Early-Infantile Developmental and Epileptic Encephalopathies

name: Early-Infantile Developmental and Epileptic Encephalopathies
creation_date: "2026-07-31T23:55:00Z"
description: >-
  Early-infantile developmental and epileptic encephalopathy (EIDEE) is the ILAE
  electroclinical syndrome defined by frequent, drug-resistant seizures beginning
  at or before three months of age, together with an abnormal interictal EEG
  (classically burst-suppression in the Ohtahara and early myoclonic
  encephalopathy presentations) and abnormal neurological examination, in which
  the epileptic activity itself contributes to developmental impairment beyond
  what the underlying aetiology alone would cause. The 2022 ILAE
  classification collapsed the older Ohtahara syndrome and early myoclonic
  encephalopathy labels into this single EIDEE syndrome. This grouping is a
  curated union of the molecularly defined dismech entries whose documented
  seizure-onset spectrum includes that neonatal-to-three-month window. Members
  are grouped by the ILAE age-at-onset and electroclinical convention, not by a
  shared molecular mechanism: they span potassium-channel loss of function
  (KCNQ2), sodium-channel gain of function (SCN2A), presynaptic vesicle-priming
  failure (STXBP1), an X-linked serine-threonine kinase deficiency (CDKL5), a
  recessive UDP-glucose dehydrogenase metabolic defect (UGDH), and
  heterotrimeric G-protein alpha-subunit dysfunction (GNAO1).
grouping_basis:
- CLINICAL_CONVENTION
- SHARED_PHENOTYPE
grouping_rationale: >-
  This grouping lumps by the ILAE electroclinical convention that defines EIDEE
  — seizure onset at or before three months of age with an encephalopathic
  course — and is assembled below the level of the MONDO taxonomy so that the
  onset boundary is explicit and auditable. Members are deliberately kept as
  separate Disease entries because their causal mechanisms diverge sharply and
  because the mechanism determines therapy: KCNQ2 loss of function makes
  M-current openers and sodium-channel blockers (carbamazepine, phenytoin)
  rational, SCN2A gain of function responds to the same sodium-channel blockers
  while SCN2A loss of function is worsened by them, CDKL5 deficiency has a
  disease-specific approved therapy (ganaxolone), STXBP1 haploinsufficiency is a
  presynaptic proteostasis/vesicle-priming defect, and UGDH deficiency is a
  recessive metabolic aetiology. Grouping basis is therefore CLINICAL_CONVENTION
  (ILAE age-at-onset/electroclinical nosology) plus the SHARED_PHENOTYPE of
  neonatal-onset drug-resistant seizures, not a shared mechanism.

  Membership rule, applied symmetrically to every candidate accepted and
  rejected: an entry is a member when its own dismech text documents a
  seizure-onset presentation at or before three months of age as an established
  part of that disease's phenotypic spectrum. That covers both the case where
  the in-window onset is the disease's characteristic presentation (KCNQ2,
  seizures in the first days of life; SCN2A gain of function,
  neonatal-to-early-infantile) and the case where it is a named end of a broader
  published spectrum (STXBP1 and GNAO1 both document the Ohtahara-syndrome /
  early-infantile DEE presentation; UGDH documents epilepsy ranging from
  neonatal-onset to infantile developmental epileptic encephalopathy). The rule
  is deliberately written as "the documented spectrum includes the window"
  rather than "onset is always inside the window", because a gene-level Disease
  entry describes a spectrum while EIDEE is a per-patient electroclinical
  diagnosis: no gene-level entry could uniformly satisfy the stricter reading,
  and under criteria_semantics NECESSARY (member implies criteria) a criterion
  that no member can uniformly satisfy would turn every listed membership into a
  contradiction rather than an auditable assertion.

  An onset_category of INFANTILE is explicitly NOT treated as disqualifying:
  HP:0003593 (Infantile onset) spans 28 days to one year and therefore overlaps
  this window rather than excluding it. An exclusion is asserted only on the
  absence of a documented at-or-before-three-months presentation, never on the
  presence of an INFANTILE tag.

