The nature and distribution of putative non-functional alleles suggest only two independent events at the origins of Astyanax mexicanus cavefish populations.

BACKGROUND: Several studies suggested that cavefish populations of Astyanax mexicanus settled during the Late Pleistocene. This implies that the cavefish's most conspicuous phenotypic changes, blindness and depigmentation, and more cryptic characters important for cave life, evolved rapidly. RESULTS: Using the published genomes of 47 Astyanax cavefish from la Cueva de El Pachón, El Sótano de la Tinaja, La Cueva Chica and El Sótano de Molino, we searched for putative loss-of-function mutations in previously defined sets of genes, i.e., vision, circadian clock and pigmentation genes. Putative non-functional alleles for four vision genes were identified. Then, we searched genome-wide for putative non-functional alleles in these four cave populations. Among 512 genes with segregating putative non-functional alleles in cavefish that are absent in surface fish, we found an enrichment in visual perception genes. Among cavefish populations, different levels of shared putative non-functional alleles were found. Using a subset of 12 genes for which putative loss-of-function mutations were found, we extend the analysis of shared pseudogenes to 11 cave populations. Using a subset of six genes for which putative loss-of-function mutations were found in the El Sótano del Toro population, where extensive hybridization with surface fish occurs, we found a correlation between the level of eye regression and the amount of putative non-functional alleles. CONCLUSIONS: We confirm that very few putative non-functional alleles are present in a large set of vision genes, in accordance with the recent origin of Astyanax mexicanus cavefish. Furthermore, the genome-wide analysis indicates an enrichment of putative loss-of-function alleles in genes with vision-related GO-terms, suggesting that visual perception may be the function chiefly impacted by gene losses related to the shift from a surface to a cave environment. The geographic distribution of putative loss-of-function alleles newly suggests that cave populations from Sierra de Guatemala and Sierra de El Abra share a common origin, albeit followed by independent evolution for a long period. It also supports that populations from the Micos area have an independent origin. In El Sótano del Toro, the troglomorphic phenotype is maintained despite massive introgression of the surface genome.

Exploring Epigenetic Modifications as Potential Biomarkers and Therapeutic Targets in Glaucoma.

Glaucoma, a complex and multifactorial neurodegenerative disorder, is a leading cause of irreversible blindness worldwide. Despite significant advancements in our understanding of its pathogenesis and management, early diagnosis and effective treatment of glaucoma remain major clinical challenges. Epigenetic modifications, encompassing deoxyribonucleic acid (DNA) methylation, histone modifications, and non-coding RNAs, have emerged as critical regulators of gene expression and cellular processes. The aim of this comprehensive review focuses on the emerging field of epigenetics and its role in understanding the complex genetic and molecular mechanisms underlying glaucoma. The review will provide an overview of the pathophysiology of glaucoma, emphasizing the intricacies of intraocular pressure regulation, retinal ganglion cell dysfunction, and optic nerve damage. It explores how epigenetic modifications, such as DNA methylation and histone modifications, can influence gene expression, and how these mechanisms are implicated in glaucomatous neurodegeneration and contribute to glaucoma pathogenesis. The manuscript discusses evidence from both animal models and human studies, providing insights into the epigenetic alterations associated with glaucoma onset and progression. Additionally, it discusses the potential of using epigenetic modifications as diagnostic biomarkers and therapeutic targets for more personalized and targeted glaucoma treatment.

Reconstitution of the phosphodiesterase 6 maturation process important for photoreceptor cell function.

