Tubulinopathies (Tubulin Gene Malformations of Cortical Development)

name: Tubulinopathies
display_name: Tubulinopathies (Tubulin Gene Malformations of Cortical Development)
creation_date: "2026-06-13T00:00:00Z"
description: >-
  The tubulinopathies are a group of malformations of cortical development caused
  by dominant variants in the tubulin genes that build the neuronal microtubule
  cytoskeleton: the alpha- and beta-tubulin isotypes that polymerize into the
  lattice, and gamma-tubulin (TUBG1), which nucleates it. Perturbed
  microtubule dynamics impair neuronal migration, axon guidance, and progenitor
  division, producing an overlapping spectrum of lissencephaly, polymicrogyria,
  microcephaly, dysmorphic basal ganglia, and corpus callosum and brainstem
  anomalies.
grouping_basis:
- SHARED_GENE_FAMILY
- SHARED_MECHANISM
grouping_rationale: >-
  Grouped on a shared gene family and mechanism: each member is caused by a
  variant in a tubulin gene and conforms to the
  microtubule_dependent_neuronal_migration_failure module (microtubule apparatus
  perturbation -> neuronal motility failure -> cortical dyslamination). Members
  are kept as separate Disease entries because they involve different tubulins
  (alpha and beta lattice paralogs, plus the gamma-tubulin nucleator) with
  distinct expression timing and binding partners, producing characteristic but
  overlapping malformation patterns. The criteria are NECESSARY: tubulin-gene
  causation plus migration-module conformance is entailed by membership, but
  microtubule-dependent migration failure also arises from non-tubulin genes
  (e.g., LIS1, DCX, and the gamma-tubulin complex protein TUBGCP2), so the
  mechanism alone is not sufficient to make a disorder a tubulinopathy. The
  gene-identity half of that conjunction does real work: TUBGCP2-related
  Lissencephaly Spectrum Disorder conforms to all three module nodes and is
  called a tubulinopathy in the literature, yet is excluded here because GCP2 is
  a gamma-tubulin COMPLEX protein rather than a tubulin.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0100153
      label: tubulinopathy
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      The grouping concept corresponds to the MONDO tubulinopathy class.
      exactMatch records the intended conceptual alignment; current DisMech
      coverage and sibling/no-MONDO member placements are consistency signals,
      not reasons to weaken the mapping predicate.
    consistency:
    - reference: MONDO
      consistent: CONSISTENT
      notes: >-
        2/5 listed members are is-a descendants of MONDO:0100153
        (TUBB2A/TUBB2B -> MONDO:0018763, TUBB3 -> MONDO:0100154). The other
        three are bona fide tubulinopathies whose MONDO terms sit outside that
        subtree: TUBA1A-related Tubulinopathy -> MONDO:0012703 (under
        lissencephaly type 3), TUBB/TUBB5-related Microcephaly ->
        MONDO:0014341 (CDCBM6) and TUBG1-related Tubulinopathy ->
        MONDO:0014171 (CDCBM4), both under complex cortical dysplasia with
        other brain malformations. This reflects an upstream MONDO inconsistency
        rather than a DisMech membership error: the CDCBM series is
        definitionally tubulin-caused for types 1 (TUBB3), 4 (TUBG1), 5
        (TUBB2A), 6 (TUBB) and 7 (TUBB2B), yet only CDCBM5 carries an is-a link
        to MONDO:0100153. Treat these as MONDO/member-alignment signals, while
        treating uncurated MONDO tubulinopathy descendants as DisMech curation
        gaps.
membership_criteria:
- description: >-
    A member conforms to the microtubule-dependent neuronal migration failure
    module — here driven by a variant in a tubulin isotype gene (the gene-family
    constraint that defines this grouping is conveyed by the curated member list
    and per-member differentiating_mechanisms, not by a HAS_GENE leaf, since the
    criteria are NECESSARY/audit-only; enumerating every tubulin isotype gene in
    the logic would be brittle).
  criteria_semantics: NECESSARY
  logic:
    criterion_predicate: CONFORMS_TO_MODULE
    module: microtubule_dependent_neuronal_migration_failure#Microtubule Apparatus Perturbation
    description: >-
      Conforms to the microtubule apparatus perturbation node of the migration
      module (here driven by a tubulin isotype variant).
members:
- member: TUBA1A-related Tubulinopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      TUBA1A is the major alpha-tubulin of migrating neurons; variants produce
      the most severe and common tubulinopathy — lissencephaly with cerebellar
      hypoplasia, dysmorphic basal ganglia, and corpus callosum agenesis.
    gene:
      preferred_term: TUBA1A
      term:
        id: hgnc:20766
        label: TUBA1A
- member: TUBB2A/TUBB2B-related Cortical Malformation
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Beta-tubulin 2A/2B variants classically produce asymmetric or bilateral
      polymicrogyria-like cortical malformation, distinguishing them from the
      lissencephaly-predominant TUBA1A phenotype.
    gene:
      preferred_term: TUBB2A
      term:
        id: hgnc:12412
        label: TUBB2A
