Compounding engineered mesenchymal stem cell-derived exosomes: A potential rescue strategy for retinal degeneration

The prevalence of retinal degenerative diseases, including age-related macular degeneration and retinitis pigmentosa, has been increasing globally and is linked to the aging population and improved life expectancy. These diseases are characterized by chronic, progressive neuronal damage or depletion of the photoreceptor cells in the retina, and limited effective treatment options are currently available. Mesenchymal stem cell-derived exosomes (MSC-EXOs) containing cytokines, growth factors, lipids, mRNA, and miRNA, which act as mediators of intercellular communication transferring bioactive molecules to recipient cells, offer an appealing, non-cellular nanotherapeutic approach for retinal degenerative diseases. However, treatment specificity is compromised due to their high heterogeneity in size, content, functional effects, and parental cellular source. To improve this, engineered MSC-EXOs with increased drug-loading capacity, targeting ability, and resistance to bodily degradation and elimination have been developed. This review summarizes the recent advances in miRNAs of MSC-EXOs as a treatment for retinal degeneration, discussing the strategies and methods for engineering therapeutic MSC-EXOs. Notably, to address the single functional role of engineered MSC-EXOs, we propose a novel concept called "Compound Engineered MSC-EXOs (Co-E-MSC-EXOs)" along with its derived potential therapeutic approaches. The advantages and challenges of employing Co-E-MSC-EXOs for retinal degeneration in clinical applications, as well as the strategies and issues related to them, are also highlighted.

Mechanism and ingredients prediction of Radix Salviae-Angelicae Sinensis Radix-Lycii Fructus-Rehmanniae Radix Praeparata-Ginkgo Folium for retinitis pigmentosa therapy using network pharmacology and molecular docking analysis

Background

Radix Salviae (Danshen)-Angelicae Sinensis Radix (Danggui)-Lycii Fructus (Gouqizi)-Rehmanniae Radix Praeparata (Shudihuang)-Ginkgo Folium (Yinxinye) (RALRG) are commonly used herbs in China that have shown positive effects on retinitis pigmentosa (RP). However, little research has been performed on the impact of RALRG and RP. Herein, this study aimed to predict the mechanism and potential components of RALRG in treating RP.

Methods

The ingredients of RALRG were obtained from the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP); the potential targets of RP and RALRG were obtained from TCMSP, GeneCards, and the Online Mendelian Inheritance in Man (OMIM) database. A protein-protein interaction (PPI) network was constructed to visualize PPIs. The functional enrichment was performed with the R program. A visual RALRG-RP-pathway pharmacology network was established by Cytoscape 3.9.1. Molecular docking was used to perform molecular docking and calculate the binding affinity.

Results

A total of 132 effective active ingredients in RALRG with 248 target genes were screened; 92 intersection target genes were acquired from the intersection of RP- and RALRG-related genes. Gene Ontology (GO) enrichment indicated that these intersection targets were mainly involved in oxidative stress, metal ion response, and chemical stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that the PI3K-AKT, cellular senescence, and MAPK signaling pathways were closely related to the therapy of RP. In addition, a potential pharmacology network for RALRG-RP-pathway was constructed. AKT1 and JUN were considered the primary targets. Luteolin, quercetin, and kaempferol were identified as the vital three active ingredients.

Conclusions

RALRG was found to be the main regulator for oxidative stress and PI3K/AKT signaling pathways. Luteolin, quercetin, and kaempferol were three promising complementary ingredients for RP treatment. This study may provide a theoretical basis for applying RALRG to screen potential drugs for RP.

Stem cell therapy for inherited retinal diseases: a systematic review and meta-analysis

PURPOSE

Stem cell therapy is a promising therapeutic approach for inherited retinal diseases (IRDs). This study aims to quantitatively examine the effectiveness and safety of stem cell therapy for patients with IRDs, including retinitis pigmentosa and Stargardt disease (STGD).

METHODS

We searched PubMed, EMBASE, Web of Science, Cochrane Library databases, and the ClinicalTrials.gov website. The latest retrieval time was August 20, 2023. The primary outcomes were rates and mean difference (MD) of best-corrected visual acuity (BCVA) improvement. Subgroup analyses were conducted according to administration routes and stem cell types. This study was registered with PROSPERO (CRD42022349271).

