Sneddon syndrome is a rare occlusive vasculopathy characterized by livedo reticularis or livedo racemosa and recurrent ischemic cerebrovascular events. The core disease mechanism is a chronic arteriopathy affecting skin and brain, producing transient ischemic attacks, stroke, and progressive neurologic impairment.
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Conditions with similar clinical presentations that must be differentiated from Sneddon syndrome:
name: Sneddon syndrome
creation_date: '2026-04-14T12:00:00Z'
category: Complex
description: >-
Sneddon syndrome is a rare occlusive vasculopathy characterized by livedo
reticularis or livedo racemosa and recurrent ischemic cerebrovascular events.
The core disease mechanism is a chronic arteriopathy affecting skin and brain,
producing transient ischemic attacks, stroke, and progressive neurologic
impairment.
disease_term:
preferred_term: Sneddon syndrome
term:
id: MONDO:0008436
label: Sneddon syndrome
classifications:
harrisons_chapter:
- classification_value: CARDIOVASCULAR
parents:
- disease
pathophysiology:
- name: Monogenic Endothelial and Mural Cell Injury
description: >-
Sneddon syndrome is a clinically defined, etiologically heterogeneous
syndrome, and a minority of cases have an identified monogenic cause acting
on the small-vessel wall. Biallelic loss-of-function ADA2 variants (the
disorder named deficiency of adenosine deaminase 2, curated separately in
this knowledge base) produce compromised endothelial integrity with
endothelial activation and inflammation. A homozygous NOTCH3 nonsense
variant was reported in one consanguineous family with childhood-onset
Sneddon syndrome; NOTCH3 acts in the mural cells of small vessels. Both
converge on the occlusive small- and medium-vessel arteriopathy that defines
the syndrome. Most patients referred with Sneddon syndrome carry neither
lesion.
cell_types:
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
biological_processes:
- preferred_term: Notch signaling pathway
term:
id: GO:0007219
label: Notch signaling pathway
modifier: DECREASED
genes:
- preferred_term: ADA2
term:
id: hgnc:1839
label: ADA2
- preferred_term: NOTCH3
term:
id: hgnc:7883
label: NOTCH3
evidence:
- reference: PMID:24552284
reference_title: Early-onset stroke and vasculopathy associated with mutations in ADA2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Skin, liver, and brain biopsies revealed vasculopathic changes
characterized by compromised endothelial integrity, endothelial cellular
activation, and inflammation.
explanation: >-
States the vessel-wall lesion produced by recessive ADA2 loss of function,
which is the injury this node describes.
- reference: PMID:32980981
reference_title: >-
A NOTCH3 homozygous nonsense mutation in familial Sneddon syndrome with
pediatric stroke.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Our findings suggest that impaired NOTCH3 signaling is one underlying
disease mechanism and that bi-allelic loss-of-function mutation in NOTCH3
is a cause of familial Sneddon syndrome with pediatric stroke.
explanation: >-
States the NOTCH3 arm of this node, in patients carrying the Sneddon
syndrome diagnosis itself rather than a related vasculopathy.
downstream:
- target: Occlusive vasculopathy
causal_link_type: DIRECT
description: >-
Injury to the endothelium and to the mural cells of small and medium
arteries produces the subendothelial proliferation and luminal occlusion
that define the Sneddon arteriopathy.
- name: Occlusive vasculopathy
description: >-
Sneddon syndrome is understood as an occlusive vasculopathy or thrombotic
microangiopathy affecting small- and medium-sized vessels.
cell_types:
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
biological_processes:
- preferred_term: blood coagulation
term:
id: GO:0007596
label: blood coagulation
modifier: INCREASED
evidence:
- reference: DOI:10.1111/ddg.15422
reference_title: >-
Combination therapy for Sneddon syndrome to reduce the incidence of
cerebrovascular complications
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sneddon syndrome is an occlusive vasculopathy that presents clinically
with generalized livedo racemosa on the skin and transient ischemic
attacks, strokes, and cognitive or motor deficits in the central nervous
system.
