Leber congenital amaurosis: comprehensive survey of the genetic heterogeneity, refinement of the clinical definition, and genotype-phenotype correlations as a strategy for molecular diagnosis

Screening for Autism Spectrum Disorder in Children and Adolescents With Leber's Congenital Amaurosis

PURPOSE

To investigate autism spectrum disorder (ASD) indicators in children with Leber congenital amaurosis (LCA).

STUDY DESIGN

Cross-sectional, prospective, and correlational study.

METHODS

Setting: It was conducted at the Institute of Ocular Genetics, the Department of Ophthalmology at Federal University of São Paulo (UNIFESP), and the Autism Spectrum Disorder Laboratory, in São Paulo, Brazil.

PATIENT POPULATION

Participants included patients aged 2 to 16 years with LCA confirmed by genetic testing. There were 20 individuals with ciliopathies (LCA cilio) and 26 with other gene mutations (LCA other). As intervention, the instrument used for ASD screening was the Autism Behavior Checklist (ABC). Marginal descriptive analyses, non-parametric tests, and a linear regression model were conducted. The main outcomes were the scores on the tests correlated with clinical variables.

RESULTS

Of the 46 participants, 6 had ASD scores. There was no statistically significant correlation between the different groups (LCA cilio and LCA other) (p = 0.438). There was no statistically significant correlation between age and ASD (p = 0.308). However, there was a statistically significant correlation between visual acuity and ASD (p = 0.008) and between male gender and ASD (p = 0.025).

CONCLUSIONS

This study suggests that there is no correlation between LCA cilio, LCA other and ASD. These findings bring new insights to the existing literature, which previously lacked robust data on the relationship between LCA and ASD. These data demonstrate that visual acuity plays a crucial role in the development of children with visual impairment as poorer visual acuity is associated with a higher incidence of ASD. Based on this study, early interventions can be designed, especially for individuals without light perception, with the aim of maximizing their developmental outcomes. Furthermore, such data indicates that any improvement in visual acuity outcomes in treatment clinical trials become relevant for child development. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Gene and cell therapy of human genetic diseases: Recent advances and future directions

Disruptions in normal development and the emergence of health conditions often result from the malfunction of vital genes in the human body. Decades of scientific research have focused on techniques to modify or substitute defective genes with healthy alternatives, marking a new era in disease treatment, prevention and cure. Recent strides in science and technology have reshaped our understanding of disorders, medication development and treatment recommendations, with human gene and cell therapy at the forefront of this transformative shift. Its primary objective is the modification of genes or adjustment of cell behaviour for therapeutic purposes. In this review, we focus on the latest advances in gene and cell therapy for treating human genetic diseases, with a particular emphasis on FDA and EMA-approved therapies and the evolving landscape of genome editing. We examine the current state of innovative gene editing technologies, particularly the CRISPR-Cas systems. As we explore the progress, ethical considerations and prospects of these innovations, we gain insight into their potential to revolutionize the treatment of genetic diseases, along with a discussion of the challenges associated with their regulatory pathways. This review traces the origins and evolution of these therapies, from conceptual ideas to practical clinical applications, marking a significant milestone in the field of medical science.

Relationship between genotype, phenotype, and refractive status in patients of inherited retinal degeneration

BACKGROUND

To elucidate the relationship between inherited retinal disease, visual acuity and refractive error development in Asian patients.

SUBJECTS

Five hundred phakic eyes with refractive data were analysed in this retrospective cohort. Diseases were categorized by clinical phenotypes, and the prevalent genotypes identified in the Taiwan Inherited Retinal Degeneration Project were analysed. Consecutive surveys in Taiwan have provided the rates of myopia in the general population.

RESULTS

No differences were observed among the disease phenotypes with respect to myopia (P = 0.098) and high myopia rates (P = 0.037). The comparison of refractive error between retinitis pigmentosa and diseases mainly affecting the central retina showed no difference, and the refraction analyses in diseases of different onset ages yielded no significance. Moreover, there was no difference in the myopia rate between the diseases and general population. Among the genotypes, a higher spherical equivalent was seen in RPGR and PROM1-related patients and emmetropic trends were observed in patients with CRB1 and PRPF31 mutations. Furthermore, significantly poorer visual acuity was found in ABCA4, CRB1 and PROM1-related patients, and more preserved visual acuity was seen in patients with EYS, USH2A, and RDH12 mutations.

CONCLUSIONS

No significant differences were observed in visual acuity, refractive state and myopia rate between patients with inherited retinal disease and the general population, and different subtypes of inherited retinal disease shared similar refractive state, except for higher cylindrical dioptres found in patients with Leber's congenital amaurosis. The heterogeneity of disease-causing genes in Asian patients may lead to variable refractive state.

The Extraordinary Phenotypic and Genetic Variability of Retinal and Macular Degenerations: The Relevance to Therapeutic Developments

Inherited retinal diseases (IRDs) are a clinically and genetically heterogeneous group of rare conditions leading to various degrees of visual handicap and to progressive blindness in more severe cases. Besides visual rehabilitation, educational, and socio-professional support, there are currently limited therapeutic options, but the approval of the first gene therapy product for RPE65-related IRDs raised hope for therapeutic innovations. Such developments are facing obstacles intrinsic to the disease and the affected tissue including the extreme phenotypic and genetic variability of IRDs and the fine tuning of visual processing through the complex architecture of the postmitotic neural retina. A precise phenotypic characterization is required prior to genetic testing, which now relies on high-throughput sequencing. Their challenges will be discussed within this article as well as their implications in clinical trial design.

Clinical, Ophthalmic, and Genetic Characterization of RPGRIP1-Associated Leber Congenital Amaurosis/Early-Onset Severe Retinal Dystrophy

PURPOSE

To present the clinical characteristics, retinal features, natural history, and genetics of RPGRIP1-associated early-onset severe retinal dystrophy (EOSRD)/Leber congenital amaurosis (LCA).

DESIGN

Retrospective case series.

METHODS

Review of clinical notes, multimodal retinal imaging, and molecular diagnosis of 18 patients (17 families) with EOSRD/LCA and disease-causing variants in RPGRIP1.

RESULTS

The mean age of visual symptoms onset was 0.87 ± 1 year (birth to 3 years), and the mean age at baseline visit was 11.4 ± 10.2 years (1-39 years). At the baseline visit, 44% of patients were legally blind (range, 2-39 years), and there was no significant association found between age and best-corrected visual acuity (BCVA) in cross-sectional analysis. Retinal evaluation showed an abolished electroretinogram or a cone-rod dystrophy pattern, no or minimal pigment deposits, a hyperautofluorescent ring at the posterior pole, and a largely preserved central macular architecture, with retained outer nuclear layer and ellipsoid zone island into adulthood. Eleven variants (48%) were previously unreported, and 13 families (76%) had a double-null (DN) genotype. Twelve patients (67%) had follow-up assessments over a 15.7 ± 9.5-year period. The rate of BCVA decline was 0.02 logarithm of the minimum angle of resolution (1 letter)/year.

CONCLUSIONS

RPGRIP1 EOSRD/LCA often presents at birth or early infancy, with nystagmus, decreased visual acuity, hyperopia, and photophobia. Patients with a DN genotype may develop symptoms earlier and have worse vision. Multimodal imaging may show a hyperautofluorescent posterior pole ring and relatively preserved central macular architecture, suggesting that the condition is a promising candidate for gene supplementation.