RESULTS

Twenty-one prospective studies, involving 496 eyes (404 RP and 92 STGD) of 382 patients (306 RP and 76 STGD), were included in this study. For RP, the rate of BCVA improvement was 49% and 30% at 6 months and 12 months, respectively, and the BCVA was significantly improved in the operative eyes at 6 months post-treatment (MD = - 0.12 logMAR, 95% CI .17 to - 0.06 logMAR; P < 0.001), while there was no significant difference at 12 months post-treatment (MD = -0.06 logMAR; 95% CI - 0.13 to 0.01 logMAR; P = 0.10). For STGD, the rate of BCVA improvement was 60% and 55% at 6 months and 12 months, respectively, and the BCVA was significantly improved in the operative eyes at 6 months (MD = - 0.14 logMAR, 95% CI - 0.22 to - 0.07 logMAR; P = 0.0002) and 12 months (MD = - 0.17 logMAR, 95% CI - 0.29 to - 0.04 logMAR; P = 0.01). Subgroup analyses showed suprachoroidal space injection of stem cells may be more efficient for RP. Eleven treated-related ocular adverse events from three studies and no related systemic adverse events were reported.

CONCLUSIONS

This study suggests stem cell therapy may be effective and safe for patients with RP or STGD. The long-term vision improvement may be limited for RP patients. Suprachoroidal space injection of stem cells may be a promising administration route for RP patients. Limited by the low grade of evidence, large sample size randomized clinical trials are required in the future.

Exome sequencing in retinal dystrophy patients reveals a novel candidate gene ER membrane protein complex subunit 3

Inherited retinal dystrophies (IRDs) are a heterogeneous group of visual disorders caused by different pathogenic mutations in genes and regulatory sequences. The endoplasmic reticulum (ER) membrane protein complex (EMC) subunit 3 (EMC3) is the core unit of the EMC insertase that integrates the transmembrane peptides into lipid bilayers, and the function of its cytoplasmic carboxyl terminus remains to be elucidated. In this study, an insertional mutation c.768insT in the C-terminal coding region of EMC3 was identified and associated with dominant IRDs in a five-generation family. This mutation caused a frameshift in the coding sequence and a gain of an additional 16 amino acid residues (p.L256F-fs-ext21) to form a helix structure in the C-terminus of the EMC3 protein. The mutation is heterozygous with an incomplete penetrance, and cosegregates in all patients examined. This finding indicates that the C-terminus of EMC3 is essential for EMC functions and that EMC3 may be a novel candidate gene for retinal degenerative diseases.

Voretigene Neparvovec for the Treatment of RPE65-Associated Retinal Dystrophy: Consensus and Recommendations from Korea RPE65-IRD Consensus Paper Committee

Mutations in the RPE65 gene, associated with Leber congenital amaurosis, early-onset severe retinal dystrophy and retinitis pigmentosa, gained growing attention since gene therapy for patients with RPE65-associated retinal dystrophy is available in clinical practice. RPE65 gene accounts for a very small proportion of patients with inherited retinal degeneration, especially Asians. Because RPE65-associated retinal dystrophy shares common clinical characteristics, such as early-onset severe nyctalopia, nystagmus, low vision and progressive visual field constriction, with retinitis pigmentosa by other genetic mutations, appropriate genetic testing is essential to make a correct diagnosis. Also, fundus abnormalities can be minimal in early childhood, and the phenotype is highly variable depending on the type of mutation in RPE65-associated retinal dystrophy, which makes a diagnostic difficulty. The aim of this paper is to review the epidemiology ofRPE65-associated retinal dystrophy, mutation spectrum, genetic diagnosis, clinical characteristics and voretigene neparvovec, a gene therapy product for the treatment of RPE65-related retinal dystrophy.

