Correlation of Genetic and Clinical Findings in Spanish Patients with X-linked Juvenile Retinoschisis

Strabismus in Genetic Syndromes: A Review

Strabismus is a feature of many genetic syndromes, with highly variable penetrance. The congenital cranial dysinnervation disorders (CCDDs) result in paralytic strabismus, with limited eye movements. CCDDs result from either deficits in differentiation of the cranial motor neuron precursors or from abnormal axon guidance of the cranial nerves. Although most individuals with comitant strabismus are otherwise healthy, strabismus is a variable feature of many genetic syndromes, most commonly those associated with intellectual disability. We review 255 genetic syndromes in which strabismus has been described and discuss the variable penetrance. The association with intellectual disability and neurological disorders underscores the likely neurological basis of strabismus, but the variable penetrance emphasises the complexity of strabismus pathophysiology. The syndromes described here mostly result from loss of function or change in function of the responsible genes; one hypothesis is that nonsyndromic strabismus may result from altered expression or regulation of the same genes.

Genotype-Phenotype Correlations in 83 Korean X-linked Retinoschisis Patients: Impact of Retinoschisin 1 Secretion Profiles on Clinical Phenotypes

PURPOSE

To assess the correlation between genotype and phenotype severity in X-linked juvenile retinoschisis (XLRS) by examining clinical and genetic features of a cohort of Korean XLRS patients.

DESIGN

Retrospective, observational study.

PARTICIPANTS

Data from 83 consecutive male patients with molecularly confirmed XLRS were collected retrospectively.

METHODS

Clinical evaluation included best-corrected visual acuity (BCVA), fundus photography, spectral domain OCT (SD-OCT), and full-field electroretinography (ERG).

MAIN OUTCOME MEASURES

The phenotypic characteristics of a cohort of pediatric Korean patients with XLRS, based on mutation types (truncating vs. missense) and secretory profile (secretion vs. nonsecretion), were assessed.

RESULTS

A total of 166 eyes of 83 patients were included. The mean age at diagnosis was 6.1 ± 8.8 years (range, 0.5-20.7 years), with a mean follow-up time of 9.2 ± 7.0 years (range, 0.6-24.3 years). The BCVA at first and last examination ranged from light perception to 0.1 logarithm of the minimum angle of resolution (mean ± standard deviation, 0.75 ± 0.59 and 0.82 ± 0.65, respectively). No significant differences were observed between the truncating (0.71 ± 0.51 and 0.75 ± 0.44) and missense (0.77 ± 0.59 and 0.84 ± 0.66) variants (P = 0.678 and 0.551). Clinical parameters from fundus photography, SD-OCT, and ERG showed no differences. However, BCVA was better for the secretion group (0.51 ± 0.24 and 0.61 ± 0.30) than for the nonsecretion group (0.65 ± 0.71 and 0.87 ± 0.81), with a significant difference in the last BCVA (P = 0.021). OCT revealed a higher frequency of ellipsoid zone disruption in the nonsecretion group (P = 0.030), with no significant differences in other parameters.

CONCLUSIONS

The secretion profile of Retinoschisin 1 (RS1) could influence the severity of XLRS phenotypes. Patients with RS1-secreted mutants, particularly with intact octamerization, exhibit more homogeneous phenotypes and better visual acuity than the RS1-nonsecreted group. This data provide insights for studying genotype and phenotype correlations in both clinical and research fields.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any materials discussed in this article.

Genotype-Phenotype Associations in an X-Linked Retinoschisis Patient Cohort: The Molecular Dynamic Insight and a Promising SD-OCT Indicator

Purpose

This study investigated a three-dimensional indicator in spectral-domain optical coherence tomography (SD-OCT) and established phenotype-genotype correlation in X-linked retinoschisis (XLRS).

