Phenotypic variability and long-term follow-up of patients with known and novel PRPH2/RDS gene mutations

Risk Factors for Worsening Morphology and Visual Acuity in Eyes with Adult-Onset Foveomacular Vitelliform Dystrophy

PURPOSE

To explore clinical risk factors and OCT features associated with worse visual acuity (VA), progression of disease, choroidal neovascularization (CNV), and atrophy in eyes with adult-onset foveomacular vitelliform dystrophy (AOFVD).

DESIGN

Single-center, retrospective, observational cohort study.

PARTICIPANTS

Patients seen at Duke Eye Center between January 2012 and May 2023 with a diagnosis of AOFVD confirmed via OCT and fundus autofluorescence.

METHODS

Baseline and final-visit images from eyes with AOFVD were examined. Disease stage was assigned, and presence of atrophy or CNV was determined. Clinical and OCT features associated with progression to atrophy and CNV were determined using t tests and chi-square analysis. Correlation with lower VA was determined using linear regression.

MAIN OUTCOME MEASURES

Association of clinical characteristics and OCT features with worse VA, progression of disease, CNV, and atrophy as determined by independent t tests, chi-square analysis, and linear regression (P < 0.05).

RESULTS

One hundred one eyes (63 patients) met inclusion criteria for this study, with mean follow-up duration of 48 months (standard deviation, 31 months). Fifty-one percent of eyes progressed beyond baseline staging during follow-up; among baseline stage 1 eyes, incidence of atrophy was 0.068/person-year; incidence of CNV was 0.022/person-year. Risk factors for worse final VA were baseline presence of vitreomacular traction ([VMT], P = 0.006), ellipsoid zone attenuation (P = 0.02), and increased lesion height and width (P < 0.001). Predictors of progression include diabetes mellitus (P = 0.01), statin use (P = 0.03), presence of hyperreflective foci (P = 0.01), and increased lesion width and volume (P = 0.03 and P = 0.04, respectively). Predictors of atrophy include the baseline presence of VMT (P = 0.02), decreased choroidal thickness (P = 0.03), and greater maximal height, width, and volume of the lesion (P = 0.03, P = 0.02, and P = 0.009, respectively). Lower baseline VA (P = 0.03) and increased lesion volume (P = 0.04) were associated with CNV.

CONCLUSIONS

Clinical and OCT imaging features at baseline may prove useful in stratifying patient risk for progression, atrophy, CNV, and worse VA. Features such as statin use, diabetes, baseline VA, and laterality should be accounted for. OCT features, such as lesion size, VMT, ellipsoid zone attenuation, choroidal thickness, and hyperreflective foci, may impart greater risk of poor outcomes. Future prospective analysis accounting for the time to development of atrophy and CNV is needed.

FINANCIAL DISCLOSURES

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Comparative analysis of in-silico tools in identifying pathogenic variants in dominant inherited retinal diseases

Inherited retinal diseases (IRDs) are a group of rare genetic eye conditions that cause blindness. Despite progress in identifying genes associated with IRDs, improvements are necessary for classifying rare autosomal dominant (AD) disorders. AD diseases are highly heterogenous, with causal variants being restricted to specific amino acid changes within certain protein domains, making AD conditions difficult to classify. Here, we aim to determine the top-performing in-silico tools for predicting the pathogenicity of AD IRD variants. We annotated variants from ClinVar and benchmarked 39 variant classifier tools on IRD genes, split by inheritance pattern. Using area-under-the-curve (AUC) analysis, we determined the top-performing tools and defined thresholds for variant pathogenicity. Top-performing tools were assessed using genome sequencing on a cohort of participants with IRDs of unknown etiology. MutScore achieved the highest accuracy within AD genes, yielding an AUC of 0.969. When filtering for AD gain-of-function and dominant negative variants, BayesDel had the highest accuracy with an AUC of 0.997. Five participants with variants in NR2E3, RHO, GUCA1A, and GUCY2D were confirmed to have dominantly inherited disease based on pedigree, phenotype, and segregation analysis. We identified two uncharacterized variants in GUCA1A (c.428T>A, p.Ile143Thr) and RHO (c.631C>G, p.His211Asp) in three participants. Our findings support using a multi-classifier approach comprised of new missense classifier tools to identify pathogenic variants in participants with AD IRDs. Our results provide a foundation for improved genetic diagnosis for people with IRDs.

Phenotyping and genotyping inherited retinal diseases: Molecular genetics, clinical and imaging features, and therapeutics of macular dystrophies, cone and cone-rod dystrophies, rod-cone dystrophies, Leber congenital amaurosis, and cone dysfunction syndromes

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population and in children. The scope of this review is to familiarise clinicians and scientists with the current landscape of molecular genetics, clinical phenotype, retinal imaging and therapeutic prospects/completed trials in IRD. Herein we present in a comprehensive and concise manner: (i) macular dystrophies (Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), PRPH2-associated pattern dystrophy, Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)), (ii) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4, KCNV2 and RPGR), (iii) predominant rod or rod-cone dystrophies (retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)), (iv) Leber congenital amaurosis/early-onset severe retinal dystrophy (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (v) cone dysfunction syndromes (achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6), X-linked cone dysfunction with myopia and dichromacy (Bornholm Eye disease; OPN1LW/OPN1MW array), oligocone trichromacy, and blue-cone monochromatism (OPN1LW/OPN1MW array)). Whilst we use the aforementioned classical phenotypic groupings, a key feature of IRD is that it is characterised by tremendous heterogeneity and variable expressivity, with several of the above genes associated with a range of phenotypes.

PRPH2-Related Retinal Dystrophies: Mutational Spectrum in 103 Families from a Spanish Cohort

PRPH2, one of the most frequently inherited retinal dystrophy (IRD)-causing genes, implies a high phenotypic variability. This study aims to analyze the PRPH2 mutational spectrum in one of the largest cohorts worldwide, and to describe novel pathogenic variants and genotype-phenotype correlations. A study of 220 patients from 103 families recruited from a database of 5000 families. A molecular diagnosis was performed using classical molecular approaches and next-generation sequencing. Common haplotypes were ascertained by analyzing single-nucleotide polymorphisms. We identified 56 variants, including 11 novel variants. Most of them were missense variants (64%) and were located in the D2-loop protein domain (77%). The most frequently occurring variants were p.Gly167Ser, p.Gly208Asp and p.Pro221_Cys222del. Haplotype analysis revealed a shared region in families carrying p.Leu41Pro or p.Pro221_Cys222del. Patients with retinitis pigmentosa presented an earlier disease onset. We describe the largest cohort of IRD families associated with PRPH2 from a single center. Most variants were located in the D2-loop domain, highlighting its importance in interacting with other proteins. Our work suggests a likely founder effect for the variants p.Leu41Pro and p.Pro221_Cys222del in our Spanish cohort. Phenotypes with a primary rod alteration presented more severe affectation. Finally, the high phenotypic variability in PRPH2 hinders the possibility of drawing genotype-phenotype correlations.

Phenotypic and genotypic features of POC1B-associated cone dystrophy

PURPOSE

Patients with cone dystrophy (CD) can present with virtually normal retinal appearance, which may delay diagnosis. This study describes the inconspicuous clinical features of POC1B-associated CD in two Saudi families.

METHODS

This is a retrospective case study. Clinical data analyzed included multimodal retinal imaging and electroretinography of the affected individuals. Genetic analysis was done for all probands.