- member: TUBB3-related Tubulinopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      The neuron-specific beta-tubulin TUBB3 is the member whose centre of
      gravity is axon guidance rather than neuronal migration: congenital
      fibrosis of the extraocular muscles (CFEOM3) with variable cortical
      malformation, reflecting the module's axon-wiring branch. This is a
      predominance, not a boundary - CFEOM is not exclusive to TUBB3. A TUBB2B
      p.Ile202Thr substitution has been reported with a syndromic CFEOM
      presentation, so a CFEOM phenotype does not by itself assign a patient to
      this member; the isotype does. TUBB3 is also the mildest member on
      caregiver-rated developmental profiling across the four genes.
    gene:
      preferred_term: TUBB3
      term:
        id: hgnc:20772
        label: TUBB3
    evidence:
    - reference: PMID:41153399
      reference_title: The p.Ile202Thr Substitution in TUBB2B Can Be Associated with Syndromic Presentation of Congenital Fibrosis of the Extraocular Muscles.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We describe a second individual with a severe phenotype of CFEOM
        combined with CDCBM7 carrying a pathogenic TUBB2B missense variant
        previously reported in two individuals with isolated CDCBM7.
      explanation: >-
        Reports a TUBB2B variant presenting with CFEOM, which is why the CFEOM
        differentiator is stated here as a predominance rather than a
        TUBB3-exclusive feature. Note the same source says only one such family
        had been reported before, so the phenotype remains strongly
        TUBB3-weighted.
    - reference: PMID:42593952
      reference_title: "Developmental Profiles Associated with TUBA1A, TUBB2A, TUBB2B, and TUBB3 Tubulinopathy Conditions."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Individuals with TUBB3 conditions demonstrated relatively milder degrees
        of delay
      explanation: >-
        Caregiver Developmental Profile Scales-4 ratings across all four member
        genes place TUBB3 at the milder end, substantiating a severity
        differentiator that was previously not evidenced anywhere in the KB.
- member: TUBB/TUBB5-related Microcephaly
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      TUBB (TUBB5) variants couple the migration defect to a progenitor-division
      defect, producing microcephaly with structural cortical malformation —
      overlapping the centrosome/spindle microcephaly mechanism. A subset of
      alleles additionally impairs ciliogenesis, which is what links this member
      to the ciliopathy spectrum.
    gene:
      preferred_term: TUBB
      term:
        id: hgnc:20778
        label: TUBB
- member: TUBG1-related Tubulinopathy
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      The only gamma-tubulin member, and the only one whose lesion is not in the
      microtubule lattice. TUBG1 encodes the core component of the gamma-tubulin
      ring complex, which NUCLEATES microtubules rather than polymerizing into
      them, so the failure mode is loss of nucleation fidelity rather than
      poisoning of the polymer. The consequence is a distinctive imaging
      signature: posterior-predominant pachygyria with posteriorly accentuated
      ventriculomegaly, but with basal ganglia, corpus callosum, brainstem and
      cerebellum often NORMAL — the opposite of the near-signature dysmorphic
      basal ganglia and callosal dysgenesis of the alpha- and beta-tubulin
      members. TUBG1 disease therefore resembles LIS1/PAFAH1B1 lissencephaly on
      MRI more than it resembles its own gene family.
    gene:
      preferred_term: TUBG1
      term:
        id: hgnc:12417
        label: TUBG1
    evidence:
    - reference: PMID:29706637
      reference_title: "Tubulinopathies continued: refining the phenotypic spectrum associated with variants in TUBG1."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Basal ganglia, corpus callosum, brainstem, and cerebellum were often
        normal, in contrast to patients with variants in other tubulin genes
        where these structures are frequently malformed.
      explanation: >-
        The imaging finding that differentiates this member from every other
        member of the grouping.
    - reference: PMID:29706637
      reference_title: "Tubulinopathies continued: refining the phenotypic spectrum associated with variants in TUBG1."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        This difference may, at least in part, be explained by gamma-tubulin's
        physiological function in microtubule nucleation, which differs from
        that of alpha and beta-tubulin.
      explanation: >-
        Attributes the divergence to gamma-tubulin's nucleation role, the
        mechanistic basis of this differentiator.
notes: >-
  A gene-family grouping (tubulin isotypes) that intersects the broader
  malformations-of-cortical-development space. TUBB/TUBB5 also conforms to the
  neural_progenitor_centrosome_spindle_dysfunction module and so additionally
  appears in the primary-microcephaly spectrum grouping — groupings are allowed
  to share members.

