X-linked Retinoschisis

Mendelian MONDO:0010725 Pathograph 10 Show in embeddings browser Ophthalmological Disease Inherited retinal dystrophy Vitreoretinal degeneration

X-linked retinoschisis (XLRS) is an early-onset, bilateral retinal dystrophy of males caused by loss-of-function variants in RS1, which encodes retinoschisin. Retinoschisin is an oddity among cell adhesion proteins: it is secreted rather than membrane-anchored, and it works by assembling into disulfide-linked octamers that pair into double rings and staple neighbouring retinal cell membranes together. Without it the retina literally splits - cystic schisis cavities open within the inner nuclear and outer plexiform layers, most conspicuously at the fovea, where the spoke-wheel appearance is diagnostic. The functional consequence follows from where the split runs: it severs signal transmission from photoreceptors to ON-bipolar cells, so the electroretinogram shows a b-wave reduced out of proportion to the a-wave, the "electronegative" pattern that distinguishes XLRS from a photoreceptor dystrophy. Acuity is reduced from young childhood, and the fragile split retina is prone to vitreous haemorrhage and retinal detachment. There is no approved disease-modifying therapy; topical carbonic anhydrase inhibitors reduce the cavities in a majority of eyes, and intravitreal AAV8-RS1 gene augmentation has completed a phase I/IIa dose-escalation trial. This entry deliberately declares no conforms_to on any node. XLRS is a failure of extracellular adhesion between retinal cells, not a photoreceptor degeneration, a phototransduction cascade lesion or a visual cycle defect, so none of the retinal modules currently in the KB describes its mechanism. Note in particular that it is NOT wired to phototransduction_cascade_dysfunction despite sharing an electronegative electroretinogram with the Schubert-Bornschein congenital stationary night blindness forms: that waveform is a shared readout of interrupted transmission, not evidence of a shared mechanism, and that module explicitly excludes transmission defects.

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1
Inheritance
6
Pathophys.
5
Phenotypes
1
Gaps
10
Pathograph
1
Genes
3
Medical Actions
1
Trials
1
Models
1
References
👪

Inheritance

1
X-linked recessive HP:0001419
XLRS affects males essentially exclusively; heterozygous female carriers are generally spared, and are typically identified only through family studies rather than through symptoms.
X-linked recessive inheritance
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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."
States the inheritance pattern and the observation that carrier females are generally unaffected. Evidence source is OTHER because this is a comprehensive review.
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Discussions and Knowledge Gaps

1
Why does XLRS show no reliable genotype-phenotype correlation, given that the structural basis of the disease - failure of retinoschisin octamer assembly - is comparatively well defined?
KNOWLEDGE GAP xlrs_no_genotype_phenotype_correlation
Attached to
pathophysiology#RS1 Loss of Function pathophysiology#Early-Onset Bilateral Visual Impairment
Cryo-EM localizes disease-associated residues to the octamer assembly interfaces, which would predict that variants abolishing assembly are more severe than those merely destabilizing it. Clinically no such correlation holds, and phenotype varies markedly even within families sharing a variant. Independently derived mouse lines also differ in severity. Something other than the allele - modifier loci, stochastic developmental factors, or mechanical variation in retinal architecture - dominates the outcome, and identifying it matters practically because gene therapy trials must select participants and time intervention without a severity predictor.
Proposed experiments
Intrafamilial phenotype discordance with modifier mapping in XLRS
xlrs_intrafamilial_discordance_study
Systematically quantify OCT cavity volume, ERG b/a ratio and acuity in affected relatives sharing an identical RS1 variant, and test whether residual discordance associates with common variation at candidate retinal-adhesion and Muller-glia loci.
⚙