RESULTS

Three affected males from two Saudi families with POC1B-associated CD were included. The ages at presentation ranged from 18 to 34 years. Ophthalmic examination showed decreased Snellen visual acuities (range: 20/100-20/300) and color vision bilaterally. Fundus examination showed only mild vascular attenuation. Macular optical coherence tomography showed reduced reflectivity of the external limiting membrane, ellipsoid, and interdigitation zones. Full-field electroretinography demonstrated undetectable light-adapted responses and normal dark-adapted responses in all patients. Next-generation sequencing showed one proband to be homozygous for a previously unpublished nonsense variant in POC1B (NM_172240):c.672C>G; p(Tyr224*). Whole exome sequencing for the second proband showed a novel homozygous frameshifting variant in POC1B: c.991del; p(Arg331Glufs*13).

CONCLUSION

We described two novel variants in POC1B and the associated subtle, yet significant retinal features. POC1B-associated CD is a rare cause of visual loss in patients with relatively normal fundus appearance. Deep phenotyping is necessary in formulating appropriate differential diagnosis.

Adult-onset foveomacular vitelliform dystrophy: epidemiology, pathophysiology, imaging, and prognosis

Adult-onset foveomacular dystrophy (AOFVD) is a retinal pattern dystrophy that may affect up to 1 in 7,400 individuals. There is much that is unknown regarding this disease's epidemiology, risk factors for development, and rate of progression through its four stages. Advancements in retinal imaging over the past 15 years have enabled improved characterization of the different stages of AOFVD. These imaging advancements also offer new ways of differentiating AOFVD from phenotypically similar retinal diseases like age-related macular degeneration and Best disease. This review synthesizes the most recent discoveries regarding imaging correlates within AOFVD as well as risk factors for the development of AOFVD, complications of AOFVD, and treatment options. Our aim is to provide ophthalmologists a succinct resource so that they may offer clarity, guidance, and appropriate monitoring and treatments for their patients with suspected AOFVD.

Comparative study of PRPH2 D2 loop mutants reveals divergent disease mechanism in rods and cones

Mutations in the photoreceptor-specific tetraspanin gene peripherin-2 (PRPH2) lead to widely varying forms of retinal degeneration ranging from retinitis pigmentosa to macular dystrophy. Both inter- and intra-familial phenotypic heterogeneity has led to much interest in uncovering the complex pathogenic mechanisms of PRPH2-associated disease. Majority of disease-causing mutations in PRPH2 reside in the second intradiscal loop, wherein seven cysteines control protein folding and oligomerization. Here, we utilize knockin models to evaluate the role of three D2 loop cysteine mutants (Y141C, C213Y and C150S), alone or in combination. We elucidated how these mutations affect PRPH2 properties, including oligomerization and subcellular localization, and contribute to disease processes. Results from our structural, functional and molecular studies revealed that, in contrast to our understanding from prior investigations, rods are highly affected by PRPH2 mutations interfering with oligomerization and not merely by the haploinsufficiency associated with these mutations. On the other hand, cones are less affected by the toxicity of the mutant protein and significantly reduced protein levels, suggesting that knockdown therapeutic strategies may sustain cone functionality for a longer period. This observation provides useful data to guide and simplify the current development of effective therapeutic approaches for PRPH2-associated diseases that combine knockdown with high levels of gene supplementation needed to generate prolonged rod improvement.

How to Set Up Genetic Counselling for Inherited Macular Dystrophies: Focus on Genetic Characterization

Inherited macular dystrophies refer to a group of degenerative conditions that predominantly affect the macula in the spectrum of inherited retinal dystrophies. Recent trends indicate a clear need for genetic assessment services in tertiary referral hospitals. However, establishing such a service can be a complex task due to the diverse skills required and multiple professionals involved. This review aims to provide comprehensive guidelines to enhance the genetic characterization of patients and improve counselling efficacy by combining updated literature with our own experiences. Through this review, we hope to contribute to the establishment of state-of-the-art genetic counselling services for inherited macular dystrophies.

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.

Genetic Diagnosis for 64 Patients with Inherited Retinal Disease

The overlapping genetic and clinical spectrum in inherited retinal degeneration (IRD) creates challenges for accurate diagnoses. The goal of this work was to determine the genetic diagnosis and clinical features for patients diagnosed with an IRD. After signing informed consent, peripheral blood or saliva was collected from 64 patients diagnosed with an IRD. Genetic testing was performed on each patient in a Clinical Laboratory Improvement Amendments of 1988 (CLIA) certified laboratory. Mutations were verified with Sanger sequencing and segregation analysis when possible. Visual acuity was measured with a traditional Snellen chart and converted to a logarithm of minimal angle of resolution (logMAR). Fundus images of dilated eyes were acquired with the Optos® camera (Dunfermline, UK). Horizontal line scans were obtained with spectral-domain optical coherence tomography (SDOCT; Spectralis, Heidelberg, Germany). Genetic testing combined with segregation analysis resolved molecular and clinical diagnoses for 75% of patients. Ten novel mutations were found and unique genotype phenotype associations were made for the genes RP2 and CEP83. Collective knowledge is thereby expanded of the genetic basis and phenotypic correlation in IRD.

PRPH2-Associated Retinopathy: Novel Variants and Genotype-Phenotype Correlations

PURPOSE

A broad spectrum of autosomal-dominant inherited retinal diseases (IRDs), ranging from mild macular pattern dystrophy to severe cone-rod degeneration, is associated with PRPH2 variants (peripherinopathies). We present detailed clinical and molecular characterization of patients affected by peripherinopathies, aiming to expand the mutational spectrum, and propose novel genotype-phenotype correlations.

DESIGN

Observational, retrospective case series.

PARTICIPANTS

Patients with an IRD related to a molecularly proven PRPH2 variant.

METHODS

Data from ophthalmic examinations and retinal imaging were collected for each follow-up visit. The standard imaging protocol included OCT, blue-light autofluorescence, near-infrared autofluorescence, and ultra-widefield fundus imaging. Genetic analysis was performed with a genomic approach by next-generation sequencing.

MAIN OUTCOME MEASURES

Results of ophthalmic examination, retinal imaging, and molecular genetic analysis.

RESULTS

Overall, a total of 19 patients with an IRD and a (likely) pathogenic PRPH2 variant were identified. Their age at presentation had a median of 48 years, whereas the symptomatic disease onset was in their 30s or 40s in 74% of cases. The median follow-up time was 4 years. Clinically, 6 patients were diagnosed with cone-rod dystrophy and 13 with pattern dystrophy. Among the 13 PRPH2 pathogenic variants identified in our cohort, 7 were missense, 3 nonsense, 2 frame shifting, and 1 splice site. Missense variants in the D2 loop were associated with cone-rod dystrophies and poor visual prognosis, whereas predicted loss-of-function alleles with pattern dystrophies and retention of a good visual function into adulthood. Overall, the following 7 variants were novel and never associated to a clinical phenotype: c.68delT, c.290G>A, c.413T>G, c.642C>G, c.702_706dupCAGTT, c.771_772delinsGA, and c.850C>G.

CONCLUSIONS

Here, we report the findings of a retrospective case series that provided a detailed clinical and molecular characterization of 19 patients harboring 13 different PRPH2 pathogenic variants, 7 of which were previously unreported, expanding the mutational spectrum of the PRPH2 gene. Loss-of-function variants might be preferentially associated with mild-pattern dystrophies, whereas missense dominant-negative variants might be preferentially associated with severely blinding cone-rod degenerations. Further studies are needed to better define the pathogenetic mechanisms and the functional effects of most variants to allow the development of successful gene therapy.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Application of multicolour reflectance imaging for the characterisation of inherited retinal disorders

AIM

To describe the role of multicolour reflectance images (MCI) in the phenotypic diagnosis of inherited retinal disorders (IRDs).

