STX1B-Related Epilepsy

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Inheritance

1

Autosomal Dominant HP:0000006

STX1B variants cosegregate as an autosomal dominant trait in large pedigrees; de novo variants (including a microdeletion) also occur.

Autosomal dominant inheritance

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"Whole-exome sequencing in independent large pedigrees identified cosegregating STX1B mutations predicted to cause an early truncation or an in-frame insertion or deletion."

Establishes the autosomal dominant, cosegregating inheritance of STX1B variants.

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Discussions and Knowledge Gaps

3

What is the molecular basis by which syntaxin-1B deficiency renders synaptic vesicle fusion temperature-sensitive, so that seizures cluster with fever rather than occurring uniformly across the physiological temperature range?

KNOWLEDGE GAP OPEN gap_stx1b_temperature_sensitivity_mechanism

Attached to

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion pathophysiology#Temperature-Sensitive Cortical Hyperexcitability

The defining clinical feature of STX1B-related epilepsy is fever-triggered seizures, and the zebrafish stx1b-knockdown model reproduces a highly temperature-sensitive epileptiform phenotype. Yet the biophysical mechanism linking reduced syntaxin-1B dosage to temperature-dependent release failure is unresolved: whether a partially depleted SNARE machine has reduced thermal reserve, whether syntaxin-1B/Munc18-1 chaperoning is temperature-labile, or whether excitatory and inhibitory terminals fail asymmetrically as temperature rises. Distinguishing these is prerequisite to explaining the fever specificity and to rational antipyretic-independent therapy.

Proposed experiments

Temperature-dependent release titration in syntaxin-1B-reduced neurons

temperature-dependent synaptic release titration

exp_stx1b_temperature_release_titration

In human iPSC-derived neurons with graded syntaxin-1B reduction (allelic series spanning haploinsufficiency to near-complete loss), measure evoked and spontaneous excitatory and inhibitory release across a controlled temperature ramp, correlating release probability and SNARE-complex assembly with temperature to test whether reduced dosage narrows the thermal operating range.

Perturbations

Graded syntaxin-1B reduction

pathophysiology#Syntaxin-1B t-SNARE Deficiency

Titrate syntaxin-1B levels across an allelic series in an isogenic human neuronal background.

STX1B hgnc:18539

Readouts

Temperature-resolved synaptic release and fusion

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion

calcium-dependent activation of synaptic vesicle fusion GO:0099502 ↓ DECREASED synaptic vesicle exocytosis GO:0016079 ↓ DECREASED

patch-clamp electrophysiology live-cell imaging assay

Direction: NEGATIVE

Controls

Wild-type syntaxin-1B neurons

Isogenic neurons with unperturbed syntaxin-1B across the same temperature ramp.

Decision criterion

A dosage-dependent narrowing of the thermal operating range for evoked release, emerging selectively at febrile temperatures, would support reduced thermal reserve of the depleted SNARE machine as the mechanism.

Would support

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion pathophysiology#Temperature-Sensitive Cortical Hyperexcitability

Show evidence (1 reference)

PMID:25362483 SUPPORT Model Organism

"Video and local field potential analyses of zebrafish larvae with antisense knockdown of stx1b showed seizure-like behavior and epileptiform discharges that were highly sensitive to increased temperature."

Establishes the temperature-sensitive phenotype whose molecular mechanism remains unexplained.

What determines an individual's position on the STX1B severity spectrum (simple febrile seizures, to GEFS+, to developmental and epileptic encephalopathy) - is it primarily loss-of-function dosage versus missense/dominant-negative effect, or do modifiers dominate?

OPEN QUESTION OPEN gap_stx1b_genotype_severity_determinants

Attached to

pathophysiology#Syntaxin-1B t-SNARE Deficiency

STX1B variants span early-truncating and whole-gene-deletion (clear haploinsufficiency) through in-frame indel and missense changes that could act as reduced-function or dominant-negative alleles incorporated into the SNARE complex. The reported phenotype ranges from benign febrile seizures to severe encephalopathy, but whether variant class predicts severity - or whether genetic background and other GEFS+ modifiers dominate - is unresolved. This directly affects prognostic counseling and whether a variant should be curated as a distinct severity subtype.

Proposed experiments

Variant-class functional stratification against clinical severity

variant functional stratification experiment

exp_stx1b_variant_class_functional_severity

Introduce a panel of reported STX1B variants (truncating, whole-gene loss, in-frame indel, missense) into an isogenic neuronal background and quantify release deficit and dominant-negative incorporation into the SNARE complex, then test whether the functional severity ranking correlates with the documented clinical severity of carriers.

Perturbations

STX1B allelic panel knock-in

pathophysiology#Syntaxin-1B t-SNARE Deficiency

Knock in individual STX1B variant classes into a shared human neuronal background for standardized functional comparison.

STX1B hgnc:18539

Readouts

Release deficit and SNARE-complex incorporation

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion

synaptic vesicle exocytosis GO:0016079 ↓ DECREASED

patch-clamp electrophysiology co-immunoprecipitation assay

Direction: NEGATIVE

Controls

Wild-type STX1B knock-in

Isogenic neurons carrying wild-type STX1B.