Generation of an Avian Myeloblastosis Virus (AMV) Reverse Transcriptase Prime Editor

Prime editing (PE) is a novel, double-strand break (DSB)-independent gene editing technology that represents an exciting avenue for the treatment of inherited retinal diseases (IRDs). Given the extensive and heterogenous nature of the 280 genes associated with IRDs, genome editing has presented countless complications. However, recent advances in genome editing technologies have identified PE to have tremendous potential, with the capability to ameliorate small deletions and insertions in addition to all twelve possible transition and transversion mutations. The current PE system is based on the fusion of the Streptococcus pyogenes Cas9 (SpCas9) nickase H840A mutant and an optimized Moloney murine leukemia virus (MMLV) reverse-transcriptase (RT) in conjunction with a PE guide RNA (pegRNA). In this study, we developed a prime editor based on the avian myeloblastosis virus (AMV)-RT and showed its applicability for the installation of the PRPH2 c.828+1G>A mutation in HEK293 cells.

Introduction and Discovery of Retinitis Pigmentosa

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy. There are three main characteristics of RP: night blindness, retinal pigmentation, and visual field constriction. Among these three features, night blindness was the first to be discovered, which could be dated back to the ancient Egyptians at around 1500 BC. However, the night blindness described at that time was most likely associated with vitamin A deficiency rather than RP. Retinitis pigmentosa was first described in cadaver anatomic dissection before the invention of the ophthalmoscope. However, it was not linked to RP or night blindness. It was not until the invention of the ophthalmoscope that ophthalmologists could truly look into the eye and correlate the retinal pigmentation with clinical symptoms, such as night blindness and visual field constriction. In 1983, at a RP workshop that gathered together many experts, a consensus was reached regarding the terminology and guidelines for the diagnosis of RP. In this chapter, we will introduce the history and discovery of RP along with its characteristics.

Electroretinogram (ERG) to Evaluate the Retina in Cases of Retinitis Pigmentosa (RP)

Electroretinogram (ERG) captures the electrical responses of photoreceptors, the summation of action potentials from all neurons in the retina elicited by illumination. ERG testing is an incredibly useful tool in obtaining more specific information regarding a retinal dystrophy. Specifically, ERGs are typically used to test photoreceptors and inner retinal function in humans and animals, to diagnose retinal dystrophies, and to monitor disease progression. In this chapter, we will introduce the components of ERGs and the standard ERG protocols for clinical examination. We will also introduce the various specialized ERG tests, which can help to differentiate retinitis pigmentosa (RP) from other retinal disorders. Lastly, we will elaborate on how to use ERGs to predict visual prognosis in RP.

Analysis of CRB1 Pathogenic Variants Correctable with CRISPR Base and Prime Editing

The mouse and human retina contain three major Crumbs homologue-1 (CRB1) isoforms. CRB1-A and CRB1-B have cell-type-specific expression patterns making the choice of gene augmentation strategy unclear. Gene editing may be a viable alternative for the amelioration of CRB1-associated retinal degenerations. To assess the prevalence and spectrum of CRB1-associated pathogenic variants amenable to base and prime editing, we carried out an analysis of the Leiden Open Variation Database. Editable variants accounted for 54.5% for base editing and 99.8% for prime editing of all CRB1 pathogenic variants in the Leiden Open Variation Database. The 10 most common editable pathogenic variants for CRB1 accounted for 34.95% of all pathogenic variants, with the c.2843G>A, p.(Cys948Tyr) being the most common editable CRB1 variant. These findings outline the next step toward developing base and prime editing therapeutics as an alternative to gene augmentation for the amelioration of CRB1-associated retinal degenerations.

Generation of CRB1 RP Patient-Derived iPSCs and a CRISPR/Cas9-Mediated Homology-Directed Repair Strategy for the CRB1 c.2480G>T Mutation

Mutations in the Crumbs-homologue-1 (CRB1) gene lead to a spectrum of severe inherited retinal diseases, including retinitis pigmentosa (RP). The establishment of a genotype-phenotype correlation in CRB1 patients has been difficult due to the substantial variability and phenotypic overlap between CRB1-associated diseases. This phenotypic modulation may be due to several factors, including genetic modifiers, deep intronic mutations, isoform diversity, and copy number variations. Induced pluripotent stem cell (iPSC)-derived patient retinal organoids are novel tools that can provide sensitive, quantitative, and scalable phenotypic assays. CRB1 RP patient iPSC-derived retinal organoids have shown reproducible phenotypes compared to healthy retinal organoids. However, having genetically defined iPSC isogenic controls that take into account potential phenotypic modulation is crucial. In this study, we generated iPSC from an early-onset CRB1 patient and developed a correction strategy for the c.2480G>T, p.(Gly827Val) CRB1 mutation using CRISPR/Cas9-mediated homology-directed repair.

