The X-linked retinopathies: Physiological insights, pathogenic mechanisms, phenotypic features and novel therapies

The D126G mutation contributes to the early-onset X-linked juvenile retinoschisis

X-linked juvenile retinoschisis (XLRS) is an inherited retinal disease caused by mutations in the RS1 gene, resulting in splitting of the retinal layers and visual disturbances. To provide insights on this disease in our cohort, genetic examination, clinical presentation, and functional analysis were performed. We observed three main RS1 mutations in our cohort of six unrelated patients: RS1-D126G, RS1-R209H, and RS1-R213W. The RS1-D126G mutation, exclusively reported in Thai patients so far, showed the highest prevalence. Phenotypically, the D126G mutation manifested early (0.3-4 years old), presenting as asymmetrical visual acuity and schisis. Functional analysis revealed that the molecular pathomechanism of D126G was the failure of protein secretion attributable to endoplasmic reticulum retention. The understanding of the genotype-phenotype relationship and the pathomechanisms of specific mutations in a particular population could immensely benefit the pipeline of personalised treatment design for XLRS.

Syndromic Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a progressive inherited retinal dystrophy, characterized by the degeneration of photoreceptors, presenting as a rod-cone dystrophy. Approximately 20-30% of patients with RP also exhibit extra-ocular manifestations in the context of a syndrome. This manuscript discusses the broad spectrum of syndromes associated with RP, pathogenic mechanisms, clinical manifestations, differential diagnoses, clinical management approaches, and future perspectives. Given the diverse clinical and genetic landscape of syndromic RP, the diagnosis may be challenging. However, an accurate and timely diagnosis is essential for optimal clinical management, prognostication, and potential treatment. Broadly, the syndromes associated with RP can be categorized into ciliopathies, inherited metabolic disorders, mitochondrial disorders, and miscellaneous syndromes. Among the ciliopathies associated with RP, Usher syndrome and Bardet-Biedl syndrome are the most well-known. Less common ciliopathies include Cohen syndrome, Joubert syndrome, cranioectodermal dysplasia, asphyxiating thoracic dystrophy, Mainzer-Saldino syndrome, and RHYNS syndrome. Several inherited metabolic disorders can present with RP including Zellweger spectrum disorders, adult Refsum disease, α-methylacyl-CoA racemase deficiency, certain mucopolysaccharidoses, ataxia with vitamin E deficiency, abetalipoproteinemia, several neuronal ceroid lipofuscinoses, mevalonic aciduria, PKAN/HARP syndrome, PHARC syndrome, and methylmalonic acidaemia with homocystinuria type cobalamin (cbl) C disease. Due to the mitochondria's essential role in supplying continuous energy to the retina, disruption of mitochondrial function can lead to RP, as seen in Kearns-Sayre syndrome, NARP syndrome, primary coenzyme Q10 deficiency, SSBP1-associated disease, and long chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Lastly, Cockayne syndrome and PERCHING syndrome can present with RP, but they do not fit the abovementioned hierarchy and are thus categorized as 'Miscellaneous'. Several first-in-human clinical trials are underway or in preparation for some of these syndromic forms of RP.

Single-Cell Transcriptomic Dataset of RPGR-associated Retinitis Pigmentosa Patient-Derived Retinal Organoids

X-linked retinitis pigmentosa (XLRP) is a severe hereditary retinal disorder marked by progressive vision loss due to photoreceptor dysfunction. The retinitis pigmentosa GTPase regulator (RPGR) gene, responsible for most XLRP cases, encodes a protein crucial for the transport of visual signal proteins between the photoreceptor inner and outer segments. However, the mechanism of RPGR mutation causing photoreceptor disorder is not clear and effective treatments remain elusive. This study utilized retinal organoids (ROs) derived from normal and RPGR-mutant human induced pluripotent stem cells (hiPSC) at four developmental stages (40, 90, 150, and 200 days). Single-cell RNA sequencing (scRNA-seq) was conducted on 71,096 cells, including 33,839 cells from the control group and 37,257 cells from the RPGR group. Key retinal cell types were identified and the obtained scRNAseq dataset was validated reliable and high -quality. This study has provided data resources and references for exploring the mechanism of RPGR-related retinal degeneration and support the development of targeted therapies.

Phenotypic and Genetic Spectrum in 309 Consecutive Pediatric Patients with Inherited Retinal Disease

Inherited retinal dystrophies (IRDs) are a common cause of blindness or severe visual impairment in children and may occur with or without systemic associations. The aim of the present study is to describe the phenotypic and genotypic spectrum of IRDs in a pediatric patient cohort in Retrospective single-center cross-sectional analysis. Presenting symptoms, clinical phenotype, and molecular genetic diagnosis were assessed in 309 pediatric patients with suspected IRD. Patients were grouped by age at genetic diagnosis (preschool: 0-6 years, n = 127; schoolchildren: 7-17 years, n = 182). Preschool children most frequently presented with nystagmus (34.5% isolated, 16.4% syndromic), no visual interest (20.9%; 14.5%), or nyctalopia (22.4%; 3.6%; p < 0.05); schoolchildren most frequently presented with declining visual acuity (31% isolated, 21.1% syndromic), nyctalopia (10.6%; 13.5%), or high myopia (5.3%; 13.2%). Pathogenic variants were identified in 96 different genes (n = 69 preschool, n = 73 schoolchildren). In the preschool group, 57.4% had isolated and 42.6% had syndromic IRDs, compared to 70.9% and 29.1% in schoolchildren. In the preschool group, 32.4% of the isolated IRDs were related to forms of Leber's congenital amaurosis (most frequent were RPE65 (11%) and CEP290 (8.2%)), 31.5% were related to stationary IRDs, 15.1% were related to macular dystrophies (ABCA4, BEST1, PRPH2, PROM1), and 8.2% to rod-cone dystrophies (RPGR, RPB3, RP2, PDE6A). All rod-cone dystrophies (RCDs) were subjectively asymptomatic at the time of genetic diagnosis. At schoolage, 41% were attributed to cone-dominated disease (34% ABCA4), 10.3% to BEST1, and 10.3% to RCDs (RP2, PRPF3, RPGR; IMPG2, PDE6B, CNGA1, MFRP, RP1). Ciliopathies were the most common syndromic IRDs (preschool 37%; schoolchildren 45.1%), with variants in USH2A, CEP290 (5.6% each), CDH23, BBS1, and BBS10 (3.7% each) being the most frequent in preschoolers, and USH2A (11.7%), BBS10 (7.8%), CEP290, CDHR23, CLRN1, and ICQB1 (3.9% each) being the most frequent in syndromic schoolkids. Vitreoretinal syndromic IRDs accounted for 29.6% (preschool: COL2A1, COL11A1, NDP (5.6% each)) and 23.5% (schoolage: COL2A1, KIF11 (9.8% each)), metabolic IRDs for 9.4% (OAT, HADHA, MMACHD, PMM2) and 3.9% (OAT, HADHA), mitochondriopathies for 3.7% and 7.8%, and syndromic albinism accounted for 5.6% and 3.9%, respectively. In conclusion we show here that the genotypic spectrum of IRDs and its quantitative distribution not only differs between children and adults but also between children of different age groups, with an almost equal proportion of syndromic and non-syndromic IRDs in early childhood. Ophthalmic screening visits at the preschool and school ages may aid even presymptomatic diagnosis and treatment of potential sight and life-threatening systemic sequelae.

The Electroretinogram I-Wave, a Component Originating in the Retinal OFF-Pathway, Associates With a Myopia Genetic Risk Polymorphism

Purpose

One of the strongest genetic associations with myopia is near the GJD2 gene. Recently, this locus was associated with cone-driven electroretinograms (ERGs), with findings highlighting OFF pathway signals specifically. The ERG i-wave is thought to originate in retinal OFF pathways. We explored this component and tested the hypothesis that it would be associated with the myopia risk locus.

Methods

International standard LA3 ERGs, recorded with conductive fiber electrodes, were analyzed, first from patients with rare monogenic deficits impairing the ON pathway, or both ON and OFF pathways, to explore effects on the i-wave. Responses were then analyzed from adult participants from the TwinsUK cohort: i-wave amplitudes were measured by two investigators independently, blinded to genotype at the GJD2 locus. We investigated the association between i-wave amplitude and allelic identity at this locus, adjusting for age, sex, and familial relatedness.

Results

Patient recordings showed the i-wave persisted in the absence of ON pathway signals, but was abolished when both ON and OFF pathways were impaired. For TwinsUK participants, recordings and genotypes were available in 184 individuals (95% female participants; mean standard deviation [SD] age, 64.1 [9.7] years). Mean (SD) i-wave amplitude was 14.5 (SD = 6.5) microvolts. Allelic dosage at the risk locus was significantly associated with i-wave amplitude (P = 0.027).

