NDP-Related Vitreoretinopathy

Mendelian MONDO:0700377 Pathograph 5 Show in embeddings browser Ophthalmological Disease Retinal Dystrophy Inherited retinal dystrophy

NDP-related vitreoretinopathy is an X-linked spectrum of retinal vascular diseases caused by pathogenic variants in NDP, which encodes Norrin, a secreted Wnt-family ligand required for retinal vascular development. Norrin binds the Frizzled-4 (FZD4) receptor together with the co-receptor LRP5 and the potentiator TSPAN12 to activate canonical Wnt/beta-catenin signaling in retinal vascular endothelium, driving deep retinal vascular plexus formation and inner blood-retina barrier (iBRB) maturation. NDP-related retinopathies form a clinical continuum with considerable overlap -- ranging from Norrie disease, NDP-related persistent fetal vasculature, NDP-related familial exudative vitreoretinopathy (FEVR, EVR2), NDP-related advanced retinopathy of prematurity, and NDP-related Coats disease -- unified by degenerative and proliferative retinal vascular changes evident at or near birth. Norrie disease, the first described and most severe presentation, is the only NDP-related retinopathy with extraocular manifestations (sensorineural hearing loss, cognitive disability), reflecting a parallel requirement for Norrin-Wnt signaling in cochlear vascular development.

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1
Inheritance
4
Pathophys.
5
Phenotypes
5
Pathograph
1
Genes
3
Medical Actions
2
Subtypes
1
Models
👪

Inheritance

1
X-linked inheritance HP:0001417
NDP-related retinopathies are inherited in an X-linked manner. The majority of affected males have an NDP pathogenic variant inherited from their carrier mother, who has a 50% transmission risk per pregnancy; affected males transmit the variant to all daughters (who become carriers) and no sons. Rarely, heterozygous females have clinical manifestations.
X-linked inheritance
Show evidence (1 reference)
PMID:20301506 SUPPORT Human Clinical
"males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be heterozygous and may rarely have clinical manifestations. Affected males transmit the NDP pathogenic variant to all of their daughters and none of their sons."
GeneReviews confirms the X-linked transmission pattern, including the rare occurrence of clinical manifestations in heterozygous females.
◆

Subtypes

2
Norrie Disease MONDO:0010691
The first described and most severe NDP-related phenotype, presenting at birth with bilateral grayish-yellow, glistening, elevated retrolental masses of immature retinal cells; foveal development is always incomplete. Norrie disease is the only NDP-related retinopathy with extraocular findings, which can variably include cognitive disability, mental health and behavior disorders, seizures, sensorineural hearing loss (typically childhood/adult onset, distinct from the congenital blindness), and peripheral vascular disease.
Show evidence (3 references)
PMID:20301506 SUPPORT Human Clinical
"The eye findings of Norrie disease, the first described and best characterized of these disorders, are typically bilateral grayish-yellow, glistening, elevated retrolental masses composed of immature retinal cells usually visible through clear lenses; foveal development is always incomplete."
GeneReviews describes the pathognomonic Norrie disease fundus finding of bilateral grayish-yellow, glistening, elevated retrolental masses.
PMID:20301506 SUPPORT Human Clinical
"In addition, Norrie disease is the only NDP-related retinopathy with associated extraocular findings, which can variably include cognitive disability, mental health and behavior disorders, seizures, sensorineural hearing loss, and peripheral vascular disease."
Establishes Norrie disease as the sole NDP-related phenotype with extraocular manifestations, distinguishing it from the milder NDP-related FEVR/PFV/ROP/Coats presentations.
PMID:28602015 SUPPORT Human Clinical
"NDP-related retinopathies are a group of X-linked disorders characterized by degenerative and proliferative changes of the neuroretina, occasionally accompanied with varying degrees of mental retardation and sensorineural hearing loss."
Clinical cohort confirms the dual degenerative/proliferative retinal pathology and occasional systemic (mental retardation, hearing loss) involvement in NDP-related retinopathies.
⚙

