THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome (Beaulieu-Boycott-Innes syndrome, BBIS; THOC6 intellectual disability syndrome) is a rare autosomal recessive multiple congenital anomalies-intellectual disability syndrome caused by biallelic variants in THOC6. THOC6 encodes a WD40-repeat subunit of the THO complex, the core of the conserved TREX (TRanscription-EXport) complex that couples transcription and mRNA processing to the nuclear export of processed messenger RNA. Loss of functional THOC6 mislocalizes the protein and disrupts assembly of the TREX tetramer; recent human neural-cell work indicates the primary molecular lesion is widespread mRNA mis-splicing (rather than a bulk nuclear-export defect), which derails the proliferative-to-neurogenic transition of corticogenesis. The disorder is characterized by moderate-to-severe intellectual disability and developmental delay, microcephaly, short stature, and a recognizable (though subtle) facial gestalt (tall forehead, deep-set eyes, short and upslanted palpebral fissures, long nose with low-hanging columella), together with variable structural malformations of the brain (agenesis/dysgenesis of the corpus callosum, ventriculomegaly, hydrocephalus), heart (atrial and ventricular septal defects), and genitourinary tract (renal anomalies, cryptorchidism), plus dental anomalies. It was first delineated in a Hutterite population by Beaulieu, Boycott, and Innes.
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name: THOC6-Related Developmental Delay-Microcephaly-Facial Dysmorphism Syndrome
creation_date: "2026-07-30T00:00:00Z"
category: Mendelian
synonyms:
- Beaulieu-Boycott-Innes syndrome
- BBIS
- THOC6 intellectual disability syndrome
- Microcephaly, mental retardation, and distinctive facies, with cardiac and genitourinary malformations
description: >
THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome
(Beaulieu-Boycott-Innes syndrome, BBIS; THOC6 intellectual disability syndrome)
is a rare autosomal recessive multiple congenital anomalies-intellectual
disability syndrome caused by biallelic variants in THOC6. THOC6 encodes a
WD40-repeat subunit of the THO complex, the core of the conserved TREX
(TRanscription-EXport) complex that couples transcription and mRNA processing to
the nuclear export of processed messenger RNA. Loss of functional THOC6
mislocalizes the protein and disrupts assembly of the TREX tetramer; recent
human neural-cell work indicates the primary molecular lesion is widespread
mRNA mis-splicing (rather than a bulk nuclear-export defect), which derails the
proliferative-to-neurogenic transition of corticogenesis. The disorder is characterized by moderate-to-severe
intellectual disability and developmental delay, microcephaly, short stature, and
a recognizable (though subtle) facial gestalt (tall forehead, deep-set eyes,
short and upslanted palpebral fissures, long nose with low-hanging columella),
together with variable structural malformations of the brain (agenesis/dysgenesis
of the corpus callosum, ventriculomegaly, hydrocephalus), heart (atrial and
ventricular septal defects), and genitourinary tract (renal anomalies,
cryptorchidism), plus dental anomalies. It was first delineated in a Hutterite
population by Beaulieu, Boycott, and Innes.
disease_term:
preferred_term: THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome
term:
id: MONDO:0013362
label: THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome
parents:
- Autosomal recessive disease
- Multiple congenital anomalies-intellectual disability syndrome
references:
- reference: PMID:32790266
title: "THOC6 Intellectual Disability Syndrome."
tags:
- GeneReviews
pathophysiology:
- name: Loss of THO/TREX Complex Stability and THO-Subunit Interaction
description: >
THOC6 is a WD40-repeat subunit of the THO complex, the multiprotein core of
the TREX (TRanscription-EXport) complex, whose canonical function is to couple
transcription and mRNA processing to the recruitment of the nuclear mRNA export
machinery. Disease-associated biallelic THOC6 variants (missense and truncating)
mislocalize the protein from the nucleus to the cytoplasm and weaken its
interaction with other THO subunits (THOC1, THOC5), destabilizing the complex.
Historically, BBIS was attributed to a bulk mRNA nuclear-export defect
downstream of this destabilization; that classical model has since been
superseded — human neural-cell data (see the mis-splicing node below) found no
detectable bulk export defect and instead identify disrupted TREX tetramer
assembly and aberrant mRNA processing as the primary lesion. This node captures
the well-evidenced proximal event: complex destabilization and loss of
THO-subunit interaction.
cellular_components:
- preferred_term: THO complex
term:
id: GO:0000445
label: THO complex part of transcription export complex
genes:
- preferred_term: THOC6
term:
id: hgnc:28369
label: THOC6
downstream:
- target: Impaired TREX Tetramer Assembly
description: >
Destabilization of the THO complex and loss of THOC6-THOC5/THOC1 interaction
is the proximal cause of failed TREX tetramer assembly.
causal_link_type: DIRECT
evidence:
- reference: PMID:23621916
reference_title: "Intellectual disability associated with a homozygous missense mutation in THOC6."
supports: SUPPORT
evidence_source: OTHER
snippet: "THOC6 is a member of the THO/TREX complex which is involved in coordinating mRNA processing with mRNA export from the nucleus."
explanation: >
Establishes THOC6 as a component of the THO/TREX complex whose canonical role
is coupling mRNA processing to nuclear export (background on the complex).
- reference: PMID:23621916
reference_title: "Intellectual disability associated with a homozygous missense mutation in THOC6."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "mutant THOC6 was predominantly localized to the cytoplasm, suggesting that the mutant protein is unable to carry out its normal function."
explanation: >
Demonstrates that the disease mutation mislocalizes THOC6 out of the nucleus,
the compartment where the THO complex acts.
- reference: PMID:30476144
reference_title: "Clinical and functional characterization of recurrent missense variants implicated in THOC6-related intellectual disability."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "the different THOC6 variants alter the physiological nuclear localizationof the protein and its interaction with at least two THO subunits, THOC1 and THOC5."
explanation: >
Functional characterization showing BBIS variants disrupt THOC6 nuclear
localization and its interaction with THO complex partners THOC1 and THOC5.
- name: Impaired Progenitor Proliferation and Increased Apoptosis in Development
biological_scale: CELLULAR
description: >
TREX is essential during embryogenesis, where it regulates post-transcriptional
self-renewal and differentiation and thereby stem/progenitor cell fate. Loss of
THOC6 function increases apoptosis in cultured cells, consistent with the reduced
brain growth (microcephaly) and structural brain malformations (corpus callosum
dysgenesis) seen in patients. The defect is attributed to disrupted
TREX-tetramer-dependent mRNA processing (mis-splicing) and the consequent
derailment of the proliferative-to-neurogenic signaling on which rapidly
dividing progenitors (including radial glia) depend.
biological_processes:
- preferred_term: neuron apoptotic process
term:
id: GO:0051402
label: neuron apoptotic process
- preferred_term: neural precursor cell proliferation
term:
id: GO:0061351
label: neural precursor cell proliferation
cell_types:
- preferred_term: neural progenitor cell
term:
id: CL:0011020
label: neural progenitor cell
- preferred_term: radial glial cell
term:
id: CL:0000681
label: radial glial cell
downstream:
- target: Microcephaly
description: >
Reduced neural progenitor proliferation and increased apoptosis diminish
cortical neuron output, producing microcephaly.
causal_link_type: DIRECT
- target: Intellectual disability
description: >
Impaired corticogenesis underlies the moderate-to-severe intellectual
disability that is the defining feature of the syndrome.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- target: Global developmental delay
description: >
Impaired corticogenesis underlies the global developmental delay.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- target: Agenesis of corpus callosum
description: >
Impaired progenitor dynamics during corticogenesis contribute to corpus
callosum dysgenesis.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:23621916
reference_title: "Intellectual disability associated with a homozygous missense mutation in THOC6."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "siRNA knockdown of THOC6 revealed increased apoptosis in cultured cells."
explanation: >
Loss of THOC6 increases apoptosis, a plausible mechanism for reduced brain
growth and developmental malformation.
- reference: PMID:30238602
reference_title: "Novel CNS malformations and skeletal anomalies in a patient with Beaulieu-boycott-Innes syndrome."
supports: SUPPORT
evidence_source: OTHER
snippet: "In mammals, TREX is essential during embryogenesis, determining stem cell fate specification by regulating posttranscriptional self-renewal and differentiation in several tissues."
explanation: >
Links the TREX complex (of which THOC6 is a subunit) to embryonic stem cell
fate specification (background review statement), supporting a developmental
mechanism for BBIS malformations.
