RD3-related retinopathy is an autosomal recessive, congenital-onset inherited retinal dystrophy caused by biallelic loss-of-function variants in RD3, which encodes a small photoreceptor protein that binds the retinal membrane guanylyl cyclases (RetGC1/GUCY2D and RetGC2/GUCY2F). It presents as Leber congenital amaurosis type 12 (LCA12): congenital nystagmus, vision reduced to counting fingers or light perception, sluggish pupils, eye poking and hyperopia, with an atrophic macula and early loss of the photoreceptor layer. RD3 has two separable jobs in the photoreceptor inner segment. It escorts newly made guanylyl cyclase out of the endoplasmic reticulum to the outer segment, and it holds the cyclase inactive until it gets there. Losing the first leaves the outer segment unable to make cGMP, so rods and cones cannot generate or recover a light response. In the rd3 mouse, losing the second lets calcium-sensor proteins (GCAPs) activate the cyclase in the wrong compartment, which drives endoplasmic reticulum stress and unusually rapid photoreceptor death; this branch has not been examined in human retina. The disease is very rare, mostly reported in consanguineous families, with one recurrent truncating founder allele (p.Arg38Ter) around the Mediterranean, and has no extraocular features. Gene augmentation restores cyclase trafficking, function and photoreceptor survival in the rd3 mouse, but no human treatment exists.
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name: RD3-Related Retinopathy
creation_date: "2026-10-15T16:00:00Z"
category: Mendelian
description: >-
RD3-related retinopathy is an autosomal recessive, congenital-onset inherited
retinal dystrophy caused by biallelic loss-of-function variants in RD3, which
encodes a small photoreceptor protein that binds the retinal membrane guanylyl
cyclases (RetGC1/GUCY2D and RetGC2/GUCY2F). It presents as Leber congenital
amaurosis type 12 (LCA12): congenital nystagmus, vision reduced to counting
fingers or light perception, sluggish pupils, eye poking and hyperopia, with an
atrophic macula and early loss of the photoreceptor layer. RD3 has two
separable jobs in the photoreceptor inner segment. It escorts newly made
guanylyl cyclase out of the endoplasmic reticulum to the outer segment, and it
holds the cyclase inactive until it gets there. Losing the first leaves the
outer segment unable to make cGMP, so rods and cones cannot generate or recover
a light response. In the rd3 mouse, losing the second lets calcium-sensor
proteins (GCAPs) activate the cyclase in the wrong compartment, which drives
endoplasmic reticulum stress and unusually rapid photoreceptor death; this
branch has not been examined in human retina. The disease is very rare, mostly
reported in consanguineous families, with one recurrent truncating founder
allele (p.Arg38Ter) around the Mediterranean, and has no extraocular
features. Gene augmentation restores cyclase trafficking,
function and photoreceptor survival in the rd3 mouse, but no human treatment
exists.
disease_term:
preferred_term: RD3-related retinopathy
term:
id: MONDO:0700235
label: RD3-related retinopathy
synonyms:
- Leber congenital amaurosis 12
- Leber congenital amaurosis type 12
- LCA12
- RD3 Leber congenital amaurosis
- RD3-associated early-onset severe retinal dystrophy
parents:
- Inherited Retinal Dystrophy
- Leber Congenital Amaurosis
notes: >-
MONDO:0700235 is a gene-level spectrum term created by the ClinGen ocular
clinical domain working group; at the time of curation its only child is
Leber congenital amaurosis 12 (MONDO:0012525), which is carried here as a
has_subtypes row rather than a separate entry. Almost every reported patient
carries biallelic truncating alleles and has LCA; the exception is a single
Spanish family with retinitis pigmentosa and a homozygous missense variant
(p.Lys87Glu), supported only by in-silico prediction, which is recorded under
genetic variants rather than as a subtype. The phenotype overlaps closely with
GUCY2D-related recessive retinopathy (LCA1), which is expected: RD3 acts on
the GUCY2D gene product. There is no RD3-specific GeneReviews chapter; the
applicable one is the nonsyndromic LCA/EOSRD overview (PMID:30285347), whose
PubMed abstract lists no clinical findings, so the phenotypes here come from
the RD3 case series (Perrault et al. 2013, Preising et al. 2012) and case
reports. None of the sources cited here reports full-field ERG results for
RD3 patients specifically, so no ERG phenotype is recorded. RD3 is neither a cascade
component nor a GCAP; the trigger node conforms to the phototransduction
module's component-defect node because RD3 is the cyclase's obligatory
trafficking partner and inhibitor, and its loss removes the cyclase from the
cascade.
has_subtypes:
- name: LCA12
display_name: Leber congenital amaurosis 12
subtype_term:
preferred_term: Leber congenital amaurosis 12
term:
id: MONDO:0012525
label: Leber congenital amaurosis 12
description: >-
The only named presentation of RD3-related retinopathy: severe congenital
visual impairment with nystagmus, eye poking and early macular atrophy,
caused by biallelic truncating RD3 variants.
genes:
- preferred_term: RD3
term:
id: hgnc:19689
label: RD3
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "RD3 (LCA12) was implicated as a LCA gene based on the identification of homozygous truncating mutations in two LCA families despite the screening of large cohorts of patients."
explanation: >-
Identifies RD3 as the LCA12 gene, defined by homozygous truncating
variants in families with Leber congenital amaurosis.
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Similar to LCA1, LCA12 patients have no extraocular symptoms despite complete inactivation of both RD3 alleles"
explanation: >-
LCA12 is non-syndromic: no extraocular features despite complete loss of
RD3.
inheritance:
- name: Autosomal recessive
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
description: >-
Every reported patient carries biallelic RD3 variants, usually homozygous
truncating alleles in consanguineous families.
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We identified three RD3 mutations in seven unrelated consanguineous LCA families - i.e., a 2 bp deletion and two nonsense mutations - predicted to cause complete loss of function."
explanation: >-
Recessive segregation of predicted null RD3 alleles in seven
consanguineous families.
- reference: PMID:22531706
reference_title: "Mutations in RD3 are associated with an extremely rare and severe form of early onset retinal dystrophy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Direct sequencing of RD3 revealed a homozygous nonsense mutation (c.180C > A) in all affected members tested."
explanation: >-
Homozygous nonsense variant segregating with disease in a consanguineous
Kurdish family.
prevalence:
- population: Published literature (worldwide)
measure_type: CASES_IN_LITERATURE
prevalence_class: ULTRA_RARE
notes: >-
No population prevalence has been published. Perrault et al. (2013) found
RD3 variants in seven families after screening 852 patients with LCA or
early-onset severe retinal dystrophy; a later case report puts RD3 at under
1% of LCA.
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Here we provide a comprehensive survey of RD3 mutations and of their clinical expression through the screening of a cohort of 852 patients originating worldwide affected with LCA or early-onset and severe RD."
explanation: >-
The worldwide screen that found RD3 variants in only seven of 852
LCA/early-onset severe retinal dystrophy probands.
- reference: PMID:32083505
reference_title: "Optical coherence tomography and fundus autofluorescence imaging in an infant with RD3-related leber congenital amaurosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Mutations in retinal degeneration 3 (RD3) have been reported as an infrequent cause of LCA which account for less than 1% of all known LCA cases."
explanation: >-
States the share of LCA attributable to RD3 as under 1%.
pathophysiology:
- name: RD3 Biallelic Loss of Function
conforms_to: "phototransduction_cascade_dysfunction#Phototransduction Cascade Component Defect"
biological_scale: MOLECULAR
description: >-
Biallelic truncating RD3 variants (nonsense, frameshift and splice-site
alleles, including the Mediterranean founder p.Arg38Ter) produce unstable,
non-functional C-terminally truncated protein or none at all. RD3 is a
195-residue four-helix-bundle protein expressed in rods and cones; it binds
RetGC1 and RetGC2 through a central helical interface and needs its
C-terminal region to couple the cyclase to intracellular trafficking.
genes:
- preferred_term: RD3
term:
id: hgnc:19689
label: RD3
genetic_context:
variant_origin: GERMLINE
functional_impact_category: LOSS_OF_FUNCTION
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
molecular_functions:
- preferred_term: guanylate cyclase inhibitor activity
modifier: DECREASED
term:
id: GO:0030251
label: guanylate cyclase inhibitor activity
evidence:
- reference: PMID:21928830
reference_title: "Retinal degeneration 3 (RD3) protein inhibits catalytic activity of retinal membrane guanylyl cyclase (RetGC) and its stimulation by activating proteins."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "The RD3 mutant lacking the carboxy-terminal half of the protein and associated with Leber congenital amaurosis type 12 (LCA12) is unable to suppress the activity of the RetGC1/GCAP complex."
explanation: >-
The LCA12 truncation loses RD3's guanylyl cyclase inhibitor activity, the
molecular function bound on this node.
- reference: PMID:24904271
reference_title: "Insights into the role of RD3 in guanylate cyclase trafficking, photoreceptor degeneration, and Leber congenital amaurosis."
supports: SUPPORT
evidence_source: OTHER
quote_role: REVIEW_SYNTHESIS
snippet: "Mutations in the gene encoding RD3 resulting in unstable non-functional C-terminal truncated proteins are responsible for early onset photoreceptor degeneration in Leber Congenital Amaurosis 12 patients, the rd3 mice, and the rcd2 collies."
explanation: >-
Review summarising that disease alleles in humans, mice and dogs all yield
unstable, non-functional truncated RD3.
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Five families originating from the Southern Shores of the Mediterranean segregated a similar mutation (c.112C>T, p.R38*) suggesting that this change may have resulted from an ancient founder effect."
explanation: >-
Recurrent truncating founder allele in RD3 retinopathy.
