[Analysis of a child with CLN1 neuronal ceroid lipofuscinosis in conjunct with Hereditary hyperferinemia cataract syndrome].

OBJECTIVE: To analyze the clinical data and genetic characteristics of a child with CLN1 neuronal ceroid lipofuscinosis in conjunct with Hereditary hyperferritinemia cataract syndrome (HHCS). METHODS: A child who was admitted to the PICU of the First Affiliated Hospital of Zhengzhou University in November 2020 was selected as the study subject. Clinical data of the child was collected. Genetic testing was carried out for the child, and the result was analyzed in the light of literature review to explore the clinical and genetic characteristics to facilitate early identification. RESULTS: The patient, a 3-year-old male, had mainly presented with visual impairment, progressive cognitive and motor regression, and epilepsy. Cranial magnetic resonance imaging revealed deepened sulci in bilateral cerebral hemispheres, and delayed myelination. The activity of palmitoyl protein thioesterase was low (8.4 nmol/g/min, reference range: 132.2 ~ 301.4 nmol/g/min), whilst serum ferritin was increased (2417.70 ng/mL, reference range: 30 ~ 400 ng/ml). Fundoscopy has revealed retinal pigment degeneration. Whole exome sequencing revealed that he has harbored c.280A>C and c.124-124+3delG compound heterozygous variants of the PPT1 gene, which were respectively inherited from his father and mother. Neither variant has been reported previously. The child has also harbored a heterozygous c.-160A>G variant of the FTL gene, which was inherited from his father. Based on the clinical phenotype and results of genetic testing, the child was diagnosed as CLN1 and HHCS. CONCLUSION: The compound heterozygous variants of the PPT1 gene probably underlay the disorders in this child. For children with CLN1 and rapidly progressing visual impairment, ophthalmological examination should be recommended, and detailed family history should be taken For those suspected for HHCS, genetic testing should be performed to confirm the diagnosis.

The Role of Epigenetics in Accelerated Aging: A Reconsideration of Later-Life Visual Loss After Early Optic Neuropathy.

BACKGROUND: In 2005, we reported 3 patients with bilateral optic nerve damage early in life. These patients had stable vision for decades but then experienced significant bilateral vision loss with no obvious cause. Our hypothesis, novel at that time, was that the late decline of vision was due to age-related attrition of retinal ganglion cells superimposed on a reduced neuronal population due to the earlier injury. EVIDENCE ACQUISITION: The field of epigenetics provides a new paradigm with which to consider the normal aging process and the impact of neuronal injury, which has been shown to accelerate aging. Late-in-life decline in function after early neuronal injury occurs in multiple sclerosis due to dysregulated inflammation and postpolio syndrome. Recent studies by our group in mice have also demonstrated the possibility of partial reversal of cellular aging and the potential to mitigate anatomical damage after injury and even improve visual function. RESULTS: The results in mice and nonhuman primates published elsewhere have shown enhanced neuronal survival and visual function after partial epigenetic reprogramming. CONCLUSIONS: Injury promotes epigenetic aging , and this finding can be observed in several clinically relevant scenarios. An understanding of the epigenetic mechanisms at play opens the opportunity to restore function in the nervous system and elsewhere with cellular rejuvenation therapies. Our earlier cases exemplify how reconsideration of previously established concepts can motivate inquiry of new paradigms.

Allele-specific gene-editing approach for vision loss restoration in RHO-associated retinitis pigmentosa.