METHODS

A retrospective review of consecutive patients affected by IRDs examined with MCI techniques from January to December 2019 at a tertiary care referral centre. All patients had MCI, fundus autofluorescence and optical coherence tomography taken at the same time point. The ability of each modality to highlight clinical features was assessed. Lesions' size was also measured and compared among imaging modalities.

RESULTS

Thirty eyes of 15 patients were included in the study, 6 males and 9 females, with a mean age of 44 years (range: 19-57.5). The most frequent clinical diagnosis were: pattern dystrophies, and late-onset retinal degeneration. Next-generation or Sanger sequencing analysis was carried out in all patients. Blue and green reflectance were relevant in highlighting peripheral mottling in fundus albipunctatus, pseudoreticular drusen in late-onset retinal degeneration, parafoveal hyperreflective area in bull's eye maculopathy and crystals in Bietti's crystalline dystrophy. Likewise, it is to mention the ability of infrared reflectance to detect hyperreflective patches in posterior pole in neurofibromatosis type 1 and retinal changes in pattern dystrophies and cone dystrophies.

CONCLUSION

Multicolour imaging technique enables the detection of clinical features that could be overlooked by other imaging modalities, allowing accurate phenotypic characterisation of IRDs and guiding genetic diagnose, and may become a meaningful monitoring tool for future treatments.

New Insights on the Regulatory Gene Network Disturbed in Central Areolar Choroidal Dystrophy-Beyond Classical Gene Candidates

Central areolar choroidal dystrophy (CACD) is a rare hereditary disease that mainly affects the macula, resulting in progressive and usually profound visual loss. Being part of congenital retinal dystrophies, it may have an autosomal dominant or recessive inheritance and, until now, has no effective treatment. Given the shortage of genotypic information about the disease, this work systematically reviews the literature for CACD-causing genes. Three independent researchers selected 33 articles after carefully searching and filtering the Scielo, Pubmed, Lilacs, Web of Science, Scopus, and Embase databases. Mutations of six genes (PRPH2, GUCA1A, GUCY2D, CDHR1, ABCA4, and TTLL5) are implicated in the monogenic dominant inheritance of CACD. They are functionally related to photoreceptors (either in the phototransduction process, as in the case of GUCY2D, or the recovery of retinal photodegradation in photoreceptors for GUCA1A, or the formation and maintenance of specific structures within photoreceptors for PRPH2). The identified genetic variants do not explain all observed clinical features, calling for further whole-genome and functional studies for this disease. A network analysis with the CACD-related genes identified in the systematic review resulted in the identification of another 20 genes that may influence CACD onset and symptoms. Furthermore, an enrichment analysis allowed the identification of 13 transcription factors and 4 long noncoding RNAs interacting with the products of the previously mentioned genes. If mutated or dysregulated, they may be directly involved in CACD development and related disorders. More than half of the genes identified by bioinformatic tools do not appear in commercial gene panels, calling for more studies about their role in the maintenance of the retina and phototransduction process, as well as for a timely update of these gene panels.

PRPH2-Associated Macular Dystrophy in 4 Family Members with a Novel Mutation

Peripherin-2 (PRPH2) gene variants are a well-established cause of multiple inherited maculopathies including central areolar choroidal dystrophy (CACD) and pattern dystrophy. In this familial case study, we present a 63-year-old proband who presented with visual acuity of 20/63 right eye and 20/100 left eye with a complaint of lowered visual acuity in the left eye for unknown duration. Fundus examination presented with unifocal atrophic lesions bilaterally. Multi-modal imaging was obtained and genetic testing (My Retina Tracker; Blueprint Genetics) was performed. The proband was monoallelic for a novel missense mutation within the PRPH2 gene (Arg203Pro) not previously found in the literature or large databases (gnomAD, ClinVar, and HGMD). Subsequent examination of the proband's mother, older sister (65 years old), younger sister (53), and daughter (35) found the novel mutation to segregate with maculopathy ranging from speckled fundus autofluorescence with EZ disruption and RPE attenuation on spectral domain optical coherence tomography to large unifocal atrophic lesions throughout the macula bilaterally. The purpose of this case report is to add to the literature of PRPH2-associated disease by providing a comprehensive fundus examination of a family with autosomal dominant PRPH2-associated maculopathy diagnosed as central areolar choroidal dystrophy and pattern dystrophy.

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.

Impairments of Photoreceptor Outer Segments Renewal and Phototransduction Due to a Peripherin Rare Haplotype Variant: Insights from Molecular Modeling

BACKGROUND

Retinitis pigmentosa punctata albescens (RPA) is a particular form of retinitis pigmentosa characterized by childhood onset night blindness and areas of peripheral retinal atrophy. We investigated the genetic cause of RPA in a family consisting of two affected Egyptian brothers with healthy consanguineous parents.

METHODS

Mutational analysis of four RPA causative genes was realized by Sanger sequencing on both probands, and detected variants were subsequently genotyped in their parents. Afterwards, found variants were deeply, statistically, and in silico characterized to determine their possible effects and association with RPA.

RESULTS

Both brothers carry three missense PRPH2 variants in a homozygous condition (c.910C > A, c.929G > A, and c.1013A > C) and two promoter variants in RHO (c.-26A > G) and RLBP1 (c.-70G > A) genes, respectively. Haplotype analyses highlighted a PRPH2 rare haplotype variant (GAG), determining a possible alteration of PRPH2 binding with melanoregulin and other outer segment proteins, followed by photoreceptor outer segment instability. Furthermore, an altered balance of transcription factor binding sites, due to the presence of RHO and RLBP1 promoter variants, might determine a comprehensive downregulation of both genes, possibly altering the PRPH2 shared visual-related pathway.

CONCLUSIONS

Despite several limitations, the study might be a relevant step towards detection of novel scenarios in RPA etiopathogenesis.

Imaging in inherited retinal disorders

Inherited retinal diseases, which results from mutations in over 260 identified genes, affect more than 2 million people globally. The diseases mostly cause severe vision loss in young working population and have severe impact on social economic status of the population. Advances in retinal imaging techniques along with developments in gene identification and cell biology techniques have yielded to a better understanding of the genetic and biochemical mechanisms causing these diseases. Retinal imaging along with through ophthalmological examination is essential to make an accurate diagnosis, to decrease the burden of unneccessary anciliary tests and to select the potential patients that can get benefit from the gene treatment. The purpose of the review is to yield an update on inherited retinal diseases by highlighting microstructural changes in retina and to summarize the retinal changes detected by currently available multimodal imaging techniques.

Retinal imaging in inherited retinal diseases

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population. The advances in ocular genetics, retinal imaging and molecular biology, have conspired to create the ideal environment for establishing treatments for IRD, with the first approved gene therapy and the commencement of multiple therapy trials. The scope of this review is to familiarize clinicians and scientists with the current landscape of retinal imaging in IRD. Herein we present in a comprehensive and concise manner the imaging findings of: (I) macular dystrophies (MD) [Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), pattern dystrophy (PRPH2), Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)], (II) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4 and RPGR), (III) cone dysfunction syndromes [achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6], blue-cone monochromatism (OPN1LW/OPN1MW array), oligocone trichromacy, bradyopsia (RGS9/R9AP) and Bornholm eye disease (OPN1LW/OPN1MW), (IV) Leber congenital amaurosis (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (V) rod-cone dystrophies [retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)], (VI) rod dysfunction syndromes (congenital stationary night blindness, fundus albipunctatus (RDH5), Oguchi disease (SAG, GRK1), and (VII) chorioretinal dystrophies [choroideremia (CHM), gyrate atrophy (OAT)].

