Retinoid Synthesis Regulation by Retinal Cells in Health and Disease

Vision starts in retinal photoreceptors when specialized proteins (opsins) sense photons via their covalently bonded vitamin A derivative 11cis retinaldehyde (11cis-RAL). The reaction of non-enzymatic aldehydes with amino groups lacks specificity, and the reaction products may trigger cell damage. However, the reduced synthesis of 11cis-RAL results in photoreceptor demise and suggests the need for careful control over 11cis-RAL handling by retinal cells. This perspective focuses on retinoid(s) synthesis, their control in the adult retina, and their role during retina development. It also explores the potential importance of 9cis vitamin A derivatives in regulating retinoid synthesis and their impact on photoreceptor development and survival. Additionally, recent advancements suggesting the pivotal nature of retinoid synthesis regulation for cone cell viability are discussed.

Posterior microphthalmos with retinal involvement related to MFRP gene: a report of 10 Brazilian patients

BACKGROUND

To describe the phenotype and genotype of 10 Brazilian patients with variants in MFRP, posterior microphthalmos and retinal findings.

METHODS

Complete ophthalmological evaluation was done at 4 different Brazilian centers. Genetic analysis was performed using commercial next generation sequencing panels for inherited retinal disorders.

RESULTS

Ages of the patients ranged from 10 to 65 years and visual acuities from 0,05 to no perception of light. All were hyperopes (+4,25 to + 17,50) with a short axial length (14,4 mm to 18 mm). Common posterior segment features, though not present in all, were optic disc drusen (5/10), foveoschisis (5/10) and retinal pigmentary changes (8/10). Isolated patients presented with macular atrophy, serous retinal detachment, and chorioretinal folds. The most common variant in MFRP found in our patients was a deletion in exon 5 (c.498delC; p.Asn267Thrfs *25), present in all except 2 patients. Other variants found were c.523C>T (p.Gln175*), c.298delG (p.Ala100Argfs *37), c.666del (p.Thr223Argfs *83) and the novel variant c.257C>A (p.Ala86Asp).

CONCLUSIONS

This is the first report of Brazilian patients with posterior microphthalmos and pathogenic variants in MFRP and the first describe of the variant p.Ala86Asp in literature. Our cases confirm the previously reported phenotype of high hyperopia, optic disc drusen, alterations in foveal architecture, retinal pigmentary changes with loss of photoreceptor function and visual field constriction. Report of such a rare condition is important to increase awareness to the phenotype of posterior microphthalmia with associated retinal conditions.

Bridging Retinal and Cerebral Neurodegeneration: A Focus on Crosslinks between Alzheimer-Perusini's Disease and Retinal Dystrophies

In the early stages of Alzheimer-Perusini's disease (AD), individuals often experience vision-related issues such as color vision impairment, reduced contrast sensitivity, and visual acuity problems. As the disease progresses, there is a connection with glaucoma and age-related macular degeneration (AMD) leading to retinal cell death. The retina's involvement suggests a link with the hippocampus, where most AD forms start. A thinning of the retinal nerve fiber layer (RNFL) due to the loss of retinal ganglion cells (RGCs) is seen as a potential AD diagnostic marker using electroretinography (ERG) and optical coherence tomography (OCT). Amyloid beta fragments (Aβ), found in the eye's vitreous and aqueous humor, are also present in the cerebrospinal fluid (CSF) and accumulate in the retina. Aβ is known to cause tau hyperphosphorylation, leading to its buildup in various retinal layers. However, diseases like AD are now seen as mixed proteinopathies, with deposits of the prion protein (PrP) and α-synuclein found in affected brains and retinas. Glial cells, especially microglial cells, play a crucial role in these diseases, maintaining immunoproteostasis. Studies have shown similarities between retinal and brain microglia in terms of transcription factor expression and morphotypes. All these findings constitute a good start to achieving better comprehension of neurodegeneration in both the eye and the brain. New insights will be able to bring the scientific community closer to specific disease-modifying therapies.

An Optical Coherence Tomography-Based Measure as an Independent Estimate of Retinal Function in Retinitis Pigmentosa

BACKGROUND

With the clinical advances in the field of gene therapy, the development of objective measures of visual function of patients with inherited retinal dystrophies (IRDs) is of utmost importance. Here, we propose one such measure.

METHODS

We retrospectively analyzed data from a cohort of 194 eyes of 97 genetically diagnosed patients with retinitis pigmentosa (RP), the most common IRD, followed at the UPMC Vision Institute. The analyzed data included the reflectivity ratio (RR) of the retinal nerve fiber layer (RNFL) to that of the entire retina, visual acuity (VA) and the thickness of the retinal outer nuclear layer (ONL) and the RNFL.