Mutant RHO is the most frequent genetic cause of autosomal dominant retinitis pigmentosa (adRP). Here, we developed an allele-specific gene-editing therapeutic drug to selectively target the human T17M RHO mutant allele while leaving the wild-type RHO allele intact for the first time. We identified a Staphylococcus aureus Cas9 (SaCas9) guide RNA that was highly active and specific to the human T17M RHO allele. In vitro experiments using HEK293T cells and patient-specific induced pluripotent stem cells (iPSCs) demonstrated active nuclease activity and high specificity. Subretinal delivery of a single adeno-associated virus serotype 2/8 packaging SaCas9 and single guide RNA (sgRNA) to the retinas of the RHO humanized mice showed that this therapeutic drug targeted the mutant allele selectively, thereby downregulating the mutant RHO mRNA expression. Administration of this therapeutic drug resulted in a long-term (up to 11 months after treatment) improvement of retinal function and preservation of photoreceptors in the heterozygous mutant humanized mice. Our study demonstrated a dose-dependent therapeutic effect in vivo. Unwanted off-target effects were not observed at the whole-genome sequencing level. Our study provides strong support for the further development of this effective therapeutic drug to treat RHO-T17M-associated adRP, also offers a generalizable framework for developing gene-editing medicine. Furthermore, our success in restoring the vision loss in the suffering RHO humanized mice verifies the feasibility of allele-specific CRISPR/Cas9-based medicines for other autosomal dominant inherited retinal dystrophies.

Natural History of Visual Dysfunction in ABCA4 Retinopathy and Its Genetic Correlates.

PURPOSE: To systematically assess the ability to detect change and retest reliability for a panel of visual function assessments in ABCA4 retinopathy. DESIGN: Prospective natural history study (NCT01736293). METHODS: Patients with at least 1 documented pathogenic ABCA4 variant and a clinical phenotype consistent with ABCA4 retinopathy were recruited from a tertiary referral center. Participants underwent longitudinal, multifaceted functional testing, including measures of function at fixation (best-corrected visual acuity, low-vision Cambridge Color Test), macular function (microperimetry), and retina-wide function (full-field electroretinography [ERG]). Two- and 5-year ability to detect change was determined based on the η2 statistic. RESULTS: A total of 134 eyes from 67 participants with a mean follow-up of 3.65 years were included. In the 2-year interval, the microperimetry-derived perilesional sensitivity (η2 of 0.73 [0.53, 0.83]; -1.79 dB/y [-2.2, -1.37]) and mean sensitivity (η2 of 0.62 [0.38, 0.76]; -1.28 dB/y [-1.67, -0.89]) showed most change over time, but could only be recorded in 71.6% of the participants. In the 5-year interval, the dark-adapted ERG a- and b-wave amplitude showed marked change over time as well (eg, DA 30 a-wave amplitude with an η2 of 0.54 [0.34, 0.68]; -0.02 log10(µV)/y [-0.02, -0.01]). The genotype explained a large fraction of variability in the ERG-based age of disease initiation (adjusted R2 of 0.73) CONCLUSIONS: Microperimetry-based clinical outcome assessments were most sensitive to change but could only be acquired in a subset of participants. Across a 5-year interval, the ERG DA 30 a-wave amplitude was sensitive to disease progression, potentially allowing for more inclusive clinical trial designs encompassing the whole ABCA4 retinopathy spectrum.

FDXR-Associated Oculopathy: Congenital Amaurosis and Early-Onset Severe Retinal Dystrophy as Common Presenting Features in a Chinese Population.

Variants in FDXR reportedly cause autosomal recessive auditory neuropathy and optic atrophy, expanding to retinal dystrophy. This study aimed to further clarify associated phenotypes. FDXR variants were selected from our in-house whole-exome sequencing dataset of 6397 families with different eye conditions. The clinical data of the identified patients were summarized. Biallelic pathogenic or likely pathogenic FDXR variants were identified in 11 unrelated patients, including 14 missense variants of which 10 were novel. Fundus observation showed complete optic disc pallor, silver wiring or severe attenuation of retinal vessels, and varying degrees of generalized retinal degeneration. Before the detection of FDXR variants, four patients were clinically diagnosed as congenital amaurosis due to the presence of nystagmus a few months after birth, while seven were diagnosed as early-onset severe retinal dystrophy due to the presence of nyctalopia and/or poor vision in early childhood. Biallelic FDXR variants are a frequent cause of congenital or early-onset severe retinal dystrophy, especially for patients with severe optic atrophy and retinal dystrophy in early childhood.