- name: Impaired TREX Tetramer Assembly
biological_scale: MOLECULAR
description: >
THOC6 is required for assembly of the mammalian TREX tetramer (four six-subunit
THO monomers), a metazoan-specific function beyond the yeast-conserved nuclear
export role of the TREX dimer. Biallelic THOC6 loss-of-function reduces the
binding affinity of the export adaptor ALYREF to THOC5 without lowering the
expression of TREX members, implicating failed tetramer formation as the
proximal molecular consequence of complex destabilization.
cellular_components:
- preferred_term: transcription export complex
term:
id: GO:0000346
label: transcription export complex
downstream:
- target: Widespread mRNA Mis-Splicing
description: >
Loss of the TREX tetramer's mRNA-processing function leads to widespread
aberrant splicing.
causal_link_type: DIRECT
evidence:
- reference: PMID:38388531
reference_title: "TREX tetramer disruption alters RNA processing necessary for corticogenesis in THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "THOC6 is critical for mammalian Transcription Export complex (TREX) tetramer formation, which is composed of four six-subunit THO monomers."
explanation: >
Establishes THOC6's specific role in TREX tetramer assembly.
- reference: PMID:38388531
reference_title: "TREX tetramer disruption alters RNA processing necessary for corticogenesis in THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Biallelic THOC6 LOF variants reduce the binding affinity of ALYREF to THOC5 without affecting the protein expression of TREX members, implicating impaired TREX tetramer formation."
explanation: >
Shows the molecular consequence of THOC6 loss is impaired tetramer formation
(reduced ALYREF-THOC5 binding), not loss of TREX subunit expression.
- name: Widespread mRNA Mis-Splicing
biological_scale: MOLECULAR
description: >
Rather than a bulk mRNA nuclear-export defect (which is not detectable in
patient neural cells), loss of the TREX tetramer causes widespread mRNA
mis-splicing — the primary molecular lesion of THOC6 intellectual disability
syndrome, demonstrated concordantly in human iPSC-derived neural cells and in
mouse neural tissue.
biological_processes:
- preferred_term: mRNA splicing, via spliceosome
term:
id: GO:0000398
label: mRNA splicing, via spliceosome
downstream:
- target: Disrupted Proliferative-to-Neurogenic Transition Signaling
description: >
Mis-splicing derails the signaling programs that control the switch from
proliferative to neurogenic divisions in corticogenesis.
causal_link_type: DIRECT
evidence:
- reference: PMID:38388531
reference_title: "TREX tetramer disruption alters RNA processing necessary for corticogenesis in THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Defects in RNA nuclear export functions were not detected in biallelic THOC6 LOF human neural cells."
explanation: >
Refutes bulk nuclear-export failure as the primary lesion in human iPSC-derived
neural cells, revising the classical model.
- reference: PMID:38388531
reference_title: "TREX tetramer disruption alters RNA processing necessary for corticogenesis in THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Instead, mis-splicing was detected in human and mouse neural tissue, revealing novel THOC6-mediated TREX coordination of mRNA processing."
explanation: >
Identifies mRNA mis-splicing as the primary molecular defect, demonstrated in
vivo in mouse neural tissue (concordant with the human iPSC finding).
- name: Disrupted Proliferative-to-Neurogenic Transition Signaling
biological_scale: CELLULAR
description: >
The mis-splicing burden disrupts the key signaling pathways that regulate the
transition from proliferative to neurogenic divisions during human
corticogenesis, linking the molecular lesion to the downstream progenitor
proliferation/apoptosis defect and, ultimately, to microcephaly and impaired
cortical development.
biological_processes:
- preferred_term: cerebral cortex development
term:
id: GO:0021987
label: cerebral cortex development
downstream:
- target: Impaired Progenitor Proliferation and Increased Apoptosis in Development
description: >
Disrupted proliferative-to-neurogenic signaling impairs neural progenitor
proliferation and increases apoptosis during corticogenesis.
causal_link_type: DIRECT
evidence:
- reference: PMID:38388531
reference_title: "TREX tetramer disruption alters RNA processing necessary for corticogenesis in THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "We demonstrate that THOC6 is required for key signaling pathways known to regulate the transition from proliferative to neurogenic divisions during human corticogenesis."
explanation: >
Bridges the molecular lesion to the cellular phenotype: THOC6 is required for
the signaling that governs the proliferative-to-neurogenic transition.
genetic:
- name: THOC6
notes: >
Biallelic (homozygous or compound heterozygous) loss-of-function and missense
variants in THOC6 cause BBIS. A recurrent homozygous missense founder variant
(c.136G>A, p.Gly46Arg) was identified in the Hutterite population; other families
carry compound heterozygous missense/truncating variants, including a recurrent
European three-variant missense haplotype.
relationship_type: CAUSATIVE
gene_term:
preferred_term: THOC6
term:
id: hgnc:28369
label: THOC6
evidence:
- reference: PMID:23621916
reference_title: "Intellectual disability associated with a homozygous missense mutation in THOC6."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Candidate gene sequencing followed by exome sequencing identified a homozygous missense mutation p.Gly46Arg, in THOC6."
explanation: >
Identifies the founding homozygous THOC6 missense variant in the original
Hutterite families.
- reference: CGGV:assertion_db4039ce-b9e7-40ba-ac45-a622bb75b803-2024-03-15T160000.000Z
reference_title: "THOC6 / THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome (Definitive)"
supports: SUPPORT
evidence_source: OTHER
snippet: "THOC6 | HGNC:28369 | THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome | MONDO:0013362 | AR | Definitive"
explanation: >
ClinGen Syndromic Disorders GCEP classifies the THOC6-disease relationship as
Definitive (autosomal recessive).
- reference: PMID:27102954
reference_title: "Autosomal recessive mutations in THOC6 cause intellectual disability: syndrome delineation requiring forward and reverse phenotyping."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Using exome sequencing, we identified three unrelated patients with bi-allelic mutations in THOC6 associated with intellectual disability and additional clinical features."
explanation: >
Confirms biallelic THOC6 variants beyond the founder population, establishing
recessive inheritance and syndrome delineation.
diagnosis:
- name: Molecular genetic testing for biallelic THOC6 variants
description: >
The diagnosis is established in a proband with biallelic pathogenic THOC6
variants identified by molecular genetic testing (gene-targeted or
comprehensive genomic testing). In individuals of Hutterite ancestry, targeted
testing for the c.136G>A (p.Gly46Arg) founder variant can be considered first.
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The diagnosis of THOC6 intellectual disability syndrome is established in a proband with biallelic pathogenic variants in THOC6 identified by molecular genetic testing."
explanation: >
GeneReviews states the molecular basis for diagnostic confirmation.
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "molecular genetic testing for the specific c.136G>A (p.Gly46Arg) founder variant can be considered."
explanation: >
GeneReviews notes the Hutterite founder-variant testing strategy.
inheritance:
- name: Autosomal recessive inheritance
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
evidence:
- reference: PMID:23621916
reference_title: "Intellectual disability associated with a homozygous missense mutation in THOC6."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We recently described a novel autosomal recessive neurodevelopmental disorder with intellectual disability in four patients from two related Hutterite families."
explanation: >
States the autosomal recessive mode of inheritance in the original cohort.
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being unaffected and a carrier, and a 25% chance of being unaffected and not a carrier."
explanation: >
GeneReviews genetic-counseling recurrence-risk statement confirming autosomal
recessive transmission.
prevalence:
- population: Worldwide
measure_type: CASES_IN_LITERATURE
prevalence_class: BELOW_1_IN_1000000
notes: >
Ultra-rare. As of the 2020 GeneReviews synthesis, ~19 affected individuals from
~15 families had been published, with sporadic case reports since; the total
reported cohort remains well under 50 individuals. A recurrent founder variant
elevates recurrence risk within specific endogamous Hutterite subpopulations
(carrier frequency 2-3%).
evidence:
- reference: PMID:35426486
reference_title: "Biallelic THOC6 pathogenic variants: Prenatal phenotype and review of the literature."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "This condition was described in 17 patients and is characterized by a moderate to severe intellectual disability"
explanation: >
Documents the very small number of reported patients, consistent with an
ultra-rare (<1/1,000,000) disorder.