RESULTS

There was a strong positive correlation between the RR and VA. Both VA and the RR were negatively correlated with disease duration; VA, but not the RR, was negatively correlated with age. The RR correlated with the ONL but not with the RNFL thickness or the intraocular pressure. Age, RR, disease duration and ONL thickness were found to be independent predictors of VA by multivariate analysis.

CONCLUSION

The OCT RR could serve as an independent predictor of visual acuity, and by extension of retinal function, in genetically diagnosed RP patients. Such objective measures can be of great value in patient selection for therapeutic trials.

Examination under anesthesia: Preferred Practice

Pediatric ocular examinations are often a challenge in the outpatient setting due to limited cooperation of the child. Hence an evaluation under anesthesia (EUA) or sedation is important for a holistic ophthalmic examination. It can be combined with short procedures, such as suture removal and corneal scrappings, both for diagnosis and for the management of several ophthalmic disorders. It can also be performed before planning a surgical intervention to record the baseline characters and formulate or refine a surgical plan. Every EUA must be used as a chance to perform a complete ophthalmic examination rather than perform a single task such as recording the intraocular pressure. This article aims to provide a protocol that can be followed for a complete EUA.

Very Large Cystoid Macular Lesions Identified Using Outlier Analysis of Genetically Confirmed Inherited Retinal Disease Cases

BACKGROUND

Cystoid macular lesions (CML) in inherited retinal diseases (IRDs) can contribute to vision impairment. Studying the morphologic range and outlier presentations of CML may inform clinical associations, mechanistic research, and trial design. Thus, we aim to describe the distribution of optical coherence tomography (OCT) parameters in IRD cases with CML and identify phenotype-genotype associations in very large cystoid macular lesions (VLCML).

MATERIALS AND METHODS

This cross-sectional study retrieved clinical information from electronic records from January 2020 to December 2021. VLCML cases were identified using the robust distance (Mahalanobis) of the correlation between central foveal thickness (CFT) and total macular volume (TMV) and a 99.9% probability ellipse. The distribution of OCT parameters was calculated by genotype and phenotype.

RESULTS

We included 173 eyes of 103 subjects. The median age was 55.9 (interquartile range [IQR], 37.9, 63.7) and 47.6% (49/103) were females. Patients had disease-causing mutations in 30 genes. The most common genes included USH2A (n = 18), RP1 (n = 12), and ABCA4 (n = 11). Robust distance analysis showed that the prevalence of VLCML was 1.94% (n = 2 patients, 4 eyes). VLCML was seen in cases of NR2E3 (119-2A>C) and BEST1 (1120_1121insG) mutations. The median CFT in cases without VLCML was 269 µm (IQR 209, 318.50) while the median for VLCML cases was 1,490 µm (IQR 1,445.50, 1,548.00) (P < .001).

CONCLUSIONS

Subjects with different IRD genotypes may develop VLCMLs. Future studies could consider the range and outlier values of CML foveal thickness when determining inclusion criteria and biostatistical plans for observational and interventional studies.

Gene-agnostic approaches to treating inherited retinal degenerations

Most patients with inherited retinal degenerations (IRDs) have been waiting for treatments that are "just around the corner" for decades, with only a handful of seminal breakthroughs happening in recent years. Highlighting the difficulties in the quest for curative therapeutics, Luxturna required 16 years of development before finally obtaining United States Food and Drug Administration (FDA) approval and its international equivalents. IRDs are both genetically and phenotypically heterogeneous. While this diversity offers many opportunities for gene-by-gene precision medicine-based approaches, it also poses a significant challenge. For this reason, alternative (or parallel) strategies to identify more comprehensive, across-the-board therapeutics for the genetically and phenotypically diverse IRD patient population are very appealing. Even when gene-specific approaches may be available and become approved for use, many patients may have reached a disease stage whereby these approaches may no longer be viable. Thus, alternate visual preservation or restoration therapeutic approaches are needed at these stages. In this review, we underscore several gene-agnostic approaches that are being developed as therapeutics for IRDs. From retinal supplementation to stem cell transplantation, optogenetic therapy and retinal prosthetics, these strategies would bypass at least in part the need for treating every individual gene or mutation or provide an invaluable complement to them. By considering the diverse patient population and treatment strategies suited for different stages and patterns of retinal degeneration, gene agnostic approaches are very well poised to impact favorably outcomes and prognosis for IRD patients.

