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Classifications

Harrison's Part

ISDS Skeletal Nosology

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Mappings

MONDO

MONDO:0030500 Loeys-Dietz syndrome 6

MONDO:0030500 is an is_a child of Loeys-Dietz syndrome (MONDO:0018954), carries the exact synonym "LDS6" attributed to OMIM:619656, cross-refers to OMIM:619656, and asserts SMAD2 (HGNC:6768) as the causal gene via RO:0004003. Because the MONDO term carries no definition text, disease identity for this entry was anchored on the OMIM:619656 cross-reference and the OAK-verified RO:0004003 causal-gene assertion rather than on any narrative source - a deliberate precaution given that the Loeys-Dietz numbered series is a high Named-Entity-Confusion-risk disease class.

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Definitions

1

Molecular and clinical diagnosis

The diagnosis of Loeys-Dietz syndrome is established either clinically, in a proband with characteristic findings, or by identification of a heterozygous pathogenic variant in one of the six autosomal dominant LDS genes; SMAD2 is the gene defining subtype 6. In the absence of formal LDS diagnostic criteria, a pathogenic variant in an LDS gene together with arterial aneurysm or dissection is generally considered sufficient.

DIAGNOSTIC_CRITERIA

Show evidence (2 references)

PMID:20301312 SUPPORT Human Clinical

"The diagnosis of LDS is established in (1) a proband with characteristic clinical findings or (2) by the identification of a heterozygous pathogenic variant in SMAD2, SMAD3, TGFB2, TGFB3, TGFBR1, or TGFBR2 or biallelic pathogenic variants in IPO8 in a proband with aortic root enlargement, type A..."

GeneReviews names SMAD2 among the genes whose heterozygous pathogenic variants establish a molecular diagnosis of Loeys-Dietz syndrome. Quoted in full through the clinical qualifier, because the molecular finding is required to occur in a proband with aortic root enlargement, dissection, other characteristic features, or a positive family history - it is not sufficient on its own.

PMID:29392890 SUPPORT Human Clinical

"It is thus suggested that a mutation in any of these six genes in combination with the presence of arterial aneurysm or dissection should be sufficient for the diagnosis of LDS"

States the working sufficiency criterion used in the absence of formal LDS diagnostic criteria, which the description paraphrases.

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Inheritance

1

Autosomal dominant inheritance HP:0000006

SMAD2-related Loeys-Dietz syndrome is inherited in an autosomal dominant manner. Both familial transmission over three generations and de novo occurrence in probands with unaffected parents have been documented.

Autosomal dominant inheritance

Show evidence (3 references)

PMID:20301312 SUPPORT Human Clinical

"LDS caused by a pathogenic variant in SMAD2, SMAD3, TGFB2, TGFB3, TGFBR1, or TGFBR2 is inherited in an autosomal dominant manner."

GeneReviews states the autosomal dominant inheritance of SMAD2-related Loeys-Dietz syndrome explicitly.

PMID:26247899 SUPPORT Human Clinical

"Moreover, one variant occurred de novo in a proband with unaffected parents."

Documents de novo occurrence of a SMAD2 variant, consistent with dominant inheritance and with a proportion of sporadic presentations.

PMID:29967133 SUPPORT Human Clinical

"This variant was also found in his affected daughter with hypertelorism and arterial tortuosity, as well as his affected mother."

Three-generation segregation of a SMAD2 missense variant with the phenotype, supporting autosomal dominant transmission.

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Discussions and Knowledge Gaps

4

Where does SMAD2-related Loeys-Dietz syndrome sit in the LDS severity ranking, and can a SMAD2-specific surveillance and surgical-threshold protocol be justified?

KNOWLEDGE GAP OPEN lds6_severity_placement

Attached to

pathophysiology#Progressive Aortic and Arterial Dilation pathophysiology#Arterial Dissection and Rupture

The Loeys-Dietz subtypes are informally ordered by severity, and that ordering drives imaging intervals and the diameter at which prophylactic repair is offered. LDS6 is the one subtype left unplaced: the published denominator is a few families and a handful of reported variants, so no genotype-specific growth rate, dissection diameter or age-at-event distribution exists. Management is therefore extrapolated wholesale from Loeys-Dietz syndrome generally. Because the gap is one of cohort size rather than of mechanism, it is closable by systematic registry accrual of SMAD2-positive probands rather than by new experimental work.

Proposed experiments

SMAD2-stratified HTAD registry analysis

smad2_registry_stratification

Pool SMAD2-positive probands across heritable-thoracic-aortic-disease registries and report age at first aneurysm, aortic growth rate, diameter at dissection and extra-aortic arterial involvement, so that LDS6 can be placed against the other subtypes on the measures that actually govern management.

Show evidence (1 reference)

PMID:31569402 SUPPORT Human Clinical

"there are not enough data on LDS caused by heterozygous mutations in SMAD2 to place this form (LDS6) in this spectrum"

States the gap explicitly, and is also the source that names the SMAD2 subtype LDS6.

Why do heterozygous SMAD2 variants produce two developmentally distinct presentations - complex congenital heart disease with laterality defects on the one hand, and late-onset arterial aneurysm with connective-tissue findings on the other - and does allele class predict which a carrier gets?

KNOWLEDGE GAP OPEN smad2_two_phenotype_split

Attached to

pathophysiology#Disrupted SMAD2-Dependent Transcriptional Programme pathophysiology#Impaired Cardiac Morphogenesis and Laterality Specification

Two phenotypes have been delineated for the same gene at very different developmental stages, and the difference is not yet explained. The leading hypothesis is allele-class-specific molecular consequence: isogenic stem-cell models show that haploinsufficiency and missense alleles produce partly distinct chromatin-accessibility and transcription-factor-binding signatures. That is a plausible mechanism but not a demonstrated one, and it has not been tested against the clinical split - the aneurysm literature is dominated by MH2 missense alleles while truncating and splice alleles are prominent in the congenital-heart-disease series, but nobody has shown that the correlation holds prospectively or that it is causal rather than an artefact of how the two literatures ascertained their patients. The question is directly actionable: a truncating SMAD2 variant found on a congenital-heart-disease panel raises the question of whether that child needs lifelong aortic surveillance, and the answer is currently unknown.

Proposed experiments

Allele-class-stratified phenotype comparison

smad2_allele_class_phenotype

Assemble all reported SMAD2 carriers, classify each allele as truncating, splice or MH2 missense, and test whether allele class predicts congenital heart disease versus late-onset aortopathy - including systematic aortic imaging of SMAD2-positive congenital-heart-disease probands, who have generally not been imaged for aneurysm.

Show evidence (2 references)

PMID:30157302 SUPPORT Human Clinical

"Our data suggest two distinct phenotypes associated with pathogenic variants in SMAD2: complex CHD with or without laterality defects and other congenital anomalies, and a late-onset vascular phenotype characterized by arterial aneurysms with connective tissue abnormalities."

The primary statement of the two-phenotype split that this gap is about.

PMID:40028843 SUPPORT In Vitro

"Heterozygous SMAD2 loss-of-function and missense variants are identified in patients with congenital heart disease (CHD) or arterial aneurysms. Mechanisms that cause distinct cardiovascular phenotypes remain unknown."

Confirms that the mechanism separating the two presentations was still unknown as of the most recent functional study.

Does the paradoxical increase in aortic TGF-beta signalling seen in other Loeys-Dietz subtypes also occur in SMAD2-variant aortic tissue, or does losing the effector itself break the paradox?

KNOWLEDGE GAP OPEN smad2_aortic_tgfb_paradox_untested

Attached to

pathophysiology#Impaired Canonical TGF-beta SMAD2 Signal Transduction

The defining paradox of Loeys-Dietz syndrome is that loss-of-function variants in positive components of the TGF-beta pathway are accompanied by increased SMAD phosphorylation and increased TGF-beta-driven gene expression in the aortic media. That observation has been made for TGFBR1/2, SMAD3, TGFB2 and TGFB3 - but not for SMAD2, because no SMAD2-variant aortic tissue series has been published. The case matters mechanistically rather than merely completing a set: SMAD2 is itself the phosphorylated effector, so a readout of increased pSMAD2 cannot mean the same thing when the SMAD2 allele is the lesion. Curating this entry's central signalling node as dysregulation rather than as loss of signalling is an inference from the other subtypes, and is flagged here rather than asserted. A further complication is that "increased aortic TGF-beta signalling" is not uniform across the aortic wall: in the Tgfbr1 mouse model of Loeys-Dietz syndrome the direction of the effect is lineage-specific, with second-heart-field derived aortic-root smooth muscle cells showing *defective* ligand-induced Smad2/3 activation while the neighbouring cardiac-neural-crest-derived cells retain signalling potential and show *increased* Smad2/3 phosphorylation in vivo - and lineage-restricted deletion of Smad2 in the neural-crest compartment alone was protective. So a whole-tissue pSMAD2 readout can average two opposite lineage-level effects, which is a second reason the paradox cannot simply be assumed to carry over to a SMAD2 lesion, and a reason any SMAD2 aortic-tissue study should be resolved by lineage rather than reported as a bulk measurement.

Proposed experiments

SMAD2-variant aortic media signalling readout

smad2_aortic_media_signalling

Obtain aortic wall tissue at elective repair from SMAD2-variant patients and quantify pSMAD2, pSMAD3, pERK1/2 and CTGF against non-syndromic and other-LDS-subtype controls, to establish whether the TGF-beta paradox holds when the mutated gene is the effector itself. Resolve the readout by smooth-muscle-cell lineage (second heart field versus cardiac neural crest) rather than reporting a bulk aortic-wall value, since the two compartments move in opposite directions in the Tgfbr1 mouse model.

Show evidence (4 references)

PMID:29392890 SUPPORT Human Clinical

"Aortic wall tissue of TGFBR1 or 2 mutant patients showed increased nuclear accumulation of phosphorylated SMAD2 (pSMAD2) and enhanced expression of TGF‐β driven gene products such as connective tissue growth factor (CTGF), illustrating enhanced TGF‐β signaling."

Establishes the paradox in the subtypes where aortic tissue was available, which is the comparison SMAD2 is missing from.

PMID:34807423 SUPPORT Human Clinical

"Despite the loss of function nature of these mutations, the patient-derived aortic tissues show evidence of increased (rather than decreased) TGFβ signalling"

A recent review states the paradox generically over the whole Loeys-Dietz gene set, SMAD2 included, without a SMAD2-specific aortic tissue series behind it - which is precisely the unexamined generalisation this gap flags rather than a resolution of it.

PMID:30614814 SUPPORT Model Organism

"Secondary heart field-derived (SHF-derived), but not neighboring cardiac neural crest-derived (CNC-derived), VSMCs showed impaired Smad2/3 activation in response to TGF-β"

Shows the defective-signalling half of the lineage split in the Tgfbr1 Loeys-Dietz mouse model: the aortic-root lineage that actually dilates is the one with impaired, not excessive, Smad2/3 activation.

+ 1 more reference

Can any existing animal model of SMAD2 loss address the LDS6 aortopathy, given that Smad2-null mouse embryos die before the aorta can be assessed?

HUMAN MODEL MISMATCH OPEN smad2_no_viable_animal_model

Attached to

pathophysiology#Aortic Medial Degeneration and Wall Weakening

Every other Loeys-Dietz gene has a mouse model whose aorta was examinable and which reproduced aspects of the human aortopathy - Smad3 knockouts die of ruptured aneurysm, Tgfb2 heterozygotes dilate the aortic root. Smad2 is the exception: knockout embryos die before E8.5 from defective egg-cylinder elongation and germ-layer formation, so aortic size cannot be measured at all. This is a genuine model-fidelity gap rather than an absence of evidence - the null model exists and has been characterised, but the developmental stage at which it fails is upstream of the tissue in question, which is exactly why a SMAD2-specific aortic mechanism has never been tested in vivo. The available human-relevant functional models are instead iPSC-based and report on cardiac development rather than on the aortic wall.

Proposed experiments

Conditional and knock-in Smad2 aortic models

smad2_conditional_aortic_model

Build smooth-muscle-lineage conditional Smad2 knockouts and knock-in mice carrying a human MH2 missense allele, bypassing the peri-implantation lethality, and phenotype the aorta for dilation, elastic fibre fragmentation and SMAD/ERK signalling.

Show evidence (2 references)

PMID:29392890 SUPPORT Model Organism

"Mouse models for SMAD2 have also been developed but Smad2 knockout mice embryos die before E8,5, due to defective egg cylinder elongation and germ layer formation, which entangles aortic size examination"

States the mismatch precisely: the Smad2-null mouse exists but dies before the aorta can be assessed, so it cannot serve as an LDS6 aortopathy model.

PMID:42380922 SUPPORT Other

"We critically evaluate the extent to which each model recapitulates the diverse LDS phenotypes and discuss their respective advantages and limitations."

A 2026 review surveying the in vivo and in vitro models available across Loeys-Dietz syndrome and assessing how far each recapitulates the human phenotypes. Cited as PARTIAL/OTHER because it is a narrative review of the model landscape rather than a SMAD2-specific experimental result; it is included because the SMAD2 gap is a claim about that landscape.

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Pathophysiology

7

Heterozygous SMAD2 Loss-of-Function Variant

The primary lesion is a heterozygous loss-of-function variant in SMAD2. Reported alleles include nonsense, frameshift and splice variants that remove one functional copy outright, and missense variants. The missense alleles reported in the aneurysm literature cluster in the MH2 domain - the conserved surface responsible for oligomerisation of SMAD2 with SMAD4 and for subsequent SMAD-dependent transcriptional activation - so an MH2 missense allele attacks the same step as haploinsufficiency, by disabling complex assembly rather than by removing protein. That clustering is not a property of SMAD2 missense variants in general: in a large congenital-heart-disease cohort the missense variants were instead concentrated in exon 4, and the modelled p.Arg114Cys allele lies in the MH1 domain.

SMAD2 hgnc:6768

Downstream

Impaired Canonical TGF-beta SMAD2 Signal Transduction Loss of one functional SMAD2 allele, or of MH2-mediated complex assembly, reduces the capacity of the canonical TGF-beta pathway to transduce signal from the activated receptor to the nucleus.

Show evidence (5 references)

PMID:29967133 SUPPORT Human Clinical

"Using gene panel sequencing, we identified a SMAD2 nonsense variant and four SMAD2 missense variants, all affecting highly conserved amino acids in the MH2 domain."

Establishes the variant classes and the MH2-domain localisation of the reported missense alleles.

PMID:29392890 SUPPORT Human Clinical

"No mutational hotspot is observed for SMAD2 and SMAD3 mutations, but the majority (100% and 63%) reside in the MH2 domain, a well conserved region responsible for the oligomerization of SMAD2 or SMAD3 with SMAD4 and subsequent Smad‐dependent activation of downstream transcription"

Gives the functional rationale for the MH2 clustering: this domain mediates SMAD2-SMAD4 oligomerisation and downstream transcriptional activation, so MH2 missense alleles are predicted to be loss-of-function.

PMID:30157302 SUPPORT Human Clinical

"WES identified pathogenic truncating variants, a splice variant, and a predicted deleterious missense variant in SMAD2."

Documents truncating and splice alleles in addition to missense variants, supporting a loss-of-function mechanism.

+ 2 more references

Impaired Canonical TGF-beta SMAD2 Signal Transduction

SMAD2 is the receptor-regulated SMAD phosphorylated by the activated type I TGF-beta receptor; with SMAD3 it carries the signal to the nucleus in complex with SMAD4. Halving functional SMAD2, or disabling its MH2 oligomerisation surface, degrades this canonical arm. As in every other Loeys-Dietz subtype the net tissue-level consequence is not a simple reduction: heterozygous loss-of-function alleles in the upstream LDS genes are associated with paradoxically increased TGF-beta pathway output in the aortic wall, evidenced by raised SMAD phosphorylation and TGF-beta-driven gene expression. The node is therefore curated as dysregulation of the pathway rather than as loss of pathway activity, matching the module it conforms to.

vascular smooth muscle cell CL:0000359

SMAD protein signal transduction GO:0060395 ⚠ ABNORMAL transforming growth factor beta receptor signaling pathway GO:0007179 ⚠ ABNORMAL

Downstream

Disrupted SMAD2-Dependent Transcriptional Programme A degraded canonical signal reaches the nucleus as an altered SMAD2-dependent transcriptional output.

Aortic Medial Degeneration and Wall Weakening Dysregulated TGF-beta signalling in the aortic wall drives medial degeneration, the substrate for aneurysm formation.

Show evidence (3 references)

PMID:29392890 SUPPORT Human Clinical

"In the canonical pathway, TGFβRI then phosphorylates SMAD2 and SMAD3 proteins that transmit the TGFβ signal to the nucleus upon association with SMAD4."

Establishes the normal position of SMAD2 in canonical TGF-beta signal transduction, the step disrupted by pathogenic SMAD2 variants.

PMID:29392890 SUPPORT Human Clinical

"heterozygous loss-of-function mutations associate with paradoxical activation of TGF‐β signaling, which was demonstrated by increased phosphorylation of Smad proteins and increased output of TGF‐β‐driven genes."

Documents the TGF-beta paradox across the Loeys-Dietz genes, justifying curating this node as dysregulation rather than loss of signalling. PARTIAL because the cited demonstration is in TGFBR1/2 and ligand-gene patients, not in SMAD2-variant aortic tissue, which has not been reported.

PMID:29967133 SUPPORT Human Clinical

"Missense variants in SMAD2, encoding a key transcriptional regulator of transforming growth factor beta signalling, were recently reported to cause arterial aneurysmal disease."

Identifies SMAD2 as a transcriptional regulator of TGF-beta signalling whose disruption causes arterial aneurysmal disease.

Disrupted SMAD2-Dependent Transcriptional Programme

SMAD2 acts in the nucleus as a co-regulator that binds many different transcription factors. Isogenic induced pluripotent stem cell models show that SMAD2 haploinsufficiency changes chromatin accessibility at promoters, dysregulates hundreds of SMAD-regulated genes including known congenital-heart-disease genes, and disrupts predicted interactions with NANOG, ETS, TEAD3/4, CREB1 and AP1. Loss-of-function and missense alleles produce partly distinct accessibility and transcription-factor-binding signatures, which is the leading explanation offered for why SMAD2 variants give rise to more than one cardiovascular phenotype.

regulation of transcription by RNA polymerase II GO:0006357 ⚠ ABNORMAL

Experimental models

Isogenic SMAD2 variant iPSC and iPSC-derived cardiomyocyte panel IPSC DERIVED MODEL Directly measures the chromatin-accessibility and transcriptional consequences of SMAD2 dosage loss in a human isogenic background.

Downstream

Impaired Cardiac Morphogenesis and Laterality Specification Among the genes whose expression falls with SMAD2 dosage are NODAL, LEFTY1 and LEFTY2 - components of the activin/nodal pathway that establishes the left-right axis - so the dysregulated transcriptional programme reaches cardiac morphogenesis and left-right patterning.

Show evidence (3 references)

PMID:40028843 SUPPORT In Vitro

"SMAD2 haploinsufficiency altered chromatin accessibility at promoters and dysregulated expression of 385 SMAD regulated genes, including 10 CHD-associated genes."

Direct measurement of the epigenetic and transcriptional consequence of SMAD2 haploinsufficiency in an isogenic human cell model.

PMID:40028843 SUPPORT In Vitro

"SMAD2 haploinsufficiency disrupts transcription factor binding and chromatin interactions critical for cardiovascular development."

States the mechanistic conclusion linking SMAD2 dosage to a disrupted transcriptional programme required for cardiovascular development.

PMID:40028843 SUPPORT In Vitro

"Differences between the molecular consequences of loss-of-function and missense variants likely contribute to phenotypic heterogeneity."

Offers allele-class-specific transcriptional consequences as an explanation for the two SMAD2 phenotypes. PARTIAL because the authors frame it as a likely contribution rather than a demonstrated cause, and the model is pluripotent stem cells rather than patient aortic tissue.

