Meester-Loeys Syndrome

Mendelian MONDO:0010515 Pathograph 10 Show in embeddings browser Heritable Thoracic Aortic Disease

Meester-Loeys syndrome (MRLS) is an X-linked syndromic aortopathy caused by loss-of-function variants in BGN, which encodes biglycan, a small leucine-rich proteoglycan of the arterial extracellular matrix. Biglycan binds and sequesters latent TGF-beta in the matrix, so losing it releases TGF-beta signalling: affected aortic wall shows increased nuclear pSMAD2. Two features make it worth separating from the Marfan and Loeys-Dietz syndromes it overlaps clinically. First, the histology is unusual for an aneurysm syndrome: elastic fibres are *preserved* rather than fragmented, which is the opposite of what a Marfan-like reading would predict. Second, the disease is not confined to the thoracic aorta. As the cohort grew from five probands to eighteen, aneurysms and dissections were found throughout the arterial tree, and cardiovascular disease was found coexisting with non-specific connective-tissue features such as joint hypermobility, so patients can be, and have been, labelled Ehlers-Danlos syndrome first. Dissections occur at young ages and males are affected more severely and more penetrantly than females. Only loss-of-function alleles are established: no pathogenic missense variant without an additional splice effect has been reported, and the discoverers recommend proving loss of function at RNA or protein level before calling a missense variant pathogenic.

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1
Inheritance
4
Pathophys.
1
Histopath.
8
Phenotypes
2
Gaps
10
Pathograph
1
Genes
1
Medical Actions
4
Differentials
2
Models
4
References
1
Deep Research
👪

Inheritance

1
X-Linked HP:0001417
X-linked. Males are affected more severely and more penetrantly; female carriers range from unaffected to minor manifestations, and two of the eighteen reported probands are female.
X-linked inheritance
Show evidence (3 references)
PMID:27632686 SUPPORT Human Clinical
"In conclusion, BGN gene defects in humans cause an X-linked syndromic form of severe TAAD that is associated with preservation of elastic fibers and increased TGF-β signaling."
States the inheritance mode, and in the same sentence the two mechanistic claims this entry turns on.
PMID:38531898 SUPPORT Human Clinical
"Furthermore, the clinical presentation is more severe and penetrant in males compared to females."
The sex difference this block records, from the larger cohort.
PMID:41465473 SUPPORT Human Clinical
"Female carriers had no or only minor manifestations."
Independent confirmation of the carrier picture in a three-generation family.
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Discussions and Knowledge Gaps

2
Is TGF-beta dysregulation in MRLS a property of the aortic wall specifically, and can patient dermal fibroblasts report it at all?
CONTROVERSY mrls_tgfbeta_tissue_discordance
Attached to
pathophysiology#Increased TGF-beta Signaling in the Aortic Wall
The aortic-wall finding is replicated: increased nuclear pSMAD2 in 2017, TGF-beta/SMAD dysregulation in a second family in 2025. But in that same 2025 study, reporter assays in cell lines expressing mutant biglycan showed *reduced* canonical Wnt and TGF-beta activity, and the patients' own dermal fibroblasts showed no consistent difference in nuclear beta-catenin or p-SMAD2/3 against controls. Three results, three directions. The most economical reading is that the signalling change is tissue-specific to the arterial media and that dermal fibroblasts are simply the wrong cell, which would matter because fibroblasts are the accessible tissue and the one the iPSC line is derived from. The alternative, that the increase is a downstream consequence of wall injury rather than a driver, is not excluded. The pathophysiology node states the observation and the review's own verdict that the functional consequences remain largely elusive, rather than asserting a mechanism.
Show evidence (2 references)
PMID:41465473 REFUTE Human Clinical
"However, patients' dermal fibroblasts did not show consistent differences in the nuclear abundance of β-catenin or p-SMAD2/3 compared to cells from controls."
Refutes the expectation that the aortic-wall signalling change is detectable in patient fibroblasts, which is the discordance this discussion is about.
PMID:41465473 SUPPORT INDIRECT In Vitro
"assays with reporter vectors revealed reduced canonical Wnt and TGF-β activity in cell lines expressing mutant biglycan"
The reporter result, whose direction is opposite to the aortic-wall finding. Graded INDIRECT because it is an overexpression reporter assay in a heterologous cell line rather than a measurement in affected tissue.
Is the absence of missense-only pathogenic BGN alleles a real constraint on the mechanism, or ascertainment?
KNOWLEDGE GAP mrls_no_missense_only_alleles
Attached to
pathophysiology#Loss-of-Function BGN Variants genetic#BGN
Across 18 probands, every pathogenic variant is truncating, splice-affecting or a deletion; not one is a missense change without an additional splice effect. If real, that says the disease requires absence of the protein rather than an altered one, and rules out a dominant-negative or gain-of-function contribution. But the group that reports it also recommends proving loss of function before calling a missense variant pathogenic, which is a filter that would systematically exclude any missense-only allele acting by another route. The 2025 family carries a "novel missense variant" in its title, which sharpens rather than settles the question. The entry records the observation without asserting the constraint.
⚙

Pathophysiology

4
Loss-of-Function BGN Variants
Reported disease alleles are loss-of-function: truncating, splice-affecting or whole-gene deletions. Notably, no pathogenic missense variant *without* an additional predicted or demonstrated splice effect has been found across 18 probands, which is why the reporting group recommends proving loss of function at cDNA or protein level before calling a BGN missense variant pathogenic.
Genetic context BGN hgnc:1044 HUGO Gene Nomenclature Committee (hgnc) Relation: this genetic context concerns this gene This genetic context concerns BGN (hgnc:1044). hgnc:1044 is a gene from the HUGO Gene Nomenclature Committee. functional_impact_category: LOSS_OF_FUNCTION
Downstream
Loss of Biglycan from the Arterial Extracellular Matrix Loss-of-function alleles remove the proteoglycan from the matrix.
Show evidence (2 references)
PMID:38531898 SUPPORT Human Clinical
"The identified BGN variants were shown to lead to loss-of-function by cDNA and Western Blot analyses of skin fibroblasts or were strongly predicted to lead to loss-of-function based on the nature of the variant."
Establishes loss of function as the mechanism, and how it was demonstrated rather than assumed.
PMID:38531898 SUPPORT Human Clinical
"No (likely) pathogenic missense variants without additional (predicted) splice effects were identified."
The negative result behind this node's claim about missense alleles, and the reason the variant-interpretation caveat is in the description.
Loss of Biglycan from the Arterial Extracellular Matrix
Biglycan is a small leucine-rich proteoglycan of the arterial media. Its loss changes the matrix without destroying its elastic architecture: the elastic fibres are preserved. That distinguishes Meester-Loeys histology from the elastic-fibre fragmentation of classical medial degeneration and is a point where the disease diverges from its clinical mimics.
Vascular smooth muscle cell CL:0000359 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Vascular smooth muscle cell, annotated with vascular associated smooth muscle cell (CL:0000359). CL:0000359 is a cell type from the Cell Ontology.
extracellular matrix organization GO:0030198 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal extracellular matrix organization (GO:0030198). GO:0030198 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Increased TGF-beta Signaling in the Aortic Wall Biglycan sequesters latent TGF-beta in the matrix; without it, signalling is released.
Show evidence (2 references)
PMID:27632686 SUPPORT Human Clinical
"We found five individuals with loss-of-function mutations in BGN encoding the small leucine-rich proteoglycan biglycan."
Identifies biglycan as the lost matrix component.
PMID:27632686 SUPPORT Human Clinical
"In conclusion, BGN gene defects in humans cause an X-linked syndromic form of severe TAAD that is associated with preservation of elastic fibers and increased TGF-β signaling."
The preservation of elastic fibres, which is what makes this node's claim about the matrix specific rather than generic.
Increased TGF-beta Signaling in the Aortic Wall
Fluorescent staining of the aortic wall shows increased nuclear pSMAD2, the canonical readout of active TGF-beta signalling. This is the mechanistic link to the wider heritable-aortopathy literature, where TGF-beta dysregulation is the recurring theme. It is also the least settled part of the model: how loss of biglycan produces it is described by the discoverers themselves as largely unresolved, and a 2025 family found the aortic-wall signal without a matching change in patient dermal fibroblasts.
transforming growth factor beta receptor signaling pathway GO:0007179 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased transforming growth factor beta receptor signaling pathway (GO:0007179). GO:0007179 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Medial Weakening and Progressive Arterial Dilatation Sustained TGF-beta signalling accompanies the wall remodelling that permits dilatation, but the earlier wording put it in the wrong layer: the increase in the media was slight, and significantly more pronounced in the adventitia, which is the major site of biglycan deposition.
Show evidence (3 references)
PMID:27632686 SUPPORT Human Clinical
"Fluorescent staining revealed an increase in TGF-β signaling, evidenced by an increase in nuclear pSMAD2 in the aortic wall."
The direct measurement, in the affected tissue, that this node asserts.
PMID:41465473 SUPPORT Human Clinical
"Studies of the aortic wall were consistent with a dysregulation of the TGF-β/SMAD pathway"
Independent replication of the aortic-wall finding in a second family, nine years later.
PMID:34807424 SUPPORT INDIRECT Other
"Although functional consequences of these mutations remain largely elusive, increased TGF-β signaling has been observed."
The reviewers' own assessment of how well this step is understood, quoted because it is the honest calibration for this node: the observation is solid, the causal path to it is not.
Medial Weakening and Progressive Arterial Dilatation
The clinical endpoint, and it is not confined to the thoracic aorta. The expanded cohort found aneurysms and dissections across the arterial tree, and one family presented with multiple visceral artery aneurysms in a proband initially diagnosed as Ehlers-Danlos syndrome. Dissection occurs at young ages.
Animal models
Bgn-deficient BALB/cA mouse Mouse recapitulates Fatal aortic rupture in hemizygous males reproduces the severe, male-predominant vascular endpoint of the human disease.
Downstream
Aortic root aneurysm
Aortic dissection
Arterial aneurysm and dilatation
Show evidence (2 references)
PMID:38531898 SUPPORT Human Clinical
"This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features."
The finding that widens this node beyond the thoracic aorta, and the diagnostic trap it creates.
PMID:27632686 SUPPORT Human Clinical
"The clinical phenotype is characterized by early-onset aortic aneurysm and dissection."
Establishes the early onset of the cardiovascular endpoint.
✶

Histopathology

1
Preserved elastic fibres with low to normal collagen content
The finding that separates this disease from the classic TGF-beta vasculopathies it resembles clinically. The paper draws the contrast with both Marfan and Loeys-Dietz, where collagen content increases and elastic fibres break; in the MRLS probands the elastin was normal and collagen was low to normal. Of the evidence below, the first item is the staining description itself; the two that follow it are the paper's Results and Discussion statements of the contrast, the Results naming Loeys-Dietz only and the Discussion naming both syndromes. A mechanism routed only through TGF-beta would predict the opposite, so this is the histological constraint any account of the disease has to satisfy.
Show evidence (3 references)
PMID:27632686 SUPPORT Human Clinical
"The staining revealed low to normal collagen content; elastin fibers appeared normal"
The direct histological description of the probands' aortic wall.
PMID:27632686 SUPPORT Human Clinical
"This is in contrast to what is observed in LDS individuals, in whom an increase in collagen production and fragmentation of elastic fibers are typically present"
The comparator the finding is meaningful against, in the paper's own words, in its Results section. This sentence names Loeys-Dietz only; the Discussion sentence quoted next extends it to Marfan.
PMID:27632686 SUPPORT Human Clinical
"This is in contrast to what has been described for MFS and LDS aortic tissue, where an increase in collagen content and an increase in elastic fiber breaks are typically observed"
The same contrast in the paper's Discussion, naming Marfan as well as Loeys-Dietz. This is the citation for the two-syndrome claim in the description.
⬡

