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Classifications

Harrison's Part

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Inheritance

1

X-linked inheritance HP:0001417

THOC2 is on the X chromosome and the disorder is X-linked, with affected males and typically milder or unaffected carrier females. Both inherited and de novo variants occur: the original families were ascertained through X-linked intellectual disability pedigrees, and a de novo variant has been documented in a female with epileptic encephalopathy, so the disorder is not confined to transmitting families. Heterozygous carrier mothers are clinically unaffected and, where tested, show highly skewed X-chromosome inactivation, which is the proposed explanation for their non-penetrance; the one severely affected female reported carried a de novo variant and her XCI status could not be assessed.

X-linked inheritance Expressivity: VARIABLE

Show evidence (3 references)

PMID:26166480 SUPPORT Human Clinical

"Here, we report that variants in THOC2, which encodes a subunit of the highly conserved TREX mRNA-export complex, cause syndromic intellectual disability (ID)."

The defining report establishing THOC2 as a cause of syndromic intellectual disability, ascertained through X-linked intellectual disability families.

PMID:29851191 SUPPORT Human Clinical

"We present detailed clinical assessment and functional studies on a de novo variant in a female with an epileptic encephalopathy"

Documents a de novo THOC2 variant in an affected female, showing the disorder is not restricted to inherited male-transmitted cases.

PMID:29851191 SUPPORT Human Clinical

"heterozygous mothers were clinically unaffected, and, where available, X-chromosome inactivation (XCI) was highly skewed"

Establishes skewed X-inactivation in carrier mothers as the observed correlate of their non-penetrance, which is the substance of the X-linked expressivity claim.

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Discussions and Knowledge Gaps

1

Is perturbed R-loop homeostasis with consequent DNA damage the mechanism of THOC2 syndrome in humans, or is it specific to the mouse model?

HUMAN MODEL MISMATCH OPEN thoc2_rloop_human_validation

Attached to

pathophysiology#Perturbed R-Loop Homeostasis and DNA Damage

The R-loop/DNA-damage model is the only mechanistic account on offer for why partial loss of a ubiquitously required transcription-export factor produces a brain-predominant phenotype, and it nominates a druggable axis (R-loop-resolving helicases, DNA-damage-response modulation). It is better evidenced than a purely murine claim: R-loops were shown to accumulate in fibroblasts from the very patient whose allele the mouse carries, and RNase H1 overexpression reduced both R-loops and comet-assay DNA damage, which orders the two events causally. Three gaps nonetheless keep this open. First, the rescue was performed in mouse neural stem cells, not in the patient cells, so the causal ordering is established in mouse and only the phenotype is established in human cells. Second, only one allele has been interrogated - the exon 37-38 deletion - whereas THOC2 alleles fall into two structurally different classes (destabilising missense versus C-terminal RNA-binding-domain truncation), so it is not established that both converge on R-loops. Third, the authors themselves frame the conclusion as a suggestion covering "mice and the patient", and no R-loop or DNA-damage measurement exists in human brain tissue. A fourth, sharper tension is that an earlier study reported the opposite cellular outcome from acute THOC2 knockdown in rodent neural cells - increased progenitor proliferation with no change in apoptosis - which is not obviously reconcilable with the germline-hypomorph finding of progenitor cell death, though the two differ in species, timing and the acuteness of the depletion.

Proposed experiments

R-loop and DNA-damage profiling across both THOC2 allele classes

thoc2_rloop_allele_classes

Quantify R-loop burden (DRIP-seq and S9.6 immunofluorescence) and DNA-damage markers in patient-derived lymphoblastoid or fibroblast lines carrying destabilising missense alleles, and compare against the already-characterised exon 37-38 deletion line and sex-matched controls. Then perform the RNase H1 rescue directly in the human patient lines rather than in mouse neural stem cells.

Decision criterion

Elevated R-loops with RNase H1 rescue in patient cells of both allele classes would establish the mechanism in human cells and unify the allele classes; an effect confined to the truncation class would mean the two classes act through different proximal mechanisms and that the entry's single causal chain needs to be split.

Reconciling increased progenitor proliferation with progenitor cell death

thoc2_proliferation_vs_apoptosis

Directly compare acute shRNA knockdown of THOC2 against a germline hypomorphic allele in the same neural progenitor system, measuring proliferation rate, apoptosis, R-loop burden and DNA damage in parallel and over a time course.

Decision criterion

If the germline hypomorph produces apoptosis where acute knockdown produces proliferation, the discrepancy is a kinetic/adaptive effect and the entry's cell-death node stands; if acute knockdown also produces apoptosis under matched conditions, the earlier report is the outlier and the chain is simpler than currently curated.

Mechanistic characterisation of the severe-profound subset

thoc2_severe_subset_mechanism

Compare THOC2 protein levels, TREX subunit abundance and R-loop burden between individuals with the severe-profound phenotype (persistent hypotonia and respiratory abnormalities) and those with the milder language-predominant phenotype.

Decision criterion

A quantitative relationship between residual THOC2 or TREX abundance and clinical severity would answer the cohort authors' explicit call for the pathophysiological basis of the severe phenotype.

Show evidence (4 references)

PMID:38331934 SUPPORT Model Organism

"Overall, we suggest that perturbed R-loop homeostasis, in stem cells and/or differentiated cells in mice and the patient, and DNA damage-associated functional alterations are at the root of THOC2 syndrome."

The mechanism is offered as a suggestion, and the human half of the claim is extrapolated from the mouse rather than measured, which is the substance of this open question.

PMID:32116545 SUPPORT Human Clinical

"Further investigations to elucidate the pathophysiological basis for this severe phenotype are warranted."

The largest cohort's authors explicitly state that the mechanism of the severe subset is unexplained, which is part of what keeps this discussion open.

PMID:38331934 SUPPORT Model Organism

"reduced R-loop accumulation (Fig. 7e) and comet tail formation (Fig. 7f) in Thoc2"

The RNase H1 rescue that orders R-loops upstream of DNA damage was performed in mutant mouse neural stem cells, not in patient cells - which is precisely the residual human-model gap the first proposed experiment closes.

+ 1 more reference

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Pathophysiology

6

Hypomorphic THOC2 Variants Reducing Protein Stability

Every disease-associated THOC2 allele is hypomorphic rather than null, because THOC2 is an essential gene. Two mechanistic classes are documented. Missense variants at evolutionarily conserved residues reduce THOC2 protein stability - 9 of 14 tested missense variants did so across current and published studies. Splice-site and intragenic-deletion variants instead produce C-terminally truncated THOC2 with loss of small regions of the C-terminal RNA-binding domain. Structural modelling places the altered residues in RNA-binding domains of two THOC2 conformations, interpreted as different intermediate RNA-binding states during RNA transport.

THOC2 hgnc:19073

Downstream

TREX Complex Destabilisation Reduced THOC2 stability has a flow-on effect on the stability of its partner TREX subunits.

Show evidence (4 references)

PMID:32116545 SUPPORT In Vitro

"Ex vivo missense variant testing and patient-derived cell line data from current and published studies show 9 of the 14 missense THOC2 variants result in reduced protein stability."

Quantifies the proportion of tested missense variants that destabilise THOC2, establishing reduced protein stability as the dominant missense mechanism.

PMID:32116545 SUPPORT Human Clinical

"The splicing-defective and deletion variants result in a loss of small regions of the C-terminal THOC2 RNA binding domain (RBD)."

Defines the second allele class - splice and deletion variants removing part of the C-terminal RNA-binding domain. This is a molecular variant-consequence finding derived from patient-cell cDNA and protein analysis, hence IN_VITRO rather than HUMAN_CLINICAL.

PMID:26166480 SUPPORT In Vitro

"We show that two variants lead to decreased stability of THOC2 and its TREX-complex partners in cells derived from the affected individuals."

Patient-derived cells demonstrate reduced stability of both THOC2 and its complex partners, the first functional evidence for the mechanism.

+ 1 more reference

TREX Complex Destabilisation

THOC2 is the largest subunit of the TREX complex, which couples transcription to mRNA export. Reduced THOC2 stability propagates to the complex: the stability of the other TREX/THOC subunits - specifically those themselves associated with neurodevelopmental disorders - falls as a consequence. The disorder is therefore a complex-level lesion rather than a single-protein one, which is one reason the phenotype overlaps other THOC-subunit disorders. Scope of the export claim. The 2015 discovery paper framed the disorder as a disturbance of the canonical mRNA-export pathway, and that framing survives at the level of the pathway. It does NOT survive as a claim of measurable bulk nuclear mRNA retention: when the exon 37-38 deletion allele was tested directly, neither mutant mouse primary neurons nor the corresponding patient fibroblasts showed overt nuclear retention of mRNAs. The GO annotation below is therefore left without a DECREASED modifier - the pathway is the affected one, but a quantitative reduction in bulk export has not been demonstrated for a disease allele, and the measured downstream consequence is loss of R-loop and genome homeostasis rather than transcript sequestration.

mRNA export from nucleus GO:0006406

Downstream

Perturbed R-Loop Homeostasis and DNA Damage Compromised THOC2/TREX function leads to R-loop accumulation, the proposed root of the disorder. The intermediates between complex destabilisation and hybrid accumulation - whether co-transcriptional RNA packaging, R-loop resolution or 3' processing is the failing step - have not been determined.

Impaired Neurodevelopment Disturbance of the canonical mRNA-export pathway is compatible with life but results in altered neuronal development. This edge is retained alongside the better-characterised route through R-loop accumulation and cortical neurogenesis because the 2015 discovery paper asserts the pathway-to-phenotype link directly, without committing to the intervening genome-instability steps.

Multi-Organ Developmental Involvement THOC subunits are ubiquitously expressed, and the congenital anomalies seen across several organ systems are attributed by the largest cohort to a role for THOC2 in multi-organ development rather than to a secondary consequence of the neurological phenotype.

Show evidence (4 references)

PMID:32116545 SUPPORT In Vitro

"Interestingly, reduced stability of THOC2 variant proteins has a flow-on effect on the stability of the multi-protein TREX complex; specifically on the other NDD-associated THOC subunits."

Establishes the complex-level consequence - destabilised THOC2 destabilises its partner THOC subunits, particularly the other NDD-associated ones.

PMID:38331934 SUPPORT Other

"We implicated the X-chromosome THOC2 gene, which encodes the largest subunit of the highly-conserved TREX (Transcription-Export) complex, in a clinically complex neurodevelopmental disorder with intellectual disability as the core phenotype."

States THOC2's identity as the largest TREX subunit and confirms intellectual disability as the core phenotype of the disorder.

PMID:26166480 SUPPORT Human Clinical

"Our results show that disturbance of the canonical molecular pathway of mRNA export is compatible with life but results in altered neuronal development with other comorbidities."

States the central paradox of the disorder - an essential housekeeping pathway can be partially disturbed compatibly with life, at the cost of altered neurodevelopment.

+ 1 more reference

Multi-Organ Developmental Involvement

The non-neurological arm of the disorder. THOC subunits are ubiquitously expressed, and the largest cohort concluded that THOC2-related disorder should be considered multisystemic in a significant proportion of individuals: congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems are each present in 10-30%, and the cohort authors attribute these to a role for THOC2 in multi-organ development and function rather than to a secondary consequence of the neurological phenotype. The molecular route from TREX destabilisation to organ malformation has not been investigated - no non-neural tissue has been examined in the mouse model or in patient material - so this node records a well-evidenced clinical observation with an unevidenced mechanism.

Downstream

Congenital Cardiac Anomaly Congenital anomalies of the cardiorespiratory system occur in a significant minority.

Genitourinary Anomaly Congenital anomalies of the genitourinary tract occur in a significant minority.

Skeletal Anomaly Congenital anomalies of the skeletal system occur in a significant minority.

Laryngomalacia and Tracheomalacia Airway malacia is among the congenital anomalies with increased risk in the severe neuromuscular subgroup.

Show evidence (3 references)

PMID:32116545 SUPPORT Human Clinical

"THOC2-related disorder should be considered a multi-systemic disorder in a significant proportion of individuals"

The largest cohort's explicit conclusion that the disorder is multisystemic, which is the claim this node represents.

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Enumerates the organ systems affected and gives the 10-30% frequency range shared by the phenotypes downstream of this node.

PMID:32116545 SUPPORT Human Clinical

"Further research to explore the underlying pathophysiological basis for these more severe phenotypes is warranted, but likely reflect the involvement of THOC2 in multi-organ development and function."

The mechanistic half of this node is the cohort authors' explicitly hedged inference ("likely reflect"), with the accompanying statement that further research is warranted - which is why the node carries PROVISIONAL confidence and is curated as PARTIAL.

Perturbed R-Loop Homeostasis and DNA Damage

The best-supported root mechanism, derived from a mouse model carrying a patient allele together with cells from the patient who carries it. Compromised THOC2/TREX function allows R-loops (RNA:DNA hybrids with a displaced single strand) to accumulate, producing DNA damage and consequent cell death during brain development. Two pieces of evidence lift this above a purely model-organism inference: R-loops accumulate in the patient's own fibroblasts as well as in mutant mouse neural stem cells, and forced RNase H1 expression - which degrades the RNA strand of RNA:DNA hybrids - reduces both the R-loop burden and the comet-assay DNA damage, placing R-loops upstream of the damage rather than alongside it. Confidence is nonetheless held at PROVISIONAL: the rescue experiment was performed in mouse neural stem cells rather than patient cells, only the exon 37-38 deletion allele has been tested, and no R-loop or DNA-damage measurement exists in human brain tissue.

neural progenitor cell CL:0011020

DNA damage response GO:0006974 ↑ INCREASED apoptotic process GO:0006915 ↑ INCREASED

Downstream

Disrupted Cortical Neurogenesis and Neuronal Maturation DNA damage and progenitor cell death during corticogenesis translate into measurable structural and maturational deficits in the developing cortex. The known intermediate is loss of ventricular-zone neural stem cells.

Show evidence (4 references)

PMID:38331934 SUPPORT Model Organism

"The Thoc2Δ/Y mouse brain development is significantly impacted by compromised THOC2/TREX function resulting in R-loop accumulation, DNA damage and consequent cell death."

Direct in vivo demonstration of the R-loop, DNA-damage and cell-death chain in the brain of a mouse carrying a patient THOC2 allele.

PMID:38331934 SUPPORT In Vitro

"indicating R-loops also accumulate in the patient cells"

R-loop accumulation is not confined to the mouse - it is reproduced in fibroblasts from the patient whose allele the mouse carries, which is the strongest available human anchor for this node.

PMID:38331934 SUPPORT In Vitro

"reduced R-loop accumulation (Fig. 7e) and comet tail formation (Fig. 7f) in Thoc2"

RNase H1 overexpression lowers both R-loop burden and comet-assay DNA damage in cultured mutant neural stem cells, establishing the R-loop as an upstream cause of the damage rather than a co-occurring marker. Tagged IN_VITRO rather than MODEL_ORGANISM because the rescue was done in cultured cells, not in the animal.

+ 1 more reference

Disrupted Cortical Neurogenesis and Neuronal Maturation

The tissue-level consequence measured in the patient-allele mouse. Loss of neural stem cells from the cortical ventricular zone thins the progenitor compartment at embryonic day 18.5, and the cortical plate and corpus callosum are correspondingly thinner. Neurons that do form show perturbed migration, altered electrophysiological properties and impaired synapse formation. This node is what connects the molecular genome-instability lesion to a brain-predominant clinical phenotype: the affected compartment is the proliferating progenitor pool of the developing cortex, which is why a ubiquitously required housekeeping factor produces a predominantly neurodevelopmental disease. This node accounts for the neurological arm only - the largest cohort concluded that THOC2 disease is also multisystemic in a significant proportion of individuals, which is modelled separately in the Multi-Organ Developmental Involvement node. All measurements are murine; the corresponding human neuroimaging findings are inconsistent: structural MRI was normal in three of the five individuals imaged in the 2018 series, and the 2020 pooled cohort found no unifying neuroradiological abnormality across the individuals it reviewed.

neural stem cell CL:0000047

neuron migration GO:0001764 ⚠ ABNORMAL synapse organization GO:0050808 ⚠ ABNORMAL

Downstream

Impaired Neurodevelopment Reduced cortical progenitor pool, thinner cortical plate and corpus callosum, and impaired neuronal migration and synapse formation produce the organism-level neurodevelopmental phenotype.

Show evidence (4 references)

PMID:38331934 SUPPORT Model Organism

"reduction in the thickness of the ventricular zone (VZ) of the E18.5 Thoc2"

Documents thinning of the cortical progenitor compartment in the patient-allele mouse, the proximal tissue-level lesion of this node.

PMID:38331934 SUPPORT Model Organism

"reduced overall thickness of the cortical plate and corpus callosum"

The cortical plate and corpus callosum are correspondingly thinner, showing that progenitor loss propagates to the mature cortical structures. Note this particular measurement is made in the post-natal day 30 brain rather than at E18.5.

PMID:38331934 SUPPORT In Vitro

"Thoc2Δ/Y neurons show perturbed in vitro neural migration, electrophysiological properties and synapse formation"

Establishes the neuronal-maturation arm of this node - migration, electrophysiology and synapse formation are all disturbed in mutant neurons. Tagged IN_VITRO because the source states these were in vitro assays.

+ 1 more reference

Impaired Neurodevelopment

The organism-level consequence is a neurodevelopmental disorder with intellectual disability as the core phenotype, accompanied by disorders of growth. Severity spans language disorder without frank intellectual disability at one end to severe-profound intellectual disability with persistent hypotonia and respiratory abnormalities at the other. Movement and seizure disorders are prominent in the more severely affected. The mouse carrying a patient allele recapitulates the core features - smaller size and weight, and deficits in spatial learning, working memory and sensorimotor function - which supports the causal chain.

neuron CL:0000540

Downstream

Intellectual Disability Intellectual disability is the core phenotype.

Speech and Language Disorder Language disorder is part of the refined core phenotype and can occur with or without frank intellectual disability.

Seizures Seizure disorders occur, particularly in the severe group.

Hypotonia Persistent hypotonia characterises the severe-profound end of the spectrum.

Tremor Tremor is among the commonly observed movement features.

Gait Disturbance Gait disturbance is among the commonly observed motor features.

Short Stature Disorders of growth are part of the refined core phenotype, and the mouse model is smaller and lighter than wild type.

Small for Gestational Age Growth restriction is already present at birth in a substantial minority, indicating a prenatal onset of the growth arm of the phenotype.

Increased Body Mass Index Elevated BMI with truncal obesity emerges in older affected males, the second growth feature that gives the disorder its MONDO name; the intervening mechanism between the THOC2 lesion and the body-composition change is unknown.

Microcephaly Reduced cortical progenitor pool and thinner cortical structures in the mouse provide a plausible route to the reduced head circumference seen in a minority of affected individuals.

Atypical Behavior Behavioural problems, including autism spectrum disorder in one individual, are among the common findings of the disorder.

Autism Spectrum Disorder One individual in the quantified cohort met diagnostic criteria for autism spectrum disorder.

Inability to Walk At the severe end of the motor spectrum, affected individuals never achieve independent ambulation.

Respiratory Abnormalities Respiratory abnormalities accompany persistent hypotonia in the severe-profound subset; the cohort authors explicitly flagged the pathophysiological basis of this severe presentation as unexplained.

Arthrogryposis Multiplex Congenita Allele-specific extreme of the phenotype. A recurrent canonical acceptor splice-site variant has produced lethal fetal akinesia with congenital joint contractures in male fetuses from two unrelated families, with a myopathic muscle phenotype showing cytoplasmic bodies. The intermediate steps between the THOC2 lesion and reduced fetal movement have not been established.

Abnormality of Movement Abnormal motor coordination, stereotypies and involuntary movements are the most common neurological feature after the cognitive and language phenotype, and emerge or worsen with age in a subset.

Hypertonia and Spasticity A minority develop hypertonia with spasticity or contractures with age, the opposite tone pole from the infantile hypotonia of early presentation.

Recurrent Aspiration and Respiratory Infection In the severe neuromuscular subgroup, persistent muscular hypotonia together with feeding difficulty and airway malacia leads to recurrent aspiration and respiratory tract infection.

Sialorrhea Excessive salivation follows from the oromotor component of the persistent hypotonia in the severe neuromuscular subgroup.

Feeding Difficulties Severe feeding difficulty follows from oromotor dysfunction in the hypotonic subgroup, and travels with gastroesophageal reflux and aspiration risk.

Gastroesophageal Reflux Gastroesophageal reflux occurs in a significant minority and contributes to the feeding and aspiration morbidity of the severe subgroup.

Visual Impairment Visual impairment occurs in a significant minority; cortical visual impairment was documented in the severely affected female.

Hearing Impairment Hearing impairment occurs in a significant minority and compounds the language phenotype.

Show evidence (3 references)

PMID:32116545 SUPPORT Human Clinical

"Our current, expanded cohort refines the core phenotype of THOC2 NDDs to language disorder and/or ID, with a variable severity, and disorders of growth."

The largest cohort's explicit refinement of the core phenotype, which this node represents.

PMID:38331934 SUPPORT Model Organism

"The Thoc2 exon 37-38 deletion male (Thoc2Δ/Y) mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight, and significant deficits in spatial learning, working memory and sensorimotor functions."

The patient-allele mouse reproduces the cognitive, sensorimotor and growth features, supporting the causal chain from the molecular lesion to the organism-level phenotype.

PMID:29851191 SUPPORT Human Clinical

"Severe neurocognitive features, including movement and seizure disorders, were observed in this cohort."

Documents the severe end of the spectrum with prominent movement and seizure disorders.

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Pathograph

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Phenotypes

27

Cardiovascular 1

Congenital Cardiac Anomaly OCCASIONAL Abnormal heart morphology HP:0001627

Show evidence (2 references)

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Cardiorespiratory congenital anomalies are named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.

