CHD8-Related Neurodevelopmental Disorder with Overgrowth

Mendelian MONDO:0014017 Pathograph 21 Show in embeddings browser Neurodevelopmental Disorder Genetic Disease

CHD8-related neurodevelopmental disorder with overgrowth (CHD8-NDD; MONDO:0014017, OMIM 615032, also catalogued as "intellectual developmental disorder with autism and macrocephaly"/IDDAM) is an autosomal dominant, highly penetrant monogenic neurodevelopmental syndrome caused by heterozygous loss-of-function variants in CHD8 (HGNC:20153) at 14q11.2. CHD8 encodes chromodomain helicase DNA-binding protein 8, an ATP-dependent chromatin remodeller that binds the promoters of a large network of neurodevelopmental and autism risk genes. Haploinsufficiency produces a recognisable clinical gestalt: generalised overgrowth with macrocephaly (usually apparent in infancy) and tall stature (usually emerging around puberty), developmental delay with disproportionate speech and motor delay, intellectual disability that is most often mild to moderate, autism spectrum disorder, a characteristic facies (broad forehead with prominent supraorbital ridges, hypertelorism/widely spaced eyes, depressed nasal bridge, long philtrum, large ears), sleep disturbance affecting both sleep initiation and maintenance, and gastrointestinal dysfunction dominated by constipation. Less frequent features include hypotonia (about 30%), seizures (10%-15%), and rarely dystonia and Chiari I malformation. Most probands carry a de novo variant, but inherited variants with markedly variable expressivity are documented. Entity scope (NEC boundary, see `discussions` and `differential_diagnoses`): this entry is the MONOGENIC CHD8 haploinsufficiency syndrome anchored on MONDO:0014017 / OMIM:615032 / RO:0004003 HGNC:20153. It is deliberately kept distinct from (i) broad multifactorial autism spectrum disorder, in which CHD8 is merely one of many risk genes recovered by large-scale exome studies - that polygenic/multifactorial entity is curated separately and must not be conflated with this syndrome; and (ii) the CHD paralogue disorders that are the most common sources of citation confusion - CHD7 (CHARGE syndrome), CHD2 (developmental and epileptic encephalopathy), and CHD4 (Sifrim-Hitz-Weiss syndrome). Large-scale autism exome-sequencing cohorts are cited here only for gene discovery and gene-level burden, never for CHD8-specific phenotype frequencies; those come from the GeneReviews chapter and CHD8-ascertained clinical series.

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Classifications

Harrison's Chapter

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Mappings

MONDO

MONDO:0014017 intellectual developmental disorder with autism and macrocephaly

MONDO:0014017 carries OMIM:615032 as an xref, asserts a causal gene relationship (RO:0004003) to HGNC:20153 (CHD8), and lists "CHD8 overgrowth syndrome" (Orphanet:642675) and AUTS18 among its synonyms. All three anchors were verified with OAK before curation began; this is the NEC anchor for the entry.

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Inheritance

Autosomal dominant inheritance HP:0000006

CHD8-NDD segregates as an autosomal dominant trait. The great majority of reported probands carry a de novo CHD8 pathogenic variant, but transmitted variants occur and can be associated with strikingly milder parental presentations, indicating variable expressivity.

Autosomal dominant inheritance Expressivity: VARIABLE

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"CHD8-NDD is inherited in an autosomal dominant fashion. However, most probands reported to date whose parents have undergone molecular genetic testing have the disorder as the result of a de novo CHD8 pathogenic variant."

GeneReviews states autosomal dominant inheritance with a predominance of de novo variants.

PMID:41407309 SUPPORT Human Clinical

"We describe the case of IDDAM caused by a paternally inherited CHD8 variant. Our findings highlight the importance of considering parental inheritance in IDDAM diagnoses"

Documents transmitted (non-de novo) inheritance with variable expressivity in an IDDAM family.

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Mechanistic Hypotheses

Canonical CHD8 haploinsufficiency

chd8_canonical_haploinsufficiency CANONICAL

The mainstream model: a heterozygous loss-of-function variant halves CHD8 protein, reducing ATP-dependent chromatin remodelling at CHD8-bound promoters and dysregulating a large secondary network of neurodevelopmental and autism risk genes. Supported by the complete absence of truncating CHD8 variants in 8,792 controls, by the DNA-methylation episignature associated with CHD8 haploinsufficiency, and by dose-matched heterozygous animal models. This is the model the main pathophysiology chain in this entry represents.

Remodelling-independent mechanism for a subset of missense alleles

chd8_remodeling_independent_missense EMERGING

Evidence balance 1 support 1 partial

A minority model with real support: not every CHD8 missense variant found in autism patients is causal, and among those that are, some act by a mechanism that does NOT involve loss of chromatin-remodelling function. Independently, one individual in the largest cohort showed a possible gain-of-function methylation signature rather than the expected haploinsufficiency signature. Together these imply that "haploinsufficiency" is an incomplete description of the molecular etiology and that the pathophysiology graph should not be read as forcing every pathogenic allele through the single remodelling node.

Show evidence (2 references)

PMID:38438524 SUPPORT Model Organism

"Furthermore, we found that mutations with high scores cause ASD by mechanisms either dependent on or independent of loss of chromatin-remodeling function."

Direct functional demonstration that some pathogenic CHD8 missense alleles act independently of chromatin-remodelling loss.

PMID:36182950 PARTIAL Human Clinical

"one analysis was inconclusive, and one showing a possible gain-of-function signature instead of the expected haploinsufficiency signature was observed"

A single human episignature observation consistent with a non-haploinsufficiency mechanism; PARTIAL because it is one individual and the signature is described only as "possible".

Discussions and Knowledge Gaps

Where exactly is the boundary between this monogenic CHD8 entity and the broad multifactorial autism spectrum disorder entry that also lists CHD8 as a risk gene?

INTERPRETATION chd8_nec_boundary_vs_multifactorial_asd

kb/disorders/Autism_Spectrum_Disorder.yaml lists CHD8 among many autism risk genes. That entry models the polygenic/multifactorial disease. This entry models the syndromic, autosomal dominant, highly penetrant disorder in which a single heterozygous CHD8 loss-of-function variant is sufficient. The two must not be merged, and evidence should not be moved between them: large-scale autism exome cohorts (e.g. PMID:22495309) belong in both as gene-discovery evidence, but CHD8-ascertained phenotype frequencies (macrocephaly, overgrowth, GI, sleep) belong only here. Practical rule applied during curation: any claim sourced from a cohort that was NOT ascertained on CHD8 genotype is admissible here only for gene-level statements.

Is brain overgrowth causally upstream of the autistic and cognitive phenotype in CHD8-NDD, or are the two parallel consequences of the same progenitor lesion?

KNOWLEDGE GAP chd8_brain_overgrowth_causality_for_behaviour

Attached to

pathophysiology#Brain Overgrowth and Megalencephaly

Macrocephaly and autism co-segregate tightly in CHD8-NDD, and both are downstream of altered progenitor proliferation, but no experiment separates them. The edge from Brain Overgrowth and Megalencephaly to the behavioural outcome is therefore modelled as INDIRECT_UNKNOWN_INTERMEDIATES rather than as a supported direct cause.

Proposed experiments

Temporally restricted CHD8 restoration in a Chd8+/- mouse that normalises brain size after the neurogenic window, testing whether behaviour is rescued independently of size.

chd8_exp_brain_size_vs_behaviour_rescue

Human imaging-genetics comparison of CHD8 variant carriers stratified by head circumference against behavioural severity.

chd8_exp_imaging_genetics_ohc_vs_severity

Does the gut-to-brain contribution to behaviour demonstrated in Chd8 haploinsufficient mice operate in humans with CHD8-NDD?

HUMAN MODEL MISMATCH chd8_gut_brain_axis_human_translation

Attached to

pathophysiology#Gastrointestinal Dysmotility and Barrier Dysfunction

In mice, gut-epithelial-restricted Chd8 haploinsufficiency alters anxiety-related behaviour and antibiotic treatment attenuates social deficits, implying a microbiota-dependent gut-to-brain arm. Nothing equivalent has been shown in humans, and the human GI phenotype is documented clinically (constipation) without any demonstrated behavioural consequence. Evidence exists in the model but its translational validity is the open question, so this is a HUMAN_MODEL_MISMATCH rather than a plain knowledge gap.

