Corpus callosum agenesis-intellectual disability-coloboma-micrognathia syndrome (Graham-Cox syndrome; X-linked syndromic intellectual disability 28, MRXS28) is an ultra-rare X-linked recessive multiple congenital anomalies-intellectual disability syndrome. It was delineated in two brothers with the recurrent pattern of ocular coloboma (iris and optic nerve), facial dysmorphism (high forehead, severe retrognathia/micrognathia, low-set cupped ears), intellectual disability, agenesis of the corpus callosum, sensorineural hearing loss, skeletal anomalies (pectus excavatum, scoliosis) and short stature. The affected brothers carried adjacent variants in the 5' regulatory region of IGBP1 (the Alpha 4 gene) at Xq13. IGBP1/Alpha 4 is a regulatory subunit of protein phosphatase 2A (PP2A) that interacts with MID1, the E3 ubiquitin-ligase product of the gene mutated in X-linked Opitz GBBB syndrome, and the disorder shows clinical overlap with Opitz GBBB syndrome.
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name: Corpus Callosum Agenesis-Intellectual Disability-Coloboma-Micrognathia Syndrome
category: Mendelian
creation_date: "2026-07-30T00:00:00Z"
synonyms:
- Graham-Cox syndrome
- MRXS28
- Intellectual disability, X-linked, syndromic 28
- Mental retardation, X-linked, syndromic 28
- Agenesis of the corpus callosum-intellectual disability-coloboma-micrognathia syndrome
- Corpus callosum, agenesis of, with impaired intellectual development, ocular coloboma and micrognathia, X-linked recessive
description: >
Corpus callosum agenesis-intellectual disability-coloboma-micrognathia
syndrome (Graham-Cox syndrome; X-linked syndromic intellectual disability 28,
MRXS28) is an ultra-rare X-linked recessive multiple congenital
anomalies-intellectual disability syndrome. It was delineated in two brothers
with the recurrent pattern of ocular coloboma (iris and optic nerve), facial
dysmorphism (high forehead, severe retrognathia/micrognathia, low-set cupped
ears), intellectual disability, agenesis of the corpus callosum, sensorineural
hearing loss, skeletal anomalies (pectus excavatum, scoliosis) and short
stature. The affected brothers carried adjacent variants in the 5' regulatory
region of IGBP1 (the Alpha 4 gene) at Xq13. IGBP1/Alpha 4 is a regulatory
subunit of protein phosphatase 2A (PP2A) that interacts with MID1, the E3
ubiquitin-ligase product of the gene mutated in X-linked Opitz GBBB syndrome,
and the disorder shows clinical overlap with Opitz GBBB syndrome.
disease_term:
preferred_term: Corpus callosum agenesis-intellectual disability-coloboma-micrognathia syndrome
term:
id: MONDO:0010333
label: corpus callosum agenesis-intellectual disability-coloboma-micrognathia syndrome
parents:
- X-linked syndromic intellectual disability
- Disorder of development or morphogenesis
mappings:
mondo_mappings:
- term:
id: MONDO:0010333
label: corpus callosum agenesis-intellectual disability-coloboma-micrognathia syndrome
mapping_predicate: skos:exactMatch
mapping_source: OMIM:300472
mapping_justification: >
MONDO:0010333 lists OMIM:300472 (MRXS28) and Orphanet:52055 (Graham-Cox
syndrome) as exact cross-references for this X-linked syndromic
intellectual disability.
inheritance:
- name: X-linked recessive inheritance
description: >
The disorder segregated in an X-linked recessive pattern in the two affected
brothers, with the causative IGBP1 (Alpha 4) locus at Xq13. It is cataloged
in OMIM as X-linked syndromic intellectual disability 28 (MRXS28).
inheritance_term:
preferred_term: X-linked recessive inheritance
term:
id: HP:0001419
label: X-linked recessive inheritance
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "in both we have identified adjacent alterations (-57delT and T-55A) in the Alpha 4 gene located within this interval"
explanation: The two affected brothers share variants at the X-linked Alpha 4 (IGBP1) locus, consistent with X-linked recessive inheritance.
prevalence:
- population: Worldwide
measure_type: CASES_IN_LITERATURE
prevalence_class: NOT_YET_DOCUMENTED
notes: >-
No population prevalence or incidence estimate exists. The syndrome has been
reported in a single family (two affected brothers) in the original 2003
description, with no independently published second family identified. Curated
as cases-in-literature / not-yet-documented; no numeric rate is asserted.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We describe two brothers with a unique pattern of malformations"
explanation: The defining report describes a single family of two affected brothers, the only cases documented in the literature.
mechanistic_hypotheses:
- hypothesis_group_id: igbp1_pp2a_dosage_developmental_mechanism
hypothesis_label: IGBP1/Alpha 4 dosage dysregulation of PP2A as the developmental mechanism
status: EMERGING
description: >-
The proposed disease mechanism is that the 5'-regulatory IGBP1 (Alpha 4)
variants alter Alpha 4 protein dosage (via changed translational efficiency,
mRNA stability, or splicing), perturbing PP2A-regulated dephosphorylation
during embryonic midline and craniofacial development. Because Alpha 4 is
itself regulated by MID1 - the E3 ubiquitin ligase mutated in the
phenotypically overlapping X-linked Opitz GBBB syndrome - dysregulated Alpha 4
dosage is proposed as a shared mechanistic node for the callosal, ocular, and
craniofacial malformations. This remains a hypothesis stated in the primary
literature: no knock-in mouse or patient-cell functional confirmation of the
specific variants has been reported, and the IGBP1-XLID gene association
itself has been flagged as needing replication.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Altered expression of Alpha 4, through either a change in translational efficiency, mRNA stability or splicing, could explain the clinical phenotype in these boys and the phenotypic overlap with Opitz GBBB syndrome"
explanation: The primary report frames the Alpha 4 dosage-dysregulation mechanism as a hypothesis, consistent with an EMERGING status.
