Stickler syndrome type 4 (STL4) is the autosomal recessive Stickler syndrome caused by biallelic loss-of-function variants in COL9A1, the gene for the alpha-1 chain of collagen IX. It was the first recessive Stickler syndrome described and the fourth Stickler gene found, reported in 2006 in a consanguineous Moroccan family homozygous for the nonsense allele R295X. Collagen IX is a heterotrimer of the alpha-1, alpha-2 and alpha-3 chains, so a null in COL9A1 removes the normal molecule rather than one component of it — which is why COL9A1, COL9A2 and COL9A3 nulls give one clinical entity in three genes, curated here as STL4, STL5 and STL6. Collagen IX is a FACIT collagen that decorates the surface of collagen II fibrils and bridges them to the surrounding matrix. Its absence is felt where a collagen II network has to be spaced and stabilised: the vitreous gel, which becomes hypoplastic and architecturally abnormal alongside an enlarged, highly myopic globe; hyaline cartilage, where it produces epiphyseal dysplasia and a much milder skeletal and orofacial phenotype than the dominant collagen II and XI forms; and the cochlea, where COL9A1 is highly expressed and where the hearing loss is both more frequent and more severe than in dominant Stickler syndrome. Two things distinguish STL4 clinically. Sensorineural hearing loss is near-universal and is usually what brings a child to attention, to the point that the literature recommends adding the collagen IX genes to congenital hearing loss panels — and a biallelic COL9A1 deletion has been reported in siblings with apparently nonsyndromic hearing loss, so the allelic spectrum reaches beyond the full syndrome. Retinal detachment, in contrast, occurs at a far lower rate than in type 1 Stickler syndrome and through horseshoe rather than giant retinal tears, so the prophylactic retinopexy protocol that is standard in type 1 does not transfer here and is offered case by case.
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name: Stickler Syndrome Type 4
creation_date: "2026-09-17T16:17:48Z"
description: >-
Stickler syndrome type 4 (STL4) is the autosomal recessive Stickler syndrome
caused by biallelic loss-of-function variants in COL9A1, the gene for the
alpha-1 chain of collagen IX. It was the first recessive Stickler syndrome
described and the fourth Stickler gene found, reported in 2006 in a
consanguineous Moroccan family homozygous for the nonsense allele R295X.
Collagen IX is a heterotrimer of the alpha-1, alpha-2 and alpha-3 chains, so a
null in COL9A1 removes the normal molecule rather than one component of it —
which is why COL9A1, COL9A2 and COL9A3 nulls give one clinical entity in three
genes, curated here as STL4, STL5 and STL6.
Collagen IX is a FACIT collagen that decorates the surface of collagen II
fibrils and bridges them to the surrounding matrix. Its absence is felt where a
collagen II network has to be spaced and stabilised: the vitreous gel, which
becomes hypoplastic and architecturally abnormal alongside an enlarged, highly
myopic globe; hyaline cartilage, where it produces epiphyseal dysplasia and a
much milder skeletal and orofacial phenotype than the dominant collagen II and
XI forms; and the cochlea, where COL9A1 is highly expressed and where the
hearing loss is both more frequent and more severe than in dominant Stickler
syndrome.
Two things distinguish STL4 clinically. Sensorineural hearing loss is
near-universal and is usually what brings a child to attention, to the point
that the literature recommends adding the collagen IX genes to congenital
hearing loss panels — and a biallelic COL9A1 deletion has been reported in
siblings with apparently nonsyndromic hearing loss, so the allelic spectrum
reaches beyond the full syndrome. Retinal detachment, in contrast, occurs at a
far lower rate than in type 1 Stickler syndrome and through horseshoe rather
than giant retinal tears, so the prophylactic retinopexy protocol that is
standard in type 1 does not transfer here and is offered case by case.
synonyms:
- STL4
- Stickler syndrome, type 4
- STICKLER syndrome, type IV
- COL9A1 autosomal recessive Stickler syndrome
- autosomal recessive Stickler syndrome caused by mutation in COL9A1
- type IX collagen recessive Stickler syndrome
category: Mendelian
disease_term:
preferred_term: Stickler syndrome, type 4
term:
id: MONDO:0013590
label: Stickler syndrome, type 4
mappings:
mondo_mappings:
- term:
id: MONDO:0013590
label: Stickler syndrome, type 4
mapping_predicate: skos:exactMatch
mapping_source: MONDO
parents:
- Stickler syndrome
classifications:
harrisons_chapter:
- classification_value: GENETICS_ENVIRONMENT_DISEASE
- classification_value: DISORDER_OF_EAR
inheritance:
- name: Autosomal recessive inheritance
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
description: >-
STL4 requires two defective COL9A1 alleles. The founding pedigree is the
clearest statement of it: four homozygous children affected, the two parents
and four sibs heterozygous and unaffected, and two sibs homozygous wild type.
Reported families are predominantly consanguineous.
evidence:
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The parents and four unaffected children were heterozygous carriers of the
R295X mutation.
explanation: >-
Unaffected heterozygous carriers on both parental sides, which is the
segregation argument that the disease is recessive rather than dominant
with reduced penetrance.
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In contrast to the three previously reported Stickler syndrome-causing
genes, this gene causes a form of Stickler syndrome with an autosomal
recessive inheritance pattern.
explanation: >-
States the inheritance mode explicitly and contrasts it with the dominant
collagen II and XI forms, which is the nosological point of STL4.
- reference: PMID:20301479
reference_title: Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Stickler
syndrome caused by pathogenic variants in COL9A1, COL9A2, or COL9A3 is
inherited in an autosomal recessive manner.
explanation: >-
The GeneReviews statement of inheritance for the collagen IX subgroup,
which is the expert-curated baseline for this entry.
prevalence:
- population: Published COL9A1 Stickler syndrome cases, reviewed to 2022
measure_type: CASES_IN_LITERATURE
prevalence_class: ULTRA_RARE
notes: >-
Eight patients from four families with COL9A1 variants had been published as
of the 2022 review of recessive Stickler syndrome. This is the one published
count that is COL9A1-specific rather than pooled across the three collagen IX
genes; every other quantitative figure in this entry is a type IX figure and
is labelled as such where it is used.
evidence:
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Table 1, Table 2 and Table 3 show the reported features of eight patients
from four families with COL9A1 variants, seven patients from four families
with COL9A2 variants and seven patients from four families with COL9A3
variants.
explanation: >-
The per-gene breakdown of published recessive Stickler cases, which is what
makes a COL9A1-specific count possible at all.
- population: Published recessive Stickler syndrome cases across all causative genes, reviewed to 2022
measure_type: CASES_IN_LITERATURE
prevalence_class: ULTRA_RARE
notes: >-
Forty patients from 23 families with recessive Stickler syndrome of any
cause. That figure spans COL9A1, COL9A2, COL9A3, COL11A1, LRP2, LOXL3 and
GZF1, so COL9A1 is a fifth of it. Recorded for context rather than as a
figure for this disease.
evidence:
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
We review the published cases of recessive SS, which comprise 40 patients
from 23 families.
explanation: >-
The published case count for recessive Stickler syndrome as a whole, which
bounds how much evidence any one of its genes can have.
progression:
- phase: Congenital ocular and auditory presentation
notes: >-
High myopia, an enlarged globe and an abnormal hypoplastic vitreous are
present from early life, and the sensorineural hearing loss is congenital or
early. The ear typically brings the child to attention before the eye does,
which is the argument for adding the collagen IX genes to congenital hearing
loss panels.
evidence:
- reference: PMID:31090205
reference_title: Homozygous Type IX collagen variants (COL9A1, COL9A2, and COL9A3) causing recessive Stickler syndrome-Expanding the phenotype.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients were highly myopic with congenital megalophthalmos and
abnormal, hypoplastic vitreous gel, and all had sensorineural hearing loss.
explanation: >-
Complete penetrance of the ocular and auditory features across the type IX
series, which included one COL9A1 patient.
- phase: Later retinal and joint complications
notes: >-
Retinal detachment, when it occurs, comes later — in the national type IX
cohort at ages 24 and 36, through horseshoe tears secondary to posterior
vitreous detachment. Arthropathy is uncommon and variable. The published
cohorts are young, mean age 11 years in the 2022 review, so both lifetime
risks are probably underestimated.
evidence:
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
However, the mean age of this cohort is 11 years old, so the lifetime
incidence of both problems may be underestimated.
explanation: >-
The authors' own caveat on their retinal detachment and joint pain figures.
It is what makes those figures usable rather than misleading, so it is
curated beside them rather than left in the paper.
pathophysiology:
- name: COL9A1 Loss of Function
biological_scale: MOLECULAR
description: >-
Biallelic loss-of-function variants abolish the alpha-1 chain of collagen IX.
The reported alleles are nonsense changes (R295X in the founding Moroccan
family, R507X in a Turkish family), a frameshift (p.Pro657fs), and a 44.6 kb
in-frame deletion removing exons 6 to 33.
genes:
- preferred_term: COL9A1
term:
id: hgnc:2217
label: COL9A1
genetic_context:
variant_origin: GERMLINE
zygosity: HOMOZYGOUS
functional_impact_category: LOSS_OF_FUNCTION
downstream:
- target: Collagen IX Heterotrimer Failure
causal_link_type: DIRECT
description: >-
Collagen IX assembles from the alpha-1, alpha-2 and alpha-3 chains, so
losing the alpha-1 chain prevents assembly of the normal molecule. The
remaining two chains may form an alternative heterotrimer that covers some
of its functions, which is the proposed reason a collagen IX null is
survivable where a collagen II null is not.
evidence:
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
This may suggest that the remaining two α chains are able to form an
alternative heterotrimer, which can fulfil some, but not all, of the
functions of the normal heterotrimer.
explanation: >-
Supports the edge and qualifies it in the same sentence: losing one chain
removes the normal heterotrimer, but not necessarily all collagen IX
function. The entry follows the source rather than asserting a clean
obligate-heterotrimer null.
evidence:
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Mutation analysis of the coding region of the COL9A1 gene showed a
homozygous R295X mutation in the four affected children.
explanation: The founding COL9A1 allele and its nonsense, loss-of-function character.