Pathophysiology

4
Norrin-FZD4-LRP5-TSPAN12 Retinal Vascular Wnt Signaling Deficiency
Loss-of-function NDP variants impair Norrin ligand activity, disrupting Norrin-FZD4-LRP5-TSPAN12 canonical Wnt/beta-catenin signaling in retinal vascular endothelium. This signaling axis is required for deep retinal vascular plexus formation and stabilization of endothelial junctional complexes that maintain the inner blood-retinal barrier; its loss produces the combined degenerative and proliferative retinal vascular pathology (incomplete vascularization with secondary neovascularization and exudation) seen across the NDP-related retinopathy spectrum.
Endothelial cell CL:0000115 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Endothelial cell (CL:0000115). CL:0000115 is a cell type from the Cell Ontology.
Canonical Wnt signaling pathway GO:0060070 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Canonical Wnt signaling pathway (GO:0060070). GO:0060070 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Failure of Intraretinal Capillary Formation
Cochlear Vascular Pathology Underlying Sensorineural Hearing Loss
Show evidence (2 references)
PMID:37947657 SUPPORT Human Clinical
"The early angiogenesis of the retina and its iBRB is a delicate process that is mediated by the canonical Norrin Wnt-signaling pathway in retinal endothelial cells. Pathogenic variants in genes that play key roles within this pathway, such as NDP, FZD4, TSPAN12, and LRP5, have been associated..."
Establishes NDP, FZD4, TSPAN12, and LRP5 as components of the shared canonical Norrin-Wnt signaling pathway required for normal retinal vascular development.
PMID:41862006 SUPPORT Other
"Interest in norrin signaling within the Wnt/β-catenin pathway arises from its crucial role in maintaining BRB integrity through the activation of the FZD4 receptor and LRP5/6 co-receptors, leading to the stabilization of endothelial junctional complexes and the maintenance and restoration of..."
Documents that Norrin-FZD4-LRP5/6 signaling stabilizes retinal endothelial junctional complexes, mechanistically linking pathway loss to blood-retinal barrier breakdown. Evidence source is OTHER because this is a review.
Failure of Intraretinal Capillary Formation
The retinal consequence of the signalling deficit, and the step at which this disease separates from an ordinary vasculopathy. Norrin is secreted by Muller glia and acts on the endothelium beside them, so the affected cell and the signalling cell are different; the vessels never receive the instruction to grow inward from the superficial plexus and form the deep intraretinal capillary beds. In Ndp-null mice intraretinal capillary formation is abolished outright rather than merely reduced. Severity in humans scales with residual signal, from a peripheral avascular zone in X-linked FEVR to near-total retinal hypovascularization in Norrie disease.
retinal blood vessel endothelial cell CL:0002585 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves retinal blood vessel endothelial cell (CL:0002585). CL:0002585 is a cell type from the Cell Ontology. Mueller cell CL:0000636 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Mueller cell (CL:0000636). CL:0000636 is a cell type from the Cell Ontology.
Retinal blood vessel morphogenesis GO:0061304 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Retinal blood vessel morphogenesis (GO:0061304). GO:0061304 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
Ndp knockout mouse Mouse rescues Intravitreal AAV expressing norrin restored intraretinal capillary growth, vessel density and plexus organization, preserved the blood-retinal barrier and rescued visual function, establishing that the vascular defect is correctable postnatally rather than fixed at birth.
Downstream
Retinal Hypovascularization, Dysplasia and Congenital Blindness
Show evidence (2 references)
PMID:42436854 SUPPORT Model Organism
"Norrin, secreted by retinal Müller cells, activates canonical Wnt signaling via Frizzled-4 and co-receptors."
Establishes the paracrine arrangement this node describes, in which the Muller glial cell is the source and the endothelium the target.
PMID:42436854 SUPPORT Model Organism
"Loss-of-function mutations abolish intraretinal capillary formation in mice."
States the severity of the developmental failure this node asserts: intraretinal capillary formation is abolished, not merely impaired.
Retinal Hypovascularization, Dysplasia and Congenital Blindness
At the severe end of the spectrum the avascular retina is also dysplastic, producing the retrolental fibrovascular mass historically called pseudoglioma, with retinal detachment usually present at or shortly after birth and blindness from infancy. The same lesion at higher residual signal gives X-linked FEVR, whose peripheral avascularity and exudative complications resemble retinopathy of prematurity - a resemblance that is phenotypic convergence on ischaemic retina, not shared aetiology, since ROP begins with hyperoxic vessel arrest rather than with a Norrin lesion.
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
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:42436854 SUPPORT Model Organism
"In humans, mutations in NDP, which encodes norrin, cause Norrie disease, characterized by retinal hypovascularization and congenital blindness, and X-linked familial exudative vitreoretinopathy (FEVR), resembling retinopathy of prematurity (ROP)."
Supports both ends of the continuum this node describes and is the source of the stated resemblance between X-linked FEVR and retinopathy of prematurity.
Cochlear Vascular Pathology Underlying Sensorineural Hearing Loss
Norrin-Wnt signaling is also required for cochlear vascular development. In Norrie disease, early malformation of the cochlear microvasculature precedes loss of vessel integrity, decline of the endocochlear potential, and subsequent hair cell death, explaining why hearing loss in Norrie disease has a later, progressive onset distinct from the congenital retinal blindness.
Endothelial cell CL:0000115 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Endothelial cell (CL:0000115). CL:0000115 is a cell type from the Cell Ontology.
Show evidence (2 references)
PMID:35132964 SUPPORT Model Organism
"We found that cochlear vascular pathology occurs earlier than previously reported and precedes sensorineural hearing loss."
Mouse model study demonstrates that cochlear microvascular pathology precedes, and therefore is not a consequence of, the sensorineural hearing loss of Norrie disease.
PMID:35132964 SUPPORT Model Organism
"The work defines a disease mechanism whereby early malformation of the cochlear microvasculature precedes loss of vessel integrity and decline of endocochlear potential, leading to hearing loss and hair cell death while sparing spiral ganglion cells."
Defines the mechanistic sequence: microvascular malformation, loss of endocochlear potential, then hair cell death, with spiral ganglion cells relatively spared.
⬡