Proposed experiments

Prospective characterisation of GI symptom burden, intestinal permeability and microbiome composition in a CHD8-NDD cohort with paired behavioural measures.

chd8_exp_human_gut_brain_cohort

Why do the reported CHD8-related dystonia cases show an apparent female preponderance, and how frequent is dystonia in unselected CHD8-NDD cohorts?

KNOWLEDGE GAP chd8_dystonia_female_preponderance

Every reported CHD8-related young-onset dystonia case to date has been female, and these individuals had minimal or absent cognitive and autistic features - the opposite of the classical presentation. Because the observation comes from small case series with obvious ascertainment bias, both the sex skew and the true frequency of dystonia remain unresolved; the frequency band here is taken from the GeneReviews "rare" descriptor, not from these series.

Show evidence (1 reference)

PMID:38441608 SUPPORT Human Clinical

"This work validates our previous observation that dystonia is part of the phenotypic spectrum of CHD8-related"

Source of the dystonia observation and the female-preponderance suggestion.

Is CHD8-related brain overgrowth in humans driven mainly by excess glial production, as the non-human primate data indicate, or by excess neural progenitor/neuronal output, as the rodent models are usually read to show?

HUMAN MODEL MISMATCH chd8_megalencephaly_rodent_vs_primate_mechanism

Attached to

pathophysiology#Increased Gliogenesis and White Matter Expansion pathophysiology#Brain Overgrowth and Megalencephaly

Rodent models produced inconsistent accounts of the macrocephaly mechanism, and mouse cortex is enlarged without a proportionate increase in neuron number. In cynomolgus monkey, CHD8 disruption before the gliogenic switch increases glial number and enlarges the brain. Because primate brains have a far larger glial complement and a much more protracted gliogenic period than rodent brains, this is plausibly a real species difference rather than a technical discrepancy - so the question is not whether the mouse result is reproducible but whether it translates. That is a translational-validity question about existing model evidence, which is why this is a HUMAN_MODEL_MISMATCH rather than a plain knowledge gap. Practical consequence: the entry keeps both the progenitor-proliferation route and the gliogenesis route as parallel edges into brain overgrowth rather than committing to one.

Proposed experiments

Cell-type-resolved quantification (single-nucleus RNA-seq or stereology) of glial versus neuronal number in post-mortem cortex from CHD8 variant carriers versus matched controls.

chd8_exp_human_postmortem_glia_neuron_ratio

Systematic volumetric and white-matter MRI characterisation of a CHD8-NDD cohort, testing whether white-matter expansion accounts for the increased head circumference as it does in the monkey.

chd8_exp_human_white_matter_imaging

Show evidence (1 reference)

PMID:36878905 SUPPORT Model Organism

"However, studies of small animal models showed inconsistent findings about the mechanisms for CHD8 deficiency-mediated autism symptoms and macrocephaly."

States the rodent inconsistency that the primate work was designed to resolve.

Which phenotype frequencies should this entry assert, given that CHD8 cohorts were ascertained in systematically different ways and report materially different numbers for the same features?

INTERPRETATION chd8_frequency_ascertainment_discrepancy

The published cohorts disagree in a patterned, non-random way. Cohorts recruited through overgrowth clinics report near-universal overgrowth and intellectual disability; cohorts recruited through autism cohorts report high autism rates; the largest series is a literature aggregation across both and regresses toward lower values. Concretely: macrocephaly is 62.5% in the truncating-variant series and about 80% in GeneReviews; sleep disturbance is 50% versus 29%; hypotonia is 27%-29% across two cohorts versus "about 30%" in GeneReviews. The convention applied in this entry is to band on the figure defensible across sources rather than the highest available one, to cite the quantitative statement itself as evidence for each band per the project's frequency-evidence guidelines, and to record the disagreeing figure alongside it rather than suppress it. Where the sources cannot be reconciled into a band at all, `frequency:` is omitted.

Show evidence (1 reference)

PMID:31001818 SUPPORT Human Clinical

"a pattern of common features: macrocephaly (62.5%), tall stature (47%), developmental delay and/or intellectual disability (81%), ASDs (84%), sleep difficulties (50%), gastrointestinal problems (40%), and distinct facial features"

The protein-truncating-variant cohort figures used as the primary quantitative anchor for several bands in this entry.

Does CHD8-NDD carry an increased tumour risk, and should tumour surveillance be recommended?

KNOWLEDGE GAP chd8_neoplasia_not_established

Two separate literatures could be mistaken for one. Somatic CHD8 alterations occur in sporadic microsatellite-instability-high gastric and colorectal cancers, and a retrospective aggregation of CHD8-NDD individuals recorded neoplasia in a minority. Neither establishes a germline tumour predisposition: the tumour types, comparison to population baseline, and causality are not established, and the GeneReviews management section - which would be expected to flag a tumour risk - does not recommend tumour surveillance. This entry therefore asserts no tumour phenotype and no surveillance recommendation. The point matters clinically because two conditions in this entry's differential (PTEN hamartoma tumor syndrome and Beckwith-Wiedemann syndrome) do carry defined tumour risk, so conflating them with CHD8-NDD in either direction would be harmful.

Proposed experiments

Registry linkage of a molecularly confirmed CHD8-NDD cohort to national cancer registries, with age- and sex-standardised incidence ratios against population baseline.

chd8_exp_cancer_incidence_registry_linkage

Is the marked clinical variability of CHD8-NDD - which extends from severe intellectual disability with autism to an isolated adult focal dystonia in a cognitively intact individual - driven by genetic background rather than chance?

OPEN QUESTION chd8_genetic_background_modifier

Crossing a Chd8 mutation across a mouse genetic reference panel produced strain- and sex-dependent trait disruptions, including effects in opposite directions on different backgrounds and frank resilience on others. That is a designed experiment rather than a post-hoc observation, and it makes modifier-driven variability a serious hypothesis for the human disorder. No human modifier locus has been mapped, so no MODIFIER-typed gene record is asserted in the `genetic:` section. The practical implication for counselling is that intrafamilial variability should be expected, as the documented paternal-transmission case shows.

Proposed experiments

Polygenic background and rare-variant modifier analysis within a molecularly confirmed CHD8-NDD cohort phenotyped on a common severity instrument.

chd8_exp_human_polygenic_modifier_analysis

Show evidence (1 reference)

PMID:36738737 SUPPORT Model Organism

"Some strains exhibited large effect-size trait disruptions, sometimes in opposite directions, and-remarkably-others expressed resilience."

Demonstrates background-dependent modification of the same Chd8 lesion, including resilience.

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Pathophysiology

CHD8 Haploinsufficiency

A heterozygous loss-of-function variant in CHD8 (nonsense, frameshift, splice, or a whole-gene 14q11.2 deletion) reduces functional chromodomain helicase DNA-binding protein 8 to roughly half of the normal dose. CHD8 is the root molecular lesion of the syndrome; the disorder is a dosage disease rather than a dominant-negative or gain-of-function condition, and truncating variants are essentially absent from population controls.

CHD8 hgnc:20153

ATP-dependent chromatin remodelling activity GO:0008094 ↓ DECREASED chromatin binding GO:0003682 ↓ DECREASED

Downstream

Failure of Chromatin Remodelling at CHD8 Target Promoters Halving CHD8 protein reduces occupancy and remodelling activity at the thousands of promoters CHD8 normally binds.

Show evidence (3 references)

PMID:36302072 SUPPORT Human Clinical

"The diagnosis of CHD8-NDD is established in a proband by identification of a heterozygous pathogenic (or likely pathogenic) variant in CHD8 by molecular genetic testing."

Establishes the heterozygous CHD8 variant as the defining molecular lesion.

PMID:24998929 SUPPORT Human Clinical

"we resequenced the ASD-associated gene CHD8 in 3,730 children with developmental delay or ASD. We identified a total of 15 independent mutations; no truncating events were identified in 8,792 controls, including 2,289 unaffected siblings."

Complete absence of truncating CHD8 events in 8,792 controls supports loss-of-function/haploinsufficiency as the disease mechanism.

PMID:30670789 SUPPORT Human Clinical

"confirms our suggestion that this is a syndromic disorder caused by haploinsufficiency or heterozygous loss of function of CHD8"

States haploinsufficiency explicitly as the mechanism.