Pathograph

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

Phenotypes

8
Cardiovascular 3
Aortic root aneurysm HP:0002616 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Aortic root aneurysm (HP:0002616), qualified as course progressive. HP:0002616 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:41465473 SUPPORT Human Clinical
"A brother of the proband had an aortic root aneurysm."
Documents aortic root aneurysm in an affected male.
Aortic dissection HP:0002647 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Aortic dissection (HP:0002647). HP:0002647 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34807424 SUPPORT Human Clinical
"Aortic dissections occur typically at young ages and are most often observed in males."
States both the age of dissection and the sex distribution.
Arterial aneurysm and dilatation Vascular dilatation HP:0002617 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is aneurysms throughout the arterial tree, annotated with Vascular dilatation (HP:0002617). HP:0002617 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:38531898 SUPPORT Human Clinical
"This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features."
Establishes involvement beyond the thoracic aorta.
PMID:41465473 SUPPORT Human Clinical
"The index male, initially diagnosed with Ehlers-Danlos syndrome, had joint hypermobility, multiple visceral artery aneurysms, and recurrent musculoskeletal problems."
A concrete instance of extra-aortic aneurysmal disease, in a patient who had been given a different diagnosis.
Eye 1
Hypertelorism HP:0000316 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypertelorism (HP:0000316). HP:0000316 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:27632686 SUPPORT Human Clinical
"Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
Lists hypertelorism among the recurrent findings.
Musculoskeletal 4
Pectus deformity Abnormal sternum morphology HP:0000766 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is pectus deformity, annotated with Abnormal sternum morphology (HP:0000766). HP:0000766 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:27632686 SUPPORT Human Clinical
"Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
Lists pectus deformity among the recurrent findings, without specifying excavatum or carinatum.
Joint hypermobility HP:0001382 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Joint hypermobility (HP:0001382). HP:0001382 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:27632686 SUPPORT Human Clinical
"Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
Lists joint hypermobility among the recurrent findings.
PMID:41465473 SUPPORT Human Clinical
"The index male, initially diagnosed with Ehlers-Danlos syndrome, had joint hypermobility, multiple visceral artery aneurysms, and recurrent musculoskeletal problems."
Documents the hypermobility and, in the same sentence, the misdiagnosis it caused.
Flexion contracture HP:0001371 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is contractures, annotated with Flexion contracture (HP:0001371). HP:0001371 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:27632686 SUPPORT Human Clinical
"Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
Lists contractures among the recurrent findings.
Skeletal dysplasia HP:0002652 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is mild skeletal dysplasia, annotated with Skeletal dysplasia (HP:0002652), qualified as severity mild. HP:0002652 is a phenotype from the Human Phenotype Ontology.
Severity: MILD
Show evidence (1 reference)
PMID:27632686 SUPPORT Human Clinical
"Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
Lists mild skeletal dysplasia among the recurrent findings and grades it.
🧬

Genetic Associations

1
BGN
Gene: BGN hgnc:1044 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is BGN (hgnc:1044). hgnc:1044 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (2 references)
PMID:38531898 SUPPORT INDIRECT Human Clinical
"Interestingly, a male proband with a deletion spanning the coding sequence of BGN and the 5' untranslated region of the downstream gene (ATP2B3) presented with a more severe skeletal phenotype."
The observation behind these notes. Graded INDIRECT because the attribution of the extra severity to ATP2B3 is an inference from one patient, and the authors offer it with "may possibly be explained by".
PMID:38531898 SUPPORT Human Clinical
"In conclusion, distinct mechanisms may underlie the wide phenotypic spectrum of MRLS patients carrying loss-of-function variants in BGN."
The authors' own conclusion that one loss-of-function mechanism does not account for the whole spectrum.
💊

Medical Actions

1
Cardiovascular Surveillance of the Whole Arterial Tree
Action: cardiovascular imaging surveillanceNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is cardiovascular imaging surveillance, annotated with Diagnostic Imaging Testing (NCIT:C16502). NCIT:C16502 is a clinical intervention from the NCI Thesaurus. Ontology label: Diagnostic Imaging Testing NCIT:C16502
Platform: Other
The one management step that is specific to this disease rather than borrowed from Marfan or Loeys-Dietz practice, and the reason molecular diagnosis matters. Two things make it MRLS-specific: the vascular risk is substantially higher than that of the hypermobility syndromes these patients are otherwise labelled with, and the imaging field has to cover the whole arterial tree rather than the aortic root alone, because aneurysms and dissections occur throughout it.
Mechanism Target:
Medial Weakening and Progressive Arterial Dilatation — Surveillance does not modify the mechanism; it detects its consequence in time to intervene. The link is recorded because that is the node surveillance is aimed at.
Show evidence (3 references)
PMID:41465473 SUPPORT Human Clinical
"Early molecular diagnosis is crucial, as it enables targeted cardiovascular surveillance and appropriate counselling for at-risk relatives."
States surveillance as the actionable consequence of diagnosis.
PMID:41465473 SUPPORT Human Clinical
"recognition of MLS, which carries a substantially higher vascular risk and, consequently, different surveillance and management implications"
Gives the reason surveillance differs from that of the hypermobility syndromes these patients are commonly labelled with.
PMID:38531898 SUPPORT Human Clinical
"This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features."
Establishes why the surveillance field must be the whole arterial tree rather than the aortic root alone.
🔬

Diagnosis

1
BGN sequencing in aortopathy and in hypermobility syndromes
The actionable diagnostic point is where to look, not how. A patient with joint hypermobility and a hypermobility-syndrome label may have MRLS, and the consequence of missing it is an unsurveilled aorta in a young male. The 2025 family makes exactly this argument. Interpreting a BGN missense variant requires demonstrating loss of function at RNA, cDNA or protein level before calling it pathogenic.
Show evidence (3 references)
PMID:41465473 SUPPORT Human Clinical
"underscores the importance of considering BGN testing in hypermobility syndromes to enable early surveillance and targeted management"
Makes the case for BGN testing in hypermobility syndromes, and names early surveillance as the reason it matters.
PMID:41465473 SUPPORT Human Clinical
"that this disorder should be considered in the differential diagnosis of joint hypermobility syndromes, particularly when there is any evidence of arterial involvement, even if mild"
Gives the specific trigger for considering the diagnosis: hypermobility plus any arterial involvement, however mild.
PMID:38531898 SUPPORT Human Clinical
"Extensive analysis at RNA, cDNA, and/or protein level is recommended to prove a loss-of-function effect before determining the pathogenicity of identified BGN missense and non-canonical splice variants."
The variant-interpretation recommendation, which is the practical consequence of no missense-only pathogenic allele having been found.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
Eighteen probands (16 male, 2 female) as of 2024, plus 36 further variant-carrying family members identified by segregation analysis. No population estimate exists.
Show evidence (2 references)
PMID:38531898 SUPPORT Human Clinical
"Since the initial publication of five probands in 2017, we have considerably expanded our MRLS cohort to a total of 18 probands (16 males and 2 females)."
Gives the proband count and sex distribution this record is based on.
PMID:38531898 SUPPORT Human Clinical
"Segregation analyses identified 36 additional BGN variant-harboring family members (9 males and 27 females)."
The additional carriers, which are relevant to counselling but are not probands.
🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Meester-Loeys Syndrome:

Marfan syndrome
Overlapping Features Clear clinical overlap. Marfan is autosomal dominant FBN1 disease; MRLS is X-linked. Histology also differs: elastic fibres are preserved in MRLS, where medial degeneration with elastic fibre fragmentation is the Marfan picture. MRLS was found by resequencing a cohort of molecularly unexplained Marfan probands, so the overlap is not theoretical.
Show evidence (2 references)
PMID:34807424 SUPPORT Other
"Clear clinical overlap with Marfan syndrome and Loeys-Dietz syndrome is observed."
States the overlap that makes these the first differentials.
PMID:27632686 SUPPORT Human Clinical
"We performed targeted resequencing of 368 candidate genes in a cohort of 11 molecularly unexplained Marfan probands."
Shows the gene was found among patients carrying a Marfan label, which is the strongest possible statement of how confusable they are.
Loeys-Dietz syndrome
Overlapping Features Shares hypertelorism, skeletal features, early aortic dissection and TGF-beta pathway involvement. Separated by inheritance (autosomal dominant TGFBR1/2, SMAD3, TGFB2/3) and by molecular testing.
Ehlers-Danlos syndromes
Overlapping Features The practically dangerous differential, because it is the one MRLS patients actually receive. Joint hypermobility plus musculoskeletal complaints in a young man reads as hypermobile EDS; the aneurysms are what should redirect the workup. The vascular EDS differential (COL3A1) matters separately because it also gives arterial rupture at young ages.
Show evidence (1 reference)
PMID:41465473 SUPPORT Human Clinical
"The index male, initially diagnosed with Ehlers-Danlos syndrome, had joint hypermobility, multiple visceral artery aneurysms, and recurrent musculoskeletal problems."
A documented instance of the misdiagnosis this differential warns about.
🧫

Experimental Models

1
MRLS patient iPSC line BBANTWi009-A CELL_LINE
An induced pluripotent stem cell line reprogrammed from dermal fibroblasts of a boy with a hemizygous BGN deletion. It is a characterised resource rather than a result: the report establishes normal karyotype, pluripotency markers, trilineage differentiation and retention of the genotype, and does not model any disease mechanism. It is recorded here so the resource is discoverable, and it deliberately carries no `modeled_mechanisms` link, because asserting one would claim more than the paper shows.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:36599284
Show evidence (1 reference)
PMID:36599284 SUPPORT In Vitro
"Here, we report an iPSC line (BBANTWi009-A) of a boy carrying a hemizygous BGN mutation (chrX:153502980-153530518del, GRCh38) causing MRLS."
Establishes the line's existence, its genotype and its disease attribution, which is the whole of what this entry claims for it.
🐁

Animal Models

1
Bgn-deficient BALB/cA mouse
Biglycan-deficient male mice on a BALB/cA background die of aortic rupture. This model predates the human disease and is what made BGN a candidate gene worth resequencing in unexplained thoracic aortic disease.
Species
Mouse
Genotype
Bgn null, hemizygous male
Publication
PMID:27632686
Pathograph links
Medial Weakening and Progressive Arterial Dilatation recapitulates fidelity: moderate observes: organism Fatal aortic rupture in hemizygous males reproduces the severe, male-predominant vascular endpoint of the human disease.
Limitations: The phenotype is strain-dependent (reported on BALB/cA), and the mouse endpoint is rupture rather than the progressive dilatation-then-dissection course that is surveilled in patients. The syndromic features that make this a syndrome rather than an isolated aortopathy, the craniofacial and skeletal findings, are not part of the cited mouse result.
Show evidence (1 reference)
PMID:27632686 SUPPORT Model Organism
"Our results are in line with those of prior reports demonstrating that Bgn-deficient male BALB/cA mice die from aortic rupture."
The mouse result and its strain and sex qualifiers, cited by the human discovery paper as corroboration.
{ }

Source YAML

click to show 
name: Meester-Loeys Syndrome
creation_date: "2026-09-06T19:15:00Z"
category: Mendelian
description: >-
  Meester-Loeys syndrome (MRLS) is an X-linked syndromic aortopathy caused by
  loss-of-function variants in BGN, which encodes biglycan, a small
  leucine-rich proteoglycan of the arterial extracellular matrix. Biglycan
  binds and sequesters latent TGF-beta in the matrix, so losing it releases
  TGF-beta signalling: affected aortic wall shows increased nuclear pSMAD2.

