Chromosome 18q Deletion Syndrome

Genetic MONDO:0011147 Pathograph 14 Show in embeddings browser hereditary disease chromosomal disorder

Chromosome 18q deletion syndrome (18q-, de Grouchy syndrome) is a contiguous-gene chromosomal disorder caused by heterozygous deletion of part of the long arm of chromosome 18, producing haploinsufficiency of a contiguous set of dosage-sensitive genes. The recurrent core comprises intellectual disability and developmental delay, short stature (often with growth hormone deficiency), hypotonia, hearing loss (frequently conductive, from congenital aural atresia or stenosis of the external auditory canal), abnormal cerebral white-matter MRI signal, foot deformities, characteristic facial features, and variable congenital anomalies. Phenotype severity and the specific manifestations correlate with deletion breakpoint and the genes lost, including TCF4 (neurodevelopment), MBP (white matter), and TSHZ1 (aural atresia). Most cases are de novo; a minority arise from a parental balanced rearrangement.

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6
Pathophys.
14
Phenotypes
1
Gaps
14
Pathograph
1
Genes
3
Medical Actions
2
Differentials
8
References
1
Deep Research
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Discussions and Knowledge Gaps

1
Is the abnormal cerebral white-matter MRI signal in 18q deletion syndrome caused by MBP-haploinsufficiency dysmyelination, or by gliosis with intact myelin? A single autopsy study of a ring-18 patient with confirmed MBP haploinsufficiency found the brain to be well myelinated and attributed the MRI signal to gliosis, contradicting the long-standing dysmyelination model.
HUMAN MODEL MISMATCH OPEN gap_18q_mbp_myelination_vs_gliosis
Attached to
pathophysiology#Reduced central white-matter myelination
The MBP-dysmyelination hypothesis is mechanistically attractive (MBP lies in the deleted 18q23 region and is required for myelin compaction), but human pathology evidence is limited to a single autopsy case in which myelin was histologically and ultrastructurally intact despite confirmed MBP haploinsufficiency, with the MRI signal instead reflecting gliosis. This is a model/observation mismatch rather than absent evidence: the imaging finding is real and reproducible, but its cellular basis (dysmyelination vs gliosis) is unresolved, which matters for interpreting MBP dosage as the driver of the white-matter phenotype.
Proposed experiments
Quantitative MBP immunohistochemistry and electron microscopy in confirmed terminal 18q23 deletion
exp_18q_mbp_autopsy_quantitative_ihc
Conduct additional autopsy studies with quantitative myelin basic protein immunohistochemistry and electron microscopy in patients with confirmed terminal 18q23 deletion (not ring chromosome) to determine whether the gliosis finding generalizes beyond the single ring-18 case, or whether true dysmyelination is detectable when MBP haploinsufficiency arises from a simple terminal deletion rather than a ring rearrangement.
Diffusion tensor imaging and magnetization transfer ratio cohort study
exp_18q_mbp_dti_mtr_invivo
Perform diffusion tensor imaging (DTI) and magnetization transfer ratio studies to distinguish dysmyelination from gliosis in vivo across a cohort of 18q deletion patients with varying breakpoints, testing whether white-matter microstructural metrics track with the extent of the deleted 18q23 interval and the presence of MBP haploinsufficiency.
Show evidence (1 reference)
PMID:21669507 SUPPORT Human Clinical
"the brain was well myelinated, contrary to established hypotheses about this disorder. The MRI signal abnormalities in 18q-syndrome could be attributed to gliosis and not to dysmyelination."
Single-autopsy human pathology contradicting the MBP-dysmyelination model and proposing gliosis as the basis of the MRI signal.
⚙

Pathophysiology

6
18q contiguous-gene haploinsufficiency
Heterozygous terminal or interstitial deletion of the long arm of chromosome 18 removes one copy of a contiguous set of genes, producing a haploinsufficiency syndrome. The clinical spectrum reflects which dosage-sensitive genes fall within the deleted interval, so the phenotype varies with breakpoint position and deletion size. The syndrome is conventionally split into a common distal (terminal) form and a rarer proximal interstitial form (18q11.2-q21.1).
Downstream
Neurodevelopmental dysregulation Haploinsufficiency of dosage-sensitive neurodevelopmental genes (including TCF4) perturbs brain development.
Reduced central white-matter myelination Loss of one MBP copy reduces myelin basic protein dosage at 18q23.
Aural and craniofacial developmental dysregulation TSHZ1 haploinsufficiency disrupts external/middle-ear and palate development.
Cardiac morphogenesis dysregulation Loss of 18q22.3-q23 genes contributes to congenital heart defects.
Growth-axis dysregulation Growth hormone deficiency from haploinsufficiency of 18q genes contributes to short stature.
Show evidence (2 references)
PMID:34956087 SUPPORT Human Clinical
"18q- syndrome is a rare chromosomal disease caused by the deletion of the long arm of chromosome 18."
Establishes the deletion of 18q as the upstream cause of the syndrome.
PMID:31390163 SUPPORT Human Clinical
"Chromosome 18q deletion syndrome is commonly classified into distal deletion and a much rarer proximal interstitial deletion spanning the 18q11.2-q21.1 region."
Supports the distal-versus-proximal architecture that underlies the breakpoint-dependent phenotype.
Neurodevelopmental dysregulation
Deletion of 18q neurodevelopmental genes produces developmental delay, intellectual disability, and behavioral abnormalities. TCF4 haploinsufficiency is a major contributor when the 18q21 region is included (full TCF4 deletion causes Pitt-Hopkins syndrome).
neuron CL:0000540
TCF4 hgnc:11634
nervous system development GO:0007399 ↓ DECREASED
Downstream
Intellectual disability Persistent neurodevelopmental disruption causes intellectual disability.
Global developmental delay Developmental neurobiologic disruption presents as global delay.
Behavioral abnormality Altered brain development contributes to autism-spectrum and behavioral features.
Show evidence (1 reference)
PMID:31390163 SUPPORT Human Clinical
"Common presentations of 18q11-q12 deletions include developmental delay/intellectual disability (DD/ID) (82%); speech delay/autism/attention deficit and hyperactivity/other behavioral problems (30%); conotruncal heart defects (15%)"
Supports developmental delay/intellectual disability and behavioral problems as the dominant neurodevelopmental output of 18q deletion.
Reduced central white-matter myelination
The distal 18q region (18q23) includes MBP, encoding myelin basic protein. 18q deletion is classically associated with reduced white-matter myelination and abnormal cerebral white-matter MRI signal. Note that the mechanistic basis is debated: a single autopsy study of a ring-18 patient with confirmed MBP haploinsufficiency found intact myelin and attributed the MRI signal to gliosis rather than dysmyelination (see discussions).
oligodendrocyte CL:0000128
MBP hgnc:6925
myelination GO:0042552 ↓ DECREASED
Downstream
Abnormal CNS myelination Reduced MBP dosage is associated with abnormal central white-matter signal.
Show evidence (2 references)
PMID:22152683 SUPPORT Human Clinical
"CAA is frequently seen in individuals with an 18q deletion, which is characterized by intellectual disability, reduced white-matter myelination, foot deformities, and distinctive facial features."
Identifies reduced white-matter myelination as a characteristic feature of the 18q deletion phenotype.
PMID:21669507 SUPPORT Human Clinical
"this syndrome involves the deletion of the myelin basic protein (MBP) gene in 18q23"
Links the white-matter phenotype to deletion of the MBP gene at 18q23.
Aural and craniofacial developmental dysregulation
TSHZ1, in the 18q22.3 critical region, is required for middle-ear and palate development. TSHZ1 haploinsufficiency disrupts development of the external and middle ear, producing congenital aural atresia and conductive hearing loss, and contributes to palatal and midface anomalies.
TSHZ1 hgnc:10669
roof of mouth development GO:0060021 ⚠ ABNORMAL
Downstream
Atresia of the external auditory canal TSHZ1 dosage loss disrupts external auditory canal development.
Cleft palate 18q22.3 dosage loss contributes to palatal clefting and high-arched palate.
Show evidence (2 references)
PMID:22152683 SUPPORT Human Clinical
"these results demonstrate that hemizygosity of TSHZ1 leads to congenital aural atresia as a result of haploinsufficiency."
Establishes TSHZ1 haploinsufficiency as the mechanism of congenital aural atresia in 18q deletion.
PMID:19157891 SUPPORT Model Organism
"gene deficient mouse models for Sall3 or Tshz1 genes, which are located at the 18q22.3 critical region, displayed palate abnormality phenotype."
Mouse knockouts of 18q22.3 critical-region genes recapitulate the palate phenotype, supporting their dosage role in craniofacial development.
Cardiac morphogenesis dysregulation
Congenital heart defects occur in roughly a quarter to a third of affected individuals, with a shared distal 18q22.3-q23 overlap region; the most common lesions are pulmonary valve anomalies and atrial septal defects. In proximal deletions, cardiac defects often map distal to GATA6, implying an alternative mechanism rather than GATA6 haploinsufficiency.
heart morphogenesis GO:0003007 ⚠ ABNORMAL
Downstream
Congenital heart disease Loss of distal 18q cardiac developmental genes produces congenital heart defects.
Show evidence (2 references)
PMID:23707655 SUPPORT Human Clinical
"All 19 individuals shared a small overlapping deletion region between 18q22.3q23. The most common cardiac defects detected were pulmonary valve anomalies and atrial septal defects."
Defines the distal critical region and the predominant cardiac lesions in 18q deletion.
PMID:31390163 SUPPORT Human Clinical
"The deletion in four out of five cases with cardiac defect was distal to GATA6, suggesting an alternative mechanism other than haploinsufficiency of GATA6 as an underlying cause of cardiac malformations."
Refines the genotype-phenotype basis of cardiac defects, arguing against a simple GATA6 dosage mechanism in proximal deletions.
Growth-axis dysregulation
Short stature is recurrent and frequently associated with growth hormone deficiency, with additional contributions from hypothyroidism and skeletal/feeding factors. Growth hormone deficiency is listed among the characteristic features of the syndrome, and affected individuals respond to recombinant human growth hormone.
Downstream
Short stature Growth hormone deficiency and skeletal factors produce short stature.
Show evidence (2 references)
PMID:19157891 SUPPORT Human Clinical
"The 18q deletion syndrome (18q-) is a multiple-anomaly disorder associated with mental retardation, white matter anomalies in the brain, growth hormone deficiency, congenital aural atresia, orofacial cleft (OFC), and palate abnormalities."
Lists growth hormone deficiency among the characteristic features of the syndrome.
PMID:34956087 SUPPORT Human Clinical
"Some cases with 18q- syndrome can be combined with growth hormone deficiency (GHD)"
Confirms growth hormone deficiency as a recognized endocrine component of the syndrome.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Chromosome 18q Deletion Syndrome Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

