Genetic and Clinical Findings in a Large Cohort of Chinese Patients with Suspected Retinitis Pigmentosa

Clinical and molecular findings in children with retinitis pigmentosa

PURPOSE

To study the clinical and genetic features of a cohort of RP children.

METHODS

We identified 46 RP patients with pathogenic or likely pathogenic mutations among 96 patients with a clinical diagnosis of retinitis pigmentosa. All of the patients underwent comprehensive clinical examinations and genetic testing. A retrospective study was conducted on 46 children with retinitis pigmentosa. The genetic and clinical characteristics of children with different genotypes were analyzed.

RESULTS

Among the 46 children, 13 inherited X-linked gene mutations, including 9 RPGR and 4 RP2 mutations. There were 10 cases of autosomal dominant genes and 23 cases of autosomal recessive genes. XLRP accounted for a larger proportion of children, as observed in previous studies on RP. We found that RPGR genes were the most commonly mutated genes in RP children. The most frequently mutated gene was RPGR (9.3%), followed by RP2 (4.2%) and RPE65 (4.2%). Forty-six patients had mutations in 21 different genes, 19 of which were novel mutations.Most children with XLRP have a high degree of myopia, poor vision, and severe clinical symptoms. Frameshift mutations were more common in XLRP, followed by nonsense mutations. The onset of XLRP is relatively serious since childhood. Most children with ADRP have relatively good visual acuity and mild clinical symptoms, and missense mutations are common. The clinical manifestations of ARRP in children are more severe than those of ADRP in children but milder than those of XLRP in children, and missense mutations are common. The manifestations of RPE65 mutations are also severe and appear early.

CONCLUSIONS

Our results revealed that XLRP gene mutations were more common in children than in adults, as observed in previous studies on RP. The proportion of RP children with ADRP is relatively small. The new findings in our study polished the spectrum of novel mutations and the proportions of different genotypes in pediatric patients. The onset of XLRP occurred earlier. The genes with a high incidence in children were all relatively severe gene types of RP. This comprehensive database may provide essential information regarding the initial stage of RP.

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.

Disease-specific variant interpretation highlighted the genetic findings in 2325 Japanese patients with retinitis pigmentosa and allied diseases

BACKGROUND

As gene-specific therapy for inherited retinal dystrophy (IRD) advances, unified variant interpretation across institutes is becoming increasingly important. This study aims to update the genetic findings of 86 retinitis pigmentosa (RP)-related genes in a large number of Japanese patients with RP by applying the standardised variant interpretation guidelines for Japanese patients with IRD (J-IRD-VI guidelines) built upon the American College of Medical Genetics and Genomics and the Association for Molecular Pathology rules, and assess the contribution of these genes in RP-allied diseases.

METHODS

We assessed 2325 probands with RP (n=2155, including n=1204 sequenced previously with the same sequencing panel) and allied diseases (n=170, newly analysed), including Usher syndrome, Leber congenital amaurosis and cone-rod dystrophy (CRD). Target sequencing using a panel of 86 genes was performed. The variants were interpreted according to the J-IRD-VI guidelines.

RESULTS

A total of 3564 variants were detected, of which 524 variants were interpreted as pathogenic or likely pathogenic. Among these 524 variants, 280 (53.4%) had been either undetected or interpreted as variants of unknown significance or benign variants in our earlier study of 1204 patients with RP. This led to a genetic diagnostic rate in 38.6% of patients with RP, with EYS accounting for 46.7% of the genetically solved patients, showing a 9% increase in diagnostic rate from our earlier study. The genetic diagnostic rate for patients with CRD was 28.2%, with RP-related genes significantly contributing over other allied diseases.

CONCLUSION

A large-scale genetic analysis using the J-IRD-VI guidelines highlighted the population-specific genetic findings for Japanese patients with IRD; these findings serve as a foundation for the clinical application of gene-specific therapies.

Genetic Characterization of 191 Probands with Inherited Retinal Dystrophy by Targeted NGS Analysis

Inherited retinal diseases (IRDs) represent a frequent cause of blindness in children and adults. As a consequence of the phenotype and genotype heterogeneity of the disease, it is difficult to have a specific diagnosis without molecular testing. To date, over 340 genes and loci have been associated with IRDs. We present the molecular finding of 191 individuals with IRD, analyzed by targeted next-generation sequencing (NGS). For 67 of them, we performed a family segregation study, considering a total of 126 relatives. A total of 359 variants were identified, 44 of which were novel. Genetic diagnostic yield was 41%. However, after stratifying the patients according to their clinical suspicion, diagnostic yield was higher for well-characterized diseases such as Stargardt disease (STGD), at 65%, and for congenital stationary night blindness 2 (CSNB2), at 64%. Diagnostic yield was higher in the patient group where family segregation analysis was possible (68%) and it was higher in younger (55%) than in older patients (33%). The results of this analysis demonstrated that targeted NGS is an effective method for establishing a molecular genetic diagnosis of IRDs. Furthermore, this study underlines the importance of segregation studies to understand the role of genetic variants with unknow pathogenic role.

In vivo genome editing via CRISPR/Cas9-mediated homology-independent targeted integration for Bietti crystalline corneoretinal dystrophy treatment

Bietti crystalline corneoretinal dystrophy (BCD) is an autosomal recessive chorioretinal degenerative disease without approved therapeutic drugs. It is caused by mutations in CYP4V2 gene, and about 80% of BCD patients carry mutations in exon 7 to 11. Here, we apply CRISPR/Cas9 mediated homology-independent targeted integration (HITI)-based gene editing therapy in HEK293T cells, BCD patient derived iPSCs, and humanized Cyp4v3 mouse model (h-Cyp4v3mut/mut) using two rAAV2/8 vectors via sub-retinal administration. We find that sgRNA-guided Cas9 generates double-strand cleavage on intron 6 of the CYP4V2 gene, and the HITI donor inserts the carried sequence, part of intron 6, exon 7-11, and a stop codon into the DNA break, achieving precise integration, effective transcription and translation both in vitro and in vivo. HITI-based editing restores the viability of iPSC-RPE cells from BCD patient, improves the morphology, number and metabolism of RPE and photoreceptors in h-Cyp4v3mut/mut mice. These results suggest that HITI-based editing could be a promising therapeutic strategy for those BCD patients carrying mutations in exon 7 to 11, and one injection will achieve lifelong effectiveness.

Gene replacement therapy in Bietti crystalline corneoretinal dystrophy: an open-label, single-arm, exploratory trial

Bietti crystalline corneoretinal dystrophy is an inherited retinal disease caused by mutations in CYP4V2, which results in blindness in the working-age population, and there is currently no available treatment. Here, we report the results of the first-in-human clinical trial (NCT04722107) of gene therapy for Bietti crystalline corneoretinal dystrophy, including 12 participants who were followed up for 180-365 days. This open-label, single-arm exploratory trial aimed to assess the safety and efficacy of a recombinant adeno-associated-virus-serotype-2/8 vector encoding the human CYP4V2 protein (rAAV2/8-hCYP4V2). Participants received a single unilateral subretinal injection of 7.5 × 1010 vector genomes of rAAV2/8-hCYP4V2. Overall, 73 treatment-emergent adverse events were reported, with the majority (98.6%) being of mild or moderate intensity and considered to be procedure- or corticosteroid-related; no treatment-related serious adverse events or local/systemic immune toxicities were observed. Compared with that measured at baseline, 77.8% of the treated eyes showed improvement in best-corrected visual acuity (BCVA) on day 180, with a mean ± standard deviation increase of 9.0 ± 10.8 letters in the 9 eyes analyzed (p = 0.021). By day 365, 80% of the treated eyes showed an increase in BCVA, with a mean increase of 11.0 ± 10.6 letters in the 5 eyes assessed (p = 0.125). Importantly, the patients' improvement observed using multifocal electroretinogram, microperimetry, and Visual Function Questionnaire-25 further supported the beneficial effects of the treatment. We conclude that the favorable safety profile and visual improvements identified in this trial encourage the continued development of rAAV2/8-hCYP4V2 (named ZVS101e).

Molecular and phenotypic characteristics of Bardet-Biedl syndrome in Chinese patients

BACKGROUND

Bardet-Biedl syndrome (BBS) is a type of non-motile ciliopathy. To date, 26 genes have been reported to be associated with BBS. However, BBS is genetically heterogeneous, with significant clinical overlap with other ciliopathies, which complicates diagnosis. Disability and mortality rates are high in BBS patients; therefore, it is urgent to improve our understanding of BBS. Thus, our study aimed to describe the genotypic and phenotypic spectra of BBS in China and to elucidate genotype-phenotype correlations.

METHODS

Twenty Chinese patients diagnosed with BBS were enrolled in this study. We compared the phenotypes of Chinese BBS patients in this study with those from other countries to analyze the phenotypic differences across patients worldwide. In addition, genotype-phenotype correlations were described for our cohort. We also summarized all previously reported cases of BBS in Chinese patients (71 patients) and identified common and specific genetic variants in the Chinese population.