Methods

Thirty-seven patients with XLRS underwent comprehensive ophthalmic examinations, including visual acuity (VA), fundus examination, electroretinogram (ERG), and SD-OCT. SD-OCT parameters of central foveal thickness (CFT), cyst cavity volume (CCV), and photoreceptor outer segment length were assessed. CCV was defined as the sum of the areas of cyst cavities in uential B-scans, measured automatically by self-developed software (OCT-CCSEG). Structural changes of the protein associated with missense variants were quantified by molecular dynamics (MD). The correlation between genotype and phenotype was analyzed.

Results

Twenty-seven different RS1 variants were identified, including a novel variant c.336_337insT(p.L113Sfs*8). The average age of onset was 14.76 ± 15.75 years, and the mean VA was 0.84 ± 0.43 logMAR. The mean CCV was 1.69 ± 1.87 mm3, correlating significantly with CFT (R = 0.66; P < 0.01). In the genotype-phenotype analysis of missense variants, CCV significantly correlated with the structural effect on the protein of mutational changes referred to as wild type, including root-mean-square deviation (R = 0.34; P = 0.04), solvent accessible surface area (R = 0.38; P = 0.02), and surface hydrophobic area (R = 0.37; P = 0.03). The amplitude of scotopic 3.0 ERG a-waves and b-waves significantly correlated with the percentage change of the β-strand in the secondary structure (a-wave: R = -0.58, P < 0.01; b-wave: R = -0.53, P < 0.01).

Conclusions

CCV is a promising indicator to quantify the structural disorganization of XLRS retina. The OCT-CCSEG software calculated CCV automatically, potentially facilitating prognosis assessment and development of personalized treatment. Moreover, MD-involved genotype-phenotype analysis suggests an association between protein structural alterations and XLRS severity measured by CCV and ERG.

Vitreous Hemorrhage in Pediatric Patients With X-Linked Retinoschisis: Characteristics and Outcomes

OBJECTIVE

To report the management and outcomes of vitreous hemorrhage in pediatric patients with X-linked retinoschisis (XLRS).

MATERIALS AND METHODS

Retrospective case series of pediatric patients with XLRS with vitreous hemorrhage between January 2000 and January 2022 at the Bascom Palmer Eye Institute.

RESULTS

Nine patients (12 eyes) met inclusion criteria. The average age at presentation was 5.75 years and mean follow-up time was 6 years. All eyes (58.3%) that underwent fluorescein angiography exhibited peripheral capillary dropout. Six of 12 eyes (50%) were observed without intervention. Four of 12 eyes (33.3%) underwent intravitreal injection of bevacizumab and 2 (16.6%) underwent vitreoretinal surgery. Seven of 12 eyes (58.3%) had documented recurrence of vitreous hemorrhage during follow-up. All retinas were attached and had clear media at final follow-up.

CONCLUSION

Fluorescein angiography is a helpful tool to evaluate the vascular phenotype in XLRS. Favorable anatomic outcomes were noted in this cohort, but recurrence of vitreous hemorrhage was common. [Ophthalmic Surg Lasers Imaging Retina 2023;54:513-518.].

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.

Typical and atypical clinical presentations of X-Linked retinoschisis: A case series and literature review

X-linked retinoschisis (XLRS) is an X-linked inherited retinal dystrophy characterized by mild-to-severe visual impairment, splitting of the retinal layers, and a reduction in the dark-adapted b-wave amplitude on the electroretinogram. Typical clinical features include macular and peripheral schisis. Relatively common features reported include rhegmatogenous or tractional retinal detachment, vitreous hemorrhage, retinal pigment epithelial changes, vitreous veils, and various retinal vascular abnormalities with or without exudation. Macular hole and macular folds are atypical presentations of XLRS, along with several other rare findings. Here, we report 4 cases of XLRS with atypical clinical presentations and review the literature on XLRS, with a focus on the variable clinical features of this condition.

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.

Phenotype Heterogeneity and the Association Between Visual Acuity and Outer Retinal Structure in a Cohort of Chinese X-Linked Juvenile Retinoschisis Patients

Purpose: X-linked juvenile retinoschisis (XLRS), caused by mutations in the RS1 gene, is an X-linked recessive inherited disease that typically involves both eyes in the first 2 decades of life. Recently, the phenotype heterogeneity of this condition has drawn increasing attention. We reported various phenotypes caused by RS1 gene mutations in eleven patients from ten Chinese families.