14
Cardiovascular 1
Congenital heart disease OCCASIONAL Abnormal heart morphology HP:0001627
Show evidence (1 reference)
PMID:23707655 SUPPORT Human Clinical
"Individuals with the 18q deletion syndrome are presented with various clinical characteristics, including cardiac anomalies in 24-36% of the reported cases."
Quantifies the prevalence of cardiac anomalies in 18q deletion.
Ear 2
Hearing impairment FREQUENT Hearing impairment HP:0000365
Show evidence (1 reference)
PMID:24637311 SUPPORT Human Clinical
"The main features of the syndrome are short stature, hearing loss, hypotonia, mental retardation, endocrine disorders and autoimmunity."
Lists hearing loss among the main features of the syndrome.
Atresia of the external auditory canal FREQUENT Atresia of the external auditory canal HP:0000413
Show evidence (1 reference)
PMID:22152683 SUPPORT Human Clinical
"CAA is frequently seen in individuals with an 18q deletion, which is characterized by intellectual disability, reduced white-matter myelination, foot deformities, and distinctive facial features."
States that congenital aural atresia is frequently seen in 18q deletion.
Head and Neck 2
Abnormal facial shape FREQUENT Abnormal facial shape HP:0001999
Show evidence (2 references)
PMID:22152683 SUPPORT Human Clinical
"CAA is frequently seen in individuals with an 18q deletion, which is characterized by intellectual disability, reduced white-matter myelination, foot deformities, and distinctive facial features."
Lists distinctive facial features as characteristic.
PMID:34956087 SUPPORT Human Clinical
"The main clinical manifestations of 18q- syndrome include characteristic appearance, intellectual disability, and abnormal genital development."
Independently lists characteristic appearance among the main manifestations.
Cleft palate OCCASIONAL Cleft palate HP:0000175
Show evidence (1 reference)
PMID:19157891 SUPPORT Human Clinical
"The frequency of CP/L and CL among 18q- individuals is about 25%; when high/arched palate cases are included, the frequency rises to about 43%."
Quantifies orofacial clefting at about 25% (occasional), rising to 43% when high-arched palate is included.
Immune 1
Autoimmunity Autoimmunity HP:0002960
Show evidence (1 reference)
PMID:24637311 SUPPORT Human Clinical
"The main features of the syndrome are short stature, hearing loss, hypotonia, mental retardation, endocrine disorders and autoimmunity."
Lists autoimmunity among the main features of the syndrome.
Musculoskeletal 1
Hypotonia FREQUENT Hypotonia HP:0001252
Show evidence (1 reference)
PMID:24637311 SUPPORT Human Clinical
"The main features of the syndrome are short stature, hearing loss, hypotonia, mental retardation, endocrine disorders and autoimmunity."
Lists hypotonia among the main features of the syndrome.
Nervous System 3
Intellectual disability VERY_FREQUENT Intellectual disability HP:0001249
Show evidence (2 references)
PMID:31390163 SUPPORT Human Clinical
"Common presentations of 18q11-q12 deletions include developmental delay/intellectual disability (DD/ID) (82%)"
Quantitative support for intellectual disability as a very frequent feature (82%).
PMID:34956087 SUPPORT Human Clinical
"The main clinical manifestations of 18q- syndrome include characteristic appearance, intellectual disability, and abnormal genital development."
Independently lists intellectual disability among the main manifestations.
Global developmental delay VERY_FREQUENT Global developmental delay HP:0001263
Show evidence (1 reference)
PMID:31390163 SUPPORT Human Clinical
"Common presentations of 18q11-q12 deletions include developmental delay/intellectual disability (DD/ID) (82%)"
Quantitative support for developmental delay as a very frequent feature (82%).
Behavioral abnormality FREQUENT Atypical behavior HP:0000708
Show evidence (1 reference)
PMID:31390163 SUPPORT Human Clinical
"speech delay/autism/attention deficit and hyperactivity/other behavioral problems (30%)"
Supports behavioral/autism-spectrum problems in roughly a third of proximal-deletion cases.
Growth 1
Short stature FREQUENT Short stature HP:0004322
Show evidence (1 reference)
PMID:24637311 SUPPORT Human Clinical
"The main features of the syndrome are short stature, hearing loss, hypotonia, mental retardation, endocrine disorders and autoimmunity."
Lists short stature among the main features of the syndrome.
Other 3
Abnormal CNS myelination FREQUENT Abnormal CNS myelination HP:0011400
Show evidence (1 reference)
PMID:22152683 SUPPORT Human Clinical
"CAA is frequently seen in individuals with an 18q deletion, which is characterized by intellectual disability, reduced white-matter myelination, foot deformities, and distinctive facial features."
Identifies reduced white-matter myelination as a characteristic feature.
Foot deformity FREQUENT Abnormal foot morphology HP:0001760
Show evidence (1 reference)
PMID:22152683 SUPPORT Human Clinical
"CAA is frequently seen in individuals with an 18q deletion, which is characterized by intellectual disability, reduced white-matter myelination, foot deformities, and distinctive facial features."
Lists foot deformities as a characteristic feature.
Abnormal genital system morphology Abnormality of the genital system HP:0000078
Show evidence (1 reference)
PMID:34956087 SUPPORT Human Clinical
"The main clinical manifestations of 18q- syndrome include characteristic appearance, intellectual disability, and abnormal genital development."
Lists abnormal genital development among the main manifestations.
🧬

Genetic Associations

1
18q deletion (Causal chromosomal deletion)
Show evidence (1 reference)
PMID:33817732 SUPPORT Human Clinical
"About 94% of cases with 18q deletion syndrome appearance are de novo, and the remaining 6% are the inherited from a parent carrying a balanced chromosomal translocation."
Supports the de novo predominance and the minority inherited via parental balanced translocation.
💊

Medical Actions

3
Supportive and multidisciplinary care
Action: supportive care MAXO:0000950
Management is supportive and symptom-directed, with no therapy that corrects the deletion; care is coordinated across developmental, audiologic, cardiac, endocrine, orthopedic, and immunologic services.
Recombinant human growth hormone therapy
Action: Pharmacotherapy NCIT:C15986
Agent: somatropin NCIT:C837
Recombinant human growth hormone is effective for documented growth hormone deficiency and short stature in 18q- syndrome, with significant height gains and no significant adverse effects reported in a case-plus-literature review.
Show evidence (1 reference)
PMID:34956087 SUPPORT Human Clinical
"the average height SDS significantly increased from -3.12 ± 0.94 SDS to -1.38 ± 1.29 SDS after the rhGH treatment (p < 0.0001)."
Demonstrates a significant height benefit from long-term rhGH treatment in 18q- syndrome.
Genetic counseling
Action: Genetic Counseling NCIT:C15240
Genetic counseling addresses recurrence risk; parental karyotyping is recommended because a subset of cases arise from a parental balanced translocation.
Show evidence (1 reference)
PMID:33817732 SUPPORT Human Clinical
"in order to establish the recurrence risk, parental karyotypes are recommended."
Supports parental karyotyping and genetic counseling for recurrence-risk assessment.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Chromosome 18q Deletion Syndrome:

Pitt-Hopkins syndrome MONDO:0012589
Overlapping Features Pitt-Hopkins syndrome is caused by TCF4 haploinsufficiency and overlaps the severe neurodevelopmental phenotype seen when 18q deletions include TCF4.
trisomy 18 Not Yet Curated MONDO:0018071
Overlapping Features Trisomy 18 (and mosaic forms / ring chromosome 18) shares dysmorphism, cardiac defects, and rocker-bottom feet and enters the differential, particularly in mosaic or dicentric rearrangements.
{ }

