Next-generation sequencing-based molecular diagnosis of 82 retinitis pigmentosa probands from Northern Ireland

Copy number variant detection using next-generation sequencing in EYS-associated retinitis pigmentosa

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy and a major cause of blindness. RP is caused by several variants of multiple genes, and genetic diagnosis by identifying these variants is important for optimizing treatment and estimating patient prognosis. Next-generation sequencing (NGS), which is currently widely used for diagnosis, is considered useful but is known to have limitations in detecting copy number variations (CNVs). In this study, we re-evaluated CNVs in EYS, the main causative gene of RP, identified via NGS using multiplex ligation-dependent probe amplification (MLPA). CNVs were identified in NGS samples of eight patients. To identify potential CNVs, MLPA was also performed on samples from 42 patients who were undiagnosed by NGS but carried one of the five major pathogenic variants reported in Japanese EYS-RP cases. All suspected CNVs based on NGS data in the eight patients were confirmed via MLPA. CNVs were found in 2 of the 42 NGS-undiagnosed RP cases. Furthermore, results showed that 121 of the 661 patients with RP had EYS as the causative gene, and 8.3% (10/121 patients with EYS-RP) had CNVs. Although NGS using the CNV calling criteria utilized in this study failed to identify CNVs in two cases, no false-positive results were detected. Collectively, these findings suggest that NGS is useful for CNV detection during clinical diagnosis of RP.

Identification of RPGR ORF15 mutation for X-linked retinitis pigmentosa in a large Chinese family and in vitro correction with prime editor

X-linked retinitis pigmentosa (XLRP) is the most severe form of Retinitis Pigmentosa (RP) and one of the leading causes of blindness in the world. Currently, there is no effective treatment for RP. In the present study, we recruited a XLRP family and identified a 4 bp deletion mutation (c. 2234_2237del) in RPGR ORF15 with Sanger sequencing, which was located in the exact same region as the missing XES (X chromosome exome sequencing) coverage. Then, we generated cell lines harboring the identified mutation and corrected it via enhanced prime editing system (ePE). Collectively, Sanger sequencing identified a pathogenic mutation in RPGR ORF15 for XLRP which was corrected with ePE. This study provides a valuable insight for genetic counseling of the afflicted family members and prenatal diagnosis, also paves a way for applying prime editing based gene therapy in those patients.

Effective smMIPs-Based Sequencing of Maculopathy-Associated Genes in Stargardt Disease Cases and Allied Maculopathies from the UK

Macular dystrophies are a group of individually rare but collectively common inherited retinal dystrophies characterised by central vision loss and loss of visual acuity. Single molecule Molecular Inversion Probes (smMIPs) have proved effective in identifying genetic variants causing macular dystrophy. Here, a previously established smMIPs panel tailored for genes associated with macular diseases has been used to examine 57 UK macular dystrophy cases, achieving a high solve rate of 63.2% (36/57). Among 27 bi-allelic STGD1 cases, only three novel ABCA4 variants were identified, illustrating that the majority of ABCA4 variants in Caucasian STGD1 cases are currently known. We examined cases with ABCA4-associated disease in detail, comparing our results with a previously reported variant grading system, and found this model to be accurate and clinically useful. In this study, we showed that ABCA4-associated disease could be distinguished from other forms of macular dystrophy based on clinical evaluation in the majority of cases (34/36).

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.

Mutation spectrum of non-syndromic hearing loss in the UAE, a retrospective cohort study and literature review

BACKGROUND

Hearing loss (HL) is a heterogeneous condition that causes partial or complete hearing impairment. Hundreds of variants in >60 genes have been reported to be associated with Hereditary HL (HHL), variants of the GJB2 gene are the most common cause of congenital SNHL, with >100 variants reported. The HHL prevalence is thought to be high in the Arab population; however, the genetic epidemiology of HHL among Emirati populations is understudied.

AIMS

To shed light on the mutational spectrum of NSHL in Emirati patients seen in the genetic clinic over 10 years and to capture founder mutation(s) if any were identified.

METHODS

Retrospective chart review of all Emirati patients assessed by clinical geneticists due to NSHL during the period between January 2010 to December 2020. Genetic tests were done based on clinical phenotypes of the patient and family history including targeted mutation testing, next-generation sequencing, or whole-exome sequencing (solo or trio). The authors did literature reviews using PubMed for all previously reported articles related to NSHL genes from UAE.

RESULTS

A total of 162 patients with HL, were evaluated during the period between January 2010 to December 2020. There were 82 patients with NSHL, and only 72 patients who completed the genetic evaluations were included in this retrospective study. Among the studied group, 42 (51.2%) were males and 40 (48.78%) were females. The youngest patient was 2 years old and the oldest patient was 50 years old. Consanguinity was documented in 76 patients (92.68%). A total of 14 mutations reported here are novel (23/72 i.e., 31.9%). Twelve missense mutations, 6 nonsense mutations, 6 frameshift mutations, 2 in-frame deletion mutations, and 1 splice site mutation was found. Variants in the GJB2 gene are the most commonly identified cause of NSHL, with c.35delG being the most followed by c.506G > A. The second commonly found variant is c.934C > G (p.Arg312Gly) in the CDC14A gene, found in 9 patients. This was followed by variants in OTOF and SLC26A4 genes, found in 8 patients, respectively. Chromosomal microdeletions encompassing genes causing NSHL were found in 3 patients. No mitochondrial mutations were found in this study group. A total of 11 previous reports about Emirati patients with NSHL were reviewed, with a total of 35 patients.

CONCLUSION

Emirati patients with NSHL have several mutations, most notably missense mutations. Novel mutations are worth further testing and represent the area for future researches.

Likely pathogenic structural variants in genetically unsolved patients with retinitis pigmentosa revealed by long-read sequencing

Despite the successful identification of causative genes and genetic variants of retinitis pigmentosa (RP), many patients have not been molecularly diagnosed. Our recent study using targeted short-read sequencing showed that the proportion of carriers of pathogenic variants in EYS, the cause of autosomal recessive RP, was unexpectedly high in Japanese patients with unsolved RP. This result suggested that causative genetic variants, which are difficult to detect by short-read sequencing, exist in such patients. Using long-read sequencing technology (Oxford Nanopore), we analysed the whole genomes of 15 patients with RP with one heterozygous pathogenic variant in EYS detected in our previous study along with structural variants (SVs) in EYS and another 88 RP-associated genes. Two large exon-overlapping deletions involving six exons were identified in EYS in two patients with unsolved RP. An analysis of an independent patient set (n=1189) suggested that these two deletions are not founder mutations. Our results suggest that searching for SVs by long-read sequencing in genetically unsolved cases benefits the molecular diagnosis of RP.

Exome sequencing of families from Ghana reveals known and candidate hearing impairment genes

We investigated hearing impairment (HI) in 51 families from Ghana with at least two affected members that were negative for GJB2 pathogenic variants. DNA samples from 184 family members underwent whole-exome sequencing (WES). Variants were found in 14 known non-syndromic HI (NSHI) genes [26/51 (51.0%) families], five genes that can underlie either syndromic HI or NSHI [13/51 (25.5%)], and one syndromic HI gene [1/51 (2.0%)]. Variants in CDH23 and MYO15A contributed the most to HI [31.4% (16/51 families)]. For DSPP, an autosomal recessive mode of inheritance was detected. Post-lingual expression was observed for a family segregating a MARVELD2 variant. To our knowledge, seven novel candidate HI genes were identified (13.7%), with six associated with NSHI (INPP4B, CCDC141, MYO19, DNAH11, POTEI, and SOX9); and one (PAX8) with Waardenburg syndrome. MYO19 and DNAH11 were replicated in unrelated Ghanaian probands. Six of the novel genes were expressed in mouse inner ear. It is known that Pax8-/- mice do not respond to sound, and depletion of Sox9 resulted in defective vestibular structures and abnormal utricle development. Most variants (48/60; 80.0%) have not previously been associated with HI. Identifying seven candidate genes in this study emphasizes the potential of novel HI genes discovery in Africa.

Screening of single nucleotide polymorphisms among fuchs’ endothelial corneal dystrophy subjects in Malaysia

Background

The pathophysiology underlying Fuchs' Endothelial Corneal Dystrophy (FECD), especially in older individuals, remains unclear, with a genetic predisposition being reported as the single best predictor of the disease. Genetic studies have shown that several genes in various loci such as COL8A2, SLC4A11, TCF8/ZEB1 and TCF4 are associated with FECD in different populations and ethnicities. A case–control study was conducted to determine the association between genetic variants and FECD in a tertiary care setting in Malaysia. A total number of 12 patients with clinically diagnosed FECD and 12 age, gender and race matched control subjects were recruited. Extracted genomic DNA were genotyped using Infinium Global Screening Array (GSA)-24 version 1.0 BeadChip with iScan high-throughput system. Illumina GenomeStudio 2.0 Data Analysis and PLINK version 1.9 software were used to perform association tests and determine the distribution of obtained variants among the cases and controls.

