Synaptic Vesicle Cycle Disorders (Presynaptic SNAREopathies)

name: Synaptic Vesicle Cycle Disorders
display_name: Synaptic Vesicle Cycle Disorders (Presynaptic SNAREopathies)
creation_date: "2026-07-06T00:00:00Z"
description: >-
  A curated union of monogenic neurodevelopmental disorders caused by defects in
  the presynaptic synaptic vesicle cycle — the trafficking cycle by which neurons
  load, dock, prime, fuse (Ca2+-triggered, SNARE-mediated), and recycle synaptic
  vesicles to release neurotransmitter. Members are distinct Disease entries that
  each disrupt a different component of the same integrated release machine
  (Munc18-1/STXBP1 and Munc13-1/UNC13A in docking/priming; the SNARE proteins,
  synaptotagmin-1, and complexin in fusion; dynamin-1/DNM1 and synaptojanin-1/SYNJ1
  in endocytic recycling). They converge on reduced or dysregulated neurotransmitter
  release and impaired synaptic transmission, manifesting as developmental and
  epileptic encephalopathy, presynaptic congenital myasthenic syndrome, and/or
  movement disorder. This grouping is the disease-level counterpart of the
  synaptic_vesicle_cycle mechanism module, and overlaps the "SNAREopathies" concept
  for the fusion-machinery subset.
grouping_basis:
- SHARED_MECHANISM
- SHARED_PATHWAY
grouping_rationale: >-
  Grouped on a shared presynaptic mechanism — a defect in the synaptic vesicle
  cycle reducing Ca2+-triggered neurotransmitter release — rather than on a single
  gene or a single clinical phenotype. The members are lumped because they act on
  the same integrated release machine and share a differential-diagnostic frame
  (early-onset developmental and epileptic encephalopathy with, in some, a
  presynaptic neuromuscular-transmission defect), but kept as separate entries
  because the specific vesicle-cycle step, gene, mode of inheritance, and the mix
  of epilepsy, myasthenia, and movement disorder differ. The criterion is NECESSARY
  (membership entails conformance to the synaptic_vesicle_cycle module) rather than
  NECESSARY_AND_SUFFICIENT: presynaptic vesicle-release proteins are numerous and a
  disorder can involve the vesicle cycle secondarily, so module conformance is
  required of members but does not by itself define the grouping. Membership is
  aspirational for entries that do not yet declare the conforms_to edge; the
  advisory evaluator flags those for follow-up.
membership_criteria:
- description: >-
    A synaptic vesicle cycle disorder is caused by a defect in a component of the
    presynaptic synaptic vesicle cycle (loading, clustering, docking, priming,
    Ca2+-triggered SNARE-mediated fusion, or endocytic recycling), such that
    neurotransmitter release is reduced or dysregulated. Every member conforms to
    the synaptic vesicle cycle module.
  criteria_semantics: NECESSARY
  logic:
    criterion_predicate: CONFORMS_TO_MODULE
    module: synaptic_vesicle_cycle
    description: >-
      Conforms to the synaptic vesicle cycle module (a presynaptic vesicle-cycle
      protein defect impairing Ca2+-triggered neurotransmitter release).
members:
- member: STXBP1 Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      De novo heterozygous STXBP1 haploinsufficiency reduces Munc18-1, the
      Sec1/Munc18 protein that chaperones syntaxin-1 and templates SNARE-complex
      assembly for vesicle fusion. Presents as early-onset developmental and
      epileptic encephalopathy (frequently Ohtahara or West syndrome) with
      severe-to-profound intellectual disability and frequent movement disorders,
      without a defining neuromuscular-junction phenotype.
    gene:
      preferred_term: STXBP1
      term:
        id: hgnc:11444
        label: STXBP1
    module: synaptic_vesicle_cycle
- member: UNC13A-Related Congenital NDD with Epilepsy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Biallelic loss-of-function of UNC13A abolishes Munc13-1, the vesicle-priming
      factor, depleting the readily releasable pool at both central synapses and
      cholinergic neuromuscular junctions. The recessive congenital form combines
      severe epileptic encephalopathy with a presynaptic (Lambert-Eaton-like)
      congenital myasthenic syndrome — the neuromuscular arm that distinguishes it
      from STXBP1 disease.
    gene:
      preferred_term: UNC13A
      term:
        id: hgnc:23150
        label: UNC13A
    module: synaptic_vesicle_cycle
- member: DNM1 Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      De novo dominant-negative variants in DNM1 (clustering in the GTPase/middle
      domains) poison the dynamin-1 fission GTPase that retrieves and recycles
      synaptic vesicles, impairing the endocytic arm of the cycle. Presents as a
      relatively homogeneous epileptic encephalopathy with infantile spasms
      evolving to Lennox-Gastaut syndrome — the vesicle-endocytosis/recycling
      member, distinct from the docking/priming and fusion members.