Analysis of Immediate Early Gene Expression Levels to Interrogate Changes in Cortical Neuronal Activity Patterns upon Vision Loss.

Mapping immediate early gene (IEG) expression levels to characterize changes in neuronal activity patterns has become a golden standard in neuroscience research. Due to straightforward detection methods such as in situ hybridization and immunohistochemistry, changes in IEG expression can be easily visualized across brain regions and in response to physiological and pathological stimulation. Based on in-house experience and existing literature, zif268 represents itself as the IEG of choice to investigate the neuronal activity dynamics induced by sensory deprivation. In the monocular enucleation mouse model of partial vision loss, zif268 in situ hybridization can be implemented to study cross-modal plasticity by charting the initial decline and subsequent rise in neuronal activity in visual cortical territory deprived of direct retinal visual input. Here, we describe a protocol for high-throughput radioactive zif268 in situ hybridization as a readout for cortical neuronal activity dynamics in response to partial vision loss in mice.

Leber Mitochondrial Optic Neuropathy in Pediatric Females With Focus on Very Early Onset Cases.

The aim of this study was to describe the phenotype of Leber hereditary optic neuropathy occurring in pediatric females. This disease generally affects young adult males, but it can occur also in females, and research data in this population is lacking. The very early onset can challenge the diagnosis and delay treatment. We searched PubMed through February 2021 and identified 226 pediatric females with genetically confirmed Leber hereditary optic neuropathy and added a new case of a 3-year-old female. The male-female ratio was 1.8:1; the mean onset age in females was 11 years with the onset at 3 years of age occurring in 3 females only. Acute onset with mild visual impairment was the most common presentation, associated with optic disc edema in 16%. Differential diagnoses are pseudotumor cerebri, optic nerve drusen and optic neuritis. The outcome is poor with partial recovery in 50%, despite some receiving Idebenone therapy.

Neurovisual profile in children affected by Angelman syndrome.

BACKGROUND: Angelman syndrome (AS) is a rare neurogenetic disorder caused by altered expression of the maternal copy of the UBE3A gene. Together with motor, cognitive, and speech impairment, ophthalmological findings including strabismus, and ocular fundus hypopigmentation characterize the clinical phenotype. The aim of this study was to detail the neurovisual profile of children affected by AS and to explore any possible genotype-phenotype correlations. METHODS: Thirty-seven children (23 females, mean age 102.8 ± 54.4 months, age range 22 to 251 months) with molecular confirmed diagnosis of AS were enrolled in the study. All underwent a comprehensive video-recorded neurovisual evaluation including the assessment of ophthalmological aspects, oculomotor functions, and basic visual abilities. RESULTS: All children had visual impairments mainly characterized by refractive errors, ocular fundus changes, strabismus, discontinuous/jerky smooth pursuit and altered saccadic movements, and/or reduced visual acuity. Comparing the neurovisual profiles between the deletion and non-deletion genetic subgroups, we found a significant statistical correlation between genotype and ocular fundus hypopigmentation (p = 0.03), discontinuous smooth pursuit (p < 0.05), and contrast sensitivity abnormalities (p < 0.01) being more frequent in the deletion subgroup. CONCLUSIONS: Subjects affected by AS present a wide spectrum of neurovisual impairments that lead to a clinical profile consistent with cerebral visual impairment (CVI). Moreover, subjects with a chromosome deletion show a more severe visual phenotype with respect to ocular fundus changes, smooth pursuit movements, and contrast sensitivity. Early detection of these impaired visual functions may help promote the introduction of neurovisual habilitative programs which can improve children's visual, neuromotor, and cognitive outcomes.

Childhood-Onset Leber Hereditary Optic Neuropathy-Clinical and Prognostic Insights.

