Pre-Descemet Corneal Dystrophy

Genetic MONDO:0017392 Pathograph 8 Show in embeddings browser Stromal Corneal Dystrophy Corneal Dystrophy Ophthalmological Disease

Pre-Descemet corneal dystrophy (PDCD) is characterised by focal, fine, polymorphic grey opacities confined to the deep stroma immediately anterior to Descemet membrane. It involves the posterior stroma and nothing else, is bilateral, usually appears after the age of 30, and does not affect vision. Its status as a dystrophy is contested, and this entry curates the dispute rather than resolving it. The IC3D classification assigns PDCD to category 4, its lowest evidence tier, and states plainly that isolated PDCD is neither a well-defined entity nor clearly hereditary or degenerative. No gene, locus or MIM number is assigned. What ultrastructure exists points toward degeneration rather than storage of a genetically determined product: transmission electron microscopy shows membrane-bound intracellular vacuoles holding electron-dense material suggestive of secondary lysosomes, together with inclusions of a lipofuscin-like lipoprotein, and no extracellular deposits at all. That last detail is what most sharply separates PDCD from the classical stromal dystrophies it sits beside in the ontology, which are defined by abnormal material accumulating in the extracellular matrix and progressively opacifying the cornea. Against a purely degenerative reading, PDCD has been described in families over two to four generations, and some forms progress. Deep corneal deposits closely resembling PDCD are also frequently seen in X-linked ichthyosis, where they appear in the first decade and where every genetically characterised family carries a point mutation, partial deletion or complete deletion of STS at Xp22.31. Much of the ophthalmological literature labels those cases PDCD. IC3D explicitly declines to, on the ground that XLI is a systemic disease with corneal manifestations and therefore not a corneal dystrophy. Both arms are curated here, because MONDO:0017392 is the concept the clinical literature uses for both and because the two are told apart by skin examination, age of onset and STS analysis rather than by the corneal appearance - but the disagreement is recorded explicitly rather than smoothed over.

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1
Mappings
1
Inheritance
6
Pathophys.
3
Histopath.
4
Phenotypes
3
Gaps
8
Pathograph
1
Genes
2
Subtypes
3
Differentials
1
Models
8
References
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Deep Research
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Classifications

Harrison's Part
GENETICS ENVIRONMENT DISEASE DERMATOLOGY
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Mappings

MONDO
MONDO:0017392 pre-descemet corneal dystrophy
skos:exactMatch MONDO
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Inheritance

1
X-linked recessive inheritance HP:0001419
In the XLI-associated subtype the lesion is at Xp22.3 and the reported affected individuals are men, including two brothers in one family. The corneal finding therefore segregates with X-linked ichthyosis itself, whose causative gene STS lies at that locus. This inheritance block describes the XLI-associated arm only; isolated PDCD has no established mode of inheritance, which is part of why IC3D rates it category 4.
X-linked recessive inheritance
Show evidence (2 references)
PMID:37287641 SUPPORT Human Clinical
"Genetic examination of the STS locus on the X chromosome in Case 1 revealed a deletion that spanned across DNA markers DXS1130-DXS237, which includes all the coding exons (exons 1-10) of STS."
Places the causal lesion on the X chromosome in an affected male.
PMID:39086014 SUPPORT Human Clinical
"The causative gene for XLI is the steroid sulfatase gene (STS), located on Xp22.3."
Confirms the gene and cytoband of the associated X-linked disorder.
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Subtypes

2
Isolated PDCD (IC3D category 4)
PDCD occurring without ichthyosis and without an identified gene - the entity MONDO and Orphanet actually define, and the one IC3D rates category 4. IC3D assigns it no MIM number, no locus and no gene, and describes it as neither well defined nor clearly hereditary or degenerative. The countervailing observation is that it has been reported in families across two to four generations, so a purely degenerative reading is not settled either. Onset is usually after age 30, which distinguishes it from the XLI-associated deposits of the other subtype.
Show evidence (3 references)
PMID:38359414 SUPPORT Other
"Isolated pre-Descemet corneal dystrophy (PDCD) is neither a well-defined entity nor is it clearly a hereditary or degenerative disorder (known as cornea farinata, "flour-like cornea")."
The classifying committee's own statement of the entity's uncertain status.
PMID:38359414 SUPPORT Human Clinical
"Although no definite pattern of inheritance is established, it has been described in families over 2 to 4 generations."
Records the familial clustering that argues against reading isolated PDCD as purely degenerative, while noting no inheritance pattern is established.
PMID:38359414 SUPPORT Human Clinical
"Usually after age 30 years; although PPPCD has been found in children as young as age 3 years."
Gives the age of onset of this subtype, which is one of the features that separates it from the XLI-associated deposits.
Deep corneal deposits of X-linked ichthyosis (STS)
STS hgnc:11425 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in STS (hgnc:11425). hgnc:11425 is a gene from the HUGO Gene Nomenclature Committee.
The genetically characterised arm, and the contested one. Affected men have bilateral punctate posterior stromal opacities anterior to Descemet membrane together with the dry, coarse, scaly skin of X-linked ichthyosis, and STS analysis shows a point mutation, a partial deletion of the coding exons, or a complete deletion of the locus at Xp22.31. That three different classes of lesion produce an indistinguishable corneal phenotype is itself the argument that they all act through loss of steroid sulfatase function. It is named "deep corneal deposits" rather than "PDCD" deliberately. Much of the ophthalmological literature - including every primary report cited here - calls these cases PDCD, but IC3D expressly refuses the label because XLI is a systemic disease with corneal manifestations. The subtype is retained under this MONDO concept because that is how the clinical literature indexes it, with the dissent recorded as evidence rather than suppressed.
Show evidence (5 references)
PMID:37287641 SUPPORT Human Clinical
"The slit-lamp examination of three affected men (two of whom were brothers) from two families revealed bilateral punctate posterior corneal stromal opacities anterior to the Descemet membrane."
Defines the corneal phenotype of this subtype in genetically confirmed individuals.
PMID:37287641 SUPPORT Human Clinical
"PDCD with XLI may be associated with either partial or complete deletion of STS."
States the allelic spectrum that defines this subtype, and shows the primary literature does apply the PDCD label to it.
PMID:38359414 REFUTE Other
"Similar deep corneal deposits to PDCD are also frequently seen in X-linked ichthyosis (MIM #308100) which results from mutations in the steroid sulfatase gene (STS) at genetic locus Xp22.31."
IC3D describes these deposits as merely SIMILAR to PDCD rather than as PDCD, which is the first half of its refusal to classify them together.
+ 2 more references
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Discussions and Knowledge Gaps

3
Do the two arms of this entity store the same material - and specifically, is the deposit in the STS-deficient cornea cholesterol sulfate, or the same lipofuscin-like lipoprotein described in isolated PDCD?
KNOWLEDGE GAP OPEN pdcd_deposit_identity
Attached to
pathophysiology#Cholesterol Sulfate Accumulation pathophysiology#Keratocyte Lysosomal Lipofuscin-Like Lipoprotein Accumulation pathophysiology#Intracellular Deposition in Posterior Keratocytes
The two arms of this entry converge on an identical-looking cellular lesion from two different proposed substrates, and neither has been measured where it matters. In the STS-deficient arm, cholesterol sulfate is the natural candidate, but the accumulation has only ever been demonstrated in the stratum corneum; no chemical or metabolomic characterisation of an STS-deficient cornea exists. In the isolated arm, the material that has actually been characterised ultrastructurally is a lipofuscin-like lipoprotein in secondary lysosomes - not a sulfated sterol - and IC3D warns that even those studies are inconsistent. Three outcomes are possible and they are not equivalent. If both arms store cholesterol sulfate, the isolated cases become candidates for occult sulfatase pathway defects. If both store lipofuscin-like lipoprotein, the STS lesion is acting through a general lysosomal-degradation failure rather than through its own substrate, and the entity is a degeneration with a genetic accelerator. If they store different things, the resemblance is coincidental and the two should not share a MONDO concept at all - which is close to IC3D's position.
Proposed experiments
Comparative lipidomics and electron microscopy of PDCD and STS-deficient corneas
pdcd_deposit_lipidomics
Apply mass-spectrometry lipidomics and transmission electron microscopy to corneal tissue from an STS-deleted donor and from a donor with isolated PDCD, comparing sulfated sterol and lipofuscin content of posterior versus anterior stroma against age-matched controls, to establish whether the two arms store the same material.
Show evidence (2 references)
PMID:38359414 SUPPORT Human Clinical
"Membrane-bound intracellular vacuoles containing electron-dense material suggestive of secondary lysosomes and inclusions of a lipofuscin-like lipoprotein consistent with a degenerative process are seen in PDCD."
Characterises the deposit in isolated PDCD as lipofuscin-like lipoprotein, which is not the substrate the STS arm predicts.
PMID:39086014 SUPPORT Human Clinical
"STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation in the stratum corneum (SC)."
The competing substrate, established in skin and never measured in cornea.
Should the deep corneal deposits of X-linked ichthyosis be classified as pre-Descemet corneal dystrophy at all, or as a corneal manifestation of a systemic disease?
KNOWLEDGE GAP OPEN pdcd_entity_boundary_xli
Attached to
pathophysiology#Loss of Steroid Sulfatase Function pathophysiology#Intracellular Deposition in Posterior Keratocytes
This is a live disagreement between two authorities that this entry deliberately does not resolve. The primary ophthalmological literature - every case series cited here, from 2013 through 2023 - labels these cases "pre-Descemet corneal dystrophy associated with X-linked ichthyosis". IC3D edition 3 explicitly refuses that label, describing the deposits as merely similar to PDCD and stating that XLI is a systemic disease with corneal manifestations and therefore not a corneal dystrophy. MONDO:0017392 carries the generic name and no gene, so it does not settle the question either way. It matters for what this record is. If IC3D is right, the STS arm belongs to an X-linked ichthyosis entry and this concept should shrink to the isolated category-4 finding; if the clinical literature is right, STS is the only identified genetic cause of anything called PDCD and the concept's centre of gravity is the STS arm. The empirical question underneath the nomenclature is the deposit-identity one recorded separately: if the two arms store different material, IC3D's separation is vindicated on mechanism and not merely on classification convention.
Proposed experiments
Systematic corneal survey of a genotyped X-linked ichthyosis cohort
pdcd_xli_corneal_survey
Examine an STS-genotyped XLI cohort with slit lamp, AS-OCT and confocal microscopy against age-matched controls, quantifying the prevalence, depth distribution and morphology of pre-Descemet opacities, to establish whether the XLI corneal phenotype is quantitatively distinguishable from isolated PDCD rather than only nominally separated from it.
Show evidence (2 references)
PMID:38359414 SUPPORT Other
"This is a systemic disease with corneal manifestations and therefore is not a corneal dystrophy."
One side of the disagreement, stated by the classifying committee.
PMID:37287641 REFUTE Human Clinical
"Pre-Descemet corneal dystrophy (PDCD) with X-linked ichthyosis (XLI) is associated with mutations in or deletions of the steroid sulfatase gene (STS)."
The other side: the primary literature treats these cases as PDCD, using the label IC3D declines to apply.
Is isolated PDCD a corneal dystrophy at all, or an age-related degeneration that has been classified with the dystrophies by appearance alone?
KNOWLEDGE GAP OPEN pdcd_is_it_a_dystrophy
Attached to
pathophysiology#Keratocyte Lysosomal Lipofuscin-Like Lipoprotein Accumulation pathophysiology#Deep Stromal Punctate Opacification Anterior to Descemet Membrane
IC3D assigns PDCD to category 4, the tier reserved for entities with the least evidence for being a corneal dystrophy, and assigns it no MIM number, no locus and no gene. The ultrastructure - lipofuscin-like lipoprotein in secondary lysosomes - is read by the reporting authors as degenerative, an independent in vivo imaging series reached the same conclusion, and onset after age 30 fits a degeneration better than a dystrophy. What keeps the question open rather than closed is that the same source reports PDCD in families across two to four generations, and that some forms progress. A purely age-related degeneration should not cluster in pedigrees. The contrast with the neighbouring entity is instructive: PPPCD occupies the same corneal layer, has autosomal dominant pedigrees and a gene (PRDX3), and is rated category 1 - so the classification machinery is capable of recognising a dystrophy here when the evidence supports one, and has declined to for PDCD.
Proposed experiments
Age-stratified prevalence of pre-Descemet opacities in an unselected population
pdcd_age_stratified_prevalence
Determine the prevalence of pre-Descemet punctate opacities by decade in an unselected adult population with slit-lamp and AS-OCT, with STS copy-number analysis and dermatological examination in those affected. A prevalence rising steadily with age in individuals without STS lesions would support degeneration; familial clustering beyond chance would support dystrophy.
Show evidence (3 references)
PMID:38359414 SUPPORT Other
"Isolated pre-Descemet corneal dystrophy (PDCD) is neither a well-defined entity nor is it clearly a hereditary or degenerative disorder (known as cornea farinata, "flour-like cornea")."
The classifying committee's own statement that the question is unresolved.
PMID:38359414 SUPPORT Other
"PDCD has historically been described as having several subgroups, many of which may represent sporadic, age-related degenerative and secondary changes."
Records the specific suspicion that much of what is called PDCD is degenerative or secondary rather than a primary dystrophy.
PMID:31298040 SUPPORT Human Clinical
"The clinical presentation and structural anomalies found in isolated sporadic pre-Descemet corneal dystrophy are in favor of a degenerative process affecting corneal keratocytes with no epithelial or endothelial involvement."
An independent imaging series arguing for the degenerative reading.
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Pathophysiology