Development of a Genotype Assay for Age-Related Macular Degeneration: The EYE-RISK Consortium

PURPOSE

To develop a genotype assay to assess associations with common and rare age-related macular degeneration (AMD) risk variants, to calculate an overall genetic risk score (GRS), and to identify potential misdiagnoses with inherited macular dystrophies that mimic AMD.

DESIGN

Case-control study.

PARTICIPANTS

Individuals (n = 4740) from 5 European cohorts.

METHODS

We designed single-molecule molecular inversion probes for target selection and used next generation sequencing to sequence 87 single nucleotide polymorphisms (SNPs), coding and splice-site regions of 10 AMD-(related) genes (ARMS2, C3, C9, CD46, CFB, CFH, CFI, HTRA1, TIMP3, and SLC16A8), and 3 genes that cause inherited macular dystrophies (ABCA4, CTNNA1, and PRPH2). Genetic risk scores for common AMD risk variants were calculated based on effect size and genotype of 52 AMD-associated variants. Frequency of rare variants was compared between late AMD patients and control individuals with logistic regression analysis.

MAIN OUTCOME MEASURES

Genetic risk score, association of genetic variants with AMD, and genotype-phenotype correlations.

RESULTS

We observed high concordance rates between our platform and other genotyping platforms for the 69 successfully genotyped SNPs (>96%) and for the rare variants (>99%). We observed a higher GRS for patients with late AMD compared with patients with early/intermediate AMD (P < 0.001) and individuals without AMD (P < 0.001). A higher proportion of pathogenic variants in the CFH (odds ratio [OR] = 2.88; P = 0.006), CFI (OR = 4.45; P = 0.005), and C3 (OR = 6.56; P = 0.0003) genes was observed in late AMD patients compared with control individuals. In 9 patients, we identified pathogenic variants in the PRPH2, ABCA4, and CTNNA1 genes, which allowed reclassification of these patients as having inherited macular dystrophy.

CONCLUSIONS

This study reports a genotype assay for common and rare AMD genetic variants, which can identify individuals at intermediate to high genetic risk of late AMD and enables differential diagnosis of AMD-mimicking dystrophies. Our study supports sequencing of CFH, CFI, and C3 genes because they harbor rare high-risk variants. Carriers of these variants could be amendable for new treatments for AMD that currently are under development.

Phenotypical Characteristics of POC1B-Associated Retinopathy in Japanese Cohort: Cone Dystrophy With Normal Funduscopic Appearance

Purpose

Cone/cone-rod dystrophy is a large group of retinal disorders with both phonotypic and genetic heterogeneity. The purpose of this study was to characterize the phenotype of eight patients from seven families harboring POC1B mutations in a cohort of the Japan Eye Genetics Consortium (JEGC).

Methods

Whole-exome sequencing with targeted analyses identified homozygous or compound heterozygous mutations of the POC1B gene in 7 of 548 families in the JEGC database. Ophthalmologic examinations including the best-corrected visual acuity, perimetry, fundus photography, fundus autofluorescence imaging, optical coherence tomography, and full-field and multifocal electroretinography (ERGs) were performed.

Results

There were four men and four women whose median age at the onset of symptoms was 15.6 years (range, 6-23 years) and that at the time of examination was 40.3 years (range, 22-67 years). The best-corrected visual acuity ranged from -0.08 to 1.52 logMAR units. The funduscopic appearance was normal in all the cases except in one case with faint mottling in the fovea. Optical coherence tomography revealed an absence of the interdigitation zone and blurred ellipsoid zone in the posterior pole, but the foveal structures were preserved in three cases. The full-field photopic ERGs were reduced or extinguished with normal scotopic responses. The central responses of the multifocal ERGs were preserved in two cases. The diagnosis was either generalized cone dystrophy in five cases or cone dystrophy with foveal sparing in three cases.

Conclusions

Generalized or peripheral cone dystrophy with normal funduscopic appearance is the representative phenotype of POC1B-associated retinopathy in our cohort.

Macular dystrophies: clinical and imaging features, molecular genetics and therapeutic options

Macular dystrophies (MDs) consist of a heterogeneous group of disorders that are characterised by bilateral symmetrical central visual loss. Advances in genetic testing over the last decade have led to improved knowledge of the underlying molecular basis. The developments in high-resolution multimodal retinal imaging have also transformed our ability to make accurate and more timely diagnoses and more sensitive quantitative assessment of disease progression, and allowed the design of optimised clinical trial endpoints for novel therapeutic interventions. The aim of this review was to provide an update on MDs, including Stargardt disease, Best disease, X-linked r etinoschisis, pattern dystrophy, Sorsby fundus dystrophy and autosomal dominant drusen. It highlights the range of innovations in retinal imaging, genotype-phenotype and structure-function associations, animal models of disease and the multiple treatment strategies that are currently in clinical trial or planned in the near future, which are anticipated to lead to significant changes in the management of patients with MDs.

PRPH2 mutation as the cause of various clinical manifestations in a family affected with inherited retinal dystrophy

Background/Objectives: To reveal the underlying genetic defect in a complex family affected with different clinical features of inherited retinal dystrophy, we carried out whole exome sequencing followed by confirmatory molecular tests.Materials and Methods: Complete ophthalmic examinations were performed for available affected family members. Whole exome sequencing, bioinformatics analysis, Sanger sequencing confirmation, and segregation analysis were done to identify the causative mutation.Results: Clinical findings suggested fundus flavimaculatus as an early clinical feature progressing to an extensive chorioretinal atrophy involving the macula and mid-periphery of the fundus in one parent and central areolar chorioretinal dystrophy (CACD) as the most probable clinical diagnosis in another parent. Macular pattern dystrophy for one of their daughters and a Leber congenital amaurosis (LCA) like phenotype for the daughter with an early onset retinal dystrophy (EORD) phenotype was suggested. We found a known pathogenic nonsense variation in the PRPH2 gene (NM_000322: p.Gln239Ter). The parents with end stage fundus flavimaculatus and CACD diagnosis and their daughter with macular pattern dystrophy were heterozygous for the identified variant. The daughter affected with EORD/LCA like retinal dystrophy was homozygous for the same variation.Conclusions: In this family, the same pathogenic variant in PRPH2 gene showed a wide range of clinical features of extensive chorioretinal macular atrophy with flecks as fundus falvimaculatus to CACD and macular pattern dystrophy in the heterozygous inheritance pattern and early onset/LCA like retinal dystrophy in the patient who was homozygous for the causative variant.

Phenotype Analysis of Retinal Dystrophies in Light of the Underlying Genetic Defects: Application to Cone and Cone-Rod Dystrophies

Phenotypes observed in a large cohort of patients with cone and cone-rod dystrophies (COD/CORDs) are described based on multimodal retinal imaging features in order to help in analyzing massive next-generation sequencing data. Structural abnormalities of 58 subjects with molecular diagnosis of COD/CORDs were analyzed through specific retinal imaging including spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (BAF/IRAF). Findings were analyzed with the underlying genetic defects. A ring of increased autofluorescence was mainly observed in patients with CRX and GUCY2D mutations (33% and 22% of cases respectively). “Speckled” autofluorescence was observed with mutations in three different genes (ABCA4 64%; C2Orf71 and PRPH2, 18% each). Peripapillary sparing was only found in association with mutations in ABCA4, although only present in 40% of such genotypes. Regarding SD-OCT, specific outer retinal abnormalities were more commonly observed in particular genotypes: focal retrofoveal interruption and GUCY2D mutations (50%), foveal sparing and CRX mutations (50%), and outer retinal atrophy associated with hyperreflective dots and ABCA4 mutations (69%). This study outlines the phenotypic heterogeneity of COD/CORDs hampering statistical correlations. A larger study correlating retinal imaging with genetic results is necessary to identify specific clinical features that may help in selecting pathogenic variants generated by high-throughput sequencing.