RESULTS

Twenty-eight variants, of which 10 are novel, in 5 different BBS-associated genes were identified in 20 Chinese BBS patients. By comparing the phenotypes of BBSome-coding genes (BBS2,7,9) with those of chaperonin-coding genes (BBS10,12), we found that patients with mutations in BBS10 and 12 had an earlier age of onset (1.10 Vs. 2.20, p < 0.01) and diagnosis (4.64 Vs. 13.17, p < 0.01), whereas patients with mutations in BBS2, 7, and 9 had a higher body mass index (28.35 Vs. 24.21, p < 0.05) and more vision problems (p < 0.05). Furthermore, in 91 Chinese BBS patients, mutations were predominant in BBS2 (28.89%) and BBS7 (15.56%), and the most frequent variants were in BBS2: c.534 + 1G > T (10/182 alleles) and BBS7: c.1002delT (7/182 alleles), marking a difference from the genotypic spectra of BBS reported abroad.

CONCLUSIONS

We recruited 20 Chinese patients with BBS for genetic and phenotypic analyses, and identified common clinical manifestations, pathogenic genes, and variants. We also described the phenotypic differences across patients worldwide and among different BBS-associated genes. This study involved the largest cohort of Chinese patients with BBS, and provides new insights into the distinctive clinical features of specific pathogenic variants.

Establishment of the induced pluripotent stem cell line SJTUGHi002-A from a CNGA1-related recessive retinitis pigmentosa patient

Retinitis pigmentosa (RP) is the most common inherited retinal diseases, characterized by photoreceptor cell death and retinal pigment epithelial atrophy. Mutations in cyclic nucleotide gated channel subunit alpha 1 (CNGA1) have been reported to cause retinitis pigmentosa. Here, we established the human induced pluripotent stem cell line (iPSC) SJTUGHi002-A, generated from peripheral blood mononuclear cells of a 36-year-old male RP patient, who carried a homozygous frameshift variant in CNGA1 gene (c.265delC; p.L89Ffs*4). The cell line can serve as a patient-derived disease model for exploring the pathogenesis and drug development of CNGA1-RP.

Mutation analysis of RHO in patients with non-syndromic retinitis pigmentosa

PURPOSE

To identify RHO mutations in patients with non-syndromic retinitis pigmentosa (NS-RP).

METHODS

A total of 143 probands (46 family history and 97 sporadic cases) with NS-RP were recruited from Southeast China. The coding exons and adjacent intronic regions of RHO were PCR-amplified and sequenced by Sanger sequencing. The candidate variant was evaluated by the guidelines of American College of Medical Genetics and further validated through co-segregation analysis within the family.

RESULTS

Five heterozygous mutations in RHO were detected in 5 out of 143 probands, where the frequency of RHO mutations in our cohort was approximately 3.5% (5/143) and 10.8% (5/46) for probands and families with NS-RP, respectively. Three known disease-causing mutations including c.C1030T (p.Q344X), c.C173G (p.T58R), and c.G266A (p.G89D) were identified in three unrelated families. The other two previously unreported mutations c.557C>A (p.S186X) and c.944delA (p.N315TfsX43) were confirmed in Family RP-087 and Family RP-139, respectively. These mutations co-segregated with available affected individuals in each family were not observed in the unaffected family members or in the 112 unrelated controls.

CONCLUSIONS

This report expands the mutational spectrum of RHO gene associated with NS-RP and demonstrates the frequency of RP RHO mutations in Southeast Chinese populations.

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

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

Screening Mutations of the Monogenic Syndromic High Myopia by Whole Exome Sequencing From MAGIC Project

Purpose

This observational study aimed to identify mutations in monogenic syndromic high myopia (msHM) using data from reported samples (n = 9370) of the Myopia Associated Genetics and Intervention Consortium (MAGIC) project.

Methods

The targeted panel containing 298 msHM-related genes was constructed and screening of clinically actionable variants was performed based on whole exome sequencing. Capillary sequencing was used to verify the identified gene mutations in the probands and perform segregation analysis with their relatives.

Results

A total of 381 candidate variants in 84 genes and 85 eye diseases were found to contribute to msHM in 3.6% (335/9370) of patients with HM. Among them, the 22 genes with the most variations accounted for 62.7% of the diagnostic cases. In the genotype-phenotype association analysis, 60% (201/335) of suspected msHM cases were recalled and 25 patients (12.4%) received a definitive genetic diagnosis. Pathogenic variants were distributed in 18 msHM-related diseases, mainly involving retinal dystrophy genes (e.g. TRPM1, CACNA1F, and FZD4), connective tissue disease genes (e.g. FBN1 and COL2A1), corneal or lens development genes (HSF4, GJA8, and MIP), and other genes (TEK). The msHM gene mutation types were allocated to four categories: nonsense mutations (36%), missense mutations (36%), frameshift mutations (20%), and splice site mutations (8%).

Conclusions

This study highlights the importance of thorough molecular subtyping of msHM to provide appropriate genetic counselling and multispecialty care for children and adolescents with HM.

Clinical and Genetic Characterization of RDH12-Retinal Dystrophy in a South American Cohort

PURPOSE

To characterize the largest cohort of individuals with retinol dehydrogenase 12 (RDH12)-retinal dystrophy to date, and the first one from South America.

DESIGN

Retrospective multicenter international study.

SUBJECTS

Seventy-eight patients (66 families) with an inherited retinal dystrophy and biallelic variants in RDH12.

METHODS

Review of clinical notes, ophthalmic images, and molecular diagnosis.

MAIN OUTCOME MEASURES

Visual function, retinal imaging, and characteristics were evaluated and correlated.

RESULTS

Thirty-seven individuals self-identified as Latino (51%) and 34 as White (47%). Sixty-nine individuals (88%) had Leber congenital amaurosis (LCA)/early-onset severe retinal dystrophy. Macular and midperipheral atrophy were seen in all patients from 3 years of age. A novel retinal finding was a hyperautofluorescent ring in 2 young children with LCA. Thirty-nine patients (50%) had subsequent visits, with mean follow-up of 6.8 ± 7.3 (range, 0-29) years. Eight variants (21%) were previously unreported, and the most frequent variant was c.295C>A, p.Leu99Ile, present in 52 alleles of 32 probands. Individuals with LCA homozygous for p.Leu99Ile (31%) had a later age of onset, a slower rate of best-corrected visual acuity decrease, the largest percentage of patients with mild visual impairment, and were predicted to reach legal blindness at an older age than the rest of the cohort.

CONCLUSIONS

By describing the largest molecularly confirmed cohort to date, improved understanding of disease progression was possible. Our detailed characterization aims to support research and the development of novel therapies that may have the potential to reduce or prevent vision loss in individuals with RDH12-associated retinal dystrophy.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures.

Whole genome sequencing enables new genetic diagnosis for inherited retinal diseases by identifying pathogenic variants

Inherited retinal diseases (IRDs) are a group of common primary retinal degenerative disorders. Conventional genetic testing strategies, such as panel-based sequencing and whole exome sequencing (WES), can only elucidate the genetic etiology in approximately 60% of IRD patients. Studies have suggested that unsolved IRD cases could be attributed to previously undetected structural variants (SVs) and intronic variants in IRD-related genes. The aim of our study was to obtain a definitive genetic diagnosis by employing whole genome sequencing (WGS) in IRD cases where the causative genes were inconclusive following an initial screening by panel sequencing. A total of 271 unresolved IRD patients and their available family members (n = 646) were screened using WGS to identify pathogenic SVs and intronic variants in 792 known ocular disease genes. Overall, 13% (34/271) of IRD patients received a confirmed genetic diagnosis, among which 7% were exclusively attributed to SVs, 4% to a combination of single nucleotide variants (SNVs) and SVs while another 2% were linked to intronic variants. 22 SVs, 3 deep-intronic variants, and 2 non-canonical splice-site variants across 14 IRD genes were identified in the entire cohort. Notably, all of these detected SVs and intronic variants were novel pathogenic variants. Among those, 74% (20/27) of variants were found in genes causally linked to Retinitis Pigmentosa (RP), with the gene EYS being the most frequently affected by SVs. The identification of SVs and intronic variants through WGS enhances the genetic diagnostic yield of IRDs and broadens the mutational spectrum of known IRD-associated genes.

Diagnostic genome sequencing improves diagnostic yield: a prospective single-centre study in 1000 patients with inherited eye diseases

PURPOSE

Genome sequencing (GS) is expected to reduce the diagnostic gap in rare disease genetics. We aimed to evaluate a scalable framework for genome-based analyses 'beyond the exome' in regular care of patients with inherited retinal degeneration (IRD) or inherited optic neuropathy (ION).

METHODS

PCR-free short-read GS was performed on 1000 consecutive probands with IRD/ION in routine diagnostics. Complementary whole-blood RNA-sequencing (RNA-seq) was done in a subset of 74 patients. An open-source bioinformatics analysis pipeline was optimised for structural variant (SV) calling and combined RNA/DNA variation interpretation.

RESULTS

A definite genetic diagnosis was established in 57.4% of cases. For another 16.7%, variants of uncertain significance were identified in known IRD/ION genes, while the underlying genetic cause remained unresolved in 25.9%. SVs or alterations in non-coding genomic regions made up for 12.7% of the observed variants. The RNA-seq studies supported the classification of two unclear variants.

