Retinoschisis: a retrospective study of an uncommon retinal change in cats and dogs

Retinoschisis is a poorly documented form of retinal degeneration characterized by cyst-like splitting that occurs between the inner nuclear and outer plexiform layers. The pathogenesis of retinoschisis is incompletely understood, but congenital, acquired and secondary aetiologies (glaucoma, inflammation, neoplasia) are described in humans. This retrospective study investigated the prevalence and associated histological and clinical features of retinoschisis in cats and dogs submitted for biopsy over a 10-year period. Of 140 samples with documented 'retinal vacuolation', four out of 120 (3%) canine samples and one out of 20 (5%) feline samples had changes consistent with retinoschisis. In most cases (80%), there was concurrent retinal detachment. In cases with available histories, increased intraocular pressure, proptosis and retinal detachment were reported clinical findings. In cats and dogs, retinoschisis is a retinal change that is generally secondary to other ocular lesions.

Concurrent Foveoschisis and Atrophy in a Patient With X-Linked Retinoschisis and Type 1 Diabetes Mellitus

We report the case of a 28-year-old man with X-linked retinoschisis (XLRS) and type I diabetes mellitus. The patient had bilateral foveoschisis with a tractional retinal fold in the right eye. Optical coherence tomography (OCT) revealed hyperreflective material within the inner nuclear and outer plexiform layers, photoreceptor atrophy, and retinal pigment epithelium irregularities in both eyes. Fluorescein angiography showed hyperfluorescent foveal spots corresponding to the hyperreflective material observed on OCT. This is a unique presentation of XLRS, with concurrent foveoschisis and photoreceptor atrophy in both eyes. The hyperreflective material on OCT serves as a distinctive feature of XLRS. [Ophthalmic Surg Lasers Imaging Retina 2023;54:603-606.].

Phenotypic expansion of KCNJ13-associated snowflake vitreoretinal degeneration

INTRODUCTION

An 18-year old highly myopic woman presented with bilateral retinoschisis associated with a unilateral macular hole in the right eye and vitreomacular traction in the left eye.

METHODS

Genetic studies disclosed a heterozygous pathogenic variant in the KCNJ13 gene was identified (c.484C>T (p.Arg162Trp)), consistent with a diagnosis of snowflake vitreoretinal degeneration (SVD).

RESULTS

While there were no corneal guttata, juvenile cataracts, or perivascular sheathing in this case, salient features of SVD included a fibrillar vitreous structure, crystalline retinopathy, and flattened optic nerves. The patient developed a FTMH in the left eye at 17 months follow up, followed by a rhegmatogenous retinal detachment (RRD) requiring 2 surgical repairs.

CONCLUSION

This case expands on the spectrum of clinical features in SVD, including retinoschisis and FTMH. It also characterizes optical coherence tomography findings in this rare disease entity. We emphasize the importance of using panel-based genetic testing to clinically distinguish and further define atypical vitreoretinopathies.

Single-capture ultra-widefield guided swept-source optical coherence tomography in the management of rhegmatogenous retinal detachment and associated peripheral vitreoretinal pathology

BACKGROUND/AIM

To assess the utility of single-capture ultra-widefield confocal scanning laser ophthalmoscope with integrated swept-source optical coherence tomography (UWF-SS-OCT) in the management of rhegmatogenous retinal detachment (RRD) and associated peripheral pathology.

METHODS

138 eyes of 101 consecutive patients with RRD and/or associated peripheral pathology at a vitreoretinal practice in Toronto, Canada between December 2020 and February 2021 that had UWF-SS-OCT with interpretable scans were included. A 200 degree fundus photograph was used to navigate a built-in 100 kHz UWF-SS-OCT to image pathology with a high-density 23 mm line scan and/or volume scan. Main outcomes were the microstructural details of the RRD and/or associated peripheral pathology and longitudinal assessment of response to laser retinopexy and cryopexy with UWF-SS-OCT.

RESULTS

56.5% (78/138) of eyes had prior or current RRD (6 eyes had combined retinoschisis detachment), 31.1% (43/138) had retinal tears/holes and 14.5% (20/138) had lattice degeneration. UWF-SS-OCT impacted management and was useful in determining the presence or absence of vitreoretinal traction with retinal holes or tears. It was also helpful in differentiating retinal detachment, schisis-detachment and retinoschisis in cases where it was not apparent clinically. There were also several novel findings such as vitreous adhesion at the posterior border of a retinal dialysis. UWF-SS-OCT was performed longitudinally before and immediately following laser retinopexy (n=22) and cryopexy (n=4). Microstructural changes were consistent with chorioretinal adhesion immediately following laser versus postprocedure day 6 following cryopexy.

CONCLUSION

Single-capture UWF-SS-OCT enabled novel insights in RRD and associated peripheral vitreoretinal pathology.

NOVEL METHOD FOR VISUALIZING PERIPHERAL RETINAL STRUCTURES WITH MICROSCOPE-INTEGRATED OPTICAL COHERENCE TOMOGRAPHY

BACKGROUND/PURPOSE

Visualization of peripheral retinal structures with optical coherence tomography (OCT) can be challenging but can offer valuable clinical information. We describe a method for intraoperative OCT of the peripheral retina.

METHODS

An investigational microscope-integrated OCT system with real-time 4D volumetric imaging was used in conjunction with a Goldmann style mirrored contact lens intraoperatively to capture peripheral images in three patients.

RESULTS

We identified retinoschisis, a retinal break, and areas of focal retinal detachment using our peripheral OCT method.

CONCLUSION

Use of a Goldmann lens in conjunction with intraoperative OCT offers surgeons the ability to resolve peripheral pathology that cannot be easily evaluated with OCT otherwise.