  Two features make it worth separating from the Marfan and Loeys-Dietz
  syndromes it overlaps clinically. First, the histology is unusual for an
  aneurysm syndrome: elastic fibres are *preserved* rather than fragmented,
  which is the opposite of what a Marfan-like reading would predict. Second,
  the disease is not confined to the thoracic aorta. As the cohort grew from
  five probands to eighteen, aneurysms and dissections were found throughout
  the arterial tree, and cardiovascular disease was found coexisting with
  non-specific connective-tissue features such as joint hypermobility, so
  patients can be, and have been, labelled Ehlers-Danlos syndrome first.

  Dissections occur at young ages and males are affected more severely and
  more penetrantly than females. Only loss-of-function alleles are established:
  no pathogenic missense variant without an additional splice effect has been
  reported, and the discoverers recommend proving loss of function at RNA or
  protein level before calling a missense variant pathogenic.
disease_term:
  preferred_term: Meester-Loeys syndrome
  term:
    id: MONDO:0010515
    label: Meester-Loeys syndrome
synonyms:
- MRLS
- BGN-related thoracic aortic aneurysm and dissection
- X-linked syndromic thoracic aortic aneurysm
parents:
- Heritable Thoracic Aortic Disease
references:
- reference: PMID:27632686
  title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
  findings: []
- reference: PMID:38531898
  title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
  findings: []
- reference: PMID:34807424
  title: "Meester-Loeys Syndrome."
  findings: []
- reference: PMID:41465473
  title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
  findings: []
inheritance:
- name: X-Linked
  description: >-
    X-linked. Males are affected more severely and more penetrantly; female
    carriers range from unaffected to minor manifestations, and two of the
    eighteen reported probands are female.
  inheritance_term:
    preferred_term: X-linked inheritance
    term:
      id: HP:0001417
      label: X-linked inheritance
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In conclusion, BGN gene defects in humans cause an X-linked syndromic form of severe TAAD that is associated with preservation of elastic fibers and increased TGF-β signaling."
    explanation: >-
      States the inheritance mode, and in the same sentence the two mechanistic
      claims this entry turns on.
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, the clinical presentation is more severe and penetrant in males compared to females."
    explanation: >-
      The sex difference this block records, from the larger cohort.
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Female carriers had no or only minor manifestations."
    explanation: >-
      Independent confirmation of the carrier picture in a three-generation
      family.
pathophysiology:
- name: Loss-of-Function BGN Variants
  biological_scale: MOLECULAR
  description: >-
    Reported disease alleles are loss-of-function: truncating, splice-affecting
    or whole-gene deletions. Notably, no pathogenic missense variant *without*
    an additional predicted or demonstrated splice effect has been found across
    18 probands, which is why the reporting group recommends proving loss of
    function at cDNA or protein level before calling a BGN missense variant
    pathogenic.
  genetic_context:
    gene:
      preferred_term: BGN
      term:
        id: hgnc:1044
        label: BGN
    functional_impact_category: LOSS_OF_FUNCTION
  evidence:
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The identified BGN variants were shown to lead to loss-of-function by cDNA and Western Blot analyses of skin fibroblasts or were strongly predicted to lead to loss-of-function based on the nature of the variant."
    explanation: >-
      Establishes loss of function as the mechanism, and how it was
      demonstrated rather than assumed.
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No (likely) pathogenic missense variants without additional (predicted) splice effects were identified."
    explanation: >-
      The negative result behind this node's claim about missense alleles, and
      the reason the variant-interpretation caveat is in the description.
  downstream:
  - target: Loss of Biglycan from the Arterial Extracellular Matrix
    description: >-
      Loss-of-function alleles remove the proteoglycan from the matrix.
- name: Loss of Biglycan from the Arterial Extracellular Matrix
  biological_scale: TISSUE
  description: >-
    Biglycan is a small leucine-rich proteoglycan of the arterial media. Its
    loss changes the matrix without destroying its elastic architecture: the
    elastic fibres are preserved. That distinguishes Meester-Loeys histology
    from the elastic-fibre fragmentation of classical medial degeneration and
    is a point where the disease diverges from its clinical mimics.
  cell_types:
  - preferred_term: Vascular smooth muscle cell
    term:
      id: CL:0000359
      label: vascular associated smooth muscle cell
  biological_processes:
  - preferred_term: extracellular matrix organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found five individuals with loss-of-function mutations in BGN encoding the small leucine-rich proteoglycan biglycan."
    explanation: >-
      Identifies biglycan as the lost matrix component.
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In conclusion, BGN gene defects in humans cause an X-linked syndromic form of severe TAAD that is associated with preservation of elastic fibers and increased TGF-β signaling."
    explanation: >-
      The preservation of elastic fibres, which is what makes this node's
      claim about the matrix specific rather than generic.
  downstream:
  - target: Increased TGF-beta Signaling in the Aortic Wall
    description: >-
      Biglycan sequesters latent TGF-beta in the matrix; without it, signalling
      is released.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Increased TGF-beta Signaling in the Aortic Wall
  biological_scale: TISSUE
  description: >-
    Fluorescent staining of the aortic wall shows increased nuclear pSMAD2, the
    canonical readout of active TGF-beta signalling. This is the mechanistic
    link to the wider heritable-aortopathy literature, where TGF-beta
    dysregulation is the recurring theme. It is also the least settled part of
    the model: how loss of biglycan produces it is described by the discoverers
    themselves as largely unresolved, and a 2025 family found the aortic-wall
    signal without a matching change in patient dermal fibroblasts.
  biological_processes:
  - preferred_term: transforming growth factor beta receptor signaling pathway
    term:
      id: GO:0007179
      label: transforming growth factor beta receptor signaling pathway
    modifier: INCREASED
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fluorescent staining revealed an increase in TGF-β signaling, evidenced by an increase in nuclear pSMAD2 in the aortic wall."
    explanation: >-
      The direct measurement, in the affected tissue, that this node asserts.
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Studies of the aortic wall were consistent with a dysregulation of the TGF-β/SMAD pathway"
    explanation: >-
      Independent replication of the aortic-wall finding in a second family,
      nine years later.
  - reference: PMID:34807424
    reference_title: "Meester-Loeys Syndrome."
    supports: SUPPORT
    evidence_source: OTHER
    directness: INDIRECT
    snippet: "Although functional consequences of these mutations remain largely elusive, increased TGF-β signaling has been observed."
    explanation: >-
      The reviewers' own assessment of how well this step is understood, quoted
      because it is the honest calibration for this node: the observation is
      solid, the causal path to it is not.
  downstream:
  - target: Medial Weakening and Progressive Arterial Dilatation
    description: >-
      Sustained TGF-beta signalling accompanies the wall remodelling that
      permits dilatation, but the earlier wording put it in the wrong layer:
      the increase in the media was slight, and significantly more pronounced
      in the adventitia, which is the major site of biglycan deposition.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:27632686
      reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "we observed a slight increase in TGF-β signaling in the media; however, this increase was significantly more pronounced in the adventitia (Supplementary Figure S2 online)."
      explanation: >-
        The measurement behind the corrected wording: slight in the media,
        significantly more pronounced in the adventitia.
    - reference: PMID:27632686
      reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "lack of biglycan increases TGF-β signaling, especially in the adventitia, the major site of biglycan deposition in the aortic wall."
      explanation: >-
        The authors' own interpretation, tying the adventitial predominance to
        where biglycan actually sits in the wall.
- name: Medial Weakening and Progressive Arterial Dilatation
  biological_scale: ORGANISM
  description: >-
    The clinical endpoint, and it is not confined to the thoracic aorta. The
    expanded cohort found aneurysms and dissections across the arterial tree,
    and one family presented with multiple visceral artery aneurysms in a
    proband initially diagnosed as Ehlers-Danlos syndrome. Dissection occurs at
    young ages.
  evidence:
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features."
    explanation: >-
      The finding that widens this node beyond the thoracic aorta, and the
      diagnostic trap it creates.
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical phenotype is characterized by early-onset aortic aneurysm and dissection."
    explanation: >-
      Establishes the early onset of the cardiovascular endpoint.
  downstream:
  - target: Aortic root aneurysm
  - target: Aortic dissection
  - target: Arterial aneurysm and dilatation
phenotypes:
- category: Cardiovascular
  name: Aortic root aneurysm
  description: >-
    Aortic root dilatation, the presenting cardiovascular lesion.
  phenotype_term:
    preferred_term: Aortic root aneurysm
    term:
      id: HP:0002616
      label: Aortic root aneurysm
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A brother of the proband had an aortic root aneurysm."
    explanation: >-
      Documents aortic root aneurysm in an affected male.
- category: Cardiovascular
  name: Aortic dissection
  description: >-
    Dissection at young ages, most often in males. This is the event the
    disease is diagnosed and surveilled to prevent.
  phenotype_term:
    preferred_term: Aortic dissection
    term:
      id: HP:0002647
      label: Aortic dissection
  evidence:
  - reference: PMID:34807424
    reference_title: "Meester-Loeys Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Aortic dissections occur typically at young ages and are most often observed in males."
    explanation: >-
      States both the age of dissection and the sex distribution.
- category: Cardiovascular
  name: Arterial aneurysm and dilatation
  description: >-
    Aneurysmal disease beyond the aortic root, including visceral arteries.
    Bound to the general vascular dilatation term because HPO has no term for
    the tree-wide arterial involvement the expanded cohort describes, and the
    aortic terms would contradict evidence that is explicitly about vessels
    beyond the aorta; the specific visceral-artery finding is quoted in the
    evidence.
  phenotype_term:
    preferred_term: aneurysms throughout the arterial tree
    term:
      id: HP:0002617
      label: Vascular dilatation
  evidence:
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features."
    explanation: >-
      Establishes involvement beyond the thoracic aorta.
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The index male, initially diagnosed with Ehlers-Danlos syndrome, had joint hypermobility, multiple visceral artery aneurysms, and recurrent musculoskeletal problems."
    explanation: >-
      A concrete instance of extra-aortic aneurysmal disease, in a patient who
      had been given a different diagnosis.
- category: Craniofacial
  name: Hypertelorism
  phenotype_term:
    preferred_term: Hypertelorism
    term:
      id: HP:0000316
      label: Hypertelorism
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
    explanation: >-
      Lists hypertelorism among the recurrent findings.
- category: Skeletal
  name: Pectus deformity
  description: >-
    Pectus deformity. Bound to the parent sternum-morphology term because the
    source says only "pectus deformity" without specifying direction, so
    binding either carinatum or excavatum would assert a direction nothing
    supports; `preferred_term` records what the source actually says.
  phenotype_term:
    preferred_term: pectus deformity
    term:
      id: HP:0000766
      label: Abnormal sternum morphology
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
    explanation: >-
      Lists pectus deformity among the recurrent findings, without specifying
      excavatum or carinatum.
- category: Skeletal
  name: Joint hypermobility
  description: >-
    Joint hypermobility, which is why one proband was initially diagnosed with
    Ehlers-Danlos syndrome. Its practical importance is diagnostic rather than
    clinical: it is the feature that routes patients away from aortic
    surveillance.
  phenotype_term:
    preferred_term: Joint hypermobility
    term:
      id: HP:0001382
      label: Joint hypermobility
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
    explanation: >-
      Lists joint hypermobility among the recurrent findings.
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The index male, initially diagnosed with Ehlers-Danlos syndrome, had joint hypermobility, multiple visceral artery aneurysms, and recurrent musculoskeletal problems."
    explanation: >-
      Documents the hypermobility and, in the same sentence, the misdiagnosis
      it caused.
- category: Skeletal
  name: Flexion contracture
  phenotype_term:
    preferred_term: contractures
    term:
      id: HP:0001371
      label: Flexion contracture
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
    explanation: >-
      Lists contractures among the recurrent findings.
- category: Skeletal
  name: Skeletal dysplasia
  phenotype_term:
    preferred_term: mild skeletal dysplasia
    term:
      id: HP:0002652
      label: Skeletal dysplasia
    severity: MILD
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia."
    explanation: >-
      Lists mild skeletal dysplasia among the recurrent findings and grades it.
genetic:
- name: BGN
  gene_term:
    preferred_term: BGN
    term:
      id: hgnc:1044
      label: BGN
  relationship_type: CAUSATIVE
  notes: >-
    One reported male carries a deletion spanning the BGN coding sequence and
    the 5' untranslated region of the downstream gene ATP2B3, and has a more
    severe skeletal phenotype. The proposed explanation is that the remnant BGN
    promoter drives ectopic expression of ATP2B3, which is normally repressed
    in skin fibroblasts. This is a contiguous-gene effect proposed as a
    possibility, not demonstrated, and it is the reason the discoverers write
    that distinct mechanisms may underlie the phenotypic spectrum.
  evidence:
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: "Interestingly, a male proband with a deletion spanning the coding sequence of BGN and the 5' untranslated region of the downstream gene (ATP2B3) presented with a more severe skeletal phenotype."
    explanation: >-
      The observation behind these notes. Graded INDIRECT because the
      attribution of the extra severity to ATP2B3 is an inference from one
      patient, and the authors offer it with "may possibly be explained by".
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In conclusion, distinct mechanisms may underlie the wide phenotypic spectrum of MRLS patients carrying loss-of-function variants in BGN."
    explanation: >-
      The authors' own conclusion that one loss-of-function mechanism does not
      account for the whole spectrum.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Eighteen probands (16 male, 2 female) as of 2024, plus 36 further
    variant-carrying family members identified by segregation analysis. No
    population estimate exists.
  evidence:
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since the initial publication of five probands in 2017, we have considerably expanded our MRLS cohort to a total of 18 probands (16 males and 2 females)."
    explanation: >-
      Gives the proband count and sex distribution this record is based on.
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Segregation analyses identified 36 additional BGN variant-harboring family members (9 males and 27 females)."
    explanation: >-
      The additional carriers, which are relevant to counselling but are not
      probands.
treatments:
- name: Cardiovascular Surveillance of the Whole Arterial Tree
  description: >-
    The one management step that is specific to this disease rather than
    borrowed from Marfan or Loeys-Dietz practice, and the reason molecular
    diagnosis matters. Two things make it MRLS-specific: the vascular risk is
    substantially higher than that of the hypermobility syndromes these
    patients are otherwise labelled with, and the imaging field has to cover
    the whole arterial tree rather than the aortic root alone, because
    aneurysms and dissections occur throughout it.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: cardiovascular imaging surveillance
    term:
      id: NCIT:C16502
      label: Diagnostic Imaging Testing
  target_mechanisms:
  - target: Medial Weakening and Progressive Arterial Dilatation
    description: >-
      Surveillance does not modify the mechanism; it detects its consequence in
      time to intervene. The link is recorded because that is the node
      surveillance is aimed at.
  evidence:
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Early molecular diagnosis is crucial, as it enables targeted cardiovascular surveillance and appropriate counselling for at-risk relatives."
    explanation: >-
      States surveillance as the actionable consequence of diagnosis.
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "recognition of MLS, which carries a substantially higher vascular risk and, consequently, different surveillance and management implications"
    explanation: >-
      Gives the reason surveillance differs from that of the hypermobility
      syndromes these patients are commonly labelled with.
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features."
    explanation: >-
      Establishes why the surveillance field must be the whole arterial tree
      rather than the aortic root alone.
animal_models:
- name: Bgn-deficient BALB/cA mouse
  species: Mouse
  genotype: Bgn null, hemizygous male
  publication: PMID:27632686
  description: >-
    Biglycan-deficient male mice on a BALB/cA background die of aortic rupture.
    This model predates the human disease and is what made BGN a candidate gene
    worth resequencing in unexplained thoracic aortic disease.
  modeled_mechanisms:
  - target: Medial Weakening and Progressive Arterial Dilatation
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Fatal aortic rupture in hemizygous males reproduces the severe,
      male-predominant vascular endpoint of the human disease.
    limitations: >-
      The phenotype is strain-dependent (reported on BALB/cA), and the mouse
      endpoint is rupture rather than the progressive dilatation-then-dissection
      course that is surveilled in patients. The syndromic features that make
      this a syndrome rather than an isolated aortopathy, the craniofacial and
      skeletal findings, are not part of the cited mouse result.
    evidence:
    - reference: PMID:27632686
      reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Our results are in line with those of prior reports demonstrating that Bgn-deficient male BALB/cA mice die from aortic rupture."
      explanation: >-
        The mouse result and its strain and sex qualifiers, cited by the human
        discovery paper as corroboration.
experimental_models:
- name: MRLS patient iPSC line BBANTWi009-A
  experimental_model_type: CELL_LINE
  description: >-
    An induced pluripotent stem cell line reprogrammed from dermal fibroblasts
    of a boy with a hemizygous BGN deletion. It is a characterised resource
    rather than a result: the report establishes normal karyotype, pluripotency
    markers, trilineage differentiation and retention of the genotype, and does
    not model any disease mechanism. It is recorded here so the resource is
    discoverable, and it deliberately carries no `modeled_mechanisms` link,
    because asserting one would claim more than the paper shows.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:36599284
  evidence:
  - reference: PMID:36599284
    reference_title: "Generation of an induced pluripotent stem cell (iPSC) line (BBANTWi009-A) from a Meester-Loeys syndrome patient carrying a BGN mutation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here, we report an iPSC line (BBANTWi009-A) of a boy carrying a hemizygous BGN mutation (chrX:153502980-153530518del, GRCh38) causing MRLS."
    explanation: >-
      Establishes the line's existence, its genotype and its disease
      attribution, which is the whole of what this entry claims for it.
histopathology:
- name: Preserved elastic fibres with low to normal collagen content
  description: >-
    The finding that separates this disease from the classic TGF-beta
    vasculopathies it resembles clinically. The paper draws the contrast with
    both Marfan and Loeys-Dietz, where collagen content increases and elastic
    fibres break; in the MRLS probands the elastin was normal and collagen was
    low to normal. Of the evidence below, the first item is the staining
    description itself; the two that follow it are the paper's Results and
    Discussion statements of the contrast, the Results naming Loeys-Dietz only
    and the Discussion naming both syndromes.
    A mechanism routed only through TGF-beta would predict the opposite, so
    this is the histological constraint any account of the disease has to
    satisfy.
  finding_term:
    preferred_term: preserved elastic fibres with low to normal collagen content in the aortic wall
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The staining revealed low to normal collagen content; elastin fibers appeared normal"
    explanation: >-
      The direct histological description of the probands' aortic wall.
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is in contrast to what is observed in LDS individuals, in whom an increase in collagen production and fragmentation of elastic fibers are typically present"
    explanation: >-
      The comparator the finding is meaningful against, in the paper's own
      words, in its Results section. This sentence names Loeys-Dietz only;
      the Discussion sentence quoted next extends it to Marfan.
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is in contrast to what has been described for MFS and LDS aortic tissue, where an increase in collagen content and an increase in elastic fiber breaks are typically observed"
    explanation: >-
      The same contrast in the paper's Discussion, naming Marfan as well
      as Loeys-Dietz. This is the citation for the two-syndrome claim in
      the description.