6
Keratocyte Lysosomal Lipofuscin-Like Lipoprotein Accumulation
The proposed initiating lesion of the isolated arm, and the reason that arm reads as a degeneration. Transmission electron microscopy of PDCD corneas shows membrane-bound intracellular vacuoles containing electron-dense material that has the appearance of secondary lysosomes, together with inclusions of a lipofuscin-like lipoprotein. Lipofuscin is the classic marker of accumulated, incompletely degraded material in long-lived post-mitotic cells, and its presence is what the reporting authors read as evidence of a degenerative process rather than of a genetically determined storage product. Consistent with that, onset is usually after age 30. It is curated PROVISIONAL rather than established because IC3D itself reports that the histopathological studies of PDCD are not consistent, and because no gene, locus or metabolic defect has been assigned that would explain why the material accumulates.
Posterior stromal keratocyte CL:0002363 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Posterior stromal keratocyte, annotated with keratocyte (CL:0002363). CL:0002363 is a cell type from the Cell Ontology.
lysosome GO:0005764 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves increased lysosome (GO:0005764). GO:0005764 is a cellular component from the Gene Ontology.
Downstream
Intracellular Deposition in Posterior Keratocytes Undegraded lipoprotein retained in secondary lysosomes is the material that renders the keratocyte hyperreflective.
Show evidence (3 references)
PMID:38359414 SUPPORT Human Clinical
"Membrane-bound intracellular vacuoles containing electron-dense material suggestive of secondary lysosomes and inclusions of a lipofuscin-like lipoprotein consistent with a degenerative process are seen in PDCD."
The ultrastructural basis of this node, including the authors' own reading of it as degenerative.
PMID:38359414 SUPPORT Human Clinical
"Histopathologic studies of PDCD are not consistent."
The explicit caveat that makes this node provisional rather than established.
PMID:31298040 SUPPORT Human Clinical
"The clinical presentation and structural anomalies found in isolated sporadic pre-Descemet corneal dystrophy are in favor of a degenerative process affecting corneal keratocytes with no epithelial or endothelial involvement."
An independent in vivo imaging series reaching the same degenerative, keratocyte-centred conclusion.
Loss of Steroid Sulfatase Function
The trigger of the genetically characterised arm. STS at Xp22.31 encodes steroid sulfatase, the enzyme that hydrolyses cholesterol sulfate, dehydroepiandrosterone sulfate and estrone sulfate. Three classes of lesion have been found in families with pre-Descemet deposits and X-linked ichthyosis - point mutations, partial deletions removing some of the ten coding exons, and complete deletion of the locus, in one case a 4.4 Mb hemizygous deletion taking three further genes with it. The informative observation is that the corneal phenotype does not differ between these classes, which is the argument that all of them converge on loss of enzyme function rather than on some deletion-size-dependent contiguous-gene effect.
STS hgnc:11425 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves STS (hgnc:11425). hgnc:11425 is a gene from the HUGO Gene Nomenclature Committee.
Genetic context variant_origin: GERMLINE zygosity: HEMIZYGOUS functional_impact_category: LOSS_OF_FUNCTION
Hemizygous point mutations, partial deletions (exons 1-7 reported) and complete deletions of STS at Xp22.31 in affected males.
steryl-sulfatase activity GO:0004773 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves steryl-sulfatase activity (GO:0004773), qualified as loss of function. GO:0004773 is a molecular function from the Gene Ontology. ⇓ LOSS OF FUNCTION
Downstream
Cholesterol Sulfate Accumulation Steroid sulfatase is the enzyme that hydrolyses cholesterol sulfate, so its loss allows the substrate to accumulate.
Show evidence (4 references)
PMID:37287641 SUPPORT Human Clinical
"Genetic screening of Cases 2 and 3 revealed a partial deletion of the STS locus involving exons 1-7 and flanking DNA marker DXS1130 on the X chromosome."
Documents a partial-deletion allele in two affected brothers.
PMID:37287641 SUPPORT Human Clinical
"Despite the identification of point mutations, partial deletion, and complete deletion of STS in different affected families reported to date, there was no apparent difference in the affected phenotype between the families, suggesting that the identified variants likely all resulted in loss of..."
The allelic-heterogeneity-with-uniform-phenotype argument that identifies loss of enzyme function, rather than deletion extent, as the mechanism.
PMID:23807007 SUPPORT Human Clinical
"aCGH performed on genomic DNA revealed a microdeletion in the Xp22.31 cytoband of approximately 1.7 megabases, containing STS."
Documents a whole-locus microdeletion in an affected individual.
+ 1 more reference
Cholesterol Sulfate Accumulation
Steroid sulfatase hydrolyses cholesterol sulfate, so loss of the enzyme allows the sulfated sterol to accumulate. This is firmly established in the skin, where excess cholesterol sulfate in the stratum corneum is what produces the barrier dysfunction and scaling of X-linked ichthyosis, and it is the natural candidate for the corneal deposit as well. It is curated as PROVISIONAL because that last step is an inference, and because there is a competing candidate. No study has chemically identified the material inside the posterior keratocytes of an STS-deficient cornea; what has been shown is that the deposit is there, that it is intracellular, and that the patient lacks steroid sulfatase. Meanwhile the ultrastructural material characterised in isolated PDCD is a lipofuscin-like lipoprotein, not a sulfated sterol. Whether the two arms share a stored substance or merely a location is unresolved, and the knowledge-gap discussion on this entry keeps that open rather than assuming it.
Downstream
Intracellular Deposition in Posterior Keratocytes Accumulated sulfated sterol is the proposed identity of the hyperreflective material seen within posterior keratocytes in this arm; the link is inferred from skin, not demonstrated in cornea.
Show evidence (3 references)
PMID:39086014 SUPPORT Human Clinical
"STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation in the stratum corneum (SC)."
Establishes substrate accumulation as the direct consequence of enzyme loss - but in stratum corneum, not cornea. Recorded as PARTIAL rather than SUPPORT so the support level itself carries the tissue mismatch, instead of leaving it to the surrounding prose.
PMID:39086014 SUPPORT Human Clinical
"Excess CS induces epidermal permeability barrier dysfunction and scaling abnormalities."
Shows the downstream consequence of the accumulated substrate is characterised in epidermis, not in cornea - the reason this node is provisional for the eye.
PMID:38359414 SUPPORT Human Clinical
"inclusions of a lipofuscin-like lipoprotein consistent with a degenerative process are seen in PDCD"
The competing substrate identity characterised in isolated PDCD, which is why a shared cholesterol-sulfate deposit cannot be assumed across both arms.
Intracellular Deposition in Posterior Keratocytes
The shared cellular lesion, and the observation that most sharply separates this entity from the classical stromal dystrophies. In vivo confocal microscopy shows enlarged, hyperreflective keratocytes in the posterior stroma carrying intracellular dots, with activated keratocytes as far forward as the very anterior stroma; the same is seen in the STS-deficient arm, where hyperreflective particles sit inside enlarged and activated posterior keratocytes. The stromal dystrophies in the same MONDO branch - macular, Schnyder, congenital stromal, the TGFBI forms - deposit abnormal material in the extracellular matrix and progressively opacify the cornea. Here the cell is the affected compartment, the cells are enlarged and activated rather than lost, and the epithelium and endothelium are spared. The extracellular contribution is not nil, and the entry does not pretend otherwise: diffuse small extracellular stromal deposits are described in vivo, even though transmission electron microscopy of PDCD reports none. That is one of the inconsistencies IC3D flags in the histopathology.
Posterior stromal keratocyte CL:0002363 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Posterior stromal keratocyte, annotated with keratocyte (CL:0002363). CL:0002363 is a cell type from the Cell Ontology.
Corneal stroma UBERON:0001777 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Corneal stroma, annotated with substantia propria of cornea (UBERON:0001777). UBERON:0001777 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
Spontaneous canine posterior stromal dystrophy (comparative phenocopy) Canis lupus familiaris partially recapitulates The canine cornea reproduces the cellular lesion this node curates - intracellular hyperreflective deposits in enlarged posterior keratocytes, graded toward Descemet membrane - independently of any human tissue.
Downstream
Deep Stromal Punctate Opacification Anterior to Descemet Membrane Light-scattering, particle-laden keratocytes concentrated in the deepest stroma are what the slit lamp resolves as discrete punctate opacities.
Show evidence (4 references)
PMID:31298040 SUPPORT Human Clinical
"Diffuse small extracellular stromal deposits, presence of enlarged hyperreflective keratocytes in the posterior stroma with either hyperreflective or hyporeflective intracellular dots, and presence of activated keratocytes in the very anterior stroma were observed in all corneas with in vivo..."
The defining cellular finding, present in all eight corneas of a four-patient series, including the extracellular component.
PMID:28302098 SUPPORT Human Clinical
"IVCM revealed regular distributed hyperreflective particles inside the enlarged and activated keratocytes in the posterior stroma."
The same intracellular posterior-keratocyte lesion in the STS-deficient arm, which is what makes the two arms clinically indistinguishable.
PMID:38359414 SUPPORT Human Clinical
"Normal cornea except for enlarged keratocytes in the posterior stroma containing vacuoles and intracytoplasmic inclusions of lipid-like material."
Light-microscopic confirmation that the abnormality is confined to enlarged, inclusion-bearing posterior keratocytes.
+ 1 more reference
Deep Stromal Punctate Opacification Anterior to Descemet Membrane
The tissue-level endpoint and the diagnostic finding: focal, fine, polymorphic grey opacities - central, annular or diffuse - confined to the deep stroma immediately anterior to Descemet membrane, bilaterally. Cross-sectional imaging resolves the same thing as a hyperreflective line running limbus to limbus just anterior to Descemet's membrane, and Scheimpflug tomography shows a second, posterior light-scattering peak that does not belong in a normal cornea. The name is a slight misdescription that is worth stating explicitly: the opacities are visible pre-Descemet, but multimodal imaging finds fine hyperreflective particles through the posterior, mid and anterior stroma. The disorder affects the whole stroma; the pre-Descemet location is where the damage is maximal, not where it is confined.
Descemet's membrane UBERON:0004367 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Descemet's membrane (UBERON:0004367). UBERON:0004367 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Visually Silent Corneal Finding Because the opacities are fine, deep and non-confluent they do not degrade the retinal image, so the finding presents as a sign rather than as visual loss.
Show evidence (4 references)
PMID:38359414 SUPPORT Human Clinical
"Focal, fine, polymorphic gray opacities that may be central, annular, or diffuse are visible in the deep stroma immediately anterior to Descemet membrane"
The reference description of the defining lesion and its variants.
PMID:31298040 SUPPORT Human Clinical
"Spectral domain optical coherence tomography scans showed a hyperreflective line anterior to Descemet's membrane running from limbus to limbus and associated with a second thinner hyperreflective line just beneath Bowman's layer."
Confirms the depth-restricted lesion on cross-sectional imaging and records a second anterior line, evidence that the process is not confined posteriorly.
PMID:31298040 SUPPORT Human Clinical
"Multimodal imaging of cornea reveals that the disorder affects the whole stroma"
Directly qualifies the "pre-Descemet" name: the visible opacities are deep, but the process is panstromal.
+ 1 more reference
Visually Silent Corneal Finding
The organism-level outcome, unusual in being an absence of disability. Vision is usually unaffected and patients are typically asymptomatic, so PDCD requires no treatment; IC3D lists it among the dystrophies that are typically asymptomatic and need none. The qualifier "usually" is theirs and is kept here, because one adult in a recently described pedigree did complain of glare. The clinical value of the finding is therefore diagnostic rather than therapeutic, and it runs in both directions: pre-Descemet opacities in a male - especially a child, since the XLI-associated deposits appear in the first decade - are a reason to examine the skin and consider copy-number analysis of STS, and known ichthyosis is a reason to look at the cornea.
Show evidence (4 references)
PMID:38359414 SUPPORT Human Clinical
"Vision is usually unaffected, and patients are typically asymptomatic. One adult member of a recently described pedigree complained of glare."
States the visual outcome together with the single reported exception.
PMID:38359414 SUPPORT Human Clinical
"Several corneal dystrophies including FCD, PACD, CCDF, and PDCD are typically asymptomatic and do not require treatment."
Establishes that no treatment is indicated, which is why this entry curates none.
PMID:32482962 SUPPORT Human Clinical
"This report demonstrates that PDCD-associated XLI may present in children and that the diagnosis may be confirmed through multimodal imaging in conjunction with genetic analysis."
Establishes the diagnostic value of the corneal sign, including its presence in childhood.
+ 1 more reference
✶

Histopathology

3
Enlarged Posterior Keratocytes with Intracytoplasmic Lipid-Like Inclusions
Light microscopy of a PDCD cornea is normal apart from the posterior keratocytes, which are enlarged and contain vacuoles and intracytoplasmic inclusions of lipid-like material. The negative half of that description is as informative as the positive half: epithelium, Bowman layer, Descemet membrane and endothelium are unremarkable, so the lesion is a keratocyte lesion and not a corneal one in general.
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"Normal cornea except for enlarged keratocytes in the posterior stroma containing vacuoles and intracytoplasmic inclusions of lipid-like material."
The reference light-microscopic description of PDCD.
Membrane-Bound Vacuoles with Lipofuscin-Like Lipoprotein on Electron Microscopy
Transmission electron microscopy resolves the vacuoles as membrane-bound structures containing electron-dense material with the appearance of secondary lysosomes, plus inclusions of a lipofuscin-like lipoprotein - a pattern the reporting authors read as degenerative. No extracellular deposits are seen. That is the ultrastructural point on which PDCD parts company with the classical stromal dystrophies, every one of which is defined by extracellular accumulation.
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"Membrane-bound intracellular vacuoles containing electron-dense material suggestive of secondary lysosomes and inclusions of a lipofuscin-like lipoprotein consistent with a degenerative process are seen in PDCD. No extracellular deposits are noted."
The ultrastructural description, including the absence of extracellular deposit.
Inconsistent Histopathology Across Reported Cases
Recorded as a finding in its own right because it constrains every other histopathological claim on this entry. IC3D states that the histopathological studies of PDCD are not consistent, which is part of why the entity sits in category 4 and why the ultrastructural mechanism above is curated as provisional rather than established.
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"Histopathologic studies of PDCD are not consistent."
The classifying committee's own assessment of the reliability of the histopathology.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Pre-Descemet Corneal Dystrophy 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

4
Integument 1
Ichthyosis HP:0008064 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ichthyosis (HP:0008064). HP:0008064 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:37287641 SUPPORT Human Clinical
"Cutaneous examination demonstrated dry, coarse, scaly ichthyotic changes characteristic of XLI in all individuals."
Documents the ichthyotic skin phenotype in every affected individual of the two families.
PMID:28302098 SUPPORT Human Clinical
"Dermatological examination revealed that the skin over the patient's entire body was dry and coarse, with thickening and scaling of the skin in the extensor side of the extremities."
Records the distribution of the ichthyotic changes in a PDCD patient.
Other 3
Punctate Posterior Stromal Corneal Opacities Punctate opacification of the cornea HP:0007856 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Punctate opacification of the cornea (HP:0007856). HP:0007856 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:37287641 SUPPORT Human Clinical
"The slit-lamp examination of three affected men (two of whom were brothers) from two families revealed bilateral punctate posterior corneal stromal opacities anterior to the Descemet membrane."
Documents the bilateral punctate posterior stromal opacities in three genetically confirmed affected men.
PMID:23807007 SUPPORT Human Clinical
"The slit-lamp examination revealed punctate opacities in the posterior corneal stroma of each eye."
Independent documentation of the same bilateral finding.
Abnormal Posterior Corneal Stroma Abnormal corneal stroma morphology HP:0011492 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal corneal stroma morphology (HP:0011492). HP:0011492 is a phenotype from the Human Phenotype Ontology.
Carried alongside the punctate-opacity phenotype (HP:0007856) on purpose, even though HP:0011492 is that term's generic ancestor. The two record different observations at different resolutions: HP:0007856 is what the slit lamp sees (discrete grey punctae at a defined depth), while this entry is what confocal microscopy sees (enlarged, activated, particle-laden keratocytes). HPO has no term for the latter, so the generic parent is the closest available anchor and the specificity lives in the description. If a keratocyte-inclusion term is ever added, this binding should move to it.
Show evidence (1 reference)
PMID:28302098 SUPPORT Human Clinical
"Slit-lamp biomicroscopy showed the presence of tiny and pleomorphic opacities in the posterior stroma immediately anterior to Descemet membrane bilaterally."
Documents the abnormal posterior stromal morphology on which the confocal findings were made.
Glare
Left unbound deliberately. HPO has no term for glare - light scatter degrading image quality - and the nearest candidate, Photophobia (HP:0000613), is defined as "Excessive sensitivity to light with the sensation of discomfort or pain in the eyes due to exposure to bright light", which is a different complaint from glare produced by a light-scattering cornea. `sqlite:obo:hp` was searched for "glare" and for the Photophobia and abnormal-visual-function neighbourhoods; no suitable term exists. `frequency` is likewise omitted: the source describes a single adult in one pedigree, which is below the resolution of any FrequencyEnum band.
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"Vision is usually unaffected, and patients are typically asymptomatic. One adult member of a recently described pedigree complained of glare."
Records the single reported symptomatic individual against the general statement that patients are asymptomatic.
🧬

Genetic Associations

1
STS
Gene: STS hgnc:11425 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is STS (hgnc:11425). hgnc:11425 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (3 references)
PMID:37287641 SUPPORT Human Clinical
"Pre-Descemet corneal dystrophy (PDCD) with X-linked ichthyosis (XLI) is associated with mutations in or deletions of the steroid sulfatase gene (STS)."
States the gene-disease association for the XLI-associated arm.
PMID:37287641 SUPPORT Human Clinical
"As only three cases of genetically confirmed PDCD associated with XLI have been reported, we sought to expand our understanding of the genetic basis of PDCD by screening STS in two previously unreported families."
Records how few genetically confirmed cases existed, which bounds the strength of the gene-disease claim.
PMID:32482962 SUPPORT Human Clinical
"Copy number analysis identified a 4389 kbp hemizygous deletion on the X chromosome (chr. X: 6,540,898-8,167,604), resulting in the deletion of 4 genes, including the known locus of XLI, the STS gene."
Documents a large contiguous deletion encompassing STS in a PDCD patient.
🔬

Diagnosis

3
Slit-Lamp Biomicroscopy
The primary diagnostic examination. Depth is what matters: fine punctate opacities confined to the stroma immediately anterior to Descemet membrane, bilaterally, distinguish PDCD from opacities at any other corneal level.
Show evidence (1 reference)
PMID:32482962 SUPPORT Human Clinical
"Corneal opacities characteristic of PDCD located in the posterior corneal stroma just anterior to Descemet membrane were identified by slit-lamp biomicroscopy."
Establishes slit-lamp biomicroscopy as the examination that makes the diagnosis.
In Vivo Confocal Microscopy
Resolves the lesion at cellular level, showing the hyperreflective particles within enlarged and activated posterior keratocytes. This is what distinguishes PDCD mechanistically from the extracellular-deposition stromal dystrophies, and it is the modality that can characterise a lesion too fine for other techniques. It is not universally informative: in one reported child with genetically confirmed PDCD the confocal findings were unremarkable while slit-lamp, AS-OCT and Scheimpflug were all abnormal.
Show evidence (2 references)
PMID:28302098 SUPPORT Human Clinical
"In vivo confocal microscopy (IVCM) is a useful tool to examine the minimal lesions of the cornea at the cellular level."
States the diagnostic role of the modality for lesions of this scale.
PMID:32482962 REFUTE Human Clinical
"In vivo confocal microscopy findings were unremarkable."
A negative result in a genetically confirmed case, showing the modality does not always detect the lesion; recorded so the diagnostic claim is not overstated.
Copy Number Variation Analysis of STS
Array CGH or cytogenomic array analysis of the Xp22.31 region converts a presumptive clinical diagnosis into a confirmed one. It is the necessary test rather than exon PCR alone, because the commonest lesion is a deletion - and a complete deletion produces exactly the same result as failed amplification for any other reason, so absence of amplicons has to be followed by copy-number analysis to be interpretable.
Show evidence (2 references)
PMID:23807007 SUPPORT Human Clinical
"Polymerase chain reaction amplification using primers designed to amplify each of the 10 exons of STS failed to produce any amplicons."
Shows the PCR result that prompted, but could not by itself establish, the deletion diagnosis.
PMID:23807007 SUPPORT Human Clinical
"The identification of a microdeletion within Xp22.3 containing STS with aCGH in an individual with suspected pre-Descemet corneal dystrophy and X-linked ichthyosis demonstrates the clinical utility of copy number variation analysis in confirming a presumptive clinical diagnosis."
States the diagnostic utility of copy-number analysis for this entity.
🩻