pathophysiology:
- name: IGBP1 5'-Regulatory Variants
biological_scale: MOLECULAR
description: >
The two affected brothers carried adjacent nucleotide changes (-57delT and
T-55A) in the 5' regulatory region of IGBP1 (the Alpha 4 gene) at Xq13, not
present in 410 control chromosomes. As non-coding regulatory variants they
are proposed to act on IGBP1 expression rather than to alter Alpha 4 protein
structure.
genes:
- preferred_term: IGBP1
term:
id: hgnc:5461
label: IGBP1
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "in both we have identified adjacent alterations (-57delT and T-55A) in the Alpha 4 gene located within this interval"
explanation: Identifies the adjacent 5'-regulatory IGBP1 (Alpha 4) variants shared by the two affected brothers.
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The double nucleotide change identified in this family was not observed in 410 control chromosomes, suggesting that it may be a pathogenetic change"
explanation: Absence from 410 control chromosomes supports pathogenicity of the regulatory variants.
downstream:
- target: Altered Alpha 4 (IGBP1) Protein Dosage
description: >
The 5'-regulatory variants are proposed to change IGBP1 expression through
altered translational efficiency, mRNA stability, or splicing, shifting
Alpha 4 protein dosage.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
hypothesis_groups:
- igbp1_pp2a_dosage_developmental_mechanism
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Altered expression of Alpha 4, through either a change in translational efficiency, mRNA stability or splicing"
explanation: The authors propose the regulatory variants change Alpha 4 expression/dosage.
- name: Altered Alpha 4 (IGBP1) Protein Dosage
biological_scale: MOLECULAR
description: >
Changed Alpha 4 (IGBP1) protein dosage resulting from the regulatory
variants. Alpha 4 is a regulatory subunit of protein phosphatase 2A (PP2A),
so altered Alpha 4 levels are proposed to feed forward into PP2A regulation.
genes:
- preferred_term: IGBP1
term:
id: hgnc:5461
label: IGBP1
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Alpha 4 is a regulatory subunit of the major cellular phosphatase, PP2A, that has recently been shown to interact with MID1, the product of the gene mutated in X-linked Opitz GBBB syndrome"
explanation: Establishes Alpha 4 (IGBP1) as a PP2A regulatory subunit whose dosage change would act through PP2A.
downstream:
- target: Dysregulated PP2A Holoenzyme Dephosphorylation
description: >
Because Alpha 4 binds and modulates the PP2A catalytic subunit, altered
Alpha 4 dosage is proposed to dysregulate PP2A-dependent dephosphorylation.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
hypothesis_groups:
- igbp1_pp2a_dosage_developmental_mechanism
evidence:
- reference: PMID:9792806
reference_title: "Regulation of protein phosphatase 2A catalytic activity by alpha4 protein and its yeast homolog Tap42."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "The association of alpha4 and Tap42 with PP2A-C inhibited the phosphatase activity toward 4E-BP1"
explanation: Alpha 4 binding of the PP2A catalytic subunit changes its phosphatase activity, the link from Alpha 4 dosage to PP2A dysregulation.
- name: Dysregulated PP2A Holoenzyme Dephosphorylation
biological_scale: MOLECULAR
description: >
Perturbed PP2A-dependent protein dephosphorylation, the major cellular
serine/threonine phosphatase activity that Alpha 4 regulates (including
toward mTOR-pathway substrates such as 4E-BP1). This is the proposed
proximal biochemical consequence that couples to developmental morphogenesis.
molecular_functions:
- preferred_term: PP2A regulatory (Alpha 4) subunit activity
term:
id: GO:0019888
label: protein phosphatase regulator activity
modifier: ABNORMAL
cellular_components:
- preferred_term: protein phosphatase type 2A complex
term:
id: GO:0000159
label: protein phosphatase type 2A complex
biological_processes:
- preferred_term: protein dephosphorylation
term:
id: GO:0006470
label: protein dephosphorylation
modifier: ABNORMAL
evidence:
- reference: PMID:9792806
reference_title: "Regulation of protein phosphatase 2A catalytic activity by alpha4 protein and its yeast homolog Tap42."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "a potential regulatory role of alpha4 and Tap42 to inibit the phosphatase activity of PP2A-C toward the physiologically relevant substrate in the mTOR signaling"
explanation: Defines the dysregulated PP2A dephosphorylation (including toward mTOR-pathway substrates) that Alpha 4 controls.
downstream:
- target: Impaired Forebrain Commissural Morphogenesis
description: >
Dysregulated PP2A signaling during embryogenesis is proposed to disrupt
forebrain commissural development, producing agenesis of the corpus
callosum.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
hypothesis_groups:
- igbp1_pp2a_dosage_developmental_mechanism
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Altered expression of Alpha 4, through either a change in translational efficiency, mRNA stability or splicing, could explain the clinical phenotype in these boys and the phenotypic overlap with Opitz GBBB syndrome"
explanation: The authors propose the Alpha 4/PP2A perturbation explains the callosal and other malformations.
- target: Impaired Craniofacial and Optic Fissure Morphogenesis
description: >
Dysregulated PP2A signaling is proposed to disrupt craniofacial and optic
fissure development, producing coloboma, micrognathia/retrognathia, and ear
anomalies, paralleling the midline defects of Opitz GBBB syndrome.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
hypothesis_groups:
- igbp1_pp2a_dosage_developmental_mechanism
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "could explain the clinical phenotype in these boys and the phenotypic overlap with Opitz GBBB syndrome"
explanation: The proposed mechanism extends to the craniofacial/ocular malformations shared with Opitz GBBB syndrome.