Pathograph

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

Phenotypes

5
Ear 1
Sensorineural hearing impairment HP:0000407 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensorineural hearing impairment (HP:0000407). HP:0000407 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35132964 SUPPORT Human Clinical
"Norrie disease is caused by mutation of the NDP gene, presenting as congenital blindness followed by later onset of hearing loss."
Confirms progressive, later-onset sensorineural hearing loss as a hallmark extraocular feature of Norrie disease.
Nervous System 2
Intellectual disability HP:0001249 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intellectual disability (HP:0001249). HP:0001249 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301506 SUPPORT Human Clinical
"In addition, Norrie disease is the only NDP-related retinopathy with associated extraocular findings, which can variably include cognitive disability, mental health and behavior disorders, seizures, sensorineural hearing loss, and peripheral vascular disease."
GeneReviews lists cognitive disability among the variable extraocular findings of Norrie disease.
Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301506 SUPPORT Human Clinical
"behavior disorders, seizures, sensorineural hearing loss, and peripheral"
GeneReviews lists seizures among the variable extraocular findings of Norrie disease.
Other 2
Congenital blindness VERY_FREQUENT HP:0007875 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Congenital blindness (HP:0007875). HP:0007875 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301506 SUPPORT Human Clinical
"of these disorders, are typically bilateral grayish-yellow, glistening, elevated"
Describes the congenital, bilateral retrolental masses that are evident at birth and cause congenital blindness in Norrie disease.
Hypoplasia of the fovea HP:0007750 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypoplasia of the fovea (HP:0007750). HP:0007750 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301506 SUPPORT Human Clinical
"clear lenses; foveal development is always"
GeneReviews states foveal development is always incomplete in Norrie disease.
🧬

Genetic Associations

1
NDP
Gene: NDP hgnc:7678 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is NDP (hgnc:7678). hgnc:7678 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:28602015 SUPPORT Human Clinical
"The whole NDP gene was deleted in patient I, while a missense NDP"
Documents that both whole-gene deletion and missense NDP variants produce the classical Norrie disease ocular phenotype.
💊

Medical Actions

3
Low Vision Rehabilitation
Action: low vision rehabilitationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is low vision rehabilitation, annotated with Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Supportive low-vision aids and rehabilitation for the congenital retinal blindness of Norrie disease and low vision in milder NDP-related phenotypes.
Hearing Surveillance and Audiologic Management
Action: audiologic surveillanceNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is audiologic surveillance, annotated with Audiometric Test (NCIT:C38036). NCIT:C38036 is a clinical intervention from the NCI Thesaurus. Ontology label: Audiometric Test NCIT:C38036
Routine audiologic monitoring for progressive sensorineural hearing loss, with avoidance of loud noises and sound-amplifying listening devices that could exacerbate hearing loss.
Show evidence (1 reference)
PMID:20301506 SUPPORT Human Clinical
"avoid: Situations that could exacerbate hearing loss such as loud noises and use of listening devices that amplify sound."
GeneReviews specifically identifies loud-noise exposure and sound amplification devices as agents/circumstances to avoid because they can exacerbate hearing loss in Norrie disease.
Genetic Counseling
Action: genetic counselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is genetic counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. Ontology label: Genetic Counseling NCIT:C15240
Genetic counseling addressing X-linked inheritance, carrier testing for at-risk female relatives, and surveillance recommendations (fluorescein angiography) for carriers.
Show evidence (1 reference)
PMID:20301506 SUPPORT Human Clinical
"to undergo fluorescein angiography to detect peripheral retinal vascular changes"
GeneReviews recommends fluorescein angiography surveillance for at-risk female carriers to detect peripheral retinal vascular changes requiring monitoring or prophylactic treatment.
🐁