Imaging Findings

1
Pre-Descemet Hyperreflective Line on OCT
Spectral-domain OCT shows a hyperreflective line immediately anterior to Descemet's membrane running limbus to limbus, with a second, thinner line beneath Bowman's layer and fine hyperreflective particles distributed through the posterior, mid and anterior stroma.
Oct
Show evidence (2 references)
PMID:31298040 SUPPORT Human Clinical
"Fine hyperreflective particles were observed in the posterior, mid, and anterior stroma on optical coherence tomography scans."
Documents the panstromal distribution of particles on OCT, beyond the pre-Descemet line that names the entity.
PMID:32482962 SUPPORT Human Clinical
"A pre-Descemet hyper-reflective line, consistent with these opacities, was seen with anterior segment optical coherence tomography."
Independent documentation of the pre-Descemet line in the STS-deficient arm.
📈

Progression

2
Onset
Isolated PDCD
Isolated PDCD usually appears after the age of 30, which is one of the practical discriminators from the XLI-associated deposits (first decade) and from PPPCD (reported as young as 3).
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"Usually after age 30 years; although PPPCD has been found in children as young as age 3 years."
Gives the age of onset for this entity, with the contrast to PPPCD.
Onset
XLI-Associated Deep Corneal Deposits
The deep corneal deposits of X-linked ichthyosis have been described in the first decade of life, and a genetically confirmed case has been reported in an 11-year-old boy - so an early-onset pre-Descemet finding should prompt a skin examination rather than a diagnosis of isolated PDCD.
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"It has been described in the first decade of life."
Gives the age of onset of the STS-associated arm.
📊

Prevalence

1
Males with X-linked ichthyosis (an upper bound on the XLI-associated subtype, not a measurement of PDCD)
Point Prevalence 16.7–50.0 per 100,000 1–9 per 10,000 XLI-Associated Deep Corneal Deposits
This is the prevalence of X-linked ichthyosis itself, 1/6,000 to 1/2,000 in males, recorded deliberately as a ceiling rather than as a measurement. PDCD occurs in only some XLI patients, so the true rate of the XLI-associated subtype is lower by an undetermined factor - the proportion of XLI patients with pre-Descemet opacities is not established in the cited literature, and is not invented here. The prevalence of isolated PDCD is not documented at all.
Show evidence (1 reference)
PMID:39086014 SUPPORT Human Clinical
"It is the second most common type of ichthyosis, with a prevalence of 1/6,000 to 1/2,000 in males and without any racial or geographical differences."
Gives the prevalence of the associated skin disorder, which bounds the XLI-associated subtype from above but does not measure it.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Pre-Descemet Corneal Dystrophy:

Cornea farinata
Overlapping Features An age-related degeneration producing many fine, dust-like grey-brown to white opacities bilaterally in the posterior stroma near Descemet membrane, best seen on retroillumination. IC3D includes it in the same template as PDCD, and the distinction from isolated PDCD is not sharp - the IC3D text treats "cornea farinata" as a name applied to the same finding.
Distinguishing Features
  • Opacities are finer and more dust-like than those of PDCD, and are best seen on retroillumination; confocal shows highly reflective particles in the cytoplasm of some keratocytes but only in the deep stroma, whereas in PDCD hyperreflective inclusions are both intracellular and extracellular.
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"In the degenerative condition, cornea farinata, many fine, dust-like gray-brown to white opacities are best seen on retroillumination and are located bilaterally in the posterior stroma near Descemet membrane."
Describes the appearance that has to be distinguished from PDCD.
Punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD)
Overlapping Features A separate entity, IC3D category 1, autosomal dominant, caused by PRDX3 variants at 10q26.11, with its own MONDO term (MONDO:0859248) and OMIM entry (#619871). It occupies the same corneal layer as PDCD and is the single most likely thing to be confused with it. Nothing about PRDX3 is curated on this entry.
Distinguishing Features
  • PPPCD deposits are polychromatic, larger and more punctate, and more uniform within an otherwise normal cornea; onset can be as young as age 3 against PDCD's usual onset after 30; PPPCD is non-progressive or mildly progressive where other forms of PDCD progress; and PPPCD has an identified gene and autosomal dominant pedigrees where PDCD has neither.
Show evidence (2 references)
PMID:38359414 SUPPORT Human Clinical
"In PPPCD, the pre-Descemet deposits are more uniform and polychromatic within the otherwise normal cornea."
Gives the phenotypic distinction between PPPCD and PDCD.
PMID:38359414 SUPPORT Human Clinical
"PPPCD is nonprogressive or possibly shows mild progression. Other forms of PDCD show progression."
Gives the progression distinction between the two entities.
Similar deep opacities in other ocular and systemic disease
Overlapping Features Deep pre-Descemet opacities are not specific to this entity. IC3D notes similar opacities in pseudoxanthoma elasticum, keratoconus, posterior polymorphous corneal dystrophy, epithelial basement membrane dystrophy and central cloudy dystrophy of Francois. The finding is therefore a starting point for a differential rather than a diagnosis on its own.
Distinguishing Features
  • Each of these carries its own additional corneal or systemic findings; isolated PDCD is a diagnosis of exclusion once they are absent.
Show evidence (1 reference)
PMID:38359414 SUPPORT Human Clinical
"Similar opacities have been noted in association with other ocular and systemic diseases such as pseudoxanthoma elasticum, keratoconus, posterior polymorphous corneal dystrophy (PPCD), EBMD, and central cloudy dystrophy of François (CCDF)."
Enumerates the conditions in which the same corneal appearance occurs.
🐁

Animal Models

1
Spontaneous canine posterior stromal dystrophy (comparative phenocopy)
A naturally occurring canine case, not an engineered model, and included here for what it does and does not establish. In vivo confocal microscopy of a dog with bilateral, non-inflammatory posterior corneal stromal opacities showed hyperreflective deposits inside keratocytes, with the number of enlarged deposit-containing keratocytes increasing toward the posterior stroma - the same cellular pattern, in the same corneal layer, with the same posterior-increasing gradient described in human PDCD. The reporting ophthalmologists say so themselves. No gene was identified and no orthologous variant demonstrated, so this is a comparative phenocopy rather than a validated natural model.
Species
Canis lupus familiaris
Genotype
Not determined - no orthologous mutation demonstrated
Publication
PMID:35346188
Pathograph links
Intracellular Deposition in Posterior Keratocytes partially recapitulates fidelity: low The canine cornea reproduces the cellular lesion this node curates - intracellular hyperreflective deposits in enlarged posterior keratocytes, graded toward Descemet membrane - independently of any human tissue.
Limitations: A single spontaneous case with no genotype: no STS variant, no orthologous mutation of any kind, and no demonstration that the stored material is the same. The resemblance is at the level of imaging phenotype only, and the reporting authors describe it as "reminiscent of" rather than as the same disease. It therefore cannot support any causal or therapeutic inference about the human entity; its value is that the cellular pattern recurs in a second species, which is weak evidence that the pattern is a real biological entity rather than an artefact of human imaging convention.
Readouts
Intra-keratocyte hyperreflective deposits on in vivo confocal microscopy
Direction: INCREASED
Interpretation: Deposits are intracellular and the affected keratocytes are enlarged, matching the human confocal description.
Show evidence (1 reference)
PMID:35346188 SUPPORT Model Organism
"With IVCM, hyperreflective deposits were identified within keratocytes and the number of enlarged keratocytes containing hyperreflective deposits increased towards the posterior stroma."
The confocal readout, including the posterior-increasing gradient that matches the human lesion.
Show evidence (1 reference)
PMID:35346188 SUPPORT Model Organism
"The bilateral, non-inflammatory nature and unique appearance with IVCM is most consistent with a posterior stromal dystrophy reminiscent of pre-Descemet corneal dystrophy described in humans."
The authors' own comparison to human PDCD, stated as a resemblance rather than an identity - which is exactly the strength of claim this link makes.
Recorded deliberately at LOW fidelity with `PARTIALLY_RECAPITULATES` rather than omitted or overstated. The deep-research report for this entry mentioned the observation but gave no identifier; the PMID was recovered by an independent PubMed search and the abstract read before curating.
{ }

Source YAML

click to show 
name: Pre-Descemet Corneal Dystrophy
creation_date: "2026-08-25T00:00:00Z"
description: >-
  Pre-Descemet corneal dystrophy (PDCD) is characterised by focal, fine,
  polymorphic grey opacities confined to the deep stroma immediately anterior to
  Descemet membrane. It involves the posterior stroma and nothing else, is
  bilateral, usually appears after the age of 30, and does not affect vision.

  Its status as a dystrophy is contested, and this entry curates the dispute
  rather than resolving it. The IC3D classification assigns PDCD to category 4,
  its lowest evidence tier, and states plainly that isolated PDCD is neither a
  well-defined entity nor clearly hereditary or degenerative. No gene, locus or
  MIM number is assigned. What ultrastructure exists points toward degeneration
  rather than storage of a genetically determined product: transmission electron
  microscopy shows membrane-bound intracellular vacuoles holding electron-dense
  material suggestive of secondary lysosomes, together with inclusions of a
  lipofuscin-like lipoprotein, and no extracellular deposits at all. That last
  detail is what most sharply separates PDCD from the classical stromal
  dystrophies it sits beside in the ontology, which are defined by abnormal
  material accumulating in the extracellular matrix and progressively opacifying
  the cornea. Against a purely degenerative reading, PDCD has been described in
  families over two to four generations, and some forms progress.

  Deep corneal deposits closely resembling PDCD are also frequently seen in
  X-linked ichthyosis, where they appear in the first decade and where every
  genetically characterised family carries a point mutation, partial deletion or
  complete deletion of STS at Xp22.31. Much of the ophthalmological literature
  labels those cases PDCD. IC3D explicitly declines to, on the ground that XLI is
  a systemic disease with corneal manifestations and therefore not a corneal
  dystrophy. Both arms are curated here, because MONDO:0017392 is the concept the
  clinical literature uses for both and because the two are told apart by skin
  examination, age of onset and STS analysis rather than by the corneal
  appearance - but the disagreement is recorded explicitly rather than smoothed
  over.

category: Genetic
parents:
- Stromal Corneal Dystrophy
- Corneal Dystrophy
- Ophthalmological Disease
synonyms:
- PDCD
- pre-Descemet corneal dystrophy
- pre-Descemet's membrane corneal dystrophy
- deep filiform dystrophy
- deep punctiform dystrophy
disease_term:
  preferred_term: pre-descemet corneal dystrophy
  term:
    id: MONDO:0017392
    label: pre-descemet corneal dystrophy
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0017392
      label: pre-descemet corneal dystrophy
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:37287641
      reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Pre-Descemet corneal dystrophy (PDCD) with X-linked ichthyosis (XLI) is
        associated with mutations in or deletions of the steroid sulfatase gene
        (STS).
      explanation: >-
        Establishes a defined single-gene lesion behind the best-characterised
        arm of this entity.
  - classification_value: DERMATOLOGY
    evidence:
    - reference: PMID:37287641
      reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Cutaneous examination demonstrated dry, coarse, scaly ichthyotic changes
        characteristic of XLI in all individuals.
      explanation: >-
        The corneal finding in this arm is one manifestation of a systemic
        keratinisation disorder, so the entity is also a dermatological one.
references:
- reference: PMID:37287641
  title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
- reference: PMID:32482962
  title: "Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene."
- reference: PMID:28302098
  title: "In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report."
- reference: PMID:23807007
  title: "Pre-Descemet corneal dystrophy and X-linked ichthyosis associated with deletion of Xp22.31 containing the STS gene."
- reference: PMID:38359414
  title: "IC3D Classification of Corneal Dystrophies-Edition 3."
- reference: PMID:39086014
  title: "Revisiting X-linked congenital ichthyosis."
- reference: PMID:31298040
  title: "Multimodal imaging of pre-Descemet corneal dystrophy."
- reference: PMID:35346188
  title: "Multimodal ocular imaging of known and novel corneal stromal disorders in dogs."
has_subtypes:
- name: Isolated PDCD
  display_name: Isolated PDCD (IC3D category 4)
  description: >-
    PDCD occurring without ichthyosis and without an identified gene - the
    entity MONDO and Orphanet actually define, and the one IC3D rates category 4.
    IC3D assigns it no MIM number, no locus and no gene, and describes it as
    neither well defined nor clearly hereditary or degenerative. The
    countervailing observation is that it has been reported in families across
    two to four generations, so a purely degenerative reading is not settled
    either. Onset is usually after age 30, which distinguishes it from the
    XLI-associated deposits of the other subtype.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Isolated pre-Descemet corneal dystrophy (PDCD) is neither a well-defined
      entity nor is it clearly a hereditary or degenerative disorder (known as
      cornea farinata, "flour-like cornea").
    explanation: >-
      The classifying committee's own statement of the entity's uncertain status.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Although no definite pattern of inheritance is established, it has been
      described in families over 2 to 4 generations.
    explanation: >-
      Records the familial clustering that argues against reading isolated PDCD
      as purely degenerative, while noting no inheritance pattern is established.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Usually after age 30 years; although PPPCD has been found in children as
      young as age 3 years.
    explanation: >-
      Gives the age of onset of this subtype, which is one of the features that
      separates it from the XLI-associated deposits.
- name: XLI-Associated Deep Corneal Deposits
  display_name: Deep corneal deposits of X-linked ichthyosis (STS)
  description: >-
    The genetically characterised arm, and the contested one. Affected men have
    bilateral punctate posterior stromal opacities anterior to Descemet membrane
    together with the dry, coarse, scaly skin of X-linked ichthyosis, and STS
    analysis shows a point mutation, a partial deletion of the coding exons, or
    a complete deletion of the locus at Xp22.31. That three different classes of
    lesion produce an indistinguishable corneal phenotype is itself the argument
    that they all act through loss of steroid sulfatase function.

    It is named "deep corneal deposits" rather than "PDCD" deliberately. Much of
    the ophthalmological literature - including every primary report cited here -
    calls these cases PDCD, but IC3D expressly refuses the label because XLI is a
    systemic disease with corneal manifestations. The subtype is retained under
    this MONDO concept because that is how the clinical literature indexes it,
    with the dissent recorded as evidence rather than suppressed.
  genes:
  - preferred_term: STS
    term:
      id: hgnc:11425
      label: STS
  evidence:
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The slit-lamp examination of three affected men (two of whom were
      brothers) from two families revealed bilateral punctate posterior corneal
      stromal opacities anterior to the Descemet membrane.
    explanation: >-
      Defines the corneal phenotype of this subtype in genetically confirmed
      individuals.
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PDCD with XLI may be associated with either partial or complete deletion
      of STS.
    explanation: >-
      States the allelic spectrum that defines this subtype, and shows the
      primary literature does apply the PDCD label to it.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: REFUTE
    evidence_source: OTHER
    snippet: >-
      Similar deep corneal deposits to PDCD are also frequently seen in X-linked
      ichthyosis (MIM #308100) which results from mutations in the steroid
      sulfatase gene (STS) at genetic locus Xp22.31.
    explanation: >-
      IC3D describes these deposits as merely SIMILAR to PDCD rather than as
      PDCD, which is the first half of its refusal to classify them together.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: REFUTE
    evidence_source: OTHER
    snippet: >-
      This is a systemic disease with corneal manifestations and therefore is
      not a corneal dystrophy.
    explanation: >-
      The explicit IC3D position that this arm is not a corneal dystrophy at
      all - recorded as REFUTE against its inclusion as a subtype of PDCD.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It has been described in the first decade of life.
    explanation: >-
      Gives the early onset of this arm, in contrast to the post-30 onset of
      isolated PDCD - a practical discriminator between the two.
inheritance:
- name: X-linked recessive inheritance
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  description: >-
    In the XLI-associated subtype the lesion is at Xp22.3 and the reported
    affected individuals are men, including two brothers in one family. The
    corneal finding therefore segregates with X-linked ichthyosis itself, whose
    causative gene STS lies at that locus. This inheritance block describes the
    XLI-associated arm only; isolated PDCD has no established mode of
    inheritance, which is part of why IC3D rates it category 4.
  evidence:
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genetic examination of the STS locus on the X chromosome in Case 1
      revealed a deletion that spanned across DNA markers DXS1130-DXS237, which
      includes all the coding exons (exons 1-10) of STS.
    explanation: >-
      Places the causal lesion on the X chromosome in an affected male.
  - reference: PMID:39086014
    reference_title: "Revisiting X-linked congenital ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The causative gene for XLI is the steroid sulfatase gene (STS), located on
      Xp22.3.
    explanation: >-
      Confirms the gene and cytoband of the associated X-linked disorder.
pathophysiology:
- name: Keratocyte Lysosomal Lipofuscin-Like Lipoprotein Accumulation
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: PROVISIONAL
  subtypes:
  - Isolated PDCD
  description: >-
    The proposed initiating lesion of the isolated arm, and the reason that arm
    reads as a degeneration. Transmission electron microscopy of PDCD corneas
    shows membrane-bound intracellular vacuoles containing electron-dense
    material that has the appearance of secondary lysosomes, together with
    inclusions of a lipofuscin-like lipoprotein. Lipofuscin is the classic
    marker of accumulated, incompletely degraded material in long-lived
    post-mitotic cells, and its presence is what the reporting authors read as
    evidence of a degenerative process rather than of a genetically determined
    storage product. Consistent with that, onset is usually after age 30.