- name: Impaired Forebrain Commissural Morphogenesis
biological_scale: TISSUE
description: >
Disrupted development of the forebrain commissures, the distal developmental
lesion underlying agenesis of the corpus callosum in the syndrome.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "mental retardation, and agenesis of the corpus callosum (ACC)"
explanation: The commissural morphogenesis defect manifests as agenesis of the corpus callosum in both brothers.
- name: Impaired Craniofacial and Optic Fissure Morphogenesis
biological_scale: TISSUE
description: >
Disrupted craniofacial and optic fissure development, the distal
developmental lesion underlying the ocular coloboma, micrognathia/
retrognathia, high forehead, and ear anomalies.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "coloboma (iris, optic nerve), high forehead, severe retrognathia"
explanation: The craniofacial/optic-fissure morphogenesis defect manifests as coloboma, high forehead, and retrognathia.
phenotypes:
- name: Agenesis of corpus callosum
category: Neurologic
description: Complete absence of the corpus callosum, a defining feature of the syndrome.
phenotype_term:
preferred_term: Agenesis of corpus callosum
term:
id: HP:0001274
label: Agenesis of corpus callosum
onset:
onset_category: CONGENITAL
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "coloboma (iris, optic nerve), high forehead, severe retrognathia, mental retardation, and agenesis of the corpus callosum (ACC)"
explanation: Both affected brothers had agenesis of the corpus callosum.
- name: Intellectual disability
category: Neurologic
description: Intellectual disability was present in both affected brothers.
phenotype_term:
preferred_term: Intellectual disability
term:
id: HP:0001249
label: Intellectual disability
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "high forehead, severe retrognathia, mental retardation, and agenesis of the corpus callosum (ACC)"
explanation: Mental retardation (intellectual disability) was a core feature in both brothers.
- name: Iris coloboma
category: Ophthalmologic
description: Coloboma of the iris, one of the two ocular coloboma components.
phenotype_term:
preferred_term: Iris coloboma
term:
id: HP:0000612
label: Iris coloboma
onset:
onset_category: CONGENITAL
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "a unique pattern of malformations that includes coloboma (iris, optic nerve)"
explanation: The coloboma explicitly involved the iris in the affected brothers.
- name: Optic disc coloboma
category: Ophthalmologic
description: Coloboma of the optic nerve/disc.
phenotype_term:
preferred_term: Optic nerve coloboma
term:
id: HP:0000588
label: Optic disc coloboma
onset:
onset_category: CONGENITAL
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "a unique pattern of malformations that includes coloboma (iris, optic nerve)"
explanation: The coloboma involved the optic nerve in addition to the iris.
- name: Retrognathia
category: Craniofacial
description: Severe retrognathia (micrognathia/retrognathia) contributing to the facial gestalt.
phenotype_term:
preferred_term: Severe retrognathia
term:
id: HP:0000278
label: Retrognathia
severity: SEVERE
onset:
onset_category: CONGENITAL
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "high forehead, severe retrognathia, mental retardation"
explanation: Severe retrognathia was documented in the affected brothers; the syndrome name emphasizes micrognathia.
- name: Micrognathia
category: Craniofacial
description: >
Micrognathia (small mandible) is the eponymous craniofacial feature named in
the disease, MONDO, OMIM, and primary-paper titles; the brothers' jaw anomaly
was characterized as severe retrognathia/micrognathia.
phenotype_term:
preferred_term: Micrognathia
term:
id: HP:0000347
label: Micrognathia
onset:
onset_category: CONGENITAL
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13"
explanation: Micrognathia is named as a cardinal feature in the report's own title.
- name: High forehead
category: Craniofacial
description: High/prominent forehead as part of the facial dysmorphism.
phenotype_term:
preferred_term: High forehead
term:
id: HP:0000348
label: High forehead
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "coloboma (iris, optic nerve), high forehead, severe retrognathia"
explanation: High forehead is part of the described craniofacial pattern.
- name: Low-set ears
category: Craniofacial
description: Low-set, cupped ears.
phenotype_term:
preferred_term: Low-set ears
term:
id: HP:0000369
label: Low-set ears
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Both boys have low-set cupped ears with sensorineural hearing loss"
explanation: Both brothers had low-set cupped ears.
- name: Cupped ear
category: Craniofacial
description: Cupped (protruding, abnormally shaped) ears.
phenotype_term:
preferred_term: Cupped ears
term:
id: HP:0000378
label: Cupped ear
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Both boys have low-set cupped ears with sensorineural hearing loss"
explanation: The ears were described as cupped in both brothers.
- name: Sensorineural hearing loss
category: Auditory
description: Sensorineural hearing loss accompanying the ear anomalies.
phenotype_term:
preferred_term: Sensorineural hearing loss
term:
id: HP:0000407
label: Sensorineural hearing impairment
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "low-set cupped ears with sensorineural hearing loss"
explanation: Sensorineural hearing loss was present in both brothers.
- name: Pectus excavatum
category: Skeletal
description: Sunken chest deformity.
phenotype_term:
preferred_term: Pectus excavatum
term:
id: HP:0000767
label: Pectus excavatum
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "normal phallus, pectus excavatum, scoliosis, and short stature"
explanation: Pectus excavatum was documented in the affected brothers.
- name: Scoliosis
category: Skeletal
description: Lateral curvature of the spine.
phenotype_term:
preferred_term: Scoliosis
term:
id: HP:0002650
label: Scoliosis
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "pectus excavatum, scoliosis, and short stature"
explanation: Scoliosis was part of the skeletal phenotype.
- name: Short stature
category: Growth
description: Reduced stature relative to age-matched peers.
phenotype_term:
preferred_term: Short stature
term:
id: HP:0004322
label: Short stature
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "pectus excavatum, scoliosis, and short stature"
explanation: Short stature was documented in the affected brothers.