Benign population variant

A population variant incompatible with disease causality.

Decision criterion

If functional severity rank (dominant-negative missense worst, haploinsufficiency intermediate) tracks clinical severity, variant class is a primary determinant; a weak correlation implicates modifiers.

Would support

pathophysiology#Syntaxin-1B t-SNARE Deficiency

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"Three additional nonsense or missense mutations and a de novo microdeletion encompassing STX1B were then identified in 449 familial or sporadic cases."

Documents the heterogeneous variant spectrum (truncating, missense, whole-gene deletion) whose relation to severity is the open question.

Does the closely related paralog syntaxin-1A partially compensate for syntaxin-1B loss, and could its regional/developmental expression explain phenotype variability and offer a therapeutic lever (upregulating STX1A to rescue release)?

EMERGING HYPOTHESIS OPEN gap_stx1b_stx1a_redundancy_therapeutic_lever

Attached to

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion

Syntaxin-1A and syntaxin-1B are highly homologous plasma-membrane t-SNAREs that can both support calcium-triggered fusion, so residual release in STX1B-deficient neurons may depend on syntaxin-1A availability. If compensation is incomplete and varies with the regional and developmental expression ratio of the two paralogs, that could contribute to the fever-dependence and phenotypic variability - and raising syntaxin-1A expression or function becomes a candidate disease-modifying strategy. This is an emerging, largely untested hypothesis for STX1B disease rather than an established mechanism.

Proposed experiments

Syntaxin-1A dosage compensation of syntaxin-1B loss

paralog compensation rescue experiment

exp_stx1b_stx1a_compensation_rescue

In syntaxin-1B-deficient human neurons, titrate syntaxin-1A expression and measure whether increased syntaxin-1A restores evoked release and rescues the temperature-sensitive release deficit, and profile the native STX1A:STX1B expression ratio across neuronal subtypes to test the regional-compensation model.

Perturbations

Syntaxin-1A overexpression on STX1B-deficient background

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion

Increase syntaxin-1A expression in syntaxin-1B-deficient neurons to test functional compensation.

STX1A hgnc:11433

Readouts

Rescue of evoked release

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion

calcium-dependent activation of synaptic vesicle fusion GO:0099502 ↓ DECREASED

patch-clamp electrophysiology

Direction: POSITIVE

Controls

STX1B-deficient neurons without STX1A manipulation

Matched syntaxin-1B-deficient neurons at baseline syntaxin-1A levels.

Wild-type neurons

Isogenic neurons with intact syntaxin-1B.

Decision criterion

Dose-dependent rescue of evoked release and temperature sensitivity by syntaxin-1A would support paralog compensation as a determinant of severity and a therapeutic lever; failure to rescue would argue against it.

Would support

pathophysiology#Impaired SNARE-Mediated Vesicle Fusion

Show evidence (1 reference)

PMID:32559416 SUPPORT Other

"Neuronal SNAREs and their key regulators together drive synaptic vesicle exocytosis and synaptic transmission as a single integrated membrane fusion machine."

Frames syntaxin-1B within an integrated SNARE machine in which paralog substitution by syntaxin-1A is a plausible compensatory route.

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Pathophysiology

3

Syntaxin-1B t-SNARE Deficiency

STX1B encodes syntaxin-1B, a plasma-membrane t-SNARE of the presynaptic release machinery. Truncating, in-frame indel, missense, and whole-gene-deletion variants reduce or impair syntaxin-1B function. Syntaxin-1B is chaperoned by Munc18-1 and partners with SNAP-25 and VAMP2 in the SNARE complex, so its deficiency degrades the fusion machinery.

neuron CL:0000540

synaptic vesicle cycle GO:0099504 ⚠ ABNORMAL

brain UBERON:0000955

Downstream

Impaired SNARE-Mediated Vesicle Fusion Syntaxin-1B is a core SNARE, so variants that unfold it, deplete it, or disturb its Munc18-1 interface degrade the fusion machinery itself.

Show evidence (2 references)

PMID:25362483 SUPPORT Human Clinical

"Here we report the identification of mutations in STX1B, encoding syntaxin-1B, that are associated with both febrile seizures and epilepsy."

Identifies STX1B/syntaxin-1B as the presynaptic-release-machinery gene whose variants cause the disorder.

PMID:25362483 SUPPORT Human Clinical

"Three additional nonsense or missense mutations and a de novo microdeletion encompassing STX1B were then identified in 449 familial or sporadic cases."

Defines the loss-of-function variant spectrum, including a whole-gene microdeletion.

Impaired SNARE-Mediated Vesicle Fusion

Syntaxin-1B is one of the three core neuronal SNAREs whose calcium-triggered zippering fuses the synaptic vesicle with the presynaptic membrane. Impaired syntaxin-1B function degrades SNARE-complex assembly and disturbs neurotransmitter release, implicating the presynaptic release machinery in the disorder. This is the module's key conformance target — the fusion-machinery arm.

neuron CL:0000540

calcium-dependent activation of synaptic vesicle fusion GO:0099502 ↓ DECREASED synaptic vesicle exocytosis GO:0016079 ↓ DECREASED

Downstream

Temperature-Sensitive Cortical Hyperexcitability Degraded presynaptic release disturbs the excitatory/inhibitory balance of cortical circuits, and the resulting hyperexcitability is temperature sensitive.