Conclusions

Patient ERGs were consistent with the i-wave arising from cone-driven OFF pathways. Amplitudes associated significantly with allelic dosage at the myopia risk locus, supporting the importance of cone-driven signaling in myopia development and further highlighting relevance of the OFF pathway in relation to this locus.

Phase 1/2 AAV5-hRKp.RPGR (Botaretigene Sparoparvovec) Gene Therapy: Safety and Efficacy in RPGR-Associated X-Linked Retinitis Pigmentosa

PURPOSE

To assess the safety and efficacy of AAV5-hRKp.RPGR in participants with retinitis pigmentosa GTPase regulator (RPGR)-associated X-linked retinitis pigmentosa (XLRP).

DESIGN

Open-label, phase 1/2 dose escalation/expansion study (ClinicalTrials.gov Identifier: NCT03252847).

METHODS

Males (≥5 years old) with XLRP-RPGR were evaluated. In the dose escalation phase, subretinal AAV5-hRKp.RPGR (low: 1.0 × 1011 vg/ml; intermediate: 2.0 × 1011 vg/ml; high: 4.0 × 1011 vg/ml) was administered to the poorer-seeing eye (n = 10). Dose confirmation (intermediate dose) was carried out in 3 pediatric participants. In the dose expansion phase, 36 participants were randomized 1:1:1 to immediate (low or intermediate dose) or deferred (control) treatment. The primary outcome was safety. Secondary efficacy outcomes included static perimetry, microperimetry, vision-guided mobility, best corrected visual acuity, and contrast sensitivity. Safety and efficacy outcomes were assessed for 52 weeks for immediate treatment participants and 26 weeks for control participants.

RESULTS

AAV5-hRKp.RPGR was safe and well tolerated, with no reported dose-limiting events. Most adverse events (AEs) were transient and related to the surgical procedure, resolving without intervention. Two serious AEs were reported with immediate treatment (retinal detachment, uveitis). A third serious AE (increased intraocular pressure) was reported outside the reporting period. All ocular inflammation-related AEs responded to corticosteroids. Treatment with AAV5-hRKp.RPGR resulted in improvements in retinal sensitivity and functional vision compared with the deferred group at Week 26; similar trends were observed at Week 52.

CONCLUSIONS

AAV5-hRKp.RPGR demonstrated an anticipated and manageable AE profile through 52 weeks. Safety and efficacy findings support investigation in a phase 3 trial.

Infantile Nystagmus Syndrome-Associated Inherited Retinal Diseases: Perspectives from Gene Therapy Clinical Trials

Inherited retinal diseases (IRDs) are a clinically and genetically diverse group of progressive degenerative disorders that can result in severe visual impairment or complete blindness. Despite their predominantly monogenic inheritance patterns, the genetic complexity of over 300 identified disease-causing genes presents a significant challenge in correlating clinical phenotypes with genotypes. Achieving a molecular diagnosis is crucial for providing patients with definitive diagnostic clarity and facilitating access to emerging gene-based therapies and ongoing clinical trials. Recent advances in next-generation sequencing technologies have markedly enhanced our ability to identify genes and genetic defects leading to IRDs, thereby propelling the development of gene-based therapies. The clinical success of voretigene neparvovec (Luxturna), the first approved retinal gene therapy for RPE65-associated Leber congenital amaurosis (LCA), has spurred considerable research and development in gene-based therapies, highlighting the importance of reviewing the current status of gene therapy for IRDs, particularly those utilizing adeno-associated virus (AAV)-based therapies. As novel disease-causing mutations continue to be discovered and more targeted gene therapies are developed, integrating these treatment opportunities into the standard care for IRD patients becomes increasingly critical. This review provides an update on the diverse phenotypic-genotypic landscape of IRDs, with a specific focus on recent advances in the understanding of IRDs in children with infantile nystagmus syndrome (INS). We highlight the complexities of the genotypic-phenotypic landscape of INS-associated IRDs, including conditions such as achromatopsia, LCA, congenital stationary night blindness, and subtypes of retinitis pigmentosa. Additionally, we provide an updated overview of AAV-based gene therapies for these diseases and discuss the potential of gene-based therapies for underlying IRDs that lead to INS, offering a valuable resource for pediatric patients potentially eligible for ongoing clinical trials.

From onset to blindness: a comprehensive analysis of RPGR-associated X-linked retinopathy in a large cohort in China

BACKGROUND

Variants in the RPGR are the leading cause of X-linked retinopathies (XLRPs). Further in-depth investigation is needed to understand the natural history.

METHODS

Review of all case records, molecular genetic testing results, best-corrected visual acuity (BCVA), retinal imaging data (including fundus autofluorescence imaging and optical coherence tomography (OCT)), static visual field (VF) assessments and full-field electroretinogram.

RESULTS

Genetic testing was conducted on 104 male patients from 89 family pedigrees, identifying 22 novel variants and 1 de novo variant. The initial symptoms appeared in 78.2% of patients at a median age of 5 years. BCVA declined at a mean rate of 0.02 (IQR, 0-0.04) logarithm of the minimum angle of resolution per year, with a gradual, non-linear decrease over the first 40 years. Autofluorescence imaging revealed macular atrophy at a median age of 36.1 (IQR, 29.9-43.2) years. Patients experienced blindness at a median age of 42.5 (IQR, 32.9-45.2) years according to WHO visual impairment categories. OCT analysis showed a mean ellipsoid zone narrowing rate of 23.3 (IQR, -1.04-22.29) µm/month, with an accelerated reduction in the first 40 years (p<0.01). The median age at which ERG no longer detected a waveform was 26.5 (IQR, 20.5-32.8) years. Comparison by variant location indicated faster progression in patients with exon 1-14 variants during the initial two decades, while those with ORF15 variants showed accelerated progression from the third decade.

CONCLUSIONS

We provide a foundation for determining the treatment window and an objective basis for evaluating the therapeutic efficacy of gene therapy for XLRP.

Pseudodominant inheritance of retinitis pigmentosa in a family with mutations in the Eyes Shut Homolog (EYS) gene

Sequence variants in Eyes Shut Homolog (EYS) gene are one of the most frequent causes of autosomal recessive retinitis pigmentosa (RP). Herein, we describe an Italian RP family characterized by EYS-related pseudodominant inheritance. The female proband, her brother, and both her sons showed typical RP, with diminished or non-recordable full-field electroretinogram, narrowing of visual field, and variable losses of central vision. To investigate this apparently autosomal dominant pedigree, next generation sequencing (NGS) of a custom panel of RP-related genes was performed, further enhanced by bioinformatic detection of copy-number variations (CNVs). Unexpectedly, all patients had a compound heterozygosity involving two known pathogenic EYS variants i.e., the exon 33 frameshift mutation c.6714delT and the exon 29 deletion c.(5927þ1_5928-1)_(6078þ1_6079-1)del, with the exception of the youngest son who was homozygous for the above-detailed frameshift mutation. No pathologic eye conditions were instead observed in the proband's husband, who was a heterozygous healthy carrier of the same c.6714delT variant in exon 33 of EYS gene. These findings provide evidence that pseudodominant pattern of inheritance can hide an autosomal recessive RP partially or totally due to CNVs, recommending CNVs study in those pedigrees which remain genetically unsolved after the completion of NGS or whole exome sequencing analysis.

PRPS1-associated retinopathy: a diagnostic odyssey

PURPOSE

This study describes how the diagnosis of Usher syndrome was revised to PRPS1-associated retinopathy and Charcot-Marie-Tooth disease type 5.

CASE REPORT

A 38-year-old female with bilaterally subnormal vision and non-congenital hearing loss was initially diagnosed with Usher syndrome, based on finding variants in three genes (MYO7A, USH2A, and PCDH15), was re-evaluated at the inherited retinal disorders clinic. She had asymmetric retinopathy and right macular pseudocoloboma. She was also found to have myopathic facies, poor grip strength and atrophy of the calf muscles. Whole exome sequencing including variants in PRPS1 showed a variant (NM_002764.4:c.287 G > A; p.Arg96Gln), which was not detected by targeted Sanger sequencing of the DNA from her mother and sister.

CONCLUSION

The constellation of asymmetric retinopathy and non-congenital hearing impairment should prompt the clinician to search for other diagnoses that may not be covered by an Usher syndrome next generation sequencing panel. Interpretation of genetic testing results should be correlated with a detailed clinical phenotype.

Impacts of X-linked Retinitis Pigmentosa and Patient Pathways in European Countries: Results from the Cross-sectional EXPLORE XLRP-1 Physician Survey

INTRODUCTION

X-linked retinitis pigmentosa (XLRP) is a rare, incurable, vision-threatening, genetic disease. In this study, we aimed to reveal the real-world burden of this disease from the viewpoint of retina specialists and geneticists involved directly in XLRP care and to identify unique insights that may not otherwise be available through typical clinical studies or health economic research.

