KCNV2-Related Retinopathy

Mendelian MONDO:1040063 Pathograph 6 Show in embeddings browser Ophthalmological Disease Retinal Dystrophy Inherited retinal dystrophy

KCNV2-related retinopathy, classically known as cone dystrophy with supernormal rod electroretinogram (CDSRR), is an autosomal recessive retinal channelopathy caused by biallelic pathogenic variants in KCNV2, which encodes Kv8.2, a modulatory (non-conducting alone) voltage-gated potassium channel alpha-subunit expressed in rod and cone photoreceptor inner segments. Kv8.2 heteromerizes with Kv2.1 to form the native photoreceptor delayed-rectifier potassium current that shapes the photoreceptor light response; its loss produces the disease's pathognomonic paradoxical electrophysiology, in which rod b-wave amplitudes on electroretinography are larger than normal under bright-flash conditions despite progressive cone-mediated visual loss.

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1
Inheritance
5
Pathophys.
4
Phenotypes
6
Pathograph
1
Genes
2
Medical Actions
👪

Inheritance

1
Autosomal recessive inheritance HP:0000007
KCNV2-related retinopathy is inherited in an autosomal recessive manner, requiring biallelic pathogenic KCNV2 variants.
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:18235024 SUPPORT Human Clinical
"The mutations concordantly segregate in all available families according a recessive mode of inheritance."
Segregation analysis across 13 families confirms autosomal recessive inheritance of KCNV2-related CDSRR.
⚙