Show evidence (2 references)

PMID:25362483 SUPPORT Human Clinical

"Our results thus implicate STX1B and the presynaptic release machinery in fever-associated epilepsy syndromes."

Directly implicates syntaxin-1B and the presynaptic release (fusion) machinery in the disorder.

PMID:32559416 SUPPORT Other

"Neuronal SNAREs and their key regulators together drive synaptic vesicle exocytosis and synaptic transmission as a single integrated membrane fusion machine."

Establishes syntaxin-1B (a core SNARE) as part of the integrated fusion machine.

Temperature-Sensitive Cortical Hyperexcitability

Impaired presynaptic release disturbs cortical excitatory/inhibitory balance, producing neuronal hyperexcitability with a characteristic temperature sensitivity: in a zebrafish stx1b-knockdown model, seizure-like behavior and epileptiform discharges are highly sensitive to increased temperature, mirroring the fever-triggered seizures in patients.

neuron CL:0000540

chemical synaptic transmission GO:0007268 ⚠ ABNORMAL

brain UBERON:0000955

Downstream

Febrile Seizures Because the hyperexcitability is temperature dependent, a rise in body temperature is what tips the network into a seizure - the fever-associated presentation.

Epilepsy The same hyperexcitability also produces afebrile, unprovoked seizures, so the disorder spans a spectrum from GEFS+ through generalized and focal epilepsies to developmental and epileptic encephalopathy.

Show evidence (1 reference)

PMID:25362483 SUPPORT Model Organism

"Video and local field potential analyses of zebrafish larvae with antisense knockdown of stx1b showed seizure-like behavior and epileptiform discharges that were highly sensitive to increased temperature."

A zebrafish model links stx1b loss to temperature-sensitive seizures, the mechanistic basis of the fever-associated phenotype.

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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

2

Febrile Seizures Clinical HP:0002373

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"Here we report the identification of mutations in STX1B, encoding syntaxin-1B, that are associated with both febrile seizures and epilepsy."

Documents febrile seizures as a core phenotype of STX1B variants.

Epilepsy Clinical HP:0001250

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"mutations in STX1B, encoding syntaxin-1B, that are associated with both febrile seizures and epilepsy."

Documents afebrile epilepsy in addition to febrile seizures.

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Genetic Associations

1

STX1B (Loss-of-Function Mutations)

Gene: STX1B hgnc:18539 variant_origin: GERMLINE

Autosomal Dominant

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"Three additional nonsense or missense mutations and a de novo microdeletion encompassing STX1B were then identified in 449 familial or sporadic cases."

Defines the STX1B loss-of-function variant spectrum across a large cohort.

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Medical Actions

2

Antiseizure Medication

Action: Pharmacotherapy NCIT:C15986

Agent: levetiracetam CHEBI:6437

Seizures are managed with antiseizure medications, guided by the specific epilepsy syndrome.

Genetic Counseling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Genetic counseling addresses the autosomal dominant inheritance and variable expressivity within families.

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Diagnosis

1

STX1B Molecular Diagnosis

Diagnosis is established by identifying a pathogenic STX1B variant (truncating, indel, missense, or whole-gene deletion) in an individual with febrile seizures and/or epilepsy, often with a dominant family history.

molecular genetic testing NCIT:C19770

Results: A pathogenic STX1B variant establishes the diagnosis.

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"Three additional nonsense or missense mutations and a de novo microdeletion encompassing STX1B were then identified in 449 familial or sporadic cases."

Molecular identification of STX1B variants establishes the diagnosis.

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Progression

1

Childhood

Presentation is typically with febrile seizures in early childhood, which may be followed by afebrile seizures (GEFS+); a subset progress to a more severe developmental and epileptic encephalopathy.

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"Febrile seizures affect 2-4% of all children and have a strong genetic component."

Contextualizes the childhood febrile-seizure presentation.

📊

Prevalence

1

Worldwide

Unknown Ultra Rare

Rare presynaptic (SNAREopathy) epilepsy syndrome within the fever-associated / GEFS+ spectrum; precise population prevalence not established.

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Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from STX1B-Related Epilepsy:

Other GEFS+ genes (SCN1A, SCN1B, GABRG2)

Overlapping Features Generalized epilepsy with febrile seizures plus is genetically heterogeneous; SCN1A, SCN1B, and GABRG2 are the classic GEFS+ genes and are distinguished from STX1B by molecular testing.

Distinguishing Features

A pathogenic STX1B variant favors this disorder.
A variant in SCN1A, SCN1B, or GABRG2 favors that GEFS+ subtype.

Show evidence (1 reference)

PMID:25362483 SUPPORT Human Clinical

"Recurrent mutations in three main genes (SCN1A, SCN1B and GABRG2) have been identified that cause febrile seizures with or without epilepsy."

Names the classic GEFS+ genes that constitute the molecular differential diagnosis.

Other SNAREopathies and synaptic vesicle cycle disorders

Overlapping Features Other SNARE-machinery and synaptic vesicle cycle disorders (SNAP25, VAMP2, STXBP1) overlap through early-onset epilepsy and developmental impairment and are distinguished by molecular testing.