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A novel homozygous COL9A1 mutation (p.R507X) was identified in two affected
Turkish sisters, and the previously published mutation (p.R295X) was found
in a Moroccan boy.
explanation: >-
A second independent nonsense allele, which is what moved COL9A1 from a
single-family observation to an established disease gene.
- reference: PMID:31315069
reference_title: Exome-wide copy number variation analysis identifies a COL9A1 in frame deletion that is associated with hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A 44.6 kb homozygous in-frame deletion spanning exons 6 to 33 of COL9A1 was
detected via exome-based copy number variation analysis.
explanation: >-
A structural allele rather than a point mutation, which matters because it
is invisible to the sequencing analyses that found the nonsense alleles.
- name: Collagen IX Heterotrimer Failure
biological_scale: MOLECULAR
description: >-
Without the alpha-1 chain, the normal collagen IX heterotrimer is not formed.
Collagen IX is a FACIT collagen assembled onto the surface of the collagen
II/XI fibril and covalently linked to collagen II, so it acts as a bridge
between fibrils and the surrounding matrix. Its loss is therefore felt
wherever a collagen II fibril network has to be spaced and stabilised: the
vitreous gel, hyaline cartilage, and the cochlea.
cellular_components:
- preferred_term: collagen trimer
modifier: DECREASED
term:
id: GO:0005581
label: collagen trimer
downstream:
- target: Vitreous Gel Architectural Failure
causal_link_type: DIRECT
- target: Cartilage and Craniofacial Matrix Disorganization
causal_link_type: DIRECT
- target: Tectorial Membrane Collagen Disorganization
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
biallelic loss of any one of the α chains for type IX collagen results in
the milder skeletal SS phenotype.
explanation: >-
States that a null in any single collagen IX chain produces the Stickler
phenotype, which is the claim this node makes and the reason three genes
give one disease.
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We considered the COL9A1 gene, located on chromosome 6q13, to be a
candidate gene on the basis of the structural association with collagen
types II and XI and because of the high expression in the human inner ear
indicated by cDNA microarray.
explanation: >-
States both facts this node rests on: collagen IX associates structurally
with collagens II and XI, and COL9A1 is highly expressed in the human inner
ear. The candidate-gene reasoning is the authors' own and preceded the
mutation finding.
- name: Vitreous Gel Architectural Failure
biological_scale: TISSUE
description: >-
The vitreous is hypoplastic with abnormal architecture and the globe is
enlarged with high axial myopia. Unlike the dominant forms, which each carry
a characteristic membranous or beaded vitreous phenotype used to subclassify
them, the collagen IX vitreous is described simply as hypoplastic and
abnormal — although the 2011 COL9A1 families were reported to show vitreous
changes distinctive enough to suggest the gene.
biological_processes:
- preferred_term: collagen fibril organization
modifier: DECREASED
term:
id: GO:0030199
label: collagen fibril organization
locations:
- preferred_term: vitreous humor
term:
id: UBERON:0001797
label: vitreous humor
downstream:
- target: High myopia
causal_link_type: DIRECT
- target: Abnormal vitreous humor morphology
causal_link_type: DIRECT
- target: Retinal detachment
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: >-
Detachment follows posterior vitreous detachment and horseshoe tear
formation rather than the giant retinal tears of type 1 Stickler syndrome,
so the vitreous lesion reaches the retina by a different route here.
evidence:
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
These were both due to horseshoe tears, secondary to posterior vitreous
detachment, occurring at the ages of 24 and 36 respectively.
explanation: >-
Names the intermediate steps between the vitreous lesion and the
detachment in this genotype group, which is what the edge claims.
- target: Progressive chorioretinal degeneration
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:31090205
reference_title: Homozygous Type IX collagen variants (COL9A1, COL9A2, and COL9A3) causing recessive Stickler syndrome-Expanding the phenotype.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All patients were highly myopic with congenital megalophthalmos and
abnormal, hypoplastic vitreous gel
explanation: >-
The vitreous and globe phenotype, present in every patient of the type IX
series.
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Although the overall phenotype was comparable to autosomal dominant
Stickler, vitreous changes that may enable recognition of patients who are
likely to carry mutations in COL9A1 were identified
explanation: >-
A COL9A1-specific claim about the vitreous, from the paper that described
the second family. It is the one report suggesting the collagen IX vitreous
is recognisable rather than merely abnormal.
- name: Cartilage and Craniofacial Matrix Disorganization
biological_scale: TISSUE
description: >-
Collagen IX loss in hyaline cartilage produces epiphyseal dysplasia and a
markedly milder skeletal and orofacial phenotype than the dominant collagen
II and XI Sticklers. Midface hypoplasia is present in a minority, arthropathy
is uncommon and variable, and cleft palate — a defining feature of the
collagen XI forms — has not been reported in any collagen IX patient.
Intervertebral disc bulging was seen in one COL9A1 patient and, notably, in
two heterozygous carriers.
cell_types:
- preferred_term: chondrocyte
term:
id: CL:0000138
label: chondrocyte
locations:
- preferred_term: cartilage tissue
term:
id: UBERON:0002418
label: cartilage tissue
downstream:
- target: Epiphyseal dysplasia
causal_link_type: DIRECT
- target: Midface retrusion
causal_link_type: DIRECT
- target: Arthralgia
causal_link_type: DIRECT
evidence:
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All three had sensorineural hearing loss and epiphyseal dysplasia.
explanation: >-
Epiphyseal dysplasia in all three genotyped COL9A1 patients of that report,
which is the cartilage readout this node predicts.
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
No patients had cleft palate, and 30.8% had midfacial hypoplasia.
explanation: >-
The craniofacial phenotype quantified in the national type IX cohort,
including the negative cleft palate finding that separates collagen IX from
collagen XI recessive Stickler syndrome.
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Cleft palate is associated with type XI collagen variants, as well as the
non-collagen genes, but is so far unreported with type IX collagen
variants.
explanation: >-
States the gene-specific absence of cleft palate, which is the cleanest
single discriminator between the collagen IX and collagen XI recessive
forms.
- name: Tectorial Membrane Collagen Disorganization
biological_scale: TISSUE
description: >-
The mechanistic step between collagen IX loss and deafness, worked out in the
Col9a1 knockout mouse rather than in humans. Type IX collagen is present in
the tectorial membrane and co-localizes there with type II collagen; in
knockout mice the tectorial membrane is misshapen, its collagen fibrils are
disorganized on electron microscopy, and an anti-type-II-collagen antibody
fails to detect type II collagen in it at all. So the same
surface-decoration failure that disorganizes the vitreous and cartilage
matrices removes the type II collagen network from the structure that
transduces sound onto the hair cells. The human counterpart has not been
examined; the human-side evidence is that COL9A1 is highly expressed in the
inner ear.
locations:
- preferred_term: tectorial membrane
term:
id: UBERON:0002233
label: tectorial membrane of cochlea
downstream:
- target: Sensorineural hearing impairment
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: >-
A disorganized tectorial membrane stripped of its type II collagen network
degrades mechanotransduction. The intermediate steps between that and a
measured threshold shift are not worked out, but the lesion and the
auditory brainstem response deficit were demonstrated in the same animals.
evidence:
- reference: PMID:15802199
reference_title: Type IX collagen is crucial for normal hearing.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Mice with targeted disruption of the col9a1 gene were shown through
assessment by auditory brain stem response to have hearing loss,
suggesting an important role of type IX collagen in maintaining normal
hearing.
explanation: >-
The functional deficit measured in the same knockout that carries the
tectorial membrane lesion, which is what makes this an edge rather than
two unconnected observations.
evidence:
- reference: PMID:15802199
reference_title: Type IX collagen is crucial for normal hearing.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
An antibody against type II collagen failed to detect type II collagen in
the tectorial membrane of type IX collagen knock-out mice, suggesting that
a lack of type IX collagen may affect the three-dimensional structure of
type II collagen molecules.
explanation: >-
The finding this node is named for: without collagen IX, the type II
collagen network is not merely disordered in the tectorial membrane, it is
undetectable. It is a mouse result and is graded as one.
- reference: PMID:15802199
reference_title: Type IX collagen is crucial for normal hearing.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: >-
Immunocytochemical analysis also revealed that type IX collagen is
distributed in the tectorial membrane, where it co-localizes with type II
collagen, indicating that type IX collagen may contribute to the
three-dimensional integrated structure of type II collagen molecules.
explanation: >-
The localization result that makes the tectorial membrane the right place
to look. It is immunocytochemistry on tissue rather than an in vivo
measurement, so it is graded IN_VITRO and separated from the knockout
finding above.
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Hearing loss was more prevalent (91.7%) than in dominant SS.
explanation: >-
The quantified comparison with the dominant forms, from the largest type IX
cohort assembled.
- reference: PMID:31090205
reference_title: Homozygous Type IX collagen variants (COL9A1, COL9A2, and COL9A3) causing recessive Stickler syndrome-Expanding the phenotype.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We suggest that COL9A1, COL9A2, and COL9A3 be added to genetic screening
panels for patients with congenital hearing loss.
explanation: >-
The practical consequence the authors draw from the hearing phenotype, and
the reason this node matters clinically more than the ocular one at
presentation.
- reference: PMID:31315069
reference_title: Exome-wide copy number variation analysis identifies a COL9A1 in frame deletion that is associated with hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The present study emphasizes the importance of exome-wide copy number
variation analysis in molecular diagnosis and provides supporting evidence
to associate COL9A1 with autosomal recessive non-syndromic HL.
explanation: >-
The cochlear phenotype can occur without the rest of the syndrome, which is
the strongest available statement that the ear is not simply carried along
by a generalised connective tissue defect.
phenotypes:
- category: Ophthalmologic
name: High myopia
description: >-
High myopia, usually beyond -6 dioptres, accompanying congenital enlargement
of the globe. It is present in essentially every reported patient, although
the founding COL9A1 family was described as moderate-to-high rather than
uniformly high.
phenotype_term:
preferred_term: High myopia
term:
id: HP:0011003
label: High myopia
frequency: VERY_FREQUENT
evidence:
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
High myopia is near-universal, and sensorineural hearing loss is very
common in patients with variants in genes for type IX or XI collagen
explanation: >-
The review's synthesis across published recessive Stickler patients with
collagen IX or XI variants.
