Expanding the genotypic and phenotypic spectra with a novel variant in the ciliopathy gene, CFAP410, associated with selective cone degeneration.

BACKGROUND: CFAP410 (Cilia and Flagella Associated Protein 410) encodes a protein that has an important role in the development and function of cilia. In ophthalmology, pathogenic variants in CFAP410 have been described in association with cone rod dystrophy, retinitis pigmentosa, with or without macular staphyloma, or with systemic abnormalities such as skeletal dysplasia and amyotrophic lateral sclerosis. Herein, we report a consanguineous family with a novel homozygous CFAP410 c.335_346del variant with cone only degeneration and no systemic features. METHODS: A retrospective analysis of ophthalmic history, examination, retinal imaging, electrophysiology and microperimetry was performed as well as genetic testing with in silico pathogenicity predictions and a literature review. RESULTS: A systemically well 28-year-old female of Pakistani ethnicity with parental consanguinity and no relevant family history, presented with childhood-onset poor central vision and photophobia. Best-corrected visual acuity and colour vision were reduced (0.5 LogMAR, 6/17 Ishihara plates (right) and 0.6 LogMAR, 3/17 Ishihara plates (left). Fundus examination showed no pigmentary retinopathy, no macular staphyloma and autofluorescence was unremarkable. Optical coherence tomography showed subtle signs of intermittent disruption of the ellipsoid zone. Microperimetry demonstrated a reduction in central retinal sensitivity. Electrodiagnostic testing confirmed a reduction in cone-driven responses. Whole-genome sequencing identified an in-frame homozygous deletion of 12 base pairs at c.335_346del in CFAP410. CONCLUSIONS: The non-syndromic cone dystrophy phenotype reported herein expands the genotypic and phenotypic spectra of CFAP410-associated ciliopathies and highlights the need for light of potential future genetic therapies.

Establishing Clinical Trial Endpoints in Selecting Patients for RPGR Retinal Gene Therapy.

Purpose: Clinical trials for X-linked retinitis pigmentosa (RP) often assess retinal structure using optical coherence tomography (OCT) and function using microperimetry to evaluate initial eligibility and endpoints. Therefore, we seek to determine which parameters might be most sensitive in screening new patients for enrollment. Methods: Thirty-one patients (62 eyes) with confirmed retinitis pigmentosa GTPase regulator (RPGR) mutations attending Oxford Eye Hospital were included in this retrospective analysis. Outer retinal structure was investigated by measuring the remaining ellipsoid zone (EZ) and external limiting membrane (ELM) on OCT. Visual function was evaluated by using 10-2 microperimetry mean sensitivity. Results: The median age of patients with RPGR was 31 years (interquartile range [IQR] = 22-39 years). For the right and left eyes, respectively, the median EZ length through the foveal section was 921 µm (IQR = 607-1570) and 865 µm (IQR = 508-1442) and median ELM length was 2056 µm (IQR = 1336-2764) and 1860 µm (IQR = 1152-2680). Similarly, the median microperimetry sensitivity (MS) was 2.0 decibel (dB; IQR = 0.4-5.4) and 1.1 dB (IQR = 0.1-5.4). Linear mixed model regression analysis showed that EZ was significantly positively correlated to ELM (P < 0.001, R² = 0.931). EZ and ELM were significantly correlated with the microperimetry sensitivity with exponential relationship (P < 0.001, R² = 0.71 and 0.72, respectively). Using the exponential equation of regression line, EZ below approximately 600 µm (RE = 637 µm, 95% confidence interval [CI] = 397-877, LE = 586 µm, 95% CI = 356-817) results in microperimetry sensitivity of approximately 0 dB. There was high degree of inter-eye symmetry for progression of EZ, ELM, and microperimetry sensitivity. Age was significantly correlated with the analyzed parameters (P < 0.001), although with low R² for each of them. Discussion: EZ may comprise a surrogate biomarker for prediction of visual function in X-linked RP caused by mutations in RPGR and, in turn, identification of appropriate patients for enrollment in clinical trials. As expected, age plays a role in predicting potential biomarkers and visual function, however, it should not be used to preclude patients for gene therapy due to the poor correlation and heterogeneity of disease onset. Translational Relevance: Biomarkers of visual function in RPGR-associated RP may lead to identification of appropriate patients for enrollment in clinical trials.

