Guillouet-Gordon syndrome (GGNS) is a rare autosomal recessive multiple congenital anomalies-intellectual disability syndrome caused by biallelic variants in MED16, a subunit of the tail module of the Mediator transcriptional coactivator complex. First described in 2025, it is the most recently delineated MEDopathy. Intellectual disability, speech delay, and/or motor delay of variable severity are constant, associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot); visual impairment, deafness, and MRI abnormalities are also frequent. Most disease-causing variants cause nuclear-to-cytoplasmic mislocalization of MED16, and med16 zebrafish and Med16 knockout mice confirm a conserved developmental requirement.
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name: Guillouet-Gordon Syndrome
creation_date: '2026-07-31T00:00:00Z'
category: Mendelian
synonyms:
- GGNS
- MED16-related MEDopathy
- MED16-related multiple congenital anomalies-intellectual disability syndrome
description: >
Guillouet-Gordon syndrome (GGNS) is a rare autosomal recessive multiple congenital
anomalies-intellectual disability syndrome caused by biallelic variants in MED16, a subunit
of the tail module of the Mediator transcriptional coactivator complex. First described in
2025, it is the most recently delineated MEDopathy. Intellectual disability, speech delay,
and/or motor delay of variable severity are constant, associated with variable combinations
of craniofacial defects (micro/retrognathia, cleft palate, preauricular tags), anomalies of
the extremities, and heart defects (predominantly tetralogy of Fallot); visual impairment,
deafness, and MRI abnormalities are also frequent. Most disease-causing variants cause
nuclear-to-cytoplasmic mislocalization of MED16, and med16 zebrafish and Med16 knockout mice
confirm a conserved developmental requirement.
disease_term:
preferred_term: Guillouet-Gordon syndrome
term:
id: MONDO:0979227
label: Guillouet-Gordon syndrome
parents:
- Autosomal recessive intellectual disability
- Neurodevelopmental disorder
- Mediator complex-associated disorder
classifications:
harrisons_chapter:
- classification_value: GENETICS_ENVIRONMENT_DISEASE
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Overall, we describe an autosomal recessive MCAs-intellectual disability MEDopathy"
explanation: Supports classification as a heritable autosomal recessive genetic disorder.
- classification_value: NEUROLOGIC
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Supports classification as a neurodevelopmental / neurologic multiple-congenital-anomaly disorder.
prevalence:
- population: Worldwide
measure_type: CASES_IN_LITERATURE
prevalence_class: BELOW_1_IN_1000000
notes: >-
Ultra-rare. The defining 2025 cohort comprised 25 individuals from 18 families. No
population-based prevalence estimate is available.
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we report the identification of 25 individuals from 18 families with bi-allelic MED16 variants who have a multiple congenital anomalies (MCAs)-intellectual disability syndrome."
explanation: Documents the defining cohort size establishing MED16 as an ultra-rare disease gene.
pathophysiology:
- name: MED16 Mediator mislocalization
description: >
MED16 is a subunit of the tail module of the Mediator complex. Most disease-causing
variants cause mislocalization of MED16 from the nucleus to the cytoplasm, and 3D modeling
indicates a destabilizing effect on protein structural elements, disrupting
Mediator-dependent transcription of developmental gene-expression programs. Homozygous
med16 zebrafish and Med16 knockout mice confirm a conserved developmental requirement.
MED16 belongs to the group of Mediator complex-associated disease genes.
genes:
- preferred_term: MED16
term:
id: hgnc:17556
label: MED16
biological_processes:
- preferred_term: transcription by RNA polymerase II
term:
id: GO:0006366
label: transcription by RNA polymerase II
- preferred_term: regulation of gene expression
term:
id: GO:0010468
label: regulation of gene expression
modifier: DYSREGULATED
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Immunofluorescence assays demonstrated protein mislocalization from the nucleus to the cytoplasm for 16 of the 17 variants studied."
explanation: Establishes nuclear-to-cytoplasmic mislocalization as the disease mechanism for most MED16 variants.
downstream:
- target: Multisystem developmental dysregulation
description: >-
MED16 mislocalization disrupts Mediator-dependent transcription across neurodevelopmental,
craniofacial, cardiac, and limb developmental programs.
- name: Multisystem developmental dysregulation
description: >
Downstream of MED16 mislocalization, developmental gene-expression programs are dysregulated
across multiple systems, producing intellectual disability, speech and motor delay,
craniofacial defects (micro/retrognathia, cleft palate, preauricular tags), extremity
anomalies, congenital heart defects (predominantly tetralogy of Fallot), visual impairment,
and deafness.
cell_types:
- preferred_term: neuron
term:
id: CL:0000540
label: neuron
biological_processes:
- preferred_term: regulation of neuron differentiation
term:
id: GO:0045664
label: regulation of neuron differentiation
modifier: DYSREGULATED
- preferred_term: heart morphogenesis
term:
id: GO:0003007
label: heart morphogenesis
modifier: DYSREGULATED
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Documents the multisystem developmental phenotype downstream of MED16 dysfunction.
downstream:
- target: Intellectual disability
description: Disrupted neuronal developmental programs contribute to intellectual disability.
- target: Cleft palate
description: Disrupted craniofacial developmental programs contribute to cleft palate and other craniofacial defects.