Methods: Data on the medical history of the patients from ten Han families of central China were collected. Ophthalmic examinations including best-corrected visual acuity (BCVA), fundus photography, ultra-wide-angle sweep source optical coherence tomography (SS-OCT), and electroretinography (ERG) were performed. Adaptive optics (AO) images were acquired to evaluate the cone photoreceptor mosaic when applicable. Venous blood of the probands and their family members was collected, and DNA was subjected to sequencing based on next-generation sequencing with a custom-designed targeted gene panel PS400 for inherited retinal diseases. Validation was performed by Sanger sequencing and cosegregation. Pathogenicity was determined in accordance with the American College of Medical Genetics and Genomics (ACMG) guidelines.

Results: Ten RS1 mutations, including eight missense mutations and two terminator mutations, were identified in 10 XLRS families. c.657C > A (p.C219X) was a novel mutation in this cohort. These patients showed a variety of clinical phenotypes, including fovea schisis, bullous retinoschisis, and macular or peripheral atrophy. Fifteen eyes of eight patients exhibited macular retinoschisis, and twelve eyes of seven patients exhibited peripheral retinoschisis. In addition, three patients showed asymmetrical fundus manifestations. Of importance, three patients without macular retinoschisis were misdiagnosed until genetic testing results were obtained. AO showed a decrease in cone density and loss of regularity in the cystic schisis macular of XLRS. Furthermore, the BCVA was associated with the photoreceptor inner segment and outer segment (IS/OS) thickness.

Conclusion: With complicated clinical manifestations, a considerable portion of XLRS patients may present various phenotypes. It should be noted that asymmetry in fundus appearance in both eyes could lead to misdiagnosis easily. Thus, genetic testing is crucial for making a final diagnosis in those patients who are suspected of having amblyopia, bilateral or unilateral macular atrophy, or conditions presenting an asymmetric fundus appearance. In addition, the residual cone photoreceptor structure was critical for the maintenance of useful vision.

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.

Gene Therapy in Inherited Retinal Diseases: An Update on Current State of the Art

Background: Gene therapy cannot be yet considered a far perspective, but a tangible therapeutic option in the field of retinal diseases. Although still confined in experimental settings, the preliminary results are promising and provide an overall scenario suggesting that we are not so far from the application of gene therapy in clinical settings. The main aim of this review is to provide a complete and updated overview of the current state of the art and of the future perspectives of gene therapy applied on retinal diseases.

Methods: We carefully revised the entire literature to report all the relevant findings related to the experimental procedures and the future scenarios of gene therapy applied in retinal diseases. A clinical background and a detailed description of the genetic features of each retinal disease included are also reported.

Results: The current literature strongly support the hope of gene therapy options developed for retinal diseases. Although being considered in advanced stages of investigation for some retinal diseases, such as choroideremia (CHM), retinitis pigmentosa (RP), and Leber's congenital amaurosis (LCA), gene therapy is still quite far from a tangible application in clinical practice for other retinal diseases.

Conclusions: Gene therapy is an extremely promising therapeutic tool for retinal diseases. The experimental data reported in this review offer a strong hope that gene therapy will be effectively available in clinical practice in the next years.

X-Linked Retinoschisis: Novel Clinical Observations and Genetic Spectrum in 340 Patients

PURPOSE

To describe the natural course, phenotype, and genotype of patients with X-linked retinoschisis (XLRS).

DESIGN

Retrospective cohort study.

PARTICIPANTS

Three hundred forty patients with XLRS from 178 presumably unrelated families.

METHODS

This multicenter, retrospective cohort study reviewed medical records of patients with XLRS for medical history, symptoms, visual acuity (VA), ophthalmoscopy, full-field electroretinography, and retinal imaging (fundus photography, spectral-domain [SD] OCT, fundus autofluorescence).

MAIN OUTCOME MEASURES

Age at onset, age at diagnosis, severity of visual impairment, annual visual decline, and electroretinography and imaging findings.