METHODS

In this exploratory, cross-sectional study (EXPLORE XLRP-1), retina specialists (n = 20) and geneticists (n = 5) in France, Germany, Italy, Spain, and the UK provided anonymized insights on their experiences managing patients with XLRP (n = 80) via an online survey and 60-min telephone interview.

RESULTS

Survey respondents reported that patient independence decreased over time, where 37% of patients were considered "completely autonomous" at diagnosis versus 23% at the last consultation. At their last visit, 45% of patients were active in the workforce; 67% (12/18) of "completely autonomous" patients had active working status compared with 13% (1/8) of "completely dependent" patients. The average time from onset of symptoms to diagnosis was 4 years and varied among countries. In 78% of patients, XLRP was confirmed by genetic testing, the rate of which varied among countries (range, 50-94%), taking up to 6 months to receive results. Specialists identified unmet needs in XLRP management including more standardized assessments of quality of life (QoL) as well as easier and earlier access to specialists, genetic testing, patient support programs, and effective treatment options.

CONCLUSIONS

The diagnosis, genetic testing, and management pathways among patients with XLRP can vary considerably. There is a need for more standardized diagnosis and management pathways, and QoL assessments, due to the major impact that XLRP has on patients' lives.

S-cone contribution to oscillatory potentials in patients with blue cone monochromacy

PURPOSE

The aim of this exploratory study is to investigate the role of S-cones in oscillatory potentials (OPs) generation by individuals with blue-cone monochromacy (BCM), retaining S-cones, and achromatopsia (ACHM), lacking cone functions.

METHODS

This retrospective study analyzed data from 39 ACHM patients, 20 BCM patients, and 26 controls. Central foveal thickness was obtained using spectral-domain optical coherence tomography, while amplitude and implicit time (IT) of a- and b-waves were extracted from the ISCEV Standard dark-adapted 3 cd.s.m-2 full-field ERG (ffERG). Time-frequency analysis of the same measurement enabled the extraction of OPs, providing insights into the dynamic characteristics of the recorded signal.

RESULTS

Both ACHM and BCM groups showed a significant reduction (p < .00001) of a- and b-wave amplitudes and ITs as well as the power of the OPs compared to the control groups. The comparison between ACHM and BCM didn't show any statistically significant differences in the electrophysiological parameters. The analysis of covariance revealed significantly reduced central foveal thickness in the BCM group compared to ACHM and controls (p < .00001), and in ACHM compared to controls (p < .00001), after age correction and Tukey post-hoc analysis.

CONCLUSIONS

S-cones do not significantly influence OPs, and the decline in OPs' power is not solely due to a reduced a-wave. This suggests a complex non-linear network influenced by photoreceptor inputs. Morphological changes don't correlate directly with functional alterations, prompting further exploration of OPs' function and physiological role.

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

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

RP2-Associated X-linked Retinopathy: Clinical Findings, Molecular Genetics, and Natural History in a Large Cohort of Female Carriers

PURPOSE

RP2-associated retinopathy typically causes severe early onset retinitis pigmentosa (RP) in affected males. However, there is a scarcity of reports describing the clinical phenotype of female carriers. We tested the hypothesis that RP2 variants manifest in female carriers with a range of functional and anatomic characteristics.

DESIGN

Retrospective case series.

METHODS

Females with disease-causing variants in RP2 were identified from investigation of pedigrees affected by RP2 retinopathy. All case notes and results of molecular genetic testing, retinal imaging (fundus autofluorescence imaging, optical coherence tomography (OCT)), and electrophysiology were reviewed.

RESULTS

Forty pedigrees were investigated. Twenty-nine pedigrees had obligate carriers or molecularly confirmed female members with recorded relevant history and/or examination. For 8 pedigrees, data were available only from history, with patients reporting affected female relatives with RP in 4 cases and unaffected female relatives in the other 4 cases. Twenty-seven females from 21 pedigrees were examined by a retinal genetics specialist. Twenty-three patients (85%) reported no complaints and had normal vision and 4 patients had RP-associated complaints (15%). Eight patients had normal fundus examination (30%), 10 had a tapetal-like reflex (TLR; 37%), 5 had scattered peripheral pigmentation (19%), and the 4 symptomatic patients had fundus findings compatible with RP (15%). All asymptomatic patients with normal fundus, TLR, or asymptomatic pigmentary changes had a continuous ellipsoid zone on OCT when available. The electroretinograms revealed mild to severe photoreceptor dysfunction in 9 of 11 subjects, often asymmetrical, including 5 with pattern electroretinogram evidence of symmetrical (n = 4) or unilateral (n = 1 subject) macular dysfunction.

CONCLUSIONS

Most carriers were asymptomatic, exhibiting subclinical characteristics such as TLR and pigmentary changes. However, female carriers of RP2 variants can manifest RP. Family history of affected females with RP does not exclude X-linked disease. The phenotypic spectrum as described herein has prognostic and counselling implications for RP2 carriers and patients.

Investigating G-quadruplex structures in RPGR gene: Implications for understanding X-linked retinal degeneration

Aims

This pilot study investigates the potential pathogenic role of G-quadruplex (G4) structures in RPGR-associated retinal degeneration, starting from a case of suspected X-linked form affected family. We hypothesize that the stabilization of these structures might alter DNA replication and transcription, inducing genetic instability and influencing gene expression.

Main methods

We conducted whole genome amplification experiments and next-generation sequencing to detect the blockade of polymerase activity by G4 structures. Our specific focus was the RPGR gene, which hosts a high concentration of predicted G4-forming motifs and is implicated in most X-linked retinal degeneration cases. To understand the potential interference of G4 structures, we applied computational and 3D molecular modeling to visualize interferences in DNA replication and transcription regulation.

Key findings

Our data confirmed the obstruction of DNA polymerase enzymes by G4 structures, particularly when stabilized by the compound pyridostatin. This obstruction was evident in the reduced amplification of RPGR gene regions and a shift in the start/end sites of putative G4 motifs. Moreover, the modeling indicated a potential disruption of critical promoter elements and RNA polymerase binding, which could drastically alter gene expression.

Significance

Our findings suggest that G4 formation in the RPGR gene could lead to genetic instability and affect the expression of RPGR, contributing to retinal dystrophy. Moreover, this study underscores the broader implications of G4 structures in other genetic disorders. Improved understanding of G4 structures could reveal novel therapeutic targets to combat genetic disorders, promoting the advancement of personalized medicine and precision health.

Retinal Imaging Findings in Inherited Retinal Diseases

Inherited retinal diseases (IRDs) represent one of the major causes of progressive and irreversible vision loss in the working-age population. Over the last few decades, advances in retinal imaging have allowed for an improvement in the phenotypic characterization of this group of diseases and have facilitated phenotype-to-genotype correlation studies. As a result, the number of clinical trials targeting IRDs has steadily increased, and commensurate to this, the need for novel reproducible outcome measures and endpoints has grown. This review aims to summarize and describe the clinical presentation, characteristic imaging findings, and imaging endpoint measures that are being used in clinical research on IRDs. For the purpose of this review, IRDs have been divided into four categories: (1) panretinal pigmentary retinopathies affecting rods or cones; (2) macular dystrophies; (3) stationary conditions; (4) hereditary vitreoretinopathies.

Female carrier of RPGR mutation presenting with high myopia

BACKGROUND

Inherited retinopathies can initially present with high refractive error in the first decade of life, before accompanying signs or symptoms are evident.

CASE PRESENTATION

A 4-year-old girl with high myopia (S-12.00 C-4.00 × 20 in the right and S-14.50 C-2.75 × 160 in the left eye), moderate visual acuity (0.3 logMAR in the right and 0.4 logMAR in the left eye), and left esotropia, presented with unremarkable past medical history and no family history of high refractive error or low vision. In optical coherence tomography imaging, macular thinning was evident, while morphology was normal. Full-field electroretinogram revealed normal implicit time recordings with reduced amplitudes in scotopic and photopic conditions. Fundus autofluorescence showed a radial pattern in both eyes. During a 5-year follow-up, significant myopia progression ensued (S-17.25 C-3.00 × 20 in the right and S-17.25 C-2.00 × 160 in the left eye), with a corresponding increase in axial length and an unchanged visual acuity. Whole-exome sequencing revealed a heterozygous termination codon variant c.212C>G (p.Ser71Ter) in RPGR, considered to be pathogenic. Segregation analysis precluded the variation in the mother and sister. A random pattern of X-chromosome inactivation was detected in the proband, without X-chromosome inactivation deviation.

CONCLUSION

This is the second report associating this specific RPGR mutation with high myopia and the first report to identify it in a female proband. This case provides additional evidence on the genotypic-phenotypic correlation between RPGR c.212C>G mutation and high myopia.