Distinguishing Features

A pathogenic STX1B variant favors this disorder.
A variant in another SNARE/vesicle-cycle gene favors the corresponding SNAREopathy.

🐁

Animal Models

1

stx1b antisense knockdown (morphant) Zebrafish (Danio rerio)

Zebrafish larvae with antisense knockdown of stx1b show seizure-like behavior and epileptiform discharges that are highly sensitive to increased temperature; wild-type human syntaxin-1B, but not a mutated protein, rescues the phenotype, demonstrating the loss-of-function, temperature-sensitive mechanism.

Species

Zebrafish (Danio rerio)

Genotype

stx1b antisense knockdown (morphant)

Show evidence (1 reference)

PMID:25362483 SUPPORT Model Organism

"Wild-type human syntaxin-1B but not a mutated protein rescued the effects of stx1b knockdown in zebrafish."

Rescue by wild-type but not mutant syntaxin-1B confirms the loss-of-function disease mechanism.

{ }

Source YAML

click to show

name: STX1B-Related Epilepsy
creation_date: "2026-07-06T00:00:00Z"
description: >-
  An epilepsy spectrum caused by variants in STX1B, which encodes syntaxin-1B, a
  core plasma-membrane (t-)SNARE of the presynaptic release machinery. With its
  partners SNAP-25 and synaptobrevin-2/VAMP2, syntaxin-1B forms the neuronal SNARE
  complex that drives calcium-triggered synaptic vesicle fusion; it is also
  chaperoned by Munc18-1 (STXBP1). Truncating, in-frame indel, missense, and
  whole-gene-deletion variants impair the release machinery, producing
  fever-associated epilepsy syndromes ranging from simple febrile seizures to
  generalized epilepsy with febrile seizures plus (GEFS+), and in some individuals
  a more severe developmental and epileptic encephalopathy. It is one of the
  SNAREopathies and completes the three core neuronal SNAREs among the synaptic
  vesicle cycle disorders (the plasma-membrane t-SNARE, alongside SNAP-25 and the
  v-SNARE VAMP2).
category: Mendelian
parents:
- Neurodevelopmental Disorder
- Epilepsy
disease_term:
  preferred_term: generalized epilepsy with febrile seizures plus, type 9
  term:
    id: MONDO:0014517
    label: generalized epilepsy with febrile seizures plus, type 9
prevalence:
- population: Worldwide
  measure_type: UNKNOWN
  prevalence_class: ULTRA_RARE
  notes: >-
    Rare presynaptic (SNAREopathy) epilepsy syndrome within the fever-associated / GEFS+ spectrum; precise population prevalence not established.
references:
- reference: PMID:25362483
  title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
- reference: PMID:32559416
  title: "SNAREopathies: Diversity in Mechanisms and Symptoms."
inheritance:
- name: Autosomal Dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    STX1B variants cosegregate as an autosomal dominant trait in large pedigrees;
    de novo variants (including a microdeletion) also occur.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Whole-exome sequencing in independent large pedigrees identified
      cosegregating STX1B mutations predicted to cause an early truncation or an
      in-frame insertion or deletion.
    explanation: >-
      Establishes the autosomal dominant, cosegregating inheritance of STX1B
      variants.
pathophysiology:
- name: Syntaxin-1B t-SNARE Deficiency
  conforms_to: "synaptic_vesicle_cycle#Synaptic Vesicle Cycle Protein Deficiency"
  description: >-
    STX1B encodes syntaxin-1B, a plasma-membrane t-SNARE of the presynaptic release
    machinery. Truncating, in-frame indel, missense, and whole-gene-deletion
    variants reduce or impair syntaxin-1B function. Syntaxin-1B is chaperoned by
    Munc18-1 and partners with SNAP-25 and VAMP2 in the SNARE complex, so its
    deficiency degrades the fusion machinery.
  role: trigger
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: synaptic vesicle cycle
    term:
      id: GO:0099504
      label: synaptic vesicle cycle
    modifier: ABNORMAL
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here we report the identification of mutations in STX1B, encoding
      syntaxin-1B, that are associated with both febrile seizures and epilepsy.
    explanation: >-
      Identifies STX1B/syntaxin-1B as the presynaptic-release-machinery gene whose
      variants cause the disorder.
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Three additional nonsense or missense mutations and a de novo microdeletion
      encompassing STX1B were then identified in 449 familial or sporadic cases.
    explanation: >-
      Defines the loss-of-function variant spectrum, including a whole-gene
      microdeletion.
  downstream:
  - target: Impaired SNARE-Mediated Vesicle Fusion
    causal_link_type: DIRECT
    description: >-
      Syntaxin-1B is a core SNARE, so variants that unfold it, deplete it, or
      disturb its Munc18-1 interface degrade the fusion machinery itself.
    evidence:
    - reference: PMID:32572454
      reference_title: "Epilepsy-causing STX1B mutations translate altered protein functions into distinct phenotypes in mouse neurons."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "STX1BG226R, causing epileptic encephalopathies, strongly compromises the interaction with Munc18-1 and reduces expression of both proteins, the size of the readily releasable pool of vesicles, and Ca2+-triggered neurotransmitter release when expressed in STX1-null neurons."
      explanation: >-
        Electrophysiology in STX1-null neurons shows an epilepsy-causing STX1B
        variant shrinking the readily releasable vesicle pool and reducing
        calcium-triggered release, which is the fusion defect this edge asserts.
    - reference: PMID:32572454
      reference_title: "Epilepsy-causing STX1B mutations translate altered protein functions into distinct phenotypes in mouse neurons."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "leads to an unfolded protein unable to sustain neurotransmission"
      explanation: >-
        Shows the milder fever-associated indel variant acting through the same
        route - a syntaxin-1B protein that cannot support release.
- name: Impaired SNARE-Mediated Vesicle Fusion
  conforms_to: "synaptic_vesicle_cycle#Impaired Calcium-Triggered SNARE-Mediated Vesicle Fusion"
  description: >-
    Syntaxin-1B is one of the three core neuronal SNAREs whose calcium-triggered
    zippering fuses the synaptic vesicle with the presynaptic membrane. Impaired
    syntaxin-1B function degrades SNARE-complex assembly and disturbs
    neurotransmitter release, implicating the presynaptic release machinery in the
    disorder. This is the module's key conformance target — the fusion-machinery
    arm.
  role: central_effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: calcium-dependent activation of synaptic vesicle fusion
    term:
      id: GO:0099502
      label: calcium-dependent activation of synaptic vesicle fusion
    modifier: DECREASED
  - preferred_term: synaptic vesicle exocytosis
    term:
      id: GO:0016079
      label: synaptic vesicle exocytosis