- name: Choanal atresia
category: Craniofacial
description: Choanal atresia in one of the two affected brothers.
phenotype_term:
preferred_term: Choanal atresia
term:
id: HP:0000453
label: Choanal atresia
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "One brother had choanal atresia and cardiac defects consisting of ventricular septal defect (VSD) and patent ductus arteriosus (PDA)"
explanation: One brother had choanal atresia (variable feature).
- name: Ventricular septal defect
category: Cardiovascular
description: Ventricular septal defect in one brother, which resolved spontaneously.
phenotype_term:
preferred_term: Ventricular septal defect
term:
id: HP:0001629
label: Ventricular septal defect
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "cardiac defects consisting of ventricular septal defect (VSD) and patent ductus arteriosus (PDA) which resolved spontaneously"
explanation: One brother had a ventricular septal defect that resolved spontaneously.
- name: Patent ductus arteriosus
category: Cardiovascular
description: Patent ductus arteriosus in one brother, which resolved spontaneously.
phenotype_term:
preferred_term: Patent ductus arteriosus
term:
id: HP:0001643
label: Patent ductus arteriosus
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "ventricular septal defect (VSD) and patent ductus arteriosus (PDA) which resolved spontaneously"
explanation: One brother had a patent ductus arteriosus that resolved spontaneously.
genetic:
- name: IGBP1
association: Causal 5'-regulatory-region variants (Alpha 4 gene)
relationship_type: CAUSATIVE
variant_origin: GERMLINE
gene_term:
preferred_term: IGBP1
term:
id: hgnc:5461
label: IGBP1
notes: >
IGBP1 (the Alpha 4 gene) at Xq13 encodes a regulatory subunit of protein
phosphatase 2A (PP2A). The two affected brothers carried adjacent changes
(-57delT and T-55A) in the gene's 5' regulatory region, not present in 410
control chromosomes.
variants:
- name: -57delT and T-55A (adjacent 5'-regulatory IGBP1/Alpha 4 variants)
description: >
Adjacent single-nucleotide changes in the 5' regulatory region of IGBP1
(Alpha 4), proposed to alter translational efficiency, mRNA stability, or
splicing. Absent from 410 control chromosomes.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The double nucleotide change identified in this family was not observed in 410 control chromosomes, suggesting that it may be a pathogenetic change"
explanation: The adjacent IGBP1 variants were absent from controls, supporting pathogenicity.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "in both we have identified adjacent alterations (-57delT and T-55A) in the Alpha 4 gene located within this interval"
explanation: Identifies IGBP1 (Alpha 4) as the candidate causative gene at Xq13.
- name: MID1
association: Mechanistic interactor (not mutated in the reported family)
relationship_type: COOPERATING
gene_term:
preferred_term: MID1
term:
id: hgnc:7095
label: MID1
notes: >
MID1 is not mutated in the reported family but is the mechanistic bridge to
the syndrome's phenotypic overlap with X-linked Opitz GBBB syndrome: MID1 is
the microtubule-associated E3 ubiquitin ligase (mutated in Opitz GBBB) that
physically interacts with Alpha 4 (IGBP1) to regulate PP2A. It is modeled as
a cooperating locus in the shared Alpha 4/PP2A developmental pathway rather
than a causative gene for this disorder.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Alpha 4 is a regulatory subunit of the major cellular phosphatase, PP2A, that has recently been shown to interact with MID1, the product of the gene mutated in X-linked Opitz GBBB syndrome"
explanation: Establishes the Alpha 4 (IGBP1)-MID1 interaction as the mechanistic link to the overlapping Opitz GBBB phenotype.
discussions:
- discussion_id: disc_ccaidc_igbp1_causality_replication
prompt: >-
Is IGBP1 (the Alpha 4 gene) definitively the cause of corpus callosum
agenesis-intellectual disability-coloboma-micrognathia syndrome, or does the
gene-disease relationship still require independent replication?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- pathophysiology#IGBP1 5'-Regulatory Variants
rationale: >-
The IGBP1 assignment rests on a single family (two brothers) with adjacent
5'-regulatory variants and a proposed, not demonstrated, functional
consequence. A systematic reassessment of X-linked intellectual disability
genes against large-scale control exome data placed IGBP1 among genes for
which replication studies are warranted, so the causal relationship should
be treated as provisional until additional families or functional data are
reported.
evidence:
- reference: PMID:23871722
reference_title: "XLID-causing mutations and associated genes challenged in light of data from large-scale human exome sequencing."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We also highlight 15 other genes (CCDC22, CLIC2, CNKSR2, FRMPD4, HCFC1, IGBP1, KIAA2022, KLF8, MAOA, NAA10, NLGN3, RPL10, SHROOM4, ZDHHC15, and ZNF261) for which replication studies are warranted"
explanation: A large-scale XLID reassessment explicitly lists IGBP1 among genes whose disease implication needs independent replication.
posed_date: "2026-07-30T00:00:00Z"
notes: >-
Consistent with the ultra-rare, single-family basis of the syndrome; the
IGBP1/Alpha 4 mechanism (PP2A regulation, MID1 interaction) is biologically
plausible but the human genetic evidence remains limited.
