Progressive_Retinal_Dystrophy_Due_To_Retinol_Transport_Defect

Disease MONDO:0014060 Pathograph 16 Show in embeddings browser

An autosomal recessive inherited retinal degeneration caused by biallelic loss-of-function variants in RBP4, the gene encoding serum retinol-binding protein 4. RBP4 is the specific plasma carrier that mobilises all-trans-retinol out of hepatic stores and delivers it to peripheral tissues. Without it the liver's vitamin A stores stay full while the circulation is empty, so the retina is starved of the chromophore precursor it needs to regenerate visual pigment. The result is a systemic vitamin A deficiency with a retina-dominant phenotype - childhood night blindness, then progressive rod-cone and retinal pigment epithelial degeneration - accompanied by severe comedogenic acne and, in some patients, iris and chorioretinal coloboma. What separates this from ordinary dietary vitamin A deficiency is a biochemical signature rather than a clinical one: serum RBP4 is undetectable, serum retinol is about one sixth of normal, retinyl esters and transthyretin are normal, and serum retinol fails to rise when vitamin A is given by mouth, because the carrier needed to mobilise it does not exist.

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1
Inheritance
8
Pathophys.
7
Phenotypes
2
Gaps
16
Pathograph
1
Genes
2
Medical Actions
1
Differentials
1
Models
1
Deep Research
👪

Inheritance

1
Autosomal recessive inheritance HP:0000007
Reported pedigrees are consanguineous or compound heterozygous, and the mode of inheritance tracks the variant class: recessive, largely truncating alleles give retinal degeneration, which is this entry. Dominant, almost exclusively missense RBP4 alleles give a different phenotype - ocular malformation of the microphthalmia-anophthalmia-coloboma spectrum - and are not curated here.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:37586836 SUPPORT Human Clinical
"dominantly inherited, almost exclusively missense, associated with ocular malformations, in contrast to recessive, mainly truncating, associated with retinal degeneration"
States the genotype-to-inheritance-to-phenotype split directly, and is the reason this entry is scoped to the recessive retinal-degeneration arm.
PMID:23189188 SUPPORT Human Clinical
"This change segregated with early onset, progressive, and severe autosomal recessive retinitis pigmentosa (arRP) in an eight member consanguineous pedigree of European ancestry."
Segregation in an eight-member consanguineous pedigree establishes the recessive mode for the degenerative phenotype.
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Discussions and Knowledge Gaps

2
Does pharmacological oral vitamin A improve retinal function in RBP4 deficiency, given that serum retinol does not rise on loading?
KNOWLEDGE GAP oral_vitamin_a_efficacy
Attached to
treatments#High-Dose Vitamin A Supplementation
The two pieces of evidence point opposite ways and neither is decisive. The rescue was obtained in Stra6-null mice, where the plasma carrier is intact and only uptake fails - the reverse of this disorder. The human measurement was made in RBP4-deficient patients and showed no rise in serum retinol at all. So the question is whether tissue delivery can improve without a measurable change in the circulating pool, by carrier-independent routes such as chylomicron-borne retinyl esters. The founding paper independently proposed exactly such an alternative source to explain why these patients are not more severely affected systemically.
Proposed experiments
Vitamin A loading in an Rbp4-null model with ocular functional readout
rbp4_null_vitamin_a_ocular_readout
Dose Rbp4-null C57BL/6 mice with pharmacological vitamin A and measure electroretinographic response and ocular retinoid content, rather than serum retinol alone. This tests delivery at the organ that matters in the genotype that matches the human disease.
Would support
pathophysiology#Chromophore Substrate Deprivation at the Retinal Pigment Epithelium
Supporting outcome
  • Recovery of a- and b-wave amplitudes and measurable ocular retinoid content despite unchanged serum retinol.
Refuting outcome
  • No change in ocular retinoid content or electroretinographic response at tolerated doses.
Why do recessive truncating RBP4 alleles cause retinal degeneration while dominant missense alleles cause ocular malformation?
KNOWLEDGE GAP recessive_versus_dominant_arm
Attached to
genetic#RBP4
A single gene producing two phenotypes that differ in inheritance mode, variant class and developmental timing is unusual enough to need an explanation. The proposed mechanism is dominant-negative action of missense alleles on retinoic-acid signalling during eye morphogenesis, with a maternal-effect component from maternal RBP4 status in pregnancy. That would make the malformation arm a developmental disorder of retinoic-acid supply and this entry's arm a postnatal disorder of chromophore supply, from lesions in the same protein. The two arms are not curated as one disease here for that reason.
Show evidence (1 reference)
PMID:37586836 SUPPORT Human Clinical
"The retinoic acid (RA) pathway plays a crucial role in both eye morphogenesis and the visual cycle."
Names the dual role that makes one gene capable of both a developmental and a degenerative phenotype.
⚙

Pathophysiology

8
Biallelic RBP4 Loss of Function
Splice-site, nonsense or destabilising missense variants on both RBP4 alleles. The shared consequence is a null protein outcome rather than a partially functional carrier.
Genetic context variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: LOSS_OF_FUNCTION
Downstream
Absent Circulating Retinol-Binding Protein 4 Message or protein instability leaves no secreted carrier in plasma.
Show evidence (1 reference)
PMID:32323592 SUPPORT Human Clinical
"Homozygous mutations in the RBP4 gene lead to severe retinitis pigmentosa that is phenotypically indistinguishable from retinitis pigmentosa caused by other recessive mutations."
Establishes biallelic RBP4 loss as a cause of the retinal phenotype, and notes that the fundus appearance alone does not identify it.
Absent Circulating Retinol-Binding Protein 4
Serum RBP4 is below detection threshold in every reported patient. This is the node the entry's diagnostic signature reads out directly.
retinol transport GO:0034633 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves retinol transport (GO:0034633), qualified as loss of function. GO:0034633 is a biological process from the Gene Ontology. ⇓ LOSS OF FUNCTION
Downstream
Failure to Mobilise Hepatic Retinol into Plasma RBP4 is the specific carrier for retinol in blood, so its absence removes the only route out of the hepatic store.
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"RBP was below detection threshold, and retinyl esters were normal."
Records the defining pair - no carrier, intact ester stores - in the founding family.
Failure to Mobilise Hepatic Retinol into Plasma
Retinol accumulates in the liver while serum retinol falls. The inverse relation is the point: this is a distribution failure, not a deficiency of vitamin A itself, which is what separates it from dietary deficiency.
Animal models
Rbp4-deficient mouse on the C57BL/6 background Mouse recapitulates Reproduces the defining biochemical dissociation - hepatic retinol retained, serum retinol undetectable.
Downstream
Systemic Retinol Deprivation with Intact Hepatic Stores Circulating retinol falls to roughly one sixth of the normal range.
Show evidence (1 reference)
PMID:26974396 SUPPORT Model Organism
"Our Rbp4-deficient mice accumulated retinol in the liver but it was undetectable in the serum, indicating an inverse relation between serum and liver retinol levels."
Demonstrates the retained-store / empty-circulation dissociation in a controlled model, which human sampling cannot show directly.
Systemic Retinol Deprivation with Intact Hepatic Stores
A whole-organism retinoid shortage in the face of normal intake and normal liver reserves. Tissues that depend on delivered retinol are affected; the retina most severely.
retinoid metabolic process GO:0001523 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased retinoid metabolic process (GO:0001523). GO:0001523 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Chromophore Substrate Deprivation at the Retinal Pigment Epithelium The retinal pigment epithelium depends on delivered retinol as the substrate for the visual cycle.
Reduced Retinoid Tone in Skin Severe childhood-onset acne segregates with the RBP4 genotype. The intermediate steps between low systemic retinoid delivery and follicular keratinisation are not established in these patients, so the edge is typed as having unknown intermediates rather than asserted as direct.
Show evidence (1 reference)
PMID:27892788 SUPPORT Human Clinical
"Bi-allelic mutations in RBP4 were identified (c.248+1G>A), consistent with a diagnosis of inherited vitamin A deficiency."
Frames the disorder as an inherited vitamin A deficiency, which is the claim this node carries.
Chromophore Substrate Deprivation at the Retinal Pigment Epithelium
With no ligand arriving, the retinal pigment epithelium cannot supply 11-cis-retinal to photoreceptors. The uptake machinery at the blood-retina barrier is intact in this disease; it simply has nothing to take up.
retinal pigment epithelial cell CL:0002586 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves retinal pigment epithelial cell (CL:0002586). CL:0002586 is a cell type from the Cell Ontology.
Downstream
Impaired Rhodopsin Regeneration in Rod Photoreceptors Rods are the most retinoid-dependent photoreceptor, so chromophore shortage reaches them first.
Show evidence (1 reference)
PMID:24852372 SUPPORT INDIRECT Model Organism
"This receptor, identified as the Stimulated by retinoic acid gene 6 (Stra6) gene product, is highly expressed in epithelia that constitute blood-tissue barriers."
Establishes that retinol entry into the retinal pigment epithelium is receptor-mediated at a blood-tissue barrier, which is what makes the ligand shortage in this disease bite at this compartment. Graded INDIRECT because the study characterises the receptor, not RBP4 deficiency.
Impaired Rhodopsin Regeneration in Rod Photoreceptors
Without 11-cis-retinal, rod visual pigment cannot be regenerated after bleaching. This is the step that produces the disease's first and most characteristic symptom, and it is functional before it is degenerative - dark-adaptation thresholds rise while photoreceptors are still present.
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.
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
Downstream
Nyctalopia Failure of rod pigment regeneration presents as night blindness from early childhood.
Progressive Photoreceptor and Retinal Pigment Epithelial Degeneration Sustained chromophore starvation is followed by structural loss. The steps between chronic functional deprivation and cell death are not established in this disease, so the edge is typed as having unknown intermediates.
Show evidence (1 reference)
PMID:32323592 SUPPORT Human Clinical
"A 49-year old Caucasian man with a family history of retinitis pigmentosa, presented with low vision and night blindness from early childhood."
Night blindness from early childhood is the presenting complaint this node predicts.
Progressive Photoreceptor and Retinal Pigment Epithelial Degeneration
Structural loss follows the functional deficit: retinal pigment epithelial atrophy, photoreceptor layer loss and peripheral choroidal loss, producing a fundus indistinguishable from other recessive retinitis pigmentosa. The historical name for the appearance is "fundus xerophthalmicus".
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
Animal models
Rbp4-deficient mouse on the C57BL/6 background Mouse recapitulates Reproduces structural loss of the photoreceptor layer and peripheral choroid, persisting to 40 weeks.
Downstream
Reduced visual acuity Loss of photoreceptors and retinal pigment epithelium reduces central acuity, measured at 20/25 to 20/40 in the founding sisters.
Retinal dystrophy Progressive degeneration of photoreceptors and retinal pigment epithelium is the clinical retinal dystrophy.
Show evidence (1 reference)
PMID:23189188 SUPPORT Human Clinical
"Retinitis Pigmentosa (RP) is a common form of retinal degeneration characterized by photoreceptor degeneration and retinal pigment epithelium (RPE) atrophy causing loss of visual field and acuities."
Defines the two-compartment degeneration this node carries.
Reduced Retinoid Tone in Skin
Severe comedogenic acne from childhood, segregating with the genotype within families. It is curated as its own node because it is the one extraocular feature reproducibly tied to the genotype, and because it is what most often brings the systemic nature of the disorder to attention.
Downstream
Acne Reduced retinoid signalling in skin presents as severe childhood-onset acne vulgaris.
Show evidence (1 reference)
PMID:23189188 SUPPORT Human Clinical
"The presence of developmental abnormalities and severe acne in patients with retinal degeneration may indicate the involvement of genes that regulate vitamin A absorption, transport and metabolism."
The authors' own reading of the skin phenotype as a marker of disturbed vitamin A handling.
⬡