Lessons learned from quantitative fundus autofluorescence

Quantitative fundus autofluorescence (qAF) is an approach that is built on a confocal scanning laser platform and used to measure the intensity of the inherent autofluorescence of retina elicited by short-wavelength (488 nm) excitation. Being non-invasive, qAF does not interrupt tissue architecture, thus allowing for structural correlations. The spectral features, cellular origin and topographic distribution of the natural autofluorescence of the fundus indicate that it is emitted from retinaldehyde-adducts that form in photoreceptor cells and accumulate, under most conditions, in retinal pigment epithelial cells. The distributions and intensities of fundus autofluorescence deviate from normal in many retinal disorders and it is widely recognized that these changing patterns can aid in the diagnosis and monitoring of retinal disease. The standardized protocol employed by qAF involves the normalization of fundus grey levels to a fluorescent reference installed in the imaging instrument. Together with corrections for magnification and anterior media absorption, this approach facilitates comparisons with serial images and images acquired within groups of patients. Here we provide a comprehensive summary of the principles and practice of qAF and we highlight recent efforts to elucidate retinal disease processes by combining qAF with multi-modal imaging.

Deep Scleral Exposure: A Degenerative Outcome of End-Stage Stargardt Disease

PURPOSE

To describe a distinct phenotypic outcome of outer retinal degeneration in a cohort of genetically confirmed patients with recessive Stargardt disease (STGD1).

DESIGN

Retrospective case series.

METHODS

Twelve patients, who were clinically diagnosed with STGD1 and exhibited a unique degenerative phenotype, were included in the study. Two disease-causing mutations were found in all patients by direct sequencing of the ABCA4 gene. Clinical characterization of patients were defined on fundus photographs, autofluorescence images (488-nm and 532-nm excitation), spectral-domain optical coherence tomography (SD-OCT), and full-field electroretinogram (ffERG) testing.

RESULTS

Mean age at initial presentation was 67.8 years and reported age of symptomatic onset was 14.1 years (mean disease duration = 53.8 years). Best-corrected visual acuity ranged from 20/400 to hand motion. All patients exhibited advanced degeneration across the posterior pole resulting in a reflectively pale, blonde fundus owing to unobstructed exposure of the underlying sclera. SD-OCT revealed complete loss of the outer retinal bands (external limiting membrane, ellipsoid zone, interdigitation zone, and retinal pigment epithelium) and choroidal layers. Scotopic and photopic waveforms on ffERG were nonrecordable or severely attenuated in 8 patients who were tested.

CONCLUSIONS

Widespread scleral exposure is a clinical outcome in a subset of STGD1 following a long duration of disease progression (∼50 years). The blonde fundus in such cases may exhibit phenotypic overlap and shared therapeutic implications with other aggressive chorioretinal dystrophies such as end-stage choroideremia, gyrate atrophy, or RPE65-Leber congenital amaurosis.

LRRTM4-C538Y novel gene mutation is associated with hereditary macular degeneration with novel dysfunction of ON-type bipolar cells

The macula is a unique structure in higher primates, where cone and rod photoreceptors show highest density in the fovea and the surrounding area, respectively. The hereditary macular dystrophies represent a heterozygous group of rare disorders characterized by central visual loss and atrophy of the macula and surrounding retina. Here we report an atypical absence of ON-type bipolar cell response in a Japanese patient with autosomal dominant macular dystrophy (adMD). To identify a causal genetic mutation for the adMD, we performed whole-exome sequencing (WES) on four affected and four-non affected members of the family for three generations, and identified a novel p.C538Y mutation in a post-synaptic gene, LRRTM4. WES analysis revealed seven rare genetic variations in patients. We further referred to our in-house WES data from 1360 families with inherited retinal diseases, and found that only p.C538Y mutation in LRRTM4 was associated with adMD-affected patients. Combinatorial filtration using public database of single-nucleotide polymorphism frequency and genotype-phenotype annotated database identified novel mutation in atypical adMD.

Temporal progression of PARP activity in the Prph2 mutant rd2 mouse: Neuroprotective effects of the PARP inhibitor PJ34

Peripherin (peripherin/rds) is a membrane-associated protein that plays a critical role in the morphogenesis of rod and cone photoreceptor outer segments. Mutations in the corresponding PRPH2 gene cause different types of retinal dystrophies characterized by a loss of photoreceptors. Over activation of poly-ADP-ribose polymerase (PARP) was previously shown to be involved in different animal models for hereditary retinal dystrophies. This includes the rd2 mouse, which suffers from a human homologous mutation in the PRPH2 gene. In the present study, we show that increased retinal PARP activity and poly-ADP-ribosylation of proteins occurs before the peak of rd2 photoreceptor degeneration. Inhibition of PARP activity with the well-characterized PARP inhibitor PJ34 decreased the levels of poly-ADP-ribosylation and photoreceptor cell death. These results suggest a causal involvement of PARP in photoreceptor degeneration caused by peripherin mutations and highlight the possibility to use PARP inhibition for the mutation-independent treatment of hereditary retinal dystrophies.

A Report on Molecular Diagnostic Testing for Inherited Retinal Dystrophies by Targeted Genetic Analyses

AIM

To test the utility of targeted sequencing as a method of clinical molecular testing in patients diagnosed with inherited retinal degeneration (IRD).

METHODS

After genetic counseling, peripheral blood was drawn from 188 probands and 36 carriers of IRD. Single gene testing was performed on each patient in a Clinical Laboratory Improvement Amendment (CLIA) certified laboratory. DNA was isolated, and all exons in the gene of interest were analyzed along with 20 base pairs of flanking intronic sequence. Genetic testing was most often performed on ABCA4, CTRP5, ELOV4, BEST1, CRB1, and PRPH2. Pathogenicity of novel sequence changes was predicted by PolyPhen2 and sorting intolerant from tolerant (SIFT).

RESULTS

Of the 225 genetic tests performed, 150 were for recessive IRD, and 75 were for dominant IRD. A positive molecular diagnosis was made in 70 (59%) of probands with recessive IRD and 19 (26%) probands with dominant IRD. Analysis confirmed 12 (34%) of individuals as carriers of familial mutations associated with IRD. Thirty-two novel variants were identified; among these, 17 sequence changes in four genes were predicted to be possibly or probably damaging including: ABCA4 (14), BEST1 (2), PRPH2 (1), and TIMP3 (1).

CONCLUSIONS

Targeted analysis of clinically suspected genes in 225 subjects resulted in a positive molecular diagnosis in 26% of patients with dominant IRD and 59% of patients with recessive IRD. Novel damaging mutations were identified in four genes. Single gene screening is not an ideal method for diagnostic testing given the phenotypic and genetic heterogeneity among IRD cases. High-throughput sequencing of all genes associated with retinal degeneration may be more efficient for molecular diagnosis.