The sixth family phosphodiesterases (PDE6) are principal effector enzymes of the phototransduction cascade in rods and cones. Maturation of nascent PDE6 protein into a functional enzyme relies on a coordinated action of ubiquitous chaperone HSP90, its specialized cochaperone aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1), and the regulatory Pγ-subunit of PDE6. Deficits in PDE6 maturation and function underlie severe visual disorders and blindness. Here, to elucidate the roles of HSP90, AIPL1, and Pγ in the maturation process, we developed the heterologous expression system of human cone PDE6C in insect cells allowing characterization of the purified enzyme. We demonstrate that in the absence of Pγ, HSP90, and AIPL1 convert the inactive and aggregating PDE6C species into dimeric PDE6C that is predominantly misassembled. Nonetheless, a small fraction of PDE6C is properly assembled and fully functional. From the analysis of mutant mice that lack both rod Pγ and PDE6C, we conclude that, in contrast to the cone enzyme, no maturation of rod PDE6AB occurs in the absence of Pγ. Co-expression of PDE6C with AIPL1 and Pγ in insect cells leads to a fully mature enzyme that is equivalent to retinal PDE6. Lastly, using immature PDE6C and purified chaperone components, we reconstituted the process of the client maturation in vitro. Based on this analysis we propose a scheme for the PDE6 maturation process.

Novel mutation in the NDP gene associated with Norrie disease in a Chinese pedigree.

PURPOSE: Norrie disease (ND) is a rare X-linked recessive disorder characteristic of early childhood blindness. While several mutations in the NDP gene have been reported as causative for ND, the genetic etiology remains unknown for many patients. This study aims to describe a novel mutation and explore the clinical manifestations in a Chinese family with two affected males. METHODS: Exome sequencing (ES) was employed to identify the causative gene in a four-generation pedigree. Sanger sequencing was subsequently utilized to validate the mutation detected by ES in additional family members. Ophthalmologic examination and diagnostic imaging relevant to ND were conducted. RESULTS: The proband (IV:2), an 8-month-old male infant, presented with binocular retinal detachment. DNA sequencing revealed a novel heterozygous missense mutation (c.174G>C) within the NDP gene in the proband. This mutation affected highly conserved residues and was predicted to disrupt the normal protein structure. Furthermore, the variant co-segregated with the disease phenotypes within the family. CONCLUSIONS: Our findings identified a novel missense mutation in the NDP gene associated with Norrie disease in China, expanding the mutation spectrum associated with ND. This discovery holds diagnostic, prognostic, and genetic counseling implications for affected individuals.

Mitochondrially Targeted Gene Therapy Rescues Visual Loss in a Mouse Model of Leber's Hereditary Optic Neuropathy.

Leber's hereditary optic neuropathy (LHON) is a common mitochondrial genetic disease, causing irreversible blindness in young individuals. Current treatments are inadequate, and there is no definitive cure. This study evaluates the effectiveness of delivering wildtype human NADH ubiquinone oxidoreductase subunit 4 (hND4) gene using mito-targeted AAV(MTSAAV) to rescue LHOH mice. We observed a declining pattern in electroretinograms amplitudes as mice aged across all groups (p < 0.001), with significant differences among groups (p = 0.023; Control vs. LHON, p = 0.008; Control vs. Rescue, p = 0.228). Inner retinal thickness and intraocular pressure did not change significantly with age or groups. Compared to LHON mice, those rescued with wildtype hND4 exhibited improved retinal visual acuity (0.29 ± 0.1 cy/deg vs. 0.15 ± 0.1 cy/deg) and increased functional hyperemia response (effect of flicker, p < 0.001, effect of Group, p = 0.004; Interaction Flicker × Group, p < 0.001). Postmortem analysis shows a marked reduction in retinal ganglion cell density in the LHON group compared to the other groups (Effect of Group, p < 0.001, Control vs. LHON, p < 0.001, Control vs. Rescue, p = 0.106). These results suggest that MTSAAV-delivered wildtype hND4 gene rescues, at least in part, visual impairment in an LHON mouse model and has the therapeutic potential to treat this disease.

Losing, preserving, and restoring vision from neurodegeneration in the eye.