Animal Models

1
Ndp knockout mouse
The standard model of Norrie disease, lacking norrin and therefore intraretinal capillary formation. Used both to define the vascular pathophysiology and to test AAV-mediated norrin replacement delivered intravitreally at postnatal day 7.
Species
Mouse
Genotype
Ndp knockout (norrin-deficient)
Publication
PMID:42436854
Pathograph links
Failure of Intraretinal Capillary Formation rescues fidelity: moderate Intravitreal AAV expressing norrin restored intraretinal capillary growth, vessel density and plexus organization, preserved the blood-retinal barrier and rescued visual function, establishing that the vascular defect is correctable postnatally rather than fixed at birth.
Limitations: Mouse retinal vascularization is largely postnatal whereas human retinal vascularization completes before term, so the postnatal-day-7 treatment window has no straightforward human equivalent; and the mouse lacks the retrolental fibrovascular mass and retinal detachment that define severe human Norrie disease.
Readouts
Intraretinal capillary growth and deep plexus organization after AAV-norrin
Direction: RESTORED
Interpretation: Structural confirmation that resupplying the ligand reverses the developmental vascular failure this node models.
Show evidence (1 reference)
PMID:42436854 SUPPORT Model Organism
"Both vectors fully restored intraretinal capillary growth in Ndp KO mice, normalizing vessel density and plexus organization, preserving the blood-retinal barrier, and rescuing visual function."
Reports the readout and its restoration directly, across both vector serotypes tested.
Show evidence (1 reference)
PMID:42436854 SUPPORT Model Organism
"Loss-of-function mutations abolish intraretinal capillary formation in mice."
Establishes that the model reproduces the human developmental vascular failure, supporting its use as informative for this node.
{ }