Pathograph

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

7
Cardiovascular 1
Patent ductus arteriosus OCCASIONAL HP:0001643 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Patent ductus arteriosus (HP:0001643). HP:0001643 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23189188 SUPPORT Human Clinical
"Additionally, one patient exhibited developmental abnormalities including patent ductus arteriosus and chorioretinal and iris colobomas."
The single reported occurrence, quoted as reported.
Eye 5
Nyctalopia VERY_FREQUENT HP:0000662 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nyctalopia (HP:0000662). HP:0000662 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32323592 SUPPORT Human Clinical
"A 49-year old Caucasian man with a family history of retinitis pigmentosa, presented with low vision and night blindness from early childhood."
Night blindness with childhood onset in a molecularly confirmed patient.
Retinal dystrophy VERY_FREQUENT HP:0000556 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Retinal dystrophy (HP:0000556). HP:0000556 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23189188 SUPPORT Human Clinical
"This change segregated with early onset, progressive, and severe autosomal recessive retinitis pigmentosa (arRP) in an eight member consanguineous pedigree of European ancestry."
Establishes the retinal phenotype and its severity in a segregating pedigree.
Reduced visual acuity 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:9888420 SUPPORT Human Clinical
"Visual acuity was reduced to 20/40 (BR) and 20/25 (MR)."
Quantifies the acuity loss in the founding sisters.
Iris coloboma OCCASIONAL HP:0000612 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Iris coloboma (HP:0000612). HP:0000612 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"Anterior segments were normal except for a discrete iris coloboma."
Records the coloboma as discrete and otherwise isolated, which is what distinguishes it from the dominant malformation phenotype.
Chorioretinal coloboma OCCASIONAL HP:0000567 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Chorioretinal coloboma (HP:0000567). HP:0000567 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23189188 SUPPORT Human Clinical
"Additionally, one patient exhibited developmental abnormalities including patent ductus arteriosus and chorioretinal and iris colobomas."
Reports chorioretinal coloboma in one patient of the pedigree.
Immune 1
Acne FREQUENT HP:0001061 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Acne (HP:0001061). HP:0001061 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32323592 SUPPORT Human Clinical
"Examination of patient's back showed widespread scaring and hyperpigmentation secondary to severe childhood-onset acne vulgaris."
Documents severity and childhood onset of the skin phenotype.
🧬

Genetic Associations

1
RBP4
Gene: RBP4 hgnc:9922 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is RBP4 (hgnc:9922). hgnc:9922 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (3 references)
PMID:23189188 SUPPORT Human Clinical
"Exome sequencing identified a novel homozygous splice site variant (c.111+1G>A) in the gene encoding retinol binding protein 4 (RBP4)."
Identifies the causal gene and a splice-site allele.
PMID:27892788 SUPPORT Human Clinical
"Bi-allelic mutations in RBP4 were identified (c.248+1G>A), consistent with a diagnosis of inherited vitamin A deficiency."
Independent pedigree with a second biallelic splice-site allele.
PMID:9888420 SUPPORT Human Clinical
"To describe the phenotype caused by a retinol deficiency in a family with compound heterozygous missense mutations (Ile41Asn and Gly75Asp) in the gene for serum retinol binding protein (RBP)."
The founding family, and the reason destabilising missense alleles are included in the recessive spectrum rather than only truncating ones.
💊

Medical Actions

2
High-Dose Vitamin A Supplementation
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: all-trans-retinol CHEBI:17336 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses all-trans-retinol (CHEBI:17336). CHEBI:17336 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Empirical, and the evidence for it is genuinely mixed rather than merely thin. The rationale is mass action: enough retinol in the gut may reach tissues by carrier-independent routes even with no RBP4. Against that sits the founding family's dose-response test, in which serum retinol did not rise at all on oral loading - the single most direct human measurement of whether this strategy raises circulating substrate, and it was negative. The supporting rescue result comes from Stra6-null mice, which model the receptor at the far side of the same axis, not RBP4 deficiency itself.
Mechanism Target:
BYPASSES Systemic Retinol Deprivation with Intact Hepatic Stores — Pharmacological dosing aims to raise tissue retinoid delivery without restoring the missing carrier, so it bypasses the lesion rather than correcting it.
Show evidence (2 references)
PMID:24852372 SUPPORT INDIRECT Model Organism
"Notably, treatment with pharmacological doses of vitamin A restored vitamin A transport across these barriers and rescued the vision of Stra6(-/-) mice."
The strongest translational result available, and it is about the wrong gene. Graded INDIRECT because Stra6-null mice lack the uptake receptor while these patients lack the plasma carrier - the same axis, a different lesion, and rescue of one does not establish rescue of the other.
PMID:9888420 REFUTE Human Clinical
"All-trans retinol levels were 0.19 microM and 0.18 microM (normal range, 0.7-1.5 microM) for BR and MR, respectively, and did not increase in a dose-response test."
Graded REFUTE against the claim that oral vitamin A raises circulating retinol in this disorder: it was measured in affected patients and did not.
Show evidence (1 reference)
PMID:24852372 SUPPORT INDIRECT Model Organism
"under conditions mimicking vitamin A excess and deficiency, our analyses revealed that STRA6-mediated vitamin A uptake is a regulated process mandatory for ocular vitamin A uptake when RBP4 constitutes the only transport mode in vitamin A deficiency"
Describes the uptake step this treatment depends on. Graded INDIRECT for the same reason as above - the experiment characterises STRA6, not RBP4 deficiency.
Low Vision Support and Ophthalmological Surveillance
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Platform: Behavioral / lifestyle
Supportive care for a progressive rod-cone dystrophy. No disease-modifying therapy exists, so serial functional assessment - dark adaptometry, electroretinography, acuity and fields - is what management consists of.
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"The two affected sisters, 17 (BR) and 13 (MR) years old, were examined clinically and with perimetry, color vision tests, dark adaptometry, rod- and cone-isolated electroretinograms (ERGs), multifocal ERGs, electrooculograms (EOGs), and laboratory tests."
Enumerates the functional assessments that constitute surveillance in this disorder.
🔬

Biochemical Markers

3
Serum retinol-binding protein 4
Pathograph Readouts
Readout Of Absent Circulating Retinol-Binding Protein 4 Negative
The assay measures the node directly: undetectable serum RBP4 is the absent carrier. Direction is NEGATIVE in the association sense - a higher measured value means less of the linked event.
Show evidence (1 reference)
PMID:23189188 SUPPORT Human Clinical
"Both patients had undetectable levels of RBP4 in the serum suggesting that this mutation led to either mRNA or protein instability resulting in a null phenotype."
The measurement behind this readout, in molecularly confirmed patients.
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"RBP was below detection threshold, and retinyl esters were normal."
Records both the absent carrier and the intact ester pool in one sentence.
Serum all-trans-retinol
Pathograph Readouts
Readout Of Systemic Retinol Deprivation with Intact Hepatic Stores Negative
Serum retinol measures the systemic deprivation node. Its unresponsiveness to oral loading is what distinguishes this node from dietary deficiency, where the same assay rises.
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"All-trans retinol levels were 0.19 microM and 0.18 microM (normal range, 0.7-1.5 microM) for BR and MR, respectively, and did not increase in a dose-response test."
The quantified measurement and its non-response, which is what this readout reports.
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"All-trans retinol levels were 0.19 microM and 0.18 microM (normal range, 0.7-1.5 microM) for BR and MR, respectively, and did not increase in a dose-response test."
Gives the measured deficit against a stated reference range, and the non-response that is diagnostically decisive.
Serum retinyl esters and transthyretin
Show evidence (1 reference)
PMID:23189188 SUPPORT Human Clinical
"Circulating transthyretin levels were normal."
Excludes a transthyretin-side defect in the transport complex.
🔬

Diagnosis

3
Serum retinol-binding protein, retinol and retinyl ester panel
The pattern, not any single value, makes the diagnosis: undetectable RBP4, markedly low retinol, normal retinyl esters, normal transthyretin.
retinoid transport laboratory panel NCIT:C25294 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"Both affected siblings had no detectable serum RBP, one sixth of normal retinol levels, and normal retinyl esters."
States the three-part signature as a single finding.
Oral vitamin A dose-response test
Ordered to separate this disorder from dietary vitamin A deficiency. In dietary deficiency serum retinol rises on loading; here it does not, because the carrier needed to mobilise hepatic stores is absent. A negative result is the informative one.
oral vitamin A loading test NCIT:C25294 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:9888420 SUPPORT Human Clinical
"did not increase in a dose-response test"
The non-response that gives the test its discriminating value.
RBP4 molecular genetic testing
Confirms the diagnosis and, because variant class tracks with phenotype and inheritance mode, also predicts which arm of the RBP4 spectrum the family is in.
RBP4 sequencing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:32323592 SUPPORT Human Clinical
"Next generation sequencing analysis revealed a novel homozygous RBP4 c.67 C > T variant."
Molecular confirmation in a clinically diagnosed patient.
🔀

Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from Progressive_Retinal_Dystrophy_Due_To_Retinol_Transport_Defect:

Dietary vitamin A deficiency
Overlapping Features The phenocopy that matters, and the reason the biochemical panel is ordered the way it is. Acquired hypovitaminosis A produces overlapping retinal dysfunction - impaired scotopic responses, constricted fields - but it is corrected by supplementation, features prominent xerophthalmia, and leaves RBP4 present and retinyl esters low. The inherited transport defect inverts all three: RBP4 undetectable, retinyl esters normal, and no response to oral loading. Notably the founding patients had no xerophthalmia at all, which the authors attributed to normal retinol in tear fluid.
Show evidence (3 references)
PMID:9888420 SUPPORT Human Clinical
"The normal retinol levels in the tear fluid explain the lack of xerophthalmia."
Explains the absence of the one sign that would be expected in dietary deficiency, which is the clinical half of the discriminator.
PMID:17646742 SUPPORT Human Clinical
"The ophthalmologic findings were keratoconjunctival xerosis with bilateral corneal ulcerations. The visual field showed a concentric bilateral restriction of isopters with tubular central vision, a similar aspect to retinitis pigmentosa."
A worked case of the acquired phenocopy. It shows both halves of the comparison at once - a field defect that mimics retinitis pigmentosa, and the corneal xerosis that inherited transport failure does not produce.
PMID:17646742 SUPPORT Human Clinical
"Corneoconjunctival improvement was obtained with vitamin supplementation, but no campimetric improvement was observed."
The response to supplementation is the decisive discriminator: in dietary deficiency the ocular surface recovers on vitamin A, whereas in RBP4 deficiency serum retinol does not even rise. Worth noting that the retinal field defect did not recover here either, which is why the distinction rests on the biochemistry rather than on treatment response alone.
🐁

