Leber congenital amaurosis: genes, proteins and disease mechanisms

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, multi-modal 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-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, none 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 genotype (DN). Twelve patients (67%) had follow up assessments over a 15.7 ± 9.5 year period. The rate of BCVA decline was 0.02 LogMAR (1 letter)/year.

CONCLUSIONS

RPGRIP1-EOSRD/LCA often presents at birth or early infancy, with nystagmus, decreased VA, 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.

Nationwide Prevalence of Inherited Retinal Diseases in the Israeli Population

Importance

Data regarding the prevalence of various inherited retinal diseases (IRDs) are limited and vary across populations; moreover, nationwide prevalence studies may be limited to a specific IRD phenotype, potentially leading to inaccurate prevalence estimations. Therefore, nationwide prevalence data are needed.

Objective

To determine the prevalence of 67 IRD phenotypes in the Israeli population.

Design, Setting, and Participants

This cohort study collected nationwide data regarding the number of individuals affected with IRD phenotypes assessed in 10 clinical and academic centers in Israel as part of the research activity of the Israeli inherited retinal disease consortium. Data were collected in May 2023 on 9396 individuals residing in Israel who were diagnosed by an ophthalmologist with an IRD using either electroretinography or retinal imaging where included. Individuals with retinal diseases known to have a nonmendelian basis or without a clear genetic basis and those who were reported as deceased at the time of data collection were excluded from this study.

Main Outcomes and Measures

Prevalence of 67 IRD phenotypes.

Results

Among the 9396 participants in our cohort, the most common IRD in Israel was retinitis pigmentosa with a disease prevalence of approximately 1:2400 individuals, followed by cone-rod dystrophy (approximately 1:14 000), Stargardt disease (approximately 1:16 000), Usher syndrome (approximately 1:16,000), and congenital stationary night blindness (approximately 1:18 000). The prevalence of all IRDs combined was 1:1043 individuals.

Conclusions and Relevance

The current study provides large prevalence dataset of 67 IRD phenotypes, some of which are extremely rare, with only a single identified case. This analysis highlights the potential importance of performing additional nationwide prevalence studies to potentially assist with determining the prevalence of IRDs worldwide.

IFT88 maintains sensory function by localising signalling proteins along Drosophila cilia

Ciliary defects cause several ciliopathies, some of which have late onset, suggesting cilia are actively maintained. Still, we have a poor understanding of the mechanisms underlying their maintenance. Here, we show Drosophila melanogaster IFT88 (DmIFT88/nompB) continues to move along fully formed sensory cilia. We further identify Inactive, a TRPV channel subunit involved in Drosophila hearing and negative-gravitaxis behaviour, and a yet uncharacterised Drosophila Guanylyl Cyclase 2d (DmGucy2d/CG34357) as DmIFT88 cargoes. We also show DmIFT88 binding to the cyclase´s intracellular part, which is evolutionarily conserved and mutated in several degenerative retinal diseases, is important for the ciliary localisation of DmGucy2d. Finally, acute knockdown of both DmIFT88 and DmGucy2d in ciliated neurons of adult flies caused defects in the maintenance of cilium function, impairing hearing and negative-gravitaxis behaviour, but did not significantly affect ciliary ultrastructure. We conclude that the sensory ciliary function underlying hearing in the adult fly requires an active maintenance program which involves DmIFT88 and at least two of its signalling transmembrane cargoes, DmGucy2d and Inactive.

Clinical and genetic studies for a cohort of patients with Leber congenital amaurosis

PURPOSE

Leber congenital amaurosis (LCA) is a group of early-onset retinal degenerative disorders, resulting in blindness in children. This study aimed to describe the clinical and genetic characteristics of a cohort of patients with LCA and to investigate the retinal vascular characteristics in LCA patients.

METHODS

Fifty-two children with LCA were included in the study. All patients underwent detailed ocular examinations. Electroretinography (ERG) was used to evaluate the retinal function. Optical coherence tomography (OCT) was used to assess the structure change of the retina for those patients who were able to cooperate very well. Panel-based next-generation sequencing was performed to identify pathogenic variants in genes associated with LCA. Diameters of the retinal vessels were measured using the EVision AI screening system with an artificial intelligence (AI) technique. An ultrasound Doppler was used to evaluate hemodynamic parameters, including peak systolic velocity (PSV), resistive index (RI), and pulsatility index (PI), in the ophthalmic, central retinal, posterior ciliary, carotid, and internal carotid as well as external carotid arteries in 12 patients aged from 3 to 14 years.

RESULTS

We detected 75 pathogenic variants from ten genes of RPGRIP1, CEP290, GUCY2D, LCA5, AIPL1, CRB1, RPE65, CRX, RDH12, and TULP1, including 29 novel and 36 previously reported variants in 52 affected children with LCA, with the highest detective rate in RPGRIP1 (26.9%). Fundus appearance is diverse in patients with LCA, ranging from normal to severe peripheral or central retinopathy. Retinal vasculature was evaluated in 12 patients with different gene variants, showing narrowed arteries with an average diameter of 43.6 ± 3.8 μm compared to that of 51.7 ± 2.6 μm in the normal controls (P < 0.001, n = 12). Meanwhile, their hemodynamic parameters were changed as well in the ophthalmic artery (OA), with a decreased PSV (P = 0.0132, n = 12) and slightly increased PI (P = 0.0488, n = 12) compared to the normal controls. However, the hemodynamic parameters did not change significantly in the other vessels.

CONCLUSIONS

Blood supply to the eyeball is predicted to be reduced in patients with LCA, presumably due to photoreceptor cell degeneration. The novel identified variants will expand the spectrum of variants in LCA-related genes and be useful for studying the molecular mechanisms of LCA.

Optical coherence tomography in children with inherited retinal disease

Recent advances have led to therapeutic options becoming available for people with inherited retinal disease. In particular, gene therapy has been shown to hold great promise for slowing vision loss from inherited retinal disease. Recent studies suggest that gene therapy is likely to be most effective when implemented early in the disease process, making consideration of paediatric populations important. It is therefore necessary to have a comprehensive understanding of retinal imaging in children with inherited retinal diseases, in order to monitor disease progression and to determine which early retinal biomarkers may be used as outcome measures in future clinical trials. In addition, as many optometrists will review children with an inherited retinal disease, an understanding of the expected imaging outcomes can improve clinical care. This review focuses on the most common imaging modality used in research assessment of paediatric inherited retinal diseases: optical coherence tomography. Optical coherence tomography findings can be used in both the clinical and research setting. In particular, the review discusses current knowledge of optical coherence tomography findings in eight paediatric inherited retinal diseases - Stargardt disease, Bests disease, Leber's congenital amaurosis, choroideremia, RPGR related retinitis pigmentosa, Usher syndrome, X-linked retinoschisis and, Batten disease.