  Candidates considered and excluded under that same rule: CACNA1E-Related DEE
  (median seizure onset about 4.5 months, with no at-or-before-three-months
  presentation documented anywhere in its entry); SCN8A-Related DEE (its entry
  documents focal seizures "often beginning in infancy" and nothing earlier, so
  the exclusion rests on that absence rather than on its INFANTILE tag); and
  AFG2A-Related Encephalopathy (its "early-infantile onset" describes congenital
  microcephaly, sensorineural hearing loss and developmental delay, whereas the
  documented seizure onset is an infantile epileptic spasms syndrome with a mean
  onset around 9 to 14 months, outside the window). KCNA2-Related DEE is a
  deliberate borderline hold-out rather than a clean exclusion: its only
  in-window statement is hedged - severe gain-and-loss-of-function presentations
  "may begin in the neonatal period" - and is evidenced by a single case report,
  and its entry annotates intellectual disability but no
  global-developmental-delay term, so listing it today would create a
  NOT_SATISFIED contradiction against the NECESSARY developmental-impairment
  leaf instead of an honest membership. All four remain candidates should their
  entries later document an in-window presentation (and, for KCNA2, the
  accompanying developmental impairment).

  This grouping is intentionally distinct from four neighbouring constructs and
  is not a duplicate of any of them. Nearest is the Disease entry Early-Infantile
  Developmental and Epileptic Encephalopathy, which carries the same
  MONDO:0800491 term as its disease_term: it models the whole syndrome concept -
  the conserved mechanism chain, the ILAE 2022 diagnostic criteria, the
  epidemiology and the etiology-guided treatment approach, including the
  structural and metabolic aetiologies that have no gene-level entry - none of
  which the Grouping class can carry. That is the pattern CLAUDE.md records for
  diabetes mellitus, where a Grouping carries a skos mapping to a MONDO umbrella
  term while a retained umbrella Disease carries that same term as its
  disease_term, and the cross-reference here is reciprocal: that entry names this
  grouping in its own notes.
  Beyond it, the Disease entry Genetic Developmental and Epileptic
  Encephalopathy (MONDO:0100062) is the aetiologic umbrella regardless of onset
  age; Childhood-Onset Epilepsy Syndromes is the broader ILAE age-at-onset
  grouping spanning infancy through childhood and including self-limited
  syndromes; and Epilepsy Excitation-Inhibition Imbalance Disorders groups by
  converging pathomechanism irrespective of onset. Onset-window convention
  (here), the syndrome concept itself, broad age-at-onset convention, aetiologic
  class, and pathomechanism are orthogonal axes.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0800491
      label: early-infantile DEE
    mapping_predicate: skos:broadMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0800491 (early-infantile DEE) is the umbrella MONDO class for the
      ILAE early-infantile developmental and epileptic encephalopathy syndrome,
      defined by drug-resistant seizures beginning at or before three months of
      age. This grouping is a curated union of six molecularly defined member
      entries and does not attempt to recapitulate the full set of genetic,
      structural, and metabolic aetiologies that satisfy the syndrome
      definition, so the mapping is asserted as broadMatch.
    consistency:
    - reference: MONDO
      consistent: CONSISTENT
      notes: >-
        All six members are developmental and epileptic encephalopathies whose
        entries document a seizure-onset presentation in the neonatal period or
        the first three months of life, consistent with the MONDO:0800491
        umbrella class, though the grouping covers only a small subset of its
        aetiologies.
membership_criteria:
- description: >-
    A member is a developmental and epileptic encephalopathy (seizures are a
    defining feature, accompanied by developmental impairment attributable in
    part to the epileptic activity) whose documented seizure-onset spectrum
    includes the at-or-before-three-months window.
  criteria_semantics: NECESSARY
  logic:
    operator: AND
    operands:
    - operator: OR
      description: >-
        Seizures are a defining feature of the syndrome. Enumerated as a
        disjunction of the specific seizure phenotypes the member entries
        actually assert, because the membership evaluator matches terms exactly
        and does not apply HPO subsumption — several members annotate only a
        specific seizure semiology (epileptic spasm, tonic seizure, focal-onset
        seizure) rather than the generic Seizure parent.
      operands:
      - criterion_predicate: HAS_PHENOTYPE
        description: Seizure (generic).
