Cornelia de Lange Syndrome 5 (CdLS5, HDAC8-related) — Comprehensive Disease Report

MONDO:0010471 · OMIM #300882 · Orphanet ORPHA:199 (CdLS group) · Gene: HDAC8 (Xq13.1)

Evidence source key: [H] human clinical/genetic; [M] model organism; [V] in vitro/biochemical; [C] computational/epigenomic. PMIDs cited throughout.

1. Disease Information

Overview. Cornelia de Lange syndrome type 5 (CdLS5) is the X-linked form of Cornelia de Lange syndrome caused by loss-of-function variants in HDAC8, the gene encoding histone deacetylase 8, the enzyme that deacetylates the cohesin subunit SMC3. CdLS is a multisystem congenital malformation and neurodevelopmental disorder characterized by distinctive facial features, growth restriction (pre- and postnatal), intellectual disability, upper-limb anomalies, hirsutism/hypertrichosis, and involvement of the cardiac, gastrointestinal, genitourinary and other systems [H, PMID 29995837; 30614194]. CdLS is a "cohesinopathy" and, more broadly, a disorder of transcriptional regulation (DTR) [H, PMID 37377026]. HDAC8-related CdLS is frequently non-classic/atypical, and in many patients the clinical diagnosis was not suspected before genomic testing [H, PMID 24403048].

Key identifiers. - MONDO: MONDO:0010471 (Cornelia de Lange syndrome 5) - OMIM phenotype: #300882; OMIM gene HDAC8: 300269 - Orphanet: ORPHA:199 (Cornelia de Lange syndrome, umbrella) - Gene: HDAC8, HGNC:13315, NCBI Gene 55869, Ensembl ENSG00000147099, UniProt Q9BY41; cytoband Xq13.1 - ICD-10: Q87.1 (congenital malformation syndromes predominantly associated with short stature); ICD-11: LD2F.1Y/typically coded under multiple-anomaly syndromes; MeSH: D003635 (De Lange Syndrome)

Synonyms/alternative names. CdLS5; HDAC8-related Cornelia de Lange syndrome; X-linked Cornelia de Lange syndrome; Cornelia de Lange syndrome due to HDAC8 deficiency; historically overlapping terms: Brachmann–de Lange syndrome. "Wilson–Turner-like" X-linked ID has been noted for some HDAC8 variants in the differential.

Data provenance. This report is compiled from aggregated disease-level resources (OMIM, Orphanet, HPO, consensus statements) and published patient cohorts (e.g., 38-patient HDAC8 cohort [PMID 24403048]; 716-proband CdLS cohort [PMID 37377026]); not from individual EHR data.

2. Etiology

Primary cause — genetic. Hemizygous (males) or heterozygous (females) loss-of-function variants in HDAC8 [H, PMID 24403048; 22885700]. HDAC8 is the vertebrate SMC3 deacetylase; CdLS-causing variants abolish enzymatic activity ("all cause a loss of enzymatic function") [H/V, PMID 24403048].

Genetic risk factors. - Causal variants: predominantly missense and largely de novo; also nonsense, frameshift, splice, and deletions [H, PMID 24403048]. - Modifier of expressivity in females: pattern of X-chromosome inactivation (XCI). Skewed XCI silencing the mutant allele attenuates phenotype; random/unfavorable XCI increases severity [H, PMID 24403048; 26671848]. - Broader locus heterogeneity: other CdLS genes (NIPBL, SMC1A, SMC3, RAD21, BRD4, ANKRD11) cause overlapping phenotypes; genetic background may modify.

Environmental risk factors. None established. CdLS is a monogenic Mendelian disorder; no confirmed toxic, infectious, dietary, or occupational cause. Male sex is a risk factor for greater severity in HDAC8-CdLS (hemizygosity, no XCI buffering) [H, PMID 24403048]. Family history relevant when a carrier mother is mosaic.

Protective factors. The principal "protective" mechanism is favorable (skewed) X-inactivation in heterozygous females, which can render carriers mildly affected or clinically unaffected [H, PMID 26671848]. No dietary/lifestyle protective factors are known. gnomAD constraint (HDAC8 highly intolerant to LoF) argues against benign LoF variation.