    It is curated PROVISIONAL rather than established because IC3D itself
    reports that the histopathological studies of PDCD are not consistent, and
    because no gene, locus or metabolic defect has been assigned that would
    explain why the material accumulates.
  cellular_components:
  - preferred_term: lysosome
    modifier: INCREASED
    term:
      id: GO:0005764
      label: lysosome
  cell_types:
  - preferred_term: Posterior stromal keratocyte
    term:
      id: CL:0002363
      label: keratocyte
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Membrane-bound intracellular vacuoles containing electron-dense material
      suggestive of secondary lysosomes and inclusions of a lipofuscin-like
      lipoprotein consistent with a degenerative process are seen in PDCD.
    explanation: >-
      The ultrastructural basis of this node, including the authors' own reading
      of it as degenerative.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Histopathologic studies of PDCD are not consistent.
    explanation: >-
      The explicit caveat that makes this node provisional rather than
      established.
  - reference: PMID:31298040
    reference_title: "Multimodal imaging of pre-Descemet corneal dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The clinical presentation and structural anomalies found in isolated
      sporadic pre-Descemet corneal dystrophy are in favor of a degenerative
      process affecting corneal keratocytes with no epithelial or endothelial
      involvement.
    explanation: >-
      An independent in vivo imaging series reaching the same degenerative,
      keratocyte-centred conclusion.
  downstream:
  - target: Intracellular Deposition in Posterior Keratocytes
    causal_link_type: DIRECT
    description: >-
      Undegraded lipoprotein retained in secondary lysosomes is the material
      that renders the keratocyte hyperreflective.
- name: Loss of Steroid Sulfatase Function
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: ESTABLISHED
  subtypes:
  - XLI-Associated Deep Corneal Deposits
  description: >-
    The trigger of the genetically characterised arm. STS at Xp22.31 encodes
    steroid sulfatase, the enzyme that hydrolyses cholesterol sulfate,
    dehydroepiandrosterone sulfate and estrone sulfate. Three classes of lesion
    have been found in families with pre-Descemet deposits and X-linked
    ichthyosis - point mutations, partial deletions removing some of the ten
    coding exons, and complete deletion of the locus, in one case a 4.4 Mb
    hemizygous deletion taking three further genes with it. The informative
    observation is that the corneal phenotype does not differ between these
    classes, which is the argument that all of them converge on loss of enzyme
    function rather than on some deletion-size-dependent contiguous-gene effect.
  genes:
  - preferred_term: STS
    term:
      id: hgnc:11425
      label: STS
  genetic_context:
    functional_impact_category: LOSS_OF_FUNCTION
    variant_origin: GERMLINE
    zygosity: HEMIZYGOUS
    description: >-
      Hemizygous point mutations, partial deletions (exons 1-7 reported) and
      complete deletions of STS at Xp22.31 in affected males.
  molecular_functions:
  - preferred_term: steryl-sulfatase activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0004773
      label: steryl-sulfatase activity
  evidence:
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genetic screening of Cases 2 and 3 revealed a partial deletion of the STS
      locus involving exons 1-7 and flanking DNA marker DXS1130 on the X
      chromosome.
    explanation: >-
      Documents a partial-deletion allele in two affected brothers.
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Despite the identification of point mutations, partial deletion, and
      complete deletion of STS in different affected families reported to date,
      there was no apparent difference in the affected phenotype between the
      families, suggesting that the identified variants likely all resulted in
      loss of function of steroid sulfatase.
    explanation: >-
      The allelic-heterogeneity-with-uniform-phenotype argument that identifies
      loss of enzyme function, rather than deletion extent, as the mechanism.
  - reference: PMID:23807007
    reference_title: "Pre-Descemet corneal dystrophy and X-linked ichthyosis associated with deletion of Xp22.31 containing the STS gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      aCGH performed on genomic DNA revealed a microdeletion in the Xp22.31
      cytoband of approximately 1.7 megabases, containing STS.
    explanation: >-
      Documents a whole-locus microdeletion in an affected individual.
  - reference: PMID:28302098
    reference_title: "In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PCR results demonstrated that all ten exons and part flanking sequences of
      STS gene failed to produce any amplicons in the patient.
    explanation: >-
      Independent confirmation of complete loss of the STS coding sequence in a
      patient with pre-Descemet deposits.
  downstream:
  - target: Cholesterol Sulfate Accumulation
    causal_link_type: DIRECT
    description: >-
      Steroid sulfatase is the enzyme that hydrolyses cholesterol sulfate, so
      its loss allows the substrate to accumulate.
    evidence:
    - reference: PMID:39086014
      reference_title: "Revisiting X-linked congenital ichthyosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation
        in the stratum corneum (SC).
      explanation: >-
        Establishes the enzyme-to-substrate step, demonstrated in skin.
- name: Cholesterol Sulfate Accumulation
  biological_scale: MOLECULAR
  role: central_effector
  mechanism_confidence: PROVISIONAL
  subtypes:
  - XLI-Associated Deep Corneal Deposits
  description: >-
    Steroid sulfatase hydrolyses cholesterol sulfate, so loss of the enzyme
    allows the sulfated sterol to accumulate. This is firmly established in the
    skin, where excess cholesterol sulfate in the stratum corneum is what
    produces the barrier dysfunction and scaling of X-linked ichthyosis, and it
    is the natural candidate for the corneal deposit as well.

    It is curated as PROVISIONAL because that last step is an inference, and
    because there is a competing candidate. No study has chemically identified
    the material inside the posterior keratocytes of an STS-deficient cornea;
    what has been shown is that the deposit is there, that it is intracellular,
    and that the patient lacks steroid sulfatase. Meanwhile the ultrastructural
    material characterised in isolated PDCD is a lipofuscin-like lipoprotein,
    not a sulfated sterol. Whether the two arms share a stored substance or
    merely a location is unresolved, and the knowledge-gap discussion on this
    entry keeps that open rather than assuming it.
  chemical_entities:
  - preferred_term: cholesterol sulfate
    modifier: INCREASED
    term:
      id: CHEBI:41321
      label: cholesterol sulfate
  evidence:
  - reference: PMID:39086014
    reference_title: "Revisiting X-linked congenital ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation in
      the stratum corneum (SC).
    explanation: >-
      Establishes substrate accumulation as the direct consequence of enzyme
      loss - but in stratum corneum, not cornea. Recorded as PARTIAL rather than
      SUPPORT so the support level itself carries the tissue mismatch, instead of
      leaving it to the surrounding prose.
  - reference: PMID:39086014
    reference_title: "Revisiting X-linked congenital ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Excess CS induces epidermal permeability barrier dysfunction and scaling
      abnormalities.
    explanation: >-
      Shows the downstream consequence of the accumulated substrate is
      characterised in epidermis, not in cornea - the reason this node is
      provisional for the eye.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      inclusions of a lipofuscin-like lipoprotein consistent with a degenerative
      process are seen in PDCD
    explanation: >-
      The competing substrate identity characterised in isolated PDCD, which is
      why a shared cholesterol-sulfate deposit cannot be assumed across both
      arms.
  downstream:
  - target: Intracellular Deposition in Posterior Keratocytes
    causal_link_type: DIRECT
    description: >-
      Accumulated sulfated sterol is the proposed identity of the
      hyperreflective material seen within posterior keratocytes in this arm;
      the link is inferred from skin, not demonstrated in cornea.
- name: Intracellular Deposition in Posterior Keratocytes
  biological_scale: CELLULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  description: >-
    The shared cellular lesion, and the observation that most sharply separates
    this entity from the classical stromal dystrophies. In vivo confocal
    microscopy shows enlarged, hyperreflective keratocytes in the posterior
    stroma carrying intracellular dots, with activated keratocytes as far
    forward as the very anterior stroma; the same is seen in the STS-deficient
    arm, where hyperreflective particles sit inside enlarged and activated
    posterior keratocytes. The stromal dystrophies in the same MONDO branch -
    macular, Schnyder, congenital stromal, the TGFBI forms - deposit abnormal
    material in the extracellular matrix and progressively opacify the cornea.
    Here the cell is the affected compartment, the cells are enlarged and
    activated rather than lost, and the epithelium and endothelium are spared.

    The extracellular contribution is not nil, and the entry does not pretend
    otherwise: diffuse small extracellular stromal deposits are described in
    vivo, even though transmission electron microscopy of PDCD reports none.
    That is one of the inconsistencies IC3D flags in the histopathology.
  cell_types:
  - preferred_term: Posterior stromal keratocyte
    term:
      id: CL:0002363
      label: keratocyte
  locations:
  - preferred_term: Corneal stroma
    term:
      id: UBERON:0001777
      label: substantia propria of cornea
  evidence:
  - reference: PMID:31298040
    reference_title: "Multimodal imaging of pre-Descemet corneal dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Diffuse small extracellular stromal deposits, presence of enlarged
      hyperreflective keratocytes in the posterior stroma with either
      hyperreflective or hyporeflective intracellular dots, and presence of
      activated keratocytes in the very anterior stroma were observed in all
      corneas with in vivo confocal microscopy.
    explanation: >-
      The defining cellular finding, present in all eight corneas of a
      four-patient series, including the extracellular component.
  - reference: PMID:28302098
    reference_title: "In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      IVCM revealed regular distributed hyperreflective particles inside the
      enlarged and activated keratocytes in the posterior stroma.
    explanation: >-
      The same intracellular posterior-keratocyte lesion in the STS-deficient
      arm, which is what makes the two arms clinically indistinguishable.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Normal cornea except for enlarged keratocytes in the posterior stroma
      containing vacuoles and intracytoplasmic inclusions of lipid-like
      material.
    explanation: >-
      Light-microscopic confirmation that the abnormality is confined to
      enlarged, inclusion-bearing posterior keratocytes.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      No extracellular deposits are noted.
    explanation: >-
      The electron-microscopic finding of no extracellular deposit, which
      conflicts with the in vivo confocal observation of diffuse extracellular
      deposits and is recorded here rather than reconciled.
  downstream:
  - target: Deep Stromal Punctate Opacification Anterior to Descemet Membrane
    causal_link_type: DIRECT
    description: >-
      Light-scattering, particle-laden keratocytes concentrated in the deepest
      stroma are what the slit lamp resolves as discrete punctate opacities.
- name: Deep Stromal Punctate Opacification Anterior to Descemet Membrane
  biological_scale: TISSUE
  role: consequence
  mechanism_confidence: ESTABLISHED
  description: >-
    The tissue-level endpoint and the diagnostic finding: focal, fine,
    polymorphic grey opacities - central, annular or diffuse - confined to the
    deep stroma immediately anterior to Descemet membrane, bilaterally.
    Cross-sectional imaging resolves the same thing as a hyperreflective line
    running limbus to limbus just anterior to Descemet's membrane, and
    Scheimpflug tomography shows a second, posterior light-scattering peak that
    does not belong in a normal cornea.

    The name is a slight misdescription that is worth stating explicitly: the
    opacities are visible pre-Descemet, but multimodal imaging finds fine
    hyperreflective particles through the posterior, mid and anterior stroma.
    The disorder affects the whole stroma; the pre-Descemet location is where
    the damage is maximal, not where it is confined.
  locations:
  - preferred_term: Descemet's membrane
    term:
      id: UBERON:0004367
      label: Descemet's membrane
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Focal, fine, polymorphic gray opacities that may be central, annular, or
      diffuse are visible in the deep stroma immediately anterior to Descemet
      membrane
    explanation: >-
      The reference description of the defining lesion and its variants.
  - reference: PMID:31298040
    reference_title: "Multimodal imaging of pre-Descemet corneal dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Spectral domain optical coherence tomography scans showed a
      hyperreflective line anterior to Descemet's membrane running from limbus
      to limbus and associated with a second thinner hyperreflective line just
      beneath Bowman's layer.
    explanation: >-
      Confirms the depth-restricted lesion on cross-sectional imaging and
      records a second anterior line, evidence that the process is not confined
      posteriorly.
  - reference: PMID:31298040
    reference_title: "Multimodal imaging of pre-Descemet corneal dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Multimodal imaging of cornea reveals that the disorder affects the whole
      stroma
    explanation: >-
      Directly qualifies the "pre-Descemet" name: the visible opacities are
      deep, but the process is panstromal.
  - reference: PMID:32482962
    reference_title: "Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Scheimpflug tomography revealed a bimodal peak light scattering.
    explanation: >-
      Provides an objective optical measurement of the extra posterior
      scattering layer.
  downstream:
  - target: Visually Silent Corneal Finding
    causal_link_type: DIRECT
    description: >-
      Because the opacities are fine, deep and non-confluent they do not degrade
      the retinal image, so the finding presents as a sign rather than as visual
      loss.
- name: Visually Silent Corneal Finding
  biological_scale: ORGANISM
  role: consequence
  mechanism_confidence: ESTABLISHED
  description: >-
    The organism-level outcome, unusual in being an absence of disability.
    Vision is usually unaffected and patients are typically asymptomatic, so
    PDCD requires no treatment; IC3D lists it among the dystrophies that are
    typically asymptomatic and need none. The qualifier "usually" is theirs and
    is kept here, because one adult in a recently described pedigree did
    complain of glare.