Impaired Cardiac Morphogenesis and Laterality Specification

SMAD2 haploinsufficiency lowers expression of NODAL, LEFTY1 and LEFTY2 - activin/nodal pathway components that establish the left-right axis - and the authors of that work propose the resulting epigenetic and transcriptional changes as the mechanism by which SMAD2 haploinsufficiency causes congenital heart disease and vascular anomalies. Clinically, heterozygous SMAD2 variants are recovered in large congenital-heart-disease cohorts and the presentation is complex structural heart disease with or without heterotaxy - a developmentally much earlier consequence than the aortopathy, and the arm of LDS6 that is least like the other Loeys-Dietz subtypes.

heart development GO:0007507 ⚠ ABNORMAL determination of left/right symmetry GO:0007368 ⚠ ABNORMAL

Experimental models

Isogenic SMAD2 variant iPSC and iPSC-derived cardiomyocyte panel IPSC DERIVED MODEL Reproduces the cell-autonomous cardiac consequences - impaired cardiomyocyte contractility and reduced activin/nodal pathway gene expression - but not the structural malformation or the laterality defect itself, which require an intact embryo.

Downstream

Complex Congenital Heart Disease Disrupted cardiac morphogenesis presents as complex structural congenital heart disease.

Heterotaxy Failure of left-right axis specification presents as a laterality defect.

Show evidence (4 references)

PMID:30157302 SUPPORT Human Clinical

"Pathogenic variants in SMAD2 have been reported in association with arterial aneurysms and dissections and in large cohorts of subjects with complex congenital heart disease (CHD)."

Establishes the congenital-heart-disease arm of the SMAD2 phenotype alongside the vascular arm.

PMID:30157302 SUPPORT Human Clinical

"Patient 3 was a fetus with complex CHD and heterotaxy."

Documents the laterality defect that implicates SMAD2 in left-right axis specification as well as in cardiac morphogenesis.

PMID:40028843 SUPPORT In Vitro

"SMAD2 haploinsufficiency in induced pluripotent stem cells impairs cardiac contractility and alters epigenetic and transcriptional processes that cause dysregulation of genes required for normal heart development"

Provides the cellular counterpart of the clinical congenital heart disease: SMAD2 dosage loss dysregulates genes required for normal heart development and impairs cardiomyocyte contractility.

+ 1 more reference

Aortic Medial Degeneration and Wall Weakening

Dysregulated TGF-beta signalling in the aortic media alters the smooth muscle cell phenotype and extracellular matrix homeostasis, weakening the wall. This is the shared, conserved step of every Loeys-Dietz subtype and of heritable thoracic aortic disease generally; it is curated here by conformance to the `aortopathy_tgfbeta_dysregulation` module rather than re-derived, because no SMAD2-specific aortic histopathology series has been published.

aortic smooth muscle cell CL:0002539

extracellular matrix organization GO:0030198 ⚠ ABNORMAL

Downstream

Progressive Aortic and Arterial Dilation A weakened media dilates progressively under haemodynamic load.

Arterial Tortuosity Loss of medial structural integrity along the arterial tree manifests as the elongation and tortuosity characteristic of Loeys-Dietz syndrome.

Show evidence (1 reference)

PMID:31569402 SUPPORT Human Clinical

"LDS is caused by pathogenic variants in transforming growth factor β (TGF-β) signaling pathway-related genes, i.e., TGFBR1, TGFBR2, SMAD2, SMAD3, TGFB2, and TGFB3, which alter the physiological development and function of the extracellular matrix, leading to cardiovascular and multisystem abnormalities"

States the shared route from TGF-beta pathway gene disruption - SMAD2 included - through altered extracellular matrix development and function to cardiovascular disease.

Progressive Aortic and Arterial Dilation

Progressive dilation is not confined to the aortic root in SMAD2-related disease: reported patients show aortic root aneurysm together with tortuosity and aneurysm throughout the arterial tree, including the neck vessels and the coronary arteries. The arterial-tree-wide distribution is what makes root-only surveillance inadequate.

Downstream

Arterial Dissection and Rupture A progressively dilated, structurally weakened artery is at risk of dissection and rupture.

Arterial Aneurysm Progressive dilation presents clinically as arterial aneurysm.

Aortic Root Aneurysm Dilation at the aortic root is the segment most often imaged and the usual trigger for referral.

Show evidence (2 references)

PMID:31569402 SUPPORT Human Clinical

"To date, 9 (likely) pathogenic variants in SMAD2 have now been described in 15 subjects displaying a broad range of features, including aneurysms, tortuosity of the entire arterial tree, and coronary artery dissections, even in the absence of prominent connective tissue characteristics"

Summarises the reported SMAD2 vascular phenotype across all published subjects: aneurysm, whole-arterial-tree tortuosity and coronary dissection.

PMID:29967133 SUPPORT Human Clinical

"In a man clinically diagnosed with Loeys-Dietz syndrome (LDS) that presents with aortic root dilatation and marked tortuosity of the neck vessels, another missense variant, p.(Ser397Tyr), was identified."

A worked case pairing aortic root dilatation with extra-aortic arterial tortuosity in a SMAD2-variant patient given a clinical LDS diagnosis.

Arterial Dissection and Rupture

Dissection is the principal life-threatening endpoint. In SMAD2-related disease it has been documented in the aorta and, distinctively, in the coronary arteries. As for Loeys-Dietz syndrome generally, dissection can occur at smaller aortic diameters and at younger ages than in Marfan syndrome, which is why the intervention thresholds used for Marfan syndrome are not transferable.

Downstream

Aortic and Arterial Dissection The dissection event as it presents clinically.

Coronary Artery Dissection Dissection of a coronary artery, a presenting event reported in this subtype.

Show evidence (3 references)

PMID:26247899 SUPPORT Human Clinical

"Our findings indicate that SMAD2 mutations are associated with arterial aneurysms and dissections"

The founding report establishing dissection as part of the SMAD2 phenotype.

PMID:29967133 SUPPORT Human Clinical

"The third missense variant, p.(Asn361Thr), was discovered in a man presenting with coronary artery dissection."

Documents coronary artery dissection as a presenting event in a SMAD2-variant patient.

PMID:20301312 SUPPORT Human Clinical

"aortic dissection can occur at smaller aortic diameters and at younger ages than observed in Marfan syndrome"

The management-critical property of Loeys-Dietz dissection risk that governs surveillance and surgical thresholds in this subtype too.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

13

Cardiovascular 5

Arterial Aneurysm Aortic aneurysm HP:0004942

Show evidence (1 reference)

PMID:26247899 SUPPORT Human Clinical

"We report three families with arterial aneurysms and dissections in which variants predicted to be pathogenic were identified in SMAD2."

The founding cohort establishing arterial aneurysm as the presenting phenotype of SMAD2 variants.

Aortic Root Aneurysm HP:0002616

Show evidence (2 references)

PMID:29967133 SUPPORT Human Clinical

"The premature stop codon (c.612dup; p.(Asn205*)) was identified in a marfanoid patient with aortic root dilatation and in his affected father."

Documents aortic root dilatation in a SMAD2 nonsense-variant family.

PMID:30157302 SUPPORT Human Clinical

"The fourth patient is an adult female with aortic root aneurysm and physical features suggestive of a connective tissue disorder."

An independently ascertained SMAD2 patient with aortic root aneurysm and connective-tissue features.

Aortic and Arterial Dissection Aortic dissection HP:0002647

Show evidence (1 reference)

PMID:26247899 SUPPORT Human Clinical

"Our findings indicate that SMAD2 mutations are associated with arterial aneurysms and dissections"

Establishes dissection as a core feature of the SMAD2 phenotype.

Arterial Tortuosity HP:0005116

Show evidence (2 references)

PMID:29967133 SUPPORT Human Clinical

"In a man clinically diagnosed with Loeys-Dietz syndrome (LDS) that presents with aortic root dilatation and marked tortuosity of the neck vessels, another missense variant, p.(Ser397Tyr), was identified."

Documents marked arterial tortuosity of the neck vessels in a SMAD2-variant patient with a clinical LDS diagnosis.

PMID:31569402 SUPPORT Human Clinical

"To date, 9 (likely) pathogenic variants in SMAD2 have now been described in 15 subjects displaying a broad range of features, including aneurysms, tortuosity of the entire arterial tree, and coronary artery dissections"

Characterises the tortuosity in SMAD2 subjects as involving the entire arterial tree rather than one segment. Quoted with its SMAD2 attribution intact rather than as a bare fragment.

Complex Congenital Heart Disease Abnormal heart morphology HP:0001627

Show evidence (2 references)

PMID:30157302 SUPPORT Human Clinical

"Patients 1 and 2 presented with complex CHD, developmental delay, seizures, dysmorphic features, short stature, and poor weight gain."

Documents complex congenital heart disease as the presenting feature in two SMAD2-variant probands.

PMID:40028843 SUPPORT Human Clinical

"Thirty participants with CHD had heterozygous loss-of-function or missense SMAD2 variants."

Cohort-scale confirmation from exome sequencing of 11,336 congenital-heart-disease participants.

Eye 1

Hypertelorism HP:0000316

Show evidence (2 references)

PMID:29967133 SUPPORT Human Clinical

"This variant was also found in his affected daughter with hypertelorism and arterial tortuosity, as well as his affected mother."

Documents hypertelorism in a SMAD2-variant family member.

PMID:20301312 SUPPORT Human Clinical

"craniofacial features (hypertelorism, strabismus, bifid uvula / cleft palate, and craniosynostosis that can involve any sutures)"

The GeneReviews Clinical Characteristics section lists hypertelorism among the craniofacial features of Loeys-Dietz syndrome, of which SMAD2-related disease is subtype 6. The other craniofacial features in this list are not curated as LDS6 phenotypes because no SMAD2-specific report documents them; see notes.

Head and Neck 1

Dysmorphic Facial Features Abnormal facial shape HP:0001999

Show evidence (1 reference)

PMID:30157302 SUPPORT Human Clinical

"Patients 1 and 2 presented with complex CHD, developmental delay, seizures, dysmorphic features, short stature, and poor weight gain."

Lists dysmorphic features in the congenital presentation.

Nervous System 2

Global Developmental Delay HP:0001263

Show evidence (1 reference)

PMID:30157302 SUPPORT Human Clinical

"Patients 1 and 2 presented with complex CHD, developmental delay, seizures, dysmorphic features, short stature, and poor weight gain."

Lists developmental delay among the features of the congenital presentation.

Seizure HP:0001250

Show evidence (1 reference)

PMID:30157302 SUPPORT Human Clinical

"Patients 1 and 2 presented with complex CHD, developmental delay, seizures, dysmorphic features, short stature, and poor weight gain."

Lists seizures among the features of the congenital presentation.

Growth 2

Marfanoid Habitus Disproportionate tall stature HP:0001519

Show evidence (1 reference)

PMID:29967133 SUPPORT Human Clinical

"A p.(Asn318Lys) missense variant was found in a Marfan syndrome (MFS)-like case who presented with aortic root aneurysm and in her affected daughter with marfanoid features and mild aortic dilatation."

Documents marfanoid features in a SMAD2-variant mother-daughter pair. Curated against HP:0001519, whose exact HPO synonyms include "Marfanoid habitus".

Short Stature HP:0004322

Show evidence (1 reference)

PMID:30157302 SUPPORT Human Clinical

"Patients 1 and 2 presented with complex CHD, developmental delay, seizures, dysmorphic features, short stature, and poor weight gain."

Lists short stature and poor weight gain in the congenital presentation.

Other 2

Coronary Artery Dissection HP:0006702

Show evidence (2 references)

PMID:29967133 SUPPORT Human Clinical

"The third missense variant, p.(Asn361Thr), was discovered in a man presenting with coronary artery dissection."

A SMAD2-variant patient whose presenting event was coronary artery dissection.

PMID:31569402 SUPPORT Human Clinical

"To date, 9 (likely) pathogenic variants in SMAD2 have now been described in 15 subjects displaying a broad range of features, including aneurysms, tortuosity of the entire arterial tree, and coronary artery dissections"

Confirms coronary artery dissection as a recurrent feature across all published SMAD2 subjects, not a single-case observation.

Heterotaxy HP:0030853

Show evidence (2 references)

PMID:30157302 SUPPORT Human Clinical

"Patient 3 was a fetus with complex CHD and heterotaxy."

Documents heterotaxy in a SMAD2-variant fetus.

PMID:40028843 SUPPORT In Vitro

"can contribute to left–right asymmetry disorders such as heterotaxy, a prominent CHD phenotype in patients with SMAD2 variants."

Supplies the mechanistic account of the heterotaxy phenotype from the isogenic iPSC models, complementing the clinical observation.

🧬

Genetic Associations

1

SMAD2 (Causative)

Gene: SMAD2 hgnc:6768 relationship_type: CAUSATIVE

Show evidence (5 references)

PMID:26247899 SUPPORT Human Clinical

"SMAD2 is a strong candidate gene for arterial aneurysms and dissections given its role in the TGF-β signaling pathway."

The founding gene-disease assertion, grounded in SMAD2's position in the TGF-beta pathway shared by the other Loeys-Dietz genes.

PMID:29392890 SUPPORT Human Clinical

"In addition to the three previously reported SMAD2 mutations, we identified four new missense mutations, bringing the total to seven missense mutations identified so far"

Quantifies the reported SMAD2 allele set at the time of the mutation update and shows it is dominated by missense variants.

PMID:29392890 SUPPORT Human Clinical

"More recently, TGF-β ligands, TGFB2 and TGFB3, as well as intracellular downstream effectors of the TGF-β pathway, SMAD2 and SMAD3, were shown to be involved in LDS."

Places SMAD2 within the Loeys-Dietz gene set as an intracellular downstream effector of the TGF-beta pathway.

+ 2 more references

💊

Medical Actions

7

Whole-Arterial-Tree Imaging Surveillance

Category: Monitoring Action: supportive care Ontology label: Supportive Care NCIT:C15747

Serial echocardiography of the aortic root and ascending aorta together with magnetic resonance or computed tomography angiography of the entire arterial tree. Root-only surveillance is inadequate in SMAD2-related disease, where tortuosity and aneurysm involve the whole arterial tree and coronary artery dissection has been a presenting event.

Show evidence (2 references)

PMID:20301312 SUPPORT Human Clinical

"Echocardiography to monitor the status of the aortic root and ascending aorta (at least annually) and magnetic resonance angiography or computerized tomography angiography to assess the entire arterial tree"

GeneReviews specifies the whole-arterial-tree surveillance regimen for Loeys-Dietz syndrome, of which SMAD2-related disease is subtype 6.

PMID:31569402 SUPPORT Human Clinical

"To date, 9 (likely) pathogenic variants in SMAD2 have now been described in 15 subjects displaying a broad range of features, including aneurysms, tortuosity of the entire arterial tree, and coronary artery dissections"

The subtype-specific reason whole-tree imaging matters here: SMAD2 patients have whole-tree tortuosity and coronary dissection.

Beta-Adrenergic Blocker Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: beta-adrenergic antagonist NCIT:C29576

Beta-adrenergic receptor blockade to reduce heart rate, blood pressure and pulsatile wall stress, with the aim of slowing aneurysm progression.

Show evidence (1 reference)

PMID:20301312 SUPPORT Human Clinical

"angiotensin receptor blockers, beta-adrenergic receptor blockers, or other medications are used to reduce hemodynamic stress"

GeneReviews documents beta-adrenergic blockade for haemodynamic stress reduction in Loeys-Dietz syndrome.

Angiotensin Receptor Blocker Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: losartan CHEBI:6541

Angiotensin receptor blockers such as losartan reduce haemodynamic stress and are proposed to act additionally on maladaptive TGF-beta signalling. Their mechanistic rationale in SMAD2-related disease is weaker than in other subtypes, because whether the aortic TGF-beta paradox holds when the mutated gene is the SMAD effector itself has never been tested.

Show evidence (1 reference)

PMID:20301312 SUPPORT Human Clinical

"angiotensin receptor blockers, beta-adrenergic receptor blockers, or other medications are used to reduce hemodynamic stress"

GeneReviews documents angiotensin receptor blockade in Loeys-Dietz syndrome.

Prophylactic Aortic Surgery

Action: surgical procedure Ontology label: Surgical Procedure NCIT:C15329

Elective repair of the aortic root or other aneurysmal segment before dissection. Loeys-Dietz aneurysms are amenable to early and aggressive surgical intervention, and because dissection can occur at smaller diameters than in Marfan syndrome the Marfan thresholds are not transferable.

Show evidence (3 references)

PMID:20301312 SUPPORT Human Clinical

"aneurysms are amenable to early and aggressive surgical intervention"

GeneReviews establishes early aggressive surgical repair as the definitive preventive intervention in Loeys-Dietz syndrome.

PMID:20301312 SUPPORT Human Clinical

"aortic dissection can occur at smaller aortic diameters and at younger ages than observed in Marfan syndrome"

Directly substantiates the comparative claim in the description: the Marfan operative diameter thresholds are not transferable because Loeys-Dietz dissection happens at smaller diameters.

PMID:34807423 SUPPORT Human Clinical

"Natural history is significant for aortic dissection at smaller aortic diameter and arterial aneurysms throughout the arterial tree"

Independent statement of the same natural-history point in a review co-authored by Dietz and Loeys, and the reason surveillance and repair must cover the whole arterial tree rather than the root alone.

Activity Restriction and Avoidance of Cardiovascular Stimulants

Category: Counseling / Informational Action: supportive care Ontology label: Supportive Care NCIT:C15747

Avoidance of contact and competitive sports, isometric exercise, and agents that stimulate the cardiovascular system, all of which acutely raise aortic wall stress.

Show evidence (1 reference)

PMID:20301312 SUPPORT Human Clinical

"Agents/circumstances to avoid: Contact sports, competitive sports, and isometric exercise; agents that stimulate the cardiovascular system including routine use of decongestants or triptan medications for the management of migraine headache"

The GeneReviews "Agents/circumstances to avoid" guidance, applicable to SMAD2-related Loeys-Dietz syndrome.

Genetic Counseling and Cascade Testing

Category: Counseling / Informational Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Autosomal dominant transmission carries a 50% recurrence risk for each child. Once the familial SMAD2 variant is known, at-risk relatives can be clarified by targeted testing so that carriers enter cardiovascular surveillance before an aneurysm is symptomatic.

Show evidence (2 references)

PMID:20301312 SUPPORT Human Clinical

"Each child of an individual with LDS has a 50% chance of inheriting the pathogenic variant and the disorder."

States the recurrence risk that genetic counselling communicates.

PMID:20301312 SUPPORT Human Clinical

"Clarify the genetic status of at-risk relatives of any age either by molecular genetic testing"

Establishes cascade testing of at-risk relatives as standard Loeys-Dietz management.

Pregnancy Surveillance and Counseling

Category: Monitoring Action: supportive care Ontology label: Supportive Care NCIT:C15747

Pregnancy and the puerperium carry an increased risk of aortic dissection or rupture and of uterine rupture, and require intensified aortic imaging during pregnancy and in the weeks after delivery.

Show evidence (1 reference)

PMID:20301312 SUPPORT Human Clinical

"Pregnancy and the postpartum period can be dangerous for women with LDS because of increased risk of aortic dissection/rupture and uterine rupture."

Establishes the pregnancy-associated risk that drives intensified surveillance and pre-pregnancy counselling.

📈

Progression

3

Prenatal and neonatal

Age: Prenatal to neonatal

In the congenital-anomaly presentation the disorder is manifest before or at birth, with complex structural heart disease that may be accompanied by a laterality defect and detected in the fetus.

Show evidence (1 reference)

PMID:30157302 SUPPORT Human Clinical

"Patient 3 was a fetus with complex CHD and heterotaxy."

Documents fetal detection of the congenital presentation.