Pathophysiology

6
RS1 Loss of Function
A hemizygous loss-of-function variant in RS1 abolishes or cripples retinoschisin. Because the protein works as an assembly, the disease is not confined to variants that stop production: missense changes at the interfaces within and between the octamer rings are themselves pathogenic, and mutations that prevent correct subunit assembly cause XLRS just as null alleles do. RS1 is expressed principally by photoreceptors and inner nuclear layer bipolar neurons - the two cell classes on either side of the layer that subsequently splits.
photoreceptor cell CL:0000210 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves photoreceptor cell (CL:0000210). CL:0000210 is a cell type from the Cell Ontology. retinal bipolar neuron CL:0000748 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves retinal bipolar neuron (CL:0000748). CL:0000748 is a cell type from the Cell Ontology.
Cell-cell adhesion GO:0098609 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Cell-cell adhesion (GO:0098609). GO:0098609 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion
Show evidence (2 references)
PMID:34390869 SUPPORT Other
"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."
Establishes both the expressing cell types this node names and the adhesion function whose loss initiates the cascade. Evidence source is OTHER because this is a review.
PMID:15644328 SUPPORT In Vitro
"Because mutations that disrupt subunit assembly cause X-linked retinoschisis, the assembly of RS1 into a disulfide-linked homo-octamer appears to be critical for its function as a retinal cell adhesion protein."
Supports the specific claim that assembly-disrupting variants, not only null alleles, cause the disease - the reason this node is framed as loss of a functional assembly rather than loss of a protein.
Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion
Retinoschisin is secreted as a soluble protein and then does something no other known cell adhesion molecule does: it assembles extracellularly into disulfide-linked octamers that pair into double rings, and couples neighbouring membranes together through octamer-octamer contacts. Cryo-EM places the residues implicated in XLRS at the interfaces within and between those rings, which is direct structural evidence that the disease mechanism is failure of the assembly rather than failure of secretion alone. Without the staple, the mechanical cohesion of the inner retina is lost.
photoreceptor cell CL:0000210 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves photoreceptor cell (CL:0000210). CL:0000210 is a cell type from the Cell Ontology. retinal bipolar neuron CL:0000748 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves retinal bipolar neuron (CL:0000748). CL:0000748 is a cell type from the Cell Ontology.
Cell adhesion GO:0007155 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Cell adhesion (GO:0007155). GO:0007155 is a biological process from the Gene Ontology. ↓ DECREASED
retina UBERON:0000966 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in retina (UBERON:0000966). UBERON:0000966 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
RS1 mutant XLRS mouse Mouse rescues AAV8-RS1 delivery under the native promoter restores retinal structure and synaptic function in the mutant mouse, providing the rescue arm that motivated the human trial.
Downstream
Intraretinal Schisis Cavity Formation
Show evidence (2 references)
PMID:27114531 SUPPORT In Vitro
"Retinoschisin (RS1) is involved in cell-cell junctions in the retina, but is unique among known cell-adhesion proteins in that it is a soluble secreted protein."
Establishes the unusual secreted-adhesion mechanism this node models.
PMID:27114531 SUPPORT In Vitro
"The interfaces internal to and between rings feature residues implicated in X-linked retinoschisis, indicating the importance of correct assembly."
Provides the structural evidence that disease-causing residues map to the assembly interfaces, which is the specific claim this node rests on.
Intraretinal Schisis Cavity Formation
Loss of adhesion allows the neurosensory retina to split, opening cystic cavities within the inner nuclear and outer plexiform layers. The fovea is affected most conspicuously, giving the spoke-wheel foveoschisis seen on fundus examination and the petaloid cystic cavities resolved on optical coherence tomography; peripheral schisis occurs in about half of patients. Splitting is present from early childhood rather than developing over decades, which is why XLRS presents at school age with poor vision rather than with progressive later loss.
Retina layer formation GO:0010842 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Retina layer formation (GO:0010842). GO:0010842 is a biological process from the Gene Ontology. ⚠ ABNORMAL
retina UBERON:0000966 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in retina (UBERON:0000966). UBERON:0000966 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
RS1 mutant XLRS mouse Mouse recapitulates Reproduces the cavities in the same retinal layers as the human disease, with the same electrophysiological signature.
Downstream
Disrupted Photoreceptor-to-Bipolar Synaptic Transmission
Retinal Fragility, Haemorrhage and Detachment
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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)."
Localizes the cavities to the specific retinal layers this node names and confirms the early-childhood onset. Evidence source is OTHER because this is a review.
Disrupted Photoreceptor-to-Bipolar Synaptic Transmission
The functional heart of the disease, and a direct consequence of where the split runs. The outer plexiform layer is the synaptic layer connecting photoreceptor terminals to bipolar dendrites; a cavity opening there and in the inner nuclear layer disorganizes that connection and interrupts signal transmission to ON-bipolar cells. The electroretinographic signature is therefore a b-wave reduced out of proportion to the a-wave - the electronegative ERG - which is what separates XLRS from a primary photoreceptor dystrophy at the bedside. Note that this places XLRS mechanistically alongside the Schubert-Bornschein forms of congenital stationary night blindness as a transmission defect, not a phototransduction defect, although the lesion here is structural rather than synaptic.
retinal bipolar neuron CL:0000748 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves retinal bipolar neuron (CL:0000748). CL:0000748 is a cell type from the Cell Ontology. photoreceptor cell CL:0000210 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves photoreceptor cell (CL:0000210). CL:0000210 is a cell type from the Cell Ontology.
Chemical synaptic transmission GO:0007268 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Chemical synaptic transmission (GO:0007268). GO:0007268 is a biological process from the Gene Ontology. ↓ DECREASED Synapse organization GO:0050808 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Synapse organization (GO:0050808). GO:0050808 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Early-Onset Bilateral Visual Impairment
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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."
States this node's mechanism and its objective electrophysiological readout in one sentence. Evidence source is OTHER because this is a review.
Retinal Fragility, Haemorrhage and Detachment
A split retina is a mechanically weak retina. Vessels bridging a schisis cavity may rupture into the vitreous, and the inner wall of a large cavity may tear, so vitreous haemorrhage and rhegmatogenous or combined retinal detachment are the acute complications that threaten sudden, sometimes permanent, vision loss on top of the stable baseline deficit. These events are the reason XLRS requires ongoing surveillance despite being an essentially non-progressive dystrophy in most patients.
retina UBERON:0000966 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in retina (UBERON:0000966). UBERON:0000966 is an anatomical location from the Uberon multi-species anatomy ontology.
Show evidence (1 reference)
PMID:30196853 SUPPORT Human Clinical
"Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment."
Names susceptibility to retinal detachment as a direct consequence of the cavities, supporting this node's placement downstream of schisis formation.
Early-Onset Bilateral Visual Impairment
Acuity is bilaterally reduced from young childhood, typically to the 20/60 to 20/120 range. The course is not flat: acuity often deteriorates through the first and second decades and only then remains relatively stable, until the fifth or sixth decade. Presentation ranges from infancy to school age. There are no reliable genotype-phenotype correlations, so the causative variant does not predict severity and cannot be used to counsel prognosis - a notable contrast with most inherited retinal dystrophies.
Visual perception GO:0007601 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Visual perception (GO:0007601). GO:0007601 is a biological process from the Gene Ontology. ↓ DECREASED
Show evidence (2 references)
PMID:34390869 SUPPORT Other
"XLRS manifests between infancy and school-age with variable phenotypic presentation and without reliable genotype-phenotype correlations."
Supports both the age range and the specific negative claim about genotype-phenotype correlation that this node makes. Evidence source is OTHER because this is a review.
PMID:20301401 SUPPORT Other
"Affected males typically have 20/60 to 20/120 vision. Visual acuity often deteriorates during the first and second decades of life but then remains relatively stable until the fifth or sixth decade."
GeneReviews supplies the acuity range this node states, which was previously uncited, and corrects its trajectory claim: the deficit is not flat from childhood but deteriorates through the first two decades before stabilising. The node description was amended accordingly. Evidence source is OTHER because GeneReviews is an expert-curated clinical synthesis.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for X-linked Retinoschisis Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