  Scope boundary (2026-08-20 review). The grouping is deliberately scoped to
  tubulin-gene MALFORMATIONS OF CORTICAL DEVELOPMENT, as the display_name says,
  not to every disease caused by a tubulin-family gene. Tubulin disorders that
  are knowingly OUT of scope, because they do not conform to the
  microtubule_dependent_neuronal_migration_failure module that the NECESSARY
  criterion tests: TUBB4A (H-ABC hypomyelinating leukodystrophy / DYT4 dystonia
  — a myelin and microtubule-stability disorder; entry TUBB4A-related Neurologic
  Disorder); TUBB4B (Leber congenital amaurosis with early-onset deafness,
  curated separately and modeled as a ciliopathy); TUBA4A (ALS/FTD, and the
  myo-tubulinopathies delineated in PMID:41678358, most of which have no CNS
  involvement at all; entry TUBA4A-related Disorder); TUBB8 (oocyte maturation
  arrest, a meiotic spindle disease with no neural phenotype); TUBB1
  (macrothrombocytopenia, a megakaryocyte marginal-band disease); and TUBA8,
  whose polymicrogyria claim is refuted (entry TUBA8-related Polymicrogyria with
  Optic Nerve Hypoplasia).

  A second exclusion class turns on gene identity rather than mechanism: the
  gamma-tubulin COMPLEX protein genes TUBGCP2, TUBGCP4 and TUBGCP6, all now
  curated as separate entries. TUBGCP4 and TUBGCP6 disease would fail the
  criterion anyway (microcephaly with chorioretinopathy, structurally normal
  cortex). TUBGCP2 would NOT: it causes pachygyria and subcortical band
  heterotopia and conforms to all three migration-module nodes, and both
  PMID:40448381 and the 2026 Turkish cohort PMID:42472988 call it a
  tubulinopathy. It is excluded here solely because GCP2 is a complex protein,
  not a tubulin — a lumping decision, recorded so it can be revisited. Widening
  to "microtubule-nucleation-and-lattice genes" would admit it and is the
  obvious alternative scope; that should be an explicit decision rather than a
  drift, as should adding any of the entries above.

  TUBG1 (2026-08-20). The gamma-tubulin member was curated and added as the
  fifth member in this pass, closing what the review identified as the
  grouping's one clear membership gap. It is the only member whose lesion is not
  in the microtubule lattice — gamma-tubulin nucleates microtubules rather than
  polymerizing into them — and the only one whose imaging phenotype spares the
  basal ganglia and corpus callosum, so it materially widens what this grouping
  asserts about its members.

  Uner Tan syndrome (2026-08-20/22). MONDO:0100144 — a TUBB2B p.Arg390Gln entity
  that IS an is-a descendant of MONDO:0100153 — now has its own DisMech entry,
  Uner Tan Syndrome, so it is no longer an uncovered concept. It is deliberately
  NOT a member here and is mapped as relatedMatch on the TUBB2A/TUBB2B entry
  rather than folded in: it is biallelic/recessive where every other allele in
  this grouping is heterozygous de novo, and it explicitly LACKS the basal
  ganglia malformation that entry curates as a core feature. Its allele also
  does not block heterodimer formation or polymer incorporation, so the
  microtubule-apparatus lesion the NECESSARY criterion tests is not established
  for it. See the gap_tubb2b_uner_tan_boundary discussion there.