Infancy and childhood

Age: Infancy to childhood

Children with the congenital-anomaly presentation come to attention through complex congenital heart disease together with developmental delay, seizures, dysmorphism and growth failure. Whether these children also need lifelong aortic surveillance is unresolved.

Show evidence (1 reference)

PMID:30157302 SUPPORT Human Clinical

"Patients 1 and 2 presented with complex CHD, developmental delay, seizures, dysmorphic features, short stature, and poor weight gain."

Characterises the childhood presentation of the congenital-anomaly arm.

Adulthood

Age: Adulthood

The vascular presentation is typically recognised in adulthood, when aortic root dilatation, arterial aneurysm, whole-tree tortuosity or a dissection event brings the patient to attention. Coronary artery dissection has been a presenting event.

Show evidence (2 references)

PMID:30157302 SUPPORT Human Clinical

"a late-onset vascular phenotype characterized by arterial aneurysms with connective tissue abnormalities"

Establishes the vascular arm as late-onset relative to the congenital arm.

PMID:29967133 SUPPORT Human Clinical

"The third missense variant, p.(Asn361Thr), was discovered in a man presenting with coronary artery dissection."

An adult presenting event in the vascular arm.

📊

Prevalence

1

Worldwide

Cases In Literature Unknown

Loeys-Dietz syndrome 6 is ultra-rare and no population prevalence has been established; broader Loeys-Dietz prevalence figures must not be reassigned to the SMAD2 subtype. The published denominator for the vascular presentation is small: three families in the discovery report, five further families in the 2019 series, and a literature total of nine likely pathogenic variants in fifteen subjects at the time of the 2019 genotypic review. Separately, thirty participants carrying heterozygous SMAD2 loss-of-function or missense variants were identified in exome sequencing of 11,336 congenital-heart-disease participants, but that ascertainment is by congenital heart disease rather than by the LDS6 phenotype and the two counts should not be added together. The deep-research report additionally offered a figure of roughly 1-5% of all Loeys-Dietz syndrome being SMAD2-related; it was seen and deliberately not curated, because the figure is review-sourced rather than traceable to a denominator-bearing cohort, and a fraction-of-LDS share cannot be converted into an LDS6 population prevalence without an LDS prevalence that is itself unestablished.

Show evidence (2 references)

PMID:31569402 SUPPORT Human Clinical

"To date, 9 (likely) pathogenic variants in SMAD2 have now been described in 15 subjects"

The literature case count for the vascular presentation; no population prevalence is derivable from it.

PMID:40028843 SUPPORT Human Clinical

"Rare SMAD2 variants (minor allele frequency ≤10-5) were identified in exome sequencing of 11 336 participants with CHD."

Gives the denominator for the congenital-heart-disease ascertainment. PARTIAL because a SMAD2 carrier rate within a congenital-heart-disease cohort is not a population prevalence of Loeys-Dietz syndrome 6.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Loeys-Dietz Syndrome 6:

Marfan syndrome MONDO:0007947

Overlapping Features Several SMAD2-variant patients were clinically diagnosed as, or worked up for, Marfan syndrome before molecular testing - they share aortic root aneurysm and a marfanoid habitus. Marfan syndrome is the single most likely misassignment for the vascular presentation of LDS6.

Distinguishing Features

Marfan syndrome is caused by FBN1 variants; LDS6 by SMAD2 variants, so molecular testing is definitive.
Ectopia lentis is a Marfan feature and is not part of the reported SMAD2 phenotype.
Hypertelorism and marked arterial tortuosity point away from Marfan syndrome and towards the Loeys-Dietz spectrum.
Aortic dissection in Loeys-Dietz syndrome can occur at smaller diameters and younger ages than in Marfan syndrome, so the distinction changes the surveillance and surgical thresholds applied.

Show evidence (2 references)

PMID:29967133 SUPPORT Human Clinical

"A p.(Asn318Lys) missense variant was found in a Marfan syndrome (MFS)-like case who presented with aortic root aneurysm and in her affected daughter with marfanoid features and mild aortic dilatation."

Documents a SMAD2-variant patient presenting as Marfan-syndrome-like, establishing the differential.

PMID:20301312 SUPPORT Human Clinical

"aortic dissection can occur at smaller aortic diameters and at younger ages than observed in Marfan syndrome"

The management consequence of resolving this differential correctly.

Loeys-Dietz syndrome (other genetic subtypes) MONDO:0018954

Overlapping Features The TGFBR1-, TGFBR2-, SMAD3-, TGFB2-, TGFB3- and IPO8-related subtypes share the aortic aneurysm, arterial tortuosity, hypertelorism and skeletal findings of LDS6, and are separable only by identifying the causal gene.

Distinguishing Features

Discrimination requires molecular testing; SMAD2 defines subtype 6.
LDS6 has not been placed in the LDS severity ranking because too few patients have been reported, so subtype-specific management cannot yet be inferred from the label (see discussion `lds6_severity_placement`).
The congenital-heart-disease-with-laterality-defect presentation reported for SMAD2 has no close counterpart in the other autosomal dominant subtypes.

Show evidence (2 references)

PMID:20301312 SUPPORT Human Clinical

"The diagnosis of LDS is established in (1) a proband with characteristic clinical findings or (2) by the identification of a heterozygous pathogenic variant in SMAD2, SMAD3, TGFB2, TGFB3, TGFBR1, or TGFBR2"

Establishes that the subtypes are separated by the causal gene rather than by clinical criteria.

PMID:31569402 SUPPORT Human Clinical

"there are not enough data on LDS caused by heterozygous mutations in SMAD2 to place this form (LDS6) in this spectrum"

Explains why identifying the subtype as LDS6 does not yet carry the prognostic weight that identifying LDS1 or LDS2 does.

🧫

Experimental Models

1

Isogenic SMAD2 variant iPSC and iPSC-derived cardiomyocyte panel IPSC_DERIVED_MODEL

CRISPR-edited isogenic induced pluripotent stem cell lines carrying heterozygous or homozygous SMAD2 loss-of-function alleles and the congenital-heart-disease-derived missense alleles p.Arg114Cys and p.Trp274Cys, profiled by bulk RNA sequencing and ATAC chromatin accessibility against published SMAD2/3 ChIP data, with cardiomyocyte differentiation and contractility assessed. This is the only human-relevant functional system reported for SMAD2 variants, and it exists because the Smad2-null mouse dies before the cardiovascular phenotype can be examined (see discussion `smad2_no_viable_animal_model`).

Organism

human NCBITaxon:9606

Cell source

CRISPR/Cas9-edited isogenic induced pluripotent stem cell lines

Culture

Pluripotent stem cell culture with directed cardiomyocyte differentiation

Publication

PMID:40028843

Pathograph links

Disrupted SMAD2-Dependent Transcriptional Programme recapitulates fidelity: moderate Directly measures the chromatin-accessibility and transcriptional consequences of SMAD2 dosage loss in a human isogenic background.

Limitations: Pluripotent stem cells and stem-cell-derived cardiomyocytes, not aortic wall tissue; the transcriptional programme measured is the developmental one, so the model speaks to the congenital arm of the disease and not to the adult aortopathy.

Readouts

Dysregulated SMAD-regulated gene expression

Direction: ALTERED

Interpretation: 385 SMAD-regulated genes, including 10 congenital-heart-disease genes, change expression under SMAD2 haploinsufficiency.

Show evidence (1 reference)

PMID:40028843 SUPPORT In Vitro

"SMAD2 haploinsufficiency altered chromatin accessibility at promoters and dysregulated expression of 385 SMAD regulated genes, including 10 CHD-associated genes."

The quantified transcriptional and chromatin readout of this model.

Show evidence (1 reference)

PMID:40028843 SUPPORT In Vitro

"SMAD2 haploinsufficiency disrupts transcription factor binding and chromatin interactions critical for cardiovascular development."

Supports treating this isogenic system as informative for the transcriptional-programme node.

Impaired Cardiac Morphogenesis and Laterality Specification partially recapitulates fidelity: low Reproduces the cell-autonomous cardiac consequences - impaired cardiomyocyte contractility and reduced activin/nodal pathway gene expression - but not the structural malformation or the laterality defect itself, which require an intact embryo.

Limitations: A dish of cardiomyocytes cannot form a malformed heart or a body axis, so the structural and laterality phenotypes are inferred from gene expression rather than observed. The p.Arg114Cys and p.Trp274Cys alleles were variants of uncertain significance at the time of modelling.

Readouts

Cardiomyocyte contractility

Direction: DECREASED

Interpretation: Contractility of SMAD2-haploinsufficient iPSC-derived cardiomyocytes is impaired relative to isogenic wild type.

Show evidence (1 reference)

PMID:40028843 SUPPORT In Vitro

"SMAD2 haploinsufficiency in induced pluripotent stem cells impairs cardiac contractility"

The functional cardiomyocyte readout of this model.

Show evidence (1 reference)

PMID:40028843 SUPPORT In Vitro

"can contribute to left–right asymmetry disorders such as heterotaxy, a prominent CHD phenotype in patients with SMAD2 variants."

The authors link the model's transcriptional findings to the heterotaxy phenotype. PARTIAL because the model reports gene expression, not an observed laterality defect.