- discussion_id: disc_ccaidc_igbp1_mouse_model_gap
prompt: >-
Does any Igbp1 (Alpha 4) mouse model recapitulate the human corpus callosum
agenesis-coloboma-craniofacial phenotype, and can such a model confirm the
proposed Alpha 4 dosage/PP2A developmental mechanism?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- pathophysiology#Dysregulated PP2A Holoenzyme Dephosphorylation
rationale: >-
No Igbp1 mouse allele has been shown to reproduce the syndrome's central
developmental phenotype (agenesis of the corpus callosum, coloboma,
craniofacial anomalies); reported Igbp1 mouse phenotypes concern other
systems. The absence of a phenotype-recapitulating animal model leaves the
proposed Alpha 4 dosage/PP2A developmental mechanism functionally
unconfirmed and is a distinct gap from the human-genetics replication gap.
posed_date: "2026-07-30T00:00:00Z"
notes: >-
Surfaced by the deep-research model-organism review; complements the
IGBP1 replication-gap discussion.
classifications:
harrisons_chapter:
- classification_value: NEUROLOGIC
- classification_value: GENETICS_ENVIRONMENT_DISEASE
progression:
- phase: Congenital, static course
age_range: Birth onward
notes: >
The structural malformations (agenesis of the corpus callosum, coloboma,
micrognathia/retrognathia, ear anomalies) are congenital and non-progressive;
intellectual disability and sensorineural hearing loss are lifelong. The one
documented dynamic exception was the cardiac involvement in one brother, whose
ventricular septal defect and patent ductus arteriosus resolved spontaneously.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "ventricular septal defect (VSD) and patent ductus arteriosus (PDA) which resolved spontaneously"
explanation: The spontaneously-resolving cardiac defects are the one dynamic exception to an otherwise static congenital course.
diagnosis:
- name: Brain MRI
description: Neuroimaging demonstrating agenesis of the corpus callosum.
diagnosis_term:
preferred_term: magnetic resonance imaging procedure
term:
id: NCIT:C16809
label: Magnetic Resonance Imaging
results: Brain MRI showing agenesis of the corpus callosum.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "mental retardation, and agenesis of the corpus callosum (ACC)"
explanation: Agenesis of the corpus callosum is an imaging-defined feature of the syndrome.
- name: Ophthalmologic examination
description: Slit-lamp and fundoscopic examination identifying iris and optic nerve coloboma.
diagnosis_term:
preferred_term: eye examination
term:
id: NCIT:C38060
label: Eye Examination
results: Iris and optic nerve coloboma on ophthalmologic examination.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "a unique pattern of malformations that includes coloboma (iris, optic nerve)"
explanation: Ophthalmologic examination detects the iris and optic nerve coloboma.
- name: Audiometry
description: Hearing assessment demonstrating sensorineural hearing loss.
diagnosis_term:
preferred_term: hearing examination
term:
id: NCIT:C38036
label: Audiometric Test
results: Sensorineural hearing loss on audiometric testing.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "low-set cupped ears with sensorineural hearing loss"
explanation: Audiometry confirms the sensorineural hearing loss.
- name: IGBP1 molecular genetic testing
description: >
Targeted IGBP1 (Alpha 4) sequencing that must include the 5' regulatory
region, since the reported pathogenic variants are non-coding 5'-region
changes that standard whole-exome capture under-represents.
diagnosis_term:
preferred_term: molecular genetic testing
term:
id: NCIT:C19770
label: Molecular Analysis
results: Identification of the causative IGBP1 5'-regulatory variant.
evidence:
- reference: PMID:14556245
reference_title: "A new X-linked syndrome with agenesis of the corpus callosum, mental retardation, coloboma, micrognathia, and a mutation in the Alpha 4 gene at Xq13."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "in both we have identified adjacent alterations (-57delT and T-55A) in the Alpha 4 gene located within this interval"
explanation: Molecular genetic testing identifies the IGBP1 (Alpha 4) 5'-regulatory variants.
treatments:
- name: Choanal atresia repair
description: Surgical correction of choanal atresia when present.
therapeutic_modality: SURGERY
treatment_term:
preferred_term: surgical procedure
term:
id: NCIT:C15329
label: Surgical Procedure
- name: Cardiac surgical repair
description: >
Cardiac monitoring with surgical repair reserved for a ventricular septal
defect or patent ductus arteriosus that does not resolve spontaneously.
therapeutic_modality: SURGERY
treatment_term:
preferred_term: surgical procedure
term:
id: NCIT:C15329
label: Surgical Procedure
- name: Hearing amplification
description: Hearing aids or cochlear implantation for sensorineural hearing loss.
therapeutic_modality: DEVICE
treatment_term:
preferred_term: hearing aid usage
- name: Speech-language therapy and early intervention
description: >
Developmental early-intervention and speech-language therapy for
intellectual disability and communication support.
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: speech therapy
term:
id: NCIT:C159273
label: Speech Language Therapy
- name: Scoliosis orthopedic surgery
description: >
Orthopedic surgical correction (e.g., spinal fusion) for progressive
scoliosis.
therapeutic_modality: SURGERY
treatment_term:
preferred_term: orthopedic surgical procedure
term:
id: NCIT:C16186
label: Orthopedic Surgical Procedure
- name: Ophthalmologic supportive care
description: >
Ophthalmologic monitoring and low-vision aids for coloboma-related visual
impairment.
therapeutic_modality: DEVICE
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
- name: Genetic counseling
description: >
Genetic counseling for the family given X-linked recessive inheritance,
including carrier-risk assessment for at-risk female relatives.
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: genetic counseling
term:
id: NCIT:C15240
label: Genetic Counseling
| Identifier | Value |
|---|---|
| OMIM (Phenotype) | #300472 — "Corpus Callosum, Agenesis of, with Impaired Intellectual Development, Ocular Coloboma, and Micrognathia" |
| OMIM (Gene) | *300139 — IGBP1 (Immunoglobulin-Binding Protein 1) |
| MONDO | MONDO:0010333 |
| Orphanet | ORPHA:52055 |
| MedGen / UMLS | C1845446 (MedGen UID 335185) |
| Disease Ontology | DOID:0060816 |
| GARD | GARD 12486 |
| Gene | IGBP1 (a.k.a. Alpha4/α4), Xq13.1, HGNC:5342 |
| Common synonym | Graham-Cox syndrome |
| Other synonym | Mental Retardation, X-linked, Syndromic 28 (MRXS28) |
| Causal variant | 5′UTR: -57delT and -55T>A (adjacent, immediately upstream of the AUG initiation codon), OMIM allele 300139.0001 |
| Inheritance | X-linked (recessive) |
Important curation caveat: This is an extremely rare, essentially single-family condition. Since its original description, this literature search found no independently published second family or additional case series — the entire clinical and molecular record rests on one 2003 report (Graham et al., PMID:14556245) describing two affected brothers. This should be reflected in a dismech entry as very sparse evidence/prevalence — do not infer generalizable frequencies from an n=2 case series, and flag evidence_source: HUMAN_CLINICAL for all clinical claims (there is no model-organism disease-recapitulation study).