5
Foveoschisis VERY_FREQUENT Ocular HP:0012152 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Foveoschisis (HP:0012152). HP:0012152 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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)"
Documents foveomacular schisis as the characteristic imaging finding. VERY_FREQUENT is a Pattern C mapping of the source's definitional framing ("characteristic"/"hallmark" -> VERY_FREQUENT, see docs/frequency-evidence-guidelines.md); no proportion is reported.
Retinoschisis Ocular HP:0030502 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Retinoschisis (HP:0030502). HP:0030502 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30196853 SUPPORT Human Clinical
"Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment."
Names retinal cavity formation as the direct structural consequence of retinoschisin absence.
PMID:20301401 SUPPORT Other
"Schisis of the peripheral retina, predominantly inferotemporally, occurs in approximately 50% of individuals."
Quantifies the peripheral component at approximately 50% and localizes it inferotemporally, supporting the "about half of patients" statement made in the pathophysiology description, which was previously uncited. Evidence source is OTHER because GeneReviews is an expert-curated clinical synthesis.
Electronegative Electroretinogram Ocular HP:0000512 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal electroretinogram (HP:0000512). HP:0000512 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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."
States the disproportionate b-wave reduction that defines the electronegative waveform.
Reduced Visual Acuity VERY_FREQUENT Ocular HP:0007663 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Reduced visual acuity (HP:0007663). HP:0007663 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"XLRS causes bilateral reduced acuities from young age"
States bilateral early acuity reduction as a defining feature of the condition. VERY_FREQUENT is a Pattern C mapping of that definitional framing (docs/frequency-evidence-guidelines.md); no proportion is reported.
Retinal Detachment Ocular HP:0000541 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Retinal detachment (HP:0000541). HP:0000541 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30196853 SUPPORT Human Clinical
"Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment."
Establishes susceptibility to detachment. No frequency band is asserted: the source says only that patients are susceptible, which carries no frequency information and maps to no band in the DisMech qualitative mapping (docs/frequency-evidence-guidelines.md).
🧬

Genetic Associations

1
RS1 (Hemizygous loss-of-function variants in males)
Gene: RS1 hgnc:10457 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is RS1 (hgnc:10457). hgnc:10457 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (2 references)
PMID:34390869 SUPPORT Other
"It results from loss-of-function RS1 gene mutations on the X-chromosome."
Assigns causation to loss-of-function RS1 variants. Evidence source is OTHER because this is a comprehensive review.
PMID:15644328 SUPPORT In Vitro
"Our results indicate that RS1 exists as a novel octamer in which the eight subunits are joined together by Cys(59)-Cys(223) intermolecular disulfide bonds."
Establishes the octameric, disulfide-linked architecture referenced in this gene's notes and in the central effector node.
💊

Medical Actions

3
Topical Carbonic Anhydrase Inhibitor (Dorzolamide)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: dorzolamide CHEBI:4702 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses dorzolamide (CHEBI:4702). CHEBI:4702 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Topical dorzolamide 2% reduces the cystic macular cavities in a majority of treated eyes, presumably by promoting fluid transport out of the retina across the retinal pigment epithelium. It does not address the adhesion defect, response is not universal, and rebound of cysts on continued therapy is described, so it is symptomatic management of the cavity rather than disease modification.
Mechanism Target:
INHIBITS Intraretinal Schisis Cavity Formation — Carbonic anhydrase inhibition reduces the size of established schisis cavities without correcting the upstream adhesion failure that produced them, which is why it is wired to this node rather than to the central effector.
Show evidence (1 reference)
PMID:20142541 SUPPORT Human Clinical
"Among the 15 patients with XLRS, 20 eyes (69%) of 11 patients showed a positive response to treatment."
Quantifies the cavity response rate in the retrospective series that established this practice.
Show evidence (1 reference)
PMID:20142541 SUPPORT Human Clinical
"Patients with XLRS have the potential to experience a beneficial effect from sustained treatment with dorzolamide, 2%."
The authors' own hedged conclusion. Marked PARTIAL because the study is a retrospective uncontrolled analysis of 29 eyes reporting the potential for benefit, not a controlled demonstration of it.
AAV8-RS1 Gene Augmentation Therapy
Action: gene therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is gene therapy (NCIT:C15238). NCIT:C15238 is a clinical intervention from the NCI Thesaurus. Ontology label: Gene Therapy NCIT:C15238
Platform: Gene therapy
Intravitreal delivery of an AAV8 vector carrying RS1 under its own promoter, intended to restore retinoschisin and with it retinal adhesion. In XLRS mice it restores retinal structure and synaptic function and quiets the schisis-induced microglial response. A phase I/IIa three-dose-escalation trial in nine men found the vector generally tolerated with dose-related ocular inflammation that resolved on corticosteroids; cavities closed transiently in one participant. Investigational, not approved.
Mechanism Target:
RESTORES Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion — Supplying wild-type RS1 restores the secreted adhesion protein itself, acting on the disease's central effector rather than on a downstream consequence.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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)."
Demonstrates in the mouse model that restoring the gene restores both the structural and the synaptic consequences of the adhesion failure. Evidence source is OTHER because this is a review.
Show evidence (1 reference)
PMID:30196853 SUPPORT Human Clinical
"Ocular events included dose-related inflammation that resolved with topical and oral corticosteroids."
Reports the principal safety finding of the first-in-human trial. Marked PARTIAL because the trial established tolerability with only transient cavity closure in one participant, not efficacy.
Avoidance of Head Trauma and Contact Sports
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Platform: Behavioral / lifestyle
Because the split retina is mechanically fragile, avoiding head trauma and high-contact sports reduces the risk of the two acute complications that threaten sudden vision loss. This is the only intervention in XLRS directed at preventing the complications rather than managing the established lesion.
Mechanism Target:
INHIBITS Retinal Fragility, Haemorrhage and Detachment — Reducing mechanical insult to a structurally fragile retina lowers the probability of the haemorrhage and detachment this node models; it does not affect the underlying adhesion defect.
Show evidence (1 reference)
PMID:20301401 SUPPORT Other
"Agents/circumstances to avoid: Head trauma and high-contact sports to reduce risk of retinal detachment and vitreous hemorrhage."
GeneReviews states this avoidance recommendation and the specific complications it targets. Evidence source is OTHER because GeneReviews is an expert-curated clinical synthesis rather than a primary study.
🔬