Retinal Focal Nodular Gliosis (Vasoproliferative Tumors) Have Varied Clinical Courses Requiring Tailored Management: A Case Series.

Introduction: Retinal focal nodular gliosis (FNG), also known as vasoproliferative tumors (VPTs), are rare, benign vascular tumors associated with exudation with no current consensus on management. Herein, we describe the varied clinical course and management of 3 patients with retinal FNG, one of whom is associated with retinitis pigmentosa. Case Presentations: Case 1 is a 76-year-old female who presented with reduced vision and distortion secondary to a vitreous hemorrhage and epiretinal membrane (ERM) as complications of a known small peripheral retinal FNG. She underwent vitrectomy for the hemorrhage to relieve vascular traction and the ERM peel, and the tumor was kept under observation. Case 2 is a 24-year-old female with genetically uncharacterized retinitis pigmentosa-like phenotype who presented with gradual loss of central vision in one eye due to cystoid macular oedema (CMO). She was found to have two peripheral retinal areas of FNG located inferonasally. Tumors were treated with cryotherapy and adjuvant intraocular steroid implant to control the CMO. Case 3 is a 28-year-old female with retinitis pigmentosa secondary to genetically confirmed variant in CRB1 gene who presented with intractable right eye CMO and localized inferior serous retinal detachment secondary to a large inferotemporal FNG. Her left eye has no light perception vision due to previous extensive serous retinal detachment and anterior segment ischemia. The right eye tumor was managed with multiple rounds of cryotherapy and laser therapy to control the serous detachment. Despite this, the condition progressed and was ultimately treated with plaque brachytherapy. Unfortunately, this resulted in extensive retinal inflammation causing annular tractional retinal detachment which was treated with combined pars plana vitrectomy and scleral buckle. Conclusion: We characterized the retinal phenotype of 3 patients with retinal FNG (VPTs) and found them to have varied clinical courses requiring tailored surgical management. The case associated with retinitis pigmentosa had a known pathogenic variant in Crumbs homolog-1 (CRB1) gene affecting retinal structure and exhibited a more severe clinical course. It is therefore important for patients with retinal dystrophies to undergo thorough peripheral examinations and detect FNG early as they may require prompt, aggressive treatment.

Longitudinal assessment of female carriers of choroideremia using multimodal retinal imaging.

BACKGROUND/AIMS: Female choroideremia carriers present with a spectrum of disease severity. Unlike in men, the rate of disease progression has not been well characterised in carriers. This longitudinal study aimed to determine the rate of retinal degeneration in choroideremia carriers, using multimodal imaging and microperimetry. METHODS: Choroideremia carriers previously seen at Oxford Eye Hospital (United Kingdom) between 2012 and 2017 returned for testing between 2015 and 2023, providing up to 11 years' follow-up data. Participants had optical coherence tomography, fundus-tracked microperimetry and fundus autofluorescence (FAF) imaging performed. RESULTS: Thirty-four eyes of 17 choroideremia carriers were examined using multimodal imaging. Median age was 44 (range: 15-73) years at baseline and median follow-up duration was 7 (range: 1-11) years. At baseline, phenotype was classified as fine (n=5 eyes), coarse (n=13 eyes), geographic (n=12 eyes) or male pattern (n=4 eyes). Thirteen patients showed no change in phenotype classification, four showed slight changes associated with choroideremia-related retinal degeneration. Despite this, carriers with severe retinal phenotypes had a statistically significant decline in average retinal sensitivity (-0.7 dB and -0.8 dB per year, respectively, p<0.001), area of geographic loss defined by FAF (+2.5 mm2 and +3.7 mm2 per year, respectively, p<0.001) and thinning of the photoreceptor complex (up to -2.8 microns and -10.3 microns per year, p<0.001). CONCLUSION: Choroideremia carriers, particularly those with severe retinal phenotypes, exhibit progressive retinal degeneration, as evident by multimodal imaging biomarkers and functional testing. Clinicians should not rely on retinal severity classification alone to assess disease progression.

Genetic therapies and potential therapeutic applications of CRISPR activators in the eye.