Source YAML

click to show 
name: Chromosome 18q Deletion Syndrome
creation_date: "2026-06-30T12:00:00Z"
synonyms:
- 18q- syndrome
- Monosomy 18q
- De Grouchy syndrome
- Distal monosomy 18q
description: >-
  Chromosome 18q deletion syndrome (18q-, de Grouchy syndrome) is a
  contiguous-gene chromosomal disorder caused by heterozygous deletion of part
  of the long arm of chromosome 18, producing haploinsufficiency of a contiguous
  set of dosage-sensitive genes. The recurrent core comprises intellectual
  disability and developmental delay, short stature (often with growth hormone
  deficiency), hypotonia, hearing loss (frequently conductive, from congenital
  aural atresia or stenosis of the external auditory canal), abnormal cerebral
  white-matter MRI signal, foot deformities, characteristic facial features, and
  variable congenital anomalies. Phenotype severity and the specific
  manifestations correlate with deletion breakpoint and the genes lost,
  including TCF4 (neurodevelopment), MBP (white matter), and TSHZ1 (aural
  atresia). Most cases are de novo; a minority arise from a parental balanced
  rearrangement.
category: Genetic
parents:
- hereditary disease
- chromosomal disorder
disease_term:
  preferred_term: chromosome 18q deletion syndrome
  term:
    id: MONDO:0011147
    label: chromosome 18q deletion syndrome
pathophysiology:
- name: 18q contiguous-gene haploinsufficiency
  description: >-
    Heterozygous terminal or interstitial deletion of the long arm of chromosome
    18 removes one copy of a contiguous set of genes, producing a
    haploinsufficiency syndrome. The clinical spectrum reflects which
    dosage-sensitive genes fall within the deleted interval, so the phenotype
    varies with breakpoint position and deletion size. The syndrome is
    conventionally split into a common distal (terminal) form and a rarer
    proximal interstitial form (18q11.2-q21.1).
  evidence:
  - reference: PMID:34956087
    reference_title: "Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      18q- syndrome is a rare chromosomal disease caused by the deletion of the
      long arm of chromosome 18.
    explanation: >-
      Establishes the deletion of 18q as the upstream cause of the syndrome.
  - reference: PMID:31390163
    reference_title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Chromosome 18q deletion syndrome is commonly classified into distal
      deletion and a much rarer proximal interstitial deletion spanning the
      18q11.2-q21.1 region.
    explanation: >-
      Supports the distal-versus-proximal architecture that underlies the
      breakpoint-dependent phenotype.
  downstream:
  - target: Neurodevelopmental dysregulation
    description: >-
      Haploinsufficiency of dosage-sensitive neurodevelopmental genes (including
      TCF4) perturbs brain development.
  - target: Reduced central white-matter myelination
    description: >-
      Loss of one MBP copy reduces myelin basic protein dosage at 18q23.
  - target: Aural and craniofacial developmental dysregulation
    description: >-
      TSHZ1 haploinsufficiency disrupts external/middle-ear and palate
      development.
  - target: Cardiac morphogenesis dysregulation
    description: >-
      Loss of 18q22.3-q23 genes contributes to congenital heart defects.
  - target: Growth-axis dysregulation
    description: >-
      Growth hormone deficiency from haploinsufficiency of 18q genes contributes
      to short stature.
- name: Neurodevelopmental dysregulation
  description: >-
    Deletion of 18q neurodevelopmental genes produces developmental delay,
    intellectual disability, and behavioral abnormalities. TCF4 haploinsufficiency
    is a major contributor when the 18q21 region is included (full TCF4 deletion
    causes Pitt-Hopkins syndrome).
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: nervous system development
    modifier: DECREASED
    term:
      id: GO:0007399
      label: nervous system development
  genes:
  - preferred_term: TCF4
    term:
      id: hgnc:11634
      label: TCF4
  evidence:
  - reference: PMID:31390163
    reference_title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common presentations of 18q11-q12 deletions include developmental
      delay/intellectual disability (DD/ID) (82%); speech delay/autism/attention
      deficit and hyperactivity/other behavioral problems (30%); conotruncal
      heart defects (15%)
    explanation: >-
      Supports developmental delay/intellectual disability and behavioral
      problems as the dominant neurodevelopmental output of 18q deletion.
  downstream:
  - target: Intellectual disability
    description: Persistent neurodevelopmental disruption causes intellectual disability.
  - target: Global developmental delay
    description: Developmental neurobiologic disruption presents as global delay.
  - target: Behavioral abnormality
    description: Altered brain development contributes to autism-spectrum and behavioral features.
- name: Reduced central white-matter myelination
  description: >-
    The distal 18q region (18q23) includes MBP, encoding myelin basic protein.
    18q deletion is classically associated with reduced white-matter myelination
    and abnormal cerebral white-matter MRI signal. Note that the mechanistic
    basis is debated: a single autopsy study of a ring-18 patient with confirmed
    MBP haploinsufficiency found intact myelin and attributed the MRI signal to
    gliosis rather than dysmyelination (see discussions).
  cell_types:
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  biological_processes:
  - preferred_term: myelination
    modifier: DECREASED
    term:
      id: GO:0042552
      label: myelination
  genes:
  - preferred_term: MBP
    term:
      id: hgnc:6925
      label: MBP
  evidence:
  - reference: PMID:22152683
    reference_title: "Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CAA is frequently seen in individuals with an 18q deletion, which is
      characterized by intellectual disability, reduced white-matter
      myelination, foot deformities, and distinctive facial features.
    explanation: >-
      Identifies reduced white-matter myelination as a characteristic feature of
      the 18q deletion phenotype.
  - reference: PMID:21669507
    reference_title: "Abnormal brain MRI signal in 18q-syndrome not due to dysmyelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      this syndrome involves the deletion of the myelin basic protein (MBP) gene
      in 18q23
    explanation: >-
      Links the white-matter phenotype to deletion of the MBP gene at 18q23.
  downstream:
  - target: Abnormal CNS myelination
    description: Reduced MBP dosage is associated with abnormal central white-matter signal.
- name: Aural and craniofacial developmental dysregulation
  description: >-
    TSHZ1, in the 18q22.3 critical region, is required for middle-ear and palate
    development. TSHZ1 haploinsufficiency disrupts development of the external
    and middle ear, producing congenital aural atresia and conductive hearing
    loss, and contributes to palatal and midface anomalies.
  biological_processes:
  - preferred_term: roof of mouth development
    modifier: ABNORMAL
    term:
      id: GO:0060021
      label: roof of mouth development
  genes:
  - preferred_term: TSHZ1
    term:
      id: hgnc:10669
      label: TSHZ1
  evidence:
  - reference: PMID:22152683
    reference_title: "Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      these results demonstrate that hemizygosity of TSHZ1 leads to congenital
      aural atresia as a result of haploinsufficiency.
    explanation: >-
      Establishes TSHZ1 haploinsufficiency as the mechanism of congenital aural
      atresia in 18q deletion.
  - reference: PMID:19157891
    reference_title: "The 18q deletion syndrome and analysis of the critical region for orofacial cleft at 18q22.3."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      gene deficient mouse models for Sall3 or Tshz1 genes, which are located at
      the 18q22.3 critical region, displayed palate abnormality phenotype.
    explanation: >-
      Mouse knockouts of 18q22.3 critical-region genes recapitulate the palate
      phenotype, supporting their dosage role in craniofacial development.
  downstream:
  - target: Atresia of the external auditory canal
    description: TSHZ1 dosage loss disrupts external auditory canal development.
  - target: Cleft palate
    description: 18q22.3 dosage loss contributes to palatal clefting and high-arched palate.
- name: Cardiac morphogenesis dysregulation
  description: >-
    Congenital heart defects occur in roughly a quarter to a third of affected
    individuals, with a shared distal 18q22.3-q23 overlap region; the most common
    lesions are pulmonary valve anomalies and atrial septal defects. In proximal
    deletions, cardiac defects often map distal to GATA6, implying an alternative
    mechanism rather than GATA6 haploinsufficiency.
  biological_processes:
  - preferred_term: heart morphogenesis
    modifier: ABNORMAL
    term:
      id: GO:0003007
      label: heart morphogenesis
  evidence:
  - reference: PMID:23707655
    reference_title: "Cardiac anomalies in individuals with the 18q deletion syndrome; report of a child with Ebstein anomaly and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All 19 individuals shared a small overlapping deletion region between
      18q22.3q23. The most common cardiac defects detected were pulmonary valve
      anomalies and atrial septal defects.
    explanation: >-
      Defines the distal critical region and the predominant cardiac lesions in
      18q deletion.
  - reference: PMID:31390163
    reference_title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The deletion in four out of five cases with cardiac defect was distal to
      GATA6, suggesting an alternative mechanism other than haploinsufficiency of
      GATA6 as an underlying cause of cardiac malformations.
    explanation: >-
      Refines the genotype-phenotype basis of cardiac defects, arguing against a
      simple GATA6 dosage mechanism in proximal deletions.
  downstream:
  - target: Congenital heart disease
    description: Loss of distal 18q cardiac developmental genes produces congenital heart defects.
- name: Growth-axis dysregulation
  description: >-
    Short stature is recurrent and frequently associated with growth hormone
    deficiency, with additional contributions from hypothyroidism and
    skeletal/feeding factors. Growth hormone deficiency is listed among the
    characteristic features of the syndrome, and affected individuals respond to
    recombinant human growth hormone.
  evidence:
  - reference: PMID:19157891
    reference_title: "The 18q deletion syndrome and analysis of the critical region for orofacial cleft at 18q22.3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The 18q deletion syndrome (18q-) is a multiple-anomaly disorder associated
      with mental retardation, white matter anomalies in the brain, growth
      hormone deficiency, congenital aural atresia, orofacial cleft (OFC), and
      palate abnormalities.
    explanation: >-
      Lists growth hormone deficiency among the characteristic features of the
      syndrome.
  - reference: PMID:34956087
    reference_title: "Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Some cases with 18q- syndrome can be combined with growth hormone
      deficiency (GHD)
    explanation: >-
      Confirms growth hormone deficiency as a recognized endocrine component of
      the syndrome.
  downstream:
  - target: Short stature
    description: Growth hormone deficiency and skeletal factors produce short stature.
phenotypes:
- name: Intellectual disability
  frequency: VERY_FREQUENT
  description: >-
    Intellectual disability of variable severity is a core feature; severity
    broadly correlates with deletion size and content.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:31390163
    reference_title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common presentations of 18q11-q12 deletions include developmental
      delay/intellectual disability (DD/ID) (82%)
    explanation: >-
      Quantitative support for intellectual disability as a very frequent
      feature (82%).
  - reference: PMID:34956087
    reference_title: "Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main clinical manifestations of 18q- syndrome include characteristic
      appearance, intellectual disability, and abnormal genital development.
    explanation: >-
      Independently lists intellectual disability among the main manifestations.
- name: Global developmental delay
  frequency: VERY_FREQUENT
  description: Developmental delay is present in the large majority of affected individuals.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:31390163
    reference_title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common presentations of 18q11-q12 deletions include developmental
      delay/intellectual disability (DD/ID) (82%)
    explanation: >-
      Quantitative support for developmental delay as a very frequent feature
      (82%).
- name: Short stature
  frequency: FREQUENT
  description: >-
    Short stature is common and frequently associated with growth hormone
    deficiency that responds to growth hormone therapy.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:24637311
    reference_title: "Features of two cases with 18q deletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main features of the syndrome are short stature, hearing loss,
      hypotonia, mental retardation, endocrine disorders and autoimmunity.
    explanation: >-
      Lists short stature among the main features of the syndrome.
- name: Hypotonia
  frequency: FREQUENT
  description: Generalized hypotonia is a common early feature.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:24637311
    reference_title: "Features of two cases with 18q deletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main features of the syndrome are short stature, hearing loss,
      hypotonia, mental retardation, endocrine disorders and autoimmunity.
    explanation: >-
      Lists hypotonia among the main features of the syndrome.
- name: Hearing impairment
  frequency: FREQUENT
  description: >-
    Hearing loss, frequently conductive, is characteristic and an important
    contributor to communication and educational difficulty.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:24637311
    reference_title: "Features of two cases with 18q deletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main features of the syndrome are short stature, hearing loss,
      hypotonia, mental retardation, endocrine disorders and autoimmunity.
    explanation: >-
      Lists hearing loss among the main features of the syndrome.
- name: Atresia of the external auditory canal
  frequency: FREQUENT
  description: >-
    Congenital aural atresia or stenosis of the external auditory canal is a
    characteristic structural ear anomaly underlying much of the conductive
    hearing loss, attributable to TSHZ1 haploinsufficiency.