Pseudodominant Inheritance of Retinitis Pigmentosa Due to Mutations in the Phosphodiesterase 6B Gene: A Case Report

Mutations in the phosphodiesterase 6B (PDE6B) gene are a rare cause of autosomal recessive retinitis pigmentosa (arRP). We report on a non-consanguineous family with a pseudodominant inheritance of RP due to PDE6B mutations. We conducted a chart review of four members of a Puerto Rican family who underwent a comprehensive ophthalmic evaluation by at least one of the authors. The mutational screening was done using a genotyping microarray provided by Invitae Corporation, using next-generation sequencing (NGS) technology. Genomic DNA obtained from saliva samples is enriched for targeted regions using a hybridization-based protocol and sequenced using Illumina technology. A descriptive analysis was done. Patient 1A had a normal ophthalmic examination and a heterozygous pathogenic variant in the PDE6B gene c.1540del PLeu514Trpfs*61. Patients 1B, 2A, and 2B had mid-peripheral retinitis pigmentosa, concentric visual field ring scotomata in both eyes (OU), extinguished electroretinogram (ERG), and homozygous pathogenic variants in the PDE6B gene c.1540del PLeu514Trpfs*61. Even though mutations in the PDE6B gene usually lead to arRP, they may be inherited in a pseudodominant pattern in geographically isolated populations. Genotyping studies in patients with RP are warranted to classify inheritance mode correctly.

The First Homozygote Mutation c.499G>T (Asp167Tyr) in the RPE65 Gene Encoding Retinoid Isomerohydrolase Causing Retinal Dystrophy

RPE65, an abundant membrane-associated protein present in the retinal pigment epithelium (RPE), is a vital retinoid isomerase necessary for regenerating 11-cis-retinaldehyde from all-trans retinol in the visual cycle. In patients with inherited retinal dystrophy (IRD), precise genetic diagnosis is an indispensable approach as it is required to establish eligibility for the genetic treatment of RPE65-associated IRDs. This case report aims to report the specific phenotype−genotype correlation of the first patient with a homozygous missense variant RPE65 c.499G>T, p. (Asp167Tyr). We report a case of a 66-year-old male who demonstrated a unique phenotype manifesting less severe functional vision deterioration in childhood and adolescence, and extensive nummular pigment clusters. The underlying causes of the differences in the typical bone spicule and atypical nummular pigment clumping are unknown, but suggest that the variant itself influenced the rate of photoreceptor death. Functional studies are needed to define whether the substitution of aspartate impairs the folding of the tertiary RPE65 structure only and does not lead to the complete abolishment of chromophore production, thus explaining the less severe phenotype in adolescence.

RPE65 c.353G>A, p.(Arg118Lys): A Novel Point Mutation Associated with Retinitis Pigmentosa and Macular Atrophy

Precise genetic diagnosis in RPE65-mediated retinitis pigmentosa (RP) is necessary to establish eligibility for genetic treatment with voretigene neparvovec: a recombinant adeno-associated viral vector providing a functional RPE65 gene. This case report aims to report a novel RP-related point mutation RPE65 c.353G>A, p.(Arg118Lys), a variant of uncertain significance associated with a severe clinical presentation and the striking phenotypic feature of complete macular atrophy. We report the case of a 40-year-old male with inherited retinal dystrophy, all features typical for the RPE65-associated RP, and marked macular atrophy. Genetic testing identified that the patient was a compound heterozygote in trans form with two heterozygous variants: RPE65 c.499G>T, p.(Asp167Tyr) and RPE65 c.353G>A, p.(Arg118Lys). Furthermore, short-wavelength and near-infrared autofluorescence patterns exhibited deficiencies specific to mutations in the visual cycle genes. To the best of our knowledge, RPE65 c.353G>A, p.(Arg118Lys) is the first described point mutation on this locus, among all other reported insertional mutations, currently classified as likely benign and of uncertain significance. We concluded that this variant contributed to the pathological phenotype, demonstrating its significance clearly to be reclassified as likely pathogenic. This being the case, patients with this specific variant in homozygous or compound heterozygous form would be likely candidates for genetic treatment with voretigene neparvovec.

Evaluating vision-specific quality of life and functional vision in a Brazilian population with Stargardt disease

PURPOSE

To compare the vision-specific quality of life (QoL) of individuals with Stargardt disease (STGD) with that of healthy individuals and to investigate the association between vision-specific QoL and functional vision.

METHODS

This cross-sectional study included 41 patients with STGD and 46 healthy volunteers matched by age and gender. Best corrected visual acuity (BCVA) was used to calculate the Functional Acuity Score (FAS) and Goldmann perimetry the Functional Field Score (FFS). These scores were combined to obtain the Functional Vision Score (FVS). Vision-specific QoL was assessed using the 25-item version of the National Eye Institute Visual Function Questionnaire (NEI VFQ-25).

RESULTS

The groups had similar sociodemographic and clinical characteristics. There were significant differences in BCVA, vision-specific QoL assessed by the NEI VFQ-25, and FVS (p < 0.001) between individuals with STGD and controls. The final total score and all the subscales of the NEI VQF-25 questionnaire were significantly lower in the STGD group (p < 0.001), except for the subscales general health, color vision, and ocular pain. NEI VFQ-25 results in the STGD group were positively correlated with family income, FVS, and FFS. FVS was the score best correlated with the NEI VFQ-25 total score.