Conventional gene therapy involving supplementation only treats loss-of-function diseases and is limited by viral packaging sizes, precluding therapy of large genes. The discovery of CRISPR/Cas has led to a paradigm shift in the field of genetic therapy, with the promise of precise gene editing, thus broadening the range of diseases that can be treated. The initial uses of CRISPR/Cas have focused mainly on gene editing or silencing of abnormal variants via utilising Cas endonuclease to trigger the target cell endogenous non-homologous end joining. Subsequently, the technology has evolved to modify the Cas enzyme and even its guide RNA, leading to more efficient editing tools in the form of base and prime editing. Further advancements of this CRISPR/Cas technology itself have expanded its functional repertoire from targeted editing to programmable transactivation, shifting the therapeutic focus to precise endogenous gene activation or upregulation with the potential for epigenetic modifications. In vivo experiments using this platform have demonstrated the potential of CRISPR-activators (CRISPRa) to treat various loss-of-function diseases, as well as in regenerative medicine, highlighting their versatility to overcome limitations associated with conventional strategies. This review summarises the molecular mechanisms of CRISPRa platforms, the current applications of this technology in vivo, and discusses potential solutions to translational hurdles for this therapy, with a focus on ophthalmic diseases.

Single-cell transcriptomic analysis of retinal immune regulation and blood-retinal barrier function during experimental autoimmune uveitis.

Uveitis is characterised by breakdown of the blood-retinal barrier (BRB), allowing infiltration of immune cells that mediate intraocular inflammation, which can lead to irreversible damage of the neuroretina and the loss of sight. Treatment of uveitis relies heavily on corticosteroids and systemic immunosuppression due to limited understanding of disease pathogenesis. We performed single-cell RNA-sequencing of retinas, as well as bulk RNA-sequencing of retinal pigment epithelial (RPE) cells from mice with experimental autoimmune uveitis (EAU) versus healthy control. This revealed that the Th1/Th17-driven disease induced strong gene expression changes in response to inflammation in rods, cones, Müller glia and RPE. In particular, Müller glia and RPE cells were found to upregulate expression of chemokines, complement factors, leukocyte adhesion molecules and MHC class II, thus highlighting their contributions to immune cell recruitment and antigen presentation at the inner and outer BRB, respectively. Additionally, ligand-receptor interaction analysis with CellPhoneDB revealed key interactions between Müller glia and T cell / natural killer cell subsets via chemokines, galectin-9 to P4HB/TIM-3, PD-L1 to PD-1, and nectin-2/3 to TIGIT signalling axes. Our findings elucidate mechanisms contributing to breakdown of retinal immune privilege during uveitis and identify novel targets for therapeutic interventions.

Investigating the impact of asymmetric macular sensitivity on visual acuity chart reading in choroideremia.

INTRODUCTION: Degeneration in choroideremia, unlike typical centripetal photoreceptor degenerations, is centred temporal to the fovea. Once the fovea is affected, the nasal visual field (temporal retina) is relatively spared, and the preferred retinal locus shifts temporally. Therefore, when reading left to right, only the right eye reads into a scotoma. We investigate how this unique property affects the ability to read an eye chart. METHODS: Standard- and low-luminance visual acuity (VA) for right and left eyes were measured with the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart. Letters in each line were labelled by column position. The numbers of letter errors for each position across the whole chart were summed to produce total column error scores for each participant. Macular sensitivity was assessed using microperimetry. Central sensitivity asymmetry was determined by the temporal-versus-nasal central macular difference and subsequently correlated to a weighted ETDRS column error score. Healthy volunteers and participants with X-linked retinitis pigmentosa GTPase regulator associated retinitis pigmentosa (RPGR-RP) were used as controls. RESULTS: Thirty-nine choroideremia participants (median age 44.9 years [IQR 35.7-53.5]), 23 RPGR-RP participants (median age 30.8 years [IQR 26.5-40.5]) and 35 healthy controls (median age 23.8 years [IQR 20.3-29.0]) were examined. In choroideremia, standard VA in the right eye showed significantly greater ETDRS column errors on the temporal side compared with the nasal side (p = 0.002). This significantly correlated with greater asymmetry in temporal-versus-nasal central macular sensitivity (p = 0.04). No significant patterns in ETDRS column errors or central macular sensitivity were seen in the choroideremia left eyes, nor in RPGR-RP and control eyes. CONCLUSION: Difficulty in tracking across lines during ETDRS VA testing may cause excess errors independent of true VA. VA assessment with single-letter optotype systems may be more suitable, particularly for patients with choroideremia, and potentially other retinal diseases with asymmetric central macular sensitivity or large central scotomas including geographic atrophy.