PMID:32116545 SUPPORT Human Clinical

"that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"

Cardiac anomalies are specifically enumerated among the congenital malformations enriched in the severe neuromuscular subgroup.

Digestive 2

Feeding Difficulties OCCASIONAL HP:0011968

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

The pooled cohort reports severe feeding difficulties within a group of multisystem features each present in 10-30%, which falls in the OCCASIONAL band (5-29%) at its upper edge.

Gastroesophageal Reflux OCCASIONAL HP:0002020

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Gastroesophageal reflux is named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.

Ear 1

Hearing Impairment OCCASIONAL HP:0000365

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Hearing impairment is named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.

Eye 1

Visual Impairment OCCASIONAL HP:0000505

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Visual impairment is named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.

Genitourinary 1

Genitourinary Anomaly OCCASIONAL Abnormality of the genitourinary system HP:0000119

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Genitorenal congenital anomalies are named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.

Head and Neck 2

Microcephaly FREQUENT HP:0000252

Show evidence (3 references)

PMID:38331934 SUPPORT Human Clinical

"we generated a mouse model based on a hypomorphic Thoc2 exon 37-38 deletion variant of a patient with ID, speech delay, hypotonia, and microcephaly"

Documents microcephaly in the index patient whose allele was modelled, establishing the association.

PMID:29851191 SUPPORT Human Clinical

"Growth abnormalities were common including low birth weight (3/7), microcephaly (2/7) and short stature (2/7)."

Documents microcephaly as part of the growth-abnormality cluster in the 2018 series; the pooled-cohort rate below is what sets the band.

PMID:32116545 SUPPORT Human Clinical

"a half (52%) have persistent short stature, a third (34%) are microcephalic and 29% have intrauterine growth restriction (IUGR)"

The pooled 38-individual cohort gives microcephaly in 34%, which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here.

Sialorrhea Drooling HP:0002307

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"

Names excessive salivation as a component of the severe neuromuscular phenotype. Qualitative statement, so no frequency band is assigned.

Immune 1

Recurrent Aspiration and Respiratory Infection Recurrent respiratory infections HP:0002205

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"

Enumerates recurrent aspiration and respiratory tract infections as components of the severe neuromuscular phenotype. The statement is qualitative, which is why no frequency band is assigned.

Musculoskeletal 3

Hypotonia FREQUENT HP:0001252

Show evidence (2 references)

PMID:29851191 SUPPORT Human Clinical

"Four of the seven had infantile hypotonia and two of the seven had tremor."

Gives the direct numerator, 4 of 7 (57%), which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here.

PMID:32116545 SUPPORT Human Clinical

"A subset of affected individuals' has severe-profound ID, persistent hypotonia and respiratory abnormalities."

Documents the persistent, severe form of the hypotonia that characterises the severe-profound subset, distinct from the more general infantile hypotonia counted above.

Hypertonia and Spasticity OCCASIONAL HP:0001276

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"in the expanded cohort 13% develop hypertonia and spasticity or contractures, and 53% have some abnormality of motor coordination, stereotypic or involuntary movements"

Gives the pooled-cohort rate of 13%, which falls in the OCCASIONAL band (5-29%). The verb "develop" is the basis for the PROGRESSIVE qualifier.

Skeletal Anomaly OCCASIONAL Abnormality of the skeletal system HP:0000924

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Skeletal congenital anomalies are named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.

Nervous System 8

Intellectual Disability VERY_FREQUENT HP:0001249

Show evidence (4 references)

PMID:38331934 SUPPORT Other

"in a clinically complex neurodevelopmental disorder with intellectual disability as the core phenotype"

States intellectual disability as the core phenotype of the disorder.

PMID:26166480 SUPPORT Human Clinical

"Affected individuals presented with variable degrees of ID and commonly observed features included speech delay, elevated BMI, short stature, seizure disorders, gait disturbance, and tremors."

The defining cohort documents intellectual disability in all affected individuals with variable degree, alongside the associated features.

PMID:29851191 SUPPORT Human Clinical

"ID was universal and at least moderate in severity: 2/7 were non-ambulatory and 3/7 non-verbal."

Intellectual disability was present in 7 of 7 individuals in this series, the direct quantitative basis for the VERY_FREQUENT band.

+ 1 more reference

Speech and Language Disorder VERY_FREQUENT Delayed speech and language development HP:0000750

Show evidence (4 references)

PMID:26166480 SUPPORT Human Clinical

"commonly observed features included speech delay, elevated BMI, short stature, seizure disorders, gait disturbance, and tremors"

Speech delay heads the list of commonly observed features in the defining cohort.

PMID:32116545 SUPPORT Human Clinical

"refines the core phenotype of THOC2 NDDs to language disorder and/or ID"

Language disorder is explicitly one half of the refined core phenotype, which is why it is banded alongside intellectual disability.

PMID:29851191 SUPPORT Human Clinical

"ID was universal and at least moderate in severity: 2/7 were non-ambulatory and 3/7 non-verbal."

Quantifies the severe end of the language phenotype - 3 of 7 individuals were non-verbal rather than merely speech-delayed.

+ 1 more reference

Seizures OCCASIONAL HP:0001250

Show evidence (4 references)

PMID:26166480 SUPPORT Human Clinical

"short stature, seizure disorders, gait disturbance, and tremors"

Seizure disorders are listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified.

PMID:29851191 SUPPORT Human Clinical

"Severe neurocognitive features, including movement and seizure disorders, were observed in this cohort."

Confirms seizure disorders as a prominent feature of the severe cohort.

PMID:29851191 SUPPORT Human Clinical

"Confirmed seizure disorder was only present in the affected female (individual 7) but suspected in individual 2."

Within the 2018 series seizures were confirmed in 1 of 7 and suspected in a second, consistent with the pooled-cohort rate below.

+ 1 more reference

Tremor OCCASIONAL HP:0001337

Show evidence (3 references)

PMID:26166480 SUPPORT Human Clinical

"seizure disorders, gait disturbance, and tremors"

Tremors are listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified.

PMID:29851191 SUPPORT Human Clinical

"Four of the seven had infantile hypotonia and two of the seven had tremor."

Gives the tremor-specific numerator, 2 of 7 (29%), which is the direct basis for the OCCASIONAL band. The larger pooled cohort does not break tremor out separately from the composite movement category.

PMID:29851191 SUPPORT Human Clinical

"nystagmus, tremor and an ataxic broad-based gait for individual 6, in the absence of significant cerebellar abnormalities on MRI"

Characterises the tremor as part of a cerebellar-type sign complex occurring without structural cerebellar abnormality, which is the clinically distinctive form the movement disorder takes in this disease.

Gait Disturbance FREQUENT HP:0001288

Show evidence (3 references)

PMID:26166480 SUPPORT Human Clinical

"seizure disorders, gait disturbance, and tremors"

Gait disturbance is listed among the commonly observed features of the defining cohort.

PMID:38331934 SUPPORT Model Organism

"significant deficits in spatial learning, working memory and sensorimotor functions"

The mouse model shows sensorimotor deficits corresponding to the human motor phenotype.

PMID:29851191 SUPPORT Human Clinical

"They have a core phenotype of ID, and common findings of behavioural disorders, infantile hypotonia, gait disturbance and growth impairment"

Gait disturbance is stated to be a common finding of the disorder; mapping the qualitative term "common" to the enum gives the FREQUENT band (30-79%).

Atypical Behavior FREQUENT HP:0000708

Show evidence (2 references)

PMID:29851191 SUPPORT Human Clinical

"Behavioural problems were reported in four individuals, with one meeting diagnostic criteria for autism spectrum disorder."

Direct numerator of 4 of 7 (57%), which falls in the FREQUENT band (30-79%).

PMID:29851191 SUPPORT Human Clinical

"They have a core phenotype of ID, and common findings of behavioural disorders, infantile hypotonia, gait disturbance and growth impairment"

The cohort's own summary lists behavioural disorders among the common findings, corroborating the band derived from the numerator.

Autism Spectrum Disorder OCCASIONAL HP:0000717

Show evidence (1 reference)

PMID:29851191 SUPPORT Human Clinical

"Behavioural problems were reported in four individuals, with one meeting diagnostic criteria for autism spectrum disorder."

One of seven individuals (14%) met diagnostic criteria for autism spectrum disorder, which falls in the OCCASIONAL band (5-29%).

Abnormality of Movement FREQUENT HP:0100022

Course: PROGRESSIVE

Show evidence (2 references)

PMID:32116545 SUPPORT Human Clinical

"in the expanded cohort 13% develop hypertonia and spasticity or contractures, and 53% have some abnormality of motor coordination, stereotypic or involuntary movements"

Gives the pooled-cohort rate of 53% for the composite movement abnormality, which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here.

PMID:32116545 SUPPORT Human Clinical

"although for many individuals the phenotype is static, a more complex neurological phenotype also emerges with age in several males"

Supports the PROGRESSIVE clinical course qualifier on this phenotype, and notes explicitly that progression is not universal.

Growth 2

Short Stature FREQUENT HP:0004322

Show evidence (3 references)

PMID:26166480 SUPPORT Human Clinical

"speech delay, elevated BMI, short stature, seizure disorders, gait disturbance, and tremors"

Short stature is listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified and so cannot itself set the band.

PMID:32116545 SUPPORT Human Clinical

"a half (52%) have persistent short stature, a third (34%) are microcephalic and 29% have intrauterine growth restriction (IUGR)"

The pooled 38-individual cohort gives persistent short stature in 52%, which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here. This supersedes the smaller 2/7 count in the 2018 series, which was a subset of this pooled denominator.

PMID:38331934 SUPPORT Model Organism

"mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight"

The mouse model reproduces the growth restriction, supporting it as a genuine consequence of the THOC2 lesion rather than an ascertainment artefact.

Small for Gestational Age OCCASIONAL HP:0001518

Show evidence (2 references)

PMID:32116545 SUPPORT Human Clinical

"a half (52%) have persistent short stature, a third (34%) are microcephalic and 29% have intrauterine growth restriction (IUGR)"

The pooled 38-individual cohort gives intrauterine growth restriction in 29%, which falls at the top of the OCCASIONAL band (5-29%) and is the basis for the frequency assigned here.

PMID:29851191 SUPPORT Human Clinical

"Growth abnormalities were common including low birth weight (3/7), microcephaly (2/7) and short stature (2/7)."

The 2018 subset reported low birth weight in 3 of 7. Low birth weight and intrauterine growth restriction are related but not identical concepts, both captured by HP:0001518; the pooled IUGR figure above is what sets the band.

Other 5

Increased Body Mass Index OCCASIONAL HP:0031418

Show evidence (3 references)

PMID:26166480 SUPPORT Human Clinical

"commonly observed features included speech delay, elevated BMI, short stature"

Elevated BMI is listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified.

PMID:32116545 SUPPORT Human Clinical

"26% of the expanded cohort have increased body weight, with obesity in older males particularly noted"

The pooled 38-individual cohort gives increased body weight in 26%, which falls in the OCCASIONAL band (5-29%) and is the basis for the frequency assigned here.

PMID:29851191 SUPPORT Human Clinical

"The affected individuals had a syndromic NDD, characterized by borderline to severe ID, speech delay, short stature and adult onset truncal obesity"

States explicitly that the obesity component is adult-onset and truncal rather than a constant feature. Note that this sentence is the 2018 paper's own recap of the 2015 cohort, so it is secondary characterisation of that earlier series rather than a new observation.

Respiratory Abnormalities OCCASIONAL Abnormality of the respiratory system HP:0002086

Show evidence (2 references)

PMID:32116545 SUPPORT Human Clinical

"A subset of affected individuals' has severe-profound ID, persistent hypotonia and respiratory abnormalities."

Respiratory abnormalities are reported specifically in the severe-profound subset, supporting an OCCASIONAL band.

PMID:32116545 SUPPORT Human Clinical

"Further investigations to elucidate the pathophysiological basis for this severe phenotype are warranted."

The cohort authors explicitly flag the severe subset's mechanism as unexplained, which is recorded as a knowledge gap in this entry.

Inability to Walk OCCASIONAL HP:0002540

Show evidence (1 reference)

PMID:29851191 SUPPORT Human Clinical

"ID was universal and at least moderate in severity: 2/7 were non-ambulatory and 3/7 non-verbal."

Direct numerator of 2 of 7 (29%), which falls at the top of the OCCASIONAL band (5-29%).

Arthrogryposis Multiplex Congenita HP:0002804

Show evidence (4 references)

PMID:34976470 SUPPORT Human Clinical

"Here, we describe for the first time a recurrent arthrogryposis multiplex congenita phenotype (AMC) in two male fetuses in a family."

First description of arthrogryposis multiplex congenita caused by a THOC2 variant, in two affected male fetuses of one family.

PMID:34976470 SUPPORT Human Clinical

"This is the most severe phenotype described in THOC2 gene-related disease till date."

Places this presentation at the extreme severe end of the THOC2 phenotypic spectrum, which is why the entry treats it as an allele-specific extreme rather than a general disease feature.

PMID:37945483 SUPPORT Human Clinical

"We report a family with the same splice site mutation in the THOC2 gene involved in fetal arthrogryposis as well."

Independent replication of the arthrogryposis phenotype with the identical splice-site variant in a second, unrelated family, which converts a single case report into a reproducible genotype-phenotype association.

+ 1 more reference

Laryngomalacia and Tracheomalacia HP:0001601

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"

Names laryngomalacia and tracheomalacia among the congenital anomalies enriched in the severe neuromuscular subgroup. Qualitative statement, so no frequency band is assigned.

🧬

Genetic Associations

1

THOC2 (Causal - X-linked hypomorphic variants)

Gene: THOC2 hgnc:19073 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (6 references)

PMID:26166480 SUPPORT Human Clinical

"we report that variants in THOC2, which encodes a subunit of the highly conserved TREX mRNA-export complex, cause syndromic intellectual disability (ID)"

The gene-discovery statement establishing THOC2 as the cause of this syndromic intellectual disability.

PMID:29851191 SUPPORT Human Clinical

"THOC2 variants that affect evolutionarily conserved amino acid residues and reduce protein stability and two with canonical splice-site THOC2 variants that result in C-terminally truncated THOC2 proteins."

Enumerates the two allele classes - destabilising missense at conserved residues, and splice variants producing C-terminal truncation.

PMID:32116545 SUPPORT Human Clinical

"including the first case of a recurrent variant (p.Arg77Cys), and an additional individual with an intragenic THOC2 microdeletion (Del-Ex37-38)"

Documents the first recurrent THOC2 variant and an intragenic microdeletion, expanding the variant spectrum beyond private missense alleles.

+ 3 more references

💊

Medical Actions

6

Multidisciplinary Supportive Care

Action: supportive care Ontology label: Supportive Care NCIT:C15747

There is no disease-modifying therapy and none is in development. Management is supportive and symptom-directed - developmental and educational support, speech and language therapy, antiseizure medication where epilepsy is present, management of the movement disorder, growth and nutritional monitoring, and respiratory support for the severe-profound subset. No treatment has been evaluated in a THOC2-specific study.

Show evidence (1 reference)

PMID:29851191 SUPPORT Other

"frequently have limited or no specific therapies for their core symptoms"

Background statement from the THOC2 cohort paper's introduction about intellectual disability generally; curated as PARTIAL/OTHER because it is framing rather than a THOC2-specific treatment finding, and it is the only citable statement on therapy available for this disorder.

Speech and Language Therapy

Action: speech and language therapy Ontology label: Speech Language Therapy NCIT:C159273

Language disorder is half of the refined core phenotype and speech delay is among the most consistently reported features, making speech-language therapy the intervention most directly matched to the disorder's dominant morbidity.

Target Phenotypes: Delayed speech and language development HP:0000750

Show evidence (1 reference)

PMID:32116545 SUPPORT Human Clinical

"refines the core phenotype of THOC2 NDDs to language disorder and/or ID"

Establishes language disorder as a core phenotype and therefore a primary intervention target; no THOC2-specific trial of speech therapy exists, so this supports the indication rather than the efficacy.

Multisystem Surveillance at Diagnosis

Action: multisystem screening evaluation at diagnosis Ontology label: Diagnosis Assessment NCIT:C15220

Because congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, feeding difficulties, and visual and hearing impairment are each present in 10-30% of affected individuals, the largest cohort explicitly recommends that every newly diagnosed individual receives a comprehensive evaluation - a detailed systems review by a paediatrician, a cardiac echocardiogram, hearing screening and ophthalmological review. This is the only concrete management recommendation issued in the THOC2 literature. Hearing and vision assessment matter disproportionately here because the population already has a language disorder, so remediable sensory deficits would otherwise be attributed to the neurodevelopmental diagnosis.

Target Phenotypes: Congenital cardiac anomaly HP:0001627 Hearing impairment HP:0000365 Visual impairment HP:0000505

Show evidence (2 references)

PMID:32116545 SUPPORT Human Clinical

"comprehensive evaluation including detailed systems review by a pediatrician, cardiac echocardiogram, hearing screening and ophthalmological review in all newly diagnosed patients is highly recommended"

An explicit, specific management recommendation issued by the largest THOC2 cohort, naming the exact investigations - this is a direct recommendation rather than an inferred indication.

PMID:32116545 SUPPORT Human Clinical

"Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"

Gives the prevalence of the multisystem findings that justify screening for them at diagnosis.

Physical and Occupational Therapy

Action: physical therapy Ontology label: Physical Therapy NCIT:C15302

Hypotonia and gait disturbance are among the common findings of the disorder, and a subset of individuals are non-ambulatory, so motor rehabilitation is a standing component of management. No THOC2-specific rehabilitation study exists; the indication rests on the documented motor phenotype rather than on any evaluated outcome.

Target Phenotypes: Hypotonia HP:0001252 Gait disturbance HP:0001288

Show evidence (1 reference)

PMID:29851191 SUPPORT Human Clinical

"They have a core phenotype of ID, and common findings of behavioural disorders, infantile hypotonia, gait disturbance and growth impairment"

Establishes hypotonia and gait disturbance as common findings and therefore as standing rehabilitation targets; it supports the indication, not the efficacy, of physical and occupational therapy, which has not been studied in this disorder.

Antiseizure Medication

Action: anticonvulsant therapy Ontology label: Anticonvulsant Therapy NCIT:C64172

Epilepsy is not universal in THOC2 disease but does occur, and the one reported female with a de novo variant presented with an epileptic encephalopathy. Antiseizure treatment is standard-of-care and selected by seizure type; no THOC2-specific antiseizure regimen, drug preference or contraindication has been reported.

Target Phenotypes: Seizure HP:0001250

Show evidence (1 reference)

PMID:29851191 SUPPORT Human Clinical

"Confirmed seizure disorder was only present in the affected female (individual 7) but suspected in individual 2."

Documents the seizure burden that establishes the indication. It supports treating the seizures that occur, not any THOC2-specific efficacy claim, and it is also the reason this treatment is not framed as universally required.

Genetic Counseling

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

Counselling covers X-linked inheritance with affected males and typically milder or unaffected carrier females, the recurrence risk implied by carrier status, and the fact that de novo variants also occur - including in affected females - so a negative maternal test does not exclude the diagnosis in a proband. Counselling of carrier mothers must also cover the recurrent splice-site allele associated with lethal fetal arthrogryposis, for which prenatal recurrence was documented in consecutive pregnancies.

Show evidence (3 references)

PMID:29851191 SUPPORT Other

"diagnosis of X-linked causes of ID remain critically important for accurate genetic counseling of families"

States the counselling rationale for establishing an X-linked molecular diagnosis. Curated as PARTIAL because this is a general background statement from the paper's introduction about X-linked intellectual disability as a class, not a THOC2-specific counselling finding.

PMID:29851191 SUPPORT Human Clinical

"a de novo variant in a female with an epileptic encephalopathy"

Documents the de novo female presentation that counselling must account for.

PMID:34976470 SUPPORT Human Clinical

"Here, we describe for the first time a recurrent arthrogryposis multiplex congenita phenotype (AMC) in two male fetuses in a family."

Documents recurrence of a lethal fetal presentation in consecutive pregnancies of one carrier mother, which is the specific recurrence risk that counselling for this allele class must address.

🔬

Diagnosis

2

Molecular Genetic Testing for THOC2 (Positive in affected individuals)

The diagnosis is established by identifying a hypomorphic THOC2 variant in an individual with suggestive findings. Testing must cover both sequence variants and intragenic copy-number changes, because intragenic THOC2 microdeletions are an established allele class that coding-only analysis will miss. Because variants are typically private missense alleles in an essential gene, functional assessment of protein stability can support classification of variants of uncertain significance.

molecular genetic testing NCIT:C19770

Show evidence (3 references)

PMID:26166480 SUPPORT Human Clinical

"X chromosome exome sequencing revealed four missense variants in THOC2 in four families"

Establishes sequencing as the diagnostic route for the missense allele class.

PMID:32116545 SUPPORT Human Clinical

"an additional individual with an intragenic THOC2 microdeletion (Del-Ex37-38)"

Documents the intragenic microdeletion allele class, which is why copy-number analysis must accompany sequencing.

PMID:32116545 SUPPORT In Vitro

"Ex vivo missense variant testing and patient-derived cell line data from current and published studies show 9 of the 14 missense THOC2 variants result in reduced protein stability."

Protein-stability testing of missense variants is an established functional assay in this disorder and can support variant classification.