{ }

Source YAML

click to show

name: Loeys-Dietz Syndrome 6
creation_date: "2026-08-18T00:00:00Z"
category: Mendelian
description: >
  Loeys-Dietz syndrome 6 (LDS6) is the SMAD2-related subtype of Loeys-Dietz
  syndrome, an autosomal dominant heritable connective tissue disorder of the
  TGF-beta signalling pathway. SMAD2 encodes a receptor-regulated SMAD that is
  phosphorylated by the type I TGF-beta receptor and, in complex with SMAD4,
  carries the canonical TGF-beta signal into the nucleus. Heterozygous
  loss-of-function SMAD2 variants - nonsense, frameshift, splice and missense
  alleles, with the missense variants reported in the aneurysm literature
  clustering in the MH2 oligomerization domain - cause a wide spectrum of
  aortic and arterial aneurysmal disease with
  connective-tissue findings reminiscent of Marfan and Loeys-Dietz syndromes:
  aortic root dilatation, thoracic and more distal arterial aneurysm and
  dissection, tortuosity of the entire arterial tree, coronary artery
  dissection, hypertelorism and a marfanoid habitus. A second, developmentally
  earlier presentation has been delineated in which SMAD2 variants cause complex
  congenital heart disease with or without laterality defects, together with
  developmental delay, seizures, dysmorphic features and growth failure. Whether
  these are two ends of one spectrum or genotype-separable entities is
  unresolved, and LDS6 has explicitly not been placed in the LDS severity
  ranking because too few patients have been reported. This entry curates the
  SMAD2 subtype specifically; the shared Loeys-Dietz clinical picture and its
  cross-subtype management are curated in the umbrella entry Loeys-Dietz
  Syndrome, and the conserved aortopathy mechanism in the
  `aortopathy_tgfbeta_dysregulation` module.
disease_term:
  preferred_term: Loeys-Dietz syndrome 6
  term:
    id: MONDO:0030500
    label: Loeys-Dietz syndrome 6
synonyms:
- LDS6
- Loeys-Dietz syndrome type 6
- SMAD2-related Loeys-Dietz syndrome
- SMAD2-related aortic and arterial aneurysm syndrome
classifications:
  harrisons_chapter:
  - classification_value: CARDIOVASCULAR
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
  isds_skeletal_category:
  - classification_value: overgrowth_syndromes_with_skeletal_involvement
    notes: >-
      ISDS Nosology and Classification of Genetic Skeletal Disorders, 2019
      revision (Mortier et al., PMID:31633310), Table 1 group 30 "Overgrowth
      (tall stature) syndromes with skeletal involvement"; the entry is listed
      as "Loeys-Dietz syndrome (types 1-6)", which includes the SMAD2 locus.
      Recorded for consistency with the sibling Loeys-Dietz subtype entries;
      the skeletal involvement curated here is the marfanoid habitus.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0030500
      label: Loeys-Dietz syndrome 6
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0030500 is an is_a child of Loeys-Dietz syndrome (MONDO:0018954),
      carries the exact synonym "LDS6" attributed to OMIM:619656, cross-refers
      to OMIM:619656, and asserts SMAD2 (HGNC:6768) as the causal gene via
      RO:0004003. Because the MONDO term carries no definition text, disease
      identity for this entry was anchored on the OMIM:619656 cross-reference
      and the OAK-verified RO:0004003 causal-gene assertion rather than on any
      narrative source - a deliberate precaution given that the Loeys-Dietz
      numbered series is a high Named-Entity-Confusion-risk disease class.
definitions:
- name: Molecular and clinical diagnosis
  definition_type: DIAGNOSTIC_CRITERIA
  description: >-
    The diagnosis of Loeys-Dietz syndrome is established either clinically, in a
    proband with characteristic findings, or by identification of a heterozygous
    pathogenic variant in one of the six autosomal dominant LDS genes; SMAD2 is
    the gene defining subtype 6. In the absence of formal LDS diagnostic
    criteria, a pathogenic variant in an LDS gene together with arterial
    aneurysm or dissection is generally considered sufficient.
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of LDS is established in (1) a proband with characteristic
      clinical findings or (2) by the identification of a heterozygous
      pathogenic variant in SMAD2, SMAD3, TGFB2, TGFB3, TGFBR1, or TGFBR2 or
      biallelic pathogenic variants in IPO8 in a proband with aortic root
      enlargement, type A dissection, other characteristic clinical features of
      LDS, or a family history of an established diagnosis of LDS.
    explanation: >-
      GeneReviews names SMAD2 among the genes whose heterozygous pathogenic
      variants establish a molecular diagnosis of Loeys-Dietz syndrome. Quoted
      in full through the clinical qualifier, because the molecular finding is
      required to occur in a proband with aortic root enlargement, dissection,
      other characteristic features, or a positive family history - it is not
      sufficient on its own.
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is thus suggested that a mutation in any of these six genes in
      combination with the presence of arterial aneurysm or dissection should be
      sufficient for the diagnosis of LDS
    explanation: >-
      States the working sufficiency criterion used in the absence of formal LDS
      diagnostic criteria, which the description paraphrases.
references:
- reference: PMID:20301312
  title: "Loeys-Dietz Syndrome."
  tags:
  - GeneReviews
inheritance:
- name: Autosomal dominant inheritance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    SMAD2-related Loeys-Dietz syndrome is inherited in an autosomal dominant
    manner. Both familial transmission over three generations and de novo
    occurrence in probands with unaffected parents have been documented.
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      LDS caused by a pathogenic variant in SMAD2, SMAD3, TGFB2, TGFB3, TGFBR1,
      or TGFBR2 is inherited in an autosomal dominant manner.
    explanation: >-
      GeneReviews states the autosomal dominant inheritance of SMAD2-related
      Loeys-Dietz syndrome explicitly.
  - reference: PMID:26247899
    reference_title: "SMAD2 Mutations Are Associated with Arterial Aneurysms and Dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Moreover, one variant occurred de novo in a proband with unaffected
      parents.
    explanation: >-
      Documents de novo occurrence of a SMAD2 variant, consistent with dominant
      inheritance and with a proportion of sporadic presentations.
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This variant was also found in his affected daughter with hypertelorism
      and arterial tortuosity, as well as his affected mother.
    explanation: >-
      Three-generation segregation of a SMAD2 missense variant with the
      phenotype, supporting autosomal dominant transmission.
pathophysiology:
- name: Heterozygous SMAD2 Loss-of-Function Variant
  biological_scale: MOLECULAR
  description: >-
    The primary lesion is a heterozygous loss-of-function variant in SMAD2.
    Reported alleles include nonsense, frameshift and splice variants that
    remove one functional copy outright, and missense variants. The missense
    alleles reported in the aneurysm literature cluster in the MH2 domain - the
    conserved surface responsible for oligomerisation of SMAD2 with SMAD4 and
    for subsequent SMAD-dependent transcriptional activation - so an MH2
    missense allele attacks the same step as haploinsufficiency, by disabling
    complex assembly rather than by removing protein. That clustering is not a
    property of SMAD2 missense variants in general: in a large
    congenital-heart-disease cohort the missense variants were instead
    concentrated in exon 4, and the modelled p.Arg114Cys allele lies in the MH1
    domain.
  genes:
  - preferred_term: SMAD2
    term:
      id: hgnc:6768
      label: SMAD2
  evidence:
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Using gene panel sequencing, we identified a SMAD2 nonsense variant and
      four SMAD2 missense variants, all affecting highly conserved amino acids
      in the MH2 domain.
    explanation: >-
      Establishes the variant classes and the MH2-domain localisation of the
      reported missense alleles.
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      No mutational hotspot is observed for SMAD2 and SMAD3 mutations, but the
      majority (100% and 63%) reside in the MH2 domain, a well conserved region
      responsible for the oligomerization of SMAD2 or SMAD3 with SMAD4 and
      subsequent Smad‐dependent activation of downstream transcription
    explanation: >-
      Gives the functional rationale for the MH2 clustering: this domain
      mediates SMAD2-SMAD4 oligomerisation and downstream transcriptional
      activation, so MH2 missense alleles are predicted to be loss-of-function.
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      WES identified pathogenic truncating variants, a splice variant, and a
      predicted deleterious missense variant in SMAD2.
    explanation: >-
      Documents truncating and splice alleles in addition to missense variants,
      supporting a loss-of-function mechanism.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Three loss‐of‐function (underlined) and 11 missense variants have been
      reported in earlier studies; 10 of these missense variants are located at
      the MH2 domain of the SMAD2 gene (P=0.01).
    explanation: >-
      Quantifies the MH2 clustering of the previously reported (aneurysm-era)
      missense alleles - 10 of 11 - and by counting them separately from the
      congenital-heart-disease cohort it also shows the clustering is not a
      property of SMAD2 missense variants in general. PARTIAL because it
      qualifies rather than simply supports the claim.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SMAD2 variants identified in participants with CHD were prevalent in exon
      4 (binomial P=0.05).
    explanation: >-
      The congenital-heart-disease allele distribution differs from the
      aneurysm-literature MH2 clustering, which is why the MH2 statement is
      scoped rather than stated of SMAD2 missense alleles generally.
  downstream:
  - target: Impaired Canonical TGF-beta SMAD2 Signal Transduction
    description: >-
      Loss of one functional SMAD2 allele, or of MH2-mediated complex assembly,
      reduces the capacity of the canonical TGF-beta pathway to transduce signal
      from the activated receptor to the nucleus.
    evidence:
    - reference: PMID:29967133
      reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Taken together, our data suggest that heterozygous loss-of-function
        SMAD2 variants can cause a wide spectrum of autosomal dominant aortic
        and arterial aneurysmal disease
      explanation: >-
        Frames the reported SMAD2 alleles as loss-of-function with respect to
        the canonical pathway they serve.
- name: Impaired Canonical TGF-beta SMAD2 Signal Transduction
  biological_scale: MOLECULAR
  conforms_to: "aortopathy_tgfbeta_dysregulation#TGF-beta Signaling Dysregulation"
  description: >-
    SMAD2 is the receptor-regulated SMAD phosphorylated by the activated type I
    TGF-beta receptor; with SMAD3 it carries the signal to the nucleus in
    complex with SMAD4. Halving functional SMAD2, or disabling its MH2
    oligomerisation surface, degrades this canonical arm. As in every other
    Loeys-Dietz subtype the net tissue-level consequence is not a simple
    reduction: heterozygous loss-of-function alleles in the upstream LDS genes
    are associated with paradoxically increased TGF-beta pathway output in the
    aortic wall, evidenced by raised SMAD phosphorylation and TGF-beta-driven
    gene expression. The node is therefore curated as dysregulation of the
    pathway rather than as loss of pathway activity, matching the module it
    conforms to.
  biological_processes:
  - preferred_term: SMAD protein signal transduction
    term:
      id: GO:0060395
      label: SMAD protein signal transduction
    modifier: ABNORMAL
  - preferred_term: transforming growth factor beta receptor signaling pathway
    term:
      id: GO:0007179
      label: transforming growth factor beta receptor signaling pathway
    modifier: ABNORMAL
  cell_types:
  - preferred_term: vascular smooth muscle cell
    term:
      id: CL:0000359
      label: vascular associated smooth muscle cell
  evidence:
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the canonical pathway, TGFβRI then phosphorylates SMAD2 and SMAD3
      proteins that transmit the TGFβ signal to the nucleus upon association
      with SMAD4.
    explanation: >-
      Establishes the normal position of SMAD2 in canonical TGF-beta signal
      transduction, the step disrupted by pathogenic SMAD2 variants.
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      heterozygous loss-of-function mutations associate with paradoxical
      activation of TGF‐β signaling, which was demonstrated by increased
      phosphorylation of Smad proteins and increased output of TGF‐β‐driven
      genes.
    explanation: >-
      Documents the TGF-beta paradox across the Loeys-Dietz genes, justifying
      curating this node as dysregulation rather than loss of signalling.
      PARTIAL because the cited demonstration is in TGFBR1/2 and ligand-gene
      patients, not in SMAD2-variant aortic tissue, which has not been reported.
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Missense variants in SMAD2, encoding a key transcriptional regulator of
      transforming growth factor beta signalling, were recently reported to
      cause arterial aneurysmal disease.
    explanation: >-
      Identifies SMAD2 as a transcriptional regulator of TGF-beta signalling
      whose disruption causes arterial aneurysmal disease.
  downstream:
  - target: Disrupted SMAD2-Dependent Transcriptional Programme
    description: >-
      A degraded canonical signal reaches the nucleus as an altered
      SMAD2-dependent transcriptional output.
  - target: Aortic Medial Degeneration and Wall Weakening
    description: >-
      Dysregulated TGF-beta signalling in the aortic wall drives medial
      degeneration, the substrate for aneurysm formation.
- name: Disrupted SMAD2-Dependent Transcriptional Programme
  biological_scale: MOLECULAR
  description: >-
    SMAD2 acts in the nucleus as a co-regulator that binds many different
    transcription factors. Isogenic induced pluripotent stem cell models show
    that SMAD2 haploinsufficiency changes chromatin accessibility at promoters,
    dysregulates hundreds of SMAD-regulated genes including known
    congenital-heart-disease genes, and disrupts predicted interactions with
    NANOG, ETS, TEAD3/4, CREB1 and AP1. Loss-of-function and missense alleles
    produce partly distinct accessibility and transcription-factor-binding
    signatures, which is the leading explanation offered for why SMAD2 variants
    give rise to more than one cardiovascular phenotype.
  biological_processes:
  - preferred_term: regulation of transcription by RNA polymerase II
    term:
      id: GO:0006357
      label: regulation of transcription by RNA polymerase II
    modifier: ABNORMAL
  evidence:
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      SMAD2 haploinsufficiency altered chromatin accessibility at promoters and
      dysregulated expression of 385 SMAD regulated genes, including 10
      CHD-associated genes.
    explanation: >-
      Direct measurement of the epigenetic and transcriptional consequence of
      SMAD2 haploinsufficiency in an isogenic human cell model.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      SMAD2 haploinsufficiency disrupts transcription factor binding and
      chromatin interactions critical for cardiovascular development.
    explanation: >-
      States the mechanistic conclusion linking SMAD2 dosage to a disrupted
      transcriptional programme required for cardiovascular development.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Differences between the molecular consequences of loss-of-function and
      missense variants likely contribute to phenotypic heterogeneity.
    explanation: >-
      Offers allele-class-specific transcriptional consequences as an
      explanation for the two SMAD2 phenotypes. PARTIAL because the authors
      frame it as a likely contribution rather than a demonstrated cause, and
      the model is pluripotent stem cells rather than patient aortic tissue.
  downstream:
  - target: Impaired Cardiac Morphogenesis and Laterality Specification
    description: >-
      Among the genes whose expression falls with SMAD2 dosage are NODAL, LEFTY1
      and LEFTY2 - components of the activin/nodal pathway that establishes the
      left-right axis - so the dysregulated transcriptional programme reaches
      cardiac morphogenesis and left-right patterning.
    evidence:
    - reference: PMID:40028843
      reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        RNA levels of NODAL, LEFTY1, and LEFTY2, components of the activin/nodal
        signaling pathway,
      explanation: >-
        Identifies the nodal-pathway genes whose RNA levels the paper reports as
        significantly reduced in SMAD2-haploinsufficient and SMAD2 p.Arg114Cys
        iPSCs, which is the measured link from the transcriptional node to
        left-right patterning. Quoted as the sentence fragment the cached record
        preserves contiguously; the reduction it reports is stated in the
        adjacent clause of the same sentence.
- name: Impaired Cardiac Morphogenesis and Laterality Specification
  biological_scale: TISSUE
  description: >-
    SMAD2 haploinsufficiency lowers expression of NODAL, LEFTY1 and LEFTY2 -
    activin/nodal pathway components that establish the left-right axis - and
    the authors of that work propose the resulting epigenetic and
    transcriptional changes as the mechanism by which SMAD2 haploinsufficiency
    causes congenital heart disease and vascular anomalies. Clinically,
    heterozygous SMAD2 variants are recovered in large congenital-heart-disease
    cohorts and the presentation is complex structural heart disease with or
    without heterotaxy - a developmentally much earlier consequence than the
    aortopathy, and the arm of LDS6 that is least like the other Loeys-Dietz
    subtypes.
  biological_processes:
  - preferred_term: heart development
    term:
      id: GO:0007507
      label: heart development
    modifier: ABNORMAL
  - preferred_term: determination of left/right symmetry
    term:
      id: GO:0007368
      label: determination of left/right symmetry
    modifier: ABNORMAL
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pathogenic variants in SMAD2 have been reported in association with
      arterial aneurysms and dissections and in large cohorts of subjects with
      complex congenital heart disease (CHD).
    explanation: >-
      Establishes the congenital-heart-disease arm of the SMAD2 phenotype
      alongside the vascular arm.
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patient 3 was a fetus with complex CHD and heterotaxy.
    explanation: >-
      Documents the laterality defect that implicates SMAD2 in left-right axis
      specification as well as in cardiac morphogenesis.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      SMAD2 haploinsufficiency in induced pluripotent stem cells impairs cardiac
      contractility and alters epigenetic and transcriptional processes that
      cause dysregulation of genes required for normal heart development
    explanation: >-
      Provides the cellular counterpart of the clinical congenital heart
      disease: SMAD2 dosage loss dysregulates genes required for normal heart
      development and impairs cardiomyocyte contractility.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      can contribute to left–right asymmetry disorders such as heterotaxy, a
      prominent CHD phenotype in patients with SMAD2 variants. We suggest that
      these epigenetic and transcriptional changes provide a mechanism by which
      haploinsufficiency of SMAD2 cause CHD and vascular anomalies.
    explanation: >-
      The authors' own statement of the mechanism connecting SMAD2
      haploinsufficiency to left-right asymmetry disorders and heterotaxy. This
      is the evidence behind the GO:0007368 left/right determination annotation
      on this node - previously the node asserted a NODAL-SMAD2 link with no
      citation at all.
  downstream:
  - target: Complex Congenital Heart Disease
    description: >-
      Disrupted cardiac morphogenesis presents as complex structural congenital
      heart disease.
  - target: Heterotaxy
    description: >-
      Failure of left-right axis specification presents as a laterality defect.
- name: Aortic Medial Degeneration and Wall Weakening
  biological_scale: TISSUE
  conforms_to: "aortopathy_tgfbeta_dysregulation#Aortic Medial Degeneration and Wall Weakening"
  description: >-
    Dysregulated TGF-beta signalling in the aortic media alters the smooth
    muscle cell phenotype and extracellular matrix homeostasis, weakening the
    wall. This is the shared, conserved step of every Loeys-Dietz subtype and of
    heritable thoracic aortic disease generally; it is curated here by
    conformance to the `aortopathy_tgfbeta_dysregulation` module rather than
    re-derived, because no SMAD2-specific aortic histopathology series has been
    published.
  cell_types:
  - preferred_term: aortic smooth muscle cell
    term:
      id: CL:0002539
      label: aortic smooth muscle cell
  biological_processes:
  - preferred_term: extracellular matrix organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      LDS is caused by pathogenic variants in transforming growth factor β
      (TGF-β) signaling pathway-related genes, i.e., TGFBR1, TGFBR2, SMAD2,
      SMAD3, TGFB2, and TGFB3, which alter the physiological development and
      function of the extracellular matrix, leading to cardiovascular and
      multisystem abnormalities
    explanation: >-
      States the shared route from TGF-beta pathway gene disruption - SMAD2
      included - through altered extracellular matrix development and function
      to cardiovascular disease.
  downstream:
  - target: Progressive Aortic and Arterial Dilation
    description: >-
      A weakened media dilates progressively under haemodynamic load.
  - target: Arterial Tortuosity
    description: >-
      Loss of medial structural integrity along the arterial tree manifests as
      the elongation and tortuosity characteristic of Loeys-Dietz syndrome.
- name: Progressive Aortic and Arterial Dilation
  biological_scale: ORGANISM
  conforms_to: "aortopathy_tgfbeta_dysregulation#Progressive Aortic Dilation and Aneurysm"
  description: >-
    Progressive dilation is not confined to the aortic root in SMAD2-related
    disease: reported patients show aortic root aneurysm together with
    tortuosity and aneurysm throughout the arterial tree, including the neck
    vessels and the coronary arteries. The arterial-tree-wide distribution is
    what makes root-only surveillance inadequate.
  evidence:
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To date, 9 (likely) pathogenic variants in SMAD2 have now been described
      in 15 subjects displaying a broad range of features, including aneurysms,
      tortuosity of the entire arterial tree, and coronary artery dissections,
      even in the absence of prominent connective tissue characteristics
    explanation: >-
      Summarises the reported SMAD2 vascular phenotype across all published
      subjects: aneurysm, whole-arterial-tree tortuosity and coronary
      dissection.
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a man clinically diagnosed with Loeys-Dietz syndrome (LDS) that
      presents with aortic root dilatation and marked tortuosity of the neck
      vessels, another missense variant, p.(Ser397Tyr), was identified.
    explanation: >-
      A worked case pairing aortic root dilatation with extra-aortic arterial
      tortuosity in a SMAD2-variant patient given a clinical LDS diagnosis.
  downstream:
  - target: Arterial Dissection and Rupture
    description: >-
      A progressively dilated, structurally weakened artery is at risk of
      dissection and rupture.
  - target: Arterial Aneurysm
    description: >-
      Progressive dilation presents clinically as arterial aneurysm.
  - target: Aortic Root Aneurysm
    description: >-
      Dilation at the aortic root is the segment most often imaged and the usual
      trigger for referral.
- name: Arterial Dissection and Rupture
  biological_scale: ORGANISM
  conforms_to: "aortopathy_tgfbeta_dysregulation#Aortic Dissection and Rupture"
  description: >-
    Dissection is the principal life-threatening endpoint. In SMAD2-related
    disease it has been documented in the aorta and, distinctively, in the
    coronary arteries. As for Loeys-Dietz syndrome generally, dissection can
    occur at smaller aortic diameters and at younger ages than in Marfan
    syndrome, which is why the intervention thresholds used for Marfan syndrome
    are not transferable.
  evidence:
  - reference: PMID:26247899
    reference_title: "SMAD2 Mutations Are Associated with Arterial Aneurysms and Dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings indicate that SMAD2 mutations are associated with arterial
      aneurysms and dissections
    explanation: >-
      The founding report establishing dissection as part of the SMAD2
      phenotype.
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The third missense variant, p.(Asn361Thr), was discovered in a man
      presenting with coronary artery dissection.
    explanation: >-
      Documents coronary artery dissection as a presenting event in a
      SMAD2-variant patient.
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      aortic dissection can occur at smaller aortic diameters and at younger
      ages than observed in Marfan syndrome
    explanation: >-
      The management-critical property of Loeys-Dietz dissection risk that
      governs surveillance and surgical thresholds in this subtype too.
  downstream:
  - target: Aortic and Arterial Dissection
    description: >-
      The dissection event as it presents clinically.
  - target: Coronary Artery Dissection
    description: >-
      Dissection of a coronary artery, a presenting event reported in this
      subtype.
discussions:
- discussion_id: lds6_severity_placement
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Where does SMAD2-related Loeys-Dietz syndrome sit in the LDS severity
    ranking, and can a SMAD2-specific surveillance and surgical-threshold
    protocol be justified?
  attaches_to:
  - pathophysiology#Progressive Aortic and Arterial Dilation
  - pathophysiology#Arterial Dissection and Rupture
  rationale: >-
    The Loeys-Dietz subtypes are informally ordered by severity, and that
    ordering drives imaging intervals and the diameter at which prophylactic
    repair is offered. LDS6 is the one subtype left unplaced: the published
    denominator is a few families and a handful of reported variants, so no
    genotype-specific growth rate, dissection diameter or age-at-event
    distribution exists. Management is therefore extrapolated wholesale from
    Loeys-Dietz syndrome generally. Because the gap is one of cohort size rather
    than of mechanism, it is closable by systematic registry accrual of
    SMAD2-positive probands rather than by new experimental work.
  evidence:
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      there are not enough data on LDS caused by heterozygous mutations in
      SMAD2 to place this form (LDS6) in this spectrum
    explanation: >-
      States the gap explicitly, and is also the source that names the SMAD2
      subtype LDS6.
  proposed_experiments:
  - experiment_id: smad2_registry_stratification
    name: SMAD2-stratified HTAD registry analysis
    description: >-
      Pool SMAD2-positive probands across heritable-thoracic-aortic-disease
      registries and report age at first aneurysm, aortic growth rate, diameter
      at dissection and extra-aortic arterial involvement, so that LDS6 can be
      placed against the other subtypes on the measures that actually govern
      management.
- discussion_id: smad2_two_phenotype_split
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why do heterozygous SMAD2 variants produce two developmentally distinct
    presentations - complex congenital heart disease with laterality defects on
    the one hand, and late-onset arterial aneurysm with connective-tissue
    findings on the other - and does allele class predict which a carrier gets?
  attaches_to:
  - pathophysiology#Disrupted SMAD2-Dependent Transcriptional Programme
  - pathophysiology#Impaired Cardiac Morphogenesis and Laterality Specification
  rationale: >-
    Two phenotypes have been delineated for the same gene at very different
    developmental stages, and the difference is not yet explained. The leading
    hypothesis is allele-class-specific molecular consequence: isogenic
    stem-cell models show that haploinsufficiency and missense alleles produce
    partly distinct chromatin-accessibility and transcription-factor-binding
    signatures. That is a plausible mechanism but not a demonstrated one, and it
    has not been tested against the clinical split - the aneurysm literature is
    dominated by MH2 missense alleles while truncating and splice alleles are
    prominent in the congenital-heart-disease series, but nobody has shown that
    the correlation holds prospectively or that it is causal rather than an
    artefact of how the two literatures ascertained their patients. The question
    is directly actionable: a truncating SMAD2 variant found on a
    congenital-heart-disease panel raises the question of whether that child
    needs lifelong aortic surveillance, and the answer is currently unknown.
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our data suggest two distinct phenotypes associated with pathogenic
      variants in SMAD2: complex CHD with or without laterality defects and
      other congenital anomalies, and a late-onset vascular phenotype
      characterized by arterial aneurysms with connective tissue abnormalities.
    explanation: >-
      The primary statement of the two-phenotype split that this gap is about.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Heterozygous SMAD2 loss-of-function and missense variants are identified
      in patients with congenital heart disease (CHD) or arterial aneurysms.
      Mechanisms that cause distinct cardiovascular phenotypes remain unknown.
    explanation: >-
      Confirms that the mechanism separating the two presentations was still
      unknown as of the most recent functional study.
  proposed_experiments:
  - experiment_id: smad2_allele_class_phenotype
    name: Allele-class-stratified phenotype comparison
    description: >-
      Assemble all reported SMAD2 carriers, classify each allele as truncating,
      splice or MH2 missense, and test whether allele class predicts congenital
      heart disease versus late-onset aortopathy - including systematic aortic
      imaging of SMAD2-positive congenital-heart-disease probands, who have
      generally not been imaged for aneurysm.
- discussion_id: smad2_aortic_tgfb_paradox_untested
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does the paradoxical increase in aortic TGF-beta signalling seen in other
    Loeys-Dietz subtypes also occur in SMAD2-variant aortic tissue, or does
    losing the effector itself break the paradox?
  attaches_to:
  - pathophysiology#Impaired Canonical TGF-beta SMAD2 Signal Transduction
  rationale: >-
    The defining paradox of Loeys-Dietz syndrome is that loss-of-function
    variants in positive components of the TGF-beta pathway are accompanied by
    increased SMAD phosphorylation and increased TGF-beta-driven gene expression
    in the aortic media. That observation has been made for TGFBR1/2, SMAD3,
    TGFB2 and TGFB3 - but not for SMAD2, because no SMAD2-variant aortic tissue
    series has been published. The case matters mechanistically rather than
    merely completing a set: SMAD2 is itself the phosphorylated effector, so a
    readout of increased pSMAD2 cannot mean the same thing when the SMAD2 allele
    is the lesion. Curating this entry's central signalling node as
    dysregulation rather than as loss of signalling is an inference from the
    other subtypes, and is flagged here rather than asserted. A further
    complication is that "increased aortic TGF-beta signalling" is not uniform
    across the aortic wall: in the Tgfbr1 mouse model of Loeys-Dietz syndrome
    the direction of the effect is lineage-specific, with second-heart-field
    derived aortic-root smooth muscle cells showing *defective* ligand-induced
    Smad2/3 activation while the neighbouring cardiac-neural-crest-derived
    cells retain signalling potential and show *increased* Smad2/3
    phosphorylation in vivo - and lineage-restricted deletion of Smad2 in the
    neural-crest compartment alone was protective. So a whole-tissue pSMAD2
    readout can average two opposite lineage-level effects, which is a second
    reason the paradox cannot simply be assumed to carry over to a SMAD2
    lesion, and a reason any SMAD2 aortic-tissue study should be resolved by
    lineage rather than reported as a bulk measurement.
  evidence:
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Aortic wall tissue of TGFBR1 or 2 mutant patients showed increased nuclear
      accumulation of phosphorylated SMAD2 (pSMAD2) and enhanced expression of
      TGF‐β driven gene products such as connective tissue growth factor (CTGF),
      illustrating enhanced TGF‐β signaling.
    explanation: >-
      Establishes the paradox in the subtypes where aortic tissue was available,
      which is the comparison SMAD2 is missing from.
  - reference: PMID:34807423
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Despite the loss of function nature of these mutations, the patient-derived
      aortic tissues show evidence of increased (rather than decreased) TGFβ
      signalling
    explanation: >-
      A recent review states the paradox generically over the whole Loeys-Dietz
      gene set, SMAD2 included, without a SMAD2-specific aortic tissue series
      behind it - which is precisely the unexamined generalisation this gap
      flags rather than a resolution of it.
  - reference: PMID:30614814
    reference_title: "Lineage-specific events underlie aortic root aneurysm pathogenesis in Loeys-Dietz syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Secondary heart field-derived (SHF-derived), but not neighboring cardiac
      neural crest-derived (CNC-derived), VSMCs showed impaired Smad2/3
      activation in response to TGF-β
    explanation: >-
      Shows the defective-signalling half of the lineage split in the Tgfbr1
      Loeys-Dietz mouse model: the aortic-root lineage that actually dilates is
      the one with impaired, not excessive, Smad2/3 activation.
  - reference: PMID:30614814
    reference_title: "Lineage-specific events underlie aortic root aneurysm pathogenesis in Loeys-Dietz syndrome."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The preserved TGF-β signaling potential in CNC-derived VSMCs
      associated, in vivo, with increased Smad2/3 phosphorylation. CNC-, but not
      SHF-specific, deletion of Smad2 preserved aortic wall architecture and
      reduced aortic dilation in this mouse model of LDS
    explanation: >-
      Shows the excessive-signalling half of the same split, and that removing
      Smad2 from that compartment alone is protective - so a bulk aortic pSMAD2
      measurement in a SMAD2 patient would average two opposite lineage effects.
  proposed_experiments:
  - experiment_id: smad2_aortic_media_signalling
    name: SMAD2-variant aortic media signalling readout
    description: >-
      Obtain aortic wall tissue at elective repair from SMAD2-variant patients
      and quantify pSMAD2, pSMAD3, pERK1/2 and CTGF against non-syndromic and
      other-LDS-subtype controls, to establish whether the TGF-beta paradox
      holds when the mutated gene is the effector itself. Resolve the readout by
      smooth-muscle-cell lineage (second heart field versus cardiac neural
      crest) rather than reporting a bulk aortic-wall value, since the two
      compartments move in opposite directions in the Tgfbr1 mouse model.
- discussion_id: smad2_no_viable_animal_model
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Can any existing animal model of SMAD2 loss address the LDS6 aortopathy,
    given that Smad2-null mouse embryos die before the aorta can be assessed?
  attaches_to:
  - pathophysiology#Aortic Medial Degeneration and Wall Weakening
  rationale: >-
    Every other Loeys-Dietz gene has a mouse model whose aorta was examinable
    and which reproduced aspects of the human aortopathy - Smad3 knockouts die
    of ruptured aneurysm, Tgfb2 heterozygotes dilate the aortic root. Smad2 is
    the exception: knockout embryos die before E8.5 from defective egg-cylinder
    elongation and germ-layer formation, so aortic size cannot be measured at
    all. This is a genuine model-fidelity gap rather than an absence of
    evidence - the null model exists and has been characterised, but the
    developmental stage at which it fails is upstream of the tissue in question,
    which is exactly why a SMAD2-specific aortic mechanism has never been
    tested in vivo. The available human-relevant functional models are instead
    iPSC-based and report on cardiac development rather than on the aortic wall.
  evidence:
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Mouse models for SMAD2 have also been developed but Smad2 knockout mice
      embryos die before E8,5, due to defective egg cylinder elongation and germ
      layer formation, which entangles aortic size examination
    explanation: >-
      States the mismatch precisely: the Smad2-null mouse exists but dies before
      the aorta can be assessed, so it cannot serve as an LDS6 aortopathy model.
  - reference: PMID:42380922
    reference_title: "Preclinical modeling of Loeys-Dietz syndrome: insights into mechanisms and therapy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      We critically evaluate the extent to which each model recapitulates the
      diverse LDS phenotypes and discuss their respective advantages and
      limitations.
    explanation: >-
      A 2026 review surveying the in vivo and in vitro models available across
      Loeys-Dietz syndrome and assessing how far each recapitulates the human
      phenotypes. Cited as PARTIAL/OTHER because it is a narrative review of the
      model landscape rather than a SMAD2-specific experimental result; it is
      included because the SMAD2 gap is a claim about that landscape.
  proposed_experiments:
  - experiment_id: smad2_conditional_aortic_model
    name: Conditional and knock-in Smad2 aortic models
    description: >-
      Build smooth-muscle-lineage conditional Smad2 knockouts and knock-in mice
      carrying a human MH2 missense allele, bypassing the peri-implantation
      lethality, and phenotype the aorta for dilation, elastic fibre
      fragmentation and SMAD/ERK signalling.
phenotypes:
- name: Arterial Aneurysm
  category: Cardiovascular
  description: >-
    Aneurysmal dilation of the aorta and other arteries is the defining
    manifestation of the vascular presentation of SMAD2-related disease, and was
    the phenotype through which the gene was discovered.
  phenotype_term:
    preferred_term: Aortic aneurysm
    term:
      id: HP:0004942
      label: Aortic aneurysm
  evidence:
  - reference: PMID:26247899
    reference_title: "SMAD2 Mutations Are Associated with Arterial Aneurysms and Dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report three families with arterial aneurysms and dissections in which
      variants predicted to be pathogenic were identified in SMAD2.
    explanation: >-
      The founding cohort establishing arterial aneurysm as the presenting
      phenotype of SMAD2 variants.
- name: Aortic Root Aneurysm
  category: Cardiovascular
  description: >-
    Dilatation of the aortic root, the site most commonly imaged and the usual
    trigger for referral, reported in both the aneurysm-ascertained and the
    connective-tissue-ascertained SMAD2 patients.
  phenotype_term:
    preferred_term: Aortic root aneurysm
    term:
      id: HP:0002616
      label: Aortic root aneurysm
  evidence:
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The premature stop codon (c.612dup; p.(Asn205*)) was identified in a
      marfanoid patient with aortic root dilatation and in his affected father.
    explanation: >-
      Documents aortic root dilatation in a SMAD2 nonsense-variant family.
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The fourth patient is an adult female with aortic root aneurysm and
      physical features suggestive of a connective tissue disorder.
    explanation: >-
      An independently ascertained SMAD2 patient with aortic root aneurysm and
      connective-tissue features.
- name: Aortic and Arterial Dissection
  category: Cardiovascular
  description: >-
    Dissection is the principal life-threatening event. It is reported in the
    aorta and, distinctively for this subtype, in the coronary arteries.
  phenotype_term:
    preferred_term: Aortic dissection
    term:
      id: HP:0002647
      label: Aortic dissection
  evidence:
  - reference: PMID:26247899
    reference_title: "SMAD2 Mutations Are Associated with Arterial Aneurysms and Dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings indicate that SMAD2 mutations are associated with arterial
      aneurysms and dissections
    explanation: >-
      Establishes dissection as a core feature of the SMAD2 phenotype.
- name: Coronary Artery Dissection
  category: Cardiovascular
  description: >-
    Spontaneous dissection of a coronary artery has been a presenting event in
    SMAD2-variant patients and is recurrent across the reported literature, a
    feature that argues for arterial-tree-wide rather than root-focused
    assessment.
  phenotype_term:
    preferred_term: Coronary artery dissection
    term:
      id: HP:0006702
      label: Coronary artery dissection
  evidence:
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The third missense variant, p.(Asn361Thr), was discovered in a man
      presenting with coronary artery dissection.
    explanation: >-
      A SMAD2-variant patient whose presenting event was coronary artery
      dissection.
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To date, 9 (likely) pathogenic variants in SMAD2 have now been described
      in 15 subjects displaying a broad range of features, including aneurysms,
      tortuosity of the entire arterial tree, and coronary artery dissections
    explanation: >-
      Confirms coronary artery dissection as a recurrent feature across all
      published SMAD2 subjects, not a single-case observation.
- name: Arterial Tortuosity
  category: Cardiovascular
  description: >-
    Tortuosity of the arterial tree, including the neck vessels, is a
    characteristic Loeys-Dietz imaging sign and is reported in SMAD2 patients.
  phenotype_term:
    preferred_term: Arterial tortuosity
    term:
      id: HP:0005116
      label: Arterial tortuosity
  evidence:
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a man clinically diagnosed with Loeys-Dietz syndrome (LDS) that
      presents with aortic root dilatation and marked tortuosity of the neck
      vessels, another missense variant, p.(Ser397Tyr), was identified.
    explanation: >-
      Documents marked arterial tortuosity of the neck vessels in a
      SMAD2-variant patient with a clinical LDS diagnosis.
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To date, 9 (likely) pathogenic variants in SMAD2 have now been described
      in 15 subjects displaying a broad range of features, including aneurysms,
      tortuosity of the entire arterial tree, and coronary artery dissections
    explanation: >-
      Characterises the tortuosity in SMAD2 subjects as involving the entire
      arterial tree rather than one segment. Quoted with its SMAD2 attribution
      intact rather than as a bare fragment.
- name: Hypertelorism
  category: Craniofacial
  description: >-
    Increased interpupillary distance, one of the classic Loeys-Dietz
    craniofacial features, is reported in SMAD2-variant patients.
  phenotype_term:
    preferred_term: Hypertelorism
    term:
      id: HP:0000316
      label: Hypertelorism
  evidence:
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This variant was also found in his affected daughter with hypertelorism
      and arterial tortuosity, as well as his affected mother.
    explanation: >-
      Documents hypertelorism in a SMAD2-variant family member.
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      craniofacial features (hypertelorism, strabismus, bifid uvula / cleft
      palate, and craniosynostosis that can involve any sutures)
    explanation: >-
      The GeneReviews Clinical Characteristics section lists hypertelorism among
      the craniofacial features of Loeys-Dietz syndrome, of which SMAD2-related
      disease is subtype 6. The other craniofacial features in this list are not
      curated as LDS6 phenotypes because no SMAD2-specific report documents
      them; see notes.
- name: Marfanoid Habitus
  category: Musculoskeletal
  description: >-
    A marfanoid body habitus - tall, slim build with disproportionately long
    limbs - is repeatedly noted in SMAD2 patients, several of whom were
    initially given a clinical diagnosis of Marfan syndrome before molecular
    testing.
  phenotype_term:
    preferred_term: Marfanoid habitus
    term:
      id: HP:0001519
      label: Disproportionate tall stature
  evidence:
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A p.(Asn318Lys) missense variant was found in a Marfan syndrome
      (MFS)-like case who presented with aortic root aneurysm and in her
      affected daughter with marfanoid features and mild aortic dilatation.
    explanation: >-
      Documents marfanoid features in a SMAD2-variant mother-daughter pair.
      Curated against HP:0001519, whose exact HPO synonyms include "Marfanoid
      habitus".
- name: Complex Congenital Heart Disease
  category: Cardiovascular
  description: >-
    The second, developmentally earlier presentation of SMAD2 variants is
    complex structural congenital heart disease, recovered both in individual
    probands and in large congenital-heart-disease exome cohorts. This arm is
    what distinguishes LDS6 most sharply from the other Loeys-Dietz subtypes.
  phenotype_term:
    preferred_term: Complex congenital heart disease
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients 1 and 2 presented with complex CHD, developmental delay,
      seizures, dysmorphic features, short stature, and poor weight gain.
    explanation: >-
      Documents complex congenital heart disease as the presenting feature in
      two SMAD2-variant probands.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thirty participants with CHD had heterozygous loss-of-function or missense
      SMAD2 variants.
    explanation: >-
      Cohort-scale confirmation from exome sequencing of 11,336
      congenital-heart-disease participants.
- name: Heterotaxy
  category: Cardiovascular
  description: >-
    A laterality defect accompanying complex congenital heart disease. The
    isogenic stem-cell work proposes reduced activin/nodal pathway expression
    under SMAD2 haploinsufficiency as the route to this phenotype.
  phenotype_term:
    preferred_term: Heterotaxy
    term:
      id: HP:0030853
      label: Heterotaxy
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patient 3 was a fetus with complex CHD and heterotaxy.
    explanation: >-
      Documents heterotaxy in a SMAD2-variant fetus.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      can contribute to left–right asymmetry disorders such as heterotaxy, a
      prominent CHD phenotype in patients with SMAD2 variants.
    explanation: >-
      Supplies the mechanistic account of the heterotaxy phenotype from the
      isogenic iPSC models, complementing the clinical observation.
- name: Global Developmental Delay
  category: Neurological
  description: >-
    Developmental delay accompanies the congenital-heart-disease presentation of
    SMAD2 variants. It is not a feature of the late-onset vascular presentation.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients 1 and 2 presented with complex CHD, developmental delay,
      seizures, dysmorphic features, short stature, and poor weight gain.
    explanation: >-
      Lists developmental delay among the features of the congenital
      presentation.
- name: Seizure
  category: Neurological
  description: >-
    Seizures were reported in both probands of the congenital-anomaly
    presentation; no seizure phenotype has been described in the vascular
    presentation.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients 1 and 2 presented with complex CHD, developmental delay,
      seizures, dysmorphic features, short stature, and poor weight gain.
    explanation: >-
      Lists seizures among the features of the congenital presentation.
- name: Short Stature
  category: Growth
  description: >-
    Short stature with poor weight gain in the congenital-anomaly presentation -
    the opposite direction of growth from the marfanoid habitus seen in the
    vascular presentation, which is part of why the two arms are curated
    separately.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients 1 and 2 presented with complex CHD, developmental delay,
      seizures, dysmorphic features, short stature, and poor weight gain.
    explanation: >-
      Lists short stature and poor weight gain in the congenital presentation.
- name: Dysmorphic Facial Features
  category: Craniofacial
  description: >-
    Non-specific facial dysmorphism accompanying the congenital-anomaly
    presentation.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients 1 and 2 presented with complex CHD, developmental delay,
      seizures, dysmorphic features, short stature, and poor weight gain.
    explanation: >-
      Lists dysmorphic features in the congenital presentation.
genetic:
- name: SMAD2
  gene_term:
    preferred_term: SMAD2
    term:
      id: hgnc:6768
      label: SMAD2
  association: Causative
  relationship_type: CAUSATIVE
  notes: >-
    SMAD2 (HGNC:6768, chromosome 18q) encodes a receptor-regulated SMAD with an
    N-terminal MH1 and a C-terminal MH2 domain. Heterozygous SMAD2 variants
    define Loeys-Dietz syndrome 6. The reported alleles fall into two groups.
    The aneurysm literature is dominated by missense variants, all of which so
    far lie in the MH2 domain that mediates oligomerisation with SMAD4 and
    downstream transcriptional activation, plus one nonsense allele
    (c.612dup; p.Asn205*). The congenital-heart-disease literature reports
    truncating and splice alleles in addition to missense variants. Whether that
    difference in allele spectrum explains the two clinical presentations is
    open (see discussion `smad2_two_phenotype_split`). Gene identity for this
    entry was established from the MONDO:0030500 RO:0004003 causal-gene
    assertion verified with OAK, together with the OMIM:619656 cross-reference,
    rather than from any narrative source.
  evidence:
  - reference: PMID:26247899
    reference_title: "SMAD2 Mutations Are Associated with Arterial Aneurysms and Dissections."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SMAD2 is a strong candidate gene for arterial aneurysms and dissections
      given its role in the TGF-β signaling pathway.
    explanation: >-
      The founding gene-disease assertion, grounded in SMAD2's position in the
      TGF-beta pathway shared by the other Loeys-Dietz genes.
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In addition to the three previously reported SMAD2 mutations, we
      identified four new missense mutations, bringing the total to seven
      missense mutations identified so far
    explanation: >-
      Quantifies the reported SMAD2 allele set at the time of the mutation
      update and shows it is dominated by missense variants.
  - reference: PMID:29392890
    reference_title: "A mutation update on the LDS-associated genes TGFB2/3 and SMAD2/3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      More recently, TGF-β ligands, TGFB2 and TGFB3, as well as intracellular
      downstream effectors of the TGF-β pathway, SMAD2 and SMAD3, were shown to
      be involved in LDS.
    explanation: >-
      Places SMAD2 within the Loeys-Dietz gene set as an intracellular
      downstream effector of the TGF-beta pathway.
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Heterozygous mutations in 6 genes (TGFBR1/2, TGFB2/3, SMAD2/3), encoding
      components of the TGF-β pathway, cause LDS.
    explanation: >-
      Confirms SMAD2 among the six Loeys-Dietz genes; this is also the source
      that assigns the SMAD2 subtype the designation LDS6.
  - reference: ORPHA:60030
    reference_title: "Loeys-Dietz syndrome"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SMAD2 | SMAD family member 2 | hgnc:6768 | Disease-causing germline mutation(s) in"
    explanation: >-
      Orphanet independently curates SMAD2 as a disease-causing gene for
      Loeys-Dietz syndrome, and supplies the HGNC identifier used here.
differential_diagnoses:
- name: Marfan syndrome
  disease_term:
    preferred_term: Marfan syndrome
    term:
      id: MONDO:0007947
      label: Marfan syndrome
  description: >-
    Several SMAD2-variant patients were clinically diagnosed as, or worked up
    for, Marfan syndrome before molecular testing - they share aortic root
    aneurysm and a marfanoid habitus. Marfan syndrome is the single most likely
    misassignment for the vascular presentation of LDS6.
  distinguishing_features:
  - >-
    Marfan syndrome is caused by FBN1 variants; LDS6 by SMAD2 variants, so
    molecular testing is definitive.
  - >-
    Ectopia lentis is a Marfan feature and is not part of the reported SMAD2
    phenotype.
  - >-
    Hypertelorism and marked arterial tortuosity point away from Marfan syndrome
    and towards the Loeys-Dietz spectrum.
  - >-
    Aortic dissection in Loeys-Dietz syndrome can occur at smaller diameters and
    younger ages than in Marfan syndrome, so the distinction changes the
    surveillance and surgical thresholds applied.
  evidence:
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A p.(Asn318Lys) missense variant was found in a Marfan syndrome
      (MFS)-like case who presented with aortic root aneurysm and in her
      affected daughter with marfanoid features and mild aortic dilatation.
    explanation: >-
      Documents a SMAD2-variant patient presenting as Marfan-syndrome-like,
      establishing the differential.
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      aortic dissection can occur at smaller aortic diameters and at younger
      ages than observed in Marfan syndrome
    explanation: >-
      The management consequence of resolving this differential correctly.
- name: Loeys-Dietz syndrome (other genetic subtypes)
  disease_term:
    preferred_term: Loeys-Dietz syndrome
    term:
      id: MONDO:0018954
      label: Loeys-Dietz syndrome
  description: >-
    The TGFBR1-, TGFBR2-, SMAD3-, TGFB2-, TGFB3- and IPO8-related subtypes share
    the aortic aneurysm, arterial tortuosity, hypertelorism and skeletal
    findings of LDS6, and are separable only by identifying the causal gene.
  distinguishing_features:
  - >-
    Discrimination requires molecular testing; SMAD2 defines subtype 6.
  - >-
    LDS6 has not been placed in the LDS severity ranking because too few
    patients have been reported, so subtype-specific management cannot yet be
    inferred from the label (see discussion `lds6_severity_placement`).
  - >-
    The congenital-heart-disease-with-laterality-defect presentation reported for
    SMAD2 has no close counterpart in the other autosomal dominant subtypes.
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of LDS is established in (1) a proband with characteristic
      clinical findings or (2) by the identification of a heterozygous
      pathogenic variant in SMAD2, SMAD3, TGFB2, TGFB3, TGFBR1, or TGFBR2
    explanation: >-
      Establishes that the subtypes are separated by the causal gene rather than
      by clinical criteria.
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      there are not enough data on LDS caused by heterozygous mutations in
      SMAD2 to place this form (LDS6) in this spectrum
    explanation: >-
      Explains why identifying the subtype as LDS6 does not yet carry the
      prognostic weight that identifying LDS1 or LDS2 does.
treatments:
- name: Whole-Arterial-Tree Imaging Surveillance
  description: >-
    Serial echocardiography of the aortic root and ascending aorta together with
    magnetic resonance or computed tomography angiography of the entire arterial
    tree. Root-only surveillance is inadequate in SMAD2-related disease, where
    tortuosity and aneurysm involve the whole arterial tree and coronary artery
    dissection has been a presenting event.
  action_category: MONITORING
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Echocardiography to monitor the status of the aortic root and ascending
      aorta (at least annually) and magnetic resonance angiography or
      computerized tomography angiography to assess the entire arterial tree
    explanation: >-
      GeneReviews specifies the whole-arterial-tree surveillance regimen for
      Loeys-Dietz syndrome, of which SMAD2-related disease is subtype 6.
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To date, 9 (likely) pathogenic variants in SMAD2 have now been described
      in 15 subjects displaying a broad range of features, including aneurysms,
      tortuosity of the entire arterial tree, and coronary artery dissections
    explanation: >-
      The subtype-specific reason whole-tree imaging matters here: SMAD2
      patients have whole-tree tortuosity and coronary dissection.
  notes: >-
    Imaging intervals are extrapolated from Loeys-Dietz syndrome generally. No
    SMAD2-specific surveillance interval has been validated; see discussion
    `lds6_severity_placement`.
- name: Beta-Adrenergic Blocker Therapy
  description: >-
    Beta-adrenergic receptor blockade to reduce heart rate, blood pressure and
    pulsatile wall stress, with the aim of slowing aneurysm progression.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: beta-adrenergic antagonist
      term:
        id: NCIT:C29576
        label: Beta-Adrenergic Antagonist
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      angiotensin receptor blockers, beta-adrenergic receptor blockers, or
      other medications are used to reduce hemodynamic stress
    explanation: >-
      GeneReviews documents beta-adrenergic blockade for haemodynamic stress
      reduction in Loeys-Dietz syndrome.
  notes: >-
    No randomised trial has demonstrated reduced aortic growth or dissection
    specifically in SMAD2-related disease; this is a syndrome-level
    recommendation.
- name: Angiotensin Receptor Blocker Therapy
  description: >-
    Angiotensin receptor blockers such as losartan reduce haemodynamic stress
    and are proposed to act additionally on maladaptive TGF-beta signalling.
    Their mechanistic rationale in SMAD2-related disease is weaker than in other
    subtypes, because whether the aortic TGF-beta paradox holds when the mutated
    gene is the SMAD effector itself has never been tested.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: losartan
      term:
        id: CHEBI:6541
        label: losartan
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      angiotensin receptor blockers, beta-adrenergic receptor blockers, or
      other medications are used to reduce hemodynamic stress
    explanation: >-
      GeneReviews documents angiotensin receptor blockade in Loeys-Dietz
      syndrome.
  notes: >-
    Angiotensin receptor blockers are contraindicated in pregnancy. See
    discussion `smad2_aortic_tgfb_paradox_untested` for why the pathway-directed
    rationale is less secure in this subtype than in the others.
- name: Prophylactic Aortic Surgery
  description: >-
    Elective repair of the aortic root or other aneurysmal segment before
    dissection. Loeys-Dietz aneurysms are amenable to early and aggressive
    surgical intervention, and because dissection can occur at smaller diameters
    than in Marfan syndrome the Marfan thresholds are not transferable.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      aneurysms are amenable to early and aggressive surgical intervention
    explanation: >-
      GeneReviews establishes early aggressive surgical repair as the definitive
      preventive intervention in Loeys-Dietz syndrome.
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      aortic dissection can occur at smaller aortic diameters and at younger
      ages than observed in Marfan syndrome
    explanation: >-
      Directly substantiates the comparative claim in the description: the
      Marfan operative diameter thresholds are not transferable because
      Loeys-Dietz dissection happens at smaller diameters.
  - reference: PMID:34807423
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Natural history is significant for aortic dissection at smaller aortic
      diameter and arterial aneurysms throughout the arterial tree
    explanation: >-
      Independent statement of the same natural-history point in a review
      co-authored by Dietz and Loeys, and the reason surveillance and repair
      must cover the whole arterial tree rather than the root alone.
  notes: >-
    No SMAD2-specific operative diameter threshold has been published; decisions
    are individualised on absolute diameter, growth rate, body size, family
    history and pregnancy plans.
- name: Activity Restriction and Avoidance of Cardiovascular Stimulants
  description: >-
    Avoidance of contact and competitive sports, isometric exercise, and agents
    that stimulate the cardiovascular system, all of which acutely raise aortic
    wall stress.
  action_category: COUNSELING_INFORMATIONAL
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Agents/circumstances to avoid: Contact sports, competitive sports, and
      isometric exercise; agents that stimulate the cardiovascular system
      including routine use of decongestants or triptan medications for the
      management of migraine headache
    explanation: >-
      The GeneReviews "Agents/circumstances to avoid" guidance, applicable to
      SMAD2-related Loeys-Dietz syndrome.
- name: Genetic Counseling and Cascade Testing
  description: >-
    Autosomal dominant transmission carries a 50% recurrence risk for each
    child. Once the familial SMAD2 variant is known, at-risk relatives can be
    clarified by targeted testing so that carriers enter cardiovascular
    surveillance before an aneurysm is symptomatic.
  action_category: COUNSELING_INFORMATIONAL
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each child of an individual with LDS has a 50% chance of inheriting the
      pathogenic variant and the disorder.
    explanation: >-
      States the recurrence risk that genetic counselling communicates.
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Clarify the genetic status of at-risk relatives of any age either by
      molecular genetic testing
    explanation: >-
      Establishes cascade testing of at-risk relatives as standard Loeys-Dietz
      management.
- name: Pregnancy Surveillance and Counseling
  description: >-
    Pregnancy and the puerperium carry an increased risk of aortic dissection or
    rupture and of uterine rupture, and require intensified aortic imaging
    during pregnancy and in the weeks after delivery.
  action_category: MONITORING
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301312
    reference_title: "Loeys-Dietz Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pregnancy and the postpartum period can be dangerous for women with LDS
      because of increased risk of aortic dissection/rupture and uterine
      rupture.
    explanation: >-
      Establishes the pregnancy-associated risk that drives intensified
      surveillance and pre-pregnancy counselling.
progression:
- phase: Prenatal and neonatal
  age_range: Prenatal to neonatal
  notes: >-
    In the congenital-anomaly presentation the disorder is manifest before or at
    birth, with complex structural heart disease that may be accompanied by a
    laterality defect and detected in the fetus.
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patient 3 was a fetus with complex CHD and heterotaxy.
    explanation: >-
      Documents fetal detection of the congenital presentation.
- phase: Infancy and childhood
  age_range: Infancy to childhood
  notes: >-
    Children with the congenital-anomaly presentation come to attention through
    complex congenital heart disease together with developmental delay,
    seizures, dysmorphism and growth failure. Whether these children also need
    lifelong aortic surveillance is unresolved.
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients 1 and 2 presented with complex CHD, developmental delay,
      seizures, dysmorphic features, short stature, and poor weight gain.
    explanation: >-
      Characterises the childhood presentation of the congenital-anomaly arm.
- phase: Adulthood
  age_range: Adulthood
  notes: >-
    The vascular presentation is typically recognised in adulthood, when aortic
    root dilatation, arterial aneurysm, whole-tree tortuosity or a dissection
    event brings the patient to attention. Coronary artery dissection has been a
    presenting event.
  evidence:
  - reference: PMID:30157302
    reference_title: "Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a late-onset vascular phenotype characterized by arterial aneurysms with
      connective tissue abnormalities
    explanation: >-
      Establishes the vascular arm as late-onset relative to the congenital arm.
  - reference: PMID:29967133
    reference_title: "Novel pathogenic SMAD2 variants in five families with arterial aneurysm and dissection: further delineation of the phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The third missense variant, p.(Asn361Thr), was discovered in a man
      presenting with coronary artery dissection.
    explanation: >-
      An adult presenting event in the vascular arm.
experimental_models:
- name: Isogenic SMAD2 variant iPSC and iPSC-derived cardiomyocyte panel
  description: >-
    CRISPR-edited isogenic induced pluripotent stem cell lines carrying
    heterozygous or homozygous SMAD2 loss-of-function alleles and the
    congenital-heart-disease-derived missense alleles p.Arg114Cys and
    p.Trp274Cys, profiled by bulk RNA sequencing and ATAC chromatin
    accessibility against published SMAD2/3 ChIP data, with cardiomyocyte
    differentiation and contractility assessed. This is the only human-relevant
    functional system reported for SMAD2 variants, and it exists because the
    Smad2-null mouse dies before the cardiovascular phenotype can be examined
    (see discussion `smad2_no_viable_animal_model`).
  experimental_model_type: IPSC_DERIVED_MODEL
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_source: CRISPR/Cas9-edited isogenic induced pluripotent stem cell lines
  culture_system: Pluripotent stem cell culture with directed cardiomyocyte differentiation
  conditions:
  - SMAD2 heterozygous loss of function
  - SMAD2 p.Arg114Cys missense
  - SMAD2 p.Trp274Cys missense
  - isogenic wild-type control
  publication: PMID:40028843
  modeled_mechanisms:
  - target: Disrupted SMAD2-Dependent Transcriptional Programme
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Directly measures the chromatin-accessibility and transcriptional
      consequences of SMAD2 dosage loss in a human isogenic background.
    limitations: >-
      Pluripotent stem cells and stem-cell-derived cardiomyocytes, not aortic
      wall tissue; the transcriptional programme measured is the developmental
      one, so the model speaks to the congenital arm of the disease and not to
      the adult aortopathy.
    readouts:
    - name: Dysregulated SMAD-regulated gene expression
      target: Disrupted SMAD2-Dependent Transcriptional Programme
      direction: ALTERED
      interpretation: >-
        385 SMAD-regulated genes, including 10 congenital-heart-disease genes,
        change expression under SMAD2 haploinsufficiency.
      evidence:
      - reference: PMID:40028843
        reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          SMAD2 haploinsufficiency altered chromatin accessibility at promoters
          and dysregulated expression of 385 SMAD regulated genes, including 10
          CHD-associated genes.
        explanation: >-
          The quantified transcriptional and chromatin readout of this model.
    evidence:
    - reference: PMID:40028843
      reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        SMAD2 haploinsufficiency disrupts transcription factor binding and
        chromatin interactions critical for cardiovascular development.
      explanation: >-
        Supports treating this isogenic system as informative for the
        transcriptional-programme node.
  - target: Impaired Cardiac Morphogenesis and Laterality Specification
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      Reproduces the cell-autonomous cardiac consequences - impaired
      cardiomyocyte contractility and reduced activin/nodal pathway gene
      expression - but not the structural malformation or the laterality defect
      itself, which require an intact embryo.
    limitations: >-
      A dish of cardiomyocytes cannot form a malformed heart or a body axis, so
      the structural and laterality phenotypes are inferred from gene expression
      rather than observed. The p.Arg114Cys and p.Trp274Cys alleles were
      variants of uncertain significance at the time of modelling.
    readouts:
    - name: Cardiomyocyte contractility
      target: Impaired Cardiac Morphogenesis and Laterality Specification
      direction: DECREASED
      interpretation: >-
        Contractility of SMAD2-haploinsufficient iPSC-derived cardiomyocytes is
        impaired relative to isogenic wild type.
      evidence:
      - reference: PMID:40028843
        reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          SMAD2 haploinsufficiency in induced pluripotent stem cells impairs
          cardiac contractility
        explanation: >-
          The functional cardiomyocyte readout of this model.
    evidence:
    - reference: PMID:40028843
      reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        can contribute to left–right asymmetry disorders such as heterotaxy, a
        prominent CHD phenotype in patients with SMAD2 variants.
      explanation: >-
        The authors link the model's transcriptional findings to the heterotaxy
        phenotype. PARTIAL because the model reports gene expression, not an
        observed laterality defect.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: UNKNOWN
  notes: >-
    Loeys-Dietz syndrome 6 is ultra-rare and no population prevalence has been
    established; broader Loeys-Dietz prevalence figures must not be reassigned
    to the SMAD2 subtype. The published denominator for the vascular
    presentation is small: three families in the discovery report, five further
    families in the 2019 series, and a literature total of nine likely
    pathogenic variants in fifteen subjects at the time of the 2019 genotypic
    review. Separately, thirty participants carrying heterozygous SMAD2
    loss-of-function or missense variants were identified in exome sequencing of
    11,336 congenital-heart-disease participants, but that ascertainment is by
    congenital heart disease rather than by the LDS6 phenotype and the two
    counts should not be added together. The deep-research report additionally
    offered a figure of roughly 1-5% of all Loeys-Dietz syndrome being
    SMAD2-related; it was seen and deliberately not curated, because the figure
    is review-sourced rather than traceable to a denominator-bearing cohort, and
    a fraction-of-LDS share cannot be converted into an LDS6 population
    prevalence without an LDS prevalence that is itself unestablished.
  evidence:
  - reference: PMID:31569402
    reference_title: "Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To date, 9 (likely) pathogenic variants in SMAD2 have now been described
      in 15 subjects
    explanation: >-
      The literature case count for the vascular presentation; no population
      prevalence is derivable from it.
  - reference: PMID:40028843
    reference_title: "Modeling SMAD2 Mutations in Induced Pluripotent Stem Cells Provides Insights Into Cardiovascular Disease Pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Rare SMAD2 variants (minor allele frequency ≤10-5) were identified in
      exome sequencing of 11 336 participants with CHD.
    explanation: >-
      Gives the denominator for the congenital-heart-disease ascertainment.
      PARTIAL because a SMAD2 carrier rate within a congenital-heart-disease
      cohort is not a population prevalence of Loeys-Dietz syndrome 6.
datasets: []