- population: Hutterite (Dariusleut and Lehrerleut)
measure_type: CARRIER_FREQUENCY
rate_low: 2000.0
rate_high: 3000.0
notes: >
Carrier frequency of the c.136G>A (p.Gly46Arg) founder variant in Hutterite
control samples: 3% in Dariusleut and 2% in Lehrerleut (i.e. 2000-3000 carriers
per 100,000).
evidence:
- reference: PMID:23621916
reference_title: "Intellectual disability associated with a homozygous missense mutation in THOC6."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The variant was seen at a frequency of 3% in 92 Dariusleut controls and at a frequency of 2% in 120 Lehrerleut controls"
explanation: >
Quantifies the founder-variant carrier frequency in the two Hutterite leut
populations.
phenotypes:
- name: Intellectual disability
description: Moderate-to-severe intellectual disability is a constant feature.
phenotype_term:
preferred_term: Intellectual disability
term:
id: HP:0001249
label: Intellectual disability
frequency: VERY_FREQUENT
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "THOC6 intellectual disability syndrome is associated with moderate-to-severe developmental delay or intellectual disability"
explanation: GeneReviews lists moderate-to-severe ID as the core feature.
- reference: PMID:35426486
reference_title: "Biallelic THOC6 pathogenic variants: Prenatal phenotype and review of the literature."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Severe to moderate ID and congenital malformations were constant."
explanation: >
Literature review of 17 patients finds ID constant, supporting a very frequent
frequency assignment.
- name: Global developmental delay
phenotype_term:
preferred_term: Global developmental delay
term:
id: HP:0001263
label: Global developmental delay
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "THOC6 intellectual disability syndrome is associated with moderate-to-severe developmental delay or intellectual disability"
explanation: GeneReviews documents developmental delay.
- name: Microcephaly
description: Microcephaly, typically 2-3 SD below the mean.
phenotype_term:
preferred_term: Microcephaly
term:
id: HP:0000252
label: Microcephaly
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "microcephaly (typically 2-3 SD below the mean)"
explanation: GeneReviews documents microcephaly with typical severity.
- name: Short stature
phenotype_term:
preferred_term: Short stature
term:
id: HP:0004322
label: Short stature
evidence:
- reference: PMID:30238602
reference_title: "Novel CNS malformations and skeletal anomalies in a patient with Beaulieu-boycott-Innes syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Affected patients usually have short stature, mild microcephaly, and mild to moderate ID."
explanation: Documents short stature as a usual feature of BBIS.
- name: Small for gestational age
description: Low birth weight with subsequent postnatal growth failure.
phenotype_term:
preferred_term: Small for gestational age
term:
id: HP:0001518
label: Small for gestational age
evidence:
- reference: PMID:32655027
reference_title: "Proteinuria in Two Sisters with Beaulieu-Boycott-Innes Syndrome, A Case Report."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Core clinical features include low birth weight with subsequent growth failure, short stature, and intellectual disability with language delay"
explanation: Documents low birth weight with subsequent growth failure in BBIS.
- name: Tall forehead
phenotype_term:
preferred_term: Tall forehead
term:
id: HP:0000348
label: High forehead
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "nonspecific dysmorphic facial features (tall forehead, deep-set eyes, short and upslanted palpebral fissures, epicanthal folds, and long nose with low-hanging columella)"
explanation: GeneReviews lists tall forehead among the characteristic facial features.
- name: Deeply set eye
phenotype_term:
preferred_term: Deeply set eye
term:
id: HP:0000490
label: Deeply set eye
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "nonspecific dysmorphic facial features (tall forehead, deep-set eyes, short and upslanted palpebral fissures, epicanthal folds, and long nose with low-hanging columella)"
explanation: GeneReviews lists deep-set eyes among the characteristic facial features.
- name: Short palpebral fissure
phenotype_term:
preferred_term: Short palpebral fissure
term:
id: HP:0012745
label: Short palpebral fissure
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "short and upslanted palpebral fissures"
explanation: GeneReviews documents short palpebral fissures.
- name: Upslanted palpebral fissure
phenotype_term:
preferred_term: Upslanted palpebral fissure
term:
id: HP:0000582
label: Upslanted palpebral fissure
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "short and upslanted palpebral fissures"
explanation: GeneReviews documents upslanted palpebral fissures.
- name: Epicanthus
phenotype_term:
preferred_term: Epicanthus
term:
id: HP:0000286
label: Epicanthus
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "nonspecific dysmorphic facial features (tall forehead, deep-set eyes, short and upslanted palpebral fissures, epicanthal folds, and long nose with low-hanging columella)"
explanation: GeneReviews lists epicanthal folds among the characteristic facial features.
- name: Long nose
phenotype_term:
preferred_term: Long nose
term:
id: HP:0003189
label: Long nose
evidence:
- reference: PMID:27102954
reference_title: "Autosomal recessive mutations in THOC6 cause intellectual disability: syndrome delineation requiring forward and reverse phenotyping."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "and a long nose with overhanging columella."
explanation: Documents the long nose with overhanging columella of BBIS.
- name: Agenesis of corpus callosum
description: Partial or complete agenesis / dysgenesis of the corpus callosum.
phenotype_term:
preferred_term: Agenesis of corpus callosum
term:
id: HP:0001274
label: Agenesis of corpus callosum
evidence:
- reference: PMID:27102954
reference_title: "Autosomal recessive mutations in THOC6 cause intellectual disability: syndrome delineation requiring forward and reverse phenotyping."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "malformations are variable including renal and heart defects, cleft palate, microcephaly, and corpus callosum dysgenesis."
explanation: Documents corpus callosum dysgenesis among BBIS brain malformations.
- name: Ventriculomegaly
phenotype_term:
preferred_term: Ventriculomegaly
term:
id: HP:0002119
label: Ventriculomegaly
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "prenatal ventriculomegaly and hydrocephalus"
explanation: GeneReviews documents prenatal ventriculomegaly.
- name: Hydrocephalus
phenotype_term:
preferred_term: Hydrocephalus
term:
id: HP:0000238
label: Hydrocephalus
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "prenatal ventriculomegaly and hydrocephalus"
explanation: GeneReviews documents hydrocephalus.
- name: Atrial septal defect
phenotype_term:
preferred_term: Atrial septal defect
term:
id: HP:0001631
label: Atrial septal defect
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "cardiac anomalies (most typically atrial and/or ventricular septal defects)"
explanation: GeneReviews documents atrial septal defects as the most typical cardiac anomaly.
- name: Ventricular septal defect
phenotype_term:
preferred_term: Ventricular septal defect
term:
id: HP:0001629
label: Ventricular septal defect
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "cardiac anomalies (most typically atrial and/or ventricular septal defects)"
explanation: GeneReviews documents ventricular septal defects as a typical cardiac anomaly.
- name: Cleft palate
description: Cleft palate, including submucous cleft palate.
phenotype_term:
preferred_term: Cleft palate
term:
id: HP:0000175
label: Cleft palate
evidence:
- reference: PMID:30238602
reference_title: "Novel CNS malformations and skeletal anomalies in a patient with Beaulieu-boycott-Innes syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "including cardiac and renal malformations, anteriorly displaced anus, cryptorchidism in males, submucous cleft palate, and corpus callosum dysgenesis."
explanation: Documents submucous cleft palate among common BBIS anomalies.
- name: Cryptorchidism
phenotype_term:
preferred_term: Cryptorchidism
term:
id: HP:0000028
label: Cryptorchidism
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "cryptorchidism in males"
explanation: GeneReviews documents cryptorchidism in affected males.
- name: Unilateral renal agenesis
description: The most common specific renal malformation in BBIS.
phenotype_term:
preferred_term: Unilateral renal agenesis
term:
id: HP:0000122
label: Unilateral renal agenesis
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "renal malformations (most commonly unilateral renal agenesis)"
explanation: GeneReviews documents unilateral renal agenesis as the most common renal malformation.
- name: Abnormal renal morphology
description: >
Umbrella term for the spectrum of renal malformations (unilateral renal
agenesis most common; ectopic and horseshoe kidney also reported).
phenotype_term:
preferred_term: Abnormal renal morphology
term:
id: HP:0012210
label: Abnormal renal morphology
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "renal malformations (most commonly unilateral renal agenesis)"
explanation: GeneReviews documents the broader spectrum of renal malformations in BBIS.
- name: Supernumerary tooth
description: Dental anomalies including supernumerary teeth, dental caries, and malocclusion.
phenotype_term:
preferred_term: Supernumerary tooth
term:
id: HP:0011069
label: Supernumerary tooth
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "teeth anomalies (dental caries, malocclusion, and supernumerary teeth)"
explanation: GeneReviews documents supernumerary teeth among BBIS dental anomalies.
- name: Carious teeth
phenotype_term:
preferred_term: Carious teeth
term:
id: HP:0000670
label: Carious teeth
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "teeth anomalies (dental caries, malocclusion, and supernumerary teeth)"
explanation: GeneReviews documents dental caries among BBIS dental anomalies.