XLRS Rat with Rs1-/Y Exon-1-Del Shows Failure of Early Postnatal Outer Retina Development

We generated a Long Evans transgenic rat with targeted deletion of the whole Rs1 exon-1 and evaluated the pathological retinal phenotype of this Rs1-/Y rat model of X-linked retinoschisis (XLRS). The Rs1-/Y rat exhibited very early onset and rapidly progressive photoreceptor degeneration. The outer limiting membrane (OLM) was disrupted and discontinuous by post-natal day (P15) and allowed photoreceptor nuclei to dislocate from the outer nuclear layers (ONL) into the sub-retinal side of the OLM. Dark-adapted electroretinogram (ERG) a-wave and b-wave amplitudes were considerably reduced to only 20-25% of WT by P17. Microglia and Müller glial showed cell marker activation by P7. Intravitreal application of AAV8-RS1 at P5-6 induced RS1 expression by P15 and rescued the inner nuclear layer (INL) and outer plexiform layer (OPL) cavity formation otherwise present at P15, and the outer-retinal structure was less disrupted. This Rs1-/Y exon-1-del rat model displays substantially faster rod cell loss compared to the exon-1-del Rs1-KO mouse. Most unexpected was the rapid appearance of schisis cavities between P7 and P15, and then cavities rapidly disappeared by P21/P30. The rat model provides clues on the molecular and cellular mechanisms underlying XLRS pathology in this model and points to a substantial and early changes to normal retinal development.

Retinoschisin and novel Na/K-ATPase interaction partners Kv2.1 and Kv8.2 define a growing protein complex at the inner segments of mammalian photoreceptors

The RS1 gene on Xp 22.13 encodes retinoschisin which is known to directly interact with the retinal Na/K-ATPase at the photoreceptor inner segments. Pathologic mutations in RS1 cause X-linked juvenile retinoschisis (XLRS), a hereditary retinal dystrophy in young males. To further delineate the retinoschisin-Na/K-ATPase complex, co-immunoprecipitation was performed with porcine and murine retinal lysates targeting the ATP1A3 subunit. This identified the voltage-gated potassium (Kv) channel subunits Kv2.1 and Kv8.2 as direct interaction partners of the retinal Na/K-ATPase. Colocalization of the individual components of the complex was demonstrated at the membrane of photoreceptor inner segments. We further show that retinoschisin-deficiency, a frequent consequence of molecular pathology in XLRS, causes mislocalization of the macromolecular complex during postnatal retinal development with a simultaneous reduction of Kv2.1 and Kv8.2 protein expression, while the level of retinal Na/K-ATPase expression remains unaffected. Patch-clamp analysis revealed no effect of retinoschisin-deficiency on Kv channel mediated potassium ion currents in vitro. Together, our data suggest that Kv2.1 and Kv8.2 together with retinoschisin and the retinal Na/K-ATPase are integral parts of a macromolecular complex at the photoreceptor inner segments. Defective compartmentalization of this complex due to retinoschisin-deficiency may be a crucial step in initial XLRS pathogenesis.

Predominant Founder Effect among Recurrent Pathogenic Variants for an X-Linked Disorder

For disorders with X-linked inheritance, variants may be transmitted through multiple generations of carrier females before an affected male is ascertained. Pathogenic RS1 variants exclusively cause X-linked retinoschisis (XLRS). While RS1 is constrained to variation, recurrent variants are frequently observed in unrelated probands. Here, we investigate recurrent pathogenic variants to determine the relative burden of mutational hotspot and founder allele events to this phenomenon. A cohort RS1 variant analysis and standardized classification, including variant enrichment in the XLRS cohort and in RS1 functional domains, were performed on 332 unrelated XLRS probands. A total of 108 unique RS1 variants were identified. A subset of 19 recurrently observed RS1 variants were evaluated in 190 probands by a haplotype analysis, using microsatellite and single nucleotide polymorphisms. Fourteen variants had at least two probands with common variant-specific haplotypes over ~1.95 centimorgans (cM) flanking RS1. Overall, 99/190 of reportedly unrelated probands had 25 distinct shared haplotypes. Examination of this XLRS cohort for common RS1 haplotypes indicates that the founder effect plays a significant role in this disorder, including variants in mutational hotspots. This improves the accuracy of clinical variant classification and may be generalizable to other X-linked disorders.

[Analysis of RS1 gene variant in a Chinese pedigree affected with X-linked congenital retinal splitters]

OBJECTIVE

To explore the genetic basis for a Chinese pedigree affected with X-linked retinoschisis.

METHODS

Clinical data of the pedigree was collected. Following DNA extraction, PCR and Sanger sequencing were carried out to detect potential variant in the RS1 gene. The result was verified by using PCR and restriction fragment length polymorphism assay.

RESULTS

All male patients were found to harbor a c.458T>G (p.Val153Gly) variant of the RS1 gene, for which Their mothers were heterozygous carriers. The same variant was not detected among unaffected members of the pedigree as well as 100 healthy controls. Bioinformatic analysis suggested the variant to be pathogenic.

CONCLUSION

The c.458T>G (p.Val153Gly) variant of the RS1 gene probably underlay the X-linked retinoschisis in this pedigree.

Clinical and Genetic Study of X-Linked Juvenile Retinoschisis in the Czech Population

The aim of this study was to identify RS1 pathogenic variants in Czech patients with X-linked retinoschisis (XLRS) and to describe the associated phenotypes, including natural history, in some cases. Twenty-one affected males from 17 families were included. The coding region of RS1 was directly sequenced and segregation of the identified mutations was performed in available family members. In total, 12 disease-causing variants within RS1 were identified; of these c.20del, c.275G>A, c.[375_379del; 386A>T], c.539C>A and c.575_576insT were novel, all predicted to be null alleles. The c.539C>A mutation occurred de novo. Three patients (aged 8, 11 and 19 years) were misdiagnosed as having intermediate uveitis and treated with systemic steroids. Repeat spectral domain optical coherence tomography examinations in four eyes documented the transition from cystoid macular lesions to macular atrophy in the fourth decade of life. Four individuals were treated with topical dorzolamide and in two of them, complete resolution of the cystic macular lesions bilaterally was achieved, while one patient was noncompliant. Rebound phenomenon after discontinuation of dorzolamide for 7 days was documented in one case. Misdiagnosis of XLRS for uveitis is not uncommon; therefore, identification of disease-causing variants is of considerable benefit to the affected individuals.