Animal Models

1
Rbp4-deficient mouse on the C57BL/6 background
The strain that made the model informative. Rbp4-null mice on a mixed 129xC57BL/6J background have only a transient b-wave deficit that recovers by 24 weeks; moving the same null onto pure C57BL/6 produced a severe, non-recovering phenotype. Background choice, not the null itself, is what separates a model that recapitulates the human disease from one that appears to outgrow it.
Species
Mouse
Genotype
Rbp4 knockout, C57BL/6 genetic background
Publication
PMID:26974396
Pathograph links
Failure to Mobilise Hepatic Retinol into Plasma recapitulates fidelity: high Reproduces the defining biochemical dissociation - hepatic retinol retained, serum retinol undetectable.
Limitations: Mice were maintained on a vitamin A-sufficient diet, so the model speaks to transport failure under adequate intake and not to how the disorder behaves when dietary supply is also limited.
Readouts
Serum versus hepatic retinol
Direction: DECREASED
Interpretation: Serum retinol undetectable while liver retinol accumulates, establishing the direction of the block as export rather than uptake or storage.
Show evidence (1 reference)
PMID:26974396 SUPPORT Model Organism
"Our Rbp4-deficient mice accumulated retinol in the liver but it was undetectable in the serum, indicating an inverse relation between serum and liver retinol levels."
Reports the paired measurement behind this readout.
Show evidence (1 reference)
PMID:26974396 SUPPORT Model Organism
"Our results suggest that RBP4 is critical for the mobilization of retinol from hepatic storage pools, and that such mobilization is necessary for ocular development and visual function."
Supports treating this model as informative for the mobilisation node.
Progressive Photoreceptor and Retinal Pigment Epithelial Degeneration recapitulates fidelity: moderate Reproduces structural loss of the photoreceptor layer and peripheral choroid, persisting to 40 weeks.
Limitations: The mouse phenotype includes developmental abnormalities - retinal depigmentation, optic disc abnormality and a persistent hyaloid artery - that are not features of the human recessive disorder, so the model runs ahead of the human phenotype on the developmental axis while matching it on the degenerative one.
Readouts
Peripheral choroid and photoreceptor layer
Direction: DECREASED
Interpretation: Structural correlate of the degeneration node, present on the C57BL/6 background and absent on the mixed background.
Show evidence (1 reference)
PMID:26974396 SUPPORT Model Organism
"loss of the peripheral choroid and photoreceptor layer in the peripheral retinas"
The histological measurement behind this readout.
Show evidence (1 reference)
PMID:26974396 SUPPORT Model Organism
"All these abnormalities had not recovered even at 40 weeks of age."
Persistence to 40 weeks is what makes this strain a model of progressive degeneration rather than of transient developmental delay.
{ }

Source YAML

click to show 
name: Progressive_Retinal_Dystrophy_Due_To_Retinol_Transport_Defect
category: Disease
creation_date: "2026-09-01T22:40:00Z"
description: >-
  An autosomal recessive inherited retinal degeneration caused by biallelic
  loss-of-function variants in RBP4, the gene encoding serum retinol-binding
  protein 4. RBP4 is the specific plasma carrier that mobilises all-trans-retinol
  out of hepatic stores and delivers it to peripheral tissues. Without it the
  liver's vitamin A stores stay full while the circulation is empty, so the
  retina is starved of the chromophore precursor it needs to regenerate visual
  pigment. The result is a systemic vitamin A deficiency with a retina-dominant
  phenotype - childhood night blindness, then progressive rod-cone and retinal
  pigment epithelial degeneration - accompanied by severe comedogenic acne and,
  in some patients, iris and chorioretinal coloboma.

  What separates this from ordinary dietary vitamin A deficiency is a
  biochemical signature rather than a clinical one: serum RBP4 is undetectable,
  serum retinol is about one sixth of normal, retinyl esters and transthyretin
  are normal, and serum retinol fails to rise when vitamin A is given by mouth,
  because the carrier needed to mobilise it does not exist.
disease_term:
  preferred_term: progressive retinal dystrophy due to retinol transport defect
  term:
    id: MONDO:0014060
    label: progressive retinal dystrophy due to retinol transport defect

inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Reported pedigrees are consanguineous or compound heterozygous, and the
    mode of inheritance tracks the variant class: recessive, largely truncating
    alleles give retinal degeneration, which is this entry. Dominant, almost
    exclusively missense RBP4 alleles give a different phenotype - ocular
    malformation of the microphthalmia-anophthalmia-coloboma spectrum - and are
    not curated here.
  evidence:
  - reference: PMID:37586836
    reference_title: Clinical, genetic and biochemical signatures of RBP4-related ocular malformations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      dominantly inherited, almost exclusively missense, associated with ocular
      malformations, in contrast to recessive, mainly truncating, associated
      with retinal degeneration
    explanation: >-
      States the genotype-to-inheritance-to-phenotype split directly, and is the
      reason this entry is scoped to the recessive retinal-degeneration arm.
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This change segregated with early onset, progressive, and severe autosomal
      recessive retinitis pigmentosa (arRP) in an eight member consanguineous
      pedigree of European ancestry.
    explanation: >-
      Segregation in an eight-member consanguineous pedigree establishes the
      recessive mode for the degenerative phenotype.

genetic:
- name: RBP4
  gene_term:
    preferred_term: RBP4
    term:
      id: hgnc:9922
      label: RBP4
  relationship_type: CAUSATIVE
  notes: >-
    Reported recessive alleles span splice-site (c.111+1G>A, c.248+1G>A),
    nonsense (c.67C>T) and destabilising missense (Ile41Asn, Gly75Asp)
    variants. What unites them is the biochemical outcome rather than the
    variant class: serum RBP4 is undetectable in every reported patient, so the
    mechanism is absence of the carrier rather than a defective transport
    complex.
  evidence:
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Exome sequencing identified a novel homozygous splice site variant
      (c.111+1G>A) in the gene encoding retinol binding protein 4 (RBP4).
    explanation: Identifies the causal gene and a splice-site allele.
  - reference: PMID:27892788
    reference_title: "Vitamin A deficiency due to bi-allelic mutation of RBP4: There's more to it than meets the eye."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Bi-allelic mutations in RBP4 were identified (c.248+1G>A), consistent with
      a diagnosis of inherited vitamin A deficiency.
    explanation: Independent pedigree with a second biallelic splice-site allele.
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To describe the phenotype caused by a retinol deficiency in a family with
      compound heterozygous missense mutations (Ile41Asn and Gly75Asp) in the
      gene for serum retinol binding protein (RBP).
    explanation: >-
      The founding family, and the reason destabilising missense alleles are
      included in the recessive spectrum rather than only truncating ones.

pathophysiology:
- name: Biallelic RBP4 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Splice-site, nonsense or destabilising missense variants on both RBP4
    alleles. The shared consequence is a null protein outcome rather than a
    partially functional carrier.
  genetic_context:
    functional_impact_category: LOSS_OF_FUNCTION
    zygosity: HOMOZYGOUS
    variant_origin: GERMLINE
  downstream:
  - target: Absent Circulating Retinol-Binding Protein 4
    causal_link_type: DIRECT
    description: >-
      Message or protein instability leaves no secreted carrier in plasma.
    evidence:
    - reference: PMID:23189188
      reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Both patients had undetectable levels of RBP4 in the serum suggesting
        that this mutation led to either mRNA or protein instability resulting
        in a null phenotype.
      explanation: >-
        Directly links the genotype to absence of circulating protein, and names
        the null mechanism.
  evidence:
  - reference: PMID:32323592
    reference_title: A novel homozygous c.67C>T variant in retinol binding protein 4 (RBP4) associated with retinitis pigmentosa and childhood acne vulgaris.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Homozygous mutations in the RBP4 gene lead to severe retinitis pigmentosa
      that is phenotypically indistinguishable from retinitis pigmentosa caused
      by other recessive mutations.
    explanation: >-
      Establishes biallelic RBP4 loss as a cause of the retinal phenotype, and
      notes that the fundus appearance alone does not identify it.

- name: Absent Circulating Retinol-Binding Protein 4
  biological_scale: MOLECULAR
  description: >-
    Serum RBP4 is below detection threshold in every reported patient. This is
    the node the entry's diagnostic signature reads out directly.
  biological_processes:
  - preferred_term: retinol transport
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0034633
      label: retinol transport
  downstream:
  - target: Failure to Mobilise Hepatic Retinol into Plasma
    causal_link_type: DIRECT
    description: >-
      RBP4 is the specific carrier for retinol in blood, so its absence removes
      the only route out of the hepatic store.
    evidence:
    - reference: PMID:26974396
      reference_title: Severe ocular phenotypes in Rbp4-deficient mice in the C57BL/6 genetic background.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our results suggest that RBP4 is critical for the mobilization of
        retinol from hepatic storage pools, and that such mobilization is
        necessary for ocular development and visual function.
      explanation: >-
        The authors' own conclusion that mobilisation, not synthesis or storage,
        is the step RBP4 carries.
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: RBP was below detection threshold, and retinyl esters were normal.
    explanation: >-
      Records the defining pair - no carrier, intact ester stores - in the
      founding family.

- name: Failure to Mobilise Hepatic Retinol into Plasma
  biological_scale: ORGANISM
  description: >-
    Retinol accumulates in the liver while serum retinol falls. The inverse
    relation is the point: this is a distribution failure, not a deficiency of
    vitamin A itself, which is what separates it from dietary deficiency.
  downstream:
  - target: Systemic Retinol Deprivation with Intact Hepatic Stores
    causal_link_type: DIRECT
    description: >-
      Circulating retinol falls to roughly one sixth of the normal range.
    evidence:
    - reference: PMID:9888420
      reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All-trans retinol levels were 0.19 microM and 0.18 microM (normal range,
        0.7-1.5 microM) for BR and MR, respectively, and did not increase in a
        dose-response test.
      explanation: >-
        Quantifies the deficit and, in the same sentence, shows it cannot be
        corrected by oral loading.
  evidence:
  - reference: PMID:26974396
    reference_title: Severe ocular phenotypes in Rbp4-deficient mice in the C57BL/6 genetic background.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Our Rbp4-deficient mice accumulated retinol in the liver but it was
      undetectable in the serum, indicating an inverse relation between serum
      and liver retinol levels.
    explanation: >-
      Demonstrates the retained-store / empty-circulation dissociation in a
      controlled model, which human sampling cannot show directly.