Clinical Trials

1
NCT02317887 PHASE_I COMPLETED
Single-center, prospective, open-label, three-dose-escalation phase I/IIa trial of intravitreal AAV8-RS1 gene augmentation in nine men with pathogenic RS1 variants, at 1e9, 1e10 and 1e11 vector genomes per eye.
Target Phenotypes: Retinoschisis HP:0030502 Human Phenotype Ontology (HP) Relation: this clinical trial targets this phenotype This clinical trial targets Retinoschisis (HP:0030502). HP:0030502 is a phenotype from the Human Phenotype Ontology. Reduced visual acuity HP:0007663 Human Phenotype Ontology (HP) Relation: this clinical trial targets this phenotype This clinical trial targets Reduced visual acuity (HP:0007663). HP:0007663 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30196853 SUPPORT Human Clinical
"This phase I/IIa single-center, prospective, open-label, three-dose-escalation clinical trial administered vector to nine participants with pathogenic RS1 mutations."
Describes the trial design and enrolment reported under this NCT number.
🐁

Animal Models

1
RS1 mutant XLRS mouse
Several independently generated Rs1 mutant mouse lines reproduce the human disease with outer plexiform and inner nuclear layer schisis cavities, early onset, phenotypic variability across lines, and a reduced b-wave to a-wave amplitude ratio. The fidelity of the model is what allowed the pathophysiology to be worked out and the gene therapy to be tested preclinically.
Species
Mouse
Genotype
Rs1 loss-of-function (multiple independent mutant lines)
Publication
PMID:34390869
Pathograph links
Intraretinal Schisis Cavity Formation recapitulates fidelity: high Reproduces the cavities in the same retinal layers as the human disease, with the same electrophysiological signature.
Limitations: The mouse retina has no fovea, so the foveoschisis that dominates the human presentation and determines human acuity has no counterpart in the model; phenotype also varies across independently derived mutant lines.
Readouts
ERG b-wave to a-wave amplitude ratio
Direction: DECREASED
Interpretation: Electrophysiological correlate of the transmission failure produced by the cavities, matching the electronegative ERG of affected men.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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."
Reports the readout and its direction across the independent mutant lines. Evidence source is OTHER because the publication is a review synthesizing results from several independently derived mouse lines, not a primary report of one of them.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"The faithful phenotype of the XLRS mouse has assisted in delineating the disease pathophysiology."
Supports treating this model as informative for the human mechanism. Evidence source is OTHER because this is a review of the mouse literature rather than a primary model-organism report.
Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion rescues fidelity: moderate AAV8-RS1 delivery under the native promoter restores retinal structure and synaptic function in the mutant mouse, providing the rescue arm that motivated the human trial.
Limitations: Rescue was achieved by subretinal-scale exposure in a small eye; the human trial used intravitreal delivery, where vector must cross the inner limiting membrane, and produced only transient cavity closure in one of nine participants.
Readouts
Schisis-associated retinal microglial activation
Direction: DECREASED
Interpretation: Restoring the adhesion protein quiets the inflammatory response the cavities provoke, indicating the microglial phenotype is downstream of the adhesion failure rather than an independent process.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"It also ameliorates the schisis-induced inflammatory microglia phenotype toward a state of immune quiescence."
Reports the microglial readout and the direction of change after gene delivery. Evidence source is OTHER because this is a review.
Show evidence (1 reference)
PMID:34390869 SUPPORT Other
"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)."
Documents the rescue on which this link rests. Evidence source is OTHER because this is a review.
{ }

Source YAML

click to show 
name: X-linked Retinoschisis
creation_date: "2026-08-22T00:00:00Z"
category: Mendelian
description: >
  X-linked retinoschisis (XLRS) is an early-onset, bilateral retinal dystrophy of
  males caused by loss-of-function variants in RS1, which encodes retinoschisin.
  Retinoschisin is an oddity among cell adhesion proteins: it is secreted rather
  than membrane-anchored, and it works by assembling into disulfide-linked
  octamers that pair into double rings and staple neighbouring retinal cell
  membranes together. Without it the retina literally splits - cystic schisis
  cavities open within the inner nuclear and outer plexiform layers, most
  conspicuously at the fovea, where the spoke-wheel appearance is diagnostic.
  The functional consequence follows from where the split runs: it severs signal
  transmission from photoreceptors to ON-bipolar cells, so the electroretinogram
  shows a b-wave reduced out of proportion to the a-wave, the "electronegative"
  pattern that distinguishes XLRS from a photoreceptor dystrophy. Acuity is
  reduced from young childhood, and the fragile split retina is prone to
  vitreous haemorrhage and retinal detachment. There is no approved
  disease-modifying therapy; topical carbonic anhydrase inhibitors reduce the
  cavities in a majority of eyes, and intravitreal AAV8-RS1 gene augmentation has
  completed a phase I/IIa dose-escalation trial.