Results

A significant novel genetic variant, rs11626651, a variant of the LOC105370676 gene or known as the LINC02320 gene, located at chromosome 14, has been identified as a suggestive association with FECD (p < 5 × 10−6). Further analysis in this study suggested that candidate genes such as COL8A2, ZEB1/TCF8, TCF4 and SLC4A11 had no significant associations with FECD.

Conclusions

The discovery of a novel variant may influence the underlying pathogenic basis of FECD in Malaysia. The current study is the first genetic study on FECD to use Infinium GSA. It is the first comprehensive report in Malaysia to provide genetic information of potential relevance to FECD, which may pave the way for new therapeutic strategies in the future. A detailed analysis with a larger sample size is recommended for further evaluation.

Clinical/Demographic Functional Testing and Multimodal Imaging Differences between Genetically Solved and Unsolved Retinitis Pigmentosa

INTRODUCTION

The purpose of this study was to compare clinical/demographic functional testing and multimodal imaging features between genetically solved and genetically unsolved nonsyndromic retinitis pigmentosa (nsRP) patients.

METHODS

A cross-sectional study was conducted at an inherited retinal dystrophies reference center. Consecutive patients with nsRP and available genetic testing results performed between 2018 and 2020 were included. Genetic testing was clinically oriented, and variants were classified according to the American College of Medical Genetics and Genomics. Only class IV or V variants were considered disease-causing. Clinical/demographic, functional, and imaging features were compared between genetically unsolved (G1) and genetically solved (G2) patients.

RESULTS

A total of 175 patients (146 families) were included: 68 patients (59 families) in G1 and 107 patients (87 families) in G2. First symptoms <25 years, consanguinity, evidence for a particular inheritance pattern, and the absence of indicators for phenocopies were significantly more prevalent in G2. No significant differences were observed on best-corrected visual acuity. The visual field index and mean central retinal layer thickness were significantly higher in G1. The frequency of atypical features on multimodal imaging did not differ between groups.

CONCLUSION

Individual clinical/demographic functional testing and multimodal imaging features should be considered when counseling patients about the probability of identifying disease-causing variants.

Toward the Treatment of Inherited Diseases of the Retina Using CRISPR-Based Gene Editing

Inherited retinal dystrophies [IRDs] are a common cause of severe vision loss resulting from pathogenic genetic variants. The eye is an attractive target organ for testing clinical translational approaches in inherited diseases. This has been demonstrated by the approval of the first gene supplementation therapy to treat an autosomal recessive IRD, RPE65-linked Leber congenital amaurosis (type 2), 4 years ago. However, not all diseases are amenable for treatment using gene supplementation therapy, highlighting the need for alternative strategies to overcome the limitations of this supplementation therapeutic modality. Gene editing has become of increasing interest with the discovery of the CRISPR-Cas9 platform. CRISPR-Cas9 offers several advantages over previous gene editing technologies as it facilitates targeted gene editing in an efficient, specific, and modifiable manner. Progress with CRISPR-Cas9 research now means that gene editing is a feasible strategy for the treatment of IRDs. This review will focus on the background of CRISPR-Cas9 and will stress the differences between gene editing using CRISPR-Cas9 and traditional gene supplementation therapy. Additionally, we will review research that has led to the first CRISPR-Cas9 trial for the treatment of CEP290-linked Leber congenital amaurosis (type 10), as well as outline future directions for CRISPR-Cas9 technology in the treatment of IRDs.

Deletion of prominin-1 in mice results in disrupted photoreceptor outer segment protein homeostasis

AIM

To illustrate the underlying mechanism how prominin-1 (also known as Prom1) mutation contribute to progressive photoreceptor degeneration.

METHODS

A CRISPR-mediated Prom1 knockout (Prom1-KO) mice model in the C57BL/6 was generated and the photoreceptor degeneration phenotypes by means of structural and functional tests were demonstrated. Immunohistochemistry and immunoblot analysis were performed to reveal the localization and quantity of related outer segment (OS) proteins.

RESULTS

The Prom1-KO mice developed the photoreceptor degeneration phenotype including the decreased outer nuclear layer (ONL) thickness and compromised electroretinogram amplitude. Immunohistochemistry analysis revealed impaired trafficking of photoreceptor OS proteins. Immunoblot data demonstrated decreased photoreceptor OS proteins.

CONCLUSION

Prom1 deprivation causes progressive photoreceptor degeneration. Prom1 is essential for maintaining normal trafficking and normal quantity of photoreceptor OS proteins. The new light is shed on the pathogenic mechanism underlying photoreceptor degeneration caused by Prom1 mutation.

PRPH2 mutation update: In silico assessment of 245 reported and 7 novel variants in patients with retinal disease

Mutations in PRPH2, encoding peripherin-2, are associated with the development of a wide variety of inherited retinal diseases (IRDs). To determine the causality of the many PRPH2 variants that have been discovered over the last decades, we surveyed all published PRPH2 variants up to July 2020, describing 720 index patients that in total carried 245 unique variants. In addition, we identified seven novel PRPH2 variants in eight additional index patients. The pathogenicity of all variants was determined using the ACMG guidelines. With this, 107 variants were classified as pathogenic, 92 as likely pathogenic, one as benign, and two as likely benign. The remaining 50 variants were classified as variants of uncertain significance. Interestingly, of the total 252 PRPH2 variants, more than half (n = 137) were missense variants. All variants were uploaded into the Leiden Open source Variation and ClinVar databases. Our study underscores the need for experimental assays for variants of unknown significance to improve pathogenicity classification, which would allow us to better understand genotype-phenotype correlations, and in the long-term, hopefully also support the development of therapeutic strategies for patients with PRPH2-associated IRD.

Molecular Epidemiology in 591 Italian Probands With Nonsyndromic Retinitis Pigmentosa and Usher Syndrome

Purpose

To describe the molecular epidemiology of nonsyndromic retinitis pigmentosa (RP) and Usher syndrome (US) in Italian patients.

Methods

A total of 591 probands (315 with family history and 276 sporadics) were analyzed. For 155 of them, we performed a family segregation study, considering a total of 382 relatives. Probands were analyzed by a customized multigene panel approach. Sanger sequencing was used to validate all genetic variants and to perform family segregation studies. Copy number variants of selected genes were analyzed by multiplex ligation-dependent probe amplification. Four patients who tested negative to targeted next-generation sequencing analysis underwent clinical exome sequencing.

Results

The mean diagnostic yield of molecular testing among patients with a family history of retinal disorders was 55.2% while the diagnostic yield including sporadic cases was 37.4%. We found 468 potentially pathogenic variants, 147 of which were unpublished, in 308 probands and 66 relatives. Mean ages of onset of the different classes of RP were autosomal dominant RP, 19.3 ± 12.6 years; autosomal recessive RP, 23.2 ± 16.6 years; X-linked RP, 13.9 ± 9.9 years; and Usher syndrome, 18.9 ± 9.5 years. We reported potential new genotype-phenotype correlations in three probands, two revealed by TruSight One testing. All three probands showed isolated RP caused by biallelic variants in genes usually associated with syndromes such as PERCHING and Senior-Loken or with retinal dystrophy, iris coloboma, and comedogenic acne syndrome.

Conclusions

This is the largest molecular study of Italian patients with RP in the literature, thus reflecting the epidemiology of the disease in Italy with reasonable accuracy.

Clinical Evidence for the Importance of the Wild-Type PRPF31 Allele in the Phenotypic Expression of RP11

PRPF31-associated retinopathy (RP11) is a common form of autosomal dominant retinitis pigmentosa (adRP) that exhibits wide variation in phenotype ranging from non-penetrance to early-onset RP. Herein, we report inter-familial and intra-familial variation in the natural history of RP11 using multimodal imaging and microperimetry. Patients were recruited prospectively. The age of symptom onset, best-corrected visual acuity, microperimetry mean sensitivity (MS), residual ellipsoid zone span and hyperautofluorescent ring area were recorded. Genotyping was performed using targeted next-generation and Sanger sequencing and copy number variant analysis. PRPF31 mutations were found in 14 individuals from seven unrelated families. Four disease patterns were observed: (A) childhood onset with rapid progression (N = 4), (B) adult-onset with rapid progression (N = 4), (C) adult-onset with slow progression (N = 4) and (D) non-penetrance (N = 2). Four different patterns were observed in a family harbouring c.267del; patterns B, C and D were observed in a family with c.772_773delins16 and patterns A, B and C were observed in 3 unrelated individuals with large deletions. Our findings suggest that the RP11 phenotype may be related to the wild-type PRPF31 allele rather than the type of mutation. Further studies that correlate in vitro wild-type PRPF31 allele expression level with the disease patterns are required to investigate this association.