Pathophysiology

5
Kv8.2/Kv2.1 Heteromeric Photoreceptor Potassium Channel Dysfunction
Biallelic KCNV2 variants disrupt Kv8.2, a modulatory alpha-subunit that cannot form functional channels on its own but heteromerizes with Kv2.1 in rod and cone photoreceptor inner segments to form the native delayed-rectifier potassium current. Loss-of-function KCNV2 variants follow at least two distinct molecular mechanisms: pore-domain mutations that yield non-conducting Kv2.1/Kv8.2 heteromers, and tetramerization-domain mutations that prevent heteromer assembly altogether, leaving only homomeric Kv2.1 channels with altered gating properties. Either route alters photoreceptor membrane excitability and light-response kinetics, producing the disease's pathognomonic supernormal rod b-wave and progressive cone-mediated visual loss.
Retinal cone cell CL:0000573 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Retinal cone cell (CL:0000573). CL:0000573 is a cell type from the Cell Ontology. Retinal rod cell CL:0000604 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Retinal rod cell (CL:0000604). CL:0000604 is a cell type from the Cell Ontology.
Potassium ion transmembrane transport GO:0071805 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Potassium ion transmembrane transport (GO:0071805). GO:0071805 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Disrupted Photoreceptor Light Adaptation
Show evidence (2 references)
PMID:23115240 SUPPORT In Vitro
"KCNV2 codes for the modulatory voltage-gated potassium channel α-subunit, Kv8.2, which is incapable of forming functional channels on its own. Functional heteromeric channels are however formed with Kv2.1 in heterologous expression systems, with both α-subunit genes expressed in rod and cone..."
Establishes that Kv8.2 requires heteromerization with Kv2.1 to form a functional photoreceptor potassium channel.
PMID:23115240 SUPPORT In Vitro
"We found that two pore mutations (W467G and G478R) led to the formation of nonconducting heteromeric Kv2.1/Kv8.2 channels, whereas the mutations localized in the tetramerization domain prevented heteromer generation and resulted in the formation of homomeric Kv2.1 channels only. Consequently,..."
Functional heterologous expression studies demonstrate the two distinct loss-of-function mechanisms (non-conducting heteromer vs. failed heteromer assembly) by which KCNV2 missense variants cause disease.
Disrupted Photoreceptor Light Adaptation
Kv8.2 does not carry current itself; it shifts the activation range of the photoreceptor inner-segment potassium channels it heteromerizes into. Losing that modulation leaves the photoreceptor unable to set its operating point appropriately for the ambient light level, so what fails is adaptation rather than phototransduction. This is why the disease produces a paradoxical rather than a simply reduced electroretinogram, and why the a-wave is delayed even where its amplitude is preserved: the rod is responding, but on the wrong timescale and from the wrong baseline.
Retinal rod cell CL:0000604 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Retinal rod cell (CL:0000604). CL:0000604 is a cell type from the Cell Ontology. Retinal cone cell CL:0000573 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Retinal cone cell (CL:0000573). CL:0000573 is a cell type from the Cell Ontology.
Response to light stimulus GO:0009416 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Response to light stimulus (GO:0009416). GO:0009416 is a biological process from the Gene Ontology. ⚠ ABNORMAL
photoreceptor inner segment GO:0001917 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves photoreceptor inner segment (GO:0001917). GO:0001917 is a cellular component from the Gene Ontology.
Downstream
Paradoxical Supernormal Scotopic b-Wave with Delayed Response Timing
Progressive Cone and Outer Nuclear Layer Loss
Show evidence (2 references)
PMID:32441199 SUPPORT Other
"This gene encodes Kv8.2, a voltage-gated potassium channel subunit that acts as a modulator by shifting the activation range of the K+ channels in photoreceptor inner segments."
Establishes the modulatory, activation-range-shifting role in the inner segment that this node asserts is lost. Evidence source is OTHER because this is a review.
PMID:30820446 SUPPORT Model Organism
"The CDSRR disease phenotype indicates that photoreceptor adaptation is disrupted."
States the interpretation this node rests on: the primary functional lesion is one of adaptation rather than of light detection.
Paradoxical Supernormal Scotopic b-Wave with Delayed Response Timing
The pathognomonic electrophysiology, and the reason the disease was recognized before its gene was. Rod b-wave amplitude rises disproportionately over a narrow range of stimulus intensity, most steeply between the two dimmest flashes, and at bright flash exceeds normal - hence "supernormal" - while the a-wave is depressed or normal in amplitude but delayed at every intensity. The resulting b:a ratio sits at or above the upper reference limit. These are not merely diagnostic curiosities: the amplitude jump, the peak-time delay and the b:a ratio have each been proposed as trial biomarkers, because they are quantitative and present before structural change.
Retinal rod cell CL:0000604 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Retinal rod cell (CL:0000604). CL:0000604 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.
Detection of light stimulus GO:0009583 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Detection of light stimulus (GO:0009583). GO:0009583 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Show evidence (3 references)
PMID:38443311 SUPPORT Human Clinical
"There was a disproportionate increase in b-wave amplitude with a relatively small light intensity increase, especially between the two dimmest stimuli of DA 0.002 and 0.01 (-2.7 and -2.0 log cd.s/m2)."
Quantifies the disproportionate amplitude jump at the specific stimulus intensities where it is steepest.
PMID:38443311 SUPPORT Human Clinical
"The a-wave peak time was delayed in all stimuli."
Supports the timing abnormality this node asserts, which is the photoreceptor-level signature distinguishing an adaptation defect from a simple loss of response.
PMID:38443311 SUPPORT Human Clinical
"We identified three potential electrophysiology biomarkers to assist in evaluating future therapies: the disproportionate b-wave amplitude jump, delayed a-wave and b-wave peak time, and the higher than normal b:a wave ratio."
Establishes the three measures named in this node as candidate trial biomarkers.
Progressive Cone and Outer Nuclear Layer Loss
Beyond the functional lesion, photoreceptors are progressively lost. In the Kv8.2 knockout mouse the structural change at six months is largely confined to the outer nuclear layer while outer segments remain intact, with increased TUNEL-positive cells throughout the retina - a pattern of photoreceptor cell death rather than outer-segment failure. In that model the loss is in fact rod-predominant (cones reduced only to about 80% of wild-type versus about 60% overall photoreceptor-layer thinning); the cone-predominant pattern in this node reflects the human macular disease rather than the mouse. In patients this is seen as a bull's-eye maculopathy on fundus autofluorescence with foveal ellipsoid zone disruption on optical coherence tomography.
Retinal cone cell CL:0000573 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Retinal cone cell (CL:0000573). CL:0000573 is a cell type from the Cell Ontology.
Photoreceptor cell maintenance GO:0045494 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Photoreceptor cell maintenance (GO:0045494). GO:0045494 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.
Downstream
Early-Onset Progressive Central Visual Loss
Show evidence (3 references)
PMID:30820446 SUPPORT Model Organism
"Optical coherence tomography (OCT) imaging and immunohistochemistry indicate that the changes in six-month-old Kv8.2 KO retinae are largely limited to the outer nuclear layer (ONL), while outer segments appear intact."
Localizes the structural change to the photoreceptor cell body layer rather than the outer segment, supporting the cell-death rather than outer-segment-failure claim this node makes.
PMID:30820446 SUPPORT Model Organism
"In addition, there is a significant increase in TUNEL-positive cells throughout the retina."
Provides the direct cell-death readout underlying this node.
PMID:38443311 SUPPORT Human Clinical
"FAF bull's eye maculopathy pattern was prominent and variable foveal disruption on OCT was apparent in all patients. Legal blindness was reached before the age of 25."
Documents the human structural correlate - foveal disruption apparent in all patients of this eight-patient cohort - together with the functional endpoint of legal blindness before age 25.
Early-Onset Progressive Central Visual Loss
Reduced acuity and colour vision loss, progressing such that legal blindness was reached before the age of 25 in a molecularly confirmed cohort of eight patients. That trajectory defines the therapeutic window: intervention aimed at preserving rather than restoring vision has to happen in the first three decades, which is why the natural-history biomarkers matter as much as the mechanism.
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 (1 reference)
PMID:38443311 SUPPORT Human Clinical
"The BCVA natural history data suggests the probable optimum therapeutic window in the first three decades of life."
States the therapeutic-window conclusion this node draws from the trajectory.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for KCNV2-Related Retinopathy 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