Metabolomics facilitates differential diagnosis in common inherited retinal degenerations by exploring their profiles of serum metabolites

The diagnosis of inherited retinal degeneration (IRD) is challenging owing to its phenotypic and genotypic complexity. Clinical information is important before a genetic diagnosis is made. Metabolomics studies the entire picture of bioproducts, which are determined using genetic codes and biological reactions. We demonstrated that the common diagnoses of IRD, including retinitis pigmentosa (RP), cone-rod dystrophy (CRD), Stargardt disease (STGD), and Bietti's crystalline dystrophy (BCD), could be differentiated based on their metabolite heatmaps. Hundreds of metabolites were identified in the volcano plot compared with that of the control group in every IRD except BCD, considered as potential diagnosing markers. The phenotypes of CRD and STGD overlapped but could be differentiated by their metabolomic features with the assistance of a machine learning model with 100% accuracy. Moreover, EYS-, USH2A-associated, and other RP, sharing considerable similar characteristics in clinical findings, could also be diagnosed using the machine learning model with 85.7% accuracy. Further study would be needed to validate the results in an external dataset. By incorporating mass spectrometry and machine learning, a metabolomics-based diagnostic workflow for the clinical and molecular diagnoses of IRD was proposed in our study.

Transcriptional precision in photoreceptor development and diseases - Lessons from 25 years of CRX research

The vertebrate retina is made up of six specialized neuronal cell types and one glia that are generated from a common retinal progenitor. The development of these distinct cell types is programmed by transcription factors that regulate the expression of specific genes essential for cell fate specification and differentiation. Because of the complex nature of transcriptional regulation, understanding transcription factor functions in development and disease is challenging. Research on the Cone-rod homeobox transcription factor CRX provides an excellent model to address these challenges. In this review, we reflect on 25 years of mammalian CRX research and discuss recent progress in elucidating the distinct pathogenic mechanisms of four CRX coding variant classes. We highlight how in vitro biochemical studies of CRX protein functions facilitate understanding CRX regulatory principles in animal models. We conclude with a brief discussion of the emerging systems biology approaches that could accelerate precision medicine for CRX-linked diseases and beyond.

Novel CRB1 pathogenic variant in Chuuk families with Leber congenital amaurosis

The purpose of this article is to determine the cause of Leber congenital amaurosis (LCA) in Chuuk state, Federated States of Micronesia (FSM). In this prospective observational case series, five patients with early-onset vision loss were examined in Chuuk state, FSM, during an ocular genetics visit to study the elevated incidence of microphthalmia. Because of their low vision these patients were incorrectly assumed to have microphthalmia. A complete ophthalmological exam established a clinical diagnosis of LCA. Candidate gene exons were sequenced with a targeted retinal dystrophy panel. Five subjects in three related families were diagnosed with LCA. All five were from Tonoas Island, within the Chuuk Lagoon, with ages ranging from 6 months to 16 years. DNA sequencing of affected individuals revealed a homozygous CRB1 NM_201253.3:c.3134del pathogenic variant, which was heterozygous in their parents. CRB1 genotypes were confirmed by a PCR restriction assay. We report identification of a founder pathogenic variant in CRB1 responsible for autosomal recessive LCA in this isolated community. This discovery will lead to appropriate recurrence risk counseling.

A novel nonsense variant (c.1499C>G) in CRB1 caused Leber congenital amaurosis-8 in a Chinese family and a literature review

Background

Leber’s congenital amaurosis (LCA) is a severe hereditary retinopathy disease that is characterized by early and severe reduction of vision, nystagmus, and sluggish or absent pupillary responses. To date, the pathogenesis of LCA remains unclear, and the majority of cases are caused by autosomal recessive inheritance. In this study, we explored the variant in the Crumbs homologue 1 (CRB1) gene in a Chinese family with LCA.

Methods

We conducted comprehensive ocular examinations and collected 5 ml of blood samples from members of a Chinese family with LCA. A pathogenic variant was identified by capturing (the panel in NGS) and Sanger sequencing validation.

Results

A nonsense variant (c.1499C>G) in the 6th exon of CRB1 gene in a Chinese family with LCA was identified, which predicted a change in the protein p. S500*, may lead to loss of gene function. We summarized the 76 variants reported thus far in CRB1 that caused LCA8.

Conclusions

This study reported a novel variant c.1499C>G (p. S500*) of the CRB1 gene occurred in a Chinese family with LCA, thus expanding the spectrum of CRB1 variants causing LCA.

Clinical and genetic spectrums of 413 North African families with inherited retinal dystrophies and optic neuropathies

Background

Inherited retinal dystrophies (IRD) and optic neuropathies (ION) are the two major causes world-wide of early visual impairment, frequently leading to legal blindness. These two groups of pathologies are highly heterogeneous and require combined clinical and molecular diagnoses to be securely identified. Exact epidemiological studies are lacking in North Africa, and genetic studies of IRD and ION individuals are often limited to case reports or to some families that migrated to the rest of the world. In order to improve the knowledge of their clinical and genetic spectrums in North Africa, we reviewed published data, to illustrate the most prevalent pathologies, genes and mutations encountered in this geographical region, extending from Morocco to Egypt, comprising 200 million inhabitants.

Main body

We compiled data from 413 families with IRD or ION together with their available molecular diagnosis. The proportion of IRD represents 82.8% of index cases, while ION accounted for 17.8%. Non-syndromic IRD were more frequent than syndromic ones, with photoreceptor alterations being the main cause of non-syndromic IRD, represented by retinitis pigmentosa, Leber congenital amaurosis, and cone-rod dystrophies, while ciliopathies constitute the major part of syndromic-IRD, in which the Usher and Bardet Biedl syndromes occupy 41.2% and 31.1%, respectively. We identified 71 ION families, 84.5% with a syndromic presentation, while surprisingly, non-syndromic ION are scarcely reported, with only 11 families with autosomal recessive optic atrophies related to OPA7 and OPA10 variants, or with the mitochondrial related Leber ION. Overall, consanguinity is a major cause of these diseases within North African countries, as 76.1% of IRD and 78.8% of ION investigated families were consanguineous, explaining the high rate of autosomal recessive inheritance pattern compared to the dominant one. In addition, we identified many founder mutations in small endogamous communities.

Short conclusion

As both IRD and ION diseases constitute a real public health burden, their under-diagnosis in North Africa due to the absence of physicians trained to the identification of inherited ophthalmologic presentations, together with the scarcity of tools for the molecular diagnosis represent major political, economic and health challenges for the future, to first establish accurate clinical diagnoses and then treat patients with the emergent therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02340-7.

RPE65 c.393T>A, p.(Asn131Lys): Novel Sequence Variant Detected

Background

Leber congenital amaurosis (LCA) is a monogenic, but genetically heterogenous disease, and at least 27 genes are implicated. This case report is aimed at providing evidence to link the novel variant RPE65 c.393T>A, p.(Asn131Lys), variant of uncertain significance (VUS), to clinical phenotype and to set the ground for objective assignment of pathogenicity confidence. Case Presentation. A case report of a female patient with LCA who manifested with nystagmus, night blindness, profound visual deficiency, and peripheral involvement of the retina consistent with RPE65 dystrophy. A thorough clinical examination, diagnostic evaluation, and genetic testing were performed. The patient was a compound heterozygote in trans form: RPE65 c.304G>T, p.(Glu102∗) pathogenic, and RPE65 c.393T>A, p.(Asn131Lys), VUS. The latter variant is absent in healthy controls and is considered harmful on in silico prediction.