📚

References & Deep Research

References

1

PMID:20301312

Loeys-Dietz Syndrome.

No top-level findings curated for this source.

Deep Research

1

Falcon ▸

Loeys–Dietz Syndrome 6 (SMAD2-Related) — Disease Characteristics Research Report

Edison Scientific Literature 25 citations 2026-08-18T09:47:34.261646

Loeys–Dietz Syndrome 6 (SMAD2-Related) — Disease Characteristics Research Report

Scope and evidence grading. Loeys–Dietz syndrome type 6 (LDS6) is exceptionally rare, and “LDS6” is not used consistently. This report therefore distinguishes: [Direct LDS6] evidence involving germline SMAD2 variants; [Pan-LDS] evidence from genetically heterogeneous Loeys–Dietz syndrome; and [HTAD/model] evidence extrapolated from hereditary thoracic aortic disease or other TGF-β-pathway LDS models. Quantitative phenotype frequencies, penetrance, treatment response, and prognosis specific to LDS6 are largely unavailable.

A compact knowledge-base summary follows.

Domain	Best-supported LDS6-specific statement	Suggested ontology/identifier	Evidence scope/caveat
Disease identity	Loeys-Dietz syndrome type 6 is the rarely used designation for monoallelic SMAD2-related syndromic aortopathy within the broader Loeys-Dietz syndrome spectrum; some authors note the subtype label is inconsistently used. (asta2023geneticbasisnew pages 3-5, ebeling2024differentiationpurificationand pages 9-11, OpenTargets Search: Loeys-Dietz syndrome-SMAD2)	SMAD2 (HGNC approved symbol); broader disease MONDO:0018954 Loeys-Dietz syndrome; MeSH D055947	Direct for SMAD2 as LDS6; broader MONDO/MeSH refer to pan-LDS, not subtype-specific LDS6.
Core molecular cause	LDS6 is caused by heterozygous pathogenic variants in SMAD2, a receptor-regulated SMAD in canonical TGF-β signaling; Open Targets links SMAD2 to Loeys-Dietz syndrome with supportive genetic literature and monoallelic inheritance evidence. (OpenTargets Search: Loeys-Dietz syndrome-SMAD2, asta2023geneticbasisnew pages 3-5)	NCBI/Ensembl target: SMAD2 / ENSG00000175387; pathway TGF-β signaling	Direct association supported; variant-level LDS6 details remain sparse in retrieved sources.
Inheritance	Inheritance is autosomal dominant / monoallelic; across LDS, ~25% have an affected parent and many cases are de novo, with familial cases often milder. (OpenTargets Search: Loeys-Dietz syndrome-SMAD2, ebeling2024differentiationpurificationand pages 9-11, zaza2022cleftpalateand pages 2-5)	HPO inheritance term analogous to Autosomal dominant inheritance; MONDO broader LDS	Monoallelic inheritance supported for SMAD2/LDS association; de novo/familial proportions are from pan-LDS, not LDS6-only cohorts.
Hallmark vascular phenotype	The best-supported disease-defining manifestation for LDS6 is thoracic aortic aneurysm/dissection predisposition within a syndromic aortopathy phenotype. SMAD2 mutations were linked to a new LDS form after study of families with aneurysm/dissection and increased aortic-wall SMAD2 expression. (asta2023geneticbasisnew pages 3-5)	HPO: Aortic root dilatation, Thoracic aortic aneurysm, Aortic dissection, Arterial tortuosity	Direct but limited foundational LDS6 evidence; frequencies/age-specific penetrance not available in retrieved subtype-specific data.
Extra-aortic syndromic features	LDS6 is expected to overlap with classic LDS features such as hypertelorism, bifid uvula/cleft palate, skeletal/connective-tissue findings, and mitral valve disease. (asta2023geneticbasisnew pages 3-5, zaza2022cleftpalateand pages 2-5)	HPO: Hypertelorism, Bifid uvula, Cleft palate, Arachnodactyly, Joint hypermobility/stiffness, Mitral valve disease	Mostly extrapolated from pan-LDS and TGFB3/TGFBR2 examples; LDS6-specific frequencies unavailable.
Pathway mechanism	SMAD2 acts downstream of TGFBR1/2; after receptor activation, phosphorylated SMAD2/3 complexes regulate transcription. LDS/related aortopathy literature supports paradoxical tissue-level increased pSMAD2/3 despite impaired signaling in some cell contexts. (liu2025anoveltgfbr2 pages 7-8, asta2023geneticbasisnew pages 3-5, macfarlane2019lineagespecificeventsunderlie pages 2-5, NCT05472519 chunk 1)	GO: TGF-beta receptor signaling pathway, SMAD protein signal transduction, regulation of transcription by RNA polymerase II	Mostly pathway-level and non-LDS6-specific mechanistic inference; direct SMAD2-LDS6 functional assays were not retrieved.
Cellular context	Aortic disease mechanisms center on vascular smooth muscle cells (VSMCs) and likely endothelial/fibroblast contributions; lineage-specific LDS mouse work shows defective TGF-β/Smad induction in a susceptible VSMC lineage can localize root aneurysm. (macfarlane2019lineagespecificeventsunderlie pages 2-5, ganizada2024unveilingcellularand pages 14-15)	CL: vascular smooth muscle cell, endothelial cell, fibroblast	Strong for LDS pathway biology, but model used Tgfbr1-LDS rather than SMAD2-LDS6.
Anatomy affected	Primary site is the aortic root/ascending thoracic aorta; broader LDS may also involve aortic arch, descending aorta, branch vessels, and craniofacial/connective tissues. (macfarlane2019lineagespecificeventsunderlie pages 2-5, spaziani2024hereditarythoracicaortic pages 7-9, zaza2022cleftpalateand pages 2-5)	UBERON: aortic root, ascending aorta, aortic arch, descending aorta, palate, arterial vasculature	LDS6-specific anatomic distribution unresolved; broader LDS/HTAD imaging evidence used.
Diagnostics	Recommended workup is syndrome recognition plus genetic testing and multimodality aortic imaging. In HTAD/LDS, testing often uses multigene panels/WES, with cascade testing of first-degree relatives when positive; echo is first-line, CT/CMR define full aortic extent. (asta2023geneticbasisnew pages 5-8, spaziani2024hereditarythoracicaortic pages 7-9, zaza2022cleftpalateand pages 2-5)	Diagnostic resources: multigene HTAD/LDS panel, WES; imaging TTE, CT/CCTA, CMR/MRA	This is current practice extrapolated from pan-LDS/HTAD; no LDS6-specific diagnostic criteria were retrieved.
Differential diagnosis	Important differentials include Marfan syndrome, other Loeys-Dietz subtypes, vascular Ehlers-Danlos syndrome, and non-syndromic/familial HTAD. (asta2023geneticbasisnew pages 5-8, ebeling2024differentiationpurificationand pages 9-11, NCT01322165 chunk 1)	MONDO/HPO differential set; genes commonly contrasted: FBN1, TGFBR1, TGFBR2, SMAD3, TGFB2, TGFB3, COL3A1	Extrapolated from broader inherited aortopathy literature.
Management	No randomized LDS-specific medical therapy trials were identified; current guidance is blood-pressure control, avoidance of stimulants/vasoconstrictors, exercise restriction, and multidisciplinary surveillance. Use of ARBs (especially losartan), beta-blockers, or ACE inhibitors is commonly extrapolated from Marfan/LDS management. (spaziani2024hereditarythoracicaortic pages 7-9, spaziani2024hereditarythoracicaortic pages 9-10, zaza2022cleftpalateand pages 2-5)	NCIT-style interventions: Losartan, Angiotensin receptor blocker, Beta-adrenergic blocker, ACE inhibitor, Aortic surgery	Pan-LDS/HTAD extrapolation; no LDS6-specific efficacy data retrieved.
Surgical intervention	Elective aortic surgery is used when anatomy or growth rate indicates high risk; retrieved LDS-oriented material notes intervention for critical aortic size/rapid growth, but subtype-specific diameter thresholds for LDS6 were not retrieved. (ebeling2024differentiationpurificationand pages 9-11, spaziani2024hereditarythoracicaortic pages 9-10)	NCIT: Aortic root replacement, Vascular surgical procedure	Threshold details here are not LDS6-specific and should not be overinterpreted.
Prevention/counseling	Secondary/tertiary prevention relies on early diagnosis, cascade family screening, serial imaging, and counseling on pregnancy/exertion risk. Prenatal diagnosis is possible when the familial pathogenic variant is known. (asta2023geneticbasisnew pages 5-8, zaza2022cleftpalateand pages 2-5)	Counseling concepts: cascade screening, prenatal testing, genetic counseling	Mostly pan-LDS evidence; LDS6-specific pregnancy outcome data not retrieved.
Epidemiology	LDS overall is rare; retrieved sources estimate prevalence as below 1 in 100,000 or 1/25,000-1/100,000. One recent review table estimated LDS6/SMAD2 accounts for ~1-5% of LDS. (ebeling2024differentiationpurificationand pages 9-11, NCT05472519 chunk 1)	Broader disease epidemiology for Loeys-Dietz syndrome	Estimates are broad and not population-based for LDS6 specifically.
Models and translational resources	Relevant resources include GenTAC registry infrastructure for genetically triggered thoracic aortopathy and a completed I-LoDiS immunopathology study in LDS; patient-specific iPSC/endothelial disease-modeling work exists for LDS broadly. (NCT01322165 chunk 1, NCT05472519 chunk 1, ebeling2024differentiationpurificationand pages 9-11)	Clinical trials/registries: NCT01322165 GenTAC; NCT05472519 I-LoDiS	Valuable for LDS research, but not specific to SMAD2/LDS6 in the retrieved records.
Major evidence gaps	Major LDS6 gaps include: lack of subtype-specific prevalence, penetrance, phenotype frequencies, validated biomarkers, surgical thresholds, pregnancy outcomes, treatment response data, and retrieved direct SMAD2 functional variant studies. (OpenTargets Search: Loeys-Dietz syndrome-SMAD2, ebeling2024differentiationpurificationand pages 9-11)	Evidence-gap annotation	Important to distinguish direct LDS6 evidence from broader LDS/HTAD extrapolation in any knowledge base entry.