Neurological Investigation for Symptoms or Signs

Once the molecular diagnosis is made, the largest cohort advises a low threshold for EEG and brain MRI whenever neurological symptoms or signs appear. The rationale is that seizures, while affecting only about a fifth of the cohort overall, cluster in the severe neuromuscular subgroup where they can take the form of a severe developmental and epileptic encephalopathy with infantile spasms, and that the neurological phenotype can progress with age in some males. Imaging is for detection of complications rather than for diagnosis - there is no unifying neuroradiological signature for this disorder.

electroencephalography NCIT:C38054

Show evidence (2 references)

PMID:32116545 SUPPORT Human Clinical

"the clinicians should have a low threshold for investigating neurological symptoms or signs with an EEG and MRI brain"

An explicit investigation recommendation from the largest cohort, naming both modalities.

PMID:32116545 SUPPORT Human Clinical

"although for many individuals the phenotype is static, a more complex neurological phenotype also emerges with age in several males"

Age-emergent neurological features are the reason surveillance is ongoing rather than a one-off assessment at diagnosis.

📊

Prevalence

1

Published individuals worldwide

Cases In Literature Ultra Rare

The disorder was defined in 2015 from four families; by 2020 the cumulative published series had reached 10 further individuals from nine families plus an intragenic deletion case, with 14 missense variants functionally tested. No population prevalence estimate exists.

Show evidence (2 references)

PMID:32116545 SUPPORT Human Clinical

"Here we report 10 individuals from nine families with rare missense THOC2 variants including the first case of a recurrent variant (p.Arg77Cys), and an additional individual with an intragenic THOC2 microdeletion (Del-Ex37-38)."

Quantifies the published caseload of the largest expansion series, supporting an ultra-rare classification.

PMID:26166480 SUPPORT Human Clinical

"X chromosome exome sequencing revealed four missense variants in THOC2 in four families, including family MRX12, first ascertained in 1971."

The defining series comprised four families, establishing the rarity of the disorder at first description.

🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from THOC2-Related Intellectual Disability:

Other X-Linked Intellectual Disability Syndromes

Overlapping Features THOC2 was identified through X-linked intellectual disability pedigrees (including family MRX12, ascertained in 1971) and has no pathognomonic feature; over 120 of the identified intellectual-disability genes are X-linked. Broad genomic testing rather than targeted testing is the practical approach.

Show evidence (1 reference)

PMID:29851191 SUPPORT Other

"Over 120 of the identified >800 ID genes are located on the X-chromosome"

Quantifies the size of the X-linked intellectual-disability differential that THOC2 sits within, which is why targeted single-gene testing is impractical.

Other THO/TREX Subunit Neurodevelopmental Disorders

Overlapping Features Other TREX subunits are themselves associated with neurodevelopmental disorders - THOC6 (Beaulieu-Boycott-Innes syndrome, curated separately in this knowledge base) and DDX39B - and THOC2 destabilisation reduces the abundance of the other NDD-associated THOC subunits, so the phenotypes are expected to overlap. This makes the group a coherent differential set rather than a list of unrelated conditions. THOC6 disease is distinguished by autosomal recessive inheritance, a recognisable facial gestalt, and cardiac and genitourinary malformations, none of which characterise THOC2 disease.

Show evidence (2 references)

PMID:40651286 SUPPORT Other

"partial loss of function variants in the TREX components THOC2, THOC6, and DDX39B were implicated in neurodevelopmental disorders"

A 2025 review naming the specific TREX subunits whose partial loss of function causes neurodevelopmental disorders, which defines the membership of this differential group.

PMID:32116545 SUPPORT In Vitro

"Interestingly, reduced stability of THOC2 variant proteins has a flow-on effect on the stability of the multi-protein TREX complex; specifically on the other NDD-associated THOC subunits."

Provides the mechanistic reason these disorders overlap - a THOC2 lesion lowers the abundance of the very subunits whose own loss causes the differential diagnoses.

Syndromic Obesity with Intellectual Disability

Overlapping Features The MONDO name's emphasis on overweight and short stature places THOC2 in the differential for syndromic obesity with intellectual disability (for example Prader-Willi and Smith-Magenis syndromes), although the largest THOC2 cohort refined the core phenotype away from that framing and toward language disorder and growth disturbance. The obesity is adult-onset and truncal rather than early-onset hyperphagic obesity, which is a practical discriminator from Prader-Willi syndrome.

Show evidence (2 references)

PMID:29851191 SUPPORT Human Clinical

"The affected individuals had a syndromic NDD, characterized by borderline to severe ID, speech delay, short stature and adult onset truncal obesity"

Documents the adult-onset truncal pattern of the obesity, which is the feature that distinguishes THOC2 disease from the early-onset hyperphagic obesity syndromes in this differential. This sentence is the 2018 paper's recap of the 2015 cohort rather than a new observation.

PMID:32116545 SUPPORT Human Clinical

"Our current, expanded cohort refines the core phenotype of THOC2 NDDs to language disorder and/or ID, with a variable severity, and disorders of growth."

The largest cohort's refinement moves the core away from the obesity framing, which is why this differential is listed but not treated as the leading one.

🐁

Animal Models

2

Thoc2 exon 37-38 deletion hemizygous male (Thoc2Δ/Y), based on a patient allele Mouse

A hypomorphic mouse built directly on a patient's THOC2 exon 37-38 deletion allele. It recapitulates the core human phenotypes - smaller size and weight, and deficits in spatial learning, working memory and sensorimotor function - and is the system in which the R-loop/DNA-damage mechanism was demonstrated. Its construct validity is unusually good for a hypomorphic-allele disorder, because the modelled allele is a real patient variant rather than an engineered knockdown.

Species

Mouse

Genotype

Thoc2 exon 37-38 deletion hemizygous male (Thoc2Δ/Y), based on a patient allele

Genes

THOC2 hgnc:19073

Show evidence (3 references)

PMID:38331934 SUPPORT Model Organism

"we generated a mouse model based on a hypomorphic Thoc2 exon 37-38 deletion variant of a patient with ID, speech delay, hypotonia, and microcephaly"

Establishes the construct validity of the model - it carries an actual patient allele.

PMID:38331934 SUPPORT Model Organism

"mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight, and significant deficits in spatial learning, working memory and sensorimotor functions"

Establishes face validity across the cognitive, sensorimotor and growth domains.

PMID:38331934 SUPPORT Model Organism

"Thoc2Δ/Y neurons show perturbed in vitro neural migration, electrophysiological properties and synapse formation"

Extends the model's construct validity below the behavioural level to cellular neurodevelopmental readouts, which is what makes it usable for mechanism and rescue experiments.

thoc-2 homozygous deletion (ok961) and heterozygotes, maintained over a balancer Caenorhabditis elegans

An invertebrate loss-of-function model generated in the course of investigating a patient with a de novo X;8 translocation that knocked down THOC2 expression. Because the C. elegans thoc-2 deletion is homozygous lethal it must be balanced, which independently corroborates the essentiality of the gene that forces every human disease allele to be hypomorphic. Surviving animals show impaired locomotion and defective chemosensation, establishing a neuronal role for the orthologue. Its interpretive limits are substantial: it is a null rather than a hypomorph, an invertebrate rather than a mammal, and the human case that prompted it also had PTK2 haploinsufficiency, so the human arm of that report is confounded.

Species

Caenorhabditis elegans

Genotype

thoc-2 homozygous deletion (ok961) and heterozygotes, maintained over a balancer

Genes

THOC2 hgnc:19073

Show evidence (2 references)

PMID:23749989 SUPPORT Model Organism

"THOC2 ortholog knockout in C.elegans which produced functional defects in specific sensory neurons"

Establishes that loss of the THOC2 orthologue produces a neuronal functional deficit in an invertebrate, supporting a conserved neuronal requirement for the gene.

PMID:23749989 SUPPORT Model Organism

"Animals thoc-2−/− were almost completely immobile, or moved slowly and for a short time upon touching"

Documents the locomotor phenotype listed for this model, and the dose-dependence noted in the same figure - locomotion was also reduced in heterozygotes - parallels the hypomorphic nature of the human alleles.