Conclusions

We conclude that RPE65 c.393T>A, p.(Asn131Lys) contributed to the pathologic phenotype, demonstrating its significance clearly in the case presented, and should be reclassified according to the criteria of evidence as likely pathogenic. This being the case, patients with this specific variant are likely candidates for genetic treatment.

Epidemiology of Mutations in the 65-kDa Retinal Pigment Epithelium (RPE65) Gene-Mediated Inherited Retinal Dystrophies: A Systematic Literature Review

INTRODUCTION

Inherited retinal dystrophies (IRDs) represent a genetically diverse group of progressive, visually debilitating diseases. Adult and paediatric patients with vision loss due to IRD caused by biallelic mutations in the 65-kDa retinal pigment epithelium (RPE65) gene are often clinically diagnosed as retinitis pigmentosa (RP), and Leber congenital amaurosis (LCA). This study aimed to understand the epidemiological landscape of RPE65 gene-mediated IRD through a systematic review of the literature, as the current evidence base for its epidemiology is very limited.

METHODS

Medline, Embase, and other databases were searched for articles on the epidemiology of RPE65 gene-mediated IRDs from inception until June 2021. Studies were included if they were original research articles reporting the epidemiology of RP and LCA and/or proportion of RPE65 gene mutations in these clinically diagnosed or molecularly confirmed IRDs patients.

RESULTS

A total of 100 studies with relevant data were included in this systematic review. The range for prevalence of LCA and RP in the literature was 1.20-2.37 and 11.09-26.43 per 100,000, respectively. The proportion of RPE65 mutations in clinically diagnosed patients with LCA was found to be between ~ 2-16% within the US and major European countries (France, Germany, Italy, Spain, and the UK). This range was also comparable to our findings in the Asian region for RPE65-LCA (1.26-16.67%). Similarly, for these European countries, RPE65-RP was estimated between 0.23 and 1.94%, and RPE65-IRD range was 1.2-14%. Further, in the Americas region, mutations in RPE65 were reported to cause 1-3% of RP and 0.8-3.7% of IRD cases. Lastly, the RPE65-IRD range was 4.81-8% in the Middle East region.

CONCLUSIONS

There are significant variations in reporting of RPE65 proportions within countries as well as regions. Generating robust epidemiological evidence on RPE65 gene-mediated IRDs would be fundamental to support rare disease awareness, timely therapeutic intervention, and public health decision-making.

GUCY2D-Related Retinal Dystrophy with Autosomal Dominant Inheritance—A Multicenter Case Series and Review of Reported Data

To report the clinical phenotype and associated genotype of a European patient cohort with GUCY2D-related autosomal-dominant (AD) cone–/cone–rod dystrophy (COD/CORD), we retrospectively analyzed 25 patients (17 female, range 12–68) with GUCY2D-related AD-COD/CORD from three major academic centers in Europe and reviewed the previously published data of 148 patients (visual acuity (VA), foveal thickness, age of first symptoms, and genetic variant). Considering all the patients, the onset of first symptoms was reported at a median age of 7 years (interquartile range 5–19 years, n = 78), and mainly consisted of reduced VA, photophobia and color vision abnormality. The disease showed a high degree of inter-eye symmetry in terms of VA (n = 165, Spearman’s ρ = 0.85, p < 0.0001) and foveal thickness (Spearman’s ρ = 0.96, n = 38, p < 0.0001). Disease progression was assessed by plotting VA as a function of age (n = 170). A linear best-fit analysis suggested a loss of 0.17 logMAR per decade (p < 0.0001). We analyzed the largest cohort described so far (n = 173), and found that the most common mutations were p.(Arg838Cys) and p.(Arg838His). Furthermore, the majority of patients suffered severe vision loss in adulthood, highlighting a window of opportunity for potential intervention. The emerging patterns revealed by this study may aid in designing prospective natural history studies to further define endpoints for future interventional trials.

A novel c.1937T>C (p.Leu646Pro) missense mutation in a patient with Leber congenital amaurosis

Over 21 genes have been associated with the inherited retinal dystrophy, Leber congenital amaurosis (LCA). A comprehensive genotype-phenotype correlation in such heterogenous cases helps guide further genetic studies and therapies. We report 2 children (10-month-old girl and an 8-month-old boy) who presented with low vision in the first year of life. Both patients manifested nystagmus, sluggish pupillary reactions, hyperopia, and normal fundus. Focussed exome sequencing was performed because LCA was suspected. A novel c.1937T>C (p.Leu646Pro) missense mutation was found in exon 9 of the tyrosine kinase domain of the GUCY2D gene in both patients.

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.

CRB1-Related Retinal Dystrophies in a Cohort of 50 Patients: A Reappraisal in the Light of Specific Müller Cell and Photoreceptor CRB1 Isoforms

Pathogenic variants in CRB1 lead to diverse recessive retinal disorders from severe Leber congenital amaurosis to isolated macular dystrophy. Until recently, no clear phenotype-genotype correlation and no appropriate mouse models existed. Herein, we reappraise the phenotype-genotype correlation of 50 patients with regards to the recently identified CRB1 isoforms: a canonical long isoform A localized in Müller cells (12 exons) and a short isoform B predominant in photoreceptors (7 exons). Twenty-eight patients with early onset retinal dystrophy (EORD) consistently had a severe Müller impairment, with variable impact on the photoreceptors, regardless of isoform B expression. Among them, two patients expressing wild type isoform B carried one variant in exon 12, which specifically damaged intracellular protein interactions in Müller cells. Thirteen retinitis pigmentosa patients had mainly missense variants in laminin G-like domains and expressed at least 50% of isoform A. Eight patients with the c.498_506del variant had macular dystrophy. In one family homozygous for the c.1562C>T variant, the brother had EORD and the sister macular dystrophy. In contrast with the mouse model, these data highlight the key role of Müller cells in the severity of CRB1-related dystrophies in humans, which should be taken into consideration for future clinical trials.

Retinal Degeneration Associated With RPGRIP1: A Review of Natural History, Mutation Spectrum, and Genotype-Phenotype Correlation in 228 Patients

Purpose:RPGRIP1 encodes a ciliary protein expressed in the photoreceptor connecting cilium. Mutations in this gene cause ∼5% of Leber congenital amaurosis (LCA) worldwide, but are also associated with cone–rod dystrophy (CRD) and retinitis pigmentosa (RP) phenotypes. Our purpose was to clinically characterize RPGRIP1 patients from our cohort, collect clinical data of additional RPGRIP1 patients reported previously in the literature, identify common clinical features, and seek genotype–phenotype correlations.

Methods: Clinical data were collected from 16 patients of our cohort and 212 previously reported RPGRIP1 patients and included (when available) family history, best corrected visual acuity (BCVA), refraction, comprehensive ocular examination, optical coherence tomography (OCT) imaging, visual fields (VF), and full-field electroretinography (ffERG).