Source YAML

click to show 
name: NDP-Related Vitreoretinopathy
creation_date: "2026-07-07T00:00:00Z"
category: Mendelian
description: >
  NDP-related vitreoretinopathy is an X-linked spectrum of retinal vascular
  diseases caused by pathogenic variants in NDP, which encodes Norrin, a
  secreted Wnt-family ligand required for retinal vascular development. Norrin
  binds the Frizzled-4 (FZD4) receptor together with the co-receptor LRP5 and
  the potentiator TSPAN12 to activate canonical Wnt/beta-catenin signaling in
  retinal vascular endothelium, driving deep retinal vascular plexus formation
  and inner blood-retina barrier (iBRB) maturation. NDP-related retinopathies
  form a clinical continuum with considerable overlap -- ranging from Norrie
  disease, NDP-related persistent fetal vasculature, NDP-related familial
  exudative vitreoretinopathy (FEVR, EVR2), NDP-related advanced retinopathy
  of prematurity, and NDP-related Coats disease -- unified by degenerative and
  proliferative retinal vascular changes evident at or near birth. Norrie
  disease, the first described and most severe presentation, is the only
  NDP-related retinopathy with extraocular manifestations (sensorineural
  hearing loss, cognitive disability), reflecting a parallel requirement for
  Norrin-Wnt signaling in cochlear vascular development.
disease_term:
  preferred_term: NDP-related vitreoretinopathy
  term:
    id: MONDO:0700377
    label: NDP-related vitreoretinopathy
synonyms:
- NDP-related retinopathy
- NDP-related vitreoretinopathy including Norrie syndrome
parents:
- Ophthalmological Disease
- Retinal Dystrophy
- Inherited retinal dystrophy
has_subtypes:
- name: Norrie disease
  display_name: Norrie Disease
  subtype_term:
    preferred_term: Norrie disease
    term:
      id: MONDO:0010691
      label: Norrie disease
  description: >
    The first described and most severe NDP-related phenotype, presenting at
    birth with bilateral grayish-yellow, glistening, elevated retrolental
    masses of immature retinal cells; foveal development is always
    incomplete. Norrie disease is the only NDP-related retinopathy with
    extraocular findings, which can variably include cognitive disability,
    mental health and behavior disorders, seizures, sensorineural hearing
    loss (typically childhood/adult onset, distinct from the congenital
    blindness), and peripheral vascular disease.
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The eye findings of Norrie disease, the first described and best characterized of these disorders, are typically bilateral grayish-yellow, glistening, elevated retrolental masses composed of immature retinal cells usually visible through clear lenses; foveal development is always incomplete."
    explanation: >
      GeneReviews describes the pathognomonic Norrie disease fundus finding of
      bilateral grayish-yellow, glistening, elevated retrolental masses.
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, Norrie disease is the only NDP-related retinopathy with associated extraocular findings, which can variably include cognitive disability, mental health and behavior disorders, seizures, sensorineural hearing loss, and peripheral vascular disease."
    explanation: >
      Establishes Norrie disease as the sole NDP-related phenotype with
      extraocular manifestations, distinguishing it from the milder
      NDP-related FEVR/PFV/ROP/Coats presentations.
  - reference: PMID:28602015
    reference_title: "Clinical and genetic analysis of Indian patients with NDP-related retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "NDP-related retinopathies are a group of X-linked disorders characterized by degenerative and proliferative changes of the neuroretina, occasionally accompanied with varying degrees of mental retardation and sensorineural hearing loss."
    explanation: >
      Clinical cohort confirms the dual degenerative/proliferative retinal
      pathology and occasional systemic (mental retardation, hearing loss)
      involvement in NDP-related retinopathies.
- name: NDP-related FEVR
  display_name: NDP-Related Familial Exudative Vitreoretinopathy (EVR2)
  description: >
    Milder end of the NDP phenotypic spectrum, with peripheral retinal
    vascular abnormalities (avascular zones, neovascularization, exudation,
    tractional detachment) but without the extraocular features of Norrie
    disease. Modeled in detail as the EVR2 subtype of
    Familial_Exudative_Vitreoretinopathy.yaml; referenced here to place it
    within the broader NDP-related retinopathy continuum.
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The spectrum of NDP-related retinopathies appears to be a continuum with considerable overlap, ranging from Norrie disease, NDP-related persistent fetal vasculature, NDP-related familial exudative vitreoretinopathy, NDP-related advanced retinopathy of prematurity, and NDP-related Coats disease."
    explanation: >
      GeneReviews places NDP-related FEVR within the continuum of NDP-related
      retinopathies alongside Norrie disease.
inheritance:
- name: X-linked inheritance
  inheritance_term:
    preferred_term: X-linked inheritance
    term:
      id: HP:0001417
      label: X-linked inheritance
  description: >
    NDP-related retinopathies are inherited in an X-linked manner. The
    majority of affected males have an NDP pathogenic variant inherited from
    their carrier mother, who has a 50% transmission risk per pregnancy;
    affected males transmit the variant to all daughters (who become
    carriers) and no sons. Rarely, heterozygous females have clinical
    manifestations.
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be heterozygous and may rarely have clinical manifestations. Affected males transmit the NDP pathogenic variant to all of their daughters and none of their sons."
    explanation: >
      GeneReviews confirms the X-linked transmission pattern, including the
      rare occurrence of clinical manifestations in heterozygous females.
pathophysiology:
- name: Norrin-FZD4-LRP5-TSPAN12 Retinal Vascular Wnt Signaling Deficiency
  conforms_to: "norrin_fzd4_retinal_vascular_development#Insufficient Norrin-FZD4-beta-catenin Signalling in Retinal Endothelium"
  role: trigger
  description: >
    Loss-of-function NDP variants impair Norrin ligand activity, disrupting
    Norrin-FZD4-LRP5-TSPAN12 canonical Wnt/beta-catenin signaling in retinal
    vascular endothelium. This signaling axis is required for deep retinal
    vascular plexus formation and stabilization of endothelial junctional
    complexes that maintain the inner blood-retinal barrier; its loss
    produces the combined degenerative and proliferative retinal vascular
    pathology (incomplete vascularization with secondary neovascularization
    and exudation) seen across the NDP-related retinopathy spectrum.
  cell_types:
  - preferred_term: Endothelial cell
    term:
      id: CL:0000115
      label: endothelial cell
  biological_processes:
  - preferred_term: Canonical Wnt signaling pathway
    term:
      id: GO:0060070
      label: canonical Wnt signaling pathway
    modifier: DECREASED
  evidence:
  - reference: PMID:37947657
    reference_title: "Mechanisms Underlying Rare Inherited Pediatric Retinal Vascular Diseases: FEVR, Norrie Disease, Persistent Fetal Vascular Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The early angiogenesis of the retina and its iBRB is a delicate process that is mediated by the canonical Norrin Wnt-signaling pathway in retinal endothelial cells. Pathogenic variants in genes that play key roles within this pathway, such as NDP, FZD4, TSPAN12, and LRP5, have been associated with the incidence of these retinal diseases."
    explanation: >
      Establishes NDP, FZD4, TSPAN12, and LRP5 as components of the shared
      canonical Norrin-Wnt signaling pathway required for normal retinal
      vascular development.
  - reference: PMID:41862006
    reference_title: "Therapeutic potential of norrin/FZD4/β-catenin signaling in blood-retinal barrier protection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Interest in norrin signaling within the Wnt/β-catenin pathway arises from its crucial role in maintaining BRB integrity through the activation of the FZD4 receptor and LRP5/6 co-receptors, leading to the stabilization of endothelial junctional complexes and the maintenance and restoration of retinal vascular barrier properties"
    explanation: >
      Documents that Norrin-FZD4-LRP5/6 signaling stabilizes retinal
      endothelial junctional complexes, mechanistically linking pathway loss
      to blood-retinal barrier breakdown. Evidence source is OTHER because this
      is a review.
  downstream:
  - target: Failure of Intraretinal Capillary Formation
    causal_link_type: DIRECT
  - target: Cochlear Vascular Pathology Underlying Sensorineural Hearing Loss
    causal_link_type: DIRECT