- reference: PMID:17186464
reference_title: "Premature truncation of a novel protein, RD3, exhibiting subnuclear localization is associated with retinal degeneration."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we identified a homozygous alteration in the invariant G nucleotide of the RD3 exon 2 donor splice site in two siblings with Leber congenital amaurosis."
explanation: >-
The first human RD3 allele, a homozygous canonical splice-site variant
predicted to truncate the protein.
downstream:
- target: Failure of Guanylate Cyclase Export to the Outer Segment
causal_link_type: DIRECT
- target: Loss of RD3 Inhibition of Guanylate Cyclase in the Inner Segment
causal_link_type: DIRECT
evidence:
- reference: PMID:21928830
reference_title: "Retinal degeneration 3 (RD3) protein inhibits catalytic activity of retinal membrane guanylyl cyclase (RetGC) and its stimulation by activating proteins."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "The RD3 mutant lacking the carboxy-terminal half of the protein and associated with Leber congenital amaurosis type 12 (LCA12) is unable to suppress the activity of the RetGC1/GCAP complex."
explanation: >-
The LCA12 truncation abolishes RD3's ability to inhibit the
GCAP-stimulated cyclase.
- name: Failure of Guanylate Cyclase Export to the Outer Segment
biological_scale: CELLULAR
description: >-
RD3 binds RetGC1 and RetGC2 in the inner segment and carries them out of the
endoplasmic reticulum toward the outer segment. Without RD3 the cyclases are
not exported from the endoplasmic reticulum, are not stably expressed, and
are essentially absent from rod and cone outer segments. The C-terminal
Arg158-Ser170 region of RD3 is required for this trafficking step but not for
cyclase inhibition, which is why trafficking and degeneration can be
separated experimentally.
genes:
- preferred_term: GUCY2D
term:
id: hgnc:4689
label: GUCY2D
- preferred_term: GUCY2F
term:
id: hgnc:4691
label: GUCY2F
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: protein localization to photoreceptor outer segment
modifier: DECREASED
term:
id: GO:1903546
label: protein localization to photoreceptor outer segment
cellular_components:
- preferred_term: endoplasmic reticulum
term:
id: GO:0005783
label: endoplasmic reticulum
- preferred_term: photoreceptor outer segment
term:
id: GO:0001750
label: photoreceptor outer segment
evidence:
- reference: PMID:21078983
reference_title: "RD3, the protein associated with Leber congenital amaurosis type 12, is required for guanylate cyclase trafficking in photoreceptor cells."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "GC1 and GC2 are undetectable in photoreceptors of the rd3 mouse deficient in RD3 by immunofluorescence microscopy."
explanation: >-
In RD3-deficient mouse photoreceptors both retinal guanylyl cyclases are
lost from their normal location.
- reference: PMID:21078983
reference_title: "RD3, the protein associated with Leber congenital amaurosis type 12, is required for guanylate cyclase trafficking in photoreceptor cells."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Cell expression studies show that RD3 mediates the export of GC1 from the endoplasmic reticulum to endosomal vesicles, and that the C terminus of GC1 is required for RD3 binding."
explanation: >-
Cell-culture evidence that RD3 is what moves GC1 out of the endoplasmic
reticulum.
- reference: PMID:42331110
reference_title: "The C-terminal domain of RD3 enables accumulation of retinal membrane guanylyl cyclase (RetGC) in photoreceptor outer segment."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Extending RD3 polypeptide to Ser170 restored RetGC accumulation in the outer segment of rescued Rd3-/- rods and enabled their photoresponse."
explanation: >-
Transgenic rescue maps the trafficking function to the RD3 C-terminal
region and ties outer-segment cyclase delivery to rod function.
downstream:
- target: Deficient Outer Segment cGMP Synthesis
causal_link_type: DIRECT
evidence:
- reference: PMID:31980596
reference_title: "GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress."
supports: SUPPORT
directness: INDIRECT
quote_role: BACKGROUND
evidence_source: MODEL_ORGANISM
snippet: "As a consequence, there is reduced cGMP synthesis that results in closure of cyclic nucleotide-gated channels (CNG-channels) and presumed chronic hyperpolarization of rd3 photoreceptors"
explanation: >-
States that the loss of outer-segment cyclase in rd3 photoreceptors
reduces cGMP synthesis and closes the cGMP-gated channels.
- name: Deficient Outer Segment cGMP Synthesis
conforms_to: "phototransduction_cascade_dysfunction#Loss of Outer-Segment cGMP and Calcium Set-Point Control"
biological_scale: CELLULAR
description: >-
With little cyclase in the outer segment, guanylyl cyclase activity in the
rd3 retina is drastically reduced and photoreceptors cannot raise cGMP to the
dark-state level. cGMP-gated channels stay closed, the dark current is lost,
and the outer segment cannot reset after light.
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
molecular_functions:
- preferred_term: guanylate cyclase activity
modifier: DECREASED
term:
id: GO:0004383
label: guanylate cyclase activity
biological_processes:
- preferred_term: cGMP biosynthetic process
modifier: DECREASED
term:
id: GO:0006182
label: cGMP biosynthetic process
evidence:
- reference: PMID:31346032
reference_title: "Retinal guanylyl cyclase activation by calcium sensor proteins mediates photoreceptor degeneration in an rd3 mouse model of congenital human blindness."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "RetGC activity in rd3/rd3 retinas was drastically reduced but stimulated by the endogenous GCAPs at low Ca2+ concentrations."
explanation: >-
Direct measurement of the cyclase deficit in RD3-deficient retina.
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
directness: INDIRECT
evidence_source: HUMAN_CLINICAL
snippet: "inability to increase cytoplasmic cGMP concentration in outer segments and thus to recover the dark-state"
explanation: >-
The authors infer this shared mechanism from the near-identical LCA12 and
LCA1 (GUCY2D) phenotypes; cGMP was not measured in patients.
downstream:
- target: Failure of Rod and Cone Phototransduction
causal_link_type: DIRECT
- target: Chronically Low Photoreceptor Intracellular Calcium
causal_link_type: DIRECT
evidence:
- reference: PMID:21078983
reference_title: "RD3, the protein associated with Leber congenital amaurosis type 12, is required for guanylate cyclase trafficking in photoreceptor cells."
supports: SUPPORT
directness: INDIRECT
evidence_source: MODEL_ORGANISM
snippet: "The resulting deficiency in cGMP synthesis and the constitutive closure of cGMP-gated channels might cause a reduction in intracellular Ca(2+) to a level below that required for long-term photoreceptor cell survival."
explanation: >-
Proposes that closed cGMP-gated channels lower intracellular calcium;
stated as a hypothesis in this paper and later supported by the GCAP2
phosphorylation-state data.
- name: Failure of Rod and Cone Phototransduction
conforms_to: "phototransduction_cascade_dysfunction#Failure of Photoreceptor Light-Response Generation or Timely Recovery"
biological_scale: CELLULAR
description: >-
Without outer-segment cGMP, rods and cones cannot generate a normal light
response from birth, which is why vision is profoundly reduced from the first
months of life and does not recover when photoreceptor death is slowed by
other means (GCAP deletion preserves rd3 photoreceptors but not their
function).
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: phototransduction
modifier: DECREASED
term:
id: GO:0007602
label: phototransduction
evidence:
- reference: PMID:31980596
reference_title: "GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Although this substantial morphological rescue does not correlate with recovery of visual function due to very diminished guanylate cyclase activity in rd3 mice, it is very informative of the mechanisms underlying photoreceptor cell death."
explanation: >-
Separates the functional deficit (cyclase-dependent) from the
degeneration (GCAP-dependent): rescued photoreceptors still do not work.
- reference: PMID:31346032
reference_title: "Retinal guanylyl cyclase activation by calcium sensor proteins mediates photoreceptor degeneration in an rd3 mouse model of congenital human blindness."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "RetGC activity completely failed to accelerate in rd3/rd3GCAPs-/- hybrid photoreceptors, whose photoresponses remained drastically suppressed compared with the WT."
explanation: >-
Photoresponses stay suppressed in surviving RD3-deficient photoreceptors.
- reference: PMID:31980596
reference_title: "GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress."
supports: SUPPORT
quote_role: BACKGROUND
evidence_source: HUMAN_CLINICAL
snippet: "LCA12 is characterized by rod and cone impaired function and severe vision loss from an early age, as well as rapid retinal degeneration."
explanation: >-
Background statement of the human phenotype: rod and cone function is
impaired from an early age in LCA12.
- reference: PMID:33539922
reference_title: "Retinal degeneration-3 protein promotes photoreceptor survival by suppressing activation of guanylyl cyclase rather than accelerating GMP recycling."
supports: SUPPORT
quote_role: BACKGROUND
evidence_source: HUMAN_CLINICAL
snippet: "making rods and cones dysfunctional from birth in recessive human Leber’s congenital amaurosis-12 (LCA12)"
explanation: >-
Background statement that rods and cones are dysfunctional from birth in
human LCA12.
downstream:
- target: Ultra-low vision
- target: Congenital nystagmus
- target: Slow pupillary light response
- target: Absent smooth pursuit
- target: Eye poking
- name: Loss of RD3 Inhibition of Guanylate Cyclase in the Inner Segment
biological_scale: MOLECULAR
description: >-
RD3 is a high-affinity, noncompetitive inhibitor of RetGC1 and RetGC2 that
opposes their activation by GCAPs. Its alpha-helical core (N-terminal to
Gly148) binds the cyclase through two surface clusters and keeps it inactive
while it is in the inner segment, before the RetGC:GCAP complex forms in the
outer segment. Truncated disease alleles lose this inhibition.