Effective AAV-mediated gene replacement therapy in retinal organoids modeling AIPL1-associated LCA4

Biallelic variations in the aryl hydrocarbon receptor interacting protein-like 1 (AIPL1) gene cause Leber congenital amaurosis subtype 4 (LCA4), an autosomal recessive early-onset severe retinal dystrophy that leads to the rapid degeneration of retinal photoreceptors and the severe impairment of sight within the first few years of life. Currently, there is no treatment or cure for AIPL1-associated LCA4. In this study, we investigated the potential of adeno-associated virus-mediated AIPL1 gene replacement therapy in two previously validated human retinal organoid (RO) models of LCA4. We report here that photoreceptor-specific AIPL1 gene replacement therapy, currently being tested in a first-in-human application, effectively rescued molecular features of AIPL1-associated LCA4 in these models. Notably, the loss of retinal phosphodiesterase 6 was rescued and elevated cyclic guanosine monophosphate (cGMP) levels were reduced following treatment. Transcriptomic analysis of untreated and AAV-transduced ROs revealed transcriptomic changes in response to elevated cGMP levels and viral infection, respectively. Overall, this study supports AIPL1 gene therapy as a promising therapeutic intervention for LCA4.

Breaking genetic shackles: The advance of base editing in genetic disorder treatment

The rapid evolution of gene editing technology has markedly improved the outlook for treating genetic diseases. Base editing, recognized as an exceptionally precise genetic modification tool, is emerging as a focus in the realm of genetic disease therapy. We provide a comprehensive overview of the fundamental principles and delivery methods of cytosine base editors (CBE), adenine base editors (ABE), and RNA base editors, with a particular focus on their applications and recent research advances in the treatment of genetic diseases. We have also explored the potential challenges faced by base editing technology in treatment, including aspects such as targeting specificity, safety, and efficacy, and have enumerated a series of possible solutions to propel the clinical translation of base editing technology. In conclusion, this article not only underscores the present state of base editing technology but also envisions its tremendous potential in the future, providing a novel perspective on the treatment of genetic diseases. It underscores the vast potential of base editing technology in the realm of genetic medicine, providing support for the progression of gene medicine and the development of innovative approaches to genetic disease therapy.

Adaptive Optics Retinal Imaging in RDH12-Associated Early Onset Severe Retinal Dystrophy

Purpose

RDH12 is among the most common genes found in individuals with early-onset severe retinal (EOSRD). Adaptive optics scanning light ophthalmoscopy (AOSLO) enables resolution of individual rod and cone photoreceptors in the retina. This study presents the first AOSLO imaging of individuals with RDH12-associated EOSRD.

Methods

Case series of patients who attended Moorfields Eye Hospital (London, UK). Spectral-domain optical coherence tomography, near-infrared reflectance (NIR), and blue autofluorescence imaging were analyzed. En face image sequences of photoreceptors were recorded using either of two AOSLO modalities. Cross-sectional analysis was undertaken for seven patients and longitudinal analysis for one patient.

Results

Nine eyes from eight patients are presented in this case series. The mean age at the time of the assessment was 11.2 ± 6.5 years of age (range 7-29). A subfoveal continuous ellipsoid zone (EZ) line was present in eight eyes. Posterior pole AOSLO revealed patches of cone mosaics. Average cone densities at regions of interest 0.5° to the fovea ranged from 12,620 to 23,660 cells/mm2, whereas intercell spacing ranged from 7.0 to 9.7 µm.

Conclusions

This study demonstrates that AOSLO can provide useful high-quality images in patients with EOSRD, even during childhood, with nystagmus, and early macular atrophy. Cones at the posterior pole can appear as scattered islands or, possibly later in life, as a single subfoveal conglomerate. Detailed image analysis suggests that retinal pigment epithelial stress and dysfunction may be the initial step toward degeneration, with NIR being a useful tool to assess retinal well-being in RDH12-associated EOSRD.

Multi-luminance mobility testing after gene therapy in the context of retinal functional diagnostics

BACKGROUND

Voretigene neparvovec (Luxturna®) is the first approved gene therapy for RPE65-linked Leber congenital amaurosis (LCA). Though individual effects are highly variable, most recipients report improved vision in everyday life. To describe such effects, visual navigation tests are now frequently used in clinical trials. However, it is still unclear how their results should be interpreted compared to conventional parameters of visual function.

METHODS

Seven LCA patients underwent a multi-luminance visual navigation test (Ora-VNCTM) before and 3 months after receiving Luxturna gene therapy. Their performance was rated based on the luminance level at which they passed the course. Differences between the first and second test were correlated to changes in visual acuity, full-field stimulus thresholds, chromatic pupil campimetry, and dark-adapted perimetry.

RESULTS

A few patients displayed notable improvements in conventional measures of visual function whereas patients with advanced retinal degeneration showed no relevant changes. Independent of these results, almost all participants improved in the visual navigation task by one or more levels. The improvement in the mobility test was best correlated to the change in full-field stimulus thresholds. Other measures of visual functions showed no clear correlation with visual navigation.

DISCUSSION

In patients who passed the test's more difficult levels, improved visual navigation can be attributed to the reactivation of rods. However, the performance of patients with low vision seemed to depend much more on confounding factors in the easier levels. In sum, such tests might only be meaningful for patients with better preserved visual functions.

Comparison of Worldwide Disease Prevalence and Genetic Prevalence of Inherited Retinal Diseases and Variant Interpretation Considerations

One of the considerations in planning the development of novel therapeutic modalities is disease prevalence that is usually defined by studying large national/regional populations. Such studies are rare and might suffer from inaccuracies and challenging clinical characterization in heterogeneous diseases, such as inherited retinal diseases (IRDs). Here we collected reported disease prevalence information on various IRDs in different populations. The most common IRD, retinitis pigmentosa, has an average disease prevalence of ∼1:4500 individuals, Stargardt disease ∼1:17,000, Usher syndrome ∼1:25,000, Leber congenital amaurosis ∼1:42,000, and all IRDs ∼1:3450. We compared these values to genetic prevalence (GP) calculated based on allele frequency of autosomal-recessive IRD mutations. Although most values did correlate, some differences were observed that can be explained by discordant, presumably null mutations that are likely to be either nonpathogenic or hypomorphic. Our analysis highlights the importance of performing additional disease prevalence studies and to couple them with population-dependent allele frequency data.

The Clinical Findings, Pathogenic Variants, and Gene Therapy Qualifications Found in a Leber Congenital Amaurosis Phenotypic Spectrum Patient Cohort

This retrospective study examines the clinical characteristics and underlying genetic variants that exist in a Leber congenital amaurosis (LCA) patient cohort evaluated at the inherited retinal disease (IRD) clinic at the University of Minnesota (UMN)/M Health System. Our LCA cohort consisted of 33 non-syndromic patients and one patient with Joubert syndrome. We report their relevant history, clinical findings, and genetic testing results. We monitored disease presentation utilizing ocular coherence tomography (OCT) and fundus autofluorescence (FAF). Electroretinogram testing (ERG) was performed in patients when clinically indicated. Next-generation sequencing (NGS) and genetic counseling was offered to all evaluated patients. Advanced photoreceptor loss was noted in 85.7% of the subjects. All patients who underwent FAF had findings of either a ring of macular hypo/hyper AF or peripheral hypo-AF. All patients had abnormal ERG findings. A diagnostic genetic test result was identified in 74.2% of the patients via NGS single-gene testing or panel testing. Two patients in our cohort qualified for Luxturna® and both received treatment at the time of this study. These data will help IRD specialists to understand the genetic variants and clinical presentations that characterize our patient population in the Midwest region of the United States.