Table: This table summarizes the best-supported findings for SMAD2-related Loeys-Dietz syndrome 6, while clearly separating subtype-specific evidence from broader Loeys-Dietz syndrome and hereditary thoracic aortic disease extrapolations. It is useful as a compact knowledge-base scaffold for curation and evidence-gap tracking.

1. Disease information

Definition

[Direct LDS6] LDS6 is a Mendelian, autosomal-dominant syndromic aortopathy caused by a heterozygous pathogenic variant in SMAD2, which encodes a receptor-regulated intracellular effector of TGF-β signaling. Its defining clinical risk is progressive arterial disease—particularly thoracic/aortic-root aneurysm, dissection, or rupture—with variable craniofacial, skeletal, cutaneous, and cardiac-valvular connective-tissue manifestations. A 2023 review states that “type 6 [is] determined by the SMAD2 mutation” and attributes the initial association to families with aneurysm/dissection and abnormal aortic-wall SMAD2 expression. (asta2023geneticbasisnew pages 3-5)

Because SMAD2-related disease has been reported only rarely, some authors use “SMAD2-related syndromic thoracic aortic aneurysm and dissection” rather than LDS6. A 2024 dissertation reviewing LDS disease models explicitly notes that “LDS type 6 is not consistently used in literature.” (ebeling2024differentiationpurificationand pages 9-11)

Identifiers and synonyms

MONDO: No subtype-specific MONDO identifier was verified in the retrieved evidence. The broader Loeys–Dietz syndrome term is MONDO:0018954.
MeSH: D055947, Loeys-Dietz Syndrome, broader disease term. (NCT05472519 chunk 1)
OMIM: Broader LDS entries cited by the retrieved literature include 609192 and 610168, historically corresponding to receptor-defined LDS forms rather than a confirmed subtype-specific LDS6 record. These should not be assigned to LDS6 without independent OMIM verification. (ebeling2024differentiationpurificationand pages 9-11)
ICD-10: No dedicated LDS6 code. LDS is commonly grouped under Q87.4 in the retrieved source; local coding may instead use congenital malformation/connective-tissue or aortic-disease codes. (ebeling2024differentiationpurificationand pages 9-11)
ICD-11: No verified subtype-specific code retrieved.
Synonyms: Loeys-Dietz syndrome type 6, LDS type 6, LDS6, SMAD2-related Loeys-Dietz syndrome, SMAD2-related syndromic aortopathy, SMAD2-related hereditary thoracic aortic disease.
Gene: SMAD2, Ensembl ENSG00000175387. Open Targets reports five genetic evidence items and an LDS–SMAD2 association score of approximately 0.76. (OpenTargets Search: Loeys-Dietz syndrome-SMAD2)

Data provenance

The entry is based primarily on aggregated disease resources, published families/case series, reviews, and registries, not individual-level EHR data. GenTAC collected longitudinal clinical data and biospecimens from 3,706 people with genetically triggered aortic conditions, including LDS, but the retrieved record does not provide an LDS6 subgroup. (NCT01322165 chunk 1)

2. Etiology

Causal factor and genetic risk

[Direct LDS6] The primary cause is a germline heterozygous pathogenic/likely pathogenic SMAD2 variant. Open Targets/Genomics England evidence supports monoallelic inheritance and includes stop-gained and splice-acceptor variant records, although complete HGVS descriptions were not present in the retrieved material. (OpenTargets Search: Loeys-Dietz syndrome-SMAD2)

Reported pathogenic classes include missense, nonsense/truncating, and splice-disrupting variants. The 2023 review particularly associates missense and nonsense SMAD2 variants with LDS6. Exact domain-specific genotype–phenotype relationships remain insufficiently established. (asta2023geneticbasisnew pages 3-5)

The strongest risk factors are therefore:

A pathogenic germline SMAD2 allele.
An affected first-degree relative or family history of thoracic aortic aneurysm/dissection or sudden unexplained death.
Established aneurysm, rapid arterial growth, hypertension, and pregnancy-related hemodynamic stress—clinically important modifiers extrapolated from pan-LDS/HTAD.

Environmental and lifestyle risk factors

No environmental exposure causes LDS6. Hypertension, stimulant or vasoconstrictor exposure, smoking, and high-static/straining exercise may add mechanical stress to a genetically vulnerable arterial wall; however, no LDS6-specific effect sizes are available. Current HTAD management emphasizes blood-pressure control, avoidance of stimulants/vasoconstrictors, and exercise restriction. (spaziani2024hereditarythoracicaortic pages 7-9)

No infectious trigger is recognized. LDS6 is not contagious or zoonotic.

Protective factors

No genetically protective SMAD2 allele or validated modifier gene has been established. Clinically protective measures are secondary/tertiary rather than etiologic: early molecular diagnosis, serial whole-arterial imaging, strict blood-pressure control, avoidance of high-strain activity, and appropriately timed prophylactic surgery. Evidence for beta-blockers or angiotensin-receptor blockers in LDS is indirect; no randomized LDS trial has shown reduced dissection risk. (spaziani2024hereditarythoracicaortic pages 9-10)

Gene–environment interaction

The working model is that SMAD2 dysfunction lowers arterial resilience while blood pressure, pulse-wave stress, pregnancy, and intense isometric exertion increase wall loading. This interaction may accelerate dilation or precipitate dissection, but it has not been quantified for LDS6.

3. Phenotypes

The following are reasonable curation targets. Unless stated otherwise, frequencies and age distributions are unknown for LDS6.

Vascular and cardiac

Aortic-root/ascending thoracic aortic dilatation or aneurysm — clinical sign/imaging abnormality; congenital through adult onset; progressive and potentially severe. Suggested HPO: Aortic root dilatation, Thoracic aortic aneurysm.
Aortic dissection/rupture — acute vascular complication superimposed on lifelong susceptibility; life-threatening. HPO: Aortic dissection, Aortic rupture.
Aneurysms/dissections outside the proximal aorta and arterial tortuosity — expected within the broader LDS phenotype but LDS6-specific distribution is unresolved. HPO: Arterial tortuosity, Generalized arterial tortuosity, Arterial aneurysm.
Mitral-valve disease and possibly aortic regurgitation — HPO: Mitral valve prolapse, Mitral regurgitation, Aortic regurgitation. The literature associates SMAD2-mutant families primarily with aneurysm/dissection, while valvular manifestations are better documented across LDS. (asta2023geneticbasisnew pages 3-5)

A pan-LDS neonatal example illustrates that disease can be evident at birth: a TGFBR2-positive newborn had a 16–17-mm aortic root with z-scores of +7.46 to +8.65 and tortuous major branches. This is not LDS6 evidence but demonstrates the possible congenital end of the LDS spectrum. (zaza2022cleftpalateand pages 2-5)

Craniofacial, skeletal, and cutaneous

Possible features include:

Hypertelorism — HPO: Hypertelorism.
Bifid uvula or cleft palate — HPO: Bifid uvula, Cleft palate.
Arachnodactyly, joint hypermobility or contractures, scoliosis, pectus deformity, and clubfoot — corresponding HPO terms should be assigned when observed.
Translucent/soft skin, easy bruising, or abnormal scarring — pan-LDS features; use phenotype-specific HPO terms rather than assuming presence.

These features are diagnostically supportive but neither necessary nor sufficient for LDS6. Their frequency in SMAD2-positive individuals is unknown. (asta2023geneticbasisnew pages 3-5, zaza2022cleftpalateand pages 2-5)

Allergic, gastrointestinal, neurologic, and behavioral features

Asthma, eczema, food allergy, elevated IgE/eosinophilia, eosinophilic gastrointestinal disease, and inflammatory bowel disease occur in pan-LDS, especially receptor-associated LDS, but have not been established as defining LDS6 features. The completed I-LoDiS study enrolled only TGFBR1/TGFBR2-positive participants, so its findings should not be directly transferred to SMAD2-related disease. (NCT05472519 chunk 1)

No characteristic behavioral or psychiatric phenotype, laboratory abnormality, or neurodevelopmental syndrome is established for LDS6.

Quality of life

No LDS6-specific EQ-5D, SF-36, PROMIS, or disease-specific patient-reported outcome data were found. Likely burdens include anxiety about dissection, repeated imaging, exercise and pregnancy restrictions, chronic musculoskeletal symptoms, and recovery from major vascular surgery. These should be recorded as anticipated consequences, not measured LDS6 statistics.

4. Genetic and molecular information

Gene and protein

Gene: SMAD2, HGNC-approved symbol; chromosome 18q21.1.
Protein: Mothers against decapentaplegic homolog 2/SMAD family member 2, a receptor-regulated SMAD.
Function: Following TGFBR1-mediated phosphorylation, SMAD2 associates with SMAD3/SMAD4-containing complexes, enters the nucleus, and regulates transcription. (liu2025anoveltgfbr2 pages 7-8)

Variant interpretation

Testing laboratories should classify variants using ACMG/AMP criteria. Evidence expected for pathogenicity includes rarity/absence in population databases, segregation or de novo occurrence, predicted loss of function where applicable, location in a critical functional domain, and validated functional impairment. A VUS must not by itself establish LDS6 or direct prophylactic surgery.

Open Targets summarizes stop-gained and splice-acceptor disease records and monoallelic inheritance evidence, but the retrieved sources do not provide a complete curated list of SMAD2 HGVS variants or their gnomAD frequencies. (OpenTargets Search: Loeys-Dietz syndrome-SMAD2)

Origin: Germline; somatic SMAD2 variants in cancer are not the cause of constitutional LDS6.
Mechanistic class: Likely loss of normal canonical signaling, dominant-negative effects for some alleles, or haploinsufficiency for truncating/splice variants. Variant-specific mechanisms require functional confirmation.
Structural variants: Large deletions/rearrangements disrupting SMAD2 are biologically plausible; no recurrent LDS6 chromosomal abnormality was established in the retrieved evidence.
Modifier genes/epigenetics: No validated LDS6 modifier gene, methylation signature, or clinical epigenetic biomarker was found.

5. Environmental information

No toxin, radiation exposure, occupational agent, diet, infection, alcohol use, or smoking exposure is known to initiate LDS6. Smoking and uncontrolled hypertension should nevertheless be minimized because of general adverse vascular effects. Contact/collision sports, heavy weightlifting, intense isometric exercise, and activities requiring Valsalva maneuvers are generally restricted in heritable aortopathy; recommendations should be individualized to arterial dimensions, prior surgery, and blood-pressure response. (spaziani2024hereditarythoracicaortic pages 7-9)

6. Mechanism and pathophysiology

Causal chain

Upstream trigger: constitutional heterozygous SMAD2 pathogenic variant.
Primary biochemical defect: altered transmission of signals from activated TGFBR1/2 through phosphorylated SMAD2/3 complexes to nuclear transcriptional programs.
Cellular dysfunction: disturbed vascular smooth-muscle-cell differentiation/contractile homeostasis, stress responses, and communication with extracellular matrix, endothelial cells, fibroblasts, and immune cells.
Tissue remodeling: reduced elastic integrity, diffuse medial degeneration, elastic-fiber fragmentation, collagen and amorphous extracellular-matrix accumulation, and maladaptive matrix turnover.
Biomechanical consequence: progressive arterial-wall weakening and altered compliance.
Clinical manifestations: aortic-root/arterial dilatation → aneurysm → dissection or rupture; associated valve, craniofacial, skeletal, and cutaneous abnormalities reflect broader developmental TGF-β dysregulation. (asta2023geneticbasisnew pages 3-5)

The signaling paradox

TGF-β-pathway mutations may reduce ligand-induced signaling cell-autonomously yet coexist with increased tissue pSMAD2/3 at sites of aneurysm. In a Tgfbr1 LDS mouse, second-heart-field-derived aortic-root VSMCs had defective ligand-induced pSmad2/3, while diseased aortic-root tissue later showed localized increases in pSmad2/3 and TGF-β1/TGF-β3 that tracked with dilation. This supports secondary compensatory or non-cell-autonomous signaling rather than a simple global “gain” or “loss” model. (macfarlane2019lineagespecificeventsunderlie pages 2-5)

Cells, tissues, and ontology suggestions

CL: vascular smooth muscle cell; endothelial cell; fibroblast; macrophage; T lymphocyte.
GO Biological Process: transforming growth factor beta receptor signaling pathway; SMAD protein signal transduction; regulation of transcription by RNA polymerase II; extracellular matrix organization; elastic fiber assembly; smooth muscle cell differentiation; response to mechanical stimulus.
GO Cellular Component: cytosol, nucleus, SMAD protein complex, receptor complex, extracellular matrix.

Molecular profiling and advanced technologies

No LDS6-specific single-cell, spatial-transcriptomic, proteomic, metabolomic, or lipidomic signature was found. Broader ascending-aortic studies report candidate circulating markers such as MMP-1/2/3/9, IL-6, GDF-15, miR-574-5p, C18-ceramide, aggrecan, and alpha-2-HS-glycoprotein, but none is validated for diagnosing or forecasting LDS6. (ganizada2024unveilingcellularand pages 14-15)

Patient-specific iPSC-derived endothelial cells are being developed for LDS modeling, offering a platform for genotype-specific endothelial phenotyping and drug testing. The retrieved 2024 work is methodological and does not establish a validated LDS6 biomarker or treatment. (ebeling2024differentiationpurificationand pages 9-11)

7. Anatomical structures affected

Organ/system level

Primary: aortic root and ascending thoracic aorta; potentially the entire aorta and medium/large arterial tree.
Secondary: heart valves; craniofacial skeleton and palate; axial/appendicular skeleton; skin and connective tissues.
Systems: cardiovascular, musculoskeletal, craniofacial, integumentary; possible allergic/gastrointestinal involvement based on pan-LDS.

UBERON suggestions

Aortic root, ascending aorta, aortic arch, descending thoracic aorta, abdominal aorta, arterial wall, tunica media of artery, heart valve, palate, skin, vertebral column.

Aortic medial VSMCs are the principal implicated cell population. The relevant subcellular route spans plasma-membrane TGF-β receptor complexes, cytosolic SMAD phosphorylation/complex assembly, and nuclear transcription. No characteristic lateralization exists; vascular and skeletal findings may be bilateral or asymmetric depending on manifestation.

8. Temporal development

LDS6 is a congenital genetic condition with lifelong risk, even when no abnormality is visible at birth. Clinical onset ranges from prenatal/neonatal aortic dilation to childhood or adult discovery of aneurysm/dissection. Progression is chronic but highly variable; acute dissection is a catastrophic event superimposed on this chronic substrate.

No validated LDS6 staging system exists. A practical clinical course is:

Genotype-positive/no detectable arterial disease.
Stable or enlarging arterial tortuosity/dilatation.
Clinically significant aneurysm or rapid growth.
Dissection/rupture or prophylactic/emergency repair.
Lifelong post-repair surveillance for residual native-vessel disease.

There is no spontaneous remission. Critical intervention windows are before dissection, during family cascade screening, after detection of rapid growth, and before/during pregnancy. Pan-LDS literature reports nonpenetrance and mosaicism, underscoring that a normal early examination does not eliminate later risk. (zaza2022cleftpalateand pages 2-5)

9. Inheritance and population

Inheritance

Pattern: autosomal dominant/monoallelic.
Recurrence: an affected heterozygous individual has a 50% probability of transmitting the variant in each pregnancy.
De novo disease: Across LDS, approximately 25% have an affected parent and the remainder are described as de novo; another retrieved review states roughly 75% are de novo. These are pan-LDS estimates, not LDS6-specific rates. (ebeling2024differentiationpurificationand pages 9-11, zaza2022cleftpalateand pages 2-5)
Penetrance: incompletely defined and probably age dependent; nonpenetrance has been reported across LDS.
Expressivity: markedly variable.
Anticipation: not established.
Germline mosaicism: theoretically relevant to apparently de novo recurrence, but no LDS6 rate is available.
Founder effects, consanguinity, carrier frequency: none established; consanguinity is not expected to drive an autosomal-dominant disorder.

Epidemiology

LDS overall has been estimated at <1 in 100,000 or approximately 1 in 25,000–100,000, but robust population-based incidence and prevalence are lacking. A recent summary estimated SMAD2/LDS6 at 1–5% of LDS, which is an approximate relative fraction rather than a population prevalence. (ebeling2024differentiationpurificationand pages 9-11, NCT05472519 chunk 1)

No reproducible ethnic, geographic, sex, or founder enrichment has been established for LDS6. All sexes can be affected. Pregnancy creates an additional vascular/uterine risk for affected women, while the germline transmission probability is sex independent.

10. Diagnostics

Clinical evaluation

Diagnosis begins with personal/family history, three-generation pedigree, physical examination, and cardiovascular imaging. Suspicion should increase with early-onset aortic aneurysm/dissection, arterial tortuosity, bifid uvula/cleft palate, hypertelorism, marfanoid skeletal features, or a family history of sudden aortic death.