Prime Editing for the Installation and Correction of Mutations Causing Inherited Retinal Disease: A Brief Methodology

Inherited retinal diseases (IRDs) encompass a large heterogeneous group of rare blinding disorders whose etiology originates from mutations in the 280 genes identified to date. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems represent a promising avenue for the treatment of IRDs, as exemplified by FDA clinical trial approval of EDIT-101 (AGN-151587), which removes a deep intronic variant in the CEP290 gene that causes Leber congenital amaurosis (LCA) type 10. Prime editing is a novel double-strand break (DSB) independent CRISPR/Cas system which has the potential to correct all 12 possible transition and transversion mutations in addition to small deletions and insertions. Here, as a proof-of-concept study, we describe a methodology using prime editing for the in vitro installation and correction of the classical Pde6b^rd10 c.1678C > T (p.Arg560Cys) mutation which causes autosomal recessive retinitis pigmentosa (RP) in mice.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pluripotent stem cell therapy for retinal diseases

Pluripotent stem cells (PSCs), which include human embryonic stem cells (hESCs) and induced pluripotent stem cell (iPSC), have been used to study development of disease processes, and as potential therapies in multiple organ systems. In recent years, there has been increasing interest in the use of PSC-based transplantation to treat disorders of the retina in which retinal cells have been functionally damaged or lost through degeneration. The retina, which consists of neuronal tissue, provides an excellent system to test the therapeutic utility of PSC-based transplantation due to its accessibility and the availability of high-resolution imaging technology to evaluate effects. Preclinical trials in animal models of retinal diseases have shown improvement in visual outcomes following subretinal transplantation of PSC-derived photoreceptors or retinal pigment epithelium (RPE) cells. This review focuses on preclinical studies and clinical trials exploring the use of PSCs for retinal diseases. To date, several phase I/II clinical trials in patients with age-related macular degeneration (AMD) and Stargardt disease (STGD1) have demonstrated the safety and feasibility of PSC-derived RPE transplantation. Additional phase I/II clinical trials using PSC-derived RPE or photoreceptor cells for the treatment of AMD, STGD1, and also retinitis pigmentosa (RP) are currently in the pipeline. As this field continues to evolve, additional technologies may enhance PSC-derived cell transplantation through gene-editing of autologous cells, transplantation of more complex cellular structures such as organoids, and monitoring of transplanted cells through novel imaging technologies.

A novel mutation in the PRPH2 gene in a Chinese pedigree with retinitis pigmentosa and angle-closure glaucoma

Background

Retinitis pigmentosa (RP) is a rare, progressive, and hereditary disorder that leads to the progressive loss of vision and visual field, and in some cases blindness. The specific relationship between RP and glaucoma has been debated for decades.

Methods

In this study, we examined a Han RP family with concomitant angle-closure glaucoma (ACG), performed an inductive analysis of their clinical features and assistant results, and applied whole-exome sequencing (WES) technology for a molecular diagnosis.

Results

A novel transversion mutation (c.626 T > A) was identified in the peripherin-2 (PRPH2) gene in the proband, resulting in the substitution of Valine to aspartic acid in codon 209. A full ophthalmic examination showed that the proband with the c.626 T > A mutation had a typical RP manifestation, with close angles; however, the proband’s elder brother, who lacked the novel mutation, had a normal fundus and open angles.

Conclusion

Our results extend the genetic mutation spectrum of PRPH2 in RP, and provide evidence to support a genetic correlation between RP and ACG.