CONCLUSION

GS is feasible in clinical practice and reliably identifies causal variants in a substantial proportion of individuals. GS extends the diagnostic yield to rare non-coding variants and enables precise determination of SVs. The added diagnostic value of RNA-seq is limited by low expression levels of the major IRD disease genes in blood.

Genotype-phenotype associations in Alström syndrome: a systematic review and meta-analysis

BACKGROUND

Alström syndrome (ALMS; #203800) is an ultrarare monogenic recessive disease. This syndrome is associated with variants in the ALMS1 gene, which encodes a centrosome-associated protein involved in the regulation of several ciliary and extraciliary processes, such as centrosome cohesion, apoptosis, cell cycle control and receptor trafficking. The type of variant associated with ALMS is mostly complete loss-of-function variants (97%) and they are mainly located in exons 8, 10 and 16 of the gene. Other studies in the literature have tried to establish a genotype-phenotype correlation in this syndrome with limited success. The difficulty in recruiting a large cohort in rare diseases is the main barrier to conducting this type of study.

METHODS

In this study we collected all cases of ALMS published to date. We created a database of patients who had a genetic diagnosis and an individualised clinical history. Lastly, we attempted to establish a genotype-phenotype correlation using the truncation site of the patient's longest allele as a grouping criteria.

RESULTS

We collected a total of 357 patients, of whom 227 had complete clinical information, complete genetic diagnosis and meta-information on sex and age. We have seen that there are five variants with high frequency, with p.(Arg2722Ter) being the most common variant, with 28 alleles. No gender differences in disease progression were detected. Finally, truncating variants in exon 10 seem to be correlated with a higher prevalence of liver disorders in patients with ALMS.

CONCLUSION

Pathogenic variants in exon 10 of the ALMS1 gene were associated with a higher prevalence of liver disease. However, the location of the variant in the ALMS1 gene does not have a major impact on the phenotype developed by the patient.

Clinical Characteristics and Genetic Variants in Taiwanese Patients With PROM1-Related Inherited Retinal Disorders

Purpose

This study investigated the clinical characteristics of patients with PROM1-related inherited retinal diseases (IRDs).

Methods

Patients diagnosed with IRDs who had mutations in PROM1 were identified at Linkou Chang Gung Memorial Hospital and Kaohsiung Medical University Hospital in Taiwan. Information on clinical characteristics and best-corrected visual acuity was recorded. Color fundus (CF) images, fundus autofluorescence photography (FAF), spectral-domain optical coherence tomography (SD-OCT), and electroretinograms (ERGs) were analyzed to examine patient phenotypes. PROM1 variants were detected using whole exome sequencing and verified by Sanger sequencing.

Results

Fourteen patients from nine families with PROM1-related IRDs were analyzed. Most patients exhibited chorioretinal atrophy in the macular area, with or without extramacular involvement on CF. Similarly, hypo-autofluorescence confined to the macular area, with or without extramacular involvement, was present for most patients on FAF. Furthermore, SD-OCT revealed outer retinal tubulations and focal or diffuse retinal thinning. ERGs showed variable findings, including maculopathy with normal ERG, subnormal cone response, and extinguished rod and cone responses. We detected five variants of the PROM1 gene, including c.139del, c.794del, c.1238T>A, c.2110C>T, and c.1117C>T.

Conclusions

In this study, we evaluated 14 Taiwanese patients with five PROM1 variants. Additionally, incomplete penetrance of heterozygous PROM1 variants was observed. Furthermore, patients with autosomal dominant PROM1 variants had lesions in the macular area and the peripheral region of the retina. SD-OCT serves as a useful tool for early detection of PROM1-related IRDs, as it captures certain signs of such diseases.

Mutations in VWA8 cause autosomal-dominant retinitis pigmentosa via aberrant mitophagy activation

BACKGROUND

Although retinitis pigmentosa (RP) is the most common type of hereditary retinal dystrophy, approximately 25%-45% of cases remain without a molecular diagnosis. von Willebrand factor A domain containing 8 (VWA8) encodes a mitochondrial matrix-targeted protein; its molecular function and pathogenic mechanism in RP remain unexplained.

METHODS

Family members of patients with RP underwent ophthalmic examinations, and peripheral blood samples were collected for exome sequencing, ophthalmic targeted sequencing panel and Sanger sequencing. The importance of VWA8 in retinal development was demonstrated by a zebrafish knockdown model and cellular and molecular analysis.

RESULTS

This study recruited a Chinese family of 24 individuals with autosomal-dominant RP and conducted detailed ophthalmic examinations. Exome sequencing analysis of six patients revealed heterozygous variants in VWA8, namely, the missense variant c.3070G>A (p.Gly1024Arg) and nonsense c.4558C>T (p.Arg1520Ter). Furthermore, VWA8 expression was significantly decreased both at the mRNA and protein levels. The phenotypes of zebrafish with VWA8 knockdown are similar to those of clinical individuals harbouring VWA8 variants. Moreover, VWA8 defects led to severe mitochondrial damage, resulting in excessive mitophagy and the activation of apoptosis.

CONCLUSIONS

VWA8 plays a significant role in retinal development and visual function. This finding may provide new insights into RP pathogenesis and potential genes for molecular diagnosis and targeted therapy.

Mutational spectrum in a Chinese cohort with congenital cataracts

BACKGROUND

To identify the mutational spectrum in a Chinese cohort with congenital cataracts.

METHODS

Probands (n = 164) with congenital cataracts and their affected or unaffected available family members were recruited for clinical examinations and panel-based next-generation sequencing, then classified into a cohort for further mutational analysis.

RESULTS

After recruitment (n = 442; 228 males and 214 females), 49.32% (218/442) of subjects received a clinical diagnosis of congenital cataracts, and 56.88% (124/218) of patients received a molecular diagnosis. Eighty-four distinct variants distributed among 43 different genes, including 42 previously reported variants and 42 novel variants, were detected, and 49 gene variants were causally associated with patient phenotypes; 27.37% of variants (23/84) were commonly detected in PAX6, GJA8 and CRYGD, and the three genes covered 33.06% of cases (41/124) with molecular diagnosis. The majority of genes were classified as genes involved in nonsyndromic congenital cataracts (19/43, 44.19%) and were responsible for 56.45% of cases (70/124). The majority of functional and nucleotide changes were missense variants (53/84, 63.10%) and substitution variants (74/84, 88.10%), respectively. Nine de novo variants were identified.

CONCLUSION

This study provides a reference for individualized genetic counseling and further extends the mutational spectrum of congenital cataracts.

Clinical and genetic features of Koreans with retinitis pigmentosa associated with mutations in rhodopsin

Purpose: To investigate the clinical features, natural course, and genetic characteristics of Koreans with rhodopsin-associated retinitis pigmentosa (RHO-associated RP). Design: We conducted a retrospective, multicenter, observational cohort study. Participants: We reviewed the medical records of 42 patients with RHO-associated RP of 36 families who visited 4 hospitals in Korea. Methods: Patients with molecular confirmation of pathogenic variants of the RHO gene were included. The patients were divided into two subgroups: the generalized and sector RP groups. A central visual field of the better-seeing eye of <10° or a best-corrected visual acuity of the better-seeing eye <20/40 indicated the progression to late-stage RP. Results: The mean age at which symptoms first appeared was 26.3 ± 17.9 years (range: 8-78 years), and the mean follow-up period was 80.9 ± 68.7 months (range: 6-268 months). At the last follow-up visit, the generalized RP group showed a significantly higher rate of visual field impairment progression to late-stage RP than that of the sector RP group (22 of 35 [62.9%] vs. 0 of 7 [0.0%], p = 0.003). No cases in the sector RP group progressed to generalized RP. Best-corrected visual acuity deterioration to late-stage RP was observed only in the generalized RP group (13 of 35 patients; 37.1%), whereas no deterioration was observed in the sector RP group. We identified 16 known and three novel RHO mutations, including two missense mutations (p.T108P and p.G121R) and one deletion mutation (p.P347_A348del). The pathogenic variants were most frequently detected in exon 1 (14 of 36 [38.9%]). The most common pathogenic variants were p.P347L and T17M (5 of 36 [13.9%] families). Among 42 patients of 36 families, 35 patients of 29 families (80.6%) presented with the generalized RP phenotype, and seven patients of seven families (19.4%) presented with the sector RP phenotype. Three variants (p.T17M, p.G101E, and p.E181K) presented with both the generalized and sector RP phenotypes. Conclusion: This multicenter cohort study provided information on the clinical and genetic features of RHO-associated RP in Koreans. It is clinically important to expand the genetic spectrum and understand genotype-phenotype correlations to ultimately facilitate the development of gene therapy.

Development of a novel prediction model based on protein structure for identifying RPE65-associated inherited retinal disease (IRDs) of missense variants

Purpose

This study aimed to develop a prediction model to classify RPE65-mediated inherited retinal disease (IRDs) based on protein secondary structure and to analyze phenotype-protein structure correlations of RPE65 missense variants in a Chinese cohort.

Methods

Pathogenic or likely pathogenic missense variants of RPE65 were obtained from UniProt, ClinVar, and HGMD databases. The three-dimensional structure of RPE65 was retrieved from the Protein Data Bank (PDB) and modified with Pymol software. A novel prediction model was developed using LASSO regression and multivariate logistic regression to identify RPE65-associated IRDs. A total of 21 Chinese probands with RPE65 variants were collected to analyze phenotype-protein structure correlations of RPE65 missense variants.