Imaging

Transthoracic echocardiography: first-line measurement of aortic root/ascending aorta and valve function.
CT angiography: rapid, high-resolution evaluation of the entire aorta and branch vessels; useful for acute disease and surgical planning but entails radiation/contrast.
CMR/MRA: preferred for repeated longitudinal imaging in many children and young adults because it avoids ionizing radiation and can characterize the full aorta and hemodynamics. (asta2023geneticbasisnew pages 5-8, spaziani2024hereditarythoracicaortic pages 7-9)

Whole-arterial baseline imaging is important because echocardiography does not visualize every vulnerable segment. Imaging intervals should be individualized by genotype, age, dimensions, growth, family history, and prior surgery.

Genetic testing

Use a comprehensive heritable thoracic aortic disease panel including at least SMAD2, TGFBR1, TGFBR2, SMAD3, TGFB2, TGFB3, FBN1, COL3A1, ACTA2, MYH11, MYLK, LOX, PRKG1, and other validated HTAD genes.
Ensure sequencing plus deletion/duplication analysis.
Use exome or genome sequencing when panel testing is negative, phenotype is atypical, or structural/noncoding disease is suspected.
Confirm candidate variants and perform segregation/de novo analysis where possible.
Offer targeted cascade testing to relatives when a pathogenic familial variant is identified. If testing is negative or yields only a VUS, at-risk relatives may still require imaging based on family history. (asta2023geneticbasisnew pages 5-8)

CMA, karyotype, or FISH is not first-line for isolated suspected LDS6 but may be appropriate for syndromic developmental abnormalities or suspected larger rearrangements. Mitochondrial and repeat-expansion testing are not indicated. RNA sequencing may help resolve splice variants but is not standard primary diagnosis.

Differential diagnosis

Other LDS subtypes: TGFBR1, TGFBR2, SMAD3, TGFB2, TGFB3.
Marfan syndrome: FBN1, commonly ectopia lentis and classic Ghent phenotype.
Vascular Ehlers–Danlos syndrome: COL3A1, marked tissue/arterial fragility.
Shprintzen–Goldberg syndrome: SKI, craniosynostosis and developmental phenotype.
Arterial tortuosity syndrome: SLC2A10, autosomal recessive.
Familial nonsyndromic HTAD and bicuspid-aortic-valve aortopathy.

No single biochemical blood test or histopathologic criterion diagnoses LDS6. Candidate circulating ATAA biomarkers remain investigational. (ganizada2024unveilingcellularand pages 14-15)

11. Outcome and prognosis

The principal morbidity and mortality arise from aortic or arterial dissection/rupture, emergency surgery, stroke/malperfusion, valve disease, and repeated vascular interventions. Untreated acute type-A dissection is highly lethal; a general aortic-disease source cited mortality of 54% untreated versus 12–26% after surgery, but these are not LDS6-specific figures. (ebeling2024differentiationpurificationand pages 9-11)

No LDS6-specific life expectancy, 5-/10-year survival, mortality rate, or validated prognostic model was found. Prognosis is expected to improve substantially with early diagnosis, blood-pressure control, surveillance, and prophylactic repair. Adverse prognostic factors likely include early or diffuse arterial disease, rapid enlargement, family history of dissection at small diameter, uncontrolled hypertension, pregnancy, and residual native aorta after repair. These are clinically plausible pan-HTAD factors rather than quantified LDS6 predictors.

No validated prognostic biomarker exists. Aortic diameter and growth remain central but imperfect risk measures.

12. Treatment

Medical therapy

No medication corrects the germline defect, and no randomized trial has demonstrated reduced aortic growth or dissection specifically in LDS or LDS6. Current practice extrapolates from Marfan syndrome and mechanistic models:

Beta-blocker—reduces heart rate, blood pressure, and pulsatile wall stress.
Angiotensin II receptor blocker, commonly losartan—reduces blood pressure and may influence maladaptive TGF-β/ERK signaling.
ACE inhibitor—alternative/additional blood-pressure control.

A 2024 HTAD review concludes that ARBs, beta-blockers, or ACE inhibitors are reasonable to lessen hemodynamic stress and that prophylactic ARB use may be considered in genotype-positive LDS with relevant family/variant history, while explicitly acknowledging the absence of LDS efficacy studies. (spaziani2024hereditarythoracicaortic pages 9-10)

Suggested NCIT-style intervention concepts: Beta Adrenergic Blocker, Angiotensin II Receptor Antagonist, Losartan, Angiotensin-Converting Enzyme Inhibitor, Antihypertensive Therapy.

Doxycycline, statins, MMP inhibition, direct TGF-β inhibition, and other pathway-directed agents remain experimental for inherited aortopathy and should not be represented as established LDS6 treatment. Calcium-channel blockers should be used cautiously in syndromic aortopathy. (spaziani2024hereditarythoracicaortic pages 9-10)

Surgery

Elective valve-sparing aortic-root replacement or composite graft replacement is the definitive preventive intervention when risk becomes unacceptable. Decisions should be genotype- and patient-specific, incorporating absolute diameter, body size/z-score, growth rate, family history, valve function, pregnancy plans, and surgical expertise. The retrieved sources did not provide a validated SMAD2-specific threshold; therefore, generic 40–50-mm statements must not be treated as an LDS6 rule. (ebeling2024differentiationpurificationand pages 9-11)

Suggested NCIT concepts: Aortic Root Replacement, Valve-Sparing Aortic Root Replacement, Aortic Aneurysm Repair, Vascular Surgery.

Supportive care

Multidisciplinary care may include cardiology/aortopathy, cardiovascular surgery, medical genetics, maternal–fetal medicine, orthopedics, craniofacial/ENT, allergy/gastroenterology, physiotherapy, occupational therapy, pain management, and psychological support.

Advanced and experimental therapeutics

No approved gene therapy, CRISPR treatment, cell therapy, RNA therapy, or LDS6-specific targeted biologic was found. Editing a dominant SMAD2 allele would require allele-specific safety, delivery to the arterial wall, and careful avoidance of disrupting essential TGF-β functions.

Trials and real-world implementations

GenTAC, NCT01322165: completed prospective registry; 3,706 participants across genetic aortopathies; longitudinal outcomes and biospecimens. (NCT01322165 chunk 1)
I-LoDiS, NCT05472519: completed 2023, 60 participants; investigated immune populations and pSMAD2/3, but eligibility was restricted to TGFBR1/TGFBR2-positive LDS and therefore does not directly study LDS6. (NCT05472519 chunk 1)
No LDS6-specific therapeutic interventional trial was identified.

13. Prevention

Primary prevention

The inherited variant cannot presently be prevented after conception. Reproductive options after identification of a familial pathogenic variant include genetic counseling, preimplantation genetic testing, chorionic-villus sampling, or amniocentesis. Prenatal ultrasound has low sensitivity for many LDS manifestations, though severe prenatal aortic dilation may occasionally be detected. (zaza2022cleftpalateand pages 2-5)

Secondary prevention

Cascade genetic testing and baseline cardiovascular imaging of first-degree relatives.
Early whole-aorta/arterial imaging in genotype-positive individuals.
Regular blood-pressure assessment and treatment.
Pregnancy risk assessment before conception.

Tertiary prevention

Serial multimodality imaging.
Medical reduction of hemodynamic stress.
Avoidance of smoking, stimulants/vasoconstrictors, collision sports, heavy isometric exertion, and Valsalva-heavy lifting.
Timely prophylactic vascular surgery.
Lifelong surveillance after repair because unrepaired arterial segments remain at risk. (spaziani2024hereditarythoracicaortic pages 7-9, spaziani2024hereditarythoracicaortic pages 9-10)

No immunization, infectious prophylaxis, newborn biochemical screening, or population-wide screening program is applicable. Targeted familial screening is the appropriate public-health strategy.

14. Other species and natural disease

No well-established naturally occurring veterinary LDS6 caused by an orthologous SMAD2 variant was identified. SMAD2 is evolutionarily conserved across vertebrates, consistent with conserved TGF-β developmental and vascular functions, but conservation alone does not demonstrate natural disease.

Human: Homo sapiens, NCBI Taxonomy 9606.
Common experimental comparison species include Mus musculus (10090) and Danio rerio (7955).
No breed-specific VBO annotation, veterinary prevalence, cross-species transmission, or zoonotic potential applies.

15. Model organisms and experimental systems

Available/related models

No well-characterized Smad2 knock-in model reproducing a specific human LDS6 allele was found in the retrieved literature. Because complete Smad2 loss has major developmental consequences, constitutive knockout models may poorly represent viable heterozygous human LDS6 and conditional or allele-specific models are preferable.

A highly informative Tgfbr1-M318R/+ LDS mouse develops aortic-root dilation and demonstrates lineage-specific pathogenesis: second-heart-field-derived VSMCs show deficient TGF-β-induced pSmad2/3 and target-gene activation, while later diseased tissue exhibits localized excess pSmad2/3 and TGF-β ligand. This recapitulates LDS pathway biology but is not a SMAD2/LDS6 model. (macfarlane2019lineagespecificeventsunderlie pages 2-5)

Cellular models

Patient fibroblasts and induced myofibroblasts.
iPSC-derived vascular smooth-muscle cells.
iPSC-derived endothelial cells.
Isogenic CRISPR-corrected or knock-in pairs.
Aortic organoids/tissue-engineered vessels.

A 2024 LDS iPSC-endothelial methodology project highlights these systems as alternatives to rodent models with limited clinical transferability. Applications include variant functional classification, cell-lineage studies, extracellular-matrix and mechanotransduction assays, and drug screening. (ebeling2024differentiationpurificationand pages 9-11)

Model limitations

Models must reproduce heterozygosity, relevant SMAD2 isoform/domain effects, human arterial-cell lineage, pulsatile mechanical loading, and long disease latency. TGFBR1/TGFBR2/SMAD3 or Marfan models illuminate shared pathways but cannot establish an LDS6-specific phenotype or treatment response.

Recent developments, authoritative interpretation, and key gaps

Recent 2023–2024 work emphasizes three developments: expanding gene-informed HTAD diagnosis, increasingly comprehensive CT/CMR surveillance, and cell/lineage-specific modeling rather than treating TGF-β signaling as uniformly increased or decreased. MRI/CMR is particularly valuable for repeated imaging because it avoids ionizing radiation and supports biomechanical measurements; next-generation sequencing enables cascade diagnosis across genetically heterogeneous aortopathies. (asta2023geneticbasisnew pages 5-8, spaziani2024hereditarythoracicaortic pages 7-9)

The most important expert-level conclusion is that SMAD2 is credibly associated with Loeys–Dietz-spectrum aortopathy, but LDS6 remains too sparsely described for independent evidence-based thresholds or outcome estimates. Open Targets supports the gene–disease association, yet current surveillance and treatment are necessarily extrapolated from broader LDS/HTAD practice. (OpenTargets Search: Loeys-Dietz syndrome-SMAD2)

Priority research needs are: an international SMAD2 registry; standardized variant and domain annotation; age-specific penetrance and phenotype frequencies; whole-arterial natural history; pregnancy outcomes; patient-derived VSMC/endothelial and allele-specific animal models; validated circulating/imaging biomarkers; and genotype-specific treatment and surgical-threshold studies.

Selected dated sources and URLs

Asta L, et al. Genetic Basis, New Diagnostic Approaches, and Updated Therapeutic Strategies of the Syndromic Aortic Diseases. Published August 2023. DOI/URL: https://doi.org/10.3390/ijerph20166615. (asta2023geneticbasisnew pages 5-8, asta2023geneticbasisnew pages 3-5)
Spaziani G, et al. Hereditary Thoracic Aortic Diseases. Published January 2024. DOI/URL: https://doi.org/10.3390/diagnostics14010112. (spaziani2024hereditarythoracicaortic pages 7-9, spaziani2024hereditarythoracicaortic pages 9-10)
Ganizada BH, et al. Unveiling cellular and molecular aspects of ascending thoracic aortic aneurysms and dissections. Published May 2024. DOI/URL: https://doi.org/10.1007/s00395-024-01053-1. (ganizada2024unveilingcellularand pages 14-15)
MacFarlane EG, et al. Lineage-specific events underlie aortic root aneurysm pathogenesis in Loeys-Dietz syndrome. Published January 2019. DOI/URL: https://doi.org/10.1172/JCI123547. (macfarlane2019lineagespecificeventsunderlie pages 2-5)
Zaza P, et al. Cleft Palate and Aortic Dilatation as Clues for Loeys–Dietz Syndrome. Published August 2022. DOI/URL: https://doi.org/10.3390/children9091290. (zaza2022cleftpalateand pages 2-5)
ClinicalTrials.gov NCT05472519, Immunopathology of Loeys-Dietz Syndrome, completed June 7, 2023: https://clinicaltrials.gov/study/NCT05472519. (NCT05472519 chunk 1)
ClinicalTrials.gov NCT01322165, GenTAC Registry, completed September 2016: https://clinicaltrials.gov/study/NCT01322165. (NCT01322165 chunk 1)

Abstract/direct-text support: The clearest retrieved subtype statement is: “Type 6 shows mutations in SMAD2,” accompanied by the caution that “LDS type 6 is not consistently used in literature.” (ebeling2024differentiationpurificationand pages 9-11) The I-LoDiS trial record characterizes LDS as a “rare vascular genetic disorder” and describes the broader hypothesis of intracellular TGF-β pathway hyperactivation measured by pSMAD2/3; because that study enrolled receptor-positive LDS, this quote is mechanistically relevant but not direct LDS6 evidence. (NCT05472519 chunk 1)

References

(asta2023geneticbasisnew pages 3-5): Laura Asta, Gianluca A. D’Angelo, Daniele Marinelli, and Umberto Benedetto. Genetic basis, new diagnostic approaches, and updated therapeutic strategies of the syndromic aortic diseases: marfan, loeys–dietz, and vascular ehlers–danlos syndrome. International Journal of Environmental Research and Public Health, 20:6615, Aug 2023. URL: https://doi.org/10.3390/ijerph20166615, doi:10.3390/ijerph20166615. This article has 40 citations.
(ebeling2024differentiationpurificationand pages 9-11): Differentiation, purification, and characterisation of patient iPSC-derived endothelial cells for Loeys-Dietz-Syndrome disease modelling This article has 1 citations and is from a peer-reviewed journal.
(OpenTargets Search: Loeys-Dietz syndrome-SMAD2): Open Targets Query (Loeys-Dietz syndrome-SMAD2, 1 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(zaza2022cleftpalateand pages 2-5): Pierluigi Zaza, Flavia Indrio, Annalisa Fracchiolla, Matteo Rinaldi, Giovanni Meliota, Alessia Salatto, Antonio Bonacaro, and Gianfranco Maffei. Cleft palate and aortic dilatation as clues for loeys–dietz syndrome. Children, 9:1290, Aug 2022. URL: https://doi.org/10.3390/children9091290, doi:10.3390/children9091290. This article has 2 citations.
(liu2025anoveltgfbr2 pages 7-8): Xin Liu, Kaiqing Liu, Lifu Hu, Zixiao Liu, Xinhua Liu, and Jiantao Wang. A novel tgfbr2 mutation causes loeys-dietz syndrome in a chinese infant: a case report. Heliyon, Jan 2025. URL: https://doi.org/10.1016/j.heliyon.2025.e42116, doi:10.1016/j.heliyon.2025.e42116. This article has 1 citations.
(macfarlane2019lineagespecificeventsunderlie pages 2-5): Elena Gallo MacFarlane, Sarah J. Parker, Joseph Y. Shin, Shira G. Ziegler, Tyler J. Creamer, Rustam Bagirzadeh, Djahida Bedja, Yichun Chen, Juan F. Calderon, Katherine Weissler, Pamela A. Frischmeyer-Guerrerio, Mark E. Lindsay, Jennifer P. Habashi, and Harry C. Dietz. Lineage-specific events underlie aortic root aneurysm pathogenesis in loeys-dietz syndrome. Journal of Clinical Investigation, 129:659-675, Jan 2019. URL: https://doi.org/10.1172/jci123547, doi:10.1172/jci123547. This article has 142 citations and is from a highest quality peer-reviewed journal.
(NCT05472519 chunk 1): Immunopathology of Loeys-Dietz Syndrome. Hospices Civils de Lyon. 2022. ClinicalTrials.gov Identifier: NCT05472519
(ganizada2024unveilingcellularand pages 14-15): Berta H. Ganizada, Rogier J. A. Veltrop, Asim C. Akbulut, Rory R. Koenen, Ryan Accord, Roberto Lorusso, Jos G. Maessen, Koen Reesink, Elham Bidar, and Leon J. Schurgers. Unveiling cellular and molecular aspects of ascending thoracic aortic aneurysms and dissections. Basic Research in Cardiology, 119:371-395, May 2024. URL: https://doi.org/10.1007/s00395-024-01053-1, doi:10.1007/s00395-024-01053-1. This article has 63 citations and is from a domain leading peer-reviewed journal.
(spaziani2024hereditarythoracicaortic pages 7-9): Gaia Spaziani, Francesca Chiara Surace, Francesca Girolami, Francesco Bianco, Valentina Bucciarelli, Francesca Bonanni, Elena Bennati, Luigi Arcieri, and Silvia Favilli. Hereditary thoracic aortic diseases. Diagnostics, 14:112, Jan 2024. URL: https://doi.org/10.3390/diagnostics14010112, doi:10.3390/diagnostics14010112. This article has 7 citations.
(asta2023geneticbasisnew pages 5-8): Laura Asta, Gianluca A. D’Angelo, Daniele Marinelli, and Umberto Benedetto. Genetic basis, new diagnostic approaches, and updated therapeutic strategies of the syndromic aortic diseases: marfan, loeys–dietz, and vascular ehlers–danlos syndrome. International Journal of Environmental Research and Public Health, 20:6615, Aug 2023. URL: https://doi.org/10.3390/ijerph20166615, doi:10.3390/ijerph20166615. This article has 40 citations.
(NCT01322165 chunk 1): National Registry of Genetically Triggered Thoracic Aortic Aneurysms and Cardiovascular Conditions. National Heart, Lung, and Blood Institute (NHLBI). 2007. ClinicalTrials.gov Identifier: NCT01322165
(spaziani2024hereditarythoracicaortic pages 9-10): Gaia Spaziani, Francesca Chiara Surace, Francesca Girolami, Francesco Bianco, Valentina Bucciarelli, Francesca Bonanni, Elena Bennati, Luigi Arcieri, and Silvia Favilli. Hereditary thoracic aortic diseases. Diagnostics, 14:112, Jan 2024. URL: https://doi.org/10.3390/diagnostics14010112, doi:10.3390/diagnostics14010112. This article has 7 citations.

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Inheritance

Discussions and Knowledge Gaps

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Medical Actions

Progression

Prevalence

Differential Diagnoses

Experimental Models

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Loeys–Dietz Syndrome 6 (SMAD2-Related) — Disease Characteristics Research Report

1. Disease information

Definition

Identifiers and synonyms

Data provenance

2. Etiology

Causal factor and genetic risk

Environmental and lifestyle risk factors

Protective factors

Gene–environment interaction

3. Phenotypes

Vascular and cardiac

Craniofacial, skeletal, and cutaneous

Allergic, gastrointestinal, neurologic, and behavioral features

Quality of life

4. Genetic and molecular information

Gene and protein

Variant interpretation

5. Environmental information

6. Mechanism and pathophysiology

Causal chain

The signaling paradox

Cells, tissues, and ontology suggestions

Molecular profiling and advanced technologies

7. Anatomical structures affected

Organ/system level

UBERON suggestions

8. Temporal development

9. Inheritance and population

Inheritance

Epidemiology

10. Diagnostics

Clinical evaluation

Imaging

Genetic testing

Differential diagnosis

11. Outcome and prognosis

12. Treatment

Medical therapy

Surgery

Supportive care

Advanced and experimental therapeutics

Trials and real-world implementations

13. Prevention

Primary prevention

Secondary prevention

Tertiary prevention

14. Other species and natural disease

15. Model organisms and experimental systems

Available/related models

Cellular models

Model limitations

Recent developments, authoritative interpretation, and key gaps

Selected dated sources and URLs

Artifacts

Reference Validation