RESULTS

Three hundred forty patients were included with a mean follow-up time of 13.2 years (range, 0.1-50.1 years). The median ages to reach mild visual impairment and low vision were 12 and 25 years, respectively. Severe visual impairment and blindness were observed predominantly in patients older than 40 years, with a predicted prevalence of 35% and 25%, respectively, at 60 years of age. The VA increased slightly during the first 2 decades of life and subsequently transitioned into an average annual decline of 0.44% (P < 0.001). No significant difference was found in decline of VA between variants that were predicted to be severe and mild (P = 0.239). The integrity of the ellipsoid zone (EZ) as well as the photoreceptor outer segment (PROS) length in the fovea on SD OCT correlated significantly with VA (Spearman's ρ = -0.759 [P < 0.001] and -0.592 [P = 0.012], respectively). Fifty-three different RS1 variants were found. The most common variants were the founder variant c.214G→A (p.(Glu72Lys)) (101 patients [38.7%]) and a deletion of exon 3 (38 patients [14.6%]).

CONCLUSIONS

Large variabilities in phenotype and natural course of XLRS were seen in this study. In most patients, XLRS showed a slow deterioration starting in the second decade of life, suggesting an optimal window of opportunity for treatment within the first 3 decades of life. The integrity of EZ as well as the PROS length on SD OCT may be important in choosing optimal candidates for treatment and as potential structural end points in future therapeutic studies. No clear genotype-phenotype correlation was found.

Comprehensive analysis of genetic and clinical characteristics of 30 patients with X-linked juvenile retinoschisis in China

Purpose

To provides the clinical and genetic characteristics of a series of Chinese patients with X‐linked juvenile retinoschisis (XLRS) through multimodal imaging and next‐generation sequencing.

Methods

Thirty patients (60 eyes) from 29 unrelated families of Chinese origin with XLRS were screened using multigene panel testing, and underwent a complete clinical evaluation. All variants identified in this study and reported in the Human Gene Mutation Database were analysed.

Results

Twenty‐five distinct variants in the retinoschisin gene were identified, of which eight were novel, and one was de novo. Missense mutations were the most prevalent type, and mutation hot spot was localized in the discoidin domain. The mean Snellen best‐corrected visual acuity was 0.28 ± 0.17. Of all eyes presenting with schisis, 92.86% had lamellar schisis and 62.5% had peripheral schisis. Schisis changes mostly involved inner and outer nuclear layers. X‐linked juvenile retinoschisis (XLRS) patients had a high incidence of complications, and peripheral schisis was a risk factor for it. No obvious genotype–phenotype association was observed.

Conclusion

This study provides comprehensive analyses of the genetic and clinical characteristics of XLRS in a cohort of Chinese patients. The fourth de novo mutation in RS1 was identified. And we show that XLRS has a wide spectrum of clinical characteristics; hence, molecular diagnosis is crucial for its diagnosis, differential diagnosis and genetic counselling. Peripheral schisis is a risk factor for the high incidence of complications, and no clear genotype–phenotype correlations were found.

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

X-linked retinoschisis (XLRS) is a leading cause of hereditary juvenile macular degeneration in males resulting in significant vision impairment. Outcome measures to monitor disease progression or therapeutic interventions have evolved with technology. A systematic review was undertaken to evaluate outcome measures for XLRS. Inclusion criteria were all publications examining outcome measures for natural history studies or following an interventional approach for patients with XLRS. Studies which did not present follow-up data were excluded. We searched medical databases including CENTRAL, Ovid Medline, pre-Medline and ahead of Print up to February 2019. Two authors independently assessed the risk of bias. Twelve studies meet the inclusion criteria with four prospective and eight retrospective case series. Five series were natural history observational studies and seven were interventional series using either topical or systemic carbonic anhydrase inhibitors. Visual acuity (VA) declined very slowly in the natural history studies equivalent to 0.22-0.5 letters per year. Five of the six interventional studies showed an improvement in VA and four a reduction in spectral domain optical coherence tomography (SD-OCT) parameters for central macular thickness (CMT). The full-field electroretinogram identified the 30-Hz latency as a further parameter to monitor function. VA was the measure most likely to show a statistically significant outcome. How functionally meaningful this is, requires further evaluation. CMT SD-OCT outcomes are variable depending on cystic changes. More refined measures are required to better correlate structure with function.