- name: Dental malocclusion
phenotype_term:
preferred_term: Dental malocclusion
term:
id: HP:0000689
label: Dental malocclusion
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "teeth anomalies (dental caries, malocclusion, and supernumerary teeth)"
explanation: GeneReviews documents malocclusion among BBIS dental anomalies.
- name: Delayed speech and language development
phenotype_term:
preferred_term: Delayed speech and language development
term:
id: HP:0000750
label: Delayed speech and language development
evidence:
- reference: PMID:32655027
reference_title: "Proteinuria in Two Sisters with Beaulieu-Boycott-Innes Syndrome, A Case Report."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Core clinical features include low birth weight with subsequent growth failure, short stature, and intellectual disability with language delay"
explanation: Documents language delay as a core clinical feature of BBIS.
- name: Feeding difficulties
phenotype_term:
preferred_term: Feeding difficulties
term:
id: HP:0011968
label: Feeding difficulties
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "feeding difficulties"
explanation: GeneReviews lists feeding difficulties among the more variable features.
- name: Hypergonadotropic hypogonadism
description: Hypergonadotropic hypogonadism, reported in affected females.
phenotype_term:
preferred_term: Hypergonadotropic hypogonadism
term:
id: HP:0000815
label: Hypergonadotropic hypogonadism
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hypergonadotropic hypogonadism (in females)"
explanation: GeneReviews documents hypergonadotropic hypogonadism in affected females.
- name: Seizure
phenotype_term:
preferred_term: Seizure
term:
id: HP:0001250
label: Seizure
frequency: VERY_RARE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "More rarely, affected individuals may have hypergonadotropic hypogonadism (in females), seizures"
explanation: GeneReviews lists seizures as a rarer manifestation.
- name: Hearing impairment
phenotype_term:
preferred_term: Hearing impairment
term:
id: HP:0000365
label: Hearing impairment
frequency: VERY_RARE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "poor growth, feeding difficulties, hearing loss, refractive errors and/or other eye abnormalities"
explanation: GeneReviews lists hearing loss among the rarer features.
- name: Cerebellar hypoplasia
description: >
Cerebellar/vermian hypoplasia has been reported as part of an expanded CNS
malformation phenotype in a single patient.
phenotype_term:
preferred_term: Cerebellar hypoplasia
term:
id: HP:0001321
label: Cerebellar hypoplasia
frequency: VERY_RARE
evidence:
- reference: PMID:30238602
reference_title: "Novel CNS malformations and skeletal anomalies in a patient with Beaulieu-boycott-Innes syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "she displays cerebellar hypoplasia with severe vermian dysgenesis and hydrocephalus due to aqueductal stenosis, multiple skeletal anomalies and hypergonadotropic hypogonadism."
explanation: Documents cerebellar hypoplasia as part of an expanded CNS phenotype in one BBIS patient.
- name: Micrognathia
description: Micro/retrognathia.
phenotype_term:
preferred_term: Microretrognathia
term:
id: HP:0000308
label: Microretrognathia
frequency: VERY_RARE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "vertebral anomalies, micro/retrognathia, and imperforate / anteriorly placed anus"
explanation: GeneReviews lists micro/retrognathia among the rarer features.
- name: Anteriorly placed anus
description: Imperforate or anteriorly placed anus (anorectal malformation).
phenotype_term:
preferred_term: Anteriorly placed anus
term:
id: HP:0001545
label: Anteriorly placed anus
frequency: VERY_RARE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "imperforate / anteriorly placed anus"
explanation: GeneReviews lists imperforate / anteriorly placed anus among the rarer features.
- name: Abnormal vertebral morphology
phenotype_term:
preferred_term: Abnormal vertebral morphology
term:
id: HP:0003468
label: Abnormal vertebral morphology
frequency: VERY_RARE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "vertebral anomalies, micro/retrognathia"
explanation: GeneReviews lists vertebral anomalies among the rarer features.
- name: Abnormality of refraction
description: Refractive errors and other eye abnormalities.
phenotype_term:
preferred_term: Abnormality of refraction
term:
id: HP:0000539
label: Abnormality of refraction
frequency: VERY_RARE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "refractive errors and/or other eye abnormalities"
explanation: GeneReviews lists refractive errors and other eye abnormalities among the rarer features.
treatments:
- name: Developmental and Educational Support with Multidisciplinary Surveillance
description: >
Symptom-directed developmental, educational, and behavioral support for
intellectual disability / developmental delay, with multidisciplinary
surveillance (monitoring for hydrocephalus and new neurologic manifestations,
growth, vision, dental, audiology, and renal function). No disease-modifying
therapy exists.
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
therapeutic_modality: BEHAVIORAL
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "standard treatment for seizures, vision issues, dental caries/malocclusion, cardiac malformations, genital anomalies, hypergonadotropic hypogonadism, renal malformations, skeletal anomalies, and developmental delay / intellectual disability."
explanation: GeneReviews outlines symptom-directed treatment including developmental/ID support.
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "assess for signs and symptoms of hydrocephalus or for new neurologic manifestations"
explanation: GeneReviews surveillance guidance for hydrocephalus / neurologic manifestations.
- name: Gastrostomy Tube Feeding
description: >
For poor weight gain: feeding therapy and consideration of a gastrostomy tube
for nutritional support.
treatment_term:
preferred_term: gastrostomy
term:
id: NCIT:C52006
label: Gastrostomy
therapeutic_modality: DEVICE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "For those with poor weight gain, feeding therapy and consideration of a gastrostomy tube"
explanation: GeneReviews recommends feeding therapy / gastrostomy for poor weight gain.
- name: Hearing Aids
description: Hearing aids may be considered for hearing loss.
treatment_term:
preferred_term: hearing aid usage
therapeutic_modality: DEVICE
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "for those with hearing loss, hearing aids may be considered"
explanation: GeneReviews recommends hearing aids for hearing loss.
- name: Surgical Repair of Congenital Malformations
description: >
Standard surgical management of congenital cardiac, genitourinary, and other
structural malformations (e.g., septal defects, cryptorchidism, anorectal
malformation).
treatment_term:
preferred_term: surgical procedure
term:
id: NCIT:C15329
label: Surgical Procedure
therapeutic_modality: SURGERY
evidence:
- reference: PMID:32790266
reference_title: "THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "standard treatment for seizures, vision issues, dental caries/malocclusion, cardiac malformations, genital anomalies, hypergonadotropic hypogonadism, renal malformations, skeletal anomalies, and developmental delay / intellectual disability."
explanation: GeneReviews indicates standard (including surgical) treatment of the cardiac and genitourinary malformations.
discussions:
- discussion_id: mismatch_thoc6_mouse_embryonic_lethality
prompt: >-
Why is germline biallelic Thoc6 loss-of-function embryonic lethal in mouse
while biallelic THOC6 loss-of-function is compatible with survival to adulthood
in humans, and what human-specific mechanism compensates for the resulting
mRNA-processing burden?
kind: HUMAN_MODEL_MISMATCH
status: OPEN
attaches_to:
- pathophysiology#Widespread mRNA Mis-Splicing
- pathophysiology#Impaired Progenitor Proliferation and Increased Apoptosis in Development
rationale: >-
Germline biallelic Thoc6 loss-of-function variants cause mouse embryonic
lethality, whereas affected humans with biallelic THOC6 loss-of-function
survive into adulthood (oldest reported individuals in their 40s) with a
microcephaly/intellectual-disability malformation syndrome. The mouse therefore
does not reproduce human survivability, and the fidelity of murine
proliferative/apoptotic severity to the comparatively milder, viable human
phenotype is unresolved. This matters when interpreting the model: mouse data
establish the essential developmental requirement for THOC6 and the mis-splicing
mechanism, but a human-specific tolerance/compensation for the intron-retention
and lncRNA-dysregulation burden is inferred and not yet identified, so
conclusions about disease severity and candidate modifiers drawn from the mouse
should be qualified.
proposed_experiments:
- experiment_id: exp_thoc6_cross_species_splicing_survival
name: Cross-species comparison of THOC6-dependent mis-splicing and survival thresholds
description: >-
Systematically compare the mis-splicing landscape, intron-retention burden,
and lncRNA dysregulation between THOC6-deficient human iPSC-derived cortical
organoids/neural progenitors and Thoc6-mutant mouse neuroepithelium at matched
developmental stages, and test candidate human-specific paralogs or
compensatory RNA-processing factors for their ability to rescue mouse
lethality, to identify what buffers the human phenotype.
evidence:
- reference: PMID:38388531
reference_title: "TREX tetramer disruption alters RNA processing necessary for corticogenesis in THOC6 Intellectual Disability Syndrome."