  This entry deliberately declares no conforms_to on any node. XLRS is a
  failure of extracellular adhesion between retinal cells, not a photoreceptor
  degeneration, a phototransduction cascade lesion or a visual cycle defect, so
  none of the retinal modules currently in the KB describes its mechanism. Note
  in particular that it is NOT wired to phototransduction_cascade_dysfunction
  despite sharing an electronegative electroretinogram with the
  Schubert-Bornschein congenital stationary night blindness forms: that waveform
  is a shared readout of interrupted transmission, not evidence of a shared
  mechanism, and that module explicitly excludes transmission defects.
disease_term:
  preferred_term: X-linked retinoschisis
  term:
    id: MONDO:0010725
    label: X-linked retinoschisis
synonyms:
- juvenile X-linked retinoschisis
- XLRS
- retinoschisis 1, X-linked, juvenile
- congenital retinoschisis
parents:
- Ophthalmological Disease
- Inherited retinal dystrophy
- Vitreoretinal degeneration
inheritance:
- name: X-linked recessive
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  description: >
    XLRS affects males essentially exclusively; heterozygous female carriers are
    generally spared, and are typically identified only through family studies
    rather than through symptoms.
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "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."
    explanation: >
      States the inheritance pattern and the observation that carrier females
      are generally unaffected. Evidence source is OTHER because this is a
      comprehensive review.
pathophysiology:
- name: RS1 Loss of Function
  description: >
    A hemizygous loss-of-function variant in RS1 abolishes or cripples
    retinoschisin. Because the protein works as an assembly, the disease is not
    confined to variants that stop production: missense changes at the interfaces
    within and between the octamer rings are themselves pathogenic, and mutations
    that prevent correct subunit assembly cause XLRS just as null alleles do.
    RS1 is expressed principally by photoreceptors and inner nuclear layer
    bipolar neurons - the two cell classes on either side of the layer that
    subsequently splits.
  role: trigger
  biological_scale: MOLECULAR
  cell_types:
  - preferred_term: photoreceptor cell
    term:
      id: CL:0000210
      label: photoreceptor cell
  - preferred_term: retinal bipolar neuron
    term:
      id: CL:0000748
      label: retinal bipolar neuron
  biological_processes:
  - preferred_term: Cell-cell adhesion
    term:
      id: GO:0098609
      label: cell-cell adhesion
    modifier: DECREASED
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "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."
    explanation: >
      Establishes both the expressing cell types this node names and the
      adhesion function whose loss initiates the cascade. Evidence source is
      OTHER because this is a review.
  - reference: PMID:15644328
    reference_title: "RS1, a discoidin domain-containing retinal cell adhesion protein associated with X-linked retinoschisis, exists as a novel disulfide-linked octamer."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Because mutations that disrupt subunit assembly cause X-linked retinoschisis, the assembly of RS1 into a disulfide-linked homo-octamer appears to be critical for its function as a retinal cell adhesion protein."
    explanation: >
      Supports the specific claim that assembly-disrupting variants, not only
      null alleles, cause the disease - the reason this node is framed as loss
      of a functional assembly rather than loss of a protein.
  downstream:
  - target: Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion
    causal_link_type: DIRECT

- name: Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion
  description: >
    Retinoschisin is secreted as a soluble protein and then does something no
    other known cell adhesion molecule does: it assembles extracellularly into
    disulfide-linked octamers that pair into double rings, and couples
    neighbouring membranes together through octamer-octamer contacts. Cryo-EM
    places the residues implicated in XLRS at the interfaces within and between
    those rings, which is direct structural evidence that the disease mechanism
    is failure of the assembly rather than failure of secretion alone. Without
    the staple, the mechanical cohesion of the inner retina is lost.
  role: central_effector
  biological_scale: MOLECULAR
  cell_types:
  - preferred_term: photoreceptor cell
    term:
      id: CL:0000210
      label: photoreceptor cell
  - preferred_term: retinal bipolar neuron
    term:
      id: CL:0000748
      label: retinal bipolar neuron
  biological_processes:
  - preferred_term: Cell adhesion
    term:
      id: GO:0007155
      label: cell adhesion
    modifier: DECREASED
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:27114531
    reference_title: "Paired octamer rings of retinoschisin suggest a junctional model for cell-cell adhesion in the retina."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Retinoschisin (RS1) is involved in cell-cell junctions in the retina, but is unique among known cell-adhesion proteins in that it is a soluble secreted protein."
    explanation: >
      Establishes the unusual secreted-adhesion mechanism this node models.
  - reference: PMID:27114531
    reference_title: "Paired octamer rings of retinoschisin suggest a junctional model for cell-cell adhesion in the retina."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The interfaces internal to and between rings feature residues implicated in X-linked retinoschisis, indicating the importance of correct assembly."
    explanation: >
      Provides the structural evidence that disease-causing residues map to the
      assembly interfaces, which is the specific claim this node rests on.
  downstream:
  - target: Intraretinal Schisis Cavity Formation
    causal_link_type: DIRECT

- name: Intraretinal Schisis Cavity Formation
  description: >
    Loss of adhesion allows the neurosensory retina to split, opening cystic
    cavities within the inner nuclear and outer plexiform layers. The fovea is
    affected most conspicuously, giving the spoke-wheel foveoschisis seen on
    fundus examination and the petaloid cystic cavities resolved on optical
    coherence tomography; peripheral schisis occurs in about half of patients.
    Splitting is present from early childhood rather than developing over
    decades, which is why XLRS presents at school age with poor vision rather
    than with progressive later loss.
  role: effector
  biological_scale: TISSUE
  biological_processes:
  - preferred_term: Retina layer formation
    term:
      id: GO:0010842
      label: retina layer formation
    modifier: ABNORMAL
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "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)."
    explanation: >
      Localizes the cavities to the specific retinal layers this node names and
      confirms the early-childhood onset. Evidence source is OTHER because this
      is a review.
  downstream:
  - target: Disrupted Photoreceptor-to-Bipolar Synaptic Transmission
    causal_link_type: DIRECT
  - target: Retinal Fragility, Haemorrhage and Detachment
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES

- name: Disrupted Photoreceptor-to-Bipolar Synaptic Transmission
  description: >
    The functional heart of the disease, and a direct consequence of where the
    split runs. The outer plexiform layer is the synaptic layer connecting
    photoreceptor terminals to bipolar dendrites; a cavity opening there and in
    the inner nuclear layer disorganizes that connection and interrupts signal
    transmission to ON-bipolar cells. The electroretinographic signature is
    therefore a b-wave reduced out of proportion to the a-wave - the
    electronegative ERG - which is what separates XLRS from a primary
    photoreceptor dystrophy at the bedside. Note that this places XLRS
    mechanistically alongside the Schubert-Bornschein forms of congenital
    stationary night blindness as a transmission defect, not a phototransduction
    defect, although the lesion here is structural rather than synaptic.
  role: effector
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: retinal bipolar neuron
    term:
      id: CL:0000748
      label: retinal bipolar neuron
  - preferred_term: photoreceptor cell
    term:
      id: CL:0000210
      label: photoreceptor cell
  biological_processes:
  - preferred_term: Chemical synaptic transmission
    term:
      id: GO:0007268
      label: chemical synaptic transmission
    modifier: DECREASED
  - preferred_term: Synapse organization
    term:
      id: GO:0050808
      label: synapse organization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "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."
    explanation: >
      States this node's mechanism and its objective electrophysiological
      readout in one sentence. Evidence source is OTHER because this is a
      review.
  downstream:
  - target: Early-Onset Bilateral Visual Impairment
    causal_link_type: DIRECT