RNA-Seq Analysis of Trans-Differentiated ARPE-19 Cells Transduced by AAV9-AIPL1 Vectors

Inherited retinal disorders (IRD) have become a primary focus of gene therapy research since the success of adeno-associated virus-based therapeutics (voretigene neparvovec-rzyl) for Leber congenital amaurosis type 2 (LCA2). Dozens of monogenic IRDs could be potentially treated with a similar approach using an adeno-associated virus (AAV) to transfer a functional gene into the retina. Here, we present the results of the design, production, and in vitro testing of the AAV serotype 9 (AAV9) vector carrying the codon-optimized (co) copy of aryl hydrocarbon receptor-interacting protein like-1 (AIPL1) as a possible treatment for LCA4. The pAAV-AIPL1co was able to successfully transduce retinal pigment epithelium cells (ARPE-19) and initiate the expression of human AIPL1. Intriguingly, cells transduced with AAV9-AIPL1co showed much less antiviral response than AAV9-AIPL1wt (wild-type AIPL1) transduced. RNA-sequencing (RNA-seq) analysis of trans-differentiated ARPE-19 cells transduced with AAV9-AIPL1co demonstrated significant differences in the expression of genes involved in the innate immune response. In contrast, AAV9-AIPL1wt induced the prominent activation of multiple interferon-stimulated genes. The key part of the possible regulatory molecular mechanism is the activation of dsRNA-responsive antiviral oligoadenylate synthetases, and a significant increase in the level of histone coding genes' transcripts overrepresented in RNA-seq data (i.e., H1, H2A, H2B, H3, and H4). The RNA-seq data suggests that AAV9-AIPL1co exhibiting less immunogenicity than AAV9-AIPL1wt can be used for potency testing, using relevant animal models to develop future therapeutics for LCA4.

AAV for Gene Therapy in Ocular Diseases: Progress and Prospects

Owing to the promising therapeutic effect and one-time treatment advantage, gene therapy may completely change the management of eye diseases, especially retinal diseases. Adeno-associated virus (AAV) is considered one of the most promising viral gene delivery tools because it can infect various types of tissues and is considered as a relatively safe gene delivery vector. The eye is one of the most popular organs for gene therapy, since its limited volume is suitable for small doses of AAV stably transduction. Recently, an increasing number of clinical trials of AAV-mediated gene therapy are underway. This review summarizes the biological functions of AAV and its application in the treatment of various ocular diseases, as well as the characteristics of different AAV delivery routes in clinical applications. Here, the latest research progresses in AAV-mediated gene editing and silencing strategies to modify that the genetic ocular diseases are systematically outlined, especially by base editing and prime editing. We discuss the progress of AAV in ocular optogenetic therapy. We also summarize the application of AAV-mediated gene therapy in animal models and the difficulties in its clinical transformation.

RPGRIP1-related retinal disease presenting as isolated cone dysfunction

PURPOSE

Bialleic RPGRIP1 pathogenic variants are typically associated with severe Leber congenital amaurosis (non-recordable electroretinography [ERG]) and less commonly with cone-rod dystrophy. This report highlights isolated cone dysfunction as an alternative RPGRIP1-related presenting phenotype.

METHODS

Retrospective case series.

RESULTS

Four individuals (two sibships from two unrelated families) had low vision, nystagmus, photophobia, and a grossly normal retinal appearance since soon after birth. ERG confirmed non-recordable photopic function with normal scotopic function. Genetic testing revealed affected members from the two families to harbor two different homozygous RPGRIP1 variants (Family 1: c.3565C>T; p.Arg1189*; Family 2: c.2711_2741delinsATATTAG; p.Gly904_Lys914delinsAspIIeArg). Follow-up for Family 1 revealed deterioration of pan-retinal function (non-recordable ERGs by 11 and 7 years old) and thus a final diagnosis of cone-rod dystrophy. Follow-up for Family 2 showed stable retinal function (normal ERG scotopic tracings maintained at 12 and 21 years old) and thus a diagnosis of isolated cone dysfunction.

CONCLUSIONS

Isolated cone dysfunction that progresses to pan-retinal dysfunction or remains relatively stationary is an alternative phenotype related to biallelic RPGRIP1 pathogenic variants.

A novel pathogenic CRB1 variant presenting as Leber Congenital Amaurosis 8 and evaluation of gene editing feasibility

INTRODUCTION

Leber Congenital Amaurosis (LCA) is an inherited retinal disease that presents in infancy with severely decreased vision, nystagmus, and extinguished electroretinography findings. LCA8 is linked to variants in the Crumbs homolog 1 (CRB1) gene.

CASE DESCRIPTION

We report a novel CRB1 variant in a 14-year-old male presenting with nystagmus, worsening vision, and inability to fixate on toys in his infancy. Color fundus photography revealed nummular pigments in the macula and periphery. Imaging studies revealed thickened retina on standard domain optical coherence tomography and widespread atrophy of the retinal pigment epithelium on autofluorescence. Full-field electroretinography revealed extinguished scotopic and significantly reduced photopic responses. Genetic testing demonstrated a novel homozygous variant, c.3057 T > A; p.(Tyr1019Ter), in the CRB1 gene. This variant is not currently amenable to base editing, however, in silico analysis revealed several potential prime editing strategies for correction.

CONCLUSION

This case presentation is consistent with LCA8, suggesting pathogenicity of this novel variant and expanding our knowledge of disease-causing CRB1 variants.

Patient stem cell-derived in vitro disease models for developing novel therapies of retinal ciliopathies

Primary cilia are specialized organelles on the surface of almost all cells in vertebrate tissues and are primarily involved in the detection of extracellular stimuli. In retinal photoreceptors, cilia are uniquely modified to form outer segments containing components required for the detection of light in stacks of membrane discs. Not surprisingly, vision impairment is a frequent phenotype associated with ciliopathies, a heterogeneous class of conditions caused by mutations in proteins required for formation, maintenance and/or function of primary cilia. Traditionally, immortalized cell lines and model organisms have been used to provide insights into the biology of ciliopathies. The advent of methods for reprogramming human somatic cells into pluripotent stem cells has enabled the generation of in vitro disease models directly from patients suffering from ciliopathies. Such models help us in investigating pathological mechanisms specific to human physiology and in developing novel therapeutic approaches. In this article, we review current protocols to differentiate human pluripotent stem cells into retinal cell types, and discuss how these cellular and/or organoid models can be utilized to interrogate pathobiology of ciliopathies affecting the retina and for testing prospective treatments.

Therapeutic applications of CRISPR/Cas9 gene editing technology for the treatment of ocular diseases

Ocular diseases are a highly heterogeneous group of phenotypes, caused by a spectrum of genetic variants and environmental factors that exhibit diverse clinical symptoms. As a result of its anatomical location, structure and immune privilege, the eye is an ideal system to assess and validate novel genetic therapies. Advances in genome editing have revolutionized the field of biomedical science, enabling researchers to understand the biology behind disease mechanisms and allow the treatment of several health conditions, including ocular pathologies. The advent of clustered regularly interspaced short palindromic repeats (CRISPR)-based gene editing facilitates efficient and specific genetic modifications in the nucleic acid sequence, resulting in permanent changes at the genomic level. This approach has advantages over other treatment strategies and is promising for the treatment of various genetic and non-genetic ocular conditions. This review provides an overview of the CRISPR/CRISPR-associated protein 9 (Cas9) system and summarizes recent advances in the therapeutic application of CRISPR/Cas9 for the treatment of various ocular pathologies, as well as future challenges.