4
Reduced visual acuity Ophthalmologic 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:18235024 SUPPORT Human Clinical
"The CDSRR phenotype was associated with reduced visual acuity of variable degree and color vision defects."
Clinical cohort study of 17 molecularly confirmed CDSRR patients reports reduced visual acuity as a core phenotype.
Color vision defect Ophthalmologic HP:0000551 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Color vision defect (HP:0000551). HP:0000551 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18235024 SUPPORT Human Clinical
"The CDSRR phenotype was associated with reduced visual acuity of variable degree and color vision defects."
Color vision defects are a core clinical feature of CDSRR.
Foveal atrophy Ophthalmologic HP:0025010 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Foveal atrophy (HP:0025010). HP:0025010 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18235024 SUPPORT Human Clinical
"Macular defects ranging from mild pigmentary changes to distinct foveal atrophy were present in nine patients."
Optical coherence tomography and fundus examination of the cohort documented macular defects (ranging from mild pigmentary changes to distinct foveal atrophy) in nine of the seventeen patients examined.
Abnormal full-field electroretinogram Ophthalmologic HP:0030466 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Supernormal rod electroretinogram response, annotated with Abnormal full-field electroretinogram (HP:0030466). HP:0030466 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18235024 SUPPORT Human Clinical
"Cone dystrophy with supernormal rod response (CDSRR) is a retinal disorder characterized by reduced visual acuity, color vision defects, and specific alterations of ERG responses that feature elevated scotopic b-wave amplitudes at high luminance intensities."
Defines the pathognomonic supernormal-rod ERG finding that gives the disease its name.
🧬

Genetic Associations

1
KCNV2
Gene: KCNV2 hgnc:19698 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is KCNV2 (hgnc:19698). hgnc:19698 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:18235024 SUPPORT Human Clinical
"Whereas no mutations were detected in the PDE6H gene, mutations in KCNV2 were identified in all patients, in either the homozygous or compound heterozygous state."
Direct sequencing of 13 CDSRR families found biallelic KCNV2 variants in all patients, establishing KCNV2 as the gene strictly associated with the CDSRR phenotype (title of the cited study).
💊

Medical Actions

2
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.
Show evidence (1 reference)
PMID:32441199 SUPPORT Other
"Currently, no treatment is available for the condition."
2020 review of KCNV2 retinopathy states no disease-modifying treatment is currently available, supporting a supportive-care-only management approach.
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 for autosomal recessive inheritance, carrier detection, and family planning.
{ }