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
molecular_functions:
- preferred_term: guanylate cyclase inhibitor activity
modifier: DECREASED
term:
id: GO:0030251
label: guanylate cyclase inhibitor activity
biological_processes:
- preferred_term: negative regulation of guanylate cyclase activity
modifier: DECREASED
term:
id: GO:0031283
label: negative regulation of guanylate cyclase activity
cellular_components:
- preferred_term: photoreceptor inner segment
term:
id: GO:0001917
label: photoreceptor inner segment
evidence:
- reference: PMID:21928830
reference_title: "Retinal degeneration 3 (RD3) protein inhibits catalytic activity of retinal membrane guanylyl cyclase (RetGC) and its stimulation by activating proteins."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "We present evidence that a different RetGC binding protein, retinal degeneration 3 protein (RD3), is a high-affinity allosteric modulator of the cyclase which inhibits RetGC activity at submicromolar concentrations."
explanation: >-
Establishes RD3 as a potent cyclase inhibitor.
- reference: PMID:42331110
reference_title: "The C-terminal domain of RD3 enables accumulation of retinal membrane guanylyl cyclase (RetGC) in photoreceptor outer segment."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Retinal degeneration-3 protein (RD3) plays a dual role in photoreceptors - prevents their degeneration by suppressing aberrant activity of retinal membrane guanylyl cyclase (RetGC) in the inner segment and enables photoreceptor function by facilitating delivery of RetGC to the outer segment."
explanation: >-
States the two separable RD3 functions that this entry models as two
branches.
downstream:
- target: Aberrant GCAP-Stimulated Guanylate Cyclase Activity in the Inner Segment
causal_link_type: DIRECT
evidence:
- reference: PMID:31346032
reference_title: "Retinal guanylyl cyclase activation by calcium sensor proteins mediates photoreceptor degeneration in an rd3 mouse model of congenital human blindness."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "These results support the hypothesis that an essential biological function of RD3 is competition with GCAPs that inhibits premature cyclase activation in the inner segment."
explanation: >-
In vivo support that RD3 normally blocks GCAP activation of the cyclase
in the inner segment.
- name: Chronically Low Photoreceptor Intracellular Calcium
biological_scale: CELLULAR
description: >-
Closed cGMP-gated channels stop calcium entry, so free calcium in rd3 rods
stays low. Inferred in rd3 mice from GCAP2 being held mostly in its
calcium-free, phosphorylated state; low calcium also keeps the GCAPs in
their cyclase-activating conformation in the inner segment.
cell_types:
- preferred_term: retinal rod cell
term:
id: CL:0000604
label: retinal rod cell
chemical_entities:
- preferred_term: calcium(2+)
modifier: DECREASED
term:
id: CHEBI:29108
label: calcium(2+)
evidence:
- reference: PMID:31980596
reference_title: "GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress."
supports: SUPPORT
directness: INDIRECT
evidence_source: MODEL_ORGANISM
snippet: "By showing that GCAP2 is mostly in its Ca2+-free-phosphorylated state in rd3 mice"
explanation: >-
The authors infer from this GCAP2 state that free calcium in rod inner
segments is permanently low; calcium was not measured directly.
downstream:
- target: Aberrant GCAP-Stimulated Guanylate Cyclase Activity in the Inner Segment
causal_link_type: DIRECT
evidence:
- reference: PMID:31980596
reference_title: "GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "GCAPs are therefore retained at the inner segment in their Ca2+-free, guanylate cyclase activator state."
explanation: >-
Low calcium holds GCAPs in their activating state where RD3 would
normally be restraining the cyclase.
- name: Aberrant GCAP-Stimulated Guanylate Cyclase Activity in the Inner Segment
biological_scale: CELLULAR
description: >-
With RD3 absent, calcium-free GCAP1 and GCAP2 activate the residual RetGC in
the inner segment, a compartment where the cyclase should be silent. This is
the main driver of the rapid photoreceptor death: deleting GCAPs preserves
most rd3 photoreceptors, and RD3 fragments that still inhibit the cyclase but
cannot traffic it prevent degeneration without restoring function. Whether
the toxicity comes from the misplaced cyclase activity itself or from a
cyclase-independent action of calcium-free GCAPs is not settled.
genes:
- preferred_term: GUCA1A
term:
id: hgnc:4678
label: GUCA1A
- preferred_term: GUCA1B
term:
id: hgnc:4679
label: GUCA1B
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
molecular_functions:
- preferred_term: guanylate cyclase activator activity
modifier: ABNORMAL
term:
id: GO:0030250
label: guanylate cyclase activator activity
cellular_components:
- preferred_term: photoreceptor inner segment
term:
id: GO:0001917
label: photoreceptor inner segment
evidence:
- reference: PMID:33539922
reference_title: "Retinal degeneration-3 protein promotes photoreceptor survival by suppressing activation of guanylyl cyclase rather than accelerating GMP recycling."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Deletion of GCAP1 or GCAP2 alone preserved 68% and 57% of photoreceptors, respectively, whereas deletion of GCAP1 and GCAP2 together preserved 86%."
explanation: >-
Genetic deletion of the cyclase activators largely prevents rd3
degeneration.
- reference: PMID:33539922
reference_title: "Retinal degeneration-3 protein promotes photoreceptor survival by suppressing activation of guanylyl cyclase rather than accelerating GMP recycling."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Taken together, our in vitro and in vivo results support the hypothesis that RD3 prevents photoreceptor death primarily by suppressing activation of RetGC by both GCAP1 and GCAP2"
explanation: >-
Concludes that RD3 protects photoreceptors by suppressing GCAP activation
of the cyclase, not by speeding GMP recycling through guanylate kinase
(an alternative this paper tested and did not support).
- reference: PMID:42331110
reference_title: "The C-terminal domain of RD3 enables accumulation of retinal membrane guanylyl cyclase (RetGC) in photoreceptor outer segment."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "The human RD3 truncated after Gly148 or Arg158 not only inhibited RetGC activation by the guanylyl cyclase activating protein (GCAP) in vitro but also prevented rapid degeneration of the RD3-deficient rods in transgenic mice."
explanation: >-
An RD3 fragment that inhibits the cyclase but cannot traffic it is enough
to prevent rapid degeneration.
downstream:
- target: Photoreceptor Endoplasmic Reticulum Stress and Mitochondrial Swelling
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:31980596
reference_title: "GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "We show that in this conformational state GCAPs induce endoplasmic reticulum (ER) stress, mitochondrial swelling, and cell death."
explanation: >-
Calcium-free GCAPs in the inner segment trigger ER stress and
mitochondrial swelling.
- name: Photoreceptor Endoplasmic Reticulum Stress and Mitochondrial Swelling
biological_scale: CELLULAR
description: >-
ER stress and mitochondrial swelling are early features of rd3 retinas,
present before photoreceptors die, and are largely prevented by deleting the
GCAPs.
cell_types:
- preferred_term: retinal rod cell
term:
id: CL:0000604
label: retinal rod cell
biological_processes:
- preferred_term: response to endoplasmic reticulum stress
modifier: INCREASED
term:
id: GO:0034976
label: response to endoplasmic reticulum stress
cellular_components:
- preferred_term: endoplasmic reticulum
term:
id: GO:0005783
label: endoplasmic reticulum
evidence:
- reference: PMID:31980596
reference_title: "GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "ER stress and mitochondrial swelling are early hallmarks of rd3 retinas preceding photoreceptor cell death, that are substantially rescued by GCAPs ablation."
explanation: >-
Places ER stress and mitochondrial swelling before photoreceptor death in
the GCAP-dependent chain.
downstream:
- target: Rapid Rod and Cone Photoreceptor Degeneration
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Rapid Rod and Cone Photoreceptor Degeneration
conforms_to: "photoreceptor_degeneration#Rod Photoreceptor Apoptosis"
biological_scale: TISSUE
description: >-
Photoreceptors develop nearly normally and then degenerate quickly. In the
rd3 mouse, apoptosis begins around eye opening, rod loss is essentially
complete by 5 weeks and remnant cones persist to about 7 weeks, with the
rate differing between strains. Patients present clinically as a cone-rod
dystrophy, and in one infant the photoreceptor layer was already missing at
the fovea.
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: retinal rod cell apoptotic process
modifier: INCREASED
term:
id: GO:0097473
label: retinal rod cell apoptotic process
- preferred_term: retinal cone cell apoptotic process
modifier: INCREASED
term:
id: GO:0097474
label: retinal cone cell apoptotic process
- preferred_term: photoreceptor cell maintenance
modifier: DECREASED
term:
id: GO:0045494
label: photoreceptor cell maintenance
locations:
- preferred_term: photoreceptor layer of retina
term:
id: UBERON:0001787
label: photoreceptor layer of retina
evidence:
- reference: PMID:8486383
reference_title: "New mouse primary retinal degeneration (rd-3)."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "The rod photoreceptor loss is essentially complete by 5 weeks, whereas remnant cone cells are seen through 7 weeks."
explanation: >-
Original description of the rapid rod and cone loss in the rd-3 mouse.
- reference: PMID:16469183
reference_title: "Morphological characterization of the retinal degeneration in three strains of mice carrying the rd-3 mutation."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "TUNEL-positive cells appear in the outer nuclear layer (ONL) by P14, and reach a maximum in all three mutant strains around P21."
explanation: >-
Photoreceptor apoptosis in three rd-3 strains.
- reference: PMID:31346032
reference_title: "Retinal guanylyl cyclase activation by calcium sensor proteins mediates photoreceptor degeneration in an rd3 mouse model of congenital human blindness."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "However, ∼70% of the hybrid rd3/rd3GCAPs-/- photoreceptors survived past 6 months, in stark contrast to <5% in the nonhybrid rd3/rd3 retinas."
explanation: >-
Fewer than 5% of RD3-deficient photoreceptors survive to 6 months, and
survival depends on GCAPs.