CONCLUSIONS

Individuals with STGD had significant impairment of vision-specific QoL and functional vision compared with controls and the FVS was the objective evaluation method most correlated with vision-specific QoL in this population.

Approach to inherited retinal diseases

Inherited retinal diseases (IRDs) are a group of phenotypically diverse disorders with varied genetic mutations, which result in retinal degeneration leading to visual impairment. When a patient presents to a clinician who is not an IRD expert, establishing a correct diagnosis can be challenging. The patient and the family members are often anxious about further vision loss. They are eager to know the prognosis and chance of further worsening of the vision. It is important for every eye specialist to educate himself/herself about the basics of IRD. It would help to familiarize oneself about how to approach a patient with an IRD. An early and accurate diagnosis can help predict the vision loss and also help the patient plan his/her education and choose appropriate career choices. An updated knowledge about the genetic mutations, mode of inheritance, and possible therapies would empower the eye specialist to help his/her patients. This article gives a broad plan of how to approach a patient with IRD with regards to characterization and diagnosis of the disorder, visual rehabilitation, and possible therapy.

Genetics of Inherited Retinal Diseases in Understudied Populations

Retinitis pigmentosa is one of the major forms of inherited retinal dystrophy transmitted in all Mendelian and non-Mendelian forms of inheritance. It involves the loss of retinal photoreceptor cells with severe loss of vision or blindness within the first 2 decades of life. RP occurs at a relatively high prevalence in India and is often associated with consanguinity in certain South Asian communities where this practice is customary. This review describes the studies that have been published with regard to genetics of retinitis pigmentosa in India and neighboring South Asian countries. These populations have been understudied in these aspects although to a variable degree from one country to another. Genetic studies on RP in India have been carried out with a range of methods aimed at detecting specific mutations, to screening of candidate genes or selected genomic regions, homozygosity mapping to whole genome sequencing. These efforts have led to a molecular genetic characterization of RP in Indian families. Similar studies on large extended families from Pakistan have provided insight into several novel genes underlying the pathogenesis of these diseases. The extreme degree of clinical and genetic heterogeneity of RP renders it challenging to identify the associated genes in these populations, and to translate the research output towards better management of the disease, as there are no unifying genetic features that are characteristic of any population so far.

An inherited night blindness in Wiltshire sheep

Twelve cases of adult-onset blindness were identified in a flock of 130 polled Wiltshire sheep in New Zealand over a 3-year period. Affected sheep developed night blindness between 2 and 3 years of age, which progressed to complete blindness by 4 to 5 years of age. Fundic examination findings included progressive tapetal hyperreflectivity and attenuation of retinal blood vessels. Histologically, the retinas had a selective loss of rod photoreceptors with initial preservation of cone photoreceptors. Retinal degeneration was not accompanied by any other ocular or central nervous system abnormalities, and pedigree analysis suggested an inherited basis for the disease. Mating an affected Wiltshire ram to 2 affected Wiltshire ewes resulted in 6 progeny that all developed retinal degeneration by 2 years of age, while mating of the same affected ram to 6 unaffected ewes resulted in 8 unaffected progeny, consistent with autosomal recessive inheritance. Homozygosity mapping of 5 affected Wiltshire sheep and 1 unaffected Wiltshire sheep using an OvineSNP50 Genotyping BeadChip revealed an identical-by-descent region on chromosome 5, but none of the genes within this region were considered plausible candidate genes. Whole-genome sequencing of 2 affected sheep did not reveal any significant mutations in any of the genes associated with retinitis pigmentosa in humans or progressive retinal atrophy in dogs. Inherited progressive retinal degeneration affecting rod photoreceptors has not been previously reported in sheep, but this disease has several similarities to inherited retinal dystrophies in other species.

The Clinical Contribution of Full-Field Electroretinography and 8-Year Experiences of Application in a Tertiary Medical Center

Electroretinography (ERG) is an important and well-established examination for retinal and visual pathway diseases. This study reviewed the medical records of patients who received full-field ERG (ffERG) at a single medical center between 2012 and 2019, which was an 8-year experience in the clinical contribution of ERG. Based on the indication for scheduling ffERG and the final diagnosis, patients could be classified into six groups: ‘retinal dystrophies’, ‘other retinal or macular diseases’, ‘optic neuropathies’, ‘visual complaints’, ‘systemic diseases’, and ‘others’. A total of 1921 full-field electroretinograms (ffERGs) (1655 patients) were included. The average number of ffERGs performed per year was 262 and the number of annual ffERGs was constant. The ‘retinal dystrophies’ group accounted for 36.5% of the studied population, followed by the ‘other retinal or macular diseases’ group (20.2%). The most common systemic disease was central nervous system disease. The rates of abnormal ffERGs in the ‘systemic diseases’, ‘optic neuropathies’, and ‘visual complaints’ groups were 27.3%, 22.6%, and 10.1%, respectively (p < 0.001). Higher rates were found in patients <20 years old in the ‘systemic diseases’ and ‘optic neuropathies’ groups; epilepsy and optic nerve atrophy were the most common diagnoses, respectively. In brief, by quantifying the functional response in the retina, ffERG is indispensable for diagnosis and prognosis in ophthalmologic and multidisciplinary practice.