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Four children showed symptoms characteristic of Stickler syndrome,
including moderate-to-severe sensorineural hearing loss, moderate-to-high
myopia with vitreoretinopathy, and epiphyseal dysplasia.
explanation: >-
The founding COL9A1 family's ocular phenotype. It is quoted rather than
paraphrased because it says moderate-to-high, which is weaker than the
review's near-universal high myopia.
- category: Ophthalmologic
name: Abnormal vitreous humor morphology
description: >-
A hypoplastic vitreous gel with abnormal architecture. In recessive Stickler
syndrome it is not assigned to the membranous or beaded categories used to
subclassify the dominant forms.
phenotype_term:
preferred_term: Abnormal vitreous humor morphology
term:
id: HP:0004327
label: Abnormal vitreous humor morphology
frequency: VERY_FREQUENT
evidence:
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
92.3% of patients exhibited an abnormal hypoplastic vitreous architecture.
explanation: The vitreous finding quantified in the national type IX cohort.
- category: Otologic
name: Sensorineural hearing impairment
description: >-
Moderate-to-severe sensorineural hearing loss, more prevalent and more severe
than in dominant Stickler syndrome, and usually the feature that brings a
child to attention first. Biallelic COL9A1 deletion has also been reported in
siblings with apparently nonsyndromic hearing loss.
phenotype_term:
preferred_term: Sensorineural hearing impairment
term:
id: HP:0000407
label: Sensorineural hearing impairment
frequency: VERY_FREQUENT
evidence:
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Four children showed symptoms characteristic of Stickler syndrome,
including moderate-to-severe sensorineural hearing loss, moderate-to-high
myopia with vitreoretinopathy, and epiphyseal dysplasia.
explanation: >-
The severity grading in the founding COL9A1 family, which is where the
claim that hearing loss is severe in this genotype originates.
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Hearing loss was more prevalent (91.7%) than in dominant SS.
explanation: Frequency in the largest type IX cohort.
- category: Musculoskeletal
name: Epiphyseal dysplasia
description: >-
Radiographic epiphyseal dysplasia, reported in the founding family and in all
three patients of the second report. It is the skeletal signature of collagen
IX loss and is milder than the spondyloepiphyseal changes of the dominant
collagen II form.
phenotype_term:
preferred_term: Epiphyseal dysplasia
term:
id: HP:0002656
label: Epiphyseal dysplasia
frequency: FREQUENT
evidence:
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
All three had sensorineural hearing loss and epiphyseal dysplasia.
explanation: >-
Epiphyseal dysplasia in all three genotyped COL9A1 patients of that report.
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Four children showed symptoms characteristic of Stickler syndrome,
including moderate-to-severe sensorineural hearing loss, moderate-to-high
myopia with vitreoretinopathy, and epiphyseal dysplasia.
explanation: The same finding in the founding family.
- category: Ophthalmologic
name: Retinal detachment
description: >-
Retinal detachment occurs but at a far lower rate than in type 1 Stickler
syndrome, and by a different mechanism: horseshoe tears after posterior
vitreous detachment rather than giant retinal tears, with no bilateral cases
in the national cohort. This is the single most consequential difference
between the collagen IX Sticklers and the dominant forms, because giant-tear
detachment is what prophylactic retinopexy exists to prevent. Exudative as
well as rhegmatogenous detachment has been reported in COL9A1 patients.
phenotype_term:
preferred_term: Retinal detachment
term:
id: HP:0000541
label: Retinal detachment
frequency: OCCASIONAL
evidence:
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
15.4% of patients developed RD secondary to horseshoe retinal tears, with
no cases of bilateral RD or giant retinal tears (GRTs).
explanation: >-
The rate and the tear morphology together, which is what distinguishes this
from the type 1 detachment risk.
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Ophthalmic assessment revealed myopia, cataracts, distinct vitreous
changes, progressive chorioretinal degeneration, and exudative and
rhegmatogenous retinal detachments.
explanation: >-
Detachment of both kinds in genotyped COL9A1 patients. Exudative detachment
was reported by these authors as a new finding in Stickler syndrome.
- category: Ophthalmologic
name: Progressive chorioretinal degeneration
description: >-
Progressive chorioretinal degeneration, reported in the COL9A1 families of the
2011 series alongside the vitreous changes and detachments. HPO carries no
"chorioretinal degeneration" term; the binding is to Chorioretinal dystrophy,
which is the progressive chorioretinal term HPO does have, and the reported
wording is kept in preferred_term.
phenotype_term:
preferred_term: progressive chorioretinal degeneration
term:
id: HP:0001135
label: Chorioretinal dystrophy
evidence:
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Ophthalmic assessment revealed myopia, cataracts, distinct vitreous
changes, progressive chorioretinal degeneration, and exudative and
rhegmatogenous retinal detachments.
explanation: >-
The chorioretinal finding in genotyped COL9A1 patients, listed among the
ophthalmic assessment results.
- category: Ophthalmologic
name: Cataract
description: >-
Cataract, reported in the COL9A1 families of the 2011 series and listed among
the ocular findings of Stickler syndrome generally. No source located states
a mechanism connecting it to a node in this pathograph, so it is left
causally unwired.
phenotype_term:
preferred_term: Cataract
term:
id: HP:0000518
label: Cataract
evidence:
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Ophthalmic assessment revealed myopia, cataracts, distinct vitreous
changes, progressive chorioretinal degeneration, and exudative and
rhegmatogenous retinal detachments.
explanation: Cataract among the ophthalmic findings in genotyped COL9A1 patients.
- category: Craniofacial
name: Midface retrusion
description: >-
Midfacial hypoplasia, present in a minority. It is much milder than in the
dominant collagen II and XI forms, and unlike them it is not accompanied by
cleft palate or Pierre Robin sequence in any reported collagen IX patient.
phenotype_term:
preferred_term: Midface retrusion
term:
id: HP:0011800
label: Midface retrusion
frequency: OCCASIONAL
evidence:
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
No patients had cleft palate, and 30.8% had midfacial hypoplasia.
explanation: >-
Frequency in the national type IX cohort, quoted with the cleft palate
negative that belongs with it.
- category: Musculoskeletal
name: Arthralgia
description: >-
Joint pain, uncommon and variable in manifestation. The 2022 review reports it
in 15% of all recessive Stickler patients; the cohorts are young, so the
lifetime figure is likely higher.
phenotype_term:
preferred_term: Arthralgia
term:
id: HP:0002829
label: Arthralgia
frequency: OCCASIONAL
evidence:
- reference: PMID:35885918
reference_title: Autosomal Recessive Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Retinal detachment has occurred in 18% of all cases, and joint pain in 15%.
explanation: >-
The joint pain frequency across all published recessive Stickler cases, of
any causative gene.
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Arthropathy was uncommon but variable in manifestation.
explanation: >-
The qualitative characterisation in the national type IX cohort, which is
what the OCCASIONAL band rests on rather than either percentage.
genetic:
- name: COL9A1
gene_term:
preferred_term: COL9A1
term:
id: hgnc:2217
label: COL9A1
relationship_type: CAUSATIVE
notes: >-
COL9A1 on chromosome 6q13 encodes the alpha-1 chain of collagen IX. Biallelic
loss of function causes STL4. Heterozygous carriers are clinically
unaffected, although intervertebral disc bulging was noted in two carriers of
R507X.
Note that COL9A1 variants in other allelic and dosage contexts have
separately been associated with multiple epiphyseal dysplasia and with
intervertebral disc disease. Those are different diseases on the same gene
and are not curated here.
variants:
- name: p.R295X
description: >-
Homozygous in the founding consanguineous Moroccan family of four affected
children. A nonsense allele, and the first COL9A1 variant reported in
Stickler syndrome. It was later found again in an unrelated Moroccan boy.
- name: p.R507X
description: >-
Homozygous in two affected Turkish sisters. The second independent nonsense
allele, which established COL9A1 as a disease gene rather than a
single-family observation.
- name: c.1970delC, p.(Pro657fs)
description: >-
A frameshift allele reported in the NHS England type IX cohort, in a patient
who also carried an ARID1B variant.
- name: g.70,948,188_70,997,277del
description: >-
A 44.6 kb homozygous in-frame deletion spanning exons 6 to 33, found by
copy-number analysis of exome data in two Iranian siblings reported as
having nonsyndromic hearing loss. It is the only structural COL9A1 allele
reported and the only one not associated with the full syndrome.
evidence:
- reference: PMID:16909383
reference_title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Therefore, COL9A1 is the fourth identified gene that can cause Stickler
syndrome.
explanation: >-
The gene-disease assertion itself, from the report that established it.
- reference: PMID:31315069
reference_title: Exome-wide copy number variation analysis identifies a COL9A1 in frame deletion that is associated with hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Pathogenic variants in COL9A1 are primarily associated with autosomal
recessive Stickler syndrome.
explanation: >-
An independent restatement of the gene-disease relationship from a group
approaching COL9A1 from the hearing loss side rather than the Stickler side.
- reference: PMID:21421862
reference_title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Intervertebral disc bulging was observed in one patient and in two
heterozygous carriers of the p.R507X mutation.
explanation: >-
The one reported finding in heterozygotes. It is a single observation in two
people and is recorded as such, not as an established carrier phenotype.
diagnosis:
- name: Molecular genetic testing for biallelic COL9A1 variants
description: >-
The diagnosis is established by identifying biallelic pathogenic COL9A1
variants in a proband with characteristic features. Sequencing alone is not
sufficient: one of the reported alleles is a 44.6 kb deletion found only by
copy-number analysis of exome data.
evidence:
- reference: PMID:20301479
reference_title: Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
The diagnosis of Stickler syndrome can be established in a proband with
characteristic clinical features and/or a heterozygous pathogenic
variant in COL2A1, COL11A1, or COL11A2 or biallelic pathogenic variants in
COL9A1, COL9A2, or COL9A3 identified by molecular genetic testing.
explanation: >-
The GeneReviews diagnostic criterion, which names biallelic COL9A1 variants
as establishing the diagnosis.
