Outcome measures in juvenile X-linked retinoschisis: A systematic review

Retinal organoids with X-linked retinoschisis RS1 (E72K) mutation exhibit a photoreceptor developmental delay and are rescued by gene augmentation therapy

BACKGROUND

X-linked juvenile retinoschisis (XLRS) is an inherited disease caused by RS1 gene mutation, which leads to retinal splitting and visual impairment. The mechanism of RS1-associated retinal degeneration is not fully understood. Besides, animal models of XLRS have limitations in the study of XLRS. Here, we used human induced pluripotent stem cell (hiPSC)-derived retinal organoids (ROs) to investigate the disease mechanisms and potential treatments for XLRS.

METHODS

hiPSCs reprogrammed from peripheral blood mononuclear cells of two RS1 mutant (E72K) XLRS patients were differentiated into ROs. Subsequently, we explored whether RS1 mutation could affect RO development and explore the effectiveness of RS1 gene augmentation therapy.

RESULTS

ROs derived from RS1 (E72K) mutation hiPSCs exhibited a developmental delay in the photoreceptor, retinoschisin (RS1) deficiency, and altered spontaneous activity compared with control ROs. Furthermore, the delays in development were associated with decreased expression of rod-specific precursor markers (NRL) and photoreceptor-specific markers (RCVRN). Adeno-associated virus (AAV)-mediated gene augmentation with RS1 at the photoreceptor immature stage rescued the rod photoreceptor developmental delay in ROs with the RS1 (E72K) mutation.

CONCLUSIONS

The RS1 (E72K) mutation results in the photoreceptor development delay in ROs and can be partially rescued by the RS1 gene augmentation therapy.

Efficacy of carbonic anhydrase inhibitors on cystoid fluid collections and visual acuity in patients with X-linked retinoschisis

PURPOSE

To date, there is no standard treatment regimen for carbonic anhydrase inhibitors (CAI) in X-linked retinoschisis (XLRS) patients. This retrospective study aims to evaluate the efficacy of CAI on visual acuity and cystoid fluid collections (CFC) in XRLS patients in Dutch and Belgian tertiary referral centers.

DESIGN

Retrospective cohort study PARTICIPANTS: Forty-two patients with X-linked retinoschisis METHODS: In total, 42 patients were enrolled. To be included, patients had to have previous treatment with oral CAI (acetazolamide), topical CAI (brinzolamide/dorzolamide), or a combination of oral and topical CAI for at least 4 consecutive weeks. We evaluated the effect of the CAI on best-corrected visual acuity (BCVA) and central foveal thickness (CFT) on optical coherence tomography (OCT).

MAIN OUTCOME MEASURES

Central foveal thickness and best corrected visual acuity RESULTS: The median age at the baseline visit of the patients in this cohort study was 14.7 years (range 43.6 years) with a median follow-up period of 4.0 years (Q1: 2.2 years, Q3: 5.2 years). During the follow-up period, 25 patients were treated once with an oral CAI (60%), 24 once with a topical CAI (57%), and 11 patients once with a combination of both topical and oral CAI (26%). We observed a significant reduction of CFT for oral CAI by 14.37 μm per 100 mg a day (P < 0.001, 95% CI -19.62 to -9.10 μm) and for topical CAI by 7.52 μm per drop a day (p = 0.017, 95% CI -13.67 to -1.32 μm). The visual acuity changed significantly while on treatment with oral CAI by -0.0059 logMAR per 100 mg (p= 0.0083, 95% CI -0.010 to -0.0013 logMAR). Seven patients (17%) had side effects leading to treatment discontinuation.

CONCLUSION

Our data indicate that treatment with (oral) CAI may be beneficial for short-term management of CFC in patients with XLRS. Despite a significant reduction in CFT, the change in visual acuity was modest and not of clinical significance. Nonetheless, the anatomical improvement of the central retina in these patients may be of value to create an optimal retinal condition for future potential treatment options such as gene therapy.