Results

The study found that both pathogenic and population missense variants were associated with structural features of RPE65. Pathogenic variants were linked to sheet, β-sheet, strands, β-hairpins, Fe2+ (iron center), and active site cavity, while population variants were related to helix, loop, helices, and helix-helix interactions. The novel prediction model showed accuracy and confidence in predicting the disease type of RPE65 variants (AUC = 0.7531). The study identified 25 missense variants in Chinese patients, accounting for 72.4% of total mutations. A significant correlation was observed between clinical characteristics of RPE65-associated IRDs and changes in amino acid type, specifically for missense variants of F8 (H68Y, P419S).

Conclusion

The study developed a novel prediction model based on the protein structure of RPE65 and investigated phenotype-protein structure correlations of RPE65 missense variants in a Chinese cohort. The findings provide insights into the precise diagnosis of RPE65-mutated IRDs.

Pathogenic Variants in CEP290 or IQCB1 Cause Earlier-Onset Retinopathy in Senior-Loken Syndrome Compared to Those in INVS, NPHP3, or NPHP4

PURPOSE

Senior-Loken syndrome (SLSN) is an autosomal recessive disorder characterized by retinopathy and nephronophthisis. This study aimed to evaluate whether different phenotypes are associated with different variants or subsets of 10 SLSN-associated genes based on an in-house data set and a literature review.

DESIGN

Retrospective case series.

METHODS

Patients with biallelic variants in SLSN-associated genes, including NPHP1, INVS, NPHP3, NPHP4, IQCB1, CEP290, SDCCAG8, WDR19, CEP164, and TRAF3IP1, were recruited. Ocular phenotypes and nephrology medical records were collected for comprehensive analysis.

RESULTS

Variants in 5 genes were identified in 74 patients from 70 unrelated families, including CEP290 (61.4%), IQCB1 (28.6%), NPHP1 (4.2%), NPHP4 (2.9%), and WDR19 (2.9%). The median age at the onset of retinopathy was approximately 1 month (since birth). Nystagmus was the most common initial sign in patients with CEP290 (28 of 44, 63.6%) or IQCB1 (19 of 22, 86.4%) variants. Cone and rod responses were extinguished in 53 of 55 patients (96.4%). Characteristic fundus changes were observed in CEP290- and IQCB1-associated patients. During follow-up, 70 of the 74 patients were referred to nephrology, among whom nephronophthisis was not detected in 62 patients (88.6%) at a median age of 6 years but presented in 8 patients (11.4%) aged approximately 9 years.

CONCLUSIONS

Patients with pathogenic variants in CEP290 or IQCB1 presented early with retinopathy, whereas other patients with INVS, NPHP3, or NPHP4 variants first developed nephropathy. Therefore, awareness of the genetic and clinical features may facilitate the clinical management of SLSN, especially early intervention of kidney problems for patients with eyes affected first.

Nuclear Receptor Subfamily 2 Group E Member 3 (NR2E3): Role in Retinal Development and Disease

NR2E3 is a nuclear hormone receptor gene required for the correct development of the retinal rod photoreceptors. Expression of NR2E3 protein in rod cell precursors suppresses cone-specific gene expression and, in concert with other transcription factors including NRL, activates the expression of rod-specific genes. Pathogenic variants involving NR2E3 cause a spectrum of retinopathies, including enhanced S-cone syndrome, Goldmann-Favre syndrome, retinitis pigmentosa, and clumped pigmentary retinal degeneration, with limited evidence of genotype-phenotype correlations. A common feature of NR2E3-related disease is an abnormally high number of cone photoreceptors that are sensitive to short wavelength light, the S-cones. This characteristic has been supported by mouse studies, which have also revealed that loss of Nr2e3 function causes photoreceptors to develop as cells that are intermediate between rods and cones. While there is currently no available cure for NR2E3-related retinopathies, there are a number of emerging therapeutic strategies under investigation, including the use of viral gene therapy and gene editing, that have shown promise for the future treatment of patients with NR2E3 variants and other inherited retinal diseases. This review provides a detailed overview of the current understanding of the role of NR2E3 in normal development and disease, and the associated clinical phenotypes, animal models, and therapeutic studies.

Unravelling the genetic basis of retinal dystrophies in Pakistani consanguineous families

BACKGROUND

Retinitis Pigmentosa (RP) is a clinically and genetically progressive retinal dystrophy associated with severe visual impairments and sometimes blindness, the most common syndromic form of which is Usher syndrome (USH). This study aimed to further increase understanding of the spectrum of RP in the Khyber Pakhtunkhwa region of Pakistan.

METHODOLOGY

Four consanguineous families of Pashtun ethnic group were investigated which were referred by the local collaborating ophthalmologists. In total 42 individuals in four families were recruited and investigated using whole exome and dideoxy sequencing. Among them, 20 were affected individuals including 6 in both family 1 and 2, 5 in family 3 and 3 in family 4.

RESULT

Pathogenic gene variants were identified in all four families, including two in cone dystrophy and RP genes in the same family (PDE6C; c.480delG, p.Asn161ThrfsTer33 and TULP1; c.238 C > T, p.Gln80Ter) with double-homozygous individuals presenting with more severe disease. Other pathogenic variants were identified in MERTK (c.2194C > T, p.Arg732Ter), RHO (c.448G > A, p.Glu150Lys) associated with non-syndromic RP, and MYO7A (c.487G > A, p.Gly163Arg) associated with USH. In addition, the reported variants were of clinical significance as the PDE6C variant was detected novel, whereas TULP1, MERTK, and MYO7A variants were detected rare and first time found segregating with retinal dystrophies in Pakistani consanguineous families.

CONCLUSIONS

This study increases knowledge of the genetic basis of retinal dystrophies in families from Pakistan providing information important for genetic testing and diagnostic provision particularly from the Khyber Pakhtunkhwa region.

New Insight into the Genotype-Phenotype Correlation of PRPH2-Related Diseases Based on a Large Chinese Cohort and Literature Review

Variants in PRPH2 are a common cause of inherited retinal dystrophies with high genetic and phenotypic heterogeneity. In this study, variants in PRPH2 were selected from in-house exome sequencing data, and all reported PRPH2 variants were evaluated with the assistance of online prediction tools and the comparative validation of large datasets. All variants were classified based on the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines. Individuals with pathogenic or likely pathogenic variants of PRPH2 were confirmed by Sanger sequencing. Clinical characteristics were summarized. Ten pathogenic or likely pathogenic variants of PRPH2 were identified in 14 families. In our cohort, the most frequent variant was p.G305Afs*19, accounting for 33.3% (5/15) of alleles, in contrast to the literature, where p.R172G (11.6%, 119/1028) was the most common variant. Nine in-house families (63.8%) were diagnosed with retinitis pigmentosa (RP), distinct from the phenotypic spectrum in the literature, which shows that RP accounts for 27.9% (283/1013) and macular degeneration is more common (45.2%, 458/1013). Patients carrying missense variants predicted as damaging by all seven prediction tools and absent in the gnomAD database were more likely to develop RP compared to those carrying missense variants predicted as damaging with fewer tools or with more than one allele number in the gnomAD database (p = 0.001). The population-specific genetic and phenotypic spectra of PRPH2 were explored, and novel insight into the genotype–phenotype correlation of PRPH2 was proposed. These findings demonstrated the importance of assessing PRPH2 variants in distinct populations and the value of providing practical suggestions for the genetic interpretation of PRPH2 variants.

Characterizing the genotypic spectrum of retinitis pigmentosa in East Asian populations: a systematic review

BACKGROUND

Ongoing trials for retinitis pigmentosa (RP) are genotype-specific, with most trials conducted on European cohorts. Due to genetic differences across diverse ancestries and populations, these therapies may not be efficacious in East Asians.

MATERIALS AND METHODS

A literature search was conducted from 1966 to September 2022 for cohort studies on East Asian populations reporting on non-syndromic RP genotypes and variants. Population-weighted prevalence was used to determine the genotypes and individual variants across the entire cohort. The carrier prevalence of common variants was compared against those in Europe.

RESULTS

A total of 12 articles describing 2,932 clinically diagnosed East Asian RP probands were included. We identified 876 variants across 54 genes. The most common genotypes included USH2A, EYS, RPGR, ABCA4, PRPF31, RHO, RP1, RP2, PDE6B and SNRNP200, with USH2A as the most common (17.1%). Overall, 60.5% of probands with clinically relevant variants were found to have one of the genotypes above, with 543/876 (62.0%) of the variants occurring in these genes. The most frequently reported variant was USH2A missense variant c.2802T>G/p.C934W (4.9%). Carrier prevalence of these variants was significantly different (p < 0.0001) than in Europe.

CONCLUSIONS

USH2A was the most commonly affected RP gene in this East Asian cohort, although sub-population analysis revealed distinct genotype prevalence patterns. While the genotypes are similar between East Asia and European cohorts, variants are specific to East Asia. The identification of several prevalent variants in USH2A and EYS provides an opportunity for the development of therapeutics that are relevant for East Asia patients.