explanation: >-
This directly supports occlusive vasculopathy as the central disease
mechanism.
downstream:
- target: Cerebral ischemic injury
description: >-
Occlusive cerebrovascular disease produces recurrent transient ischemic
attacks and strokes.
causal_link_type: DIRECT
evidence:
- reference: DOI:10.1111/ddg.15422
reference_title: >-
Combination therapy for Sneddon syndrome to reduce the incidence of
cerebrovascular complications
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sneddon syndrome is an occlusive vasculopathy that presents clinically
with generalized livedo racemosa on the skin and transient ischemic
attacks, strokes, and cognitive or motor deficits in the central
nervous system.
explanation: >-
The abstract directly links the vasculopathy to recurrent cerebral
ischemic events.
- target: Cutaneous livedo
description: >-
The same vasculopathy produces the characteristic generalized livedo skin
findings.
causal_link_type: DIRECT
evidence:
- reference: DOI:10.1111/ddg.15422
reference_title: >-
Combination therapy for Sneddon syndrome to reduce the incidence of
cerebrovascular complications
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sneddon syndrome is an occlusive vasculopathy that presents clinically
with generalized livedo racemosa on the skin and transient ischemic
attacks, strokes, and cognitive or motor deficits in the central
nervous system.
explanation: >-
This directly supports livedo as a cutaneous consequence of the
vasculopathy.
- name: Cerebral ischemic injury
description: >-
Recurrent occlusive cerebrovascular events produce stroke, cerebral
atrophy, and long-term neurologic impairment.
cell_types:
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
biological_processes:
- preferred_term: response to hypoxia
term:
id: GO:0001666
label: response to hypoxia
modifier: ABNORMAL
evidence:
- reference: PMID:17665002
reference_title: Clinical, neurovascular and neuropathological features in Sneddon's syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The patients had repeated ischemic cerebral episodes, livedo
reticularis and thrombocytopenia. CT and MRI showed strokes and cerebral
atrophy.
explanation: >-
This directly supports recurrent ischemic brain injury as a central
downstream mechanism.
downstream:
- target: Ischemic stroke
description: Recurrent cerebral ischemic injury manifests clinically as ischemic stroke.
causal_link_type: DIRECT
- name: Cutaneous livedo
description: >-
Generalized livedo reticularis or livedo racemosa is the characteristic
dermatologic expression of the underlying vasculopathy.
cell_types:
- preferred_term: endothelial cell
term:
id: CL:0000115
label: endothelial cell
biological_processes:
- preferred_term: vasoconstriction
term:
id: GO:0042310
label: vasoconstriction
modifier: ABNORMAL
evidence:
- reference: PMID:17665002
reference_title: Clinical, neurovascular and neuropathological features in Sneddon's syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sneddon's syndrome (SS) is characterized by ischemic cerebrovascular
episodes and livedo reticularis.
explanation: >-
This directly supports livedo as a defining cutaneous manifestation.
downstream:
- target: Livedo reticularis
description: The cutaneous vascular phenotype is expressed clinically as livedo reticularis.
causal_link_type: DIRECT
phenotypes:
- name: Livedo reticularis
category: Dermatologic
diagnostic: true
description: >-
Persistent livedo reticularis or livedo racemosa is a defining skin finding
in Sneddon syndrome.
phenotype_term:
preferred_term: Livedo reticularis
term:
id: HP:0033505
label: Livedo reticularis
evidence:
- reference: PMID:17665002
reference_title: Clinical, neurovascular and neuropathological features in Sneddon's syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Sneddon's syndrome (SS) is characterized by ischemic cerebrovascular
episodes and livedo reticularis.
explanation: >-
This directly supports livedo reticularis as a defining phenotype.