Whole exome sequencing reveals putatively novel associations in retinopathies and drusen formation

Inherited retinal dystrophies (IRDs) affect 1 in 3000 individuals worldwide and are genetically heterogeneous, with over 270 identified genes and loci; however, there are still many identified disorders with no current genetic etiology. Whole exome sequencing (WES) provides a hypothesis-free first examination of IRD patients in either a clinical or research setting to identify the genetic cause of disease. We present a study of IRD in ten families from Alberta, Canada, through the lens of novel gene discovery. We identify the genetic etiology of IRDs in three of the families to be variants in known disease-associated genes, previously missed by clinical investigations. In addition, we identify two potentially novel associations: LRP1 in early-onset drusen formation and UBE2U in a multi-system condition presenting with retinoschisis, cataracts, learning disabilities, and developmental delay. We also describe interesting results in our unsolved cases to provide further information to other investigators of these blinding conditions.

Diagnosis of Peripheral Retinoschisis Using Ultrasound Biomicroscopy

BACKGROUND AND OBJECTIVE

Retinal imaging can help differentiate retinoschisis (RS) from retinal detachment (RD). This study describes new sonographic features of RS using ultrasound biomicroscopy (UBM) and evaluates their diagnostic value.

PATIENTS AND METHODS

Medical records of subjects diagnosed with RS and RD who underwent imaging prior to intervention were reviewed. Images were evaluated for detachment shape ultrasound (US) B-mode, as well as presence of intraretinal pillars, retinal layers split, and intraretinal cysts on UBM.

RESULTS

Of 48 eyes from 48 patients in the study, 25 were diagnosed as RS and 23 as RD. "Retinal layers split" was the most common UBM finding in the RS group (72%), followed by intraretinal pillars (64%) and intraretinal cysts (36%). No RD case exhibited these findings (P < .001).

CONCLUSIONS

UBM might assist in difficult cases to differentiate between RS and RD by detection of the unique sonographic features of RS described herein. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:e196-e202.].

Establishment of CSUASOi001-A, a non-integrated induced pluripotent stem cell line from urine-derived cells of a Chinese patient carrying RS1 gene mutation

X-linked juvenile retinoschisis (XLRS) is one of the most severely affected genetic causes of irreversible retinal degeneration diseases in young males, especially school-age boys. Here, we generated induced pluripotent stem cells (iPSCs) from a Chinese 11-year-old male with clinically diagnosed XLRS. Urine sample was collected with appropriate cooperation, then isolated cells were expanded for subsequent reprogramming procedure using integration-free Sendai virus. The newly derived CSUASOi001-A iPS cell line harboring the c.304C > T mutation in the RS1 gene (p.R102W) provides a useful resource to investigate pathogenic mechanisms in XLRS.

Variegated yet non-random rod and cone photoreceptor disease patterns in RPGR-ORF15-associated retinal degeneration

Mutations in the ORF15 exon of the RPGR gene cause a common form of X-linked retinitis pigmentosa, which often results in severe loss of vision. In dogs and mice, gene augmentation therapy has been shown to arrest the progressive degeneration of rod and cone photoreceptors. However, the distribution of potentially treatable photoreceptors across the human retinas and the rate of degeneration are not known. Here, we have defined structural and functional features of the disease in 70 individuals with ORF15 mutations. We also correlated the features observed in patients with those of three Rpgr-mutant (Rpgr-ko, Rd9, and Rpgr-cko) mice. In patients, there was pronounced macular disease. Across the retina, rod and cone dysfunction showed a range of patterns and a spectrum of severity between individuals, but a high symmetry was observed between eyes of each individual. Genotype was not related to disease expression. In the Rpgr-ko mice, there were intra-retinal differences in rhodopsin and cone opsin trafficking. In Rd9 and Rpgr-cko mice, retinal degeneration showed inter-ocular symmetry. Longitudinal results in patients revealed localized rod and cone dysfunction with progression rates of 0.8 to 1.3 log per decade in sensitivity loss. Relatively retained rod and cone photoreceptors in mid- and far-peripheral temporal-inferior and nasal-inferior visual field regions should be good targets for future localized gene therapies in patients.

Cog-Wheel Octameric Structure of RS1, the Discoidin Domain Containing Retinal Protein Associated with X-Linked Retinoschisis

RS1, also known as retinoschisin, is a disulphide-linked, discoidin domain containing homo-oligomeric protein that plays a crucial role in maintaining the cellular and synaptic organization of the retina. This is highlighted by the finding that over 130 mutations in RS1 cause X-linked retinoschisis, a retinal degenerative disease characterized by the splitting of the retinal cell layers, disruption of the photoreceptor-bipolar synapses, degeneration of photoreceptors, and severe loss in central vision. In this study, we investigated the arrangement of the RS1 subunits within the oligomer complex using single particle electron microscopy. RS1 was seen as two stacked rings with each ring displaying a symmetrical cog wheel-like structure with eight teeth or projections corresponding to the RS1 subunits. Three dimensional reconstruction and molecular modelling indicated that the discoidin domain, the principal functional unit of RS1, projects outward, and the Rs1 domain and C-terminal segment containing intermolecular disulphide bonds are present in the inner ring to form the core octameric structure. These studies provide a basis for further understanding the role of the novel core RS1 octameric complex in retinal cell biology and X-linked retinoschisis.

Restoration of synaptic function in sight for degenerative retinal disease

Synaptic disorganization is a prominent feature of many neurological diseases of the CNS, including Parkinson's disease, intellectual development disorders, and autism. Although synaptic plasticity is critical for learning and memory, it is unclear whether this innate property helps restore synaptic function in disease once the primary cause of disease is abrogated. An answer to this question may come from a recent investigation in X-linked retinoschisis, a currently untreatable retinopathy. In this issue of the JCI, Ou, Vijayasarathy, and colleagues showed progressive disorganization of key functional elements of the synapse between photoreceptors and ON-bipolar cells in a retinoschisin-deficient mouse model. Moreover, they demonstrated that adeno-associated virus-mediated (AAV-mediated) delivery of the retinoschisin gene restores structure and function to the photoreceptor to ON-bipolar cell synapse in mouse models, even in adults at advanced stages of the disease. The results of this study hold promise that AAV-based supplemental gene therapy will benefit patients with X-linked retinoschisis in a forthcoming clinical trial.