IMPDH1-associated autosomal dominant retinitis pigmentosa: natural history of novel variant Lys314Gln and a comprehensive literature search

BACKGROUND

Inosine monophosphate dehydrogenase (IMPDH) is a key regulatory enzyme in the de novo synthesis of the purine base guanine. Mutations in the inosine monophosphate dehydrogenase 1 gene (IMPDH1) are causative for RP10 autosomal dominant retinitis pigmentosa (adRP). This study reports a novel variant in a family with IMPDH1-associated retinopathy. We also performed a comprehensive review of all reported IMPDH1 disease causing variants with their associated phenotype.

MATERIALS AND METHODS

Multimodal imaging and functional studies documented the phenotype including best-corrected visual acuity (BCVA), fundus photograph, fundus autofluorescence (FAF), full field electroretinogram (ffERG), optical coherence tomography (OCT) and visual field (VF) data were collected. A literature search was performed in the PubMed and LOVD repositories.

RESULTS

We report 3 cases from a 2-generation family with a novel heterozygous likely pathogenic variant p. (Lys314Gln) (exon 10). The ophthalmic phenotype showed diffuse outer retinal atrophy with mild pigmentary changes with sparse pigmentary changes. FAF showed early macular involvement with macular hyperautofluorescence (hyperAF) surrounded by hypoAF. Foveal ellipsoid zone island can be found in the youngest patient but not in the older ones. The literature review identified a further 56 heterozygous, 1 compound heterozygous, and 2 homozygous variant. The heterozygous group included 43 missense, 3 in-frame, 1 nonsense, 2 frameshift, 1 synonymous, and 6 intronic variants. Exon 10 was noted as a hotspot harboring 18 variants.

CONCLUSIONS

We report a novel IMPDH1 variant. IMPDH1-associated retinopathy presents most frequently in the first decade of life with early macular involvement.

The Structural Abnormalities Are Deeply Involved in the Cause of RPGRIP1-Related Retinal Dystrophy in Japanese Patients

Leber congenital amaurosis (LCA) is the most severe form of inherited retinal dystrophy. RPGRIP1-related LCA accounts for 5-6% of LCA. We performed whole-exome sequencing and whole-genome sequencing (WGS) on 29 patients with clinically suspected LCA and examined ophthalmic findings in patients with biallelic pathogenic variants of RPGRIP1. In addition to five previously reported cases, we identified five cases from four families with compound heterozygous RPGRIP1 variants using WGS. Five patients had null variants comprising frameshift variants, an Alu insertion, and microdeletions. A previously reported 1339 bp deletion involving exon 18 was found in four cases, and the deletion was relatively prevalent in the Japanese population (allele frequency: 0.002). Microdeletions involving exon 1 were detected in four cases. In patients with RPGRIP1 variants, visual acuity remained low, ranging from light perception to 0.2, and showed no correlation with age. In optical coherence tomography images, the ellipsoid zone (EZ) length decreased with age in all but one case of unimpaired EZ. The retinal structure was relatively preserved in all cases; however, there were cases with great differences in visual function compared to their siblings and a 56-year-old patient who still had a faint EZ line. Structural abnormalities may be important genetic causes of RPGRIP1-related retinal dystrophy in Japanese patients, and WGS was useful for detecting them.

Revisiting Retinal Degeneration Hallmarks: Insights from Molecular Markers and Therapy Perspectives

Visual impairment and blindness are a growing public health problem as they reduce the life quality of millions of people. The management and treatment of these diseases represent scientific and therapeutic challenges because different cellular and molecular actors involved in the pathophysiology are still being identified. Visual system components, particularly retinal cells, are extremely sensitive to genetic or metabolic alterations, and immune responses activated by local insults contribute to biological events, culminating in vision loss and irreversible blindness. Several ocular diseases are linked to retinal cell loss, and some of them, such as retinitis pigmentosa, age-related macular degeneration, glaucoma, and diabetic retinopathy, are characterized by pathophysiological hallmarks that represent possibilities to study and develop novel treatments for retinal cell degeneration. Here, we present a compilation of revisited information on retinal degeneration, including pathophysiological and molecular features and biochemical hallmarks, and possible research directions for novel treatments to assist as a guide for innovative research. The knowledge expansion upon the mechanistic bases of the pathobiology of eye diseases, including information on complex interactions of genetic predisposition, chronic inflammation, and environmental and aging-related factors, will prompt the identification of new therapeutic strategies.

Genome editing in the treatment of ocular diseases

Genome-editing technologies have ushered in a new era in gene therapy, providing novel therapeutic strategies for a wide range of diseases, including both genetic and nongenetic ocular diseases. These technologies offer new hope for patients suffering from previously untreatable conditions. The unique anatomical and physiological features of the eye, including its immune-privileged status, size, and compartmentalized structure, provide an optimal environment for the application of these cutting-edge technologies. Moreover, the development of various delivery methods has facilitated the efficient and targeted administration of genome engineering tools designed to correct specific ocular tissues. Additionally, advancements in noninvasive ocular imaging techniques and electroretinography have enabled real-time monitoring of therapeutic efficacy and safety. Herein, we discuss the discovery and development of genome-editing technologies, their application to ocular diseases from the anterior segment to the posterior segment, current limitations encountered in translating these technologies into clinical practice, and ongoing research endeavors aimed at overcoming these challenges.

A multidisciplinary approach to inherited retinal dystrophies from diagnosis to initial care: a narrative review with inputs from clinical practice

BACKGROUND

Non-syndromic inherited retinal dystrophies (IRDs) such as retinitis pigmentosa or Leber congenital amaurosis generally manifest between early childhood and late adolescence, imposing profound long-term impacts as a result of vision impairment or blindness. IRDs are highly heterogeneous, with often overlapping symptoms among different IRDs, and achieving a definite diagnosis is challenging. This narrative review provides a clinical overview of the non-syndromic generalized photoreceptor dystrophies, particularly retinitis pigmentosa and Leber congenital amaurosis. The clinical investigations and genetic testing needed to establish a diagnosis are outlined, and current management approaches are discussed, focusing on the importance of the involvement of an interdisciplinary team from diagnosis and initial care to long-term follow-up and support.

RESULTS

The effective management of IRDs requires a multidisciplinary, and ideally interdisciplinary, team of experts knowledgeable about IRDs, with experienced professionals from fields as diverse as ophthalmology, neuropsychiatry, psychology, neurology, genetics, orthoptics, developmental therapy, typhlology, occupational therapy, otolaryngology, and orientation and mobility specialties. Accurate clinical diagnosis encompasses a range of objective and subjective assessments as a prerequisite for the genetic testing essential in establishing an accurate diagnosis necessary for the effective management of IRDs, particularly in the era of gene therapies. Improvements in genome sequencing techniques, such as next-generation sequencing, have greatly facilitated the complex process of determining IRD-causing gene variants and establishing a molecular diagnosis. Genetic counseling is essential to help the individual and their family understand the condition, the potential risk for offspring, and the implications of a diagnosis on visual prognosis and treatment options. Psychological support for patients and caregivers is important at all stages of diagnosis, care, and rehabilitation and is an essential part of the multidisciplinary approach to managing IRDs. Effective communication throughout is essential, and the patient and caregivers' needs and expectations must be acknowledged and discussed.