Inner segment ellipsoid band length is a prognostic factor in retinitis pigmentosa associated with EYS mutations: 5-year observation of retinal structure

PurposeTo evaluate whether the length of the inner segment ellipsoid (ISe) band can be used as a prognostic factor for disease course in retinitis pigmentosa (RP) patients with EYS mutations by observation over a period of 5 years.MethodsTwelve RP patients with EYS mutations were studied. The horizontal and vertical ISe length of the right eye was manually measured at five time points annually, using spectral domain optical coherence tomography. A regression line through the five points from baseline to the final measurement was drawn and the ratio of the length (%) at each point to the baseline length was calculated; the slope was defined as the rate of ISe shortening (%/year). The correlation between the rate of ISe shortening and age, visual acuity, and mean deviation (MD) value were evaluated. The intraclass correlation coefficient (ICC) for the measurements was calculated.ResultsThe mean rate of ISe shortening was -4.65±2.89% per year and the decline was statistically significant. The rate of shortening was significantly negatively correlated with the baseline length (P=0.046, r=0.58), but not with the baseline age, visual acuity, and MD value. The ICC (2, 1) was 0.999.ConclusionsISe of all RP patients with EYS mutations shortened during the 5 years of annual observation. The measurement of the length of ISe is a simple and convenient method with high repeatability, and the length is a sensitive prognostic factor for the rate of ISe shortening in RP patients with EYS mutations.

Isolated and Syndromic Retinal Dystrophy Caused by Biallelic Mutations in RCBTB1, a Gene Implicated in Ubiquitination

Inherited retinal dystrophies (iRDs) are a group of genetically and clinically heterogeneous conditions resulting from mutations in over 250 genes. Here, homozygosity mapping and whole-exome sequencing (WES) in a consanguineous family revealed a homozygous missense mutation, c.973C>T (p.His325Tyr), in RCBTB1. In affected individuals, it was found to segregate with retinitis pigmentosa (RP), goiter, primary ovarian insufficiency, and mild intellectual disability. Subsequent analysis of WES data in different cohorts uncovered four additional homozygous missense mutations in five unrelated families in whom iRD segregates with or without syndromic features. Ocular phenotypes ranged from typical RP starting in the second decade to chorioretinal dystrophy with a later age of onset. The five missense mutations affect highly conserved residues either in the sixth repeat of the RCC1 domain or in the BTB1 domain. A founder haplotype was identified for mutation c.919G>A (p.Val307Met), occurring in two families of Mediterranean origin. We showed ubiquitous mRNA expression of RCBTB1 and demonstrated predominant RCBTB1 localization in human inner retina. RCBTB1 was very recently shown to be involved in ubiquitination, more specifically as a CUL3 substrate adaptor. Therefore, the effect on different components of the CUL3 and NFE2L2 (NRF2) pathway was assessed in affected individuals’ lymphocytes, revealing decreased mRNA expression of NFE2L2 and several NFE2L2 target genes. In conclusion, our study puts forward mutations in RCBTB1 as a cause of autosomal-recessive non-syndromic and syndromic iRD. Finally, our data support a role for impaired ubiquitination in the pathogenetic mechanism of RCBTB1 mutations.

In Vivo Analysis of Disease-Associated Point Mutations Unveils Profound Differences in mRNA Splicing of Peripherin-2 in Rod and Cone Photoreceptors

Point mutations in peripherin-2 (PRPH2) are associated with severe retinal degenerative disorders affecting rod and/or cone photoreceptors. Various disease-causing mutations have been identified, but the exact contribution of a given mutation to the clinical phenotype remains unclear. Exonic point mutations are usually assumed to alter single amino acids, thereby influencing specific protein characteristics; however, they can also affect mRNA splicing. To examine the effects of distinct PRPH2 point mutations on mRNA splicing and protein expression in vivo, we designed PRPH2 minigenes containing the three coding exons and relevant intronic regions of human PRPH2. Minigenes carrying wild type PRPH2 or PRPH2 exon 2 mutations associated with rod or cone disorders were expressed in murine photoreceptors using recombinant adeno-associated virus (rAAV) vectors. We detect three PRPH2 splice isoforms in rods and cones: correctly spliced, intron 1 retention, and unspliced. In addition, we show that only the correctly spliced isoform results in detectable protein expression. Surprisingly, compared to rods, differential splicing leads to lower expression of correctly spliced and higher expression of unspliced PRPH2 in cones. These results were confirmed in qRT-PCR experiments from FAC-sorted murine rods and cones. Strikingly, three out of five cone disease-causing PRPH2 mutations profoundly enhanced correct splicing of PRPH2, which correlated with strong upregulation of mutant PRPH2 protein expression in cones. By contrast, four out of six PRPH2 mutants associated with rod disorders gave rise to a reduced PRPH2 protein expression via different mechanisms. These mechanisms include aberrant mRNA splicing, protein mislocalization, and protein degradation. Our data suggest that upregulation of PRPH2 levels in combination with defects in the PRPH2 function caused by the mutation might be an important mechanism leading to cone degeneration. By contrast, the pathology of rod-specific PRPH2 mutations is rather characterized by PRPH2 downregulation and impaired protein localization.

Photoreceptors are the light sensing cells of the retina and consist of dim light and night vision mediating rods and daylight and color vision mediating cones. PRPH2 is crucial for the structural and functional integrity of photoreceptors. Some point mutations in PRPH2 lead to degeneration of rods, whereas others only affect cones. We examined the potential effects of 11 disease-linked PRPH2 mutations on mRNA splicing and protein expression in vivo. For this, we expressed six PRPH2 mutants associated with degeneration of rods in murine rods and five additional mutants linked to cone diseases in murine cones. We demonstrate that different splicing efficiencies of PRPH2 lead to its high expression in rods and to its low expression in cones. Furthermore, we show that the majority of PRPH2 mutants associated with cone disorders results in an upregulation of PRPH2 expression in cones by increasing the mRNA splicing efficiency. By contrast, the majority of PRPH2 mutants associated with rod diseases leads to a downregulation of PRPH2 expression in rods via different mechanisms including aberrant mRNA splicing. These results provide novel insights into the pathobiology of mRNA splicing in photoreceptors and might contribute to explain the differential penetrance of PRPH2 mutants in rods and cones.

Quantitative Fundus Autofluorescence and Optical Coherence Tomography in PRPH2/RDS- and ABCA4-Associated Disease Exhibiting Phenotypic Overlap

PURPOSE

To assess whether quantitative fundus autofluorescence (qAF), a measure of RPE lipofuscin, and spectral-domain optical coherence tomography (SD-OCT) can aid in the differentiation of patients with fundus features that could either be related to ABCA4 mutations or be part of the phenotypic spectrum of pattern dystrophies.

METHODS

Autofluorescence images (30°, 488-nm excitation) from 39 patients (67 eyes) were acquired with a confocal scanning laser ophthalmoscope equipped with an internal fluorescent reference and were quantified as previously described. In addition, horizontal SD-OCT images through the fovea were obtained. Patients were screened for ABCA4 and PRPH2/RDS mutations.

RESULTS

ABCA4 mutations were identified in 19 patients (mean age, 37 ± 12 years) and PRPH2/RDS mutations in 8 patients (mean age, 48 ± 13 years); no known ABCA4 or PRPH2/RDS mutations were found in 12 patients (mean age, 48 ± 9 years). Differentiation of the groups using phenotypic SD-OCT and AF features (e.g., peripapillary sparing, foveal sparing) was not reliable. However, patients with ABCA4 mutations could be discriminated reasonably well from other patients when qAF values were corrected for age and race. In general, ABCA4 patients had higher qAF values than PRPH2/RDS patients, while most patients without mutations in PRPH2/RDS or ABCA4 had qAF levels within the normal range.