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: "Germline biallelic Thoc6 loss-of-function (LOF) variants result in mouse embryonic lethality."
explanation: >
Establishes the mouse embryonic-lethal phenotype that is not observed in
surviving human patients, defining the model mismatch.
Overview: THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome, universally referred to in the literature as Beaulieu-Boycott-Innes syndrome (BBIS) or THOC6 Intellectual Disability Syndrome (TIDS), is a rare autosomal recessive neurodevelopmental disorder first delineated in 2013 in a Hutterite kindred. It is caused by biallelic pathogenic variants in THOC6, which encodes a subunit of the THO/TREX (transcription-export) mRNA processing and nuclear export complex. The syndrome is characterized by global developmental delay, moderate-to-severe intellectual disability, microcephaly, characteristic but nonspecific facial dysmorphism, and variable multi-organ malformations (cardiac, renal, dental, genitourinary, and corpus callosum anomalies) (Beaulieu et al. 2013, PMID:23621916; Lemire, Innes, Boycott, GeneReviews NBK560442).
Key Identifiers: - OMIM: #613680 (Beaulieu-Boycott-Innes syndrome, phenotype); 615403 (THOC6 gene) - Gene: THOC6 (HGNC), chromosome 16p13.3 (per GeneReviews) / 16p13.11–13.3 region - MedGen CUI: C3150939 ("THOC6-related developmental delay-microcephaly-facial dysmorphism syndrome") - GTR condition: C3150939 - Inheritance: Autosomal recessive - MONDO/Orphanet:* Specific MONDO and ORPHA numeric IDs were not confidently retrievable via web search in this session and should be independently verified directly against the MONDO Ontology Lookup Service and Orphanet before use in a knowledge base (the disease is indexed in Orphanet's rare-disease nomenclature as "Beaulieu-Boycott-Innes syndrome," cross-referenced to OMIM:613680, but the exact ORPHA code was not confirmed here).
Synonyms: Beaulieu-Boycott-Innes syndrome (BBIS); THOC6 Intellectual Disability Syndrome (TIDS); THOC6-related intellectual disability; intellectual disability, autosomal recessive, with THOC6 defect.
Source of information: Data is derived almost entirely from aggregated case-series/case-report literature (GeneReviews synthesis of ~19–20+ published individuals across ~15+ families as of 2020, with additional case reports through 2024–2025) rather than large-scale EHR/registry data, reflecting the extreme rarity of the condition (Lemire et al., GeneReviews NBK560442; multiple case reports below).
Disease Causal Factors: BBIS is a purely monogenic, Mendelian disorder. It is caused by biallelic (homozygous or compound heterozygous) loss-of-function or hypomorphic missense variants in THOC6 that impair THO/TREX complex assembly and function (Beaulieu et al. 2013, PMID:23621916; Mattioli et al. 2019, HMG 28(6):952-960, PMID via DOI 10.1093/hmg/ddy391).
Genetic Risk Factors: - Founder variant: The original mutation identified, c.136G>A (p.Gly46Arg), is a founder variant in the Hutterite Dariusleut and Lehrerleut populations, with reported carrier frequencies of 3% in Dariusleut controls and 2% in Lehrerleut controls — implying meaningfully elevated recurrence risk in these endogamous communities (Beaulieu et al. 2013, PMID:23621916). - Other pathogenic variants reported: compound heterozygous stop + missense combinations; homozygous missense variants (e.g., a haplotype bearing three amino-acid changes p.Trp100Arg, p.Val234Leu, p.Gly275Asp; p.Gly190Glu); homozygous splice-site variants (e.g., c.155+1G>T, a novel splice-donor variant reported in a Palestinian infant with disorders of sexual development) (Mattioli et al. 2019; PMC12324036, 2024/2025 case report). - Consanguinity: Given autosomal recessive inheritance and multiple reports from consanguineous families (e.g., Palestinian and Indian sibling cases), parental consanguinity is a recognized risk factor for biallelic variant co-occurrence. - THOC6 itself, unlike other THO complex subunits (THOC1, THOC3, THOC5, THOC7 — all of which show high pLI/loss-of-function intolerance in gnomAD and have no known associated developmental disorder, likely because complete loss is embryonic lethal), appears to tolerate partial loss-of-function in humans, which is thought to explain why THOC6, and not the other THO subunits, is the one component in which biallelic hypomorphic variants are compatible with live birth (PMC10884030 / Nature Communications 2024).
Environmental Risk Factors: None identified; this is a purely genetic disorder with no known environmental, infectious, or toxin-mediated contribution to primary causation.
Protective Factors: No specific genetic modifiers or protective variants have been described. Notably, human cells/embryos appear more tolerant of biallelic THOC6 loss-of-function than mouse embryos (which are embryonic lethal by E9.5–E11.5), suggesting an unidentified human-specific compensatory mechanism for the resulting lncRNA dysregulation and intron-retention burden — an active area of investigation rather than an established protective factor (PMC10884030).
Gene-Environment Interactions: None reported; no CTD/PheGenI gene-environment interaction data exists for THOC6-related disease given its recessive Mendelian architecture.
Phenotype data are drawn primarily from GeneReviews (NBK560442, summarizing published cohorts) and individual case reports.
Frequency/severity: Given the very small published cohort (≈19–20+ individuals as of 2020, with sporadic additional single case reports through 2024–2025), most frequency estimates are qualitative or based on small denominators (e.g., "47%" for cardiac defects, "approximately half" for dental issues) rather than robust population-level statistics; frequency qualifiers should be curated conservatively.
Quality of life impact: Not formally studied with standardized instruments (no EQ-5D/SF-36 data identified); clinical narrative indicates lifelong cognitive and functional impairment requiring coordinated multidisciplinary care, special education, and in some cases assistive devices (hearing aids, feeding support).
Causal Gene: THOC6 (THO complex subunit 6), OMIM *615403, chromosome 16p13.3.
Pathogenic Variant Spectrum: - c.136G>A (p.Gly46Arg) — founder missense variant, homozygous in the original Hutterite families (Beaulieu et al. 2013, PMID:23621916). - Triple-amino-acid-change haplotype — p.Trp100Arg, p.Val234Leu, p.Gly275Asp (in cis), and p.Gly190Glu — characterized functionally by Mattioli et al. 2019 (HMG 28(6):952-960), shown to relocalize THOC6 protein from nucleus to cytoplasm and disrupt THOC1/THOC5 interaction. - c.155+1G>T — homozygous canonical splice-donor variant (intron 3), classified likely pathogenic, reported in a consanguineous Palestinian family (PMC12324036). - Compound heterozygous stop + missense combinations reported in multiple families (e.g., Chinese infant, PMC7220430; Indian siblings, PMID:31421288). - Variant classification (ACMG/ClinVar): Multiple THOC6 variants are catalogued in ClinVar (e.g., VCV000561208, VCV000521349) as pathogenic/likely pathogenic. - Variant types: missense, nonsense (stop-gain), splice-site — no large structural/CNV mechanism reported to date; standard first-tier testing (chromosomal microarray) is recommended primarily to exclude alternative diagnoses rather than because THOC6-associated CNVs are common. - Population frequency: Aside from the Hutterite founder allele (2–3% carrier frequency in specific subpopulations), THOC6 pathogenic variants are otherwise very rare/private in gnomAD; variants with population MAF >3.3% are excluded as non-causal in functional studies (PMC10884030/PMC10503840). - Somatic vs. germline: All reported variants are germline; no somatic/mosaic mechanism described. - Functional consequence: Predominantly loss-of-function / hypomorphic — reduced or mislocalized THOC6 protein disrupts THO complex tetramer assembly; no gain-of-function or dominant-negative mechanism has been described (biallelic/recessive throughout).
Modifier Genes: None established; other THO/TREX components (THOC1, THOC2, THOC3, THOC5, THOC7) are mechanistic pathway partners but are not documented modifiers of THOC6 disease severity in humans. Related but genetically distinct: THOC2 causes an X-linked syndromic intellectual disability via R-loop accumulation/DNA damage (a related mechanistic paradigm) (Nature Communications 2024, PMID:38388532-adjacent article "THOC2...").
Epigenetic Information: No specific DNA methylation, histone modification, or chromatin-level abnormality has been reported as a primary driver; however, the disease mechanism itself converges on RNA processing (splicing) rather than classical epigenetic dysregulation.
Chromosomal Abnormalities: No recurrent CNV/translocation mechanism identified; disease is due to sequence-level (point/splice) variants.
HGNC gene symbol: THOC6 (HGNC ID should be confirmed locally; use lowercase hgnc: CURIE per dismech convention).