- reference: PMID:31315069
reference_title: Exome-wide copy number variation analysis identifies a COL9A1 in frame deletion that is associated with hearing loss.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
This is also the first reported copy number variation in COL9A1 that was
identified through an exome data set in an Iranian family with apparent
non-syndromic HL.
explanation: >-
The case for adding copy-number analysis to the diagnostic workup rather
than stopping at sequence variants.
treatments:
- name: Prophylactic retinopexy, genotype-scoped
description: >-
Prophylactic retinopexy is the standard of care in type 1 Stickler syndrome,
where it prevents giant-tear detachment. It does not transfer to the collagen
IX Sticklers on current evidence: the national type IX cohort found no giant
retinal tears and no bilateral detachments, and its authors recommend
offering prophylaxis case by case rather than routinely. Both the general
recommendation and its genotype-specific restriction are curated here so a
reader meets them together.
therapeutic_modality: SURGERY
treatment_term:
preferred_term: prophylactic retinopexy
term:
id: NCIT:C15329
label: Surgical Procedure
target_mechanisms:
- target: Retinal detachment
description: >-
Creates a chorioretinal adhesion at the sites where tears form, which
reduces but does not eliminate detachment risk.
evidence:
- reference: PMID:39406934
reference_title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Prophylactic retinopexy should only be offered case-by-case for fellow eyes
of patients presenting with GRT detachments in their first eye.
explanation: >-
The genotype-scoped recommendation, from the only cohort study that
addressed the question in collagen IX patients.
- reference: PMID:35885933
reference_title: Prevention of Blindness in Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Based on the current body of literature, there is extremely strong evidence
from cohort comparison studies demonstrating the efficacy and safety of
prophylactic retinopexy to reduce, but not eliminate, the risk of retinal
detachment in Stickler syndrome patients.
explanation: >-
The general case for prophylaxis in Stickler syndrome, which is what the
collagen IX restriction above restricts. The same review names absence of
molecular sub-typing as a source of historic uncertainty, and the type IX
cohort is that sub-typing carried out.
- name: Retinal detachment repair
description: >-
Surgical repair of established detachment. Outcomes of detachment surgery in
Stickler syndrome are poor compared with the general population, which is the
stated argument for prevention where prevention is justified.
therapeutic_modality: SURGERY
treatment_term:
preferred_term: retinal detachment repair
term:
id: NCIT:C15329
label: Surgical Procedure
target_mechanisms:
- target: Retinal detachment
description: Reattaches the retina after a tear has produced a detachment.
evidence:
- reference: PMID:35885933
reference_title: Prevention of Blindness in Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Although retinal detachment surgery in the general population has a high
success rate, outcomes from surgical repair in Stickler syndrome patients
are notoriously poor, providing a strong argument for prophylactic
intervention.
explanation: >-
The outcome caveat that makes repair an unsatisfactory fallback.
- name: Annual vitreoretinal and audiologic surveillance
description: >-
Annual examination by a vitreoretinal specialist and annual audiologic
evaluation, with orthopaedic assessment as needed. Because the detachments in
this genotype group occurred in adulthood, surveillance is lifelong rather
than paediatric.
therapeutic_modality: OTHER
treatment_term:
preferred_term: clinical surveillance
term:
id: NCIT:C49236
label: Therapeutic Procedure
target_mechanisms:
- target: Retinal detachment
description: >-
Detects tears and early detachment while they are still treatable. It
modifies outcome rather than the underlying collagen defect.
evidence:
- reference: PMID:20301479
reference_title: Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Annual
examination by a vitreoretinal specialist; audiologic evaluations annually;
clinical, radiographic, and/or orthopedic assessment as needed.
explanation: >-
The GeneReviews surveillance schedule for Stickler syndrome.
- name: Avoidance of contact sports
description: >-
GeneReviews lists activities that may cause traumatic retinal detachment,
such as contact sports, among circumstances to avoid in Stickler syndrome.
The recommendation is written for Stickler syndrome as a whole; no collagen
IX-specific study of trauma risk exists.
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: activity restriction
term:
id: NCIT:C15747
label: Supportive Care
target_mechanisms:
- target: Retinal detachment
description: >-
Removes the traumatic trigger for detachment. It does not address the
vitreous lesion that makes the retina vulnerable.
evidence:
- reference: PMID:20301479
reference_title: Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
Activities such as contact sports that may lead to traumatic retinal
detachment.
explanation: >-
The GeneReviews agents-and-circumstances-to-avoid entry for Stickler
syndrome.
- name: Hearing loss management
description: >-
Standard management of sensorineural hearing loss, with prompt treatment of
otitis media. In this genotype the hearing loss is the earliest and most
consistent manifestation, and dual sensory impairment is what early diagnosis
is meant to prevent.
therapeutic_modality: OTHER
treatment_term:
preferred_term: hearing loss management
term:
id: NCIT:C15747
label: Supportive Care
target_mechanisms:
- target: Sensorineural hearing impairment
description: >-
Amplification and aural rehabilitation address the functional deficit, not
the cochlear matrix lesion.
evidence:
- reference: PMID:20301479
reference_title: Stickler Syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: REVIEW_SYNTHESIS
snippet: >-
standard treatment of sensorineural and
conductive hearing loss; prompt treatment of otitis media
explanation: >-
The GeneReviews management recommendation for the auditory phenotype.
- reference: PMID:31090205
reference_title: Homozygous Type IX collagen variants (COL9A1, COL9A2, and COL9A3) causing recessive Stickler syndrome-Expanding the phenotype.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Although recessive SS is rare, early diagnosis would have a high impact for
children with potentially dual sensory impairment, as well as identifying
risk to future children.
explanation: >-
The stated reason early auditory diagnosis matters in this disease
specifically.
animal_models:
- name: Col9a1 knockout mouse
species: Mouse
genotype: Col9a1 targeted disruption, homozygous null
publication: PMID:15802199
description: >-
The germline Col9a1 null mouse is the model that supplies this entry's
cochlear and cartilage mechanism. Reading it across to human STL4 requires
one step the literature does not take for you: the mouse is a Col9a1 null and
so is the human disease, but almost every human cohort pools the three
collagen IX genes, so the mouse is gene-matched to this entry in a way the
human evidence is not.
modeled_mechanisms:
- target: Tectorial Membrane Collagen Disorganization
relationship: RECAPITULATES
fidelity: HIGH
model_scale: TISSUE
description: >-
The knockout reproduces the lesion and the deficit together: a misshapen
tectorial membrane with disorganized collagen fibrils, no detectable type
II collagen in it, and measurable hearing loss on auditory brainstem
response.
limitations: >-
No human tectorial membrane from a COL9A1 patient has been examined, so the
claim that the human deafness has this mechanism is an extrapolation from
the mouse. The human-side support is expression rather than structure:
COL9A1 is highly expressed in the human inner ear.
readouts:
- name: Auditory brainstem response threshold
target: Tectorial Membrane Collagen Disorganization
direction: ALTERED
interpretation: Functional hearing deficit in the knockout.
evidence:
- reference: PMID:15802199
reference_title: Type IX collagen is crucial for normal hearing.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Mice with targeted disruption of the col9a1 gene were shown through
assessment by auditory brain stem response to have hearing loss,
suggesting an important role of type IX collagen in maintaining normal
hearing.
explanation: The auditory measurement, stated with the method used.
- name: Tectorial membrane type II collagen immunoreactivity
target: Tectorial Membrane Collagen Disorganization
direction: ABOLISHED
interpretation: >-
Type II collagen is undetectable in the knockout tectorial membrane, which
is the structural readout behind the node.
evidence:
- reference: PMID:15802199
reference_title: Type IX collagen is crucial for normal hearing.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
An antibody against type II collagen failed to detect type II collagen
in the tectorial membrane of type IX collagen knock-out mice, suggesting
that a lack of type IX collagen may affect the three-dimensional
structure of type II collagen molecules.
explanation: The immunohistochemical result, in the knockout tissue.
evidence:
- reference: PMID:15802199
reference_title: Type IX collagen is crucial for normal hearing.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
These findings indicate that genes encoding each chain of type IX
collagen may fulfill an important function associated with the tectorial
membrane in the auditory system.
explanation: >-
The authors' own conclusion, which is a claim about all three collagen IX
chains and therefore about this entry's gene.
- target: Cartilage and Craniofacial Matrix Disorganization
relationship: PARTIALLY_RECAPITULATES
fidelity: MODERATE
model_scale: ORGANISM
description: >-
The knockout develops premature osteoarthritis and intervertebral disc
degeneration with cartilage erosion, raised serum hyaluronan, gait changes
and increased mechanical sensitivity.
limitations: >-
The human COL9A1 skeletal phenotype is epiphyseal dysplasia in children,
not premature osteoarthritis in adults, and human arthropathy in this
genotype is reported as uncommon. The mouse therefore models the cartilage
matrix defect but expresses it as a degenerative joint phenotype the human
cohorts do not consistently show. Intervertebral disc degeneration is the
one place the two converge: disc bulging was reported in a COL9A1 patient
and in two heterozygous carriers.
readouts:
- name: Knee and spine histologic degeneration grade
target: Cartilage and Craniofacial Matrix Disorganization
direction: INCREASED
interpretation: Cartilage erosion and disc degeneration in the knockout.
evidence:
- reference: PMID:19714629
reference_title: Decreased physical function and increased pain sensitivity in mice deficient for type IX collagen.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
Male Col9a1(-/-) mice had the highest mean serum hyaluronan levels and
strong histologic evidence of cartilage erosion.
explanation: The histological and biochemical cartilage readout.
evidence:
- reference: PMID:19714629
reference_title: Decreased physical function and increased pain sensitivity in mice deficient for type IX collagen.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
In mice with Col9a1 gene inactivation (Col9a1(-/-)), osteoarthritis (OA)
and intervertebral disc degeneration develop prematurely.
explanation: >-
The skeletal phenotype of the knockout, stated as the premise of that
study rather than as its own finding.
quote_role: BACKGROUND
- reference: PMID:18163498
reference_title: Early-onset degeneration of the intervertebral disc and vertebral end plate in mice deficient in type IX collagen.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: >-
There was evidence of more degeneration of the disc and end plate in the
spines of Col9a1(-/-) mice compared with those of WT controls, at most
time points.