diagnosis:
- name: BGN sequencing in aortopathy and in hypermobility syndromes
  description: >-
    The actionable diagnostic point is where to look, not how. A patient with
    joint hypermobility and a hypermobility-syndrome label may have MRLS, and
    the consequence of missing it is an unsurveilled aorta in a young male. The
    2025 family makes exactly this argument. Interpreting a BGN missense
    variant requires demonstrating loss of function at RNA, cDNA or protein
    level before calling it pathogenic.
  evidence:
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "underscores the importance of considering BGN testing in hypermobility syndromes to enable early surveillance and targeted management"
    explanation: >-
      Makes the case for BGN testing in hypermobility syndromes, and names
      early surveillance as the reason it matters.
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "that this disorder should be considered in the differential diagnosis of joint hypermobility syndromes, particularly when there is any evidence of arterial involvement, even if mild"
    explanation: >-
      Gives the specific trigger for considering the diagnosis: hypermobility
      plus any arterial involvement, however mild.
  - reference: PMID:38531898
    reference_title: "Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Extensive analysis at RNA, cDNA, and/or protein level is recommended to prove a loss-of-function effect before determining the pathogenicity of identified BGN missense and non-canonical splice variants."
    explanation: >-
      The variant-interpretation recommendation, which is the practical
      consequence of no missense-only pathogenic allele having been found.
differential_diagnoses:
- name: Marfan syndrome
  description: >-
    Clear clinical overlap. Marfan is autosomal dominant FBN1 disease; MRLS is
    X-linked. Histology also differs: elastic fibres are preserved in MRLS,
    where medial degeneration with elastic fibre fragmentation is the Marfan
    picture. MRLS was found by resequencing a cohort of molecularly unexplained
    Marfan probands, so the overlap is not theoretical.
  evidence:
  - reference: PMID:34807424
    reference_title: "Meester-Loeys Syndrome."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Clear clinical overlap with Marfan syndrome and Loeys-Dietz syndrome is observed."
    explanation: >-
      States the overlap that makes these the first differentials.
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We performed targeted resequencing of 368 candidate genes in a cohort of 11 molecularly unexplained Marfan probands."
    explanation: >-
      Shows the gene was found among patients carrying a Marfan label, which is
      the strongest possible statement of how confusable they are.
- name: Loeys-Dietz syndrome
  description: >-
    Shares hypertelorism, skeletal features, early aortic dissection and
    TGF-beta pathway involvement. Separated by inheritance (autosomal dominant
    TGFBR1/2, SMAD3, TGFB2/3) and by molecular testing.
- name: Ehlers-Danlos syndromes
  description: >-
    The practically dangerous differential, because it is the one MRLS patients
    actually receive. Joint hypermobility plus musculoskeletal complaints in a
    young man reads as hypermobile EDS; the aneurysms are what should redirect
    the workup. The vascular EDS differential (COL3A1) matters separately
    because it also gives arterial rupture at young ages.
  evidence:
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The index male, initially diagnosed with Ehlers-Danlos syndrome, had joint hypermobility, multiple visceral artery aneurysms, and recurrent musculoskeletal problems."
    explanation: >-
      A documented instance of the misdiagnosis this differential warns about.
- name: FLNA-related periventricular nodular heterotopia with Ehlers-Danlos features
  description: >-
    The other X-linked cause of thoracic aortic disease, and the only one known
    before BGN. Distinguished by the periventricular nodular heterotopia on
    neuroimaging.
  evidence:
  - reference: PMID:27632686
    reference_title: "Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "So far, the only known X-linked gene is FLNA, which is associated with the periventricular nodular heterotopia type of Ehlers-Danlos syndrome."
    explanation: >-
      Names the alternative X-linked cause and its distinguishing feature.
discussions:
- discussion_id: mrls_tgfbeta_tissue_discordance
  kind: CONTROVERSY
  attaches_to:
  - pathophysiology#Increased TGF-beta Signaling in the Aortic Wall
  prompt: >-
    Is TGF-beta dysregulation in MRLS a property of the aortic wall
    specifically, and can patient dermal fibroblasts report it at all?
  rationale: >-
    The aortic-wall finding is replicated: increased nuclear pSMAD2 in 2017,
    TGF-beta/SMAD dysregulation in a second family in 2025. But in that same
    2025 study, reporter assays in cell lines expressing mutant biglycan showed
    *reduced* canonical Wnt and TGF-beta activity, and the patients' own dermal
    fibroblasts showed no consistent difference in nuclear beta-catenin or
    p-SMAD2/3 against controls. Three results, three directions. The most
    economical reading is that the signalling change is tissue-specific to the
    arterial media and that dermal fibroblasts are simply the wrong cell, which
    would matter because fibroblasts are the accessible tissue and the one the
    iPSC line is derived from. The alternative, that the increase is a
    downstream consequence of wall injury rather than a driver, is not
    excluded. The pathophysiology node states the observation and the review's
    own verdict that the functional consequences remain largely elusive, rather
    than asserting a mechanism.
  evidence:
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "However, patients' dermal fibroblasts did not show consistent differences in the nuclear abundance of β-catenin or p-SMAD2/3 compared to cells from controls."
    explanation: >-
      Refutes the expectation that the aortic-wall signalling change is
      detectable in patient fibroblasts, which is the discordance this
      discussion is about.
  - reference: PMID:41465473
    reference_title: "A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: INDIRECT
    snippet: "assays with reporter vectors revealed reduced canonical Wnt and TGF-β activity in cell lines expressing mutant biglycan"
    explanation: >-
      The reporter result, whose direction is opposite to the aortic-wall
      finding. Graded INDIRECT because it is an overexpression reporter assay in
      a heterologous cell line rather than a measurement in affected tissue.
- discussion_id: mrls_no_missense_only_alleles
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Loss-of-Function BGN Variants
  - genetic#BGN
  prompt: >-
    Is the absence of missense-only pathogenic BGN alleles a real constraint on
    the mechanism, or ascertainment?
  rationale: >-
    Across 18 probands, every pathogenic variant is truncating, splice-affecting
    or a deletion; not one is a missense change without an additional splice
    effect. If real, that says the disease requires absence of the protein
    rather than an altered one, and rules out a dominant-negative or
    gain-of-function contribution. But the group that reports it also
    recommends proving loss of function before calling a missense variant
    pathogenic, which is a filter that would systematically exclude any
    missense-only allele acting by another route. The 2025 family carries a
    "novel missense variant" in its title, which sharpens rather than settles
    the question. The entry records the observation without asserting the
    constraint.
notes: >-
  On the deep-research report. The entry was drafted from primary literature
  retrieved via PubMed, because the openscientist run had not returned; the
  report arrived before the pull request was opened and was reconciled into the
  entry, which is where the `treatments:` entry came from.