Novel compound heterozygous EYS variants may be associated with arRP in a large Chinese pedigree

As a genetically heterogeneous ocular dystrophy, gene mutations with autosomal recessive retinitis pigmentosa (arRP) in patients have not been well described. We aimed to detect the disease-causing genes and variants in a Chinese arRP family. In the present study, a large Chinese pedigree consisting of 31 members including a proband and another two patients was recruited; clinical examinations were conducted; next-generation sequencing using a gene panel was used for identifying pathogenic genes, and Sanger sequencing was performed for verification of mutations. Novel compound heterozygous variants c.G2504A (p.C835Y) and c.G6557A (p.G2186E) for the EYS gene were identified, which co-segregated with the clinical RP phenotypes. Sequencing of 100 ethnically matched normal controls didn't found these mutations in EYS. Therefore, our study identified pathogenic variants in EYS that may cause arRP in this Chinese family. This is the first study to reveal the novel mutation in the EYS gene (c.G2504A, p.C835Y), extending its mutation spectrum. Thus, the EYS c.G2504A (p.C835Y) and c.G6557A (p.G2186E) variants may be the disease-causing missense mutations for RP in this large arRP family. These findings should be helpful for molecular diagnosis, genetic counseling and clinical management of arRP disease.

Intravitreal autologous mesenchymal stem cell transplantation: a non-randomized phase I clinical trial in patients with retinitis pigmentosa

Background

Retinitis pigmentosa (RP) is a progressive inherited retinal disease with great interest for finding effective treatment modalities. Stem cell-based therapy is one of the promising candidates. We aimed to investigate the safety, feasibility, and short-term efficacy of intravitreal injection of bone marrow-derived mesenchymal stem cells (BM-MSCs) in participants with advanced stage RP.

Methods

This non-randomized phase I clinical trial enrolled 14 participants, categorized into three groups based on a single dose intravitreal BM-MSC injection of 1 × 10⁶, 5 × 10⁶, or 1 × 10⁷ cells. We evaluated signs of inflammation and other adverse events (AEs). We also assessed the best corrected visual acuity (BCVA), visual field (VF), central subfield thickness (CST), and subjective experiences.

Results

During the 12-month period, we noticed several mild and transient AEs. Interestingly, we found statistically significant improvements in the BCVA compared to baseline, although they returned to the baseline at 12 months. The VF and CST were stable, indicating no remarkable disease progression. We followed 12 participants beyond the study period, ranging from 1.5 to 7 years, and observed one severe but manageable AE at year 3.

Conclusion

Intravitreal injection of BM-MSCs appears to be safe and potentially effective. All adverse events during the 12-month period required observation without any intervention. For the long-term follow-up, only one participant needed surgical treatment for a serious adverse event and the vision was restored. An enrollment of larger number of participants with less advanced RP and long-term follow-up is required to evaluate the safety and efficacy of this intervention.

Trial registration

ClinicalTrials.gov, NCT01531348. Registered on February 10, 2012

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-020-02122-7.

Unilaterally extinguished electroretinograms in an eye with normal visual acuity and visual field

PURPOSE

This study reports a case of unilateral retinopathy with extinguished full-field ERGs (ffERGs), wherein the visual acuity was 16/16 and the visual field was spared.

METHODS

Observational case report.

RESULTS

A 39-year-old female had developed nyctalopia in her left eye. Two years later, she visited an ophthalmologist who noted a bilaterally reduced pigmentation of the fundus. Her best-corrected visual acuity was 16/16 in both the eyes. Goldmann perimetry demonstrated that her visual field was bilaterally fully spared. ffERGs measurement was performed in accordance with the ISCEV standard protocol and indicated that her right eye was normal. However, all ERG responses were severely attenuated in her left eye. Multifocal ERG responses were found to be normal in the right eye and extinguished in the left eye except for residual responses that were exclusively located at the center. During the 7 years of the follow-up period, the visual field in the left eye, which was once normal, became shaded, and the development of a ring scotoma was identified. The visual field in the right eye is still full.

CONCLUSIONS

The pathogenesis of this patient's condition still remains unknown, while unilateral retinitis pigmentosa, unilateral pigmentary retinopathy, acute zonal occult outer retinopathy, and autoimmune retinopathy can all be considered as possible explanations. The uniqueness of this case study is that the extinguished ERG responses are predictive of the functional alteration in the affected eye, when the initial visual acuity and the visual field were normal.