        phenotype_term:
          preferred_term: Seizure
          term:
            id: HP:0001250
            label: Seizure
      - criterion_predicate: HAS_PHENOTYPE
        description: Epileptic spasm.
        phenotype_term:
          preferred_term: Epileptic spasm
          term:
            id: HP:0011097
            label: Epileptic spasm
      - criterion_predicate: HAS_PHENOTYPE
        description: Infantile spasms.
        phenotype_term:
          preferred_term: Infantile spasms
          term:
            id: HP:0012469
            label: Infantile spasms
      - criterion_predicate: HAS_PHENOTYPE
        description: Tonic seizure.
        phenotype_term:
          preferred_term: Tonic seizure
          term:
            id: HP:0032792
            label: Tonic seizure
      - criterion_predicate: HAS_PHENOTYPE
        description: Focal-onset seizure.
        phenotype_term:
          preferred_term: Focal-onset seizure
          term:
            id: HP:0007359
            label: Focal-onset seizure
    - operator: OR
      description: >-
        Developmental impairment accompanies the epilepsy, distinguishing a
        developmental and epileptic encephalopathy from a self-limited neonatal
        or infantile epilepsy syndrome. Enumerated as a disjunction because
        members annotate either the generic or the severity-qualified term.
      operands:
      - criterion_predicate: HAS_PHENOTYPE
        description: Global developmental delay.
        phenotype_term:
          preferred_term: Global developmental delay
          term:
            id: HP:0001263
            label: Global developmental delay
      - criterion_predicate: HAS_PHENOTYPE
        description: Severe global developmental delay.
        phenotype_term:
          preferred_term: Severe global developmental delay
          term:
            id: HP:0011344
            label: Severe global developmental delay
    - criterion_predicate: OTHER
      description: >-
        The member entry documents a seizure-onset presentation at or before
        three months of age - the neonatal-to-early-infantile window that
        defines EIDEE under the 2022 ILAE classification - as an established
        part of its phenotypic spectrum. Stated as "the documented spectrum
        includes the window" so that the criterion is uniformly satisfiable by a
        gene-level entry, which describes a spectrum rather than a single
        per-patient onset age. Onset age is not currently expressible as a
        structured leaf predicate, so it is asserted as an OTHER criterion; the
        advisory evaluator reports this leaf as UNKNOWN per member, which is
        expected.
members:
- member: KCNQ2 Developmental and Epileptic Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      KCNQ2 developmental and epileptic encephalopathy is caused by de novo,
      typically dominant-negative missense variants in KCNQ2 (Kv7.2), which
      reduce the neuronal M-current that normally dampens repetitive firing at
      the axon initial segment. Seizures begin in the first days of life, giving
      this member the earliest and most reliably neonatal onset in the grouping,
      and the loss-of-function M-current mechanism is what makes sodium-channel
      blockers such as carbamazepine effective. The instructive contrast is with
      the SCN2A loss-of-function variant class, which this grouping excludes on
      onset grounds and which is worsened by those same drugs: KCNQ2 loss of
      function and the SCN2A gain of function that is a member here arrive at
      sodium-channel-blocker responsiveness from opposite channel lesions.
    gene:
      preferred_term: KCNQ2
      term:
        id: hgnc:6296
        label: KCNQ2
- member: SCN2A-Related Developmental and Epileptic Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      SCN2A-related developmental and epileptic encephalopathy separates by
      variant functional class, and age at onset is the bedside proxy for that
      split: gain-of-function Nav1.2 variants produce the
      neonatal-to-early-infantile presentation that qualifies for this
      grouping and respond to
      sodium-channel blockers, whereas loss-of-function variants present after
      three months and are worsened by the same drugs. It is the only member
      whose grouping membership is defined by a functional subclass rather than
      by the gene as a whole.
    gene:
      preferred_term: SCN2A
      term:
        id: hgnc:10588
        label: SCN2A
- member: STXBP1 Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      STXBP1 encephalopathy is caused by heterozygous loss-of-function variants
      in STXBP1 (Munc18-1) acting through haploinsufficiency and protein
      destabilisation. Unlike the channelopathy members, the primary lesion is
      presynaptic: impaired syntaxin-1 chaperoning and SNARE-complex assembly
      degrade synaptic vesicle docking and priming, so neurotransmitter release
      fails rather than membrane excitability being directly altered. Onset is
      typically in the first months of life.