- reference: PMID:32083505
reference_title: "Optical coherence tomography and fundus autofluorescence imaging in an infant with RD3-related leber congenital amaurosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This study indicates that RD3-related LCA has a very severe phenotype with foveal development arrest and very early loss of all photoreceptor layer and external limiting membrane at the fovea."
explanation: >-
Early photoreceptor loss documented by OCT in an infant patient.
downstream:
- target: Photoreceptor layer loss on macular OCT
- target: Abnormal macular morphology
- target: Macular atrophy
- target: Retinal pigment epithelial mottling
- target: Attenuation of retinal blood vessels
- target: Spicular pigmentation of the retina
- target: Cone-rod dystrophy
- target: Abnormal fundus autofluorescence
- target: Perifoveal ring of hyperautofluorescence
phenotypes:
- name: Ultra-low vision
category: Ophthalmological
frequency: VERY_FREQUENT
description: >-
Vision is profoundly reduced from the first months of life, to counting
fingers, hand movements or light perception in all ten patients of the
largest series whose acuity was recorded.
phenotype_term:
preferred_term: Ultra-low vision
term:
id: HP:0032123
label: Ultra-low vision
onset:
onset_category: CONGENITAL
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Visual acuity, when measurable, was reduced to counting fingers, hand-movements or light perception."
explanation: >-
Visual acuity in the 11-patient RD3 series.
- reference: PMID:22531706
reference_title: "Mutations in RD3 are associated with an extremely rare and severe form of early onset retinal dystrophy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "BCVA was severely reduced from the earliest examinations (as early as 3 months), never exceeding 1.3 LogMAR."
directness: INDIRECT
explanation: >-
Bounds best-corrected acuity at 1.3 logMAR or worse from 3 months of age
in the Kurdish family; consistent with, but not by itself establishing,
the ultra-low range.
- name: Congenital nystagmus
category: Ophthalmological
frequency: VERY_FREQUENT
phenotype_term:
preferred_term: Congenital nystagmus
term:
id: HP:0006934
label: Congenital nystagmus
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Patients consistently presented with congenital nystagmus, low vision, sluggish pupillary reflexes, absence of ocular pursuit since birth"
explanation: >-
Congenital nystagmus was consistent across the RD3 series.
- name: Slow pupillary light response
category: Ophthalmological
frequency: FREQUENT
description: >-
Sluggish pupillary reflexes. The series text calls them consistent; its
Table 2 records altered pupillary reflexes for 5 of 11 patients.
phenotype_term:
preferred_term: Sluggish pupillary reflexes
term:
id: HP:0030211
label: Slow pupillary light response
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Patients consistently presented with congenital nystagmus, low vision, sluggish pupillary reflexes, absence of ocular pursuit since birth"
explanation: >-
Sluggish pupils in the RD3 series summary.
- name: Absent smooth pursuit
category: Ophthalmological
description: >-
No visual pursuit from birth. The series text calls this consistent, but
its Table 2 records it for only 2 of 11 patients, so no frequency is
given.
phenotype_term:
preferred_term: Absence of ocular pursuit since birth
term:
id: HP:0007179
label: Absent smooth pursuit
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Patients consistently presented with congenital nystagmus, low vision, sluggish pupillary reflexes, absence of ocular pursuit since birth"
explanation: >-
Absent ocular pursuit since birth in the RD3 series.
- name: Eye poking
category: Ophthalmological
description: >-
Early-onset and long-lasting oculodigital signs of Franceschetti (eye
pressing and poking). The series text calls these consistent, but its
Table 2 records them for only 2 of 11 patients, so no frequency is given.
phenotype_term:
preferred_term: Oculodigital sign of Franceschetti
term:
id: HP:0001483
label: Eye poking
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "early-onset and long-lasting digito-ocular signs of Franceschetti, photoaversion (one exception) and mild to moderate hyperopia"
explanation: >-
Digito-ocular signs in the RD3 series summary.
- name: Photophobia
category: Ophthalmological
frequency: VERY_FREQUENT
description: >-
Photoaversion, recorded in 8 of the 9 patients with data in the largest
series.
phenotype_term:
preferred_term: Photoaversion
term:
id: HP:0000613
label: Photophobia
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "early-onset and long-lasting digito-ocular signs of Franceschetti, photoaversion (one exception) and mild to moderate hyperopia"
explanation: >-
Photoaversion in all but one patient.
- name: Hypermetropia
category: Ophthalmological
frequency: VERY_FREQUENT
description: >-
Mild to moderate hyperopia, recorded in 6 of the 7 patients with
refraction data (the seventh was measured without cycloplegia).
phenotype_term:
preferred_term: Hyperopia
term:
id: HP:0000540
label: Hypermetropia
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "early-onset and long-lasting digito-ocular signs of Franceschetti, photoaversion (one exception) and mild to moderate hyperopia"
explanation: >-
Hyperopia in the RD3 series summary.
- name: Retinal pigment epithelial mottling
category: Ophthalmological
frequency: FREQUENT
description: >-
Salt-and-pepper retina, recorded in 3 of the 7 patients with fundus data;
three others had a dull retina without pigment migration.
phenotype_term:
preferred_term: Salt-and-pepper retinopathy
term:
id: HP:0007814
label: Retinal pigment epithelial mottling
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Macular atrophy, RPE atrophy with salt and pepper aspect, some bone-spicule pigment in the mid periphery"
explanation: >-
Table 2 fundus entry for one of the three patients with a salt-and-pepper
retina.
- name: Attenuation of retinal blood vessels
category: Ophthalmological
frequency: VERY_FREQUENT
description: Thin retinal vessels in 6 of the 7 patients with fundus data.
phenotype_term:
preferred_term: Thin retinal vessels
term:
id: HP:0007843
label: Attenuation of retinal blood vessels
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Fundus consistently showed dull retina with salt and pepper aspect, thin retinal vessels and an early macular rearrangement (maculopathy, Figure 2)."
explanation: >-
Thin retinal vessels on fundoscopy.
- name: Abnormal macular morphology
category: Ophthalmological
frequency: VERY_FREQUENT
description: >-
Early macular rearrangement (maculopathy) in all 7 patients with fundus
data, recorded as macular rearrangement in four and macular atrophy in
three.
phenotype_term:
preferred_term: Maculopathy
term:
id: HP:0001103
label: Abnormal macular morphology
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Fundus consistently showed dull retina with salt and pepper aspect, thin retinal vessels and an early macular rearrangement (maculopathy, Figure 2)."
explanation: >-
Early maculopathy in the RD3 series.
- name: Macular atrophy
category: Ophthalmological
frequency: FREQUENT
description: >-
Macular or central foveal atrophy, recorded in 3 of the 7 patients with
fundus data in the largest series and in an infant case.
phenotype_term:
preferred_term: Macular atrophy
term:
id: HP:0007401
label: Macular atrophy
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Salt and pepper retina, thin vessels, marked macular atrophy"
explanation: >-
Table 2 fundus entry recording marked macular atrophy in one of the three
affected patients.
- reference: PMID:32083505
reference_title: "Optical coherence tomography and fundus autofluorescence imaging in an infant with RD3-related leber congenital amaurosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Well-demarcated central foveal atrophy was noted in the infrared imaging."
explanation: >-
Central foveal atrophy in an infant with homozygous p.Arg38Ter.
- name: Photoreceptor layer loss on macular OCT
category: Ophthalmological
description: >-
Spectral-domain OCT shows the photoreceptor layer missing with relatively
preserved inner retina; in an infant, the outer nuclear layer, external
limiting membrane, ellipsoid zone and interdigitation zone were absent at
the fovea.
phenotype_term:
preferred_term: Photoreceptor layer loss on macular OCT
term:
id: HP:0030609
label: Photoreceptor layer loss on macular OCT
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The photoreceptor layer was missing, the inner segment/outer segment border was diminished and an increased backscatter from the choroid was observed due to RPE-atrophy."
explanation: >-
OCT in the one patient of the series who was imaged.
- reference: PMID:32083505
reference_title: "Optical coherence tomography and fundus autofluorescence imaging in an infant with RD3-related leber congenital amaurosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "An arrest in foveal development and loss of outer retinal structure including outer nuclear layer, external limiting membrane, ellipsoid zone and interdigitation zone at the fovea were detected in the OCT imaging."
explanation: >-
Loss of all outer retinal layers at the fovea in infancy.
- name: Hypoplasia of the fovea
category: Ophthalmological
description: Arrest of foveal development, reported in an infant case.
phenotype_term:
preferred_term: Foveal development arrest
term:
id: HP:0007750
label: Hypoplasia of the fovea
evidence:
- reference: PMID:32083505
reference_title: "Optical coherence tomography and fundus autofluorescence imaging in an infant with RD3-related leber congenital amaurosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "An arrest in foveal development and loss of outer retinal structure including outer nuclear layer, external limiting membrane, ellipsoid zone and interdigitation zone at the fovea were detected in the OCT imaging."
explanation: >-
Foveal development arrest in a single infant; frequency unknown.
- name: Abnormal fundus autofluorescence
category: Ophthalmological
description: >-
Fundus autofluorescence severely reduced, in the one patient of the
largest series who was imaged.
phenotype_term:
preferred_term: Severely reduced fundus autofluorescence
term:
id: HP:0030602
label: Abnormal fundus autofluorescence imaging
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Fundus autofluorescence (FAF) was severely reduced, a proper image could not be taken."
explanation: >-
Severely reduced autofluorescence in an imaged RD3 patient.