Efficacy of topical brinzolamide in children with retinal dystrophies

Background: Inherited retinal dystrophies are a leading cause of irreversible blindness in children in the United States. Topical carbonic anhydrase inhibitors have improved central vision and cystoid macular edema in patients with retinal dystrophies, but few studies have assessed their efficacy in children. Materials and Methods: A retrospective chart review was performed with Institutional Review Board approval to identify pediatric patients with inherited retinal dystrophies who received topical brinzolamide at a single university center between 2008 and 2015. Serial visual acuity and central macular thicknesses were compared to assess the efficacy of brinzolamide. Results: Seven subjects were identified who met the inclusion criteria. Four had juvenile X-linked retinoschisis, two had retinitis pigmentosa, and one had Leber congenital amaurosis. All were prescribed brinzolamide thrice daily; however, one patient was completely non-compliant. Four of the six treated patients exhibited a mild decrease in central macular thickness in both eyes during the study with all six treated patients having significantly improved vision at the first endpoint, 33.2 ± 8.2 months after treatment initiation. For treated patients, average visual acuity (LogMAR) ± standard error of the mean improved from 0.5 ± 0.04 pre-treatment to 0.3 ± 0.1 at the second endpoint, 50.2 ± 7.3 months after treatment initiation. Conclusions: Mild anatomic improvement of macular cysts was seen in pediatric patients using brinzolamide. Visual acuity improvement occurred even without significant reduction in macular cysts. Further studies are needed to determine whether the beneficial effects of carbonic anhydrase inhibitors are sustained in children with inherited retinal degenerations.

Detection of Large Structural Variants Causing Inherited Retinal Diseases

Current application of next-generation sequencing (NGS) leads to detection of the underlying disease-causing gene and mutation or mutations in from 60% to 85% of patients with inherited retinal diseases (IRDs), depending on the methods used, disease type, and population tested. In a cohort of 320 families with autosomal dominant retinitis pigmentosa (adRP), we have detected the mutation in 82% of cases using a variety of methods, leaving more than 50 families with "elusive" disease genotypes. All of the remaining families have been screened for mutations in known IRD genes using retinal-targeted-capture NGS, and most have been tested by whole-exome NGS. Linkage mapping has been conducted in several large families. In one of these families, with DNA samples from ten affected family members and six unaffected, linking members, we observed substantial maximum two-point LOD scores for linkage to both chromosomes 2 and 4. Subsequent 10X Genomics Chromium™ sequencing, which facilitates linked-read, phase-known chromosomal analysis, revealed a balanced translocation of the q terminus arms of chromosomes 2 and 4 involving 35 Mb and 73 Mb of 2 and 4, respectively. The balanced translocation is present in all affected family members and absent from all unaffected individuals. Family histories suggest multiple miscarriages are associated with the translocation. The breakpoint on chromosome 4 is within or 5' to the LRAT gene, whereas the chromosome 2 break is in a gene-poor region. We conclude that the balanced translocation is the cause of adRP in this family, which may lead to dysregulation of the LRAT gene. Since multiple miscarriages are a hallmark of balanced translocations, this possibility should be considered in evaluating family histories. Further, large structural variants, which are not easily detected by conventional sequencing methods, may account for a significant fraction of the remaining unsolved families.

A Novel FLVCR1 Variant Implicated in Retinitis Pigmentosa

Here we describe the identification and evaluation of a rare novel autosomal recessive mutation in FLVCR1 which is implicated solely in RP, with no evidence of posterior column ataxia in a number of affected patients. The mutation was detected as part of an ongoing target capture NGS study (Target 5000), aimed at identifying candidate variants in pedigrees with inherited retinal degenerations (IRDs) in Ireland. The mutation, FLVCR1 p.Tyr341Cys, was observed homozygously in seven affected patients across four pedigrees. FLVCR1 p.Tyr341Cys is a very rare mutation, with no previous reports of pathogenicity and no homozygous cases reported in online allele frequency databases. Our sequencing study identified seven homozygotes across multiple pedigrees, all with similar clinical presentations of RP without ataxia, a scenario extremely unlikely to occur by chance for a benign allele, particularly given the low population frequency of p.Tyr341Cys.