Generation of a gene-corrected isogenic iPSC cell line from an X-linked retinoschisis patient with a hemizygous mutation c.304C > T (p.R102W) in RS1 gene

X-linked retinoschisis (XLRS) is one of the most common retinal genetic diseases with progressive visual impairment in childhood affecting males. It is manifested with macular and/or peripheral schisis in neural retinas with no effective treatment. Previously, we successfully generated a human-induced pluripotent stem cell (iPSC) line from an XLRS patient carrying the hemizygous RS1 c. 304C > T (p.R102W) mutation. Here, we corrected the c.304C > T mutation in the RS1 gene using CRISPR/Cas9 technology to generate an isogenic control. This cell line is valuable for the study of XLRS.

Visual Acuity-Related Outer Retinal Structural Parameters on Swept Source Optical Coherence Tomography and Angiography in XLRS Patients and Carriers

Purpose

To assess the quantitative differences in vessel density and retinal thickness of X-linked retinoschisis (XLRS) patients and RS1 mutation carriers, and the correlation with best-corrected visual acuity (BCVA) with swept source optical coherence tomography (SS-OCT) and OCT angiography (OCTA).

Methods

We analyzed the correlation between the BCVA of XLRS patients and the SS-OCT and OCTA findings including the detailed structural characteristics of XLRS patients.

Results

Besides the schitic changes in various retinal layers, the structural disturbance of outer retina was universally found. In 29 eyes included in the quantitative analysis, XLRS patients showed lower vessel density of the superficial capillary plexus, deep capillary plexus and lower thickness of the outer nuclear layer. BCVA was correlated with the thickness of the outer plexiform layer and outer nuclear layer and the thickness from the outer limiting membrane to the retinal pigment epithelium. Carriers showed higher thickness of outer plexiform layer and smaller foveal avascular zone area.

Conclusions

SS-OCT and OCTA could identify the pathological alterations of the individual retinal layers and capillaries, which could pinpoint the exact location of the damages related to visual impairment. In the carriers, the subtle alterations that can be detected with SS-OCT, despite their normal visual acuity, may be caused by the lyonization.

Translational Relevance

Swept source optical coherence tomography can be used as an efficient technique to expose the retinal damage related to visual impairment for prognosis and follow-up.

Long-term functional and structural outcomes in X-linked retinoschisis: implications for clinical trials

Introduction

X-linked retinoschisis (XLRS) is an inherited retinal disease (IRD) caused by pathogenic mutations in the retinoschisin gene, RS1. Affected individuals develop retinal layer separation, leading to loss of visual acuity (VA). Several XLRS gene therapy trials have been attempted but none have met their primary endpoints. An improved understanding of XLRS natural history and clinical outcomes may better inform future trials. Here, we report the long-term functional and structural outcomes of XLRS and the relevance of RS1 genotypes to the visual prognosis of affected individuals.

Methods

A retrospective chart review of patients with molecularly confirmed X-linked retinoschisis was performed. Functional and structural outcomes, and RS1 genotype data, were included for analysis.

Results

Fifty-two patients with XLRS from 33 families were included in the study. Median age at symptom onset was 5 years (range 0-49) and median follow-up was 5.7 years (range 0.1-56.8). Macular retinoschisis occurred in 103 of 104 eyes (99.0%), while peripheral retinoschisis occurred in 48 of 104 eyes (46.2%), most often in the inferotemporal quadrant (40.4%). Initial and final VA were similar (logMAR 0.498 vs. 0.521; p = 0.203). Fifty of 54 eyes (92.6%) developed detectable outer retinal loss by age 20, and 29 of 66 eyes (43.9%) had focal or diffuse outer retinal atrophy (ORA) by age 40. ORA but not central subfield thickness (CST) was associated with reduced VA. Inter-eye correlation was modest for VA (r-squared = 0.03; p = 0.08) and CST (r-squared = 0.15; p = 0.001). Carbonic anhydrase inhibitors (CAIs) improved CST (p = 0.026), but not VA (p = 0.380). Eight of 104 eyes (7.7%) had XLRS-related retinal detachment (RD), which was associated with poorer outcomes compared to eyes without RD (median final VA 0.875 vs. 0.487; p <0.0001). RS1 null genotypes had greater odds of at least moderate visual impairment at final follow-up (OR 7.81; 95% CI 2.17, 28.10; p = 0.002) which was independent of age at onset, initial CST, initial ORA, or previous RD.