- name: Systemic Retinol Deprivation with Intact Hepatic Stores
  biological_scale: ORGANISM
  description: >-
    A whole-organism retinoid shortage in the face of normal intake and normal
    liver reserves. Tissues that depend on delivered retinol are affected; the
    retina most severely.
  biological_processes:
  - preferred_term: retinoid metabolic process
    modifier: DECREASED
    term:
      id: GO:0001523
      label: retinoid metabolic process
  downstream:
  - target: Chromophore Substrate Deprivation at the Retinal Pigment Epithelium
    causal_link_type: DIRECT
    description: >-
      The retinal pigment epithelium depends on delivered retinol as the
      substrate for the visual cycle.
    evidence:
    - reference: PMID:32323592
      reference_title: A novel homozygous c.67C>T variant in retinol binding protein 4 (RBP4) associated with retinitis pigmentosa and childhood acne vulgaris.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The retinol binding protein 4 (RBP4) is essential in delivering retinol
        to the retinal pigment epithelium and normal functioning of the visual
        cycle.
      explanation: >-
        Names the delivery step and the compartment that fails when it is lost.
  - target: Reduced Retinoid Tone in Skin
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Severe childhood-onset acne segregates with the RBP4 genotype. The
      intermediate steps between low systemic retinoid delivery and follicular
      keratinisation are not established in these patients, so the edge is typed
      as having unknown intermediates rather than asserted as direct.
    evidence:
    - reference: PMID:32323592
      reference_title: A novel homozygous c.67C>T variant in retinol binding protein 4 (RBP4) associated with retinitis pigmentosa and childhood acne vulgaris.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Patient's affected brother, positive for the same homozygous variant,
        also had a history of severe acne vulgaris whereas the unaffected
        brother did not, confirming that mutations in RBP4 segregated with the
        acne vulgaris phenotype in this family.
      explanation: >-
        Within-family segregation ties the skin phenotype to the genotype.
        Graded INDIRECT because co-segregation establishes that the lesion
        causes the phenotype without showing the retinoid step that mediates it.
  evidence:
  - reference: PMID:27892788
    reference_title: "Vitamin A deficiency due to bi-allelic mutation of RBP4: There's more to it than meets the eye."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Bi-allelic mutations in RBP4 were identified (c.248+1G>A), consistent with
      a diagnosis of inherited vitamin A deficiency.
    explanation: >-
      Frames the disorder as an inherited vitamin A deficiency, which is the
      claim this node carries.

- name: Chromophore Substrate Deprivation at the Retinal Pigment Epithelium
  biological_scale: TISSUE
  description: >-
    With no ligand arriving, the retinal pigment epithelium cannot supply
    11-cis-retinal to photoreceptors. The uptake machinery at the blood-retina
    barrier is intact in this disease; it simply has nothing to take up.
  cell_types:
  - preferred_term: retinal pigment epithelial cell
    term:
      id: CL:0002586
      label: retinal pigment epithelial cell
  downstream:
  - target: Impaired Rhodopsin Regeneration in Rod Photoreceptors
    causal_link_type: DIRECT
    description: >-
      Rods are the most retinoid-dependent photoreceptor, so chromophore
      shortage reaches them first.
    evidence:
    - reference: PMID:24852372
      reference_title: STRA6 is critical for cellular vitamin A uptake and homeostasis.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Vitamin A must be adequately distributed within the body to maintain the
        functions of retinoids in the periphery and chromophore production in
        the eyes.
      explanation: >-
        States the dependency this edge asserts - ocular chromophore production
        requires adequate systemic distribution. Graded INDIRECT because it is a
        general statement of the dependency rather than a measurement made in
        RBP4 deficiency.
  evidence:
  - reference: PMID:24852372
    reference_title: STRA6 is critical for cellular vitamin A uptake and homeostasis.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      This receptor, identified as the Stimulated by retinoic acid gene 6
      (Stra6) gene product, is highly expressed in epithelia that constitute
      blood-tissue barriers.
    explanation: >-
      Establishes that retinol entry into the retinal pigment epithelium is
      receptor-mediated at a blood-tissue barrier, which is what makes the
      ligand shortage in this disease bite at this compartment. Graded INDIRECT
      because the study characterises the receptor, not RBP4 deficiency.

- name: Impaired Rhodopsin Regeneration in Rod Photoreceptors
  biological_scale: CELLULAR
  description: >-
    Without 11-cis-retinal, rod visual pigment cannot be regenerated after
    bleaching. This is the step that produces the disease's first and most
    characteristic symptom, and it is functional before it is degenerative -
    dark-adaptation thresholds rise while photoreceptors are still present.
  cell_types:
  - preferred_term: retinal rod cell
    term:
      id: CL:0000604
      label: retinal rod cell
  biological_processes:
  - preferred_term: visual perception
    modifier: DECREASED
    term:
      id: GO:0007601
      label: visual perception
  downstream:
  - target: Nyctalopia
    causal_link_type: DIRECT
    description: >-
      Failure of rod pigment regeneration presents as night blindness from early
      childhood.
    evidence:
    - reference: PMID:9888420
      reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Dark adaptation thresholds were elevated. In the scotopic ERG, only
        reduced mixed responses were recordable.
      explanation: >-
        Elevated dark-adaptation thresholds with reduced scotopic responses is
        the functional signature of impaired rod pigment regeneration.
  - target: Progressive Photoreceptor and Retinal Pigment Epithelial Degeneration
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Sustained chromophore starvation is followed by structural loss. The steps
      between chronic functional deprivation and cell death are not established
      in this disease, so the edge is typed as having unknown intermediates.
    evidence:
    - reference: PMID:41829974
      reference_title: "The Liver-Eye Axis of Dietary Vitamin A Homeostasis: A Review of Mechanisms, Receptors, and Visual Outcomes."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: OTHER
      snippet: >-
        Tight regulation of retinoid delivery to peripheral tissues is crucial
        for metabolic function and photoreceptor integrity.
      explanation: >-
        Links delivery to structural integrity rather than to function alone.
        Graded INDIRECT because it is a review's framing statement, and OTHER
        because the source is a review rather than a primary study.
  evidence:
  - reference: PMID:32323592
    reference_title: A novel homozygous c.67C>T variant in retinol binding protein 4 (RBP4) associated with retinitis pigmentosa and childhood acne vulgaris.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 49-year old Caucasian man with a family history of retinitis pigmentosa,
      presented with low vision and night blindness from early childhood.
    explanation: >-
      Night blindness from early childhood is the presenting complaint this node
      predicts.

- name: Progressive Photoreceptor and Retinal Pigment Epithelial Degeneration
  biological_scale: TISSUE
  description: >-
    Structural loss follows the functional deficit: retinal pigment epithelial
    atrophy, photoreceptor layer loss and peripheral choroidal loss, producing a
    fundus indistinguishable from other recessive retinitis pigmentosa. The
    historical name for the appearance is "fundus xerophthalmicus".
  cell_types:
  - preferred_term: retinal cone cell
    term:
      id: CL:0000573
      label: retinal cone cell
  biological_processes:
  - preferred_term: photoreceptor cell maintenance
    modifier: DECREASED
    term:
      id: GO:0045494
      label: photoreceptor cell maintenance
  downstream:
  - target: Reduced visual acuity
    causal_link_type: DIRECT
    description: >-
      Loss of photoreceptors and retinal pigment epithelium reduces central
      acuity, measured at 20/25 to 20/40 in the founding sisters.
    evidence:
    - reference: PMID:9888420
      reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Visual acuity was reduced to 20/40 (BR) and 20/25 (MR).
      explanation: >-
        Quantifies the acuity endpoint in the same patients whose retinal
        pigment epithelial atrophy is documented.
  - target: Retinal dystrophy
    causal_link_type: DIRECT
    description: >-
      Progressive degeneration of photoreceptors and retinal pigment epithelium
      is the clinical retinal dystrophy.
    evidence:
    - reference: PMID:9888420
      reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Both patients showed a typical "fundus xerophthalmicus," featuring a
        progressed atrophy of the retinal pigment epithelium.
      explanation: >-
        Records the structural endpoint at the retinal pigment epithelium in the
        founding family.
  evidence:
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Retinitis Pigmentosa (RP) is a common form of retinal degeneration
      characterized by photoreceptor degeneration and retinal pigment epithelium
      (RPE) atrophy causing loss of visual field and acuities.
    explanation: >-
      Defines the two-compartment degeneration this node carries.

- name: Reduced Retinoid Tone in Skin
  biological_scale: TISSUE
  description: >-
    Severe comedogenic acne from childhood, segregating with the genotype within
    families. It is curated as its own node because it is the one extraocular
    feature reproducibly tied to the genotype, and because it is what most often
    brings the systemic nature of the disorder to attention.
  downstream:
  - target: Acne
    causal_link_type: DIRECT
    description: >-
      Reduced retinoid signalling in skin presents as severe childhood-onset
      acne vulgaris.
    evidence:
    - reference: PMID:23189188
      reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The second patient developed acne from young age and extending into the
        5(th) decade.
      explanation: >-
        Documents the onset and persistence of the skin phenotype.
  evidence:
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The presence of developmental abnormalities and severe acne in patients
      with retinal degeneration may indicate the involvement of genes that
      regulate vitamin A absorption, transport and metabolism.
    explanation: >-
      The authors' own reading of the skin phenotype as a marker of disturbed
      vitamin A handling.

phenotypes:
- category: Ocular
  name: Nyctalopia
  description: >-
    Night blindness from early childhood is the presenting symptom and the
    earliest functional consequence of chromophore deprivation.
  phenotype_term:
    preferred_term: Nyctalopia
    term:
      id: HP:0000662
      label: Nyctalopia
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:32323592
    reference_title: A novel homozygous c.67C>T variant in retinol binding protein 4 (RBP4) associated with retinitis pigmentosa and childhood acne vulgaris.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 49-year old Caucasian man with a family history of retinitis pigmentosa,
      presented with low vision and night blindness from early childhood.
    explanation: Night blindness with childhood onset in a molecularly confirmed patient.
- category: Ocular
  name: Retinal dystrophy
  description: >-
    Progressive rod-cone degeneration with retinal pigment epithelial atrophy,
    clinically indistinguishable from other recessive retinitis pigmentosa.
  phenotype_term:
    preferred_term: Retinal dystrophy
    term:
      id: HP:0000556
      label: Retinal dystrophy
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This change segregated with early onset, progressive, and severe autosomal
      recessive retinitis pigmentosa (arRP) in an eight member consanguineous
      pedigree of European ancestry.
    explanation: Establishes the retinal phenotype and its severity in a segregating pedigree.
- category: Ocular
  name: Reduced visual acuity
  phenotype_term:
    preferred_term: Reduced visual acuity
    term:
      id: HP:0007663
      label: Reduced visual acuity
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Visual acuity was reduced to 20/40 (BR) and 20/25 (MR).
    explanation: Quantifies the acuity loss in the founding sisters.
- category: Ocular
  name: Iris coloboma
  description: >-
    Reported in recessive patients as a discrete defect, distinct from the
    severe microphthalmia-anophthalmia-coloboma spectrum seen with dominant
    missense alleles.
  phenotype_term:
    preferred_term: Iris coloboma
    term:
      id: HP:0000612
      label: Iris coloboma
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Anterior segments were normal except for a discrete iris coloboma.
    explanation: >-
      Records the coloboma as discrete and otherwise isolated, which is what
      distinguishes it from the dominant malformation phenotype.
- category: Ocular
  name: Chorioretinal coloboma
  phenotype_term:
    preferred_term: Chorioretinal coloboma
    term:
      id: HP:0000567
      label: Chorioretinal coloboma
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Additionally, one patient exhibited developmental abnormalities including
      patent ductus arteriosus and chorioretinal and iris colobomas.
    explanation: Reports chorioretinal coloboma in one patient of the pedigree.
- category: Dermatological
  name: Acne
  description: >-
    Severe comedogenic acne beginning in childhood and persisting into adult
    life, segregating with the RBP4 genotype within families.
  phenotype_term:
    preferred_term: Acne
    term:
      id: HP:0001061
      label: Acne
  frequency: FREQUENT
  evidence:
  - reference: PMID:32323592
    reference_title: A novel homozygous c.67C>T variant in retinol binding protein 4 (RBP4) associated with retinitis pigmentosa and childhood acne vulgaris.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Examination of patient's back showed widespread scaring and
      hyperpigmentation secondary to severe childhood-onset acne vulgaris.
    explanation: Documents severity and childhood onset of the skin phenotype.
- category: Cardiovascular
  name: Patent ductus arteriosus
  description: >-
    Reported in a single patient. Curated because retinoid signalling has an
    established role in organogenesis, but the frequency is a single case and it
    is not part of the core phenotype.
  phenotype_term:
    preferred_term: Patent ductus arteriosus
    term:
      id: HP:0001643
      label: Patent ductus arteriosus
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Additionally, one patient exhibited developmental abnormalities including
      patent ductus arteriosus and chorioretinal and iris colobomas.
    explanation: The single reported occurrence, quoted as reported.