- name: Failure of Intraretinal Capillary Formation
  description: >
    The retinal consequence of the signalling deficit, and the step at which
    this disease separates from an ordinary vasculopathy. Norrin is secreted by
    Muller glia and acts on the endothelium beside them, so the affected cell
    and the signalling cell are different; the vessels never receive the
    instruction to grow inward from the superficial plexus and form the deep
    intraretinal capillary beds. In Ndp-null mice intraretinal capillary
    formation is abolished outright rather than merely reduced. Severity in
    humans scales with residual signal, from a peripheral avascular zone in
    X-linked FEVR to near-total retinal hypovascularization in Norrie disease.
  role: central_effector
  biological_scale: TISSUE
  conforms_to: "norrin_fzd4_retinal_vascular_development#Incomplete Retinal Vascularization with Peripheral Avascular Retina"
  cell_types:
  - preferred_term: retinal blood vessel endothelial cell
    term:
      id: CL:0002585
      label: retinal blood vessel endothelial cell
  - preferred_term: Mueller cell
    term:
      id: CL:0000636
      label: Mueller cell
  biological_processes:
  - preferred_term: Retinal blood vessel morphogenesis
    term:
      id: GO:0061304
      label: retinal blood vessel morphogenesis
    modifier: DECREASED
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:42436854
    reference_title: "AAV-norrin gene therapy rescues retinal defects in mice with Norrie disease and oxygen-induced retinopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Norrin, secreted by retinal Müller cells, activates canonical Wnt signaling via Frizzled-4 and co-receptors."
    explanation: >
      Establishes the paracrine arrangement this node describes, in which the
      Muller glial cell is the source and the endothelium the target.
  - reference: PMID:42436854
    reference_title: "AAV-norrin gene therapy rescues retinal defects in mice with Norrie disease and oxygen-induced retinopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Loss-of-function mutations abolish intraretinal capillary formation in mice."
    explanation: >
      States the severity of the developmental failure this node asserts:
      intraretinal capillary formation is abolished, not merely impaired.
  downstream:
  - target: Retinal Hypovascularization, Dysplasia and Congenital Blindness
    causal_link_type: DIRECT