- name: Ischemic stroke
category: Neurologic
diagnostic: true
description: >-
Recurrent ischemic cerebral events are a central neurologic manifestation of
Sneddon syndrome.
phenotype_term:
preferred_term: Ischemic stroke
term:
id: HP:0002140
label: Ischemic stroke
evidence:
- reference: PMID:17665002
reference_title: Clinical, neurovascular and neuropathological features in Sneddon's syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The patients had repeated ischemic cerebral episodes, livedo
reticularis and thrombocytopenia. CT and MRI showed strokes and cerebral
atrophy.
explanation: >-
This directly supports stroke as a major neurologic consequence.
- name: Thrombocytopenia
category: Hematologic
description: >-
Thrombocytopenia can accompany the vascular syndrome in some affected
patients.
phenotype_term:
preferred_term: Thrombocytopenia
term:
id: HP:0001873
label: Thrombocytopenia
evidence:
- reference: PMID:17665002
reference_title: Clinical, neurovascular and neuropathological features in Sneddon's syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
The patients had repeated ischemic cerebral episodes, livedo
reticularis and thrombocytopenia.
explanation: >-
This directly supports thrombocytopenia as an associated phenotype in the
described cases.
biochemical: []
genetic:
- name: ADA2
relationship_type: UNKNOWN
gene_term:
preferred_term: ADA2
term:
id: hgnc:1839
label: ADA2
notes: >-
Graded UNKNOWN, which needs explaining, because the underlying biology is
not uncertain at all. Biallelic loss-of-function ADA2 variants cause
deficiency of adenosine deaminase 2 (DADA2) - ClinGen Definitive - and
DADA2 is curated in this knowledge base as its own entry (MONDO:0014306).
What is unclassified is the relationship between ADA2 and *this* disease
term. CAUSATIVE asserts the ClinGen Definitive or Strong tier for the
gene-disease pair the entry denotes, and no panel has curated ADA2 against
Sneddon syndrome; the Definitive call belongs to the other term. Grading
this CAUSATIVE would have the entry assert in a controlled field the exact
claim the rest of this note withdraws.
ADA2 is recorded here because a minority of patients carrying the Sneddon
syndrome diagnosis prove on testing to have DADA2: in the only series that
genotyped an adult Sneddon-spectrum cohort, 6 of the 32 genotyped patients
were biallelic. Plasma ADA2 activity separated the two groups with 100%
sensitivity and specificity in that series, so in current practice DADA2 is
the diagnosis that testing establishes rather than a subtype of Sneddon
syndrome. Note the naming history: ADA2 was formerly CECR1, which is the
symbol used throughout the 2014-2018 literature quoted below.
evidence:
- reference: PMID:30645994
reference_title: >-
Adenosine Deaminase Two and Immunoglobulin M Accurately Differentiate
Adult Sneddon's Syndrome of Unknown Cause.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
A total of 73 participants were included in the study: 26 patients with
PSnS with no CECR1 mutation (PSnS), 6 bi-allelic (DADA2 patients) and 7
HHZ CECR1 mutations and 34 HC.
explanation: >-
Quantifies the ADA2-attributable share of an adult Sneddon-spectrum
referral cohort, and is the source of the 6-of-32 figure in the note.
- reference: PMID:30645994
reference_title: >-
Adenosine Deaminase Two and Immunoglobulin M Accurately Differentiate
Adult Sneddon's Syndrome of Unknown Cause.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Serum IgM levels might be used as a triage tool and plasma ADA2 activity
performs perfectly as a diagnostic test for DADA2 in adult patients within
the SnS spectrum.
explanation: >-
Supports treating DADA2 as a diagnosis to be separated out of the Sneddon
spectrum by testing, which is why this gene is recorded with that caveat
rather than as a plain Sneddon syndrome subtype.
- reference: PMID:30645994
reference_title: >-
Adenosine Deaminase Two and Immunoglobulin M Accurately Differentiate
Adult Sneddon's Syndrome of Unknown Cause.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
With the use of the best indexes, plasma ADA2 activity differentiated PSnS
from DADA2 with a sensitivity and specificity of 100.0%
explanation: >-
Sources the diagnostic-accuracy figure quoted in the note above.