Results: Out of 228 patients, the majority (197, 86%) were diagnosed with LCA, 18 (7%) with RP, and 13 (5%) with CRD. Age of onset was during early childhood (n = 133, average of 1.7 years). All patients but 6 had moderate hyperopia (n = 59, mean of 4.8D), and average BCVA was 0.06 Snellen (n = 124; only 10 patients had visual acuity [VA] > 0.10 Snellen). On funduscopy, narrowing of blood vessels was noted early in life. Most patients had mild bone spicule-like pigmentation starting in the midperiphery and later encroaching upon the posterior pole. OCT showed thinning of the outer nuclear layer (ONL), while cystoid changes and edema were relatively rare. VF were usually very constricted from early on. ffERG responses were non-detectable in the vast majority of cases. Most of the mutations are predicted to be null (363 alleles), and 93 alleles harbored missense mutations. Missense mutations were identified only in two regions: the RPGR-interacting domain and the C2 domains. Biallelic null mutations are mostly associated with a severe form of the disease, whereas biallelic missense mutations usually cause a milder disease (mostly CRD).

Conclusion: Our results indicate that RPGRIP1 biallelic mutations usually cause severe retinal degeneration at an early age with a cone–rod pattern. However, most of the patients exhibit preservation of some (usually low) BCVA for a long period and can potentially benefit from gene therapy. Missense changes appear only in the conserved domains and are associated with a milder phenotype.

Retinal pigment epithelium 65 kDa protein (RPE65): An update

Vertebrate vision critically depends on an 11-cis-retinoid renewal system known as the visual cycle. At the heart of this metabolic pathway is an enzyme known as retinal pigment epithelium 65 kDa protein (RPE65), which catalyzes an unusual, possibly biochemically unique, reaction consisting of a coupled all-trans-retinyl ester hydrolysis and alkene geometric isomerization to produce 11-cis-retinol. Early work on this isomerohydrolase demonstrated its membership to the carotenoid cleavage dioxygenase superfamily and its essentiality for 11-cis-retinal production in the vertebrate retina. Three independent studies published in 2005 established RPE65 as the actual isomerohydrolase instead of a retinoid-binding protein as previously believed. Since the last devoted review of RPE65 enzymology appeared in this journal, major advances have been made in a number of areas including our understanding of the mechanistic details of RPE65 isomerohydrolase activity, its phylogenetic origins, the relationship of its membrane binding affinity to its catalytic activity, its role in visual chromophore production for rods and cones, its modulation by macromolecules and small molecules, and the involvement of RPE65 mutations in the development of retinal diseases. In this article, I will review these areas of progress with the goal of integrating results from the varied experimental approaches to provide a comprehensive picture of RPE65 biochemistry. Key outstanding questions that may prove to be fruitful future research pursuits will also be highlighted.

Emerging evidence implicating a role for neurexins in neurodegenerative and neuropsychiatric disorders

Synaptopathies are brain disorders characterized by dysfunctional synapses, which are specialized junctions between neurons that are essential for the transmission of information. Synaptic dysfunction can occur due to mutations that alter the structure and function of synaptic components or abnormal expression levels of a synaptic protein. One class of synaptic proteins that are essential to their biology are cell adhesion proteins that connect the pre- and post-synaptic compartments. Neurexins are one type of synaptic cell adhesion molecule that have, recently, gained more pathological interest. Variants in both neurexins and their common binding partners, neuroligins, have been associated with several neuropsychiatric disorders. In this review, we summarize some of the key physiological functions of the neurexin protein family and the protein networks they are involved in. Furthermore, examination of published literature has implicated neurexins in both neuropsychiatric and neurodegenerative disorders. There is a clear link between neurexins and neuropsychiatric disorders, such as autism spectrum disorder and schizophrenia. However, multiple expression studies have also shown changes in neurexin expression in several neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Therefore, this review highlights the potential importance of neurexins in brain disorders and the importance of doing more targeted studies on these genes and proteins.

Deciphering the genetic architecture and ethnographic distribution of IRD in three ethnic populations by whole genome sequence analysis

Patients with inherited retinal dystrophies (IRDs) were recruited from two understudied populations: Mexico and Pakistan as well as a third well-studied population of European Americans to define the genetic architecture of IRD by performing whole-genome sequencing (WGS). Whole-genome analysis was performed on 409 individuals from 108 unrelated pedigrees with IRDs. All patients underwent an ophthalmic evaluation to establish the retinal phenotype. Although the 108 pedigrees in this study had previously been examined for mutations in known IRD genes using a wide range of methodologies including targeted gene(s) or mutation(s) screening, linkage analysis and exome sequencing, the gene mutations responsible for IRD in these 108 pedigrees were not determined. WGS was performed on these pedigrees using Illumina X10 at a minimum of 30X depth. The sequence reads were mapped against hg19 followed by variant calling using GATK. The genome variants were annotated using SnpEff, PolyPhen2, and CADD score; the structural variants (SVs) were called using GenomeSTRiP and LUMPY. We identified potential causative sequence alterations in 61 pedigrees (57%), including 39 novel and 54 reported variants in IRD genes. For 57 of these pedigrees the observed genotype was consistent with the initial clinical diagnosis, the remaining 4 had the clinical diagnosis reclassified based on our findings. In seven pedigrees (12%) we observed atypical causal variants, i.e. unexpected genotype(s), including 4 pedigrees with causal variants in more than one IRD gene within all affected family members, one pedigree with intrafamilial genetic heterogeneity (different affected family members carrying causal variants in different IRD genes), one pedigree carrying a dominant causative variant present in pseudo-recessive form due to consanguinity and one pedigree with a de-novo variant in the affected family member. Combined atypical and large structural variants contributed to about 20% of cases. Among the novel mutations, 75% were detected in Mexican and 50% found in European American pedigrees and have not been reported in any other population while only 20% were detected in Pakistani pedigrees and were not previously reported. The remaining novel IRD causative variants were listed in gnomAD but were found to be very rare and population specific. Mutations in known IRD associated genes contributed to pathology in 63% Mexican, 60% Pakistani and 45% European American pedigrees analyzed. Overall, contribution of known IRD gene variants to disease pathology in these three populations was similar to that observed in other populations worldwide. This study revealed a spectrum of mutations contributing to IRD in three populations, identified a large proportion of novel potentially causative variants that are specific to the corresponding population or not reported in gnomAD and shed light on the genetic architecture of IRD in these diverse global populations.

Whole exome sequencing in 17 consanguineous Iranian pedigrees expands the mutational spectrum of inherited retinal dystrophies

Inherited retinal dystrophies (IRDs) constitute one of the most heterogeneous groups of Mendelian human disorders. Using autozygome-guided next-generation sequencing methods in 17 consanguineous pedigrees of Iranian descent with isolated or syndromic IRD, we identified 17 distinct genomic variants in 11 previously-reported disease genes. Consistent with a recessive inheritance pattern, as suggested by pedigrees, variants discovered in our study were exclusively bi-allelic and mostly in a homozygous state (in 15 families out of 17, or 88%). Out of the 17 variants identified, 5 (29%) were never reported before. Interestingly, two mutations (GUCY2D:c.564dup, p.Ala189ArgfsTer130 and TULP1:c.1199G > A, p.Arg400Gln) were also identified in four separate pedigrees (two pedigrees each). In addition to expanding the mutational spectrum of IRDs, our findings confirm that the traditional practice of endogamy in the Iranian population is a prime cause for the appearance of IRDs.