Synaptic pathology and therapeutic repair in adult retinoschisis mouse by AAV-RS1 transfer

Strategies aimed at invoking synaptic plasticity have therapeutic potential for several neurological conditions. The human retinal synaptic disease X-linked retinoschisis (XLRS) is characterized by impaired visual signal transmission through the retina and progressive visual acuity loss, and mice lacking retinoschisin (RS1) recapitulate human disease. Here, we demonstrate that restoration of RS1 via retina-specific delivery of adeno-associated virus type 8-RS1 (AAV8-RS1) vector rescues molecular pathology at the photoreceptor-depolarizing bipolar cell (photoreceptor-DBC) synapse and restores function in adult Rs1-KO animals. Initial development of the photoreceptor-DBC synapse was normal in the Rs1-KO retina; however, the metabotropic glutamate receptor 6/transient receptor potential melastatin subfamily M member 1-signaling (mGluR6/TRPM1-signaling) cascade was not properly maintained. Specifically, the TRPM1 channel and G proteins Gαo, Gβ5, and RGS11 were progressively lost from postsynaptic DBC dendritic tips, whereas the mGluR6 receptor and RGS7 maintained proper synaptic position. This postsynaptic disruption differed from other murine night-blindness models with an electronegative electroretinogram response, which is also characteristic of murine and human XLRS disease. Upon AAV8-RS1 gene transfer to the retina of adult XLRS mice, TRPM1 and the signaling molecules returned to their proper dendritic tip location, and the DBC resting membrane potential was restored. These findings provide insight into the molecular plasticity of a critical synapse in the visual system and demonstrate potential therapeutic avenues for some diseases involving synaptic pathology.

Peripapillary retinoschisis in glaucomatous eyes

Purpose

To investigate the structural and clinical characteristics of peripapillary retinoschisis observed in glaucomatous eyes using spectral-domain optical coherence tomography (SD-OCT).

Methods

Circumpapillary retinal nerve fiber layer (cpRNFL) and macular cross-hair SD-OCT scans and infrared fundus images of the glaucoma patients from the Investigating Glaucoma Progression Study (IGPS) and healthy volunteers were reviewed. Optic disc images obtained using enhanced depth imaging (EDI) SD-OCT were also evaluated. The structural characteristics and clinical course of the retinoschisis associated with glaucoma were investigated.

Results

Twenty-five retinoschisis areas were found in 22 of the 372 patients (5.9%) included in the IGPS, and in 1 area in 1 of 187 healthy control subjects (0.5%). In the 22 glaucomatous eyes with retinoschisis, the schisis was attached to the optic disc and overlapped with the retinal nerve fiber layer (RNFL) defect. The RNFL was the layer most commonly affected by the retinoschisis, either alone or together with other deeper layers. Acquired optic disc pit was identified in 8 eyes on disc photography and/or B-scan images obtained by EDI SD-OCT. Spontaneous resolution of this condition was observed in nine eyes. No retinal detachment or macular involvement of the retinoschisis was observed in any of the eyes. Multivariate analysis showed a significant influence of a higher intraocular pressure at SD-OCT scanning on the presence of retinoschisis (Odds ratio  = 1.418, P = 0.001).

Conclusions

The present study investigated 22 cases of peripapillary retinoschisis in glaucomatous eyes. The retinoschisis was attached to the optic nerve and topographically correlated with RNFL defect. It often resolved spontaneously without causing severe visual disturbance. Care should be taken not to overestimate the RNFL thickness in eyes with retinoschisis, and also not to misinterpret the resolution of retinoschisis as a rapid glaucomatous RNFL deterioration.

[Potential of ultrasound biomicroscopy of retinal periphery in cataract of different etiology]

Presence and pattern of peripheral retinal changes were studied using ultrasound biomicroscopy (UBM) in patients with cataract of different etiology. UBM was performed in 85 eyes of 65 patients. Mean age was 65, 75+8, 19 years old. UBM was performed using "Sonomed" equipment (USA). Morphology of revealed by means of UBM peripheral retinal changes was made in 5 eyes with uveal melanoma. The signs of retinoschisis were found in 82 eyes (96.5%) using UBM. The initial UBM signs represent inclusions in the inner retinal layers. With the progressing of schisis cystic splitting of retina was found. Confluence of distinct cysts into one schisis zone was characteristic for further progressing. Thus peripheral retinoschisis has acoustic stages, that are confirmed morphologicaly and can be revealed by means of UBM in the majority of old patients with cataract of different etiology.

[Alternative of laser treatment optimization in retinoschisis]

In this study a new original technique is proposed for treatment of II-III retinoschisis using diode laser Milon Lachta (Saint-Petersburg). Laser radiation parameters were wave length 0,83 microm, energy 350-850 m W, time 0,2-0,3 s, spot diameter 150-200 microm. Original technique of gradual progressive laser coagulation was performed in 72 patients with II-I1 retinoschisis using diode laser. This treatment allowed to preserve macular function to the maximum.

Intraocular gas treatment for myopic foveoschisis

PURPOSE

To report a case of symptomatic myopic retinoschisis with foveolar detachment and lamellar macular hole, treated with expansible gas.

METHODS

Interventional case report. A myopic patient presented with a history of decreased vision and metamorphopsia in his right eye. Optical coherence tomography (OCT) revealed an increased macular thickness, thinning and separation of the inner and external retina (retinoschisis or foveoschisis), foveolar detachment, lamellar hole, and foveolar vitreous traction. We treated the patient with a single dose of 0.2 mL of perfluoroethane (C2F6), performed under retrobulbar anesthesia, followed by prone posturing for 15 days.

RESULTS

OCT showed reattachment of the foveolar retina, disappearance of the retinoschisis, and visual acuity improvement.

CONCLUSIONS

Intraocular expansible gas and prone posturing, without vitrectomy, could be an alternative treatment in selected cases of symptomatic macular foveoschisis with foveolar detachment, in the absence of dense epiretinal membranes.