  phenotype_term:
    preferred_term: Atresia of the external auditory canal
    term:
      id: HP:0000413
      label: Atresia of the external auditory canal
  evidence:
  - reference: PMID:22152683
    reference_title: "Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CAA is frequently seen in individuals with an 18q deletion, which is
      characterized by intellectual disability, reduced white-matter
      myelination, foot deformities, and distinctive facial features.
    explanation: >-
      States that congenital aural atresia is frequently seen in 18q deletion.
- name: Abnormal CNS myelination
  frequency: FREQUENT
  description: >-
    Abnormal cerebral white-matter MRI signal, historically attributed to
    reduced myelination from MBP haploinsufficiency, is a characteristic
    neuroimaging finding.
  phenotype_term:
    preferred_term: Abnormal CNS myelination
    term:
      id: HP:0011400
      label: Abnormal CNS myelination
  evidence:
  - reference: PMID:22152683
    reference_title: "Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CAA is frequently seen in individuals with an 18q deletion, which is
      characterized by intellectual disability, reduced white-matter
      myelination, foot deformities, and distinctive facial features.
    explanation: >-
      Identifies reduced white-matter myelination as a characteristic feature.
- name: Foot deformity
  frequency: FREQUENT
  description: Foot deformities, including clubfoot and vertical talus, are characteristic.
  phenotype_term:
    preferred_term: Abnormal foot morphology
    term:
      id: HP:0001760
      label: Abnormal foot morphology
  evidence:
  - reference: PMID:22152683
    reference_title: "Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CAA is frequently seen in individuals with an 18q deletion, which is
      characterized by intellectual disability, reduced white-matter
      myelination, foot deformities, and distinctive facial features.
    explanation: >-
      Lists foot deformities as a characteristic feature.
- name: Abnormal facial shape
  frequency: FREQUENT
  description: >-
    Distinctive/characteristic facial features aid clinical recognition of the
    syndrome.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:22152683
    reference_title: "Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CAA is frequently seen in individuals with an 18q deletion, which is
      characterized by intellectual disability, reduced white-matter
      myelination, foot deformities, and distinctive facial features.
    explanation: >-
      Lists distinctive facial features as characteristic.
  - reference: PMID:34956087
    reference_title: "Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main clinical manifestations of 18q- syndrome include characteristic
      appearance, intellectual disability, and abnormal genital development.
    explanation: >-
      Independently lists characteristic appearance among the main
      manifestations.
- name: Congenital heart disease
  frequency: OCCASIONAL
  description: >-
    Congenital heart defects, most commonly pulmonary valve anomalies and atrial
    septal defects, occur in a substantial minority of affected individuals.
  phenotype_term:
    preferred_term: Abnormal heart morphology
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  evidence:
  - reference: PMID:23707655
    reference_title: "Cardiac anomalies in individuals with the 18q deletion syndrome; report of a child with Ebstein anomaly and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Individuals with the 18q deletion syndrome are presented with various
      clinical characteristics, including cardiac anomalies in 24-36% of the
      reported cases.
    explanation: >-
      Quantifies the prevalence of cardiac anomalies in 18q deletion.
- name: Cleft palate
  frequency: OCCASIONAL
  description: >-
    Cleft palate with or without cleft lip is a characteristic craniofacial
    feature, occurring in about a quarter of affected individuals (a higher
    fraction when high-arched palate is also counted).
  phenotype_term:
    preferred_term: Cleft palate
    term:
      id: HP:0000175
      label: Cleft palate
  evidence:
  - reference: PMID:19157891
    reference_title: "The 18q deletion syndrome and analysis of the critical region for orofacial cleft at 18q22.3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The frequency of CP/L and CL among 18q- individuals is about 25%; when
      high/arched palate cases are included, the frequency rises to about 43%.
    explanation: >-
      Quantifies orofacial clefting at about 25% (occasional), rising to 43% when
      high-arched palate is included.
- name: Behavioral abnormality
  frequency: FREQUENT
  description: >-
    Autism-spectrum features, attention deficit and hyperactivity, and other
    behavioral problems are reported.
  phenotype_term:
    preferred_term: Behavioral abnormality
    term:
      id: HP:0000708
      label: Atypical behavior
  evidence:
  - reference: PMID:31390163
    reference_title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      speech delay/autism/attention deficit and hyperactivity/other behavioral
      problems (30%)
    explanation: >-
      Supports behavioral/autism-spectrum problems in roughly a third of
      proximal-deletion cases.
- name: Abnormal genital system morphology
  description: >-
    Genital anomalies (e.g., cryptorchidism, micropenis, hypoplastic labia) are
    reported among the main manifestations.
  phenotype_term:
    preferred_term: Abnormality of the genital system
    term:
      id: HP:0000078
      label: Abnormality of the genital system
  evidence:
  - reference: PMID:34956087
    reference_title: "Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main clinical manifestations of 18q- syndrome include characteristic
      appearance, intellectual disability, and abnormal genital development.
    explanation: >-
      Lists abnormal genital development among the main manifestations.
- name: Autoimmunity
  description: >-
    Autoimmune disease and humoral immunodeficiency are recognized associated
    features; autoimmune thyroiditis is reported.
  phenotype_term:
    preferred_term: Autoimmunity
    term:
      id: HP:0002960
      label: Autoimmunity
  evidence:
  - reference: PMID:24637311
    reference_title: "Features of two cases with 18q deletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The main features of the syndrome are short stature, hearing loss,
      hypotonia, mental retardation, endocrine disorders and autoimmunity.
    explanation: >-
      Lists autoimmunity among the main features of the syndrome.
genetic:
- name: 18q deletion
  association: Causal chromosomal deletion
  notes: >-
    Most affected individuals have a terminal deletion of the long arm of
    chromosome 18; deletion size and breakpoint determine which dosage-sensitive
    genes are lost and therefore the phenotype. About 94% of cases are de novo;
    around 6% are inherited from a parent carrying a balanced chromosomal
    translocation, so parental karyotyping is recommended for recurrence-risk
    assessment.
  evidence:
  - reference: PMID:33817732
    reference_title: "Case report of a novel phenotype in 18q deletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      About 94% of cases with 18q deletion syndrome appearance are de novo, and
      the remaining 6% are the inherited from a parent carrying a balanced
      chromosomal translocation.
    explanation: >-
      Supports the de novo predominance and the minority inherited via parental
      balanced translocation.
treatments:
- name: Supportive and multidisciplinary care
  description: >-
    Management is supportive and symptom-directed, with no therapy that corrects
    the deletion; care is coordinated across developmental, audiologic,
    cardiac, endocrine, orthopedic, and immunologic services.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
- name: Recombinant human growth hormone therapy
  description: >-
    Recombinant human growth hormone is effective for documented growth hormone
    deficiency and short stature in 18q- syndrome, with significant height gains
    and no significant adverse effects reported in a case-plus-literature review.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: somatropin
      term:
        id: NCIT:C837
        label: Somatropin
  evidence:
  - reference: PMID:34956087
    reference_title: "Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the average height SDS significantly increased from -3.12 ± 0.94 SDS to
      -1.38 ± 1.29 SDS after the rhGH treatment (p < 0.0001).
    explanation: >-
      Demonstrates a significant height benefit from long-term rhGH treatment in
      18q- syndrome.
- name: Genetic counseling
  description: >-
    Genetic counseling addresses recurrence risk; parental karyotyping is
    recommended because a subset of cases arise from a parental balanced
    translocation.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:33817732
    reference_title: "Case report of a novel phenotype in 18q deletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      in order to establish the recurrence risk, parental karyotypes are
      recommended.
    explanation: >-
      Supports parental karyotyping and genetic counseling for recurrence-risk
      assessment.
diagnosis:
- name: Chromosomal microarray and karyotype analysis
  description: >-
    Chromosomal microarray (array-CGH / SNP array) is first-line for defining
    deletion breakpoints and size for genotype-phenotype mapping; karyotype and
    parental karyotyping detect larger rearrangements and balanced parental
    translocations.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: MAXO:0000127
      label: genetic testing
  evidence:
  - reference: PMID:31390163
    reference_title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Since the establishment of chromosomal microarrays in clinical practice,
      many new microdeletion/microduplication syndromes have been identified,
      including 18q11.2 microdeletion.
    explanation: >-
      Supports chromosomal microarray as the diagnostic modality that delineates
      18q deletions.
differential_diagnoses:
- name: Pitt-Hopkins syndrome
  description: >-
    Pitt-Hopkins syndrome is caused by TCF4 haploinsufficiency and overlaps the
    severe neurodevelopmental phenotype seen when 18q deletions include TCF4.
  disease_term:
    preferred_term: Pitt-Hopkins syndrome
    term:
      id: MONDO:0012589
      label: Pitt-Hopkins syndrome
- name: trisomy 18
  description: >-
    Trisomy 18 (and mosaic forms / ring chromosome 18) shares dysmorphism,
    cardiac defects, and rocker-bottom feet and enters the differential,
    particularly in mosaic or dicentric rearrangements.
  disease_term:
    preferred_term: trisomy 18
    term:
      id: MONDO:0018071
      label: trisomy 18
discussions:
- discussion_id: gap_18q_mbp_myelination_vs_gliosis
  prompt: >-
    Is the abnormal cerebral white-matter MRI signal in 18q deletion syndrome
    caused by MBP-haploinsufficiency dysmyelination, or by gliosis with intact
    myelin? A single autopsy study of a ring-18 patient with confirmed MBP
    haploinsufficiency found the brain to be well myelinated and attributed the
    MRI signal to gliosis, contradicting the long-standing dysmyelination model.
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Reduced central white-matter myelination
  rationale: >-
    The MBP-dysmyelination hypothesis is mechanistically attractive (MBP lies in
    the deleted 18q23 region and is required for myelin compaction), but human
    pathology evidence is limited to a single autopsy case in which myelin was
    histologically and ultrastructurally intact despite confirmed MBP
    haploinsufficiency, with the MRI signal instead reflecting gliosis. This is a
    model/observation mismatch rather than absent evidence: the imaging finding
    is real and reproducible, but its cellular basis (dysmyelination vs gliosis)
    is unresolved, which matters for interpreting MBP dosage as the driver of the
    white-matter phenotype.
  evidence:
  - reference: PMID:21669507
    reference_title: "Abnormal brain MRI signal in 18q-syndrome not due to dysmyelination."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the brain was well myelinated, contrary to established hypotheses about
      this disorder. The MRI signal abnormalities in 18q-syndrome could be
      attributed to gliosis and not to dysmyelination.
    explanation: >-
      Single-autopsy human pathology contradicting the MBP-dysmyelination model
      and proposing gliosis as the basis of the MRI signal.
  proposed_experiments:
  - experiment_id: exp_18q_mbp_autopsy_quantitative_ihc
    name: Quantitative MBP immunohistochemistry and electron microscopy in confirmed terminal 18q23 deletion
    description: >-
      Conduct additional autopsy studies with quantitative myelin basic protein
      immunohistochemistry and electron microscopy in patients with confirmed
      terminal 18q23 deletion (not ring chromosome) to determine whether the
      gliosis finding generalizes beyond the single ring-18 case, or whether true
      dysmyelination is detectable when MBP haploinsufficiency arises from a
      simple terminal deletion rather than a ring rearrangement.
  - experiment_id: exp_18q_mbp_dti_mtr_invivo
    name: Diffusion tensor imaging and magnetization transfer ratio cohort study
    description: >-
      Perform diffusion tensor imaging (DTI) and magnetization transfer ratio
      studies to distinguish dysmyelination from gliosis in vivo across a cohort
      of 18q deletion patients with varying breakpoints, testing whether
      white-matter microstructural metrics track with the extent of the deleted
      18q23 interval and the presence of MBP haploinsufficiency.
datasets: []
references:
- reference: PMID:22152683
  title: "Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
- reference: PMID:21669507
  title: "Abnormal brain MRI signal in 18q-syndrome not due to dysmyelination."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
- reference: PMID:23707655
  title: "Cardiac anomalies in individuals with the 18q deletion syndrome; report of a child with Ebstein anomaly and review of the literature."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
- reference: PMID:19157891
  title: "The 18q deletion syndrome and analysis of the critical region for orofacial cleft at 18q22.3."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
- reference: PMID:31390163
  title: "Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
- reference: PMID:33817732
  title: "Case report of a novel phenotype in 18q deletion syndrome."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
- reference: PMID:34956087
  title: "Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
- reference: PMID:24637311
  title: "Features of two cases with 18q deletion syndrome."
  found_in:
  - Chromosome_18q_Deletion_Syndrome-deep-research-claude_code.md
  findings: []
📚