A novel mutation of the RPGR gene in a Chinese X-linked retinitis pigmentosa family and possible involvement of X-chromosome inactivation

OBJECTIVES

The objective of this study is to investigate the molecular mechanisms and genotype-phenotype correlations of a Chinese family with X-linked retinitis pigmentosa (XLRP).

METHODS

A four-generation family with a total of 41 individuals including 7 affected males was recruited. All subjects in this pedigree underwent a complete ophthalmic examination. Targeted capture and next-generation sequencing were performed on the proband using a multigene panel containing 57 known causative genes of retinitis pigmentosa (RP), including RP1, RP2, RPGR, RHO, PRPH2, CRB1 among others. All variants were verified in the remaining family members by polymerase chain reaction amplification and Sanger sequencing. Blood DNA was used for X-chromosome inactivation analysis in female carriers.

RESULTS

All the affected individuals were diagnosed with RP. The affected males showed symptoms from the first decade, while the female carriers had onset in the second decade or later. A frameshift mutation c.345_348delTGAA in the RPGR gene was identified in all affected males and female carriers. By XCI analysis, we found that there was little correlation between their phenotype and the methylation status of their X chromosomes.

CONCLUSIONS

A novel mutation c.345_348delTGAA of the RPGR gene was identified, expanding the spectrum of RPGR mutations causing XLRP. In this pedigree, the phenotype extended to female carriers, in whom RP was milder and its onset delayed compared to hemizygous males. Although lack of strong correlation between X-inactivation and the severity of the disease, the milder, variable effects in female carriers still could reflect X-inactivation patterns in the retina of each individual.

Next-Generation Sequencing Applications for Inherited Retinal Diseases

Inherited retinal diseases (IRDs) represent a collection of phenotypically and genetically diverse conditions. IRDs phenotype(s) can be isolated to the eye or can involve multiple tissues. These conditions are associated with diverse forms of inheritance, and variants within the same gene often can be associated with multiple distinct phenotypes. Such aspects of the IRDs highlight the difficulty met when establishing a genetic diagnosis in patients. Here we provide an overview of cutting-edge next-generation sequencing techniques and strategies currently in use to maximise the effectivity of IRD gene screening. These techniques have helped researchers globally to find elusive causes of IRDs, including copy number variants, structural variants, new IRD genes and deep intronic variants, among others. Resolving a genetic diagnosis with thorough testing enables a more accurate diagnosis and more informed prognosis and should also provide information on inheritance patterns which may be of particular interest to patients of a child-bearing age. Given that IRDs are heritable conditions, genetic counselling may be offered to help inform family planning, carrier testing and prenatal screening. Additionally, a verified genetic diagnosis may enable access to appropriate clinical trials or approved medications that may be available for the condition.

Genotype-Phenotype Correlations in RP1-Associated Retinal Dystrophies: A Multi-Center Cohort Study in JAPAN

Background: Little is known about genotype–phenotype correlations of RP1-associated retinal dystrophies in the Japanese population. We aimed to investigate the genetic spectrum of RP1 variants and provide a detailed description of the clinical findings in Japanese patients. Methods: In total, 607 patients with inherited retinal diseases were examined using whole-exome/whole-genome sequencing (WES/WGS). PCR-based screening for an Alu element insertion (c.4052_4053ins328/p.Tyr1352AlafsTer9) was performed in 18 patients with autosomal-recessive (AR)-retinitis pigmentosa (RP) or AR-cone dystrophy (COD)/cone-rod dystrophy (CORD), including seven patients with heterozygous RP1 variants identified by WES/WGS analysis, and 11 early onset AR-RP patients, in whom no pathogenic variant was identified. We clinically examined 25 patients (23 families) with pathogenic RP1 variants, including five patients (five families) with autosomal-dominant (AD)-RP, 13 patients (11 families) with AR-RP, and seven patients (seven families) with AR-COD/CORD. Results: We identified 18 pathogenic RP1 variants, including seven novel variants. Interestingly, the Alu element insertion was the most frequent variant (32.0%, 16/50 alleles). The clinical findings revealed that the age at onset and disease progression occurred significantly earlier and faster in AR-RP patients compared to AD-RP or AR-COD/CORD patients. Conclusions: Our results suggest a genotype–phenotype correlation between variant types/locations and phenotypes (AD-RP, AR-RP, and AR-COD/CORD), and the Alu element insertion was the most major variant in Japanese patients with RP1-associated retinal dystrophies.

Noncoding mutation in RPGRIP1 contributes to inherited retinal degenerations

Purpose

Despite the extensive use of next-generation sequencing (NGS) technology to identify disease-causing genomic variations, a major gap in our understanding of Mendelian diseases is the unidentified molecular lesion in a significant portion of patients. For inherited retinal degenerations (IRDs), although currently close to 300 disease-associated genes have been identified, the mutations in approximately one-third of patients remain unknown. With mounting evidence that noncoding mutations might contribute significantly to disease burden, we aimed to systematically investigate the contributions of noncoding regions in the genome to IRDs.

Methods

In this study, we focused on RPGRIP1, which has been linked to various IRD phenotypes, including Leber congenital amaurosis (LCA), retinitis pigmentosa (RP), and macular dystrophy (MD). As several noncoding mutant alleles have been reported in RPGRIP1, and we observed that the mutation carrier frequency of RPGRIP1 is higher in patient cohorts with unsolved IRDs, we hypothesized that mutations in the noncoding regions of RPGRIP1 might be a significant contributor to pathogenicity. To test this hypothesis, we performed whole-genome sequencing (WGS) for 25 patients with unassigned IRD who carry a single mutation in RPGRIP1.

Results

Three noncoding variants in RPGRIP1, including a 2,890 bp deletion and two deep-intronic variants (c.2710+233G>A and c.1468-263G>C), were identified as putative second hits of RPGRIP1 in three patients with LCA. The mutant alleles were validated with direct sequencing or in vitro assays.

Conclusions

The results highlight the significance of the contribution of noncoding pathogenic variants to unsolved IRD cases.

Identification of Deep-Intronic Splice Mutations in a Large Cohort of Patients With Inherited Retinal Diseases

High throughput sequencing technologies have revolutionized the identification of mutations responsible for a diverse set of Mendelian disorders, including inherited retinal disorders (IRDs). However, the causal mutations remain elusive for a significant proportion of patients. This may be partially due to pathogenic mutations located in non-coding regions, which are largely missed by capture sequencing targeting the coding regions. The advent of whole-genome sequencing (WGS) allows us to systematically detect non-coding variations. However, the interpretation of these variations remains a significant bottleneck. In this study, we investigated the contribution of deep-intronic splice variants to IRDs. WGS was performed for a cohort of 571 IRD patients who lack a confident molecular diagnosis, and potential deep intronic variants that affect proper splicing were identified using SpliceAI. A total of six deleterious deep intronic variants were identified in eight patients. An in vitro minigene system was applied to further validate the effect of these variants on the splicing pattern of the associated genes. The prediction scores assigned to splice-site disruption positively correlated with the impact of mutations on splicing, as those with lower prediction scores demonstrated partial splicing. Through this study, we estimated the contribution of deep-intronic splice mutations to unassigned IRD patients and leveraged in silico and in vitro methods to establish a framework for prioritizing deep intronic variant candidates for mechanistic and functional analyses.

CHM mutation spectrum and disease: An update at the time of human therapeutic trials

Choroideremia is an X-linked inherited retinal disorder (IRD) characterized by the degeneration of retinal pigment epithelium, photoreceptors, choriocapillaris and choroid affecting males with variable phenotypes in female carriers. Unlike other IRD, characterized by a large clinical and genetic heterogeneity, choroideremia shows a specific phenotype with causative mutations in only one gene, CHM. Ongoing gene replacement trials raise further interests in this disorder. We describe here the clinical and genetic data from a French cohort of 45 families, 25 of which carry novel variants, in the context of 822 previously reported choroideremia families. Most of the variants represent loss-of-function mutations with eleven families having large (i.e. ≥6 kb) genomic deletions, 18 small insertions, deletions or insertion deletions, six showing nonsense variants, eight splice site variants and two missense variants likely to affect splicing. Similarly, 822 previously published families carry mostly loss-of-function variants. Recurrent variants are observed worldwide, some of which linked to a common ancestor, others arisen independently in specific CHM regions prone to mutations. Since all exons of CHM may harbor variants, Sanger sequencing combined with quantitative polymerase chain reaction or multiplex ligation-dependent probe amplification experiments are efficient to achieve the molecular diagnosis in patients with typical choroideremia features.