explanation: >-
The disc and end-plate phenotype with its comparison group, measured by
two blinded graders at three ages. This is the finding rather than the
paper's framing, which is why it replaced an earlier draft snippet that
quoted the title.
discussions:
- discussion_id: gap_stl4_collagen_ix_gene_equivalence
kind: KNOWLEDGE_GAP
status: OPEN
prompt: >-
Are STL4 (COL9A1), STL5 (COL9A2) and STL6 (COL9A3) clinically
distinguishable, or is the three-way split an artefact of gene-by-gene
discovery?
attaches_to:
- "pathophysiology#Collagen IX Heterotrimer Failure"
rationale: >-
The mechanistic argument says they should be indistinguishable: collagen IX
assembles from all three chains, and a null in any one removes the normal
molecule. Every cohort study to date has pooled them and reported figures for
"type IX recessive Stickler syndrome" rather than per gene, so there is no
published comparison that could detect a difference — and the absence of a
reported difference is not evidence of equivalence. A chain-specific effect
is not impossible: COL9A2 and COL9A3 have separate associations with multiple
epiphyseal dysplasia, COL9A1 has one with nonsyndromic hearing loss that the
other two do not, and the 2022 review itself proposes that the two remaining
chains may form an alternative heterotrimer, which would make the identity of
the missing chain matter. The practical stake is whether a clinician seeing a
COL9A1 patient may use a pooled type IX cohort's numbers, which is exactly
what this entry has had to do for most of its frequencies. The same gap is
recorded on Stickler_Syndrome_Type_5; it is restated here rather than
cross-referenced because the two entries are curated independently and a
reader of either should meet it.
proposed_experiments:
- experiment_id: exp_stl4_gene_stratified_reanalysis
name: Gene-stratified reanalysis of the pooled collagen IX cohorts
description: >-
Reanalyse the published type IX recessive Stickler cases stratified by gene
rather than pooled, comparing hearing threshold, axial length, retinal
detachment rate and arthropathy, and report whether the combined cohorts
are large enough to exclude a clinically meaningful difference.
- discussion_id: gap_stl4_nonsyndromic_hearing_loss_boundary
kind: KNOWLEDGE_GAP
status: OPEN
prompt: >-
Why does a biallelic COL9A1 deletion give apparently nonsyndromic hearing
loss where the nonsense alleles give full Stickler syndrome?
attaches_to:
- "pathophysiology#Tectorial Membrane Collagen Disorganization"
- "genetic#COL9A1"
rationale: >-
The Iranian siblings carried a homozygous 44.6 kb in-frame deletion of exons
6 to 33 and were reported as having nonsyndromic hearing loss, while the
nonsense alleles R295X and R507X give the full ocular, skeletal and auditory
syndrome. Two readings are open and the published data do not separate them.
An in-frame deletion may leave a partially functional chain that the cochlea
tolerates less well than the eye, in which case the phenotype is genuinely
allele-specific. Alternatively the ocular features may not have been looked
for: the study was a hearing loss study, and high myopia and a hypoplastic
vitreous are not findings a hearing clinic records. Distinguishing these
decides whether COL9A1 belongs on nonsyndromic hearing loss panels as a
nonsyndromic gene or as a Stickler gene whose patients need ophthalmic
referral.
proposed_experiments:
- experiment_id: exp_stl4_ophthalmic_assessment_of_nonsyndromic_probands
name: Ophthalmic assessment of COL9A1 probands ascertained through hearing loss
description: >-
Perform refraction, axial length measurement and dilated vitreoretinal
examination on probands with biallelic COL9A1 variants ascertained through
hearing loss panels, and report whether the ocular phenotype is absent or
merely unascertained.
notes: >-
Scope and lump/split. This entry covers biallelic COL9A1 Stickler syndrome.
Separate per-type entries are the settled shape here — Stickler_Syndrome_Type_1,
_Type_2, _Type_5 and _Type_6 already exist alongside the Stickler_Syndrome
umbrella — and MONDO:0013590 was bound nowhere in kb/ before this entry.
Whether the three collagen IX genes deserve three entries is genuinely open and
is curated as a KNOWLEDGE_GAP rather than settled here.
Cohort attribution, and why it is prose. Almost every published cohort pools
COL9A1, COL9A2 and COL9A3 as "type IX recessive Stickler syndrome", so most
quantitative claims here — 91.7% hearing loss, 15.4% retinal detachment, 30.8%
midfacial hypoplasia, 92.3% abnormal vitreous — are type IX figures and not
COL9A1 figures. Each description says so. There is no schema slot that records
the population a phenotype frequency was measured in as structured data, so a
query for "frequency of retinal detachment in STL4" reads 15.4% off a
three-gene cohort with nothing machine-readable marking it as such. The
COL9A1-specific claims here are the two family reports (PMID:16909383,
PMID:21421862), the deletion report (PMID:31315069), and the case count of
eight patients from four families.
The clinically important negative. The prophylactic retinopexy protocol that is
standard in type 1 Stickler syndrome does not transfer here, and that is
curated as a restriction with its evidence rather than by omitting the
treatment. Getting it wrong in either direction has a cost: assuming Stickler
syndrome means high giant-tear risk leads to unnecessary bilateral prophylaxis
in children, while omitting the treatment entirely would hide the general
recommendation from a reader who arrives at this entry first.
Phenotypes left unwired, deliberately. Cataract carries no causal inlink. No
source located states a mechanism connecting it to a node in this pathograph;
collagen IX is not a lens collagen, and the reports list cataract among ocular
findings without proposing a route from the vitreous lesion. An edge drawn to
satisfy a connectivity metric would assert a causal claim no paper makes.
One binding that is not exact. "Progressive chorioretinal degeneration", the
wording used by the 2011 COL9A1 report, has no HPO term. It is bound to
Chorioretinal dystrophy (HP:0001135), the progressive chorioretinal term HPO
does carry, with the reported wording kept in preferred_term. Chorioretinal
atrophy (HP:0000533) was considered and rejected as naming the endpoint rather
than the process.
GeneReviews. PMID:20301479, Stickler Syndrome, is the baseline chapter and is
tagged in references:. It is written around the dominant forms, so it is mined
for what applies here — the diagnostic criterion, the recessive inheritance
statement for the collagen IX genes, the surveillance schedule, the hearing
loss management recommendation and the contact-sport restriction — and each is
quoted as REVIEW_SYNTHESIS, because the chapter is an expert synthesis and not
a study of this genotype. Features it describes that belong to the dominant
subtypes, notably cleft palate and Pierre Robin sequence and the high
giant-retinal-tear risk, are deliberately not curated here, because the
collagen IX literature reports them as absent or different.
What is deliberately absent. No datasets: block — no COL9A1 Stickler-specific
dataset was identified, and a COL9A1 search surfaces the far larger multiple
epiphyseal dysplasia and intervertebral disc degeneration literature, which is
a different disease on the same gene. No clinical_trials: block — none found
for recessive Stickler syndrome. No environmental: block. No
experimental_models: block — no non-animal system (organoid, organ-chip, cell
line) modelling this disease was located.
Deep research. One OpenScientist run, committed; its reference validation
reports 25 of 25 references resolved with no failed quotes. `just preflight-dr`
was not usable for the Named Entity Confusion check because MONDO records no
causal gene for MONDO:0013590; the manual fallback is the report's own gene
counts, which are COL9A1-dominant throughout, and its OMIM identifiers (#614134
disease, *120210 gene) are this disease's. The run's contribution to the entry
is specific and large: the Col9a1 knockout mouse literature, which supplies the
tectorial membrane mechanism above. Before reading it, the cochlear node in
this entry said the step from collagen IX loss to deafness was not
mechanistically worked out, which was wrong; it was worked out in mouse in 2005.
What was not taken from the report. Its term validation flagged HP:0012609,
offered as "Megalophthalmos", which HPO actually calls Hypomagnesiuria; that
identifier is not bound here. It also proposes the naturally occurring canine
oculoskeletal dysplasia as a large-animal model. That dysplasia is caused by
COL9A2 and COL9A3 variants, not COL9A1, so listing it as an animal model of
this entry's gene would misstate the genotype, and it is left out.
references:
- reference: PMID:20301479
title: Stickler Syndrome.
tags:
- GeneReviews
- reference: PMID:16909383
title: A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene.
- reference: PMID:21421862
title: Autosomal recessive Stickler syndrome in two families is caused by mutations in the COL9A1 gene.
- reference: PMID:31315069
title: Exome-wide copy number variation analysis identifies a COL9A1 in frame deletion that is associated with hearing loss.
- reference: PMID:39406934
title: Retinal detachment in Type IX collagen recessive Stickler syndrome.
- reference: PMID:15802199
title: Type IX collagen is crucial for normal hearing.
datasets: []
Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.