Gene–environment interactions. Not established; disease is essentially fully genetically determined. The main "gene–gene/epigenetic" interaction is XCI × mutant allele.

3. Phenotypes

HDAC8-CdLS overlaps classic CdLS but is often milder and has discriminating features. Frequencies below are drawn from CdLS-spectrum and HDAC8 cohorts [PMID 24403048; 30614194; 29995837]; HDAC8-specific frequencies are smaller-N.

Craniofacial (near-universal; congenital). - Synophrys / arched eyebrows — HP:0000664 / HP:0000574 (characteristic across CdLS) [PMID 30614194] - Short nose with anteverted nares, depressed bridge — HP:0003196 / HP:0000463 [PMID 30614194] - Long philtrum, thin upper vermilion — HP:0000343 / HP:0000219 [PMID 30614194] - Micrognathia — HP:0000347; low-set/posteriorly rotated ears - HDAC8-discriminating: delayed anterior fontanelle closure (HP:0001476), ocular hypertelorism (HP:0000316), hooding of eyelids, broader nose, dental anomalies (HP:0000164) [H, PMID 24403048]. "often displays delayed anterior fontanelle closure, ocular hypertelorism, hooding of the eyelids, a broader nose and dental anomalies, which may be useful discriminating features" [PMID 24403048].

Growth (congenital/childhood, chronic). Prenatal and postnatal growth restriction — HP:0001511 / HP:0001510; microcephaly (often postnatal) — HP:0000252 [PMID 30614194]. Severity generally milder in HDAC8 than NIPBL.

Neurodevelopment (childhood, lifelong). Intellectual disability — HP:0001249; global developmental delay — HP:0001263; speech delay — HP:0000750. HDAC8 cases trend milder cognitively than NIPBL but ID is typical.

Neurobehavioral/psychiatric (childhood → adult; persistent). - Autism spectrum features — HP:0000717 (significantly elevated vs comparison syndromes) [H, PMID 23937369]; ASD criteria may increase over time [PMID 30941551] - Anxiety — HP:0000739 (common, persistent; intolerance of uncertainty a driver) [PMID 36199025; 40878447] - Self-injurious behavior — HP:0100716; stereotypies — HP:0000733 - Catatonia-like attenuated behavior in ~30.3% of CdLS [PMID 29536582]

Limb (congenital). Upper-limb reduction defects (oligodactyly, absent forearm) — HP:0009821/HP:0002984 are characteristic of severe NIPBL CdLS but typically ABSENT or mild in HDAC8-CdLS [PMID 24403048; 30158690]. Small hands/feet, 5th-finger clinodactyly (HP:0004209) may occur.

Other systems. Hirsutism/hypertrichosis — HP:0001007; congenital heart defects — HP:0001627 (e.g., septal defects, pulmonary stenosis); gastro-esophageal reflux and GI dysmotility — HP:0002020; cryptorchidism/genital anomalies — HP:0000028; hearing loss — HP:0000365; ptosis — HP:0000508; myopia/ophthalmologic issues; seizures — HP:0001250 (subset). Male hemizygotes more severely affected [PMID 24403048].

Quality-of-life impact. Substantial: lifelong intellectual disability, communication limits, anxiety, self-injury, GI symptoms, and feeding difficulty impair adaptive functioning and caregiver burden [PMID 36199025; 29536582]. Disease-specific/formal QoL instrument data (EQ-5D/SF-36) are limited for CdLS5 specifically — not available at HDAC8 subtype resolution.

4. Genetic / Molecular Information

Causal gene. HDAC8 (HGNC:13315; OMIM 300269), Xq13.1, encoding a class I zinc-dependent histone/lysine deacetylase; physiological substrate for the CdLS mechanism is cohesin subunit SMC3 (acetyl-K105/K106) [H/V, PMID 22885700].

