Chromosome 18q Deletion Syndrome

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 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).

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.