Failure of Chromatin Remodelling at CHD8 Target Promoters

CHD8 binds chromatin very widely - thousands of replicated promoter-proximal sites in neural progenitors - and its target set is strongly enriched for other autism risk genes and for chromatin-modification and transcription-regulation genes. Reduced CHD8 dose therefore acts as a hub lesion: a limited set of direct binding-site effects is amplified into a far larger secondary transcriptional network.

neural progenitor cell CL:0011020

chromatin remodeling GO:0006338 ↓ DECREASED regulation of transcription by RNA polymerase II GO:0006357 ⚠ ABNORMAL

Downstream

Dysregulation of Neurodevelopmental Gene Networks

Show evidence (2 references)

PMID:25294932 SUPPORT In Vitro

"CHD8 showed widespread binding to chromatin, with 7,324 replicated sites that marked 5,658 genes."

Quantifies the breadth of CHD8 chromatin occupancy in human neural progenitor cells.

PMID:25752243 SUPPORT In Vitro

"CHD8 targets are strongly enriched for other ASD risk genes in both human and mouse neurodevelopment, and converge in ASD-associated co-expression networks in human midfetal cortex."

Shows the CHD8 target set is an autism risk-gene regulatory hub during human neurodevelopment.

Dysregulation of Neurodevelopmental Gene Networks

Reducing CHD8 to single-allele levels perturbs the expression of well over a thousand genes. Directly bound genes are dominated by chromatin and transcriptional regulators, while the indirectly down-regulated secondary network is dominated by brain-development programmes - synapse formation, neuron differentiation, cell adhesion, and axon guidance. This secondary network, not any single target, is the proximate cause of the neurodevelopmental phenotype.

synapse assembly GO:0007416 ↓ DECREASED axon guidance GO:0007411 ↓ DECREASED brain development GO:0007420 ⚠ ABNORMAL

Downstream

Impaired Wnt/beta-Catenin Signal Transduction

REST-Mediated Repression of Neuronal Genes

Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation

Glial and Serotonergic Disruption of Sleep Architecture

Striatal Circuit Dysfunction

Enteric Neural Crest and Gut Epithelial Dysfunction

Show evidence (3 references)

PMID:25294932 SUPPORT In Vitro

"Suppressing CHD8 to levels comparable with the loss of a single allele caused altered expression of 1,756 genes, 64.9% of which were up-regulated."

Establishes the scale and directionality of transcriptional dysregulation at a haploinsufficient CHD8 dose.

PMID:25294932 SUPPORT In Vitro

"Genes indirectly down-regulated (i.e., without CHD8-binding sites) reflect pathways involved in brain development, including synapse formation, neuron differentiation, cell adhesion, and axon guidance, whereas CHD8-bound genes are strongly associated with chromatin modification and..."

Identifies the specific neurodevelopmental programmes carried by the secondary network.

PMID:29668850 SUPPORT Model Organism

"Genes involved in cell adhesion and axon guidance are particularly prominent amongst the downregulated transcripts."

Independent replication in the postnatal neocortex of Chd8 heterozygous mice.

Impaired Wnt/beta-Catenin Signal Transduction

CHD8 interacts with beta-catenin and regulates the expression of key transducers of the Wnt pathway. Chd8 knockdown disrupts Wnt signalling during cortical development, and restoring Wnt signalling rescues the resulting transcriptional and behavioural deficits, making this a mechanistically load-bearing branch rather than a correlate. Wnt/chromatin-remodelling connectivity is also the network into which the most disruptive de novo autism mutations fall.

canonical Wnt signaling pathway GO:0060070 ⚠ ABNORMAL

Downstream

Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation

Show evidence (2 references)

PMID:27694995 SUPPORT Model Organism

"knockdown of Chd8 disrupts the expression of key transducers of Wnt signaling, and enhancing Wnt signaling rescues the transcriptional and behavioral deficits caused by Chd8 knockdown"

Rescue by Wnt enhancement establishes the causal role of the Wnt branch.

PMID:22495309 PARTIAL Human Clinical

"39% (49 of 126) of the most severe or disruptive de novo mutations map to a highly interconnected β-catenin/chromatin remodelling protein network ranked significantly for autism candidate genes"

Places CHD8 within the beta-catenin/chromatin-remodelling network at the level of autism genetics; PARTIAL because this is cohort-level network evidence, not a CHD8-specific functional assay.

REST-Mediated Repression of Neuronal Genes

CHD8 physically interacts with the RE-1 silencing transcription factor (REST). When CHD8 is reduced, REST is abnormally activated and represses the transcription of many neuronal genes, providing one route by which a chromatin dosage lesion is converted into a global delay of the neuronal differentiation programme. REST activation has also been observed in autism brain tissue.

negative regulation of transcription by RNA polymerase II GO:0000122 ↑ INCREASED

Downstream

Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation

Show evidence (1 reference)

PMID:27602517 SUPPORT Model Organism

"reduced expression of CHD8 was associated with abnormal activation of RE-1 silencing transcription factor (REST), which suppresses the transcription of many neuronal genes"

Identifies REST derepression of the neuronal programme as a CHD8-dosage consequence.

Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation

The convergent cellular consequence of the transcriptional lesion. CHD8 normally stimulates cell-cycle gene transcription while restraining premature induction of neural-specific genes; at reduced dose the balance between progenitor proliferation and differentiation is disturbed and neurodevelopment is globally delayed. In mouse models the effect is dosage-graded: heterozygous and mildly hypomorphic animals show increased proliferation of intermediate progenitors and brain hyperplasia, whereas severe depletion flips the phenotype to p53-driven apoptosis and brain hypoplasia.

neural progenitor cell CL:0011020 radial glial cell CL:0000681

neural precursor cell proliferation GO:0061351 ↑ INCREASED neuron differentiation GO:0030182 ↓ DECREASED cell cycle GO:0007049 ⚠ ABNORMAL

Downstream

Brain Overgrowth and Megalencephaly

Excitatory-Inhibitory Neuronal Trajectory Imbalance

Increased Gliogenesis and White Matter Expansion In primates the same progenitor-level lesion is expressed predominantly as excess glial rather than excess neuronal output.

Show evidence (3 references)

PMID:27694995 SUPPORT Model Organism

"Here we report that Chd8 knockdown during cortical development results in defective neural progenitor proliferation and differentiation that ultimately manifests in abnormal neuronal morphology and behaviors in adult mice."

Directly demonstrates the progenitor proliferation/differentiation defect and its behavioural consequence.

PMID:33627187 SUPPORT Model Organism

"We identify increased proliferation of non-ventricular zone TBR2+ intermediate progenitors as one potential cause of brain hyperplasia in these mutants."

Identifies the specific progenitor population whose excess proliferation drives brain overgrowth in a dosage-graded Chd8 allelic series.

PMID:27602517 SUPPORT Model Organism

"Gene set enrichment analysis revealed that neurodevelopment was delayed in the mutant mouse embryos."

Supports global delay of the neurodevelopmental programme.

Brain Overgrowth and Megalencephaly

Expansion of the progenitor pool translates into increased brain size, which is the tissue-level substrate of the clinical macrocephaly. This is one of the most robustly cross-validated nodes in the entry: chd8 suppression enlarges the forebrain/midbrain in zebrafish, Chd8 heterozygous mice have increased brain size, and CHD8-haploinsufficient human cerebral organoids are enlarged.

brain development GO:0007420 ⚠ ABNORMAL

brain UBERON:0000955

Downstream

Autistic, Cognitive and Neuropsychiatric Phenotype Macrocephaly and the autism/cognitive phenotype co-segregate in CHD8-NDD, but whether brain overgrowth is itself causal for the behavioural phenotype or is a parallel consequence of the same progenitor lesion is not established.

Show evidence (3 references)

PMID:24998929 SUPPORT Model Organism

"chd8 disruption in zebrafish recapitulates features of the human phenotype, including increased head size as a result of expansion of the forebrain/midbrain and impairment of gastrointestinal motility due to a reduction in postmitotic enteric neurons."

Model-organism recapitulation of both the head-size and the gastrointestinal arms of the human phenotype.

PMID:29668850 SUPPORT Model Organism

"Here, we report that Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli."

Mouse heterozygote recapitulates brain overgrowth and hypertelorism.

PMID:35385734 SUPPORT In Vitro

"This imbalance is consistent with an enlargement of cerebral organoids as an in vitro correlate of patients' macrocephaly."

Human cerebral organoid model links the cellular imbalance to enlargement, the in vitro correlate of macrocephaly.

Excitatory-Inhibitory Neuronal Trajectory Imbalance

In isogenic human cerebral organoids, CHD8 haploinsufficiency accelerates generation of inhibitory neurons and delays generation of excitatory neurons, producing symmetrically opposite, time-dependent distortions of their proportions. The effect is cell-autonomous and reflects abnormal proliferation and alternative-splicing programmes rather than a static shift in cell identity.