    modifier: DECREASED
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our results thus implicate STX1B and the presynaptic release machinery in
      fever-associated epilepsy syndromes.
    explanation: >-
      Directly implicates syntaxin-1B and the presynaptic release (fusion)
      machinery in the disorder.
  - reference: PMID:32559416
    reference_title: "SNAREopathies: Diversity in Mechanisms and Symptoms."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Neuronal SNAREs and their key regulators together drive synaptic vesicle
      exocytosis and synaptic transmission as a single integrated membrane fusion
      machine.
    explanation: >-
      Establishes syntaxin-1B (a core SNARE) as part of the integrated fusion
      machine.
  downstream:
  - target: Temperature-Sensitive Cortical Hyperexcitability
    causal_link_type: DIRECT
    description: >-
      Degraded presynaptic release disturbs the excitatory/inhibitory balance of
      cortical circuits, and the resulting hyperexcitability is temperature
      sensitive.
    evidence:
    - reference: PMID:25362483
      reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Wild-type human syntaxin-1B but not a mutated protein rescued the effects of stx1b knockdown in zebrafish."
      explanation: >-
        The rescue arm is what makes this a causal rather than correlative link:
        restoring functional syntaxin-1B abolishes the hyperexcitable phenotype,
        while the mutant protein does not.
- name: Temperature-Sensitive Cortical Hyperexcitability
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Neuronal Hyperexcitability and Hypersynchrony"
  description: >-
    Impaired presynaptic release disturbs cortical excitatory/inhibitory balance,
    producing neuronal hyperexcitability with a characteristic temperature
    sensitivity: in a zebrafish stx1b-knockdown model, seizure-like behavior and
    epileptiform discharges are highly sensitive to increased temperature,
    mirroring the fever-triggered seizures in patients.
  role: effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: chemical synaptic transmission
    term:
      id: GO:0007268
      label: chemical synaptic transmission
    modifier: ABNORMAL
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Video and local field potential analyses of zebrafish larvae with antisense
      knockdown of stx1b showed seizure-like behavior and epileptiform discharges
      that were highly sensitive to increased temperature.
    explanation: >-
      A zebrafish model links stx1b loss to temperature-sensitive seizures, the
      mechanistic basis of the fever-associated phenotype.
  downstream:
  - target: Febrile Seizures
    causal_link_type: DIRECT
    description: >-
      Because the hyperexcitability is temperature dependent, a rise in body
      temperature is what tips the network into a seizure - the fever-associated
      presentation.
    evidence:
    - reference: PMID:25362483
      reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "epileptiform discharges that were highly sensitive to increased temperature"
      explanation: >-
        Establishes temperature as the trigger converting the hyperexcitable
        state into discharges, which is the fever dependence this edge asserts.
  - target: Epilepsy
    causal_link_type: DIRECT
    description: >-
      The same hyperexcitability also produces afebrile, unprovoked seizures,
      so the disorder spans a spectrum from GEFS+ through generalized and focal
      epilepsies to developmental and epileptic encephalopathy.
    evidence:
    - reference: PMID:30737342
      reference_title: "Clinical spectrum of STX1B-related epileptic disorders."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This work suggests a role for ultrarare STX1B variants in the pathogenesis of a broad range of both common and rare epilepsies."
      explanation: >-
        A 23-family cohort establishes that STX1B variants cause epilepsy beyond
        the febrile presentation, supporting an afebrile epilepsy outcome of the
        same hyperexcitable state.
phenotypes:
- name: Febrile Seizures
  category: Clinical
  description: >-
    Fever-associated (febrile) seizures, the hallmark early presentation, reflecting
    temperature-sensitive cortical hyperexcitability.
  diagnostic: true
  phenotype_term:
    preferred_term: Febrile seizure
    term:
      id: HP:0002373
      label: Febrile seizure (within the age range of 3 months to 6 years)
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here we report the identification of mutations in STX1B, encoding
      syntaxin-1B, that are associated with both febrile seizures and epilepsy.
    explanation: >-
      Documents febrile seizures as a core phenotype of STX1B variants.
- name: Epilepsy
  category: Clinical
  description: >-
    Epilepsy spanning generalized epilepsy with febrile seizures plus (GEFS+) and,
    in some individuals, a more severe developmental and epileptic encephalopathy.
  diagnostic: true
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      mutations in STX1B, encoding syntaxin-1B, that are associated with both
      febrile seizures and epilepsy.
    explanation: >-
      Documents afebrile epilepsy in addition to febrile seizures.
genetic:
- name: STX1B
  gene_term:
    preferred_term: STX1B
    term:
      id: hgnc:18539
      label: STX1B
  association: Loss-of-Function Mutations
  presence: Positive
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal Dominant
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
  notes: >-
    Variants include early-truncating, in-frame insertion/deletion, nonsense, and
    missense changes, as well as a de novo whole-gene microdeletion, consistent
    with a loss-of-function mechanism affecting syntaxin-1B.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Three additional nonsense or missense mutations and a de novo microdeletion
      encompassing STX1B were then identified in 449 familial or sporadic cases.
    explanation: >-
      Defines the STX1B loss-of-function variant spectrum across a large cohort.
diagnosis:
- name: STX1B Molecular Diagnosis
  description: >-
    Diagnosis is established by identifying a pathogenic STX1B variant (truncating,
    indel, missense, or whole-gene deletion) in an individual with febrile seizures
    and/or epilepsy, often with a dominant family history.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
    qualifiers:
    - predicate:
        preferred_term: has participant
        term:
          id: RO:0000057
          label: has participant
      value:
        preferred_term: STX1B
        term:
          id: hgnc:18539
          label: STX1B
  results: A pathogenic STX1B variant establishes the diagnosis.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Three additional nonsense or missense mutations and a de novo microdeletion