PURPOSE: To investigate the clinical and molecular genetic features of childhood-onset Leber hereditary optic neuropathy (LHON) to gain a better understanding of the factors influencing the visual outcome in this atypical form of the disease. DESIGN: Retrospective cohort study. METHODS: We retrospectively included 2 cohorts of patients with LHON with onset of visual loss before the age of 12 years from Italy and the United Kingdom. Ophthalmologic evaluation, including best-corrected visual acuity, orthoptic evaluation, slit-lamp biomicroscopy, visual field testing, and optical coherence tomography, was considered. Patients were classified based on both the age of onset and the pattern of visual loss. RESULTS: A total of 68 patients were stratified based on the age of onset of visual loss: group 1 (<3 years): 14 patients (20.6%); group 2 (≥3 to <9 years): 27 patients (39.7%); and group 3 (≥9 to ≤12 years): 27 patients (39.7%). Patients in group 2 achieved a better visual outcome than those in group 3. Patients in groups 1 and 2 had better mean deviation on visual field testing than those in group 3. The mean ganglion cell layer thickness on optical coherence tomography in group 2 was higher than those in groups 1 and 3. Patients were also categorized based on the pattern of visual loss as follows: Subacute Bilateral: 54 patients (66.7%); Insidious Bilateral: 14 patients (17.3%); Unilateral: 9 patients (11.1%); and Subclinical Bilateral: 4 patients (4.9%). CONCLUSIONS: Children who lose vision from LHON before the age of 9 years have a better visual prognosis than those who become affected in later years, likely representing a "form frustre" of the disease.

Precision genome editing in the eye.

CRISPR-Cas-based genome editing technologies could, in principle, be used to treat a wide variety of inherited diseases, including genetic disorders of vision. Programmable CRISPR-Cas nucleases are effective tools for gene disruption, but they are poorly suited for precisely correcting pathogenic mutations in most therapeutic settings. Recently developed precision genome editing agents, including base editors and prime editors, have enabled precise gene correction and disease rescue in multiple preclinical models of genetic disorders. Additionally, new delivery technologies that transiently deliver precision genome editing agents in vivo offer minimized off-target editing and improved safety profiles. These improvements to precision genome editing and delivery technologies are expected to revolutionize the treatment of genetic disorders of vision and other diseases. In this Perspective, we describe current preclinical and clinical genome editing approaches for treating inherited retinal degenerative diseases, and we discuss important considerations that should be addressed as these approaches are translated into clinical practice.

Experiences of genetic testing among individuals with retinitis pigmentosa.

BACKGROUND: Retinitis pigmentosa (RP) is a genetically heterogeneous retinal dystrophy which results in progressive vision loss. There is scant literature on the experiences of genetic testing in patients with RP. MATERIALS AND METHODS: Patients with a clinical diagnosis of RP who received genetic testing at the Wills Eye Ocular Genetics clinic between 2016 and 2020 were recruited. Telephone interviews were conducted using a semi-structured guide designed to elicit participant experiences with genetic testing. A thematic analysis was performed to describe patterns in participant responses. RESULTS: Twelve patients participated. Seven participants identified as female and five as male, with ages ranging from 22 to 70. Ten patients had positive genetic test results, while two had negative genetic testing. Reported motivations for genetic testing included qualification for clinical trials (58% of total participants), determination of etiology or usal gene (50%), reproductive concerns (50%), and prognostic outlook (50%). Most participants (75%) expressed satisfaction about their decision to pursue genetic testing. Participants with both positive and negative genetic testing reported persistent uncertainty regarding their prognosis for visual decline (50%). Genetic confirmation of disease leads to initiation of safety and vision-protecting health behaviors (42%). CONCLUSION: Patients with RP are generally satisfied with their testing experience, despite approaching testing with a wide range of motivations and expectations. Future research can leverage this methodology to identify targets for improvement in pre- and post-test education and counselling.

Vision-related convergent gene losses reveal SERPINE3's unknown role in the eye.