Exome sequencing identified five novel USH2A variants in Korean patients with retinitis pigmentosa

BACKGROUND

Retinitis pigmentosa (RP) is an inherited disorder that causes progressive loss of vision. This study aimed to describe the possible causative variants of the USH2A gene in Korean RP families and their associated phenotypes.

MATERIALS AND METHODS

We recruited 94 RP families (220 subjects, including 94 probands and 126 family members) in a Korean cohort, and analyzed USH2A gene variants through whole-exome sequencing. The pathogenicity of the variants was classified according to American College of Medical Genetics and Genomics and Association for Molecular Pathology guidelines.

RESULTS

We found 14 USH2A disease-causing variants, including 5 novel variants. Disease causing variants were identified in 10 probands with RP, accounting for 10.6% (10/94) of the Korean RPs in the cohort. To visually represent the structural changes induced by novel variants, we modeled the three-dimensional structures of the wild-type and mutant proteins.

CONCLUSIONS

This study expands the spectrum of USH2A variants and provides information for future therapeutic strategies for RP.

Volume-accumulated reflectivity of the outer retina (integral) on spectral domain optical coherence tomography as a predictor of cone cell density: a pilot study

BACKGROUND

The study aims to investigate the relationship between the volume-accumulated reflectivity (termed "integral") on spectral domain optical coherence tomography (SD-OCT) and cone density on adaptive optics (AO) imaging.

METHODS

In this cross-sectional study, both eyes of 32 healthy subjects and 5 patients with inherited retinal diseases (IRD) were studied. The parameter, integral, was defined as the volume-accumulated reflectivity values in a selected region on OCT images; integrals of the ellipsoid zone (EZ) and interdigitation zone (IZ) were measured at 2°, 3°, 4°, 5°and 6° eccentricity along the four meridians on fovea-centered OCT B-scans. Cone density in the same region was measured using a flood illumination adaptive optics camera RTX1.

RESULTS

Integrals of EZ, IZ and cone density shared similar distribution patterns. Integral of the IZ was better correlated with cone density in both healthy people (r = 0.968, p < 0.001) and those with IRD (r = 0.823, p < 0.001) than direct measurements of reflectivity on OCT images. A strong correlation was found between best corrected visual acuity (BCVA) and cone density at 2° eccentricity (r = -0.857, p = 0.002). BCVA was also correlated with the integral of the IZ at the foveola (r = -0.746, p = 0.013) and fovea (r = -0.822, p = 0.004).

CONCLUSIONS

The new parameter "integral" of the photoreceptor outer segment measured from SD-OCT was noted to correlate with cone density and visual function in this pilot study.

Genetic characteristics of suspected retinitis pigmentosa in a cohort of Chinese patients

The study aimed to screen for the causative variants in Chinese patients with suspected retinitis pigmentosa (RP). A cohort of 75 unrelated Chinese patients with a clinical diagnosis of RP and their available family members were enrolled in this study. Genomic DNA of all subjects was extracted and whole-exome sequencing (WES) was applied. Candidate variants were identified, and minigene assays were conducted to evaluate the pathogenicity of novel splicing variants. Totally, the diagnostic yield was 44 % (33/75) and 16 novel variants that had not been reported previously were found. Among the genetically solved 33 cases, 31 patients were identified as carrying causative variants of RP and 2 patients carried pathogenic variants implicated in other retinal diseases. USH2A, CYP4V2, and RPGR were the most common causative genes, accounting for about half of the genetically solved cases. Moreover, minigene assays validated that the novel splicing variants were detrimental. Additionally, 9 patients carried a single deleterious heterozygous variant in 6 genes with autosomal recessive hereditary patterns, and no corresponding copy number variants (CNVs) was detected. The findings of this study revealed the genetic landscape of RP in China and provided guidance for clinicians.

Eyes Shut Homolog-Associated Retinal Degeneration: Natural History, Genetic Landscape, and Phenotypic Spectrum

PURPOSE

To describe the natural history, genetic landscape, and phenotypic spectrum of Eyes shut homolog (EYS)-associated retinal degeneration (EYS-RD).

DESIGN

Retrospective, single-center cohort study complemented by a cross-sectional examination.

SUBJECTS

Patients with biallelic EYS variants were recruited at an inherited RD referral center in Portugal.

METHODS

Every patient underwent a cross-sectional examination comprising a comprehensive ophthalmic examination including best-corrected visual acuity (BCVA), dilated slit-lamp anterior segment, and fundus biomicroscopy; ultrawide-field color fundus photography and fundus autofluorescence imaging; and spectral domain-OCT. In the setting of a retinitis pigmentosa (RP) diagnosis, every patient was classified as typical or atypical RP according to imaging criteria. Baseline demographics, age at onset of symptoms, family history, history of consanguinity, symptoms, age at diagnosis, BCVA at baseline and throughout follow-up, and EYS variants were collected from each individual patient file.

MAIN OUTCOME MEASURES

Clinical/demographic, genetic, multimodal imaging data, and BCVA variation were compared between typical and atypical RP. Additionally, BCVA variation during follow-up was used as an endpoint to describe EYS-RD natural history.

RESULTS

Fifty-eight patients (59% men; mean age 52 ± 14 years) from 48 White families of Portuguese ancestry were included. Twenty distinct EYS variants were identified, 8 of which are novel. In 32.8% of patients, onset of symptoms was in early adulthood (21-30 years). A clinical diagnosis of RP was established in 57 patients and cone-rod dystrophy in 1 patient. Regarding RP, 75.0% of the patients were graded as typical and 25.0% as atypical. Atypical EYS-RP commonly presents with inferior crescent-shaped macular atrophy with superior midperipheral sparing. In EYS-RD, a negative correlation was found between age and BCVA (r = -0.50; P < 0.001), with an average loss of 1.45 letters per year. When stratifying for RP phenotype, lower average loss of letters per year (P < 0.001), higher BCVA (P < 0.001), and larger ellipsoid zone widths (P < 0.001) were found in atypical RP.

CONCLUSIONS

This study expands the genetic spectrum of EYS-RD by reporting 8 novel variants. A high frequency of atypical phenotypes was identified. These patients have better BCVA and larger ellipsoidal zone widths, thus presenting an overall better prognosis.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

De Novo Mutations Contributes Approximately 7% of Pathogenicity in Inherited Eye Diseases

Purpose

The purpose of this study was to describe genotype-phenotype associations and novel insights into genetic characteristics in a trio-based cohort of inherited eye diseases (IEDs).

Methods

To determine the etiological role of de novo mutations (DNMs) and genetic profile in IEDs, we retrospectively reviewed a large cohort of proband-parent trios of Chinese origin. The patients underwent a detailed examination and was clinically diagnosed by an ophthalmologist. Panel-based targeted exome sequencing was performed on DNA extracted from blood samples, containing coding regions of 792 IED-causative genes and their flanking exons. All participants underwent genetic testing.

Results

All proband-parent trios were divided into 22 subgroups, the overall diagnostic yield was 48.67% (605/1243), ranging from 4% to 94.44% for each of the subgroups. A total of 108 IED-causative genes were identified, with the top 24 genes explaining 67% of the 605 genetically solved trios. The genetic etiology of 6.76% (84/1243) of the trio was attributed to disease-causative DNMs, and the top 3 subgroups with the highest incidence of DNM were aniridia (n = 40%), Marfan syndrome/ectopia lentis (n = 38.78%), and retinoblastoma (n = 37.04%). The top 10 genes have a diagnostic yield of DNM greater than 3.5% in their subgroups, including PAX6 (40.00%), FBN1 (38.78%), RB1 (37.04%), CRX (10.34%), CHM (9.09%), WFS1 (8.00%), RP1L1 (5.88%), RS1 (5.26%), PCDH15 (4.00%), and ABCA4 (3.51%). Additionally, the incidence of DNM in offspring showed a trend of correlation with paternal age at reproduction, but not statistically significant with paternal (P = 0.154) and maternal (P = 0.959) age at reproduction.

Conclusions

Trios-based genetic analysis has high accuracy and validity. Our study helps to quantify the burden of the full spectrum IED caused by each gene, offers novel potential for elucidating etiology, and plays a crucial role in genetic counseling and patient management.

Novel compound heterozygous variants in the USH2A gene associated with autosomal recessive retinitis pigmentosa without hearing loss

Background: Retinitis pigmentosa (RP) is a group of progressive inherited retinal dystrophies characterized by the primary degeneration of rod photoreceptors and the subsequent loss of cone photoreceptors because of cell death. It is caused by different mechanisms, including inflammation, apoptosis, necroptosis, pyroptosis, and autophagy. Variants in the usherin gene (USH2A) have been reported in autosomal recessive RP with or without hearing loss. In the present study, we aimed to identify causative variants in a Han-Chinese pedigree with autosomal recessive RP. Methods: A six-member, three-generation Han-Chinese family with autosomal recessive RP was recruited. A full clinical examination, whole exome sequencing, and Sanger sequencing, as well as co-segregation analysis were performed. Results: Three heterozygous variants in the USH2A gene, c.3304C>T (p.Q1102*), c.4745T>C (p.L1582P), and c.14740G>A (p.E4914K), were identified in the proband, which were inherited from parents and transmitted to the daughters. Bioinformatics analysis supported the pathogenicity of the c.3304C>T (p.Q1102*) and c.4745T>C (p.L1582P) variants. Conclusions: Novel compound heterozygous variants in the USH2A gene, c.3304C>T (p.Q1102*) and c.4745T>C (p.L1582P), were identified as the genetic causes of autosomal recessive RP. The findings may enhance the current knowledge of the pathogenesis of USH2A-associated phenotypes, expand the spectrum of the USH2A gene variants, and contribute to improved genetic counseling, prenatal diagnosis, and disease management.