GABAergic (inhibitory) neuron CL:0000617 ↑ INCREASED glutamatergic (excitatory) neuron CL:0000679 ↓ DECREASED

cerebral cortex neuron differentiation GO:0021895 ⚠ ABNORMAL

Downstream

Aberrant Long-Range Functional Connectivity

Show evidence (1 reference)

PMID:35385734 SUPPORT In Vitro

"we find that CHD8 haploinsufficiency disrupted neurodevelopmental trajectories with an accelerated and delayed generation of, respectively, inhibitory and excitatory neurons that yields, at days 60 and 120, symmetrically opposite expansions in their proportions."

Directly demonstrates the excitatory-inhibitory trajectory imbalance in a human isogenic model of CHD8 haploinsufficiency.

Aberrant Long-Range Functional Connectivity

Downregulation of the cell-adhesion and axon-guidance programme that builds long-range projections is followed by measurable changes in functional brain connectivity. Resting-state fMRI in Chd8 heterozygous mice shows increased synchronised activity in cortico-hippocampal and auditory-parietal networks, suggesting that CHD8-NDD is a subtype of autism characterised by long-range OVER-connectivity, in contrast to the under-connectivity more often reported in idiopathic autism.

axon guidance GO:0007411 ↓ DECREASED

Downstream

Autistic, Cognitive and Neuropsychiatric Phenotype

Show evidence (2 references)

PMID:29668850 SUPPORT Model Organism

"Resting-state functional MRI identified increased synchronized activity in cortico-hippocampal and auditory-parietal networks in Chd8 heterozygous mutant mice, implicating altered connectivity as a potential mechanism underlying the behavioral phenotypes."

Provides the functional-imaging evidence for altered long-range connectivity.

PMID:29668850 SUPPORT Model Organism

"Our data suggest that CHD8 haploinsufficiency represents a specific subtype of ASD where neuropsychiatric symptoms are underpinned by long-range over-connectivity."

States the over-connectivity interpretation that distinguishes this subtype.

Autistic, Cognitive and Neuropsychiatric Phenotype

The organism-level neurobehavioural endpoint: autism spectrum disorder, developmental delay with disproportionate speech and motor involvement, intellectual disability usually in the mild-to-moderate range, and neuropsychiatric comorbidity including anxiety, ADHD, and aggressive or self-injurious behaviour. Chd8 heterozygous mice recapitulate the behavioural domain with increased anxiety, repetitive behaviour and altered social behaviour.

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays. When present, ID is most often in the mild-to-moderate range."

GeneReviews description of the cognitive/developmental endpoint.

PMID:27602517 SUPPORT Model Organism

"Here we show that mice heterozygous for Chd8 mutations manifest ASD-like behavioural characteristics including increased anxiety, repetitive behaviour, and altered social behaviour."

Model-organism recapitulation of the autistic and anxiety phenotype at the same gene dosage as the human disorder.

Enteric Neural Crest and Gut Epithelial Dysfunction

CHD8 is also required outside the CNS. In zebrafish, chd8 loss reduces the number of vagal neural crest cells and enteric neural/glial progenitors emigrating from the neural tube and impairs their early migration, later yielding fewer serotonergic enteric neurons and enterochromaffin cells, a thinner intestinal epithelium and fewer goblet cells. In mice, Chd8L haploinsufficiency increases intestinal permeability and reduces tuft and goblet cell counts. This is the mechanistic basis of the gastrointestinal arm of the syndrome, which is not explained by the CNS phenotype.

enteric neuron CL:0007011 ↓ DECREASED intestinal goblet cell CL:0000160 ↓ DECREASED intestinal tuft cell CL:0019032 ↓ DECREASED

enteric nervous system development GO:0048484 ⚠ ABNORMAL

Downstream

Gastrointestinal Dysmotility and Barrier Dysfunction

Show evidence (3 references)

PMID:36375841 SUPPORT Model Organism

"we found that the loss of chd8 leads to a reduced number of vagal neural crest cells (NCCs), enteric neural and glial progenitors, emigrating from the neural tube, and that their early migration capability was altered."

Establishes the enteric neural crest developmental defect downstream of chd8 loss.

PMID:36375841 SUPPORT Model Organism

"The tissue examination of chd8 mutants revealed a thinner intestinal epithelium accompanied by an accumulation of neutrophils and the decreased numbers of goblet cells and eosinophils."

Documents the intestinal epithelial and immune-balance component.

PMID:37783686 SUPPORT Model Organism

"The current study found that mice haploinsufficient for the large isoform of Chd8 (Chd8L) exhibited increased intestinal permeability, transcriptomic dysregulation in gut epithelial cells, reduced tuft cell and goblet cell counts in the gut, and an overall increase in microbial load."

Mammalian replication of the gut epithelial defect at a haploinsufficient Chd8 dose.

Gastrointestinal Dysmotility and Barrier Dysfunction

The clinical gastrointestinal endpoint: impaired gut motility (clinically, constipation with or without diarrhoea) attributable to reduced postmitotic enteric innervation, together with barrier compromise and altered microbial load. Gut-restricted manipulations in mice show this arm also feeds back on behaviour, though that gut-brain link remains a model-organism finding.

intestine UBERON:0000160

Show evidence (2 references)

PMID:24998929 SUPPORT Model Organism

"impairment of gastrointestinal motility due to a reduction in postmitotic enteric neurons"

Links reduced enteric innervation to the motility defect in the zebrafish model of the human phenotype.

PMID:37783686 SUPPORT Model Organism

"Antibiotic treatment of Chd8L haploinsufficient mice attenuated social behavioral deficits."

Supports a gut-to-brain contribution to behaviour in the mouse model; not yet demonstrated in humans.

Increased Gliogenesis and White Matter Expansion

A primate-specific arm of the overgrowth mechanism. CRISPR/Cas9 disruption of CHD8 in cynomolgus monkey embryos increases gliogenesis and the number of glial cells in newborn monkeys, and knockdown in organotypic newborn-monkey brain slices enhances glial proliferation. Because rodent studies gave inconsistent accounts of how CHD8 loss enlarges the brain - and because mouse cortex is enlarged without a proportionate increase in neuron number - glial expansion rather than neuronal excess may be the dominant driver of megalencephaly in primates, including humans. This node is retained deliberately as a parallel, species-qualified route into brain overgrowth; see the HUMAN_MODEL_MISMATCH discussion.

glial cell CL:0000125 ↑ INCREASED

gliogenesis GO:0042063 ↑ INCREASED

white matter UBERON:0002316

Downstream

Brain Overgrowth and Megalencephaly

Show evidence (2 references)

PMID:36878905 SUPPORT Model Organism

"we found that CRISPR/Cas9-mediated CHD8 mutations in the embryos of cynomolgus monkeys led to increased gliogenesis to cause macrocephaly in cynomolgus monkeys"

Establishes increased gliogenesis as the route from CHD8 disruption to macrocephaly in a non-human primate.

PMID:36878905 SUPPORT Model Organism

"However, studies of small animal models showed inconsistent findings about the mechanisms for CHD8 deficiency-mediated autism symptoms and macrocephaly."

States the rodent inconsistency that motivates treating the primate glial mechanism as a distinct, better-supported route in primates.

Glial and Serotonergic Disruption of Sleep Architecture

A mechanistically distinct arm accounting for the sleep phenotype. In Drosophila, the single CHD8/CHD7 ortholog kismet is required in glia - specifically the subperineurial glia that constitute the blood-brain barrier - for both developmental and adult sleep architecture, and the sleep disturbance is caused by elevated serotonin during development. Critically, despite this developmental origin the defect is reversible in adulthood by a behavioural regime resembling human sleep restriction therapy, which supplies a mechanistic rationale for the behavioural sleep interventions GeneReviews already recommends empirically.

blood-brain-barrier glia (Drosophila subperineurial glia) CL:0000125

Downstream

Autistic, Cognitive and Neuropsychiatric Phenotype Disrupted sleep architecture is a component of the organism-level neurobehavioural burden; whether it also worsens the cognitive and behavioural phenotype in CHD8-NDD is untested.

Show evidence (3 references)

PMID:34088660 SUPPORT Model Organism

"We show that Kismet is required in glia for early developmental and adult sleep architecture. This role localizes to subperineurial glia constituting the blood-brain barrier."