Genetic characteristics and epidemiology of inherited retinal degeneration in Taiwan

Inherited retinal degenerations (IRDs) are a group of phenotypically and genotypically heterogeneous disorders with substantial socioeconomic impact. In this cohort study, we tried to address the genetic characteristics and epidemiology of IRDs in Taiwan. Totally, 312 families with IRDs were identified and recruited and genetic testing was performed via probe capture-based NGS targeting 212 IRD-related genes. Statistical analysis was based on the proband of each affected family. Disease-causing genotypes were identified in 178 families (57.1%). ABCA4 variants were the most common cause of disease in this cohort (27 families, 15.2%), whereas CYP4V2 variants were the most common cause for the single phenotype—Bietti’s crystalline dystrophy (12 families, 3.8%). Some variants such as ABCA4:c.1804C>T, CYP4V2:c.802-8_810delinsGC, and EYS:c6416G>A were population-specific disease-causing hotspots. Probands affected by ABCA4, RPGR, RP1L1, and CEP290 sought medical help earlier while patients affected by EYS and CYP4V2 visited our clinic at an older age. To evaluate the representativeness of our cohort in the genetic epidemiology of IRDs in Taiwan, our demographic data were compared with that of the total IRD population in Taiwan, obtained from the National Health Insurance Research Database. This is currently the largest-scale, comprehensive study investigating the genetic characteristics and epidemiology of IRD in Taiwan. These data could help patients and caregivers to adopt precision genomic medicine and novel gene therapies in near future.

Roles of HIF and 2-Oxoglutarate-Dependent Dioxygenases in Controlling Gene Expression in Hypoxia

Simple Summary

Hypoxia—reduction in oxygen availability—plays key roles in both physiological and pathological processes. Given the importance of oxygen for cell and organism viability, mechanisms to sense and respond to hypoxia are in place. A variety of enzymes utilise molecular oxygen, but of particular importance to oxygen sensing are the 2-oxoglutarate (2-OG) dependent dioxygenases (2-OGDs). Of these, Prolyl-hydroxylases have long been recognised to control the levels and function of Hypoxia Inducible Factor (HIF), a master transcriptional regulator in hypoxia, via their hydroxylase activity. However, recent studies are revealing that such dioxygenases are involved in almost all aspects of gene regulation, including chromatin organisation, transcription and translation.

Abstract

Hypoxia—reduction in oxygen availability—plays key roles in both physiological and pathological processes. Given the importance of oxygen for cell and organism viability, mechanisms to sense and respond to hypoxia are in place. A variety of enzymes utilise molecular oxygen, but of particular importance to oxygen sensing are the 2-oxoglutarate (2-OG) dependent dioxygenases (2-OGDs). Of these, Prolyl-hydroxylases have long been recognised to control the levels and function of Hypoxia Inducible Factor (HIF), a master transcriptional regulator in hypoxia, via their hydroxylase activity. However, recent studies are revealing that dioxygenases are involved in almost all aspects of gene regulation, including chromatin organisation, transcription and translation. We highlight the relevance of HIF and 2-OGDs in the control of gene expression in response to hypoxia and their relevance to human biology and health.

EYS is a major gene involved in retinitis pigmentosa in Japan: genetic landscapes revealed by stepwise genetic screening

Next-generation sequencing (NGS) has greatly advanced the studies of causative genes and variants of inherited diseases. While it is sometimes challenging to determine the pathogenicity of identified variants in NGS, the American College of Medical Genetics and Genomics established the guidelines to help the interpretation. However, as to the genetic screenings for patients with retinitis pigmentosa (RP) in Japan, none of the previous studies utilized the guidelines. Considering that EYS is the major causative gene of RP in Japan, we conducted stepwise genetic screening of 220 Japanese patients with RP utilizing the guidelines. Step 1-4 comprised the following, in order: Sanger sequencing for two major EYS founder mutations; targeted sequencing of all coding regions of EYS; whole genome sequencing; Sanger sequencing for Alu element insertion in RP1, a recently determined founder mutation for RP. Among the detected variants, 2, 19, 173, and 1 variant(s) were considered pathogenic and 8, 41, 44, and 5 patients were genetically solved in step 1, 2, 3, and 4, respectively. Totally, 44.5% (98/220) of the patients were genetically solved, and 50 (51.0%) were EYS-associated and 5 (5.1%) were Alu element-associated. Among the unsolved 122 patients, 22 had at least one possible pathogenic variant.

Molecular diagnosis based on comprehensive genetic testing in 800 Chinese families with non-syndromic inherited retinal dystrophies

IMPORTANCE

Inherited retinal dystrophies (IRDs) are a group of monogenic diseases, one of the leading causes of blindness.

BACKGROUND

Introducing a comprehensive genetic testing strategy by combining single gene Sanger sequencing, next-generation sequencing (NGS) including whole exome sequencing (WES), and a specific hereditary eye disease enrichment panel (HEDEP) sequencing, to identify the disease-causing variants of 800 Chinese probands affected with non-syndromic IRDs.

DESIGN

Retrospective analysis.

PARTICIPANTS

Eight hundred Chinese non-syndromic IRDs probands and their families.

METHODS

A total of 149 patients were subjected to Sanger sequencing. Of the 651 patients subjected to NGS, 86 patients underwent WES and 565 underwent HEDEP. Patients that likely carried copy number variations (CNVs) detected by HEDEP were further validated by multiplex ligation-dependent probe amplification (MLPA) or quantitative fluorescence PCR (QF-PCR).

MAIN OUTCOME MEASURES

The diagnostic rate.

RESULTS

(Likely) pathogenic variants were determined in 481 cases (60.13% detection rate). The detection rates of single gene Sanger sequencing, WES and HEDEP were 86.58%, 31.40% and 56.99%, respectively. Approximately 11.64% of 481 cases carried autosomal dominant variants, 72.97% carried AR variants and 15.39% were found to be X-linked. CNVs were confirmed by MLPA or QF-PCR in 17 families. Fourteen genes that each caused disease in 1% or more of the cohort were detected, and these genes were collectively responsible for disease in almost one half (46.38%) of the families.

CONCLUSIONS AND RELEVANCE

Sanger sequencing is ideal to detect pathogenic variants of clinical homogeneous diseases, whereas NGS is more appropriate for patients without an explicit clinical diagnosis.

[Comparison study of whole exome sequencing and targeted panel sequencing in molecular diagnosis of inherited retinal dystrophies]

OBJECTIVE

To evaluate and compare whole exome sequencing (WES) and targeted panel sequencing in the clinical molecular diagnosis of the Chinese families affected with inherited retinal dystrophies (IRDs).

METHODS

The clinical information of 182 probands affected with IRDs was collected, including their family history and the ophthalmic examination results. Blood samples of all probands and their relatives were collected and genomic DNA was extracted by standard protocols. The first 91 cases were subjected to the WES and the other 91 cases were subjected to a specific hereditary eye disease enrichment panel (HEDEP) designed by us. All likely pathogenic and pathogenic variants in the candidate genes were determined by Sanger sequencing and co-segregation analyses were performed in available family members. Copy number variations (CNVs) detected by HEDEP were further validated by multiplex ligation-dependent probe amplification (MLPA). As PRGR ORF15 was difficult to capture by next generation sequencing (NGS), all the samples were subjected to Sanger sequencing for this region. All sequence changes identified by NGS were classified according to the American College of Medical Gene-tics and Genomics and the Association for Molecular Pathology (ACMG/AMP) variant interpretation guidelines. In this study, only variants identified as pathogenic or likely pathogenic were included, while those variants of uncertain significance, likely benign or benign were not included.

RESULTS

In 91 cases with WES, pathogenic or likely pathogenic variants were determined in 30 cases, obtaining a detection rate of 33.00% (30/91); While in 91 cases with HEDEP sequencing, pathogenic or likely pathogenic variants were determined in 51 cases, achieving the diagnostic rate of 56.04% (51/91), and totally, the diagnostic rate was 44.51%. HEDEP had better sequencing coverage and read depth than WES, therefore HEDEP had higher detection rate. In addition, HEDEP could detect CNVs. In this study, we detected disease-causing variants in 29 distinct IRD-associated genes, USH2A, ABCA4 and RPGR were the three most common disease-causing genes, and the frequency of these genes in Chinese IRDs population was 11.54% (21/182), 6.59% (12/182) and 3.85% (7/182), respectively. We found 43 novel variants and 6 cases carried variants in RPGR ORF15.

CONCLUSION

NGS in conjunction with Sanger sequencing offers a reliable and effective approach for the genetic diagnosis of IRDs, and after evaluating the pros and cons of the two sequencing methods, we conclude that HEDEP should be used as a first-tier test for IRDs patients, WES can be used as a supplementary molecular diagnostic method due to its merit of detecting novel IRD-associated genes if HEDEP or other methods could not detect disease-causing va-riants in reported genes. In addition, our results enriched the mutational spectra of IRDs genes, and our methods paves the way of genetic counselling, family planning and up-coming gene-based therapies for these families.