Primary Ciliary Dyskinesia and Retinitis Pigmentosa: Novel RPGR Variant and Possible Modifier Gene

We report a novel RPGR missense variant co-segregated with a familial X-linked retinitis pigmentosa (XLRP) case. The brothers were hemizygous for this variant, but only the proband presented with primary ciliary dyskinesia (PCD). Thus, we aimed to elucidate the role of the RPGR variant and other modifier genes in the phenotypic variability observed in the family and its impact on motile cilia. The pathogenicity of the variant on the RPGR protein was evaluated by in vitro studies transiently transfecting the mutated RPGR gene, and immunofluorescence analysis on nasal brushing samples. Whole-exome sequencing was conducted to identify potential modifier variants. In vitro studies showed that the mutated RPGR protein could not localise to the cilium and impaired cilium formation. Accordingly, RPGR was abnormally distributed in the siblings' nasal brushing samples. In addition, a missense variant in CEP290 was identified. The concurrent RPGR variant influenced ciliary mislocalisation of the protein. We provide a comprehensive characterisation of motile cilia in this XLRP family, with only the proband presenting PCD symptoms. The variant's pathogenicity was confirmed, although it alone does not explain the respiratory symptoms. Finally, the CEP290 gene may be a potential modifier for respiratory symptoms in patients with RPGR mutations.

Characterization of a novel heterozygous frameshift variant in NDP gene that causes familial exudative vitreoretinopathy in female patients

Familial exudative vitreoretinopathy (FEVR) is a severe inherited disease characterized by defective retinal vascular development. With genetic and clinical heterogeneity, FEVR can be inherited in different patterns and characterized by phenotypes ranging from moderate visual defects to complete vision loss. This study was conducted to unravel the genetic and functional etiology of a 4-month-old female FEVR patient. Targeted gene panel and Sanger sequencing were utilized for genetic evaluation. Luciferase assays, western blot, quantitive real-time PCR, and immunocytochemistry were performed to verify the functional defects in the identified candidate variant. Here, we report a 4-month-old girl with bilateral retinal folds and peripheral avascularization, and identified a novel frameshift heterozygous variant c.37dup (p.Leu13ProfsTer13) in NDP. In vitro experiments revealed that the Leu13ProfsTer13 variant led to a prominent decrease in protein levels instead of mRNA levels, resulting in compromised Norrin/β-catenin signaling activity. Human androgen receptor assay further revealed that a slight skewing of X chromosome inactivation could partially cause FEVR. Thus, the pathogenic mechanism by which heterozygous frameshift or nonsense variants in female carriers cause FEVR might largely result from a loss-of-function variant in one X chromosome allele and a slightly skewed X-inactivation. Further recruitment of more FEVR-affected females carrying NDP variants and genotype-phenotype correlation analysis can ultimately offer valuable information for the prognosis prediction of FEVR.

Aland Island Eye Disease with Retinoschisis in the Clinical Spectrum of CACNA1F-Associated Retinopathy-A Case Report

Aland island eye disease (AIED), an incomplete form of X-linked congenital stationary night blindness (CSNB2A), and X-linked cone-rod dystrophy type 3 (CORDX3) display many overlapping clinical findings. They result from mutations in the CACNA1F gene encoding the α1F subunit of the Cav1.4 channel, which plays a key role in neurotransmission from rod and cone photoreceptors to bipolar cells. Case report: A 57-year-old Caucasian man who had suffered since his early childhood from nystagmus, nyctalopia, low visual acuity and high myopia in both eyes (OU) presented to expand the diagnostic process, because similar symptoms had occurred in his 2-month-old grandson. Additionally, the patient was diagnosed with protanomalous color vision deficiency, diffuse thinning, and moderate hypopigmentation of the retina. Optical coherence tomography of the macula revealed retinoschisis in the right eye and foveal hypoplasia in the left eye. Dark-adapted (DA) 3.0 flash full-field electroretinography (ffERG) amplitudes of a-waves were attenuated, and the amplitudes of b-waves were abolished, which resulted in a negative pattern of the ERG. Moreover, the light-adapted 3.0 and 3.0 flicker ffERG as well as the DA 0.01 ffERG were consistent with severely reduced responses OU. Genetic testing revealed a hemizygous form of a stop-gained mutation (c.4051C>T) in exon 35 of the CACNA1F gene. This pathogenic variant has so far been described in combination with a phenotype corresponding to CSNB2A and CORDX3. This report contributes to expanding the knowledge of the clinical spectrum of CACNA1F-related disease. Wide variability and the overlapping clinical manifestations observed within AIED and its allelic disorders may not be explained solely by the consequences of different mutations on proteins. The lack of distinct genotype-phenotype correlations indicates the presence of additional, not yet identified, disease-modifying factors.

Clinical and genetic risk factors underlying severe consequence identified in 75 families with unilateral high myopia

BACKGROUNDS

Unilateral high myopia (uHM), commonly observed in patients with retinal diseases or only with high myopia, is frequently associated with amblyopia with poor prognosis. This study aims to reveal the clinical and genetic spectrum of uHM in a large Chinese cohort.

METHODS

A total of 75 probands with simplex uHM were included in our Pediatric and Genetic Eye Clinic. Patients with significant posterior anomalies other than myopic fundus changes were excluded. Variants were detected by exome sequencing and then analyzed through multiple-step bioinformatic and co-segregation analysis and finally confirmed by Sanger sequencing. Genetic findings were correlated with associated clinical data for analysis.

RESULTS

Among the 75 probands with a mean age of 6.21 ± 4.70 years at the presentation, myopic fundus of C1 and C2 was observed in 73 (97.3%) probands. Surprisingly, specific peripheral changes were identified in 63 eyes involving 36 (48.0%) probands after extensive examination, including peripheral retinal avascular zone (74.6%, 47/63 eyes), neovascularization (54.0%), fluorescein leakage (31.7%), peripheral pigmentary changes (31.7%), and others. Exome sequencing identified 21 potential pathogenic variants of 13 genes in 20 of 75 (26.7%) probands, including genes for Stickler syndrome (COL11A1 and COL2A1; 6/20), FEVR (FZD4, LRP5, and TSPAN12; 5/20), and others (FBN1, GPR179, ZEB2, PAX6, GPR143, OPN1LW, FRMD7, and CACNA1F; 9/20). For the peripheral retinal changes in the 20 probands, variants in Stickler syndrome-related genes were predominantly associated with retinal pigmentary changes, lattice degeneration, and retinal avascular region, while variants in genes related to FEVR were mainly associated with the avascular zone, neovascularization, and fluorescein leakage.

CONCLUSIONS

Genetic defects were identified in about one-fourth of simplex uHM patients in which significant consequences may be hidden under a classic myopic fundus in up to half. To our knowledge, this is the first systematic genetic study on simplex uHM to date. In addition to routine care of strabismus and amblyopia, careful examination of the peripheral retina and genetic screening is warranted for patients with uHM in order to identify signs of risk for retinal detachment and other complications and provide meaningful genetic counseling.

Morphological and functional parameters in X-linked retinoschisis patients-A multicentre retrospective cohort study

Introduction

X-linked retinoschisis (XLRS) is a potential target for gene supplementation approaches. To establish potential structural and functional endpoints for clinical trials, a comprehensive understanding of the inter-eye symmetry, relationship between structural and functional parameters, and disease progression is vital.

Methods

In this retrospective multicentre study, 118 eyes of 59 XLRS patients with RS1 mutations were assessed. Information from center databases included: RS1 variant; age at presentation; best-corrected visual acuity (BCVA), central retinal thickness (CRT), macular volume (MV) at presentation and at the last follow up; full-field electroretinogram (ERG) findings; presence of peripheral retinoschisis and complications (vitreous hemorrhage, retinal detachment); treatment with systemic or topical carbonic anhydrase inhibitors (CAI).

Results

Inter-eye symmetry revealed strong correlation in CRT (r = 0.77; p < 0.0001) and moderate correlations in MV (r = 0.51, p < 0.0001) and BCVA (r = 0.49; p < 0.0001). Weak or no correlations were observed between BCVA and structural parameters (CRT, MV). Peripheral retinoschisis was observed in 40 (68%), retinal detachment in 9 (15%), and vitreous hemorrhage in 5 (8%) patients, respectively. Longitudinal examinations (mean, 4.3 years) showed no BCVA changes; however, a reduction of the CRT (p = 0.02), and MV (p = 0.01) was observed. Oral and/or topical CAI treatment did not significantly alter the CRT (p = 0.34).

Discussion

The XLRS phenotype demonstrates a strong CRT symmetry between the eyes within individual patients and stable BCVA over several years. BCVA exhibits a weak correlation with the morphological parameters of retinal thickness (CRT MV). In our cohort, longitudinal functional changes were not significant, likely attributed to the short average follow-up period. Furthermore, CAI treatment didn't influence both morphological and functional outcomes.