biochemical:
- name: Serum retinol-binding protein 4
  readouts:
  - target: Absent Circulating Retinol-Binding Protein 4
    relationship: READOUT_OF
    direction: NEGATIVE
    interpretation: >-
      The assay measures the node directly: undetectable serum RBP4 is the
      absent carrier. Direction is NEGATIVE in the association sense - a higher
      measured value means less of the linked event.
    evidence:
    - reference: PMID:23189188
      reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Both patients had undetectable levels of RBP4 in the serum suggesting
        that this mutation led to either mRNA or protein instability resulting
        in a null phenotype.
      explanation: The measurement behind this readout, in molecularly confirmed patients.
  notes: >-
    Decreased - undetectable rather than merely low. This is the single most discriminating
    laboratory finding, and it is what separates the disorder from dietary
    vitamin A deficiency, where RBP4 is present.
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: RBP was below detection threshold, and retinyl esters were normal.
    explanation: Records both the absent carrier and the intact ester pool in one sentence.
- name: Serum all-trans-retinol
  readouts:
  - target: Systemic Retinol Deprivation with Intact Hepatic Stores
    relationship: READOUT_OF
    direction: NEGATIVE
    interpretation: >-
      Serum retinol measures the systemic deprivation node. Its
      unresponsiveness to oral loading is what distinguishes this node from
      dietary deficiency, where the same assay rises.
    evidence:
    - reference: PMID:9888420
      reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All-trans retinol levels were 0.19 microM and 0.18 microM (normal range,
        0.7-1.5 microM) for BR and MR, respectively, and did not increase in a
        dose-response test.
      explanation: >-
        The quantified measurement and its non-response, which is what this
        readout reports.
  notes: >-
    Decreased to roughly one sixth of the normal range, and - critically - it does not rise
    on oral vitamin A loading, because the carrier required to mobilise hepatic
    stores is absent.
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All-trans retinol levels were 0.19 microM and 0.18 microM (normal range,
      0.7-1.5 microM) for BR and MR, respectively, and did not increase in a
      dose-response test.
    explanation: >-
      Gives the measured deficit against a stated reference range, and the
      non-response that is diagnostically decisive.
- name: Serum retinyl esters and transthyretin
  notes: >-
    Both normal. Recorded as a normal result because their normality is
    informative: it localises the lesion to the carrier rather than to intake,
    storage, or the stabilising partner.
  evidence:
  - reference: PMID:23189188
    reference_title: Exome analysis identified a novel mutation in the RBP4 gene in a consanguineous pedigree with retinal dystrophy and developmental abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Circulating transthyretin levels were normal.
    explanation: Excludes a transthyretin-side defect in the transport complex.

animal_models:
- name: Rbp4-deficient mouse on the C57BL/6 background
  species: Mouse
  genotype: Rbp4 knockout, C57BL/6 genetic background
  publication: PMID:26974396
  description: >-
    The strain that made the model informative. Rbp4-null mice on a mixed
    129xC57BL/6J background have only a transient b-wave deficit that recovers
    by 24 weeks; moving the same null onto pure C57BL/6 produced a severe,
    non-recovering phenotype. Background choice, not the null itself, is what
    separates a model that recapitulates the human disease from one that
    appears to outgrow it.
  modeled_mechanisms:
  - target: Failure to Mobilise Hepatic Retinol into Plasma
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces the defining biochemical dissociation - hepatic retinol
      retained, serum retinol undetectable.
    limitations: >-
      Mice were maintained on a vitamin A-sufficient diet, so the model speaks
      to transport failure under adequate intake and not to how the disorder
      behaves when dietary supply is also limited.
    readouts:
    - name: Serum versus hepatic retinol
      target: Failure to Mobilise Hepatic Retinol into Plasma
      direction: DECREASED
      interpretation: >-
        Serum retinol undetectable while liver retinol accumulates, establishing
        the direction of the block as export rather than uptake or storage.
      evidence:
      - reference: PMID:26974396
        reference_title: Severe ocular phenotypes in Rbp4-deficient mice in the C57BL/6 genetic background.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Our Rbp4-deficient mice accumulated retinol in the liver but it was
          undetectable in the serum, indicating an inverse relation between
          serum and liver retinol levels.
        explanation: Reports the paired measurement behind this readout.
    evidence:
    - reference: PMID:26974396
      reference_title: Severe ocular phenotypes in Rbp4-deficient mice in the C57BL/6 genetic background.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our results suggest that RBP4 is critical for the mobilization of
        retinol from hepatic storage pools, and that such mobilization is
        necessary for ocular development and visual function.
      explanation: Supports treating this model as informative for the mobilisation node.
  - target: Progressive Photoreceptor and Retinal Pigment Epithelial Degeneration
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces structural loss of the photoreceptor layer and peripheral
      choroid, persisting to 40 weeks.
    limitations: >-
      The mouse phenotype includes developmental abnormalities - retinal
      depigmentation, optic disc abnormality and a persistent hyaloid artery -
      that are not features of the human recessive disorder, so the model runs
      ahead of the human phenotype on the developmental axis while matching it
      on the degenerative one.
    readouts:
    - name: Peripheral choroid and photoreceptor layer
      target: Progressive Photoreceptor and Retinal Pigment Epithelial Degeneration
      direction: DECREASED
      interpretation: >-
        Structural correlate of the degeneration node, present on the C57BL/6
        background and absent on the mixed background.
      evidence:
      - reference: PMID:26974396
        reference_title: Severe ocular phenotypes in Rbp4-deficient mice in the C57BL/6 genetic background.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          loss of the peripheral choroid and photoreceptor layer in the
          peripheral retinas
        explanation: The histological measurement behind this readout.
    evidence:
    - reference: PMID:26974396
      reference_title: Severe ocular phenotypes in Rbp4-deficient mice in the C57BL/6 genetic background.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        All these abnormalities had not recovered even at 40 weeks of age.
      explanation: >-
        Persistence to 40 weeks is what makes this strain a model of progressive
        degeneration rather than of transient developmental delay.

diagnosis:
- name: Serum retinol-binding protein, retinol and retinyl ester panel
  diagnosis_term:
    preferred_term: retinoid transport laboratory panel
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  description: >-
    The pattern, not any single value, makes the diagnosis: undetectable RBP4,
    markedly low retinol, normal retinyl esters, normal transthyretin.
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both affected siblings had no detectable serum RBP, one sixth of normal
      retinol levels, and normal retinyl esters.
    explanation: States the three-part signature as a single finding.
- name: Oral vitamin A dose-response test
  diagnosis_term:
    preferred_term: oral vitamin A loading test
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  description: >-
    Ordered to separate this disorder from dietary vitamin A deficiency. In
    dietary deficiency serum retinol rises on loading; here it does not, because
    the carrier needed to mobilise hepatic stores is absent. A negative result
    is the informative one.
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: did not increase in a dose-response test
    explanation: The non-response that gives the test its discriminating value.
- name: RBP4 molecular genetic testing
  diagnosis_term:
    preferred_term: RBP4 sequencing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: >-
    Confirms the diagnosis and, because variant class tracks with phenotype and
    inheritance mode, also predicts which arm of the RBP4 spectrum the family is
    in.
  evidence:
  - reference: PMID:32323592
    reference_title: A novel homozygous c.67C>T variant in retinol binding protein 4 (RBP4) associated with retinitis pigmentosa and childhood acne vulgaris.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Next generation sequencing analysis revealed a novel homozygous RBP4 c.67
      C > T variant.
    explanation: Molecular confirmation in a clinically diagnosed patient.

treatments:
- name: High-Dose Vitamin A Supplementation
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Empirical, and the evidence for it is genuinely mixed rather than merely
    thin. The rationale is mass action: enough retinol in the gut may reach
    tissues by carrier-independent routes even with no RBP4. Against that sits
    the founding family's dose-response test, in which serum retinol did not
    rise at all on oral loading - the single most direct human measurement of
    whether this strategy raises circulating substrate, and it was negative.
    The supporting rescue result comes from Stra6-null mice, which model the
    receptor at the far side of the same axis, not RBP4 deficiency itself.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: all-trans-retinol
      term:
        id: CHEBI:17336
        label: all-trans-retinol
  target_mechanisms:
  - target: Systemic Retinol Deprivation with Intact Hepatic Stores
    treatment_effect: BYPASSES
    description: >-
      Pharmacological dosing aims to raise tissue retinoid delivery without
      restoring the missing carrier, so it bypasses the lesion rather than
      correcting it.
    evidence:
    - reference: PMID:24852372
      reference_title: STRA6 is critical for cellular vitamin A uptake and homeostasis.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Notably, treatment with pharmacological doses of vitamin A restored
        vitamin A transport across these barriers and rescued the vision of
        Stra6(-/-) mice.
      explanation: >-
        The strongest translational result available, and it is about the wrong
        gene. Graded INDIRECT because Stra6-null mice lack the uptake receptor
        while these patients lack the plasma carrier - the same axis, a
        different lesion, and rescue of one does not establish rescue of the
        other.
    - reference: PMID:9888420
      reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
      supports: REFUTE
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All-trans retinol levels were 0.19 microM and 0.18 microM (normal range,
        0.7-1.5 microM) for BR and MR, respectively, and did not increase in a
        dose-response test.
      explanation: >-
        Graded REFUTE against the claim that oral vitamin A raises circulating
        retinol in this disorder: it was measured in affected patients and did
        not.
  evidence:
  - reference: PMID:24852372
    reference_title: STRA6 is critical for cellular vitamin A uptake and homeostasis.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      under conditions mimicking vitamin A excess and deficiency, our analyses
      revealed that STRA6-mediated vitamin A uptake is a regulated process
      mandatory for ocular vitamin A uptake when RBP4 constitutes the only
      transport mode in vitamin A deficiency
    explanation: >-
      Describes the uptake step this treatment depends on. Graded INDIRECT for
      the same reason as above - the experiment characterises STRA6, not RBP4
      deficiency.