X-linked peripheral retinoschisis without macular involvement: a case series with RS1 genetic confirmation

Background: Juvenile X-linked Retinoschisis (JXLRS) is a hereditary retinopathy that commonly presents with macular retinoschisis. In this study, we describe a group of patients who presented with peripheral retinoschisis with no macular schisis.Materials and Methods: A retrospective case series of three JXLRS patients with genetically confirmed RS1 genotypes was identified. Presence of macular and/or peripheral retinoschisis as assessed by optical coherence tomography (OCT), wide-field fluorescein angiography, clinical ophthalmoscopy, and color fundus photography.Results: The eyes of the three JXLRS patients with peripheral retinoschisis had no macular schisis or atrophy on OCT. ERG was available in one patient and showed no reduced b-waves on scotopic combined rod-cone response.Conclusions: RS1 mutations can cause a macular-sparing JXLRS phenotype. The diagnosis of JXLRS should be considered for young males presenting with peripheral retinoschisis even if there is no evidence of macular schisis.

X-linked juvenile retinoschisis: phenotypic and genetic characterization

Juvenile X-linked retinoschisis (XLRS, MIM#312700) belongs to a group of the vitreoretinal dystrophies. We aimed to describe the phenotype-genotype correlation of three XLRS cases in juveniles with different novel mutations from the Lithuanian population. The patients demonstrated macular retinoschisis and typical cyst-like cavities on spectral-domain optical coherence tomography (SD-OCT) images. The mean central foveal thickness was 569.7 µm. Two patients presented with peripheral retinoschisis. Flash electroretinogram demonstrated a reduced b/a ratio (<1.0) in all patients. RS1 (NM_000330.3) gene coding exons Sanger sequencing was performed. RS1 c.599G>T (p.R200L) mutation was detected in one case, showing to be pathogenic in silico analysis. c. (92_97) insC (p.W33fs) mutation was identified for another patient, indicating the variant is possibly damaging in silico analysis. The third case was identified with a pathogenic mutation c.422C>G (p.R141H), HGMD CM981753. These are the first cases of XLRS in the Lithuanian population confirmed by molecular genotyping. Presented patients had a different genotype but similar phenotypic traits.

Optical Coherence Tomography Angiography Findings in X-Linked Retinoschisis

BACKGROUND AND OBJECTIVE

The aim of the study was to determine optical coherence tomography angiography (OCTA) findings and to identify mutations in the RS1 gene in a three-generation family with X-linked juvenile retinoschisis (XLRS).

PATIENTS AND METHODS

Clinical and genetic assessments were performed in 12 family members. OCTA was performed at baseline (12 members including cases and carriers) and after acetazolamide administration (three cases). Twenty healthy subjects (20 eyes, controls) were chosen for comparison. Molecular genetic analysis of the RS1 gene was performed in all family members.

RESULTS

Deep capillary plexus density was reduced in cases compared with controls (P < .01) and was negatively related with retinal thickness (P < .05). After treatment, retinal thickness decreased (P < .05) and deep capillary plexus density increased (P < .05) in cases. In three cases and in four carriers, p.Arg197 His mutation was found.

CONCLUSION

OCTA shows reduced macular deep vessel density in patients with XLRS probably related to vessel displacement and disruption due to schitic cysts. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:e20-e31.].