Inducible Pluripotent Stem Cells to Model and Treat Inherited Degenerative Diseases of the Outer Retina: 3D-Organoids Limitations and Bioengineering Solutions

Inherited retinal degenerations (IRD) affecting either photoreceptors or pigment epithelial cells cause progressive visual loss and severe disability, up to complete blindness. Retinal organoids (ROs) technologies opened up the development of human inducible pluripotent stem cells (hiPSC) for disease modeling and replacement therapies. However, hiPSC-derived ROs applications to IRD presently display limited maturation and functionality, with most photoreceptors lacking well-developed outer segments (OS) and light responsiveness comparable to their adult retinal counterparts. In this review, we address for the first time the microenvironment where OS mature, i.e., the subretinal space (SRS), and discuss SRS role in photoreceptors metabolic reprogramming required for OS generation. We also address bioengineering issues to improve culture systems proficiency to promote OS maturation in hiPSC-derived ROs. This issue is crucial, as satisfying the demanding metabolic needs of photoreceptors may unleash hiPSC-derived ROs full potential for disease modeling, drug development, and replacement therapies.

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.

Gene therapy in retinal diseases: A review

Over 2 million people worldwide are suffering from gene-related retinal diseases, inherited or acquired, and over 270 genes have been identified which are found to be responsible for these conditions. This review article touches upon the mechanisms of gene therapy, various enzymes of the visual cycle responsible for different genetic diseases, Luxturna—the first US Food and Drug Administration (FDA)-approved therapeutic gene product, and several ongoing trials of gene therapy for age-related macular degeneration. Gene therapy has tremendous potential for retinal conditions due to its ease of accessibility, immune-privileged status, and tight blood-retinal barriers, limiting systemic side effects of the drug. In recent years, advances in gene therapy in retinal conditions have increasing significantly, with progress in cell-specific targeting and transduction efficiency of gene products through the use of adeno-associated viral vectors (AAVs), suggesting that even greater success in future clinical trials is possible.

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.

Investigation of genotype-phenotype relationship in Turkish patients with inherited retinal disease by next generation sequencing

BACKGROUND

Inherited retinal dystrophies (IRDs) are a group of retinal diseases genetically and clinically highly heterogeneous and associated with more than 300 genes. This study aims to investigate the genetic basis of Turkish patients with IRDs.

MATERIALS AND METHODS

In the study, genes related to retinal diseases in 86 IRDs patients were analyzed using the Next Generations Sequencing method (NGS).

RESULTS

The mean age of 86 patients was 35 and the mean age at diagnosis was 18. There was consanguinity between the parents of 62% of these patients. Fifty-six retinal disease-associated genes of 46 patients and 230 retinal disease-associated genes of 40 patients were examined. Genetic analysis provides a molecular diagnosis in a total of 53 (61.6%) patients. The genes responsible for the IRDs phenotype were frequently identified as ABCA4 (25%), EYS (11%), and RDH12 (9%). There was no significant difference between those with and without a molecular diagnosis in terms of demographic characteristics and family history.

CONCLUSIONS

Determination of genetic cause by NGS method in IRDs subgroups that are difficult to define by ophthalmic examination ensures that patients receive accurate diagnosis, treatment and counseling. This study contributed to the understanding of the genotype-phenotype relationship of Turkish patients with IRDs.

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.

Spectrum of Disease Severity in Nonsyndromic Patients With Mutations in the CEP290 Gene: A Multicentric Longitudinal Study

Purpose

The purpose of this study was to perform a detailed longitudinal phenotyping and genetic characterization of 32 Italian patients with a nonsyndromic retinal dystrophy and mutations in the CEP290 gene.

Methods

We reviewed the clinical history and examinations of 32 patients with a nonsyndromic retinal dystrophy due to mutations in the CEP290 gene, followed up (mean follow-up: 5.9 years) at 3 Italian centers. The clinical examinations included: best corrected visual acuity (BCVA), optical coherence tomography (OCT), and full-field electroretinogram (ERG).

Results

Patients (mean age = 19.0 ± 3.4 years) had a mean BCVA of 1.73 ± 0.20 logMAR. Longitudinal analysis of BCVA showed a nonsignificant decline. Central retinal thickness (CRT) declined significantly with age at an exponential rate of 1.0%/year (P = 0.001). At disease onset, most patients (19/32; 49.4%) had nystagmus. The absence of nystagmus was significantly associated with better BCVA and more preserved CRT (P < 0.05). ERG showed undetectable responses in most patients (64.0%), whereas reduced scotopic and photopic responses were observed in four patients (16.0%) who had no nystagmus. We identified 35 different variants, among which 12 were novel. Our genotype-phenotype correlation analysis shows a significantly worse BCVA in patients harboring a loss-of-function mutation and the deep-intronic variant c.2991+1655A>G.

Conclusions

Our study highlights a mild phenotype of the disease, characterized by absence of nystagmus, good visual acuity, considerably preserved retinal morphology, and recordable ERG, confirming the wide spectrum of CEP290-related retinal dystrophies. Finally, in our cohort, the deep intronic variant c.2991+1655A>G was associated with a more severe phenotype.

Novel variants in GUCY2D causing retinopathy and the genotype-phenotype correlation

Leber congenital amaurosis (LCA) is the most severe form of retinopathy and cone/cone-rod dystrophy (CORD) is a common form of inherited retinopathy. Variants in GUCY2D constitute the most common cause of LCA and autosomal dominant CORD (ADCORD). The purpose of this study was to reveal novel variants and document associated phenotypes of patients with GUCY2D-associated retinopathy. Fifty-two potentially pathogenic variants (PPVs), including 12 novel ones (p.Gly144_Ala164del, p.Trp154Glyfs*12, p.Leu186Pro, p.Ala207Pro, p.Ala229Asp, p.Ala353Glu, p.Trp372*, p.Arg528*, p.Arg660Pro, p.Ile682Thr, p.Trp788Cys, and c.1026 + 171_*486del), were identified in 16 families with ADCORD and 34 families with autosomal recessive LCA (ARLCA). The novel variant c.1026 + 171_*486del is a large-scale (16.3 kb) deletion involving exons 4-20 of GUCY2D, and was identified in an ARLCA family in heterozygous status mimicking a homozygous p.Trp788Cys variant. Among the detected 52 PPVs, 32 (61.5%) were missense, seven (13.5%) were splicing, six (11.5%) were nonsense, four (7.7%) were inframe indel, and three (5.8%) were frameshift deletion. The median age of examination in 27 patients with ADCORD was 21.0 years (ranges 3-54) with a median visual acuity (VA) of 0.10 (ranges 0.02-0.90). There were 48.0% of patients with macular atrophy, 86.4% with severe reduced or extinguished cone responses, 77.3% with normal or mildly reduced rod responses, and 60.9% with high myopia. Visual impairment, macular dystrophy, and cone dysfunction deteriorated with age. The median age of examination in 34 patients with ARLCA was 1.1 years (ranges 0.3-25). There were 55.9% of patients with roving nystagmus, 68.2% with VA of worse than hand motion, 59.4% with almost normal fundus, 90.6% with extinguished rod and cone responses, and 50.0% with high hyperopia. In conclusions, twelve novel PPVs in GUCY2D (including a novel large-scale deletion) were identified. Most (32/52, 61.5%) of causative GUCY2D variants were missense. Progressive development of macular atrophy, cone dysfunction, visual impairment, and myopia are four major characteristics of GUCY2D-associated ADCORD. Normal fundus, roving nystagmus, and hypermetropia in early age are common findings specific to GUCY2D-associated ARLCA. The obtained data in this study will be of value in counselling patients and designing future therapeutic approaches.