- name: Low Vision Support and Ophthalmological Surveillance
  therapeutic_modality: BEHAVIORAL
  description: >-
    Supportive care for a progressive rod-cone dystrophy. No disease-modifying
    therapy exists, so serial functional assessment - dark adaptometry,
    electroretinography, acuity and fields - is what management consists of.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The two affected sisters, 17 (BR) and 13 (MR) years old, were examined
      clinically and with perimetry, color vision tests, dark adaptometry, rod-
      and cone-isolated electroretinograms (ERGs), multifocal ERGs,
      electrooculograms (EOGs), and laboratory tests.
    explanation: >-
      Enumerates the functional assessments that constitute surveillance in this
      disorder.

differential_diagnoses:
- name: Dietary vitamin A deficiency
  description: >-
    The phenocopy that matters, and the reason the biochemical panel is ordered
    the way it is. Acquired hypovitaminosis A produces overlapping retinal
    dysfunction - impaired scotopic responses, constricted fields - but it is
    corrected by supplementation, features prominent xerophthalmia, and leaves
    RBP4 present and retinyl esters low. The inherited transport defect inverts
    all three: RBP4 undetectable, retinyl esters normal, and no response to oral
    loading. Notably the founding patients had no xerophthalmia at all, which
    the authors attributed to normal retinol in tear fluid.
  evidence:
  - reference: PMID:9888420
    reference_title: Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The normal retinol levels in the tear fluid explain the lack of
      xerophthalmia.
    explanation: >-
      Explains the absence of the one sign that would be expected in dietary
      deficiency, which is the clinical half of the discriminator.
  - reference: PMID:17646742
    reference_title: "[The eye and anorexia nervosa. A case report]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The ophthalmologic findings were keratoconjunctival xerosis with bilateral
      corneal ulcerations. The visual field showed a concentric bilateral
      restriction of isopters with tubular central vision, a similar aspect to
      retinitis pigmentosa.
    explanation: >-
      A worked case of the acquired phenocopy. It shows both halves of the
      comparison at once - a field defect that mimics retinitis pigmentosa, and
      the corneal xerosis that inherited transport failure does not produce.
  - reference: PMID:17646742
    reference_title: "[The eye and anorexia nervosa. A case report]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Corneoconjunctival improvement was obtained with vitamin supplementation,
      but no campimetric improvement was observed.
    explanation: >-
      The response to supplementation is the decisive discriminator: in dietary
      deficiency the ocular surface recovers on vitamin A, whereas in RBP4
      deficiency serum retinol does not even rise. Worth noting that the retinal
      field defect did not recover here either, which is why the distinction
      rests on the biochemistry rather than on treatment response alone.

discussions:
- discussion_id: oral_vitamin_a_efficacy
  kind: KNOWLEDGE_GAP
  attaches_to:
  - treatments#High-Dose Vitamin A Supplementation
  prompt: >-
    Does pharmacological oral vitamin A improve retinal function in RBP4
    deficiency, given that serum retinol does not rise on loading?
  rationale: >-
    The two pieces of evidence point opposite ways and neither is decisive. The
    rescue was obtained in Stra6-null mice, where the plasma carrier is intact
    and only uptake fails - the reverse of this disorder. The human measurement
    was made in RBP4-deficient patients and showed no rise in serum retinol at
    all. So the question is whether tissue delivery can improve without a
    measurable change in the circulating pool, by carrier-independent routes
    such as chylomicron-borne retinyl esters. The founding paper independently
    proposed exactly such an alternative source to explain why these patients
    are not more severely affected systemically.
  proposed_experiments:
  - experiment_id: rbp4_null_vitamin_a_ocular_readout
    name: Vitamin A loading in an Rbp4-null model with ocular functional readout
    description: >-
      Dose Rbp4-null C57BL/6 mice with pharmacological vitamin A and measure
      electroretinographic response and ocular retinoid content, rather than
      serum retinol alone. This tests delivery at the organ that matters in the
      genotype that matches the human disease.
    would_support:
    - pathophysiology#Chromophore Substrate Deprivation at the Retinal Pigment Epithelium
    supporting_outcome:
    - >-
      Recovery of a- and b-wave amplitudes and measurable ocular retinoid
      content despite unchanged serum retinol.
    refuting_outcome:
    - >-
      No change in ocular retinoid content or electroretinographic response at
      tolerated doses.

- discussion_id: recessive_versus_dominant_arm
  kind: KNOWLEDGE_GAP
  attaches_to:
  - genetic#RBP4
  prompt: >-
    Why do recessive truncating RBP4 alleles cause retinal degeneration while
    dominant missense alleles cause ocular malformation?
  rationale: >-
    A single gene producing two phenotypes that differ in inheritance mode,
    variant class and developmental timing is unusual enough to need an
    explanation. The proposed mechanism is dominant-negative action of missense
    alleles on retinoic-acid signalling during eye morphogenesis, with a
    maternal-effect component from maternal RBP4 status in pregnancy. That would
    make the malformation arm a developmental disorder of retinoic-acid supply
    and this entry's arm a postnatal disorder of chromophore supply, from
    lesions in the same protein. The two arms are not curated as one disease
    here for that reason.
  evidence:
  - reference: PMID:37586836
    reference_title: Clinical, genetic and biochemical signatures of RBP4-related ocular malformations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The retinoic acid (RA) pathway plays a crucial role in both eye
      morphogenesis and the visual cycle.
    explanation: >-
      Names the dual role that makes one gene capable of both a developmental
      and a degenerative phenotype.

notes: >-
  Scope. This entry is the recessive, retinal-degeneration arm of the RBP4
  spectrum. Dominant missense RBP4 alleles cause the
  microphthalmia-anophthalmia-coloboma spectrum with skewed maternal
  inheritance and are a different clinical entity;
  they are recorded in the discussion rather than curated as a subtype, because
  they differ in inheritance mode, variant class, developmental timing and
  proposed mechanism.

  Evidence discipline worth flagging for the next curator. The most quotable
  therapeutic result in this literature - pharmacological vitamin A rescuing
  vision - was obtained in Stra6-null mice. STRA6 is the uptake receptor on the
  far side of the same vitamin A axis; these patients lack the plasma carrier
  instead. Rescuing a model that has a carrier but no receptor does not
  establish rescue in a disease that has a receptor but no carrier, so every use
  of PMID:24852372 in this entry is graded INDIRECT, and the human dose-response
  failure is curated as a REFUTE item on the same treatment link rather than
  omitted. The same reasoning excludes the Rbpr2-null mouse from
  animal_models: it is a third gene in the axis, informative about the axis and
  not about this disease. Its reference cache is deliberately not shipped
  either, because an uncited cache belongs to no entry.

  Deliberately not curated. No prevalence record: the literature is a handful of
  consanguineous pedigrees and no population rate has been published, and
  ORPHA has no code that maps cleanly to the recessive arm alone. No datasets.
  No CHEBI binding for retinyl esters on the biochemical record, because the
  claim there is that a class of compounds was normal rather than a measurement
  of one species. PMID:34440435 (Leber congenital amaurosis genotype-phenotype)
  was returned by the research run as background framing for visual-cycle gene
  therapy. It is named here only to record that it was read and set aside: it
  does not mention RBP4, no evidence item cites it, and its cache is
  deliberately not shipped.

  Term corrections made against the research report. The report proposed
  HP:0031287 for acne; that identifier is Seborrheic keratosis, and the correct
  term is HP:0001061. It also transposed two retinol identifiers, calling
  CHEBI:17336 "retinol / vitamin A" and CHEBI:50211 "all-trans-retinol", when
  CHEBI:17336 is all-trans-retinol and CHEBI:50211 is retinol; the entry binds
  CHEBI:17336 for the supplement. Both were caught by checking each identifier
  against the ontology rather than against the report's own naming, and neither
  would have been caught by the report's confabulation rate, which was 0.0.
📚

References & Deep Research

Deep Research

1

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OpenScientist ▸
Progressive Retinal Dystrophy Due To Retinol Transport Defect — Comprehensive Disease Report
openscientist-autonomous 11 citations 2026-09-01T22:15:27.609440

Progressive Retinal Dystrophy Due To Retinol Transport Defect — Comprehensive Disease Report

Summary

Progressive retinal dystrophy due to a retinol transport defect is a rare inherited retinal degeneration caused primarily by biallelic (autosomal recessive) loss-of-function variants in RBP4, the gene encoding serum retinol-binding protein 4 (chromosome 10q23.33). RBP4 is the sole specific plasma carrier that mobilizes vitamin A (all-trans retinol) from hepatic stores and delivers it to peripheral tissues, most critically the eye. When circulating RBP4 is absent or non-functional, the retina is starved of the retinoid chromophore required to regenerate visual pigment, even though liver vitamin A stores remain intact. The result is a systemic ("inherited") vitamin A deficiency with a retina-dominant phenotype: childhood-onset night blindness (nyctalopia), reduced visual acuity, and progressive rod–cone/retinal pigment epithelium (RPE) degeneration, frequently accompanied by iris and chorioretinal colobomata, severe comedogenic acne, and, in some pedigrees, developmental anomalies such as patent ductus arteriosus.

The distinctive diagnostic biochemical signature separates this disorder from ordinary dietary vitamin A deficiency: serum RBP4 is undetectable, serum retinol is very low (~1/6 of normal), retinyl esters are normal, transthyretin is normal, and serum retinol fails to rise with oral vitamin A dosing because there is no carrier to mobilize the vitamin from the liver. Electrophysiology shows reduced scotopic ERG responses and elevated dark-adaptation thresholds. Mechanistically related disease arises from defects in the retinol uptake receptors STRA6 and RBPR2, which extract retinol from RBP4 at blood–tissue barriers (RPE, choroid plexus). These genes define a broader "liver–eye vitamin A axis."

A key refinement discovered across the investigation is a genotype–inheritance–phenotype dichotomy: recessive, mainly truncating RBP4 alleles produce retinal degeneration, whereas dominant, almost exclusively missense alleles produce ocular malformations (microphthalmia–anophthalmia–coloboma, MAC), with a maternal-effect component—consistent with the dual role of the retinoic-acid/vitamin-A pathway in both eye morphogenesis and the visual cycle. Management is empirical high-dose vitamin A supplementation (rescue demonstrated in Stra6-knockout mice), with AAV gene therapy proposed given the small size of RBP4.

Key Findings

Finding 1 — RBP4 is the causal gene; biallelic loss-of-function drives disease via vitamin A transport failure

Multiple independent consanguineous pedigrees establish recessive RBP4 variants as the cause of progressive retinal dystrophy. Reported pathogenic alleles include a homozygous splice-site variant c.111+1G>A (PMID: 23189188), a homozygous variant c.67C>T (PMID: 32323592), and biallelic c.248+1G>A (PMID: 27892788). Across these families, affected patients had undetectable serum RBP4, severe vitamin A deficiency, and low serum retinol, with normal transthyretin—collectively establishing a null / loss-of-function mechanism rather than a transport-complex assembly defect.