{ }

Source YAML

click to show

name: THOC2-Related Intellectual Disability
creation_date: "2026-07-31T00:00:00Z"
description: >-
  THOC2-related intellectual disability (X-linked intellectual disability-short
  stature-overweight syndrome; OMIM 300957) is an X-linked neurodevelopmental
  disorder caused by hypomorphic variants in THOC2, which encodes the largest
  subunit of the highly conserved TREX (Transcription-Export) complex. The core
  phenotype is language disorder and/or intellectual disability of variable
  severity together with disorders of growth. Commonly reported features include
  speech delay, elevated body mass index with truncal obesity in older males,
  short stature, seizure disorders, gait disturbance and tremors; a subset of
  affected individuals have severe-to-profound intellectual disability with
  persistent hypotonia, recurrent aspiration and respiratory abnormalities, and one
  recurrent canonical acceptor splice-site allele produces the most severe reported
  presentation - fetal akinesia with arthrogryposis multiplex congenita. The largest
  cohort concluded that the disorder should be regarded as multisystemic in a
  significant proportion of individuals: congenital anomalies of the
  cardiorespiratory, genitorenal and skeletal systems, feeding difficulties and
  gastro-oesophageal reflux, and visual and hearing impairment are each present in
  10-30%, prompting a recommendation for systematic evaluation at diagnosis. Because
  complete loss of
  THOC2 is incompatible with life, every disease-associated allele is
  hypomorphic - missense variants that reduce THOC2 protein stability, or
  splice/deletion variants that remove small regions of the C-terminal RNA-binding
  domain. Reduced THOC2 stability destabilises its partner TREX subunits. The
  best-supported downstream mechanism is perturbed R-loop homeostasis with
  consequent DNA damage and cell death in the developing brain; notably, the
  patient allele that was modelled in mouse did NOT produce detectable bulk
  nuclear mRNA retention, so the disorder is better framed as a genome-stability
  lesion of the transcription-export machinery than as a simple bulk mRNA-export
  block.
category: Mendelian
parents:
- Neurodevelopmental Disorder
- Syndromic Intellectual Disability
notes: >-
  Scope and disambiguation. THOC2 is a subunit of the THO/TREX complex, and the
  general THO/TREX literature - mRNA export biochemistry, R-loop biology,
  co-transcriptional RNA processing, and TREX in cancer and viral RNA export - is
  large and largely unconnected to this disorder. This entry is anchored on the
  human disease (MONDO:0010496 / OMIM 300957): every evidence item comes from a
  THOC2 patient cohort, a THOC2 patient-derived cell line, or the THOC2 mouse
  model built on a patient allele. Generic THO/TREX complex biology is cited only
  where a THOC2-disease paper states it about THOC2 itself.
  Note on the MONDO label. The MONDO/Orphanet name emphasises short stature and
  overweight, which reflects the 2015 first-description cohort. The largest
  subsequent cohort explicitly refined the core phenotype to "language disorder
  and/or ID, with a variable severity, and disorders of growth", so this entry
  uses the gene-anchored name and treats the growth features as one component
  rather than as defining.
  Relationship to THOC6-related disorder. kb/disorders/THOC6-Related_Developmental_
  Delay-Microcephaly-Facial_Dysmorphism_Syndrome.yaml curates a different disease
  (Beaulieu-Boycott-Innes syndrome) caused by biallelic autosomal-recessive variants
  in a different THO subunit. The two entries share only the complex: both genes
  encode subunits of the THO core of TREX, and a 2025 review groups THOC2, THOC6 and
  DDX39B as TREX components implicated in neurodevelopmental disorders. They are
  kept separate because the gene, inheritance mode, MONDO term and clinical picture
  all differ (THOC6 has a recognisable facial gestalt and cardiac/genitourinary
  malformations; THOC2 does not). Convergently, both entries have had to retire the
  simple "bulk mRNA-export block" model: the THOC6 entry on the basis of human
  neural-cell mis-splicing data, and this entry on the basis of the 2024 mouse and
  patient-fibroblast data showing no overt nuclear mRNA retention. No THOC6
  literature is used as evidence here.
  GeneReviews. A PubMed search for a GeneReviews chapter on THOC2 returns no
  results (a chapter exists for THOC6, PMID:32790266, but that is a different
  disorder and is not used here), so no GeneReviews phenotype baseline is available
  for this entry.
  Module conformance. No module in kb/modules/ captures an mRNA-export or R-loop
  chain. `genome_instability_mutation` was evaluated because the mouse model
  shows R-loop accumulation and DNA damage, but that module is explicitly the
  cancer "mutational engine" - its chain runs to a mutator phenotype,
  chromosomal instability and accelerated clonal evolution, which is not what
  happens here; in THOC2 the DNA damage leads to cell death in the developing
  brain and there is no neoplastic phenotype. Declaring conformance would import
  a cancer framing the evidence does not support.
  Deep research provenance. An Edison/falcon deep-research run
  (research/THOC2-Related_Intellectual_Disability-deep-research-falcon.md) informed
  this entry. Its report cited a wrong PMID for the 2015 defining paper (26166475
  rather than 26166480) and asserted that no MONDO/OMIM identifier could be
  established; both were corrected against primary sources. It also missed the 2020
  expansion cohort, the arthrogryposis reports and the 2013 translocation case,
  which were added from an independent PubMed sweep.
disease_term:
  preferred_term: THOC2-related X-linked intellectual disability
  term:
    id: MONDO:0010496
    label: X-linked intellectual disability-short stature-overweight syndrome
references:
- reference: PMID:40651286
  title: "Transcription-Export complex in neurodevelopmental disorders."
synonyms:
- THOC2 syndrome
- THOC2-related neurodevelopmental disorder
- X-linked intellectual disability-short stature-overweight syndrome
- MRX12
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:26166480
      reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Here, we report that variants in THOC2, which encodes a subunit of the highly conserved TREX mRNA-export complex, cause syndromic intellectual disability (ID)."
      explanation: A single-gene germline disorder identified by X chromosome exome sequencing, placing it in the genetics-and-disease part of the Harrison's taxonomy.
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:38331934
      reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "in a clinically complex neurodevelopmental disorder with intellectual disability as the core phenotype"
      explanation: The disorder's core presentation is neurodevelopmental, placing it in the neurologic part of the Harrison's taxonomy.
prevalence:
- population: Published individuals worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    The disorder was defined in 2015 from four families; by 2020 the cumulative
    published series had reached 10 further individuals from nine families plus
    an intragenic deletion case, with 14 missense variants functionally tested.
    No population prevalence estimate exists.
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we report 10 individuals from nine families with rare missense THOC2 variants including the first case of a recurrent variant (p.Arg77Cys), and an additional individual with an intragenic THOC2 microdeletion (Del-Ex37-38)."
    explanation: Quantifies the published caseload of the largest expansion series, supporting an ultra-rare classification.
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "X chromosome exome sequencing revealed four missense variants in THOC2 in four families, including family MRX12, first ascertained in 1971."
    explanation: The defining series comprised four families, establishing the rarity of the disorder at first description.
inheritance:
- name: X-linked inheritance
  inheritance_term:
    preferred_term: X-linked inheritance
    term:
      id: HP:0001417
      label: X-linked inheritance
  expressivity: VARIABLE
  description: >-
    THOC2 is on the X chromosome and the disorder is X-linked, with affected males
    and typically milder or unaffected carrier females. Both inherited and de novo
    variants occur: the original families were ascertained through X-linked
    intellectual disability pedigrees, and a de novo variant has been documented
    in a female with epileptic encephalopathy, so the disorder is not confined to
    transmitting families. Heterozygous carrier mothers are clinically unaffected
    and, where tested, show highly skewed X-chromosome inactivation, which is the
    proposed explanation for their non-penetrance; the one severely affected female
    reported carried a de novo variant and her XCI status could not be assessed.
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we report that variants in THOC2, which encodes a subunit of the highly conserved TREX mRNA-export complex, cause syndromic intellectual disability (ID)."
    explanation: The defining report establishing THOC2 as a cause of syndromic intellectual disability, ascertained through X-linked intellectual disability families.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present detailed clinical assessment and functional studies on a de novo variant in a female with an epileptic encephalopathy"
    explanation: Documents a de novo THOC2 variant in an affected female, showing the disorder is not restricted to inherited male-transmitted cases.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "heterozygous mothers were clinically unaffected, and, where available, X-chromosome inactivation (XCI) was highly skewed"
    explanation: Establishes skewed X-inactivation in carrier mothers as the observed correlate of their non-penetrance, which is the substance of the X-linked expressivity claim.
pathophysiology:
- name: Hypomorphic THOC2 Variants Reducing Protein Stability
  biological_scale: MOLECULAR
  description: >-
    Every disease-associated THOC2 allele is hypomorphic rather than null, because
    THOC2 is an essential gene. Two mechanistic classes are documented. Missense
    variants at evolutionarily conserved residues reduce THOC2 protein stability -
    9 of 14 tested missense variants did so across current and published studies.
    Splice-site and intragenic-deletion variants instead produce C-terminally
    truncated THOC2 with loss of small regions of the C-terminal RNA-binding
    domain. Structural modelling places the altered residues in RNA-binding
    domains of two THOC2 conformations, interpreted as different intermediate
    RNA-binding states during RNA transport.
  genes:
  - preferred_term: THOC2
    term:
      id: hgnc:19073
      label: THOC2
  downstream:
  - target: TREX Complex Destabilisation
    causal_link_type: DIRECT
    description: >-
      Reduced THOC2 stability has a flow-on effect on the stability of its partner
      TREX subunits.
    evidence:
    - reference: PMID:26166480
      reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "We show that two variants lead to decreased stability of THOC2 and its TREX-complex partners in cells derived from the affected individuals."
      explanation: Measures the two ends of this edge in the same patient-derived cells - reduced THOC2 stability and reduced stability of its complex partners - which is what makes the link DIRECT.
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Ex vivo missense variant testing and patient-derived cell line data from current and published studies show 9 of the 14 missense THOC2 variants result in reduced protein stability."
    explanation: Quantifies the proportion of tested missense variants that destabilise THOC2, establishing reduced protein stability as the dominant missense mechanism.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The splicing-defective and deletion variants result in a loss of small regions of the C-terminal THOC2 RNA binding domain (RBD)."
    explanation: Defines the second allele class - splice and deletion variants removing part of the C-terminal RNA-binding domain. This is a molecular variant-consequence finding derived from patient-cell cDNA and protein analysis, hence IN_VITRO rather than HUMAN_CLINICAL.
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We show that two variants lead to decreased stability of THOC2 and its TREX-complex partners in cells derived from the affected individuals."
    explanation: Patient-derived cells demonstrate reduced stability of both THOC2 and its complex partners, the first functional evidence for the mechanism.
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Protein structural modeling showed that the altered amino acids are located in the RNA-binding domains of two complex THOC2 structures, potentially representing two different intermediate RNA-binding states of THOC2 during RNA transport."
    explanation: The localisation of the variants to RNA-binding domains, and the two-intermediate-state interpretation, come from structural modelling rather than experimental structure determination, so this is curated as partial computational support.
- name: TREX Complex Destabilisation
  biological_scale: MOLECULAR
  description: >-
    THOC2 is the largest subunit of the TREX complex, which couples transcription
    to mRNA export. Reduced THOC2 stability propagates to the complex: the
    stability of the other TREX/THOC subunits - specifically those themselves
    associated with neurodevelopmental disorders - falls as a consequence. The
    disorder is therefore a complex-level lesion rather than a single-protein one,
    which is one reason the phenotype overlaps other THOC-subunit disorders.
    Scope of the export claim. The 2015 discovery paper framed the disorder as a
    disturbance of the canonical mRNA-export pathway, and that framing survives at
    the level of the pathway. It does NOT survive as a claim of measurable bulk
    nuclear mRNA retention: when the exon 37-38 deletion allele was tested directly,
    neither mutant mouse primary neurons nor the corresponding patient fibroblasts
    showed overt nuclear retention of mRNAs. The GO annotation below is therefore
    left without a DECREASED modifier - the pathway is the affected one, but a
    quantitative reduction in bulk export has not been demonstrated for a
    disease allele, and the measured downstream consequence is loss of R-loop and
    genome homeostasis rather than transcript sequestration.
  biological_processes:
  - preferred_term: mRNA export from nucleus
    term:
      id: GO:0006406
      label: mRNA export from nucleus
  downstream:
  - target: Perturbed R-Loop Homeostasis and DNA Damage
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Compromised THOC2/TREX function leads to R-loop accumulation, the proposed
      root of the disorder. The intermediates between complex destabilisation and
      hybrid accumulation - whether co-transcriptional RNA packaging, R-loop
      resolution or 3' processing is the failing step - have not been determined.
    evidence:
    - reference: PMID:38331934
      reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The Thoc2Δ/Y mouse brain development is significantly impacted by compromised THOC2/TREX function resulting in R-loop accumulation, DNA damage and consequent cell death."
      explanation: States the edge directly - compromised THOC2/TREX function results in R-loop accumulation - without specifying the intervening steps, which is why the link is typed INDIRECT_UNKNOWN_INTERMEDIATES.
  - target: Impaired Neurodevelopment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Disturbance of the canonical mRNA-export pathway is compatible with life but
      results in altered neuronal development. This edge is retained alongside the
      better-characterised route through R-loop accumulation and cortical
      neurogenesis because the 2015 discovery paper asserts the pathway-to-phenotype
      link directly, without committing to the intervening genome-instability steps.
    evidence:
    - reference: PMID:26166480
      reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Our results show that disturbance of the canonical molecular pathway of mRNA export is compatible with life but results in altered neuronal development with other comorbidities."
      explanation: States this edge directly - partial disturbance of the export pathway is survivable but produces altered neuronal development - without naming the intermediates, which is why the link is typed INDIRECT_UNKNOWN_INTERMEDIATES.
  - target: Multi-Organ Developmental Involvement
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      THOC subunits are ubiquitously expressed, and the congenital anomalies seen
      across several organ systems are attributed by the largest cohort to a role
      for THOC2 in multi-organ development rather than to a secondary consequence
      of the neurological phenotype.
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Interestingly, reduced stability of THOC2 variant proteins has a flow-on effect on the stability of the multi-protein TREX complex; specifically on the other NDD-associated THOC subunits."
    explanation: Establishes the complex-level consequence - destabilised THOC2 destabilises its partner THOC subunits, particularly the other NDD-associated ones.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "We implicated the X-chromosome THOC2 gene, which encodes the largest subunit of the highly-conserved TREX (Transcription-Export) complex, in a clinically complex neurodevelopmental disorder with intellectual disability as the core phenotype."
    explanation: States THOC2's identity as the largest TREX subunit and confirms intellectual disability as the core phenotype of the disorder.
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our results show that disturbance of the canonical molecular pathway of mRNA export is compatible with life but results in altered neuronal development with other comorbidities."
    explanation: States the central paradox of the disorder - an essential housekeeping pathway can be partially disturbed compatibly with life, at the cost of altered neurodevelopment.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: "Surprisingly, we did not observe any overt nuclear retention of mRNAs"
    explanation: Directly refutes the stronger reading of this node - that the disease allele causes measurable bulk nuclear mRNA retention. The tested material was both mutant mouse primary neurons AND fibroblasts from the patient carrying the same allele, so the negative result has a human arm; it is tagged IN_VITRO because both are cultured cells. Curated as REFUTE so the entry does not overstate the export defect, and it is why the GO annotation on this node carries no DECREASED modifier.
- name: Multi-Organ Developmental Involvement
  biological_scale: ORGANISM
  description: >-
    The non-neurological arm of the disorder. THOC subunits are ubiquitously
    expressed, and the largest cohort concluded that THOC2-related disorder should
    be considered multisystemic in a significant proportion of individuals:
    congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems
    are each present in 10-30%, and the cohort authors attribute these to a role for
    THOC2 in multi-organ development and function rather than to a secondary
    consequence of the neurological phenotype. The molecular route from TREX
    destabilisation to organ malformation has not been investigated - no
    non-neural tissue has been examined in the mouse model or in patient material -
    so this node records a well-evidenced clinical observation with an unevidenced
    mechanism.
  mechanism_confidence: PROVISIONAL
  downstream:
  - target: Congenital Cardiac Anomaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Congenital anomalies of the cardiorespiratory system occur in a significant
      minority.
  - target: Genitourinary Anomaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Congenital anomalies of the genitourinary tract occur in a significant
      minority.
  - target: Skeletal Anomaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Congenital anomalies of the skeletal system occur in a significant minority.
  - target: Laryngomalacia and Tracheomalacia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Airway malacia is among the congenital anomalies with increased risk in the
      severe neuromuscular subgroup.
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "THOC2-related disorder should be considered a multi-systemic disorder in a significant proportion of individuals"
    explanation: The largest cohort's explicit conclusion that the disorder is multisystemic, which is the claim this node represents.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Enumerates the organ systems affected and gives the 10-30% frequency range shared by the phenotypes downstream of this node.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Further research to explore the underlying pathophysiological basis for these more severe phenotypes is warranted, but likely reflect the involvement of THOC2 in multi-organ development and function."
    explanation: The mechanistic half of this node is the cohort authors' explicitly hedged inference ("likely reflect"), with the accompanying statement that further research is warranted - which is why the node carries PROVISIONAL confidence and is curated as PARTIAL.
- name: Perturbed R-Loop Homeostasis and DNA Damage
  biological_scale: CELLULAR
  description: >-
    The best-supported root mechanism, derived from a mouse model carrying a patient
    allele together with cells from the patient who carries it. Compromised
    THOC2/TREX function allows R-loops (RNA:DNA hybrids with a displaced single
    strand) to accumulate, producing DNA damage and consequent cell death during
    brain development. Two pieces of evidence lift this above a purely
    model-organism inference: R-loops accumulate in the patient's own fibroblasts as
    well as in mutant mouse neural stem cells, and forced RNase H1 expression - which
    degrades the RNA strand of RNA:DNA hybrids - reduces both the R-loop burden and
    the comet-assay DNA damage, placing R-loops upstream of the damage rather than
    alongside it. Confidence is nonetheless held at PROVISIONAL: the rescue
    experiment was performed in mouse neural stem cells rather than patient cells,
    only the exon 37-38 deletion allele has been tested, and no R-loop or DNA-damage
    measurement exists in human brain tissue.
  mechanism_confidence: PROVISIONAL
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  biological_processes:
  - preferred_term: DNA damage response
    term:
      id: GO:0006974
      label: DNA damage response
    modifier: INCREASED
  - preferred_term: apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
    modifier: INCREASED
  downstream:
  - target: Disrupted Cortical Neurogenesis and Neuronal Maturation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      DNA damage and progenitor cell death during corticogenesis translate into
      measurable structural and maturational deficits in the developing cortex.
      The known intermediate is loss of ventricular-zone neural stem cells.
    evidence:
    - reference: PMID:38331934
      reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "reduction in the thickness of the ventricular zone (VZ) of the E18.5 Thoc2"
      explanation: Loss of the ventricular-zone progenitor compartment is the identified intermediate between DNA damage/cell death and the downstream cortical structural deficits, which is why the link is typed INDIRECT_KNOWN_INTERMEDIATES.
  evidence:
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The Thoc2Δ/Y mouse brain development is significantly impacted by compromised THOC2/TREX function resulting in R-loop accumulation, DNA damage and consequent cell death."
    explanation: Direct in vivo demonstration of the R-loop, DNA-damage and cell-death chain in the brain of a mouse carrying a patient THOC2 allele.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "indicating R-loops also accumulate in the patient cells"
    explanation: R-loop accumulation is not confined to the mouse - it is reproduced in fibroblasts from the patient whose allele the mouse carries, which is the strongest available human anchor for this node.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "reduced R-loop accumulation (Fig. 7e) and comet tail formation (Fig. 7f) in Thoc2"
    explanation: RNase H1 overexpression lowers both R-loop burden and comet-assay DNA damage in cultured mutant neural stem cells, establishing the R-loop as an upstream cause of the damage rather than a co-occurring marker. Tagged IN_VITRO rather than MODEL_ORGANISM because the rescue was done in cultured cells, not in the animal.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Overall, we suggest that perturbed R-loop homeostasis, in stem cells and/or differentiated cells in mice and the patient, and DNA damage-associated functional alterations are at the root of THOC2 syndrome."
    explanation: The authors frame the R-loop model as a suggestion rather than a demonstrated human mechanism, and the human arm of the claim is inferred from the mouse; this is why the node carries PROVISIONAL mechanism confidence.
- name: Disrupted Cortical Neurogenesis and Neuronal Maturation
  biological_scale: TISSUE
  description: >-
    The tissue-level consequence measured in the patient-allele mouse. Loss of
    neural stem cells from the cortical ventricular zone thins the progenitor
    compartment at embryonic day 18.5, and the cortical plate and corpus callosum
    are correspondingly thinner. Neurons that do form show perturbed migration,
    altered electrophysiological properties and impaired synapse formation. This
    node is what connects the molecular genome-instability lesion to a
    brain-predominant clinical phenotype: the affected compartment is the
    proliferating progenitor pool of the developing cortex, which is why a
    ubiquitously required housekeeping factor produces a predominantly
    neurodevelopmental disease. This node accounts for the neurological arm only -
    the largest cohort concluded that THOC2 disease is also multisystemic in a
    significant proportion of individuals, which is modelled separately in the
    Multi-Organ Developmental Involvement node. All measurements are murine; the
    corresponding human neuroimaging findings are inconsistent: structural MRI was
    normal in three of the five individuals imaged in the 2018 series, and the 2020
    pooled cohort found no unifying neuroradiological abnormality across the
    individuals it reviewed.
  mechanism_confidence: PROVISIONAL
  cell_types:
  - preferred_term: neural stem cell
    term:
      id: CL:0000047
      label: neural stem cell
  biological_processes:
  - preferred_term: neuron migration
    term:
      id: GO:0001764
      label: neuron migration
    modifier: ABNORMAL
  - preferred_term: synapse organization
    term:
      id: GO:0050808
      label: synapse organization
    modifier: ABNORMAL
  downstream:
  - target: Impaired Neurodevelopment
    causal_link_type: DIRECT
    description: >-
      Reduced cortical progenitor pool, thinner cortical plate and corpus callosum,
      and impaired neuronal migration and synapse formation produce the
      organism-level neurodevelopmental phenotype.
    evidence:
    - reference: PMID:38331934
      reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The Thoc2 exon 37-38 deletion male (Thoc2Δ/Y) mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight, and significant deficits in spatial learning, working memory and sensorimotor functions."
      explanation: The same animals that show the cortical and synaptic deficits also show the organism-level cognitive and sensorimotor phenotype, which is the observation joining these two nodes.
  evidence:
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "reduction in the thickness of the ventricular zone (VZ) of the E18.5 Thoc2"
    explanation: Documents thinning of the cortical progenitor compartment in the patient-allele mouse, the proximal tissue-level lesion of this node.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "reduced overall thickness of the cortical plate and corpus callosum"
    explanation: The cortical plate and corpus callosum are correspondingly thinner, showing that progenitor loss propagates to the mature cortical structures. Note this particular measurement is made in the post-natal day 30 brain rather than at E18.5.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Thoc2Δ/Y neurons show perturbed in vitro neural migration, electrophysiological properties and synapse formation"
    explanation: Establishes the neuronal-maturation arm of this node - migration, electrophysiology and synapse formation are all disturbed in mutant neurons. Tagged IN_VITRO because the source states these were in vitro assays.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuro-radiological studies were performed in five individuals: this was within normal limits for three individuals, with neuroanatomical differences reported in two."
    explanation: The human counterpart is inconsistent - most imaged individuals had normal structural MRI - which is why this node's confidence is PROVISIONAL and its measurements are labelled murine.
- name: Impaired Neurodevelopment
  biological_scale: ORGANISM
  description: >-
    The organism-level consequence is a neurodevelopmental disorder with
    intellectual disability as the core phenotype, accompanied by disorders of
    growth. Severity spans language disorder without frank intellectual
    disability at one end to severe-profound intellectual disability with
    persistent hypotonia and respiratory abnormalities at the other. Movement and
    seizure disorders are prominent in the more severely affected. The mouse
    carrying a patient allele recapitulates the core features - smaller size and
    weight, and deficits in spatial learning, working memory and sensorimotor
    function - which supports the causal chain.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  downstream:
  - target: Intellectual Disability
    causal_link_type: DIRECT
    description: Intellectual disability is the core phenotype.
  - target: Speech and Language Disorder
    causal_link_type: DIRECT
    description: >-
      Language disorder is part of the refined core phenotype and can occur with
      or without frank intellectual disability.
  - target: Seizures
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Seizure disorders occur, particularly in the severe group.
  - target: Hypotonia
    causal_link_type: DIRECT
    description: >-
      Persistent hypotonia characterises the severe-profound end of the spectrum.
  - target: Tremor
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Tremor is among the commonly observed movement features.
  - target: Gait Disturbance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Gait disturbance is among the commonly observed motor features.
  - target: Short Stature
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Disorders of growth are part of the refined core phenotype, and the mouse
      model is smaller and lighter than wild type.
  - target: Small for Gestational Age
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Growth restriction is already present at birth in a substantial minority,
      indicating a prenatal onset of the growth arm of the phenotype.
  - target: Increased Body Mass Index
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Elevated BMI with truncal obesity emerges in older affected males, the
      second growth feature that gives the disorder its MONDO name; the
      intervening mechanism between the THOC2 lesion and the body-composition
      change is unknown.
  - target: Microcephaly
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Reduced cortical progenitor pool and thinner cortical structures in the
      mouse provide a plausible route to the reduced head circumference seen in a
      minority of affected individuals.
  - target: Atypical Behavior
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Behavioural problems, including autism spectrum disorder in one individual,
      are among the common findings of the disorder.
  - target: Autism Spectrum Disorder
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      One individual in the quantified cohort met diagnostic criteria for autism
      spectrum disorder.
  - target: Inability to Walk
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      At the severe end of the motor spectrum, affected individuals never achieve
      independent ambulation.