- name: Retinal Hypovascularization, Dysplasia and Congenital Blindness
  description: >
    At the severe end of the spectrum the avascular retina is also dysplastic,
    producing the retrolental fibrovascular mass historically called
    pseudoglioma, with retinal detachment usually present at or shortly after
    birth and blindness from infancy. The same lesion at higher residual signal
    gives X-linked FEVR, whose peripheral avascularity and exudative
    complications resemble retinopathy of prematurity - a resemblance that is
    phenotypic convergence on ischaemic retina, not shared aetiology, since ROP
    begins with hyperoxic vessel arrest rather than with a Norrin lesion.
  role: consequence
  biological_scale: ORGANISM
  conforms_to: "norrin_fzd4_retinal_vascular_development#Ischaemia-Driven Neovascularization, Exudation and Tractional Detachment"
  biological_processes:
  - preferred_term: Visual perception
    term:
      id: GO:0007601
      label: visual perception
    modifier: DECREASED
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:42436854
    reference_title: "AAV-norrin gene therapy rescues retinal defects in mice with Norrie disease and oxygen-induced retinopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In humans, mutations in NDP, which encodes norrin, cause Norrie disease, characterized by retinal hypovascularization and congenital blindness, and X-linked familial exudative vitreoretinopathy (FEVR), resembling retinopathy of prematurity (ROP)."
    explanation: >
      Supports both ends of the continuum this node describes and is the source
      of the stated resemblance between X-linked FEVR and retinopathy of
      prematurity.