Discussion

Overall, long-term follow-up of XLRS patients demonstrated relatively stable VA, with presenting CST, development of ORA, and null RS1 mutations associated with poorer long-term visual outcomes, indicating a clinically relevant genotype-phenotype correlation in XLRS.

X-linked retinoschisis: mutation spectrum and genotype-phenotype relationship in an Italian pediatric cohort

BACKGROUND

X-linked juvenile retinoschisis (×LRS) is an X-linked vitreoretinal degenerative disease that consists of variable phenotypes ranging from severe early-onset defects to subtle abnormalities diagnosed in elderly patients. XLRS is caused by a loss of function of the protein Retinoschisin (RS1), which is essential to preserve retinal integrity and function of photoreceptor-bipolar synapse. The literature data so far mostly agree on the absence of a clear genotype-phenotype correlation in XLRS. We reviewed clinical and molecular characteristics of a cohort of Italian pediatric XLRS patients to assess the presence of a correlation between genotype and phenotype severity.

MATERIALS AND METHODS

We retrospectively examined clinical and genetic features of a cohort of 27 XLRS patients. In this study we included patients with a diagnosis of XLRS confirmed by fundus photography, spectral domain optical coherence tomography, and molecular analysis and with an onset of less than 10 years of age. We sorted RS1 variants according to their effect of RS1 structure and function in three separate groups.

RESULTS

According to previous studies, we did not observe a conclusive genotype-phenotype correlation in our cohort; nevertheless, we noticed that patients harboring RS1 variants leading to RS1-secreted mutants show a more homogeneous phenotype, with an overall good visual acuity, compared to the other two groups.

CONCLUSIONS

Our data support the hypothesis that secretion profile of RS1 could influence the severity of the phenotype. More extensive and functional studies are needed to acquire notions in view of the opportunity of gene replacement therapy for XLRS patients.

A patient with X-linked retinoschisis and exudative retinal detachment associated with a pathogenic hemizygous variant c.304c>T in RS1

BACKGROUND

X-linked retinoschisis (XLRS) is a rare retinal dystrophy due to pathogenic variants in the RS1 gene. The hallmark of the disease is a foveal spoke-wheel appearance. The purpose of this report is to expand the phenotypic spectrum of XLRS reporting a patient with atypical phenotype of XLRS associated with Coats-like phenotype.

MATERIALS AND METHODS

This is a case report of a patient diagnosed with XLRS who underwent ophthalmologic multimodal imaging and next-generation sequencing panel.

RESULTS

The proband is a 14-year-old male patient who presented at Instituto Suel Abujamra with a history of Coats Disease in the right eye treated with retinal laser in both eyes two years ago. His best-corrected visual acuity was count finger at 1 foot in the right eye and 20/40 in the left eye. Fundus exam showed an extensive area of exudation and retinal detachment in the right eye and cystic change at the fovea in a spoke-wheel pattern in the left eye. The next-generation sequencing panel targeting inherited retinal diseases with 236 genes found a pathogenic hemizygous variant c.304C>T (p.Arg102Trp) in RS1 that has already been reported.

CONCLUSIONS

The association of peripheral vascular incompetence and XLRS has already been described. Retinal exudation in the setting of XLRS is probably the result of vascular disruption and compromise. The loss of retinoschisin function that leads to foveal retinoschisis may also lead to vascular anomalies.