    The clinical value of the finding is therefore diagnostic rather than
    therapeutic, and it runs in both directions: pre-Descemet opacities in a
    male - especially a child, since the XLI-associated deposits appear in the
    first decade - are a reason to examine the skin and consider copy-number
    analysis of STS, and known ichthyosis is a reason to look at the cornea.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Vision is usually unaffected, and patients are typically asymptomatic. One
      adult member of a recently described pedigree complained of glare.
    explanation: >-
      States the visual outcome together with the single reported exception.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Several corneal dystrophies including FCD, PACD, CCDF, and PDCD are
      typically asymptomatic and do not require treatment.
    explanation: >-
      Establishes that no treatment is indicated, which is why this entry
      curates none.
  - reference: PMID:32482962
    reference_title: "Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This report demonstrates that PDCD-associated XLI may present in children
      and that the diagnosis may be confirmed through multimodal imaging in
      conjunction with genetic analysis.
    explanation: >-
      Establishes the diagnostic value of the corneal sign, including its
      presence in childhood.
  - reference: PMID:23807007
    reference_title: "Pre-Descemet corneal dystrophy and X-linked ichthyosis associated with deletion of Xp22.31 containing the STS gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The identification of a microdeletion within Xp22.3 containing STS with
      aCGH in an individual with suspected pre-Descemet corneal dystrophy and
      X-linked ichthyosis demonstrates the clinical utility of copy number
      variation analysis in confirming a presumptive clinical diagnosis.
    explanation: >-
      States the clinical use of the finding: it converts a presumptive
      diagnosis into a confirmed one via copy-number analysis.
phenotypes:
- category: Ophthalmologic
  name: Punctate Posterior Stromal Corneal Opacities
  description: >-
    Numerous fine, polymorphic, punctate opacities in the deep corneal stroma
    immediately anterior to Descemet membrane, bilateral. This is the defining
    finding of the entity; its depth restriction is what makes the diagnosis.
  phenotype_term:
    preferred_term: Punctate opacification of the cornea
    term:
      id: HP:0007856
      label: Punctate opacification of the cornea
  diagnostic: true
  evidence:
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The slit-lamp examination of three affected men (two of whom were
      brothers) from two families revealed bilateral punctate posterior corneal
      stromal opacities anterior to the Descemet membrane.
    explanation: >-
      Documents the bilateral punctate posterior stromal opacities in three
      genetically confirmed affected men.
  - reference: PMID:23807007
    reference_title: "Pre-Descemet corneal dystrophy and X-linked ichthyosis associated with deletion of Xp22.31 containing the STS gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The slit-lamp examination revealed punctate opacities in the posterior
      corneal stroma of each eye.
    explanation: >-
      Independent documentation of the same bilateral finding.
- category: Ophthalmologic
  name: Abnormal Posterior Corneal Stroma
  description: >-
    The structural abnormality underlying the visible opacities: enlarged,
    activated keratocytes in the posterior stroma laden with hyperreflective
    intracellular particles.
  notes: >-
    Carried alongside the punctate-opacity phenotype (HP:0007856) on purpose,
    even though HP:0011492 is that term's generic ancestor. The two record
    different observations at different resolutions: HP:0007856 is what the slit
    lamp sees (discrete grey punctae at a defined depth), while this entry is
    what confocal microscopy sees (enlarged, activated, particle-laden
    keratocytes). HPO has no term for the latter, so the generic parent is the
    closest available anchor and the specificity lives in the description. If a
    keratocyte-inclusion term is ever added, this binding should move to it.
  phenotype_term:
    preferred_term: Abnormal corneal stroma morphology
    term:
      id: HP:0011492
      label: Abnormal corneal stroma morphology
  evidence:
  - reference: PMID:28302098
    reference_title: "In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Slit-lamp biomicroscopy showed the presence of tiny and pleomorphic
      opacities in the posterior stroma immediately anterior to Descemet
      membrane bilaterally.
    explanation: >-
      Documents the abnormal posterior stromal morphology on which the confocal
      findings were made.
- category: Dermatologic
  name: Ichthyosis
  description: >-
    Dry, coarse, scaling skin, most marked on the extensor surfaces of the
    limbs. In the XLI-associated subtype this is not a comorbidity but the same
    disorder seen in a second organ, and it is what makes the corneal finding
    diagnostically actionable.
  subtype: XLI-Associated Deep Corneal Deposits
  phenotype_term:
    preferred_term: Ichthyosis
    term:
      id: HP:0008064
      label: Ichthyosis
  evidence:
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Cutaneous examination demonstrated dry, coarse, scaly ichthyotic changes
      characteristic of XLI in all individuals.
    explanation: >-
      Documents the ichthyotic skin phenotype in every affected individual of
      the two families.
  - reference: PMID:28302098
    reference_title: "In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dermatological examination revealed that the skin over the patient's
      entire body was dry and coarse, with thickening and scaling of the skin in
      the extensor side of the extremities.
    explanation: >-
      Records the distribution of the ichthyotic changes in a PDCD patient.
- category: Ophthalmologic
  name: Glare
  description: >-
    Vision is usually unaffected in this entity, but not invariably: one adult
    member of a recently described pedigree complained of glare. Recorded
    because "asymptomatic" is the entity's defining clinical claim, and a single
    documented exception to it is worth carrying rather than rounding away.
  phenotype_term:
    preferred_term: Glare
  notes: >-
    Left unbound deliberately. HPO has no term for glare - light scatter
    degrading image quality - and the nearest candidate, Photophobia
    (HP:0000613), is defined as "Excessive sensitivity to light with the
    sensation of discomfort or pain in the eyes due to exposure to bright
    light", which is a different complaint from glare produced by a
    light-scattering cornea. `sqlite:obo:hp` was searched for "glare" and for
    the Photophobia and abnormal-visual-function neighbourhoods; no suitable
    term exists. `frequency` is likewise omitted: the source describes a single
    adult in one pedigree, which is below the resolution of any FrequencyEnum
    band.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Vision is usually unaffected, and patients are typically asymptomatic. One
      adult member of a recently described pedigree complained of glare.
    explanation: >-
      Records the single reported symptomatic individual against the general
      statement that patients are asymptomatic.
histopathology:
- name: Enlarged Posterior Keratocytes with Intracytoplasmic Lipid-Like Inclusions
  description: >-
    Light microscopy of a PDCD cornea is normal apart from the posterior
    keratocytes, which are enlarged and contain vacuoles and intracytoplasmic
    inclusions of lipid-like material. The negative half of that description is
    as informative as the positive half: epithelium, Bowman layer, Descemet
    membrane and endothelium are unremarkable, so the lesion is a keratocyte
    lesion and not a corneal one in general.
  diagnostic: true
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Normal cornea except for enlarged keratocytes in the posterior stroma
      containing vacuoles and intracytoplasmic inclusions of lipid-like
      material.
    explanation: >-
      The reference light-microscopic description of PDCD.
- name: Membrane-Bound Vacuoles with Lipofuscin-Like Lipoprotein on Electron Microscopy
  description: >-
    Transmission electron microscopy resolves the vacuoles as membrane-bound
    structures containing electron-dense material with the appearance of
    secondary lysosomes, plus inclusions of a lipofuscin-like lipoprotein - a
    pattern the reporting authors read as degenerative. No extracellular
    deposits are seen. That is the ultrastructural point on which PDCD parts
    company with the classical stromal dystrophies, every one of which is
    defined by extracellular accumulation.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Membrane-bound intracellular vacuoles containing electron-dense material
      suggestive of secondary lysosomes and inclusions of a lipofuscin-like
      lipoprotein consistent with a degenerative process are seen in PDCD. No
      extracellular deposits are noted.
    explanation: >-
      The ultrastructural description, including the absence of extracellular
      deposit.
- name: Inconsistent Histopathology Across Reported Cases
  description: >-
    Recorded as a finding in its own right because it constrains every other
    histopathological claim on this entry. IC3D states that the
    histopathological studies of PDCD are not consistent, which is part of why
    the entity sits in category 4 and why the ultrastructural mechanism above is
    curated as provisional rather than established.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Histopathologic studies of PDCD are not consistent.
    explanation: >-
      The classifying committee's own assessment of the reliability of the
      histopathology.
imaging_findings:
- name: Pre-Descemet Hyperreflective Line on OCT
  modality: OCT
  description: >-
    Spectral-domain OCT shows a hyperreflective line immediately anterior to
    Descemet's membrane running limbus to limbus, with a second, thinner line
    beneath Bowman's layer and fine hyperreflective particles distributed
    through the posterior, mid and anterior stroma.
  evidence:
  - reference: PMID:31298040
    reference_title: "Multimodal imaging of pre-Descemet corneal dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Fine hyperreflective particles were observed in the posterior, mid, and
      anterior stroma on optical coherence tomography scans.
    explanation: >-
      Documents the panstromal distribution of particles on OCT, beyond the
      pre-Descemet line that names the entity.
  - reference: PMID:32482962
    reference_title: "Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A pre-Descemet hyper-reflective line, consistent with these opacities, was
      seen with anterior segment optical coherence tomography.
    explanation: >-
      Independent documentation of the pre-Descemet line in the STS-deficient
      arm.
differential_diagnoses:
- name: Cornea farinata
  description: >-
    An age-related degeneration producing many fine, dust-like grey-brown to
    white opacities bilaterally in the posterior stroma near Descemet membrane,
    best seen on retroillumination. IC3D includes it in the same template as
    PDCD, and the distinction from isolated PDCD is not sharp - the IC3D text
    treats "cornea farinata" as a name applied to the same finding.
  distinguishing_features:
  - >-
      Opacities are finer and more dust-like than those of PDCD, and are best seen
      on retroillumination; confocal shows highly reflective particles in the
      cytoplasm of some keratocytes but only in the deep stroma, whereas in PDCD
      hyperreflective inclusions are both intracellular and extracellular.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the degenerative condition, cornea farinata, many fine, dust-like
      gray-brown to white opacities are best seen on retroillumination and are
      located bilaterally in the posterior stroma near Descemet membrane.
    explanation: >-
      Describes the appearance that has to be distinguished from PDCD.
- name: Punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD)
  description: >-
    A separate entity, IC3D category 1, autosomal dominant, caused by PRDX3
    variants at 10q26.11, with its own MONDO term (MONDO:0859248) and OMIM entry
    (#619871). It occupies the same corneal layer as PDCD and is the single most
    likely thing to be confused with it. Nothing about PRDX3 is curated on this
    entry.
  distinguishing_features:
  - >-
      PPPCD deposits are polychromatic, larger and more punctate, and more uniform
      within an otherwise normal cornea; onset can be as young as age 3 against
      PDCD's usual onset after 30; PPPCD is non-progressive or mildly progressive
      where other forms of PDCD progress; and PPPCD has an identified gene and
      autosomal dominant pedigrees where PDCD has neither.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In PPPCD, the pre-Descemet deposits are more uniform and polychromatic
      within the otherwise normal cornea.
    explanation: >-
      Gives the phenotypic distinction between PPPCD and PDCD.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PPPCD is nonprogressive or possibly shows mild progression. Other forms of
      PDCD show progression.
    explanation: >-
      Gives the progression distinction between the two entities.
- name: Similar deep opacities in other ocular and systemic disease
  description: >-
    Deep pre-Descemet opacities are not specific to this entity. IC3D notes
    similar opacities in pseudoxanthoma elasticum, keratoconus, posterior
    polymorphous corneal dystrophy, epithelial basement membrane dystrophy and
    central cloudy dystrophy of Francois. The finding is therefore a starting
    point for a differential rather than a diagnosis on its own.
  distinguishing_features:
  - >-
      Each of these carries its own additional corneal or systemic findings;
      isolated PDCD is a diagnosis of exclusion once they are absent.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Similar opacities have been noted in association with other ocular and
      systemic diseases such as pseudoxanthoma elasticum, keratoconus, posterior
      polymorphous corneal dystrophy (PPCD), EBMD, and central cloudy dystrophy
      of François (CCDF).
    explanation: >-
      Enumerates the conditions in which the same corneal appearance occurs.
progression:
- phase: Onset
  subtype: Isolated PDCD
  notes: >-
    Isolated PDCD usually appears after the age of 30, which is one of the
    practical discriminators from the XLI-associated deposits (first decade) and
    from PPPCD (reported as young as 3).
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Usually after age 30 years; although PPPCD has been found in children as
      young as age 3 years.
    explanation: >-
      Gives the age of onset for this entity, with the contrast to PPPCD.
- phase: Onset
  subtype: XLI-Associated Deep Corneal Deposits
  notes: >-
    The deep corneal deposits of X-linked ichthyosis have been described in the
    first decade of life, and a genetically confirmed case has been reported in
    an 11-year-old boy - so an early-onset pre-Descemet finding should prompt a
    skin examination rather than a diagnosis of isolated PDCD.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It has been described in the first decade of life.
    explanation: >-
      Gives the age of onset of the STS-associated arm.
genetic:
- name: STS
  gene_term:
    preferred_term: STS
    term:
      id: hgnc:11425
      label: STS
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: PRESENT
  subtype: XLI-Associated Deep Corneal Deposits
  notes: >-
    STS (Xp22.3) encodes steroid sulfatase. It is the causative gene of X-linked
    ichthyosis, and every genetically characterised PDCD family reported to date
    carries an STS lesion. Three allele classes have been described in PDCD
    specifically - point mutations, partial deletion of the coding exons (exons
    1-7 in one family of two brothers), and complete deletion of the locus,
    including a 4389 kbp hemizygous deletion that removed four genes. The
    phenotype does not differ between these classes, which argues that all act
    through loss of enzyme function rather than through the extra genes a large
    deletion removes. Note the scope limit: STS is causative for the
    XLI-associated arm only. Isolated PDCD has no identified gene, and IC3D
    places it in category 4 for that reason.
  evidence:
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pre-Descemet corneal dystrophy (PDCD) with X-linked ichthyosis (XLI) is
      associated with mutations in or deletions of the steroid sulfatase gene
      (STS).
    explanation: >-
      States the gene-disease association for the XLI-associated arm.
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      As only three cases of genetically confirmed PDCD associated with XLI have
      been reported, we sought to expand our understanding of the genetic basis
      of PDCD by screening STS in two previously unreported families.
    explanation: >-
      Records how few genetically confirmed cases existed, which bounds the
      strength of the gene-disease claim.
  - reference: PMID:32482962
    reference_title: "Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Copy number analysis identified a 4389 kbp hemizygous deletion on the X
      chromosome (chr. X: 6,540,898-8,167,604), resulting in the deletion of 4
      genes, including the known locus of XLI, the STS gene.
    explanation: >-
      Documents a large contiguous deletion encompassing STS in a PDCD patient.
animal_models:
- name: Spontaneous canine posterior stromal dystrophy (comparative phenocopy)
  species: Canis lupus familiaris
  genotype: Not determined - no orthologous mutation demonstrated
  publication: PMID:35346188
  description: >-
    A naturally occurring canine case, not an engineered model, and included here
    for what it does and does not establish. In vivo confocal microscopy of a dog
    with bilateral, non-inflammatory posterior corneal stromal opacities showed
    hyperreflective deposits inside keratocytes, with the number of enlarged
    deposit-containing keratocytes increasing toward the posterior stroma - the
    same cellular pattern, in the same corneal layer, with the same
    posterior-increasing gradient described in human PDCD. The reporting
    ophthalmologists say so themselves.

    No gene was identified and no orthologous variant demonstrated, so this is a
    comparative phenocopy rather than a validated natural model.
  modeled_mechanisms:
  - target: Intracellular Deposition in Posterior Keratocytes
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      The canine cornea reproduces the cellular lesion this node curates -
      intracellular hyperreflective deposits in enlarged posterior keratocytes,
      graded toward Descemet membrane - independently of any human tissue.
    limitations: >-
      A single spontaneous case with no genotype: no STS variant, no orthologous
      mutation of any kind, and no demonstration that the stored material is the
      same. The resemblance is at the level of imaging phenotype only, and the
      reporting authors describe it as "reminiscent of" rather than as the same
      disease. It therefore cannot support any causal or therapeutic inference
      about the human entity; its value is that the cellular pattern recurs in a
      second species, which is weak evidence that the pattern is a real
      biological entity rather than an artefact of human imaging convention.
    readouts:
    - name: Intra-keratocyte hyperreflective deposits on in vivo confocal microscopy
      target: Intracellular Deposition in Posterior Keratocytes
      direction: INCREASED
      interpretation: >-
        Deposits are intracellular and the affected keratocytes are enlarged,
        matching the human confocal description.
      evidence:
      - reference: PMID:35346188
        reference_title: "Multimodal ocular imaging of known and novel corneal stromal disorders in dogs."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          With IVCM, hyperreflective deposits were identified within keratocytes
          and the number of enlarged keratocytes containing hyperreflective
          deposits increased towards the posterior stroma.
        explanation: >-
          The confocal readout, including the posterior-increasing gradient that
          matches the human lesion.
    evidence:
    - reference: PMID:35346188
      reference_title: "Multimodal ocular imaging of known and novel corneal stromal disorders in dogs."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The bilateral, non-inflammatory nature and unique appearance with IVCM is
        most consistent with a posterior stromal dystrophy reminiscent of
        pre-Descemet corneal dystrophy described in humans.
      explanation: >-
        The authors' own comparison to human PDCD, stated as a resemblance rather
        than an identity - which is exactly the strength of claim this link
        makes.
  notes: >-
    Recorded deliberately at LOW fidelity with `PARTIALLY_RECAPITULATES` rather
    than omitted or overstated. The deep-research report for this entry mentioned
    the observation but gave no identifier; the PMID was recovered by an
    independent PubMed search and the abstract read before curating.
diagnosis:
- name: Slit-Lamp Biomicroscopy
  description: >-
    The primary diagnostic examination. Depth is what matters: fine punctate
    opacities confined to the stroma immediately anterior to Descemet membrane,
    bilaterally, distinguish PDCD from opacities at any other corneal level.
  evidence:
  - reference: PMID:32482962
    reference_title: "Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Corneal opacities characteristic of PDCD located in the posterior corneal
      stroma just anterior to Descemet membrane were identified by slit-lamp
      biomicroscopy.
    explanation: >-
      Establishes slit-lamp biomicroscopy as the examination that makes the
      diagnosis.
- name: In Vivo Confocal Microscopy
  description: >-
    Resolves the lesion at cellular level, showing the hyperreflective particles
    within enlarged and activated posterior keratocytes. This is what
    distinguishes PDCD mechanistically from the extracellular-deposition stromal
    dystrophies, and it is the modality that can characterise a lesion too fine
    for other techniques. It is not universally informative: in one reported
    child with genetically confirmed PDCD the confocal findings were
    unremarkable while slit-lamp, AS-OCT and Scheimpflug were all abnormal.
  evidence:
  - reference: PMID:28302098
    reference_title: "In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In vivo confocal microscopy (IVCM) is a useful tool to examine the minimal
      lesions of the cornea at the cellular level.
    explanation: >-
      States the diagnostic role of the modality for lesions of this scale.
  - reference: PMID:32482962
    reference_title: "Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In vivo confocal microscopy findings were unremarkable.
    explanation: >-
      A negative result in a genetically confirmed case, showing the modality
      does not always detect the lesion; recorded so the diagnostic claim is not
      overstated.
- name: Copy Number Variation Analysis of STS
  description: >-
    Array CGH or cytogenomic array analysis of the Xp22.31 region converts a
    presumptive clinical diagnosis into a confirmed one. It is the necessary
    test rather than exon PCR alone, because the commonest lesion is a deletion
    - and a complete deletion produces exactly the same result as failed
    amplification for any other reason, so absence of amplicons has to be
    followed by copy-number analysis to be interpretable.
  evidence:
  - reference: PMID:23807007
    reference_title: "Pre-Descemet corneal dystrophy and X-linked ichthyosis associated with deletion of Xp22.31 containing the STS gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Polymerase chain reaction amplification using primers designed to amplify
      each of the 10 exons of STS failed to produce any amplicons.
    explanation: >-
      Shows the PCR result that prompted, but could not by itself establish, the
      deletion diagnosis.
  - reference: PMID:23807007
    reference_title: "Pre-Descemet corneal dystrophy and X-linked ichthyosis associated with deletion of Xp22.31 containing the STS gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The identification of a microdeletion within Xp22.3 containing STS with
      aCGH in an individual with suspected pre-Descemet corneal dystrophy and
      X-linked ichthyosis demonstrates the clinical utility of copy number
      variation analysis in confirming a presumptive clinical diagnosis.
    explanation: >-
      States the diagnostic utility of copy-number analysis for this entity.
prevalence:
- population: >-
    Males with X-linked ichthyosis (an upper bound on the XLI-associated
    subtype, not a measurement of PDCD)
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_5_PER_10000
  rate_low: 16.7
  rate_high: 50.0
  subtype: XLI-Associated Deep Corneal Deposits
  notes: >-
    This is the prevalence of X-linked ichthyosis itself, 1/6,000 to 1/2,000 in
    males, recorded deliberately as a ceiling rather than as a measurement. PDCD
    occurs in only some XLI patients, so the true rate of the XLI-associated
    subtype is lower by an undetermined factor - the proportion of XLI patients
    with pre-Descemet opacities is not established in the cited literature, and
    is not invented here. The prevalence of isolated PDCD is not documented at
    all.
  evidence:
  - reference: PMID:39086014
    reference_title: "Revisiting X-linked congenital ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is the second most common type of ichthyosis, with a prevalence of
      1/6,000 to 1/2,000 in males and without any racial or geographical
      differences.
    explanation: >-
      Gives the prevalence of the associated skin disorder, which bounds the
      XLI-associated subtype from above but does not measure it.
discussions:
- discussion_id: pdcd_deposit_identity
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Do the two arms of this entity store the same material - and specifically,
    is the deposit in the STS-deficient cornea cholesterol sulfate, or the same
    lipofuscin-like lipoprotein described in isolated PDCD?
  attaches_to:
  - "pathophysiology#Cholesterol Sulfate Accumulation"
  - "pathophysiology#Keratocyte Lysosomal Lipofuscin-Like Lipoprotein Accumulation"
  - "pathophysiology#Intracellular Deposition in Posterior Keratocytes"
  rationale: >-
    The two arms of this entry converge on an identical-looking cellular lesion
    from two different proposed substrates, and neither has been measured where
    it matters. In the STS-deficient arm, cholesterol sulfate is the natural
    candidate, but the accumulation has only ever been demonstrated in the
    stratum corneum; no chemical or metabolomic characterisation of an
    STS-deficient cornea exists. In the isolated arm, the material that has
    actually been characterised ultrastructurally is a lipofuscin-like
    lipoprotein in secondary lysosomes - not a sulfated sterol - and IC3D warns
    that even those studies are inconsistent.