Record notes
Scope and lump/split. This entry covers biallelic COL9A1 Stickler syndrome. Separate per-type entries are the settled shape here — Stickler_Syndrome_Type_1, _Type_2, _Type_5 and _Type_6 already exist alongside the Stickler_Syndrome umbrella — and MONDO:0013590 was bound nowhere in kb/ before this entry. Whether the three collagen IX genes deserve three entries is genuinely open and is curated as a KNOWLEDGE_GAP rather than settled here. Cohort attribution, and why it is prose. Almost every published cohort pools COL9A1, COL9A2 and COL9A3 as "type IX recessive Stickler syndrome", so most quantitative claims here — 91.7% hearing loss, 15.4% retinal detachment, 30.8% midfacial hypoplasia, 92.3% abnormal vitreous — are type IX figures and not COL9A1 figures. Each description says so. There is no schema slot that records the population a phenotype frequency was measured in as structured data, so a query for "frequency of retinal detachment in STL4" reads 15.4% off a three-gene cohort with nothing machine-readable marking it as such. The COL9A1-specific claims here are the two family reports (PMID:16909383, PMID:21421862), the deletion report (PMID:31315069), and the case count of eight patients from four families. The clinically important negative. The prophylactic retinopexy protocol that is standard in type 1 Stickler syndrome does not transfer here, and that is curated as a restriction with its evidence rather than by omitting the treatment. Getting it wrong in either direction has a cost: assuming Stickler syndrome means high giant-tear risk leads to unnecessary bilateral prophylaxis in children, while omitting the treatment entirely would hide the general recommendation from a reader who arrives at this entry first. Phenotypes left unwired, deliberately. Cataract carries no causal inlink. No source located states a mechanism connecting it to a node in this pathograph; collagen IX is not a lens collagen, and the reports list cataract among ocular findings without proposing a route from the vitreous lesion. An edge drawn to satisfy a connectivity metric would assert a causal claim no paper makes. One binding that is not exact. "Progressive chorioretinal degeneration", the wording used by the 2011 COL9A1 report, has no HPO term. It is bound to Chorioretinal dystrophy (HP:0001135), the progressive chorioretinal term HPO does carry, with the reported wording kept in preferred_term. Chorioretinal atrophy (HP:0000533) was considered and rejected as naming the endpoint rather than the process. GeneReviews. PMID:20301479, Stickler Syndrome, is the baseline chapter and is tagged in references:. It is written around the dominant forms, so it is mined for what applies here — the diagnostic criterion, the recessive inheritance statement for the collagen IX genes, the surveillance schedule, the hearing loss management recommendation and the contact-sport restriction — and each is quoted as REVIEW_SYNTHESIS, because the chapter is an expert synthesis and not a study of this genotype. Features it describes that belong to the dominant subtypes, notably cleft palate and Pierre Robin sequence and the high giant-retinal-tear risk, are deliberately not curated here, because the collagen IX literature reports them as absent or different. What is deliberately absent. No datasets: block — no COL9A1 Stickler-specific dataset was identified, and a COL9A1 search surfaces the far larger multiple epiphyseal dysplasia and intervertebral disc degeneration literature, which is a different disease on the same gene. No clinical_trials: block — none found for recessive Stickler syndrome. No environmental: block. No experimental_models: block — no non-animal system (organoid, organ-chip, cell line) modelling this disease was located. Deep research. One OpenScientist run, committed; its reference validation reports 25 of 25 references resolved with no failed quotes. `just preflight-dr` was not usable for the Named Entity Confusion check because MONDO records no causal gene for MONDO:0013590; the manual fallback is the report's own gene counts, which are COL9A1-dominant throughout, and its OMIM identifiers (#614134 disease, *120210 gene) are this disease's. The run's contribution to the entry is specific and large: the Col9a1 knockout mouse literature, which supplies the tectorial membrane mechanism above. Before reading it, the cochlear node in this entry said the step from collagen IX loss to deafness was not mechanistically worked out, which was wrong; it was worked out in mouse in 2005. What was not taken from the report. Its term validation flagged HP:0012609, offered as "Megalophthalmos", which HPO actually calls Hypomagnesiuria; that identifier is not bound here. It also proposes the naturally occurring canine oculoskeletal dysplasia as a large-animal model. That dysplasia is caused by COL9A2 and COL9A3 variants, not COL9A1, so listing it as an animal model of this entry's gene would misstate the genotype, and it is left out.
Create: Stickler_Syndrome_Type_4 (COL9A1 autosomal recessive Stickler syndrome) · 2026-09-17T16:53:25Z · View source
De novo curation of MONDO:0013590, biallelic COL9A1 Stickler syndrome, as the COL9A1 sibling of the existing Stickler_Syndrome_Type_5 (COL9A2) and _Type_6 (COL9A3) entries. Deep research: one OpenScientist run (research/Stickler_Syndrome_Type_4-deep-research-openscientist.md), reference validation 25/25 resolved with no failed quotes. preflight-dr could not run the Named Entity Confusion gene check because MONDO records no causal gene for this term; manual fallback used the report's gene counts and OMIM identifiers. The report's substantive contribution was the Col9a1 knockout mouse literature: before reading it the cochlear node asserted that the step from collagen IX loss to deafness was not mechanistically worked out, which was wrong. That node was rewritten as Tectorial Membrane Collagen Disorganization and an animal_models block with two modeled_mechanisms links was added. The report's term validation flagged HP:0012609 offered as Megalophthalmos, which HPO calls Hypomagnesiuria; not bound. Its proposed canine oculoskeletal dysplasia model is COL9A2/COL9A3 and was deliberately excluded. GeneReviews PMID:20301479 (Stickler Syndrome) is tagged and mined; just check-genereviews reports TAGGED. One draft snippet quoted a paper title and was replaced with a findings sentence after the reference validator flagged it. Validation run in the worktree: just validate (schema, terms, references) 57/57 snippets verified, validate-terms, check-entity-refs, check-causal-targets, check-qualifier-terms, check-duplicate-keys, check-genereviews - all clean.
Disease: Stickler Syndrome Type 4 · MONDO: MONDO:0013590 · OMIM: #614134 · Orphanet: ORPHA:90654 · Gene: COL9A1 (chromosome 6q13; OMIM 120210, HGNC:2217, UniProt P20849) · Category:* Mendelian (autosomal recessive)
Stickler syndrome type 4 (STL4) is a rare autosomal recessive collagenopathy caused by biallelic loss-of-function variants in COL9A1, the gene encoding the α1 chain of type IX collagen. Type IX collagen is a fibril-associated collagen with interrupted triple helices (FACIT) that is covalently cross-linked to the surface of type II collagen fibrils, where it restricts lateral fibril growth and mediates interactions with other extracellular matrix (ECM) components. When both COL9A1 alleles are inactivated, the entire type IX collagen heterotrimer (α1/α2/α3) cannot assemble, destabilizing the type II collagen network in the three tissues that depend on it most heavily: the vitreous humor of the eye, the hyaline/epiphyseal cartilage of the skeleton, and the tectorial membrane of the cochlea. This single molecular lesion produces the characteristic triad of the disease.
The STL4 clinical phenotype comprises high (often congenital) myopia with an abnormal, hypoplastic vitreous gel, sensorineural hearing loss (present in ~92% of cases), and epiphyseal dysplasia. Compared with the far more common dominant forms of Stickler syndrome (caused by heterozygous variants in COL2A1, COL11A1, COL11A2), STL4 carries a notably lower risk of retinal detachment (~15%, and via horseshoe tears rather than the giant retinal tears typical of type 1 disease), lacks cleft palate, and shows more prevalent hearing loss. The disease is ultra-rare — fewer than ~30–40 patients had been reported worldwide across all three type IX collagen genes as of the mid-2020s — and is enriched in consanguineous families, consistent with its recessive inheritance.
The mechanism is unusually well demonstrated for such a rare disorder. The Col9a1-knockout mouse recapitulates the human disease across all organ branches: it develops premature osteoarthritis and intervertebral disc degeneration (skeletal branch), and shows hearing loss with a disorganized tectorial membrane in which type II collagen is undetectable (auditory branch), directly proving that type IX collagen organizes the type II collagen network. A naturally occurring canine oculoskeletal dysplasia, caused by recessive COL9A2 and COL9A3 mutations in Labrador Retrievers, Samoyeds, and Northern Inuit Dogs, provides a spontaneous large-animal model that closely resembles human Stickler/Marshall syndromes. No disease-modifying therapy exists; management is multidisciplinary and supportive, with prophylactic retinopexy offered to reduce retinal-detachment risk and audiologic/orthopedic care as needed.
Overview. Stickler syndrome type 4 is one of the recessive subtypes of Stickler syndrome, a group of hereditary connective-tissue disorders ("hereditary progressive arthro-ophthalmopathy") affecting the eye, ear, skeleton, and orofacial structures. STL4 specifically denotes the form caused by biallelic COL9A1 variants. It is defined at the disease level in aggregated resources (OMIM, Orphanet, MONDO) rather than being derived from individual patient EHR data; the primary evidence base is a small number of case reports and one moderately sized case series.
Key identifiers.
| Resource | Identifier |
|---|---|
| OMIM (disease) | #614134 |
| OMIM (gene, COL9A1) | *120210 |
| MONDO | MONDO:0013590 |
| Orphanet | ORPHA:90654 (Stickler syndrome type 4 / autosomal recessive Stickler syndrome) |
| Gene / HGNC | COL9A1 / HGNC:2217 |
| UniProt (protein) | P20849 (collagen α-1(IX) chain) |
| Cytogenetic locus | 6q13 |
Synonyms / alternative names. Autosomal recessive Stickler syndrome (COL9A1-related); STL4; type IX collagen recessive Stickler syndrome. Broadly, the recessive "type IX collagen" Stickler group also encompasses STL5 (COL9A2) and the COL9A3-related recessive form.
Data provenance. Disease-level, aggregated from published literature (OMIM/Orphanet + primary case reports/series), not EHR-derived.
Primary cause (genetic). STL4 is a monogenic Mendelian disorder. It is caused by homozygous or compound heterozygous loss-of-function variants in COL9A1. The disease was first described in a consanguineous Moroccan family carrying a homozygous nonsense variant p.R295X, which co-segregated with disease in four affected children while all heterozygous carriers and wild-type homozygotes were unaffected: "Mutation analysis of the coding region of the COL9A1 gene showed a homozygous R295X mutation in the four affected children. The parents and four unaffected children were heterozygous carriers of the R295X mutation" (PMID: 16909383). A second independent family — two Turkish sisters — carried a novel homozygous p.R507X variant, confirming gene causation (PMID: 21421862).
Genetic risk factors. The overwhelming risk factor is carriage of two null COL9A1 alleles. Because inheritance is recessive, consanguinity is the dominant epidemiological risk factor — 7 of 11 families in the largest series had consanguineous parents (PMID: 39406934). Heterozygous carriers are generally unaffected for Stickler syndrome (though see Section 4 regarding the dominant multiple epiphyseal dysplasia allelic series). Related recessive Stickler disease arises from biallelic loss-of-function in the paralogous genes COL9A2 (STL5; PMID: 21671392) and COL9A3 (PMID: 24273071, PMID: 33570243); rare biallelic LOXL3 variants produce a phenotypically overlapping recessive Stickler-like disorder (PMID: 30362103).
Environmental risk factors. None identified. As a fully penetrant Mendelian disorder, STL4 has no established environmental, occupational, toxic, or infectious contributing cause.