Source YAML

click to show 
name: KCNV2-Related Retinopathy
creation_date: "2026-07-07T00:00:00Z"
category: Mendelian
description: >
  KCNV2-related retinopathy, classically known as cone dystrophy with
  supernormal rod electroretinogram (CDSRR), is an autosomal recessive
  retinal channelopathy caused by biallelic pathogenic variants in KCNV2,
  which encodes Kv8.2, a modulatory (non-conducting alone) voltage-gated
  potassium channel alpha-subunit expressed in rod and cone photoreceptor
  inner segments. Kv8.2 heteromerizes with Kv2.1 to form the native
  photoreceptor delayed-rectifier potassium current that shapes the
  photoreceptor light response; its loss produces the disease's
  pathognomonic paradoxical electrophysiology, in which rod b-wave
  amplitudes on electroretinography are larger than normal under bright-flash
  conditions despite progressive cone-mediated visual loss.
disease_term:
  preferred_term: KCNV2-related retinopathy
  term:
    id: MONDO:1040063
    label: KCNV2-related retinopathy
synonyms:
- Cone dystrophy with supernormal rod electroretinogram
- CDSRR
parents:
- Ophthalmological Disease
- Retinal Dystrophy
- Inherited retinal dystrophy
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >
    KCNV2-related retinopathy is inherited in an autosomal recessive manner,
    requiring biallelic pathogenic KCNV2 variants.
  evidence:
  - reference: PMID:18235024
    reference_title: "Cone dystrophy with supernormal rod response is strictly associated with mutations in KCNV2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mutations concordantly segregate in all available families according a recessive mode of inheritance."
    explanation: >-
      Segregation analysis across 13 families confirms autosomal recessive
      inheritance of KCNV2-related CDSRR.
pathophysiology:
- name: Kv8.2/Kv2.1 Heteromeric Photoreceptor Potassium Channel Dysfunction
  role: trigger
  biological_scale: MOLECULAR
  description: >
    Biallelic KCNV2 variants disrupt Kv8.2, a modulatory alpha-subunit that
    cannot form functional channels on its own but heteromerizes with Kv2.1
    in rod and cone photoreceptor inner segments to form the native
    delayed-rectifier potassium current. Loss-of-function KCNV2 variants
    follow at least two distinct molecular mechanisms: pore-domain mutations
    that yield non-conducting Kv2.1/Kv8.2 heteromers, and
    tetramerization-domain mutations that prevent heteromer assembly
    altogether, leaving only homomeric Kv2.1 channels with altered gating
    properties. Either route alters photoreceptor membrane excitability and
    light-response kinetics, producing the disease's pathognomonic
    supernormal rod b-wave and progressive cone-mediated visual loss.
  cell_types:
  - preferred_term: Retinal cone cell
    term:
      id: CL:0000573
      label: retinal cone cell
  - preferred_term: Retinal rod cell
    term:
      id: CL:0000604
      label: retinal rod cell
  biological_processes:
  - preferred_term: Potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: DECREASED
  evidence:
  - reference: PMID:23115240
    reference_title: "Functional analysis of missense mutations in Kv8.2 causing cone dystrophy with supernormal rod electroretinogram."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "KCNV2 codes for the modulatory voltage-gated potassium channel α-subunit, Kv8.2, which is incapable of forming functional channels on its own. Functional heteromeric channels are however formed with Kv2.1 in heterologous expression systems, with both α-subunit genes expressed in rod and cone photoreceptors."
    explanation: >-
      Establishes that Kv8.2 requires heteromerization with Kv2.1 to form a
      functional photoreceptor potassium channel.
  - reference: PMID:23115240
    reference_title: "Functional analysis of missense mutations in Kv8.2 causing cone dystrophy with supernormal rod electroretinogram."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We found that two pore mutations (W467G and G478R) led to the formation of nonconducting heteromeric Kv2.1/Kv8.2 channels, whereas the mutations localized in the tetramerization domain prevented heteromer generation and resulted in the formation of homomeric Kv2.1 channels only. Consequently, our study suggests the existence of two distinct molecular mechanisms involved in the disease pathology."
    explanation: >-
      Functional heterologous expression studies demonstrate the two
      distinct loss-of-function mechanisms (non-conducting heteromer vs.
      failed heteromer assembly) by which KCNV2 missense variants cause
      disease.
  downstream:
  - target: Disrupted Photoreceptor Light Adaptation
    causal_link_type: DIRECT