- reference: CGGV:assertion_e05f1338-6a58-4991-af3b-6433bd165a9f-2023-05-30T170000.000Z
reference_title: ADA2 / deficiency of adenosine deaminase 2 (Definitive)
supports: SUPPORT
directness: INDIRECT
evidence_source: OTHER
snippet: >-
ADA2 | HGNC:1839 | deficiency of adenosine deaminase 2 | MONDO:0100317 |
AR | Definitive | SOP9 | Antibody Deficiencies Gene Curation Expert Panel
explanation: >-
Sources the note's statement that the gene-disease relationship ClinGen
curates Definitive for ADA2 is deficiency of adenosine deaminase 2, not
Sneddon syndrome.
- reference: PMID:24552284
reference_title: Early-onset stroke and vasculopathy associated with mutations in ADA2.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Loss-of-function mutations in CECR1 were associated with a spectrum of
vascular and inflammatory phenotypes, ranging from early-onset recurrent
stroke to systemic vasculopathy or vasculitis.
explanation: >-
Establishes recessive ADA2 loss of function as causal for the vasculopathy
spectrum that includes the livedo-plus-stroke presentation.
- name: NOTCH3
relationship_type: UNKNOWN
gene_term:
preferred_term: NOTCH3
term:
id: hgnc:7883
label: NOTCH3
notes: >-
A homozygous NOTCH3 nonsense variant, p.(Arg735Ter), was identified by
exome sequencing in two affected siblings of one consanguineous family with
childhood-onset Sneddon syndrome. Graded UNKNOWN rather than CAUSATIVE:
CAUSATIVE asserts the ClinGen Definitive or Strong tier, and one
consanguineous family with no ClinGen curation for this gene-disease pair
does not reach it. The schema offers no Limited or Moderate tier, so
UNKNOWN - not yet classified - is the value that fits. Dominant NOTCH3
variants cause CADASIL, a different small-vessel disease of the brain. In the same study, exome sequencing of six further
unrelated Sneddon patients found no rare variant in NOTCH3 or in ADA2,
which is the direct evidence that neither gene accounts for most cases.
evidence:
- reference: PMID:32980981
reference_title: >-
A NOTCH3 homozygous nonsense mutation in familial Sneddon syndrome with
pediatric stroke.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We performed whole-exome sequencing (WES) in 2 affected siblings of a
consanguineous family with childhood-onset stroke and identified a
homozygous nonsense mutation within the epidermal growth factor repeat
(EGFr) 19 of NOTCH3, p.(Arg735Ter).
explanation: >-
The primary observation behind this record, including the specific allele
quoted in the note.
- reference: PMID:32980981
reference_title: >-
A NOTCH3 homozygous nonsense mutation in familial Sneddon syndrome with
pediatric stroke.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
We found none of the patients to carry a rare variant (MAF < 0.01) in the
NOTCH3 or in the ADA2 gene.
explanation: >-
The same study's negative result in six further Sneddon patients, which
bounds how much of the syndrome either gene explains.
- reference: PMID:32980981
reference_title: >-
A NOTCH3 homozygous nonsense mutation in familial Sneddon syndrome with
pediatric stroke.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
quote_role: BACKGROUND
snippet: >-
NOTCH3 encodes a transmembrane receptor predominantly expressed in mural
cells of small blood vessels that plays a critical role in their
integrity
explanation: >-
Sources the mural-cell role this entry attributes to NOTCH3. Taken from
the citing paper's introduction, where it restates established NOTCH3
biology rather than reporting a result of its own, hence BACKGROUND.