Diagnostic definition of malattia leventinese in a family from Colombia

The malattia leventinese is an autosomal dominant inherited disease whose symptoms appear between the second and fourth decades of life. It is characterized by the appearance of drusen located between the retinal pigment epithelium and the Bruch membrane. It is usually associated with low vision and may progress to blindness. The pathogenic variant p.Arg345Trp in the EFEMP1 gene has been associated with this disease. We characterized clinically and molecularly a family with malattia leventinese using a comprehensive approach that involved ophthalmologists, pediatricians, and geneticists. This approach is of great importance since the phenotype of this disease is often confused with acular degeneration. All family members underwent ophthalmological evaluation and DNA extraction from a peripheral blood sample. All exons of the EFEMP1 gene were amplified and sequenced. The pathogenic variant p.Arg345Trp was identified in affected individuals in this family. This is the first report of malattia leventinese in a family with the p.Arg345Trp pathogenic variant in Colombia. The molecular diagnosis of retinal dystrophies is essential to differentiate this type of pathology.

CRISPR Cas9 based genome editing in inherited retinal dystrophies

BACKGROUND

Precision genome engineering, with targeted therapy towards patient-specific mutations is predicted to be the future of personalized medicine. Ophthalmology is in the frontiers of development of targeted therapy since the eye is an accessible organ and has the ease of both delivery as well as monitoring effects of therapy.

MATERIALS AND METHODS

We reviewed literature using keywords CRISPR, precision medicine, genomic editing, retinal dystrophies, retinitis pigmentosa, Usher syndrome, Stargardt's Disease. Further, we collated data on current clinical trials.

RESULTS

There is growing evidence on the role of genomic editing in retinal dystrophies, the various methods used, and stage of development of different therapies have been summarized in this paper.

CONCLUSIONS

The CRISPR-Cas9 system has revolutionized genome editing, and opened avenues in drug discovery. It is important to understand the role of this system along with its applicability in the field of ophthalmology. In this review article, we briefly describe its methodology, the strategies of employing it for making genetic perturbations, and explore its applications in inherited retinal dystrophies.

Retinal Inflammation, Cell Death and Inherited Retinal Dystrophies

Inherited retinal dystrophies (IRDs) are a group of retinal disorders that cause progressive and severe loss of vision because of retinal cell death, mainly photoreceptor cells. IRDs include retinitis pigmentosa (RP), the most common IRD. IRDs present a genetic and clinical heterogeneity that makes it difficult to achieve proper treatment. The progression of IRDs is influenced, among other factors, by the activation of the immune cells (microglia, macrophages, etc.) and the release of inflammatory molecules such as chemokines and cytokines. Upregulation of tumor necrosis factor alpha (TNFα), a pro-inflammatory cytokine, is found in IRDs. This cytokine may influence photoreceptor cell death. Different cell death mechanisms are proposed, including apoptosis, necroptosis, pyroptosis, autophagy, excessive activation of calpains, or parthanatos for photoreceptor cell death. Some of these cell death mechanisms are linked to TNFα upregulation and inflammation. Therapeutic approaches that reduce retinal inflammation have emerged as useful therapies for slowing down the progression of IRDs. We focused this review on the relationship between retinal inflammation and the different cell death mechanisms involved in RP. We also reviewed the main anti-inflammatory therapies for the treatment of IRDs.

Different Phenotypes in Pseudodominant Inherited Retinal Dystrophies

Retinal dystrophies (RD) are a group of Mendelian disorders caused by rare genetic variations leading to blindness. A pathogenic variant may manifest in both dominant or recessive mode and clinical and genetic heterogeneity makes it difficult to establish a precise diagnosis. In this study, families with autosomal dominant RD in successive generations were identified, and we aimed to determine the disease's molecular origin in these consanguineous families. Whole exome sequencing was performed in the index patient of each family. The aim was to determine whether these cases truly represented examples of dominantly inherited RD, or whether another mode of inheritance might be applicable. Six potentially pathogenic variants in four genes were identified in four families. In index patient with enhanced S-cone syndrome in F1, we identified a new digenetic combination: a heterozygous variant p.[G51A];[=] in RHO and a homozygous pathogenic variant p.[R311Q];[R311Q] in NR2E3. Helicoid subretinal fibrosis associated with recessive NR2E3 variant p.[R311Q];[R311Q] was identified in F2. A new frameshift variant c.[105delG];[105delG] in RDH12 was found in F3 with cone-rod dystrophy. In F4, the compound heterozygous variants p.[R964^*];[W758^*] were observed in IMPG2 with a retinitis pigmentosa (RP) phenotype. We showed that both affected parents and the offspring, were homozygous for the same variants in all four families. Our results provide evidence that in consanguineous families, autosomal recessive can be transmitted as pseudodominant inheritance in RD patients, and further extend our knowledge of pathogenic variants in RD genes.