- name: Disrupted Photoreceptor Light Adaptation
  description: >
    Kv8.2 does not carry current itself; it shifts the activation range of the
    photoreceptor inner-segment potassium channels it heteromerizes into. Losing
    that modulation leaves the photoreceptor unable to set its operating point
    appropriately for the ambient light level, so what fails is adaptation
    rather than phototransduction. This is why the disease produces a
    paradoxical rather than a simply reduced electroretinogram, and why the
    a-wave is delayed even where its amplitude is preserved: the rod is
    responding, but on the wrong timescale and from the wrong baseline.
  role: central_effector
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: Retinal rod cell
    term:
      id: CL:0000604
      label: retinal rod cell
  - preferred_term: Retinal cone cell
    term:
      id: CL:0000573
      label: retinal cone cell
  biological_processes:
  - preferred_term: Response to light stimulus
    term:
      id: GO:0009416
      label: response to light stimulus
    modifier: ABNORMAL
  cellular_components:
  - preferred_term: photoreceptor inner segment
    term:
      id: GO:0001917
      label: photoreceptor inner segment
  evidence:
  - reference: PMID:32441199
    reference_title: "KCNV2 retinopathy: clinical features, molecular genetics and directions for future therapy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "This gene encodes Kv8.2, a voltage-gated potassium channel subunit that acts as a modulator by shifting the activation range of the K+ channels in photoreceptor inner segments."
    explanation: >-
      Establishes the modulatory, activation-range-shifting role in the inner
      segment that this node asserts is lost. Evidence source is OTHER because
      this is a review.
  - reference: PMID:30820446
    reference_title: "The Role of the Voltage-Gated Potassium Channel Proteins Kv8.2 and Kv2.1 in Vision and Retinal Disease: Insights from the Study of Mouse Gene Knock-Out Mutations."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The CDSRR disease phenotype indicates that photoreceptor adaptation is disrupted."
    explanation: >-
      States the interpretation this node rests on: the primary functional
      lesion is one of adaptation rather than of light detection.
  downstream:
  - target: Paradoxical Supernormal Scotopic b-Wave with Delayed Response Timing
    causal_link_type: DIRECT
  - target: Progressive Cone and Outer Nuclear Layer Loss
    causal_link_type: DIRECT

- name: Paradoxical Supernormal Scotopic b-Wave with Delayed Response Timing
  description: >
    The pathognomonic electrophysiology, and the reason the disease was
    recognized before its gene was. Rod b-wave amplitude rises
    disproportionately over a narrow range of stimulus intensity, most steeply
    between the two dimmest flashes, and at bright flash exceeds normal - hence
    "supernormal" - while the a-wave is depressed or normal in amplitude but
    delayed at every intensity. The resulting b:a ratio sits at or above the
    upper reference limit. These are not merely diagnostic curiosities: the
    amplitude jump, the peak-time delay and the b:a ratio have each been
    proposed as trial biomarkers, because they are quantitative and present
    before structural change.
  role: effector
  biological_scale: TISSUE
  cell_types:
  - preferred_term: Retinal rod cell
    term:
      id: CL:0000604
      label: retinal rod cell
  - preferred_term: retinal bipolar neuron
    term:
      id: CL:0000748
      label: retinal bipolar neuron
  biological_processes:
  - preferred_term: Detection of light stimulus
    term:
      id: GO:0009583
      label: detection of light stimulus
    modifier: ABNORMAL
  evidence:
  - reference: PMID:38443311
    reference_title: "Natural history and biomarkers of KCNV2-associated retinopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was a disproportionate increase in b-wave amplitude with a relatively small light intensity increase, especially between the two dimmest stimuli of DA 0.002 and 0.01 (-2.7 and -2.0 log cd.s/m2)."
    explanation: >-
      Quantifies the disproportionate amplitude jump at the specific stimulus
      intensities where it is steepest.
  - reference: PMID:38443311
    reference_title: "Natural history and biomarkers of KCNV2-associated retinopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The a-wave peak time was delayed in all stimuli."
    explanation: >-
      Supports the timing abnormality this node asserts, which is the
      photoreceptor-level signature distinguishing an adaptation defect from a
      simple loss of response.
  - reference: PMID:38443311
    reference_title: "Natural history and biomarkers of KCNV2-associated retinopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified three potential electrophysiology biomarkers to assist in evaluating future therapies: the disproportionate b-wave amplitude jump, delayed a-wave and b-wave peak time, and the higher than normal b:a wave ratio."
    explanation: >-
      Establishes the three measures named in this node as candidate trial
      biomarkers.