  `just preflight-dr` returned WARN: ATP2B3 is mentioned 11 times against 32
  for BGN. That is not a second disease leaking in, it is the contiguous-gene
  hypothesis for the one deletion patient, which this entry carries in the
  `genetic:` notes with `directness: INDIRECT`. The warning is a true positive
  about the report's content and a false alarm about entity confusion.

  The report's own Term Validation section flagged `UBERON:0035904`, which the
  report calls "ascending aorta" and UBERON calls *primary visual area, layer
  4*. No UBERON term is bound in this entry, so nothing was affected, but it is
  worth recording that the report proposed an anatomy term for the wrong
  anatomy. Two further flags in that section are false alarms from its own
  parsing rather than errors: it reports `HP:0000316` and `HP:0001371` as
  "named as a different term", where the report's name for each is a fragment
  of a quoted sentence rather than a proposed label. Both are bound correctly
  here.

  On where the reference metadata came from. The PubMed record for
  PMID:41465473 loses its italicised gene symbols when read through a metadata
  API: the title comes back as "in theGene" and the abstract as
  "consideringtesting". `just fetch-reference` produces a cache file with both
  intact, and the reference validator checks `reference_title` against that
  cache, so it catches the difference. Every title and snippet here is taken
  from the cache rather than from an API response.

  On what `treatments:` does and does not contain. It holds one entry,
  cardiovascular surveillance, because that is the only management step the
  MRLS literature states about MRLS. Beta blockade, losartan and prophylactic
  root replacement are the standard of care a patient will actually receive,
  and the deep-research report for this entry opens its treatment section by
  saying so explicitly: no MRLS-specific approved therapy or trial exists and
  management is extrapolated from heritable-TAAD, Marfan and Loeys-Dietz
  guidelines. Curating those here would attach disease-specific claims to
  citations that do not mention this disease, so they are deliberately absent.
  This is a real gap, not a tidy omission: a heritable-aortopathy guideline
  source should be found and the extrapolated management curated against it
  with `directness: INDIRECT`.

  Not curated, and why. No `datasets:`, `clinical_trials:` or `environmental:`.
  `directness` is set on four items only, where it was actually assessed.

  On the review's under-consumption finding, and what is still not curated.
  The histological finding is now a `histopathology:` section, and the
  TGF-beta edge has been corrected to the layer the measurement actually
  supports. Three things the review asked for are still absent, deliberately
  rather than by oversight.

  The cutaneous and neurological systems are named as affected by
  PMID:34807424, and the full text of PMID:27632686 lists brain aneurysms,
  striae, bifid uvula, cervical spine instability and a detailed skeletal
  dysplasia. Each is curatable and each needs its own phenotype with its own
  quote; adding a dozen phenotypes inside a review round is how a round stops
  being reviewable. They are the obvious next change to this entry.

  The collagen-fibrillogenesis arm of the mechanism is likewise absent. The
  paper's statement about fibril diameter and lateral association is a
  hypothesis in its discussion rather than a measurement, and the decorin
  substitution that would explain the preserved elastic fibres is explicitly
  speculative there. Adding it as a pathophysiology node would put a
  hypothesis on the same footing as the measured TGF-beta finding. It belongs
  as a node with a `PROVISIONAL` marker or as a discussion, and that is a
  judgement worth making deliberately rather than in passing.

  On the histopathology `finding_term` being unbound. MPATH and PATO were
  searched for a term covering preserved elastic fibres with low to normal
  collagen content and neither carries one; the finding is a conjunction of a
  normal result and a low-normal result, which is not the shape of a
  pathological-finding term. It is recorded as free text rather than bound to
  something approximate. Noted so the search is not repeated.

  A pattern worth recording for whoever edits this entry next. Twice in review,
  a `description` was found still arguing for a binding that had already been
  replaced: the aneurysm term and the pectus term. Rebinding a term means
  editing the sentence that justified the old one, and nothing in the
  toolchain checks that, because prose is not validated. Grep the phenotype's
  own description for the old term's name before considering a rebinding done.

  On accepting a review correction without checking it. Round 2 narrowed the
  histopathology contrast from "Loeys-Dietz and Marfan" to Loeys-Dietz alone,
  on the strength of a Results-section sentence that names only Loeys-Dietz.
  The Discussion of the same paper says "This is in contrast to what has been
  described for MFS and LDS aortic tissue", so the original two-syndrome
  phrasing was right and the narrowing made the entry say something its source
  contradicts. Restored, with both sentences now cited so the claim rests on
  the paper rather than on anyone's reading of it. The lesson is the one this
  entry keeps relearning: a claim about what a source says has to be checked
  against the whole source, and that applies to a reviewer's claim as much as
  to a curator's.
📚

References & Deep Research

References

4
PMID:27632686
Loss-of-function mutations in the X-linked biglycan gene cause a severe syndromic form of thoracic aortic aneurysms and dissections.
No top-level findings curated for this source.
PMID:38531898
Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome.
No top-level findings curated for this source.
PMID:34807424
Meester-Loeys Syndrome.
No top-level findings curated for this source.
PMID:41465473
A Family with Meester-Loeys Syndrome Caused by a Novel Missense Variant in the BGN Gene.
No top-level findings curated for this source.

Deep Research

1

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.

Evaluations and curation notes (2)

Record notes

On the deep-research report. The entry was drafted from primary literature retrieved via PubMed, because the openscientist run had not returned; the report arrived before the pull request was opened and was reconciled into the entry, which is where the `treatments:` entry came from. `just preflight-dr` returned WARN: ATP2B3 is mentioned 11 times against 32 for BGN. That is not a second disease leaking in, it is the contiguous-gene hypothesis for the one deletion patient, which this entry carries in the `genetic:` notes with `directness: INDIRECT`. The warning is a true positive about the report's content and a false alarm about entity confusion. The report's own Term Validation section flagged `UBERON:0035904`, which the report calls "ascending aorta" and UBERON calls *primary visual area, layer 4*. No UBERON term is bound in this entry, so nothing was affected, but it is worth recording that the report proposed an anatomy term for the wrong anatomy. Two further flags in that section are false alarms from its own parsing rather than errors: it reports `HP:0000316` and `HP:0001371` as "named as a different term", where the report's name for each is a fragment of a quoted sentence rather than a proposed label. Both are bound correctly here. On where the reference metadata came from. The PubMed record for PMID:41465473 loses its italicised gene symbols when read through a metadata API: the title comes back as "in theGene" and the abstract as "consideringtesting". `just fetch-reference` produces a cache file with both intact, and the reference validator checks `reference_title` against that cache, so it catches the difference. Every title and snippet here is taken from the cache rather than from an API response. On what `treatments:` does and does not contain. It holds one entry, cardiovascular surveillance, because that is the only management step the MRLS literature states about MRLS. Beta blockade, losartan and prophylactic root replacement are the standard of care a patient will actually receive, and the deep-research report for this entry opens its treatment section by saying so explicitly: no MRLS-specific approved therapy or trial exists and management is extrapolated from heritable-TAAD, Marfan and Loeys-Dietz guidelines. Curating those here would attach disease-specific claims to citations that do not mention this disease, so they are deliberately absent. This is a real gap, not a tidy omission: a heritable-aortopathy guideline source should be found and the extrapolated management curated against it with `directness: INDIRECT`. Not curated, and why. No `datasets:`, `clinical_trials:` or `environmental:`. `directness` is set on four items only, where it was actually assessed. On the review's under-consumption finding, and what is still not curated. The histological finding is now a `histopathology:` section, and the TGF-beta edge has been corrected to the layer the measurement actually supports. Three things the review asked for are still absent, deliberately rather than by oversight. The cutaneous and neurological systems are named as affected by PMID:34807424, and the full text of PMID:27632686 lists brain aneurysms, striae, bifid uvula, cervical spine instability and a detailed skeletal dysplasia. Each is curatable and each needs its own phenotype with its own quote; adding a dozen phenotypes inside a review round is how a round stops being reviewable. They are the obvious next change to this entry. The collagen-fibrillogenesis arm of the mechanism is likewise absent. The paper's statement about fibril diameter and lateral association is a hypothesis in its discussion rather than a measurement, and the decorin substitution that would explain the preserved elastic fibres is explicitly speculative there. Adding it as a pathophysiology node would put a hypothesis on the same footing as the measured TGF-beta finding. It belongs as a node with a `PROVISIONAL` marker or as a discussion, and that is a judgement worth making deliberately rather than in passing. On the histopathology `finding_term` being unbound. MPATH and PATO were searched for a term covering preserved elastic fibres with low to normal collagen content and neither carries one; the finding is a conjunction of a normal result and a low-normal result, which is not the shape of a pathological-finding term. It is recorded as free text rather than bound to something approximate. Noted so the search is not repeated. A pattern worth recording for whoever edits this entry next. Twice in review, a `description` was found still arguing for a binding that had already been replaced: the aneurysm term and the pectus term. Rebinding a term means editing the sentence that justified the old one, and nothing in the toolchain checks that, because prose is not validated. Grep the phenotype's own description for the old term's name before considering a rebinding done. On accepting a review correction without checking it. Round 2 narrowed the histopathology contrast from "Loeys-Dietz and Marfan" to Loeys-Dietz alone, on the strength of a Results-section sentence that names only Loeys-Dietz. The Discussion of the same paper says "This is in contrast to what has been described for MFS and LDS aortic tissue", so the original two-syndrome phrasing was right and the narrowing made the entry say something its source contradicts. Restored, with both sentences now cited so the claim rests on the paper rather than on anyone's reading of it. The lesson is the one this entry keeps relearning: a claim about what a source says has to be checked against the whole source, and that applies to a reviewer's claim as much as to a curator's.