    Three outcomes are possible and they are not equivalent. If both arms store
    cholesterol sulfate, the isolated cases become candidates for occult
    sulfatase pathway defects. If both store lipofuscin-like lipoprotein, the
    STS lesion is acting through a general lysosomal-degradation failure rather
    than through its own substrate, and the entity is a degeneration with a
    genetic accelerator. If they store different things, the resemblance is
    coincidental and the two should not share a MONDO concept at all - which is
    close to IC3D's position.
  proposed_experiments:
  - experiment_id: pdcd_deposit_lipidomics
    name: Comparative lipidomics and electron microscopy of PDCD and STS-deficient corneas
    description: >-
      Apply mass-spectrometry lipidomics and transmission electron microscopy to
      corneal tissue from an STS-deleted donor and from a donor with isolated
      PDCD, comparing sulfated sterol and lipofuscin content of posterior versus
      anterior stroma against age-matched controls, to establish whether the two
      arms store the same material.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Membrane-bound intracellular vacuoles containing electron-dense material
      suggestive of secondary lysosomes and inclusions of a lipofuscin-like
      lipoprotein consistent with a degenerative process are seen in PDCD.
    explanation: >-
      Characterises the deposit in isolated PDCD as lipofuscin-like lipoprotein,
      which is not the substrate the STS arm predicts.
  - reference: PMID:39086014
    reference_title: "Revisiting X-linked congenital ichthyosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation in
      the stratum corneum (SC).
    explanation: >-
      The competing substrate, established in skin and never measured in cornea.
- discussion_id: pdcd_entity_boundary_xli
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Should the deep corneal deposits of X-linked ichthyosis be classified as
    pre-Descemet corneal dystrophy at all, or as a corneal manifestation of a
    systemic disease?
  attaches_to:
  - "pathophysiology#Loss of Steroid Sulfatase Function"
  - "pathophysiology#Intracellular Deposition in Posterior Keratocytes"
  rationale: >-
    This is a live disagreement between two authorities that this entry
    deliberately does not resolve. The primary ophthalmological literature -
    every case series cited here, from 2013 through 2023 - labels these cases
    "pre-Descemet corneal dystrophy associated with X-linked ichthyosis". IC3D
    edition 3 explicitly refuses that label, describing the deposits as merely
    similar to PDCD and stating that XLI is a systemic disease with corneal
    manifestations and therefore not a corneal dystrophy. MONDO:0017392 carries
    the generic name and no gene, so it does not settle the question either way.

    It matters for what this record is. If IC3D is right, the STS arm belongs to
    an X-linked ichthyosis entry and this concept should shrink to the isolated
    category-4 finding; if the clinical literature is right, STS is the only
    identified genetic cause of anything called PDCD and the concept's centre of
    gravity is the STS arm. The empirical question underneath the nomenclature
    is the deposit-identity one recorded separately: if the two arms store
    different material, IC3D's separation is vindicated on mechanism and not
    merely on classification convention.
  proposed_experiments:
  - experiment_id: pdcd_xli_corneal_survey
    name: Systematic corneal survey of a genotyped X-linked ichthyosis cohort
    description: >-
      Examine an STS-genotyped XLI cohort with slit lamp, AS-OCT and confocal
      microscopy against age-matched controls, quantifying the prevalence,
      depth distribution and morphology of pre-Descemet opacities, to establish
      whether the XLI corneal phenotype is quantitatively distinguishable from
      isolated PDCD rather than only nominally separated from it.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      This is a systemic disease with corneal manifestations and therefore is
      not a corneal dystrophy.
    explanation: >-
      One side of the disagreement, stated by the classifying committee.
  - reference: PMID:37287641
    reference_title: "Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pre-Descemet corneal dystrophy (PDCD) with X-linked ichthyosis (XLI) is
      associated with mutations in or deletions of the steroid sulfatase gene
      (STS).
    explanation: >-
      The other side: the primary literature treats these cases as PDCD, using
      the label IC3D declines to apply.
- discussion_id: pdcd_is_it_a_dystrophy
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is isolated PDCD a corneal dystrophy at all, or an age-related degeneration
    that has been classified with the dystrophies by appearance alone?
  attaches_to:
  - "pathophysiology#Keratocyte Lysosomal Lipofuscin-Like Lipoprotein Accumulation"
  - "pathophysiology#Deep Stromal Punctate Opacification Anterior to Descemet Membrane"
  rationale: >-
    IC3D assigns PDCD to category 4, the tier reserved for entities with the
    least evidence for being a corneal dystrophy, and assigns it no MIM number,
    no locus and no gene. The ultrastructure - lipofuscin-like lipoprotein in
    secondary lysosomes - is read by the reporting authors as degenerative, an
    independent in vivo imaging series reached the same conclusion, and onset
    after age 30 fits a degeneration better than a dystrophy.

    What keeps the question open rather than closed is that the same source
    reports PDCD in families across two to four generations, and that some forms
    progress. A purely age-related degeneration should not cluster in pedigrees.
    The contrast with the neighbouring entity is instructive: PPPCD occupies the
    same corneal layer, has autosomal dominant pedigrees and a gene (PRDX3), and
    is rated category 1 - so the classification machinery is capable of
    recognising a dystrophy here when the evidence supports one, and has
    declined to for PDCD.
  proposed_experiments:
  - experiment_id: pdcd_age_stratified_prevalence
    name: Age-stratified prevalence of pre-Descemet opacities in an unselected population
    description: >-
      Determine the prevalence of pre-Descemet punctate opacities by decade in
      an unselected adult population with slit-lamp and AS-OCT, with STS
      copy-number analysis and dermatological examination in those affected. A
      prevalence rising steadily with age in individuals without STS lesions
      would support degeneration; familial clustering beyond chance would
      support dystrophy.
  evidence:
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Isolated pre-Descemet corneal dystrophy (PDCD) is neither a well-defined
      entity nor is it clearly a hereditary or degenerative disorder (known as
      cornea farinata, "flour-like cornea").
    explanation: >-
      The classifying committee's own statement that the question is unresolved.
  - reference: PMID:38359414
    reference_title: "IC3D Classification of Corneal Dystrophies-Edition 3."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      PDCD has historically been described as having several subgroups, many of
      which may represent sporadic, age-related degenerative and secondary
      changes.
    explanation: >-
      Records the specific suspicion that much of what is called PDCD is
      degenerative or secondary rather than a primary dystrophy.
  - reference: PMID:31298040
    reference_title: "Multimodal imaging of pre-Descemet corneal dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The clinical presentation and structural anomalies found in isolated
      sporadic pre-Descemet corneal dystrophy are in favor of a degenerative
      process affecting corneal keratocytes with no epithelial or endothelial
      involvement.
    explanation: >-
      An independent imaging series arguing for the degenerative reading.
notes: >-
  Entry-type decision. MONDO:0017392 is a leaf under MONDO:0020213 (stromal
  corneal dystrophy), and dismech already has a Stromal_Corneal_Dystrophy
  umbrella entry with six subtypes. PDCD was nonetheless curated as its own
  Disease rather than folded in as a seventh subtype, because it does not share
  that umbrella's pathograph. The umbrella is defined by progressive deposition
  of abnormal material in the EXTRACELLULAR matrix causing loss of transparency
  and visual impairment; PDCD's material is intracellular, in enlarged posterior
  keratocytes, electron microscopy reports no extracellular deposits at all, and
  vision is spared. It is linked to the umbrella through `parents` instead.

  Entity boundary - PDCD is NOT PPPCD. IC3D edition 3 groups them in one
  template but keeps them distinct: punctiform and polychromatic pre-Descemet
  corneal dystrophy (PPPCD) is category 1, autosomal dominant, caused by PRDX3
  variants at 10q26.11, with MIM #619871; PDCD proper is category 4 with "MIM:
  PDCD - None". MONDO keeps them apart too - PPPCD is MONDO:0859248 ("corneal
  dystrophy, punctiform and polychromatic pre-descemet"), which is not a
  descendant of MONDO:0020213 and is not this entry. Nothing about PRDX3 is
  curated here, and a future PPPCD entry should be a separate file rather than a
  subtype of this one. This is not a theoretical hazard: the deep-research
  report generated for this curation had PRDX3 as its single most-mentioned gene
  (27 mentions, ahead of STS at 23) and devoted a whole mechanism subsection to
  PPPCD. Nothing from that subsection was used. PPPCD is instead recorded under
  `differential_diagnoses`, which is where it belongs.

  Scope of the genetic claim. STS is curated as CAUSATIVE for the
  XLI-associated arm only. Isolated PDCD has no identified gene and IC3D records
  its locus and gene as "Unknown". Note also that the evidence base is small -
  the reporting authors describe only three genetically confirmed PDCD-with-XLI
  cases before adding their two families - which is why the strength of the
  gene-disease relationship is stated with that qualification rather than
  asserted flatly.

  Deliberately not curated: datasets. `just discover-datasets` returned 12
  candidates, all GENE_ONLY and all matched on the string "STS" - which in the
  GEO corpus overwhelmingly means *soft tissue sarcoma* or a cell line named
  STS-something (H-STS neuroendocrine tumour line, STS-109 undifferentiated
  pleomorphic sarcoma), not steroid sulfatase. Not one concerned cornea,
  ichthyosis or sulfatase biology. This is Named Entity Confusion reached
  through dataset search in its purest form: every accession resolves, and none
  is about this disease. No `datasets:` block is therefore recorded, and the
  absence is deliberate rather than an omission.

  On genetic counselling. A reviewer reasonably suggested a `NCIT:C15240 Genetic
  Counseling` treatment scoped to the XLI arm, since that arm is a confirmed
  X-linked disorder with recurrence implications for a family. It is not added,
  for one reason only: none of the seven cached references contains a quotable
  statement about counselling. The closest is PMID:23807007's remark on the
  clinical utility of copy-number analysis in confirming a presumptive diagnosis,
  which is about diagnosis and is already curated under `diagnosis:`. Adding a
  counselling treatment on the strength of it being obviously true is exactly the
  fabrication the evidence SOP forbids, so the gap is recorded here instead. If a
  citable source is found - a GeneReviews chapter for X-linked ichthyosis would be
  the natural one - this is a ready-made addition.

  Deliberately not curated: treatments. PDCD is visually silent, and IC3D lists
  it among the dystrophies that are typically asymptomatic and do not require
  treatment. Recording a treatment here would mean inventing one; the absence is
  the clinically relevant fact, and it is carried by evidence on the
  "Visually Silent Corneal Finding" node rather than by an empty section.
📚

References & Deep Research

References

8
PMID:37287641
Identification of a novel partial deletion of STS associated with pre-Descemet corneal dystrophy and X-linked ichthyosis.
No top-level findings curated for this source.
PMID:32482962
Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene.
No top-level findings curated for this source.
PMID:28302098
In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report.
No top-level findings curated for this source.
PMID:23807007
Pre-Descemet corneal dystrophy and X-linked ichthyosis associated with deletion of Xp22.31 containing the STS gene.
No top-level findings curated for this source.
PMID:38359414
IC3D Classification of Corneal Dystrophies-Edition 3.
No top-level findings curated for this source.
PMID:39086014
Revisiting X-linked congenital ichthyosis.
No top-level findings curated for this source.
PMID:31298040
Multimodal imaging of pre-Descemet corneal dystrophy.
No top-level findings curated for this source.
PMID:35346188
Multimodal ocular imaging of known and novel corneal stromal disorders in dogs.
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Pre-Descemet Corneal Dystrophy: Disease Characteristics Report
Edison Scientific Literature 21 citations 2026-08-25T19:05:20.383526

Pre-Descemet Corneal Dystrophy: Disease Characteristics Report

Scope note. “Pre-Descemet corneal dystrophy” (PDCD) is not one genetically uniform disorder. The 2024 International Committee for Classification of Corneal Dystrophies (IC3D) separates poorly defined, usually sporadic PDCD/cornea farinata-like disease (category 4) from punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD), a genetically supported autosomal-dominant disorder caused by PRDX3 variants (category 1). Similar deposits can also occur as a manifestation of STS deficiency/X-linked ichthyosis. These entities should not be merged without qualification in a knowledge base. (weiss2024ic3dclassificationof pages 48-49, weiss2024ic3dclassificationof pages 11-12)

