy for early onset retinitis pigmentosa (RP) (Leber congenital amaurosis) associated with biallelic RPE65 mutation in a 30-year-old female patient. Initially, her visual acuity (VA) was 20/200, and her visual field (VF) was severely constricted to the center in the left eye. Her electroretinography showed nearly extinct signals. Full-field stimulus threshold test (FST) revealed diminished dark-adapted light sensitivity. Voretigene neparvovec-rzyl (VN) is the first in vivo viral gene therapy agent to be approved. At 3 months after subretinal injection of VN in the left eye, VA, VF, and FST showed sustained improvement. She did not exhibit any signs of adverse effects from the treatment. Gene therapy for RP proved to be an effective and safe treatment in an advanced case of RPE65-associatied early onset RP.

Identification of a novel compound heterozygous CYP4V2 variant in a patient with autosomal recessive retinitis pigmentosa

Retinitis pigmentosa (RP) belongs to a family of retinal disorders that is characterized by the progressive degeneration of rod and cone photoreceptors. The aim of the present study was to screen for possible disease-causing genetic variants in a non-consanguineous Chinese family with non-syndromic autosomal recessive RP. Whole-exome sequencing (WES) was performed in samples from the affected individual (the proband) and those from the two children of the proband. A novel compound heterozygous variant of c.C958T (p.R320X) and c.G1355A (p.R452H) in the Cytochrome P450 family 4 subfamily V member 2 (CYP4V2) gene was identified through WES. Subsequently, this variant was validated by direct Sanger sequencing. This compound heterozygous variant was found to be absent from other unaffected family members and 400 ethnically-matched healthy control individuals. In addition, this compound variant was co-segregated with the RP phenotype in an autosomal recessive manner. In silico analysis revealed that both c.C958T (p.R320X) and c.G1355A (p.R452H) could compromise the protein function of CYP4V2. These results strongly suggest this compound variant to be a disease-causing variant, which expands upon the spectrum of currently known CYP4V2 genetic variants associated with retinal diseases.

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.

Congenital stationary night blindness: an update and review of the disease spectrum in Saudi Arabia

Congenital stationary night blindness (CSNB) is a group of rare, mainly stationary disorders of the retina, resulting from dysfunction of several specific and essential visual processing mechanisms. The inheritance is often recessive and as such, CSNB may be more common among populations with a high degree of consanguinity. Here, we present a topic update and a review of the clinical and molecular genetic spectrum of CSNB in Saudi Arabia. Since a major review article on CSNB in 2015, which described 17 genes underlying CSNB, an additional four genes have been incriminated in autosomal recessive CSNB: RIMS2, GNB3, GUCY2D and ABCA4. These have been associated with syndromic cone-rod synaptic disease, ON bipolar cell dysfunction with reduced cone sensitivity, CSNB with dysfunction of the phototransduction (Riggs type) and CSNB with cone-rod dystrophy, respectively. In Saudi Arabia, a total of 24 patients with CSNB were identified, using a combination of literature search and retrospective study of previously unpublished cases. Recessive mutations in TRPM1 and CABP4 accounted for the majority of cases (5 and 13 for each gene, respectively). These genes were associated with complete (cCSNB) and incomplete (icCSNB), respectively, and were associated with high myopia in the former and hyperopia in the latter. Four novel mutations were identified. For the first time, we describe the fundus albipunctatus in two patients from Saudi Arabia, caused by recessive mutation in RDH5 and RPE65, where the former in addition featured findings compatible with cone dystrophy. No cases were identified with any dominantly inherited CSNB.

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.

Clinical and functional analyses of AIPL1 variants reveal mechanisms of pathogenicity linked to different forms of retinal degeneration

Disease-causing sequence variants in the highly polymorphic AIPL1 gene are associated with a broad spectrum of inherited retinal diseases ranging from severe autosomal recessive Leber congenital amaurosis to later onset retinitis pigmentosa. AIPL1 is a photoreceptor-specific co-chaperone that interacts with HSP90 to facilitate the stable assembly of retinal cGMP phosphodiesterase, PDE6. In this report, we establish unequivocal correlations between patient clinical phenotypes and in vitro functional assays of uncharacterized AIPL1 variants. We confirm that missense and nonsense variants in the FKBP-like and tetratricopeptide repeat domains of AIPL1 lead to the loss of both HSP90 interaction and PDE6 activity, confirming these variants cause LCA. In contrast, we report the association of p.G122R with milder forms of retinal degeneration, and show that while p.G122R had no effect on HSP90 binding, the modulation of PDE6 cGMP levels was impaired. The clinical history of these patients together with our functional assays suggest that the p.G122R variant is a rare hypomorphic allele with a later disease onset, amenable to therapeutic intervention. Finally, we report the primate-specific proline-rich domain to be dispensable for both HSP90 interaction and PDE6 activity. We conclude that variants investigated in this domain do not cause disease, with the exception of p.A352_P355del associated with autosomal dominant cone-rod dystrophy.

Retinal Structure in RPE65-Associated Retinal Dystrophy

Purpose

RPE65-associated retinal dystrophy (RPE65-RD) is an early onset, progressive, severe retinal dystrophy. We sought to characterize the natural history of retinal degeneration in affected individuals.

Methods

We performed cross-sectional and longitudinal quantitative and qualitative assessments of retinal architecture in RPE65-RD using spectral domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF) imaging. Twenty-six subjects (mean age, 14.8 years, range, 5-24 years) with RPE65-RD underwent SD-OCT and FAF imaging, of whom 14 subjects were followed up over time. Foveal thickness (FT), outer nuclear layer thickness (ONLT), ellipsoid zone width (EZW), and ellipsoid zone area (EZA) were calculated where possible. These were correlated with age, best corrected visual acuity (BCVA), and central 30° retinal sensitivity (V30). Intra-observer agreement, test-retest repeatability, and interocular symmetry were also investigated.

Results

We identified structural interocular symmetry, the presence of autofluorescence in 46% (12/26) of subjects, and the presence of foveal hypoplasia (associated with significantly worse BCVA) in 50% of subjects. EZW and EZA were measurable in 67% (35/52) and 37% (19/52) of eyes, respectively, with both demonstrating good agreement on repeated measurement. The annual rate of progression using EZW was -300.63 µm/year, and -1.17 mm2/year in EZA. EZW was found to have a statistically significant correlation with BCVA and V30.

Conclusions

We identified the presence of autofluorescence in half of our subjects, with foveal hypoplasia also noted in half of our cohort. EZW, and to a lesser extent EZA, were robust measures of retinal degeneration and represent valuable metrics to determine the impact of intervention. (ClinicalTrials.gov number NCT02714816.).

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.