- target: Tetralogy of Fallot
description: Disrupted cardiac developmental programs contribute to congenital heart defects, predominantly tetralogy of Fallot.
- target: Limb anomalies
description: Disrupted limb developmental programs contribute to anomalies of the extremities.
phenotypes:
- category: Clinical
name: Intellectual disability
# frequency intentionally omitted: the source states the ID/speech/motor triad
# was "constant" as an "and/or" group, not per-feature; no defensible band.
description: >
Intellectual disability of variable severity is a constant feature.
phenotype_term:
preferred_term: Intellectual disability
term:
id: HP:0001249
label: Intellectual disability
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Documents intellectual disability as a constant feature.
- category: Clinical
name: Speech delay
# frequency intentionally omitted: snippet says "constant" (an "and/or" group
# claim), which does not support FREQUENT or any other per-feature band.
description: >
Speech delay of variable severity is a constant developmental feature.
phenotype_term:
preferred_term: Delayed speech and language development
term:
id: HP:0000750
label: Delayed speech and language development
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Documents speech delay as a constant developmental feature.
- category: Clinical
name: Motor delay
# frequency intentionally omitted: snippet says "constant" (an "and/or" group
# claim), which does not support FREQUENT or any other per-feature band.
description: >
Motor delay of variable severity is a constant developmental feature.
phenotype_term:
preferred_term: Motor delay
term:
id: HP:0001270
label: Motor delay
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Documents motor delay as a constant developmental feature.
- category: Craniofacial
name: Cleft palate
# frequency intentionally omitted: the source reports only "variable
# combinations" of craniofacial defects, giving no per-feature rate.
description: >
Cleft palate is among the variable craniofacial defects, alongside micro/retrognathia and
preauricular tags.
phenotype_term:
preferred_term: Cleft palate
term:
id: HP:0000175
label: Cleft palate
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Documents cleft palate among the variable craniofacial defects.
- category: Cardiovascular
name: Tetralogy of Fallot
# frequency intentionally omitted: "predominantly tetralogy of Fallot" ranks it
# among heart defects but gives no rate across the cohort.
description: >
Congenital heart defects, predominantly tetralogy of Fallot, occur in a subset of individuals.
phenotype_term:
preferred_term: Tetralogy of Fallot
term:
id: HP:0001636
label: Tetralogy of Fallot
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Documents tetralogy of Fallot as the predominant congenital heart defect.
- category: Skeletal
name: Limb anomalies
# frequency intentionally omitted: the source reports only "variable
# combinations" including extremity anomalies, giving no per-feature rate.
description: >
Anomalies of the extremities are part of the variable multiple-congenital-anomaly spectrum.
phenotype_term:
preferred_term: Limb anomalies
term:
id: HP:0002813
label: Abnormal limb bone morphology
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot)."
explanation: Documents anomalies of the extremities as part of the spectrum.
- category: Ophthalmologic
name: Visual impairment
frequency: FREQUENT
description: >
Visual impairment is a frequent feature.
phenotype_term:
preferred_term: Visual impairment
term:
id: HP:0000505
label: Visual impairment
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Visual impairment, deafness, and magnetic resonance imaging (MRI) abnormalities were also frequent."
explanation: Documents visual impairment as a frequent feature.
- category: Audiologic
name: Deafness
frequency: FREQUENT
description: >
Deafness is a frequent feature.
phenotype_term:
preferred_term: Hearing impairment
term:
id: HP:0000365
label: Hearing impairment
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Visual impairment, deafness, and magnetic resonance imaging (MRI) abnormalities were also frequent."
explanation: Documents deafness as a frequent feature.
genetic:
- name: MED16 biallelic variants
association: Causative
gene_term:
preferred_term: MED16
term:
id: hgnc:17556
label: MED16
inheritance:
- name: Autosomal Recessive
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Overall, we describe an autosomal recessive MCAs-intellectual disability MEDopathy"
explanation: Bi-allelic MED16 variants across many families support autosomal recessive inheritance.
features: >
Biallelic protein-truncating and missense/in-frame-duplication variants; most cause
nuclear-to-cytoplasmic mislocalization of MED16.
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we report the identification of 25 individuals from 18 families with bi-allelic MED16 variants who have a multiple congenital anomalies (MCAs)-intellectual disability syndrome."
explanation: Establishes the biallelic MED16 gene-disease relationship in a large multi-family cohort.
treatments:
- name: Supportive Care
description: >
Multidisciplinary supportive care including developmental therapies, cardiac and
craniofacial surgical management, and ophthalmologic and audiologic management as needed.
treatment_term:
preferred_term: Supportive Care
term:
id: NCIT:C15747
label: Supportive Care
- name: Genetic Counseling
description: >
Genetic counseling is recommended given the autosomal recessive inheritance, with carrier
testing for at-risk relatives.
treatment_term:
preferred_term: Genetic Counseling
term:
id: NCIT:C15240
label: Genetic Counseling
evidence:
- reference: PMID:40081376
reference_title: "Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Overall, we describe an autosomal recessive MCAs-intellectual disability MEDopathy"
explanation: The autosomal recessive basis established here warrants carrier and recurrence-risk counseling.