CONCLUSIONS

The high qAF levels of ABCA4-positive patients are a hallmark of ABCA4-related disease. The reason for high qAF among many PRPH2/RDS-positive patients is not known; higher RPE lipofuscin accumulation may be a primary or secondary effect of the PRPH2/RDS mutation.

Retinal dystrophies, genomic applications in diagnosis and prospects for therapy

Retinal dystrophies (RDs) are degenerative diseases of the retina which have marked clinical and genetic heterogeneity. Common presentations among these disorders include night or colour blindness, tunnel vision and subsequent progression to complete blindness. The known causative disease genes have a variety of developmental and functional roles with mutations in more than 120 genes shown to be responsible for the phenotypes. In addition, mutations within the same gene have been shown to cause different disease phenotypes, even amongst affected individuals within the same family highlighting further levels of complexity. The known disease genes encode proteins involved in retinal cellular structures, phototransduction, the visual cycle, and photoreceptor structure or gene regulation. This review aims to demonstrate the high degree of genetic complexity in both the causative disease genes and their associated phenotypes, highlighting the more common clinical manifestation of retinitis pigmentosa (RP). The review also provides insight to recent advances in genomic molecular diagnosis and gene and cell-based therapies for the RDs.

High prevalence of PRPH2 in autosomal dominant retinitis pigmentosa in france and characterization of biochemical and clinical features

PURPOSE

To assess the prevalence of PRPH2 in autosomal dominant retinitis pigmentosa (adRP), to report 6 novel mutations, to characterize the biochemical features of a recurrent novel mutation, and to study the clinical features of adRP patients.

DESIGN

Retrospective clinical and molecular genetic study.

METHODS

Clinical investigations included visual field testing, fundus examination, high-resolution spectral-domain optical coherence tomography (OCT), fundus autofluorescence imaging, and electroretinogram (ERG) recording. PRPH2 was screened by Sanger sequencing in a cohort of 310 French families with adRP. Peripherin-2 protein was produced in yeast and analyzed by Western blot.

RESULTS

We identified 15 mutations, including 6 novel and 9 previously reported changes in 32 families, accounting for a prevalence of 10.3% in this adRP population. We showed that a new recurrent p.Leu254Gln mutation leads to protein aggregation, suggesting abnormal folding. The clinical severity of the disease in examined patients was moderate with 78% of the eyes having 1-0.5 of visual acuity and 52% of the eyes retaining more than 50% of the visual field. Some patients characteristically showed vitelliform deposits or macular involvement. In some families, pericentral RP or macular dystrophy were found in family members while widespread RP was present in other members of the same families.

CONCLUSIONS

The mutations in PRPH2 account for 10.3% of adRP in the French population, which is higher than previously reported (0%-8%) This makes PRPH2 the second most frequent adRP gene after RHO in our series. PRPH2 mutations cause highly variable phenotypes and moderate forms of adRP, including mild cases, which could be underdiagnosed.

Prph2 mutations as a cause of electronegative ERG

PURPOSE

To describe the phenotypic and genotypic features in patients with PRPH2 mutations and negative electroretinograms.

METHODS

Retrospective observational case series. Records of patients with a confirmed molecular diagnosis of PRPH2 mutation, and an electronegative electroretinogram (reduced b-wave to a-wave amplitude ratio) under either photopic or scotopic conditions, were identified. Data examined included clinical history and retinal images, electrophysiology, and mutational analysis.

RESULTS

Six patients were ascertained. All had presented with clinically evident maculopathy and Snellen visual acuities in the range of 6/6 to 1/60. All had negative electroretinograms in scotopic or photopic electroretinograms or both. Four patients were heterozygous for a previously reported missense mutation c.514C>T, p.R172W; 2 were heterozygous for the frame-shifting mutations c.259_266del8, p.D87fs and c.394delC, p.Q132fs. No other cause of electronegative electroretinogram was identified in any patient. Photopic On- and Off-response recording was useful in identifying On-pathway dysfunction.

CONCLUSION

PRPH2 mutation can be associated with negative electroretinograms. This novel finding is not mutation specific and does not relate to the severity of the disease. The data add to the documented phenotypical variability of PRPH2 mutations and represent a further cause of negative electroretinogram.

OTX2 mutations cause autosomal dominant pattern dystrophy of the retinal pigment epithelium

PURPOSE

To identify the genetic cause of autosomal-dominant pattern dystrophy (PD) of the retinal pigment epithelium (RPE) in two families.

METHODS AND RESULTS

Two families with autosomal-dominant PD were identified. Eight members of family 1 (five affected) were subjected to whole-genome SNP genotyping; multipoint genome-wide linkage analysis identified 7 regions of potential linkage, and genotyping four additional individuals from family 1 resulted in a maximum logarithm of odds score of 2.09 observed across four chromosomal regions. Exome sequencing of two affected family 1 members identified 15 shared non-synonymous rare coding sequence variants within the linked regions; candidate genes were prioritised and further analysed. Sanger sequencing confirmed a novel heterozygous missense variant (E79K) in orthodenticle homeobox 2 (OTX2) that segregated with the disease phenotype. Family 2 with PD (two affected) harboured the same missense variant in OTX2. A shared haplotype of 19.68 cM encompassing OTX2 was identified between affected individuals in the two families. Within the two families, all except one affected demonstrated distinct 'patterns' at the macula. In vivo structural retinal imaging showed discrete areas of RPE-photoreceptor separation at the macula in all cases. Electroretinogram testing showed generalised photoreceptor degeneration in three cases. Mild developmental anomalies were observed, including optic nerve head dysplasia (four cases), microcornea (one case) and Rathke's cleft cyst (one case); pituitary hormone levels were normal.

CONCLUSIONS

This is the first report implicating OTX2 to underlie PD. The retinal disease resembles conditional mice models that show slow photoreceptor degeneration secondary to loss of Otx2 function in the adult RPE.

Causes and consequences of inherited cone disorders

Hereditary cone disorders (CDs) are characterized by defects of the cone photoreceptors or retinal pigment epithelium underlying the macula, and include achromatopsia (ACHM), cone dystrophy (COD), cone-rod dystrophy (CRD), color vision impairment, Stargardt disease (STGD) and other maculopathies. Forty-two genes have been implicated in non-syndromic inherited CDs. Mutations in the 5 genes implicated in ACHM explain ∼93% of the cases. On the contrary, only 21% of CRDs (17 genes) and 25% of CODs (8 genes) have been elucidated. The fact that the large majority of COD and CRD-associated genes are yet to be discovered hints towards the existence of unknown cone-specific or cone-sensitive processes. The ACHM-associated genes encode proteins that fulfill crucial roles in the cone phototransduction cascade, which is the most frequently compromised (10 genes) process in CDs. Another 7 CD-associated proteins are required for transport processes towards or through the connecting cilium. The remaining CD-associated proteins are involved in cell membrane morphogenesis and maintenance, synaptic transduction, and the retinoid cycle. Further novel genes are likely to be identified in the near future by combining large-scale DNA sequencing and transcriptomics technologies. For 31 of 42 CD-associated genes, mammalian models are available, 14 of which have successfully been used for gene augmentation studies. However, gene augmentation for CDs should ideally be developed in large mammalian models with cone-rich areas, which are currently available for only 11 CD genes. Future research will aim to elucidate the remaining causative genes, identify the molecular mechanisms of CD, and develop novel therapies aimed at preventing vision loss in individuals with CD in the future.

Miscoded Visual Processing in Degenerative Retinal Disorder?