Retinoschisin (RS1), the Protein Encoded by the X-linked Retinoschisis Gene, Is Anchored to the Surface of Retinal Photoreceptor and Bipolar Cells through Its Interactions with a Na/K ATPase-SARM1 Complex

Retinoschisin or RS1 is a discoidin domain-containing protein encoded by the gene responsible for X-linked retinoschisis (XLRS), an early onset macular degeneration characterized by a splitting of the retina. Retinoschisin, expressed and secreted from photoreceptors and bipolar cells as a homo-octameric complex, associates with the surface of these cells where it serves to maintain the cellular organization of the retina and the photoreceptor-bipolar synaptic structure. To gain insight into the role of retinoschisin in retinal cell adhesion and the pathogenesis of XLRS, we have investigated membrane components in retinal extracts that interact with retinoschisin. Unlike the discoidin domain-containing blood coagulation proteins Factor V and Factor VIII, retinoschisin did not bind to phospholipids or retinal lipids reconstituted into unilamellar vesicles or immobilized on microtiter plates. Instead, co-immunoprecipitation studies together with mass spectrometric-based proteomics and Western blotting showed that retinoschisin is associated with a complex consisting of Na/K ATPase (alpha3, beta2 isoforms) and the sterile alpha and TIR motif-containing protein SARM1. Double labeling studies for immunofluorescence microscopy confirmed the co-localization of retinoschisin with Na/K ATPase and SARM1 in photoreceptors and bipolar cells of retina tissue. We conclude that retinoschisin binds to Na/K ATPase on photoreceptor and bipolar cells. This interaction may be part of a novel SARM1-mediated cell signaling pathway required for the maintenance of retinal cell organization and photoreceptor-bipolar synaptic structure.

Retinoschisin Gene Therapy and Natural History in theRs1h-KO Mouse: Long-term Rescue from Retinal Degeneration

PURPOSE

The authors characterized the natural history of a retinoschisin gene knockout (Rs1h-KO) mouse model and evaluated the long-term effects of retinal rescue after AAV(2/2)-CMV-Rs1h gene delivery.

METHODS

Full-field scotopic electroretinograms (ERGs) were recorded from 44 male hemizygous Rs1h-KO and 44 male wild-type (WT) C57BL/6J mice at six ages between 1 and 16 months. Retinal morphometry included outer segment layer (OSL) width, photoreceptor cell count, and grading of schisis cavity severity. One eye each of seven Rs1h-KO mice at age 14 days was injected with AAV(2/2)-CMV-Rs1h, and retinal histology and ERG findings at 14 months were analyzed.

RESULTS

The outer nuclear layer (ONL) of 1-month-old Rs1h-KO mice was disorganized but had nearly normal cell counts. The OSL was thinned, rod outer segments were misaligned, and abundant schisis cavities spanned the inner nuclear and outer plexiform layers in all retinas. ERG a- and b-wave amplitudes at this age were reduced by 33% and 50%, respectively. ERG and ONL cell numbers decreased further between 1 and 16 months, with unequal changes in the a- and b-waves with age. The a-wave reduction correlated well with the steady decline in ONL cell number, whereas a rapid decline in the b-wave and a (b/a-wave) ratio less than in WT were associated with increasing severity of schisis cavities at young ages. At 4 months, the cavities were maximal, but they coalesced and disappeared at older ages. The (b/a-wave) ratio was inversely correlated with cavity severity across all ages (r = -0.74; P < 0.0001; n = 22). Considerable heterogeneity was observed at each age in the ERG amplitudes and retinal morphology. Mice injected with AAV-Rs1h at 14 days showed considerable structural and functional rescue at age 14 months, including improved rod outer and inner segment integrity, less photoreceptor cell loss, and larger ERG amplitudes compared with untreated fellow eyes.

CONCLUSIONS

The ERG of the Rs1h-KO mouse at early ages reflects disruption of photoreceptor and second-order neuron function. In mid to late ages, the ERG decline reflects primarily photoreceptor degeneration. The Rs1h-KO mouse is consistent with human clinical X-linked juvenile retinoschisis (XLRS) in showing schisis cavities, which affect primarily the b-wave, the regression of schisis cavities at older ages, and a considerable range in phenotypic severity across individuals. This mouse model also indicates the critical roll of RS-protein in photoreceptor survival consistent with decreased a-waves in some patients with XLRS. Long-term rescue of retinal morphology and function by AAV-Rs1h gene transfer may provide a basis for considering intervention in the homologous human XLRS condition.

Congenital X-linked retinoschisis classification system

PURPOSE

To establish a classification system for congenital X-linked retinoschisis (CXLRS) using clinical examination and optical coherence tomography (OCT).

METHODS

Thirty-eight eyes of 19 patients who carried a clinical diagnosis of CXLRS were examined with OCT and clinical examination. Eyes were classified into one of four types based on a combination of clinical examination and OCT.

RESULTS

All patients had bilateral OCT scanning performed at an average age of 8.64 years (range 2.24-17.4 years). Review of OCT scans revealed that 37 of 38 eyes had foveal schisis (97%) while 31 of 38 (82%) eyes had macular schisis deeper than the nerve fiber layer in areas of ophthalmoscopically normal macular retina. The authors termed this flat schisis phenomenon lamellar schisis. Thirty of 38 (79%) had peripheral bullous schisis cavities present.

CONCLUSIONS

OCT examinations of patients with CXLRS reveal lamellar schisis in areas of ophthalmoscopically normal macular retina in 82% of eyes with the clinical diagnosis of CXLRS. Using both clinical examination and OCT, the authors were able to identify foveal, lamellar, and peripheral schisis, lamellar schisis only identifiable by OCT. These findings allow the authors to propose a classification system. The authors hope this classification system will allow a better understanding of the natural history of CXLRS disease and allow testing of therapeutic options.

Genome-Wide Expression Profiling of the Retinoschisin-Deficient Retina in Early Postnatal Mouse Development

PURPOSE

The Rs1h knockout mouse displays retinal features typical for X-linked juvenile retinoschisis (RS). Consequently, this mouse line represents an excellent model to study early molecular events in RS.

METHODS

Whole genome expression profiling using DNA-microarrays was performed on total RNA extracts from retinoschisin-deficient and wild-type murine retinas from postnatal days 7, 9, 11, and 14. Quantitative real-time RT-PCR (qRT-PCR) analysis of additional time points facilitated the refinement of the temporal expression profile of differentially regulated transcripts. Differential protein expression was confirmed by Western blot analysis.