Create: Meester-Loeys Syndrome · 2026-09-06T20:03:13Z · View source

De novo curation of Meester-Loeys syndrome (MONDO:0010515, X-linked BGN-related syndromic aortopathy). Drafted from primary literature; the openscientist deep-research report arrived before the PR and was reconciled in, contributing the surveillance treatment entry. Preflight returned WARN on ATP2B3, which is the contiguous-gene hypothesis for one deletion patient rather than entity confusion. Four pathophysiology nodes run from loss-of-function BGN variants through loss of biglycan from the arterial matrix (with elastic fibres preserved, unlike Marfan medial degeneration) and increased aortic-wall TGF-beta signalling to tree-wide arterial dilatation. A CONTROVERSY discussion records that the aortic-wall TGF-beta finding is replicated but that reporter assays showed the opposite direction and patient dermal fibroblasts showed no difference at all. A second KNOWLEDGE_GAP records that no missense-only pathogenic allele exists across 18 probands and that the group reporting it uses a filter that would exclude one. Reference titles and snippets were taken from the reference cache rather than a metadata API, which is how a title mismatch was caught. Validated: just validate (40/40 snippets verified), validate-terms, check-entity-refs, check-causal-targets, check-enum-values all pass.

OpenScientist ▸
1. Disease Information
openscientist-autonomous 2026-09-06T19:53:55.476362

1. Disease Information

Overview. MRLS is a Mendelian, X-linked syndromic aortopathy/connective-tissue disorder. "Meester-Loeys syndrome is an X-linked form of syndromic thoracic aortic aneurysm, characterized by the involvement of multiple organ systems... the cardiovascular, skeletal, craniofacial, cutaneous and neurological systems are affected. Clear clinical overlap with Marfan syndrome and Loeys-Dietz syndrome is observed. Aortic dissections occur typically at young ages and are most often observed in males" (PMID 34807424).

Key identifiers. - OMIM: 300989 (Meester-Loeys syndrome) - MONDO: MONDO:0010515 - Orphanet: ORPHA:404003 (Meester-Loeys syndrome) - Gene / OMIM gene: BGN — OMIM 301870; HGNC:1044; NCBI Gene 633; Ensembl ENSG00000182492; UniProt P21810 (PGS1/biglycan) - ICD-11: best mapped under LA87 / heritable connective-tissue and thoracic-aorta disorders (no MRLS-specific code); ICD-10: Q87.4 (Marfan-like syndromes) / I71.x (aortic aneurysm/dissection) used pragmatically - MeSH: no dedicated descriptor; indexed under "Aortic Aneurysm, Thoracic" + "Genetic Diseases, X-Linked" + "Proteoglycans"

Synonyms / alternative names. Meester-Loeys syndrome; MRLS; BGN-related thoracic aortic aneurysm and dissection; X-linked syndromic TAAD (biglycan type); "biglycan-related Meester-Loeys syndrome" (PMID 38531898).

Data provenance. Disease-level aggregation from OMIM/Orphanet, built on aggregated individual-patient case series (18 probands + 36 relatives to date; PMID 38531898).

2. Etiology

Primary cause — genetic. MRLS is monogenic, caused by hemizygous (males) or heterozygous (females) loss-of-function variants in BGN. "We found five individuals with loss-of-function mutations in BGN encoding the small leucine-rich proteoglycan biglycan" (PMID 27632686). No infectious or purely environmental cause exists.

Genetic risk factors. - Causal variants: BGN loss-of-function — nonsense, frameshift, canonical splice-site, and whole-/partial-gene deletions. "The identified BGN variants were shown to lead to loss-of-function... No (likely) pathogenic missense variants without additional (predicted) splice effects were identified" (PMID 38531898) — i.e., pure missense variants are essentially not disease-causing; loss of function is the operative mechanism. - Modifier genes / contiguous-gene effects: a deletion extending from BGN into the 5′UTR of the neighboring ATP2B3 gene produced a more severe skeletal phenotype, "possibly explained by expressional activation of the downstream ATPase ATP2B3... driven by the remnant BGN promotor" (PMID 38531898). Genes in the shared ECM/TGF-β aortopathy network (FBN1, TGFBR1/2, SMAD3, TGFB2/3, COL3A1, ACTA2, MYH11) are candidate genetic-background modifiers (inferred).

Environmental / lifestyle risk factors (disease-triggering, not disease-causing). As in all heritable TAAD, hypertension and increased hemodynamic/wall stress promote aneurysm growth and dissection: "The major risk factors for the disease are increased hemodynamic forces, typically owing to poorly controlled hypertension, and heritable genetic variants" (PMID 31066871). Male sex is a strong effect modifier (X-linked dosage; see §9). Isometric/heavy resistance exercise, stimulant use, and pregnancy are conventionally avoided/monitored in TAAD (inferred by extrapolation).

Protective factors. In females, skewed (favorable) X-inactivation biasing expression toward the wild-type BGN allele is the plausible protective modifier explaining milder female phenotypes (inferred). No validated protective germline variant is described. Pharmacological "protection" (β-blockade/ARB) is discussed in §12.

Gene–environment interaction. Genetic ECM/TGF-β vulnerability × mechanical wall stress (blood pressure, exercise, pregnancy) determines dissection timing/severity; the murine model implicates "gender-related response to stress" as an interacting determinant of the male-limited catastrophe (PMID 17502576).

3. Phenotypes

Phenotype types span clinical signs/physical manifestations (cardiovascular, skeletal, craniofacial, cutaneous) and structural imaging abnormalities; onset is typically congenital-to-childhood for morphological features and childhood-to-young-adult for aortic events. Frequencies below are qualitative/approximate (small cohorts, N≈18 probands).

Cardiovascular (core, most severe). - Thoracic aortic aneurysm (aortic root/ascending) — HP:0012727 / aortic root aneurysm HP:0002616. Common, early. Severity severe; progression progressive. - Aortic dissection — HP:0002647. "early-onset aortic aneurysm and dissection" (PMID 27632686); "Aortic dissections occur typically at young ages and are most often observed in males" (PMID 34807424). - Aneurysms/dissections of the wider arterial tree (not confined to thoracic aorta) — "aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree" (PMID 38531898). HP:0004942 (arterial aneurysm), HP:0025019 (arterial dissection). - Arterial tortuosity — HP:0005116 (reported in the Marfan/LDS-overlap spectrum; frequent). - Congenital heart defects / valvular disease — including septal defects and valvular anomalies; HP:0001631 (atrial septal defect), HP:0001629 (ventricular septal defect), HP:0001634 (mitral valve prolapse), HP:0001647 (bicuspid aortic valve). Variable frequency.

Craniofacial. - Hypertelorism — HP:0000316 ("Other recurrent findings include hypertelorism", PMID 27632686). Frequent. - Additional dysmorphism (e.g., broad forehead/macrocephaly, downslanting palpebral fissures, high palate) — variable; HP:0000256 (macrocephaly), HP:0000494 (downslanting palpebral fissures).

Skeletal / connective tissue. - Pectus deformity (excavatum/carinatum) — HP:0000766. Frequent (PMID 27632686). - Joint hypermobility — HP:0001382. Frequent. - Joint contractures — HP:0001371 ("joint hypermobility, contractures", PMID 27632686). - Mild skeletal dysplasia / short stature / scoliosis / arachnodactyly-like features — HP:0002652 (mild skeletal dysplasia spectrum), HP:0002650 (scoliosis), HP:0001166 (arachnodactyly). Variable; a contiguous ATP2B3 deletion caused a more severe skeletal phenotype (PMID 38531898).

Cutaneous. Soft/hyperextensible or translucent skin, striae, easy bruising (connective-tissue fragility) — HP:0000974 (hyperextensible skin), HP:0001075 (atrophic scars/soft skin spectrum). Variable.

Neurological. Reported involvement (e.g., developmental/structural CNS findings in some patients) — the neurological system is listed among affected systems (PMID 34807424); frequency low/variable.

Quality-of-life impact. No MRLS-specific QoL (EQ-5D/SF-36/PROMIS) data exist. By analogy to Marfan/LDS: lifelong cardiovascular-event anxiety, activity restriction (avoidance of contact/heavy resistance sport), chronic musculoskeletal pain from hypermobility/pectus/scoliosis, and surgical burden reduce QoL; sudden aortic death is the dominant life-limiting concern in males.

4. Genetic / Molecular Information

Causal gene. BGN (biglycan), Xq28; HGNC:1044; NCBI Gene 633; OMIM 301870; UniProt P21810. Class I small leucine-rich proteoglycan (SLRP); "Biglycan is a Class I Small Leucine Rich Proteoglycan (SLRP) that is localized on human chromosome Xq28-ter... Biglycan contains two chondroitin sulfate glycosaminoglycan (GAG) chains attached near its NH2 terminus" (PMID 12975603). Paralog/duplication partner: decorin (DCN).

Pathogenic variants. - Type/class: predominantly loss-of-function — nonsense, frameshift indels, canonical splice-site variants, and partial/whole-gene deletions (e.g., chrX:153,502,980–153,530,518del, GRCh38; PMID 36599284). Larger deletions may extend into contiguous genes (ATP2B3). - Functional consequence: loss of function / loss of expression confirmed by cDNA and Western blot of skin fibroblasts (PMID 38531898). Pure missense variants without splice effect are not established as pathogenic (PMID 38531898) — argues against a dominant-negative missense mechanism and for haploinsufficiency/absence of protein. - Classification (ACMG/AMP): reported variants are pathogenic/likely pathogenic; loss-of-function is a recognized mechanism for BGN (PVS1 applicable), supported by segregation. - Allele frequency: private/ultra-rare; absent or vanishingly rare in gnomAD (constraint expected for an X-linked LoF disease gene). Genomic coordinates in GRCh38; ClinVar hosts the reported variants. - Somatic vs germline: germline. De novo and inherited (X-linked segregation) variants both occur (PMID 38531898).

Modifier genes / epigenetics. - ATP2B3 contiguous-gene activation modifies skeletal severity (PMID 38531898). - X-chromosome inactivation (XCI) is the principal epigenetic determinant of female expressivity (skewed XCI → variable phenotype) (inferred). - No disease-specific DNA-methylation/histone signature has been reported.

Chromosomal abnormalities. Structural deletions at Xq28 spanning BGN (± ATP2B3) are detectable by chromosomal microarray / MLPA / read-depth analysis (PMID 38531898; 36599284).

Ontology tags. Gene: HGNC:1044 (BGN). GO molecular function: GO:0005518 (collagen binding), GO:0050431 (transforming growth factor beta binding), GO:0030020 (extracellular matrix structural constituent conferring tensile strength).