Standard electrophysiological procedures for visual testing were applied to record the retinal and cortical electrophysiological responses to contrast stimulation from 35 subjects with unambiguously diagnosed retinitis pigmentosa and severe impairment of visual acuity and field. Stimuli (central 9° of visual field) were sinusoidal bars with spatial frequencies of 0.6–1.2 cycle/degree and 1.3–5.0 cycle/degree for the retinal (pattern-ERG) and cortical (pattern-VEP) responses, respectively; contrast was 80%; reversal at 2.13 Hz. Structured pattern-ERG above noise level was recorded from 29 subjects at 0.6 cycle/degree and from 24 subjects at 1.2 cycle/degree; latencies were increased and amplitude reduced. Pattern-VEP responses above noise level, with increased latencies and reduced amplitude, were observed in 92% of subjects with unilateral and in all subjects with bilateral retinal response. Both responses were phase-locked to stimulus. No correlation with the residual visual acuity or field was detected. The observation is consistent with evidence of the disease sparing the neuroretina and with unconscious visual processing and suggests miscoding of visual information processing.

Providing comprehensive genetic-based ophthalmic care

The diagnosis of an inherited retinal dystrophy can have a significant impact on both the physical and emotional lives of patients and their families. In order to optimize the health and quality of life for these individuals, a comprehensive approach to clinical care starting at the time of diagnosis and continuing throughout their lifespan is critical. A multidisciplinary team approach integrating ophthalmic and genetic counseling services can optimize the diagnostic process and long-term management of these patients. When vision loss is first appreciated, the diagnostic specificity of an ophthalmic evaluation can be enhanced by a detailed genetic work-up. This evaluation can help confirm the diagnosis and allow for accurate risk counseling of the patient and their family. Genetic counseling is critical at the time of diagnosis and is an opportunity to provide education about the diagnosis, discuss low-vision rehabilitation, and explore impacts on academics and employment. In addition, counseling can help patients deal with the current psychological aspects of their vision loss, prepare for the lifelong impact of their diagnosis and over time adjust to the impact of progressive vision loss.

Gene therapy for retinal disease

Gene therapy strategies for the treatment of inherited retinal diseases have made major advances in recent years. This review focuses on adeno-associated viral (AAV) vector approaches to treat retinal degeneration and, thus, prevent or delay the onset of blindness. Data from human clinical trials of gene therapy for retinal disease show encouraging signs of safety and efficacy from AAV vectors. Recent progress in enhancing cell-specific targeting and transduction efficiency of the various retinal layers plus the use of AAV-delivered growth factors to augment the therapeutic effect and limit cell death suggest even greater success in future human trials is possible.

Combination of retinitis pigmentosa and hearing loss caused by a novel mutation in PRPH2 and a known mutation in GJB2: importance for differential diagnosis of Usher syndrome

Purpose of this study was to molecularly characterize a family in which two brothers (46 and 36 years) presented with a combination of retinitis pigmentosa (RP) and severe sensorineural hearing loss while father and sister (71 and 41 years) presented with isolated RP. Retinal phenotype was compared with phenotype of 17 patients with Usher syndrome type 1. Ophthalmological examination included assessment of Snellen visual acuity, color vision with Ishihara tables, Goldmann perimetry (targets II/1-4) and microperimetry. Fundus autofluorescence imaging and optical coherence tomography were performed. Direct sequencing of all coding exons and flanking intronic sequences of GJB2 (gap junction protein, beta 2) and PRPH2 (peripherin 2) genes was performed in younger brother. Other family members were analyzed with sequencing (GJB2), high resolution melt analysis (GJB2) or restriction enzymes (PRPH2). Brothers with hearing loss were found to carry a homozygous c.35 delG mutation in GJB2, the most common mutation associated with recessive hearing loss. All patients were found to carry a novel heterozygous mutation c.389T>C (p.Leu130Pro) on PRPH2. Age of onset was higher in PRPH2 than USH1 patients, however with some overlap. Differentiation from retinal phenotype of USH1 could only be made in the oldest patient, who retained good central visual function after more than three decades of disease.

Good epidemiologic practice in retinitis pigmentosa: from phenotyping to biobanking

Inherited retinal dystrophies, such as retinitis pigmentosa (RP), include a group of relatively rare hereditary diseases caused by mutations in genes that code for proteins involved in the maintenance and function of the photoreceptor cells (cones and rods). The different forms of RP consist of progressive neurodegenerative disorders which are generally related to various and severe limitations of visual performances. In the course of typical RP (rod-cone dystrophy), the affected individuals first experience night-blindness and/or visual field constriction (secondary to rod dysfunctions), followed by variable alterations of the central vision (due to cone damages). On the other hand, during the atypical form of RP (cone-rod dystrophy), the cone’s functionalities are prevalently disrupted in comparison with the rod’s ones. The basic diagnosis of RP relies upon the documentation of unremitting loss in photoreceptor activity by electroretinogram and/or visual field testing. The prevalence of all RP typologies is variably reported in about one case for each 3000-5000 individuals, with a total of about two millions of affected persons worldwide. The inherited retinal dystrophies are sometimes the epiphenomenon of a complex framework (syndromic RP), but more often they represent an isolated disorder (about 85-90 % of cases). Although 200 causative RP mutations have been hitherto detected in more than 100 different genes, the molecular defect is identifiable in just about the 50% of the analyzed patients with RP. Not only the RP genotypes are very heterogeneous, but also the patients with the same mutation can be affected by different phenotypic manifestations. RP can be inherited as autosomal dominant, autosomal recessive or X-linked trait, and many sporadic forms are diagnosed in patients with no affected relatives. Dissecting the clinico-genetic complexity of RP has become an attainable objective by means of large-scale research projects, in which the collaboration between ophthalmologists, geneticists, and epidemiologists becomes a crucial aspect. In the present review, the main issues regarding clinical phenotyping and epidemiologic criticisms of RP are focused, especially highlighting the importance of both standardization of the diagnostic protocols and appropriateness of the disease’s registration systems.

Molecular diagnosis of putative Stargardt Disease probands by exome sequencing

BACKGROUND

The commonest genetic form of juvenile or early adult onset macular degeneration is Stargardt Disease (STGD) caused by recessive mutations in the gene ABCA4. However, high phenotypic and allelic heterogeneity and a small but non-trivial amount of locus heterogeneity currently impede conclusive molecular diagnosis in a significant proportion of cases.

METHODS

We performed whole exome sequencing (WES) of nine putative Stargardt Disease probands and searched for potentially disease-causing genetic variants in previously identified retinal or macular dystrophy genes. Follow-up dideoxy sequencing was performed for confirmation and to screen for mutations in an additional set of affected individuals lacking a definitive molecular diagnosis.

RESULTS

Whole exome sequencing revealed seven likely disease-causing variants across four genes, providing a confident genetic diagnosis in six previously uncharacterized participants. We identified four previously missed mutations in ABCA4 across three individuals. Likely disease-causing mutations in RDS/PRPH2, ELOVL, and CRB1 were also identified.

CONCLUSIONS

Our findings highlight the enormous potential of whole exome sequencing in Stargardt Disease molecular diagnosis and research. WES adequately assayed all coding sequences and canonical splice sites of ABCA4 in this study. Additionally, WES enables the identification of disease-related alleles in other genes. This work highlights the importance of collecting parental genetic material for WES testing as the current knowledge of human genome variation limits the determination of causality between identified variants and disease. While larger sample sizes are required to establish the precision and accuracy of this type of testing, this study supports WES for inherited early onset macular degeneration disorders as an alternative to standard mutation screening techniques.