Localises the sleep requirement to blood-brain-barrier glia in the sole CHD8/CHD7 ortholog.

PMID:34088660 SUPPORT Model Organism

"We demonstrate that Kismet-related sleep disturbances are caused by high serotonin during development, paralleling a well-established but genetically unsolved autism endophenotype."

Identifies developmental hyperserotonemia as the mediator of the sleep defect.

PMID:34088660 PARTIAL Model Organism

"Despite their developmental origin, Kismet's sleep architecture defects can be reversed in adulthood by a behavioral regime resembling human sleep restriction therapy."

Shows the sleep phenotype is reversible in adulthood in the fly. Marked PARTIAL because reversibility has not been demonstrated in humans with CHD8-NDD; the claim supports the plausibility of behavioural sleep intervention, not its proven efficacy in this disorder.

Striatal Circuit Dysfunction

Chd8 heterozygous mice show brain-region-specific dysregulation of chromatin modification, mRNA/protein processing, Wnt signalling and cell-cycle regulation, together with altered synaptic physiology in medium spiny neurons of the nucleus accumbens. Perturbing Chd8 in adult mice reproduces an altered motor-learning phenotype, indicating an ongoing adult striatal requirement for CHD8 rather than a purely developmental one.

medium spiny neuron of the nucleus accumbens CL:1001474

striatum UBERON:0002435

Downstream

Autistic, Cognitive and Neuropsychiatric Phenotype

Show evidence (1 reference)

PMID:28402856 SUPPORT Model Organism

"We also find altered synaptic physiology in medium spiny neurons of the nucleus accumbens. Perturbation of Chd8 in adult mice recapitulates improved acquired motor learning behavior found in Chd8+/- animals, suggesting a role for CHD8 in adult striatal circuits."

Establishes the striatal synaptic phenotype and an adult (post-developmental) CHD8 requirement.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

Digestive 2

Constipation FREQUENT Constipation HP:0002019

Show evidence (4 references)

PMID:36302072 SUPPORT Human Clinical

"The most common gastrointestinal issue is constipation with or without periods of diarrhea."

GeneReviews identifies constipation as the most common GI issue in a disorder in which GI issues are a listed core domain; "most common" maps to FREQUENT.

PMID:24998929 SUPPORT Human Clinical

"characteristics enriched in this group included macrocephaly, distinct faces, and gastrointestinal complaints"

Independent cohort evidence for enrichment of GI complaints.

PMID:31001818 SUPPORT Human Clinical

"gastrointestinal problems (40%)"

Quantifies gastrointestinal problems at 40%, inside the FREQUENT band.

+ 1 more reference

Diarrhea Diarrhea HP:0002014

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"The most common gastrointestinal issue is constipation with or without periods of diarrhea."

GeneReviews records diarrhoea as an intermittent accompaniment; no frequency is stated, so none is asserted.

Ear 1

Large Ears Macrotia HP:0000400

Show evidence (1 reference)

PMID:31980904 SUPPORT Human Clinical

"dysmorphic features, including broad forehead with prominent supraorbital ridges, flat nasal bridge, telecanthus and large ears"

Clinical series naming large ears.

Eye 1

Hypertelorism Hypertelorism HP:0000316

Show evidence (2 references)

PMID:30670789 SUPPORT Human Clinical

"similar dysmorphic features, including widely-spaced eyes, short nose with flat nasal bridge, long philtrum, prominent Cupid's bow of the upper lip, full lower lip, and auricular anomalies"

Clinical series describing widely spaced eyes in the CHD8 facies.

PMID:29668850 SUPPORT Model Organism

"Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli"

Hypertelorism is recapitulated in the mouse heterozygote.

Head and Neck 5

Macrocephaly FREQUENT Macrocephaly HP:0000256

Show evidence (4 references)

PMID:36302072 SUPPORT Human Clinical

"The most common findings are the development of macrocephaly (most often during infancy) and tall stature (most typically during puberty), which is often accompanied by ASD and/or DD/ID."

GeneReviews names macrocephaly as one of the two most common findings of the syndrome.

PMID:31001818 SUPPORT Human Clinical

Quantifies macrocephaly at 62.5% in a 25-person CHD8 protein-truncating-variant cohort. This is the quantitative basis for the FREQUENT (30-79%) band; VERY_FREQUENT is deliberately NOT used because cohort figures range from about 52% to 80% depending on ascertainment (see the phenotype description and the frequency-ascertainment discussion).

PMID:24998929 SUPPORT Human Clinical

"In addition to a high likelihood of an ASD diagnosis among patients bearing CHD8 mutations, characteristics enriched in this group included macrocephaly, distinct faces, and gastrointestinal complaints."

Independent CHD8-ascertained cohort confirming macrocephaly enrichment.

+ 1 more reference

Depressed Nasal Bridge Depressed nasal bridge HP:0005280

Show evidence (1 reference)

PMID:30670789 SUPPORT Human Clinical

"similar dysmorphic features, including widely-spaced eyes, short nose with flat nasal bridge, long philtrum, prominent Cupid's bow of the upper lip, full lower lip, and auricular anomalies"

Clinical series describing the flat nasal bridge.

Long Philtrum Long philtrum HP:0000343

Show evidence (1 reference)

PMID:30670789 SUPPORT Human Clinical

"similar dysmorphic features, including widely-spaced eyes, short nose with flat nasal bridge, long philtrum, prominent Cupid's bow of the upper lip, full lower lip, and auricular anomalies"

Clinical series describing the long philtrum.

Downslanted Palpebral Fissures Downslanted palpebral fissures HP:0000494

Show evidence (1 reference)

PMID:36182950 SUPPORT Human Clinical

"wide-set eyes with down slanted palpebral ﬁssures"

Named as a typical dysmorphic feature of the entity. This sentence summarises the prior literature in the introduction of the largest cohort paper rather than reporting that cohort's own counts, so no frequency is asserted.

Pointed Chin Pointed chin HP:0000307

Show evidence (1 reference)

PMID:36182950 SUPPORT Human Clinical

"a broad nose with full nasal tip, and a pointed chin"

Named as a typical dysmorphic feature of the entity. As above, this is a literature-summary sentence, so no frequency is asserted.

Musculoskeletal 1

Hypotonia OCCASIONAL Hypotonia HP:0001252

Show evidence (3 references)

PMID:36302072 SUPPORT Human Clinical

"Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare)."

GeneReviews gives an approximate 30% figure, sitting exactly on the OCCASIONAL/FREQUENT boundary.

PMID:36182950 SUPPORT Human Clinical

"Many neurological abnormalities, like intellectual disability (68%) and hypotonia (29%) were observed"

Largest cohort reports 29%.

PMID:31001818 SUPPORT Human Clinical

"some had regression of speech (37%), seizures (27%) and hypotonia (27%)"

Second independent cohort reports 27%. Two independent quantified cohorts both fall below 30%, so the OCCASIONAL (5-29%) band is used rather than rounding GeneReviews' "about 30%" upward.

Nervous System 13

Global Developmental Delay VERY_FREQUENT Global developmental delay HP:0001263

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays."

"Most, if not all" maps to VERY_FREQUENT in the project's prose-to-enum table.

PMID:31001818 SUPPORT Human Clinical

"developmental delay and/or intellectual disability (81%)"

Independent cohort quantification of developmental delay and/or intellectual disability at 81%, supporting the VERY_FREQUENT band.

Delayed Speech and Language Development VERY_FREQUENT Delayed speech and language development HP:0000750

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays."

GeneReviews identifies speech delay as one of the two most common developmental domains within a near-universal developmental delay.

Motor Delay VERY_FREQUENT Motor delay HP:0001270

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays."

GeneReviews identifies motor delay as one of the two most common developmental domains within a near-universal developmental delay.

PMID:29668850 SUPPORT Model Organism

"Here, we report that Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli."

Motor delay is recapitulated in the Chd8 heterozygous mouse.

Intellectual Disability FREQUENT Intellectual disability HP:0001249

Severity: MODERATE

Show evidence (4 references)

PMID:36302072 SUPPORT Human Clinical

"When present, ID is most often in the mild-to-moderate range."

GeneReviews qualifies ID as present in a subset ("when present") with mild-to-moderate severity, so the band is set below the near-universal developmental delay.

PMID:30670789 SUPPORT Human Clinical

"Children with the disorder present with developmental delay, intellectual disability, and/or autism spectrum disorder in addition to characteristic facies."

Independent clinical series confirming intellectual disability.