Modeling Retinitis Pigmentosa with Patient-Derived iPSCs

Retinitis pigmentosa (RP) causes blindness in 1 out of 3000-4000 individuals worldwide. Understanding the disease mechanism underlying the death of photoreceptors in RP patient is crucial for the discovery and development of therapies to prevent and stop the progression of retinal degeneration. Despite having provided valuable insight into RP pathology, several shortcomings of animal models warrant the need for a better modeling system. This review discusses the current use of patient-derived induced pluripotent stem cells (iPSCs) to model RP and its advantages over animal models. Further improvement to enhance the representativeness of iPSC RP models is also discussed.

The Diagnostic Yield of Next Generation Sequencing in Inherited Retinal Diseases: A Systematic Review and Meta-analysis

PURPOSE

Accurate genotyping of individuals with inherited retinal diseases (IRD) is essential for patient management and identifying suitable candidates for gene therapies. This study evaluated the diagnostic yield of next generation sequencing (NGS) in IRDs.

DESIGN

Systematic review and meta-analysis.

METHODS

This systematic review was prospectively registered (CRD42021293619). Ovid MEDLINE and Ovid Embase were searched on 6 June 2022. Clinical studies evaluating the diagnostic yield of NGS in individuals with IRDs were eligible for inclusion. Risk of bias assessment was performed. Studies were pooled using a random...effects inverse variance model. Sources of heterogeneity were explored using stratified analysis, meta-regression, and sensitivity analysis.

RESULTS

This study included 105 publications from 28 countries. Most studies (90 studies) used targeted gene panels. The diagnostic yield of NGS was 61.3% (95% confidence interval: 57.8-64.7%; 51 studies) in mixed IRD phenotypes, 58.2% (51.6-64.6%; 41 studies) in rod-cone dystrophies, 57.7% (46.8-68.3%; eight studies) in macular and cone/cone-rod dystrophies, and 47.6% (95% CI: 41.0-54.3%; four studies) in familial exudative vitreoretinopathy. For mixed IRD phenotypes, a higher diagnostic yield was achieved pooling studies published between 2018-2022 (64.2% [59.5-68.7%]), studies using exome sequencing (73.5% [58.9-86.1%]), and studies using the American College of Medical Genetics variant interpretation standards (65.6% [60.8-70.4%]).

CONCLUSION

The current diagnostic yield of NGS in IRDs is between 52-74%. The certainty of the evidence was judged as low or very low. A key limitation of the current evidence is the significant heterogeneity between studies. Adoption of standardized reporting guidelines could improve confidence in future meta-analyses.

A Japanese boy with Bardet-Biedl syndrome caused by a novel homozygous variant in the ARL6 gene who was initially diagnosed with retinitis punctata albescens: A case report

PURPOSE

Bardet-Biedl Syndrome (BBS) is an autosomal recessive systemic disorder characterized by retinitis pigmentosa, polydactyly, obesity, intellectual disability, renal impairments, and hypogonadism. The purpose of this study was to determine the ocular characteristics of a boy with BBS caused by a novel homozygous variant in the ARL6 (alternative named BBS3) gene who had been originally diagnosed with retinitis punctata albescens.

METHODS

This was an observational case study. The patient underwent ophthalmological examinations, electroretinography, and genetic analyses using whole-exome sequencing.

RESULTS

A 7-year-old boy was examined in our hospital with complaints of a progressive reduction of his visual acuity and night blindness in both eyes. There was no family history of eye diseases and no consanguineous marriage. Fundus examinations showed numerous white spots in the deep retina and retinal pigment epithelium. Fundus autofluorescence showed hypofluorescence consistent with these spots. Both the scotopic and photopic components of the full-field electroretinographies were non-detectable. Based on these clinical findings, this boy was suspected to have retinitis punctata albescens. Subsequent genetic testing using whole-exome sequencing revealed a novel homozygous variants in the ARL6/BBS3 gene (NM_001278293.3:c.528G>A, (p.Trp176Ter)). A systemic examination by the pediatric department revealed that this boy had a history of a surgical excision of polydactyly on his left foot when he was born, and that he was mildly obese. There were no prominent intellectual or gonadal dysfunctions, no craniofacial or dental abnormalities, no congenital heart disease, and no hearing impairment. He was then clinically and genetically diagnosed with BBS.

CONCLUSION AND IMPORTANCE

In children with night blindness and progressive visual dysfunction, it is important for ophthalmologists to consult clinical geneticists and pediatricians to rule out the possibility of systemic diseases such as BBS.

PRPF31 interacts with PRPH2 confirmed by co-immunoprecipitation and co-localization

Both PRPF31 and PRPH2 are the causative genes for retinitis pigmentosa. And both of them are associated with the balance of rhodopsin. In this study, we aim to investigate the co-expression and interaction of PRPF31 and PRPH2. We used PRPF31-eGFP, PRPF31-3xFlag and PRPH2-mCherry vectors were transfected into HEK293T and APRE-19 cells. Immunoblotting and co-immunoprecipitation (Co-IP) were used for gene expression validation and protein interaction. Immunofluorescence staining assay was used to test the co-localization analysis of PRPF31 and PRPH2. Co-IP experiments showed that PRPF31 could be pulled down with an anti-PRPH2 antibody. There was co-localization between PRPF31 and PRPH2 in HEK293T, APRE-19 and mouse retina. The Co-IP and co-localization experiments suggest that PRPF31 interacted with PRPH2.

Landscape of pathogenic variants in six pre-mRNA processing factor genes for retinitis pigmentosa based on large in-house data sets and database comparisons

PURPOSE

Variants in six genes encoding pre-mRNA processing factors (PRPFs) are a common cause of autosomal dominant retinitis pigmentosa (ADRP). This study aims to determine the characteristics of potential pathogenic variants (PPVs) in the six genes.

METHODS

Variants in six PRPF genes were identified from in-house exome sequencing data. PPVs were identified based on comparative bioinformatics analysis, clinical phenotypes and the ACMG/AMP guidelines. The features of PPVs were revealed by comparative analysis of in-house data set, gnomAD and previously published literature.

RESULTS

Totally, 36 heterozygous PPVs, including 19 novels, were detected from 45 families, which contributed to 4.4% (45/1019) of RP cases. These PPVs were distributed in PRPF31 (17/45, 37.8%), SNRNP200 (12/45, 26.7%), PRPF8 (10/45, 22.2%) and PRPF3 (6/45, 13.3%) but not in PRPF6 or PRPF4. Different types of PPVs were predominant in different PRPF genes, such as loss-of-function variants in PRPF31 and missense variants in the five remaining genes. The clustering of PPVs in specific regions was observed in SNRNP200, PRPF8 and PRPF3. The pathogenicity for certain classes of variants in these genes, such as loss-of-function variants in PRPF6 and missense variants in PRPF31 and PRPF4, requires careful consideration and further validation. The predominant fundus changes were early macular involvement, widespread RPE atrophy and pigmentation in the mid- and far-peripheral retina.

CONCLUSION

Systemic comparative analysis may shed light on the characterization of PPVs in these genes. Our findings provide a brief landscape of PPVs in PRPF genes and the associated phenotypes and emphasize the careful classification of pathogenicity for certain types of variants that warrant further characterization.

Association between retinitis pigmentosa and an increased risk of primary angle closure glaucoma: A population-based cohort study

Background

Retinitis pigmentosa (RP) is the most frequent retinal hereditary dystrophy and result in blindness if progresses. Several case reports have revealed the possible association between RP and primary angle-closure glaucoma (PACG). We conducted a population-based study to explore whether RP significantly increased the risk of PACG development.

Methods

Using the Taiwan National Health Insurance Research Database, we enrolled patients with RP into the RP group from 2001 to 2013 and included a comparison group of 1:4 age- and sex-matched individuals without RP. We performed a Cox regression analysis to estimate the crude and adjusted hazard ratios (HRs) of RP for PACG after adjustment for hypertension, diabetes, hyperlipidaemia, chronic kidney disease, and lens subluxation.

Results

We enrolled 6223 subjects with RP and 24892 subjects for comparison. The mean age of the cohort was 49.0 ± 18.1 years. The RP group had significantly higher percentages of diabetes mellitus, hypertension, and hyperlipidaemia. The cumulative incidence of PACG in patients with RP was 1.61%, which was significantly higher than that in the comparison group (0.81%, p < 0.0001). According to the univariate Cox regression analysis, the hazard of PACG development was significantly greater in the RP group, with an unadjusted HR of 2.09 (95% confidence interval [CI], 1.64–2.65). The increased risk persisted after adjusting for confounders (adjusted HR = 2.18; 95% CI, 1.76–2.72).