- name: Perifoveal ring of hyperautofluorescence
category: Ophthalmological
description: >-
Perifoveal hyperautofluorescent ring with irregular hyperautofluorescence
outside the vascular arcades, reported in an infant.
phenotype_term:
preferred_term: Perifoveal ring of hyperautofluorescence
term:
id: HP:0030629
label: Perifoveal ring of hyperautofluorescence
evidence:
- reference: PMID:32083505
reference_title: "Optical coherence tomography and fundus autofluorescence imaging in an infant with RD3-related leber congenital amaurosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "FAF imaging showed perifoveal hyperautofluorescent ring and irregular hyperautofluorescence outside the vascular arcade."
explanation: >-
Autofluorescence pattern in an infant with homozygous p.Arg38Ter.
- name: Spicular pigmentation of the retina
category: Ophthalmological
description: Peripheral bone-spicule pigment appearing as the disease progresses.
phenotype_term:
preferred_term: Bone spicules in the periphery
term:
id: HP:0007737
label: Spicular pigmentation of the retina
evidence:
- reference: PMID:22531706
reference_title: "Mutations in RD3 are associated with an extremely rare and severe form of early onset retinal dystrophy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The disease presented as cone-rod dystrophy with dystrophic changes in the macula and bone spicules in the periphery on progression."
explanation: >-
Bone spicules appeared with progression in the Kurdish family followed for
up to 22 years.
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Macular atrophy, RPE atrophy with salt and pepper aspect, some bone-spicule pigment in the mid periphery"
explanation: >-
Mid-peripheral bone-spicule pigment in a 17-year-old patient of the
largest series.
- name: Cone-rod dystrophy
category: Ophthalmological
description: >-
Where it can be characterised, the retinal dystrophy behaves as a cone-rod
dystrophy with macular involvement.
phenotype_term:
preferred_term: Cone-rod dystrophy
term:
id: HP:0000548
label: Cone/cone-rod dystrophy
evidence:
- reference: PMID:22531706
reference_title: "Mutations in RD3 are associated with an extremely rare and severe form of early onset retinal dystrophy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The disease presented as cone-rod dystrophy with dystrophic changes in the macula and bone spicules in the periphery on progression."
explanation: >-
Cone-rod pattern in a family followed longitudinally.
- name: Keratoconus
category: Ophthalmological
frequency: OCCASIONAL
description: Reported in one of eleven patients in the largest series.
phenotype_term:
preferred_term: Keratoconus
term:
id: HP:0000563
label: Keratoconus
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Nystagmus since birth altered pupillary reflexes, Keratoconus"
explanation: >-
Table 2 lists keratoconus in a 31-year-old patient from Morocco, the only
one of eleven.
- name: Optic disc pallor
category: Ophthalmological
frequency: OCCASIONAL
phenotype_term:
preferred_term: Optic disc pallor
term:
id: HP:0000543
label: Optic disc pallor
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Macular atrophy, attenuated retinal vessels, abnormal RPE in the mid-periphery, optic disk pallor"
explanation: >-
Table 2 lists optic disc pallor in one patient (p.E46*) of eleven.
genetic:
- name: RD3
gene_term:
preferred_term: RD3
term:
id: hgnc:19689
label: RD3
relationship_type: CAUSATIVE
association: Causative
inheritance:
- name: Autosomal recessive
features: >-
The LCA-causing alleles are predicted to truncate the protein (nonsense,
small frameshift and canonical splice-site variants). The c.112C>T
(p.Arg38Ter) allele recurs in families from the southern Mediterranean as
an ancient founder allele. One homozygous missense variant (p.Lys87Glu)
has been reported in a family with retinitis pigmentosa, on in-silico
evidence only.
variants:
- name: c.112C>T (p.Arg38Ter)
variant_type: single nucleotide variant
clinical_significance: PATHOGENIC
description: >-
Nonsense founder allele shared by five families from the southern shores
of the Mediterranean; also reported homozygous in an infant with
RD3-related LCA.
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Five families originating from the Southern Shores of the Mediterranean segregated a similar mutation (c.112C>T, p.R38*) suggesting that this change may have resulted from an ancient founder effect."
explanation: Founder nonsense allele segregating in five families.
- reference: PMID:32083505
reference_title: "Optical coherence tomography and fundus autofluorescence imaging in an infant with RD3-related leber congenital amaurosis."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Homozygous pathogenic variant (c.112 C > T, p.Arg38Ter) was detected in the RD3 gene."
explanation: Same allele homozygous in an independent infant case.
- name: c.180C>A
variant_type: single nucleotide variant
clinical_significance: PATHOGENIC
description: Homozygous nonsense variant in a consanguineous Kurdish family.
evidence:
- reference: PMID:22531706
reference_title: "Mutations in RD3 are associated with an extremely rare and severe form of early onset retinal dystrophy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Direct sequencing of RD3 revealed a homozygous nonsense mutation (c.180C > A) in all affected members tested."
explanation: Segregating homozygous nonsense allele.
- name: c.259A>G (p.Lys87Glu)
variant_type: single nucleotide variant
description: >-
Homozygous missense variant reported in one Spanish family with
retinitis pigmentosa rather than LCA. Pathogenicity rests on in-silico
prediction; no segregation or functional data are given. Lys87 lies in
the Lys87-Leu122 region that binds the cyclase.
evidence:
- reference: PMID:24516651
reference_title: "Combined genetic and high-throughput strategies for molecular diagnosis of inherited retinal dystrophies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Screening of the RD3 candidate, previously reported only as a LCA-causative gene, revealed a new missense mutation c.259A>G p.K87E in homozygosity."
explanation: Identifies the variant in a retinitis pigmentosa family.
- reference: PMID:24516651
reference_title: "Combined genetic and high-throughput strategies for molecular diagnosis of inherited retinal dystrophies."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Notably, RD3-up to now only associated to Leber Congenital Amaurosis- was identified as causative of Retinitis Pigmentosa."
explanation: >-
The authors' conclusion that RD3 can cause retinitis pigmentosa,
resting on this single family.
gene_disease_validity:
- validity_classification: DEFINITIVE
classified_by: CLINGEN
external_id: CGGV:assertion_67c894eb-2c16-4598-8e92-8345e562d91c-2022-01-06T050000.000Z
notes: Retina Gene Curation Expert Panel, autosomal recessive, SOP8, approved January 2022.
evidence:
- reference: CGGV:assertion_67c894eb-2c16-4598-8e92-8345e562d91c-2022-01-06T050000.000Z
reference_title: "RD3 / RD3-related retinopathy (Definitive)"
supports: SUPPORT
evidence_source: OTHER
snippet: "RD3 | HGNC:19689 | RD3-related retinopathy | MONDO:0700235 | AR | Definitive"
explanation: ClinGen classifies RD3 as definitively associated with this disease.
evidence:
- reference: PMID:17186464
reference_title: "Premature truncation of a novel protein, RD3, exhibiting subnuclear localization is associated with retinal degeneration."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This mutation is predicted to result in premature truncation of the RD3 protein, segregates with the disease, and is not detected in 121 ethnically matched control individuals."
explanation: >-
First human RD3 variant, segregating with LCA and absent from controls.
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We identified three RD3 mutations in seven unrelated consanguineous LCA families - i.e., a 2 bp deletion and two nonsense mutations - predicted to cause complete loss of function."
explanation: Replication of RD3 loss of function in seven further families.
treatments:
- name: RD3 Gene Augmentation (preclinical)
description: >-
Subretinal AAV delivery of RD3 to photoreceptors is the only disease-directed
approach and has been tested only in mice. In two rd3 strains, AAV8(Y733F)
carrying Rd3 under the rhodopsin kinase promoter moved guanylyl cyclase from
the endoplasmic reticulum to rod and cone outer segments, kept photoreceptors
alive for at least 7 months, and restored ERG responses. Transgenic RD3
expression in rods likewise restored cyclase levels and photoresponses. No
human trial has been reported; care for patients is supportive.
therapeutic_modality: GENE_THERAPY
treatment_term:
preferred_term: gene augmentation therapy
term:
id: NCIT:C15238
label: Gene Therapy
delivery_system:
delivery_platform: VIRAL_VECTOR
target_cell_types:
- preferred_term: photoreceptor cell
term:
id: CL:0000210
label: photoreceptor cell
target_mechanisms:
- target: Failure of Guanylate Cyclase Export to the Outer Segment
treatment_effect: RESTORES
- target: Rapid Rod and Cone Photoreceptor Degeneration
treatment_effect: INHIBITS
evidence:
- reference: PMID:23740938
reference_title: "RD3 gene delivery restores guanylate cyclase localization and rescues photoreceptors in the Rd3 mouse model of Leber congenital amaurosis 12."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Strong RD3 transgene expression led to the translocation of guanylate cyclase from the endoplasmic reticulum (ER) to rod and cone outer segments (OSs) as visualized by immunofluorescence microscopy."
explanation: >-
AAV-delivered RD3 restores cyclase trafficking in rd3 mice.
- reference: PMID:23740938
reference_title: "RD3 gene delivery restores guanylate cyclase localization and rescues photoreceptors in the Rd3 mouse model of Leber congenital amaurosis 12."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Guanylate cyclase expression and localization coincided with the survival of rod and cone photoreceptors for at least 7 months."
explanation: >-
Long-term photoreceptor survival after RD3 gene delivery.
- reference: PMID:31346032
reference_title: "Retinal guanylyl cyclase activation by calcium sensor proteins mediates photoreceptor degeneration in an rd3 mouse model of congenital human blindness."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "When transgenically expressed in rd3/rd3 mouse retinas under control of the rhodopsin promoter, the RD3GFP construct increased RetGC levels to near normal levels, restored dark-adapted photoresponses, and rescued rods from degeneration."
explanation: >-
Independent transgenic rescue of cyclase levels, function and survival.