RESULTS

Based on biostatistic and knowledge-based DNA-microarray analyses we have identified differentially regulated retinal genes in early postnatal stages of the Rs1h-deficient mouse defining key molecular pathways including adhesion, cytoskeleton, vesicular trafficking, and immune response. A significant upregulation of Egr1 at P11 and several microglia/glia-related transcripts starting at P11 with a peak at P14 were identified in the diseased retina. The results provided evidence that macrophage/microglia activation precedes apoptotic photoreceptor cell death. Finally, the role of Egr1 in the pathogenesis of Rs1h-deficiency was investigated, and the results indicated that activation of the MAPK Erk1/2 pathway occurs as early as P7. Analyses of Rs1h(-/Y)/Egr1(-/-) double-knockout mice suggest that Egr1 upregulation is not a prerequisite for macrophage/microglia activation or apoptosis.

CONCLUSIONS

The findings imply that microglia/glia activation may be triggering events in the photoreceptor degeneration of retinoschisin-deficient mice. Furthermore, the data point to a role of Erk1/2-Egr1 pathway activation in RS pathogenesis.

X-linked retinoschisis: an update

X-linked retinoschisis is the leading cause of macular degeneration in males and leads to splitting within the inner retinal layers leading to visual deterioration. Many missense and protein truncating mutations have now been identified in the causative retinoschisis gene (RS1) which encodes a 224 amino acid secretory retinal protein, retinoschisin. Retinoschisin octamerisation is implicated in cell-cell interactions and cell adhesion perhaps by interacting with beta2 laminin. Mutations cause loss of retinoschisin function by one of the three mechanisms: by interfering with protein secretion, by preventing its octamerisation or by reducing function in the secreted octamerised protein. The development of retinoschisis mouse models have provided a model system that closely resembles the human disease. Recent reports of RS1 gene transfer to these models and the sustained restoration of some retinal function and morphology suggest gene replacement may be a possible future therapy for patients.

An unusual X-linked retinoschisis phenotype and biochemical characterization of the W112C RS1 mutation

A 52-year-old subject harboring an RS1 gene W112C mutation presented with a prominent and asymmetric tapetal-like retinal sheen. Transient ERG responses were smaller and slower in the eye with the more extensive sheen, an association that, to our knowledge, had not been previously reported. An ON-pathway dysfunction explained the abnormalities of the transient but not those of the flicker ERGs. Although in vitro studies showed that the W112C mutant retinoschisin is present only in the cellular fraction and is not secreted, disease expression was remarkably mild, consistent with the notion of the existence of genetic and/or epigenetic disease modifiers.

The role of caspases in photoreceptor cell death of the retinoschisin-deficient mouse

Early schisis cavities in the retinal bipolar cell layer accompanied by progressive loss of cone and rod photoreceptor cells are the hallmark of the retinoschisin-deficient (Rs1h(-/Y)) murine retina. With this study we aimed at elucidating the molecular events underlying the photoreceptor cell death in this established murine model of X-linked juvenile retinoschisis. We show that photoreceptor degeneration in the Rs1h(-/Y) mouse is due to apoptotic events peaking around postnatal day 18. Cell death is accompanied by increased expression of initiator and inflammatory caspases but not by downstream effector caspases. The strong induction of caspase-1 (Casp1) prompted us to explore its involvement in the apoptotic process. We therefore generated double knock-out mice deficient for both retinoschisin and Casp1. No direct influence of the Casp1 genotype on apoptosis could be identified although striking differences in the overall number of resident microglia were observed independent of the Rs1h genotype.

[Interferon alpha-associated retinopathy in patients with chronic hepatitis C]

BACKGROUND

Interferons are a complex group of glycoproteins with antiviral, antiproliferative and immunomodulatory activity. They are used to treat different types of human neoplasms and chronic hepatitis C. Several case reports have described interferon-induced ocular side effects since the first case in 1990.

PATIENT AND METHODS

We report about a 61-year-old female undergoing interferon 2alpha treatment who developed bilateral retinopathy during systemic therapy and provide a summary about ocular side effects and their consequences.

CONCLUSIONS

Patients should be monitored by ophthalmologists before, during and after interferon therapy in order to avoid side effects like retinal neovascularisation and to prevent potential serious side effects.

[Senile retinoschisis with tearing of the deep layer--classification and pathogenic hypotheses]

The observations have been made on 52 eyes with senile retinoschisis with tearing of the deep layer. These principle studies are the aspect of tearing, in order to classify and discuss the pathogenic hypotheses. Seven types of tearing are presented. Their modes of formation seem different. We established a pathogenic classification of these tears. The risk of operation on a secondary retinal detachment is always a subject of discussion even if the symptomatic detachment may be considered very rare. From these seven observation of schisis detachment, there is proposed a pathogenic hypothesis. The vitreous have played the principal role in making a traction on the edge of the deep tears where sometimes the retinoschisis is not formed. It is recommended to observe and analyse systematically the tearing of the retinoschisis external layer.

X-LINKED RETINOSCHISIS IN THREE FEMALES FROM THE SAME FAMILY: A PHENOTYPE–GENOTYPE CORRELATION

PURPOSE

To describe the clinical findings and outcome for three homozygous females affected with X-linked retinoschisis (XLRS) in a large Colombian family with 26 affected males.

METHODS

Retrospective review of charts for females from a family with XLRS who underwent complete ophthalmologic examinations, ancillary tests, clinical genetic evaluation, and molecular studies.

RESULTS

Three female patients (6 eyes) with clinical findings of XLRS were identified. The patients' ages ranged from 10 to 37 years. Initial visual acuity was equal to or worse than 20/50 in 4 eyes (66%) of 2 patients. Four eyes (66%) were hyperopic. Intraocular pressure was normal in all eyes. Three eyes (50%) had cataracts, and vitreous veils were present in 3 (50%). The optic disk was pale in 6 eyes (100%). Foveal schisis was present in 6 eyes (100%). Peripheral retinal schisis was present in five eyes. A silvery gloss or tapetal-like retinal reflex or sheen was observed in 6 eyes (100%), and dendritic lines were found in 2 (33%). One eye had a retinal break, and one had a retinal detachment. Two eyes underwent cataract extraction; one patient underwent bilateral cryotherapy, one, laser treatment, and one, scleral buckling. Final visual acuity was 20/50 to 20/100 in 2 eyes and 20/200 to 20/400 in 4. Follow-up ranged from 7 to 22 years. Molecular analysis showed that all three female patients were homozygous for the allele 639delG of (on) the XRLS1 gene.