      encompassing STX1B were then identified in 449 familial or sporadic cases.
    explanation: >-
      Molecular identification of STX1B variants establishes the diagnosis.
differential_diagnoses:
- name: Other GEFS+ genes (SCN1A, SCN1B, GABRG2)
  description: >-
    Generalized epilepsy with febrile seizures plus is genetically heterogeneous;
    SCN1A, SCN1B, and GABRG2 are the classic GEFS+ genes and are distinguished from
    STX1B by molecular testing.
  distinguishing_features:
  - A pathogenic STX1B variant favors this disorder.
  - A variant in SCN1A, SCN1B, or GABRG2 favors that GEFS+ subtype.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recurrent mutations in three main genes (SCN1A, SCN1B and GABRG2) have been
      identified that cause febrile seizures with or without epilepsy.
    explanation: >-
      Names the classic GEFS+ genes that constitute the molecular differential
      diagnosis.
- name: Other SNAREopathies and synaptic vesicle cycle disorders
  description: >-
    Other SNARE-machinery and synaptic vesicle cycle disorders (SNAP25, VAMP2,
    STXBP1) overlap through early-onset epilepsy and developmental impairment and
    are distinguished by molecular testing.
  distinguishing_features:
  - A pathogenic STX1B variant favors this disorder.
  - A variant in another SNARE/vesicle-cycle gene favors the corresponding SNAREopathy.
animal_models:
- species: Zebrafish (Danio rerio)
  genotype: stx1b antisense knockdown (morphant)
  description: >-
    Zebrafish larvae with antisense knockdown of stx1b show seizure-like behavior
    and epileptiform discharges that are highly sensitive to increased temperature;
    wild-type human syntaxin-1B, but not a mutated protein, rescues the phenotype,
    demonstrating the loss-of-function, temperature-sensitive mechanism.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Wild-type human syntaxin-1B but not a mutated protein rescued the effects of
      stx1b knockdown in zebrafish.
    explanation: >-
      Rescue by wild-type but not mutant syntaxin-1B confirms the loss-of-function
      disease mechanism.
progression:
- phase: Childhood
  notes: >-
    Presentation is typically with febrile seizures in early childhood, which may be
    followed by afebrile seizures (GEFS+); a subset progress to a more severe
    developmental and epileptic encephalopathy.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Febrile seizures affect 2-4% of all children and have a strong genetic
      component.
    explanation: >-
      Contextualizes the childhood febrile-seizure presentation.
treatments:
- name: Antiseizure Medication
  description: >-
    Seizures are managed with antiseizure medications, guided by the specific
    epilepsy syndrome.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: levetiracetam
      term:
        id: CHEBI:6437
        label: levetiracetam
- name: Genetic Counseling
  description: >-
    Genetic counseling addresses the autosomal dominant inheritance and variable
    expressivity within families.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
discussions:
- discussion_id: gap_stx1b_temperature_sensitivity_mechanism
  prompt: >-
    What is the molecular basis by which syntaxin-1B deficiency renders synaptic
    vesicle fusion temperature-sensitive, so that seizures cluster with fever
    rather than occurring uniformly across the physiological temperature range?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Impaired SNARE-Mediated Vesicle Fusion
  - pathophysiology#Temperature-Sensitive Cortical Hyperexcitability
  rationale: >-
    The defining clinical feature of STX1B-related epilepsy is fever-triggered
    seizures, and the zebrafish stx1b-knockdown model reproduces a highly
    temperature-sensitive epileptiform phenotype. Yet the biophysical mechanism
    linking reduced syntaxin-1B dosage to temperature-dependent release failure
    is unresolved: whether a partially depleted SNARE machine has reduced thermal
    reserve, whether syntaxin-1B/Munc18-1 chaperoning is temperature-labile, or
    whether excitatory and inhibitory terminals fail asymmetrically as
    temperature rises. Distinguishing these is prerequisite to explaining the
    fever specificity and to rational antipyretic-independent therapy.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Video and local field potential analyses of zebrafish larvae with antisense
      knockdown of stx1b showed seizure-like behavior and epileptiform discharges
      that were highly sensitive to increased temperature.
    explanation: >-
      Establishes the temperature-sensitive phenotype whose molecular mechanism
      remains unexplained.
  proposed_experiments:
  - experiment_id: exp_stx1b_temperature_release_titration
    name: Temperature-dependent release titration in syntaxin-1B-reduced neurons
    description: >-
      In human iPSC-derived neurons with graded syntaxin-1B reduction (allelic
      series spanning haploinsufficiency to near-complete loss), measure
      evoked and spontaneous excitatory and inhibitory release across a
      controlled temperature ramp, correlating release probability and
      SNARE-complex assembly with temperature to test whether reduced dosage
      narrows the thermal operating range.
    experiment_type:
      preferred_term: temperature-dependent synaptic release titration
    perturbations:
    - name: Graded syntaxin-1B reduction
      target: pathophysiology#Syntaxin-1B t-SNARE Deficiency
      genes:
      - preferred_term: STX1B
        term:
          id: hgnc:18539
          label: STX1B
      description: >-
        Titrate syntaxin-1B levels across an allelic series in an isogenic
        human neuronal background.
    readouts:
    - name: Temperature-resolved synaptic release and fusion
      target: pathophysiology#Impaired SNARE-Mediated Vesicle Fusion
      biological_processes:
      - preferred_term: calcium-dependent activation of synaptic vesicle fusion
        term:
          id: GO:0099502
          label: calcium-dependent activation of synaptic vesicle fusion
        modifier: DECREASED
      - preferred_term: synaptic vesicle exocytosis
        term:
          id: GO:0016079
          label: synaptic vesicle exocytosis
        modifier: DECREASED
      assays:
      - preferred_term: patch-clamp electrophysiology
      - preferred_term: live-cell imaging assay
      direction: NEGATIVE
    controls:
    - name: Wild-type syntaxin-1B neurons
      description: Isogenic neurons with unperturbed syntaxin-1B across the same temperature ramp.
    decision_criterion: >-
      A dosage-dependent narrowing of the thermal operating range for evoked
      release, emerging selectively at febrile temperatures, would support
      reduced thermal reserve of the depleted SNARE machine as the mechanism.
    would_support:
    - pathophysiology#Impaired SNARE-Mediated Vesicle Fusion
    - pathophysiology#Temperature-Sensitive Cortical Hyperexcitability