Pathogenic variants. - Types: predominantly missense (clustered around catalytic residues/active site), plus nonsense, frameshift, splice-site, and intragenic/whole-gene deletions [H, PMID 24403048]. Recurrent examples reported include p.His180Arg, p.Gly304 region, p.Thr311Met, and catalytic-domain substitutions (variant-level detail curated in ClinVar/HGMD). - Classification (ACMG/AMP): pathogenic/likely pathogenic for LoF and functionally validated missense; some VUS resolved by enzymatic assay or DNA-methylation episignature. - Allele frequency: essentially absent from population databases (gnomAD) — consistent with a highly constrained, disease-causing gene. - Origin: germline, mostly de novo; maternal mosaicism documented (unaffected mother mosaic → two affected sibs) [H, PMID 26671848]. HDAC8 somatic mutations occur in cancers but are unrelated to CdLS. - Functional consequence: loss of function / loss of enzymatic (deacetylase) activity [H/V, PMID 24403048].

Modifier genes / factors. X-inactivation pattern is the dominant modifier in females [PMID 26671848]. NIPBL expression level correlates with severity across CdLS broadly [PMID 27125329]. No specific trans-modifier gene proven for HDAC8.

Epigenetic information. CdLS displays a reproducible genome-wide DNA-methylation "episignature" usable diagnostically; it can confirm diagnosis in mutation-negative patients and reclassify VUS, though sensitivity is heterogeneous across CdLS cases [C/H, PMID 38751117; 37872275]. Mechanistically, HDAC8 loss alters SMC3 acetylation and cohesin-dependent chromatin architecture/transcription [V, PMID 22885700].

Chromosomal abnormalities. CdLS5 is a single-gene disorder; large Xq13 deletions encompassing HDAC8 can cause it and are detectable by CMA. Otherwise no characteristic karyotypic change.

5. Environmental Information

Environmental factors: none established. Lifestyle factors: none causal (monogenic disorder). Infectious agents: not applicable. (Environmental contribution is essentially nil; disease is genetically determined.)

6. Mechanism / Pathophysiology

Causal chain (initiating lesion → clinical manifestation)

1. A loss-of-function HDAC8 variant results in loss of HDAC8 lysine-deacetylase activity [H/V, PMID 24403048].
2. Loss of HDAC8 activity leads to failure to deacetylate SMC3 (acetyl-K105/K106) during mitotic exit → increased/retained SMC3 acetylation [V, PMID 22885700].
3. Retained-acetyl SMC3 results in inefficient dissolution of the "used" cohesin complex released from chromatin (prophase and anaphase) and its improper recycling/reloading [V, PMID 22885700].
4. This leads to decreased occupancy at cohesin binding sites genome-wide → altered chromatin architecture and gene transcription (a pattern shared with NIPBL-mutant CdLS) [V, PMID 22885700].
5. Dysregulated developmental transcription results in abnormal patterning/differentiation of multiple lineages, notably cranial neural crest — (branch, demonstrated in mouse): HDAC8 loss de-represses homeobox factors Otx2 and Lhx1 in cranial neural crest, leading to skull/craniofacial malformation [M, PMID 19605684].
6. Multilineage transcriptional dysregulation during embryogenesis results in the CdLS phenotype: craniofacial dysmorphism, growth restriction, CNS/neurodevelopmental and behavioral abnormalities, limb, cardiac, and GI anomalies [H, PMID 29995837].
7. (Female branch) Skewed X-inactivation silencing the mutant HDAC8 allele attenuates the phenotype; hemizygous males lack this buffering and are more severely affected [H, PMID 24403048; 26671848].

Note on inference: Steps 1–4 are biochemically demonstrated in human cells; step 5 (Otx2/Lhx1) is demonstrated in mouse neural crest and inferred to underlie human craniofacial features; step 6 is the clinical–molecular correlation.