5. Environmental Information

  • Environmental toxins/radiation/infection: none causal or contributory established; MRLS is monogenic.
  • Lifestyle / hemodynamic factors: uncontrolled hypertension and high-intensity isometric exercise increase aortic wall stress and dissection risk in heritable TAAD generally ("increased hemodynamic forces, typically owing to poorly controlled hypertension", PMID 31066871). Smoking and stimulant drugs are conventional aggravators of aortic disease (inferred). Pregnancy is a high-risk period for aortic dissection in connective-tissue aortopathies (inferred/extrapolated).
  • Infectious agents: not applicable.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

  1. A germline loss-of-function BGN variant (nonsense/frameshift/splice/deletion) at Xq28 leads to absent or non-functional biglycan protein (loss of function demonstrated by cDNA/Western; PMID 38531898).
  2. Loss of biglycan results in defective collagen fibrillogenesis and ECM assembly — biglycan normally binds type I collagen and organizes fibrils ("able to associate specifically with type I collagen fibrils... inhibit collagen fibrillogenesis", PMID 8038266) — leading to structurally abnormal collagen fibrils and reduced tensile strength of the arterial wall (demonstrated in Bgn-null mouse aortas by TEM/biomechanics; PMID 17502576).
  3. In parallel (branch point), loss of biglycan's role as a matrix reservoir/modulator of TGF-β and BMP ("less BMP-4 binding, which reduced the sensitivity of osteoblasts to BMP-4", PMID 15173106; TGF-β binding, PMID 9731537) results in increased/dysregulated TGF-β signaling, demonstrated in the human aortic wall as increased nuclear pSMAD2 ("an increase in nuclear pSMAD2 in the aortic wall", PMID 27632686). (Whether TGF-β activation is upstream driver or downstream compensatory response is not fully resolved — inferred parallel to Marfan/LDS.)
  4. Increased canonical (SMAD2/3) and non-canonical (ERK-mediated, via AT1 receptor) TGF-β signaling leads to medial degeneration/remodeling of the aortic media (SMC phenotype change, matrix turnover) — the shared final common pathway of heritable aortopathy (PMID 25614286; 26607280).
  5. Mechanically weakened, remodeled arterial media under hemodynamic stress results in aortic root/ascending aneurysm, and, when the intima/media tears, aortic dissection and rupture — occurring across the entire arterial tree (PMID 38531898), preferentially and earlier in males ("gender-related response to stress", PMID 17502576).
  6. Loss of biglycan in bone/skeletal ECM independently leads to reduced osteoblast differentiation and low bone mass/skeletal features (PMID 9731537; 15173106), and in skin/joints to connective-tissue laxity — producing the non-cardiovascular manifestations.
  7. Branch (context-dependent): soluble biglycan is normally a TLR2/TLR4 danger signal (DAMP) engaging CD14 (pro-inflammatory) or CD44 (pro-autophagic) (PMID 30776184; 24480070). Its loss may perturb ECM-immune homeostasis; the net contribution to MRLS vascular inflammation is inferred, not demonstrated.

Detail by category

  • Molecular pathways: TGF-β/SMAD2/3 (KEGG hsa04350; Reactome R-HSA-170834), BMP signaling, angiotensin-II AT1-receptor→ERK (non-canonical). CHEBI: TGF-β is a protein (not CHEBI); losartan CHEBI:6541; angiotensin II CHEBI:2719.
  • Protein dysfunction: loss of function / absent proteoglycan (not aggregation) — UniProt P21810; SLRP leucine-rich-repeat fold (InterPro IPR000372/Pfam LRR).
  • Cellular processes: vascular smooth-muscle-cell phenotype modulation, ECM remodeling, medial degeneration; osteoblast differentiation defect; possible sterile inflammation/autophagy switch (biglycan DAMP).
  • Tissue-damage mechanism: mechanical failure of collagen-poor/disorganized media → intimomedial tear, dissection, hemorrhage (PMID 17502576).
  • Metabolic/biochemical: no primary metabolic defect; the defect is structural-ECM and growth-factor-signaling.
  • Molecular profiling: patient iPSCs (PMID 36599284) and skin-fibroblast cDNA/protein analyses (PMID 38531898) are available; no large MRLS transcriptomic/proteomic/metabolomic datasets published.
  • GO/CL suggestions: GO:0030198 (extracellular matrix organization), GO:0032964 (collagen biosynthetic process/fibril organization GO:0030199), GO:0007179 (TGF-β receptor signaling pathway), GO:0006954 (inflammatory response, branch). Cell types: CL:0000359 (vascular associated smooth muscle cell), CL:0000057 (fibroblast), CL:0000062 (osteoblast).

7. Anatomical Structures Affected

Organ level (primary). Aorta — especially aortic root/ascending aorta (UBERON:0035904 ascending aorta; UBERON:0000947 aorta); entire arterial tree including branch/peripheral arteries (UBERON:0001637 artery) (PMID 38531898). Heart/valves (UBERON:0000948) with congenital defects. Secondary/complication level. End-organ ischemia from dissection (brain, viscera, limbs); hemothorax/hemoperitoneum from rupture (PMID 17502576). Body systems. Cardiovascular (primary); musculoskeletal/skeletal; integumentary (skin); craniofacial; nervous system (variable).

Tissue and cell level. Connective tissue / ECM of the arterial wall (media and adventitia), bone, skin, joints. Key cells: vascular smooth muscle cells (CL:0000359), (myo)fibroblasts (CL:0000057/CL:0000186), osteoblasts/marrow stromal precursors (CL:0000062/CL:0000134). SLRPs including biglycan localize to medial and adventitial arterial layers (PMID 24272803).

Subcellular level. Extracellular matrix / extracellular space (GO:0031012 extracellular matrix; GO:0005615 extracellular space) is the primary compartment; secretory pathway (ER/Golgi glycosylation of GAG chains) is relevant to biosynthesis; nucleus implicated via pSMAD2 nuclear translocation (GO:0005634).

Localization / laterality. Aortic disease is central/axial and typically bilateral-symmetric in the sense of a midline great vessel; peripheral arterial aneurysms may be multifocal. Skeletal/craniofacial features are typically bilateral.

8. Temporal Development

  • Onset. Morphological (craniofacial/skeletal) features are congenital; aortic aneurysm can be detected in childhood, and dissection occurs at young ages, frequently in the first three decades in males ("Aortic dissections occur typically at young ages", PMID 34807424; the mouse model dies within the first 3 months, PMID 17502576).
  • Onset pattern. Aneurysm growth is chronic/insidious; dissection/rupture is an acute, catastrophic event.
  • Progression. Aortic dilatation is progressive; disease course is chronic and lifelong with risk of episodic acute events. Progression rate is variable and sex-dependent (faster/more severe in males; PMID 38531898).
  • Stages (pragmatic). (i) pre-aneurysmal/at-risk carrier → (ii) aortic dilatation/aneurysm → (iii) dissection/rupture (end-stage acute event) → (iv) post-surgical residual disease requiring lifelong surveillance.
  • Remission. No spontaneous remission; treatment-induced stabilization (surgery + medical therapy) is the goal.
  • Critical periods / windows of intervention. Childhood–young adulthood surveillance to intervene before dissection; peri-operative timing at diameter thresholds; pregnancy is a critical high-risk window in females.

9. Inheritance and Population

Epidemiology. Ultra-rare; prevalence unknown, not formally estimated (Orphanet lists no point prevalence). Only 18 probands + 36 variant-harboring relatives were in the largest cohort (PMID 38531898). Incidence unquantified.

Inheritance (genetic). - Pattern: X-linked (Xq28). Hemizygous males fully/severely affected; heterozygous females variably affected. "BGN gene defects in humans cause an X-linked syndromic form of severe TAAD" (PMID 27632686). - Penetrance: high/near-complete in males; reduced in females. "the clinical presentation is more severe and penetrant in males compared to females" (PMID 38531898). - Expressivity: variable, especially in females (modulated by X-inactivation). - Genetic anticipation: not described (not a repeat-expansion disorder). - Germline mosaicism: possible in principle for X-linked LoF disorders (not specifically documented for MRLS). - De novo variants: occur; both inherited and de novo variants reported. - Founder effects / consanguinity: none reported; variants are largely private. - Carrier frequency: not established; expected very low (ultra-rare gene).

Population demographics. - Sex ratio: strong male predominance of clinically significant disease (16/18 probands male; PMID 38531898). - Ethnic/geographic distribution: no enrichment; cases reported across multiple countries/ancestries (international cohort, PMID 38531898). No variant-specific geographic clustering. - Age distribution: young — pediatric to young-adult events predominate.

10. Diagnostics

Genetic testing (definitive). - Approach: molecular confirmation of a pathogenic BGN loss-of-function variant. Recommended via multigene heritable-TAAD/aortopathy NGS panels (including FBN1, TGFBR1/2, SMAD3, TGFB2/3, COL3A1, ACTA2, MYH11, LOX, BGN, etc.), WES/WGS, or single-gene BGN sequencing + deletion/duplication analysis (MLPA/CMA for the structural deletions). "Extensive analysis at RNA, cDNA, and/or protein level is recommended" to prove loss of function and resolve splice effects (PMID 38531898). - CMA / MLPA / read-depth: needed to detect partial/whole-gene BGN deletions (± ATP2B3) (PMID 38531898; 36599284). - RNA/cDNA studies & Western blot of skin fibroblasts: functionally confirm splice/LoF impact and absence of protein (PMID 38531898). - Karyotype/FISH/mtDNA/repeat-expansion testing: not indicated (not applicable).

Clinical / imaging tests. - Echocardiography (transthoracic) for aortic root/ascending dimensions — first-line surveillance. - CT angiography / MR angiography of the whole arterial tree — essential because disease "extend[s] beyond the thoracic aorta, affecting the entire arterial tree" (PMID 38531898); assesses tortuosity, distal aneurysms. - Physical exam for connective-tissue/skeletal/craniofacial signs (hypertelorism, pectus, hypermobility, contractures). - Histopathology (if tissue available): medial degeneration with preserved elastic fibers but abnormal collagen — a distinguishing feature ("preservation of elastic fibers and increased TGF-β signaling", PMID 27632686); increased nuclear pSMAD2 on IHC.

Biomarkers. No validated circulating MRLS biomarker. Increased aortic-wall pSMAD2 is a tissue marker of TGF-β activation (PMID 27632686). Circulating TGF-β/TGF-β2 is a candidate (elevated in related ECM aortopathies, PMID 26607280) — inferred, unvalidated in MRLS.

Clinical criteria / differential diagnosis. No standalone diagnostic criteria; diagnosis rests on phenotype + BGN variant. Differential diagnoses: Marfan syndrome (FBN1), Loeys-Dietz syndrome (TGFBR1/2, SMAD2/3, TGFB2/3), vascular Ehlers-Danlos (COL3A1), and the other X-linked aortopathy FLNA/filamin-A (periventricular nodular heterotopia + aortic disease; PMID 35819109). Distinguishing features of MRLS: X-linked male-predominant inheritance, preserved elastic fibers with collagen fibril abnormality, hypertelorism + pectus + hypermobility/contractures.

Screening. Cascade genetic testing of at-risk relatives once the familial BGN variant is known; prenatal/preimplantation testing feasible. No newborn screening exists.

11. Outcome / Prognosis

  • Survival/mortality. Prognosis is dominated by aortic dissection/rupture, a leading cause of early death in affected males. No formal 5-/10-year survival statistics exist (ultra-rare); the mouse model shows 50% male mortality by 3 months from aortic rupture (PMID 17502576), underscoring lethality of untreated severe disease.
  • Disease-specific mortality. Sudden cardiovascular death from dissection/rupture is the principal disease-specific cause.
  • Morbidity/disability. Post-dissection sequelae, multiple aortic/arterial surgeries, chronic musculoskeletal disability (scoliosis, pectus, hypermobility pain), and lifelong activity restriction.
  • Recovery. No cure; timely prophylactic surgery + medical therapy markedly improves outcome (extrapolated from Marfan/LDS).
  • Prognostic factors. Male sex, larger/rapidly growing aortic diameter, distal/multifocal arterial involvement, and large deletions (± ATP2B3) predict worse outcome (PMID 38531898). QoL: no MRLS-specific instrument data.

12. Treatment

No MRLS-specific approved therapy or trial exists; management is extrapolated from heritable-TAAD/Marfan/LDS guidelines.

Pharmacotherapy (medical aortic protection). - β-adrenergic blockers (e.g., atenolol, metoprolol) — reduce dP/dt and wall stress (NCIT: C2019 adrenergic beta-antagonist). Standard of care in heritable TAAD. - Angiotensin-II type-1 receptor blockers (ARBs), esp. losartan (NCIT:C61912 losartan; DrugBank DB00678; CHEBI:6541) — reduce TGF-β signaling and aortic growth in Marfan models/patients: "TGF-β2 levels were reduced after losartan treatment, an angiotensin-II type-1 receptor blocker, known to prevent aortic aneurysm formation" (PMID 26607280); clinical-trial context in PMID 31066871/27274304. Biologically rationalized in MRLS given increased aortic pSMAD2, but efficacy is unproven in MRLS. - Blood-pressure control generally to minimize hemodynamic stress (PMID 31066871). - Pharmacogenomics: none specific to MRLS.