The retina is a part of the brain that sits at the back of the eye, looking out onto the world. The first neurons of the retina are the rod and cone photoreceptors, which convert changes in photon flux into electrical signals that are the basis of vision. Rods and cones are frequent targets of heritable neurodegenerative diseases that cause visual impairment, including blindness, in millions of people worldwide. This review summarizes the diverse genetic causes of inherited retinal degenerations (IRDs) and their convergence onto common pathogenic mechanisms of vision loss. Currently, there are few effective treatments for IRDs, but recent advances in disparate areas of biology and technology (e.g., genome editing, viral engineering, 3D organoids, optogenetics, semiconductor arrays) discussed here enable promising efforts to preserve and restore vision in IRD patients with implications for neurodegeneration in less approachable brain areas.

Epilepsy plus blindness in microdeletion of GABRA1 and GABRG2 in mouse and human.

OBJECTIVE: GABAA receptor subunit gene (GABR) mutations are significant causes of epilepsy, including syndromic epilepsy. This report for the first time, describes intractable epilepsy and blindness due to optic atrophy in our patient, who has a microdeletion of the GABRA1 and GABRG2 genes. We then characterized the molecular phenotypes and determined patho-mechanisms underlying the genotype-phenotype correlations in a mouse model who is haploinsufficient for both genes (Gabra1+/-/Gabrg2+/- mouse). METHODS: Electroencephalography was conducted in both human and mice with the same gene loss. GABAA receptor expression was evaluated by biochemical and imaging approaches. Optic nerve atrophy was evaluated with fundus photography in human while electronic microscopy, visual evoked potential and electroretinography recordings were conducted in mice. RESULTS: The patient has bilateral optical nerve atrophy. Mice displayed spontaneous seizures, reduced electroretinography oscillatory potential and reduced GABAA receptor α1, ß2 and γ2 subunit expression in various brain regions. Electronic microscopy showed that mice also had optic nerve degeneration, as indicated by increased G-ratio, the ratio of the inner axonal diameter to the total outer diameter, suggesting impaired myelination of axons. More importantly, we identified that phenobarbital was the most effective anticonvulsant in mice and the patient's seizures were also controlled with phenobarbital after failing multiple anti-seizure drugs. CONCLUSIONS: This study is the first report of haploinsufficiency of two GABR epilepsy genes and visual impairment due to altered axonal myelination and resultant optic nerve atrophy. The study suggests the far-reaching impact of GABR mutations and the translational significance of animal models with the same etiology.

Factors Associated with Large Cup-to-Disc Ratio and Blindness in the Primary Open-Angle African American Glaucoma Genetics (POAAGG) Study.

BACKGROUND/AIMS: Primary open-angle glaucoma (POAG) disproportionately affects individuals of African ancestry. In these patients' eyes, a large cup-to-disc ratio (LCDR > 0.90) suggests greater retinal ganglion cell loss, though these patients often display varied visual ability. This study investigated the prevalence and risk factors associated with LCDR in African ancestry individuals with POAG and explored the differences between blind (>20/200) and not blind (≤20/200) LCDR eyes. METHODS: A case-control methodology was used to investigate the demographic, optic disc, and genetic risk factors of subjects in the Primary Open-Angle African American Glaucoma Genetics Study. Risk factors were analyzed using univariable and multivariable logistic regression models with inter-eye correlation adjusted using generalized estimating equations. RESULTS: Out of 5605 eyes with POAG, 1440 eyes (25.7%) had LCDR. In the multivariable analysis, LCDR was associated with previous glaucoma surgery (OR = 1.72), increased intraocular pressure (OR = 1.04), decreased mean deviation (OR = 1.08), increased pattern standard deviation (OR = 1.06), thinner retinal nerve fiber layer (OR = 1.05), nasalization of vessels (OR = 2.67), bayonetting of vessels (OR = 1.98), visible pores in the lamina cribrosa (OR = 1.68), and a bean-shaped cup (OR = 2.11). Of LCDR eyes, 30.1% were classified as blind (≤20/200). In the multivariable analysis, the statistically significant risk factors of blindness in LCDR eyes were previous glaucoma surgery (OR = 1.72), increased intraocular pressure (OR = 1.05), decreased mean deviation (OR = 1.04), and decreased pattern standard deviation (OR = 0.90). CONCLUSIONS: These findings underscore the importance of close monitoring of intraocular pressure and visual function in African ancestry POAG patients, particularly those with LCDR, to preserve visual function.