An Open-Label Phase II Study Assessing the Safety of Bilateral, Sequential Administration of Retinal Gene Therapy in Participants with Choroideremia: The GEMINI Study.

Choroideremia, an incurable, progressive retinal degeneration primarily affecting young men, leads to sight loss. GEMINI was a multicenter, open-label, prospective, two-period, interventional Phase II study assessing the safety of bilateral sequential administration of timrepigene emparvovec, a gene therapy, in adult males with genetically confirmed choroideremia (NCT03507686, ClinicalTrials.gov). Timrepigene emparvovec is an adeno-associated virus serotype 2 vector encoding the cDNA of Rab escort protein 1, augmented by a downstream woodchuck hepatitis virus post-transcriptional regulatory element. Up to 0.1 mL of timrepigene emparvovec, containing 1 × 1011 vector genomes, was administered by subretinal injection following vitrectomy and retinal detachment. The second eye was treated after an intrasurgery window of <6, 6-12, or >12 months. Each eye was followed at up to nine visits over 12 months. Overall, 66 participants received timrepigene emparvovec, and 53 completed the study. Visual acuity (VA) was generally maintained in both eyes, independent of intrasurgery window duration, even after bilateral retinal detachment and subretinal injection. Bilateral treatment was well tolerated, with predominantly mild or moderate treatment-emergent adverse events (TEAEs) and a low rate of serious surgical complications (7.6%). Retinal inflammation TEAEs were reported in 45.5% of participants, with similar rates in both eyes; post hoc analyses found that these were not associated with clinically significant vision loss at month 12 versus baseline. Two participants (3.0%) reported serious noninfective retinitis. Prior timrepigene emparvovec exposure did not increase the risk of serious TEAEs or serious ocular TEAEs upon injection of the second eye; furthermore, no systemic immune reaction or inoculation effect was observed. Presence of antivector neutralizing antibodies at baseline was potentially associated with a higher percentage of TEAEs related to ocular inflammation or reduced VA after injection of the first eye. The GEMINI study results may inform decisions regarding bilateral sequential administration of other gene therapies for retinal diseases.

Gene Therapies in Clinical Development to Treat Retinal Disorders.

Gene therapies have emerged as promising treatments in clinical development for various retinal disorders, offering hope to patients with inherited degenerative eye conditions. Several gene therapies have already shown remarkable success in clinical trials, with significant improvements observed in visual acuity and the preservation of retinal function. A multitude of gene therapies have now been delivered safely in human clinical trials for a wide range of inherited retinal disorders but there are some gaps in the reported trial data. Some of the most exciting treatment options are not under peer review and information is only available in press release form. Whilst many trials appear to have delivered good outcomes of safety, others have failed to meet primary endpoints and therefore not proceeded to phase III. Despite this, such trials have enabled researchers to learn how best to assess and monitor patient outcomes, which will guide future trials to greater success. In this review, we consider recent and ongoing clinical trials for a variety of potential retinal gene therapy treatments and discuss the positive and negative issues related to these trials. We discuss the treatment potential following clinical trials as well as the potential risks of some treatments under investigation. As these therapies continue to advance through rigorous testing and regulatory approval processes, they hold the potential to revolutionise the landscape of retinal disorder treatments, providing renewed vision and enhancing the quality of life for countless individuals worldwide.

Age-related macular degeneration: suitability of optogenetic therapy for geographic atrophy.

Age-related macular degeneration (AMD) is a growing public health concern given the aging population and it is the leading cause of blindness in developed countries, affecting individuals over the age of 55 years. AMD affects the retinal pigment epithelium (RPE) and Bruch's membrane in the macula, leading to secondary photoreceptor degeneration and eventual loss of central vision. Late AMD is divided into two forms: neovascular AMD and geographic atrophy (GA). GA accounts for around 60% of late AMD and has been the most challenging subtype to treat. Recent advances include approval of new intravitreally administered therapeutics, pegcetacoplan (Syfovre) and avacincaptad pegol (Iveric Bio), which target complement factors C3 and C5, respectively, which slow down the rate of enlargement of the area of atrophy. However, there is currently no treatment to reverse the central vision loss associated with GA. Optogenetics may provide a strategy for rescuing visual function in GA by imparting light-sensitivity to the surviving inner retina (i.e., retinal ganglion cells or bipolar cells). It takes advantage of residual inner retinal architecture to transmit visual stimuli along the visual pathway, while a wide range of photosensitive proteins are available for consideration. Herein, we review the anatomical changes in GA, discuss the suitability of optogenetic therapeutic sensors in different target cells in pre-clinical models, and consider the advantages and disadvantages of different routes of administration of therapeutic vectors.