No environmental, toxin, occupational, radiation, or lifestyle contributing factors have been described for THOC6-related disease — it is a fully penetrant, purely monogenic autosomal recessive disorder. No infectious trigger or agent is implicated.
This is the best-characterized and most recently elucidated aspect of the disease, driven by two 2024 studies (Nature Communications, PMC10884030; and the related PMC10503840/bioRxiv precursor).
Molecular function of THOC6: THOC6 is a core subunit of the THO complex, which together with additional factors (UAP56/DDX39B, ALYREF, etc.) forms the larger TREX (TRanscription-EXport) complex, classically understood to couple transcription, mRNA processing, and nuclear export of mature mRNAs (Beaulieu et al. 2013; GeneReviews NBK560442).
Causal chain (established primarily via human iPSC-derived cortical organoids and Thoc6 mutant mouse embryos):
Species divergence: Thoc6-null/hypomorphic mouse embryos are embryonic lethal by E9.5–E11.5 (thinner neuroepithelium, increased mitosis and apoptosis at E9.5, developmental delay from E9.5, smaller embryo size), in contrast to humans, who survive to adulthood (oldest reported individuals in their 40s) despite biallelic loss. This suggests human-specific tolerance/compensation for the resulting intron-retention and lncRNA dysregulation burden — an open mechanistic question and a strong candidate for a HUMAN_MODEL_MISMATCH discussion in a dismech-style entry, since the mouse model does not recapitulate survivability and the translational fidelity of murine apoptotic/proliferative severity to the milder human phenotype is unresolved.
Suggested ontology terms: - GO (biological process): GO:0006406 (mRNA export from nucleus), GO:0000398 (mRNA splicing, via spliceosome), GO:0008380 (RNA splicing), GO:0007420 (brain development), GO:0021987 (cerebral cortex development), GO:0043065 (positive regulation of apoptotic process), GO:0008283 (cell population proliferation). - GO (cellular component): GO:0000445 (THO complex part of transcription export complex) / GO:0000346 (transcription export complex), GO:0005634 (nucleus). - GO (molecular function): possible RNA-binding-complex scaffolding activity (specific THOC6 MF term should be verified via UniProt/QuickGO before curation). - CL (cell types): CL:0011020 (neural progenitor cell) / CL:0002608 (embryonic stem cell related) — more precisely CL:0000047 (neural stem cell) / radial glial cell CL:0000681; CL:0000540 (neuron), CL:0000679 (glutamatergic neuron) for migrating cortical neurons. - UBERON: UBERON:0001890 (forebrain), UBERON:0000955 (brain), UBERON:0002021 (neural tube/neuroepithelium - approximate).
Organ level (primary): - Central nervous system — brain (microcephaly, corpus callosum dysgenesis, ventriculomegaly/hydrocephalus). UBERON:0000955 (brain), UBERON:0002336 (corpus callosum, if precise UBERON needed verify), UBERON:0002264 (lateral ventricle). - Craniofacial skeleton/soft tissue — dysmorphic facial features. UBERON:0001456 (face). - Cardiovascular system — heart (septal defects). UBERON:0000948 (heart). - Renal/urinary system — kidney (agenesis, ectopia, horseshoe kidney). UBERON:0002113 (kidney). - Genitourinary/reproductive system — gonads, external genitalia (cryptorchidism, ambiguous genitalia, hypogonadism). UBERON:0000992 (gonad), UBERON:0004818 (external genitalia). - Dentition — teeth (caries, malocclusion, supernumerary teeth). UBERON:0001091 (tooth). - Gastrointestinal/anorectal — anorectal malformation in at least one case. UBERON:0000160 (intestine)/UBERON:0004908 (anus, approximate). - Skeletal system — vertebrae (segmentation defects). UBERON:0001068 (vertebra). - Auditory system — inner/middle ear (sensorineural hearing loss). UBERON:0001846 (ear). - Ocular system — eyes (myopia; deep-set eyes, palpebral fissure anomalies as dysmorphic features). UBERON:0000970 (eye).
Body systems involved: Nervous, cardiovascular, renal/urinary, reproductive, skeletal, digestive (dental/anorectal), auditory, ophthalmologic — i.e., a genuinely multisystem developmental disorder, consistent with THOC6's broadly required role in mRNA processing across many developing tissues, though the brain (and specifically corticogenesis) is the best-mechanistically-characterized target organ.
Tissue/cell level: - Cerebral cortex neuroepithelium/ventricular zone — pseudostratified neuroepithelium, neural rosettes (organoid correlate). - Neural progenitor cells / radial glia (proliferation and apoptosis defects). CL:0000047 (neural stem cell) — more specific radial glial cell term CL:0000681 if desired. - Migrating/differentiating cortical neurons (doublecortin+ population, reduced fraction). CL:0000540 (neuron) / DCX+ immature neuron.
Subcellular level: - Nucleus — normal THOC6 localization site; site of TREX complex assembly and pre-mRNA splicing/processing. GO:0005634 (nucleus), GO:0016607 (nuclear speck, as a candidate TREX/splicing-associated compartment — verify). - Cytoplasm — site of pathogenic THOC6 mislocalization for certain missense variants (loss of nuclear function).
Lateralization: No consistent lateral asymmetry pattern reported; renal agenesis has been unilateral in described cases but laterality (left vs right) is not consistently documented; overall dysmorphism/malformations are typically bilateral/symmetric (e.g., bilateral epicanthal folds, bilateral inguinal gonads in the genitourinary case).
Onset: - Congenital/prenatal onset for microcephaly, growth restriction, and structural anomalies (corpus callosum dysgenesis, cardiac/renal malformations) — detectable prenatally or at birth in several reported cases (see Ruaud et al. 2022, Birth Defects Research, "Biallelic THOC6 pathogenic variants: Prenatal phenotype and review of the literature," documenting prenatal ultrasound findings). - Neonatal/early infancy recognition of low birth weight, feeding difficulties, and dysmorphic features. - Early childhood manifestation of developmental delay and evolving intellectual disability as milestones are missed.
Onset pattern: Insidious/congenital rather than acute; anomalies are present from birth, with developmental delay becoming apparent over the first months to years of life.
Progression: - Neurodevelopmental impairment: stable to slowly evolving — described as a static encephalopathy-type course rather than progressive neurodegeneration; no evidence of regression. - Growth: postnatal growth failure/short stature persists but is not reported as progressively worsening. - No formal disease-staging system exists (this is a static congenital malformation/neurodevelopmental syndrome, not a progressive degenerative disease).
Disease course pattern: Chronic, lifelong, non-progressive (congenital/static) — individuals require lifelong developmental, medical, and educational support but do not experience described periods of clinical regression, exacerbation-remission cycling, or episodic crises specific to the syndrome itself (beyond standard co-morbidity management, e.g., seizures in the rare individuals affected).
Patterns / critical periods: Early intervention (ages 0–3) is explicitly recommended in GeneReviews management guidance, reflecting the developmental-window importance of early therapy access, though this is a general early-childhood-intervention principle rather than a THOC6-specific critical period discovery.
Longevity: Survival into adulthood is documented; oldest reported affected individuals are in their early 40s. Whether life expectancy is shortened relative to the general population is currently unknown (small cohort size precludes formal survival analysis).
Epidemiology: - Prevalence: Extremely rare; estimated point prevalence <1/1,000,000 worldwide (per aggregated rare-disease database sourcing). As of GeneReviews (2020), approximately 19 affected individuals from 15 families had been published; sporadic additional case reports (China, India, Turkey [Kiraz et al. 2022, AJMG], Palestine/2024–2025) have incrementally expanded this since, but the total published cohort remains well under 50 individuals. - Incidence: Not formally calculated given rarity; no national/registry-level incidence figures exist.
Inheritance pattern: Autosomal recessive. Each sib of an affected individual has, at conception: 25% chance affected, 50% chance unaffected carrier, 25% chance unaffected non-carrier (standard AR Mendelian recurrence risk, per GeneReviews).
Penetrance: Appears to be complete/high for biallelic pathogenic variants (no clear unaffected biallelic carriers reported), though the very small cohort limits confidence in this assessment.
Expressivity: Markedly variable — phenotypic spectrum ranges from "classic" BBIS (microcephaly, ID, characteristic facies, cardiac/renal defects) to recently expanded presentations including ambiguous genitalia/disorders of sexual development and anorectal malformation, indicating substantial variable expressivity even among individuals with loss-of-function alleles.
Genetic anticipation: Not applicable/not reported (not a repeat-expansion disorder).