Protective factors. No genetic or environmental protective factors are established.
Gene–environment interactions. Not established for the human disease. The closest analog is from the mouse model, where mechanical/physical loading interacts with the genetic cartilage defect: moderate forced running exercise induced cartilage adaptation but exacerbated the molecular cartilage phenotype of type IX collagen knockout mice (PMID: 42154996) — relevant to the skeletal branch but not a cause of the disease.
The STL4 phenotype is dominated by three organ systems: eye, ear, and skeleton. Frequencies below are drawn primarily from the largest cohort (13 cases / 11 families; PMID: 39406934) and a multi-family case series (PMID: 31090205).
| Phenotype | Type | Frequency | Onset | Severity/Course | Suggested HPO |
|---|---|---|---|---|---|
| High myopia | Physical/ophthalmic sign | ~Universal | Congenital / early childhood | Severe, stable-to-progressive | HP:0011003 (High myopia) |
| Abnormal / hypoplastic vitreous | Clinical sign | ~Universal | Congenital | Structural; key diagnostic sign | Vitreous anomaly (HP:0004327-related) |
| Congenital megalophthalmos (enlarged globe) | Physical manifestation | Reported in all patients in one series | Congenital | Structural | HP:0012609 (Megalophthalmos) |
| Sensorineural hearing loss | Clinical sign / lab (audiometry) | ~91.7% | Childhood, often early | Mild–moderate, progressive; may need aids/implants | HP:0000407 (SNHL) |
| Retinal detachment (horseshoe tears) | Clinical sign | ~15.4% | Childhood–adult | Sight-threatening; no bilateral RD / no GRTs reported | HP:0000541 (Retinal detachment) |
| Epiphyseal dysplasia / arthropathy | Physical/skeletal | Variable/uncommon | Childhood | Variable; early osteoarthritis possible | HP:0002656 (Epiphyseal dysplasia) |
| Midfacial hypoplasia | Physical manifestation | ~30.8% | Congenital | Mild–moderate | HP:0011800 (Midface retrusion) |
| Cleft palate | Physical manifestation | Absent (0%) | — | Distinguishes STL4 from dominant STL | HP:0000175 (Cleft palate) |
| Short stature | Physical manifestation | Variable | Childhood | Mild | HP:0004322 (Short stature) |
Key characterization quotes. In the largest series: "15.4% of patients developed RD secondary to horseshoe retinal tears, with no cases of bilateral RD or giant retinal tears (GRTs). No patients had cleft palate, and 30.8% had midfacial hypoplasia. Hearing loss was more prevalent (91.7%) than in dominant SS" (PMID: 39406934). In the multi-family series: "All patients were highly myopic with congenital megalophthalmos and abnormal, hypoplastic vitreous gel, and all had sensorineural hearing loss" (PMID: 31090205).
Hearing phenotype context. A systematic review of hearing impairment across all Stickler subtypes found hearing loss in 62.9% overall, predominantly sensorineural (67.8%), and typically mild-to-moderate (PMID: 23110709); STL4 sits at the high end of hearing-loss prevalence (~92%).
Quality of life impact. The combination of severe visual impairment (high myopia, risk of retinal detachment) and sensorineural hearing loss creates a dual sensory impairment with substantial impact on daily functioning, education, and communication — a point emphasized clinically because visually impaired Stickler patients depend heavily on hearing (PMID: 23110709). Arthropathy/early osteoarthritis, where present, adds musculoskeletal disability. No disease-specific EQ-5D/SF-36 data are available for this ultra-rare disorder.
Causal gene. COL9A1 (OMIM 120210; HGNC:2217; UniProt P20849), encoding the α1(IX) chain of type IX collagen, located at 6q13. Type IX collagen is a heterotrimer of three genetically distinct chains — α1, α2, α3 — encoded by COL9A1, COL9A2, COL9A3 respectively; all three chains are required* to form a functional molecule, so loss of any one chain via biallelic null variants produces recessive Stickler syndrome (PMID: 21671392).
Pathogenic variants (STL4, COL9A1).
| Variant | Type | Zygosity | Population | Phenotype | PMID |
|---|---|---|---|---|---|
| p.R295X (c.883C>T) | Nonsense (LoF) | Homozygous | Moroccan (consanguineous) | STL4 | 16909383 |
| p.R507X | Nonsense (LoF) | Homozygous | Turkish | STL4 | 21421862 |
| ~44.6 kb deletion of exons 6–33, p.(Phe233_Ser704del) | Large in-frame deletion | Homozygous | — | Non-syndromic hearing loss (allelic spectrum) | 31315069 |
Variant classification and type. STL4-causing variants are predominantly nonsense, frameshift, or large-deletion loss-of-function alleles, classified pathogenic/likely pathogenic under ACMG/AMP criteria (LoF is a well-established mechanism for this gene; recurrent stop-gains in multiple families provide segregation evidence). In a young Chinese retinal-detachment cohort, Stickler syndrome was the leading genetic cause (35.7%) and ~40% of variants were VUS, underscoring interpretation challenges in ophthalmic collagenopathies (PMID: 42382949).
Allele frequency. STL4 variants are private/ultra-rare; pathogenic COL9A1 stop-gains are essentially absent from population databases (gnomAD) at appreciable frequency, consistent with a recessive disorder.
Somatic vs germline. All variants are germline; no somatic involvement (non-neoplastic Mendelian disorder).
Functional consequence. Loss of function — biallelic null variants abolish α1(IX) and therefore prevent assembly of the entire type IX collagen heterotrimer.
Allelic dosage rule (key insight). COL9A1 exhibits a striking dosage-dependent, mechanism-dependent genotype–phenotype relationship:
Modifier genes. None formally established. The paralogous COL9A2/COL9A3 and the interacting type II collagen (COL2A1) are mechanistic partners rather than confirmed modifiers.
Epigenetic / chromosomal abnormalities. None reported; STL4 is not associated with methylation changes, imprinting, aneuploidy, or gross chromosomal rearrangement (aside from the intragenic 44.6 kb CNV noted above).
No environmental, toxic, occupational, lifestyle, or infectious factors are established in the causation of STL4. It is a purely genetic Mendelian disorder. The only environment-related signal in the literature is mechanical loading of cartilage, where forced running exercise in type IX collagen knockout mice both induced cartilage adaptation and exacerbated the molecular knockout phenotype (PMID: 42154996) — relevant to counseling around joint use in the skeletal branch but not a cause of the disease.
Disorganized/destabilized type II collagen network → branches into three tissue-specific manifestations:
4a — Vitreous (eye): abnormal, hypoplastic vitreous gel + high myopia + megalophthalmos → predisposition to retinal tears/detachment (demonstrated phenotype, PMID: 31090205).
COL9A1 biallelic null (p.R295X / p.R507X)
│ no α1(IX) chain
▼
Type IX collagen heterotrimer fails to assemble (α1/α2/α3 all required)
│ loss of FACIT cross-linking to type II collagen fibrils
▼
Destabilized / disorganized type II collagen ECM network
├───────────────┬────────────────────────┐
▼ ▼ ▼
VITREOUS CARTILAGE TECTORIAL MEMBRANE
hypoplastic epiphyseal dysplasia, type II collagen network absent,
vitreous, premature OA / disc membrane disorganized
high myopia, degeneration │
megalophthalmos │ ▼
│ ▼ Sensorineural hearing loss (~92%)
▼ Arthropathy, short stature
Retinal tears / detachment (~15%)
| Level | Structure | UBERON / GO / CL |
|---|---|---|
| Organ | Eye (vitreous body, retina, globe) | UBERON:0000970 (eye); UBERON:0001796 (vitreous humor); UBERON:0000966 (retina) |
| Organ | Inner ear / cochlea (tectorial membrane) | UBERON:0001846 (internal ear); UBERON:0002220 (tectorial membrane) |
| Organ/system | Skeleton — epiphyseal/articular cartilage, intervertebral disc | UBERON:0002481 (cartilage tissue); UBERON:0002103 (intervertebral disc) |
| System | Craniofacial (midface) | midface (UBERON:0002100-related) |
| Tissue | Connective tissue / hyaline cartilage; vitreous gel | connective tissue (UBERON:0002384) |
| Cell | Chondrocyte | CL:0000138 |
| Cell | Spiral-ligament fibrocyte / cochlear supporting cell | cochlear fibrocyte |
| Subcellular | Extracellular matrix; collagen type IX trimer | GO:0031012; GO:0005596 |
Body systems. Primary: sensory (visual + auditory) and musculoskeletal. Secondary: craniofacial. Lateralization: bilateral (myopia, vitreous anomaly, hearing loss are bilateral; retinal detachment may be unilateral). Type IX collagen was confirmed "within the tectorial membrane as well as fibrocytes in the spiral ligament" (PMID: 18448257).
Clinical/ophthalmic evaluation. Diagnosis is anchored by the vitreous phenotype — an abnormal, hypoplastic vitreous gel is a key diagnostic sign in Stickler syndrome (PMID: 17318849, PMID: 31090205) — combined with high myopia and audiometrically documented sensorineural hearing loss.
Audiology. Pure-tone audiometry / auditory brainstem response to characterize sensorineural hearing loss; COL9A1/COL9A2/COL9A3 should be included on congenital hearing-loss gene panels (PMID: 31090205).
Imaging. Skeletal radiographs for epiphyseal dysplasia; bone densitometry (and, in severe cases, transiliac bone biopsy) may reveal osteoporosis with disorganized trabecular network (PMID: 28159459).
Genetic testing (definitive). Next-generation sequencing using skeletal/collagen or Stickler-specific gene panels, and whole-exome/whole-genome sequencing, are the diagnostic mainstay (PMID: 31090205, PMID: 33951325). Because pathogenic COL9A1 variants include large intragenic deletions, CNV/exome copy-number analysis is important (the 44.6 kb deletion was found by exome-wide CNV analysis, PMID: 31315069). Variant interpretation follows ACMG/AMP criteria; VUS rates are high in ophthalmic collagenopathy cohorts (~40%), so integrating phenotype and family history is essential (PMID: 42382949).