    gene:
      preferred_term: STXBP1
      term:
        id: hgnc:11444
        label: STXBP1
- member: CDKL5 Deficiency Disorder
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      CDKL5 deficiency disorder is an X-linked encephalopathy caused by loss of
      the CDKL5 serine-threonine kinase, whose substrates regulate dendritic
      arborisation, synapse maturation, and microtubule dynamics. It is the only
      member whose lesion is a signalling kinase rather than an ion channel,
      vesicle protein, or metabolic enzyme, the only X-linked member, and the
      only one with a disorder-specific approved antiseizure therapy
      (ganaxolone). Seizures begin in the first months of life.
    gene:
      preferred_term: CDKL5
      term:
        id: hgnc:11411
        label: CDKL5
- member: UGDH-related developmental and epileptic encephalopathy 84
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      UGDH-related developmental and epileptic encephalopathy 84 is the sole
      autosomal-recessive and sole metabolic member: biallelic loss-of-function
      variants in UGDH deplete UDP-glucuronic acid, the shared precursor for
      glycosaminoglycan and proteoglycan synthesis, so the epileptic
      encephalopathy arises from a biosynthetic-precursor deficit rather than
      from a primary synaptic or channel lesion. Its entry documents severe
      epilepsy ranging from neonatal-onset to infantile developmental epileptic
      encephalopathy, so its documented spectrum includes this grouping's window
      at the neonatal end, satisfying the membership rule stated in the
      grouping rationale.
    gene:
      preferred_term: UGDH
      term:
        id: hgnc:12525
        label: UGDH
- member: GNAO1-Related Developmental and Epileptic Encephalopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      GNAO1-related developmental and epileptic encephalopathy is caused by de
      novo variants in GNAO1, which encodes Galpha-o, the most abundant
      heterotrimeric G-protein alpha subunit in brain. It is the only member
      whose primary lesion sits in G-protein-coupled signal transduction rather
      than in an ion channel, a presynaptic vesicle protein, a signalling kinase
      or a metabolic enzyme, and the only member whose phenotype is a two-pole
      continuum in which a hyperkinetic movement-disorder pole
      (choreoathetosis, dystonia) can dominate over the epilepsy pole and is
      addressed by pallidal deep brain stimulation rather than by antiseizure
      medication. Its entry documents epileptic spasms including an
      Ohtahara-syndrome / early-infantile DEE presentation in a subset of
      patients, which is what places its documented spectrum inside this
      grouping's window; other patients in the epilepsy pole declare later in
      infancy, and a separate cluster has focal seizure onset at ages 3 to 10
      years.
    gene:
      preferred_term: GNAO1
      term:
        id: hgnc:4389
        label: GNAO1
notes: >-
  Clinical-convention grouping by the ILAE EIDEE onset window (a documented
  seizure-onset presentation at or before three months), kept deliberately
  distinct from the umbrella Disease entry Early-Infantile Developmental and
  Epileptic Encephalopathy that carries the same MONDO term, from the aetiologic
  Disease entry Genetic Developmental and Epileptic Encephalopathy, from the
  broader Childhood-Onset Epilepsy Syndromes age-at-onset grouping, and from the
  mechanism grouping Epilepsy Excitation-Inhibition Imbalance Disorders. The
  single NECESSARY criteria block is an AND of three operands: an OR of five
  seizure leaves (Seizure, Epileptic spasm, Infantile spasms, Tonic seizure,
  Focal-onset seizure), an OR of two developmental-impairment leaves (Global
  developmental delay, Severe global developmental delay), and an OTHER
  onset-window leaf. Both disjunctions are enumerated rather than stated as a
  single parent term because the membership evaluator matches terms exactly and
  does not apply HPO subsumption, so a member annotating only a specific seizure
  semiology or only the severity-qualified delay term would otherwise read as
  NOT_SATISFIED. The advisory evaluator reports the OTHER leaf as UNKNOWN per
  member, which is expected and advisory only. Entries considered and excluded
  on onset grounds (CACNA1E, SCN8A, AFG2A), and the KCNA2 borderline hold-out,
  are named with their reasons in the grouping rationale.