A novel CRX variant (p.R98X) is identified in a Chinese family of Retinitis pigmentosa with atypical and mild manifestations

BACKGROUND

Retinitis pigmentosa (RP) is the most common form of hereditary retinal degeneration that can cause inherited blindness. RP has extreme genetic and clinical heterogeneity, which brings a major obstacle to obtaining an accurate molecular diagnosis.

OBJECTIVE

To analyze the genetic defect in a Chinese family of RP with a few atypical manifestations.

METHODS

Whole-exome sequencing (WES) was applied to identify the disease-associated genes. Sanger sequencing was performed to validate the variants of candidate genes in the patient and his parents. In vitro expression analysis was further conducted to examine the potential biological function of the gene variant.

RESULTS

A heterozygous nonsense variant c.292C > T (p.R98X) of CRX gene was identified to be present in the affected male. The c.292C > T variant of CRX was absent in all of the searched databases, including the 10,000 Chinese exome database. The nonsense variant was supposed to result in a truncated CRX protein with a destroyed homedomain (HD), which is essential for CRX translation. Interestingly, the following assay showed that the potential truncated protein was not detected, indicating that the variant may cause a loss-of-function mutation of CRX gene.

CONCLUSION

We identified a novel heterozygous null mutation in the CRX gene which was the first evidence of a nonsense mutation in the HD domain of CRX. Our finding suggested that the haploinsufficiency mutation of CRX gene contributed to the atypical and mild manifestations of the autosomal dominant RP in the Chinese family.

Molecular Findings in Families with an Initial Diagnose of Autosomal Dominant Retinitis Pigmentosa (adRP)

Genetic testing of probands in families with an initial diagnosis of autosomal dominant retinitis pigmentosa (adRP) usually confirms the diagnosis, but there are exceptions. We report results of genetic testing in a large cohort of adRP families with an emphasis on exceptional cases including X-linked RP with affected females; homozygous affected individuals in families with heterozygous, dominant disease; and independently segregating mutations in the same family. Genetic testing was conducted in more than 700 families with a provisional or probable diagnosis of adRP. Exceptions to the proposed mode of inheritance were extracted from our comprehensive patient and family database. In a subset of 300 well-characterized families with a probable diagnosis of adRP, 195 (70%) have dominant mutations in known adRP genes but 25 (8%) have X-linked mutations, 3 (1%) have multiple segregating mutations, and 3 (1%) have dominant-acting mutations in genes previously associated with recessive disease. It is currently possible to determine the underlying disease-causing gene and mutation in approximately 80% of families with an initial diagnosis of adRP, but 10% of "adRP" families have a variant mode of inheritance. Informed genetic diagnosis requires close collaboration between clinicians, genetic counselors, and laboratory scientists.

Unilateral pigmented paravenous retinochoroidal atrophy with retinitis pigmentosa in the contralateral eye: A case report

Purpose

We describe a sporadic case of unilateral pigmented paravenous retinochoroidal atrophy (PPRCA) with retinitis pigmentosa (RP) in the contralateral eye.

Observations

a 24-year-old female aware of the narrowing of visual field was examined at our hospital. Funduscopic examination revealed left eye showing retinochroidal atrophy along the retinal veins with pigment accumulation while right eye showing peripheral diffuse retinal pigmented epithelium atrophy with bone spicule pigmentation. Fundus autofluorescence, electroretinogram, visual field test and optic coherent tomography were also performed and obtained results were compatible with funduscopic observation.

Conclusions and importance

Simultaneous manifestation of PPRCA and RP observed in this case is rare and supports a shared genetic basis between the two diseases. Further genetic investigations are needed to elucidate the etiology and to properly manage PPRCA.