References & Deep Research

References

8
PMID:22152683
Disruption of teashirt zinc finger homeobox 1 is associated with congenital aural atresia in humans.
No top-level findings curated for this source.
PMID:21669507
Abnormal brain MRI signal in 18q-syndrome not due to dysmyelination.
No top-level findings curated for this source.
PMID:23707655
Cardiac anomalies in individuals with the 18q deletion syndrome; report of a child with Ebstein anomaly and review of the literature.
No top-level findings curated for this source.
PMID:19157891
The 18q deletion syndrome and analysis of the critical region for orofacial cleft at 18q22.3.
No top-level findings curated for this source.
PMID:31390163
Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects.
No top-level findings curated for this source.
PMID:33817732
Case report of a novel phenotype in 18q deletion syndrome.
No top-level findings curated for this source.
PMID:34956087
Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review.
No top-level findings curated for this source.
PMID:24637311
Features of two cases with 18q deletion syndrome.
No top-level findings curated for this source.

Deep Research

1
Claude Code ▸
1. Disease Information
claude-haiku-4-5-20251001, claude-opus-4-8[1m] 20 citations 2026-06-30T08:50:03.820030

1. Disease Information

Overview. Chromosome 18q deletion syndrome (18q−) is a rare contiguous-gene chromosomal disorder caused by partial loss of the long (q) arm of chromosome 18. It was first delineated by Jean de Grouchy and colleagues in 1964 (hence "de Grouchy syndrome"). The phenotype is highly variable and dependent on deletion size and breakpoints, but the recurrent core comprises intellectual disability/developmental delay, hypotonia, short stature, characteristic facial dysmorphism, ear canal anomalies with hearing loss, foot deformities, and abnormal cerebral white-matter MRI signal. The condition is conventionally divided into a common distal (terminal) 18q deletion form and a rarer proximal interstitial 18q deletion form (≈18q11.2–q21.1).

Key identifiers: - OMIM: #601808 (Chromosome 18q deletion syndrome) - Orphanet: ORPHA:1600 (Distal monosomy 18q); proximal form tracked separately (Orphanet "Proximal monosomy 18q") - MONDO: MONDO:0011147 (chromosome 18q deletion syndrome) - GARD: Proximal chromosome 18q deletion syndrome (GARD 10866) - MeSH: "Chromosome 18 Deletion Syndrome" (Supplementary Concept) / Chromosome Deletion; Chromosomes, Human, Pair 18 - ICD-10: Q93.5 (Other deletions of part of a chromosome); ICD-11: LD44 (structural chromosome anomaly) - UMLS/MalaCards: indexed as "Chromosome 18q Deletion Syndrome" - Suggested MONDO term for KB: MONDO:0011147

Synonyms / alternative names: 18q− syndrome; 18q deletion syndrome; de Grouchy syndrome (type 2); monosomy 18q; partial monosomy of the long arm of chromosome 18; distal 18q− / proximal 18q−.

Data provenance. Information here is principally aggregated, disease-level (OMIM/Orphanet curated summaries, cohort reviews, and genotype–phenotype case series). Several quantitative phenotype frequencies derive from patient-level aggregation (literature cohorts of ~163 cases reviewed in a 2021 report; the UT San Antonio Chromosome 18 Clinical Research Center registry is the largest deeply phenotyped cohort). It is not primarily EHR-derived.

2. Etiology

Primary cause. A structural chromosomal abnormality — heterozygous deletion of part of 18q, producing haploinsufficiency of the deleted genes. Most deletions are terminal (extending to 18qter); interstitial deletions are less common.

Mechanistic origin / inheritance of the lesion. According to PubMed, ~94% of cases are de novo, and ~6% are inherited from a parent carrying a balanced (reciprocal) translocation or other balanced rearrangement that segregates unbalanced to offspring (Bohîlțea et al., 2020, Rom J Morphol Embryol; DOI). The same source states: "An estimated incidence for all types of 18q deletions is one in 55,000 births predominant on females. About 94% of cases with 18q deletion syndrome appearance are de novo, and the remaining 6% are … inherited from a parent carrying a balanced chromosomal translocation."

Complex mechanisms also occur: terminal 18q deletions are frequently associated with inverted-duplication-deletion [inv-dup del(18q)] and ring chromosome 18 / dicentric rearrangements, and low-level mosaicism can blend 18q-deletion and trisomy-18 features (Bonaglia et al., 2022, Eur J Med Genet; DOI).

Genetic risk factors. This is a sporadic structural-variant disorder, not a multifactorial/susceptibility-allele disease. "Risk" is essentially the chance of a de novo deletion or unbalanced segregation in a balanced-translocation carrier parent.

Environmental risk factors. None established. No toxin, infection, or lifestyle exposure is causally linked. Advanced parental age has not been robustly implicated for these structural deletions.

Protective factors. None applicable (chromosomal deletion).