- name: Genetic Counseling
description: >-
Counselling for families with an affected child. Because RD3 carriers are
rare, the authors of the largest series judged the recurrence risk for LCA
in non-consanguineous unions negligible, for heterozygous and homozygous
individuals alike; the risk is in consanguineous unions.
treatment_term:
preferred_term: genetic counseling
term:
id: NCIT:C15240
label: Genetic Counseling
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Considering the low frequency of RD3 carriers, the recurrence risk for LCA in non-consanguineous unions is negligible for both heterozygote and homozygote RD3 individuals."
explanation: Basis for recurrence-risk counselling.
diagnosis:
- name: Molecular genetic testing
diagnosis_term:
preferred_term: genetic testing
term:
id: NCIT:C15709
label: Genetic Testing
description: >-
Diagnosis rests on finding biallelic RD3 variants, because the LCA12
phenotype closely resembles GUCY2D-related LCA1. In patients with LCA type
I from the Mediterranean region with moderate or no hyperopia, the authors
of the largest series recommend screening RD3 first, before GUCY2D, RPGRIP1
and CEP290. Since LCA12 is non-syndromic, they advise against routine
extraocular investigations once an RD3 diagnosis is made.
evidence:
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In LCA type I patients originating from this region with moderate or no hyperopia, RD3 should be screened for mutations first, before GUCY2D, RPGRIP1 and CEP290"
explanation: >-
Recommended screening order for Mediterranean patients, reflecting the
p.Arg38Ter founder allele.
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In these patients, anxiogenic and expensive extraocular explorations must not be systematically prescribed"
explanation: >-
Management point that follows from the absence of extraocular disease.
- reference: PMID:23308101
reference_title: "Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The LCA12 phenotype in our patients is highly similar to those of patients with mutant photoreceptor-specific guanylate cyclase (GUCY2D/LCA1)."
explanation: >-
The clinical overlap with LCA1 is why gene testing, not examination,
makes the diagnosis.
animal_models:
- name: rd3 mouse (Rd3 nonsense)
species: Mouse
genotype: Rd3 C>T nonsense, predicted stop after residue 106, homozygous
publication: PMID:17186464
description: >-
Naturally occurring retinal degeneration 3 mouse, described in 1993 and
mapped to Rd3 in 2006. Photoreceptors develop normally and then degenerate
from about postnatal week 2 to 3. Several strains carry the mutation and
differ in the rate of degeneration and, in one strain, in cone function,
which points to background modifiers.
evidence:
- reference: PMID:17186464
reference_title: "Premature truncation of a novel protein, RD3, exhibiting subnuclear localization is associated with retinal degeneration."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "The rd3 mutation results in a predicted stop codon after residue 106."
explanation: Identifies the causal Rd3 truncating mutation in the rd3 mouse.
modeled_mechanisms:
- target: Failure of Guanylate Cyclase Export to the Outer Segment
relationship: RECAPITULATES
fidelity: HIGH
model_scale: CELLULAR
description: >-
Both retinal guanylyl cyclases are lost from rd3 photoreceptors, the
defect the human truncating alleles are predicted to cause.
evidence:
- reference: PMID:21078983
reference_title: "RD3, the protein associated with Leber congenital amaurosis type 12, is required for guanylate cyclase trafficking in photoreceptor cells."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "GC1 and GC2 are undetectable in photoreceptors of the rd3 mouse deficient in RD3 by immunofluorescence microscopy."
explanation: Cyclase loss from rd3 mouse photoreceptors.
- target: Rapid Rod and Cone Photoreceptor Degeneration
relationship: RECAPITULATES
fidelity: MODERATE
model_scale: TISSUE
description: Rapid rod and cone loss within weeks of eye opening.
limitations: >-
The rate of degeneration differs between rd3 strains, and the
Rb(11.13)4Bnr/J strain appears to carry an additional cone
phototransduction defect, so strain background must be considered before
comparing rates with human disease.
evidence:
- reference: PMID:8486383
reference_title: "New mouse primary retinal degeneration (rd-3)."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "The rod photoreceptor loss is essentially complete by 5 weeks, whereas remnant cone cells are seen through 7 weeks."
explanation: Time course of rd-3 photoreceptor loss.
- name: rcd2 collie (RD3 insertion)
species: Dog
genotype: RD3 insertion altering the last 61 codons, homozygous
background: Collie
publication: PMID:19130129
description: >-
Rod-cone dysplasia type 2, an autosomal recessive retinal disease of collie
dogs, maps to an insertion in RD3 that replaces the C-terminal 61 codons and
extends the open reading frame. It is the large-animal counterpart of LCA12.
evidence:
- reference: PMID:19130129
reference_title: "Canine RD3 mutation establishes rod-cone dysplasia type 2 (rcd2) as ortholog of human and murine rd3."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "an insertion was found that cosegregates with rcd2 and is predicted to alter the last 61 codons of the normal open reading frame and further extend the open reading frame."
explanation: Identifies the canine RD3 allele that causes rcd2.
modeled_mechanisms:
- target: RD3 Biallelic Loss of Function
relationship: RECAPITULATES
fidelity: MODERATE
model_scale: MOLECULAR
description: >-
A naturally occurring RD3 allele that disrupts the C-terminal region, as
the human truncating alleles do.
limitations: >-
The canine allele replaces and extends the C terminus rather than
truncating it, and the mapping paper does not report cyclase trafficking
or ERG data for the dog.
evidence:
- reference: PMID:19130129
reference_title: "Canine RD3 mutation establishes rod-cone dysplasia type 2 (rcd2) as ortholog of human and murine rd3."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "an insertion was found that cosegregates with rcd2 and is predicted to alter the last 61 codons of the normal open reading frame and further extend the open reading frame."
explanation: The canine allele alters the RD3 C terminus.
references:
- reference: PMID:30285347
title: "Nonsyndromic Leber Congenital Amaurosis / Early-Onset Severe Retinal Dystrophy Overview."
tags:
- GeneReviews
Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.
Create: RD3-Related Retinopathy (LCA12) · 2026-10-15T16:38:57Z · View source
New gene-level entry for RD3-related retinopathy (MONDO:0700235), with Leber congenital amaurosis 12 (MONDO:0012525) as its only has_subtypes row. Deletes stubs/RD3-related_Retinopathy.yaml. Deep research: one OpenScientist report, research/RD3-Related_Retinopathy-deep-research-openscientist.md. Reference validation 22/22 resolved, 0 not found; term validation flagged only paraphrased labels and one obsolete NCIT treatment term (NCIT:C15368), none of which were used. just preflight-dr passed (RD3 mentioned 76 times). The report attributes PMID:30090012 to an RD3 case of maternal UPD6; that paper reports a TULP1 variant (RD3 is on chromosome 1q32.3), so the claim and its c.524dupC variant were not used. The report's suggested Deeply set eye phenotype (HP:0000490) has no RD3 source and was not used, and its statement that the ERG is extinguished in RD3 patients is uncited; no cited source reports patient ERG results, so no ERG phenotype is recorded. Pathograph: two branches from RD3 loss of function. (1) Failure of guanylyl cyclase export from the ER to the outer segment, then deficient cGMP synthesis, then failure of rod and cone phototransduction (Azadi 2010, Molday 2013, Olshevskaya 2026). (2) Loss of RD3 inhibition of the cyclase in the inner segment, then aberrant GCAP-stimulated cyclase activity, then ER stress and mitochondrial swelling, then rapid photoreceptor degeneration (Peshenko 2011, Dizhoor 2019 and 2021, Plana-Bonamaiso 2020). Low intracellular calcium links the two. The degenerative branch is rd3-mouse evidence and is labelled as such. Phenotypes come from Perrault 2013 (11 patients), Preising 2012 and Dikkaya 2020; the GeneReviews LCA/EOSRD overview (PMID:30285347) is tagged but its abstract lists no clinical findings. Frequencies were set from the per-patient Table 2 of Perrault 2013 rather than its summary sentence, which calls several findings consistent that the table records in only 2 of 11 patients (eye poking, absent pursuit); those two carry no frequency. Also recorded: ClinGen Definitive (CGGV assertion 67c894eb, Retina GCEP), the p.Arg38Ter founder allele, a single RP family with homozygous p.Lys87Glu (PMID:24516651, in-silico support only), rd3 mouse and rcd2 collie models, preclinical AAV gene augmentation, genetic counselling, and molecular diagnosis guidance. An independent pre-PR review found an edge citing a sentence about degeneration rather than cGMP, a REFUTE item pointing at the wrong claim, a visual-acuity binding to HP:0001141 where the cited acuities fall in HP:0032123 Ultra-low vision, overstated frequencies, and an unsupported rods-and-cones-together claim. All were corrected before the PR. Validation: just validate passes (78/78 snippets, terms, schema); check-entity-refs, check-causal-targets, check-gene-validity, check-snippet-length/grading/title, check-coarse-phenotypes, check-genereviews (TAGGED) pass. 14 of 19 phenotypes are causally connected.
Disease: RD3-Related Retinopathy / Leber Congenital Amaurosis 12 (LCA12) MONDO ID: MONDO:0700235 · OMIM: #610612 · Gene: RD3 (retinal degeneration 3; C1orf36), chromosome 1q32.3 Category: Mendelian, autosomal recessive, non-syndromic inherited retinal dystrophy
RD3-Related Retinopathy, also designated Leber Congenital Amaurosis type 12 (LCA12), is an extremely rare, autosomal recessive, congenital-onset inherited retinal dystrophy caused by biallelic truncating loss-of-function mutations in the RD3 gene on chromosome 1q32.3. RD3 encodes an evolutionarily conserved ~23 kDa α-helical protein that functions as a dual-role regulator of the retinal membrane guanylate cyclases RetGC1 (GUCY2D/GC1) and RetGC2 (GUCY2F/GC2): it stabilizes the cyclases, inhibits their premature catalytic activity in the endoplasmic reticulum (ER), and chaperones their ER exit and trafficking to the photoreceptor outer segments. Loss of functional RD3 leaves the cyclases undetectable and trapped in the ER, abolishing cGMP-based phototransduction and triggering GCAP-driven aberrant cyclase activation and ER-stress-mediated photoreceptor death.