A large family with inherited optic disc anomalies: a correlation between a new genetic locus and complex ocular phenotypes

Congenital cavitary optic disc anomalies (CODA) is clinically typified by an enlarged excavation of optic disc in diverse degrees. Here, we report the clinical and genetic findings in a four-generation Chinese family with a complicated form of autosomal dominant CODA. Cardinal manifestations included bilateral excavated optic disc with multiple cilioretinal vessels emerging and bilateral retinoschisis with great variability in the range of extension and severity. Other intra-familial phenotypic diversities were also noted, including severity in retinal atrophy, onset age of visual impairment and presence of congenital nystagmus and strabismus. Genome-wide linkage analysis and fine mapping mapped a novel locus for CODA to a 34.3 cM interval between D14S972 and D14S139 at 14q12-q22.1. A maximum multi-point log odds score of 3.901 was reached at D14S275. However, no mutation was identified by exome sequencing or direct sequencing of PAX6 and PAX2 genes, suggesting that the mutation may reside within a regulatory element. In conclusion, we find retinoschisis as a necessary consequence of optic nerve head (ONH) anomalies. The complicated phenotype observed in the family provided additional insights into the inherited ONH anomalies. Mapping of a novel locus, 14q12-q22.1, implies a new disease-causing gene and potential distinct pathogenesis for CODA.

Long-term rearrangement of retinal structures in a novel mutation of X-linked retinoschisis

The aim of the present study was to report a novel mutation in the retinoschisin 1 (RS1) gene in a Caucasian family affected by X-linked juvenile retinoschisis (XLRS) and to describe the long-term modification of retinal structure. Two brothers with an early onset maculopathy were diagnosed with XLRS. Fundus photography, fluorescein angiography, spectral domain optical coherence tomography and electroretinogram analyses were performed. Their sister was also examined. All subjects were screened for mutations in the RS1 gene. XLRS patients demonstrated a marked reduction of best-corrected visual acuity. SD-OCT scans reported a cystic degeneration primarily involving the inner nuclear layer, though some cysts were detected in the outer plexiform layer and in the ganglion cell layer. During the ten-year follow-up, a progressive retinal thickening and coalescence of the cysts was observed. Genetic testing revealed a novel mutation (p.Ile212Asn) in the RS1 gene in both XLRS patients, whereas their sister was not a genetic carrier. Several mutations of the RS1 gene were recognized to be responsible for XLRS. Although the correspondence between genotype and phenotype is still under debate, is reasonable that siblings affected by XLRS could share other genetic and/or epigenetic factors capable to influence clinical course of the disease.

The gene mutation in a Taiwanese family with X-linked retinoschisis

X-linked retinoschisis (XLRS) is one of the leading causes of macular degeneration in male children. The purpose of this study is to describe the clinical characteristics of a Taiwanese family with X-linked retinoschisis (XLRS) and to investigate the genetic mutation in the retinoschisin 1 (RS1) gene. A total of four participants in this XLRS family were analyzed. Complete ophthalmic examinations were performed, including best corrected visual acuity, optical coherence tomography (OCT), and electroretinogram (ERG). Direct DNA sequence of the RS1 gene identified one affected male and one female carrier. The affected male, had a cartwheel-like macular appearance and abnormal retinal pigment epithelium pigmentation in his bilateral eyes. The mixed scotopic ERG b-wave was more reduced than a-wave. OCT revealed typical macular microcystic schisis cavities. Direct DNA sequence analysis revealed a single base pair substitution in Exon 4, 304C > T, resulting in Arg102Trp. Our results show a RS1 (304C > T) mutation in a Taiwanese family with XLRS. This finding expands the clinical profiles of RS1 mutation and may help to further understand its pathogenesis.

X-linked juvenile retinoschisis (XLRS): a review of genotype-phenotype relationships

X-linked juvenile retinoschisis (XLRS) is one of the most common genetic causes of juvenile progressive retinal-vitreal degeneration in males. To date, more than 196 different mutations of the RS1 gene have been associated with XLRS. The mutation spectrum is large and the phenotype variable. This review will focus on the clinical features of XLRS and examine the relationship between phenotype and genotype.

A phenotype-genotype correlation study of X-linked retinoschisis

PURPOSE

To compare the clinical phenotype and detailed electroretinographic parameters in X-linked retinoschisis (XLRS).

DESIGN

Retrospective, comparative study.