Robotising vitreoretinal surgeries.

The use of robotic surgery in ophthalmology has been shown to offer many potential advantages to current surgical techniques. Vitreoretinal surgery requires complex manoeuvres and high precision, and this is an area that exceeds manual human dexterity in certain surgical situations. With the advent of advanced therapeutics such as subretinal gene therapy, precise delivery and minimising trauma is imperative to optimize outcomes. There are multiple robotic systems in place for ophthalmology in pre-clinical and clinical use, and the Preceyes Robotic Surgical System (Preceyes BV) has also gained the CE mark and is commercially available for use. Recent in-vivo and in-human surgeries have been performed successfully with robotics systems. This includes membrane peeling, subretinal injections of therapeutics, and retinal vein cannulation. There is huge potential to integrate robotic surgery into mainstream clinical practice. In this review, we summarize the existing systems, and clinical implementation so far, and highlight the future clinical applications for robotic surgery in vitreo-retina.

Robot-Assisted Eye Surgery: A Systematic Review of Effectiveness, Safety, and Practicality in Clinical Settings.

Purpose: Surgical innovation in ophthalmology is impeded by the physiological limits of human motion, and robotic assistance may facilitate an expansion of the surgical repertoire. We conducted a systematic review to identify ophthalmic procedures in which robotic systems have been trialled, evaluate their performance, and explore future directions for research and development of robotic techniques. Methods: The Cochrane Library, Embase, MEDLINE, Scopus, and Web of Science were searched. Screening adhered to five criteria: (1) English language; (2) primary research article; (3) human patients; (4) ophthalmological surgery; and (5) robot-assisted surgery. Quality assessment was conducted with Joanna Briggs Institute Tools for Critical Appraisal. The study protocol was registered prospectively (PROSPERO ID CRD42023449793). Results: Twelve studies were included. In comparative studies, there was no difference in the occurrence of ocular harms in robot-assisted procedures and conventional surgery. However, robotic assistance did not demonstrate consistent benefits over manual surgery in terms of effectiveness or practicality, likely reflecting the learning curve associated with these systems. Single studies indicated the potential of robotic assistance to improve the consistency of subretinal drug infusion and efficiency of instrument manipulation in vitreoretinal surgery. Conclusions: Proof-of-concept studies have demonstrated the potential of robotic assistance to facilitate procedures otherwise infeasible or impractical, and may broaden access to surgery. However, robot-assisted surgery has not yet demonstrated any significant benefits over standard surgical practice. Improving the speed and reducing perioperative requirements of robot-assisted surgery are particular priorities for research and innovation to improve the practicality of these novel techniques. Translational Relevance: This systematic review summarizes the potential and limitations of robotic systems for assisting eye surgery and outlines what is required for these systems to benefit patients and surgeons.

Retinal Characteristics of Female Choroideremia Carriers: Multimodal Imaging, Microperimetry, and Genetics.