Clinical and genetic characteristics of 10 Japanese patients with PROM1-associated retinal disorder: A report of the phenotype spectrum and a literature review in the Japanese population

Variants in the PROM1 gene are associated with cone (-rod) dystrophy, macular dystrophy, and other phenotypes. We describe the clinical and genetic characteristics of 10 patients from eight Japanese families with PROM1-associated retinal disorder (PROM1-RD) in a nationwide cohort. A literature review of PROM1-RD in the Japanese population was also performed. The median age at onset/examination of 10 patients was 31.0 (range, 10-45)/44.5 (22-73) years. All 10 patients showed atrophic macular changes. Seven patients (70.0%) had spared fovea to various degrees, approximately half of whom had maintained visual acuity. Generalized cone (-rod) dysfunction was demonstrated in all nine subjects with available electrophysiological data. Three PROM1 variants were identified in this study: one recurrent disease-causing variant (p.Arg373Cys), one novel putative disease-causing variant (p.Cys112Arg), and one novel variant of uncertain significance (VUS; p.Gly53Asp). Characteristic features of macular atrophy with generalized cone-dominated retinal dysfunction were shared among all 10 subjects with PROM1-RD, and the presence of foveal sparing was crucial in maintaining visual acuity. Together with the three previously reported variants [p.R373C, c.1551+1G>A (pathogenic), p.Asn580His (likely benign)] in the literature of Japanese patients, one prevalent missense variant (p.Arg373Cys, 6/9 families, 66.7%) detected in multiple studies was determined in the Japanese population, which was also frequently detected in the European population.

Next-generation sequencing and its application in diagnosis of retinitis pigmentosa

Retinitis Pigmentosa (RP) is a major cause of heritable human blindness with a high genetic heterogeneity. It is characterized by the initial degeneration of rod photoreceptors followed by cone photoreceptors. RP is also a prominent reason of visual impairment, by a global prevalence of 1:4000. RP is usually specified with nyctalopia in puberty, followed by concentric visual field loss, that reflects the main impairment of rod photoreceptors; later in the life, as disease progresses, because of cone dysfunction, central vision loss also occurs. A precise molecular diagnosis is crucial for disease characterization and clinical prognosis. DNA sequencing is a powerful tool for deciphering various causes of different human diseases. The arrival of next-generation sequencing (NGS) technologies has diminished sequencing cost and considerably augmented the throughput, making whole-genome sequencing (WGS) a conceivable way for obtaining comprehensive genomic data and a more precise clinical decision. Nevertheless, the advantages gained from NGS technologies are among a number of challenges that must be sufficiently addressed before this technique can be altered from an investigation tools to a helpful method in routine clinical practices. This article aims to provide an overview about NGS technology and its related platforms. The challenges in the analysis and choosing an appropriate NGS method likewise their potential applications in clinical diagnosis are also discussed. The merit of such technique has been reflected in some recent studies where it is shown that using NGS and molecular information could help with clinical diagnosis, providing potential treatment options or changes, up-to-date family counseling and management.

Genetic tests by next-generation sequencing in children with developmental delay and/or intellectual disability

Developments in next-generation sequencing (NGS) techogies have assisted in clarifying the diagnosis and treatment of developmental delay/intellectual disability (DD/ID) via molecular genetic testing. Advances in DNA sequencing technology have not only allowed the evolution of targeted panels but also, and more currently enabled genome-wide analyses to progress from research era to clinical practice. Broad acceptance of accuracy- guided targeted gene panel, whole-exome sequencing (WES), and whole-genome sequencing (WGS) for DD/ID need prospective analyses of the increasing cost-effectiveness versus conventional genetic testing. Choosing the appropriate sequencing method requires individual planning. Data are required to guide best-practice recommendations for genomic testing, regarding various clinical phenotypes in an etiologic approach. Targeted panel testing may be recommended as a first-tier testing approach for children with DD/ID. Family-based trio testing by WES/WGS can be used as a second test for DD/ ID in undiagnosed children who previously tested negative on a targeted panel. The role of NGS in molecular diagnostics, treatment, prediction of prognosis will continue to increase further in the coming years. Given the rapid pace of changes in the past 10 years, all medical providers should be aware of the changes in the transformative genetics field.

Copy-number variation contributes 9% of pathogenicity in the inherited retinal degenerations

PURPOSE

Current sequencing strategies can genetically solve 55-60% of inherited retinal degeneration (IRD) cases, despite recent progress in sequencing. This can partially be attributed to elusive pathogenic variants (PVs) in known IRD genes, including copy-number variations (CNVs), which have been shown as major contributors to unsolved IRD cases.

METHODS

Five hundred IRD patients were analyzed with targeted next-generation sequencing (NGS). The NGS data were used to detect CNVs with ExomeDepth and gCNV and the results were compared with CNV detection with a single-nucleotide polymorphism (SNP) array. Likely causal CNV predictions were validated by quantitative polymerase chain reaction (qPCR).

RESULTS

Likely disease-causing single-nucleotide variants (SNVs) and small indels were found in 55.6% of subjects. PVs in USH2A (11.6%), RPGR (4%), and EYS (4%) were the most common. Likely causal CNVs were found in an additional 8.8% of patients. Of the three CNV detection methods, gCNV showed the highest accuracy. Approximately 30% of unsolved subjects had a single likely PV in a recessive IRD gene.

CONCLUSION

CNV detection using NGS-based algorithms is a reliable method that greatly increases the genetic diagnostic rate of IRDs. Experimentally validating CNVs helps estimate the rate at which IRDs might be solved by a CNV plus a more elusive variant.

Mutation spectrum of PRPF31, genotype-phenotype correlation in retinitis pigmentosa, and opportunities for therapy

Pathogenic variants in pre-messenger RNA (pre-mRNA) splicing factor 31, PRPF31, are the second most common genetic cause of autosomal dominant retinitis pigmentosa (adRP) in most populations. This remains a completely untreatable and incurable form of blindness, and it can be difficult to predict the clinical course of disease. In order to design appropriate targeted therapies, a thorough understanding of the genetics and molecular mechanism of this disease is required. Here, we present the structure of the PRPF31 gene and PRPF31 protein, current understanding of PRPF31 protein function and the full spectrum of all reported clinically relevant variants in PRPF31. We delineate the correlation between specific PRPF31 genotype and RP phenotype, suggesting that, except in cases of complete gene deletion or large-scale deletions, dominant negative effects contribute to phenotype as well as haploinsufficiency. This has important impacts on design of targeted therapies, particularly the feasibility of gene augmentation as a broad approach for treatment of PRPF31-associated RP. We discuss other opportunities for therapy, including antisense oligonucleotide therapy and gene-independent approaches and offer future perspectives on treatment of this form of RP.

•

PRPF31 is the second most common cause of autosomal dominant retinitis pigmentosa and a potential target for gene therapy.

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We present all reported pathogenic variants in PRPF31 as a resource for clinicians, diagnostic genetics labs, and researchers.

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Genotype-phenotype correlations suggest that, dominant negative effects contribute to disease in addition to haploinsufficiency.

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This finding has important impacts on the suitability of gene augmentation approaches across all mutation types.

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This finding may aid prognosis of disease in PRPF31-associated RP patients.

Role of carotenoids and retinoids during heart development

The nutritional requirements of the developing embryo are complex. In the case of dietary vitamin A (retinol, retinyl esters and provitamin A carotenoids), maternal derived nutrients serve as precursors to signaling molecules such as retinoic acid, which is required for embryonic patterning and organogenesis. Despite variations in the composition and levels of maternal vitamin A, embryonic tissues need to generate a precise amount of retinoic acid to avoid congenital malformations. Here, we summarize recent findings regarding the role and metabolism of vitamin A during heart development and we survey the association of genes known to affect retinoid metabolism or signaling with various inherited disorders. A better understanding of the roles of vitamin A in the heart and of the factors that affect retinoid metabolism and signaling can help design strategies to meet nutritional needs and to prevent birth defects and disorders associated with altered retinoid metabolism. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Extensive genic and allelic heterogeneity underlying inherited retinal dystrophies in Mexican patients molecularly analyzed by next-generation sequencing

Background

Retinal dystrophies (RDs) are one of the most genetically heterogeneous monogenic disorders with ~270 associated loci identified by early 2019. The recent application of next‐generation sequencing (NGS) has greatly improved the molecular diagnosis of RD patients. Genetic characterization of RD cohorts from different ethnic groups is justified, as it would improve the knowledge of molecular basis of the disease. Here, we present the results of genetic analysis in a large cohort of 143 unrelated Mexican subjects with a variety of RDs.

Methods

A targeted NGS approach covering 199 RD genes was employed for molecular screening of 143 unrelated patients. In addition to probands, 258 relatives were genotyped by Sanger sequencing for familial segregation of pathogenic variants.