Gene–environment interactions. Not applicable as a disease-causing mechanism; phenotypic variability is driven by deletion size/breakpoints, modifier loci, and possibly stochastic/epigenetic factors rather than measured environmental exposures.

3. Phenotypes

Frequencies below are from a 2021 systematic review/case report aggregating 163 reported cases (Wu et al., 2021, Medicine (Baltimore); PMID 34956087 / cited via the PMC review) unless otherwise noted. Phenotype types are tagged for HPO.

Phenotype Frequency Type Suggested HPO
Intellectual disability 57.1% Behavioral/cognitive HP:0001249 (Intellectual disability)
Language/motor developmental delay 49.7% Developmental HP:0001263 (Global developmental delay); HP:0000750 (Delayed speech)
Ear abnormalities (incl. canal stenosis/atresia) 65.6% Physical/structural HP:0000598 (Abnormal ear morphology); HP:0000413 (Atresia of external auditory canal)
Hearing impairment (often conductive) common Sensory HP:0000405 (Conductive hearing impairment); HP:0000407 (Sensorineural)
Mid-face hypoplasia / dysplasia 47.2% Craniofacial HP:0011800 (Midface retrusion)
Abnormal hands/feet (incl. clubfoot, vertical talus) ~41% / ~39% Skeletal HP:0001837 (Broad toe); HP:0001762 (Talipes equinovarus)
Short stature 35.0% Growth HP:0004322 (Short stature)
Ocular abnormalities (strabismus, nystagmus, coloboma) 32.5% Ophthalmologic HP:0000486 (Strabismus); HP:0000589 (Coloboma)
Genital dysplasia (cryptorchidism, micropenis, hypoplastic labia) 28.2% Genitourinary HP:0000028 (Cryptorchidism); HP:0000054 (Micropenis)
Hypotonia 40.5% Neuromuscular HP:0001252 (Hypotonia)
Congenital heart disease 19.0% (literature range 24–36%) Cardiac HP:0001627 (Abnormal heart morphology); HP:0001631 (ASD); HP:0001636 (Tetralogy/conotruncal)
Abnormal cerebral white-matter MRI signal very common Neuroimaging HP:0002500 (Abnormal cerebral white matter morphology); HP:0007younger — HP:0011399
Cleft palate / lip (± high-arched palate) ~25% CP/L; ~43% incl. high palate Craniofacial HP:0000175 (Cleft palate); HP:0000159 (Abnormal lip)
Hypothyroidism 3.7% Endocrine HP:0000821 (Hypothyroidism)
IgA deficiency / humoral immunodeficiency IgA def ~4–20%; ≥1 Ig low in 50–90% Laboratory/immune HP:0002720 (Decreased circulating IgA); HP:0002721 (Immunodeficiency)
Seizures/epilepsy subset Neurologic HP:0001250 (Seizure)
Autistic traits / behavioral problems (ADHD) subset Behavioral HP:0000729 (Autistic behavior); HP:0007018 (ADHD)
Nystagmus/poor coordination, tremor subset Neurologic HP:0000639 (Nystagmus); HP:0001337 (Tremor)

Phenotype characteristics: - Age of onset: Congenital/neonatal (dysmorphism, hypotonia, structural anomalies). Developmental and growth issues manifest through infancy and childhood. Immunodeficiency and combined (cellular) immunodeficiency can present with late onset in adulthood. - Severity: Highly variable — mild to severe; broadly correlated with deletion size and content, though same-breakpoint individuals can differ markedly. - Progression: Structural anomalies are static/congenital; cognitive disability is non-progressive but lifelong; immunodeficiency can be progressive (e.g., late-onset combined immunodeficiency). - Behavioral phenotype: A 2025 retrospective cohort comparing 18p del, 18q del, and 18p tetrasomy found measurable cognitive/behavioral impairment across chromosome-18 anomalies; 18q deletion patients showed intellectual disability with adaptive deficits (Allegri et al., 2025, Ital J Pediatr; DOI).

Quality-of-life impact. Driven mainly by intellectual disability, communication/speech impairment, hearing loss (educational/social impact), short stature, motor/orthopedic limitations, and recurrent infections. No disease-specific validated QoL instrument; general pediatric/ID QoL measures apply.

4. Genetic / Molecular Information

Nature of the lesion. Heterozygous deletion of 18q producing dosage haploinsufficiency of a contiguous gene set. Deletion sizes in case series range widely — e.g., 6.6–23.0 Mb across an eight-patient microarray cohort (Feng et al., 2016, Zhonghua Yi Xue Yi Chuan Xue Za Zhi; DOI). Terminal 18q23 involvement is present in ~87% of cases.

Critical regions / candidate genes (genotype–phenotype): - Distal critical region 18q22.3–q23 (~67.7–74.9 Mb): core of the classic syndrome. - Proximal critical region 18q12.1–q12.3 (~25.2–42.9 Mb) and 18q11–q12 (interstitial form).

Gene (HGNC suggestion) Locus Implicated phenotype Evidence
TSHZ1 (teashirt zinc-finger homeobox 1) 18q22.3 (~72.9–73.4 Mb) Congenital aural atresia (CAA), middle-ear malformation, palate Feenstra et al., 2011 — "hemizygosity of TSHZ1 leads to congenital aural atresia as a result of haploinsufficiency" (DOI)
MBP (myelin basic protein) 18q23 White-matter MRI signal abnormality (historically attributed to dysmyelination) Long-standing hypothesis; challenged by Tanaka et al., 2011 (see below) (DOI)
SALL3 18q23 Palate/craniofacial (mouse knockout palate defect) Dostal et al., 2009 (DOI)
NFATC1 18q23 Congenital heart disease Feng et al., 2016 (DOI)
GALR1 (galanin receptor 1) 18q23 Growth/neuroendocrine candidate Feng et al., 2016
TCF4 18q21.2 Pitt-Hopkins syndrome when fully deleted (severe ID, breathing anomalies) — distinguishes deletions extending more proximally Established TCF4 literature
CYB5A 18q22 Gonadogenesis/genital phenotype candidate review-level
SS18 18q11.2 Skeletal/growth candidate review-level
GATA6 18q11.2 Conotruncal heart defect (but cardiac defects often distal to GATA6, suggesting alternative mechanism) Rojnueangnit et al., 2019 (DOI)
Immune cluster: MALT1, BCL2, NEDD4L, TNFRSF11A, CD226, SOCS6 18q21–qter Humoral/combined immunodeficiency, T-/B-cell regulation Late-onset combined immunodeficiency report (PMC11186878)

Variant classification / type. The pathogenic lesion is a copy-number loss (structural variant), classified pathogenic per ACMG/ClinGen CNV criteria when encompassing the established critical region. Point mutations in single genes recapitulate sub-phenotypes — e.g., loss-of-function TSHZ1 variants (c.723G>A p.Trp241X; c.946_947delinsA p.Pro316ThrfsX16) cause isolated nonsyndromic bilateral CAA (Feenstra et al., 2011, DOI).

Functional consequence: Loss of function via haploinsufficiency (dosage sensitivity). Suggested GO/biological-process annotations: GO:0042552 (myelination), GO:0007605 (sensory perception of sound), GO:0060021 (roof of mouth/palate development), GO:0001525/heart morphogenesis GO:0003007.

Modifier genes / epigenetics. Phenotypic variability among same-size deletions implicates modifier loci, allelic content on the retained homolog (unmasked recessive alleles), and possibly position effects/epigenetic dysregulation; no specific methylation signature is established for 18q−.

Somatic vs germline: Germline/constitutional (often de novo in the germline or early embryo; mosaic forms occur).

Chromosomal abnormalities. Terminal del(18q); interstitial del(18q); ring chromosome 18 [r(18)] (combines 18p and 18q loss); inv-dup del(18q); dicentric/mosaic forms (Bonaglia et al., 2022, DOI).

5. Environmental Information

No environmental, lifestyle, or infectious agents cause 18q deletion syndrome. It is a constitutional structural chromosomal disorder. Recurrent infections seen in patients are a consequence of the associated immunodeficiency, not an etiologic exposure. (Not applicable: CTD/TOXNET/lifestyle factors.)

6. Mechanism / Pathophysiology

The unifying mechanism is haploinsufficiency of dosage-sensitive developmental genes within the deleted 18q segment, disrupting multiple organ-development programs. Causal chains by domain:

1. Neurodevelopment / CNS white matter. - Upstream: deletion of 18q23 including MBP and adjacent loci → altered myelin/glial gene dosage → abnormal cerebral white-matter MRI signal → contributing to motor delay, hypotonia, cognitive impairment. - Important nuance / knowledge gap: the historical "dysmyelination" model was directly refuted by autopsy/pathology in a ring-18 patient with confirmed MBP haploinsufficiency: Tanaka et al., 2011 found "the brain was well myelinated, contrary to established hypotheses … The MRI signal abnormalities in 18q-syndrome could be attributed to gliosis and not to dysmyelination" (DOI). This is a candidate HUMAN_MODEL_MISMATCH/knowledge-gap for the KB (single autopsy case; MBP dosage confirmed but myelin intact). Cell types: oligodendrocyte (CL:0000128), astrocyte (CL:0000127, gliosis). Process: GO:0042552 (myelination), GO:0061640 gliogenesis-related.

2. Middle/external ear development (conductive hearing loss). - TSHZ1 haploinsufficiency → failure of normal middle-ear/external-auditory-canal morphogenesis → congenital aural atresia/stenosis → conductive hearing loss (Feenstra et al., 2011; mouse Tshz1 middle-ear phenotype). UBERON: external acoustic meatus (UBERON:0001352), middle ear (UBERON:0001756). Process: GO:0042472 (inner/middle ear morphogenesis).