Despite decades of research, knowledge about the genes that are important for development and function of the mammalian eye and are involved in human eye disorders remains incomplete. During mammalian evolution, mammals that naturally exhibit poor vision or regressive eye phenotypes have independently lost many eye-related genes. This provides an opportunity to predict novel eye-related genes based on specific evolutionary gene loss signatures. Building on these observations, we performed a genome-wide screen across 49 mammals for functionally uncharacterized genes that are preferentially lost in species exhibiting lower visual acuity values. The screen uncovered several genes, including SERPINE3, a putative serine proteinase inhibitor. A detailed investigation of 381 additional mammals revealed that SERPINE3 is independently lost in 18 lineages that typically do not primarily rely on vision, predicting a vision-related function for this gene. To test this, we show that SERPINE3 has the highest expression in eyes of zebrafish and mouse. In the zebrafish retina, serpine3 is expressed in Müller glia cells, a cell type essential for survival and maintenance of the retina. A CRISPR-mediated knockout of serpine3 in zebrafish resulted in alterations in eye shape and defects in retinal layering. Furthermore, two human polymorphisms that are in linkage with SERPINE3 are associated with eye-related traits. Together, these results suggest that SERPINE3 has a role in vertebrate eyes. More generally, by integrating comparative genomics with experiments in model organisms, we show that screens for specific phenotype-associated gene signatures can predict functions of uncharacterized genes.

The Relationship Between Stage of Leber's Hereditary Optic Neuropathy and Pattern Electroretinogram Latency.

Purpose: The purpose of this study was to compare the baseline steady-state pattern electroretinogram (SS-PERG) of patients with G11778A Leber hereditary optic neuropathy (LHON) with different stages of visual acuity (VA) loss before allotopic gene therapy (GT). Methods: Patients (n = 28) were enrolled into groups (GT I: chronic bilateral VA ≤35 Early Treatment Diabetic Retinopathy Study [ETDRS]; GT II: acute bilateral VA ≤35 ETDRS; GT III: acute unilateral, VA ≤35 ETDRS, and better eye VA ≥70 ETDRS) and tested with SS-PERG together with 210 age-matched normal controls (NCs). SS-PERG amplitude (nV) and latency (ms) of each eye were averaged for groups GT I, GT II, and NC. Symptomatic eyes (GT III-S) and asymptomatic eyes (GT III-A) of group GT III were included separately and accounted for by using generalized estimating equation (GEE) methods. Results: Compared to NC, SS-PERG amplitudes were reduced similarly by approximately 50% (P < 0.001) among all GT groups (NC > GT I, GT II, GT III-S, and GT III-A). SS-PERG latencies were shorter by ≥3.5 ms in all LHON groups and differed by disease stage (G III-A < NC, P = 0.002; GT III-S < GT III-A, P = 0.01; GT II < GT III-S, P = 0.03; GT I < NC, P < 0.001, but not different from other GT groups, all P > 0.1). Conclusions: Although SS-PERG amplitude reduction did not distinguish between disease stages, SS-PERG latency shortening occurred in asymptomatic eyes and symptomatic eyes and distinguished between disease stages. Translational Relevance: SS-PERG latency shortening is consistent with primary damage of smaller/slower axons and sparing of larger/faster axons and may provide an objective staging of LHON, which may be helpful to determine efficacy in LHON trials.

Foveal Hypoplasia Grading in 95 Cases of Congenital Aniridia: Correlation to Phenotype and PAX6 Genotype.