PURPOSE: To describe visual function and retinal features of female carriers of choroideremia (CHM), using multimodal imaging and microperimetry. DESIGN: Cross-sectional cohort study. PARTICIPANTS AND CONTROLS: Choroideremia carriers seen in Australia (Melbourne or Perth) or the United Kingdom (Oxford or Cambridge) between 2012 and 2023. Healthy age-matched controls seen in Melbourne, Australia, between 2022 and 2023. METHODS: Participants had visual acuity, fundus-tracked microperimetry, OCT, and fundus autofluorescence imaging performed. Choroideremia carriers were either genetically or clinically confirmed (i.e., obligate carriers). Choroideremia carriers were grouped according to their retinal phenotype and compared with healthy controls. Statistical analyses were performed on StataBE (v18.0). MAIN OUTCOME MEASURES: Best-corrected visual acuity (BCVA), low-luminance visual acuity (LLVA), average retinal sensitivity, volume of macular hill of vision (HoV), inner retinal thickness, and photoreceptor complex (PRC) thickness. RESULTS: Eighty-six eyes of 43 CHM carriers and 60 eyes of 30 healthy controls were examined using multimodal imaging and microperimetry. Median age was 54 and 48.5 years for CHM carriers and controls, respectively (P = 0.18). Most CHM carriers (86%) were genetically confirmed. Choroideremia carriers and controls had strong intereye correlation between eyes for BCVA and average retinal sensitivity (P < 0.001). Low-luminance visual acuity and macular HoV tests were sensitive tests to detect changes in CHM carriers with mild phenotypes (i.e., fine and coarse). Choroideremia carriers with geographic or male-pattern phenotypes had reduced BCVA, LLVA, retinal sensitivity, and retinal thinning, compared with healthy controls. Retinal thickening of the inner retina was observed in the central 1°, despite generalized thinning of the PRC in the central 7°, indicating retinal remodeling in CHM carriers, compared with controls. There were no genotype-phenotype correlations observed. CONCLUSIONS: Female carriers of CHM with severe retinal phenotypes (i.e., geographic or male pattern) have significantly decreased visual function and retinal structural changes when compared with age-matched controls and those carriers with milder phenotypes. Low-luminance visual acuity and volumetric measures of the macular HoV were found to be the most sensitive functional tests to detect milder retinal disease (fine and coarse phenotypes) in CHM carriers. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

In Silico CRISPR-Cas-Mediated Base Editing Strategies for Early-Onset, Severe Cone-Rod Retinal Degeneration in Three Crumbs homolog 1 Patients, including the Novel Variant c.2833G>A.

Pathogenic variants in the Crumbs homolog 1 (CRB1) gene lead to severe, childhood-onset retinal degeneration leading to blindness in early adulthood. There are no approved therapies, and traditional adeno-associated viral vector-based gene therapy approaches are challenged by the existence of multiple CRB1 isoforms. Here, we describe three CRB1 variants, including a novel, previously unreported variant that led to retinal degeneration. We offer a CRISPR-Cas-mediated DNA base editing strategy as a potential future therapeutic approach. This study is a retrospective case series. Clinical and genetic assessments were performed, including deep phenotyping by retinal imaging. In silico analyses were used to predict the pathogenicity of the novel variant and to determine whether the variants are amenable to DNA base editing strategies. Case 1 was a 24-year-old male with cone-rod dystrophy and retinal thickening typical of CRB1 retinopathy. He had a relatively preserved central outer retinal structure and a best corrected visual acuity (BCVA) of 60 ETDRS letters in both eyes. Genetic testing revealed compound heterozygous variants in exon 9: c.2843G>A, p.(Cys948Tyr) and a novel variant, c.2833G>A, p.(Gly945Arg), which was predicted to likely be pathogenic by an in silico analysis. Cases 2 and 3 were two brothers, aged 20 and 24, who presented with severe cone-rod dystrophy and a significant disruption of the outer nuclear layers. The BCVA was reduced to hand movements in both eyes in Case 2 and to 42 ETDRS letters in both eyes in Case 3. Case 2 was also affected with marked cystoid macular lesions, which are common in CRB1 retinopathy, but responded well to treatment with oral acetazolamide. Genetic testing revealed two c.2234C>T, p.(Thr745Met) variants in both brothers. As G-to-A and C-to-T variants, all three variants are amenable to adenine base editors (ABEs) targeting the forward strand in the Case 1 variants and the reverse strand in Cases 2 and 3. Available PAM sites were detected for KKH-nSaCas9-ABE8e for the c.2843G>A variant, nSaCas9-ABE8e and KKH-nSaCas9-ABE8e for the c.2833G>A variant, and nSpCas9-ABE8e for the c.2234C>T variant. In this case series, we report three pathogenic CRB1 variants, including a novel c.2833G>A variant associated with early-onset cone-rod dystrophy. We highlight the severity and rapid progression of the disease and offer ABEs as a potential future therapeutic approach for this devastating blinding condition.

Rescue of cone and rod photoreceptor function in a CDHR1-model of age-related retinal degeneration.