X-linked juvenile retinoschisis presenting with rhegmatogenous retinal detachment in a male Nigerian adolescent: A case report

A 15-year-old boy came to the eye clinic with reduced vision in the left eye of a year's duration and prior trauma. Best-corrected visual acuity was 6/9 and hand movement in both eyes, respectively. The anterior segment examination was essentially normal except for a Marcus Gunn pupil and a polar cataract in the left eye. Goldmann applanation tonometry was 10 and 06 mmHg, respectively, in the right and left eyes. Binocular indirect ophthalmoscopy of the right eye revealed pink disc, normal vessels and the Mizuo-Nakamura phenomenon with a cartwheel appearance at the macula. The left eye had a total retinal detachment with proliferative vitreoretinopathy and retinal tear at 12 o' clock. Optical coherence tomography revealed posterior vitreous detachment and schitic cavities at the macula in the left eye. A diagnosis of left rhegmatogenous retinal detachment with background X-linked juvenile retinoschisis was made. The patient was advised on a pars plana vitrectomy under guarded visual prognosis.

Electronegative electroretinogram in the modern multimodal imaging era

Background

The electronegative electroretinogram (ERG) reflecting inner retinal dysfunction can assist as a diagnostic tool to determine the anatomical location in eye disease. The aim of this study is to determine the frequency and aetiology of electronegative ERG in a tertiary ophthalmology centre and to develop a clinical algorithm to assist patient management.

Methods

Retrospective review of ERGs performed at the Save Sight Institute from January 2011 to December 2020. ERGs were performed according to ISCEV standard. The b:a ratio was analysed in dark adapted (DA) 3.0 or 12.0 recordings. Patients with ratio of ≤1.0 were included.

Results

A total of 4421 patients had ERGs performed during study period, of which 139 patients (3.1%) had electronegative ERG. The electronegative ERG patients' median age at referral time was 37 (0.7–90.6) years. The causative aetiologies were photoreceptor dystrophy (48, 34.5%), Congenital Stationary Night Blindness (CSNB) (33, 23.7%), retinal ischemia (18, 12.9%), retinoschisis (15, 10.8%), paraneoplastic autoimmune retinopathy (PAIR) and nonPAIR (14, 10.1%), batten disease (4, 2.9%), and inflammatory retinopathy (4, 2.9%). There were three patients with an unclassified diagnosis. Thirty‐two patients (23%) had good vision and a normal fundus appearance. Eleven patients (7.9%) had good vision and normal results in all multimodal imaging.

Conclusions

The frequency of electronegative ERG in our referral centre was 3.1% with photoreceptor dystrophy as the main aetiology. A significant number of the cases had good vision with normal fundus or normal multimodal imaging. This further highlights the value of an ERG in this modern multimodal imaging era.

The electrophysiological features of X-linked juvenile retinoschisis in a young male: a case report

This case report describes the detailed electrophysiological features and the corresponding relationship with the structural changes in a case of X-linked juvenile retinoschisis (XLRS). A 25-year-old male presented with a history of several years of decreased visual acuity in both eyes. The best corrected visual acuity was 20/200 in oculus dexter (OD) and 20/80 in oculus sinister. Retinoschisis was found in the macula by optical coherence tomography, which was more severe in OD. Electroretinogram revealed a similar electronegative waveform in both eyes. Visual evoked potential detected a reduced amplitude and delayed phase in P100-wave, which was worse in OD. The patient was diagnosed as XLRS and advised to undergo continuous medical observation. He was followed up for the next year, with no significant change in retinal function and structure being observed. These current findings suggest that electrophysiology permits the detailed analysis of the clinical picture of XLRS and helps to gain a deeper understanding of the pathogenesis.