Detail by category

• Molecular pathways: cohesin cycle / sister-chromatid cohesion establishment–dissolution; cohesin-mediated chromatin looping and enhancer–promoter regulation (Reactome "Cohesin Loading onto Chromatin," "Establishment of Sister Chromatid Cohesion"). Downstream developmental TF networks (Otx2, Lhx1). Not a classic signaling cascade (Wnt/MAPK) primarily, though cohesin regulates many such loci.
• Cellular processes: GO:0016575 histone deacetylation; GO:0007062 sister chromatid cohesion; GO:0006325 chromatin organization; GO:0006351 transcription; cell-fate specification/patterning; cranial neural crest migration/differentiation. Increased apoptosis of neural crest in Hdac8-null skull [M, PMID 19605684].
• Protein dysfunction: loss of catalytic deacetylase activity (Zn2+-dependent hydrolase, InterPro/Pfam PF00850 Hist_deacetyl; PDB structures of HDAC8 available). Missense variants disrupt catalysis/substrate binding → LoF [V, PMID 24403048].
• Biochemical abnormality: enzyme deficiency — SMC3-lysine deacetylase (HDAC8) [V, PMID 22885700].
• Epigenetic changes: aberrant SMC3 acetylation; altered histone deacetylation of neural-crest TF loci; reproducible blood DNA-methylation episignature [PMID 22885700; 38751117].
• Immune/metabolic involvement: not central; no primary immunodeficiency/metabolic defect characteristic of CdLS5.
• Transcriptomics: CdLS cell lines (NIPBL or HDAC8 mutant) share a consistent altered transcription profile with reduced cohesin site occupancy [V, PMID 22885700].
• Cell types (CL) / anatomy (UBERON): CL:0000333 cranial neural crest cell; UBERON:0003129 skull; UBERON:0001890 forebrain.

7. Anatomical Structures Affected

• Organ/system level (primary): craniofacial skeleton/skull (UBERON:0003129), central nervous system/brain (UBERON:0000955), musculoskeletal/limbs (upper limb UBERON:0002102). Secondary/associated: heart (UBERON:0000948), gastrointestinal tract incl. esophagus (UBERON:0001043)/gut, genitourinary tract (UBERON:0000079), ears/auditory system (UBERON:0001690), eyes (UBERON:0000970), skin/hair (hypertrichosis).
• Body systems: nervous, craniofacial/skeletal, cardiovascular, digestive, genitourinary, integumentary, sensory (auditory/visual), endocrine (growth).
• Tissue/cell level: connective/skeletal (cranial bones), nervous tissue; key developmental population = cranial neural crest cells (CL:0000333) [M, PMID 19605684].
• Subcellular (GO cellular component): GO:0005634 nucleus; GO:0000785 chromatin; GO:0008278 cohesin complex; GO:0005737 cytoplasm (HDAC8 also cytoplasmic).
• Localization/lateralization: malformations are generally bilateral/symmetric (craniofacial midline and paired structures); limb involvement, when present in the broader spectrum, can be asymmetric.

8. Temporal Development

• Onset: congenital — malformations arise in embryogenesis; growth restriction detectable prenatally; dysmorphism recognizable at birth [H, PMID 29995837]. Onset pattern: chronic/static malformation with developmental unfolding.
• Progression: Non-progressive at the malformation level; lifelong/chronic course. Neurobehavioral features (autism traits, anxiety, catatonia-like attenuation) can emerge or intensify across childhood into adulthood [H, PMID 30941551; 29536582]. Adaptive ability tends to be stable with some receptive-language gains [PMID 30941551].
• Patterns: No remission (structural/genetic). Critical period: early embryonic neural-crest/organogenesis window sets the malformation; postnatally, early developmental/behavioral intervention is the actionable window.

9. Inheritance and Population

• Epidemiology: CdLS (all genes) estimated incidence/prevalence ~1/10,000–1/30,000 [H, PMID 32800026]. HDAC8 accounts for a minority (~4–5%) of CdLS; CdLS5 is correspondingly rarer. Precise CdLS5 prevalence: not separately established.
• Inheritance: X-linked (Xq13.1). De novo in most; can be inherited from a carrier/mosaic mother [PMID 24403048; 26671848].
• Penetrance/expressivity: Highly variable expressivity; in females penetrance/severity is modulated by X-inactivation (can be near-nonpenetrant with fully skewed favorable XCI) [PMID 26671848]. Males: essentially penetrant, more severe.
• Genetic anticipation: not applicable (not a repeat-expansion disorder).
• Germline/somatic mosaicism: documented maternal mosaicism with sibling recurrence [PMID 26671848]; relevant to recurrence-risk counseling.
• Founder effects/consanguinity/carrier frequency: no founder effect; consanguinity not relevant (X-linked, mostly de novo); carrier frequency negligible in general population (gnomAD LoF depleted).
• Population demographics: No ethnic predilection; CdLS occurs across global populations with consistent core features [H, PMID 30614194]. Sex ratio: both sexes affected; males more severely affected, females often milder/atypical [PMID 24403048]. Age distribution: present from birth through adulthood.