Entity/status Inheritance / gene / variant Hallmark phenotype and course Strongest evidence / sample Mechanism confidence Management Major gaps
Isolated/classic pre-Descemet corneal dystrophy (PDCD), historically overlapping with cornea farinata; IC3D 2024 treats PDCDs as a group and notes isolated PDCD remains poorly defined / category 4 No established causal gene for isolated PDCD. Usually sporadic in modern imaging series; heredity unclear. IC3D notes prior overlap with cornea farinata/deep filiform/deep punctiform labels. DOI: https://doi.org/10.1097/ICO.0000000000003420 (2024); https://doi.org/10.1177/1120672119862505 (2020) (weiss2024ic3dclassificationof pages 48-49, alafaleq2020multimodalimagingof pages 1-2, alafaleq2020multimodalimagingof pages 4-6) Bilateral tiny gray/polymorphic punctiform opacities immediately anterior to Descemet membrane; generally asymptomatic with vision usually unaffected; nonprogressive to slowly progressive. Multimodal imaging suggests deposits throughout the stroma, maximal posteriorly. DOI: https://doi.org/10.1097/ICO.0000000000003420 (2024); https://doi.org/10.1177/1120672119862505 (2020) (weiss2024ic3dclassificationof pages 48-49, alafaleq2020multimodalimagingof pages 1-2, alafaleq2020multimodalimagingof pages 6-9) IC3D expert synthesis plus retrospective multimodal case series of 8 corneas from 4 unrelated male patients with bilateral disease; SD-OCT showed hyperreflective line anterior to Descemet membrane and IVCM showed extracellular stromal deposits plus enlarged posterior keratocytes. DOI: https://doi.org/10.1097/ICO.0000000000003420 (2024); https://doi.org/10.1177/1120672119862505 (2020) (weiss2024ic3dclassificationof pages 48-49, alafaleq2020multimodalimagingof pages 1-2, alafaleq2020multimodalimagingof pages 2-4) Moderate for a keratocyte-centered degenerative/deposition process; low for a single molecular cause. Evidence includes ultrastructural vacuoles with electron-dense/lipofuscin-like material and imaging evidence of stromal, not epithelial/endothelial, involvement. DOI: https://doi.org/10.1177/1120672119862505 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (weiss2024ic3dclassificationof pages 48-49, alafaleq2020multimodalimagingof pages 6-9, alafaleq2020multimodalimagingof pages 4-6) Usually observation/follow-up because vision is typically preserved; diagnosis supported by slit-lamp, IVCM, and anterior-segment OCT. No disease-specific therapy or trial identified. DOI: https://doi.org/10.1177/1120672119862505 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (weiss2024ic3dclassificationof pages 48-49, alafaleq2020multimodalimagingof pages 6-9) No prevalence/incidence estimates specific to isolated PDCD; no validated gene; little natural-history data; no penetrance estimates; no biomarker, trial, or pathology-standardized management pathway. Distinction from cornea farinata and secondary/systemic causes remains imperfect. (weiss2024ic3dclassificationof pages 48-49, alafaleq2020multimodalimagingof pages 6-9, alafaleq2020multimodalimagingof pages 4-6)
Punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD); genetically supported distinct subtype; IC3D category 1 in 2024 Autosomal dominant; PRDX3 is the leading causal gene. Recurrent heterozygous PRDX3 c.568G>C (p.Asp190His) identified in 4 of 5 reported families in the 2020 genetic study; PDZD8 c.872+10A>T segregated in 3 of 5 families but was not favored as the main cause. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (barrio2020punctiformandpolychromatic pages 1-8, barrio2020punctiformandpolychromatic pages 17-21, barrio2020punctiformandpolychromatic pages 26-30, weiss2024ic3dclassificationof pages 11-12) Posterior stromal/pre-Descemetic multicolored polychromatic punctiform opacities, usually bilateral; typically asymptomatic and without visual disturbance; cases reported from childhood to late adulthood, often nonprogressive or only mildly progressive. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (barrio2020punctiformandpolychromatic pages 1-8, weiss2024ic3dclassificationof pages 48-49, barrio2020punctiformandpolychromatic pages 12-17) Strongest evidence is the 2020 family-based study: 12 affected individuals from 3 previously unreported families within a larger set of 5 PPPCD families; segregation plus recurrence of PRDX3 p.Asp190His across families. Imaging showed hyperreflective posterior stromal/Descemet-level opacities; only measured biomechanical abnormality was increased corneal stiffness. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020) (barrio2020punctiformandpolychromatic pages 1-8, barrio2020punctiformandpolychromatic pages 17-21, barrio2020punctiformandpolychromatic pages 26-30) High confidence for a gene-disease relationship relative to other PDCD forms; moderate confidence for mechanism. PRDX3 encodes a mitochondrial antioxidant peroxidase regulating mitochondrial reactive oxygen species, but direct human corneal molecular profiling remains sparse. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (barrio2020punctiformandpolychromatic pages 17-21, weiss2024ic3dclassificationof pages 11-12) Observation and follow-up are usual because visual function is largely preserved; genetic counseling is reasonable given autosomal-dominant inheritance. No targeted therapy or registered clinical trial found. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (barrio2020punctiformandpolychromatic pages 1-8, weiss2024ic3dclassificationof pages 48-49) Extremely small literature base (about 10 families before 2020); prevalence unknown; penetrance and expressivity incompletely quantified; possible locus heterogeneity remains unresolved; uncertain whether extra-corneal crystals in isolated reports indicate a broader systemic process in some families. (barrio2020punctiformandpolychromatic pages 1-8, weiss2024ic3dclassificationof pages 11-12)
STS/X-linked ichthyosis-associated pre-Descemet opacities; better viewed as syndromic/secondary pre-Descemet corneal changes rather than primary isolated dystrophy X-linked recessive STS deficiency. Case report demonstrated complete deletion of all 10 STS exons and flanking sequence failure by PCR in a 34-year-old man with known X-linked ichthyosis. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (shi2017invivoconfocal pages 4-5, shi2017invivoconfocal pages 1-2, shi2017invivoconfocal pages 2-4) Bilateral tiny pleomorphic gray-brownish posterior stromal opacities anterior to Descemet membrane, with preserved corrected visual acuity (20/20 both eyes after refraction in the reported case); skin dryness/scaling from infancy; stable over 1 year in the published case. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (shi2017invivoconfocal pages 1-2, shi2017invivoconfocal pages 2-4) Single detailed human case report with slit-lamp, IVCM, dermatologic exam, and molecular confirmation of STS deletion. IVCM showed enlarged activated posterior stromal keratocytes containing regularly distributed hyperreflective particles and additional anterior stromal particles; endothelial cell density remained normal. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (shi2017invivoconfocal pages 4-5, shi2017invivoconfocal pages 1-2, shi2017invivoconfocal pages 2-4) Moderate for a secondary metabolic/deposition mechanism: authors proposed STS deficiency elevates cholesterol sulfate, causing lysosomal dysfunction and lipid accumulation in keratocytes; however this is based mainly on clinicopathologic inference and one genetically confirmed case. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (shi2017invivoconfocal pages 4-5, shi2017invivoconfocal pages 2-4) Management centers on recognition of the ocular finding within X-linked ichthyosis, observation, and systemic/genetic counseling; no cornea-specific intervention was needed in the reported case. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (shi2017invivoconfocal pages 4-5, shi2017invivoconfocal pages 1-2) Evidence limited to isolated cases; unclear prevalence among STS-deficient patients; natural history and treatment thresholds unknown; uncertain whether this should be classified with primary corneal dystrophies or as a manifestation of systemic disease. (weiss2024ic3dclassificationof pages 48-49, shi2017invivoconfocal pages 4-5, shi2017invivoconfocal pages 2-4)

Table: This table contrasts the main evidence-supported forms of pre-Descemet corneal disease: poorly defined isolated PDCD, PRDX3-associated PPPCD, and STS/X-linked ichthyosis-associated pre-Descemet opacities. It summarizes what is established, what is inferred, and where major evidence gaps remain.

1. Disease information

PDCD denotes bilateral, generally noninflammatory deposits in the deep corneal stroma immediately anterior to Descemet membrane. The classic appearance is numerous fine, gray, polymorphic opacities; PPPCD has larger punctiform opacities with a distinctive multicolored or polychromatic appearance. Vision is usually preserved. IC3D describes isolated PDCD as neither a well-defined hereditary dystrophy nor an unequivocal degeneration, whereas PRDX3-associated PPPCD now meets category-1 criteria. (weiss2024ic3dclassificationof pages 48-49, weiss2024ic3dclassificationof pages 11-12)

Names and synonyms: pre-Descemet corneal dystrophy; pre-Descemet’s membrane corneal dystrophy; deep filiform dystrophy; deep punctiform dystrophy; cornea farinata (historically overlapping, but now better regarded as a degeneration); punctiform and polychromatic pre-Descemet corneal dystrophy; posterior polychromatic corneal dystrophy. (weiss2024ic3dclassificationof pages 48-49)

Identifiers: no confidently validated disease-specific OMIM, Orphanet, MONDO, MeSH, ICD-10, or ICD-11 identifier was established in the retrieved authoritative literature. A knowledge base should therefore retain the label as an IC3D entity and avoid assigning an unverified MONDO ID. Generic coding may fall under corneal dystrophy or corneal opacity, but that is not disease-specific.

The evidence is aggregated disease-level literature—IC3D expert classification, family studies, and small case series—not individual EHR data. The core sources are IC3D Edition 3, published February 2024 (DOI), and the family/genetic study published April 2020 (DOI). PMIDs were not exposed in the retrieved records and should be verified directly in PubMed before database deposition. (barrio2020punctiformandpolychromatic pages 1-8, weiss2024ic3dclassificationof pages 48-49)

2. Etiology and risk/protective factors

Genetic causes

  • PPPCD: heterozygous PRDX3 NM_006793.4:c.568G>C, p.(Asp190His) is the principal reported causal variant. It segregated with disease and was found in four of five evaluated families. Autosomal-dominant transmission is supported. (barrio2020punctiformandpolychromatic pages 17-21, barrio2020punctiformandpolychromatic pages 26-30)
  • A rare intronic PDZD8 c.872+10A>T variant segregated in three of five families, but PRDX3 was favored as the causal gene. Possible locus heterogeneity remains unresolved. (barrio2020punctiformandpolychromatic pages 1-8, barrio2020punctiformandpolychromatic pages 17-21)
  • Isolated nonpolychromatic PDCD: no locus or causal gene is established; modern series are often sporadic. (weiss2024ic3dclassificationof pages 48-49, alafaleq2020multimodalimagingof pages 1-2)
  • Syndromic pre-Descemet opacities: complete deletion of STS was demonstrated in a man with X-linked ichthyosis. This is better annotated as a secondary ocular manifestation of STS deficiency than as PRDX3-associated PPPCD. (shi2017invivoconfocal pages 1-2, shi2017invivoconfocal pages 2-4)

Family history is the principal recognized risk indicator for PPPCD. Cases in the genetic series ranged from 8 to 79 years, showing that detectable disease may span much of life. Geographic clustering among Spanish/Spanish-ancestry and Brazilian families was observed, but the sample is too small to establish a founder effect or population-specific risk. (barrio2020punctiformandpolychromatic pages 17-21, barrio2020punctiformandpolychromatic pages 12-17)

Environmental, lifestyle, infectious, and protective factors

No reproducible toxin, diet, smoking, alcohol, occupational, infectious, or lifestyle cause has been demonstrated. No protective allele, diet, medication, or behavioral intervention is known. Age may affect detectability—classic PDCD is usually recognized after age 30—but PPPCD has been seen by age 3, so age is not a causal exposure. No validated gene–environment interaction exists. (weiss2024ic3dclassificationof pages 48-49)

A report proposing vaccine/surgical stimulation in a person with an ARSG variant is insufficient to establish causation and should not be treated as a recognized PDCD risk factor.

3. Phenotypes

Phenotype Type and characteristics Suggested HPO annotation
Deep stromal corneal opacities Objective sign; bilateral fine gray/polymorphic deposits immediately anterior to Descemet membrane, usually extending broadly across the cornea Corneal opacity, HP:0007957; bilateral qualifier; posterior/deep stromal location as free-text qualifier
Polychromatic punctiform deposits PPPCD-defining sign; multicolored punctate posterior stromal opacities Corneal opacity (HP:0007957), punctate/polychromatic morphology qualifier
Preserved visual acuity/asymptomatic state Most common clinical state; one IC3D-cited patient reported glare “Asymptomatic” should be represented as absence of symptoms rather than a positive HPO phenotype
Glare Rare symptom; frequency cannot be estimated Glare/photophobia concept if locally supported; do not infer photophobia from glare alone
Increased corneal stiffness Quantitative biomechanical abnormality in the 2020 family study; clinical significance uncertain No validated disease-specific HPO mapping identified
X-linked ichthyosis features Syndromic STS cases may have generalized dry, coarse, scaling skin Annotate under X-linked ichthyosis, not primary PPPCD

PPPCD is typically mild, bilateral, asymptomatic, and nonprogressive or only mildly progressive. Other PDCD/cornea-farinata-like forms may progress slowly. Onset is commonly recognized in adulthood, but childhood PPPCD is documented. No reliable phenotype frequencies beyond “usually” or “typically” are available because published cohorts are extremely small. (weiss2024ic3dclassificationof pages 48-49, barrio2020punctiformandpolychromatic pages 1-8)

No validated EQ-5D, SF-36, PROMIS, or vision-related quality-of-life study exists. Since corrected acuity is generally normal, everyday functional impact is expected to be minimal, although glare or diagnostic anxiety may matter in individual patients. This is clinical inference rather than measured evidence.

4. Genetic and molecular information

PRDX3 encodes mitochondrial peroxiredoxin-3, an antioxidant peroxidase that regulates mitochondrial reactive oxygen species. The recurrent p.Asp190His substitution was novel in the 2020 study, predicted damaging, and had a CADD score of 31. The retrieved record did not provide a defensible ClinVar classification or current gnomAD allele frequency; therefore “pathogenic” should be used only in the disease-association sense supported by segregation and IC3D category 1, not asserted as a current ClinVar/ACMG record without database verification. (barrio2020punctiformandpolychromatic pages 17-21, barrio2020punctiformandpolychromatic pages 12-17)

The variant is germline, heterozygous, and missense. A dominant-negative versus gain-of-function versus haploinsufficiency mechanism has not been experimentally established. No modifier gene, protective allele, chromosomal rearrangement, somatic mutation, methylation signature, histone change, or other disease-specific epigenetic mechanism is known. The PDZD8 intronic allele remains a candidate rather than a confirmed independent cause. (barrio2020punctiformandpolychromatic pages 1-8, barrio2020punctiformandpolychromatic pages 17-21)

For STS-associated disease, the reported lesion was a germline X-chromosomal deletion encompassing all ten exons and flanking sequence. In the reported male it produced the expected X-linked hemizygous deficiency. (shi2017invivoconfocal pages 1-2, shi2017invivoconfocal pages 2-4)

5. Environmental information

PDCD/PPPCD is not infectious and is not linked to pollution, radiation, smoking, diet, exercise, alcohol, or occupational exposure. Important acquired mimics include crystalline keratopathy and occupational corneal deposits such as argyrosis; these are differential diagnoses, not proven triggers of inherited PPPCD. No environmental prevention strategy is supported.

6. Mechanism and pathophysiology

PRDX3-associated PPPCD

A biologically plausible chain is:

germline PRDX3 p.Asp190His → altered mitochondrial peroxide handling in corneal keratocytes → oxidative/proteostatic stress → intracellular and extracellular deposit formation, greatest in posterior stroma → punctiform polychromatic slit-lamp opacities.

The first step—gene association—is strong; the downstream oxidative/deposition chain is plausible but not directly demonstrated by corneal transcriptomics, proteomics, metabolomics, or functional editing studies. (barrio2020punctiformandpolychromatic pages 17-21, weiss2024ic3dclassificationof pages 11-12)

Sporadic/classic PDCD

IVCM and ultrastructure support a keratocyte-centered degenerative process. Enlarged posterior keratocytes contain membrane-bound vacuoles with electron-dense, lipofuscin-like material; extracellular particles occur throughout the stroma, with maximal damage anterior to Descemet membrane. Epithelium and endothelium are largely spared. (alafaleq2020multimodalimagingof pages 1-2, alafaleq2020multimodalimagingof pages 6-9, alafaleq2020multimodalimagingof pages 4-6)

The 2020 multimodal study’s abstract concluded that findings were “in favor of a degenerative process affecting corneal keratocytes with no epithelial or endothelial involvement.” It also reported that imaging “reveals that the disorder affects the whole stroma.” (DOI, September 2020). (alafaleq2020multimodalimagingof pages 1-2)

STS-associated mechanism

A proposed chain is:

STS deletion → steroid sulfatase deficiency → cholesterol-sulfate accumulation → lysosomal dysfunction/lipid retention in keratocytes → intracellular hyperreflective particles and posterior stromal opacity.

This mechanism is supported by biochemical plausibility and one genetically confirmed clinical case, not by direct human corneal metabolomics. (shi2017invivoconfocal pages 4-5, shi2017invivoconfocal pages 2-4)

Suggested ontology terms: corneal stromal keratocyte (CL term should be curator-verified); corneal stroma and posterior corneal stroma (UBERON); mitochondrion (GO:0005739); lysosome (GO:0005764); response to oxidative stress (GO:0006979); reactive oxygen species metabolic process (GO:0072593); lipid storage/lysosomal organization as provisional biological-process annotations. No immune, inflammatory, ischemic, necrotic, or fibrotic mechanism is established.

No disease-specific bulk/single-cell RNA-seq, spatial transcriptomics, proteomics, metabolomics, lipidomics, multi-omics integration, CRISPR screen, or organoid study was found.

7. Anatomical structures affected

The disease is restricted predominantly to the cornea, especially the deep/posterior stroma immediately anterior to Descemet membrane. Imaging shows lesser deposits and activated keratocytes across anterior and middle stroma as well. Corneal epithelial thickness, Descemet membrane, endothelium, and central corneal thickness are generally normal. (alafaleq2020multimodalimagingof pages 2-4, alafaleq2020multimodalimagingof pages 6-9)

The target cell is the corneal stromal keratocyte. Relevant compartments include mitochondria for PRDX3 biology and lysosomal/vacuolar compartments for lipofuscin-like storage. Disease is typically bilateral and broadly distributed, often limbus-to-limbus, although one STS case retained a 2–3-mm clear perilimbal zone. (shi2017invivoconfocal pages 1-2, alafaleq2020multimodalimagingof pages 2-4)

Suggested anatomy annotations are cornea (UBERON:0000964), corneal stroma, Descemet membrane as an adjacency landmark, and bilateral eye involvement. No established secondary-organ involvement exists in isolated PPPCD; skin involvement belongs to syndromic STS deficiency. IC3D notes a report of crystals under the lens capsule, leaving open whether rare PPPCD may occasionally be systemic. (weiss2024ic3dclassificationof pages 11-12)

8. Temporal development

Classic PDCD is most often recognized after age 30 and develops insidiously. PPPCD can be detected in early childhood and has been documented across ages 3–79. In the 2020 family cohort, affected individuals were 8–79 years old, with mean age 42.9 years. (weiss2024ic3dclassificationof pages 48-49, barrio2020punctiformandpolychromatic pages 12-17)

There is no validated staging system. A practical descriptive sequence is: subclinical deposits detectable by IVCM/OCT; visible punctiform posterior stromal deposits; stable or mildly increasing deposit burden. End-stage corneal decompensation is not characteristic. One STS-associated case remained unchanged at one year. (weiss2024ic3dclassificationof pages 48-49, shi2017invivoconfocal pages 1-2)

The condition is chronic/lifelong once present. Spontaneous remission, relapsing-remitting behavior, critical treatment windows, and treatment-induced remission have not been documented.