Results

A solving rate of 66% (95/143) was achieved, with evidence of extensive loci (44 genes) and allelic (110 pathogenic variants) heterogeneity. Forty‐eight percent of the identified pathogenic variants were novel while ABCA4, CRB1, USH2A, and RPE65 carried the greatest number of alterations. Novel deleterious variants in IDH3B and ARL6 were identified, supporting their involvement in RD. Familial segregation of causal variants allowed the recognition of 124 autosomal or X‐linked carriers.

Conclusion

Our results illustrate the utility of NGS for genetic diagnosis of RDs of different populations for a better knowledge of the mutational landscape associated with the disease.

Expanded Phenotypic Spectrum of Retinopathies Associated with Autosomal Recessive and Dominant Mutations in PROM1

PURPOSE

To describe the genetic and phenotypic characteristics of a cohort of patients with PROM1 variants.

DESIGN

Case-case study.

METHODS

We screened a cohort of 2216 families with inherited retinal dystrophies using classical molecular techniques and next-generation sequencing approaches. The clinical histories of 25 patients were reviewed to determine age of onset of symptoms and the results of ophthalmoscopy, best-corrected visual acuity, full-field electroretinography, and visual field studies. Fundus autofluorescence and spectral-domain optical coherence tomography were further assessed in 7 patients.

RESULTS

PROM1 variants were identified in 32 families. Disease-causing variants were found in 18 autosomal recessive and 4 autosomal dominant families. Monoallelic pathogenic variants or variants of unknown significance were identified in the remaining 10 families. Comprehensive phenotyping of 25 patients from 22 families carrying likely disease-causing variants revealed clinical heterogeneity associated with the PROM1 gene. Most of these patients presented cone-rod dystrophy and some exhibited macular dystrophy or retinitis pigmentosa, while all presented with macular damage. Phenotypic association of a dominant splicing variant with late-onset mild maculopathy was established. This variant is one of the 3 likely founder variants identified in our Spanish cohort.

CONCLUSIONS

We report the largest cohort of patients with PROM1 variants, describing in detail the phenotype in 25 of them. Interestingly, within the variability of phenotypes related to this gene, macular involvement is a common feature in all patients.

Olfactory Dysfunction in Patients With CNGB1-Associated Retinitis Pigmentosa

Importance

Co-occurrence of retinitis pigmentosa (RP) and olfactory dysfunction may have a common genetic cause.

Objective

To report olfactory function and the retinal phenotype in patients with biallelic mutations in CNGB1, a gene coding for a signal transduction channel subunit expressed in rod photoreceptors and olfactory sensory neurons.

Design, Setting, and Participants

This case series was conducted from August 2015 through July 2017. The setting was a multicenter study involving 4 tertiary referral centers for inherited retinal dystrophies. Participants were 9 patients with CNGB1-associated RP.

Main Outcomes and Measures

Results of olfactory testing, ocular phenotyping, and molecular genetic testing using targeted next-generation sequencing.

Results

Nine patients were included in the study, 3 of whom were female. Their ages ranged between 34 and 79 years. All patients had an early onset of night blindness but were usually not diagnosed as having RP before the fourth decade because of slow retinal degeneration. Retinal features were characteristic of a rod-cone dystrophy. Olfactory testing revealed reduced or absent olfactory function, with all except one patient scoring in the lowest quartile in relation to age-related norms. Brain magnetic resonance imaging and electroencephalography measurements in response to olfactory stimulation were available for 1 patient and revealed no visible olfactory bulbs and reduced responses to odor, respectively. Molecular genetic testing identified 5 novel (c.1312C>T, c.2210G>A, c.2492+1G>A, c.2763C>G, and c.3044_3050delGGAAATC) and 5 previously reported mutations in CNGB1.

Conclusions and Relevance

Mutations in CNGB1 may cause an autosomal recessive RP-olfactory dysfunction syndrome characterized by a slow progression of retinal degeneration and variable anosmia or hyposmia.

Deletion of the transmembrane protein Prom1b in zebrafish disrupts outer-segment morphogenesis and causes photoreceptor degeneration

Mutations in human prominin 1 (PROM1), encoding a transmembrane glycoprotein localized mainly to plasma membrane protrusions, have been reported to cause retinitis pigmentosa, macular degeneration, and cone-rod dystrophy. Although the structural role of PROM1 in outer-segment (OS) morphogenesis has been demonstrated in Prom1-knockout mouse, the mechanisms underlying these complex disease phenotypes remain unclear. Here, we utilized a zebrafish model to further investigate PROM1's role in the retina. The Prom1 orthologs in zebrafish include prom1a and prom1b, and our results showed that prom1b, rather than prom1a, plays an important role in zebrafish photoreceptors. Loss of prom1b disrupted OS morphogenesis, with rods and cones exhibiting differences in impairment: cones degenerated at an early age, whereas rods remained viable but with an abnormal OS, even at 9 months postfertilization. Immunofluorescence experiments with WT zebrafish revealed that Prph2, an ortholog of the human transmembrane protein peripherin 2 and also associated with OS formation, is localized to the edge of OS and is more highly expressed in the cone OS than in the rod OS. Moreover, we found that Prom1b deletion causes mislocalization of Prph2 and disrupts its oligomerization. We conclude that the variation in Prph2 levels between cones and rods was one of the reasons for the different PROM1 mutation-induced phenotypes of these retinal structures. These findings expand our understanding of the phenotypes caused by PROM1 mutations and provide critical insights into its function.

Clinical and Molecular Characterization of PROM1-Related Retinal Degeneration

IMPORTANCE

The PROM1 gene, commonly associated with cone-rod dystrophies, may have dominant or recessive phenotypes that influence disease onset and severity.

OBJECTIVE

To characterize the clinical phenotype and molecular genetic variations in patients with PROM1 variants.

DESIGN, SETTING, AND PARTICIPANTS

This case-series study was conducted at 2 specialist retinal genetics clinics and examined 19 consecutively enrolled patients with PROM1-related retinal degeneration. Data were collected and analyzed from May 2018 to December 2018.

MAIN OUTCOMES AND MEASURES

Results of ophthalmic examination, retinal imaging, and molecular genetic analysis by next-generation sequencing.

RESULTS

Of 19 patients, 13 (68%) were women, and age ranged from 11 to 70 years. All patients presented with central visual loss, with or without photophobia. Individuals with recessive variants commonly had severe loss of visual acuity by their 20s, whereas the dominant variant was associated with a milder phenotype, with most patients retaining good vision into late adulthood. The recessive cases were associated with a panretinal dystrophy of cone-rod phenotype with early macular involvement, whereas the dominant variants were associated with a cone-rod phenotype that was restricted to the macula with predominantly cone dysfunction. Next-generation sequencing identified 3 novel and 9 previously reported variants in PROM1. Recessive mutations included 6 truncating variants (3 nonsense and 3 frameshift), 4 splice site variants, and 1 missense variant. All 6 dominant variants were associated with a c.1117C>T missense variant. The variants were distributed throughout the PROM1 genomic sequence with no specific clustering on protein domains.

CONCLUSIONS AND RELEVANCE

In this case-series study, PROM1 recessive variants were associated with early-onset, severe panretinal degeneration. The similar phenotypes observed in patients with homozygous missense variants and splice site variants compared with similarly aged patients with truncating variants suggests that all recessive variants have a null (or loss of function close to null) outcome on PROM1 function. In contrast, the dominant missense cases were associated with a milder, cone-driven phenotype, suggesting that the dominant disease is preferentially associated with cones. This has implications for the development of treatments for this severely blinding disease, and adeno-associated viral vector-based gene therapy and optogenetics could become successful treatment options.

Genetic testing in patients with retinitis pigmentosa: Features of unsolved cases

IMPORTANCE

Uncommon characteristics in genetically unsolved retinitis pigmentosa (RP) patients may indicate an incorrect clinical diagnosis or as yet unknown genetic causes resulting in specific retinal phenotypes. The diagnostic yield of targeted next-generation sequencing may be increased by a reasonable preselection of RP-patients.

BACKGROUND

To systematically evaluate and compare features of genetically solved and unsolved RP-patients.

DESIGN

Retrospective, observational study.

PARTICIPANTS

One-hundred and twelve consecutive RP-patients who underwent extensive molecular genetic analysis.

METHODS

Characterization of patients based on multimodal imaging and medical history.

MAIN OUTCOME MEASURES

Differences between genetically solved and unsolved RP-patients.

RESULTS

Compared to genetically solved patients (n = 77), genetically unsolved patients (n = 35) more frequently had an age of disease-onset above 30 years (60% vs 8%; P < 0.0001), showed atypical fundus features (49% vs 8%; P < 0. 0001) and indicators for phenocopies (eg, autoimmune diseases) (17% vs 0%; P < 0. 001). Evidence for a particular inheritance pattern was less common (20% vs 49%; P < 0. 01). The diagnostic yield was 84% (71/85) in patients with first symptoms below 30 years-of-age, compared to 69% (77/112) in the overall cohort. The other selection criteria alone or in combination resulted in limited further increase of the diagnostic yield (up to 89%) while excluding considerably more patients (up to 56%) from genetic testing.