RETINITIS PIGMENTOSA ASSOCIATED WITH THE EYS C2139Y VARIANT : An Important Cause of Blindness in East Asian Populations.

PURPOSE: The study aimed to describe the phenotypic features of retinitis pigmentosa (RP) associated with the previously described EYS C2139Y variant in Singaporeans and establish the importance of this variant as a prevalent cause of RP among East Asians. METHODS: A clinical phenotyping and exome-sequencing study was conducted on consecutive patients with nonsyndromic RP. Epidemiological analysis was performed using Singaporean and global population-based genetic data. RESULTS: A study of 150 consecutive unrelated individuals with nonsyndromic RP found that 87 (58%) of cases had plausible genotypes. A previously described missense variant in the EYS gene, 6416G>A (C2139Y), occurred heterozygously or homozygously in 17 of 150 families (11.3%), all with autosomal recessive RP. Symptom onset in EYS C2139Y-related RP ranged from 6 to 45 years, with visual acuity ranging from 20/20 at 21 years to no light perception by 48 years. C2139Y-related RP had typical findings, including sectoral RP in cases with EYS E2703X in trans . The median age at presentation was 45 years and visual fields declined to less than 20° (Goldmann V4e isopter) by age 65 years. Intereye correlation for visual acuity, fields, and ellipsoid band width was high (r 2 = 0.77-0.95). Carrier prevalence was 0.66% (allele frequency of 0.33%) in Singaporean Chinese and 0.34% in East Asians, suggesting a global disease burden exceeding 10,000 individuals. CONCLUSION: The EYS C2139Y variant is common in Singaporean RP patients and other ethnic Chinese populations. Targeted molecular therapy for this single variant could potentially treat a significant proportion of RP cases worldwide.

Legg-Calve-Perthes' disease: an opportunity to prevent blindness?

Legg-Calve-Perthes' disease (LCP) is defined as avascular necrosis of the femoral head in a child and may present to a variety of disciplines from general practice to orthopaedics, paediatrics, rheumatology and more. The Stickler syndromes are a group of disorders of type II, IX and XI collagen associated with hip dysplasia, retinal detachment, deafness and cleft palate. The pathogenesis of LCP disease remains an enigma but there have been a small number of cases reporting variants in the gene encoding the α1 chain of type II collagen (COL2A1). Variants in COL2A1 are known to cause type 1 Stickler syndrome (MIM 108300, 609508), which is a connective tissue disorder with a very high risk of childhood blindness, and it is also associated with dysplastic development of the femoral head. It is unclear whether COL2A1 variants make a definitive contribution to both disorders, or whether the two are indistinguishable using current clinical diagnostic techniques. In this paper, we compare the two conditions and present a case series of 19 patients with genetically confirmed type 1 Stickler syndrome presenting with a historic diagnosis of LCP. In contrast to isolated LCP, children with type 1 Stickler syndrome have a very high risk of blindness from giant retinal tear detachment, but this is now largely preventable if a timely diagnosis is made. This paper highlights the potential for avoidable blindness in children presenting to clinicians with features suggestive of LCP disease but with underlying Stickler syndrome and proposes a simple scoring system to assist clinicians.

The first genetically authenticated case of Leber hereditary optic neuropathy in Sri Lanka: a case report and review of the literature.