Surgical / interventional. Prophylactic aortic root/ascending replacement at diameter thresholds (with valve-sparing where feasible), and repair of dissections/peripheral aneurysms; lifelong surveillance of the whole arterial tree given diffuse involvement (PMID 38531898). NCIT: C157975 (aortic aneurysm repair) / C51826 (aortic surgery).

Advanced / experimental therapeutics. No gene, cell, or RNA therapy in clinical use. Patient-derived iPSCs (PMID 36599284) enable disease modeling and future therapeutic screening. Anti-TGF-β strategies are conceptually relevant but require careful timing (TGF-β neutralization can be beneficial or harmful depending on disease stage; PMID 25614286).

Supportive/rehabilitative. Physiotherapy for hypermobility/scoliosis, pectus management, pain control, cardiology + medical genetics multidisciplinary care.

Treatment strategy. Genotype-informed, risk-stratified surveillance + medical therapy + timely prophylactic surgery; avoid heavy isometric exercise; high-risk pregnancy management.

13. Prevention

  • Primary prevention: not possible (monogenic); genetic counseling and reproductive options (PGT/prenatal testing) prevent transmission (NSGC/ACMG frameworks).
  • Secondary prevention (early detection): cascade genetic testing of relatives; serial aortic imaging (echo + CT/MR angiography) in variant carriers to detect aneurysm before dissection.
  • Tertiary prevention (complication avoidance): β-blockers/ARBs, blood-pressure control, activity modification, and prophylactic surgery at threshold diameters to prevent dissection/rupture (extrapolated from PMID 31066871).
  • Risk stratification: males and large-deletion carriers prioritized for intensive surveillance (PMID 38531898).
  • Immunization / public-health / environmental measures: not applicable.
  • Counseling: X-linked recurrence-risk counseling — affected/carrier females transmit to 50% of offspring; affected males transmit the variant to all daughters (obligate carriers) and no sons.

14. Other Species / Natural Disease

  • Taxonomy / model species: Mus musculus (NCBI:txid10090) is the principal species with a described Bgn-related aortic phenotype.
  • Orthologous gene: mouse Bgn (NCBI Gene 12111; X chromosome), highly conserved with human BGN; conserved intron-exon structure shared with decorin (PMID 12975603).
  • Naturally occurring animal disease: no well-characterized spontaneous BGN-related aortic-dissection disorder in companion animals/wildlife is documented in OMIA (as of this review); the murine phenotype is engineered, though it arose on a specific genetic background (BALB/cA) revealing strain/background dependence (PMID 17502576).
  • Comparative biology / conservation: the biglycan–collagen–TGF-β ECM axis is evolutionarily conserved; the male-limited murine aortic-rupture phenotype parallels human male predominance, supporting conserved sex-dependent mechanisms (PMID 17502576).
  • Zoonosis / transmission: not applicable (genetic disease).

15. Model Organisms

Mouse (primary model). - Type: mammalian, germline knockout — Bgn-deficient (null) mice (X-linked, so hemizygous males "Bgn0/Y"). Also Bgn/Fmod double-knockout for skeletal studies. - Cardiovascular phenotype recapitulation (strong): "50% of biglycan-deficient male mice died suddenly within the first 3 months of life... aortic rupture that involved an intimal and medial tear as well as dissection between the media and adventitia"; aortas showed "structural abnormalities of collagen fibrils and reduced tensile strength" (PMID 17502576). This closely models the human early-onset, male-predominant TAAD. - Skeletal phenotype recapitulation: Bgn-null mice develop "an osteoporosis-like phenotype" with reduced bone mass increasing with age (PMID 9731537), and reduced osteoblast BMP-4 responsiveness/differentiation (PMID 15173106) — models the skeletal component. - Model limitations: aortic-rupture penetrance is strain/background-dependent (prominent on BALB/cA; PMID 17502576); craniofacial/vascular-tree features less characterized; TGF-β activation dynamics in mouse aorta not fully mapped to human. - Genetic model variants available: single Bgn KO; Bgn/Fmod and Bgn/Dcn compound mutants (MGI). Conditional/humanized BGN lines are not standard.

Cellular / in vitro models. - Patient-derived iPSC line BBANTWi009-A from an MRLS male with a BGN deletion — normal karyotype, pluripotent, tri-lineage differentiation, original genotype retained (PMID 36599284). Enables SMC/vascular disease modeling and drug screening. - Patient skin fibroblasts used for cDNA/Western LoF confirmation (PMID 38531898).

Resources. MGI (mouse Bgn), IMSR (strains), Cellosaurus/biobank (iPSC line), ClinVar (human variants).

Supported vs. Refuted Hypotheses

Supported. - MRLS is X-linked, caused by BGN loss-of-function (PMID 27632686; 38531898). - Mechanism = ECM/collagen weakening + increased TGF-β/SMAD2 signaling (PMID 27632686; 17502576; 8038266). - Male-predominant severity/penetrance; disease affects the whole arterial tree (PMID 38531898). - Bgn-null mouse recapitulates aortic dissection and skeletal phenotype (PMID 17502576; 9731537).

Refuted / not supported. - Pathogenic missense-only BGN variants driving disease via dominant-negative mechanism — not supported; LoF is the operative mechanism (PMID 38531898). - A primary metabolic/enzymatic defect — not applicable; defect is structural-ECM/signaling.

Limitations and Future Directions

  • Evidence rests on small cohorts (≈18 probands); precise phenotype frequencies, penetrance quantification, and natural-history/survival statistics are lacking.
  • No MRLS-specific clinical trials; medical therapy (β-blocker/ARB) efficacy is extrapolated, not proven.
  • Whether TGF-β hyperactivation is a primary driver vs. secondary response is unresolved.
  • Female expressivity determinants (XCI skewing) and modifier genes (beyond ATP2B3) are under-characterized.
  • Future work: iPSC-SMC and improved mouse models to define causal chain and test targeted (anti-TGF-β, ARB) and gene-based therapies; registry-based natural-history and QoL studies; validated circulating biomarkers.

Key ontology quick-reference

  • Disease: MONDO:0010515; OMIM:300989; ORPHA:404003
  • Gene/protein: HGNC:1044 (BGN); UniProt P21810; GO:0005518, GO:0050431, GO:0030198, GO:0007179
  • Phenotypes (HPO): HP:0002647 (aortic dissection), HP:0002616 (aortic root aneurysm), HP:0004942 (arterial aneurysm), HP:0005116 (arterial tortuosity), HP:0000316 (hypertelorism), HP:0000766 (pectus deformity), HP:0001382 (joint hypermobility), HP:0001371 (contractures), HP:0002650 (scoliosis)
  • Anatomy (UBERON): UBERON:0000947 (aorta), UBERON:0035904 (ascending aorta), UBERON:0001637 (artery), UBERON:0000948 (heart)
  • Cells (CL): CL:0000359 (vascular smooth muscle cell), CL:0000057 (fibroblast), CL:0000062 (osteoblast)
  • Chemicals (CHEBI): CHEBI:6541 (losartan), CHEBI:2719 (angiotensin II)
  • Treatments (NCIT): C61912 (losartan), C2019 (β-blocker), aortic aneurysm repair (surgical)

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 15
Resolved 15
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 15
Quoted claims found in source 12
Quoted claims not found in source 3
References weighed for topical relevance 15
On topic 9
Off topic 1

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

1 of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

  • PMID:38531898: "biglycan-related Meester-Loeys syndrome"
  • Text part not found as substring: 'biglycan-related Meester-Loeys syndrome'
  • PMID:38531898: "possibly explained by expressional activation of the downstream ATPase ATP2B3... driven by the remnant BGN promotor"
  • closest text in source: "This may possibly be explained by expressional activation of the downstream ATPase ATP2B3 (normally repressed in skin fibroblasts) driven by the remnant BGN promotor"
  • PMID:12975603 (abstract only): "Biglycan is a Class I Small Leucine Rich Proteoglycan (SLRP) that is localized on human chromosome Xq28-ter... Biglycan contains two chondroitin sulfate glycosaminoglycan (GAG) chains attached near its NH2 terminus"
  • closest text in source: "Biglycan is a Class I Small Leucine Rich Proteoglycans (SLRP) that is localized on human chromosome Xq28-ter"

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

  • PMID:8038266 (1 mention) - Biosynthesis and interactions of small chondroitin/dermatan sulphate proteoglycans.
  • shared terms: biglycan, collagen

Weighed against this report's own most characteristic terms: aortic, disease, dissection, bgn, mrls, aneurysm, male, skeletal, phenotype, gene, tgf, variant, arterial, biglycan, genetic, x-linked, collagen, primary, ecm, model.

Term Validation

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

Outcome Count
Terms checked 48
Resolved 44
Unresolved (possible confabulation) 0
Obsolete 1
Unverifiable 3
Terms whose name was checked 35
Terms named correctly 22
Terms named as a different term 3
Terms whose name is worth a second look 10

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • HP:0000316 (2 mentions) - the report calls it "Other recurrent findings include hypertelorism", PMID 27632686", "hypertelorism"; HP calls it Hypertelorism*
  • HP:0001371 (2 mentions) - the report calls it "joint hypermobility, contractures", PMID 27632686", "contractures"; HP calls it Flexion contracture*
  • UBERON:0035904 (2 mentions) - the report calls it "ascending aorta"; UBERON calls it primary visual area, layer 4

Obsolete terms

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

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

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • HP:0004942 (2 mentions) - the report calls it "arterial aneurysm"; HP calls it Aortic aneurysm
  • HP:0025019 (1 mention) - the report calls it "arterial dissection"; HP calls it Arterial rupture
  • HP:0000766 (2 mentions) - the report calls it "pectus deformity"; HP calls it Abnormal sternum morphology, and lists "Pectus deformity" among its other names
  • HP:0002652 (1 mention) - the report calls it "mild skeletal dysplasia spectrum"; HP calls it Skeletal dysplasia
  • HP:0001075 (1 mention) - the report calls it "atrophic scars/soft skin spectrum"; HP calls it Atrophic scars
  • CHEBI:2719 (2 mentions) - the report calls it "angiotensin II"; CHEBI calls it Ile(5)-angiotensin II, and lists "Angiotensin II" among its other names
  • GO:0007179 (2 mentions) - the report calls it "TGF-β receptor signaling pathway"; GO calls it transforming growth factor beta receptor signaling pathway, and lists "TGF-beta receptor signaling pathway" among its other names
  • GO:0006954 (1 mention) - the report calls it "inflammatory response, branch"; GO calls it inflammatory response
  • CL:0000359 (3 mentions) - the report calls it "vascular associated smooth muscle cell", "vascular smooth muscle cells", "vascular smooth muscle cell"; CL calls it vascular associated smooth muscle cell, and lists "vascular smooth muscle cell" among its other names
  • UBERON:0000948 (2 mentions) - the report calls it "Heart/valves", "heart"; UBERON calls it heart

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • HP:0000316 - called "Other recurrent findings include hypertelorism*", PMID 27632686", "hypertelorism"
  • HP:0001371 - called "joint hypermobility, contractures*", PMID 27632686", "contractures"
  • CL:0000359 - called "vascular associated smooth muscle cell", "vascular smooth muscle cells", "vascular smooth muscle cell"
  • UBERON:0000948 - called "Heart/valves", "heart"

Prefixes with no resolver

Terms 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, OMIM.