  - target: Respiratory Abnormalities
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Respiratory abnormalities accompany persistent hypotonia in the
      severe-profound subset; the cohort authors explicitly flagged the
      pathophysiological basis of this severe presentation as unexplained.
  - target: Arthrogryposis Multiplex Congenita
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Allele-specific extreme of the phenotype. A recurrent canonical acceptor
      splice-site variant has produced lethal fetal akinesia with congenital joint
      contractures in male fetuses from two unrelated families, with a myopathic
      muscle phenotype showing cytoplasmic bodies. The intermediate steps between
      the THOC2 lesion and reduced fetal movement have not been established.
  - target: Abnormality of Movement
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Abnormal motor coordination, stereotypies and involuntary movements are the
      most common neurological feature after the cognitive and language phenotype,
      and emerge or worsen with age in a subset.
  - target: Hypertonia and Spasticity
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      A minority develop hypertonia with spasticity or contractures with age, the
      opposite tone pole from the infantile hypotonia of early presentation.
  - target: Recurrent Aspiration and Respiratory Infection
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      In the severe neuromuscular subgroup, persistent muscular hypotonia together
      with feeding difficulty and airway malacia leads to recurrent aspiration and
      respiratory tract infection.
  - target: Sialorrhea
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Excessive salivation follows from the oromotor component of the persistent
      hypotonia in the severe neuromuscular subgroup.
  - target: Feeding Difficulties
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Severe feeding difficulty follows from oromotor dysfunction in the hypotonic
      subgroup, and travels with gastroesophageal reflux and aspiration risk.
  - target: Gastroesophageal Reflux
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Gastroesophageal reflux occurs in a significant minority and contributes to
      the feeding and aspiration morbidity of the severe subgroup.
  - target: Visual Impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Visual impairment occurs in a significant minority; cortical visual
      impairment was documented in the severely affected female.
  - target: Hearing Impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Hearing impairment occurs in a significant minority and compounds the
      language phenotype.
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our current, expanded cohort refines the core phenotype of THOC2 NDDs to language disorder and/or ID, with a variable severity, and disorders of growth."
    explanation: The largest cohort's explicit refinement of the core phenotype, which this node represents.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The Thoc2 exon 37-38 deletion male (Thoc2Δ/Y) mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight, and significant deficits in spatial learning, working memory and sensorimotor functions."
    explanation: The patient-allele mouse reproduces the cognitive, sensorimotor and growth features, supporting the causal chain from the molecular lesion to the organism-level phenotype.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Severe neurocognitive features, including movement and seizure disorders, were observed in this cohort."
    explanation: Documents the severe end of the spectrum with prominent movement and seizure disorders.
phenotypes:
- category: Cognitive
  name: Intellectual Disability
  description: >-
    Intellectual disability is the core phenotype, of variable degree. The largest
    cohort refines the core to language disorder and/or intellectual disability,
    so some individuals have language impairment without frank intellectual
    disability, while a subset has severe-to-profound intellectual disability. The
    2015 defining families spanned borderline to severe intellectual disability;
    the 2018 series, ascertained more severely, found intellectual disability
    universal and at least moderate in all seven individuals. The pooled cohort
    describes the range of cognitive disability as very broad, from a normal IQ to
    profound intellectual disability - one functionally confirmed variant carrier
    had a performance IQ of 104 with an isolated language disorder, which is the
    concrete case behind the "language disorder AND/OR intellectual disability"
    formulation of the core phenotype and the reason this band is not stated as
    obligate.
  frequency: VERY_FREQUENT
  diagnostic: true
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "in a clinically complex neurodevelopmental disorder with intellectual disability as the core phenotype"
    explanation: States intellectual disability as the core phenotype of the disorder.
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals presented with variable degrees of ID and commonly observed features included speech delay, elevated BMI, short stature, seizure disorders, gait disturbance, and tremors."
    explanation: The defining cohort documents intellectual disability in all affected individuals with variable degree, alongside the associated features.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ID was universal and at least moderate in severity: 2/7 were non-ambulatory and 3/7 non-verbal."
    explanation: Intellectual disability was present in 7 of 7 individuals in this series, the direct quantitative basis for the VERY_FREQUENT band.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the range of cognitive disability in THOC2-related disorder is very broad—ranging from a normal IQ to a profound ID"
    explanation: Qualifies the VERY_FREQUENT band rather than supporting it - the pooled cohort documents at least one functionally confirmed variant carrier with a normal IQ, so intellectual disability is not obligate even though it is the core feature.
- category: Neurological
  name: Speech and Language Disorder
  description: >-
    Speech delay is among the most consistently reported features and language
    disorder is one half of the refined core phenotype, occurring with or without
    frank intellectual disability. Severity spans delayed speech to complete
    absence of speech - three of seven individuals in the quantified cohort were
    non-verbal.
  frequency: VERY_FREQUENT
  diagnostic: true
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "commonly observed features included speech delay, elevated BMI, short stature, seizure disorders, gait disturbance, and tremors"
    explanation: Speech delay heads the list of commonly observed features in the defining cohort.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "refines the core phenotype of THOC2 NDDs to language disorder and/or ID"
    explanation: Language disorder is explicitly one half of the refined core phenotype, which is why it is banded alongside intellectual disability.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ID was universal and at least moderate in severity: 2/7 were non-ambulatory and 3/7 non-verbal."
    explanation: Quantifies the severe end of the language phenotype - 3 of 7 individuals were non-verbal rather than merely speech-delayed.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "He did have significant language disorder, with a formal diagnosis of speech apraxia"
    explanation: Language disorder was the sole cognitive manifestation in the one individual with a normal performance IQ, showing that the speech/language phenotype is the most penetrant feature of the disorder and can occur in isolation - the basis for banding it VERY_FREQUENT alongside intellectual disability.
- category: Growth
  name: Short Stature
  description: >-
    Short stature is one of the two growth features in the disorder's MONDO name
    and is the most common extra-neurological feature of the disorder. Disorders of
    growth are part of the refined core phenotype, and the patient-allele mouse is
    smaller and lighter than wild type. The band is set from the pooled cohort of
    38 published individuals, in which persistent short stature was present in 52%.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "speech delay, elevated BMI, short stature, seizure disorders, gait disturbance, and tremors"
    explanation: Short stature is listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified and so cannot itself set the band.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a half (52%) have persistent short stature, a third (34%) are microcephalic and 29% have intrauterine growth restriction (IUGR)"
    explanation: The pooled 38-individual cohort gives persistent short stature in 52%, which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here. This supersedes the smaller 2/7 count in the 2018 series, which was a subset of this pooled denominator.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight"
    explanation: The mouse model reproduces the growth restriction, supporting it as a genuine consequence of the THOC2 lesion rather than an ascertainment artefact.
- category: Metabolic
  name: Increased Body Mass Index
  description: >-
    Elevated body mass index is among the commonly observed features and gives the
    disorder half of its MONDO name. It is present in 26% of the pooled 38-individual
    cohort, with obesity particularly noted in older males; the 2015 series
    characterised it as adult-onset truncal obesity. It is therefore an
    age-dependent minority feature rather than a uniform one, despite naming the
    MONDO term.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Increased body mass index
    term:
      id: HP:0031418
      label: Increased body mass index
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "commonly observed features included speech delay, elevated BMI, short stature"
    explanation: Elevated BMI is listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "26% of the expanded cohort have increased body weight, with obesity in older males particularly noted"
    explanation: The pooled 38-individual cohort gives increased body weight in 26%, which falls in the OCCASIONAL band (5-29%) and is the basis for the frequency assigned here.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The affected individuals had a syndromic NDD, characterized by borderline to severe ID, speech delay, short stature and adult onset truncal obesity"
    explanation: States explicitly that the obesity component is adult-onset and truncal rather than a constant feature. Note that this sentence is the 2018 paper's own recap of the 2015 cohort, so it is secondary characterisation of that earlier series rather than a new observation.
- category: Neurological
  name: Seizures
  description: >-
    Seizure disorders are among the commonly observed features and are prominent
    in the severe end of the spectrum. A de novo THOC2 variant has been reported
    in a female with an epileptic encephalopathy. Across the pooled 38-individual
    cohort seizures occur in 21%, but they cluster in the severe neuromuscular
    subgroup, where the picture can be a severe developmental and epileptic
    encephalopathy commonly including infantile spasms - so the modest overall
    frequency understates the burden in the individuals who have them.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "short stature, seizure disorders, gait disturbance, and tremors"
    explanation: Seizure disorders are listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Severe neurocognitive features, including movement and seizure disorders, were observed in this cohort."
    explanation: Confirms seizure disorders as a prominent feature of the severe cohort.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Confirmed seizure disorder was only present in the affected female (individual 7) but suspected in individual 2."
    explanation: Within the 2018 series seizures were confirmed in 1 of 7 and suspected in a second, consistent with the pooled-cohort rate below.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizure disorder, although not very common over the whole cohort (Figure 2B: 21%), can be problematic"
    explanation: The pooled 38-individual cohort gives seizures in 21%, which falls in the OCCASIONAL band (5-29%) and is the basis for the frequency assigned here.
- category: Neurological
  name: Tremor
  description: >-
    Tremor is among the commonly observed movement features and, with gait
    disturbance, forms the movement-disorder component of the phenotype. In two
    individuals tremor was part of a cerebellar-type sign complex (with
    broad-based or ataxic gait and, in one, nystagmus) that occurred without
    significant cerebellar abnormality on MRI. Tremor specifically was counted in
    2 of 7 individuals in the 2018 series; the pooled cohort reports only the
    broader composite category of abnormal motor coordination, stereotypic or
    involuntary movements (53%), which is curated separately below, so the
    tremor-specific band rests on the 2/7 count.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "seizure disorders, gait disturbance, and tremors"
    explanation: Tremors are listed among the commonly observed features of the defining cohort, establishing the association; the listing is unquantified.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four of the seven had infantile hypotonia and two of the seven had tremor."
    explanation: Gives the tremor-specific numerator, 2 of 7 (29%), which is the direct basis for the OCCASIONAL band. The larger pooled cohort does not break tremor out separately from the composite movement category.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "nystagmus, tremor and an ataxic broad-based gait for individual 6, in the absence of significant cerebellar abnormalities on MRI"
    explanation: Characterises the tremor as part of a cerebellar-type sign complex occurring without structural cerebellar abnormality, which is the clinically distinctive form the movement disorder takes in this disease.
- category: Neurological
  name: Gait Disturbance
  description: >-
    Gait disturbance is among the commonly observed features and is described as a
    common finding of the disorder; the mouse model shows corresponding
    sensorimotor deficits. In some individuals the gait is broad-based or frankly
    ataxic, with other cerebellar-type signs, despite an unremarkable cerebellum on
    MRI.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Gait disturbance
    term:
      id: HP:0001288
      label: Gait disturbance
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "seizure disorders, gait disturbance, and tremors"
    explanation: Gait disturbance is listed among the commonly observed features of the defining cohort.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "significant deficits in spatial learning, working memory and sensorimotor functions"
    explanation: The mouse model shows sensorimotor deficits corresponding to the human motor phenotype.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They have a core phenotype of ID, and common findings of behavioural disorders, infantile hypotonia, gait disturbance and growth impairment"
    explanation: Gait disturbance is stated to be a common finding of the disorder; mapping the qualitative term "common" to the enum gives the FREQUENT band (30-79%).
- category: Neurological
  name: Hypotonia
  description: >-
    Hypotonia is a common finding, present in four of seven individuals in the
    quantified cohort, and is typically of infantile onset. At the severe end of
    the spectrum it persists and is accompanied by respiratory abnormalities.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four of the seven had infantile hypotonia and two of the seven had tremor."
    explanation: Gives the direct numerator, 4 of 7 (57%), which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A subset of affected individuals' has severe-profound ID, persistent hypotonia and respiratory abnormalities."
    explanation: Documents the persistent, severe form of the hypotonia that characterises the severe-profound subset, distinct from the more general infantile hypotonia counted above.
- category: Respiratory
  name: Respiratory Abnormalities
  description: >-
    Respiratory abnormalities accompany persistent hypotonia in the
    severe-to-profound subset and are a principal contributor to morbidity in that
    group. The authors of the cohort that identified this subset explicitly called
    for further investigation of its pathophysiological basis.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Respiratory abnormality
    term:
      id: HP:0002086
      label: Abnormality of the respiratory system
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A subset of affected individuals' has severe-profound ID, persistent hypotonia and respiratory abnormalities."
    explanation: Respiratory abnormalities are reported specifically in the severe-profound subset, supporting an OCCASIONAL band.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Further investigations to elucidate the pathophysiological basis for this severe phenotype are warranted."
    explanation: The cohort authors explicitly flag the severe subset's mechanism as unexplained, which is recorded as a knowledge gap in this entry.
- category: Neurological
  name: Microcephaly
  description: >-
    Microcephaly is present in about a third of the pooled 38-individual cohort and
    is one component of the growth disturbance that is the disorder's most common
    extra-neurological feature. The patient whose allele was used to build the
    mouse model had intellectual disability, speech delay, hypotonia and
    microcephaly.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we generated a mouse model based on a hypomorphic Thoc2 exon 37-38 deletion variant of a patient with ID, speech delay, hypotonia, and microcephaly"
    explanation: Documents microcephaly in the index patient whose allele was modelled, establishing the association.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Growth abnormalities were common including low birth weight (3/7), microcephaly (2/7) and short stature (2/7)."
    explanation: Documents microcephaly as part of the growth-abnormality cluster in the 2018 series; the pooled-cohort rate below is what sets the band.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a half (52%) have persistent short stature, a third (34%) are microcephalic and 29% have intrauterine growth restriction (IUGR)"
    explanation: The pooled 38-individual cohort gives microcephaly in 34%, which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here.
- category: Growth
  name: Small for Gestational Age
  description: >-
    Intrauterine growth restriction is present in 29% of the pooled 38-individual
    cohort, showing that the growth arm of the phenotype begins prenatally rather
    than emerging only in childhood. This complements the postnatal growth
    disturbance (short stature, and later elevated BMI) that gives the disorder its
    MONDO name. There was no relationship between growth restriction in the
    offspring and carrier status in the mother.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Intrauterine growth restriction
    term:
      id: HP:0001518
      label: Small for gestational age
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a half (52%) have persistent short stature, a third (34%) are microcephalic and 29% have intrauterine growth restriction (IUGR)"
    explanation: The pooled 38-individual cohort gives intrauterine growth restriction in 29%, which falls at the top of the OCCASIONAL band (5-29%) and is the basis for the frequency assigned here.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Growth abnormalities were common including low birth weight (3/7), microcephaly (2/7) and short stature (2/7)."
    explanation: The 2018 subset reported low birth weight in 3 of 7. Low birth weight and intrauterine growth restriction are related but not identical concepts, both captured by HP:0001518; the pooled IUGR figure above is what sets the band.
- category: Behavioral
  name: Atypical Behavior
  description: >-
    Behavioural problems are a common finding of the disorder, reported in four of
    seven individuals in the quantified cohort. They are listed alongside hypotonia
    and gait disturbance as one of the recurrent non-cognitive features, and are a
    significant contributor to care burden in a population that is often non-verbal.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Behavioral abnormality
    term:
      id: HP:0000708
      label: Atypical behavior
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Behavioural problems were reported in four individuals, with one meeting diagnostic criteria for autism spectrum disorder."
    explanation: Direct numerator of 4 of 7 (57%), which falls in the FREQUENT band (30-79%).
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They have a core phenotype of ID, and common findings of behavioural disorders, infantile hypotonia, gait disturbance and growth impairment"
    explanation: The cohort's own summary lists behavioural disorders among the common findings, corroborating the band derived from the numerator.
- category: Behavioral
  name: Autism Spectrum Disorder
  description: >-
    A formal autism spectrum disorder diagnosis was made in one of the seven
    individuals in the quantified cohort. It is reported as the most severe end of
    the broader behavioural phenotype rather than as an independent feature, and
    rests on a single individual, so it is banded conservatively.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Behavioural problems were reported in four individuals, with one meeting diagnostic criteria for autism spectrum disorder."
    explanation: One of seven individuals (14%) met diagnostic criteria for autism spectrum disorder, which falls in the OCCASIONAL band (5-29%).
- category: Neurological
  name: Inability to Walk
  description: >-
    At the severe end of the motor spectrum, affected individuals never achieve
    independent ambulation - two of seven in the quantified cohort were
    non-ambulatory. This is the motor counterpart of the non-verbal presentation
    and marks the same severe-profound subgroup that carries persistent hypotonia
    and respiratory abnormalities.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Inability to walk
    term:
      id: HP:0002540
      label: Inability to walk
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ID was universal and at least moderate in severity: 2/7 were non-ambulatory and 3/7 non-verbal."
    explanation: Direct numerator of 2 of 7 (29%), which falls at the top of the OCCASIONAL band (5-29%).
- category: Musculoskeletal
  name: Arthrogryposis Multiplex Congenita
  description: >-
    The most severe reported presentation of THOC2 disease and an allele-specific
    one. A recurrent canonical acceptor splice-site variant (c.2482-1_2484delGTCA,
    affecting the intron 22/exon 23 acceptor site) has caused lethal fetal akinesia
    with multiple congenital joint contractures in male fetuses from two unrelated
    families reported independently. Muscle histology in the second family showed a
    myopathic picture with cytoplasmic bodies - the only tissue-level muscle
    characterisation available for this disorder. No frequency is assigned: this is
    a small number of isolated fetal reports tied to one specific variant, not a
    rate within the intellectual-disability cohorts, and it would be misleading to
    band it as if it were.
  phenotype_term:
    preferred_term: Arthrogryposis multiplex congenita
    term:
      id: HP:0002804
      label: Arthrogryposis multiplex congenita
  evidence:
  - reference: PMID:34976470
    reference_title: "Novel Consensus Splice Site Pathogenic Variation in THOC2 Gene Leads to Recurrent Arthrogryposis Multiplex Congenita Phenotype: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we describe for the first time a recurrent arthrogryposis multiplex congenita phenotype (AMC) in two male fetuses in a family."
    explanation: First description of arthrogryposis multiplex congenita caused by a THOC2 variant, in two affected male fetuses of one family.
  - reference: PMID:34976470
    reference_title: "Novel Consensus Splice Site Pathogenic Variation in THOC2 Gene Leads to Recurrent Arthrogryposis Multiplex Congenita Phenotype: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the most severe phenotype described in THOC2 gene-related disease till date."
    explanation: Places this presentation at the extreme severe end of the THOC2 phenotypic spectrum, which is why the entry treats it as an allele-specific extreme rather than a general disease feature.
  - reference: PMID:37945483
    reference_title: "Muscular phenotype description of abnormal THOC2 splicing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a family with the same splice site mutation in the THOC2 gene involved in fetal arthrogryposis as well."
    explanation: Independent replication of the arthrogryposis phenotype with the identical splice-site variant in a second, unrelated family, which converts a single case report into a reproducible genotype-phenotype association.
  - reference: PMID:37945483
    reference_title: "Muscular phenotype description of abnormal THOC2 splicing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We provide the first description of the muscular phenotype of this disease which reveals the presence of cytoplasmic bodies."
    explanation: Provides the muscle histopathology accompanying the fetal akinesia - a myopathic picture with cytoplasmic bodies.
- category: Neurological
  name: Abnormality of Movement
  description: >-
    A composite movement-disorder phenotype - abnormal motor coordination,
    stereotypies or involuntary movements - is present in just over half of the
    pooled 38-individual cohort and is the single most common neurological feature
    after the cognitive and language phenotype. It is partly age-emergent: although
    the phenotype is static in many individuals, a more complex neurological
    picture appears with age in several males, and three individuals in the 2020
    cohort had received an additional diagnosis of cerebral palsy. Tremor and gait
    disturbance, curated separately above, are specific instances within this
    category.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Abnormality of movement
    term:
      id: HP:0100022
      label: Abnormality of movement
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in the expanded cohort 13% develop hypertonia and spasticity or contractures, and 53% have some abnormality of motor coordination, stereotypic or involuntary movements"
    explanation: Gives the pooled-cohort rate of 53% for the composite movement abnormality, which falls in the FREQUENT band (30-79%) and is the basis for the frequency assigned here.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "although for many individuals the phenotype is static, a more complex neurological phenotype also emerges with age in several males"
    explanation: Supports the PROGRESSIVE clinical course qualifier on this phenotype, and notes explicitly that progression is not universal.
- category: Neurological
  name: Hypertonia and Spasticity
  description: >-
    A minority of affected individuals develop hypertonia with spasticity or
    contractures, typically emerging with age rather than present from infancy.
    This is the opposite pole from the infantile hypotonia that characterises the
    early presentation, and the two are not mutually exclusive across the disease
    course - hypotonia early, spasticity later, in some individuals.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Hypertonia
    term:
      id: HP:0001276
      label: Hypertonia
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in the expanded cohort 13% develop hypertonia and spasticity or contractures, and 53% have some abnormality of motor coordination, stereotypic or involuntary movements"
    explanation: Gives the pooled-cohort rate of 13%, which falls in the OCCASIONAL band (5-29%). The verb "develop" is the basis for the PROGRESSIVE qualifier.
- category: Gastrointestinal
  name: Feeding Difficulties
  description: >-
    Severe feeding difficulties are one of the multisystem features present in a
    significant minority of affected individuals, and in the severe neuromuscular
    subgroup they co-occur with recurrent aspiration and excessive salivation.
    Together with gastroesophageal reflux they are a principal contributor to
    non-neurological morbidity.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: The pooled cohort reports severe feeding difficulties within a group of multisystem features each present in 10-30%, which falls in the OCCASIONAL band (5-29%) at its upper edge.
- category: Gastrointestinal
  name: Gastroesophageal Reflux
  description: >-
    Gastroesophageal reflux is reported among the multisystem features present in
    a significant minority, alongside severe feeding difficulties. In the severe
    neuromuscular subgroup it is clinically linked to the recurrent aspiration and
    respiratory infections that dominate that group's morbidity.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Gastroesophageal reflux
    term:
      id: HP:0002020
      label: Gastroesophageal reflux
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Gastroesophageal reflux is named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.
- category: Ophthalmological
  name: Visual Impairment
  description: >-
    Visual impairment is one of the multisystem features present in a significant
    minority of affected individuals, and cortical visual impairment was
    specifically documented in the severely affected female with a de novo variant.
    Its recognition is the reason routine ophthalmological review is recommended at
    diagnosis.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Visual impairment is named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.
- category: Auditory
  name: Hearing Impairment
  description: >-
    Hearing impairment is one of the multisystem features present in a significant
    minority of affected individuals. Because it is both common enough to matter
    and directly remediable in a population already burdened with a language
    disorder, hearing screening is recommended in all newly diagnosed individuals.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Hearing impairment is named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.
- category: Cardiovascular
  name: Congenital Cardiac Anomaly
  description: >-
    Congenital anomalies of the cardiorespiratory system occur in a significant
    minority. No specific lesion predominates in the reported series; cardiac
    anomalies are additionally listed among the congenital malformations enriched
    in the severe neuromuscular subgroup. This is the basis for the recommendation
    that all newly diagnosed individuals have an echocardiogram.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Congenital cardiac anomaly
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Cardiorespiratory congenital anomalies are named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"
    explanation: Cardiac anomalies are specifically enumerated among the congenital malformations enriched in the severe neuromuscular subgroup.
- category: Renal
  name: Genitourinary Anomaly
  description: >-
    Congenital anomalies of the genitourinary tract occur in a significant minority.
    The MONDO/Orphanet description of the disorder additionally lists microorchidism
    and microphallus among the less common manifestations, consistent with
    genitourinary involvement, although those specific findings are not quantified
    in the published cohorts.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Genitourinary anomaly
    term:
      id: HP:0000119
      label: Abnormality of the genitourinary system
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Genitorenal congenital anomalies are named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.
- category: Musculoskeletal
  name: Skeletal Anomaly
  description: >-
    Congenital anomalies of the skeletal system occur in a significant minority of
    affected individuals. These are distinct from the joint contractures of the
    lethal fetal arthrogryposis presentation, which is tied to one specific splice
    allele, and from the acquired contractures that develop with spasticity in a
    smaller subgroup.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Skeletal anomaly
    term:
      id: HP:0000924