- discussion_id: gap_stx1b_genotype_severity_determinants
  prompt: >-
    What determines an individual's position on the STX1B severity spectrum
    (simple febrile seizures, to GEFS+, to developmental and epileptic
    encephalopathy) - is it primarily loss-of-function dosage versus
    missense/dominant-negative effect, or do modifiers dominate?
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - pathophysiology#Syntaxin-1B t-SNARE Deficiency
  rationale: >-
    STX1B variants span early-truncating and whole-gene-deletion (clear
    haploinsufficiency) through in-frame indel and missense changes that could
    act as reduced-function or dominant-negative alleles incorporated into the
    SNARE complex. The reported phenotype ranges from benign febrile seizures to
    severe encephalopathy, but whether variant class predicts severity - or
    whether genetic background and other GEFS+ modifiers dominate - is
    unresolved. This directly affects prognostic counseling and whether a
    variant should be curated as a distinct severity subtype.
  evidence:
  - reference: PMID:25362483
    reference_title: "Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Three additional nonsense or missense mutations and a de novo microdeletion
      encompassing STX1B were then identified in 449 familial or sporadic cases.
    explanation: >-
      Documents the heterogeneous variant spectrum (truncating, missense,
      whole-gene deletion) whose relation to severity is the open question.
  proposed_experiments:
  - experiment_id: exp_stx1b_variant_class_functional_severity
    name: Variant-class functional stratification against clinical severity
    description: >-
      Introduce a panel of reported STX1B variants (truncating, whole-gene
      loss, in-frame indel, missense) into an isogenic neuronal background and
      quantify release deficit and dominant-negative incorporation into the
      SNARE complex, then test whether the functional severity ranking
      correlates with the documented clinical severity of carriers.
    experiment_type:
      preferred_term: variant functional stratification experiment
    perturbations:
    - name: STX1B allelic panel knock-in
      target: pathophysiology#Syntaxin-1B t-SNARE Deficiency
      genes:
      - preferred_term: STX1B
        term:
          id: hgnc:18539
          label: STX1B
      description: >-
        Knock in individual STX1B variant classes into a shared human neuronal
        background for standardized functional comparison.
    readouts:
    - name: Release deficit and SNARE-complex incorporation
      target: pathophysiology#Impaired SNARE-Mediated Vesicle Fusion
      biological_processes:
      - preferred_term: synaptic vesicle exocytosis
        term:
          id: GO:0016079
          label: synaptic vesicle exocytosis
        modifier: DECREASED
      assays:
      - preferred_term: patch-clamp electrophysiology
      - preferred_term: co-immunoprecipitation assay
      direction: NEGATIVE
    controls:
    - name: Wild-type STX1B knock-in
      description: Isogenic neurons carrying wild-type STX1B.
    - name: Benign population variant
      description: A population variant incompatible with disease causality.
    decision_criterion: >-
      If functional severity rank (dominant-negative missense worst,
      haploinsufficiency intermediate) tracks clinical severity, variant class
      is a primary determinant; a weak correlation implicates modifiers.
    would_support:
    - pathophysiology#Syntaxin-1B t-SNARE Deficiency