Müller cell metabolic chaos during retinal degeneration

Müller cells play a critical role in retinal metabolism and are among the first cells to demonstrate metabolic changes in retinal stress or disease. The timing, extent, regulation, and impacts of these changes are not yet known. We evaluated metabolic phenotypes of Müller cells in the degenerating retina. Retinas harvested from wild-type (WT) and rhodopsin Tg P347L rabbits were fixed in mixed aldehydes and resin embedded for computational molecular phenotyping (CMP). CMP facilitates small molecule fingerprinting of every cell in the retina, allowing evaluation of metabolite levels in single cells. CMP revealed signature variations in metabolite levels across Müller cells from TgP347L retina. In brief, neighboring Müller cells demonstrated variability in taurine, glutamate, glutamine, glutathione, glutamine synthetase (GS), and CRALBP. This variability showed no correlation across metabolites, implying the changes are functionally chaotic rather than simply heterogeneous. The inability of any clustering algorithm to classify Müller cell as a single class in the TgP347L retina is a formal proof of metabolic variability in the present in degenerating retina. Although retinal degeneration is certainly the trigger, Müller cell metabolic alterations are not a coherent response to the microenvironment. And while GS is believed to be the primary enzyme responsible for the conversion of glutamate to glutamine in the retina, alternative pathways appear to be unmasked in degenerating retina. Somehow, long term remodeling involves loss of Müller cell coordination and identity, which has negative implications for therapeutic interventions that target neurons alone.

Retinal remodeling in human retinitis pigmentosa

Retinitis Pigmentosa (RP) in the human is a progressive, currently irreversible neural degenerative disease usually caused by gene defects that disrupt the function or architecture of the photoreceptors. While RP can initially be a disease of photoreceptors, there is increasing evidence that the inner retina becomes progressively disorganized as the outer retina degenerates. These alterations have been extensively described in animal models, but remodeling in humans has not been as well characterized. This study, using computational molecular phenotyping (CMP) seeks to advance our understanding of the retinal remodeling process in humans. We describe cone mediated preservation of overall topology, retinal reprogramming in the earliest stages of the disease in retinal bipolar cells, and alterations in both small molecule and protein signatures of neurons and glia. Furthermore, while Müller glia appear to be some of the last cells left in the degenerate retina, they are also one of the first cell classes in the neural retina to respond to stress which may reveal mechanisms related to remodeling and cell death in other retinal cell classes. Also fundamentally important is the finding that retinal network topologies are altered. Our results suggest interventions that presume substantial preservation of the neural retina will likely fail in late stages of the disease. Even early intervention offers no guarantee that the interventions will be immune to progressive remodeling. Fundamental work in the biology and mechanisms of disease progression are needed to support vision rescue strategies.

Electrophysiological and Histologic Evaluation of the Time Course of Retinal Degeneration in the rd10 Mouse Model of Retinitis Pigmentosa

Among several animal models of retinitis pigmentosa (RP), the more recently developed rd10 mouse with later onset and slower rate of retinal degeneration than rd1 mouse is a more suitable model for testing therapeutic modalities. We therefore investigated the time course of retinal degeneration in rd10 mice before adopting this model in our interventional studies. Electroretinogram (ERG) recordings were carried out in postnatal weeks (PW) 3~5 rd10 (n=23) and wild-type (wt) mice (n=26). We compared the amplitude and implicit time of the b-wave of ERG records from wt and rd10 mice. Our results showed that b-wave amplitudes in rd10 mice were significantly lower and the implicit time of b-waves in rd10 mice were also significantly slower than that in wt mice (20~160 µV vs. 350~480 µV; 55~75 ms vs. 100~150 ms: p<0.001) through PW3 to PW5. The most drastic changes in ERG amplitudes and latencies were observed during PW3 to PW4. In multichannel recording of rd10 retina in PW2 to PW4.5, we found no significant difference in mean spike frequency, but the frequency of power spectral peak of local field potential at PW3 and PW3.5 is significantly different among other age groups (p<0.05). Histologic examination of rd10 retinae showed significant decrease in thickness of the outer nuclear layer at PW3. TUNEL positive cells were most frequently observed at PW3. From these data, we confirm that in the rd10 mouse, the most precipitous retinal degeneration occurs between PW3~PW4 and that photoreceptor degeneration is complete by PW5.