Clinical Spectrum and Genetic Diagnosis of 54 Consecutive Patients Aged 0-25 with Bilateral Cataracts

Childhood cataract affects 2.5-3.5 per 10,000 children in the UK, with a genetic mutation identified in 50-90% of bilateral cases. However, cataracts can also manifest in adolescence and early adulthood in isolation, as part of a complex ocular phenotype or with systemic features making accurate diagnosis more challenging. We investigate our real-world experience through a retrospective review of consecutive bilateral cataract patients (0-25 years) presenting to the ocular genetics service at Moorfields Eye Hospital between 2017 and 2020. Fifty-four patients from 44 unrelated families were identified, with a median age of 13.5 years (range 1 to 68 years) and a median age at diagnosis of 43.9 months IQR (1.7-140.3 months); 40.7% were female and 46.3% were Caucasian. Overall, 37 patients from 27 families (61.4%) were genetically solved (50%) or likely solved (additional 11.4%), with 26 disease-causing variants (8 were novel) in 21 genes; the most common were crystallin genes, in 8 (29.6%) families, with half occurring in the CRYBB2 gene. There was no significant difference in the molecular diagnostic rates between sporadic and familial inheritance (P = 0.287). Associated clinical diagnoses were retinal dystrophies in five (18.5%) and aniridia in three (11.1%) families. Bilateral cataracts were the presenting feature in 27.3% (6/22) of either complex or syndromic cases, and isolated cataract patients were 11.5 years younger (rank-sum Z = 3.668, P = 0.0002). Prompt genetic investigation with comprehensive panel testing can aid with diagnosis and optimise management of cataract patients.

Pattern of ocular morbidity among students in a school for visually impaired children in North India

AIMS:

The aim of this study was to identify the ocular morbidity pattern among children attending a blind school in North India and comparing the data with similar studies conducted across India and abroad.

STUDY DESIGN:

This was a cross-sectional observational study.

MATERIALS AND METHODS:

A cross-sectional study was performed during September 2017 where 94 students attending a blind school were interviewed, and a detailed ocular examination was performed by an ophthalmologist.

RESULTS:

Sixty-three (67%) children were blind since birth and 29 (30.9%) had absolute blindness. Anatomical site of blindness included retinal disorders in 38 (40.42%), whole globe pathology in 20 (21.40%), optic nerve disorders in 17 (18.09%), corneal diseases in eight (8.51%), and congenital cataract in four (4.26%). A history of consanguinity among parents was reported by 12 (12.8%) students. Blindness was potentially avoidable in 22 (23.4%) children.

CONCLUSION:

Retinal pathologies were the most common cause for blindness in the present study. The proportion of corneal scarring and congenital cataract is decreasing and majority of cases had unavoidable or incurable blindness. Health education about consanguineous marriages, establishment of pediatric ophthalmology units across the country is essential to eliminate or minimize avoidable blindness among children.

RPGR-Associated Dystrophies: Clinical, Genetic, and Histopathological Features

This study describes the clinical, genetic, and histopathological features in patients with RPGR-associated retinal dystrophies. Nine male patients from eight unrelated families underwent a comprehensive ophthalmic examination. Additionally, the histopathology of the right eye from a patient with an end-stage cone-rod-dystrophy (CRD)/sector retinitis pigmentosa (RP) phenotype was examined. All RPGR mutations causing a CRD phenotype were situated in exon ORF15. The mean best-corrected visual acuity (BCVA, decimals) was 0.58 (standard deviation (SD)): 0.34; range: 0.05-1.13); and the mean spherical refractive error was -4.1 D (SD: 2.11; range: -1.38 to -8.19). Hyperautofluorescent rings were observed in six patients. Full-field electroretinography responses were absent in all patients. The visual field defects ranged from peripheral constriction to central islands. The mean macular sensitivity on microperimetry was 11.6 dB (SD: 7.8; range: 1.6-24.4) and correlated significantly with BCVA (r = 0.907; p = 0.001). A histological examination of the donor eye showed disruption of retinal topology and stratification, with a more severe loss found in the peripheral regions. Reactive gliosis was seen in the inner layers of all regions. Our study demonstrates the highly variable phenotype found in RPGR-associated retinal dystrophies. Therapies should be applied at the earliest signs of photoreceptor degeneration, prior to the remodeling of the inner retina.