PARTICIPANTS

Fifty-seven patients (aged 1-67 years) with molecularly confirmed XLRS were clinically ascertained.

METHODS

Pattern electroretinography (PERG) and full-field electroretinography (ERG), incorporating international standard recordings, were performed in 44 cases. Thirteen patients, mostly pediatric, were tested using a simplified ERG protocol. On-Off and S-cone ERGs were performed in most adults. Fundus autofluorescence (FAF) imaging and optical coherence tomography (OCT) were available in 17 and 21 cases, respectively.

MAIN OUTCOME MEASURES

The clinical and electrophysiologic data associated with different types of mutation in the RS1 gene.

RESULTS

Forty-three patients had missense changes (group A), and 14 patients had nonsense, splice-site, or frame-shifting mutations in the RS1 gene (group B). The mean best-corrected visual acuity was better in group A than in group B (0.34 and 0.21, respectively). Fundus examination revealed foveal schisis in approximately half of both groups. The bright-flash dark-adapted (DA) ERG (11.0 candela.sec.m(-2)) waveform was electronegative in 62% of group A eyes and 100% of group B eyes. The photopic 30-Hz flicker ERG was delayed in all group B eyes and all except 6 group A eyes. On-Off ERG b-waves were subnormal in 39% of group A and 89% of group B eyes; d-waves were delayed in 14 eyes (group A = 10, group B = 4). S-cone ERGs were abnormal in 50% of both groups. The PERG was abnormal in 88% of group A and 100% of group B eyes. A spoke-wheel pattern of high and low intensity was the most common FAF abnormality observed. The OCT showed intraretinal schitic cavities in the majority of eyes.

CONCLUSIONS

There is profound phenotypic variability in patients with XLRS. Most patients have DA bright-flash ERGs with a low b:a ratio in keeping with inner retinal dysfunction. Generalized cone system dysfunction is common and associated with an abnormal On-response and less frequent additional Off-response involvement. Nonsense, splice-site, or frame-shifting mutations in RS1 consistently caused electronegative bright-flash ERG, delayed flicker response, and abnormal PERG; missense mutations result in a wider range of ERG abnormalities.

X-linked juvenile retinoschisis: clinical diagnosis, genetic analysis, and molecular mechanisms

X-linked juvenile retinoschisis (XLRS, MIM 312700) is a common early onset macular degeneration in males characterized by mild to severe loss in visual acuity, splitting of retinal layers, and a reduction in the b-wave of the electroretinogram (ERG). The RS1 gene (MIM 300839) associated with the disease encodes retinoschisin, a 224 amino acid protein containing a discoidin domain as the major structural unit, an N-terminal cleavable signal sequence, and regions responsible for subunit oligomerization. Retinoschisin is secreted from retinal cells as a disulphide-linked homo-octameric complex which binds to the surface of photoreceptors and bipolar cells to help maintain the integrity of the retina. Over 190 disease-causing mutations in the RS1 gene are known with most mutations occurring as non-synonymous changes in the discoidin domain. Cell expression studies have shown that disease-associated missense mutations in the discoidin domain cause severe protein misfolding and retention in the endoplasmic reticulum, mutations in the signal sequence result in aberrant protein synthesis, and mutations in regions flanking the discoidin domain cause defective disulphide-linked subunit assembly, all of which produce a non-functional protein. Knockout mice deficient in retinoschisin have been generated and shown to display most of the characteristic features found in XLRS patients. Recombinant adeno-associated virus (rAAV) mediated delivery of the normal RS1 gene to the retina of young knockout mice result in long-term retinoschisin expression and rescue of retinal structure and function providing a 'proof of concept' that gene therapy may be an effective treatment for XLRS.