- name: Retinal Fragility, Haemorrhage and Detachment
  description: >
    A split retina is a mechanically weak retina. Vessels bridging a schisis
    cavity may rupture into the vitreous, and the inner wall of a large cavity
    may tear, so vitreous haemorrhage and rhegmatogenous or combined retinal
    detachment are the acute complications that threaten sudden, sometimes
    permanent, vision loss on top of the stable baseline deficit. These events
    are the reason XLRS requires ongoing surveillance despite being an
    essentially non-progressive dystrophy in most patients.
  role: consequence
  biological_scale: ORGANISM
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:30196853
    reference_title: "Retinal AAV8-RS1 Gene Therapy for X-Linked Retinoschisis: Initial Findings from a Phase I/IIa Trial by Intravitreal Delivery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment."
    explanation: >
      Names susceptibility to retinal detachment as a direct consequence of the
      cavities, supporting this node's placement downstream of schisis
      formation.

- name: Early-Onset Bilateral Visual Impairment
  description: >
    Acuity is bilaterally reduced from young childhood, typically to the 20/60
    to 20/120 range. The course is not flat: acuity often deteriorates through
    the first and second decades and only then remains relatively stable, until
    the fifth or sixth decade. Presentation ranges from infancy to school age.
    There are
    no reliable genotype-phenotype correlations, so the causative variant does
    not predict severity and cannot be used to counsel prognosis - a notable
    contrast with most inherited retinal dystrophies.
  role: consequence
  biological_scale: ORGANISM
  biological_processes:
  - preferred_term: Visual perception
    term:
      id: GO:0007601
      label: visual perception
    modifier: DECREASED
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "XLRS manifests between infancy and school-age with variable phenotypic presentation and without reliable genotype-phenotype correlations."
    explanation: >
      Supports both the age range and the specific negative claim about
      genotype-phenotype correlation that this node makes. Evidence source is
      OTHER because this is a review.
  - reference: PMID:20301401
    reference_title: "X-Linked Congenital Retinoschisis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Affected males typically have 20/60 to 20/120 vision. Visual acuity often deteriorates during the first and second decades of life but then remains relatively stable until the fifth or sixth decade."
    explanation: >
      GeneReviews supplies the acuity range this node states, which was
      previously uncited, and corrects its trajectory claim: the deficit is not
      flat from childhood but deteriorates through the first two decades before
      stabilising. The node description was amended accordingly. Evidence
      source is OTHER because GeneReviews is an expert-curated clinical
      synthesis.
phenotypes:
- category: Ocular
  name: Foveoschisis
  description: >
    Splitting of the fovea into radial cystic cavities, producing the
    pathognomonic spoke-wheel appearance and resolved as petaloid cysts on
    optical coherence tomography. Present in essentially all affected males.
  phenotype_term:
    preferred_term: Foveoschisis
    term:
      id: HP:0012152
      label: Foveoschisis
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "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)"
    explanation: >
      Documents foveomacular schisis as the characteristic imaging finding.
      VERY_FREQUENT is a Pattern C mapping of the source's definitional
      framing ("characteristic"/"hallmark" -> VERY_FREQUENT, see
      docs/frequency-evidence-guidelines.md); no proportion is reported.
- category: Ocular
  name: Retinoschisis
  description: >
    Splitting of the neurosensory retina within the inner nuclear and outer
    plexiform layers, macular in essentially all patients and additionally
    peripheral in a substantial minority.
  phenotype_term:
    preferred_term: Retinoschisis
    term:
      id: HP:0030502
      label: Retinoschisis
  evidence:
  - reference: PMID:30196853
    reference_title: "Retinal AAV8-RS1 Gene Therapy for X-Linked Retinoschisis: Initial Findings from a Phase I/IIa Trial by Intravitreal Delivery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment."
    explanation: >
      Names retinal cavity formation as the direct structural consequence of
      retinoschisin absence.
  - reference: PMID:20301401
    reference_title: "X-Linked Congenital Retinoschisis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Schisis of the peripheral retina, predominantly inferotemporally, occurs in approximately 50% of individuals."
    explanation: >
      Quantifies the peripheral component at approximately 50% and localizes it
      inferotemporally, supporting the "about half of patients" statement made
      in the pathophysiology description, which was previously uncited.
      Evidence source is OTHER because GeneReviews is an expert-curated
      clinical synthesis.
- category: Ocular
  name: Electronegative Electroretinogram
  description: >
    A selectively reduced b-wave with relatively preserved a-wave, reflecting
    interrupted transmission from photoreceptors to ON-bipolar cells. This is
    the objective diagnostic discriminator between XLRS and a primary
    photoreceptor dystrophy.
  phenotype_term:
    preferred_term: Abnormal electroretinogram
    term:
      id: HP:0000512
      label: Abnormal electroretinogram
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "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."
    explanation: >
      States the disproportionate b-wave reduction that defines the
      electronegative waveform.
- category: Ocular
  name: Reduced Visual Acuity
  description: >
    Bilaterally reduced best-corrected acuity present from young childhood and
    largely stable thereafter.
  phenotype_term:
    preferred_term: Reduced visual acuity
    term:
      id: HP:0007663
      label: Reduced visual acuity
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "XLRS causes bilateral reduced acuities from young age"
    explanation: >
      States bilateral early acuity reduction as a defining feature of the
      condition. VERY_FREQUENT is a Pattern C mapping of that definitional
      framing (docs/frequency-evidence-guidelines.md); no proportion is
      reported.
- category: Ocular
  name: Retinal Detachment
  description: >
    Rhegmatogenous or combined retinal detachment arising from tears in the
    inner wall of a schisis cavity; an acute, sight-threatening complication
    rather than a baseline feature.
  phenotype_term:
    preferred_term: Retinal detachment
    term:
      id: HP:0000541
      label: Retinal detachment
  evidence:
  - reference: PMID:30196853
    reference_title: "Retinal AAV8-RS1 Gene Therapy for X-Linked Retinoschisis: Initial Findings from a Phase I/IIa Trial by Intravitreal Delivery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment."