Safety and improved efficacy signals following gene therapy in childhood blindness caused by GUCY2D mutations

A first-in-human clinical trial of gene therapy in Leber congenital amaurosis due to mutations in the GUCY2D gene is underway, and early results are summarized. A recombinant adeno-associated virus serotype 5 (rAAV5) vector carrying the human GUCY2D gene was delivered by subretinal injection to one eye in three adult patients with severe visual loss, nystagmus, but preserved retinal structure. Safety and efficacy parameters were monitored for 9 months post-operatively. No systemic toxicity was detected; there were no serious adverse events, and ocular adverse events resolved. P1 and P2 showed statistically significant rod photoreceptor vision improvement by full-field stimulus testing in the treated eye. P1 also showed improvement in pupillary responses. Visual acuity remained stable from baseline in P1 and P2. P3, however, showed a gain of 0.3 logMAR in the treated eye, indicating greater cone-photoreceptor function. The results show safety and both rod- and cone-mediated efficacy of this therapy.

Unique Variant Spectrum in a Jordanian Cohort with Inherited Retinal Dystrophies

Whole Exome Sequencing (WES) is a powerful approach for detecting sequence variations in the human genome. The aim of this study was to investigate the genetic defects in Jordanian patients with inherited retinal dystrophies (IRDs) using WES. WES was performed on proband patients' DNA samples from 55 Jordanian families. Sanger sequencing was used for validation and segregation analysis of the detected, potential disease-causing variants (DCVs). Thirty-five putatively causative variants (6 novel and 29 known) in 21 IRD-associated genes were identified in 71% of probands (39 of the 55 families). Three families showed phenotypes different from the typically reported clinical findings associated with the causative genes. To our knowledge, this is the largest genetic analysis of IRDs in the Jordanian population to date. Our study also confirms that WES is a powerful tool for the molecular diagnosis of IRDs in large patient cohorts.

Clinical and Genetic Analysis of 63 Families Demonstrating Early and Advanced Characteristic Fundus as the Signature of CRB1 Mutations

PURPOSE

To reveal the characteristics of ocular changes in patients with biallelic CRB1 mutations.

DESIGN

Comparative exome sequencing and retrospective case series on clinical data.

METHODS

Seventy-four patients from 63 families with biallelic potential pathogenic variants in CRB1 were selected from our in-house exome sequencing. The clinical data were reviewed and evaluated in detail, including best-corrected visual acuity, fundus photography, optical coherence tomography (OCT), and electroretinogram (ERG).

RESULTS

Biallelic CRB1 variants, involving 45 variants including 23 novel, were identified in 40 novel families based on exome sequencing. Analyzing clinical data of the 74 individuals from 63 families revealed the following CRB1-associated phenotypes: (1) early-onset reduced visual acuity with congenital nystagmus; (2) 2 types of characteristic retinal changes including yellowish geographic macular degeneration (YMD) or nummular pigment deposits (NPD) at posterior retina with bone-spicule pigmentation at midperipheral retina; (3) undetectable rod and cone responses on ERG; (4) cystoid macular edema or macular atrophy on OCT. YMD and NPD are unique and CRB1-associated. Long-term follow-up examination as well as age- and variant-dependent phenotypic analysis suggested YMD is the early fundus change that would gradually progress to NPD.

CONCLUSIONS

YMD and NPD are 2 major characteristic CRB1-associated fundus changes and the former one will advance to the latter with age. Recognizing such characteristic signs associated with biallelic CRB1 variants may be of value in areas without widespread access to genetic testing where a more targeted approach is needed and might be biomarkers for evaluation of effects for future intervention.

Whole Locus Sequencing Identifies a Prevalent Founder Deep Intronic RPGRIP1 Pathologic Variant in the French Leber Congenital Amaurosis Cohort

Leber congenital amaurosis (LCA) encompasses the earliest and most severe retinal dystrophies and can occur as a non-syndromic or a syndromic disease. Molecular diagnosis in LCA is of particular importance in clinical decision-making and patient care since it can provide ocular and extraocular prognostics and identify patients eligible to develop gene-specific therapies. Routine high-throughput molecular testing in LCA yields 70%–80% of genetic diagnosis. In this study, we aimed to investigate the non-coding regions of one non-syndromic LCA gene, RPGRIP1, in a series of six families displaying one single disease allele after a gene-panel screening of 722 LCA families which identified 26 biallelic RPGRIP1 families. Using trio-based high-throughput whole locus sequencing (WLS) for second disease alleles, we identified a founder deep intronic mutation (NM_020366.3:c.1468-128T>G) in 3/6 families. We employed Sanger sequencing to search for the pathologic variant in unresolved LCA cases (106/722) and identified three additional families (two homozygous and one compound heterozygous with the NM_020366.3:c.930+77A>G deep intronic change). This makes the c.1468-128T>G the most frequent RPGRIP1 disease allele (8/60, 13%) in our cohort. Studying patient lymphoblasts, we show that the pathologic variant creates a donor splice-site and leads to the insertion of the pseudo-exon in the mRNA, which we were able to hamper using splice-switching antisense oligonucleotides (AONs), paving the way to therapies.

CRB1-associated retinal dystrophies in a Belgian cohort: genetic characteristics and long-term clinical follow-up

AIM

To investigate the natural history in a Belgian cohort of CRB1-associated retinal dystrophies.

METHODS

An in-depth retrospective study focusing on visual function and retinal structure.

RESULTS

Forty patients from 35 families were included (ages: 2.5-80.1 years). In patients with a follow-up of >1 year (63%), the mean follow-up time was 12.0 years (range: 2.3-29.2 years). Based on the patient history, symptoms and/or electroretinography, 22 patients (55%) were diagnosed with retinitis pigmentosa (RP), 15 (38%) with Leber congenital amaurosis (LCA) and 3 (8%) with macular dystrophy (MD), the latter being associated with the p.(Ile167_Gly169del) mutation (in compound heterozygosity). MD later developed into a rod-cone dystrophy in one patient. Blindness at initial presentation was seen in the first decade of life in LCA, and in the fifth decade of life in RP. Eventually, 28 patients (70%) reached visual acuity-based blindness (<0.05). Visual field-based blindness (<10°) was documented in 17/25 patients (68%). Five patients (13%) developed Coats-like exudative vasculopathy. Intermediate/posterior uveitis was found in three patients (8%). Cystoid maculopathy was common in RP (9/21; 43%) and MD (3/3; 100%). Macular involvement, varying from retinal pigment epithelium alterations to complete outer retinal atrophy, was observed in all patients.