Age-related macular degeneration (AMD) is the most common cause of untreatable blindness in the developed world. Recently, CDHR1 has been identified as the cause of a subset of AMD that has the appearance of the "dry" form, or geographic atrophy. Biallelic variants in CDHR1-a specialized protocadherin highly expressed in cone and rod photoreceptors-result in blindness from shortened photoreceptor outer segments and progressive photoreceptor cell death. Here we demonstrate long-term morphological, ultrastructural, functional, and behavioral rescue following CDHR1 gene therapy in a relevant murine model, sustained to 23-months after injection. This represents the first demonstration of rescue of a monogenic cadherinopathy in vivo. Moreover, the durability of CDHR1 gene therapy seems to be near complete-with morphological findings of the rescued retina not obviously different from wildtype throughout the lifespan of the mouse model. A follow-on clinical trial in patients with CDHR1-associated retinal degeneration is warranted. Hypomorphic CDHR1 variants may mimic advanced dry AMD. Accurate clinical classification is now critical, as their pathogenesis and treatment are distinct.

CRISPR Manipulation of Age-Related Macular Degeneration Haplotypes in the Complement System: Potential Future Therapeutic Applications/Avenues.

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss among the elderly in the developed world. Whilst AMD is a multifactorial disease, the involvement of the complement system in its pathology is well documented, with single-nucleotide polymorphisms (SNPs) in different complement genes representing an increased risk factor. With several complement inhibitors explored in clinical trials showing limited success, patients with AMD are still without a reliable treatment option. This indicates that there is still a gap of knowledge in the functional implications and manipulation of the complement system in AMD, hindering the progress towards translational treatments. Since the discovery of the CRISPR/Cas system and its development into a powerful genome engineering tool, the field of molecular biology has been revolutionised. Genetic variants in the complement system have long been associated with an increased risk of AMD, and a variety of haplotypes have been identified to be predisposing/protective, with variation in complement genes believed to be the trigger for dysregulation of the cascade leading to inflammation. AMD-haplotypes (SNPs) alter specific aspects of the activation and regulation of the complement cascade, providing valuable insights into the pathogenic mechanisms of AMD with important diagnostic and therapeutic implications. The effect of targeting these AMD-related SNPs on the regulation of the complement cascade has been poorly explored, and the CRISPR/Cas system provides an ideal tool with which to explore this avenue. Current research concentrates on the association events of specific AMD-related SNPs in complement genes without looking into the effect of targeting these SNPs and therefore influencing the complement system in AMD pathogenesis. This review will explore the current understanding of manipulating the complement system in AMD pathogenesis utilising the genomic manipulation powers of the CRISPR/Cas systems. A number of AMD-related SNPs in different complement factor genes will be explored, with a particular emphasis on factor H (CFH), factor B (CFB), and complement C3 (C3).

A Prospective, Observational, Non-interventional Clinical Study of Participants With Choroideremia: The NIGHT Study.

PURPOSE: The NIGHT study aimed to assess the natural history of choroideremia (CHM), an X-linked inherited chorioretinal degenerative disease leading to blindness, and determine which outcomes would be the most sensitive for monitoring disease progression. DESIGN: A prospective, observational, multicenter cohort study. METHODS: Males aged ≥18 years with genetically confirmed CHM, visible active disease within the macular region, and best-corrected visual acuity (BCVA) ≥34 Early Treatment Diabetic Retinopathy Study (ETDRS) letters at baseline were assessed for 20 months. The primary outcome was the change in BCVA over time at Months 4, 8, 12, 16, and 20. A range of functional and anatomical secondary outcome measures were assessed up to Month 12, including retinal sensitivity, central ellipsoid zone (EZ) area, and total area of fundus autofluorescence (FAF). Additional ocular assessments for safety were performed. RESULTS: A total of 220 participants completed the study. The mean BCVA was stable over 20 months. Most participants (81.4% in the worse eye and 77.8% in the better eye) had change from baseline > -5 ETDRS letters at Month 20. Interocular symmetry was low overall. Reductions from baseline to Month 12 were observed (worse eye, better eye) for retinal sensitivity (functional outcome; -0.68 dB, -0.48 dB), central EZ area (anatomical outcome; -0.276 mm2, -0.290 mm2), and total area of FAF (anatomical outcome; -0.605 mm2, -0.533 mm2). No assessment-related serious adverse events occurred. CONCLUSIONS: Retinal sensitivity, central EZ area, and total area of FAF are more sensitive than BCVA in measuring the natural progression of CHM.