      label: Abnormality of the skeletal system
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Skeletal congenital anomalies are named in the pooled cohort's 10-30% multisystem group, which falls in the OCCASIONAL band (5-29%) at its upper edge.
- category: Respiratory
  name: Recurrent Aspiration and Respiratory Infection
  description: >-
    Part of the severe neuromuscular phenotype that emerged from the pooled cohort:
    severe-to-profound intellectual disability with persistent muscular hypotonia,
    recurrent aspiration and respiratory tract infections, excessive salivation,
    and an increased risk of congenital anomalies including laryngomalacia and
    tracheomalacia. This is the concrete clinical content behind the
    "respiratory abnormalities" of the severe-profound subset, and it is the main
    driver of morbidity in that group. No frequency is assigned: the pooled cohort
    describes this as a phenotype affecting "a proportion" of individuals without
    giving a numerator for the respiratory features specifically.
  phenotype_term:
    preferred_term: Recurrent respiratory infections
    term:
      id: HP:0002205
      label: Recurrent respiratory infections
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"
    explanation: Enumerates recurrent aspiration and respiratory tract infections as components of the severe neuromuscular phenotype. The statement is qualitative, which is why no frequency band is assigned.
- category: Neurological
  name: Sialorrhea
  description: >-
    Excessive salivation is a component of the severe neuromuscular phenotype and
    travels with the persistent hypotonia, feeding difficulty and aspiration risk
    of that subgroup rather than occurring in isolation. No frequency is assigned:
    the source describes the phenotype qualitatively as affecting a proportion of
    the cohort without a numerator.
  phenotype_term:
    preferred_term: Excessive salivation
    term:
      id: HP:0002307
      label: Drooling
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"
    explanation: Names excessive salivation as a component of the severe neuromuscular phenotype. Qualitative statement, so no frequency band is assigned.
- category: Respiratory
  name: Laryngomalacia and Tracheomalacia
  description: >-
    Airway malacia is listed among the congenital anomalies with increased risk in
    the severe neuromuscular subgroup, and is mechanistically coherent with the
    persistent hypotonia and aspiration risk of that group. No frequency is
    assigned: the source names it within a qualitative description of a subgroup
    phenotype rather than giving a rate.
  phenotype_term:
    preferred_term: Laryngomalacia
    term:
      id: HP:0001601
      label: Laryngomalacia
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "that of severe to profound ID, persistent muscular hypotonia, recurrent aspiration and respiratory tract infections, excessive salivation and an increased risk of congenital anomalies, including laryngo/tracheomalacia, cardiac and palatal anomalies"
    explanation: Names laryngomalacia and tracheomalacia among the congenital anomalies enriched in the severe neuromuscular subgroup. Qualitative statement, so no frequency band is assigned.
genetic:
- name: THOC2
  gene_term:
    preferred_term: THOC2
    term:
      id: hgnc:19073
      label: THOC2
  association: Causal - X-linked hypomorphic variants
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: Positive
  notes: >-
    THOC2 is on the X chromosome and encodes the largest subunit of the TREX
    (Transcription-Export) complex. Because THOC2 is essential, all
    disease-associated alleles are hypomorphic. Two classes are documented:
    missense variants at evolutionarily conserved residues that reduce THOC2
    protein stability (9 of 14 tested), and canonical splice-site variants or
    intragenic deletions that yield C-terminally truncated protein lacking part of
    the RNA-binding domain. A recurrent variant (p.Arg77Cys) has been described.
    Both inherited (X-linked pedigree) and de novo variants occur, including a de
    novo variant in an affected female with epileptic encephalopathy; carrier
    mothers are clinically unaffected with highly skewed X-inactivation. Allele
    class predicts the extreme of the spectrum: one specific recurrent canonical
    acceptor splice-site variant, c.2482-1_2484delGTCA at the intron 22/exon 23
    boundary, has produced lethal fetal akinesia with arthrogryposis multiplex
    congenita in two unrelated families, which is a qualitatively different and
    more severe outcome than the postnatal neurodevelopmental presentation of the
    missense alleles. Outside that one allele, no genotype-phenotype correlation
    holds: the largest cohort found no clear relationship between clinical severity
    and either variant type (missense, splicing-defective or microdeletion) or the
    region of the protein affected. The two arthrogryposis reports postdate that
    analysis and are not contradicted by it, but they should be read as a single
    allele-specific exception rather than as evidence for a general
    variant-type-to-severity rule.
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we report that variants in THOC2, which encodes a subunit of the highly conserved TREX mRNA-export complex, cause syndromic intellectual disability (ID)"
    explanation: The gene-discovery statement establishing THOC2 as the cause of this syndromic intellectual disability.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "THOC2 variants that affect evolutionarily conserved amino acid residues and reduce protein stability and two with canonical splice-site THOC2 variants that result in C-terminally truncated THOC2 proteins."
    explanation: Enumerates the two allele classes - destabilising missense at conserved residues, and splice variants producing C-terminal truncation.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "including the first case of a recurrent variant (p.Arg77Cys), and an additional individual with an intragenic THOC2 microdeletion (Del-Ex37-38)"
    explanation: Documents the first recurrent THOC2 variant and an intragenic microdeletion, expanding the variant spectrum beyond private missense alleles.
  - reference: PMID:37945483
    reference_title: "Muscular phenotype description of abnormal THOC2 splicing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a family with the same splice site mutation in the THOC2 gene involved in fetal arthrogryposis as well."
    explanation: Establishes a recurrent splice-site allele with a distinct, lethal fetal presentation in a second unrelated family, which is the basis for the allele-class-to-severity statement in the notes.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "heterozygous mothers were clinically unaffected, and, where available, X-chromosome inactivation (XCI) was highly skewed"
    explanation: Documents the carrier-female genotype-phenotype relationship - unaffected despite carrying a pathogenic allele, with skewed X-inactivation as the observed correlate.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "there is no clear genotypic-phenotypic correlation between the severity or spectrum of phenotypic differences and either the type of genetic variant"
    explanation: The largest cohort's explicit negative finding on genotype-phenotype correlation, which is why this entry does not attempt to grade severity by variant class outside the one recurrent arthrogryposis splice allele.
diagnosis:
- name: Molecular Genetic Testing for THOC2
  description: >-
    The diagnosis is established by identifying a hypomorphic THOC2 variant in an
    individual with suggestive findings. Testing must cover both sequence variants
    and intragenic copy-number changes, because intragenic THOC2 microdeletions
    are an established allele class that coding-only analysis will miss. Because
    variants are typically private missense alleles in an essential gene,
    functional assessment of protein stability can support classification of
    variants of uncertain significance.
  presence: Positive in affected individuals
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  evidence:
  - reference: PMID:26166480
    reference_title: "THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "X chromosome exome sequencing revealed four missense variants in THOC2 in four families"
    explanation: Establishes sequencing as the diagnostic route for the missense allele class.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "an additional individual with an intragenic THOC2 microdeletion (Del-Ex37-38)"
    explanation: Documents the intragenic microdeletion allele class, which is why copy-number analysis must accompany sequencing.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Ex vivo missense variant testing and patient-derived cell line data from current and published studies show 9 of the 14 missense THOC2 variants result in reduced protein stability."
    explanation: Protein-stability testing of missense variants is an established functional assay in this disorder and can support variant classification.
- name: Neurological Investigation for Symptoms or Signs
  description: >-
    Once the molecular diagnosis is made, the largest cohort advises a low threshold
    for EEG and brain MRI whenever neurological symptoms or signs appear. The
    rationale is that seizures, while affecting only about a fifth of the cohort
    overall, cluster in the severe neuromuscular subgroup where they can take the
    form of a severe developmental and epileptic encephalopathy with infantile
    spasms, and that the neurological phenotype can progress with age in some males.
    Imaging is for detection of complications rather than for diagnosis - there is
    no unifying neuroradiological signature for this disorder.
  diagnosis_term:
    preferred_term: electroencephalography
    term:
      id: NCIT:C38054
      label: Electroencephalography
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the clinicians should have a low threshold for investigating neurological symptoms or signs with an EEG and MRI brain"
    explanation: An explicit investigation recommendation from the largest cohort, naming both modalities.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "although for many individuals the phenotype is static, a more complex neurological phenotype also emerges with age in several males"
    explanation: Age-emergent neurological features are the reason surveillance is ongoing rather than a one-off assessment at diagnosis.
differential_diagnoses:
- name: Other X-Linked Intellectual Disability Syndromes
  description: >-
    THOC2 was identified through X-linked intellectual disability pedigrees
    (including family MRX12, ascertained in 1971) and has no pathognomonic
    feature; over 120 of the identified intellectual-disability genes are
    X-linked. Broad genomic testing rather than targeted testing is the practical
    approach.
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Over 120 of the identified >800 ID genes are located on the X-chromosome"
    explanation: Quantifies the size of the X-linked intellectual-disability differential that THOC2 sits within, which is why targeted single-gene testing is impractical.
- name: Other THO/TREX Subunit Neurodevelopmental Disorders
  description: >-
    Other TREX subunits are themselves associated with neurodevelopmental
    disorders - THOC6 (Beaulieu-Boycott-Innes syndrome, curated separately in this
    knowledge base) and DDX39B - and THOC2 destabilisation reduces the abundance of
    the other NDD-associated THOC subunits, so the phenotypes are expected to
    overlap. This makes the group a coherent differential set rather than a list of
    unrelated conditions. THOC6 disease is distinguished by autosomal recessive
    inheritance, a recognisable facial gestalt, and cardiac and genitourinary
    malformations, none of which characterise THOC2 disease.
  evidence:
  - reference: PMID:40651286
    reference_title: "Transcription-Export complex in neurodevelopmental disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "partial loss of function variants in the TREX components THOC2, THOC6, and DDX39B were implicated in neurodevelopmental disorders"
    explanation: A 2025 review naming the specific TREX subunits whose partial loss of function causes neurodevelopmental disorders, which defines the membership of this differential group.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Interestingly, reduced stability of THOC2 variant proteins has a flow-on effect on the stability of the multi-protein TREX complex; specifically on the other NDD-associated THOC subunits."
    explanation: Provides the mechanistic reason these disorders overlap - a THOC2 lesion lowers the abundance of the very subunits whose own loss causes the differential diagnoses.
- name: Syndromic Obesity with Intellectual Disability
  description: >-
    The MONDO name's emphasis on overweight and short stature places THOC2 in the
    differential for syndromic obesity with intellectual disability (for example
    Prader-Willi and Smith-Magenis syndromes), although the largest THOC2 cohort
    refined the core phenotype away from that framing and toward language disorder
    and growth disturbance. The obesity is adult-onset and truncal rather than
    early-onset hyperphagic obesity, which is a practical discriminator from
    Prader-Willi syndrome.
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The affected individuals had a syndromic NDD, characterized by borderline to severe ID, speech delay, short stature and adult onset truncal obesity"
    explanation: Documents the adult-onset truncal pattern of the obesity, which is the feature that distinguishes THOC2 disease from the early-onset hyperphagic obesity syndromes in this differential. This sentence is the 2018 paper's recap of the 2015 cohort rather than a new observation.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our current, expanded cohort refines the core phenotype of THOC2 NDDs to language disorder and/or ID, with a variable severity, and disorders of growth."
    explanation: The largest cohort's refinement moves the core away from the obesity framing, which is why this differential is listed but not treated as the leading one.
treatments:
- name: Multidisciplinary Supportive Care
  description: >-
    There is no disease-modifying therapy and none is in development. Management is
    supportive and symptom-directed - developmental and educational support,
    speech and language therapy, antiseizure medication where epilepsy is present,
    management of the movement disorder, growth and nutritional monitoring, and
    respiratory support for the severe-profound subset. No treatment has been
    evaluated in a THOC2-specific study.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  notes: >-
    No published THOC2-specific treatment study exists, so this entry records the
    standard-of-care framing rather than evidence of efficacy. The claim that
    intellectual disability generally lacks specific therapy is cited from the
    THOC2 cohort literature's own framing.
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "frequently have limited or no specific therapies for their core symptoms"
    explanation: Background statement from the THOC2 cohort paper's introduction about intellectual disability generally; curated as PARTIAL/OTHER because it is framing rather than a THOC2-specific treatment finding, and it is the only citable statement on therapy available for this disorder.
- name: Speech and Language Therapy
  description: >-
    Language disorder is half of the refined core phenotype and speech delay is
    among the most consistently reported features, making speech-language therapy
    the intervention most directly matched to the disorder's dominant morbidity.
  treatment_term:
    preferred_term: speech and language therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  therapeutic_modality: BEHAVIORAL
  target_phenotypes:
  - preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "refines the core phenotype of THOC2 NDDs to language disorder and/or ID"
    explanation: Establishes language disorder as a core phenotype and therefore a primary intervention target; no THOC2-specific trial of speech therapy exists, so this supports the indication rather than the efficacy.
- name: Multisystem Surveillance at Diagnosis
  description: >-
    Because congenital anomalies of the cardiorespiratory, genitorenal and skeletal
    systems, feeding difficulties, and visual and hearing impairment are each
    present in 10-30% of affected individuals, the largest cohort explicitly
    recommends that every newly diagnosed individual receives a comprehensive
    evaluation - a detailed systems review by a paediatrician, a cardiac
    echocardiogram, hearing screening and ophthalmological review. This is the only
    concrete management recommendation issued in the THOC2 literature. Hearing and
    vision assessment matter disproportionately here because the population already
    has a language disorder, so remediable sensory deficits would otherwise be
    attributed to the neurodevelopmental diagnosis.
  treatment_term:
    preferred_term: multisystem screening evaluation at diagnosis
    term:
      id: NCIT:C15220
      label: Diagnosis Assessment
  target_phenotypes:
  - preferred_term: Congenital cardiac anomaly
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  - preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  - preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
  evidence:
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "comprehensive evaluation including detailed systems review by a pediatrician, cardiac echocardiogram, hearing screening and ophthalmological review in all newly diagnosed patients is highly recommended"
    explanation: An explicit, specific management recommendation issued by the largest THOC2 cohort, naming the exact investigations - this is a direct recommendation rather than an inferred indication.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital anomalies of the cardiorespiratory, genitorenal and skeletal systems, severe feeding difficulties and gastroesophageal reflux, and visual and hearing impairments are present in a significant proportion (10–30%)"
    explanation: Gives the prevalence of the multisystem findings that justify screening for them at diagnosis.
- name: Physical and Occupational Therapy
  description: >-
    Hypotonia and gait disturbance are among the common findings of the disorder,
    and a subset of individuals are non-ambulatory, so motor rehabilitation is a
    standing component of management. No THOC2-specific rehabilitation study
    exists; the indication rests on the documented motor phenotype rather than on
    any evaluated outcome.
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  therapeutic_modality: BEHAVIORAL
  target_phenotypes:
  - preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  - preferred_term: Gait disturbance
    term:
      id: HP:0001288
      label: Gait disturbance
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They have a core phenotype of ID, and common findings of behavioural disorders, infantile hypotonia, gait disturbance and growth impairment"
    explanation: Establishes hypotonia and gait disturbance as common findings and therefore as standing rehabilitation targets; it supports the indication, not the efficacy, of physical and occupational therapy, which has not been studied in this disorder.
- name: Antiseizure Medication
  description: >-
    Epilepsy is not universal in THOC2 disease but does occur, and the one reported
    female with a de novo variant presented with an epileptic encephalopathy.
    Antiseizure treatment is standard-of-care and selected by seizure type; no
    THOC2-specific antiseizure regimen, drug preference or contraindication has
    been reported.
  treatment_term:
    preferred_term: anticonvulsant therapy
    term:
      id: NCIT:C64172
      label: Anticonvulsant Therapy
  therapeutic_modality: SMALL_MOLECULE
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Confirmed seizure disorder was only present in the affected female (individual 7) but suspected in individual 2."
    explanation: Documents the seizure burden that establishes the indication. It supports treating the seizures that occur, not any THOC2-specific efficacy claim, and it is also the reason this treatment is not framed as universally required.
- name: Genetic Counseling
  description: >-
    Counselling covers X-linked inheritance with affected males and typically
    milder or unaffected carrier females, the recurrence risk implied by carrier
    status, and the fact that de novo variants also occur - including in affected
    females - so a negative maternal test does not exclude the diagnosis in a
    proband. Counselling of carrier mothers must also cover the recurrent
    splice-site allele associated with lethal fetal arthrogryposis, for which
    prenatal recurrence was documented in consecutive pregnancies.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  therapeutic_modality: BEHAVIORAL
  evidence:
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "diagnosis of X-linked causes of ID remain critically important for accurate genetic counseling of families"
    explanation: States the counselling rationale for establishing an X-linked molecular diagnosis. Curated as PARTIAL because this is a general background statement from the paper's introduction about X-linked intellectual disability as a class, not a THOC2-specific counselling finding.
  - reference: PMID:29851191
    reference_title: "Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a de novo variant in a female with an epileptic encephalopathy"
    explanation: Documents the de novo female presentation that counselling must account for.
  - reference: PMID:34976470
    reference_title: "Novel Consensus Splice Site Pathogenic Variation in THOC2 Gene Leads to Recurrent Arthrogryposis Multiplex Congenita Phenotype: A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we describe for the first time a recurrent arthrogryposis multiplex congenita phenotype (AMC) in two male fetuses in a family."
    explanation: Documents recurrence of a lethal fetal presentation in consecutive pregnancies of one carrier mother, which is the specific recurrence risk that counselling for this allele class must address.
animal_models:
- species: Mouse
  genotype: Thoc2 exon 37-38 deletion hemizygous male (Thoc2Δ/Y), based on a patient allele
  genes:
  - preferred_term: THOC2
    term:
      id: hgnc:19073
      label: THOC2
  associated_phenotypes:
  - Reduced size and weight
  - Spatial learning and working memory deficits
  - Sensorimotor deficits
  description: >-
    A hypomorphic mouse built directly on a patient's THOC2 exon 37-38 deletion
    allele. It recapitulates the core human phenotypes - smaller size and weight,
    and deficits in spatial learning, working memory and sensorimotor function -
    and is the system in which the R-loop/DNA-damage mechanism was demonstrated.
    Its construct validity is unusually good for a hypomorphic-allele disorder,
    because the modelled allele is a real patient variant rather than an
    engineered knockdown.
  evidence:
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we generated a mouse model based on a hypomorphic Thoc2 exon 37-38 deletion variant of a patient with ID, speech delay, hypotonia, and microcephaly"
    explanation: Establishes the construct validity of the model - it carries an actual patient allele.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight, and significant deficits in spatial learning, working memory and sensorimotor functions"
    explanation: Establishes face validity across the cognitive, sensorimotor and growth domains.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Thoc2Δ/Y neurons show perturbed in vitro neural migration, electrophysiological properties and synapse formation"
    explanation: Extends the model's construct validity below the behavioural level to cellular neurodevelopmental readouts, which is what makes it usable for mechanism and rescue experiments.
- species: Caenorhabditis elegans
  genotype: thoc-2 homozygous deletion (ok961) and heterozygotes, maintained over a balancer
  genes:
  - preferred_term: THOC2
    term:
      id: hgnc:19073
      label: THOC2
  associated_phenotypes:
  - Impaired locomotion
  - Sensory neuron dysfunction (reduced chemotaxis)
  description: >-
    An invertebrate loss-of-function model generated in the course of investigating
    a patient with a de novo X;8 translocation that knocked down THOC2 expression.
    Because the C. elegans thoc-2 deletion is homozygous lethal it must be
    balanced, which independently corroborates the essentiality of the gene that
    forces every human disease allele to be hypomorphic. Surviving animals show
    impaired locomotion and defective chemosensation, establishing a neuronal role
    for the orthologue. Its interpretive limits are substantial: it is a null
    rather than a hypomorph, an invertebrate rather than a mammal, and the human
    case that prompted it also had PTK2 haploinsufficiency, so the human arm of
    that report is confounded.
  evidence:
  - reference: PMID:23749989
    reference_title: "A de novo X;8 translocation creates a PTK2-THOC2 gene fusion with THOC2 expression knockdown in a patient with psychomotor retardation and congenital cerebellar hypoplasia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "THOC2 ortholog knockout in C.elegans which produced functional defects in specific sensory neurons"
    explanation: Establishes that loss of the THOC2 orthologue produces a neuronal functional deficit in an invertebrate, supporting a conserved neuronal requirement for the gene.
  - reference: PMID:23749989
    reference_title: "A de novo X;8 translocation creates a PTK2-THOC2 gene fusion with THOC2 expression knockdown in a patient with psychomotor retardation and congenital cerebellar hypoplasia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Animals thoc-2−/− were almost completely immobile, or moved slowly and for a short time upon touching"
    explanation: Documents the locomotor phenotype listed for this model, and the dose-dependence noted in the same figure - locomotion was also reduced in heterozygotes - parallels the hypomorphic nature of the human alleles.
discussions:
- discussion_id: thoc2_rloop_human_validation
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Is perturbed R-loop homeostasis with consequent DNA damage the mechanism of
    THOC2 syndrome in humans, or is it specific to the mouse model?
  attaches_to:
  - pathophysiology#Perturbed R-Loop Homeostasis and DNA Damage
  rationale: >-
    The R-loop/DNA-damage model is the only mechanistic account on offer for why
    partial loss of a ubiquitously required transcription-export factor produces a
    brain-predominant phenotype, and it nominates a druggable axis
    (R-loop-resolving helicases, DNA-damage-response modulation). It is better
    evidenced than a purely murine claim: R-loops were shown to accumulate in
    fibroblasts from the very patient whose allele the mouse carries, and RNase H1
    overexpression reduced both R-loops and comet-assay DNA damage, which orders
    the two events causally. Three gaps nonetheless keep this open. First, the
    rescue was performed in mouse neural stem cells, not in the patient cells, so
    the causal ordering is established in mouse and only the phenotype is
    established in human cells. Second, only one allele has been interrogated -
    the exon 37-38 deletion - whereas THOC2 alleles fall into two structurally
    different classes (destabilising missense versus C-terminal
    RNA-binding-domain truncation), so it is not established that both converge on
    R-loops. Third, the authors themselves frame the conclusion as a suggestion
    covering "mice and the patient", and no R-loop or DNA-damage measurement
    exists in human brain tissue. A fourth, sharper tension is that an earlier
    study reported the opposite cellular outcome from acute THOC2 knockdown in
    rodent neural cells - increased progenitor proliferation with no change in
    apoptosis - which is not obviously reconcilable with the germline-hypomorph
    finding of progenitor cell death, though the two differ in species, timing and
    the acuteness of the depletion.
  proposed_experiments:
  - experiment_id: thoc2_rloop_allele_classes
    name: R-loop and DNA-damage profiling across both THOC2 allele classes
    description: >-
      Quantify R-loop burden (DRIP-seq and S9.6 immunofluorescence) and DNA-damage
      markers in patient-derived lymphoblastoid or fibroblast lines carrying
      destabilising missense alleles, and compare against the already-characterised
      exon 37-38 deletion line and sex-matched controls. Then perform the RNase H1
      rescue directly in the human patient lines rather than in mouse neural stem
      cells.
    decision_criterion: >-
      Elevated R-loops with RNase H1 rescue in patient cells of both allele classes
      would establish the mechanism in human cells and unify the allele classes;
      an effect confined to the truncation class would mean the two classes act
      through different proximal mechanisms and that the entry's single causal
      chain needs to be split.
  - experiment_id: thoc2_proliferation_vs_apoptosis
    name: Reconciling increased progenitor proliferation with progenitor cell death
    description: >-
      Directly compare acute shRNA knockdown of THOC2 against a germline
      hypomorphic allele in the same neural progenitor system, measuring
      proliferation rate, apoptosis, R-loop burden and DNA damage in parallel and
      over a time course.
    decision_criterion: >-
      If the germline hypomorph produces apoptosis where acute knockdown produces
      proliferation, the discrepancy is a kinetic/adaptive effect and the entry's
      cell-death node stands; if acute knockdown also produces apoptosis under
      matched conditions, the earlier report is the outlier and the chain is
      simpler than currently curated.
  - experiment_id: thoc2_severe_subset_mechanism
    name: Mechanistic characterisation of the severe-profound subset
    description: >-
      Compare THOC2 protein levels, TREX subunit abundance and R-loop burden
      between individuals with the severe-profound phenotype (persistent hypotonia
      and respiratory abnormalities) and those with the milder
      language-predominant phenotype.
    decision_criterion: >-
      A quantitative relationship between residual THOC2 or TREX abundance and
      clinical severity would answer the cohort authors' explicit call for the
      pathophysiological basis of the severe phenotype.
  evidence:
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Overall, we suggest that perturbed R-loop homeostasis, in stem cells and/or differentiated cells in mice and the patient, and DNA damage-associated functional alterations are at the root of THOC2 syndrome."
    explanation: The mechanism is offered as a suggestion, and the human half of the claim is extrapolated from the mouse rather than measured, which is the substance of this open question.
  - reference: PMID:32116545
    reference_title: "Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Further investigations to elucidate the pathophysiological basis for this severe phenotype are warranted."
    explanation: The largest cohort's authors explicitly state that the mechanism of the severe subset is unexplained, which is part of what keeps this discussion open.
  - reference: PMID:38331934
    reference_title: "Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "reduced R-loop accumulation (Fig. 7e) and comet tail formation (Fig. 7f) in Thoc2"
    explanation: The RNase H1 rescue that orders R-loops upstream of DNA damage was performed in mutant mouse neural stem cells, not in patient cells - which is precisely the residual human-model gap the first proposed experiment closes.
  - reference: PMID:23749989
    reference_title: "A de novo X;8 translocation creates a PTK2-THOC2 gene fusion with THOC2 expression knockdown in a patient with psychomotor retardation and congenital cerebellar hypoplasia."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Thoc2 knockdown in neuronal stem cells (LC1) which increased their in vitro growth rate without modifying apoptosis levels"
    explanation: Acute THOC2 knockdown in rodent neural stem cells increased proliferation and explicitly did not change apoptosis, the opposite of the progenitor cell death seen with a germline hypomorphic allele. Curated as PARTIAL because it is an in-vitro acute-knockdown result in a different system rather than a direct contradiction, but it is the substance of the second proposed experiment.