Overview. Corpus callosum agenesis-intellectual disability-coloboma-micrognathia syndrome is an X-linked developmental disorder first delineated in two brothers who shared a distinctive, non-random pattern of malformations: bilateral coloboma of the iris and optic nerve, a high/broad forehead, severe retrognathia (micrognathia), agenesis of the corpus callosum (ACC), intellectual disability, sensorineural hearing loss, skeletal anomalies, and short stature (Graham et al., 2003, PMID:14556245). Orphanet's summary states the condition is "characterized by coloboma of the iris and optic nerve, facial dysmorphism (high forehead, microretrognathia, low-set ears), intellectual deficit, agenesis of the corpus callosum (ACC), sensorineural hearing loss, skeletal anomalies and short stature."
Data provenance. All currently available clinical information is derived from individual patients — specifically the two affected brothers in the original family report — rather than from an aggregated disease-level registry or cohort. There is no birth-prevalence registry, disease-specific patient registry, or large case series behind this entry.
Common synonyms/alternative names (from MedGen/OMIM): - Corpus callosum, agenesis of, with impaired intellectual development, ocular coloboma, and micrognathia - Agenesis of the corpus callosum with mental retardation, ocular coloboma, and micrognathia - Graham-Cox syndrome - Mental retardation, X-linked, syndromic 28 (MRXS28)
Disease causal factor: monogenic, X-linked. The syndrome is caused by mutation in IGBP1 (immunoglobulin-binding protein 1; Alpha4/α4), located at Xq13.1. Graham et al. (2003) mapped the interval on X and identified "adjacent alterations (-57delT and T-55A) in the Alpha 4 gene located within this interval" — two nucleotide changes clustered in the 5′-untranslated region immediately 5′ of the ATG translation-initiation codon, present in both affected brothers (PMID:14556245).
Modifier genes: None specifically implicated for this syndrome. However, IGBP1/α4 is mechanistically linked to MID1 (mutated in X-linked Opitz G/BBB syndrome, OMIM #300000): MID1 is an E3 ubiquitin ligase that directly polyubiquitinates α4 at lysine-287, and this ubiquitination event regulates α4 stability and, in turn, PP2A activity (Watkins et al., PMC3774402 / J Biol Chem). The Graham et al. abstract notes that "Alpha 4… has recently been shown to interact with MID1, the product of the gene mutated in X-linked Opitz GBBB syndrome," offering a candidate mechanistic explanation for the clinical overlap between the two conditions (both feature agenesis/hypoplasia of the corpus callosum and other midline defects). This MID1–α4 axis is a strong candidate "modifier pathway" worth noting in a mechanism narrative even though no modifier variant has been formally reported in this family.
Phenotype data below are drawn from the OMIM Clinical Synopsis (#300472, mirrored via MedGen/GARD) and the original Graham et al. 2003 case description. Frequencies are effectively n=2 (both affected brothers), except where one feature was present in only one brother — treat all "frequency" claims as descriptive, not population-based percentages.
| Phenotype | Type | Both brothers / one brother | Suggested HPO term* |
|---|---|---|---|
| Agenesis of corpus callosum | Structural/neuroimaging | Both | HP:0001274 (Agenesis of corpus callosum) |
| Intellectual disability | Neurodevelopmental | Both | HP:0001249 (Intellectual disability) |
| Iris coloboma | Ocular, congenital malformation | Both | HP:0000612 (Iris coloboma) |
| Optic nerve/disc coloboma | Ocular, congenital malformation | Both | HP:0000588 (Optic disc coloboma) |
| High/broad forehead | Craniofacial dysmorphism | Both | HP:0000348 (High forehead) |
| Micrognathia / severe retrognathia | Craniofacial dysmorphism | Both | HP:0000347 (Micrognathia) / HP:0000278 (Retrognathia) |
| Low-set, cupped ("lop") ears | Craniofacial dysmorphism | Both | HP:0000369 (Low-set ears) |
| Sensorineural hearing loss | Auditory / laboratory-functional (audiometry) | Both | HP:0000407 (Sensorineural hearing impairment) |
| Short stature | Growth | Both | HP:0004322 (Short stature) |
| Pectus excavatum | Skeletal | Both | HP:0000767 (Pectus excavatum) |
| Scoliosis (thoracolumbar) | Skeletal | Both | HP:0002650 (Scoliosis) |
| Downslanted palpebral fissures | Craniofacial dysmorphism | Reported | HP:0000494 (Downslanted palpebral fissures) |
| Prominent nasal bridge | Craniofacial dysmorphism | Reported | HP:0000426 (Prominent nasal bridge) |
| High palate / cleft palate / bifid uvula | Craniofacial/palatal | Reported (variable) | HP:0000218 (High palate) / HP:0000175 (Cleft palate) / HP:0000193 (Bifid uvula) |
| Nystagmus | Ocular, functional | Reported | HP:0000639 (Nystagmus) |
| Macrocephaly | Growth/head | Reported | HP:0000256 (Macrocephaly) |
| Short neck | Skeletal | Reported | HP:0000470 (Short neck) |
| Choanal atresia | Structural, airway | One brother only | HP:0000453 (Choanal atresia) |
| Ventricular septal defect | Cardiac, congenital | One brother only (resolved spontaneously) | HP:0001629 (Ventricular septal defect) |
| Patent ductus arteriosus | Cardiac, congenital | One brother only (resolved spontaneously) | HP:0001643 (Patent ductus arteriosus) |
| Bilateral cryptorchidism | Genitourinary | Reported | HP:0008689 (Bilateral cryptorchidism) |
| Chronic constipation | Gastrointestinal | Reported | HP:0002019 (Constipation) |
| Recurrent aspiration pneumonia | Respiratory, secondary complication | Reported | HP:0002878 (Recurrent aspiration pneumonia) |
HPO term IDs above are provided from domain knowledge as strong candidates for the described phenotypes; before curating into dismech they must be independently verified with OAK* (uv run runoak -i sqlite:obo:hp info HP:XXXXXXX -O obo) per project policy, since I did not directly query the HPO API for this report.