Genetic Counseling For Predictive Retinal Imaging

This Viewpoint discusses genetic counseling for predictive retinal imaging.

Allogeneic HSCT for Symptomatic Female X-linked Chronic Granulomatous Disease Carriers

X-linked chronic granulomatous disease (XL-CGD) is an inherited disorder of superoxide production, causing failure to generate the oxidative burst in phagocytes. It is characterized by invasive bacterial and fungal infections, inflammation, and chronic autoimmune disease. While XL-CGD carriers were previously assumed to be healthy, a range of clinical manifestations with significant morbidity have recently been described in a subgroup of carriers with impaired neutrophil oxidative burst due to skewed lyonization. Allogeneic hematopoietic stem cell transplantation (HSCT) is the standard curative treatment for CGD but has rarely been reported in individual symptomatic carriers to date. We undertook a retrospective international survey of outcome of HSCT for symptomatic XL-CGD carriers. Seven symptomatic female XL-CGD carriers aged 1-56 years underwent HSCT in four centers, indicated for severe and recurrent infection, colitis, and autoimmunity. Two patients died from transplant-related complications, following donor engraftment and restoration of oxidative burst. All surviving patients demonstrated resolution of their neutrophil oxidative burst defect with concordant reduction in infection and inflammatory symptoms and freedom from further immunosuppressive therapy. In conclusion, allogeneic HSCT may cure the phagocyte defect in symptomatic XL-CGD carriers and improve their recurrent and disabling infective and inflammatory symptoms but risks transplant-related complications.

Losing, preserving, and restoring vision from neurodegeneration in the eye

The retina is a part of the brain that sits at the back of the eye, looking out onto the world. The first neurons of the retina are the rod and cone photoreceptors, which convert changes in photon flux into electrical signals that are the basis of vision. Rods and cones are frequent targets of heritable neurodegenerative diseases that cause visual impairment, including blindness, in millions of people worldwide. This review summarizes the diverse genetic causes of inherited retinal degenerations (IRDs) and their convergence onto common pathogenic mechanisms of vision loss. Currently, there are few effective treatments for IRDs, but recent advances in disparate areas of biology and technology (e.g., genome editing, viral engineering, 3D organoids, optogenetics, semiconductor arrays) discussed here enable promising efforts to preserve and restore vision in IRD patients with implications for neurodegeneration in less approachable brain areas.

Inherited causes of combined vision and hearing loss: clinical features and molecular genetics

Combined vision and hearing loss, also known as dual sensory impairment, can occur in several genetic conditions, including ciliopathies such as Usher and Bardet-Biedl syndrome, mitochondrial DNA disorders and systemic diseases, such as CHARGE, Stickler, Waardenburg, Alport and Alstrom syndrome. The retinal phenotype may point to the diagnosis of such disorders. Herein, we aim to provide a comprehensive review of the molecular genetics and clinical features of the most common non-chromosomal inherited disorders to cause dual sensory impairment.

Genetic and clinical landscape of ARR3-associated MYP26: the most common cause of Mendelian early-onset high myopia with a unique inheritance

AIMS

To elucidate genetic background of early-onset high myopia (eoHM) and characteristics of ARR3-associated MYP26.

METHODS

Variants in 14 genes reported to contribute to eoHM, including ARR3, were selected from exome sequencing data set and classified into different categories following American College of Medical Genetics and Genomics guidelines based on in silico prediction, associated phenotypes, confirmation and cosegregation analysis. The available clinical data of individuals were summarised.

RESULTS

Pathogenic and likely pathogenic variants in three of 14 genes were identified in 52 of 928 families with eoHM, including 29 in ARR3, 22 in OPN1LW and 1 in LRPAP1. For ARR3, 24 pathogenic variants (16 truncation and 8 missense) were identified in 66 women and 12 men, in whom 64 women and 4 men had eoHM by X-linked female-limited inheritance. Refraction ranged from -5.00 to -28.75 diopter (-12.58±4.83). Mild-to-moderately reduced cone responses were recorded in 76.9% (10/13) of patients with electroretinogram recordings. Most patients (75.9%, 41/54) had mild myopic fundus changes (C0 to C1). Genotype-phenotype analysis suggested that the myopic retinopathy degree was correlated with age and the variant's nature. Peripheral retinal degeneration was observed in 38.5% (5/13) patients using wide-field examinations.

CONCLUSION

This study reveals ARR3 as the most frequently implicated gene for Mendelian eoHM. Truncations and highly scored missense variants in ARR3 are pathogenic. Myopia due to ARR3 mutations is transmitted in X-linked female-limited inheritance, manifests with mild cone impairment and slowly progresses to pathologic myopia. Identification of the most common cause for Mendelian eoHM provides a valuable starting point into the molecular mechanism of myopia.

The Value of Electroretinography in Identifying Candidate Genes for Inherited Retinal Dystrophies: A Diagnostic Guide

Inherited retinal dystrophies (IRDs) are a group of heterogeneous diseases caused by genetic mutations that specifically affect the function of the rod, cone, or bipolar cells in the retina. Electroretinography (ERG) is a diagnostic tool that measures the electrical activity of the retina in response to light stimuli, and it can help to determine the function of these cells. A normal ERG response consists of two waves, the a-wave and the b-wave, which reflect the activity of the photoreceptor cells and the bipolar and Muller cells, respectively. Despite the growing availability of next-generation sequencing (NGS) technology, identifying the precise genetic mutation causing an IRD can be challenging and costly. However, certain types of IRDs present with unique ERG features that can help guide genetic testing. By combining these ERG findings with other clinical information, such as on family history and retinal imaging, physicians can effectively narrow down the list of candidate genes to be sequenced, thereby reducing the cost of genetic testing. This review article focuses on certain types of IRDs with unique ERG features. We will discuss the pathophysiology and clinical presentation of, and ERG findings on, these disorders, emphasizing the unique role ERG plays in their diagnosis and genetic testing.

Novel mutations of the X-linked genes associated with early-onset high myopia in five Chinese families

PURPOSE

To report novel pathogenic variants of X-linked genes in five Chinese families with early-onset high myopia (eoHM) by using whole-exome sequencing and analyzing the phenotypic features.

METHODS

5 probands with X-linked recessive related eoHM were collected in Ningxia Eye Hospital from January 2021 to June 2022. The probands and their family members received comprehensive ophthalmic examinations,and DNA was abstracted from patients and family members. Whole-exome sequencing was performed on probands to screen the causative variants, and all suspected pathogenic variants were determined by Sanger sequencing and co-segregation analysis was performed on available family members. The pathogenicity of novel variants was predicted using silico analysis and evaluated according to ACMG guidelines. RT-qPCR was used to detect differences in the relative mRNAs expression of candidate gene in mRNAs available with the proband and family members in the pedigree 2. The relationship between genetic variants and clinical features was analyzed.

RESULTS

All probands were male, and all pedigrees conformed to an X-linked recessive inheritance pattern. They were diagnosed with high myopia at their first visits between 4 and 7 years old. Spherical equivalent ranged between - 6.00D and - 11.00D.The five novel hemizygous variants were found in the probands, containing frameshift deletion variant c.797_801del (p.Val266Alafs*75) of OPN1LW gene in the pedigree 1, nonsense variant c.513G > A (p.Trp171Ter)of RP2 gene in the pedigree 2, missense variant c.98G > T (p.Cys33Phe) of GPR143 gene in the pedigree 3, frameshift deletion variant c.1876_1877del (p.Met626Valfs*22) of FRMD7 gene in the pedigree 4 and inframe deletion variant c.670_ 675del (p.Glu192_ Glu193del) of HMGB3 gene in the pedigree 5. All variants were classified as pathogenic or likely pathogenic by the interpretation principles of HGMD sequence variants and ACMG guidelines. In family 2, RT-qPCR showed that the mRNA expression of RP2 gene was lower in the proband than in other normal family members, indicating that such variant caused an effect on gene function at the mRNA expression level. Further clinical examination showed that pedigrees 1, 2, 3, and 4 were diagnosed as X-linked recessive hereditary eye disease with early-onset high myopia, including quiescent cone dysfunction, retinitis pigmentosa, ocular albinism, and idiopathic congenital nystagmus respectively. The pedigree 5 had eoHM in the right eye and ptosis in both eyes.

CONCLUSION

In this paper,we are the first to report five novel hemizygous variants in OPN1LW, RP2, GPR143, FRMD7, HMGB3 genes are associated with eoHM. Our study extends the genotypic spectrums for eoHM and better assists ophthalmologists in assessing, diagnosing, and conducting genetic screening for eoHM.

RPGR: Deep Phenotyping and Genetic Characterization With Findings Specific to the 3'-end of ORF15

Purpose

To describe a group of patients with retinitis pigmentosa GTPase regulator (RPGR)-related retinopathy with a tapetal-like retinal sheen and corresponding changes in the reflectivity of the ellipsoid zone on optical coherence tomography (OCT) imaging.