PMID:36182950 SUPPORT Human Clinical

"Many neurological abnormalities, like intellectual disability (68%) and hypotonia (29%) were observed, as well as a wide variety of behavioural abnormalities (88%)."

The largest assembled cohort (n=106) quantifies intellectual disability at 68%, within the FREQUENT (30-79%) band.

+ 1 more reference

Autism Spectrum Disorder FREQUENT Autism HP:0000717

Show evidence (4 references)

PMID:24998929 SUPPORT Human Clinical

"Our findings indicate that CHD8 disruptions define a distinct ASD subtype and reveal unexpected comorbidities between brain development and enteric innervation."

Establishes CHD8 disruption as defining a distinct, monogenic autism subtype.

PMID:33627187 SUPPORT Human Clinical

"CHD8 haploinsufficiency causes autism and macrocephaly with high penetrance in the human population."

States the high penetrance of the autism-plus-macrocephaly phenotype.

PMID:36182950 SUPPORT Human Clinical

"Most frequently observed behavioural problems included autism spectrum disorder (76%), short attention span (32%), abnormal social behaviour (31%), sleep disturbance (29%) and impaired social interactions (28%)."

The largest cohort (n=106) puts autism spectrum disorder at 76%, inside the FREQUENT (30-79%) band. FREQUENT rather than VERY_FREQUENT is used because the two largest quantified series bracket the 80% threshold (76% here, 84% in PMID:31001818) rather than clearing it.

+ 1 more reference

Sleep Disturbance FREQUENT Sleep disturbance HP:0002360

Show evidence (4 references)

PMID:36302072 SUPPORT Human Clinical

"Sleep disturbance is characterized by difficulty with both initiation (delayed sleep onset) and maintenance (frequent night awakenings) of sleep."

GeneReviews characterises the sleep phenotype qualitatively (initiation and maintenance) but does not quantify it; the FREQUENT band comes from the 50% figure in PMID:31001818 below, not from this source.

PMID:30670789 SUPPORT Human Clinical

"Gastrointestinal and sleep problems are notable."

Independent clinical series flagging sleep problems as notable.

PMID:31001818 SUPPORT Human Clinical

"sleep difficulties (50%)"

Quantifies sleep difficulties at 50%, the basis for the FREQUENT band.

+ 1 more reference

Seizures OCCASIONAL Seizure HP:0001250

Show evidence (3 references)

PMID:36302072 SUPPORT Human Clinical

"Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare)."

GeneReviews gives 10%-15%, which falls in the 5-29% OCCASIONAL band.

PMID:31001818 SUPPORT Human Clinical

"some had regression of speech (37%), seizures (27%) and hypotonia (27%)"

An independent cohort reports 27%, at the upper end of but still within the OCCASIONAL band.

PMID:31526516 SUPPORT Human Clinical

"less severe adaptive deficits in communication skills, similar functional language, more social motivation challenges in those with ASD, larger head circumference, higher weight, and lower seizure prevalence relative to the other gene group"

CHD8 carriers have LOWER seizure prevalence than other autism-risk-gene carriers, reinforcing that epilepsy is not a defining feature of this disorder.

Dystonia VERY_RARE Dystonia HP:0001332

Show evidence (3 references)

PMID:36302072 SUPPORT Human Clinical

"Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare)."

GeneReviews describes dystonia as rare, mapping to the VERY_RARE band.

PMID:38441608 SUPPORT Human Clinical

"This work validates our previous observation that dystonia is part of the phenotypic spectrum of CHD8-related"

Dedicated case series validating dystonia as part of the CHD8-NDD spectrum.

PMID:34415117 SUPPORT Human Clinical

"We further expand the CHD8-related phenotype with the description of two unrelated patients who presented with childhood-onset progressive dystonia."

The original report establishing childhood-onset progressive dystonia as a CHD8 presentation. Note this is the one phenotype in the entry described as progressive.

Anxiety Anxiety HP:0000739

Show evidence (4 references)

PMID:36302072 SUPPORT Human Clinical

"monitor for signs and symptoms of anxiety, attention-deficit/hyperactivity disorder, and aggressive or self-injurious behavior"

GeneReviews surveillance guidance identifies anxiety as an expected manifestation; no frequency is given, so none is asserted.

PMID:27602517 SUPPORT Model Organism

"mice heterozygous for Chd8 mutations manifest ASD-like behavioural characteristics including increased anxiety, repetitive behaviour, and altered social behaviour"

Anxiety is recapitulated at the same gene dosage in mice.

PMID:38622540 SUPPORT Human Clinical

"Patterns of mental health features varied by group, with anxiety most prominent for CHD8"

Genotype-first CBCL comparison across ADNP, CHD8 and DYRK1A identifies anxiety as the psychiatric feature most characteristic of CHD8 specifically. The CHD8 subgroup is n=18, so this establishes the qualitative profile, not a frequency.

+ 1 more reference

Attention Deficit Hyperactivity Disorder Attention deficit hyperactivity disorder HP:0007018

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"monitor for signs and symptoms of anxiety, attention-deficit/hyperactivity disorder, and aggressive or self-injurious behavior"

GeneReviews surveillance guidance identifies ADHD as an expected manifestation.

PMID:41407309 SUPPORT Human Clinical

"who exhibited a subtle feature, including traits consistent with attention-deficit/hyperactivity disorder"

Illustrates ADHD traits as the minimal expression in a transmitting parent.

Aggressive and Self-Injurious Behavior Self-injurious behavior HP:0100716

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"monitor for signs and symptoms of anxiety, attention-deficit/hyperactivity disorder, and aggressive or self-injurious behavior"

GeneReviews surveillance guidance identifies aggressive/self-injurious behaviour as an expected manifestation.

PMID:33175317 PARTIAL Human Clinical

"History of severe abdominal pain predicted higher rates of SIB and SIB severity after controlling for age and adaptive behavior; individuals with a history of severe abdominal pain were eight times more likely to exhibit SIB than those with no history."

In carriers of disruptive autism-risk-gene mutations, self-injury is strongly associated with severe abdominal pain, suggesting some challenging behaviour in this disorder is a pain signal from the gastrointestinal phenotype rather than a primary behavioural phenotype. Marked PARTIAL because the cohort spans multiple autism-risk genes and is not CHD8-specific.

Behavioral Abnormality VERY_FREQUENT Atypical behavior HP:0000708

Show evidence (2 references)

PMID:36182950 SUPPORT Human Clinical

"Many neurological abnormalities, like intellectual disability (68%) and hypotonia (29%) were observed, as well as a wide variety of behavioural abnormalities (88%)."

Quantifies composite behavioural abnormality at 88% in the largest cohort, supporting the VERY_FREQUENT (80-100%) band.

PMID:31721432 SUPPORT Human Clinical

"Behavioral problems were reported in the majority of patients (78%), with over half (56%) either formally diagnosed with an autistic spectrum disorder or described as having autistic traits."

Independent cohort reporting behavioural problems in 78%.

Developmental Regression FREQUENT Developmental regression HP:0002376

Show evidence (1 reference)

PMID:31001818 SUPPORT Human Clinical

"some had regression of speech (37%), seizures (27%) and hypotonia (27%)"

Quantifies speech regression at 37%, inside the FREQUENT (30-79%) band. Note the source measures regression of speech specifically; regression of social and motor skills is described qualitatively elsewhere and is not separately banded.

Growth 1

Tall Stature and Generalized Overgrowth FREQUENT Tall stature HP:0000098

Show evidence (5 references)

PMID:36302072 SUPPORT Human Clinical

"The most common findings are the development of macrocephaly (most often during infancy) and tall stature (most typically during puberty), which is often accompanied by ASD and/or DD/ID."

GeneReviews identifies tall stature as one of the two most common findings, qualified by pubertal timing.

PMID:31001818 SUPPORT Human Clinical

Quantifies tall stature at 47%, within the FREQUENT (30-79%) band.

PMID:31721432 SUPPORT Human Clinical

"85% had a height and/or head circumference >=2 standard deviations above the mean, meeting our clinical criteria for overgrowth"

The overgrowth-ascertained cohort shows that when height and head circumference are considered together, 85% meet formal overgrowth criteria - the generalised (not head-only) nature of the overgrowth is the discriminating feature versus other autism-with-macrocephaly conditions.