INTRODUCTION: Leber hereditary optic neuropathy is a genetic disease of mitochondrial inheritance characterized by bilateral irreversible vision loss, predominantly affecting males. We report the first genetically authenticated Sri Lankan case of Leber hereditary optic neuropathy, illustrating its characteristic features of male predominance and variable penetrance. CASE PRESENTATION: A 15-year-old previously healthy Sri Lankan boy presented with painless progressive vision loss in his right eye, followed by vision loss in his left eye within 3 months. There was no history of drug or toxin exposure, or a family history of vision loss. His parents were nonconsanguineous. On examination, he could only perceive light. Funduscopy revealed bilateral optic atrophy. Routine hematological and biochemical blood tests, including inflammatory markers, were normal. Cranial magnetic resonance imaging was unremarkable. Optical coherence tomography, and the clinical presentation, suggested a diagnosis of Leber hereditary optic neuropathy, which was confirmed by detection of m.14484T > C pathogenic variant in the MT-ND6 gene through targeted genetic analysis for the three common pathogenic variants in mitochondrial deoxyribonucleic acid. He was homoplasmic for the variant, and his asymptomatic mother and two female siblings were also found to be harboring the variant with homoplasmy. CONCLUSIONS: This case report is intended to increase awareness of Leber hereditary optic neuropathy, and highlights the need to consider this rare diagnosis in the appropriate clinical context. It also illustrates the phenomena of incomplete penetrance and male predominance, and suggests the possibility of an X-linked gene governing Leber hereditary optic neuropathy disease expression, which warrants further investigation.

Gata2a Mutation Causes Progressive Microphthalmia and Blindness in Nile Tilapia.

The normal development of lens fiber cells plays a critical role in lens morphogenesis and maintaining transparency. Factors involved in the development of lens fiber cells are largely unknown in vertebrates. In this study, we reported that GATA2 is essential for lens morphogenesis in Nile tilapia (Oreochromis niloticus). In this study, Gata2a was detected in the primary and secondary lens fiber cells, with the highest expression in primary fiber cells. gata2a homozygous mutants of tilapia were obtained using CRISPR/Cas9. Different from fetal lethality caused by Gata2/gata2a mutation in mice and zebrafish, some gata2a homozygous mutants of tilapia are viable, which provides a good model for studying the role of gata2 in non-hematopoietic organs. Our data showed that gata2a mutation caused extensive degeneration and apoptosis of primary lens fiber cells. The mutants exhibited progressive microphthalmia and blindness in adulthood. Transcriptome analysis of the eyes showed that the expression levels of almost all genes encoding crystallin were significantly down-regulated, while the expression levels of genes involved in visual perception and metal ion binding were significantly up-regulated after gata2a mutation. Altogether, our findings indicate that gata2a is required for the survival of lens fiber cells and provide insights into transcriptional regulation underlying lens morphogenesis in teleost fish.

Identification of a novel large multigene deletion and a frameshift indel in PDE6B as the underlying cause of early-onset recessive rod-cone degeneration.

A family, with two affected identical twins with early-onset recessive inherited retinal degeneration, was analyzed to determine the underlying genetic cause of pathology. Exome sequencing revealed a rare and previously reported causative variant (c.1923_1969delinsTCTGGG; p.Asn643Glyfs*29) in the PDE6B gene in the affected twins and their unaffected father. Further investigation, using genome sequencing, identified a novel ∼7.5-kb deletion (Chr 4:670,405-677,862del) encompassing the ATP5ME gene, part of the 5' UTR of MYL5, and a 378-bp (Chr 4:670,405-670,782) region from the 3' UTR of PDE6B in the affected twins and their unaffected mother. Both variants segregated with disease in the family. Analysis of the relative expression of PDE6B, in peripheral blood cells, also revealed a significantly lower level of PDE6B transcript in affected siblings compared to a normal control. PDE6B is associated with recessive rod-cone degeneration and autosomal dominant congenital stationary night blindness. Ophthalmic evaluation of these patients showed night blindness, fundus abnormalities, and peripheral vision loss, which are consistent with PDE6B-associated recessive retinal degeneration. These findings suggest that the loss of PDE6B transcript resulting from the compound heterozygous pathogenic variants is the underlying cause of recessive rod-cone degeneration in the study family.

CRISPR/Cas9-A Promising Therapeutic Tool to Cure Blindness: Current Scenario and Future Prospects.