Clinically, LCA12 presents as a severe congenital/early-infantile cone-rod dystrophy with profoundly reduced visual acuity from the first months of life (best-corrected visual acuity never exceeding 1.3 LogMAR, documented as early as 3 months of age), nystagmus/roving eye movements, photophobia, and a severely reduced or non-recordable full-field electroretinogram (ERG). The phenotype is clinically indistinguishable from GUCY2D-related LCA1, reflecting the shared molecular pathway, which makes molecular genetic testing (NGS panels/whole-exome sequencing) essential for diagnosis. The disorder is confined to the neural retina (rod and cone photoreceptors), is bilateral and symmetric, non-syndromic, and carries a normal life expectancy; the principal outcome is lifelong profound visual disability/legal blindness.
RD3 is a very rare cause of LCA (only 7 of 852 LCA/early-onset severe retinal dystrophy patients in a worldwide cohort), strongly associated with consanguinity, and carries a North African/Mediterranean founder allele p.R38* (c.112C>T). Etiology is purely monogenic with no environmental, infectious, or lifestyle contributions. There is currently no approved treatment; management is supportive (low-vision rehabilitation, genetic counseling). The leading experimental strategy is AAV-mediated RD3 gene augmentation, which rescued photoreceptors and restored ERG function in the rd3 mouse, and which is strongly supported by the mechanistically adjacent GUCY2D/LCA1 gene-therapy program (ATSN-101), now demonstrating safety and sustained efficacy in phase 1/2 trials.
Overview. RD3-Related Retinopathy is a congenital, severe, non-syndromic retinal dystrophy belonging to the Leber Congenital Amaurosis (LCA) spectrum, the earliest-onset and most severe group of inherited retinal diseases. It is caused by deficiency of the RD3 protein, which is required for the expression and trafficking of retinal guanylate cyclases in rod and cone photoreceptors.
Key identifiers.
| Resource | Identifier |
|---|---|
| MONDO | MONDO:0700235 |
| OMIM (phenotype) | #610612 (Leber congenital amaurosis 12) |
| Gene | RD3 (HGNC; aliases C1orf36, retinal degeneration 3) |
| Locus | 1q32.3 |
| Disease class | Autosomal recessive inherited retinal dystrophy / LCA |
Synonyms / alternative names: Leber congenital amaurosis 12; LCA12; RD3-related Leber congenital amaurosis; retinal degeneration 3-related retinopathy; early-onset severe retinal dystrophy due to RD3.
Information source type. The knowledge base for this disease is derived from aggregated disease-level resources (OMIM, ClinVar) and from a small number of individual patient/family case reports and cohort studies (notably consanguineous families), supplemented by extensive model-organism data (rd3 mouse, rcd2 collie) and in vitro/biochemical studies of the RD3–guanylate cyclase interaction. No large EHR-based cohorts exist because of the disease's rarity.
Primary cause. The disease is purely monogenic. It results from biallelic (homozygous or compound heterozygous) loss-of-function variants in RD3. Perrault et al. identified three RD3 mutations — a 2-bp deletion and two nonsense mutations — in seven unrelated consanguineous LCA families, all predicted to cause complete loss of function: "We identified three RD3 mutations in seven unrelated consanguineous LCA families - i.e., a 2 bp deletion and two nonsense mutations - predicted to cause complete loss of function" [PMID: 23308101]. Truncating mutations produce unstable, non-functional C-terminally truncated proteins [PMID: 24904271].
Genetic risk factors. The causal factor is the RD3 truncating variant itself. Consanguinity is the principal predisposing context: every published family was consanguineous or carried founder alleles [PMID: 23308101; PMID: 22531706]. No susceptibility loci or validated human modifier genes are established.
Environmental / lifestyle risk factors. None identified or mechanistically plausible. This is a classical Mendelian disorder; no toxins, infections, dietary, occupational, or lifestyle factors contribute to onset or severity.
Protective factors. No genetic or environmental protective factors are known.
Modifier genes. No human modifiers are established. In mouse models, genetic background and GCAP (guanylate cyclase-activating protein) gene dosage modulate degeneration severity, nominating GCAPs as candidate modifiers [PMID: 31346032; PMID: 27471269].
Gene–environment interactions. None reported; etiology is independent of environmental exposure.
LCA12 is a severe, congenital/early-infantile cone-rod dystrophy. Key phenotypes, with suggested HPO terms:
| Phenotype | HPO term (suggested) | Characteristics |
|---|---|---|
| Severe visual impairment / blindness from birth | HP:0000618 (Blindness); HP:0007663 (Reduced visual acuity, congenital) | BCVA severely reduced from earliest exams (≤1.3 LogMAR by 3 months); never normalizes [PMID: 22531706] |
| Nystagmus / roving eye movements | HP:0000639 (Nystagmus) | Hallmark of LCA |
| Reduced/absent electroretinogram | HP:0000512 (Abnormal electroretinogram) | Rod and cone responses extinguished or severely reduced |
| Photophobia | HP:0000613 (Photophobia) | Common LCA feature |
| Cone-rod dystrophy | HP:0000548 (Cone/cone-rod dystrophy) | Macular dystrophic changes progressing to peripheral bone spicules [PMID: 22531706] |
| Macular dystrophy | HP:0007754 (Macular dystrophy) | Dystrophic macular changes |
| Pigmentary retinopathy / bone spicules | HP:0007737 (Bone spicule pigmentation of the retina) | Appears on progression |
| Deep-set eyes | HP:0000490 (Deeply set eye) | Part of the LCA oculo-digital complex |
Age of onset: Neonatal/congenital — functional deficit present from birth. Severity: Severe (profound, lifelong). Progression: Congenital functional loss with early rapid structural photoreceptor loss, then slowly progressive macular/peripheral changes. "BCVA was severely reduced from the earliest examinations (as early as 3 months), never exceeding 1.3 LogMAR. The disease presented as cone-rod dystrophy with dystrophic changes in the macula and bone spicules in the periphery on progression" [PMID: 22531706]. Frequency among affected individuals: Core features (severe acuity loss, nystagmus, extinguished ERG) are essentially universal; pigmentary retinopathy and bone spicules appear with progression.
Quality-of-life impact. Profound, lifelong visual disability/legal blindness with major effects on education, mobility, independence, and daily functioning from infancy. Disease-specific QOL instruments have not been reported for this ultra-rare disorder.
Clinical overlap. "The LCA12 phenotype in our patients is highly similar to those of patients with mutant photoreceptor-specific guanylate cyclase (GUCY2D/LCA1)" [PMID: 23308101], reflecting the shared pathway.
Causal gene. RD3 (retinal degeneration 3; alias C1orf36), chromosome 1q32.3; phenotype LCA12 OMIM #610612. Encodes an evolutionarily conserved ~23 kDa protein.
Pathogenic variants.
| Variant (cDNA / protein) | Type | Classification | Note |
|---|---|---|---|
| c.112C>T (p.Arg38*) | Nonsense | Pathogenic | Mediterranean/North African founder allele [PMID: 23308101] |
| c.180C>A | Nonsense | Pathogenic | Homozygous, reported in LCA family [PMID: 22531706] |
| 2-bp deletion | Frameshift | Pathogenic | Among 3 mutations found in 7 families [PMID: 23308101] |
| c.524dupC (p.Pro176ThrfsTer7) | Frameshift | Likely pathogenic | Reported via maternal UPD6 case [PMID: 30090012] |
Modifier genes. GCAPs (GUCA1A/GUCA1B) are candidate modifiers based on mouse data [PMID: 31346032].
Epigenetic information: No disease-specific DNA methylation or histone-modification findings reported.
Chromosomal abnormalities: Not a feature; however, uniparental isodisomy of chromosome 6 was reported to unmask a homozygous RD3-region variant in one case of maternal UPD [PMID: 30090012] — a mechanistic curiosity rather than a typical cause.
This section is not applicable beyond confirming the purely genetic etiology [PMID: 23308101].
RD3 biallelic truncation (p.R38*)
│ loss of function
▼
RD3 protein absent / unstable
│ fails to bind & chaperone
▼
GC1 (GUCY2D) + GC2 (GUCY2F) trapped in ER ──► undetectable in outer segment
│ │
▼ (Branch A: functional) ▼ (Branch B: degenerative)
cGMP synthesis deficit aberrant GCAP activation + ER stress
│ │
▼ ▼
extinguished ERG, photoreceptor apoptosis
congenital blindness, (rods → cones)
nystagmus │
▼
retinal degeneration,
macular dystrophy, bone spicules
Why molecular testing is required. Because the LCA12 phenotype is clinically indistinguishable from GUCY2D/LCA1 and other LCA subtypes [PMID: 23308101], clinical examination alone cannot establish the gene. Diagnosis rests on molecular genetics.
Clinical / functional tests. - Electrophysiology: Full-field ERG severely reduced or non-recordable (rod and cone) — a defining feature of LCA. - Imaging: OCT shows outer-retinal (ellipsoid zone / outer nuclear layer) disruption; fundus may be near-normal early, developing macular dystrophy and peripheral bone spicules on progression [PMID: 22531706]. - Laboratory/biomarkers: No blood/urine biomarker; the molecular genetic variant is the diagnostic biomarker.
Clinical criteria & differential diagnosis. Diagnosis uses standard LCA criteria (congenital severe vision loss, nystagmus, extinguished ERG). Differential diagnosis includes all other LCA/EOSRD genes — especially GUCY2D (LCA1) given pathway identity, plus CEP290 (LCA10), RPE65 (LCA2), NMNAT1, TULP1, RPGRIP1, and others; distinction is by molecular testing [PMID: 23308101; PMID: 39710161; PMID: 36128853].