+ 2 more references

Other 5

Overweight FREQUENT Overweight HP:0025502

Show evidence (2 references)

PMID:36182950 SUPPORT Human Clinical

"being overweight (34%, 24/71)"

The largest assembled cohort (n=106) reports overweight in 34% (24/71) of individuals with a recorded weight; 24/71 = 33.8%, which falls in the FREQUENT (30-79%) band. The denominator (71 of 106) reflects incomplete weight reporting rather than selective assessment, so unlike the forehead/dental figures discussed in note (4) this proportion is interpretable as a frequency.

PMID:31980904 SUPPORT Human Clinical

"a prominent, consistent pattern of overgrowth as measured by weight, height and head circumference"

Independent confirmation that weight is one of the three axes on which the overgrowth is expressed; this series does not quantify overweight separately, so it contributes no figure to the band.

Chiari Type I Malformation VERY_RARE Chiari type I malformation HP:0007099

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare)."

GeneReviews describes Chiari I malformation as rare, mapping to VERY_RARE.

Broad Forehead with Prominent Supraorbital Ridges Broad forehead HP:0000337

Show evidence (1 reference)

PMID:31980904 SUPPORT Human Clinical

"dysmorphic features, including broad forehead with prominent supraorbital ridges, flat nasal bridge, telecanthus and large ears"

Clinical series describing the forehead and supraorbital features.

Prominent Supraorbital Ridges Prominent supraorbital ridges HP:0000336

Show evidence (1 reference)

PMID:31980904 SUPPORT Human Clinical

"dysmorphic features, including broad forehead with prominent supraorbital ridges, flat nasal bridge, telecanthus and large ears"

Clinical series naming prominent supraorbital ridges.

Musculoskeletal Abnormality FREQUENT Abnormality of the musculoskeletal system HP:0033127

Show evidence (2 references)

PMID:36182950 SUPPORT Human Clinical

"Furthermore, abnormalities in the digestive (53%), musculoskeletal (79%) and genitourinary systems (18%) were noted."

Quantifies composite musculoskeletal involvement at 79%, the top of the FREQUENT band.

PMID:31721432 SUPPORT Human Clinical

"Additional clinical features included neonatal hypotonia (33%), and less frequently seizures, pes planus, scoliosis, fifth finger clinodactyly, umbilical hernia, and glabellar hemangioma"

Enumerates the individual musculoskeletal findings that make up the composite, each individually uncommon.

🧬

Genetic Associations

CHD8

Gene: CHD8 hgnc:20153 relationship_type: CAUSATIVE variant_origin: DE_NOVO

Show evidence (6 references)

PMID:22495309 SUPPORT Human Clinical

"In proband exomes, recurrent protein-altering mutations were observed in two genes: CHD8 and NTNG1."

Gene-discovery evidence: the original sporadic-autism exome study that identified recurrent de novo CHD8 mutations. Cited for discovery only, not for CHD8-specific phenotype frequencies.

PMID:24998929 SUPPORT Human Clinical

Establishes the mutational burden and the absence of truncating CHD8 events in controls.

PMID:31980904 SUPPORT Human Clinical

"HELIC domain mutations were associated with a severe phenotype defined by a greater number of clinical features, lower verbal IQ, and a prominent, consistent pattern of overgrowth as measured by weight, height and head circumference."

Documents the HELIC-domain genotype-phenotype correlation.

+ 3 more references

💊

Medical Actions

Sleep Disturbance Management

Action: behavioral counseling Ontology label: Behavioral Counseling NCIT:C181743

GeneReviews recommends addressing sleep disturbance through behavioural interventions and/or pharmacologic treatment. Sleep is a high-yield target because the disturbance affects both sleep onset and maintenance and is a major driver of daytime behavioural burden. No CHD8-specific agent is established; management follows general neurodevelopmental-disorder practice.

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"Sleep disturbance may be addressed through behavioral interventions and/or pharmacologic treatment"

GeneReviews management recommendation for sleep disturbance.

Management of Bowel Dysfunction

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Standard treatment for bowel dysfunction, principally constipation. Because the constipation in CHD8-NDD is linked to reduced enteric innervation rather than to diet alone, it commonly requires sustained rather than episodic management, and GeneReviews recommends ongoing monitoring for constipation at surveillance visits.

Mechanism Target:

INHIBITS Gastrointestinal Dysmotility and Barrier Dysfunction — Symptomatic management of the clinical endpoint of the enteric arm of the mechanism graph.

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"standard treatment for DD/ID, seizures, and bowel dysfunction"

GeneReviews management recommendation for bowel dysfunction.

PMID:36302072 SUPPORT Human Clinical

"monitor for constipation"

GeneReviews surveillance recommendation.

Developmental and Educational Intervention

Action: speech and language therapy Ontology label: Speech Language Therapy NCIT:C159273

Standard treatment for developmental delay and intellectual disability, with assessment of developmental progress and educational needs at each visit. Given the disproportionate speech and language involvement, speech-language therapy is a particular priority.

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"standard treatment for DD/ID, seizures, and bowel dysfunction"

GeneReviews management recommendation for DD/ID.

PMID:36302072 SUPPORT Human Clinical

"assessment of developmental progress and educational needs"

GeneReviews surveillance recommendation for developmental progress.

Antiseizure Pharmacotherapy

Action: Pharmacotherapy NCIT:C15986

Standard antiseizure treatment for the 10%-15% of affected individuals who develop seizures. No CHD8-specific antiseizure medication preference is established.

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"standard treatment for DD/ID, seizures, and bowel dysfunction"

GeneReviews management recommendation for seizures.

Surgical Treatment of Chiari I Malformation

Action: surgical procedure Ontology label: Surgical Procedure NCIT:C15329

When a Chiari I malformation is present, surgical treatment may be required. Serial imaging may be considered for asymptomatic or minimally symptomatic Chiari I malformation as clinically indicated.

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"if Chiari I malformation is present, surgical treatment may be required"

GeneReviews management recommendation for Chiari I malformation.

Growth and Neurologic Surveillance

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Structured surveillance at each visit: measurement of growth parameters including head circumference; assessment of developmental progress and educational needs; monitoring for anxiety, ADHD and aggressive or self-injurious behaviour; assessment for new manifestations such as seizures, tone changes, and signs of cerebrospinal fluid obstruction or spinal cord dysfunction; screening for sleep disturbance; and monitoring for constipation.

Show evidence (2 references)

PMID:36302072 SUPPORT Human Clinical

"At each visit: measurement of growth parameters (including head circumference); assessment of developmental progress and educational needs"

GeneReviews surveillance schedule.

PMID:36302072 SUPPORT Human Clinical

"assess for new manifestations, such as seizures, changes in tone, and signs/symptoms of cerebrospinal fluid obstruction and/or spinal cord dysfunction"

GeneReviews surveillance for new neurologic manifestations.

Deep Brain Stimulation for Refractory Dystonia

Action: deep brain stimulation Ontology label: Deep Brain Stimulation NCIT:C21024

In the rare subgroup presenting with childhood-onset progressive dystonia, deep brain stimulation produced clinical improvement in both reported cases. This is the best-evidenced targeted intervention in the disorder, although the evidence base is two patients. Pharmacologic options tried in the dystonic subgroup (levodopa, tizanidine, botulinum toxin) have given inconsistent results, with levodopa ineffective in one individual and partially effective in another.

Target Phenotypes: Dystonia HP:0001332

Show evidence (1 reference)

PMID:34415117 SUPPORT Human Clinical

"Deep brain stimulation led to clinical improvement in both cases."

Both reported individuals with CHD8-related progressive dystonia improved with deep brain stimulation.

Genetic Counseling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Autosomal dominant counselling: each child of an affected individual has a 50% chance of inheriting the variant. Because most probands have a de novo variant, parental testing informs recurrence-risk estimates - and, as transmitted variants with very mild parental expression are documented, apparently unaffected parents should still be tested before recurrence risk is quoted as low. Once the familial variant is known, prenatal and preimplantation genetic testing are possible.

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"Each child of an individual with CHD8-NDD has a 50% chance of inheriting the CHD8 pathogenic variant. Once the CHD8 pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible."

GeneReviews genetic counselling guidance.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from CHD8-Related Neurodevelopmental Disorder with Overgrowth:

Autism Spectrum Disorder (multifactorial) MONDO:0005258

Overlapping Features The single most important boundary for this entry. Broad, multifactorial autism spectrum disorder lists CHD8 among many risk genes recovered by large-scale exome sequencing, and dismech curates it as a separate, polygenic entity. This entry is NOT that entity: here CHD8 haploinsufficiency is the sufficient monogenic cause of a syndromic, highly penetrant phenotype with overgrowth, macrocephaly, dysmorphism, sleep and gastrointestinal involvement.