"Exome sequencing identified a novel homozygous splice site variant (c.111+1G>A) in the gene encoding retinol binding protein 4 (RBP4)." — PMID: 23189188

"Both patients had undetectable levels of RBP4 in the serum suggesting that this mutation led to either mRNA or protein instability resulting in a null phenotype." — PMID: 23189188

"Bi-allelic mutations in RBP4 were identified (c.248+1G>A), consistent with a diagnosis of inherited vitamin A deficiency." — PMID: 27892788

Ontology anchors: Gene HGNC:9922 (RBP4); OMIM gene 180250. GO biological process: retinol transport (GO:0034633), retinoid metabolic process (GO:0001523).

Finding 2 — Characteristic multisystem phenotype

The clinical picture spans the eye and beyond. Ocular features include night blindness and low vision from early childhood with fundus findings typical of recessive retinitis pigmentosa (PMID: 32323592), and retinal dystrophy combined with iris/chorioretinal colobomata (PMID: 27892788, PMID: 23189188). Extraocular features include severe childhood-onset acne vulgaris that segregates with the RBP4 genotype (PMID: 32323592, PMID: 23189188) and developmental abnormalities such as patent ductus arteriosus (PMID: 23189188).

"presented with low vision and night blindness from early childhood" — PMID: 32323592

"confirming that mutations in RBP4 segregated with the acne vulgaris phenotype in this family" — PMID: 32323592

"one patient exhibited developmental abnormalities including patent ductus arteriosus and chorioretinal and iris colobomas" — PMID: 23189188

Suggested HPO terms: Nyctalopia/night blindness (HP:0000662); Retinal dystrophy (HP:0000556); Rod-cone dystrophy (HP:0000510); Reduced visual acuity (HP:0007663); Iris coloboma (HP:0000612); Chorioretinal coloboma (HP:0000567); Acne (HP:0031287); Patent ductus arteriosus (HP:0001643).

Finding 3 — Mouse models recapitulate the dystrophy and demonstrate rescue by pharmacological vitamin A

Rbp4-deficient mice on a C57BL/6 background show reduced ERG a- and b-wave amplitudes, loss of peripheral choroid and photoreceptor layer, fewer ganglion cells and synapses, and developmental defects (retinal depigmentation, optic disc abnormality, persistent hyaloid artery). Their biochemistry mirrors humans: serum retinol was undetectable while liver retinol accumulated (PMID: 26974396). Stra6-knockout mice show markedly reduced ocular retinoids, choroid/RPE malformations, early cone death, and short rod outer segments—and, crucially, high-dose vitamin A rescues vision (PMID: 24852372).

"loss of the peripheral choroid and photoreceptor layer in the peripheral retinas" — PMID: 26974396

"accumulated retinol in the liver but it was undetectable in the serum" — PMID: 26974396

"treatment with pharmacological doses of vitamin A restored vitamin A transport across these barriers and rescued the vision of Stra6(-/-) mice" — PMID: 24852372

This is the single strongest piece of translational evidence supporting empirical vitamin A supplementation as therapy.

Finding 4 — Genetic heterogeneity of the retinol-transport axis (RBP4 → STRA6 / RBPR2)

The disorder is one node in a multigene "liver–eye vitamin A axis." RBP4 is the blood carrier; cellular uptake of retinol is receptor-mediated. STRA6 is highly expressed in epithelia forming blood–tissue barriers (RPE, choroid plexus), and its loss causes reduced ocular retinoids, RPE malformation, and cone death (PMID: 24852372). A second systemic receptor, RBPR2, when knocked out in mice, shows decreased ocular retinoids and loss of visual function (PMID: 35745101). The axis is integrated in a recent review (PMID: 41829974).

"This receptor, identified as the Stimulated by retinoic acid gene 6 (Stra6) gene product, is highly expressed in epithelia that constitute blood-tissue barriers." — PMID: 24852372

"Blood transport of the lipophilic vitamin is mediated by the retinol-binding protein, RBP4." — PMID: 24852372

Related genes/ontology: STRA6 (HGNC:30650), RBPR2 (HGNC:34333), TTR (transthyretin, RBP4's stabilizing partner). GO cellular component: extracellular space (GO:0005615); apical plasma membrane (GO:0016324) for STRA6 at the RPE.

Finding 5 — The founding human family defines the diagnostic signature

Seeliger et al. 1999 (PMID: 9888420) described the first human RBP4 patients: two affected sisters with compound heterozygous missense mutations Ile41Asn (I41N) and Gly75Asp (G75D). Their labs defined the phenotype: all-trans retinol 0.18–0.19 µM (normal 0.7–1.5 µM) that did not increase in a dose-response test, RBP below detection threshold, and normal retinyl esters. Clinically: night vision problems, reduced acuity (20/25–20/40), discrete iris coloboma, "fundus xerophthalmicus" with RPE atrophy, elevated dark-adaptation thresholds, reduced scotopic ERG, abnormal EOG light rise, and acne.

"RBP was below detection threshold, and retinyl esters were normal." — PMID: 9888420

"did not increase in a dose-response test" — PMID: 9888420

"compound heterozygous missense mutations (Ile41Asn and Gly75Asp) in the gene for serum retinol binding protein (RBP)" — PMID: 9888420

The failure of serum retinol to rise with oral vitamin A is a pivotal treatment caveat: because RBP4 is required to mobilize hepatic retinol, systemic delivery may be limited, and the therapeutic effect (as in Stra6 mice) likely depends on mass-action/pharmacological dosing rather than restoring the physiological carrier.

Finding 6 — Genotype–inheritance dichotomy with a maternal-effect component

Plaisancié et al. 2023 (PMID: 37586836), studying 7 new families / 13 patients, resolved the phenotypic spectrum into two modes:

"dominantly inherited, almost exclusively missense, associated with ocular malformations, in contrast to recessive, mainly truncating, associated with retinal degeneration" — PMID: 37586836

"The retinoic acid (RA) pathway plays a crucial role in both eye morphogenesis and the visual cycle." — PMID: 37586836

The dominant, malformation-causing alleles show skewed (maternal) inheritance—consistent with a maternal-effect mechanism whereby maternal RBP4 status influences retinoic-acid signaling during fetal eye morphogenesis.

Mechanistic Model / Interpretation

Causal chain (initiating lesion → clinical manifestation)

  1. Biallelic loss-of-function variant in RBP4 (splice-site, nonsense, or destabilizing missense) → leads to absent or non-functional serum retinol-binding protein 4 (undetectable serum RBP4).
  2. Absent RBP4 → results in failure to mobilize all-trans retinol from hepatic stores into the bloodstream; liver retinol is retained/accumulates while serum retinol falls to ~1/6 normal (demonstrated in humans and Rbp4-KO mice).
  3. Low circulating retinol → deprives the retinal pigment epithelium of substrate for the visual (retinoid) cycle; STRA6/RBPR2-mediated uptake at the RPE has no ligand to extract.
  4. Chromophore deprivation → impairs regeneration of 11-cis-retinal / rhodopsin in rod (then cone) photoreceptors → manifests first as night blindness (rods most retinoid-dependent).
  5. Chronic chromophore starvation → causes progressive photoreceptor and RPE degeneration and peripheral choroid loss → progressive retinal dystrophy / RP-like phenotype with reduced ERG and elevated dark-adaptation thresholds.
  6. Branch (developmental / dominant-missense arm): deficient retinoic-acid signaling during embryonic eye morphogenesis → results in ocular malformations (iris/chorioretinal coloboma; microphthalmia–anophthalmia–coloboma spectrum), influenced by maternal RBP4 status (maternal effect). (Inferred from the RA-pathway role in morphogenesis rather than directly demonstrated in these pedigrees.)
  7. Branch (systemic retinoid signaling): low tissue retinoid tone in skin → contributes to dysregulated follicular keratinization and severe acne vulgaris; other developmental effects (e.g., patent ductus arteriosus) reflect retinoid-dependent organogenesis. (Skin/PDA links are phenotypically associated and mechanistically inferred.)

The liver–eye vitamin A axis (schematic)

   LIVER (retinyl ester stores)
|  hydrolysis -> retinol
v
   [ RBP4 ] <-- stabilized by TTR -->  BLOODSTREAM (retinol.RBP4.TTR)
|                                   X  <-- LESION: no RBP4 -> no carrier
v
   BLOOD-TISSUE BARRIER (RPE, choroid plexus)
|  STRA6 / RBPR2 receptor uptake
v
   RPE  -> visual (retinoid) cycle -> 11-cis-retinal
|
v
   PHOTORECEPTORS (rods > cones): rhodopsin regeneration
|  chromophore starvation
v
   Night blindness -> progressive rod-cone/RPE degeneration

Upstream vs downstream

Level Component Role Directionality
Initiating lesion RBP4 LoF variant No plasma retinol carrier Most upstream
Systemic Serum retinol ↓, liver retinol retained Substrate deprivation Upstream
Barrier/uptake STRA6, RBPR2 No ligand to import Intermediate
Tissue RPE visual cycle No chromophore regeneration Downstream
End-organ Rod → cone photoreceptors Degeneration Most downstream

Cell types and processes

  • Cell Ontology (CL): retinal rod cell (CL:0000604); retinal cone cell (CL:0000573); retinal pigment epithelial cell (CL:0002586); retinal ganglion cell (CL:0000740); hepatic stellate cell (CL:0000632, retinoid storage).
  • UBERON anatomy: retina (UBERON:0000966); retinal pigment epithelium (UBERON:0001782); choroid (UBERON:0002348); iris (UBERON:0001769); liver (UBERON:0002107).
  • GO biological processes: visual perception (GO:0007601); retinoid metabolic process (GO:0001523); retinol transport (GO:0034633); retina development in camera-type eye (GO:0060041); photoreceptor cell maintenance (GO:0045494).
  • CHEBI chemical entities: retinol / vitamin A (CHEBI:17336); all-trans-retinol (CHEBI:50211); 11-cis-retinal (CHEBI:16066); retinyl ester (CHEBI:63410); retinoic acid (CHEBI:26536).

Evidence Base

PMID Title (abbrev.) Evidence type Supports
9888420 Phenotype in retinol deficiency due to hereditary RBP defect Human clinical Founding family; diagnostic signature; missense compound-het; non-response to oral dosing (F5)
23189188 Exome analysis: novel RBP4 mutation with retinal dystrophy + developmental abnormalities Human clinical/genetic Splice variant c.111+1G>A; null phenotype; coloboma + PDA (F1, F2)
27892788 Vitamin A deficiency due to bi-allelic RBP4 mutation Human clinical/genetic Biallelic c.248+1G>A; inherited vitamin A deficiency (F1, F2)
32323592 Homozygous c.67C>T RBP4 with RP and childhood acne Human clinical/genetic Night blindness; acne segregation (F1, F2)
26974396 Severe ocular phenotypes in Rbp4-deficient mice (C57BL/6) Model organism Photoreceptor/choroid loss; serum retinol undetectable, liver retinol retained (F3)
24852372 STRA6 critical for cellular vitamin A uptake Model organism/in vitro STRA6 uptake receptor; vitamin A rescue in Stra6-KO (F3, F4)
35745101 RBPR2-null mice: decreased ocular retinoids, visual loss Model organism Second systemic receptor in the axis (F4)
41829974 The Liver-Eye Axis of Dietary Vitamin A Homeostasis Review Integrates axis mechanisms/receptors (F4)
37586836 Clinical, genetic, biochemical signatures of RBP4 disease Human clinical/genetic Genotype–inheritance dichotomy; maternal effect; RA pathway (F6)
34440435 Leber congenital amaurosis genotype–phenotype Review (context) Frames visual-cycle gene dystrophies and gene therapy landscape
17646742 The eye and anorexia nervosa (dietary vitamin A deficiency) Human case (contrast) Acquired vitamin A deficiency phenocopy; distinguishes dietary vs transport defect

Note on the anorexia case (PMID: 17646742): dietary hypovitaminosis A produces overlapping retinal dysfunction (impaired scotopic ERG, RP-like field constriction) but is corrected by supplementation and features prominent xerophthalmia—underscoring that the inherited transport defect is distinguished by undetectable RBP4, normal retinyl esters, and poor response to oral vitamin A.