CONCLUSION

Bi-allelic CRB1 mutations result in a range of progressive retinal disorders, most of which are generalised, with characteristically early macular involvement. Visual function and retinal structure analysis indicates a window for potential intervention with gene therapy before the fourth decade of life in RP and the first decade in LCA.

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.

Voretigene Neparvovec and Gene Therapy for Leber's Congenital Amaurosis: Review of Evidence to Date

Gene therapy has now evolved as the upcoming modality for management of many disorders, both inheritable and non-inheritable. Knowledge of genetics pertaining to a disease has therefore become paramount for physicians across most specialities. Inheritable retinal dystrophies (IRDs) are notorious for progressive and relentless vision loss, frequently culminating in complete blindness in both eyes. Leber’s congenital amaurosis (LCA) is a typical example of an IRD that manifests very early in childhood. Research in gene therapy has led to the development and approval of voretigene neparvovec (VN) for use in patients of LCA with a deficient biallelic RPE65 gene. The procedure involves delivery of a recombinant virus vector that carries the RPE65 gene in the subretinal space. This comprehensive review reports the evidence thus far in support of gene therapy for LCA. We explore and compare the various gene targets including but not limited to RPE65, and discuss the choice of vector and method for ocular delivery. The review details the evolution of gene therapy with VN in a phased manner, concluding with the challenges that lie ahead for its translation for use in communities that differ much both genetically and economically.

Voretigene Neparvovec for Treating Inherited Retinal Dystrophies Caused by RPE65 Gene Mutations: An Evidence Review Group Perspective of a NICE Highly Specialised Technology Appraisal

The UK National Institute for Health and Care Excellence (NICE) considered evidence for voretigene neparvovec (VN; Luxturna^®) for the treatment of RPE65-mediated inherited retinal dystrophies (IRD) within its highly specialised technology programme. This paper summarises the evidence provided by the company; the appraisal of the evidence by the Peninsula Technology Appraisal Group, who were commissioned to act as the independent evidence review group (ERG); and the development of the NICE guidance by the appraisal committee. The evidence presented by the company highlighted the significant lifelong burden of IRD for patients and carers. Evidence to support the effectiveness of VN was lacking, but the available evidence showed a modest, sustained improvement across a variety of vision-related outcomes. While patients would remain visually impaired, the committee considered that VN would prevent further deterioration in vision. The modelling approach used by the company had a number of limitations and relied heavily upon a large volume of clinical expert input to produce cost-effectiveness estimates with large uncertainty around long-term effectiveness. The ERG's main concerns revolved around these long-term outcomes and the plausibility of utility values. The NICE committee were convinced that the clinical benefits of VN were important and an appropriate use of national health service resources within a specialised service. The committee concluded that a high unmet need existed in patients with RPE65-mediated IRD and that VN represents a step change in the management of this condition.

TULP1 and TUB Are Required for Specific Localization of PRCD to Photoreceptor Outer Segments

Photoreceptor disc component (PRCD) is a small protein which is exclusively localized to photoreceptor outer segments, and is involved in the formation of photoreceptor outer segment discs. Mutations in PRCD are associated with retinal degeneration in humans, mice, and dogs. The purpose of this work was to identify PRCD-binding proteins in the retina. PRCD protein-protein interactions were identified when implementing the Ras recruitment system (RRS), a cytoplasmic-based yeast two-hybrid system, on a bovine retina cDNA library. An interaction between PRCD and tubby-like protein 1 (TULP1) was identified. Co-immunoprecipitation in transfected mammalian cells confirmed that PRCD interacts with TULP1, as well as with its homolog, TUB. These interactions were mediated by TULP1 and TUB highly conserved C-terminal tubby domain. PRCD localization was altered in the retinas of TULP1- and TUB-deficient mice. These results show that TULP1 and TUB, which are involved in the vesicular trafficking of several photoreceptor proteins from the inner segment to the outer segment, are also required for PRCD exclusive localization to photoreceptor outer segment discs.

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.

Leber Congenital Amaurosis With Coats-Like Reaction and 3 Novel Sequence Variants: A Short Report

Purpose:

This report discusses a patient with Leber congenital amaurosis who presented with severe bilateral Coats-like reaction and 3 novel sequence variants in 2 different genes.

Methods:

The patient underwent complete ophthalmic and retinal evaluations including fluorescein angiography and optical coherence tomography as well as genetic studies. She was treated with intravitreal injection of intravitreal bevacizumab and laser photocoagulation.

Results:

Genetic analysis of the patient identified 2 novel sequence variants in the CEP290 (centrosomal protein 290) gene and another novel sequence variant in the RPGRIP1 (RPGR interacting protein 1) gene.

Conclusions:

The clinical presentation of Coats-like reaction in Leber congenital amaurosis can be associated with sequence variants in certain genes. The presence of multiple gene sequence variants in this patient may have contributed to the severity of disease.

Novel mutation identified in Leber congenital amaurosis - a case report

Background

Leber congenital amaurosis (LCA) is the earliest onset and the most severe form of all inherited retinal degenerative disorders, characterized by blindness, or severe visual impairment from birth, and typically exhibits clinical and genetic heterogeneity. Recently, 14 causative genes of LCA were reported. We performed whole-exome sequencing (WES) for Japanese siblings, and identified a novel homozygous nonsense mutation in the RPGR-interacting protein 1 (RPGRIP1) gene. We also report their follow-up data over 27 years.

Case presentation

Patient 1 is a 37-year-old male. In 1992, his eye position indicated orthophoria, however, horizontal nystagmus was evident, and he complained of photophobia. His best corrected decimal visual acuity (BCVA) was 0.2 (S + 6.5/C-3.5/170°) OD and 0.1 (S + 6.0/C-2.5/10°) OS. Fundus examination revealed bisymmetrical inferior focal retinal pigment epithelium (RPE) mottling. Bright-flash electroretinogram (ERG) revealed a subnormal pattern, while 30 Hz flicker ERG was non-recordable in both eyes. At his final visit in 2019, his BCVA was 0.09 (S + 3.5/C-3.5/180°) OD and 0.09 (S + 3.0/C-4.0/10°) OS. Patient 2, a 34-year-old female, is the sibling of patient 1. In 1992, her BCVA was 0.05 (S + 6.0) OD and 0.06 (S + 5.0) OS. She was in a chin-up position during visual acuity testing. Horizontal nystagmus was evident, and she also complained of photophobia. Bright-flash ERG was severely attenuated, and 30 Hz flicker ERG was non-recordable in both eyes. At her final visit in 2019, her BCVA was 0.02 (uncorrectable) OD and 0.03 (uncorrectable) OS. There were no other patients with LCA in their family and their parents were non-consanguineous. WES revealed a homozygous, consecutive, two-nucleotide variation in the RPGRIP1 gene (NM_020366: exon15:c.G2294A and c.C2295A, p.C765X), resulting in a premature stop codon. We interpreted this variation as a novel pathogenic mutation of RPGRIP1 that contributes to LCA6 development.

Conclusions

Herein, we report a novel nonsense mutation of RPGRIP1 in two patients with LCA6 and present their long-term follow-up data. These clinical data linked to genotypes provide important information for the development of new treatments, such as gene therapy, as well as for genetic counseling.