Onset: All features are congenital/present from the neonatal-infant period (structural malformations); intellectual disability and hearing loss are ascertained/diagnosed in infancy-childhood. Severity/progression: Most anomalies are static, congenital, non-progressive structural malformations; the cardiac defects (VSD, PDA) in the one affected brother resolved spontaneously, indicating a non-progressive, self-limited course for that specific finding. Quality of life impact: Not formally measured (no EQ-5D/SF-36/disease-specific instrument data available); qualitatively, intellectual disability, sensorineural hearing loss, and visual impairment from coloboma would be expected to impose substantial functional impact, but this is inferential, not sourced from a QOL study of the reported family.
Causal gene: IGBP1 (Immunoglobulin-Binding Protein 1; a.k.a. Alpha4/α4; HGNC:5342), OMIM *300139, chromosome Xq13.1.
Pathogenic variant:
- Location: 5′-untranslated region (5′UTR), immediately upstream of (adjacent to) the ATG translation-initiation codon.
- Variants: two adjacent alterations — -57delT (a single-nucleotide deletion) and -55T>A (a single-nucleotide substitution) — reported together as OMIM allele 300139.0001.
- Variant class: regulatory/non-coding (5′UTR), not a missense/nonsense/frameshift coding change. This is mechanistically distinct from most Mendelian loss-of-function alleles.
- Proposed functional consequence: hypothesized to perturb translational efficiency, mRNA stability, or splicing of IGBP1 transcript — i.e., an expression/dosage effect on α4 protein levels rather than a structural protein defect (Graham et al., 2003).
- Zygosity/origin: hemizygous in both affected brothers (germline, X-linked); explicit segregation/carrier data for the mother were not retrievable from the abstract alone — the primary manuscript (Am J Med Genet A. 2003;123A(1):37-44) should be consulted for full pedigree/carrier-testing detail before finalizing an inheritance block.
- Population frequency: not listed in gnomAD/ExAC/1000 Genomes searches performed here as a named pathogenic variant; given the rarity of the phenotype this variant is expected to be private/family-specific or absent from population databases — should be confirmed directly in gnomAD/ClinVar at curation time.
- ClinVar/ACMG classification: not independently verified in this pass; recommend checking ClinVar for accession status of 300139.0001 before asserting a formal ACMG tier in the KB entry.
Modifier/interacting gene — MID1: Although not mutated in this family, MID1 (mutated in X-linked Opitz G/BBB syndrome, OMIM #300000, Xp22.2) is mechanistically coupled to IGBP1/α4: MID1 is a RING-finger E3 ubiquitin ligase that catalyzes polyubiquitination of α4 at lysine-287 in its C-terminal region, a modification that regulates α4 protein stability and, downstream, PP2A catalytic activity (PMC3774402, J Biol Chem). Loss of MID1 function is associated with hypospadias, cleft lip/palate, cardiac septal defects, and — notably — agenesis/hypoplasia of the corpus callosum and cerebellar vermis in a subset of Opitz G/BBB patients, providing candidate biological plausibility for a shared final-common pathway with the IGBP1 syndrome.
Epigenetic information: No DNA methylation, histone modification, or chromatin-state data specific to this syndrome were found.
Chromosomal abnormalities: None reported; this is a point-mutation (small indel/SNV) disorder, not a copy-number or structural chromosomal condition.
No environmental, lifestyle, or infectious contributing factors have been reported for this syndrome — it is modeled in the literature as a purely monogenic X-linked condition. No data available for toxin/occupational exposure, maternal lifestyle factors, or infectious triggers.
Gene product and normal function. IGBP1/α4 was originally identified as an immunoglobulin-binding protein involved in B-cell antigen receptor signal transduction in lymphocytes, but its principal, broadly conserved role is as a regulatory subunit of the PP2A family of serine/threonine phosphatases — PP2A, PP4, and PP6.
Molecular pathway.
1. α4 binds directly to the PP2A catalytic subunit (PP2Ac), displacing the canonical scaffolding subunit (PP2Aa/PR65) and regulatory B-subunit (PP2Ab) that normally form the heterotrimeric PP2A holoenzyme.
2. Within the mTOR signaling pathway, under growth-promoting conditions α4 down-regulates PP2A phosphatase activity, permitting downstream activation of eIF-4E and S6 kinase, driving translation initiation and cell-cycle progression (i.e., α4 acts as a rheostat linking nutrient/growth signaling to translational control via PP2A inhibition).
3. α4 itself is a target of ubiquitin-mediated turnover: MID1 (the Opitz G/BBB gene) is an E3 ligase that polyubiquitinates α4 at Lys-287, controlling α4 (and thus PP2A) protein levels — identified via NMR/biochemical studies of the MID1-α4 interaction (PMC3237570, PMC3774402).