Differential diagnosis. Dominant Stickler syndrome (COL2A1 = STL1, COL11A1 = STL2, COL11A2 = STL3); recessive COL9A2 (STL5) and COL9A3 forms; recessive LOXL3-related Stickler-like syndrome; Marshall syndrome; fibrochondrogenesis (severe recessive COL11A1); Marfan syndrome and familial exudative vitreoretinopathy (FEVR) in the RD differential (PMID: 42382949). Distinguishing features of STL4 versus dominant disease: absence of cleft palate, higher hearing-loss prevalence, lower/atypical RD risk (horseshoe rather than giant retinal tears), and recessive family history with consanguinity.
Screening. Cascade carrier testing in consanguineous families once the familial variant is known; prenatal/preimplantation genetic testing is feasible for known biallelic variants.
No disease-modifying or curative therapy exists. Management is multidisciplinary and supportive, targeting each organ branch.
| Domain | Intervention | Evidence / notes | Suggested NCIT |
|---|---|---|---|
| Ophthalmic — prevention | Prophylactic retinopexy (360° cryotherapy or laser) | Cryotherapy reduced RD from 73% (untreated) to 8% failure in STL1 (PMID: 17675240); laser reduced RD from 26.7% to 4.6% of eyes (PMID: 34982001); strong cohort-level evidence of efficacy/safety (PMID: 35885933). In STL4, RD risk is lower (~15%), so prophylaxis is individualized (PMID: 39406934) | Cryotherapy; Laser Therapy |
| Ophthalmic — corrective | Refractive correction of high myopia; vitreoretinal surgery for established RD | Standard of care | Retinal Reattachment Surgery |
| Audiologic | Hearing aids; cochlear implantation for severe SNHL; regular audiologic follow-up | Recommended given ~92% hearing-loss prevalence and progressive course (PMID: 23110709) | Hearing Aid; Cochlear Implant |
| Orthopedic / rehab | Physiotherapy, analgesia, joint care for arthropathy/OA; bone-health assessment | Supportive; DEXA and bone care where osteoporosis present (PMID: 28159459) | Physical Therapy |
| Genetic | Genetic counseling for families | Recessive risk counseling; carrier testing | Genetic Counseling |
Pharmacotherapy / advanced therapeutics. No approved pharmacologic, gene, cell, or RNA-based therapy. No pharmacogenomic considerations specific to STL4. Gene-replacement or ECM-directed strategies remain hypothetical.
A naturally occurring recessive oculoskeletal dysplasia (OSD) in dogs is a validated large-animal model of type IX collagen Stickler syndrome.
| Breed | Gene / variant | NCBI Taxon | Reference |
|---|---|---|---|
| Labrador Retriever (drd1) | COL9A3, exon-1 1-bp insertion | 9615 (Canis lupus familiaris) | PMID: 20686772 |
| Samoyed (drd2) | COL9A2, 5′ 1,267-bp deletion | 9615 | PMID: 20686772 |
| Northern Inuit Dog | COL9A3 nonsense variant (carrier ~15%, affected ~0.6%) | 9615 | PMID: 31415586 |
Both canine COL9A2/COL9A3 mutations affect the COL3 domain and reduce retinal RNA expression: "Positional candidate gene analysis then led to the identification of a 1-base insertional mutation in exon 1 of COL9A3 that cosegregates with drd1 and a 1,267-bp deletion mutation in the 5' end of COL9A2 that cosegregates with drd2" (PMID: 20686772). The canine phenotype — short-limbed dwarfism, angular limb deformities, cataracts, vitreopathy, retinal detachment — "resembles human hereditary arthro-ophthalmopathies such as Stickler and Marshall syndromes" (PMID: 20686772). In the Northern Inuit Dog, a COL9A3 nonsense variant was strongly associated with OSD (p = 1.41×10⁻¹¹; PMID: 31415586). Orthologous genes: canine COL9A1/COL9A2/COL9A3. This has veterinary relevance (breeding management) and confirms evolutionary conservation of the type IX collagen mechanism.
Mouse — Col9a1 knockout (primary genetic model). The Col9a1−/− mouse recapitulates the human disease across organ branches:
Dog — naturally occurring OSD (COL9A2/COL9A3): spontaneous large-animal model (Section 14) capturing the combined ocular + skeletal phenotype.
Model characteristics. The mouse strongly recapitulates the auditory (tectorial membrane) and skeletal (cartilage/disc) branches; the dog additionally recapitulates the ocular (vitreopathy, cataract, retinal detachment) branch. Limitations: mouse ocular anatomy differs from human, so the vitreous/myopia phenotype is less directly modeled in mouse; craniofacial features are minimally modeled. Resources: MGI (Col9a1), Alliance of Genome Resources; canine models via breed genetic databases.
The unifying interpretation of STL4 is a single-molecule ECM structural failure with three tissue-specific readouts. Type IX collagen is not a signaling molecule; it is a FACIT collagen that decorates the surface of type II collagen fibrils and physically organizes them. Its complete loss (from biallelic COL9A1 nulls) removes the architectural constraint on the type II collagen network in exactly the three tissues where type II collagen is the dominant fibrillar collagen and where its precise 3-D organization is functionally critical: the vitreous gel, hyaline/epiphyseal cartilage, and the cochlear tectorial membrane. The elegance of the mechanism is that the same lesion in the mouse leads to a type-II-collagen-empty tectorial membrane (hearing loss) and premature cartilage/disc degeneration, matching the human auditory and skeletal phenotypes.
The dosage/mechanism dichotomy is the second key conceptual pillar: recessive null → Stickler (STL4) versus dominant in-frame COL3-skipping → multiple epiphyseal dysplasia (dominant negative). This explains why the same gene family produces two clinically distinct disorders and why heterozygous STL4 carriers are healthy — one functional allele produces enough intact heterotrimer, whereas a dominant-negative in-frame allele poisons the trimer.
Finally, STL4's clinical distinctiveness from dominant Stickler (lower RD risk, no giant retinal tears, no cleft palate, higher hearing-loss prevalence) is mechanistically consistent: type IX collagen's role is more about fibril organization/stability than the bulk fibrillar scaffold provided by type II/XI collagen, so the vitreoretinal fragility that drives giant retinal tears in COL2A1 disease is attenuated, while the tectorial-membrane dependence on type IX collagen makes hearing loss especially prominent.
| PMID | Role in this report |
|---|---|
| 16909383 | First STL4 family; homozygous COL9A1 p.R295X co-segregates, carriers unaffected — establishes gene causation |
| 21421862 | Second COL9A1 family (p.R507X, Turkish sisters) — confirms causation |
| 21671392 | COL9A2 LoF causes recessive Stickler; all three chains required for functional collagen IX |
| 39406934 | Largest cohort (13/11 families): RD 15.4% via horseshoe tears, no GRT, no cleft palate, hearing loss 91.7%, consanguinity |
| 31090205 | Multi-family series: universal high myopia, megalophthalmos, hypoplastic vitreous, SNHL; panels should include COL9 genes |
| 42154996 | Defines FACIT function of type IX collagen; exercise-GxE cartilage study |
| 19714629 | Col9a1−/− mouse: premature OA and disc degeneration; pain/gait phenotype |
| 18163498 | Col9a1−/− mouse: early-onset disc/end-plate degeneration (P<0.01 at 3, 6 mo) |
| 15802199 | Mechanism-defining: Col9a1−/− mouse hearing loss + type-II-collagen-empty, disorganized tectorial membrane |
| 18448257 | Localizes type IX collagen to tectorial membrane and spiral-ligament fibrocytes |
| 31315069 | 44.6 kb in-frame COL9A1 deletion → non-syndromic hearing loss; allelic spectrum |
| 10364514 | Dominant type IX (COL9A2) in-frame alleles cause MED (dominant-negative) — contrasts recessive null Stickler |
| 20686772 | Canine COL9A2/COL9A3 OSD model resembling human Stickler/Marshall |
| 31415586 | Northern Inuit Dog COL9A3 nonsense OSD (p=1.41×10⁻¹¹) |
| 17675240 | Prophylactic cryotherapy: RD 73%→8% failure |
| 34982001 | Prophylactic laser retinopexy: RD 26.7%→4.6% of eyes |
| 35885933 | Review: Stickler = most common cause of childhood RD; strong evidence for prophylaxis |
| 33570243 | Rarity: ~19 type IX recessive Stickler patients reported |
| 23110709 | Systematic review of hearing impairment across Stickler subtypes |
| 24273071 | First recessive COL9A3 Stickler family |
| 42382949 | ACMG/AMP + VUS analysis in gene-related RD (Stickler leading cause) |
| 28159459 | Osteoporosis with bone histology in Stickler syndrome |
| 17318849 | Vitreous phenotype as key diagnostic sign |
| 30362103 | LOXL3 recessive Stickler-like disorder (differential) |
Evidence source types: human clinical (case reports/series, cohorts), model organism (Col9a1−/− mouse; canine OSD), and computational/variant-interpretation (ACMG/AMP, CNV analysis). Note that all disease-frequency estimates derive from small cohorts and are subject to reporting bias.
Checked with linkml-reference-validator 0.2.1.
| Outcome | Count |
|---|---|
| References checked | 25 |
| Resolved | 25 |
| Unresolved (possible confabulation) | 0 |
| Unverifiable | 0 |
| References weighed for topical relevance | 25 |
| On topic | 20 |
| Off topic | 0 |
All extracted references resolved successfully.
Checked with linkml-term-validator 0.4.5, through the ols: adapter.
| Outcome | Count |
|---|---|
| Terms checked | 29 |
| Resolved | 26 |
| Unresolved (possible confabulation) | 0 |
| Obsolete | 1 |
| Unverifiable | 2 |
| Terms whose name was checked | 11 |
| Terms named correctly | 8 |
| Terms named as a different term | 3 |
These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:
MONDO:0013590 (2 mentions) - the report calls it "MONDO"; MONDO calls it Stickler syndrome, type 4HP:0012609 (1 mention) - the report calls it "Megalophthalmos"; HP calls it HypomagnesiuriaHP:0000407 (1 mention) - the report calls it "SNHL"; HP calls it Sensorineural hearing impairmentThese terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:
UBERON:0002220 (UBERON_0002220) (1 mention) - replaced by UBERON:0002291Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.