Large Animal Models of Inherited Retinal Degenerations: A Review

Studies utilizing large animal models of inherited retinal degeneration (IRD) have proven important in not only the development of translational therapeutic approaches, but also in improving our understanding of disease mechanisms. The dog is the predominant species utilized because spontaneous IRD is common in the canine pet population. Cats are also a source of spontaneous IRDs. Other large animal models with spontaneous IRDs include sheep, horses and non-human primates (NHP). The pig has also proven valuable due to the ease in which transgenic animals can be generated and work is ongoing to produce engineered models of other large animal species including NHP. These large animal models offer important advantages over the widely used laboratory rodent models. The globe size and dimensions more closely parallel those of humans and, most importantly, they have a retinal region of high cone density and denser photoreceptor packing for high acuity vision. Laboratory rodents lack such a retinal region and, as macular disease is a critical cause for vision loss in humans, having a comparable retinal region in model species is particularly important. This review will discuss several large animal models which have been used to study disease mechanisms relevant for the equivalent human IRD.

Expanding the Clinical and Molecular Heterogeneity of Nonsyndromic Inherited Retinal Dystrophies

A cohort of 172 patients diagnosed clinically with nonsyndromic retinal dystrophies, from 110 families underwent full ophthalmologic examination, including retinal imaging, electrophysiology, and optical coherence tomography, when feasible. Molecular analysis was performed using targeted next-generation sequencing (NGS). Variants were filtered and prioritized according to the minimum allele frequency, and finally classified according to the American College of Medical Genetics and Genomics guidelines. Multiplex ligation-dependent probe amplification and array comparative genomic hybridization were performed to validate copy number variations identified by NGS. The diagnostic yield of this study was 62% of studied families. Thirty novel mutations were identified. The study found phenotypic intra- and interfamilial variability in families with mutations in C1QTNF5, CERKL, and PROM1; biallelic mutations in PDE6B in a unilateral retinitis pigmentosa patient; interocular asymmetry RP in 50% of the symptomatic RPGR-mutated females; the first case with possible digenism between CNGA1 and CNGB1; and a ROM1 duplication in two unrelated retinitis pigmentosa families. Ten unrelated cases were reclassified. This study highlights the clinical utility of targeted NGS for nonsyndromic inherited retinal dystrophy cases and the importance of full ophthalmologic examination, which allows new genotype-phenotype associations and expands the knowledge of this group of disorders. Identifying the cause of disease is essential to improve patient management, provide accurate genetic counseling, and take advantage of gene therapy-based treatments.

Unraveling the genetic cause of hereditary ophthalmic disorders in Arab societies from Israel and the Palestinian Authority

Visual impairment due to inherited ophthalmic disorders is amongst the most common disabilities observed in populations practicing consanguineous marriages. Here we investigated the molecular genetic basis of an unselected broad range of ophthalmic disorders in 20 consanguineous families from Arab villages of Israel and the Palestinian Authority. Most patients had little or very poor prior clinical workup and were recruited in a field study. Homozygosity mapping followed by candidate gene sequencing applying conventional Sanger sequencing or targeted next generation sequencing was performed in six families. In the remaining 14 families, one affected subject per family was chosen for whole exome sequencing. We discovered likely disease-causing variants, all homozygous, in 19 of 20 independent families (95%) including a previously reported novel disease gene for congenital nystagmus associated with foveal hypoplasia. Moreover, we found a family in which disease-causing variants for two collagenopathies - Stickler and Knobloch syndrome - segregate within a large sibship. Nine of the 19 distinct variants observed in this study were novel. Our study demonstrated a very high molecular diagnostic yield for a highly diverse spectrum of rare ophthalmic disorders in Arab patients from Israel and the Palestinian Authority, even with very limited prior clinical investigation. We conclude that 'genetic testing first' may be an economic way to direct clinical care and to support proper genetic counseling and risk assessment in these families.

Single-nuclei RNA-seq on human retinal tissue provides improved transcriptome profiling

Single-cell RNA-seq is a powerful tool in decoding the heterogeneity in complex tissues by generating transcriptomic profiles of the individual cell. Here, we report a single-nuclei RNA-seq (snRNA-seq) transcriptomic study on human retinal tissue, which is composed of multiple cell types with distinct functions. Six samples from three healthy donors are profiled and high-quality RNA-seq data is obtained for 5873 single nuclei. All major retinal cell types are observed and marker genes for each cell type are identified. The gene expression of the macular and peripheral retina is compared to each other at cell-type level. Furthermore, our dataset shows an improved power for prioritizing genes associated with human retinal diseases compared to both mouse single-cell RNA-seq and human bulk RNA-seq results. In conclusion, we demonstrate that obtaining single cell transcriptomes from human frozen tissues can provide insight missed by either human bulk RNA-seq or animal models.

The genetic aetiology of retinal degeneration in children in Finland - new founder mutations identified

PURPOSE

To study the genetic aetiology and phenotypes of retinal degeneration (RD) in Finnish children born during 1993-2009.

METHODS

Children with retinal degeneration (N = 68) were investigated during 2012-2014 with a targeted gene analysis or a next-generation sequencing (NGS) based gene panel. Also, a full clinical ophthalmological examination was performed.

RESULTS

The cohort covered 44% (68/153) of the Finnish children with inherited RD born 1993-2009. X-linked retinoschisis, retinitis pigmentosa, Leber congenital amaurosis and cone-rod dystrophy were the most common clinical diagnoses in the study group. Pathogenic mutations were found in 17 retinal genes. The molecular genetic aetiology was identified in 77% of the patients (in 77% of the families) analysed by NGS method. Several founder mutations were detected including three novel founder mutations c.148delG in TULP1, c.2314C>R (p.Gln772Ter) in RPGRIP1 and c.533G>A (Trp178Ter) in TYR. We also confirmed the previous tentative finding of c.2944 + 1delG in GYCU2D being the most frequent cause of Leber congenital amaurosis (LCA) in Finland.

CONCLUSIONS

Globally, RD is genetically heterogeneous with over 260 disease genes reported so far. This was shown not to be the case in Finland, where the genetic aetiology of RD is caused by a small group of genes, due to several founder mutations that are enriched in the population. We found that X-chromosomal retinoschisis constitutes the major group in Finnish paediatric RD population and is almost exclusively caused by two founder mutations. Several other founder mutations were detected including three novel founder mutations. All in all, the genetic aetiology of 77% of families was identified which is higher than previously reported from other populations, likely due to the specific genomic constitution of the Finns.

CRB1 Gene Mutation Causing Different Phenotypes of Leber Congenital Amaurosis in Siblings

Purpose

We report a rare case of CRB1gene mutation in two siblings (sisters) affected with the exact same genetic mutation on both CRB1genes resulting in varying phenotypes.

Case Report

CRB1gene mutation in this case has resulted in causing varying degrees of Leber congenital amaurosis (LCA) in both sisters with a more severe phenotype in the older sibling causing LCA-8 with retinitis pigmentosa spectrum in both eyes and a milder phenotype causing LCA-8 with less severe rod cone dystrophy in the younger sister.

Conclusion

In summary, the mechanisms of varying phenotypes resulting from CRB1 genetic mutation are still not well understood. We concluded that the presence of different phenotypes associated with identical genotypic mutation of a single gene in siblings or in a family is important especially when dealing with retinal dystrophies.