Section-by-Section Knowledge Base Content

1. Disease Information

Inherited retinal degeneration from failed plasma vitamin A transport. Synonyms: RBP4-related retinal dystrophy; inherited/systemic vitamin A deficiency; retinol-binding protein deficiency; "fundus xerophthalmicus" (historical). Identifiers: Gene RBP4 OMIM 180250; disease phenotype OMIM #615147 (RBP4-related retinal dystrophy / "Retinal dystrophy, iris coloboma, and comedogenic acne syndrome, RDCCAS"). Suggested MONDO: map to the RBP4-related inherited vitamin A deficiency / retinal-dystrophy branch. ICD-10 H35.5 (hereditary retinal dystrophy). Information is derived from aggregated disease-level resources and small pedigree case series, not large EHR cohorts.

2. Etiology

Primary cause: genetic—biallelic (recessive) LoF RBP4 variants (retinal degeneration) or monoallelic dominant missense (ocular malformation). Genetic risk factors: consanguinity (most recessive families are consanguineous). Modifier/environmental: dietary vitamin A status may modulate severity; there are no established protective alleles. Gene–environment interaction: because the block is at transport, dietary vitamin A alone does not normalize serum retinol, but pharmacological loading may partially bypass the deficit (mass-action delivery).

3. Phenotypes

Night blindness (HP:0000662, early childhood, progressive, high frequency); retinal dystrophy/rod–cone dystrophy (HP:0000556/HP:0000510, progressive); reduced visual acuity (HP:0007663); iris coloboma (HP:0000612) and chorioretinal coloboma (HP:0000567, subset); acne (HP:0031287, severe, childhood-onset, variable); patent ductus arteriosus (HP:0001643, rare). QoL impact is dominated by progressive low vision and nyctalopia affecting mobility and independence.

4. Genetic/Molecular Information

Causal gene: RBP4 (HGNC:9922; 10q23.33; OMIM 180250). Variant classes: splice-site (c.111+1G>A; c.248+1G>A), c.67C>T, and missense (I41N/G75D; dominant missense in MAC). Classification: pathogenic/likely pathogenic per ACMG for the recessive truncating alleles. Functional consequence: loss of function / null (undetectable serum RBP4) for recessive disease; the dominant missense alleles are proposed to act via altered retinoid signaling. Modifier genes: STRA6, RBPR2, TTR within the same axis. Epigenetic and chromosomal abnormalities: none established.

5. Environmental Information

Dietary vitamin A intake is the principal modifiable variable but cannot correct the transport block at physiological doses. No infectious agents. Acquired (dietary/malabsorptive) vitamin A deficiency is an important phenocopy for differential diagnosis.

6. Mechanism / Pathophysiology

See "Mechanistic Model" above for the full ordered causal chain, pathway map, and ontology anchors.

7. Anatomical Structures Affected

Primary organ: eye—retina (UBERON:0000966), RPE (UBERON:0001782), choroid (UBERON:0002348), iris (UBERON:0001769). Secondary: liver (retinoid storage; UBERON:0002107), skin (acne), cardiovascular (PDA). Cells: rods (CL:0000604), cones (CL:0000573), RPE (CL:0002586). Subcellular: RPE endosomal/visual-cycle machinery; photoreceptor outer segments. Lateralization: bilateral, generally symmetric.

8. Temporal Development

Onset: childhood (night blindness/low vision from early childhood). Course: chronic, slowly progressive rod–cone/RPE degeneration; developmental/malformation features are congenital. Critical period: embryonic eye morphogenesis (for coloboma/MAC via retinoic-acid signaling) and early postnatal photoreceptor maintenance.

9. Inheritance and Population

Inheritance: autosomal recessive (retinal degeneration; often consanguineous) vs autosomal dominant missense (ocular malformation, with maternal-effect skewing). Prevalence: ultra-rare; only a handful of families reported worldwide—no reliable population estimate. Penetrance/expressivity: variable expressivity across ocular and extraocular features. Founder effects not established; consanguinity is a strong contributor for recessive cases.

10. Diagnostics

Biochemistry (key): undetectable serum RBP4, very low serum retinol, normal retinyl esters, normal transthyretin; serum retinol does not rise with oral vitamin A. Electrophysiology: reduced scotopic ERG, elevated dark-adaptation thresholds, abnormal EOG light rise. Imaging/fundus: RP-like RPE atrophy, peripheral pigmentary change, coloboma. Genetics: WES/WGS or inherited-retinal-dystrophy gene panels including RBP4 (and STRA6, RBPR2); single-gene confirmation of biallelic RBP4 variants. Differential: dietary/malabsorptive vitamin A deficiency (normalizes with supplementation; RBP4 present), other recessive RP, Leber congenital amaurosis (visual-cycle genes; PMID: 34440435).

11. Outcome/Prognosis

Vision is progressively impaired; night blindness and low vision are the dominant disabilities. Not typically life-limiting (extraocular features—PDA—are exceptions). No large survival data; prognosis is driven by degree of retinal degeneration at diagnosis and potential responsiveness to vitamin A loading.

12. Treatment

Mainstay: empirical high-dose (pharmacological) vitamin A supplementation (NCIT: Vitamin A / Retinol Therapy). Rationale is strong preclinically—vitamin A rescued vision in Stra6-KO mice (PMID: 24852372)—but the human treatment caveat is that serum retinol may not normalize because RBP4 is absent (PMID: 9888420); benefit likely depends on mass-action delivery to the eye. Supportive: low-vision rehabilitation; dermatologic management of acne. Investigational: AAV-mediated RBP4 gene replacement is a rational strategy given the small gene and the null mechanism (no approved therapy yet; no NCT identified in this investigation).

13. Prevention

Genetic counseling for consanguineous/at-risk families; carrier and cascade testing; prenatal/preimplantation options for known family variants. Ensuring adequate maternal vitamin A status is prudent given the retinoic-acid morphogenesis link, though it does not overcome the transport block.

14. Other Species / Natural Disease

Disease modeled and mechanistically dissected in mouse (Mus musculus, NCBI:txid10090): Rbp4⁻/⁻ (PMID: 26974396), Stra6⁻/⁻ (PMID: 24852372), Rbpr2⁻/⁻ (PMID: 35745101). Orthologs: mouse Rbp4 (NCBI Gene 19662). No specific companion-animal natural disease was identified in this investigation.

15. Model Organisms

Mammalian genetic knockouts are the principal models. Rbp4⁻/⁻ mice recapitulate the human biochemical signature (serum retinol undetectable, liver retinol retained) and structural degeneration (photoreceptor/choroid loss, reduced ERG). Stra6⁻/⁻ mice add the therapeutic proof-of-concept (vitamin A rescue). Limitations: background-dependent severity (C57BL/6 shows severe ocular phenotypes); mouse retinoid handling and rod-dominance differ from human macula, so cone/macular outcomes may be imperfectly modeled.

Limitations and Knowledge Gaps

  • Ultra-rare disease, tiny N. Conclusions rest on a small number of consanguineous pedigrees and case series; there are no cohort-level prevalence, penetrance, or natural-history data.
  • Treatment evidence is largely preclinical. Vitamin A rescue is proven in Stra6-KO mice, but human treatment response—especially whether high-dose vitamin A halts or reverses retinal degeneration—is not established in controlled studies, and serum retinol may not normalize.
  • Extraocular mechanism inferred. The links from RBP4 loss to acne and to PDA are phenotypic associations with mechanistic inference (retinoid signaling) rather than direct experimental proof in these families.
  • Dominant-missense/MAC arm is newer and less mechanistically resolved; the maternal-effect basis needs functional confirmation.
  • No approved gene therapy or registered clinical trial was identified; AAV replacement remains conceptual.
  • Some cited resources (PMID: 41829974) lacked accessible abstracts, limiting verbatim support.

Proposed Follow-up Experiments / Actions

  1. Prospective vitamin A dosing trial in genetically confirmed RBP4-null patients with serial ERG, dark-adaptation, OCT, and serum retinol/RBP4 to quantify whether pharmacological loading slows degeneration and to define the effective dose.
  2. AAV-RBP4 gene-replacement proof-of-concept in Rbp4⁻/⁻ mice (liver-directed vs intravitreal/RPE-directed) measuring serum retinol restoration and ERG rescue; compare with vitamin A loading.
  3. Genotype–phenotype meta-analysis aggregating all reported RBP4 families to formalize the recessive-truncating (degeneration) vs dominant-missense (malformation) dichotomy and estimate expressivity/penetrance.
  4. Mechanistic dissection of extraocular features—retinoid profiling of skin and assessment of developmental cardiovascular phenotypes in Rbp4-KO models—to test the retinoid-signaling basis of acne and PDA.
  5. Diagnostic algorithm validation: prospectively confirm that the triad "undetectable RBP4 + low retinol + normal retinyl esters + non-response to oral vitamin A" reliably distinguishes inherited transport defect from acquired/dietary deficiency.
  6. Registry/consortium for RBP4, STRA6, and RBPR2 patients to enable natural-history and future interventional studies.

Evidence source legend: Human clinical/genetic — PMIDs 9888420, 23189188, 27892788, 32323592, 37586836. Model organism — PMIDs 26974396, 24852372, 35745101. Review/context — PMIDs 41829974, 34440435, 17646742.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 11
Resolved 11
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 16
Quoted claims found in source 16
Quoted claims not found in source 0
References weighed for topical relevance 11
On topic 9
Off topic 0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 33
Resolved 29
Unresolved (possible confabulation) 0
Obsolete 1
Unverifiable 3
Terms whose name was checked 3
Terms named correctly 0
Terms named as a different term 1
Terms whose name is worth a second look 2

Terms the report names something else

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:

  • UBERON:0000966 (2 mentions) - the report calls it "UBERON anatomy: retina"; UBERON calls it retina**

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

  • GO:0005615 (obsolete extracellular space) (1 mention) - replaced by GO:0005576

Terms whose name is worth a second look

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:

  • GO:0007601 (1 mention) - the report calls it "GO biological processes: visual perception"; GO calls it visual perception**, and lists "sensory visual perception" among its other names
  • CHEBI:17336 (1 mention) - the report calls it "CHEBI chemical entities: retinol / vitamin A"; CHEBI calls it all-trans-retinol**, and lists "all-trans-vitamin A" among its other names