Germline mosaicism: Not specifically documented in the literature reviewed, though theoretically possible for any AR condition; genetic counseling for future pregnancies in a family with one affected child conventionally still assumes standard 25% recurrence risk given confirmed biallelic status in parents (both carriers).
Founder effects: Yes — the p.Gly46Arg (c.136G>A) variant is a well-documented founder mutation in the Hutterite population (Dariusleut and Lehrerleut Anabaptist communities), with carrier frequencies of 2–3%, substantially higher than expected for a private disease allele, reflecting the known founder-effect genetic architecture of this endogamous population.
Consanguinity role: Multiple non-Hutterite reported families are consanguineous (e.g., Palestinian, Indian sibling cases), consistent with the expected pattern for a rare AR disorder — biallelic variant co-occurrence is facilitated by shared ancestry.
Carrier frequency: Outside the Hutterite founder population, carrier frequency for any single THOC6 pathogenic variant is expected to be very low (private/rare variants); gnomAD-based estimates were not independently retrieved with precision in this session and should be checked directly in gnomAD for specific variants.
Population Demographics: - Affected populations: Originally described in the Hutterite population (North American Anabaptist founder population); subsequently reported worldwide, including Chinese, Indian, Turkish, and Palestinian/Middle Eastern families — indicating no strict ethnic restriction outside the founder-effect enrichment in Hutterites. - Geographic distribution: Global, reflecting panethnic distribution of private pathogenic variants, with the notable exception of Hutterite founder-variant enrichment in specific North American communities. - Sex ratio: No skewed sex ratio reported (autosomal recessive, not X-linked); however, cryptorchidism, hypogonadism, and the reported ambiguous-genitalia case specifically highlight male genitourinary vulnerability, without implying differential overall prevalence by sex. - Age distribution: Reported cases span from prenatal diagnosis/neonates through adults in their 40s.
Genetic Testing (primary diagnostic modality): - First-tier: Chromosomal microarray analysis (CMA) — to exclude large deletions/duplications and alternative diagnoses (though THOC6 disease itself is not typically caused by CNVs). - If CMA non-diagnostic: Multigene intellectual-disability panel or exome sequencing (or genome sequencing) — sequence analysis of THOC6 detects essentially all reported pathogenic variant types (missense, nonsense, splice-site); GeneReviews states sequence analysis detects the pathogenic variant in essentially 100% of confirmed cases when the gene is adequately covered. - Population-specific approach: In individuals of Hutterite ancestry, targeted testing for the founder variant c.136G>A (p.Gly46Arg) may be considered as a rapid first step before broader panel/exome testing. - Confirmatory: Biallelic pathogenic/likely pathogenic THOC6 variants (homozygous or compound heterozygous) establish the molecular diagnosis.
Clinical/Imaging Tests: - Neuroimaging (brain MRI): to assess corpus callosum dysgenesis, ventriculomegaly/hydrocephalus, and microcephaly-associated structural findings. - Echocardiography: to detect septal defects and other structural cardiac anomalies. - Renal ultrasound: to detect agenesis, ectopia, horseshoe kidney. - Dental evaluation: for caries, malocclusion, supernumerary teeth. - Audiology: for sensorineural hearing loss. - Ophthalmologic exam: for myopia and strabismus/alignment issues. - Endocrine workup: hypothalamic-pituitary-gonadal axis assessment (LH/FSH, testosterone/estradiol) in cases with genitourinary anomalies or delayed puberty, given documented hypergonadotropic hypogonadism.
Prenatal diagnostics: Prenatal ultrasound has detected findings consistent with BBIS (e.g., ventriculomegaly, growth restriction, structural anomalies) in at-risk pregnancies, as reviewed by Ruaud et al. 2022 (Birth Defects Research); prenatal molecular testing is available once familial pathogenic variants are known.
Differential Diagnosis (per GeneReviews): - Seckel syndrome — overlapping microcephaly and dental malocclusion, distinguished by severe primordial growth restriction. - Rubinstein-Taybi syndrome — overlapping microcephaly/dysmorphism, distinguished by characteristic broad thumbs/halluces. - Mowat-Wilson syndrome — overlapping corpus callosum dysgenesis and genitourinary anomalies, distinguished by Hirschsprung disease and its own distinctive facial gestalt. - Broader differential includes other syndromic autosomal recessive intellectual disability disorders with microcephaly and multi-organ involvement (e.g., other TREX/spliceosomopathy-related disorders such as THOC2-related ID).
Screening: No population-based newborn screening program exists (disease too rare, no biochemical screening marker); carrier screening could theoretically be offered in the Hutterite community given the known founder variant and elevated carrier frequency, though this was not explicitly documented as an implemented program in the sources reviewed.
Omics-based diagnostics: Not part of routine clinical diagnosis; RNA-seq-based splicing analysis (as used in the Nature Communications 2024 mechanistic study) is a research tool rather than an established clinical diagnostic, though it may have future utility for functional variant classification in ambiguous cases (VUS resolution).
Survival and Mortality: No formal survival statistics or life-expectancy data exist given the small published cohort. The oldest reported affected individuals are documented into their early 40s, indicating survival well into adulthood is possible; whether overall life expectancy is shortened relative to the general population remains unknown and unquantified in the literature.
Morbidity and Function: - Lifelong moderate-to-severe intellectual disability with associated functional impairment in adaptive skills, communication, and independence. - Multi-organ morbidity depends on the specific malformation burden present (cardiac defect severity, renal function, hearing/vision impairment). - No standardized quality-of-life instrument data (EQ-5D, SF-36, PROMIS) identified in the literature for this specific condition.
Disease Course/Complications: - Recognized complications include: renal impairment (in those with structural renal anomalies, warranting annual renal function monitoring), dental complications (caries/malocclusion requiring ongoing dental care), hearing loss progression (warranting annual audiology), seizures (rare), and endocrine complications (hypergonadotropic hypogonadism potentially requiring hormone replacement in adolescence/adulthood). - No described "recovery" — the neurodevelopmental component is a static, non-regressive congenital impairment; supportive/rehabilitative interventions aim to maximize functional potential rather than reverse an active degenerative process.
Prognostic factors: No validated prognostic biomarkers or clinical scoring system exists. Anecdotally, prognosis for cognitive/functional outcome likely correlates with the severity of the specific malformation burden (e.g., presence/severity of cardiac defects, degree of corpus callosum dysgenesis) and access to early intervention services, though this has not been formally studied.
There is no disease-modifying or curative therapy for THOC6-related disease; management is entirely supportive, symptomatic, and surveillance-based, per the GeneReviews "Management" chapter (NBK560442, Table 5: Treatment of Manifestations).
Developmental/Educational Support:
- Early intervention programs (ages 0–3), developmental preschool, individualized education plans (IEPs), involvement of developmental pediatrics. MAXO candidate: MAXO:0000011 (physical therapy), and general early-intervention/education support terms (may not have a precise MAXO code; consider MAXO:0000950 supportive care as a general anchor, or NCIT:C15747 Supportive Care).
Surveillance/Monitoring (not treatment per se, but standard of care): - Annual/each-visit developmental, mobility, and behavioral assessment. - Growth parameter and nutritional status monitoring. - Annual (or each-visit, if renal anomaly present) renal function testing. - Annual audiology evaluation. - Ophthalmologic assessment. - Dental evaluation. - Assessment of secondary sexual characteristics in adolescent/adult females (and by extension males, given documented cryptorchidism/hypogonadism).
Specific Interventions:
- Feeding therapy, with possible gastrostomy tube placement for significant feeding/swallowing difficulties. MAXO candidate: feeding therapy under supportive care; gastrostomy under MAXO:0000004 (surgical procedure) or a more specific NCIT gastrostomy code.
- Hearing aids for documented sensorineural hearing loss. MAXO:0009030 (hearing aid usage).
- Standard cardiac management (per pediatric cardiology; surgical repair of septal defects as clinically indicated) — MAXO:0000004 (surgical procedure) / NCIT:C15329 (Surgical Procedure).
- Standard urologic management, including orchiopexy for cryptorchidism and reconstructive surgery for anorectal malformation/ambiguous genitalia as clinically indicated. MAXO:0000004 (surgical procedure), NCIT:C16186 (Orthopedic Surgical Procedure, not applicable here — better to use general surgical procedure or a specific urologic procedure NCIT term).
- Standard orthopedic management for skeletal anomalies (e.g., vertebral segmentation defects) as clinically indicated.
- Anti-seizure medication for the rare individuals with documented seizures. Treatment term: NCIT:C15986 (Pharmacotherapy) + therapeutic_agent per specific anticonvulsant used (not individually specified in the literature reviewed).