- name: Cochlear Vascular Pathology Underlying Sensorineural Hearing Loss
  role: consequence
  biological_scale: TISSUE
  description: >
    Norrin-Wnt signaling is also required for cochlear vascular development.
    In Norrie disease, early malformation of the cochlear microvasculature
    precedes loss of vessel integrity, decline of the endocochlear potential,
    and subsequent hair cell death, explaining why hearing loss in Norrie
    disease has a later, progressive onset distinct from the congenital
    retinal blindness.
  cell_types:
  - preferred_term: Endothelial cell
    term:
      id: CL:0000115
      label: endothelial cell
  evidence:
  - reference: PMID:35132964
    reference_title: "The timing of auditory sensory deficits in Norrie disease has implications for therapeutic intervention."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We found that cochlear vascular pathology occurs earlier than previously reported and precedes sensorineural hearing loss."
    explanation: >
      Mouse model study demonstrates that cochlear microvascular pathology
      precedes, and therefore is not a consequence of, the sensorineural hearing
      loss of Norrie disease.
  - reference: PMID:35132964
    reference_title: "The timing of auditory sensory deficits in Norrie disease has implications for therapeutic intervention."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The work defines a disease mechanism whereby early malformation of the cochlear microvasculature precedes loss of vessel integrity and decline of endocochlear potential, leading to hearing loss and hair cell death while sparing spiral ganglion cells."
    explanation: >
      Defines the mechanistic sequence: microvascular malformation, loss of
      endocochlear potential, then hair cell death, with spiral ganglion
      cells relatively spared.
phenotypes:
- name: Congenital blindness
  category: Ophthalmologic
  subtype: Norrie disease
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Congenital blindness
    term:
      id: HP:0007875
      label: Congenital blindness
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "of these disorders, are typically bilateral grayish-yellow, glistening, elevated"
    explanation: >
      Describes the congenital, bilateral retrolental masses that are evident
      at birth and cause congenital blindness in Norrie disease.
- name: Hypoplasia of the fovea
  category: Ophthalmologic
  subtype: Norrie disease
  phenotype_term:
    preferred_term: Hypoplasia of the fovea
    term:
      id: HP:0007750
      label: Hypoplasia of the fovea
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "clear lenses; foveal development is always"
    explanation: >
      GeneReviews states foveal development is always incomplete in Norrie
      disease.
- name: Sensorineural hearing impairment
  category: Audiologic
  subtype: Norrie disease
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:35132964
    reference_title: "The timing of auditory sensory deficits in Norrie disease has implications for therapeutic intervention."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Norrie disease is caused by mutation of the NDP gene, presenting as congenital blindness followed by later onset of hearing loss."
    explanation: >
      Confirms progressive, later-onset sensorineural hearing loss as a
      hallmark extraocular feature of Norrie disease.
- name: Intellectual disability
  category: Neurologic
  subtype: Norrie disease
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, Norrie disease is the only NDP-related retinopathy with associated extraocular findings, which can variably include cognitive disability, mental health and behavior disorders, seizures, sensorineural hearing loss, and peripheral vascular disease."
    explanation: >
      GeneReviews lists cognitive disability among the variable extraocular
      findings of Norrie disease.
- name: Seizure
  category: Neurologic
  subtype: Norrie disease
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "behavior disorders, seizures, sensorineural hearing loss, and peripheral"
    explanation: >
      GeneReviews lists seizures among the variable extraocular findings of
      Norrie disease.
genetic:
- name: NDP
  gene_term:
    preferred_term: NDP
    term:
      id: hgnc:7678
      label: NDP
  notes: >
    NDP encodes Norrin, a secreted cystine-knot growth factor that activates
    canonical Wnt/beta-catenin signaling through FZD4/LRP5/TSPAN12 in retinal
    and cochlear vascular endothelium. Disease variants act through loss of
    Norrin ligand function; whole-gene deletions and missense variants have
    both been reported to cause the classical Norrie disease ocular
    phenotype.
  evidence:
  - reference: PMID:28602015
    reference_title: "Clinical and genetic analysis of Indian patients with NDP-related retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The whole NDP gene was deleted in patient I, while a missense NDP"
    explanation: >
      Documents that both whole-gene deletion and missense NDP variants
      produce the classical Norrie disease ocular phenotype.
treatments:
- name: Low Vision Rehabilitation
  description: Supportive low-vision aids and rehabilitation for the
    congenital retinal blindness of Norrie disease and low vision in milder
    NDP-related phenotypes.
  treatment_term:
    preferred_term: low vision rehabilitation
    term:
      id: NCIT:C15747
      label: Supportive Care
- name: Hearing Surveillance and Audiologic Management
  description: Routine audiologic monitoring for progressive sensorineural
    hearing loss, with avoidance of loud noises and sound-amplifying
    listening devices that could exacerbate hearing loss.
  treatment_term:
    preferred_term: audiologic surveillance
    term:
      id: NCIT:C38036
      label: Audiometric Test
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "avoid: Situations that could exacerbate hearing loss such as loud noises and use of listening devices that amplify sound."
    explanation: >
      GeneReviews specifically identifies loud-noise exposure and sound
      amplification devices as agents/circumstances to avoid because they can
      exacerbate hearing loss in Norrie disease.
- name: Genetic Counseling
  description: Genetic counseling addressing X-linked inheritance, carrier
    testing for at-risk female relatives, and surveillance recommendations
    (fluorescein angiography) for carriers.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301506
    reference_title: "NDP-Related Retinopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "to undergo fluorescein angiography to detect peripheral retinal vascular changes"
    explanation: >
      GeneReviews recommends fluorescein angiography surveillance for at-risk
      female carriers to detect peripheral retinal vascular changes requiring
      monitoring or prophylactic treatment.
animal_models:
- name: Ndp knockout mouse
  species: Mouse
  genotype: Ndp knockout (norrin-deficient)
  description: >
    The standard model of Norrie disease, lacking norrin and therefore
    intraretinal capillary formation. Used both to define the vascular
    pathophysiology and to test AAV-mediated norrin replacement delivered
    intravitreally at postnatal day 7.
  publication: PMID:42436854
  modeled_mechanisms:
  - target: Failure of Intraretinal Capillary Formation
    relationship: RESCUES
    fidelity: MODERATE
    description: >
      Intravitreal AAV expressing norrin restored intraretinal capillary growth,
      vessel density and plexus organization, preserved the blood-retinal
      barrier and rescued visual function, establishing that the vascular defect
      is correctable postnatally rather than fixed at birth.
    limitations: >
      Mouse retinal vascularization is largely postnatal whereas human retinal
      vascularization completes before term, so the postnatal-day-7 treatment
      window has no straightforward human equivalent; and the mouse lacks the
      retrolental fibrovascular mass and retinal detachment that define severe
      human Norrie disease.
    readouts:
    - name: Intraretinal capillary growth and deep plexus organization after AAV-norrin
      target: Failure of Intraretinal Capillary Formation
      direction: RESTORED
      interpretation: >
        Structural confirmation that resupplying the ligand reverses the
        developmental vascular failure this node models.
      evidence:
      - reference: PMID:42436854
        reference_title: "AAV-norrin gene therapy rescues retinal defects in mice with Norrie disease and oxygen-induced retinopathy."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Both vectors fully restored intraretinal capillary growth in Ndp KO mice, normalizing vessel density and plexus organization, preserving the blood-retinal barrier, and rescuing visual function."
        explanation: >
          Reports the readout and its restoration directly, across both vector
          serotypes tested.
    evidence:
    - reference: PMID:42436854
      reference_title: "AAV-norrin gene therapy rescues retinal defects in mice with Norrie disease and oxygen-induced retinopathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Loss-of-function mutations abolish intraretinal capillary formation in mice."
      explanation: >
        Establishes that the model reproduces the human developmental vascular
        failure, supporting its use as informative for this node.