PURPOSE: To correlate the degree of foveal hypoplasia in congenital aniridia with visual acuity, iris phenotype, and PAX6 mutations. DESIGN: Retrospective case series. METHODS: Ninety-five consecutive patients with high-quality spectral-domain optical coherence tomography records and available genotype were included in a single referral center. Iris hypoplasia was classified as complete, presence of iris root or remnants, and mild atypical aniridia. Spectral-domain optical coherence tomography images were assessed to classify foveal hypoplasia as grade 1 to 4 and to determine mean thicknesses for retinal layers. For statistical analysis 1 eye for each patient was used and 1 member of the same family has been included (n = 76 eyes). RESULTS: Most eyes (n= 158/169, 93.5%) showed variable degree of foveal hypoplasia. PAX6-positive patients presented higher degree of foveal hypoplasia than patients negative for PAX6 (P < .0001). PAX6 deletions, PAX6 variants subjected to nonsense-mediated decay and C-terminal extension variants were mostly associated with grade 3 or 4 foveal hypoplasia. Deletions restricted to the 3' flanking regulatory regions of PAX6 were associated with grade 1 or 2 foveal hypoplasia (P < .0001). Best-corrected visual acuity was higher and foveal outer retinal layers were thicker in patients with deletions in the 3' regulatory region of PAX6 (P = .001 and P < .0001). Patients with missense mutations presented with variable degree of foveal hypoplasia. The degree of foveal hypoplasia was most frequently correlated with the severity of iris defects, with 95% of eyes with complete aniridia presenting grade 3 or 4 foveal hypoplasia (P = .005). However, among eyes with mild iris phenotype, 70% (n=9/13) showed severe foveal hypoplasia. CONCLUSIONS: All types of PAX6 variants, even those associated with mild iris defects, may be at risk for severe foveal hypoplasia with poor visual prognosis, except for deletions restricted to the 3' regulatory PAX6 regions.

TRPV4-induced Müller cell gliosis and TNF-α elevation-mediated retinal ganglion cell apoptosis in glaucomatous rats via JAK2/STAT3/NF-κB pathway.

BACKGROUND: Glaucoma, the leading cause of irreversible blindness worldwide, is a type of retinal disease characterized by the selective death of retinal ganglion cells (RGCs). However, the pathogenesis of glaucoma has not been fully elucidated. Transient receptor potential vanilloid 4 (TRPV4) is a pressure-sensitive and calcium-permeable cation channel. TRPV4 is widely distributed in the retina and its sustained activation leads to RGC death; indicating that TRPV4 may be a possible target for glaucoma treatment. Here, we investigated the effects of TRPV4 on RGC apoptosis in a rat model of chronic ocular hypertension (COH), then examined the mechanism underlying these effects. METHODS: The COH model was established by injection of micro-magnetic beads into the anterior chamber of adult male rats. The expression levels of TRPV4, glial fibrillary acidic protein, and inflammatory factors were assessed by immunohistochemistry and immunoblotting. RGC apoptosis and visual dysfunction were evaluated by TUNEL assay and photopic negative response. Functional expression of TRPV4 was examined by electrophysiology and calcium imaging. Real-time polymerase chain reaction and immunoblotting were employed to investigate the molecular mechanism underlying the effects of TRPV4 on tumor necrosis factor-α (TNF-α) release. RESULTS: We found that TRPV4 played an essential role in glaucoma, such that high levels of TRPV4 expression were associated with elevated intraocular pressure. Furthermore, TRPV4 activation was involved in glaucoma-induced RGC apoptosis and RGC-related reductions in visual function. Mechanistic investigation demonstrated that TRPV4 activation led to enhanced Müller cell gliosis and TNF-α release via the JAK2/STAT3/NF-kB pathway, while TRPV4 inhibition could reverse these effects. Finally, TRPV4 activation could lead to elevated expression of TNF receptor 1 in RGCs, while inhibition of TNF-α could reduce TRPV4-mediated RGC apoptosis. CONCLUSIONS: TRPV4 activation induces Müller cell gliosis and TNF-α elevation via the JAK2/STAT3/NF-κB pathway, which may exacerbate RGC apoptosis in glaucoma; these results suggest that TRPV4 can serve as a therapeutic target in glaucoma treatment.