Whole-exome sequencing identifies an RS1 variant in a Chinese family with X-linked retinoschisis

A notable behavioural feature of X-linked retinoschisis (XLRS) is extensive structural schisis (splitting) of the outer plexiform and inner nuclear layers of the neurosensory retina, which is partly combined with complications related to vitreous hemorrhage, macular holes and retinal detachment. The present study aimed to identify the pathogenic gene mutation in a three-generation Chinese family with XLRS by whole-exome sequencing (WES). The clinical information of a three-generation Chinese family with cases of XLRS was collected. WES was performed for the proband. A comparison with the human reference genome sequence (hg38) and bioinformatic analysis were performed to reveal putative variants and Sanger sequencing was applied to verify mutations in this family and healthy control participants. Intraretinal cystic spaces were detected by optical coherence tomography imaging. Structures of the wild-type and mutant retinoschisin 1 (RS1) protein were modelled by PyMol. Almost all patients had a history of vision loss and abnormal blue-purple colour vision; however, the phenotypes of the 4 patients were distinctly different. There was no linear correlation between phenotypic severity and age. A recurrent RS1 (Xp22.2) mutation (NM_000330: c.559C>T) was detected, resulting in the p.Q187X variant. According to the protein model, this variant is likely pathogenic. The present study was the first to report that RS1:c.559C>T induces XLRS in a three-generation Chinese pedigree, with the mutation leading to premature termination of translation of the RS1 protein. WES was able to diagnose XLRS, which has the characteristics of clinical and genetic heterogeneity.

Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling

X-linked Retinoschisis (XLRS) is an early-onset transretinal dystrophy, often with a prominent macular component, that affects males and generally spares heterozygous females because of X-linked recessive inheritance. It results from loss-of-function RS1 gene mutations on the X-chromosome. XLRS causes bilateral reduced acuities from young age, and on clinical exam and by ocular coherence tomography (OCT) the neurosensory retina shows foveo-macular cystic schisis cavities in the outer plexiform (OPL) and inner nuclear layers (INL). XLRS manifests between infancy and school-age with variable phenotypic presentation and without reliable genotype-phenotype correlations. INL disorganization disrupts synaptic signal transmission from photoreceptors to ON-bipolar cells, and this reduces the electroretinogram (ERG) bipolar b-wave disproportionately to photoreceptor a-wave changes. RS1 gene expression is localized mainly to photoreceptors and INL bipolar neurons, and RS1 protein is thought to play a critical cell adhesion role during normal retinal development and later for maintenance of retinal structure. Several independent XLRS mouse models with mutant RS1 were created that recapitulate features of human XLRS disease, with OPL-INL schisis cavities, early onset and variable phenotype across mutant models, and reduced ERG b-wave to a-wave amplitude ratio. The faithful phenotype of the XLRS mouse has assisted in delineating the disease pathophysiology. Delivery to XLRS mouse retina of an AAV8-RS1 construct under control of the RS1 promoter restores the retinal structure and synaptic function (with increase of b-wave amplitude). It also ameliorates the schisis-induced inflammatory microglia phenotype toward a state of immune quiescence. The results imply that XLRS gene therapy could yield therapeutic benefit to preserve morphological and functional retina particularly when intervention is conducted at earlier ages before retinal degeneration becomes irreversible. A phase I/IIa single-center, open-label, three-dose-escalation clinical trial reported a suitable safety and tolerability profile of intravitreally administered AAV8-RS1 gene replacement therapy for XLRS participants. Dose-related ocular inflammation occurred after dosing, but this resolved with topical and oral corticosteroids. Systemic antibodies against AAV8 increased in dose-dependent fashion, but no antibodies were observed against the RS1 protein. Retinal cavities closed transiently in one participant. Technological innovations in methods of gene delivery and strategies to further reduce immune responses are expected to enhance the therapeutic efficacy of the vector and ultimate success of a gene therapy approach.

Spontaneous resolution of schitic cavities in XLRS

X-linked retinoschisis (XLRS) is an inherited retinal condition that leads to schisis of the retina. In the past, treatment trials for XLRS have generally used OCT monitoring of the schitic cavities as the primary structural outcome measure and best corrected visual acuity as the primary functional outcome. Here, we report two cases of genetically confirmed XLRS with marked fluctuations in OCT morphology in the absence of treatment. Given this demonstration of spontaneous fluctuation in retinal structure on OCT in XLRS we suggest that alternative measures of retinal function should be used in future therapeutic trials in XLRS.