Methods

A retrospective case series of 66 patients with a disease-causing variant in RPGR was performed. An expert examiner, masked to patient demographics, clinical evaluations, and specific RPGR variant, analyzed color fundus photographs for the presence of a tapetal-like retinal sheen and assessed OCT images for the presence of an abnormally broad hyper-reflective band in the outer retina. Longitudinal reflectivity profiles were generated and compared with healthy controls.

Results

Twelve patients (18.2%) had a retinal sheen on color images that cosegregated with an abnormally broad hyper-reflective ellipsoid zone band on OCT imaging. Three-fourths of these patients were male, had a cone-rod dystrophy, and had pathogenic RPGR variants located toward the 3'-end of ORF15. This group had a different longitudinal reflectivity profile signature compared with controls. After a period of prolonged dark adaptation, the abnormal hyper-reflective band on OCT became less apparent, and the outer retinal layers adopted a more normal appearance.

Conclusions

RPGR-related retinopathy should be considered for males presenting with retinal sheen, abnormal ellipsoid zone hyper-reflectivity, and cone or cone-rod dysfunction on ERG, and pursued with molecular testing. Our results have implications for understanding the role of the C-terminal domain encoded by RPGR ORF15 in the phototransduction cascade. Further, the findings may be important to incorporate into both inclusion criteria and outcome measure developments in future RPGR-related cone or cone-rod dystrophy clinical trials.

RP2 X-LINKED RETINITIS PIGMENTOSA CARRIER STATE PRESENTING WITH VASCULAR LEAKAGE AND UNILATERAL MACULAR ATROPHY

PURPOSE

We describe the unusual clinical presentation of a 33-year-old woman subsequently identified as a carrier of RP2-associated X-linked retinitis pigmentosa.

METHODS

Case report.

RESULTS

A 33-year-old woman without a known family history of retinal disease presented with unilateral reduced visual acuity and central scotoma in the left eye. Examination showed underlying macular atrophy in the left eye and a bilateral tapetal-like reflex. Full-field electroretinogram was abnormal in the left eye but normal in the right eye. Notable findings on wide-field imaging included bilateral peripheral vascular leakage on fluorescein angiography and a bilaterally symmetric radial pattern of hyperfluorescence on fundus autofluorescence. Genetic testing demonstrated a pathogenic variant in the gene RP2 confirming that she was a carrier of X-linked retinitis pigmentosa.

CONCLUSION

We describe clinical features of the carrier state of RP2-XLRP and expand potential findings to include peripheral vascular leakage. This case highlights the importance of awareness of the carrier state, particularly if a family history cannot be provided.

NDP-related retinopathies: clinical phenotype of female carriers

BACKGROUND/AIMS

Norrin cysteine knot growth factor (NDP) located on the X chromosome, was previously reported to cause Norrie disease and familial exudative vitreoretinopathy (FEVR), which are blindness-causing ocular disorders, in males. In this study, we aimed to explore the clinical characteristics of female carriers with NDP mutations.

METHODS

Twelve female carriers from 11 unrelated families with pathogenic NDP mutations were recruited. Clinical data were collected from the NDP carriers. Comprehensive ocular examinations, including best corrected visual acuity, slit lamp examination, fundus photography and fundus fluorescein angiography (FFA) were evaluated. Targeted gene or whole exome sequencing was performed in the probands, and Sanger sequencing was performed to confirm NDP mutations in female carriers.

RESULTS

Of the 12 females, 1 (1/12, 8.3%) presented with decreased visual acuity and 11 (11/12, 91.7%) were asymptomatic. Based on the FFA, peripheral vascular changes were noted in 66.7% (16/24) of the eyes of 75.0% (9/12) of the carriers. A total of 33.3% (8/24) had typical FEVR phenotype, 33.3% (8/24) had mild vascular abnormalities and 33.3% (8/24) was unremarkable. In addition, predominant changes such as telangiectatic endings (66.7%), anomalous circumferential vessel (37.5%), supernumerary vascular branching (33.3%), fluorescein leakage (29.2%), avascular area (8.3%), retina fold (8.3%) and peripheral straightening of retinal vessels (33.3%) were noted.

CONCLUSION

Although NDP-related retinopathy is an X-linked recessive disorder, most of the female carriers of NDP exhibited clinical features of FEVR. Thus, timely examinations and lifelong monitoring should be conducted in the NDP female carriers.

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.

Blue cone monochromacy and gene therapy

Blue cone monochromacy (BCM) is a congenital vision disorder characterized by complete loss or severely reduced long- and middle-wavelength cone function, caused by mutations in the OPN1LW/OPN1MW gene cluster on the X-chromosome. BCM patients typically suffer from poor visual acuity, severely impaired color discrimination, myopia, and nystagmus. In this review, we cover the genetic causes of BCM, clinical features of BCM patients, genetic testing, and clinical outcome measurements for future BCM clinical trials. However, our emphasis is on detailing the animal models for BCM and gene therapy using adeno-associated vectors (AAV). We describe two mouse models resembling the two most common causes of BCM, current progress in proof-of-concept studies to treat BCM with deletion mutations, the challenges we face, and future directions.

The Phosphoproteome of the Rd1 Mouse Retina, a Model of Inherited Photoreceptor Degeneration, Changes after Protein Kinase G Inhibition

Retinitis pigmentosa (RP) is a frequent cause of blindness among the working population in industrial countries due to the inheritable death of photoreceptors. Though gene therapy was recently approved for mutations in the RPE65 gene, there is in general no effective treatment presently. Previously, abnormally high levels of cGMP and overactivation of its dependent protein kinase (PKG) have been suggested as causative for the fatal effects on photoreceptors, making it meaningful to explore the cGMP-PKG downstream signaling for more pathological insights and novel therapeutic target development purposes. Here, we manipulated the cGMP-PKG system in degenerating retinas from the rd1 mouse model pharmacologically via adding a PKG inhibitory cGMP-analogue to organotypic retinal explant cultures. A combination of phosphorylated peptide enrichment and mass spectrometry was then applied to study the cGMP-PKG-dependent phosphoproteome. We identified a host of novel potential cGMP-PKG downstream substrates and related kinases using this approach and selected the RAF1 protein, which may act as both a substrate and a kinase, for further validation. This showed that the RAS/RAF1/MAPK/ERK pathway may be involved in retinal degeneration in a yet unclarified mechanism, thus deserving further investigation in the future.

Choroideremia: Toward Regulatory Approval of Retinal Gene Therapy

Choroideremia is an X-linked inherited retinal degeneration characterized by primary centripetal degeneration of the retinal pigment epithelium (RPE), with secondary degeneration of the choroid and retina. Affected individuals experience reduced night vision in early adulthood with blindness in late middle age. The underlying CHM gene encodes REP1, a protein involved in the prenylation of Rab GTPases essential for intracellular vesicle trafficking. Adeno-associated viral gene therapy has demonstrated some benefit in clinical trials for choroideremia. However, challenges remain in gaining regulatory approval. Choroideremia is slowly progressive, which presents difficulties in demonstrating benefit over short pivotal clinical trials that usually run for 1-2 years. Improvements in visual acuity are particularly challenging due to the initial negative effects of surgical detachment of the fovea. Despite these challenges, great progress toward a treatment has been made since choroideremia was first described in 1872.

Overcoming the Challenges to Clinical Development of X-Linked Retinitis Pigmentosa Therapies: Proceedings of an Expert Panel

X-linked retinitis pigmentosa (XLRP) is a rare inherited retinal disease manifesting as impaired night vision and peripheral vision loss that progresses to legal blindness. Although several trials of ocular gene therapy for XLRP have been conducted or are in progress, there is currently no approved treatment. In July 2022, the Foundation Fighting Blindness convened an expert panel to examine relevant research and make recommendations for overcoming the challenges and capitalizing on the opportunities in conducting clinical trials of RPGR-targeted therapy for XLRP. Data presented concerned RPGR structure and mutation types known to cause XLRP, RPGR mutation-associated retinal phenotype diversity, patterns in genotype/phenotype relationships, disease onset and progression from natural history studies, and the various functional and structural tests used to monitor disease progression. Panel recommendations include considerations, such as genetic screening and other factors that can impact clinical trial inclusion criteria, the influence of age on defining and stratifying participant cohorts, the importance of conducting natural history studies early in clinical development programs, and the merits and drawbacks of available tests for measuring treatment outcomes. We recognize the need to work with regulators to adopt clinically meaningful end points that would best determine the efficacy of a trial. Given the promise of RPGR-targeted gene therapy for XLRP and the difficulties encountered in phase III clinical trials to date, we hope these recommendations will help speed progress to finding a cure.