CONCLUSIONS AND RELEVANCE

The medical history and retinal phenotype differ between genetically solved and a subgroup of unsolved RP-patients, which may reflect undetected genotypes or retinal conditions mimicking RP. Patient stratification may inform on the individual likelihood of identifying disease-causing mutations and may impact patient counselling.

The identification of a RNA splice variant in TULP1 in two siblings with early-onset photoreceptor dystrophy

Background

Early‐onset photoreceptor dystrophies are a major cause of irreversible visual impairment in children and young adults. This clinically heterogeneous group of disorders can be caused by mutations in many genes. Nevertheless, to date, 30%–40% of cases remain genetically unexplained. In view of expanding therapeutic options, it is essential to obtain a molecular diagnosis in these patients as well. In this study, we aimed to identify the genetic cause in two siblings with genetically unexplained retinal disease.

Methods

Whole exome sequencing was performed to identify the causative variants in two siblings in whom a single pathogenic variant in TULP1 was found previously. Patients were clinically evaluated, including assessment of the medical history, slit‐lamp biomicroscopy, and ophthalmoscopy. In addition, a functional analysis of the putative splice variant in TULP1 was performed using a midigene assay.

Results

Clinical assessment showed a typical early‐onset photoreceptor dystrophy in both the patients. Whole exome sequencing identified two pathogenic variants in TULP1, a c.1445G>A (p.(Arg482Gln)) missense mutation and an intronic c.718+23G>A variant. Segregation analysis confirmed that both siblings were compound heterozygous for the TULP1 c.718+23G>A and c.1445G>A variants, while the unaffected parents were heterozygous. The midigene assay for the c.718+23G>A variant confirmed an elongation of exon 7 leading to a frameshift.

Conclusion

Here, we report the first near‐exon RNA splice variant that is not present in a consensus splice site sequence in TULP1, which was found in a compound heterozygous manner with a previously described pathogenic TULP1 variant in two patients with an early‐onset photoreceptor dystrophy. We provide proof of pathogenicity for this splice variant by performing an in vitro midigene splice assay, and highlight the importance of analysis of noncoding regions beyond the noncanonical splice sites in patients with inherited retinal diseases.

Where are the missing gene defects in inherited retinal disorders? Intronic and synonymous variants contribute at least to 4% of CACNA1F-mediated inherited retinal disorders

Inherited retinal disorders (IRD) represent clinically and genetically heterogeneous diseases. To date, pathogenic variants have been identified in ~260 genes. Albeit that many genes are implicated in IRD, for 30-50% of the cases, the gene defect is unknown. These cases may be explained by novel gene defects, by overlooked structural variants, by variants in intronic, promoter or more distant regulatory regions, and represent synonymous variants of known genes contributing to the dysfunction of the respective proteins. Patients with one subgroup of IRD, namely incomplete congenital stationary night blindness (icCSNB), show a very specific phenotype. The major cause of this condition is the presence of a hemizygous pathogenic variant in CACNA1F. A comprehensive study applying direct Sanger sequencing of the gene-coding regions, exome and genome sequencing applied to a large cohort of patients with a clinical diagnosis of icCSNB revealed indeed that seven of the 189 CACNA1F-related cases have intronic and synonymous disease-causing variants leading to missplicing as validated by minigene approaches. These findings highlight that gene-locus sequencing may be a very efficient method in detecting disease-causing variants in clinically well-characterized patients with a diagnosis of IRD, like icCSNB.

Comparison of TCGA and GENIE genomic datasets for the detection of clinically actionable alterations in breast cancer

Whole exome sequencing (WES), targeted gene panel sequencing and single nucleotide polymorphism (SNP) arrays are increasingly used for the identification of actionable alterations that are critical to cancer care. Here, we compared The Cancer Genome Atlas (TCGA) and the Genomics Evidence Neoplasia Information Exchange (GENIE) breast cancer genomic datasets (array and next generation sequencing (NGS) data) in detecting genomic alterations in clinically relevant genes. We performed an in silico analysis to determine the concordance in the frequencies of actionable mutations and copy number alterations/aberrations (CNAs) in the two most common breast cancer histologies, invasive lobular and invasive ductal carcinoma. We found that targeted sequencing identified a larger number of mutational hotspots and clinically significant amplifications that would have been missed by WES and SNP arrays in many actionable genes such as PIK3CA, EGFR, AKT3, FGFR1, ERBB2, ERBB3 and ESR1. The striking differences between the number of mutational hotspots and CNAs generated from these platforms highlight a number of factors that should be considered in the interpretation of array and NGS-based genomic data for precision medicine. Targeted panel sequencing was preferable to WES to define the full spectrum of somatic mutations present in a tumor.

Identification of novel PROM1 mutations responsible for autosomal recessive maculopathy with rod-cone dystrophy

PURPOSE

To characterize two patients with macular and rod-cone dystrophy and identify the genetic basis for disease.

METHOD

Ophthalmic examinations were performed for the family and the peripheral blood samples were collected for whole exome sequencing. The mutated sequences of PROM1 gene were cloned and expressed in cultured cell lines after transient transfection followed by analysis with confocal microscopy and bridge-PCR.

RESULT

We reported that two patients, brothers in a family, were diagnosed with macular and rod-cone dystrophy. Phenotypically, both patients experience progressive visual impairment and nyctalopia. The fundus examination showed macular and choroid dystrophy with pigment deposits in the macular region. Functionally, photoreceptor response to electrophysiological stimulation was significantly compromised with more severe decline in rods. Genetic analysis by whole exome sequencing revealed two novel compound heterogeneous point mutations in PROM1 gene that co-segregate with patients in an autosomal recessive manner. Specifically, the c.C1902G(p.Y634X) nonsense mutation results in a truncated, labile, and mislocalized protein, while the c.C1682+3A>G intronic mutation disrupts messenger RNA splicing.

CONCLUSION

Our findings have identified two novel deleterious mutations in PROM1 gene that are associated with hereditary macular and rod-cone dystrophy in human.

Next-generation sequencing identifies unexpected genotype-phenotype correlations in patients with retinitis pigmentosa

Retinitis pigmentosa (RP) is an inherited degenerative disease causing severe retinal dystrophy and visual impairment mainly with onset in infancy or adolescence. Targeted next-generation sequencing (NGS) has become an efficient tool to encounter the enormous genetic heterogeneity of diverse retinal dystrophies, including RP. To identify disease-causing mutations in unselected, consecutive RP patients, we conducted Sanger sequencing of genes commonly involved in the suspected genetic RP subtype, followed by targeted large-panel NGS if no mutation was identified, or NGS as primary analysis. A high (70%) detection rate of disease-causing mutations was achieved in a large cohort of 116 unrelated patients. About half (48%) of the solved RP cases were explained by mutations in four genes: RPGR, EYS, PRPF31 and USH2A. Overall, 110 different mutations distributed across 30 different genes were detected, and 46 of these mutations were novel. A molecular diagnosis was achieved in the majority (82–100%) of patients if the family history was suggestive for a particular mode of inheritance, but only in 60% in cases of sporadic RP. The diagnostic potential of extensive molecular analysis in a routine setting is also illustrated by the identification of unexpected genotype-phenotype correlations for RP patients with mutations in CRX, CEP290, RPGRIP1, MFSD8. Furthermore, we identified numerous mutations in autosomal dominant (PRPF31, PRPH2, CRX) and X-linked (RPGR) RP genes in patients with sporadic RP. Variants in RP2 and RPGR were also found in female RP patients with apparently sporadic or dominant disease. In summary, this study demonstrates that massively parallel sequencing of all known retinal dystrophy genes is a valuable diagnostic approach for RP patients.

GRIPT: a novel case-control analysis method for Mendelian disease gene discovery

Despite rapid progress of next-generation sequencing (NGS) technologies, the disease-causing genes underpinning about half of all Mendelian diseases remain elusive. One main challenge is the high genetic heterogeneity of Mendelian diseases in which similar phenotypes are caused by different genes and each gene only accounts for a small proportion of the patients. To overcome this gap, we developed a novel method, the Gene Ranking, Identification and Prediction Tool (GRIPT), for performing case-control analysis of NGS data. Analyses of simulated and real datasets show that GRIPT is well-powered for disease gene discovery, especially for diseases with high locus heterogeneity.