    explanation: >
      Establishes susceptibility to detachment. No frequency band is asserted:
      the source says only that patients are susceptible, which carries no
      frequency information and maps to no band in the DisMech qualitative
      mapping (docs/frequency-evidence-guidelines.md).
genetic:
- name: RS1
  association: Hemizygous loss-of-function variants in males
  notes: >
    RS1 encodes retinoschisin, a secreted discoidin-domain cell adhesion protein
    that assembles into disulfide-linked homo-octamers. Pathogenic variants
    include null alleles and missense changes that map to the octamer assembly
    interfaces; the latter cause disease by preventing correct assembly rather
    than by preventing expression.
  gene_term:
    preferred_term: RS1
    term:
      id: hgnc:10457
      label: RS1
  relationship_type: CAUSATIVE
  evidence:
  - reference: PMID:34390869
    reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It results from loss-of-function RS1 gene mutations on the X-chromosome."
    explanation: >
      Assigns causation to loss-of-function RS1 variants. Evidence source is
      OTHER because this is a comprehensive review.
  - reference: PMID:15644328
    reference_title: "RS1, a discoidin domain-containing retinal cell adhesion protein associated with X-linked retinoschisis, exists as a novel disulfide-linked octamer."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our results indicate that RS1 exists as a novel octamer in which the eight subunits are joined together by Cys(59)-Cys(223) intermolecular disulfide bonds."
    explanation: >
      Establishes the octameric, disulfide-linked architecture referenced in
      this gene's notes and in the central effector node.
treatments:
- name: Topical Carbonic Anhydrase Inhibitor (Dorzolamide)
  description: >
    Topical dorzolamide 2% reduces the cystic macular cavities in a majority of
    treated eyes, presumably by promoting fluid transport out of the retina
    across the retinal pigment epithelium. It does not address the adhesion
    defect, response is not universal, and rebound of cysts on continued therapy
    is described, so it is symptomatic management of the cavity rather than
    disease modification.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: dorzolamide
      term:
        id: CHEBI:4702
        label: dorzolamide
  target_mechanisms:
  - target: Intraretinal Schisis Cavity Formation
    treatment_effect: INHIBITS
    description: >
      Carbonic anhydrase inhibition reduces the size of established schisis
      cavities without correcting the upstream adhesion failure that produced
      them, which is why it is wired to this node rather than to the central
      effector.
    evidence:
    - reference: PMID:20142541
      reference_title: "Efficacy of sustained topical dorzolamide therapy for cystic macular lesions in patients with X-linked retinoschisis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Among the 15 patients with XLRS, 20 eyes (69%) of 11 patients showed a positive response to treatment."
      explanation: >
        Quantifies the cavity response rate in the retrospective series that
        established this practice.
  evidence:
  - reference: PMID:20142541
    reference_title: "Efficacy of sustained topical dorzolamide therapy for cystic macular lesions in patients with X-linked retinoschisis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with XLRS have the potential to experience a beneficial effect from sustained treatment with dorzolamide, 2%."
    explanation: >
      The authors' own hedged conclusion. Marked PARTIAL because the study is a
      retrospective uncontrolled analysis of 29 eyes reporting the potential for
      benefit, not a controlled demonstration of it.
- name: AAV8-RS1 Gene Augmentation Therapy
  description: >
    Intravitreal delivery of an AAV8 vector carrying RS1 under its own promoter,
    intended to restore retinoschisin and with it retinal adhesion. In XLRS
    mice it restores retinal structure and synaptic function and quiets the
    schisis-induced microglial response. A phase I/IIa three-dose-escalation
    trial in nine men found the vector generally tolerated with dose-related
    ocular inflammation that resolved on corticosteroids; cavities closed
    transiently in one participant. Investigational, not approved.
  therapeutic_modality: GENE_THERAPY
  treatment_term:
    preferred_term: gene therapy
    term:
      id: NCIT:C15238
      label: Gene Therapy
  target_mechanisms:
  - target: Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion
    treatment_effect: RESTORES
    description: >
      Supplying wild-type RS1 restores the secreted adhesion protein itself,
      acting on the disease's central effector rather than on a downstream
      consequence.
    evidence:
    - reference: PMID:34390869
      reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "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)."
      explanation: >
        Demonstrates in the mouse model that restoring the gene restores both
        the structural and the synaptic consequences of the adhesion failure.
        Evidence source is OTHER because this is a review.
  evidence:
  - reference: PMID:30196853
    reference_title: "Retinal AAV8-RS1 Gene Therapy for X-Linked Retinoschisis: Initial Findings from a Phase I/IIa Trial by Intravitreal Delivery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ocular events included dose-related inflammation that resolved with topical and oral corticosteroids."
    explanation: >
      Reports the principal safety finding of the first-in-human trial. Marked
      PARTIAL because the trial established tolerability with only transient
      cavity closure in one participant, not efficacy.
- name: Avoidance of Head Trauma and Contact Sports
  description: >
    Because the split retina is mechanically fragile, avoiding head trauma and
    high-contact sports reduces the risk of the two acute complications that
    threaten sudden vision loss. This is the only intervention in XLRS directed
    at preventing the complications rather than managing the established
    lesion.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Retinal Fragility, Haemorrhage and Detachment
    treatment_effect: INHIBITS
    description: >
      Reducing mechanical insult to a structurally fragile retina lowers the
      probability of the haemorrhage and detachment this node models; it does
      not affect the underlying adhesion defect.
  evidence:
  - reference: PMID:20301401
    reference_title: "X-Linked Congenital Retinoschisis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Agents/circumstances to avoid: Head trauma and high-contact sports to reduce risk of retinal detachment and vitreous hemorrhage."
    explanation: >
      GeneReviews states this avoidance recommendation and the specific
      complications it targets. Evidence source is OTHER because GeneReviews is
      an expert-curated clinical synthesis rather than a primary study.
clinical_trials:
- name: NCT02317887
  phase: PHASE_I
  status: COMPLETED
  description: >
    Single-center, prospective, open-label, three-dose-escalation phase I/IIa
    trial of intravitreal AAV8-RS1 gene augmentation in nine men with pathogenic
    RS1 variants, at 1e9, 1e10 and 1e11 vector genomes per eye.
  target_phenotypes:
  - preferred_term: Retinoschisis
    term:
      id: HP:0030502
      label: Retinoschisis
  - preferred_term: Reduced visual acuity
    term:
      id: HP:0007663
      label: Reduced visual acuity
  evidence:
  - reference: PMID:30196853
    reference_title: "Retinal AAV8-RS1 Gene Therapy for X-Linked Retinoschisis: Initial Findings from a Phase I/IIa Trial by Intravitreal Delivery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This phase I/IIa single-center, prospective, open-label, three-dose-escalation clinical trial administered vector to nine participants with pathogenic RS1 mutations."
    explanation: >
      Describes the trial design and enrolment reported under this NCT number.
animal_models:
- name: RS1 mutant XLRS mouse
  species: Mouse
  genotype: Rs1 loss-of-function (multiple independent mutant lines)
  description: >
    Several independently generated Rs1 mutant mouse lines reproduce the human
    disease with outer plexiform and inner nuclear layer schisis cavities, early
    onset, phenotypic variability across lines, and a reduced b-wave to a-wave
    amplitude ratio. The fidelity of the model is what allowed the
    pathophysiology to be worked out and the gene therapy to be tested
    preclinically.
  publication: PMID:34390869
  modeled_mechanisms:
  - target: Intraretinal Schisis Cavity Formation
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >
      Reproduces the cavities in the same retinal layers as the human disease,
      with the same electrophysiological signature.
    limitations: >
      The mouse retina has no fovea, so the foveoschisis that dominates the
      human presentation and determines human acuity has no counterpart in the
      model; phenotype also varies across independently derived mutant lines.
    readouts:
    - name: ERG b-wave to a-wave amplitude ratio
      target: Intraretinal Schisis Cavity Formation
      direction: DECREASED
      interpretation: >
        Electrophysiological correlate of the transmission failure produced by
        the cavities, matching the electronegative ERG of affected men.
      evidence:
      - reference: PMID:34390869
        reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
        supports: SUPPORT
        evidence_source: OTHER
        snippet: "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."
        explanation: >
          Reports the readout and its direction across the independent mutant
          lines. Evidence source is OTHER because the publication is a review
          synthesizing results from several independently derived mouse lines,
          not a primary report of one of them.
    evidence:
    - reference: PMID:34390869
      reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "The faithful phenotype of the XLRS mouse has assisted in delineating the disease pathophysiology."
      explanation: >
        Supports treating this model as informative for the human mechanism.
        Evidence source is OTHER because this is a review of the mouse
        literature rather than a primary model-organism report.
  - target: Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion
    relationship: RESCUES
    fidelity: MODERATE
    description: >
      AAV8-RS1 delivery under the native promoter restores retinal structure and
      synaptic function in the mutant mouse, providing the rescue arm that
      motivated the human trial.
    limitations: >
      Rescue was achieved by subretinal-scale exposure in a small eye; the human
      trial used intravitreal delivery, where vector must cross the inner
      limiting membrane, and produced only transient cavity closure in one of
      nine participants.
    readouts:
    - name: Schisis-associated retinal microglial activation
      target: Failure of Retinoschisin Octamer-Mediated Retinal Cell Adhesion
      direction: DECREASED
      interpretation: >
        Restoring the adhesion protein quiets the inflammatory response the
        cavities provoke, indicating the microglial phenotype is downstream of
        the adhesion failure rather than an independent process.
      evidence:
      - reference: PMID:34390869
        reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
        supports: SUPPORT
        evidence_source: OTHER
        snippet: "It also ameliorates the schisis-induced inflammatory microglia phenotype toward a state of immune quiescence."
        explanation: >
          Reports the microglial readout and the direction of change after gene
          delivery. Evidence source is OTHER because this is a review.
    evidence:
    - reference: PMID:34390869
      reference_title: "Of men and mice: Human X-linked retinoschisis and fidelity in mouse modeling."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "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)."
      explanation: >
        Documents the rescue on which this link rests. Evidence source is OTHER
        because this is a review.
discussions:
- discussion_id: xlrs_no_genotype_phenotype_correlation
  kind: KNOWLEDGE_GAP
  prompt: >-
    Why does XLRS show no reliable genotype-phenotype correlation, given that
    the structural basis of the disease - failure of retinoschisin octamer
    assembly - is comparatively well defined?
  attaches_to:
  - "pathophysiology#RS1 Loss of Function"
  - "pathophysiology#Early-Onset Bilateral Visual Impairment"
  rationale: >-
    Cryo-EM localizes disease-associated residues to the octamer assembly
    interfaces, which would predict that variants abolishing assembly are more
    severe than those merely destabilizing it. Clinically no such correlation
    holds, and phenotype varies markedly even within families sharing a variant.
    Independently derived mouse lines also differ in severity. Something other
    than the allele - modifier loci, stochastic developmental factors, or
    mechanical variation in retinal architecture - dominates the outcome, and
    identifying it matters practically because gene therapy trials must select
    participants and time intervention without a severity predictor.
  proposed_experiments:
  - experiment_id: xlrs_intrafamilial_discordance_study
    name: Intrafamilial phenotype discordance with modifier mapping in XLRS
    description: >
      Systematically quantify OCT cavity volume, ERG b/a ratio and acuity in
      affected relatives sharing an identical RS1 variant, and test whether
      residual discordance associates with common variation at candidate
      retinal-adhesion and Muller-glia loci.
references:
- reference: PMID:20301401
  title: X-Linked Congenital Retinoschisis.
  tags:
  - GeneReviews
  findings: []
📚

References & Deep Research

References

1
PMID:20301401
X-Linked Congenital Retinoschisis.
No top-level findings curated for this source.