Mutations in the RS1 gene in a Chinese family with X-linked juvenile retinoschisis

The purpose of our study was to identify the mutations in the retinoschisis 1 (RS1) gene, which was associated with X-linked retinoschisis (XLRS) in a four-generation Chinese family, and to provide the theoretical basis for gene diagnosis and gene therapy. Genomic DNA was extracted from peripheral leukocytes. All six exons and flanking intronic regions were amplified by polymerase chain reaction (PCR), followed by direct sequencing. Through our genetic analysis, one frameshift 573delG mutation was identified in the patients of this four-generation pedigree; however, this mutation was absent in normal or non-carrier subjects. In conclusion, this 573delG mutation is reported in the Chinese population for the first time. This mutation widens the mutational spectrum of RS1 in Asians. Identification of mutations in the RS1 gene and expanded information on clinical manifestations will facilitate early diagnosis, appropriate early therapy, and genetic counseling regarding the prognosis of XLRS.

Abnormal cone structure in foveal schisis cavities in X-linked retinoschisis from mutations in exon 6 of the RS1 gene

PURPOSE

To evaluate macular cone structure in patients with X-linked retinoschisis (XLRS) caused by mutations in exon 6 of the RS1 gene.

METHODS

High-resolution macular images were obtained with adaptive optics scanning laser ophthalmoscopy (AOSLO) and spectral domain optical coherence tomography (SD-OCT) in two patients with XLRS and 27 age-similar healthy subjects. Retinal structure was correlated with best-corrected visual acuity, kinetic and static perimetry, fundus-guided microperimetry, full-field electroretinography (ERG), and multifocal ERG. The six coding exons and the flanking intronic regions of the RS1 gene were sequenced in each patient.

RESULTS

Two unrelated males, ages 14 and 29, with visual acuity ranging from 20/32 to 20/63, had macular schisis with small relative central scotomas in each eye. The mixed scotopic ERG b-wave was reduced more than the a-wave. SD-OCT showed schisis cavities in the outer and inner nuclear and plexiform layers. Cone spacing was increased within the largest foveal schisis cavities but was normal elsewhere. In each patient, a mutation in exon 6 of the RS1 gene was identified and was predicted to change the amino acid sequence in the discoidin domain of the retinoschisin protein.

CONCLUSIONS

AOSLO images of two patients with molecularly characterized XLRS revealed increased cone spacing and abnormal packing in the macula of each patient, but cone coverage and function were near normal outside the central foveal schisis cavities. Although cone density is reduced, the preservation of wave-guiding cones at the fovea and eccentric macular regions has prognostic and therapeutic implications for XLRS patients with foveal schisis. (Clinical Trials.gov number, NCT00254605.).

Foveomacular schisis in juvenile X-linked retinoschisis: an optical coherence tomography study

PURPOSE

To explore the structural features of juvenile X-linked retinoschisis using spectral-domain optical coherence tomography (OCT).

DESIGN

Retrospective, observational cross-sectional study.

METHODS

Eighteen male patients (34 eyes) who were diagnosed with juvenile X-linked retinoschisis at the Eye & ENT Hospital of Fudan University over an 18-month period were included. Their OCT images, which were obtained using spectral-domain OCT (Cirrus HD-OCT; Carl Zeiss Meditec), were analyzed. The anatomic location of the schisis cavity in juvenile X-linked retinoschisis was characterized by direct inspection of OCT images.

RESULTS

On OCT, the schisis cavity was visible at the fovea in all 34 eyes, and it was associated with increased retinal thickness. Schisis was present at the retinal nerve fiber layer in 4 eyes, at the inner nuclear layer in 29 eyes, and at the outer nuclear layer/outer plexiform layer in 22 eyes. In most cases, widespread foveomacular schisis was detected using OCT; however, in 9 eyes (6 patients), the schisis was confined to the fovea. Schisis of the inner nuclear layer and outer nuclear layer/outer plexiform layer almost always involved the foveal center, but retinal nerve fiber layer schisis was seen only in the parafoveal area.

CONCLUSIONS

Despite conventional wisdom, in patients with X-linked retinoschisis, the schisis cavity can occur in a number of different layers of the neurosensory retina (retinal nerve fiber layer, inner nuclear layer, and outer nuclear layer/outer plexiform layer). In addition, different forms of schisis may affect different locations in the macula (foveal vs parafoveal), and, in most eyes, the schisis involves the entire foveomacular region.