CONCLUSION

As IRDs can present at an early age, clinicians need to be aware of the clinical signs suggesting visual impairment and follow up with multidisciplinary support for timely diagnoses to facilitate appropriate therapeutic or rehabilitation intervention to minimize vision loss.

Progressive Cone-Rod Dystrophy and RPE Dysfunction in Mitfmi/+ Mice

Mutations in the mouse microphthalmia-associated transcription factor (Mitf) gene affect retinal pigment epithelium (RPE) differentiation and development and can lead to hypopigmentation, microphthalmia, deafness, and blindness. For instance, an association has been established between loss-of-function mutations in the mouse Mitf gene and a variety of human retinal diseases, including Waardenburg type 2 and Tietz syndromes. Although there is evidence showing that mice with the homozygous Mitfmi mutation manifest microphthalmia and osteopetrosis, there are limited or no data on the effects of the heterozygous condition in the eye. Mitf mice can therefore be regarded as an important model system for the study of human disease. Thus, we characterized Mitfmi/+ mice at 1, 3, 12, and 18 months old in comparison with age-matched wild-type mice. The light- and dark-adapted electroretinogram (ERG) recordings showed progressive cone-rod dystrophy in Mitfmi/+ mice. The RPE response was reduced in the mutant in all age groups studied. Progressive loss of pigmentation was found in Mitfmi/+ mice. Histological retinal sections revealed evidence of retinal degeneration in Mitfmi/+ mice at older ages. For the first time, we report a mouse model of progressive cone-rod dystrophy and RPE dysfunction with a mutation in the Mitf gene.

Primary cilia as dynamic and diverse signalling hubs in development and disease

Primary cilia, antenna-like sensory organelles protruding from the surface of most vertebrate cell types, are essential for regulating signalling pathways during development and adult homeostasis. Mutations in genes affecting cilia cause an overlapping spectrum of >30 human diseases and syndromes, the ciliopathies. Given the immense structural and functional diversity of the mammalian cilia repertoire, there is a growing disconnect between patient genotype and associated phenotypes, with variable severity and expressivity characteristic of the ciliopathies as a group. Recent technological developments are rapidly advancing our understanding of the complex mechanisms that control biogenesis and function of primary cilia across a range of cell types and are starting to tackle this diversity. Here, we examine the structural and functional diversity of primary cilia, their dynamic regulation in different cellular and developmental contexts and their disruption in disease.

Integrative Single-Cell Transcriptomics and Epigenomics Mapping of the Fetal Retina Developmental Dynamics

The underlying mechanisms that determine gene expression and chromatin accessibility in retinogenesis are poorly understood. Herein, single-cell RNA sequencing and single-cell assay for transposase-accessible chromatin sequencing are performed on human embryonic eye samples obtained 9-26 weeks after conception to explore the heterogeneity of retinal progenitor cells (RPCs) and neurogenic RPCs. The differentiation trajectory from RPCs to 7 major types of retinal cells are verified. Subsequently, diverse lineage-determining transcription factors are identified and their gene regulatory networks are refined at the transcriptomic and epigenomic levels. Treatment of retinospheres, with the inhibitor of RE1 silencing transcription factor, X5050, induces more neurogenesis with the regular arrangement, and a decrease in Müller glial cells. The signatures of major retinal cells and their correlation with pathogenic genes associated with multiple ocular diseases, including uveitis and age-related macular degeneration are also described. A framework for the integrated exploration of single-cell developmental dynamics of the human primary retina is provided.

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.

Clinical and Molecular Features of a Chinese Cohort With Syndromic and Nonsyndromic Retinal Dystrophies Related to the CEP290 Gene

PURPOSE

To reveal the clinical and genetic features of 54 Chinese pedigrees with syndromic or nonsyndromic retinal dystrophies related to CEP290 and to explore the genotype-phenotype correlation.

DESIGN

Retrospective cohort study.

METHODS

Patients diagnosed with nonsyndromic inherited retinal dystrophy (IRD) or syndromic ciliopathy (SCP) were enrolled. We identified 61 patients from 54 families carrying biallelic pathogenic CEP290 variants using next-generation sequencing, Sanger sequencing, and co-segregation validation. Genotype-phenotype correlation was evaluated.

RESULTS

This study included 37 IRD patients from 32 families and 24 patients with SCP from 22 pedigrees. Four retinal dystrophy phenotypes were confirmed: Leber congenital amaurosis (LCA, 46/61), early-onset severe retinal dystrophy (EOSRD, 4/61), retinitis pigmentosa (RP, 10/61), and cone-rod dystrophy (CORD, 1/61). The SCP phenotypes included Joubert syndrome (JS) (23/24) and Bardet-Biedl syndrome (BBS) (1/24). We detected 73 different CEP290 variants, of which 33 (45.2%) were not previously reported. Two novel copy number variations (CNVs) and 1 novel pathogenic synonymous change were identified. The most recurrent alterations in the IRD and SCP were p.Q123* (6/64, 9.4%) and p.I556Ffs*17 (10/44, 22.7%), respectively. IRD patients carried more stop-gain alleles (25/64, 39.1%), whereas SCP patients carried more frameshift alleles (23/44, 52.3%).

CONCLUSIONS

LCA was the most common retinal dystrophy phenotype, and JS was the most prevalent syndrome in CEP290 patients; RP/CORD and BBS may be present in early adulthood. The hot spot variants and distribution of genotypes were distinct between IRD and SCP. Our study expands the CEP290 variant spectrum and enhances the current knowledge of CEP290 heterogeneity.

Retinal Organoids from an AIPL1 CRISPR/Cas9 Knockout Cell Line Successfully Recapitulate the Molecular Features of LCA4 Disease

Aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) is expressed in photoreceptors where it facilitates the assembly of phosphodiesterase 6 (PDE6) which hydrolyses cGMP within the phototransduction cascade. Genetic variations in AIPL1 cause type 4 Leber congenital amaurosis (LCA4), which presents as rapid loss of vision in early childhood. Limited in vitro LCA4 models are available, and these rely on patient-derived cells harbouring patient-specific AIPL1 mutations. While valuable, the use and scalability of individual patient-derived LCA4 models may be limited by ethical considerations, access to patient samples and prohibitive costs. To model the functional consequences of patient-independent AIPL1 mutations, CRISPR/Cas9 was implemented to produce an isogenic induced pluripotent stem cell line harbouring a frameshift mutation in the first exon of AIPL1. Retinal organoids were generated using these cells, which retained AIPL1 gene transcription, but AIPL1 protein was undetectable. AIPL1 knockout resulted in a decrease in rod photoreceptor-specific PDE6α and β, and increased cGMP levels, suggesting downstream dysregulation of the phototransduction cascade. The retinal model described here provides a novel platform to assess functional consequences of AIPL1 silencing and measure the rescue of molecular features by potential therapeutic approaches targeting mutation-independent pathogenesis.