📚

References & Deep Research

References

1

PMID:40651286

Transcription-Export complex in neurodevelopmental disorders.

No top-level findings curated for this source.

Deep Research

1

Falcon ▸

THOC2-Related Intellectual Disability: Disease Characteristics Report

Edison Scientific Literature 22 citations 2026-07-31T23:48:04.424690

THOC2-Related Intellectual Disability: Disease Characteristics Report

Executive summary

THOC2-related intellectual disability is an ultra-rare, predominantly X-linked neurodevelopmental disorder caused by pathogenic or likely pathogenic germline variants in THOC2, which encodes the largest subunit of the nuclear TREX transcription–mRNA-export complex. Intellectual disability and speech/language impairment are central; hypotonia, gait or cerebellar-type motor abnormalities, seizures, behavioral abnormalities, short stature, microcephaly, low birth weight, and later truncal obesity occur variably. The best-supported mechanism is partial loss of THOC2/TREX function. A major 2024 study refined this to a causal chain of abnormal R-loop homeostasis, DNA damage, cell-cycle disruption and apoptosis during neurodevelopment, followed by neuronal migration, axonal, synaptic and network dysfunction. Evidence remains limited to small cohorts, patient cells and one hypomorphic mouse model; prevalence, longitudinal prognosis, validated biomarkers and disease-modifying treatments are unknown. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 1-3, bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2, bhattacharjee2024compromisedtranscriptionmrnaexport pages 13-14)

The following table summarizes the most actionable evidence and its limitations.

domain	established finding	quantitative/variant detail	evidence type and year	evidence limitation
Disease naming / identifiers	A rare Mendelian neurodevelopmental disorder caused by pathogenic THOC2 variation; retrieved evidence supports names such as THOC2-related intellectual disability, THOC2-associated neurodevelopmental disorder, and X-linked intellectual disability due to THOC2. Do not assert MONDO/OMIM IDs here because they were not established in the retrieved evidence. (kumar2018severeneurocognitiveand pages 3-5, kumar2018severeneurocognitiveand pages 1-3)	Core phenotype is intellectual disability with variable syndromic features; THOC2 is on chromosome X and encodes the largest TREX subunit. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2, kumar2018severeneurocognitiveand pages 3-5)	Human clinical cohorts/reports, 2015 and 2018; mechanistic disease framing, 2024. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 1-3, bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2)	Naming is consistent across papers, but registry identifiers were not retrieved directly.
Inheritance	Established X-linked inheritance with affected hemizygous males in multigenerational families; also de novo disease in at least one affected female and additional de novo male cases. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 1-3, kumar2018severeneurocognitiveand pages 6-8)	2015 cohort: 4 multigenerational families, 20 affected individuals. 2018 expansion: 6 affected individuals from 5 unrelated families plus 1 affected female with de novo p.Tyr517Cys. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 1-3, kumar2018severeneurocognitiveand pages 6-8)	Human pedigree/genomic evidence, 2015 and 2018.	Penetrance is not formally quantified; female manifestations appear uncommon and likely influenced by X-inactivation.
Sex effects / X-inactivation	Heterozygous mothers were usually clinically unaffected and showed highly skewed X-chromosome inactivation when tested. (kumar2018severeneurocognitiveand pages 8-10, kumar2018severeneurocognitiveand pages 6-8)	Reported XCI skewing included ~94%, 98:2%, and 99.9:0.1%. (kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 26-27)	Human clinical/molecular evidence, 2018.	Small number of carrier females studied; cannot define full female penetrance spectrum.
Core phenotypes	Intellectual disability is the consistent core phenotype, often with speech/language impairment, hypotonia, gait disturbance, tremor, seizures/epileptic encephalopathy, growth abnormalities, and occasional behavioral/autism features. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 5-6, kumar2018severeneurocognitiveand pages 8-10)	2015: severity ranged from borderline to severe; speech delay, short stature, elevated BMI/truncal obesity in older males in 2/4 families, seizure disorders, tremors, gait disturbance. (kumar2015thoc2mutationsimplicate pages 1-3) 2018 established series: all 7 had at least moderate ID; 2/7 non-ambulatory, 3/7 non-verbal, 4/7 behavioral problems, 1/7 ASD, 4/7 infantile hypotonia, 2/7 tremor, 1/7 confirmed seizures, 1/7 suspected seizures, 3/7 low birth weight, 2/7 microcephaly, 2/7 short stature. (kumar2018severeneurocognitiveand pages 5-6)	Human clinical cohort data, 2015 and 2018.	Frequencies are from small cohorts and partly enriched for severe referrals; not population estimates.
Neuroimaging / neurologic findings	Brain imaging can be normal or show nonspecific structural abnormalities; cerebellar-type signs may occur even without major cerebellar MRI abnormalities. (kumar2018severeneurocognitiveand pages 8-10, kumar2015thoc2mutationsimplicate pages 1-3)	2018: abnormal MRI in 2/5 tested—cortical gyral changes, corpus callosum hypoplasia, reduced brainstem volume, lateral ventricle dilatation, delayed myelination, periventricular white matter lesions; 3/5 were normal. (kumar2018severeneurocognitiveand pages 5-6) 2015: mild ventriculomegaly, gliosis, inferior cerebellar vermis dysplasia, cervical cord compression reported in a limited subset. (kumar2015thoc2mutationsimplicate pages 1-3)	Human imaging observations, 2015 and 2018.	Imaging numbers are very small; no disease-specific radiologic signature established.
Established pathogenic / likely pathogenic variants	Established disease-causing variants include multiple missense and splice-altering THOC2 variants that reduce protein stability or create C-terminal truncation. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 5-6, kumar2018severeneurocognitiveand pages 8-10)	2015 established missense variants: c.937C>T (p.Leu313Phe), c.1313T>C (p.Leu438Pro), c.2399T>C (p.Ile800Thr), c.3034T>C (p.Ser1012Pro). (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 3-5) 2018 established variants include p.Tyr517Cys, p.Thr696Ile, p.Gly713Asp, p.His1187Tyr, and splice variants c.4450-2A>G and c.3503+4A>C / p.Gly1168fs7*. (kumar2018severeneurocognitiveand pages 1-3, kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 5-6)	Human genomic + functional evidence, 2015 and 2018.	Variant list is restricted to retrieved papers; no contemporaneous ClinVar aggregation was retrieved.
VUS / candidate variants	Additional rare missense THOC2 variants were reported as variants of uncertain significance rather than established causes. (kumar2018severeneurocognitiveand pages 10-11)	Reported VUS: p.Arg77Cys, p.Ser1108Leu, p.Arg1121Gly, p.Asn1261His. They were rare/conserved and in silico-predicted damaging but lacked sufficient functional confirmation. (kumar2018severeneurocognitiveand pages 10-11)	Human genomic interpretation, 2018.	These should not be treated as confirmed causal variants without stronger evidence.
Population frequency	Established pathogenic variants were absent from large reference datasets, supporting rarity. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 26-27, kumar2018severeneurocognitiveand pages 10-11)	2015 variants absent in >60,000 individuals from 1000 Genomes/ExAC; 2018 variants absent in gnomAD/ExAC per report. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 26-27, kumar2018severeneurocognitiveand pages 10-11)	Human variant interpretation, 2015 and 2018.	Database versions were historical; current allele frequencies were not independently re-queried here.
Molecular mechanism	THOC2 dysfunction compromises TREX-associated RNA biology and, in the 2024 model, causes R-loop accumulation → DNA damage → cell-cycle disruption / apoptosis → adverse neurodevelopment. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2, bhattacharjee2024compromisedtranscriptionmrnaexport pages 13-14)	2024 mouse/patient study showed RNase H-sensitive R-loop accumulation in Thoc2Δ/Y neural stem cells and patient fibroblasts; RNase H1 overexpression reduced R-loops and DNA damage (****p<0.0001). (bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9, bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16)	Mouse + patient-derived cell mechanistic study, 2024.	Mechanism is strongly supported in the hypomorphic mouse model and patient fibroblasts, but not yet proven for every human variant.
2024 model-organism / cell findings	A hypomorphic Thoc2Δ/Y mouse recapitulated major syndrome features and linked them to impaired neurodevelopment. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2, bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11, bhattacharjee2024compromisedtranscriptionmrnaexport pages 4-5)	Smaller size/weight; reduced birth rate by ~33%; deficits in spatial learning, working memory, fine motor/sensorimotor tasks; reduced cortical ventricular zone, cortical plate, and corpus callosum thickness; 32% shorter primary axons; fewer mature dendritic spines; reduced electrophysiologic activity. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11, bhattacharjee2024compromisedtranscriptionmrnaexport pages 11-13, bhattacharjee2024compromisedtranscriptionmrnaexport pages 4-5)	Mouse model + primary neurons/NSCs, 2024.	A hypomorphic exon 37-38 deletion model may not reflect all missense/splice variants or full human natural history.
Diagnostics	Diagnosis has been made by family-based sequencing approaches and modern exome/genome sequencing, followed by segregation and functional RNA/protein studies when needed. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 5-6, kumar2018severeneurocognitiveand pages 3-5, kumar2018severeneurocognitiveand pages 27-27)	2015: X-chromosome exome sequencing plus linkage (combined LOD 8.1) in 4 families. (kumar2015thoc2mutationsimplicate pages 1-3) 2018: WES/WGS/trio exome with Sanger confirmation; cDNA PCR, RT-qPCR, western blotting, immunofluorescence, cycloheximide chase used for splice/protein effect resolution. (kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 5-6, kumar2018severeneurocognitiveand pages 3-5, kumar2018severeneurocognitiveand pages 27-27)	Human diagnostic genomics, 2015 and 2018.	No disease-specific consensus testing guideline or biomarker was retrieved.
Treatment / management	No disease-modifying therapy, targeted therapy, or disease-specific clinical trial was identified in the retrieved evidence; management appears supportive and symptom-based. (kumar2018severeneurocognitiveand pages 5-6, kumar2015thoc2mutationsimplicate pages 1-3)	Isolated report: one male had growth-hormone deficiency treated with replacement therapy. Supportive needs are implied by nonverbal/nonambulatory status, seizures, behavioral issues, and developmental disability. (kumar2015thoc2mutationsimplicate pages 3-4, kumar2018severeneurocognitiveand pages 5-6) Clinical trials search retrieved no relevant THOC2-specific interventional trial.	Human case management observations, 2015/2018; trial search negative.	Supportive care details were not systematically reported; no treatment outcome series or guidelines were retrieved.
Epidemiology	THOC2-related intellectual disability is ultra-rare; no prevalence or incidence estimate was identified in retrieved sources. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 1-3)	Evidence base consists of small family series and case reports: 20 affected individuals in 2015 families, plus 7 established additional cases in 2018; papers mention broader totals including previously reported individuals, but no population denominator. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 3-5, kumar2018severeneurocognitiveand pages 1-3)	Human rare-disease literature, 2015 and 2018.	No registry-based epidemiology, sex ratio estimate, or geographic prevalence study was retrieved.

Table: This table compacts the strongest retrieved evidence on THOC2-related intellectual disability, including inheritance, core phenotypes, variant classes, 2024 mechanism data, diagnostics, and major gaps. It is designed for rapid knowledge-base curation while clearly separating established findings from limited or absent evidence.

Evidence base and source provenance

The principal human evidence comprises a 2015 American Journal of Human Genetics study of four multigenerational families with 20 affected individuals and a 2018 Human Mutation expansion containing additional de novo and inherited cases. The principal recent advance is the February 2024 Nature Communications study using a hypomorphic mouse, neural stem cells, primary neurons and fibroblasts from an affected person. Thus, most clinical information is aggregated disease-level information abstracted from research cohorts, pedigrees and case reports—not EHR-derived population data. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 1-3, bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2)

Key publications are:

Kumar et al., “THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability,” published August 2015, DOI: https://doi.org/10.1016/j.ajhg.2015.05.021; PMID: 26166475. (kumar2015thoc2mutationsimplicate pages 1-3)
Kumar et al., “Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery,” published June 2018, DOI: https://doi.org/10.1002/humu.23557; PMID should be verified against PubMed before database ingestion. (kumar2018severeneurocognitiveand pages 5-6)
Bhattacharjee et al., “Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment,” published February 2024, DOI: https://doi.org/10.1038/s41467-024-45121-5; PubMed record: https://pubmed.ncbi.nlm.nih.gov/?term=10.1038%2Fs41467-024-45121-5. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2)

Representative exact abstract statements include: “We implicated the X-chromosome THOC2 gene, which encodes the largest subunit of the highly-conserved TREX (Transcription-Export) complex, in a clinically complex neurodevelopmental disorder with intellectual disability as the core phenotype” and “Overall, we suggest that perturbed R-loop homeostasis… and DNA damage-associated functional alterations are at the root of THOC2 syndrome.” (bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2)

1. Disease information

Definition and nomenclature

The condition is a Mendelian neurodevelopmental syndrome in which damaging THOC2 variants compromise an essential RNA-processing/export factor. Preferred practical label: THOC2-related neurodevelopmental disorder or THOC2-related intellectual disability. Literature alternatives include THOC2-associated intellectual disability, THOC2 syndrome, X-linked intellectual disability due to THOC2, and historically X-linked intellectual disability 12/MRX12 for one linked family. Because phenotypes extend beyond cognition, “THOC2-related neurodevelopmental disorder” is the broadest label. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 3-5, bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2)

Identifiers

Gene: THOC2; the retrieved literature establishes X-chromosomal localization but did not independently validate HGNC/NCBI identifiers.
OMIM: MRX12 is the historical family designation. The exact current OMIM disease and gene numbers should be verified directly in OMIM before knowledge-base release; they were not returned by the available evidence tools.
MONDO: no disease-specific MONDO identifier was recoverable in the searches; Open Targets also returned no matching disease entity. Do not assign an unverified MONDO ID.
Orphanet: no disease-specific ORPHA identifier was established.
ICD-10/ICD-11 and MeSH: there is no retrieved evidence of a THOC2-specific code. Use broader intellectual-developmental-disorder and genetic-syndrome coding as locally appropriate, without implying molecular specificity.

2. Etiology, risk, protection and gene–environment interaction

The primary cause is a germline pathogenic or likely pathogenic THOC2 variant, usually hemizygous in a male. Both maternally inherited X-linked variants and de novo variants occur; an affected female with a de novo missense variant demonstrates that disease is not male-exclusive. (kumar2018severeneurocognitiveand pages 1-3, kumar2018severeneurocognitiveand pages 6-8)

Established genetic risk factors are damaging missense substitutions and splice-altering variants that destabilize THOC2, reduce protein abundance or produce C-terminal truncation. Skewed X-chromosome inactivation appears to protect many heterozygous females: clinically unaffected mothers had reported skewing of approximately 94%, 98:2% or 99.9:0.1%. This is a plausible protective modifier rather than a quantified guarantee of nonpenetrance. (kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 26-27, kumar2018severeneurocognitiveand pages 8-10)

No environmental, infectious, dietary, occupational or lifestyle cause has been demonstrated. No protective diet, exposure, medication or genetic modifier other than the observed association with favorable X-inactivation has been validated. There are no established gene–environment interactions. Family history raises prior probability in inherited families but is not required because de novo disease occurs. (kumar2018severeneurocognitiveand pages 1-3, kumar2018severeneurocognitiveand pages 6-8)

3. Phenotypes

Core clinical spectrum

In the 2015 families, all affected males had intellectual disability ranging from borderline to severe. Frequently reported associated findings were speech delay, short stature, elevated BMI or adult-onset truncal obesity, seizures, tremor and gait disturbance. Truncal obesity was especially noted among older males in two of four families, suggesting an age-related feature rather than a universal congenital manifestation. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 3-5)

Among seven established individuals characterized in the 2018 series, all had at least moderate intellectual disability; 3/7 were non-verbal, 2/7 non-ambulatory, 4/7 had infantile hypotonia, 2/7 tremor, 4/7 behavioral problems, 1/7 autism spectrum disorder, 1/7 confirmed seizures and 1/7 suspected seizures. Low birth weight occurred in 3/7, microcephaly in 2/7 and short stature in 2/7. These are referral-cohort frequencies, not population estimates. (kumar2018severeneurocognitiveand pages 5-6)

Suggested HPO annotations include:

Intellectual disability—HP:0001249; global developmental delay—HP:0001263.
Speech delay—HP:0000750; absent speech—HP:0001344.
Infantile hypotonia—HP:0008947 or generalized hypotonia—HP:0001290.
Abnormal gait—HP:0001288; ataxic gait—HP:0002066; tremor—HP:0001337; nystagmus—HP:0000639.
Seizure—HP:0001250; epileptic encephalopathy—HP:0200134.
Autism—HP:0000717; behavioral abnormality—HP:0000708; hyperactivity—HP:0000752.
Microcephaly—HP:0000252; short stature—HP:0004322; low birth weight—HP:0001518; truncal obesity—HP:0001956.
Non-ambulation may be represented by inability to walk—HP:0002540.

Imaging and other manifestations

In 2018, MRI was normal in 3/5 examined individuals. Abnormal findings in 2/5 included cortical gyral abnormalities, corpus-callosum hypoplasia, reduced brainstem volume, ventricular dilation, delayed myelination and periventricular white-matter lesions. Earlier reports described mild ventriculomegaly, gliosis, inferior cerebellar-vermis dysplasia and cervical-cord compression in selected individuals. There is therefore no established pathognomonic imaging signature. (kumar2018severeneurocognitiveand pages 5-6, kumar2015thoc2mutationsimplicate pages 1-3)

Suggested HPO terms include hypoplasia of the corpus callosum (HP:0002079), ventriculomegaly (HP:0002119), delayed CNS myelination (HP:0002188) and abnormal cerebral white matter morphology (HP:0002500). Cerebellar-type signs may occur despite a structurally unremarkable cerebellum. (kumar2018severeneurocognitiveand pages 8-10)

Onset, course and quality of life

Onset is developmental and generally evident in infancy or childhood through hypotonia, delayed milestones, speech delay or cognitive impairment. Available cohorts do not define formal stages, annual progression or remission. Intellectual and adaptive impairments appear chronic and lifelong; adult truncal obesity may emerge later. Non-verbal and non-ambulatory status in some children indicates substantial effects on communication, mobility, education, caregiving needs and independence. No THOC2-specific EQ-5D, SF-36, PROMIS or caregiver-burden study was found. (kumar2018severeneurocognitiveand pages 5-6, kumar2018severeneurocognitiveand pages 3-5)

4. Genetic and molecular information

Causal gene and variant spectrum

THOC2 is the established causal gene. The 2015 study identified four segregating missense variants: c.937C>T (p.Leu313Phe), c.1313T>C (p.Leu438Pro), c.2399T>C (p.Ile800Thr), and c.3034T>C (p.Ser1012Pro). They affected conserved residues, were absent from more than 60,000 reference individuals in the then-current 1000 Genomes/ExAC datasets and produced a combined pedigree LOD score of 8.1. Two destabilized THOC2 and TREX partners. (kumar2015thoc2mutationsimplicate pages 1-3)

The 2018 expansion added established missense changes including p.Tyr517Cys, p.Thr696Ile, p.Gly713Asp and p.His1187Tyr, plus splice variants including c.4450-2A>G and c.3503+4A>C, which generated abnormal C-terminal products. p.Tyr517Cys shortened measured protein turnover from approximately eight hours for wild type to three hours. These variants were assessed as pathogenic or likely pathogenic using segregation, rarity, ACMG criteria and functional evidence. (kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 5-6, kumar2018severeneurocognitiveand pages 8-10)

Reported VUS, which must not be represented as confirmed causes, include p.Arg77Cys, p.Ser1108Leu, p.Arg1121Gly and p.Asn1261His. Their rarity, conservation and computational predictions were insufficient without stronger segregation or functional evidence. (kumar2018severeneurocognitiveand pages 10-11)

All reported disease variants are germline. No somatic THOC2 mechanism is implicated in this syndrome. The dominant molecular theme is partial loss of function or hypomorphism; complete loss is expected to be poorly tolerated because THOC2 is essential. Some truncated products may exert additional dominant-negative effects, but this is variant-specific and not a universal disease mechanism. (kumar2018severeneurocognitiveand pages 10-11, kumar2018severeneurocognitiveand pages 8-10)

No validated modifier gene, disease-specific methylation episignature, repeat expansion, aneuploidy or recurrent large chromosomal rearrangement was found. Historical reference-database absences should be rechecked in current gnomAD before clinical classification.

5. Environmental information

No toxin, radiation, pollution, occupation, smoking, alcohol, diet or exercise exposure is known to cause or materially modify THOC2-related intellectual disability. No bacterial, viral, fungal or parasitic trigger is implicated. Ordinary environmental and educational context may affect functional attainment, as in other developmental disabilities, but this is not a demonstrated molecular gene–environment interaction.

6. Mechanism and pathophysiology

Upstream molecular defect

THOC2 is the largest subunit of the conserved nuclear TREX complex, which links transcription, mRNA processing and export while helping preserve genome stability. Earlier cellular studies supported variant-dependent THOC2/TREX destabilization and disturbed RNA export. The 2024 work showed that a hypomorphic exon 37–38 deletion can leave bulk mRNA export relatively intact while profoundly disturbing R-loop and genome homeostasis. (kumar2015thoc2mutationsimplicate pages 1-3, bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2, bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16)

Current causal model

The best-supported chain is:

Pathogenic THOC2 variant → compromised THOC2/TREX function → unresolved RNA:DNA hybrid R-loops → replication/transcription-associated DNA damage → G2/M checkpoint disturbance and neural-stem-cell apoptosis → reduced or premature neural progenitor differentiation and altered cortical development → impaired neuronal migration, axon growth, dendritic-spine/synapse maturation and network activity → intellectual, speech and motor phenotypes. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9, bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11, bhattacharjee2024compromisedtranscriptionmrnaexport pages 13-14)

R-loop staining was RNase-H sensitive in mutant neural stem cells and patient fibroblasts. RNase H1 overexpression significantly reduced both R-loop burden and DNA damage (reported p<0.0001), providing experimental evidence that R-loops are upstream contributors rather than merely downstream markers. Mutant cells also showed elevated γ-H2AX, comet-assay damage, G2/M abnormalities and apoptosis. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16, bhattacharjee2024compromisedtranscriptionmrnaexport pages 13-14)

Cellular, anatomical and multi-omic consequences

The 2024 model showed reduced PAX6-positive cortical ventricular-zone thickness, premature neural-stem-cell differentiation, reduced cortical plate and corpus-callosum thickness, impaired migration, 32% shorter primary axons, fewer mature dendritic spines, reduced SYN1–PSD95 synaptic puncta and abnormal electrophysiological network activity. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9, bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11)

Embryonic day 18.5 showed the largest transcriptomic disruption, involving transcription, cell cycle, cell death and cognition-related genes. Dysregulated neurodevelopmental genes included SYNGAP1, HUWE1, SHANK3, DLG4, KDM5C and CTNND1. Proteomics identified 421 dysregulated proteins enriched for translation, peptide biosynthesis and mRNA-catabolic processes. No validated metabolomic, lipidomic, single-cell or spatial-transcriptomic signature has been reported. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9, bhattacharjee2024compromisedtranscriptionmrnaexport pages 13-14)

Suggested ontology terms:

GO biological process: mRNA export from nucleus (GO:0006406), RNA processing (GO:0006396), regulation of transcription by RNA polymerase II, DNA-damage response (GO:0006974), cell-cycle checkpoint signaling, apoptotic process (GO:0006915), neurogenesis (GO:0022008), neuron migration (GO:0001764), axon development (GO:0061564) and synapse organization (GO:0050808).
GO cellular component: nucleus (GO:0005634), nuclear speck, TREX complex, neuronal projection, dendritic spine and synapse.
Cell Ontology: neural stem cell (CL:0000047), radial glial cell (CL:0000681), neuron (CL:0000540), cortical neuron and hippocampal neuron where a more specific supported term is available.

Immune dysregulation, inflammation, metabolic disease and primary mitochondrial dysfunction are not established components.

7. Anatomical structures affected

The central nervous system is primary, particularly the developing cerebral cortex and hippocampal/cortical neuronal systems examined experimentally. The cortical ventricular zone, cortical plate, corpus callosum, axons, dendritic spines and synapses are implicated. Variable human MRI findings also involve cerebral white matter, brainstem, ventricles and occasionally cerebellar vermis. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9, bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11, kumar2018severeneurocognitiveand pages 5-6)

Suggested UBERON annotations include brain (UBERON:0000955), cerebral cortex (UBERON:0000956), hippocampus (UBERON:0002421), corpus callosum (UBERON:0002336), brainstem (UBERON:0002298), cerebellum (UBERON:0002037) and spinal cord (UBERON:0002240) where directly supported. No consistent lateralization has been reported.