3. Craniofacial / palate. - TSHZ1/SALL3 dosage → palate and midface developmental defects → cleft palate/high-arched palate, midface hypoplasia (Dostal et al., 2009). Process: GO:0060021 (roof of mouth development).

4. Cardiac morphogenesis. - Candidate NFATC1 (distal) and proximal conotruncal loci → CHD, predominantly pulmonary-valve anomalies and atrial septal defects; rarer Ebstein anomaly and conotruncal defects (van Trier et al., 2013 — "All 19 individuals shared a small overlapping deletion region between 18q22.3q23. The most common cardiac defects detected were pulmonary valve anomalies and atrial septal defects"; DOI). Process: GO:0003007 (heart morphogenesis).

5. Growth axis / short stature. - Multifactorial: growth hormone deficiency (GHD) is recurrent in 18q−, plus contributions from hypothyroidism and skeletal/feeding factors. The 18q− literature explicitly lists growth hormone deficiency as a characteristic feature (Dostal et al., 2009 — "18q- … is a multiple-anomaly disorder associated with mental retardation, white matter anomalies in the brain, growth hormone deficiency, congenital aural atresia, orofacial cleft …" DOI). GHD is thought to reflect hypothalamic-pituitary dysfunction.

6. Immune system. - Loss of immune-regulatory genes in 18q21–qter (MALT1, BCL2, NFATC1, NEDD4L, CD226, SOCS6, TNFRSF11A) → impaired B-cell maturation/immunoglobulin synthesis (humoral immunodeficiency, CVID-like) and, in some, T-cell defects (late-onset combined immunodeficiency, low TREC/KREC, depleted naïve CD4+/CD8+ T cells). Cell types: B cell (CL:0000236), CD4+ T cell (CL:0000624), CD8+ T cell (CL:0000625). Process: GO:0002377 (immunoglobulin production), GO:0030183 (B cell differentiation).

Upstream vs downstream summary: The chromosomal deletion is the single upstream cause; each organ phenotype is a downstream, largely independent consequence of haploinsufficiency of region-specific genes — a classic contiguous-gene-syndrome architecture rather than a single converging pathway.

Molecular profiling. No disease-specific transcriptomic/proteomic/metabolomic signature is established; mechanistic inference rests on gene-dosage and mouse-model data (Sall3, Tshz1 knockouts).

7. Anatomical Structures Affected

Organ / system level (UBERON suggestions): - Central nervous system / brain white matter (UBERON:0002316 white matter; corpus callosum UBERON:0002336 — agenesis reported), cerebellar vermis (partial agenesis in severe cases). - Ear — external auditory canal (UBERON:0001352), middle ear (UBERON:0001756) → atresia/stenosis, conductive hearing loss; sometimes sensorineural. - Craniofacial skeleton / palate (UBERON:0001716 secondary palate; midface). - Heart (UBERON:0000948) — septa, pulmonary valve (UBERON:0002146), conotruncus, tricuspid valve (Ebstein). - Eyes (UBERON:0000970) — strabismus, nystagmus, optic anomalies, coloboma/anophthalmia (severe cases). - Skeleton / limbs — feet (clubfoot, vertical talus), hands; hip (developmental dysplasia of the hip reported — Yu et al., 2022, DOI). - Endocrine — pituitary/hypothalamus (GH axis), thyroid (UBERON:0002046). - Genitourinary — external genitalia (cryptorchidism, micropenis, hypoplastic labia). - Immune system — bone marrow / lymphoid tissue.

Tissue/cell level: oligodendrocytes & astrocytes (CNS); B and T lymphocytes (immune); cardiomyocytes/valve mesenchyme (heart); cranial neural-crest-derived mesenchyme (palate/midface).

Subcellular (GO cellular component): myelin sheath (GO:0043209); not a primary organelle-localized disorder.

Localization / laterality: Anomalies are typically bilateral (e.g., bilateral aural atresia, bilateral foot deformities), though asymmetric findings occur, especially in mosaic cases (e.g., unilateral iris coloboma marking mosaicism; Bonaglia et al., 2022, DOI).

8. Temporal Development

  • Onset: Congenital. Many features (dysmorphism, hypotonia, structural cardiac/ear/palate anomalies) present at or before birth; prenatal detection is increasingly common via NIPT/ultrasound + microarray (Bohîlțea et al., 2020, DOI).
  • Onset pattern: Chronic, static/non-progressive for most structural and cognitive features.
  • Progression / disease course: Lifelong. Developmental disability is stable (non-degenerative). Growth deficits manifest across childhood; immunodeficiency may be progressive and can present in adulthood (late-onset combined immunodeficiency).
  • Critical windows for intervention: Early childhood for hearing rehabilitation (atresia repair / bone-conduction devices), GH therapy initiation, early developmental/speech intervention; ongoing immunologic surveillance.
  • Remission: None (constitutional deletion); symptom management only.

9. Inheritance and Population

Epidemiology. - Incidence: ~1 in 40,000 (some sources) to 1 in 55,000 live births (Bohîlțea et al., 2020, DOI); Orphanet/NORD often cite ~1/40,000. - Sex ratio: Female predominance reported.

For the genetic etiology: - Inheritance pattern: Most cases de novo (~94%); ~6% inherited via a parental balanced translocation. Recurrence risk is low for de novo cases but substantially elevated when a parent carries a balanced rearrangement — parental karyotyping is recommended. - Penetrance: Effectively complete for "having an abnormal phenotype," but expressivity is highly variable (size/breakpoint-dependent and stochastic). - Anticipation: Not applicable (not a repeat-expansion disorder). - Germline/somatic mosaicism: Occurs; can soften or asymmetrically alter phenotype (mosaic del(18q)/inv-dup del or del/trisomy mixtures). - Founder effects / consanguinity / carrier frequency: Not applicable (structural de novo events; not a recessive carrier disease).

Population demographics. Reported worldwide with no strong ethnic predilection; documented across diverse populations (China, Europe, Romania, Japan, etc.). Geographic clustering reflects ascertainment, not true prevalence variation.

10. Diagnostics

Cytogenetic / molecular (definitive): - Chromosomal microarray (CMA / array-CGH / SNP array) — first-line; defines breakpoints and deletion size and enables genotype–phenotype mapping (Feng et al., 2016, DOI; Shi et al., 2017, DOI). MAXO suggestion: comparative genomic hybridization / microarray testing. - Karyotyping (G-banding) — detects larger deletions, ring 18, translocations; complements CMA for balanced-rearrangement detection in parents. - FISH — confirms terminal deletion / specific loci. - Next-generation sequencing (WES/WGS) — refines breakpoints, detects co-occurring single-gene variants (e.g., HSPG2 explaining DDH in one case; Yu et al., 2022, DOI). - Prenatal: NIPT flag + diagnostic CMA on CVS/amniocentesis; fetal ultrasound/MRI for structural anomalies.

Adjunctive clinical workup (per organ): - Audiology + temporal-bone CT (aural atresia). - Echocardiography + ECG (CHD; van Trier et al., 2013 recommend physical exam, ECG, and ultrasound in all 18q− patients, DOI). - Brain MRI (white-matter signal, corpus callosum). - Endocrine: GH stimulation testing, IGF-1, thyroid function. - Immunologic: quantitative immunoglobulins (IgG/IgA/IgM/IgE + IgG subclasses), vaccine responses, lymphocyte subsets, TREC/KREC — important given high rate of humoral and occasional combined immunodeficiency. - Ophthalmologic and orthopedic evaluation.

Clinical criteria / differential diagnosis. Diagnosis is genetic (deletion confirmation), not clinical-criteria-based. Differentials: trisomy 18 / mosaic trisomy 18; ring 18 (combined 18p/18q features); Pitt-Hopkins syndrome (if TCF4 involved); other contiguous-gene/ID syndromes; isolated nonsyndromic CAA (TSHZ1); CHARGE syndrome (coloboma + ear); 22q11.2 deletion (conotruncal CHD).

Screening. No population newborn screen. Cascade parental karyotyping when a balanced rearrangement is suspected; prenatal CMA in at-risk pregnancies.

11. Outcome / Prognosis

  • Survival / life expectancy: Generally compatible with survival into adulthood; many patients reach adulthood (a 50-year-old patient is reported — Yapijakis et al., 2020, DOI). Prognosis worsens with severe CHD, major brain malformations (corpus callosum agenesis, severe cases with anophthalmia), or significant immunodeficiency. Severe prenatally diagnosed cases with major CNS/cardiac malformations may not survive (Bohîlțea et al., 2020).
  • Morbidity / disability: Lifelong intellectual disability (mild–severe), communication and hearing impairment, motor/orthopedic disability, short stature, and infection burden are the principal contributors to disability.
  • Complications: Recurrent respiratory (≈37%), urinary (≈19%), and gastrointestinal (≈19%) infections and sepsis (≈11%) in immunodeficient patients (PMC11186878); CHD-related complications; chronic arthritis has been reported (Kashima et al., 2015, DOI* — see note below).
  • Prognostic factors: Deletion size/content (extent of critical-region involvement), presence/severity of CHD, degree of immunodeficiency, and major CNS malformations.
  • Recovery potential: Structural and cognitive deficits are permanent; targeted therapies (GH, hearing rehabilitation, Ig replacement) measurably improve specific outcomes.

Note: Kashima et al., 2015 (Clin Exp Rheumatol, PMID 25665051) report chronic arthritis in an 18q− patient treated with tocilizumab and adalimumab (abstract not available in PubMed; cite by PMID 25665051).

12. Treatment

Management is multidisciplinary and supportive/symptom-directed — no therapy corrects the deletion. MAXO suggestions in brackets.