Screening. Cascade carrier testing in consanguineous families; carrier/pre-conception screening is relevant in high-consanguinity populations [PMID: 41567338].
Current standard of care. No approved disease-specific therapy exists. Management is supportive: low-vision rehabilitation, visual aids, educational support for the visually impaired, and genetic counseling [PMID: 23308101]. NCIT: Supportive Care (NCIT:C15277); Genetic Counseling (NCIT:C15368).
Pharmacotherapy / pharmacogenomics: None specific.
Advanced therapeutics — gene therapy (leading experimental strategy). - Preclinical proof of concept: Subretinal AAV8(Y733F)-mouse Rd3 under a rhodopsin-kinase promoter delivered to P14 rd3 mice translocated guanylate cyclase from ER to outer segments and preserved photoreceptors: "Guanylate cyclase expression and localization coincided with the survival of rod and cone photoreceptors for at least 7 months. Rod and cone visual function was restored in the In(5)30Rk/J strain of rd3 mice as measured by electroretinography (ERG)" [PMID: 23740938]. NCIT: Gene Therapy (NCIT:C15262); Adeno-associated Virus Vector (NCIT:C122200). - Translational validation from the adjacent pathway: The GUCY2D/LCA1 program demonstrates clinical translatability of the same pathway. ATSN-101 (subretinal AAV5-GUCY2D), phase 1/2: "ATSN-101 is well tolerated 12 months after treatment, with no drug-related serious adverse events. Clinically significant improvements in retinal sensitivity were sustained in patients" — high-dose dark-adapted full-field stimulus threshold mean change 20.3 dB vs 1.1 dB untreated at 12 months (p=0.012) [PMID: 39244273]. Related preclinical LCA1 work showed full restoration of cone function in the all-cone Nrl⁻/⁻Gucy2e⁻/⁻ model [PMID: 26247368].
RNA-based / cell / surgical therapies: None established for RD3.
Treatment strategy: A genotype-guided, AAV gene-augmentation approach is the rational path, best delivered early (within the therapeutic window) given rapid early degeneration [PMID: 8486383].
RD3-related retinal degeneration occurs naturally across species, underscoring strong evolutionary conservation of the RD3–guanylate-cyclase mechanism.
| Species | Model / condition | Evidence |
|---|---|---|
| Mus musculus (mouse; NCBI Taxon 10090) | rd3 naturally occurring mutant; "the only mouse homozygous retinal degeneration reported to date in which photoreceptors are initially normal" [PMID: 8486383] | Ortholog |
| Canis lupus familiaris (dog; NCBI Taxon 9615) | rod-cone dysplasia type 2 (rcd2) in collies; a canine RD3 splice-insertion "cosegregates with rcd2 and is predicted to alter the last 61 codons of the normal open reading frame" [PMID: 19130129] | Ortholog |
| Model | Type | Genetic basis | Phenotype recapitulation | Application |
|---|---|---|---|---|
| rd3 mouse | Mammalian, naturally occurring | Rd3 loss of function | Excellent: normal early differentiation, rod loss complete by ~5 wk, cones to ~7 wk; GC1/GC2 undetectable [PMID: 8486383; PMID: 21078983] | Pathogenesis, GCAP/ER-stress death mechanism, gene-therapy testing [PMID: 31980596; PMID: 23740938] |
| rcd2 collie (dog) | Mammalian, naturally occurring | Canine RD3 splice insertion, alters last 61 codons [PMID: 19130129] | Good large-animal ortholog of human/murine disease | Comparative/translational studies |
| rd3 retina (transcriptomics) | In vivo profiling | — | Downregulated phototransduction/lipid metabolism; upregulated immune response [PMID: 23687432] | Pathway discovery |
RD3-Related Retinopathy is best understood as a guanylate-cyclase-trafficking disorder. RD3 is a small, conserved photoreceptor protein that performs two coupled jobs on RetGC1/RetGC2: (1) it inhibits premature cyclase catalysis in the ER (preventing wasteful/toxic cGMP generation before the enzyme reaches its destination), and (2) it chaperones cyclase ER exit and delivery to the outer segment — "This interaction inhibits GC catalytic activity and promotes the exit of GC1 and GC2 from the endoplasmic reticulum and their trafficking to photoreceptor outer segments" [PMID: 24904271]. Biallelic truncating mutations delete the critical Lys87–Leu122 target-binding core (and the central α-helix around Cys93), abolishing both functions [PMID: 27471269]. The consequence is bilateral loss of outer-segment cyclase, collapse of cGMP phototransduction (the functional, congenital-blindness branch), and a parallel degenerative branch in which unrestrained GCAP-driven cyclase activity plus ER stress kills photoreceptors — rods first, then cones [PMID: 31980596; PMID: 31346032].
Because the terminal defect is identical to that in GUCY2D/LCA1 (no outer-segment cyclase activity), the two diseases are phenotypically indistinguishable and converge on the same gene-therapy logic: restore the missing protein to restore cyclase localization and photoreceptor survival. The rd3 mouse and rcd2 collie confirm cross-species conservation, and AAV-RD3 rescue in the mouse — mirrored by the clinical success of AAV-GUCY2D (ATSN-101) in the adjacent pathway — provides a direct, credible therapeutic rationale [PMID: 21078983; PMID: 23740938; PMID: 39244273].
| PMID | Title (abbrev.) | Contribution |
|---|---|---|
| 23308101 | Worldwide survey of RD3 mutations | Variant classes, founder p.R38*, rarity (7/852), recurrence risk, phenotype overlap with LCA1 |
| 22531706 | RD3 severe early-onset retinal dystrophy | Homozygous c.180C>A; BCVA ≤1.3 LogMAR by 3 mo; cone-rod dystrophy; 22-yr follow-up; exclusion-mapping diagnosis |
| 21078983 | RD3 required for GC trafficking | Core mechanism: RD3 mediates GC1 ER exit; cell/subcellular localization |
| 24904271 | RD3 in GC trafficking / LCA review | Dual inhibit + traffic role; unstable truncated protein across human/mouse/collie |
| 27471269 | Mapping RD3 interaction sites | Lys87–Leu122 interface; 180–700-fold affinity loss; dual chaperone/inhibitory role |
| 31980596 | GCAP-mediated death + ER stress | Downstream death mechanism in rd3 mouse |
| 31346032 | RetGC activation by calcium sensors | GCAP-driven degeneration; GCAPs as modifiers |
| 23740938 | AAV RD3 gene delivery rescue | Gene-therapy proof of concept; photoreceptor/ERG rescue ≥7 months |
| 39244273 | ATSN-101 GUCY2D phase 1/2 | Clinical translatability of adjacent-pathway AAV therapy |
| 19130129 | Canine RD3 / rcd2 | Dog ortholog model |
| 8486383 | rd3 mouse description | Degeneration time-course; therapeutic-window rationale |
| 23687432 | rd3 retinal transcriptome | Pathway changes (phototransduction down, immune up) |
| 26100624 | RetGC1 dimerization domain | RD3 vs GCAP binding determinants (distinct but overlapping) |
| 36157073 | Structural basis of RetGC regulation | Structural context of RD3/GCAP regulation |
| 30090012 | UPD6 unmasking RD3 variant | Atypical diagnostic mechanism; c.524dupC |
| 41465088 | Qatar IRD genetics | WES recommended first-tier for non-syndromic IRD |
| 40114034 | Asian IRD diagnostic yield | LCA reliably diagnosed vs heterogeneous RP/CRD |
| 41567338 | Screening in consanguineous populations | Carrier screening/counseling for prevention |
| 26247368 | AAV-retGC1 in all-cone LCA1 model | Supports cyclase-pathway gene replacement |
Evidence source legend: human clinical (patient/family cohorts: PMIDs 23308101, 22531706, 30090012, 39244273); model organism (rd3 mouse, rcd2 collie: PMIDs 8486383, 19130129, 23740938, 23687432, 31980596, 31346032); in vitro/biochemical/structural (PMIDs 21078983, 24904271, 27471269, 26100624, 36157073).
Checked with linkml-reference-validator 0.3.0.
| Outcome | Count |
|---|---|
| References checked | 22 |
| Resolved | 22 |
| Unresolved (possible confabulation) | 0 |
| Unverifiable | 0 |
| References weighed for topical relevance | 22 |
| On topic | 16 |
| Off topic | 0 |
All extracted references resolved successfully.
Checked with linkml-term-validator 0.4.5, through the ols: adapter.
| Outcome | Count |
|---|---|
| Terms checked | 27 |
| Resolved | 26 |
| Unresolved (possible confabulation) | 0 |
| Obsolete | 1 |
| Unverifiable | 0 |
| Terms whose name was checked | 11 |
| Terms named correctly | 7 |
| Terms named as a different term | 2 |
| Terms whose name is worth a second look | 2 |
These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:
MONDO:0700235 (2 mentions) - the report calls it "MONDO"; MONDO calls it RD3-related retinopathyCL:0000604 (2 mentions) - the report calls it "Cell types / GO terms: Rod photoreceptor"; CL calls it retinal rod cell**These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:
NCIT:C15368 (Treatment) (1 mention)The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:
HP:0007737 (1 mention) - the report calls it "Bone spicule pigmentation of the retina"; HP calls it Spicular pigmentation of the retina, and lists "Bone spicule pigmentation of the retina" among its other namesGO:0001750 (2 mentions) - the report calls it "Photoreceptor outer segment", "Subcellular level: Photoreceptor outer segment"; GO calls it photoreceptor outer segmentThe report gives these identifiers more than one name of its own:
GO:0001750 - called "Photoreceptor outer segment", "Subcellular level: Photoreceptor outer segment"