Unravelling the pathogenic role and genotype-phenotype correlation of the USH2A p.(Cys759Phe) variant among Spanish families

INTRODUCTION

Mutations in USH2A cause both isolated Retinitis Pigmentosa (RP) and Usher syndrome (that implies RP and hearing impairment). One of the most frequent variants identified in this gene and among these patients is the p.(Cys759Phe) change. However, the pathogenic role of this allele has been questioned since it was found in homozygosity in two healthy siblings of a Spanish family. To assess the causative role of USH2A p.(Cys759Phe) in autosomal recessive RP (ARRP) and Usher syndrome type II (USH2) and to establish possible genotype-phenotype correlations associated with p.(Cys759Phe), we performed a comprehensive genetic and clinical study in patients suffering from any of the two above-mentioned diseases and carrying at least one p.(Cys759Phe) allele.

MATERIALS AND METHODS

Diagnosis was set according to previously reported protocols. Genetic analyses were performed by using classical molecular and Next-Generation Sequencing approaches. Probands of 57 unrelated families were molecularly studied and 63 patients belonging to these families were phenotypically evaluated.

RESULTS

Molecular analysis characterized 100% of the cases, identifying: 11 homozygous patients for USH2A p.(Cys759Phe), 42 compound heterozygous patients (12 of them with another missense USH2A pathogenic variant and 30 with a truncating USH2A variant), and 4 patients carrying the p.(Cys759Phe) allele and a pathogenic variant in another RP gene (PROM1, CNGB1 or RP1). No additional causative variants were identified in symptomatic homozygous patients. Statistical analysis of clinical differences between zygosity states yielded differences (p≤0.05) in age at diagnosis of RP and hypoacusis, and progression of visual field loss. Homozygosity of p.(Cys759Phe) and compound heterozygosity with another USH2A missense variant is associated with ARRP or ARRP plus late onset hypoacusis (OR = 20.62, CI = 95%, p = 0.041).

CONCLUSIONS

The present study supports the role of USH2A p.(Cys759Phe) in ARRP and USH2 pathogenesis, and demonstrates the clinical differences between different zygosity states. Phenotype-genotype correlations may guide the genetic characterization based upon specific clinical signs and may advise on the clinical management and prognosis based upon a specific genotype.

Toward an elucidation of the molecular genetics of inherited retinal degenerations

While individually classed as rare diseases, hereditary retinal degenerations (IRDs) are the major cause of registered visual handicap in the developed world. Given their hereditary nature, some degree of intergenic heterogeneity was expected, with genes segregating in autosomal dominant, recessive, X-linked recessive, and more rarely in digenic or mitochondrial modes. Today, it is recognized that IRDs, as a group, represent one of the most genetically diverse of hereditary conditions - at least 260 genes having been implicated, with 70 genes identified in the most common IRD, retinitis pigmentosa (RP). However, targeted sequencing studies of exons from known IRD genes have resulted in the identification of candidate mutations in only approximately 60% of IRD cases. Given recent advances in the development of gene-based medicines, characterization of IRD patient cohorts for known IRD genes and elucidation of the molecular pathologies of disease in those remaining unresolved cases has become an endeavor of the highest priority. Here, we provide an outline of progress in this area.

REEP6 mediates trafficking of a subset of Clathrin-coated vesicles and is critical for rod photoreceptor function and survival

In retinal photoreceptors, vectorial transport of cargo is critical for transduction of visual signals, and defects in intracellular trafficking can lead to photoreceptor degeneration and vision impairment. Molecular signatures associated with routing of transport vesicles in photoreceptors are poorly understood. We previously reported the identification of a novel rod photoreceptor specific isoform of Receptor Expression Enhancing Protein (REEP) 6, which belongs to a family of proteins involved in intracellular transport of receptors to the plasma membrane. Here we show that loss of REEP6 in mice (Reep6^−/−) results in progressive retinal degeneration. Rod photoreceptor dysfunction is observed in Reep6^−/− mice as early as one month of age and associated with aberrant accumulation of vacuole-like structures at the apical inner segment and reduction in selected rod phototransduction proteins. We demonstrate that REEP6 is detected in a subset of Clathrin-coated vesicles and interacts with the t-SNARE, Syntaxin3. In concordance with the rod degeneration phenotype in Reep6^−/− mice, whole exome sequencing identified homozygous REEP6-E75K mutation in two retinitis pigmentosa families of different ethnicities. Our studies suggest a critical function of REEP6 in trafficking of cargo via a subset of Clathrin-coated vesicles to selected membrane sites in retinal rod photoreceptors.

Leveraging splice-affecting variant predictors and a minigene validation system to identify Mendelian disease-causing variants among exon-captured variants of uncertain significance

The genetic heterogeneity of Mendelian disorders results in a significant proportion of patients that are unable to be assigned a confident molecular diagnosis after conventional exon sequencing and variant interpretation. Here, we evaluated how many patients with an inherited retinal disease (IRD) have variants of uncertain significance (VUS) that are disrupting splicing in a known IRD gene by means other than affecting the canonical dinucleotide splice site. Three in silico splice-affecting variant predictors were leveraged to annotate and prioritize variants for splicing functional validation. An in vitro minigene system was used to assay each variant's effect on splicing. Starting with 745 IRD patients lacking a confident molecular diagnosis, we validated 23 VUS as splicing variants that likely explain disease in 26 patients. Using our results, we optimized in silico score cutoffs to guide future variant interpretation. Variants that alter base pairs other than the canonical GT-AG dinucleotide are often not considered for their potential effect on RNA splicing but in silico tools and a minigene system can be utilized for the prioritization and validation of such splice-disrupting variants. These variants can be overlooked causes of human disease but can be identified using conventional exon sequencing with proper interpretation guidelines.

Next-generation sequencing reveals the mutational landscape of clinically diagnosed Usher syndrome: copy number variations, phenocopies, a predominant target for translational read-through, and PEX26 mutated in Heimler syndrome

Background

Combined retinal degeneration and sensorineural hearing impairment is mostly due to autosomal recessive Usher syndrome (USH1: congenital deafness, early retinitis pigmentosa (RP); USH2: progressive hearing impairment, RP).

Methods

Sanger sequencing and NGS of 112 genes (Usher syndrome, nonsyndromic deafness, overlapping conditions), MLPA, and array‐CGH were conducted in 138 patients clinically diagnosed with Usher syndrome.

Results

A molecular diagnosis was achieved in 97% of both USH1 and USH2 patients, with biallelic mutations in 97% (USH1) and 90% (USH2), respectively. Quantitative readout reliably detected CNVs (confirmed by MLPA or array‐CGH), qualifying targeted NGS as one tool for detecting point mutations and CNVs. CNVs accounted for 10% of identified USH2A alleles, often in trans to seemingly monoallelic point mutations. We demonstrate PTC124‐induced read‐through of the common p.Trp3955* nonsense mutation (13% of detected USH2A alleles), a potential therapy target. Usher gene mutations were found in most patients with atypical Usher syndrome, but the diagnosis was adjusted in case of double homozygosity for mutations in OTOA and NR2E3, genes implicated in isolated deafness and RP. Two patients with additional enamel dysplasia had biallelic PEX26 mutations, for the first time linking this gene to Heimler syndrome.

Conclusion

Targeted NGS not restricted to Usher genes proved beneficial in uncovering conditions mimicking Usher syndrome.

Whole-Exome Sequencing Identifies Biallelic IDH3A Variants as a Cause of Retinitis Pigmentosa Accompanied by Pseudocoloboma

PURPOSE

To identify the genetic cause of and describe the phenotype in 4 families with autosomal recessive retinitis pigmentosa (arRP) that can be associated with pseudocoloboma.

DESIGN

Case series.

PARTICIPANTS

Seven patients from 4 unrelated families with arRP, among whom 3 patients had bilateral early-onset macular pseudocoloboma.

METHODS

We performed homozygosity mapping and whole-exome sequencing in 5 probands and 2 unaffected family members from 4 unrelated families. Subsequently, Sanger sequencing and segregation analysis were performed in additional family members. We reviewed the medical history of individuals carrying IDH3A variants and performed additional ophthalmic examinations, including full-field electroretinography, fundus photography, fundus autofluorescence imaging, and optical coherence tomography.

MAIN OUTCOME MEASURES

IDH3A variants, age at diagnosis, visual acuity, fundus appearance, visual field, and full-field electroretinography, fundus autofluorescence, and optical coherence tomography findings.

RESULTS

We identified 7 different variants in IDH3A in 4 unrelated families, that is, 5 missense, 1 nonsense, and 1 frameshift variant. All participants showed symptoms early in life, ranging from night blindness to decreased visual acuity, and were diagnosed between the ages of 1 and 11 years. Four participants with biallelic IDH3A variants displayed a typical arRP phenotype and 3 participants were diagnosed with arRP and pseudocoloboma of the macula.

CONCLUSIONS

IDH3A variants were identified as a novel cause of typical arRP in some individuals associated with macular pseudocoloboma. We observed both phenotypes in 2 siblings carrying the same compound heterozygous variants, which could be explained by variable disease expression and warrants caution when making assertions about genotype-phenotype correlations.