Growth / endocrine. - Recombinant human growth hormone (rhGH) for documented GHD/short stature — effective. A case report + literature review of 16 rhGH-treated patients showed mean height SDS improving from −3.12 ± 0.94 to −1.38 ± 1.29 over ~5.9 years (Δ +1.74 SDS, p<0.0001), with a single patient gaining +2.82 SDS over 7 years and no serious adverse events (Wu et al., 2021, Medicine, PMID 34956087). [MAXO hormone replacement therapy / pharmacotherapy; therapeutic agent CHEBI: somatropin.] - Levothyroxine for hypothyroidism. [MAXO:0000088-adjacent; pharmacotherapy.]

Hearing. - Bone-conduction/bone-anchored hearing devices; surgical canaloplasty/atresia repair for aural atresia; early amplification to support speech development. [MAXO hearing aid use; surgical procedure MAXO:0000004.]

Cardiac. - Standard medical/surgical management of specific CHD (e.g., ASD/VSD repair, valve interventions). [MAXO:0000004 surgical procedure.]

Immunologic. - Immunoglobulin replacement therapy (IVIG/SCIG) and antimicrobial prophylaxis for symptomatic humoral immunodeficiency; immunologic monitoring; in combined immunodeficiency, escalated management. [MAXO immunoglobulin therapy / supportive care MAXO:0000950.]

Developmental / rehabilitative. - Early intervention, special education, speech-language therapy, physical and occupational therapy [MAXO:0000011 physical therapy], orthopedic management of foot deformities (casting/surgery).

Other / experimental. - Anti-cytokine biologics (tocilizumab, adalimumab) used for associated chronic arthritis (Kashima et al., 2015, PMID 25665051). No gene/cell/RNA therapies exist or are in trials for the deletion itself; care is individualized via the Chromosome 18 registry/clinical research center model.

Pharmacogenomics: No disease-specific PGx guidance.

13. Prevention

  • Primary prevention: Not possible for de novo deletions. For families with a known parental balanced translocation: genetic counseling, preimplantation genetic testing (PGT-SR), and prenatal diagnosis (CVS/amniocentesis + CMA) reduce recurrence. [MAXO:0000079 genetic counseling.]
  • Secondary prevention (early detection): Prenatal NIPT/ultrasound triggering diagnostic CMA; postnatal early multidisciplinary evaluation (audiology, echo, endocrine, immunology) to intervene before complications (e.g., speech delay from undetected hearing loss; infections from undetected immunodeficiency).
  • Tertiary prevention (complication avoidance): Immunoglobulin replacement/antibiotic prophylaxis to prevent infections; GH to prevent severe short stature; routine cardiac surveillance; developmental support.
  • Counseling: Recurrence-risk assessment requires parental karyotyping; risk is low if both parents are normal, substantial if a balanced rearrangement is present.

14. Other Species / Natural Disease

  • Taxonomy: Human disorder (NCBITaxon:9606). No naturally occurring animal homolog of the chromosomal syndrome.
  • Orthologous genes / models: Mouse orthologs of critical-region genes are studied — Tshz1 (middle-ear and palate development) and Sall3 (palate) knockout mice recapitulate sub-phenotypes (Dostal et al., 2009, DOI; Feenstra et al., 2011, DOI).
  • Veterinary / OMIA: No recognized natural counterpart; not zoonotic; not applicable.

15. Model Organisms

  • Mouse (Mus musculus, NCBITaxon:10090):
  • Tshz1 knockout — middle-ear malformation modeling congenital aural atresia (supports TSHZ1 haploinsufficiency as the CAA mechanism; Feenstra et al., 2011). Evidence source: MODEL_ORGANISM.
  • Sall3 knockout — palate abnormality, supporting a craniofacial candidate at 18q22.3 (Dostal et al., 2009). MODEL_ORGANISM.
  • Mbp mutants (e.g., shiverer) — classic myelin-deficiency models; relevant to the historical MBP/white-matter hypothesis, but human autopsy data (Tanaka et al., 2011, DOI) show intact myelination with gliosis in 18q−, a human–model mismatch worth flagging.
  • Model type: Single-gene mouse knockouts modeling individual sub-phenotypes; there is no whole-syntenic-deletion mouse model reproducing the full contiguous-gene syndrome — a recognized limitation.
  • Applications: Dissecting gene-specific contributions (ear, palate, myelin) rather than the integrated multisystem phenotype.
  • Resources: MGI (mouse), IMPC for null-allele phenotyping of TSHZ1/SALL3/MBP/NFATC1.

Key Evidence Summary (citable for KB evidence items)

According to PubMed, the following are high-value, snippet-quotable sources (verify exact substrings against fetched abstracts before committing as evidence):

  1. Feenstra et al., 2011, Am J Hum Genet (PMID 22152683) — TSHZ1/CAA. Quote: "hemizygosity of TSHZ1 leads to congenital aural atresia as a result of haploinsufficiency." DOI
  2. Tanaka et al., 2011, Brain Dev (PMID 21669507) — white matter. Quote: "The MRI signal abnormalities in 18q-syndrome could be attributed to gliosis and not to dysmyelination." DOI
  3. van Trier et al., 2013, Eur J Med Genet (PMID 23707655) — cardiac. Quote: "cardiac anomalies in 24-36% of the reported cases … The most common cardiac defects detected were pulmonary valve anomalies and atrial septal defects." DOI
  4. Dostal et al., 2009, J Craniomaxillofac Surg (PMID 19157891) — palate/clefts + GHD as a feature. Quote: "The 18q deletion syndrome (18q-) is a multiple-anomaly disorder associated with mental retardation, white matter anomalies in the brain, growth hormone deficiency, congenital aural atresia, orofacial cleft …" DOI
  5. Rojnueangnit et al., 2019, Mol Genet Genomic Med (PMID 31390163) — proximal 18q11-q12 deletion. Quote: "Common presentations of 18q11-q12 deletions include developmental delay/intellectual disability (DD/ID) (82%); speech delay/autism/attention deficit and hyperactivity/other behavioral problems (30%); conotruncal heart defects (15%)." DOI
  6. Feng et al., 2016 (PMID 27060316) — candidate genes. Quote: "NFATC1, GALR1, MBP, SALL3 and TSHZ1 are likely to be causative genes for congenital heart disease, psychological, growth retardation, and cleft palate." DOI
  7. Bohîlțea et al., 2020, Rom J Morphol Embryol (PMID 33817732) — incidence/inheritance. Quote: "An estimated incidence for all types of 18q deletions is one in 55 000 births predominant on females. About 94% of cases … are de novo, and the remaining 6% are … inherited from a parent carrying a balanced chromosomal translocation." DOI
  8. Bonaglia et al., 2022, Eur J Med Genet (PMID 36064004) — mosaicism/inv-dup del. DOI
  9. Yu et al., 2022, BMC Med Genomics (PMID 36123715) — 18q22.2q23 deletion + co-occurring HSPG2 variant (DDH). DOI
  10. Allegri et al., 2025, Ital J Pediatr (PMID 40001201) — behavioral phenotype across chromosome-18 anomalies. DOI

Open knowledge gaps to encode (discussions: KNOWLEDGE_GAP / HUMAN_MODEL_MISMATCH): - MBP haploinsufficiency vs. white-matter MRI signal: human pathology shows gliosis, not dysmyelination (single autopsy case) — the mechanistic basis of the imaging finding is unresolved (HUMAN_MODEL_MISMATCH). - Cardiac defects often map distal to GATA6, implying a non-GATA6 mechanism for conotruncal CHD in proximal deletions (Rojnueangnit et al., 2019). - No syntenic mouse model of the full contiguous-gene syndrome (limits integrated mechanism study).

Suggested dismech Annotation Set (quick reference)

  • MONDO: MONDO:0011147
  • Top phenotypes (HP): HP:0001249, HP:0001263, HP:0000413, HP:0000405, HP:0011800, HP:0004322, HP:0001252, HP:0000175, HP:0001627, HP:0002500, HP:0002720, HP:0000486
  • Genes (HGNC, lowercase prefix per repo convention): TSHZ1, MBP, SALL3, NFATC1, GALR1, TCF4, GATA6, MALT1, BCL2
  • Cell types (CL): CL:0000128 (oligodendrocyte), CL:0000127 (astrocyte), CL:0000236 (B cell), CL:0000624 (CD4+ T cell), CL:0000625 (CD8+ T cell)
  • Anatomy (UBERON): UBERON:0002316 (white matter), UBERON:0001352 (external acoustic meatus), UBERON:0001716 (secondary palate), UBERON:0000948 (heart), UBERON:0002046 (thyroid)
  • GO processes: GO:0042552 (myelination), GO:0042472 (ear morphogenesis), GO:0060021 (palate development), GO:0003007 (heart morphogenesis), GO:0002377 (Ig production)
  • Treatments (MAXO): hormone/pharmacotherapy (rhGH, levothyroxine), MAXO:0000004 (surgical procedure), MAXO:0000011 (physical therapy), MAXO:0000079 (genetic counseling), MAXO:0000950 (supportive care), immunoglobulin replacement

Sources (databases): MalaCards — Chromosome 18q Deletion Syndrome · OMIM #601808 · Orphanet ORPHA:1600 · GARD — Proximal chromosome 18q deletion · NORD — Chromosome 18q− Syndrome · PMC reviews PMC8695685 (GH treatment) and PMC11186878 (immunodeficiency).

Note on data sourcing: All mechanistic and clinical claims above are attributed to articles retrieved from PubMed (DOIs linked inline). Before populating KB evidence items, run just fetch-reference PMID:XXXX and just validate-references to confirm each snippet is an exact substring of the real abstract — several frequency figures (e.g., the 163-case percentages) come from review aggregation (PMID 34956087) and the immunoglobulin percentages from PMC11186878, which should be quoted directly from those sources rather than paraphrased.