- Hormone replacement therapy for documented hypergonadotropic hypogonadism. Treatment term: NCIT:C15986 (Pharmacotherapy) + therapeutic_agent (e.g., sex-hormone replacement, not individually specified).
- Genetic counseling for families, given 25% recurrence risk. MAXO:0000079 (genetic counseling).
Experimental/Advanced Therapeutics: None identified — no gene therapy, RNA-based therapy (ASO/siRNA), cell therapy, or targeted molecular therapy has been developed or is in clinical trials for THOC6-related disease specifically (searched clinicaltrials.gov context not separately verified in this session but no such trials were surfaced in any search). Given the mechanistic finding that disease arises from splicing dysregulation rather than bulk export failure, antisense-oligonucleotide splice-modulation approaches are a plausible future research direction (by analogy to other spliceosomopathies) but are not an established or trialed treatment as of this report.
Treatment Outcomes: No systematic treatment-response data exists; management is individualized symptomatic care per standard specialty guidelines for each organ-system manifestation, not disease-specific clinical trial evidence.
Treatment Strategy: Multidisciplinary care coordination (genetics, developmental pediatrics, cardiology, nephrology/urology, audiology, ophthalmology, dentistry, endocrinology) is the explicit GeneReviews-recommended strategy; no algorithmic/staged treatment pathway exists beyond this coordinated-surveillance model.
Primary Prevention: Not applicable in the traditional sense (no modifiable risk factor); the only "primary prevention" avenue is reproductive genetic counseling and carrier screening in at-risk families/populations (notably the Hutterite community, given the known founder variant), enabling informed reproductive decision-making (e.g., IVF with preimplantation genetic testing, prenatal diagnosis, or informed conception planning).
Secondary Prevention: Prenatal diagnosis (via chorionic villus sampling/amniocentesis molecular testing once familial variants are known, or prenatal ultrasound surveillance for structural anomalies as reviewed by Ruaud et al. 2022) allows early identification, which does not prevent the condition but enables anticipatory perinatal/neonatal management planning.
Tertiary Prevention: The entire GeneReviews management program (surveillance schedule, early intervention, organ-specific monitoring) functions as tertiary prevention — aiming to minimize complications (renal deterioration, uncorrected hearing loss, dental disease, untreated hypogonadism) in individuals already diagnosed.
Immunization: No disease-specific vaccine strategy; standard immunization schedules apply.
Genetic Counseling: Central to prevention strategy — informing carrier parents of the 25% recurrence risk per pregnancy, offering prenatal/preimplantation testing options, and (in the Hutterite community specifically) potentially offering targeted carrier screening for the founder c.136G>A variant.
Public Health/Behavioral/Prophylaxis: Not applicable — this is not a condition amenable to public-health-level intervention, sanitation, vector control, or prophylactic medication strategies.
Taxonomy: No naturally-occurring THOC6-deficient disease has been reported in non-human species (no OMIA entry identified in searches conducted). The gene is broadly conserved (THO complex is conserved from yeast through mammals), but no spontaneous veterinary/companion-animal or wildlife disease phenotype has been documented.
Comparative biology: The THO/TREX complex mRNA-export/splicing-coupling function is evolutionarily conserved from Saccharomyces cerevisiae through humans, underscoring the fundamental cellular importance of this pathway; however, no comparative natural-disease models exist — all model data derives from engineered (not naturally occurring) animal models (see Section 15).
Zoonotic potential/transmission: Not applicable (non-infectious monogenic disorder).
Mouse (engineered, not natural disease): - Thoc6 loss-of-function mouse model (described as Thoc6^fs/fs in the 2024 Nature Communications mechanistic study): biallelic loss is embryonic lethal by E9.5–E11.5. Embryos show developmental delay evident from E9.5, are smaller than littermates, and display thinner neuroepithelium in the telencephalic vesicles, with increased mitosis and increased apoptosis at E9.5. This is notably more severe than the human phenotype (humans survive with biallelic loss-of-function into adulthood), representing an important human-model mismatch: the mouse model demonstrates the embryonic requirement for Thoc6 in neuroepithelial development but does not recapitulate human survivability, implying species-specific compensatory mechanisms not yet identified. Splicing-defect signatures (weak splice sites, altered events) were broadly similar in direction to human findings but the mouse showed a "broader apoptotic response" than human iPSC-derived models (PMC10884030 / Nature Communications 2024, PMID:38388531). - Available via MGI (Thoc6, MGI:2677480), which curates mouse genetic/phenotype data for this locus, though the specific engineered allele used in the corticogenesis study should be cross-referenced directly with the primary publication for exact allele nomenclature.
Human iPSC-derived cortical organoid model: - Patient-derived and CRISPR-engineered iPSC lines carrying THOC6 pathogenic variants (nonsense W100 and missense E188K alleles referenced) differentiated into dorsal forebrain-fated cortical organoids, recapitulating aspects of in vivo ventricular-zone neurogenesis (neural rosette formation, NPC proliferation, and differentiation to cortical neuron fates). This model reproduced reduced NPC proliferation, elevated apoptosis, delayed neuronal differentiation, thinner pseudostratified neuroepithelium, and smaller neural rosettes — closely mirroring the human microcephaly phenotype, making this the most disease-relevant available model system (PMC10884030/PMC10503840, Nature Communications 2024 and its bioRxiv precursor). - Model characteristics: Human iPSC-derived organoids showed milder apoptotic response than the mouse model, better recapitulating the survivable human phenotype — an important point favoring the organoid model's translational fidelity over the (embryonic lethal) mouse model for phenotype severity, though the organoid model cannot capture the full multi-organ (cardiac/renal/genitourinary) phenotype spectrum, which remains a model limitation* (organoids model cortical/neural pathology only).
Applications: These models have been used specifically to establish the TREX-tetramer-disruption / alternative-splicing mechanism (rather than the originally hypothesized bulk mRNA nuclear export defect), and to identify downstream PI3K-AKT/mTOR, TGF-β, and WNT/lncRNA pathway dysregulation as mediators of the proliferation/apoptosis/differentiation phenotype in corticogenesis.
Resources: MGI (Thoc6 mouse gene record, MGI:2677480) for mouse genetic/allele data; no dedicated ZFIN/FlyBase/WormBase THOC6 disease model was identified in this search (searches for zebrafish THOC6-specific models did not return a dedicated published zebrafish thoc6 disease model, unlike the related THOC2 gene, for which a zebrafish model exists).
| Citation | Contribution |
|---|---|
| Beaulieu et al. 2013, Orphanet J Rare Dis 8:62, PMID:23621916 | Original description; Hutterite founder variant p.Gly46Arg |
| Kumar et al. 2016 / "Autosomal recessive mutations in THOC6..." PMID:27102954 | Syndrome delineation, forward/reverse phenotyping, expanded cohort |
| Mattioli et al. 2019, Hum Mol Genet 28(6):952-960, DOI:10.1093/hmg/ddy391 | Functional characterization of recurrent missense variants; mislocalization and THOC1/THOC5 interaction loss |
| Lemire, Innes, Boycott — GeneReviews NBK560442 (2020) | Comprehensive clinical synthesis, diagnostic/management guidelines, ~19 individuals/15 families |
| Ruaud et al. 2022, Birth Defects Research, DOI:10.1002/bdr2.2011 | Prenatal phenotype and literature review |
| Kiraz et al. 2022, Am J Med Genet A, DOI:10.1002/ajmg.a.62667 | Truncating variant, new phenotypic findings |
| PMC10503840 / bioRxiv 2022.09.06.506502 | Mechanisms of mRNA processing defects — precursor mechanistic study |
| Nature Communications 2024, PMID:38388531, PMC10884030 | Definitive TREX-tetramer/splicing mechanism; mouse and human organoid models |
| PMC12324036 (2024–2025 case report) | Novel splice variant (c.155+1G>T); first report of ambiguous genitalia/DSD phenotype |
Note for dismech curation: MONDO and Orphanet numeric identifiers for this entry should be independently confirmed against the live MONDO Ontology Lookup Service and Orphanet database before entry (not reliably retrievable via general web search in this session); OMIM #613680 (phenotype) and *615403 (gene) are confirmed. All PMIDs above should be run through just fetch-reference and snippet-verified per the standard dismech evidence SOP before being committed to a knowledge-base YAML entry — several claims here (e.g., "47% cardiac defects," "approximately half" dental anomalies) originate from aggregated GeneReviews narrative text rather than a single quotable primary-source sentence, so curators should locate the specific primary cohort paper (likely Kumar et al. 2016 or the GeneReviews-cited case series) for an exact quotable snippet rather than citing the GeneReviews synthesis itself as the evidence source where a primary paper exists.