The identification of small molecules that stimulate retinal pigment epithelial cells: potential novel therapeutic options for treating retinopathies

INTRODUCTION

Combinatory strategies using pharmacology and stem cell therapy have emerged due to their potential in the treatment of retinal pigment epithelium (RPE) cell related diseases, and a variety of different stem cell sources have been evaluated both in animal models and in humans. RPE cells derived from human embryonic stem cells (hESCs) and human induced pluripotent cells (hiPSCs) are already in clinical trials, holding great promise for the treatment of age-related macular disease (AMD) and hereditary RPE-related retinal dystrophies. Highly efficient protocol for RPE generations have been developed, but they are still time-consuming and laborious. Areas covered: The authors review RPE related diseases, as well as the known functions of RPE cells in retinal homeostasis. The authors also discuss small molecules that target RPE in vivo as well as in vitro to aid RPE differentiation from pluripotent stem cells clinically. The authors base this review on literature searches performed through PubMed. Expert opinion: Using high-throughput systems, technology will provide the possibility of identifying and optimizing molecules/drugs that could lead to faster and simpler protocols for RPE differentiation. This could be crucial in moving forward to create safer and more efficient RPE-based personalized therapies.

Translation of CRISPR Genome Surgery to the Bedside for Retinal Diseases

In recent years, there has been accelerated growth of clustered regularly interspaced short palindromic repeats (CRISPR) genome surgery techniques. Genome surgery holds promise for diseases for which a cure currently does not exist. In the field of ophthalmology, CRISPR offers possibilities for treating inherited retinal dystrophies. The retina has little regenerative potential, which makes treatment particularly difficult. For such conditions, CRISPR genome surgery methods have shown great potential for therapeutic applications in animal models of retinal dystrophies. Much anticipation surrounds the potential for CRISPR as a therapeutic, as clinical trials of ophthalmic genome surgery are expected to begin as early as 2018. This mini-review summarizes preclinical CRISPR applications in the retina and current CRISPR clinical trials.

Isolation and Comparative Transcriptome Analysis of Human Fetal and iPSC-Derived Cone Photoreceptor Cells

Loss of cone photoreceptors, crucial for daylight vision, has the greatest impact on sight in retinal degeneration. Transplantation of stem cell-derived L/M-opsin cones, which form 90% of the human cone population, could provide a feasible therapy to restore vision. However, transcriptomic similarities between fetal and stem cell-derived cones remain to be defined, in addition to development of cone cell purification strategies. Here, we report an analysis of the human L/M-opsin cone photoreceptor transcriptome using an AAV2/9.pR2.1:GFP reporter. This led to the identification of a cone-enriched gene signature, which we used to demonstrate similar gene expression between fetal and stem cell-derived cones. We then defined a cluster of differentiation marker combination that, when used for cell sorting, significantly enriches for cone photoreceptors from the fetal retina and stem cell-derived retinal organoids, respectively. These data may facilitate more efficient isolation of human stem cell-derived cones for use in clinical transplantation studies.

Biallelic Mutations in GNB3 Cause a Unique Form of Autosomal-Recessive Congenital Stationary Night Blindness

Congenital stationary night blindness (CSNB) is a heterogeneous group of non-progressive inherited retinal disorders with characteristic electroretinogram (ERG) abnormalities. Riggs and Schubert-Bornschein are subtypes of CSNB and demonstrate distinct ERG features. Riggs CSNB demonstrates selective rod photoreceptor dysfunction and occurs due to mutations in genes encoding proteins involved in rod phototransduction cascade; night blindness is the only symptom and eye examination is otherwise normal. Schubert-Bornschein CSNB is a consequence of impaired signal transmission between the photoreceptors and bipolar cells. Schubert-Bornschein CSNB is subdivided into complete CSNB with an ON bipolar signaling defect and incomplete CSNB with both ON and OFF pathway involvement. Both subtypes are associated with variable degrees of night blindness or photophobia, reduced visual acuity, high myopia, and nystagmus. Whole-exome sequencing of a family screened negative for mutations in genes associated with CSNB identified biallelic mutations in the guanine nucleotide-binding protein subunit beta-3 gene (GNB3). Two siblings were compound heterozygous for a deletion (c.170_172delAGA [p.Lys57del]) and a nonsense mutation (c.1017G>A [p.Trp339(∗)]). The maternal aunt was homozygous for the nonsense mutation (c.1017G>A [p.Trp339(∗)]). Mutational analysis of GNB3 in a cohort of 58 subjects with CSNB identified a sporadic case individual with a homozygous GNB3 mutation (c.200C>T [p.Ser67Phe]). GNB3 encodes the β subunit of G protein heterotrimer (Gαβγ) and is known to modulate ON bipolar cell signaling and cone transducin function in mice. Affected human subjects showed an unusual CSNB phenotype with variable degrees of ON bipolar dysfunction and reduced cone sensitivity. This unique retinal disorder with dual anomaly in visual processing expands our knowledge about retinal signaling.