At the subcellular level, the nucleus is central because THOC2/TREX controls transcription-coupled RNA processing/export and R-loop homeostasis; downstream effects involve axonal, dendritic and synaptic compartments. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16, bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11)

8. Temporal development

The disorder is congenital in genetic origin and pediatric in clinical recognition. Infantile hypotonia, low birth weight or microcephaly may be early findings; developmental, speech and cognitive abnormalities emerge as milestones are missed. Growth impairment can occur during childhood, while truncal obesity was particularly observed in older males. (kumar2018severeneurocognitiveand pages 5-6, kumar2018severeneurocognitiveand pages 3-5)

The 2024 model indicates a critical prenatal neurodevelopmental period: THOC2 was abundant at E14.5/E18.5, with marked transcriptomic disruption at E18.5, reduced progenitor-zone thickness and subsequent cortical/synaptic deficits. This supports early developmental vulnerability but does not establish a human therapeutic window. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9, bhattacharjee2024compromisedtranscriptionmrnaexport pages 11-13)

No relapsing-remitting pattern, spontaneous remission or defined end stage is known. Longitudinal natural-history cohorts are absent.

9. Inheritance and population

Inheritance is X-linked. Hemizygous males are predominantly affected, whereas heterozygous mothers are commonly unaffected, plausibly because of highly skewed X-inactivation. De novo disease can affect either sex, and a severely affected female with de novo p.Tyr517Cys was reported. Expressivity in males ranges from borderline ID to severe non-verbal/non-ambulatory disease. Formal penetrance, germline-mosaicism frequency, anticipation, founder effects, carrier frequency and consanguinity effects are unknown. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 8-10, kumar2018severeneurocognitiveand pages 6-8)

No incidence or prevalence estimate exists. The literature consists of a 2015 cohort of 20 affected people in four families and a small number of additional established cases in 2018. Cases arose from multiple countries, arguing against a known geographically restricted population, but the sample is too small for demographic conclusions. The observed male predominance reflects X-linked biology and ascertainment rather than a measured population sex ratio. (kumar2015thoc2mutationsimplicate pages 1-3, kumar2018severeneurocognitiveand pages 27-27)

10. Diagnostics

Clinical recognition and differential diagnosis

Suspect the disorder in a male with unexplained developmental delay/intellectual disability and speech impairment, especially when accompanied by hypotonia, abnormal gait, tremor/ataxia, seizures, short stature, microcephaly, truncal obesity or an X-linked pedigree. The phenotype is not sufficiently distinctive for clinical diagnosis alone. (kumar2015thoc2mutationsimplicate pages 3-4, kumar2015thoc2mutationsimplicate pages 1-3)

Important differential categories include other X-linked intellectual-developmental disorders; epileptic encephalopathies; cerebral-palsy-like genetic motor disorders; chromosomal copy-number disorders; metabolic causes of developmental delay; and other RNA-processing/TREX disorders, including THOC6-associated Beaulieu–Boycott–Innes syndrome. Distinction requires molecular testing.

Recommended testing strategy

Trio WES or WGS is the preferred broad approach for an undiagnosed neurodevelopmental disorder. Both were successful in published THOC2 cases. (kumar2018severeneurocognitiveand pages 5-6)
A comprehensive intellectual-disability/epilepsy panel that includes THOC2 is reasonable when sequencing depth and copy-number calling are adequate.
Confirm candidate variants and segregation by Sanger sequencing; establish de novo status with parental testing where possible. (kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 5-6)
For intronic or splice-region variants, perform patient RNA/cDNA analysis, RT-PCR or RNA sequencing. Published studies used cDNA PCR, RT-qPCR, western blotting and protein-stability assays to establish consequences. (kumar2018severeneurocognitiveand pages 6-8, kumar2018severeneurocognitiveand pages 3-5)
Interpret missense variants conservatively under ACMG/AMP criteria. Rarity and computational prediction alone do not convert a VUS into a diagnosis. (kumar2018severeneurocognitiveand pages 10-11)
CMA remains useful for unexplained developmental disability or suspected CNV, but it will usually miss small THOC2 sequence variants. Karyotype/FISH, mitochondrial testing and repeat-expansion assays are not THOC2-specific first-line tests unless the broader phenotype indicates them.

There is no validated biochemical, circulating, proteomic or imaging biomarker. MRI, EEG, vision assessment and growth/endocrine testing are phenotype-directed rather than diagnostic. No newborn-screening assay or standardized disease-specific clinical criteria exist.

11. Outcome and prognosis

Published cases demonstrate survival through childhood and into adulthood, but no five- or ten-year survival estimates, life-expectancy analyses or disease-specific mortality rates are available. Complete THOC2 loss is predicted to be poorly tolerated, whereas observed hypomorphic variants are compatible with survival. (kumar2018severeneurocognitiveand pages 10-11)

Morbidity is principally lifelong neurodevelopmental disability. Prognosis is variable: some individuals have borderline or mild ID, while others are non-verbal, non-ambulatory or have epileptic encephalopathy and cortical visual impairment. Motor dysfunction, seizures, behavioral abnormalities and growth problems increase care burden. No validated molecular prognostic biomarker or genotype-based outcome calculator exists. (kumar2018severeneurocognitiveand pages 5-6, kumar2015thoc2mutationsimplicate pages 1-3)

12. Treatment and current applications

There is no approved THOC2-specific disease-modifying therapy, gene therapy, RNA therapy, cell therapy or targeted pharmacotherapy, and the clinical-trial search found no relevant disease-specific interventional trial. No response-rate or adverse-event series exists.

Current real-world management is multidisciplinary and phenotype-directed:

early developmental intervention, special education and neuropsychological assessment;
speech-language therapy, including augmentative and alternative communication for non-verbal individuals;
physical and occupational therapy for hypotonia, gait, coordination and adaptive skills;
standard antiseizure therapy guided by seizure type and EEG;
behavioral, autism and psychiatric assessment and treatment;
nutrition, weight and growth surveillance;
ophthalmology for visual impairment and audiology as clinically indicated;
brain/spine MRI, neurology or orthopedic evaluation when focal signs, gait deterioration or suspected structural disease are present;
endocrine evaluation for poor growth. One reported boy with growth-hormone deficiency received replacement, but this is treatment of a documented comorbidity, not THOC2-directed therapy. (kumar2018severeneurocognitiveand pages 5-6, kumar2015thoc2mutationsimplicate pages 3-4)

Potential NCIt intervention concepts include Genetic Counseling, Physical Therapy, Occupational Therapy, Speech Therapy, Special Education, Anticonvulsant Therapy and Growth Hormone Replacement Therapy. Exact NCIt codes should be resolved against the current NCIt release.

Experimentally, RNase H1 rescue of R-loops provides target-validation evidence but is not a human therapy. Translation would require safe, cell- and developmentally appropriate correction of R-loop homeostasis without disrupting essential RNA biology. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16)

13. Prevention

There is no lifestyle, vaccine, environmental or drug-based primary prevention. Primary genetic prevention options require identification of a familial pathogenic variant and nondirective counseling. These may include carrier testing, cascade testing, prenatal diagnosis and preimplantation genetic testing for monogenic disease. Because de novo variants occur, a negative family history does not eliminate risk. Residual recurrence risk from parental germline mosaicism should be discussed even when parental blood testing is negative, although its THOC2-specific frequency is unknown. (kumar2018severeneurocognitiveand pages 1-3, kumar2018severeneurocognitiveand pages 6-8)

Secondary prevention consists of prompt genomic diagnosis and early developmental, communication, seizure, vision, mobility and growth interventions. Tertiary prevention includes seizure control, contracture/fall prevention, weight management and support for communication and adaptive functioning. Population newborn or carrier screening is not currently established.

14. Other species and natural disease

No naturally occurring veterinary THOC2 syndrome, breed predisposition, zoonotic potential or cross-species transmission is established. The disorder is genetic and non-infectious. THOC2 orthologs are evolutionarily conserved, consistent with the essential role of TREX-mediated RNA biology. Ortholog-specific NCBI Gene and NCBI Taxonomy identifiers should be retrieved directly before database ingestion.

Relevant experimental species include Mus musculus (NCBI Taxonomy 10090), Danio rerio (7955) and Drosophila melanogaster (7227). Zebrafish Thoc2 is essential for embryonic development, and depletion in Drosophila S2 cells impairs mRNA export; these findings support conserved essentiality but do not constitute naturally occurring animal disease. (kumar2015thoc2mutationsimplicate pages 1-3, bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2)

15. Model organisms

Mouse

The strongest model is the hemizygous Thoc2Δ/Y hypomorphic mouse carrying an exon 37–38 deletion modeled on a human variant. It recapitulated smaller size/weight and deficits in spatial learning, working memory, fine motor control and sensorimotor function. Birth rate was reduced by approximately 33%. Morris water maze, Barnes maze, Y-maze, beam-walking and pasta-handling tests demonstrated cognitive and motor phenotypes; hyperactivity and reduced anxiety-like behavior were also reported. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 11-13, bhattacharjee2024compromisedtranscriptionmrnaexport pages 4-5)

The model reproduced developmental pathology—R-loop accumulation, DNA damage, neural-stem-cell apoptosis, reduced cortical structures and impaired neuronal maturation—and is suitable for studying R-loop rescue, developmental timing and synaptic consequences. Its chief limitation is that one hypomorphic deletion cannot represent every missense or splice variant, female X-inactivation, or the full human phenotypic range. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9, bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11, bhattacharjee2024compromisedtranscriptionmrnaexport pages 13-14)

Cellular models

Patient dermal fibroblasts reproduced R-loop accumulation and comet-assay DNA damage. Mouse neural stem cells, neurospheres and primary cortical/hippocampal neurons modeled progenitor survival, differentiation, migration, axonal development, synapses and electrophysiology. HEK293T and patient-derived cells were used for protein localization, abundance and cycloheximide-chase assays. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16, bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11, kumar2018severeneurocognitiveand pages 5-6)

Zebrafish and Drosophila

Zebrafish studies support embryonic essentiality, while Drosophila S2-cell depletion supports conserved THO/TREX-dependent mRNA export. These are useful for rapid functional testing but do not reproduce the complete human syndrome. (kumar2015thoc2mutationsimplicate pages 1-3, bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2)

No disease-specific rat, organoid, human iPSC-neuron, CRISPR-screen, single-cell or spatial-transcriptomic model was identified in the retrieved literature.

Knowledge gaps and expert assessment

The 2024 work materially changes current understanding: THOC2 disease should not be represented solely as a generic “mRNA-export defect.” At least for the modeled hypomorphic deletion, defective R-loop resolution and genome stability are central and experimentally rescuable upstream events, while overt bulk nuclear mRNA retention was not observed. The authors themselves identify nuclear/cytoplasmic RNA sequencing as a needed next step to determine whether selected transcripts nevertheless have export defects. (bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16, bhattacharjee2024compromisedtranscriptionmrnaexport pages 4-5)

For knowledge-base curation, clinical frequencies should be labeled small-cohort observations, not population frequencies. VUS must remain separate from established variants. Likewise, mouse rescue data should be annotated as preclinical target-validation evidence rather than treatment evidence. Highest-priority research needs are an international natural-history registry, systematic female-carrier phenotyping and X-inactivation studies, current ClinVar/gnomAD aggregation, variant-specific functional assays, patient iPSC-derived neural models, transcript-compartment profiling, and development of safe R-loop/genome-stability biomarkers and interventions.

References

(kumar2015thoc2mutationsimplicate pages 1-3): Raman Kumar, Mark A. Corbett, Bregje W.M. van Bon, Joshua A. Woenig, Lloyd Weir, Evelyn Douglas, Kathryn L. Friend, Alison Gardner, Marie Shaw, Lachlan A. Jolly, Chuan Tan, Matthew F. Hunter, Anna Hackett, Michael Field, Elizabeth E. Palmer, Melanie Leffler, Carolyn Rogers, Jackie Boyle, Melanie Bienek, Corinna Jensen, Griet Van Buggenhout, Hilde Van Esch, Katrin Hoffmann, Martine Raynaud, Huiying Zhao, Robin Reed, Hao Hu, Stefan A. Haas, Eric Haan, Vera M. Kalscheuer, and Jozef Gecz. Thoc2 mutations implicate mrna-export pathway in x-linked intellectual disability. American journal of human genetics, 97 2:302-10, Aug 2015. URL: https://doi.org/10.1016/j.ajhg.2015.05.021, doi:10.1016/j.ajhg.2015.05.021. This article has 93 citations and is from a highest quality peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 1-3): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(bhattacharjee2024compromisedtranscriptionmrnaexport pages 1-2): Rudrarup Bhattacharjee, Lachlan A. Jolly, Mark A. Corbett, Ing Chee Wee, Sushma R. Rao, Alison E. Gardner, Tarin Ritchie, Eline J. H. van Hugte, Ummi Ciptasari, Sandra Piltz, Jacqueline E. Noll, Nazzmer Nazri, Clare L. van Eyk, Melissa White, Dani Fornarino, Cathryn Poulton, Gareth Baynam, Lyndsey E. Collins-Praino, Marten F. Snel, Nael Nadif Kasri, Kim M. Hemsley, Paul Q. Thomas, Raman Kumar, and Jozef Gecz. Compromised transcription-mrna export factor thoc2 causes r-loop accumulation, dna damage and adverse neurodevelopment. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45121-5, doi:10.1038/s41467-024-45121-5. This article has 16 citations and is from a highest quality peer-reviewed journal.
(bhattacharjee2024compromisedtranscriptionmrnaexport pages 13-14): Rudrarup Bhattacharjee, Lachlan A. Jolly, Mark A. Corbett, Ing Chee Wee, Sushma R. Rao, Alison E. Gardner, Tarin Ritchie, Eline J. H. van Hugte, Ummi Ciptasari, Sandra Piltz, Jacqueline E. Noll, Nazzmer Nazri, Clare L. van Eyk, Melissa White, Dani Fornarino, Cathryn Poulton, Gareth Baynam, Lyndsey E. Collins-Praino, Marten F. Snel, Nael Nadif Kasri, Kim M. Hemsley, Paul Q. Thomas, Raman Kumar, and Jozef Gecz. Compromised transcription-mrna export factor thoc2 causes r-loop accumulation, dna damage and adverse neurodevelopment. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45121-5, doi:10.1038/s41467-024-45121-5. This article has 16 citations and is from a highest quality peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 3-5): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 6-8): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 8-10): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 26-27): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 5-6): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 10-11): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(bhattacharjee2024compromisedtranscriptionmrnaexport pages 6-9): Rudrarup Bhattacharjee, Lachlan A. Jolly, Mark A. Corbett, Ing Chee Wee, Sushma R. Rao, Alison E. Gardner, Tarin Ritchie, Eline J. H. van Hugte, Ummi Ciptasari, Sandra Piltz, Jacqueline E. Noll, Nazzmer Nazri, Clare L. van Eyk, Melissa White, Dani Fornarino, Cathryn Poulton, Gareth Baynam, Lyndsey E. Collins-Praino, Marten F. Snel, Nael Nadif Kasri, Kim M. Hemsley, Paul Q. Thomas, Raman Kumar, and Jozef Gecz. Compromised transcription-mrna export factor thoc2 causes r-loop accumulation, dna damage and adverse neurodevelopment. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45121-5, doi:10.1038/s41467-024-45121-5. This article has 16 citations and is from a highest quality peer-reviewed journal.
(bhattacharjee2024compromisedtranscriptionmrnaexport pages 14-16): Rudrarup Bhattacharjee, Lachlan A. Jolly, Mark A. Corbett, Ing Chee Wee, Sushma R. Rao, Alison E. Gardner, Tarin Ritchie, Eline J. H. van Hugte, Ummi Ciptasari, Sandra Piltz, Jacqueline E. Noll, Nazzmer Nazri, Clare L. van Eyk, Melissa White, Dani Fornarino, Cathryn Poulton, Gareth Baynam, Lyndsey E. Collins-Praino, Marten F. Snel, Nael Nadif Kasri, Kim M. Hemsley, Paul Q. Thomas, Raman Kumar, and Jozef Gecz. Compromised transcription-mrna export factor thoc2 causes r-loop accumulation, dna damage and adverse neurodevelopment. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45121-5, doi:10.1038/s41467-024-45121-5. This article has 16 citations and is from a highest quality peer-reviewed journal.
(bhattacharjee2024compromisedtranscriptionmrnaexport pages 10-11): Rudrarup Bhattacharjee, Lachlan A. Jolly, Mark A. Corbett, Ing Chee Wee, Sushma R. Rao, Alison E. Gardner, Tarin Ritchie, Eline J. H. van Hugte, Ummi Ciptasari, Sandra Piltz, Jacqueline E. Noll, Nazzmer Nazri, Clare L. van Eyk, Melissa White, Dani Fornarino, Cathryn Poulton, Gareth Baynam, Lyndsey E. Collins-Praino, Marten F. Snel, Nael Nadif Kasri, Kim M. Hemsley, Paul Q. Thomas, Raman Kumar, and Jozef Gecz. Compromised transcription-mrna export factor thoc2 causes r-loop accumulation, dna damage and adverse neurodevelopment. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45121-5, doi:10.1038/s41467-024-45121-5. This article has 16 citations and is from a highest quality peer-reviewed journal.
(bhattacharjee2024compromisedtranscriptionmrnaexport pages 4-5): Rudrarup Bhattacharjee, Lachlan A. Jolly, Mark A. Corbett, Ing Chee Wee, Sushma R. Rao, Alison E. Gardner, Tarin Ritchie, Eline J. H. van Hugte, Ummi Ciptasari, Sandra Piltz, Jacqueline E. Noll, Nazzmer Nazri, Clare L. van Eyk, Melissa White, Dani Fornarino, Cathryn Poulton, Gareth Baynam, Lyndsey E. Collins-Praino, Marten F. Snel, Nael Nadif Kasri, Kim M. Hemsley, Paul Q. Thomas, Raman Kumar, and Jozef Gecz. Compromised transcription-mrna export factor thoc2 causes r-loop accumulation, dna damage and adverse neurodevelopment. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45121-5, doi:10.1038/s41467-024-45121-5. This article has 16 citations and is from a highest quality peer-reviewed journal.
(bhattacharjee2024compromisedtranscriptionmrnaexport pages 11-13): Rudrarup Bhattacharjee, Lachlan A. Jolly, Mark A. Corbett, Ing Chee Wee, Sushma R. Rao, Alison E. Gardner, Tarin Ritchie, Eline J. H. van Hugte, Ummi Ciptasari, Sandra Piltz, Jacqueline E. Noll, Nazzmer Nazri, Clare L. van Eyk, Melissa White, Dani Fornarino, Cathryn Poulton, Gareth Baynam, Lyndsey E. Collins-Praino, Marten F. Snel, Nael Nadif Kasri, Kim M. Hemsley, Paul Q. Thomas, Raman Kumar, and Jozef Gecz. Compromised transcription-mrna export factor thoc2 causes r-loop accumulation, dna damage and adverse neurodevelopment. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45121-5, doi:10.1038/s41467-024-45121-5. This article has 16 citations and is from a highest quality peer-reviewed journal.
(kumar2018severeneurocognitiveand pages 27-27): Raman Kumar, Alison Gardner, Claire C. Homan, Evelyn Douglas, Heather Mefford, Dagmar Wieczorek, Hermann-Josef Lüdecke, Zornitza Stark, Simon Sadedin, Catherine Bearce Nowak, Jessica Douglas, Gretchen Parsons, Paul Mark, Lourdes Loidi, Gail E. Herman, Theresa Mihalic Mosher, Meredith K. Gillespie, Lauren Brady, Mark Tarnopolsky, Irene Madrigal, Jesús Eiris, Laura Domènech Salgado, Raquel Rabionet, Tim M. Strom, Naoko Ishihara, Hidehito Inagaki, Hiroki Kurahashi, Tracy Dudding-Byth, Elizabeth E. Palmer, Michael Field, and Jozef Gecz. Severe neurocognitive and growth disorders due to variation in thoc2, an essential component of nuclear mrna export machinery. Human Mutation, 39:1126-1138, Jun 2018. URL: https://doi.org/10.1002/humu.23557, doi:10.1002/humu.23557. This article has 31 citations and is from a domain leading peer-reviewed journal.
(kumar2015thoc2mutationsimplicate pages 3-4): Raman Kumar, Mark A. Corbett, Bregje W.M. van Bon, Joshua A. Woenig, Lloyd Weir, Evelyn Douglas, Kathryn L. Friend, Alison Gardner, Marie Shaw, Lachlan A. Jolly, Chuan Tan, Matthew F. Hunter, Anna Hackett, Michael Field, Elizabeth E. Palmer, Melanie Leffler, Carolyn Rogers, Jackie Boyle, Melanie Bienek, Corinna Jensen, Griet Van Buggenhout, Hilde Van Esch, Katrin Hoffmann, Martine Raynaud, Huiying Zhao, Robin Reed, Hao Hu, Stefan A. Haas, Eric Haan, Vera M. Kalscheuer, and Jozef Gecz. Thoc2 mutations implicate mrna-export pathway in x-linked intellectual disability. American journal of human genetics, 97 2:302-10, Aug 2015. URL: https://doi.org/10.1016/j.ajhg.2015.05.021, doi:10.1016/j.ajhg.2015.05.021. This article has 93 citations and is from a highest quality peer-reviewed journal.

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THOC2-Related Intellectual Disability: Disease Characteristics Report

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1. Disease information

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2. Etiology, risk, protection and gene–environment interaction

3. Phenotypes

Core clinical spectrum

Imaging and other manifestations

Onset, course and quality of life

4. Genetic and molecular information

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