Bi-allelic variants in OGDHL cause a neurodevelopmental spectrum disease featuring epilepsy, hearing loss, visual impairment, and ataxia.

The 2-oxoglutarate dehydrogenase-like (OGDHL) protein is a rate-limiting enzyme in the Krebs cycle that plays a pivotal role in mitochondrial metabolism. OGDHL expression is restricted mainly to the brain in humans. Here, we report nine individuals from eight unrelated families carrying bi-allelic variants in OGDHL with a range of neurological and neurodevelopmental phenotypes including epilepsy, hearing loss, visual impairment, gait ataxia, microcephaly, and hypoplastic corpus callosum. The variants include three homozygous missense variants (p.Pro852Ala, p.Arg244Trp, and p.Arg299Gly), three compound heterozygous single-nucleotide variants (p.Arg673Gln/p.Val488Val, p.Phe734Ser/p.Ala327Val, and p.Trp220Cys/p.Asp491Val), one homozygous frameshift variant (p.Cys553Leufs∗16), and one homozygous stop-gain variant (p.Arg440Ter). To support the pathogenicity of the variants, we developed a novel CRISPR-Cas9-mediated tissue-specific knockout with cDNA rescue system for dOgdh, the Drosophila ortholog of human OGDHL. Pan-neuronal knockout of dOgdh led to developmental lethality as well as defects in Krebs cycle metabolism, which was fully rescued by expression of wild-type dOgdh. Studies using the Drosophila system indicate that p.Arg673Gln, p.Phe734Ser, and p.Arg299Gly are severe loss-of-function alleles, leading to developmental lethality, whereas p.Pro852Ala, p.Ala327Val, p.Trp220Cys, p.Asp491Val, and p.Arg244Trp are hypomorphic alleles, causing behavioral defects. Transcript analysis from fibroblasts obtained from the individual carrying the synonymous variant (c.1464T>C [p.Val488Val]) in family 2 showed that the synonymous variant affects splicing of exon 11 in OGDHL. Human neuronal cells with OGDHL knockout exhibited defects in mitochondrial respiration, indicating the essential role of OGDHL in mitochondrial metabolism in humans. Together, our data establish that the bi-allelic variants in OGDHL are pathogenic, leading to a Mendelian neurodevelopmental disease in humans.

Establishing risk of vision loss in Leber hereditary optic neuropathy.

We conducted an updated epidemiological study of Leber hereditary optic neuropathy (LHON) in Australia by using registry data to establish the risk of vision loss among different LHON mutations, sex, age at onset, and mitochondrial haplogroup. We identified 96 genetically unrelated LHON pedigrees, including 56 unpublished pedigrees, and updated 40 previously known pedigrees, comprising 620 affected individuals and 4,948 asymptomatic carriers. The minimum prevalence of vision loss due to LHON in Australia in 2020 was one in 68,403 individuals. Although our data confirm some well-established features of LHON, the overall risk of vision loss among those with a LHON mutation was lower than reported previously-17.5% for males and 5.4% for females. Our findings confirm that women, older adults, and younger children are also at risk. Furthermore, we observed a higher incidence of vision loss in children of affected mothers as well as in children of unaffected women with at least one affected brother. Finally, we confirmed our previous report showing a generational fall in prevalence of vision loss among Australian men. Higher reported rates of vision loss in males with a LHON mutation are not supported by our work and other epidemiologic studies. Accurate knowledge of risk is essential for genetic counseling of individuals with LHON mutations. This knowledge could also inform the detection and validation of potential biomarkers and has implications for clinical trials of treatments aimed at preventing vision loss in LHON because an overestimated risk may lead to an underpowered study or a false claim of efficacy.

In vivo analysis of onset and progression of retinal degeneration in the Nr2e3rd7/rd7 mouse model of enhanced S-cone sensitivity syndrome.