Conclusion

This nationwide population-based cohort study showed that people with RP are at a significantly greater risk of developing PACG than individuals without RP.

A Novel Autosomal Recessive Variant of the NRL Gene Causing Enhanced S-Cone Syndrome: A Morpho-Functional Analysis of Two Unrelated Pediatric Patients

Enhanced S-cone syndrome (ESCS) is a rare autosomal recessive retinal degeneration mainly associated with pathogenic variations in the NR2E3 gene. Only a few pathogenic variations in the NRL gene associated with ESCS have been reported to date. Here, we describe the clinical and genetic findings of two unrelated pediatric patients with a novel frameshift homozygous variant in the NRL gene. Fundus examinations showed signs of peripheral degeneration in both patients, more severe in Proband 2, with relative sparing of the macular area. Spectral domain optical coherence tomography (SD-OCT) revealed a significant macular involvement with cysts in Proband 1, and minimal foveal alteration with peripheral retina involvement in Proband 2. Visual acuity was abnormal in both patients, but more severely affected in Proband 1 than Proband 2. The electroretinogram recordings showed reduced scotopic, mixed and single flash cone responses, with a typical supernormal S-cone response, meeting the criteria for a clinical diagnosis of ESCS in both patients. The present report expands the clinical and genetic spectrum of NRL-associated ESCS, and confirms the age-independent variability of phenotypic presentation already described in the NR2E3-associated ESCS.

Genetic Characteristics and Variation Spectrum of USH2A-Related Retinitis Pigmentosa and Usher Syndrome

Purposes: We aimed to characterize the USH2A genotypic spectrum in a Chinese cohort and provide a detailed genetic profile for Chinese patients with USH2A-IRD.

Methods: We designed a retrospective study wherein a total of 1,334 patients diagnosed with IRD were included as a study cohort, namely 1,278 RP and 56 USH patients, as well as other types of IEDs patients and healthy family members as a control cohort. The genotype-phenotype correlation of all participants with USH2A variant was evaluated.

Results: Etiological mutations in USH2A, the most common cause of RP and USH, were found in 16.34% (n = 218) genetically solved IRD patients, with prevalences of 14.87% (190/1,278) and 50% (28/56). After bioinformatics and QC processing, 768 distinct USH2A variants were detected in all participants, including 136 disease-causing mutations present in 665 alleles, distributed in 5.81% of all participants. Of these 136 mutations, 43 were novel, nine were founder mutations, and two hot spot mutations with allele count ≥10. Furthermore, 38.5% (84/218) of genetically solved USH2A-IRD patients were caused by at least one of both c.2802T&gt;G and c.8559–2 A&gt;G mutations, and 36.9% and 69.6% of the alleles in the RP and USH groups were truncating, respectively.

Conclusion: USH2A-related East Asian-specific founder and hot spot mutations were the major causes for Chinese RP and USH patients. Our study systematically delineated the genotype spectrum of USH2A-IRD, enabled accurate genetic diagnosis, and provided East Asian and other ethnicities with baseline data of a Chinese origin, which would better serve genetic counseling and therapeutic targets selection.

Clinical and Genetic Analysis of Retinitis Pigmentosa with Primary Angle Closure Glaucoma in the Chinese Population

PURPOSE

Retinitis pigmentosa (RP) constitutes a class of common inherited retinal dystrophies. Patients with RP and comorbid primary angle-closure glaucoma (PACG) have been described, but the relationship between the diseases remains unclear. This study investigated the clinical and genetic characteristics of Chinese patients with RP and comorbid PACG.

METHODS

Of 1356 patients with RP, we analyzed the genetic features of 39 RP patients with PACG using next-generation sequencing and reviewed their clinical characteristics.

RESULTS

In total, 18 patients with acute PACG and 21 patients with chronic PACG were included in this study; their age at examination was 50.54 ± 12.99 years (range, 25.0-71.0 years), and their age at PACG onset was 46.04 ± 14.50 years (range, 24.9-68.0 years). Additionally, the mean lens thickness (LT) was 4.49 ± 0.44 μm, and the mean axial length (AL) was 22.63 ± 1.17 mm. Notably, the prevalence of PACG in patients with RP was 2.88%; this was higher than the prevalence in the general population. This could be explained by nanophthalmos, thickened lentis, ectopia lentis, or zonular insufficiency. Furthermore, patients with a shorter AL, a greater LT, iridociliary cysts, or nanophthalmos exhibited earlier development of PACG. Overall, 30 disease-causing variants spanning 17 genes were identified in 56.41% of the patients, and PRPH2 was the most common mutation gene.

CONCLUSIONS

Our findings revealed that there is a strong association between RP and PACG. Furthermore, intraocular pressure (IOP) should be measured in patients with RP to protect them from the aggravated damage of an elevated IOP.

Mutation spectrum in a cohort with familial exudative vitreoretinopathy

Purpose

To expand the mutation spectrum of patients with familial exudative vitreoretinopathy (FEVR) disease.

Participants

74 probands (53 families and 21 sporadic probands) with familial exudative vitreoretinopathy (FEVR) disease and their available family members (n = 188) were recruited for sequencing.

Methods

Panel‐based targeted screening was performed on all subjects. Before sanger sequencing, variants of LRP5, NDP, FZD4, TSPAN12, ZNF408, KIF11, RCBTB1, JAG1, and CTNNA1 genes were verified by a series of bioinformatics tools and genotype–phenotype co‐segregation analysis.

Results

40.54% (30/74) of the probands were sighted to possess at least one etiological mutation of the nine FEVR‐causative genes. The etiological mutation detection rate was 37.74% (20/53) in family‐attainable probands while 47.62% (10/21) in sporadic cases. The diagnosis rate of patients in the early‐onset subgroup (≤5 years old, 45.4%) is higher than that of the children or adolescence‐onset subgroup (6–16 years old, 42.1%) and the late‐onset subgroup (≥17 years old, 39.4%). A total of 36 etiological mutations were identified in this study, comprising 26 novel mutations and 10 reported mutations. LRP5 was the most prevalent mutant gene among the 36 mutation types with a percentage of 41.67% (15/36). Followed by FZD4 (10/36, 27.78%), TSPAN12 (5/36, 13.89%), NDP (4/36, 11.11%), KIF11 (1/36, 2.78%), and RCBTB1 (1/36, 2.78%). Among these mutations, 63.89% (23/36) were missense mutations, 25.00% (9/36) were frameshift mutations, 5.56% (2/36) were splicing mutations, 5.56% (2/36) were nonsense mutations. Moreover, the clinical pathogenicity of these variants was defined according to American College of Medical Genetics (ACMG) and genomics guidelines: 41.67% (15/36) were likely pathogenic variants, 27.78% (10/36) pathogenic variants, 30.55% (11/36) variants of uncertain significance. No etiological mutations discovered in the ZNF408, JAG1, and CTNNA1 genes in this FEVR cohort.

Conclusions

We systematically screened nine FEVR disease‐associated genes in a cohort of 74 Chinese probands with FEVR disease. With a detection rate of 40.54%, 36 etiological mutations of six genes were authenticated in 30 probands, including 26 novel mutations and 10 reported mutations. The most prevalent mutated gene is LRP5, followed by FZD4, TSPAN12, NDP, KIF11, and RCBTB1. In total, a de novo mutation was confirmed. Our study significantly clarified the mutation spectrum of variants bounded up to FEVR disease.

Patients with Retinitis Pigmentosa May Have a Higher Risk of Developing Open-Angle Glaucoma

Background

Retinitis pigmentosa (RP) is the most common retinal hereditary dystrophy, which can lead to blindness if it progresses. Similarly, open-angle glaucoma (OAG) is a genetic disorder. The similarities in genetic variants and pathophysiology between RP and OAG have been reported. We sought to explore whether patients with RP have a significantly higher risk of OAG development.

Methods

We enrolled patients with RP into the RP group through Taiwan's National Health Insurance Research Database from 2001 to 2013; we included a comparison group of 1 : 4 age- and gender-matched individuals without RP. We performed a Cox regression analysis to estimate the crude and adjusted hazard ratios (HRs) for OAG. We adjusted the following confounders in the Cox regression model: age, gender, diabetes mellitus, hypertension, and chronic kidney disease.

Results

We enrolled 6,223 subjects with RP and 24,892 subjects for comparison. The mean age of the cohort was 49.0 ± 18.1 years. The RP group had significantly higher percentages of diabetes mellitus, hypertension, and hyperlipidaemia. The cumulative incidence of OAG in patients with RP was 1.57%; this was significantly higher than that in the comparison group (0.58%, p < 0.0001). On univariate Cox regression analysis, the hazard of OAG development was significantly greater in the RP group than in the comparison group with an unadjusted HR of 2.86 (95% confidence interval, 2.21–3.70). The increased risk persisted after adjusting for confounders (adjusted HR = 2.86; 95% CI, 2.21–3.70).

Conclusions

This nationwide population-based cohort study showed that people with RP are at a significantly greater risk of developing OAG than individuals without it.