10. Diagnostics

• Clinical criteria: 2018 first international consensus provides diagnostic criteria for classic and non-classic CdLS and a cardinal/suggestive feature scoring approach; recommends molecular confirmation [H, PMID 29995837]. Facial-analysis technology aids recognition across populations (sensitivity ≥95%, specificity ≥91%) [PMID 30614194].
• Genetic testing (recommended, definitive):
• Multigene NGS panel / WES / WGS covering the seven CdLS/DTR genes incl. HDAC8 — first-line; HDAC8 sequencing is "indispensable" in CdLS workup [H, PMID 26671848]. WGS adds detection of structural/deep-intronic variants.
• Single-gene HDAC8 sequencing when HDAC8 phenotype suspected.
• Chromosomal microarray (CMA) to detect Xq13 deletions/CNVs.
• Deep/mosaicism-aware sequencing of multiple tissues (buccal, fibroblasts) because somatic/parental mosaicism is common in CdLS [PMID 26671848].
• X-inactivation assay in females to interpret expressivity [PMID 24403048].
• Omics-based diagnostics: DNA-methylation episignature as an orthogonal classifier to confirm mutation-negative CdLS and reclassify VUS [C, PMID 38751117; caution on sensitivity per PMID 37872275]. Functional SMC3-deacetylation/enzyme assays can validate missense VUS [V, PMID 24403048].
• Supportive clinical tests: echocardiography (CHD), hearing and ophthalmologic evaluation, GI/reflux workup, renal ultrasound, growth monitoring, developmental/behavioral assessment (per consensus surveillance) [PMID 29995837].
• Differential diagnosis: classic NIPBL-CdLS and other cohesinopathy genes (SMC1A, SMC3, RAD21); CdLS-like DTRs (ANKRD11/KBG, EP300, AFF4/CHOPS, TAF1, BRD4); Warsaw breakage syndrome (DDX11), Roberts syndrome (ESCO2), fetal alcohol spectrum, Coffin–Siris, Rubinstein–Taybi [H, PMID 31721174; 36703504].
• Screening: No population newborn screening (not applicable). Cascade/carrier and prenatal testing offered once a familial variant is known; prenatal ultrasound may show IUGR, limb/heart anomalies.

11. Outcome / Prognosis

• Survival/life expectancy: Many individuals survive into adulthood, particularly milder (incl. many HDAC8) cases; life expectancy is influenced by complications (severe CHD, GI/aspiration, infections). Formal CdLS5-specific survival statistics: not established. Hemizygous males (more severe) have poorer prognosis than mildly affected skewed-XCI females [PMID 24403048].
• Morbidity/function: Lifelong intellectual disability and behavioral morbidity (anxiety, ASD, self-injury, catatonia-like features) dominate disability burden [PMID 36199025; 29536582]. Growth failure, feeding/GI problems, hearing/vision deficits contribute.
• Complications: GERD and GI dysmotility, aspiration, recurrent infections, congenital heart disease, seizures, behavioral crises/self-injury.
• Recovery potential: Malformations are static; developmental and behavioral outcomes are improvable with early intervention/therapy; no cure.
• Prognostic factors: genotype/gene (HDAC8 milder than NIPBL), sex and X-inactivation pattern, severity of CHD/GI disease, degree of ID. No validated molecular prognostic biomarker beyond gene/variant and XCI [PMID 24403048; 27125329].

12. Treatment

No disease-modifying/curative therapy exists; management is multidisciplinary and supportive, per the 2018 consensus [H, PMID 29995837].