- name: Progressive Cone and Outer Nuclear Layer Loss
  description: >
    Beyond the functional lesion, photoreceptors are progressively lost. In the
    Kv8.2 knockout mouse the structural change at six months is largely confined
    to the outer nuclear layer while outer segments remain intact, with
    increased TUNEL-positive cells throughout the retina - a pattern of
    photoreceptor cell death rather than outer-segment failure. In that model the
    loss is in fact rod-predominant (cones reduced only to about 80% of wild-type
    versus about 60% overall photoreceptor-layer thinning); the cone-predominant
    pattern in this node reflects the human macular disease rather than the mouse.
    In patients this is seen as a bull's-eye maculopathy on fundus
    autofluorescence with foveal ellipsoid zone disruption on optical coherence
    tomography.
  role: effector
  biological_scale: TISSUE
  cell_types:
  - preferred_term: Retinal cone cell
    term:
      id: CL:0000573
      label: retinal cone cell
  biological_processes:
  - preferred_term: Photoreceptor cell maintenance
    term:
      id: GO:0045494
      label: photoreceptor cell maintenance
    modifier: DECREASED
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:30820446
    reference_title: "The Role of the Voltage-Gated Potassium Channel Proteins Kv8.2 and Kv2.1 in Vision and Retinal Disease: Insights from the Study of Mouse Gene Knock-Out Mutations."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Optical coherence tomography (OCT) imaging and immunohistochemistry indicate that the changes in six-month-old Kv8.2 KO retinae are largely limited to the outer nuclear layer (ONL), while outer segments appear intact."
    explanation: >-
      Localizes the structural change to the photoreceptor cell body layer
      rather than the outer segment, supporting the cell-death rather than
      outer-segment-failure claim this node makes.
  - reference: PMID:30820446
    reference_title: "The Role of the Voltage-Gated Potassium Channel Proteins Kv8.2 and Kv2.1 in Vision and Retinal Disease: Insights from the Study of Mouse Gene Knock-Out Mutations."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In addition, there is a significant increase in TUNEL-positive cells throughout the retina."
    explanation: >-
      Provides the direct cell-death readout underlying this node.
  - reference: PMID:38443311
    reference_title: "Natural history and biomarkers of KCNV2-associated retinopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "FAF bull's eye maculopathy pattern was prominent and variable foveal disruption on OCT was apparent in all patients. Legal blindness was reached before the age of 25."
    explanation: >-
      Documents the human structural correlate - foveal disruption apparent in
      all patients of this eight-patient cohort - together with the functional
      endpoint of legal blindness before age 25.
  downstream:
  - target: Early-Onset Progressive Central Visual Loss
    causal_link_type: DIRECT