    gene:
      preferred_term: DNM1
      term:
        id: hgnc:2972
        label: DNM1
    module: synaptic_vesicle_cycle
- member: SYT1-Associated Neurodevelopmental Disorder
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      De novo dominant-negative C2B-domain variants in SYT1 impair synaptotagmin-1,
      the vesicular calcium sensor for fast synchronous fusion, slowing and
      desynchronizing release. Uniquely among the group it is NOT an epileptic
      encephalopathy — seizures are characteristically absent — presenting instead
      with a hyperkinetic movement disorder, ophthalmic anomalies, and a
      distinctive low-frequency-oscillation EEG (Baker-Gordon syndrome); the
      calcium-sensor/fusion member.
    gene:
      preferred_term: SYT1
      term:
        id: hgnc:11509
        label: SYT1
    module: synaptic_vesicle_cycle
- member: SNAP25-Related Developmental and Epileptic Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      De novo variants in SNAP25 impair the core t-SNARE SNAP-25, degrading
      assembly of the SNARE complex that executes vesicle fusion — a fusion-subunit
      member alongside SYT1, sharing the fusion node but substituting a SNARE
      structural component rather than the calcium sensor. Presents as a
      developmental and epileptic encephalopathy with intellectual disability,
      early-onset epilepsy, movement disorder, cerebral visual impairment, and brain
      atrophy.
    gene:
      preferred_term: SNAP25
      term:
        id: hgnc:11132
        label: SNAP25
    module: synaptic_vesicle_cycle
- member: VAMP2-Related Neurodevelopmental Disorder
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      De novo C-terminal SNARE-motif variants in VAMP2 impair synaptobrevin-2, the
      vesicle-side (v-)SNARE — the vesicle-membrane counterpart of the
      plasma-membrane t-SNAREs SNAP-25 and syntaxin-1B, completing the three core neuronal
      SNAREs in the group. Presents with congenital axial hypotonia, intellectual
      disability, and autistic features with Rett-like stereotypies; severe
      C-terminal variants add movement disorder, visual impairment, and epilepsy.
    gene:
      preferred_term: VAMP2
      term:
        id: hgnc:12643
        label: VAMP2
    module: synaptic_vesicle_cycle
- member: STX1B-Related Epilepsy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Loss-of-function variants in STX1B impair syntaxin-1B, the plasma-membrane
      t-SNARE — the third core neuronal SNARE, completing the trio with SNAP-25 and
      VAMP2. Distinctively presents as a fever-associated epilepsy spectrum (simple
      febrile seizures to GEFS+, occasionally DEE) with temperature-sensitive
      cortical hyperexcitability, rather than a neonatal encephalopathy.
    gene:
      preferred_term: STX1B
      term:
        id: hgnc:18539
        label: STX1B
    module: synaptic_vesicle_cycle
- member: CPLX1-Related Developmental and Epileptic Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Biallelic loss-of-function of CPLX1 removes complexin-1, the SNARE-complex
      regulator/fusion clamp that gates and synchronizes calcium-triggered release
      — the fusion-machinery member at the level of the SNARE regulator rather than
      a SNARE subunit or the calcium sensor. Uniquely autosomal-recessive among the
      DEE members, it presents with severe infantile migrating myoclonic epilepsy
      and developmental delay.
    gene:
      preferred_term: CPLX1
      term:
        id: hgnc:2309
        label: CPLX1
    module: synaptic_vesicle_cycle
- member: SYN1-Related Neurodevelopmental Disorder
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      X-linked loss-of-function of SYN1 impairs synapsin-1, which tethers vesicles
      into the reserve pool — the vesicle-clustering / reserve-pool arm upstream of
      docking, priming, and fusion. Uniquely X-linked among the group, it presents
      with focal epilepsy and autism spectrum disorder rather than a severe neonatal
      epileptic encephalopathy.
    gene:
      preferred_term: SYN1
      term:
        id: hgnc:11494
        label: SYN1
    module: synaptic_vesicle_cycle
- member: UNC13A-Related NDD with Seizures and Movement Disorder
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Heterozygous UNC13A gain-of-function or dysregulatory
      (second-messenger-regulation) variants alter Munc13-1-dependent priming, producing a dominant
      neurodevelopmental disorder with seizures and a prominent movement disorder
      (tremor, dyskinesia), distinct from the recessive loss-of-function congenital
      form and from STXBP1 disease.
    gene:
      preferred_term: UNC13A
      term:
        id: hgnc:23150
        label: UNC13A
    module: synaptic_vesicle_cycle