Translational Relevance

Examination of relevant data and recommendations for the successful clinical development of gene therapies for RPGR-associated XLRP.

High-Quality Chromosome-Level Genome Assembly of the Corsac Fox (Vulpes corsac) Reveals Adaptation to Semiarid and Harsh Environments

The Corsac fox (Vulpes corsac) is a species of fox distributed in the arid prairie regions of Central and Northern Asia, with distinct adaptations to dry environments. Here, we applied Oxford-Nanopore sequencing and a chromosome structure capture technique to assemble the first Corsac fox genome, which was then assembled into chromosome fragments. The genome assembly has a total length of 2.2 Gb with a contig N50 of 41.62 Mb and a scaffold N50 of 132.2 Mb over 18 pseudo-chromosomal scaffolds. The genome contained approximately 32.67% of repeat sequences. A total of 20,511 protein-coding genes were predicted, of which 88.9% were functionally annotated. Phylogenetic analyses indicated a close relation to the Red fox (Vulpes vulpes) with an estimated divergence time of ~3.7 million years ago (MYA). We performed separate enrichment analyses of species-unique genes, the expanded and contracted gene families, and positively selected genes. The results suggest an enrichment of pathways related to protein synthesis and response and an evolutionary mechanism by which cells respond to protein denaturation in response to heat stress. The enrichment of pathways related to lipid and glucose metabolism, potentially preventing stress from dehydration, and positive selection of genes related to vision, as well as stress responses in harsh environments, may reveal adaptive evolutionary mechanisms in the Corsac fox under harsh drought conditions. Additional detection of positive selection for genes associated with gustatory receptors may reveal a unique desert diet strategy for the species. This high-quality genome provides a valuable resource for studying mammalian drought adaptation and evolution in the genus Vulpes.

Asymmetric presentation with a novel RP2 gene mutation in X-Linked retinitis pigmentosa: a case report

BACKGROUND

We present the detailed multimodal imaging analysis in a case of X-linked retinitis pigmentosa (XLRP) exhibiting a markedly asymmetric presentation with a novel RP2 mutation.

CASE PRESENTATION

A 25-year-old woman complained of decreased vision in the right eye as well as night blindness. Her visual acuity was 20/100 (OD) and 20/20 (OS). Fundus examination revealed bone spicule pigmentation with tessellated changes in the fundus within the posterior pole. Optical coherence tomography (OCT) showed generalized disruption of foveal microstructures in the OD. No abnormal findings were identified, but localized ellipsoid zone band losses were observed on OCT in the OS. Fundus autofluorescence revealed multiple patchy hypo-autofluorescent lesions in the OD and a tapetal-like radial reflex against a dark background in the OS. Fluorescein angiography and OCT angiography revealed diffuse mottled hyperfluorescence with reduced retinal vessel density in the OD and no evidence of vascular compromise in the OS. Goldmann perimetry demonstrated a constricted visual field, and electrophysiological assessment revealed an extinguished rod response and a severely impaired cone response in the OD. Molecular genetic tests via next-generation sequencing revealed the pathogenic variant to be a heterozygous frameshift mutation in RP2 (RP2, p.Glu269Glyfs*7), resulting in premature termination of the protein.

CONCLUSIONS

Random X-inactivation may be attributed to interocular differences in the severity of XLRP in female carriers. A novel frameshift mutation in the RP2 gene and a comprehensive phenotypic evaluation in the current study may broaden the spectrum of the disease in XLRP carriers.

Mouse all-cone retina models of Cav1.4 synaptopathy

The voltage-gated calcium channel, Cav1.4 is localized to photoreceptor ribbon synapses and functions both in molecular organization of the synapse and in regulating release of synaptic vesicles. Mutations in Cav1.4 subunits typically present as either incomplete congenital stationary night blindness or a progressive cone-rod dystrophy in humans. We developed a cone-rich mammalian model system to further study how different Cav1.4 mutations affect cones. RPE65 R91W KI; Nrl KO "Conefull" mice were crossed to Cav1.4 α1F or α2δ4 KO mice to generate the "Conefull:α1F KO" and "Conefull:α2δ4 KO" lines. Animals were assessed using a visually guided water maze, electroretinogram (ERG), optical coherence tomography (OCT), and histology. Mice of both sexes and up to six-months of age were used. Conefull: α1F KO mice could not navigate the visually guided water maze, had no b-wave in the ERG, and the developing all-cone outer nuclear layer reorganized into rosettes at the time of eye opening with degeneration progressing to 30% loss by 2-months of age. In comparison, the Conefull: α2δ4 KO mice successfully navigated the visually guided water maze, had a reduced amplitude b-wave ERG, and the development of the all-cone outer nuclear layer appeared normal although progressive degeneration with 10% loss by 2-months of age was observed. In summary, new disease models for studying congenital synaptic diseases due to loss of Cav1.4 function have been created.

Unique Haplotypes in OPN1LW as a Common Cause of High Myopia With or Without Protanopia: A Potential Window Into Myopic Mechanism

Purpose

Specific haplotypes (LVAVA, LIVVA, and LIAVA) formed by five polymorphisms (p.L153M, p.V171I, p.A174V, p.I178V, and p.S180A in exon 3 of OPN1LW) that cause partial or complete exon skipping have been reported as unique genetic causes of high myopia with or without colorblindness. This study aimed to identify the contribution of OPN1LW to early-onset high myopia (eoHM) and the molecular basis underlying eoHM with or without colorblindness.

Methods

Comparative analysis of exome sequencing data was conducted for 1226 families with eoHM and 9304 families with other eye conditions. OPN1LW variants detected by targeted or whole exome sequencing were confirmed by long-range amplification and Sanger sequencing, together with segregation analysis. The clinical data were thoroughly analyzed.

Results

Unique haplotypes and truncation variants in OPN1LW were detected exclusively in 68 of 1226 families with eoHM but in none of the 9304 families with other visual diseases (P = 1.63 × 10-63). Four classes of variants were identified: haplotypes causing partial splicing defects in OPN1LW (LVAVA or LIVVA in 31 families), LVAVA in OPN1LW-OPN1MW hybrid gene (in 3 families), LIAVA in OPN1LW (in 29 families), and truncations in OPN1LW (in 5 families). The first class causes partial loss of red photopigments, whereas the latter three result in complete loss of red photopigments. This is different from the replacement of red with green owing to unequal re-arrangement causing red-green colorblindness alone. Of the 68 families, 42 affected male patients (31 families) with the first class of variants (LVAVA or LIVVA in OPN1LW) had eoHM alone, whereas 37 male patients with the latter 3 classes had eoHM with protanopia. Adaptive optics retinal imaging demonstrated reduced cone regularity and density in men with eoHM caused by OPN1LW variants compared to those patients with eoHM and without OPN1LW variants.

Conclusion

Based on the 68 families with unique variants in OPN1LW, our study provides firm evidence that the two different phenotypes (eoHM with or without colorblindness) are caused by two different classes of variants (partial splicing-effect haplotypes or complete splicing-effect haplotypes/truncation variants, respectively). The contribution of OPN1LW to eoHM (isolated and syndromic) was characterized by OPN1LW variants found in 5.5% (68/1226) of the eoHM families, making it the second most common cause of monogenic eoHM alone (2.4%) and a frequent cause of syndromic monogenic eoHM with colorblindness. Such haplotypes, in which each individual variant alone is considered a benign polymorphism, are potential candidates for other hereditary diseases with causes of missing genetic defects.

Genetic spectrum, retinal phenotype, and peripapillary RNFL thickness in RPGR heterozygotes

PURPOSE

Phenotypic heterogeneity with variable severity has been reported in female carriers of retinitis pigmentosa GTPase regulator (RPGR) mutations, including a male-type phenotype. A phenomenon not fully understood is peripapillary retinal nerve fiber layer (pRNFL) thickening in male patients with RPGR-associated X-linked retinitis pigmentosa, especially in the temporal sector. We aim to describe the genetic spectrum, retinal phenotypes, and pRNFL thickness in a cohort of Caucasian RPGR-mutation heterozygotes.

METHODS

A cross-sectional study was conducted at an inherited retinal degeneration (IRD) reference center in Portugal. Female patients heterozygous for clinically significant RPGR variants were identified using the IRD-PT registry. A complete ophthalmologic examination was performed, complemented by macular and peripapillary spectral domain optical coherence tomography (SD-OCT), ultra-widefield color fundus photography (UW-CFP), and ultra-widefield fundus autofluorescence (UW-FAF). The retinal phenotypes were graded according to previously described classifications. The pRNFL thickness across the superior, inferior, nasal, and temporal quadrants was compared to the Spectralis® RNFL age-adjusted reference database.