The photoreceptor-specific nuclear receptor Nr2e3 is not expressed in Nr2e3rd7/rd7 mice, a mouse model of the recessively inherited retinal degeneration enhanced S-cone sensitivity syndrome (ESCS). We characterized in detail C57BL/6J Nr2e3rd7/rd7 mice in vivo by fundus photography, optical coherence tomography and fluorescein angiography and, post mortem, by histology and immunohistochemistry. White retinal spots and so-called 'rosettes' first appear at postnatal day (P) 12 in the dorsal retina and reach maximal expansion at P21. The highest density in 'rosettes' is observed within a region located between 100 and 350 µM from the optic nerve head. 'Rosettes' disappear between 9 to 12 months. Non-apoptotic cell death markers are detected during the slow photoreceptor degeneration, at a rate of an approximately 3% reduction of outer nuclear layer thickness per month, as observed from 7 to 31 months of age. In vivo analysis of Nr2e3rd7/rd7 Cx3cr1gfp/+ retinas identified microglial cells within 'rosettes' from P21 on. Subretinal macrophages were observed in vivo and by confocal microscopy earliest in 12-months-old Nr2e3rd7/rd7 retinas. At P21, S-opsin expression and the number of S-opsin expressing dorsal cones was increased. The dorso-ventral M-cone gradient was present in Nr2e3rd7/rd7 retinas, but M-opsin expression and M-opsin expressing cones were decreased. Retinal vasculature was normal.

Intermixing the OPN1LW and OPN1MW Genes Disrupts the Exonic Splicing Code Causing an Array of Vision Disorders.

Light absorption by photopigment molecules expressed in the photoreceptors in the retina is the first step in seeing. Two types of photoreceptors in the human retina are responsible for image formation: rods, and cones. Except at very low light levels when rods are active, all vision is based on cones. Cones mediate high acuity vision and color vision. Furthermore, they are critically important in the visual feedback mechanism that regulates refractive development of the eye during childhood. The human retina contains a mosaic of three cone types, short-wavelength (S), long-wavelength (L), and middle-wavelength (M) sensitive; however, the vast majority (~94%) are L and M cones. The OPN1LW and OPN1MW genes, located on the X-chromosome at Xq28, encode the protein component of the light-sensitive photopigments expressed in the L and M cones. Diverse haplotypes of exon 3 of the OPN1LW and OPN1MW genes arose thru unequal recombination mechanisms that have intermixed the genes. A subset of the haplotypes causes exon 3- skipping during pre-messenger RNA splicing and are associated with vision disorders. Here, we review the mechanism by which splicing defects in these genes cause vision disorders.

Identification of susceptibility loci for light-induced visual impairment in rats.

Bright light exposure in animals results in the selective degeneration of the outer retina, known as "retinal photic injury" (RPI). The susceptibility to RPI differs among rat strains. WKY rats display susceptibility to RPI with extensive retinal degeneration observed in the sagittal eye specimen, whereas LEW strain rats are resistant to it, showing only slight or no degeneration. In the present study, we first established an ethological screening method using the Morris water maze to discern differential susceptibility among the living rats. WKY and LEW were crossed to produce the first filial generation (F1) offspring. Maze-trained individuals were exposed to bright, white light. The screening test results demonstrated that the susceptibility to light-induced visual impairment in rats is a dominant Mendelian susceptibility trait, as F1 rats were susceptible to visual impairment like WKY rats. Therefore, F1 rats were backcrossed with recessive LEW to produce the first backcross offspring (BC1). Subsequent recurrent backcrossing while selecting for the susceptibility, indicated a segregation ratio of ca. 24% in BC1 and BC2 generations, indicating the involvement of two or more genes in the susceptibility. Further, microsatellite analysis of BC1-to-BC4 individuals using microsatellite markers mapped two susceptibility loci on chromosome segments 5q36 and 19q11-q12, named RPI susceptibility (Rpi)1 and Rpi2, respectively. This study provides an insight into mechanisms underlying differential susceptibility, which could help decipher the mechanism underlying the onset/progression of human age-related macular degeneration.