• Supportive/medical (NCIT: C15277 Supportive Care):
• GI: anti-reflux medical therapy (proton-pump inhibitors — NCIT C29708; H2 blockers), nutritional support, fundoplication/gastrostomy for severe GERD/feeding failure.
• Cardiac: surgical/medical management of congenital heart defects.
• ENT/audiology: hearing aids, myringotomy tubes for otitis; ophthalmology for ptosis/refractive error.
• Growth/endocrine: nutritional optimization; growth monitoring.
• Neurology: anti-seizure medication if epilepsy.
• Neurobehavioral/psychiatric (NCIT C15313 Psychosocial/Behavioral therapy; C265 Pharmacotherapy): behavioral therapy for self-injury/ASD; SSRIs (e.g., sertraline — NCIT C47727) for anxiety/OCD-like symptoms; treat pain/occult GI sources of behavioral change; address intolerance of uncertainty in anxiety interventions [PMID 40878447; 36199025].
• Surgical/interventional (NCIT C15329 Surgery): cardiac repair, fundoplication/gastrostomy, orchidopexy for cryptorchidism, cleft/orthodontic and other reconstructive procedures as indicated.
• Rehabilitative: physical, occupational, and speech/language therapy; special education; early developmental intervention.
• Advanced/experimental therapeutics: None approved. No gene, cell, RNA, or targeted therapy in clinical use for CdLS5. HDAC-modulation strategies are conceptual/preclinical only; no CdLS-specific trials identified. Pharmacogenomics: no CdLS5-specific PGx guidance.
• Treatment strategy: individualized, guided by the consensus care/surveillance pathway; genotype-informed counseling but not yet genotype-targeted drug therapy [PMID 29995837].

13. Prevention

• Primary prevention: Not possible (mostly de novo genetic disorder). Prevention centers on reproductive counseling for families with a known variant.
• Secondary prevention: Early molecular diagnosis → structured surveillance (cardiac, GI, hearing, vision, growth, behavioral) to detect and treat complications early [PMID 29995837].
• Tertiary prevention: Aggressive management of GERD/aspiration, CHD, and behavioral/self-injury to prevent morbidity.
• Genetic screening/counseling: genetic counseling (X-linked risks, de novo vs mosaic recurrence), prenatal testing / PGT when a familial variant is known; test/counsel potentially mosaic mothers given documented sibling recurrence [PMID 26671848]. NSGC/ACMG counseling frameworks apply.
• Immunization/public-health/environmental measures: not applicable beyond routine pediatric care.

14. Other Species / Natural Disease

• Taxonomy/orthologs: HDAC8 is conserved across vertebrates. Mouse Hdac8 (NCBI Gene 70315; NCBI Taxon 10090); also conserved in rat, zebrafish. Cohesin/SMC3 machinery conserved from yeast (Hos1 is the yeast SMC3 deacetylase analog) to humans [PMID 22885700].
• Natural disease in other species: No well-characterized naturally occurring HDAC8-CdLS in companion/wild animals reported in OMIA; not applicable/none documented. Veterinary relevance: none established.
• Comparative biology: The cohesin acetylation cycle and neural-crest role of Hdac8 are evolutionarily conserved, underpinning cross-species disease modeling [PMID 22885700; 19605684].
• Transmission/zoonosis: not applicable (genetic disorder).

15. Model Organisms

• Mouse (Mus musculus, NCBI Taxon 10090) — primary model [M, PMID 19605684]:
• Global Hdac8 knockout: perinatal lethality due to skull instability — models the craniofacial malformation.
• Conditional (cranial neural crest–specific, e.g., Wnt1-Cre) knockout: phenocopies the skull defect, localizing pathogenesis to cranial neural crest.
• Mechanistic readout: HDAC8 represses homeobox TFs Otx2 and Lhx1; loss de-represses them → aberrant skull patterning; increased neural-crest apoptosis.
• Recapitulation: strong for craniofacial/skull patterning; limitations: global KO perinatal lethality limits study of postnatal neurobehavioral phenotypes; does not capture X-inactivation mosaicism of human females.
• Zebrafish (Danio rerio) / cohesinopathy models: cohesin (nipbl, esco2, rad21) models reproduce craniofacial and developmental gene-expression phenotypes, supporting the transcriptional-dysregulation mechanism shared with HDAC8 [M, PMID 29084713].
• In vitro / cellular models: patient-derived lymphoblastoid/fibroblast lines showing increased SMC3 acetylation, reduced cohesin occupancy, and altered transcription [V, PMID 22885700]; recombinant HDAC8 enzymatic assays to test variant activity [V, PMID 24403048]. iPSC/organoid HDAC8-CdLS models: an emerging but not yet standard resource.
• Model databases: MGI (mouse Hdac8), IMPC, ZFIN (zebrafish), Alliance of Genome Resources.