- discussion_id: gap_stx1b_stx1a_redundancy_therapeutic_lever
  prompt: >-
    Does the closely related paralog syntaxin-1A partially compensate for
    syntaxin-1B loss, and could its regional/developmental expression explain
    phenotype variability and offer a therapeutic lever (upregulating STX1A to
    rescue release)?
  kind: EMERGING_HYPOTHESIS
  status: OPEN
  attaches_to:
  - pathophysiology#Impaired SNARE-Mediated Vesicle Fusion
  rationale: >-
    Syntaxin-1A and syntaxin-1B are highly homologous plasma-membrane t-SNAREs
    that can both support calcium-triggered fusion, so residual release in
    STX1B-deficient neurons may depend on syntaxin-1A availability. If
    compensation is incomplete and varies with the regional and developmental
    expression ratio of the two paralogs, that could contribute to the
    fever-dependence and phenotypic variability - and raising syntaxin-1A
    expression or function becomes a candidate disease-modifying strategy. This
    is an emerging, largely untested hypothesis for STX1B disease rather than an
    established mechanism.
  evidence:
  - reference: PMID:32559416
    reference_title: "SNAREopathies: Diversity in Mechanisms and Symptoms."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Neuronal SNAREs and their key regulators together drive synaptic vesicle
      exocytosis and synaptic transmission as a single integrated membrane fusion
      machine.
    explanation: >-
      Frames syntaxin-1B within an integrated SNARE machine in which paralog
      substitution by syntaxin-1A is a plausible compensatory route.
  proposed_experiments:
  - experiment_id: exp_stx1b_stx1a_compensation_rescue
    name: Syntaxin-1A dosage compensation of syntaxin-1B loss
    description: >-
      In syntaxin-1B-deficient human neurons, titrate syntaxin-1A expression
      and measure whether increased syntaxin-1A restores evoked release and
      rescues the temperature-sensitive release deficit, and profile the native
      STX1A:STX1B expression ratio across neuronal subtypes to test the
      regional-compensation model.
    experiment_type:
      preferred_term: paralog compensation rescue experiment
    perturbations:
    - name: Syntaxin-1A overexpression on STX1B-deficient background
      target: pathophysiology#Impaired SNARE-Mediated Vesicle Fusion
      genes:
      - preferred_term: STX1A
        term:
          id: hgnc:11433
          label: STX1A
      description: >-
        Increase syntaxin-1A expression in syntaxin-1B-deficient neurons to test
        functional compensation.
    readouts:
    - name: Rescue of evoked release
      target: pathophysiology#Impaired SNARE-Mediated Vesicle Fusion
      biological_processes:
      - preferred_term: calcium-dependent activation of synaptic vesicle fusion
        term:
          id: GO:0099502
          label: calcium-dependent activation of synaptic vesicle fusion
        modifier: DECREASED
      assays:
      - preferred_term: patch-clamp electrophysiology
      direction: POSITIVE
    controls:
    - name: STX1B-deficient neurons without STX1A manipulation
      description: Matched syntaxin-1B-deficient neurons at baseline syntaxin-1A levels.
    - name: Wild-type neurons
      description: Isogenic neurons with intact syntaxin-1B.
    decision_criterion: >-
      Dose-dependent rescue of evoked release and temperature sensitivity by
      syntaxin-1A would support paralog compensation as a determinant of
      severity and a therapeutic lever; failure to rescue would argue against it.
    would_support:
    - pathophysiology#Impaired SNARE-Mediated Vesicle Fusion

📚

References & Deep Research

References

2

PMID:25362483

Mutations in STX1B, encoding a presynaptic protein, cause fever-associated epilepsy syndromes.

No top-level findings curated for this source.

PMID:32559416

SNAREopathies: Diversity in Mechanisms and Symptoms.

No top-level findings curated for this source.

STX1B-Related Epilepsy

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