Assessment of Visual Function with Cotoretigene Toliparvovec in X-Linked Retinitis Pigmentosa in the Randomized XIRIUS Phase 2/3 Study.

PURPOSE: Cotoretigene toliparvovec (BIIB112/AAV8-RPGR) is an investigational vector-based gene therapy designed to provide a full-length, codon-optimized retinitis pigmentosa GTPase regulator (RPGR) protein to individuals with RPGR-associated X-linked retinitis pigmentosa (XLRP). We assessed efficacy and tolerability of cotoretigene toliparvovec subretinal gene therapy. DESIGN: Part 2 of the XIRIUS trial (ClinicalTrials.gov identifier, NCT03116113) was a phase 2/3, 12-month, randomized (1:1:1) dose-expansion study. PARTICIPANTS: Male patients ≥10 years of age with RPGR-associated XLRP were included. METHODS: Participants were randomized 1:1:1 to receive low-dose subretinal cotoretigene toliparvovec (5 × 1010 vector genomes/eye), high-dose cotoretigene toliparvovec (2.5 × 1011 vector genomes/eye) or to be an untreated control participant. MAIN OUTCOME MEASURES: The primary end point was the percentage of participants meeting microperimetry responder criteria (≥ 7-dB improvement at ≥ 5 of 16 central loci). Secondary end points included change from baseline in retinal sensitivity at the central 16 loci and the entire 68 loci at 12 months and change from baseline in low-luminance visual acuity (LLVA) at 12 months, as well as the proportion of eyes with a ≥ 15-Early Treatment Diabetic Retinopathy Study ETDRS letter LLVA and ≥ 10-ETDRS letter LLVA change from baseline at month 12. RESULTS: Because of the impact of the COVID-19 pandemic, enrollment ended before reaching the initial target, leaving the trial underpowered. Twenty-nine participants were included (low-dose group, n = 10; high-dose group, n = 10; control group, n = 9). At month 12, the percentage of participants meeting microperimetry responder criteria was not significantly different between either cotoretigene toliparvovec group (low dose, 37.5% [P = 0.3181]; high dose, 25.0% [P = 0.5177]) and the control group (22.2%). However, the mean change from baseline in microperimetry sensitivity improved significantly with the low-dose group versus the control group at month 12 (P = 0.0350). Significant improvement in LLVA occurred in the low-dose group versus the control group at month 12 (33.3% difference [80% confidence interval, 14.7%-55.2%]; P = 0.0498). Three ocular-related serious adverse events (SAEs) occurred in the low-dose group versus 7 SAEs in the high-dose group. CONCLUSIONS: The primary microperimetry end point was not met. Significant improvements in LLVA and mean microperimetry were observed compared with controls and fewer SAEs occured with low-dose compared with high dose cotoretigene toliparvovec. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A hypomorphic variant of choroideremia is associated with a novel intronic mutation that leads to exon skipping.

INTRODUCTION: Molecular confirmation of pathogenic sequence variants in the CHM gene is required prior to enrolment in retinal gene therapy clinical trials for choroideremia. Individuals with mild choroideremia have been reported. The molecular basis of genotype-phenotype associations is of clinical relevance since it may impact on selection for retinal gene therapy. METHODS AND MATERIALS: Genetic testing and RNA analysis were undertaken in a patient with mild choroideremia to confirm the pathogenicity of a novel intronic variant in CHM and to explore the mechanism underlying the mild clinical phenotype. RESULTS: A 42-year-old male presented with visual field loss. Fundoscopy and autofluorescence imaging demonstrated mild choroideremia for his age. Genetic analysis revealed a variant at a splice acceptor site in the CHM gene (c.1350-3C > G). RNA analysis demonstrated two out-of-frame transcripts, suggesting pathogenicity, without any detectable wildtype transcripts. One of the two out-of-frame transcripts is present in very low levels in healthy controls. DISCUSSION: Mild choroideremia may result from +3 or -3 splice site variants in CHM. It is presumed that the resulting mRNA transcripts may be partly functional, thereby preventing the development of the null phenotype. Choroideremia patients with such variants may present challenges for gene therapy since there may be residual transcript activity which could result in long-lasting visual function which is atypical for this disease.