CONCLUSIONS

Compared with their affected male relatives, three females from a family with XLRS had similar ocular findings and a more severe course of disease. These findings are explained by the fact that these patients were homozygous for a mutation in the XLRS1 gene.

Ultrastructure of internal limiting membrane in myopic foveoschisis

PURPOSE

To reveal the pathogenesis of myopic foveoschisis (MF).

DESIGN

Clinicopathological report.

METHODS

Internal limiting membranes (ILMs) were collected from ten patients with MF and five patients with idiopathic macular hole (IMH) as a control. Samples were subjected to transmission electron microscopic study. Characteristics of the ILM were compared between the two groups.

RESULTS

Collagen fiber and cell debris were identified on the inner surface of ILM in seven eyes (70%) with MF, significantly more (P < .05) than found in IMH subjects (0%). More fibrous glial cells were likely to be found on the inner surface of ILM. No significant difference in fibroblast-like cell adhesion was observed.

CONCLUSIONS

Collagen fiber and cellular component are suggested to play an important role in developing MF. ILM peeling may be essential for vitrectomy for MF.

A Retinal Neuronal Developmental Wave of Retinoschisin Expression Begins in Ganglion Cells during Layer Formation

PURPOSE

Mutations in the retinoschisin gene, RS-1, cause juvenile X-linked retinoschisis (XLRS), a dystrophy characterized by delamination of the inner retinal layers, leading to visual impairment. Although the retinoschisin protein (RS) is expressed most abundantly in photoreceptors in the outer retina, XLRS disease affects the innermost retinal layers, including the nerve fiber layer that contains retinal ganglion cells (RGCs). Considering the histopathological and electrophysiological characteristics of the clinical disease, the present study was conducted to evaluate the local cellular expression of RS-1 during retinal development.

METHODS

RS protein and RS-1 mRNA were localized to specific retinal cell types in embryonic to adult mice by immunohistochemistry, confocal immunofluorescence microscopy, catalyzed reporter deposition in situ hybridization, and laser capture microdissection/RT-PCR.

RESULTS

RS-1 mRNA was expressed first in RGCs by postnatal day (P)1, after terminal differentiation. Expression then moved posteriorly through the retina in a spatial and temporal developmental wave, as additional neuronal classes were born and synaptic layers were formed. RS was expressed by bipolar cells at a time when these neurons were establishing functional synapses with photoreceptors, evidenced by the appearance of the electroretinogram b-wave between P12 and P14.

CONCLUSIONS

All major classes of adult retinal neurons, with the possible exception of horizontal cells, express RS protein and mRNA, strongly suggesting that retinoschisin in the inner retina is synthesized locally rather than being transported, as earlier proposed, from distal retinal photoreceptors. Continued expression of RS by mature inner-retinal neurons supports the possibility of a therapeutic strategy of protein replacement to treat both infants and adults with XLRS.

RS-1Gene Delivery to an AdultRs1hKnockout Mouse Model Restores ERG b-Wave with Reversal of the Electronegative Waveform of X-Linked Retinoschisis

PURPOSE

To create and evaluate a mouse model of human X-linked juvenile retinoschisis (XLRS) and then investigate whether supplementing with the retinoschisin protein by gene delivery can reverse the abnormal "electronegative" electroretinogram (ERG) retinal response.

METHODS

An X-linked retinoschisis mouse (Rs1h-KO) model was created by substituting a neomycin resistance cassette for exon 1 and 1.6 kb of intron 1 of Rs1h, the murine orthologue of the human RS-1 gene. RS protein was evaluated by immunohistochemistry and Western blot analysis with a polyclonal RS N-terminus antibody. Retinal function was evaluated by conventional, full-field flash ERG recordings. RS protein supplementation therapy was evaluated by gene transfer with an AAV(2/2)-CMV-Rs1h vector containing C57BL/6J Rs1h cDNA under the regulation of a CMV promoter, and ERG functional analysis was performed.

RESULTS

No RS protein was detected by Western blot analysis or immunohistochemistry in the Rs1h-KO mouse. Dark-adapted ERG responses showed an electronegative configuration, with b-wave reduction in both Rs1h(-/Y) and Rs1h-/- mice, typical of XLRS in humans. Histologic examination of Rs1h-KO mice showed disorganization of multiple retinal layers, including duplication and mislocalization of ganglion cells, laminar dissection through the inner plexiform layer, disorganization of the outer plexiform layer, loss of regularity of the outer nuclear layer, and shortening of the inner/outer segments with mislocalization of photoreceptor nuclei into this layer. After intraocular administration of AAV(2/2)-CMV-Rs1h, immunohistochemistry showed retinoschisin expression in all retinal layers of Rs1h(-/Y) mice, and ERG recordings showed reversal of the electronegative waveform and restoration of the normal positive b-wave.

CONCLUSIONS

The RS-KO mouse mimics structural features of human X-linked juvenile retinoschisis with dissection through, and disorganization of, multiple retinal layers. The Rs1h-KO functional deficit results in an electronegative ERG waveform that is characteristic of human retinoschisis disease and that implicates a synaptic transmission deficit in the absence of retinoschisin protein. Replacement therapy by supplementing normal Rs1h protein in the adult Rs1h-KO mouse restored the normal ERG configuration. This indicates that gene therapy is a viable strategy of therapeutic intervention even in the postdevelopmental adult stage of XLRS disease.

Vitreal pathogenic role in optic pit foveolar retinoschisis and central serous retinopathy

PURPOSE

To expand on current theories concerning the vitreal-induced mechanism underlying the development of foveolar retinoschisis and macular sensory detachments associated with optic nerve head pits. To propose the notion that vitreal traction may contribute to the pathogenesis of serous detachments in central serous chorioretinopathy (CSC).