Summary Answer

Cornelia de Lange syndrome 5 is the X-linked (Xq13.1) form of CdLS caused by loss-of-function variants in HDAC8, the deacetylase for the cohesin subunit SMC3. Impaired SMC3 deacetylation disrupts the cohesin acetylation/recycling cycle and cohesin-dependent transcriptional regulation during development (a "cohesinopathy"/disorder of transcriptional regulation), producing a multisystem malformation and neurodevelopmental syndrome that overlaps classic CdLS but is often milder/atypical, with discriminating features (delayed fontanelle closure, ocular hypertelorism, dental anomalies); hemizygous males are more severely affected, while heterozygous females are variably affected depending on X-inactivation. Management is multidisciplinary and supportive with no disease-modifying therapy; diagnosis rests on consensus clinical criteria plus molecular testing (with episignature/functional assays as adjuncts).

Key Limitations

• Many phenotype frequencies and prognosis/QoL data are CdLS-spectrum-level, not HDAC8-specific (small N for CdLS5).
• No CdLS5-specific survival, incidence, or clinical-trial data; therapeutics remain supportive.
• Variant-level ClinVar/gnomAD counts were not directly queried in this literature-based synthesis and should be verified in those databases for KB population.

Primary References (PMIDs)

22885700 (Deardorff 2012, Nature, HDAC8=SMC3 deacetylase/mechanism); 24403048 (Kaiser 2014, 38-patient HDAC8 cohort, X-linked, discriminating features); 26671848 (Parenti 2016, HDAC8 spectrum, skewed XCI, maternal mosaicism); 19605684 (Haberland 2009, Hdac8 mouse skull/neural crest, Otx2/Lhx1); 29995837 (Kline 2018, first international consensus); 37377026 (Kaur 2023, 716 probands, DTR framing); 30614194 (Dowsett 2019, diverse populations); 30158690 (Yuan 2019, mild end of spectrum); 27125329 (Kaur 2016, NIPBL levels/severity); 23937369, 36199025, 29536582, 30941551, 40878447 (CdLS neurobehavioral phenotype); 38751117, 37872275 (episignature diagnostics); 31721174 (chromatinopathies review); 29084713 (zebrafish cohesinopathy model).

Artifacts

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Reference Validation

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All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

• HP:0000574 (1 mention) - the report calls it "characteristic across CdLS"; HP calls it Thick eyebrow
• HP:0000463 (1 mention) - the report calls it "PMID 30614194"; HP calls it Anteverted nares
• HP:0000219 (1 mention) - the report calls it "PMID 30614194"; HP calls it Thin upper lip vermilion
• HP:0000252 (1 mention) - the report calls it "PMID 30614194"; HP calls it Microcephaly
• HP:0000717 (1 mention) - the report calls it "significantly elevated vs comparison syndromes"; HP calls it Autism
• HP:0000739 (1 mention) - the report calls it "common, persistent; intolerance of uncertainty a driver"; HP calls it Anxiety
• HP:0001250 (1 mention) - the report calls it "subset"; HP calls it Seizure

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

• GO:0016575 (obsolete histone deacetylation) (1 mention)

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• HP:0001476 (1 mention) - the report calls it "HDAC8-discriminating: delayed anterior fontanelle closure"; HP calls it Delayed closure of the anterior fontanelle**, and lists "Delayed closure of anterior fontanelle" among its other names

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.