Ocular Manifestations in a Chinese Pedigree of Familial Amyloidotic Polyneuropathy Carrying the Transthyretin Mutation c.401A>G (p.Tyr134Cys)

Familial amyloid polyneuropathy (FAP) caused by a genetic mutation in transthyretin (TTR) is an autosomal dominant hereditary disease. The retrospective, observational case series study presents the ocular clinicopathological findings of five cases carrying the TTR mutation c.401A>G (p.Tyr134Cys). Multimodal retinal imaging and electrophysiological examination, Congo red staining and immunohistochemical analysis of specimens, and genetic analyses were performed. Cases 1 and 2 were symptomatic with vitreous and retinal amyloid deposition and poor visual recovery. Case 3 had a symptomatic vitreous haze in the left eye with good postoperative visual recovery. The right eye of case 3 and the eyes of cases 4 and 5 were asymptomatic. Thicker retinal nerve fiber layer, retinal venous tortuosity with prolonged arteriovenous passage time on fluorescein angiography and retinal dysfunction detected by multifocal electroretinogram occurred even in asymptomatic eyes. Moreover, the internal limiting membrane from patients with FAP was stained positive for Congo red and transforming growth factor-β1. The results highlight the amyloid deposition of mutant TTR in the optic disc and retina, even in the asymptomatic stage. The deposited amyloid leads to increased resistance to venous return and retinal functional abnormalities. Therefore, careful follow-up of structural and functional changes in the retina is needed, even in asymptomatic patients with FAP.

Envisioning the development of a CRISPR-Cas mediated base editing strategy for a patient with a novel pathogenic CRB1 single nucleotide variant

BACKGROUND

Inherited retinal degeneration (IRD) associated with mutations in the Crumbs homolog 1 (CRB1) gene is associated with a severe, early-onset retinal degeneration for which no therapy currently exists. Base editing, with its capability to precisely catalyse permanent nucleobase conversion in a programmable manner, represents a novel therapeutic approach to targeting this autosomal recessive IRD, for which a gene supplementation is challenging due to the need to target three different retinal CRB1 isoforms.

PURPOSE

To report and classify a novel CRB1 variant and envision a possible therapeutic approach in form of base editing.

METHODS

Case report.

RESULTS

A 16-year-old male patient with a clinical diagnosis of early-onset retinitis pigmentosa (RP) and characteristic clinical findings of retinal thickening and coarse lamination was seen at the Oxford Eye Hospital. He was found to be compound heterozygous for two CRB1 variants: a novel pathogenic nonsense variant in exon 9, c.2885T>A (p.Leu962Ter), and a likely pathogenic missense change in exon 6, c.2056C>T (p.Arg686Cys). While a base editing strategy for c.2885T>A would encompass a CRISPR-pass mediated "read-through" of the premature stop codon, the resulting missense changes were predicted to be "possibly damaging" in in-silico analysis. On the other hand, the transversion missense change, c.2056C>T, is amenable to transition editing with an adenine base editor (ABE) fused to a SaCas9-KKH with a negligible chance of bystander edits due to an absence of additional Adenines (As) in the editing window.

CONCLUSIONS

This case report records a novel pathogenic nonsense variant in CRB1 and gives an example of thinking about a base editing strategy for a patient compound heterozygous for CRB1 variants.

Autosomal Dominant Retinitis Pigmentosa-Associated TOPORS Protein Truncating Variants Are Exclusively Located in the Region of Amino Acid Residues 807 to 867

Purpose

Heterozygous truncating variants of TOPORS have been reported to cause autosomal dominant retinitis pigmentosa (adRP). The purpose of this study was to investigate whether all heterozygous truncating variants, including copy number variants (CNVs), are pathogenic.

Methods

TOPORS truncating variants were collected and reviewed through an in-house dataset and existing databases. Individuals with truncating variants underwent ophthalmological evaluation.

Results

Six truncating variants were detected in seven families. Three N-terminus truncating variants were detected in three families without RP, and the other three were identified in four unrelated families with typical RP. Based on the in-house dataset and published literature, 17 truncating variants were identified in 47 families with RP. All RP-associated truncating alleles, except one, were distributed in the last exon of TOPORS and clustered in amino acid residues 807 to 867 (46/47, 97.9%). Conversely, in the gnomAD database, only one truncating allele (1/27, 3.7%) was in this region, and the others were outside (26/27, 96.3%), suggesting that the pathogenic truncating variants were significantly clustered in residues 807 to 867 (χ² = 65.6, P = 1.1 × 10^–17). Additionally, three CNVs involving the N-terminus of TOPORS were recorded in control populations but were absent in affected patients.

Conclusions

This study suggests that all pathogenic truncating variants of TOPORS were clustered in residues 807 to 867, whereas the truncating variants outside this region and the CNVs involving the N-terminus were not associated with RP. A dominant-negative effect, rather than haploinsufficiency, is speculated to be the underlying pathogenesis. These findings provide valuable information for interpreting variation in TOPORS and other genes in similar situations, especially for CNVs.

Clinical and genetic investigations in Chinese families with retinitis pigmentosa

To describe clinical and genetic characteristics in a series of Chinese patients with non-syndromic retinitis pigmentosa, a total of 20 unrelated Chinese pedigrees with non-syndromic retinitis pigmentosa were evaluated. Complete ophthalmic examinations data including the Humphrey visual field, spectral domain-optical coherence tomography, full-field electroretinography, and fundus fluorescence were collected and analyzed. Targeted exome sequencing was utilized to investigate variations in 260 known genes of inherited retinal disease, including the 90 known causative retinitis pigmentosa genes. We initially identified the potential candidate variants in the pedigrees, then validated the variants using the Sanger sequencing and performed segregation analysis to verify that the variants constituted disease-causing mutations in these pedigrees. We detected three novel (likely) pathogenic and eight previously reported (likely) pathogenic variations in nine genes reported to be related to non-syndromic retinitis pigmentosa in nine of the pedigrees. We report clinical characteristics of Chinese patients with retinitis pigmentosa and novel mutations responsible for non-syndromic retinitis pigmentosa in Chinese pedigrees, expanding the number of gene mutations associated with this disorder and clarifying its genetic basis in the Chinese population. These data will help with rapid and efficient molecular diagnosis and the study of targeted treatment for retinitis pigmentosa in this population.

Mutation Analysis of the RPGR Gene in a Chinese Cohort

Purpose: The purpose of this study was to investigate the clinical and genetic characteristics of the retinitis pigmentosa GTPase regulatory factor gene (RPGR) in a Chinese cohort.

Methods: A retrospective analysis was performed on 80 subjects with RPGR-retinal dystrophy (RPGR-RD) for detailed genetic and clinical characterization. The panel-based next-generation sequencing of 792 causative genes involved in common genetic eye diseases was conducted in all individuals, followed by clinical variant interpretation. Information, including age, sex, geographic distribution, family history, consanguineous marriage, age at symptom onset, disease duration, best corrected visual acuity (BCVA), and complete ophthalmologic examination results, was collected.

Results: This cohort (41 men and 39 women) included 26 families (26 probands and their available family members) and 13 sporadic cases. The average age of these participants was 36.35 ± 17.68 years, and the majority of the families were from eastern China (28 families, 71.79%). The average duration of disease in the probands was 22.68 ± 15.80 years. In addition, the average BCVA values of the right and left eyes in the probands were 0.96 ± 0.77 and 1.00 ± 0.77, respectively. A total of 34 RPGR variants were identified, including 6 reported variants and 28 novel variants. Among these variants, NM_001034853.1: c.2899_2902delGAAG and c.2744_2745ins24 were considered de novo variants. The majority of the RPGR variants were classified as likely pathogenic, accounting for 70.59% of the variants (24 variants). The most common nucleotide and amino acid changes identified in this study were deletions (16 variants, 45.06%) and frameshifts (17 variants, 50.00%), respectively. Genetic analysis revealed that these RPGR variants were distributed in 10 different subregions of RPGR, and 70.59% of the RPGR variants (24 variants) were located in exon 15. Four RPGR variants, NM_001034853.1: c.2405_2406delAG, c.1345C > T, c.2218G > T and c.2236_2237delGA, occurred at a very high frequency of 28.21% (11 families) among 39 unrelated families.

Conclusion: This study expands the known mutational spectrum of RPGR, and we provide a new reference for the genetic diagnosis of RPGR variants.

Gene-Based Therapeutics for Inherited Retinal Diseases

Inherited retinal diseases (IRDs) are a heterogenous group of orphan eye diseases that typically result from monogenic mutations and are considered attractive targets for gene-based therapeutics. Following the approval of an IRD gene replacement therapy for Leber's congenital amaurosis due to RPE65 mutations, there has been an intensive international research effort to identify the optimal gene therapy approaches for a range of IRDs and many are now undergoing clinical trials. In this review we explore therapeutic challenges posed by IRDs and review current and future approaches that may be applicable to different subsets of IRD mutations. Emphasis is placed on five distinct approaches to gene-based therapy that have potential to treat the full spectrum of IRDs: 1) gene replacement using adeno-associated virus (AAV) and nonviral delivery vectors, 2) genome editing via the CRISPR/Cas9 system, 3) RNA editing by endogenous and exogenous ADAR, 4) mRNA targeting with antisense oligonucleotides for gene knockdown and splicing modification, and 5) optogenetic approaches that aim to replace the function of native retinal photoreceptors by engineering other retinal cell types to become capable of phototransduction.