9. Inheritance and population

PPPCD follows autosomal-dominant inheritance. Penetrance appears substantial in reported pedigrees but has not been quantified; age-dependent ascertainment is possible. Expressivity is variable in deposit burden, age of recognition, and occasional glare, but visual function is usually preserved. Anticipation, germline mosaicism, consanguinity effects, carrier frequency, and sex bias are unknown. (barrio2020punctiformandpolychromatic pages 1-8, weiss2024ic3dclassificationof pages 48-49)

Only about ten families had been reported before the 2020 study. That study evaluated 21 relatives from three additional families, including 12 affected individuals. These counts demonstrate extreme rarity but cannot yield prevalence or incidence. No population-based rate per 100,000 is available. (barrio2020punctiformandpolychromatic pages 1-8)

Spanish/Spanish-ancestry and Brazilian clustering is reported, but founder status has not been established. Both sexes can be affected in autosomal-dominant PPPCD. The male predominance in one four-patient sporadic imaging series cannot establish a sex ratio. (barrio2020punctiformandpolychromatic pages 17-21, alafaleq2020multimodalimagingof pages 1-2)

10. Diagnostics

Clinical and imaging approach

  1. Slit-lamp biomicroscopy: identify bilateral, fine gray or polychromatic punctiform deposits in posterior stroma immediately anterior to Descemet membrane.
  2. Anterior-segment OCT: look for hyperreflective particles/line anterior to Descemet membrane; isolated PDCD may also show a thinner line below Bowman layer and particles through the stroma.
  3. In-vivo confocal microscopy: demonstrate hyperreflective intracellular inclusions in enlarged posterior keratocytes and extracellular stromal deposits; assess preservation of epithelium and endothelium.
  4. Scheimpflug densitometry/specular microscopy: supportive but not independently diagnostic.
  5. Visual acuity, refraction, pachymetry, and endothelial cell density: document preserved function and exclude endothelial disease. (barrio2020punctiformandpolychromatic pages 26-30, shi2017invivoconfocal pages 1-2, alafaleq2020multimodalimagingof pages 2-4)

In the STS-associated case, corrected acuity reached 20/20 in both eyes and endothelial densities were 3,347 and 3,095 cells/mm². IVCM localized 2.0–3.4-µm particles within posterior keratocytes at 321–494 µm depth. (shi2017invivoconfocal pages 1-2)

Genetic testing

For a convincing polychromatic familial phenotype, sequence PRDX3, preferably through an inherited corneal-dystrophy panel with deletion/duplication analysis and segregation testing. Targeted testing for c.568G>C is efficient in a known family. WES/WGS is appropriate when PRDX3 testing is negative, the phenotype is atypical, or syndromic findings suggest another diagnosis. In males with ichthyosis, test STS by copy-number analysis plus sequencing. CMA may detect a larger Xp22.3 deletion. Karyotyping, FISH, mitochondrial DNA testing, and repeat-expansion assays have no routine role unless another clinical indication exists. (barrio2020punctiformandpolychromatic pages 1-8, shi2017invivoconfocal pages 2-4)

Differential diagnosis

Important alternatives are cornea farinata; fleck corneal dystrophy; central cloudy dystrophy of François; posterior amorphous corneal dystrophy; Fuchs endothelial corneal dystrophy/cornea guttata; posterior polymorphous corneal dystrophy; crystalline infectious keratopathy; Schnyder corneal dystrophy; cystinosis; drug/toxin or silver deposits; and pre-Descemet opacities secondary to X-linked ichthyosis. Normal endothelium, lack of edema/inflammation, posterior stromal keratocyte localization, polychromasia, and PRDX3 segregation favor PPPCD. (alafaleq2020multimodalimagingof pages 6-9)

There are no universally validated numerical diagnostic criteria. Asymptomatic relatives in a PRDX3-positive family can undergo cascade slit-lamp examination and targeted testing. Population or newborn screening is not indicated.

11. Outcome and prognosis

Prognosis is excellent. Most patients remain asymptomatic with preserved corrected acuity, and the disease does not affect survival or life expectancy. No disease-specific mortality, five- or ten-year survival statistic, disability rate, or quality-of-life score exists. (weiss2024ic3dclassificationof pages 48-49, barrio2020punctiformandpolychromatic pages 1-8)

When reduced vision is present, published imaging series attributed it to other conditions such as amblyopia, cataract, or retinal pigment epitheliopathy rather than PDCD. Corneal edema, endothelial failure, recurrent erosions, ulceration, and blindness are not characteristic complications. (alafaleq2020multimodalimagingof pages 6-9)

No validated prognostic biomarker exists. Deposit burden, symptoms, acuity, and serial OCT/IVCM are reasonable monitoring measures, but their predictive value is unproven.

12. Treatment

Standard care is observation and periodic ophthalmic review. Refractive correction treats coincidental ametropia; glare can be managed symptomatically. Genetic counseling is appropriate for PRDX3-positive families and STS-associated disease. A 2025 case report likewise recommended observation/follow-up and noninvasive imaging. (nicoli2025distrofiacornealpredescemética pages 3-5)

No drug, antioxidant, lysosomal therapy, gene therapy, RNA therapy, cell therapy, PTK, keratoplasty, or other surgery has demonstrated disease-specific benefit. Because deposits are deep and visual acuity is generally preserved, PTK is anatomically inappropriate in routine PPPCD. Corneal transplantation would be considered only for exceptional, proven visually significant stromal opacity after exclusion of other causes; no response rate or recurrence estimate exists.

No relevant interventional ClinicalTrials.gov study or disease-specific NCT identifier was found. Generic patents and experimental gene-editing approaches for other corneal dystrophies do not constitute evidence for PDCD treatment. Suggested NCIT concepts are Observation, Genetic Counseling, Visual Acuity Test, Optical Coherence Tomography, and, only if exceptionally indicated, Corneal Transplantation; exact NCIT codes should be terminology-service verified.

13. Prevention

Primary prevention is unavailable for a germline disorder. No vaccine, prophylactic drug, diet, or exposure avoidance prevents PPPCD. Secondary prevention consists of cascade examination/testing in affected families, allowing early diagnosis and avoidance of unnecessary treatment. Tertiary prevention consists of routine monitoring and treatment of unrelated visual problems.

Genetic counseling should explain autosomal-dominant transmission—nominally a 50% variant-transmission probability from a heterozygous parent—while emphasizing that penetrance and severity are not adequately quantified. Prenatal or preimplantation testing is technically possible once a familial pathogenic variant is confirmed but is rarely proportionate for a usually asymptomatic, non–vision-threatening condition. STS families require X-linked counseling. No population screening or public-health intervention is justified.

14. Other species and natural disease

No genetically confirmed natural PRDX3-associated PDCD has been established in another species. A 2022 canine report described bilateral, noninflammatory posterior stromal opacities with hyperreflective deposits within keratocytes and increasing numbers of enlarged deposit-containing keratocytes toward the posterior stroma. The authors judged this “reminiscent of pre-Descemet corneal dystrophy” in humans, but no orthologous mutation was demonstrated; it is therefore a comparative phenocopy, not a validated natural model. Relevant taxonomy is domestic dog, Canis lupus familiaris (NCBI Taxon 9615). Breed/VBO assignment was not established in the retrieved evidence.

There is no zoonotic or transmissible potential.

15. Model organisms

No validated PRDX3 knock-in mouse, rat, zebrafish, invertebrate, organoid, iPSC, or corneal-cell model has been shown to reproduce human PPPCD deposits. Likewise, no STS-deficient model has been validated specifically for the corneal phenotype. The canine observation may help define comparative imaging features but cannot establish causality or therapeutic response.

Priority models would include: (1) a heterozygous PRDX3 p.Asp190His knock-in animal; (2) patient-derived keratocytes or iPSC-derived corneal stromal cells; and (3) engineered corneal stromal organoids assessing mitochondrial peroxide handling, keratocyte vacuoles, lipofuscin/lipid deposition, transparency, and biomechanics. These are research recommendations, not currently validated resources.

Recent developments and evidence-quality assessment

The key recent advance is the February 2024 IC3D reclassification: PRDX3-associated PPPCD is now category 1, while isolated nonpolychromatic PDCD remains category 4. IC3D’s abstract states: “Pre-Descemet corneal dystrophies include category 1, autosomal dominant, punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD) (PRDX3 mutations, chromosome 10)” and notes that it is “typically asymptomatic.” (DOI, February 2024). (weiss2024ic3dclassificationof pages 48-49)

The foundational genetic evidence remains the April 2020 family study: 12 affected people in three newly reported families, recurrence of PRDX3 p.Asp190His in four of five families evaluated across the study, and significantly increased corneal stiffness as the principal measured biomechanical abnormality. Its main limitations are small sample size, concentration in a few ancestries, prediction rather than direct functional proof, and unresolved locus heterogeneity. (barrio2020punctiformandpolychromatic pages 1-8, barrio2020punctiformandpolychromatic pages 17-21)

Overall, evidence is moderate-to-strong for PRDX3 as the cause of PPPCD, moderate for a keratocyte deposition/degeneration mechanism, and very low for epidemiology, quantified natural history, molecular profiling, or treatment efficacy. The most important database-curation safeguard is to keep PRDX3-associated PPPCD, category-4 isolated PDCD/cornea farinata, and STS-associated syndromic deposits as related but distinct assertions.

References

  1. (weiss2024ic3dclassificationof pages 48-49): Jayne S. Weiss, Christopher J. Rapuano, Berthold Seitz, Massimo Busin, Tero T. Kivelä, Nacim Bouheraoua, Cecilie Bredrup, Ken K. Nischal, Harshvardhan Chawla, Vincent Borderie, Kenneth R. Kenyon, Eung Kweon Kim, Hans Ulrik Møller, Francis L. Munier, Tim Berger, and Walter Lisch. Ic3d classification of corneal dystrophies—edition 3. Cornea, 43:466-527, Feb 2024. URL: https://doi.org/10.1097/ico.0000000000003420, doi:10.1097/ico.0000000000003420. This article has 119 citations and is from a peer-reviewed journal.

  2. (weiss2024ic3dclassificationof pages 11-12): Jayne S. Weiss, Christopher J. Rapuano, Berthold Seitz, Massimo Busin, Tero T. Kivelä, Nacim Bouheraoua, Cecilie Bredrup, Ken K. Nischal, Harshvardhan Chawla, Vincent Borderie, Kenneth R. Kenyon, Eung Kweon Kim, Hans Ulrik Møller, Francis L. Munier, Tim Berger, and Walter Lisch. Ic3d classification of corneal dystrophies—edition 3. Cornea, 43:466-527, Feb 2024. URL: https://doi.org/10.1097/ico.0000000000003420, doi:10.1097/ico.0000000000003420. This article has 119 citations and is from a peer-reviewed journal.

  3. (alafaleq2020multimodalimagingof pages 1-2): Munirah Alafaleq, Cristina Georgeon, Kate Grieve, and Vincent M Borderie. Multimodal imaging of pre-descemet corneal dystrophy. European Journal of Ophthalmology, 30:908-916, Sep 2020. URL: https://doi.org/10.1177/1120672119862505, doi:10.1177/1120672119862505. This article has 9 citations and is from a peer-reviewed journal.

  4. (alafaleq2020multimodalimagingof pages 4-6): Munirah Alafaleq, Cristina Georgeon, Kate Grieve, and Vincent M Borderie. Multimodal imaging of pre-descemet corneal dystrophy. European Journal of Ophthalmology, 30:908-916, Sep 2020. URL: https://doi.org/10.1177/1120672119862505, doi:10.1177/1120672119862505. This article has 9 citations and is from a peer-reviewed journal.

  5. (alafaleq2020multimodalimagingof pages 6-9): Munirah Alafaleq, Cristina Georgeon, Kate Grieve, and Vincent M Borderie. Multimodal imaging of pre-descemet corneal dystrophy. European Journal of Ophthalmology, 30:908-916, Sep 2020. URL: https://doi.org/10.1177/1120672119862505, doi:10.1177/1120672119862505. This article has 9 citations and is from a peer-reviewed journal.

  6. (alafaleq2020multimodalimagingof pages 2-4): Munirah Alafaleq, Cristina Georgeon, Kate Grieve, and Vincent M Borderie. Multimodal imaging of pre-descemet corneal dystrophy. European Journal of Ophthalmology, 30:908-916, Sep 2020. URL: https://doi.org/10.1177/1120672119862505, doi:10.1177/1120672119862505. This article has 9 citations and is from a peer-reviewed journal.

  7. (barrio2020punctiformandpolychromatic pages 1-8): Jorge L. Alió del Barrio, Doug D. Chung, Olena Al-Shymali, Alice Barrington, Kavya Jatavallabhula, Vinay S. Swamy, Pilar Yébana, Maria Angélica Henríquez-Recine, Ana Boto-de-los-Bueis, Jorge L. Alió, and Anthony J. Aldave. Punctiform and polychromatic pre-descemet corneal dystrophy: clinical evaluation and identification of the genetic basis. American Journal of Ophthalmology, 212:88-97, Apr 2020. URL: https://doi.org/10.1016/j.ajo.2019.11.024, doi:10.1016/j.ajo.2019.11.024. This article has 12 citations and is from a domain leading peer-reviewed journal.

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  9. (barrio2020punctiformandpolychromatic pages 26-30): Jorge L. Alió del Barrio, Doug D. Chung, Olena Al-Shymali, Alice Barrington, Kavya Jatavallabhula, Vinay S. Swamy, Pilar Yébana, Maria Angélica Henríquez-Recine, Ana Boto-de-los-Bueis, Jorge L. Alió, and Anthony J. Aldave. Punctiform and polychromatic pre-descemet corneal dystrophy: clinical evaluation and identification of the genetic basis. American Journal of Ophthalmology, 212:88-97, Apr 2020. URL: https://doi.org/10.1016/j.ajo.2019.11.024, doi:10.1016/j.ajo.2019.11.024. This article has 12 citations and is from a domain leading peer-reviewed journal.

  10. (barrio2020punctiformandpolychromatic pages 12-17): Jorge L. Alió del Barrio, Doug D. Chung, Olena Al-Shymali, Alice Barrington, Kavya Jatavallabhula, Vinay S. Swamy, Pilar Yébana, Maria Angélica Henríquez-Recine, Ana Boto-de-los-Bueis, Jorge L. Alió, and Anthony J. Aldave. Punctiform and polychromatic pre-descemet corneal dystrophy: clinical evaluation and identification of the genetic basis. American Journal of Ophthalmology, 212:88-97, Apr 2020. URL: https://doi.org/10.1016/j.ajo.2019.11.024, doi:10.1016/j.ajo.2019.11.024. This article has 12 citations and is from a domain leading peer-reviewed journal.

  11. (shi2017invivoconfocal pages 4-5): Hui Shi, Xiao-feng Qi, Tao-tao Liu, Qian Hao, Xiao-hong Li, Ling-ling Liang, Yi-miao Wang, and Zhi-hua Cui. In vivo confocal microscopy of pre-descemet corneal dystrophy associated with x-linked ichthyosis: a case report. BMC Ophthalmology, Mar 2017. URL: https://doi.org/10.1186/s12886-017-0423-5, doi:10.1186/s12886-017-0423-5. This article has 18 citations and is from a peer-reviewed journal.

  12. (shi2017invivoconfocal pages 1-2): Hui Shi, Xiao-feng Qi, Tao-tao Liu, Qian Hao, Xiao-hong Li, Ling-ling Liang, Yi-miao Wang, and Zhi-hua Cui. In vivo confocal microscopy of pre-descemet corneal dystrophy associated with x-linked ichthyosis: a case report. BMC Ophthalmology, Mar 2017. URL: https://doi.org/10.1186/s12886-017-0423-5, doi:10.1186/s12886-017-0423-5. This article has 18 citations and is from a peer-reviewed journal.

  13. (shi2017invivoconfocal pages 2-4): Hui Shi, Xiao-feng Qi, Tao-tao Liu, Qian Hao, Xiao-hong Li, Ling-ling Liang, Yi-miao Wang, and Zhi-hua Cui. In vivo confocal microscopy of pre-descemet corneal dystrophy associated with x-linked ichthyosis: a case report. BMC Ophthalmology, Mar 2017. URL: https://doi.org/10.1186/s12886-017-0423-5, doi:10.1186/s12886-017-0423-5. This article has 18 citations and is from a peer-reviewed journal.

  14. (nicoli2025distrofiacornealpredescemética pages 3-5): CM Nicoli and ES López. Distrofia corneal pre-descemética. Unknown journal, 2025.

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References checked 5
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Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 2
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References weighed for topical relevance 5
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