REPORTS

We describe two patients, one with macular retinoschisis and the other with central serous detachment. The first patient, a 45-year-old Hispanic female, presented with a temporally located optic nerve head pit, foveolar retinoschisis and schisis retinal spaces extending to the surrounding macula and to the disc. The second patient, a 43-year-old Haitian male, developed a central serous retinal detachment OS with decreased visual acuity one day following in-office administration of Apraclonidine (0.5 per cent Iopidine, Alcon) and Dorzolamide-Timolol Maleate (Cosopt, Merck) to lower elevated intraocular pressure (IOP). Macular retinal pigment mottling and epiretinal membrane sheen OU had been observed on his initial visit. Visual acuity improved within a three-day period with resolution of the serous detachment.

CONCLUSION

We suggest that the persistence of Cloquet's canal may permit fluid leakage into the proximal vitreous in cases of congenital optic nerve head pits. Tangential vitreal traction may promote the opening of a fistula at the optic pit and additionally thrust vitreal fluid into the pit and retinal space inducing the formation of schisis spaces, foveolar-schisis and underlying sensory serous detachment. We question whether a reduction in vitreous volume, induced by initial administration of anti-glaucoma medications, may contribute to the development and/or recurrence of central serous choroidopathy in predisposed individuals.

Retinal detachment 7 years after prophylactic schisis cavity excision in juvenile X-linked retinoschisis

A 7-year-old boy with X-linked juvenile retinoschisis developed a retinal detachment at the site of previous prophylactic excision of a schisis cavity. The patient underwent a scleral buckle procedure, pars plana vitrectomy, membrane peel, and silicone oil injection with successful reattachment. At last follow-up, the visual acuity was 20/400 and the retina was attached. Prophylactic excision of a schisis cavity may be complicated by retinal detachment several years after the surgery. Given the favorable natural history of schisis cavities in X-linked juvenile retinoschisis, the decision to perform prophylactic excision should be undertaken cautiously after full consideration of the potential complications.

Clinical features of X linked juvenile retinoschisis associated with new mutations in the XLRS1 gene in Italian families

AIMS

To describe the clinical phenotype of X linked juvenile retinoschisis in eight Italian families with six different mutations in the XLRS1 gene.

METHODS

Complete ophthalmic examinations, electroretinography and A and B-scan standardised echography were performed in 18 affected males. The coding sequences of the XLRS1 gene were amplified by polymerase chain reaction and directly sequenced on an automated sequencer.

RESULTS

Six different XLRS1 mutations were identified; two of these mutations Ile81Asn and the Trp122Cys, have not been previously described. The affected males showed an electronegative response to the standard white scotopic stimulus and a prolonged implicit time of the 30 Hz flicker. In the families with Trp112Cys and Trp122Cys mutations we observed a more severe retinoschisis (RS) clinical picture compared with the other genotypes.

CONCLUSION

The severe RS phenotypes associated with Trp112Cys and to Trp122Cys mutations suggest that these mutations determine a notable alteration in the function of the retinoschisin protein.

[Macular dystrophies]

Macular dystrophies are a group of hereditary disorders of the macula occurring in children or young adults. The most frequent in France will be presented in detail: Best disease, Stargardt macular dystrophy, cone dystrophy, X-linked retinoschisis, pattern dystrophy, and malattia leventinese. Molecular biology studies have now mapped and identified the genes involved in these macular dystrophies. Analysis of the features of fundus examination will lead to further examinations such as fluorescein angiography, indocyanine green angiography, optical coherent tomography, electroretinography, or electrooculography, in order to confirm the diagnosis. We will also present the differential diagnosis of each of these macular dystrophies.

X-linked retinoschisis: report of a family with a rare deletion in the XLRS1 gene

PURPOSE

To describe the clinical features and identify the disease causing mutation in a family with X-linked retinoschisis.

DESIGN

Cohort study.

METHODS

Genealogical investigation and mutation screening of the XLRS1 gene were performed in a four generation family of Icelandic ancestry. Three affected family members were evaluated clinically over a 29-year period.

RESULTS

A rarely reported, four base pair deletion (375- 378 del AGAT) in exon 5 of the XLRS1 gene was found in all affected males. A high degree of intrafamilial variability was observed in the progression of the disorder over 29 years.

CONCLUSIONS

Identification of the disease causing mutation in this family allows for the diagnosis of individuals at risk for this inherited macular degeneration. Furthermore, the long-term follow-up of subjects with identical mutations helps to better characterize the highly variable clinical course of this disorder.

Vitreous surgery for highly myopic eyes with foveal detachment and retinoschisis

PURPOSE

To evaluate the efficacy of vitreous surgery for highly myopic eyes with foveal detachment and retinoschisis.

DESIGN

Retrospective comparative interventional case series.

PARTICIPANTS

Seven patients (nine highly myopic eyes) with posterior staphyloma with foveal detachment and retinoschisis without macular hole. Preoperative best-corrected visual acuity in nine eyes ranged from 0.02 to 0.4 (average, 0.17).

METHODS

Vitreous surgery performed on all nine eyes consisted of core vitrectomy, surgically induced posterior vitreous detachment (three eyes), removal of the premacular vitreous cortex and internal limiting membrane in the posterior staphyloma, and 30% SF(6) gas tamponade. Patients were instructed to maintain a prone position for at least 1 day after surgery. The postoperative follow-up period ranged from 6 to 42.5 months (average, 20.4 months).

MAIN OUTCOME MEASURES

Visual acuity, retinal tomography monitored by optical coherence tomography.

RESULTS

In eight of the nine eyes, foveal detachment and retinoschisis gradually decreased in height, and these eyes finally attained foveal attachment and visual improvement within 6 months postoperatively. The postoperative best-corrected visual acuity of these eight eyes ranged from 0.4 to 0.6 (average, 0.48). One eye developed a full-thickness macular hole during vitreous surgery, and its postoperative best-corrected visual acuity was 0.08.

CONCLUSIONS

Foveal detachment and retinoschisis in highly myopic eyes resolved after vitrectomy. Vitreous surgery might have a rationale as prophylactic treatment for highly myopic eyes at high risk of macular hole development.