Polymer- and lipid-based nanocarriers for ocular drug delivery: Current status and future perspectives

Ocular diseases seriously affect patients' vision and life quality, with a global morbidity of over 43 million blindness. However, efficient drug delivery to treat ocular diseases, particularly intraocular disorders, remains a huge challenge due to multiple ocular barriers that significantly affect the ultimate therapeutic efficacy of drugs. Recent advances in nanocarrier technology offer a promising opportunity to overcome these barriers by providing enhanced penetration, increased retention, improved solubility, reduced toxicity, prolonged release, and targeted delivery of the loaded drug to the eyes. This review primarily provides an overview of the progress and contemporary applications of nanocarriers, mainly polymer- and lipid-based nanocarriers, in treating various eye diseases, highlighting their value in achieving efficient ocular drug delivery. Additionally, the review covers the ocular barriers and administration routes, as well as the prospective future developments and challenges in the field of nanocarriers for treating ocular diseases.

The application and progression of CRISPR/Cas9 technology in ophthalmological diseases

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas) system is an adaptive immune defence system that has gradually evolved in bacteria and archaea to combat invading viruses and exogenous DNA. Advances in technology have enabled researchers to enhance their understanding of the immune process in vivo and its potential for use in genome editing. Thus far, applications of CRISPR/Cas9 genome editing technology in ophthalmology have included gene therapy for corneal dystrophy, glaucoma, congenital cataract, Leber's congenital amaurosis, retinitis pigmentosa, Usher syndrome, fundus neovascular disease, proliferative vitreoretinopathy, retinoblastoma and other eye diseases. Additionally, the combination of CRISPR/Cas9 genome editing technology with adeno-associated virus vector and inducible pluripotent stem cells provides further therapeutic avenues for the treatment of eye diseases. Nonetheless, many challenges remain in the development of clinically feasible retinal genome editing therapy. This review discusses the development, as well as mechanism of CRISPR/Cas9 and its applications and challenges in gene therapy for eye diseases.

Progress in and Prospects of Genome Editing Tools for Human Disease Model Development and Therapeutic Applications

Programmable nucleases, such as zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas, are widely accepted because of their diversity and enormous potential for targeted genomic modifications in eukaryotes and other animals. Moreover, rapid advances in genome editing tools have accelerated the ability to produce various genetically modified animal models for studying human diseases. Given the advances in gene editing tools, these animal models are gradually evolving toward mimicking human diseases through the introduction of human pathogenic mutations in their genome rather than the conventional gene knockout. In the present review, we summarize the current progress in and discuss the prospects for developing mouse models of human diseases and their therapeutic applications based on advances in the study of programmable nucleases.

Cost-effective sequence analysis of 113 genes in 1,192 probands with retinitis pigmentosa and Leber congenital amaurosis

Introduction: Retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) are two groups of inherited retinal diseases (IRDs) where the rod photoreceptors degenerate followed by the cone photoreceptors of the retina. A genetic diagnosis for IRDs is challenging since >280 genes are associated with these conditions. While whole exome sequencing (WES) is commonly used by diagnostic facilities, the costs and required infrastructure prevent its global applicability. Previous studies have shown the cost-effectiveness of sequence analysis using single molecule Molecular Inversion Probes (smMIPs) in a cohort of patients diagnosed with Stargardt disease and other maculopathies. Methods: Here, we introduce a smMIPs panel that targets the exons and splice sites of all currently known genes associated with RP and LCA, the entire RPE65 gene, known causative deep-intronic variants leading to pseudo-exons, and part of the RP17 region associated with autosomal dominant RP, by using a total of 16,812 smMIPs. The RP-LCA smMIPs panel was used to screen 1,192 probands from an international cohort of predominantly RP and LCA cases. Results and discussion: After genetic analysis, a diagnostic yield of 56% was obtained which is on par with results from WES analysis. The effectiveness and the reduced costs compared to WES renders the RP-LCA smMIPs panel a competitive approach to provide IRD patients with a genetic diagnosis, especially in countries with restricted access to genetic testing.

Cellular and Molecular Mechanisms of Pathogenesis Underlying Inherited Retinal Dystrophies

Inherited retinal dystrophies (IRDs) are congenital retinal degenerative diseases that have various inheritance patterns, including dominant, recessive, X-linked, and mitochondrial. These diseases are most often the result of defects in rod and/or cone photoreceptor and retinal pigment epithelium function, development, or both. The genes associated with these diseases, when mutated, produce altered protein products that have downstream effects in pathways critical to vision, including phototransduction, the visual cycle, photoreceptor development, cellular respiration, and retinal homeostasis. The aim of this manuscript is to provide a comprehensive review of the underlying molecular mechanisms of pathogenesis of IRDs by delving into many of the genes associated with IRD development, their protein products, and the pathways interrupted by genetic mutation.

Embryonic stem cell extracellular vesicles reverse the senescence of retinal pigment epithelial cells by the p38MAPK pathway

Retinal pigment epithelial (RPE) cellular senescence is regarded as an initiator for age-related macular degeneration (AMD). We previously demonstrated that by the coculture way, embryonic stem cells (ESCs) can reverse the senescence of RPE cells, but xenograft cells can cause a plethora of adverse effects. Extracellular vesicles (EVs) derived from ESCs can act as messengers to mediate nearby cell activities and have the same potential as ESCs to reverse RPE senescence. Furthermore, ESC-EVs have achieved preliminary efficacy while treating many age-related diseases. The present study aimed to test the effect of ESC-EVs on the replicative senescence model of RPE cells as well as its mechanism. The results showed that ESC-EVs enhanced the proliferative ability and cell cycle transition of senescent RPE cells, whereas reduced the senescence-associated galactosidase (SA-β-gal) staining rate, as well as the levels of mitochondrial membrane potential (MMP) and reactive oxygen species (ROS). Moreover, classical markers of cellular senescence p21^WAF1/CIP1 (p21) and p16^INK4a (p16) were downregulated. The bioinformatic analysis and further study showed that the inhibition of the p38MAPK pathway by ESC-EVs played a pivotal role in RPE cellular senescence-reversing effect, which was ameliorated or even abolished when dehydrocorydaline were administrated simultaneously, demonstrating that ESC-EVs can effectively reverse RPE cellular senesence by inhibiting the p38MAPK pathway, thus highlights the potential of ESC-derived EVs as biomaterials for preventative and protective therapy in AMD.

Biallelic Variants in TULP1 Are Associated with Heterogeneous Phenotypes of Retinal Dystrophy

Biallelic pathogenic variants in TULP1 are mostly associated with severe rod-driven inherited retinal degeneration. In this study, we analyzed clinical heterogeneity in 17 patients and characterized the underlying biallelic variants in TULP1. All patients underwent thorough ophthalmological examinations. Minigene assays and structural analyses were performed to assess the consequences of splice variants and missense variants. Three patients were diagnosed with Leber congenital amaurosis, nine with early onset retinitis pigmentosa, two with retinitis pigmentosa with an onset in adulthood, one with cone dystrophy, and two with cone-rod dystrophy. Seventeen different alleles were identified, namely eight missense variants, six nonsense variants, one in-frame deletion variant, and two splice site variants. For the latter two, minigene assays revealed aberrant transcripts containing frameshifts and premature termination codons. Structural analysis and molecular modeling suggested different degrees of structural destabilization for the missense variants. In conclusion, we report the largest cohort of patients with TULP1-associated IRD published to date. Most of the patients exhibited rod-driven disease, yet a fraction of the patients exhibited cone-driven disease. Our data support the hypothesis that TULP1 variants do not fold properly and thus trigger unfolded protein response, resulting in photoreceptor death.