Heterozygous deep-intronic variants and deletions in ABCA4 in persons with retinal dystrophies and one exonic ABCA4 variant

Variants in ABCA4 are responsible for autosomal-recessive Stargardt disease and cone-rod dystrophy. Sequence analysis of ABCA4 exons previously revealed one causative variant in each of 45 probands. To identify the "missing" variants in these cases, we performed multiplex ligation-dependent probe amplification-based deletion scanning of ABCA4. In addition, we sequenced the promoter region, fragments containing five deep-intronic splice variants, and 15 deep-intronic regions containing weak splice sites. Heterozygous deletions spanning ABCA4 exon 5 or exons 20-22 were found in two probands, heterozygous deep-intronic variants were identified in six probands, and a deep-intronic variant was found together with an exon 20-22 deletion in one proband. Based on ophthalmologic findings and characteristics of the identified exonic variants present in trans, the deep-intronic variants V1 and V4 were predicted to be relatively mild and severe, respectively. These findings are important for proper genetic counseling and for the development of variant-specific therapies.

Contribution of mutation load to the intrafamilial genetic heterogeneity in a large cohort of Spanish retinal dystrophies families

PURPOSE

The aim of this study was to deepen our knowledge on the basis of intrafamilial genetic heterogeneity of inherited retinal dystrophies (RD) to further discern the contribution of individual alleles to the pathology.

METHODS

Families with intrafamilial locus and/or allelic heterogeneity were selected from a cohort of 873 characterized of 2468 unrelated RD families. Clinical examination included visual field assessments, electrophysiology, fundus examination, and audiogram. Molecular characterization was performed using a combination of different methods: genotyping microarray, single strand conformational polymorphism (SSCP), denaturing high pressure liquid chromatography (dHPLC), high resolution melt (HRM), multiplex ligation-dependent probe amplification (MLPA), Sanger sequencing, whole-genome homozygosity mapping, and next-generation sequencing (NGS).

RESULTS

Overall, intrafamilial genetic heterogeneity was encountered in a total of 8 pedigrees. There were 5 of 873 families (~0.6%) with causative mutations in more than one gene (locus heterogeneity), involving the genes: (1) USH2A, RDH12, and TULP1; (2) PDE6B and a new candidate gene; (3) CERKL and CRB1; (4) BBS1 and C2orf71; and (5) ABCA4 and CRB1. Typically, in these cases, each mutated gene was associated with different phenotypes. In the 3 other families (~0.35%), different mutations in the same gene (allelic heterogeneity) were found, including the frequent RD genes ABCA4 and CRB1.

CONCLUSIONS

This systematic research estimates that the frequency of overall mutation load promoting RD intrafamilial heterogeneity in our cohort of Spanish families is almost 1%. The identification of the genetic mechanisms underlying RD locus and allelic heterogeneity is essential to discriminate the real contribution of the monoallelic mutations to the disease, especially in the NGS era. Moreover, it is decisive to provide an accurate genetic counseling and in disease treatment.

Blockade of neuronal nitric oxide synthase reduces cone cell death in a model of retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of diseases in which many different mutations cause rod photoreceptor cells to die and then gradually cone photoreceptors die due to progressive oxidative damage. In this study, we have shown that peroxynitrite-induced nitrosative damage also occurs. In the rd1 mouse model of RP, there was increased staining for S-nitrosocysteine and nitrotyrosine protein adducts that are generated by peroxynitrite. Peroxynitrite is generated from nitric oxide (NO) and superoxide radicals. After degeneration of rods, injection of hydroethidine resulted in strong fluorescence in the retina of rd1 mice, indicating high levels of superoxide radicals, and this was reduced, as was nitrotyrosine staining, by apocynin, suggesting that overaction of NADP(H) oxidase is at least partially responsible. Treatment of rd1 mice with a mixture of nitric oxide synthase (NOS) inhibitors markedly reduced S-nitrosocysteine and nitrotyrosine staining and significantly increased cone survival, indicating that NO-derived peroxynitrite contributes to cone cell death. Treatment with 7-nitroindazole, a relatively specific inhibitor of neuronal NOS, also significantly reduced cone cell death, but aminoguanidine, a relatively specific inhibitor of inducible NOS, did not. These data suggest that NO generated by neuronal NOS exacerbates oxidative damage to cones in RP and that combined therapy to reduce NO and oxidative stress should be considered.