- name: F5
relationship_type: RISK_FACTOR
gene_term:
preferred_term: F5
term:
id: hgnc:3542
label: F5
notes: >-
Heterozygous factor V Leiden was found at higher frequency in
antiphospholipid-antibody-negative Sneddon syndrome than in
antibody-positive Sneddon syndrome in a single 53-patient series. This is a
thrombophilic susceptibility association in a subgroup, not a causal gene,
and no clinical difference was found between carriers and non-carriers
within the antibody-negative group. F5 is deliberately not wired to a
pathophysiology node: this entry models no thrombophilia mechanism, and
asserting one on the strength of a prevalence comparison would overstate
what the cited study measured.
evidence:
- reference: PMID:12765305
reference_title: Factor V Leiden mutation in Sneddon syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Factor V Leiden mutation was detected in six patients (11.3%),
heterozygous in all. The frequency of this mutation was statistically
higher in group 1 (6/31, 19.3%) than in group 2 (0/22; P = 0.035).
explanation: >-
The measured association, with the subgroup restriction that makes this a
risk-factor record rather than a causal one.
- reference: PMID:12765305
reference_title: Factor V Leiden mutation in Sneddon syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Within aPL-negative SNS, the comparison of patients with versus without
factor V Leiden mutation showed no difference for clinical data or
familial history of thrombosis.
explanation: >-
The same study's negative result on clinical correlates, recorded so the
association is not read as a phenotype-defining one.
environmental: []
treatments:
- name: Antiplatelet or anticoagulant therapy
description: >-
Antithrombotic pharmacotherapy is recommended to reduce recurrent ischemic
cerebrovascular complications.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
evidence:
- reference: DOI:10.1111/ddg.15422
reference_title: >-
Combination therapy for Sneddon syndrome to reduce the incidence of
cerebrovascular complications
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Antiplatelet or anticoagulant therapy is recommended.
explanation: >-
This directly supports antithrombotic therapy as standard treatment.
- name: Combination vasculoprotective pharmacotherapy
description: >-
Combination therapy adding alprostadil and captopril to standard
antithrombotic treatment may reduce recurrent ischemic events.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: alprostadil
term:
id: CHEBI:15544
label: prostaglandin E1
- preferred_term: captopril
term:
id: CHEBI:3380
label: captopril
evidence:
- reference: DOI:10.1111/ddg.15422
reference_title: >-
Combination therapy for Sneddon syndrome to reduce the incidence of
cerebrovascular complications
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Combination therapy reduces the long‐term incidence of ischemic events in
patients with primary Sneddon syndrome.
explanation: >-
This supports a more intensive combination pharmacotherapy approach in
primary disease.
diagnosis:
- name: Brain MRI
description: >-
Brain imaging is used to document stroke burden and cerebral atrophy in
suspected Sneddon syndrome.
diagnosis_term:
preferred_term: magnetic resonance imaging procedure
term:
id: NCIT:C16809
label: Magnetic Resonance Imaging
evidence:
- reference: PMID:17665002
reference_title: Clinical, neurovascular and neuropathological features in Sneddon's syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
CT and MRI showed strokes and cerebral atrophy.
explanation: >-
This directly supports neuroimaging as a core diagnostic assessment.
differential_diagnoses:
- name: Antiphospholipid syndrome
description: >-
Antiphospholipid syndrome can overlap clinically with Sneddon syndrome
because both can combine livedo and ischemic cerebrovascular disease.
disease_term:
preferred_term: antiphospholipid syndrome
term:
id: MONDO:8000010
label: antiphospholipid syndrome
evidence:
- reference: PMID:17665002
reference_title: Clinical, neurovascular and neuropathological features in Sneddon's syndrome.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Antiphospholipid antibodies may be found in some patients with ischemic
cerebrovascular events and livedo reticularis. SS may thus be associated
with antiphospholipid syndrome.
explanation: >-
This supports antiphospholipid syndrome as an important overlapping
diagnosis and differential consideration.
clinical_trials: []
datasets: []
notes: >-
Initial curation emphasizes the occlusive vasculopathy mechanism, recurrent
cerebral ischemia, and evidence-backed treatment and imaging sections from
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