Loss-of-function approach using mouse retinal explants showed pivotal roles of Nmnat2 in early and middle stages of retinal development

Nicotinamide mononucleotide adenylyltransferase (Nmnat) is a class of enzymes with three members (Nmnat1-3). Nmnat1 is in nucleus and associated with Leber congenital amaurosis, a form of early-onset retinal degeneration, while Nmnat2 is in cytoplasm and a well-characterized neuroprotective factor. The differences in their biological roles in the retina are unclear. We performed short hairpin RNA (shRNA)-based loss-of-function analysis of Nmnat2 during mouse retinal development in retinal explant cultures prepared from early (E14.5), middle (E17.5), or late (postnatal day [P]0.5) developmental stages. Nmnat2 has important roles in the survival of retinal cells in the early and middle stages of retinal development. Retinal cell death caused by Nmnat2 knockdown could be partially rescued by supplementation with NAD or nicotinamide mononucleotide (NMN). Survival of retinal cells in the late stage of retinal development was unaffected by Nmnat2, but differentiation of Müller glia was controlled by Nmnat2. RNA-Seq analyses showed perturbation of gene expression patterns by shRNAs specific for Nmnat1 or Nmnat2, but gene ontology analysis did not provide a rational explanation for the phenotype. This study showed that Nmnat2 has multiple developmental stage-dependent roles during mouse retinal development, which were clearly different from those of Nmnat1, suggesting specific roles for Nmnat1 and Nmnat2.

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

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

Ependyma: a new target for autoantibodies in neuromyelitis optica?

Neuromyelitis optica (NMO) is an autoimmune demyelinating disease of the central nervous system characterized by the presence of autoantibodies (called NMO-IgG) targeting aquaporin-4. Aquaporin-4 is expressed at the perivascular foot processes of astrocytes, in the glia limitans, but also at the ependyma. Most studies have focused on studying the pathogenicity of NMO-IgG on astrocytes, and NMO is now considered an astrocytopathy. However, periependymal lesions are observed in NMO suggesting that ependymal cells could also be targeted by NMO-IgG. Ependymal cells regulate CSF-parenchyma molecular exchanges and CSF flow, and are a niche for sub-ventricular neural stem cells. Our aim was to examine the effect of antibodies from NMO patients on ependymal cells. We exposed two models, i.e. primary cultures of rat ependymal cells and explant cultures of rat lateral ventricular wall whole mounts, to purified IgG of NMO patients (NMO-IgG) for 24 hours. We then evaluated the treatment effect using immunolabelling, functional assays, ependymal flow analysis and bulk RNA sequencing. For each experiment, the effects were compared with those of purified IgG from a healthy donors and non-treated cells. We found that: (i) NMO-IgG induced aquaporin-4 agglomeration at the surface of ependymal cells and induced cell enlargement in comparison to controls. In parallel, it induced an increase in gap junction connexin-43 plaque size; (ii) NMO-IgG altered the orientation of ciliary basal bodies and functionally impaired cilia motility; (iii) NMO-IgG activated the proliferation of sub-ventricular neural stem cells; (iv) treatment with NMO-IgG up-regulated the expression of pro-inflammatory cytokines and chemokines in the transcriptomic analysis. Our study showed that NMO-IgG can trigger an early and specific reactive phenotype in ependymal cells, with functional alterations of intercellular communication and cilia, activation of sub-ventricular stem cell proliferation and the secretion of pro-inflammatory cytokines. These findings suggest a key role for ependymal cells in the early phase of NMO lesion formation.

CRISPR-Based Tools for Fighting Rare Diseases

Rare diseases affect the life of a tremendous number of people globally. The CRISPR-Cas system emerged as a powerful genome engineering tool and has facilitated the comprehension of the mechanism and development of therapies for rare diseases. This review focuses on current efforts to develop the CRISPR-based toolbox for various rare disease therapy applications and compares the pros and cons of different tools and delivery methods. We further discuss the therapeutic applications of CRISPR-based tools for fighting different rare diseases.

Bioengineering Human Pluripotent Stem Cell-Derived Retinal Organoids and Optic Vesicle-Containing Brain Organoids for Ocular Diseases

Retinal organoids are three-dimensional (3D) structures derived from human pluripotent stem cells (hPSCs) that mimic the retina's spatial and temporal differentiation, making them useful as in vitro retinal development models. Retinal organoids can be assembled with brain organoids, the 3D self-assembled aggregates derived from hPSCs containing different cell types and cytoarchitectures that resemble the human embryonic brain. Recent studies have shown the development of optic cups in brain organoids. The cellular components of a developing optic vesicle-containing organoids include primitive corneal epithelial and lens-like cells, retinal pigment epithelia, retinal progenitor cells, axon-like projections, and electrically active neuronal networks. The importance of retinal organoids in ocular diseases such as age-related macular degeneration, Stargardt disease, retinitis pigmentosa, and diabetic retinopathy are described in this review. This review highlights current developments in retinal organoid techniques, and their applications in ocular conditions such as disease modeling, gene therapy, drug screening and development. In addition, recent advancements in utilizing extracellular vesicles secreted by retinal organoids for ocular disease treatments are summarized.

Therapeutic modulation of gene expression in the disease state: Treatment strategies and approaches for the development of next-generation of the epigenetic drugs

Epigenetic dysregulation is an important determinant of many pathological conditions and diseases. Designer molecules that can specifically target endogenous DNA sequences provide a means to therapeutically modulate gene function. The prokaryote-derived CRISPR/Cas editing systems have transformed our ability to manipulate the expression program of genes through specific DNA and RNA targeting in living cells and tissues. The simplicity, utility, and robustness of this technology have revolutionized epigenome editing for research and translational medicine. Initial success has inspired efforts to discover new systems for targeting and manipulating nucleic acids on the epigenetic level. The evolution of nuclease-inactive and RNA-targeting Cas proteins fused to a plethora of effector proteins to regulate gene expression, epigenetic modifications and chromatin interactions opened up an unprecedented level of possibilities for the development of “next-generation” gene therapy therapeutics. The rational design and construction of different types of designer molecules paired with viral-mediated gene-to-cell transfers, specifically using lentiviral vectors (LVs) and adeno-associated vectors (AAVs) are reviewed in this paper. Furthermore, we explore and discuss the potential of these molecules as therapeutic modulators of endogenous gene function, focusing on modulation by stable gene modification and by regulation of gene transcription. Notwithstanding the speedy progress of CRISPR/Cas-based gene therapy products, multiple challenges outlined by undesirable off-target effects, oncogenicity and other virus-induced toxicities could derail the successful translation of these new modalities. Here, we review how CRISPR/Cas—based gene therapy is translated from research-grade technological system to therapeutic modality, paying particular attention to the therapeutic flow from engineering sophisticated genome and epigenome-editing transgenes to delivery vehicles throughout efficient and safe manufacturing and administration of the gene therapy regimens. In addition, the potential solutions to some of the obstacles facing successful CRISPR/Cas utility in the clinical research are discussed in this review. We believe, that circumventing these challenges will be essential for advancing CRISPR/Cas-based tools towards clinical use in gene and cell therapies.