RESULTS

Forty-eight eyes from 24 females (10 families) were included in the study. Genetic analysis yielded 8 distinct clinically significant frameshift variants in RPGR gene, 3 of which herein reported for the first time. No association was found between mutation location and best-corrected visual acuity (BCVA) or retinal phenotype. Age was associated with worse BCVA and more advanced phenotypes on SD-OCT, UW-CFP, and UW-FAF. Seven women (29.17%) presented a male-type phenotype on UW-FAF in at least one eye. An association was found between UW-FAF and pRNFL thickness in the temporal sector (p = 0.003), with the most advanced fundus autofluorescence phenotypes showing increased pRNFL thickness in this sector.

CONCLUSION

This study expands the genetic landscape of RPGR-associated disease by reporting 3 novel clinically significant variants. We have shown that clinically severe phenotypes are not uncommon among female carriers. Furthermore, we provide novel insights into pRNFL changes observed in RPGR heterozygotes that mimic what has been reported in male patients.

Clinical and genetic features of retinoschisis in 120 families with RS1 mutations

BACKGROUND/AIMS

X-linked retinoschisis (XLRS), associated with RS1, is the most common type of X-linked retinopathy in children. This study aimed to identify clinical and genetic features of retinoschisis in 120 families with RS1 variants in China.

METHODS

RS1 variants were collected from our in-house exome data and were predicted by multiple-step bioinformatics analysis. Clinical data of 122 patients from 120 families with potential pathogenic RS1 variants were analysed and summarised, respectively.

RESULT

Totally, 79 hemizygous variants (53 missense, 25 truncation and 1 indel), were detected. All except one (78/79, 98.7%), including 22 novels, were classified as potential pathogenic and detected exclusively in 120 families with retinoschisis. Clinical data demonstrated an average age of presentation at 5 years (1 month-41 years). Macular changes were classified as macular schisis (87.5%), macular atrophy (10.7%), normal (0.9%) and unclassified (0.9%). Patients with macular atrophy had older age but similar visual acuity compared with macular schisis. Peripheral retinal changes included flat retinoschisis (52.4%), bullous retinoschisis (BRS) (10.7%) and normal-like (36.9%) patients. Spontaneous regression was observed in two patients with BRS on follow-up examination. Visual acuity in the peripheral retinoschisis group was worse than that without peripheral retinoschisis.

CONCLUSION

Almost all rare RS1 variants were potential pathogenic. All patients with RS1 pathogenic variants showed detectable characteristics in the macula and/or peripheral retina. Our data on RS1 variants and associated clinical phenotypes may be of value for clinical diagnosis and genetic test of retinoschisis.

Novel Exon 7 Deletions in TSPAN12 in a Three-Generation FEVR Family: A Case Report and Literature Review

Familial exudative vitreoretinopathy (FEVR) is a severe clinically and genetically heterogeneous disease that is characterized by vascular disorder. FEVR exhibits strikingly variable clinical phenotypes, ranging from asymptomatic to total blindness. In this case, we present a patient who was first treated as having high myopia and retinopathy but was finally diagnosed with FEVR caused by the heterozygous deletion of exon 7 in TSPAN12 with the aid of whole genome sequencing (WGS). Typical vascular changes, including vascular leakage and an avascular zone in the peripheral retina, were observed in the proband using fundus fluorescein angiography (FFA), and the macular dragging was shown to be progressing in the follow-up visit. Furthermore, the proband showed unreported TSPAN12-related phenotypes of FEVR: ERG (full-field electroretinogram) abnormalities and retinoschisis. Only mild vascular changes were exhibited in the FFA for the other three family members who carried the same deletion of exon 7 in TSPAN12. This case expands our understanding of the phenotype resulting from TSPAN12 mutations and signifies the importance of combining both clinical and molecular analysis approaches to establish a complete diagnosis.

Genetic Characteristics and Long-Term Follow-Up of Slovenian Patients with RPGR Retinal Dystrophy

Genetic characteristics and a long-term clinical follow-up of 18 Slovenian retinitis pigmentosa GTPase regulator (RPGR) patients from 10 families with retinitis pigmentosa (RP) or cone/cone-rod dystrophy (COD/CORD) are reported. RP (eight families) was associated with two already known (p.(Ser407Ilefs*46) and p.(Glu746Argfs*23)) and five novel variants (c.1245+704_1415-2286del, p.(Glu660*), p.(Ala153Thr), c.1506+1G>T, and p.(Arg780Serfs*54)). COD (two families) was associated with p.(Ter1153Lysext*38). The median age of onset in males with RP (N = 9) was 6 years. At the first examination (median age of 32 years), the median best corrected visual acuity (BCVA) was 0.30 logMAR, and all patients had a hyperautofluorescent ring on fundus autofluorescence (FAF) encircling preserved photoreceptors. At the last follow-up (median age of 39 years), the median BCVA was 0.48 logMAR, and FAF showed ring constriction transitioning to patch in 2/9. Among females (N = 6; median age of 40 years), two had normal/near-normal FAF, one had unilateral RP (male pattern), and three had a radial and/or focal pattern of retinal degeneration. After a median of 4 years (4-21) of follow-up, 2/6 exhibited disease progression. The median age of onset in males with COD was 25 years. At first examination (median age of 35 years), the median BCVA was 1.00 logMAR, and all patients had a hyperautofluorescent FAF ring encircling foveal photoreceptor loss. At the last follow-up (median age of 42 years), the median BCVA was 1.30 logMAR, and FAF showed ring enlargement. The majority of the identified variants (75%; 6/8) had not been previously reported in other RPGR cohorts, which suggested the presence of distinct RPGR alleles in the Slovenian population.

Profiling of visual acuity and genotype correlations in RP2 patients: a cross-sectional comparative meta-analysis between carrier females and affected males

BACKGROUND

X-linked retinitis pigmentosa (XLRP) is the most severe form of retinitis pigmentosa (RP) and accounts for 15-20% of all RP cases. In this study, we investigated the progression of visual acuity loss across age groups in female carriers and compared it to affected males.

METHODS

A PubMed literature search was conducted, and RP2 cases were included based on specific inclusion criteria. Visual acuity (VA), refractive error spherical equivalent (SE), and retinal findings were recorded. Cross-sectional analyses investigated the relationship between VA and age in carrier females and affected males. Genotype-phenotype VA correlations were studied using t-tests.

RESULTS

35 carrier females and 28 affected males with confirmed RP2 mutations were collected from 13 studies. The mean age and logMAR VA of carrier females were 44.2 ± 17.4 years, and 0.5 ± 0.5, respectively. 78.8% of carrier females showed abnormal XLRP-related fundus findings and had significantly reduced VA compared to those with normal fundi (0.6 ± 0.5 vs. 0.1 ± 0.1; p = 0.03). Compared to affected males, no statistical correlation was found between logMAR VA and advancing age in carrier females (p = 0.75). Statistically significant linear correlations were found between logMAR VA and SE in each of carrier females (p = 0.01). There were no observed differences in logMAR VA based on mutation type (p = 0.97) or mutation location (p = 0.83). Anisometropia was observed in 38% of carrier females and 68% of affected males; these prevalence numbers are statistically significant between the two groups (1.7 ± 0.3 vs. 3.9 ± 10.9 dioptres; p = 0.03).

CONCLUSIONS

RP2 carrier females generally maintain good VA throughout their lifetime, as opposed to affected males, whose vision progressively declines. Our study provides important VA prognostic data that is crucial for patient counseling.

X-linked retinoschisis: mutation spectrum and genotype-phenotype relationship in an Italian pediatric cohort

BACKGROUND

X-linked juvenile retinoschisis (×LRS) is an X-linked vitreoretinal degenerative disease that consists of variable phenotypes ranging from severe early-onset defects to subtle abnormalities diagnosed in elderly patients. XLRS is caused by a loss of function of the protein Retinoschisin (RS1), which is essential to preserve retinal integrity and function of photoreceptor-bipolar synapse. The literature data so far mostly agree on the absence of a clear genotype-phenotype correlation in XLRS. We reviewed clinical and molecular characteristics of a cohort of Italian pediatric XLRS patients to assess the presence of a correlation between genotype and phenotype severity.

MATERIALS AND METHODS

We retrospectively examined clinical and genetic features of a cohort of 27 XLRS patients. In this study we included patients with a diagnosis of XLRS confirmed by fundus photography, spectral domain optical coherence tomography, and molecular analysis and with an onset of less than 10 years of age. We sorted RS1 variants according to their effect of RS1 structure and function in three separate groups.

RESULTS

According to previous studies, we did not observe a conclusive genotype-phenotype correlation in our cohort; nevertheless, we noticed that patients harboring RS1 variants leading to RS1-secreted mutants show a more homogeneous phenotype, with an overall good visual acuity, compared to the other two groups.

CONCLUSIONS

Our data support the hypothesis that secretion profile of RS1 could influence the severity of the phenotype. More extensive and functional studies are needed to acquire notions in view of the opportunity of gene replacement therapy for XLRS patients.