- name: Early-Onset Progressive Central Visual Loss
  description: >
    Reduced acuity and colour vision loss, progressing such that legal blindness
    was reached before the age of 25 in a molecularly confirmed cohort of eight
    patients. That trajectory defines the therapeutic
    window: intervention aimed at preserving rather than restoring vision has to
    happen in the first three decades, which is why the natural-history
    biomarkers matter as much as the mechanism.
  role: consequence
  biological_scale: ORGANISM
  biological_processes:
  - preferred_term: Visual perception
    term:
      id: GO:0007601
      label: visual perception
    modifier: DECREASED
  evidence:
  - reference: PMID:38443311
    reference_title: "Natural history and biomarkers of KCNV2-associated retinopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The BCVA natural history data suggests the probable optimum therapeutic window in the first three decades of life."
    explanation: >-
      States the therapeutic-window conclusion this node draws from the
      trajectory.
phenotypes:
- name: Reduced visual acuity
  category: Ophthalmologic
  phenotype_term:
    preferred_term: Reduced visual acuity
    term:
      id: HP:0007663
      label: Reduced visual acuity
  evidence:
  - reference: PMID:18235024
    reference_title: "Cone dystrophy with supernormal rod response is strictly associated with mutations in KCNV2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The CDSRR phenotype was associated with reduced visual acuity of variable degree and color vision defects."
    explanation: >-
      Clinical cohort study of 17 molecularly confirmed CDSRR patients
      reports reduced visual acuity as a core phenotype.
- name: Color vision defect
  category: Ophthalmologic
  phenotype_term:
    preferred_term: Color vision defect
    term:
      id: HP:0000551
      label: Color vision defect
  evidence:
  - reference: PMID:18235024
    reference_title: "Cone dystrophy with supernormal rod response is strictly associated with mutations in KCNV2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The CDSRR phenotype was associated with reduced visual acuity of variable degree and color vision defects."
    explanation: Color vision defects are a core clinical feature of CDSRR.
- name: Foveal atrophy
  category: Ophthalmologic
  phenotype_term:
    preferred_term: Foveal atrophy
    term:
      id: HP:0025010
      label: Foveal atrophy
  evidence:
  - reference: PMID:18235024
    reference_title: "Cone dystrophy with supernormal rod response is strictly associated with mutations in KCNV2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Macular defects ranging from mild pigmentary changes to distinct foveal atrophy were present in nine patients."
    explanation: >-
      Optical coherence tomography and fundus examination of the cohort
      documented macular defects (ranging from mild pigmentary changes to
      distinct foveal atrophy) in nine of the seventeen patients examined.
- name: Abnormal full-field electroretinogram
  category: Ophthalmologic
  description: >
    The pathognomonic finding in KCNV2-related retinopathy: rod-mediated
    scotopic b-wave amplitudes on full-field ERG are paradoxically larger
    than normal ("supernormal") at high-luminance flash intensities, despite
    progressive cone dysfunction.
  phenotype_term:
    preferred_term: Supernormal rod electroretinogram response
    term:
      id: HP:0030466
      label: Abnormal full-field electroretinogram
  reports_on:
  - target: Kv8.2/Kv2.1 Heteromeric Photoreceptor Potassium Channel Dysfunction
    relationship: READOUT_OF
    endpoint_context: DIAGNOSTIC
    interpretation: The full-field ERG measures the photoreceptor light-response abnormality produced by the potassium-channel defect.
  evidence:
  - reference: PMID:18235024
    reference_title: "Cone dystrophy with supernormal rod response is strictly associated with mutations in KCNV2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cone dystrophy with supernormal rod response (CDSRR) is a retinal disorder characterized by reduced visual acuity, color vision defects, and specific alterations of ERG responses that feature elevated scotopic b-wave amplitudes at high luminance intensities."
    explanation: >-
      Defines the pathognomonic supernormal-rod ERG finding that gives the
      disease its name.
genetic:
- name: KCNV2
  gene_term:
    preferred_term: KCNV2
    term:
      id: hgnc:19698
      label: KCNV2
  evidence:
  - reference: PMID:18235024
    reference_title: "Cone dystrophy with supernormal rod response is strictly associated with mutations in KCNV2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Whereas no mutations were detected in the PDE6H gene, mutations in KCNV2 were identified in all patients, in either the homozygous or compound heterozygous state."
    explanation: >-
      Direct sequencing of 13 CDSRR families found biallelic KCNV2 variants
      in all patients, establishing KCNV2 as the gene strictly associated
      with the CDSRR phenotype (title of the cited study).
treatments:
- name: Low Vision Rehabilitation
  description: Supportive low-vision aids and rehabilitation.
  treatment_term:
    preferred_term: low vision rehabilitation
    term:
      id: NCIT:C15747
      label: Supportive Care
  notes: >-
    No disease-modifying treatment is currently available; management is
    supportive. An AAV-based gene replacement approach is under
    investigational (in vitro organoid) screening but has not reached
    human trials (PMID:41516321), so it is not curated here as a treatment.
  evidence:
  - reference: PMID:32441199
    reference_title: "KCNV2 retinopathy: clinical features, molecular genetics and directions for future therapy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Currently, no treatment is available for the condition."
    explanation: >-
      2020 review of KCNV2 retinopathy states no disease-modifying treatment
      is currently available, supporting a supportive-care-only management
      approach.
- name: Genetic Counseling
  description: >
    Genetic counseling for autosomal recessive inheritance, carrier
    detection, and family planning.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  notes: >-
    Standard of care for an autosomal recessive Mendelian retinopathy with
    molecularly confirmed biallelic KCNV2 variants; no KCNV2-specific
    genetic-counseling outcome study was identified to cite directly.