In vivo application of base and prime editing to treat inherited retinal diseases

Inherited retinal diseases (IRDs) are vision-threatening retinal disorders caused by pathogenic variants of genes related to visual functions. Genomic analyses in patients with IRDs have revealed pathogenic variants which affect vision. However, treatment options for IRDs are limited to nutritional supplements regardless of genetic variants or gene-targeting approaches based on antisense oligonucleotides and adeno-associated virus vectors limited to targeting few genes. Genome editing, particularly that involving clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 technologies, can correct pathogenic variants and provide additional treatment opportunities. Recently developed base and prime editing platforms based on CRISPR-Cas9 technologies are promising for therapeutic genome editing because they do not employ double-stranded breaks (DSBs), which are associated with P53 activation, large deletions, and chromosomal translocations. Instead, using attached deaminases and reverse transcriptases, base and prime editing efficiently induces specific base substitutions and intended genetic changes (substitutions, deletions, or insertions), respectively, without DSBs. In this review, we will discuss the recent in vivo application of CRISPR-Cas9 technologies, focusing on base and prime editing, in animal models of IRDs.

Retinal gene therapy in RPE-65 gene mediated inherited retinal dystrophy

BACKGROUND

Voretigene neparvovec (VN) is a gene therapeutic agent for treatment of retinal dystrophies caused by bi-allelic RPE65 mutations. We illustrate, both the benefits and pitfalls associated with ocular gene therapy in the same patient.

METHODS

Two eyes of one patient with bi-allelic RPE65 mutations have been treated with VN. The clinical examinations included visual acuity (VA, in normal and low luminance), colour vision, contrast sensitivity, International Society for Clinical Electrophysiology of Vision (ISCEV) standard retinal electrophysiology and dark-adapted full-field stimulus threshold (FST), Goldmann VF analysis and imaging studies, including optical coherence tomography (OCT) and autofluorescence. These were performed at baseline, 2-weeks, 3 and 6-months, 1 and 2-years follow-up.

RESULTS

The first eye showed improvement in rod photoreceptor function with increased peripheral and low luminance vision (baseline VA: 0.9 logMAR and 2-years post-operative VA: 0.7 logMAR). The second eye, whilst showing increased light sensitivity, suffered a drop in central vision (at 2-weeks) with loss of foveal photoreceptors as shown by the loss of ellipsoid zone on OCT scan (baseline VA: 0.6, 2-year post-operative VA: 1.2). FST improvements were maintained in both eyes indicating a sustained efficacy of VN with little waning of its effect.

CONCLUSIONS

We present a previously unreported adverse complication of subretinal VN therapy in bi-allelic RPE65, indicating a probable immune response in treatment of the second eye, resulting in loss of foveal photoreceptors. This case-series highlights the potential and pitfalls of retinal gene therapy in the same patient. The immune responses of the body to a 'foreign vector', remains a challenge.

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.

The interaction between LC8 and LCA5 reveals a novel oligomerization function of LC8 in the ciliary-centrosome system

Dynein light chain LC8 is a small dimeric hub protein that recognizes its partners through short linear motifs and is commonly assumed to drive their dimerization. It has more than 100 known binding partners involved in a wide range of cellular processes. Recent large-scale interaction studies suggested that LC8 could also play a role in the ciliary/centrosome system. However, the cellular function of LC8 in this system remains elusive. In this work, we characterized the interaction of LC8 with the centrosomal protein lebercilin (LCA5), which is associated with a specific form of ciliopathy. We showed that LCA5 binds LC8 through two linear motifs. In contrast to the commonly accepted model, LCA5 forms dimers through extensive coiled coil formation in a LC8-independent manner. However, LC8 enhances the oligomerization ability of LCA5 that requires a finely balanced interplay of coiled coil segments and both binding motifs. Based on our results, we propose that LC8 acts as an oligomerization engine that is responsible for the higher order oligomer formation of LCA5. As LCA5 shares several common features with other centrosomal proteins, the presented LC8 driven oligomerization could be widespread among centrosomal proteins, highlighting an important novel cellular function of LC8.

Exome Sequencing Identified Molecular Determinants of Retinal Dystrophies in Nine Consanguineous Pakistani Families

Inherited retinal dystrophies (IRDs) are a heterogeneous group of degenerative disorders of the retina. Retinitis Pigmentosa (RP) is a common type of IRD that causes night blindness and loss of peripheral vision and may progress to blindness. Mutations in more than 300 genes have been associated with syndromic and non-syndromic IRDs. Recessive forms are more frequent in populations where endogamy is a social preference, such as Pakistan. The aim of this study was to identify molecular determinants of IRDs with the common presentation of night blindness in consanguineous Pakistani families. This study included nine consanguineous IRD-affected families that presented autosomal recessive inheritance of the night blindness phenotype. DNA was extracted from blood samples. Targeted exome sequencing of 344 known genes for retinal dystrophies was performed. Screening of nine affected families revealed two novel (c.5571_5576delinsCTAGATand c.471dup in EYS and SPATA7 genes, respectively) and six reported pathogenic mutations (c.304C>A, c.187C>T, c.1560C>A, c.547C>T, c.109del and c.9911_11550del in PDE6A, USH2A, USH2A, NMNAT1, PAX6 and ALMS1 genes, respectively) segregating with disease phenotype in each respective family. Molecular determinants of hereditary retinal dystrophies were identified in all screened families. Identification of novel variants aid future diagnosis of retinal dystrophies and help to provide genetic counseling to affected families.

Update on Viral Gene Therapy Clinical Trials for Retinal Diseases

In 2001, the first large animal was successfully treated with a gene therapy that restored its vision. Lancelot, the Briard dog that was treated, suffered from a human childhood blindness called Leber's congenital amaurosis type 2. Sixteen years later, the gene therapy was approved by the U.S. Food and Drug Administration. The success of this gene therapy in dogs led to a fast expansion of the ocular gene therapy field. By now every class of inherited retinal dystrophy has been treated in at least one animal model and many clinical trials have been initiated in humans. In this study, we review the status of viral gene therapies for the retina, with a focus on ongoing human clinical trials. It is likely that in the next decade we will see several new viral gene therapies approved.

Investigation of PTC124-mediated translational readthrough in a retinal organoid model of AIPL1-associated Leber congenital amaurosis

Leber congenital amaurosis type 4 (LCA4), caused by AIPL1 mutations, is characterized by severe sight impairment in infancy and rapidly progressing degeneration of photoreceptor cells. We generated retinal organoids using induced pluripotent stem cells (iPSCs) from renal epithelial cells obtained from four children with AIPL1 nonsense mutations. iPSC-derived photoreceptors exhibited the molecular hallmarks of LCA4, including undetectable AIPL1 and rod cyclic guanosine monophosphate (cGMP) phosphodiesterase (PDE6) compared with control or CRISPR-corrected organoids. Increased levels of cGMP were detected. The translational readthrough-inducing drug (TRID) PTC124 was investigated as a potential therapeutic agent. LCA4 retinal organoids exhibited low levels of rescue of full-length AIPL1. However, this was insufficient to fully restore PDE6 in photoreceptors and reduce cGMP. LCA4 retinal organoids are a valuable platform for in vitro investigation of novel therapeutic agents.