4. Proposed disease mechanism in this syndrome: the 5′UTR mutations (-57delT, -55T>A) are hypothesized to alter IGBP1 mRNA translational efficiency/stability, changing α4 protein dosage during development. Because α4 normally titrates PP2A activity in growth/mTOR signaling and is itself regulated by the same MID1 pathway implicated in the phenotypically overlapping Opitz G/BBB syndrome, dysregulated α4 dosage is proposed as the shared mechanistic node explaining midline developmental anomalies (corpus callosum agenesis) and craniofacial/ocular malformations (coloboma, micrognathia) in both conditions. This remains a hypothesis stated in the primary literature, not a functionally confirmed causal chain (no knock-in mouse or patient-cell rescue experiment for this specific variant was identified) — a dismech entry should model this as a mechanistic_hypotheses block with status: EMERGING, not an established chain.
Cell types / biological processes (suggested ontology terms, to be OAK-verified): - Cellular process: protein phosphatase type 2A complex regulation, translational initiation, mTOR signaling — candidate GO terms: GO:0000159 (protein phosphatase type 2A complex), GO:0006446 (regulation of translational initiation), GO:0032008 (positive regulation of TOR signaling) - Molecular function: GO:0008601 (protein phosphatase type 2A regulator activity) - Relevant cell types for corpus callosum agenesis generally: commissural neurons, radial glia of the developing telencephalon (CL:0000030-type progenitors) — no cell-type-specific study exists for this particular syndrome; this would be an inference from general ACC biology, not this syndrome's own literature.
Biochemical abnormalities: presumptive altered α4 protein dosage/PP2A regulatory-subunit stoichiometry; no direct biochemical assay (e.g., patient-fibroblast PP2A activity assay) for this specific family was located in this search.
Advanced omics / molecular profiling: No transcriptomic, proteomic, metabolomic, or single-cell data specific to this syndrome or its patients were found. No data available.
prevalence_class: NOT_YET_DOCUMENTED or ULTRA_RARE with an explicit note that the estimate rests on a single-family report, not a population survey — do not assign a numeric rate_per_100000.No formal survival, mortality, or long-term outcome data exist for this syndrome beyond the original 2003 report. The reported clinical course to that point: - Both brothers survived with intellectual disability and sensorineural hearing loss as apparently stable, lifelong findings. - The cardiac anomalies (VSD, PDA) in the one affected brother resolved spontaneously, a favorable outcome for that specific complication. - Complications noted include recurrent aspiration pneumonia (likely related to structural airway/palatal anomalies) and chronic constipation. - No quality-of-life instrument data, formal prognostic-factor analysis, or biomarker-based prognosis exists. No data available for life expectancy or disability-adjusted outcome measures.
No disease-specific, targeted, or FDA-approved therapy exists for this syndrome (it is not a treatable inborn error of metabolism, and no gene therapy/RNA-based approach has been reported). Management, as implied by the phenotype, would be symptomatic/supportive and multidisciplinary, though the original report does not detail a treatment protocol. Reasonable inferred supportive-care components (not directly sourced to a treatment-outcomes study of this syndrome, but standard-of-care for the individual findings) would include: - Surgical correction of choanal atresia (when present) — candidate MAXO term: MAXO:0000004 (surgical procedure) - Cardiac monitoring/surgical repair if VSD/PDA do not spontaneously resolve — MAXO:0000004 - Hearing amplification/cochlear implantation for sensorineural hearing loss — candidate MAXO:0009030 (hearing aid usage) - Early intervention/special education and speech-language therapy for intellectual disability — MAXO:0000930 (speech therapy) - Ophthalmologic monitoring for coloboma-related visual impairment (low-vision aids as needed) - Orthopedic monitoring/bracing or surgery for scoliosis — MAXO:0000004 / NCIT:C16186 - Genetic counseling for the family given X-linked inheritance — MAXO:0000079 (genetic counseling)
No pharmacotherapy, gene therapy, cell therapy, RNA-based therapy, or clinical trial (no NCT identifier) targeting this syndrome specifically was found. No data available for treatment-response rates or adverse-event data, since no interventional study of this condition exists.
No primary, secondary, or tertiary prevention strategy, immunization, or prophylaxis is applicable to this monogenic congenital malformation syndrome beyond standard reproductive/genetic counseling for X-linked conditions in an affected family (risk assessment, carrier testing of at-risk female relatives, and prenatal or preimplantation genetic testing options once a familial IGBP1 variant is known). No population-level screening program exists given the syndrome's extreme rarity.
No naturally-occurring veterinary or wildlife disease recapitulating this specific human syndrome (i.e., no OMIA entry or veterinary case series linking spontaneous IGBP1 mutation to an analogous coloboma/ACC/micrognathia phenotype in animals) was identified in this search. IGBP1 is a broadly conserved gene (MGI notes strong orthology across human, mouse, rat, and zebrafish), but no spontaneous animal disease model of this human phenotype has been reported.
HUMAN_MODEL_MISMATCH-type gap once/if any Igbp1 mouse craniofacial or CNS phenotype data are located and reviewed in detail on the MGI allele pages.Overall assessment for KB population: This is a well-defined but data-sparse Mendelian entry appropriate for a minimal, tightly-evidenced dismech entry: one causal gene (IGBP1), one variant class (5′UTR, 300139.0001), one primary clinical reference (PMID:14556245) supplying essentially all phenotype and evidence items, and a strong candidate mechanistic_hypotheses/conforms_to-style link to the MID1–α4–PP2A–mTOR pathway (potentially referencing Opitz G/BBB syndrome as a related-mechanism comparator) rather than a fully independently-elaborated pathophysiology module. Given the single-family evidentiary base, curators should resist inflating prevalence, frequency, or generalizing penetrance/expressivity claims beyond what n=2 supports.