CRISPR-based targeted genome editing is bringing revolutionary changes in the research arena of biological sciences. CRISPR/Cas9 has been explored as an efficient therapeutic tool for the treatment of genetic diseases. It has been widely used in ophthalmology research by using mouse models to correct pathogenic mutations in the eye stem cells. In recent studies, CRISPR/Cas9 has been used to correct a large number of mutations related to inherited retinal disorders. In vivo therapeutic advantages for retinal diseases have been successfully achieved in some rodents. Current advances in the CRISPR-based gene-editing domain, such as modified Cas variants and delivery approaches have optimized its application to treat blindness. In this review, recent progress and challenges of the CRISPR-Cas system have been discussed to cure blindness and its prospects.

[Genetic analysis of microcephaly-cortical blind syndrome due to compound heterozygous variants of DIAPH1 gene].

OBJECTIVE: To explore the genetic etiology of a child with microcephaly-cortical blind syndrome. METHODS: Clinical data of the child was collected. The child and her parents were subjected to whole exome sequencing (WES). Candidate variants were validated by Sanger sequencing. RESULTS: WES revealed that the child has harbored compound heterozygous variants c.1051C>T and c.609delA of the DIAPH1 gene. CONCLUSION: The compound heterozygous variation c.1051C>T (p.R351X) and c.609delA (p.E203Efs*19) of the DIAPH1 gene probably underlay the microcephaly-cortical blindness syndrome in this child.

Update on Viral Gene Therapy Clinical Trials for Retinal Diseases.

In 2001, the first large animal was successfully treated with a gene therapy that restored its vision. Lancelot, the Briard dog that was treated, suffered from a human childhood blindness called Leber's congenital amaurosis type 2. Sixteen years later, the gene therapy was approved by the U.S. Food and Drug Administration. The success of this gene therapy in dogs led to a fast expansion of the ocular gene therapy field. By now every class of inherited retinal dystrophy has been treated in at least one animal model and many clinical trials have been initiated in humans. In this study, we review the status of viral gene therapies for the retina, with a focus on ongoing human clinical trials. It is likely that in the next decade we will see several new viral gene therapies approved.

Insight from OPN1LW Gene Haplotypes into the Cause and Prevention of Myopia.

Nearsightedness (myopia) is a global health problem of staggering proportions that has driven the hunt for environmental and genetic risk factors in hopes of gaining insight into the underlying mechanism and providing new avenues of intervention. Myopia is the dominant risk factor for leading causes of blindness, including myopic maculopathy and retinal detachment. The fundamental defect in myopia-an excessively elongated eyeball-causes blurry distance vision that is correctable with lenses or surgery, but the risk of blindness remains. Haplotypes of the long-wavelength and middle-wavelength cone opsin genes (OPN1LW and OPN1MW, respectively) that exhibit profound exon-3 skipping during pre-messenger RNA splicing are associated with high myopia. Cone photoreceptors expressing these haplotypes are nearly devoid of photopigment. Conversely, cones in the same retina that express non-skipping haplotypes are relatively full of photopigment. We hypothesized that abnormal contrast signals arising from adjacent cones differing in photopigment content stimulate axial elongation, and spectacles that reduce contrast may significantly slow myopia progression. We tested for an association between spherical equivalent refraction and OPN1LW haplotype in males of European ancestry as determined by long-distance PCR and Sanger sequencing and identified OPN1LW exon 3 haplotypes that increase the risk of common myopia. We also evaluated the effects of contrast-reducing spectacles lenses on myopia progression in children. The work presented here provides new insight into the cause and prevention of myopia progression.

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.

A defective structural zipper in photoreceptors causes inherited blindness.

Being able to see the beauty of this world is a wonderful thing unfortunately unavailable to people with inherited blindness. In this issue of PLOS Biology, Mercey and colleagues present optimized expansion microscopy for retinal tissue, which represents a huge step forward in our ability to study these blinding conditions.