Distinguishing Features

Presence of a heterozygous pathogenic CHD8 variant; macrocephaly and tall stature; recognisable facies; prominent sleep and gastrointestinal involvement; autosomal dominant transmission with 50% recurrence risk to offspring. Broad ASD has no single sufficient genetic cause and no consistent overgrowth phenotype.

Show evidence (1 reference)

PMID:24998929 SUPPORT Human Clinical

"Our findings indicate that CHD8 disruptions define a distinct ASD subtype and reveal unexpected comorbidities between brain development and enteric innervation."

Explicitly frames CHD8 disruption as defining a distinct subtype separable from autism at large.

CHARGE Syndrome (CHD7) MONDO:0008965

Overlapping Features Caused by the CHD paralogue CHD7, not CHD8. Cited here as an explicit named-entity-confusion guard: CHD7 and CHD8 are adjacent in the CHD family and are readily transposed in literature searches, but the diseases are distinct.

Distinguishing Features

CHARGE syndrome is characterised by coloboma, choanal atresia, cranial nerve dysfunction, characteristic external and inner ear anomalies with semicircular canal hypoplasia, and heart defects; growth retardation rather than overgrowth is typical. CHD8-NDD has none of these as core features.

CHD2-Related Developmental and Epileptic Encephalopathy MONDO:0014150

Overlapping Features Caused by the CHD paralogue CHD2. A second explicit NEC guard: CHD2 is an epilepsy gene, and seizures also occur in a minority of CHD8-NDD, so the combination of a "CHD" gene plus seizures is a known route to misattribution.

Distinguishing Features

CHD2-related disease is dominated by early-onset, often photosensitive myoclonic epilepsy and epileptic encephalopathy with developmental regression. In CHD8-NDD seizures occur in only 10%-15%, are not the defining feature, and overgrowth/macrocephaly dominates the presentation.

Show evidence (1 reference)

PMID:36302072 SUPPORT Human Clinical

"Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare)."

Quantifies seizures as a minority feature in CHD8-NDD, distinguishing it from a primary epilepsy gene.

Sifrim-Hitz-Weiss Syndrome (CHD4) MONDO:0014946

Overlapping Features Caused by the CHD paralogue CHD4. A third NEC guard within the CHD family; CHD4-related disease also involves developmental delay and macrocephaly, making it the closest phenotypic neighbour among the paralogues.

Distinguishing Features

CHD4-related Sifrim-Hitz-Weiss syndrome is typically caused by missense (largely gain-of-function-like) variants and features hearing loss, congenital heart defects, skeletal and genital anomalies, and ventriculomegaly. CHD8-NDD is a loss-of-function/haploinsufficiency disorder without that visceral malformation profile.

14q11.2 Microdeletion Syndrome

Overlapping Features A contiguous-gene deletion encompassing CHD8 and neighbouring genes. Deletion cases share the CHD8-NDD core phenotype, and the minimal critical region has been narrowed to SUPT16H and CHD8, but a deletion is not a pure CHD8 lesion.

Distinguishing Features

Detected by chromosomal microarray rather than sequencing; additional deleted genes (notably SUPT16H) may modify the phenotype, so deletion cases are held adjacent to, not inside, the intragenic-variant entity.

Show evidence (1 reference)

PMID:25257502 SUPPORT Human Clinical

"The minimal critical region, considering present and previous cases, contains the SUPT16H and CHD8 genes."

Defines the minimal critical region and shows it is not CHD8 alone.

14q11.2 Microduplication (CHD8-SUPT16H) Syndrome Not Yet Curated MONDO:0016835

Overlapping Features The reciprocal dosage disorder. Duplication of the same 14q11.2 segment containing CHD8 and SUPT16H also produces a neurodevelopmental phenotype, which is why CHD8 is described as requiring tight dosage control in both directions. Duplication cases are a separate entity and must not be folded into this entry.

Distinguishing Features

Detected as a copy-number GAIN on chromosomal microarray rather than a loss-of-function sequence variant; neurodevelopmental severity is variable and at least one reported individual had normal intelligence; the duplication also spans SUPT16H so single-gene CHD8 triplosensitivity is not established.

Show evidence (2 references)

PMID:31823155 SUPPORT Human Clinical

"Recently, a 14q11.2 microduplication syndrome, encompassing CHD8 and SUPT16H, has been described, highlighting the importance of a tight control of at least CHD8 gene-dosage for a normal development."

Establishes the duplication entity and the bidirectional dosage sensitivity.

PMID:31823155 SUPPORT Human Clinical

"Here, we report on two patients with 14q11.2 microduplication encompassing CHD8 and SUPT16H, one of whom had normal intelligence."

Documents the milder end of the duplication phenotype, distinguishing it from the deletion/loss-of-function disorder.

PTEN Hamartoma Tumor Syndrome MONDO:0017623

Overlapping Features The most important not-to-miss alternative in the macrocephaly-plus-autism presentation, because unlike CHD8-NDD it carries a defined cancer risk that changes surveillance.

Distinguishing Features

In PTEN hamartoma tumor syndrome the macrocephaly is disproportionate to height, whereas CHD8-NDD overgrowth is generalised (height and head circumference together). Hamartomas and a defined malignancy risk are features of PTEN disease and are not established in CHD8-NDD, where tumour surveillance is explicitly not recommended.

Other Overgrowth-with-Intellectual-Disability Syndromes

Overlapping Features Sotos syndrome (NSD1), Weaver syndrome (EZH2), Tatton-Brown-Rahman syndrome (DNMT3A), Malan syndrome (NFIX) and Beckwith-Wiedemann syndrome share the overgrowth-plus-developmental-impairment presentation and are the differential within which CHD8-NDD was originally delineated.

Distinguishing Features

Most of these conditions - including CHD8-NDD itself - have distinct DNA methylation episignatures, so a single episignature array can discriminate much of this differential simultaneously. Beckwith-Wiedemann syndrome is further distinguished by asymmetric/lateralised overgrowth and embryonal tumour risk.

Show evidence (1 reference)

PMID:31001818 SUPPORT Human Clinical

"CHD8 is one of the causative genes for OGID (overgrowth and ID)"

Places CHD8 explicitly within the overgrowth-and-intellectual-disability disease group that constitutes this differential.

🔬

Clinical Trials

NCT01238250 RECRUITING

Simons Searchlight - an observational, online, international registry for families with rare genetic variants causing neurodevelopmental disorders, including CHD8. It is the principal longitudinal natural-history data source for this disorder. There is no interventional trial for CHD8-NDD.

Target Phenotypes: Autism HP:0000717 Global developmental delay HP:0001263

Show evidence (1 reference)

clinicaltrials:NCT01238250 SUPPORT Human Clinical

"Simons Searchlight is an observational, online, international research program for families with rare genetic variants that cause neurodevelopmental disorders and may be associated with autism."

Describes the registry that provides longitudinal natural-history data for CHD8 variant carriers.

🧫

Experimental Models

CHD8 heterozygous human cerebral organoids

Isogenic CRISPR/Cas9 CHD8+/- iPSC-derived cerebral organoids model CHD8 haploinsufficiency in a human genetic background. They show enlargement, an accelerated/delayed split in inhibitory versus excitatory neurogenesis, and cell-autonomous, patient-mutation-specific molecular defects in proliferation and alternative splicing.

Show evidence (2 references)

PMID:35385734 SUPPORT In Vitro

"Through an isogenic design of patient-specific mutations and mosaic organoids, we define genotype-phenotype relationships and uncover their cell-autonomous nature."

Describes the isogenic organoid design and its cell-autonomous readout.

PMID:28321286 SUPPORT In Vitro

"CRISPR/Cas9-mediated heterozygous knockout of the autism gene CHD8 and characterization of its transcriptional networks in cerebral organoids derived from iPS cells."

Establishes the heterozygous CHD8 organoid model system.

{ }

Source YAML

click to show

name: CHD8-Related Neurodevelopmental Disorder with Overgrowth
creation_date: "2026-07-31T00:00:00Z"
category: Mendelian
synonyms:
- intellectual developmental disorder with autism and macrocephaly
- IDDAM
- CHD8 overgrowth syndrome
- CHD8-related neurodevelopmental disorder
- CHD8-NDD
- autism, susceptibility to, 18
- AUTS18
description: >-
  CHD8-related neurodevelopmental disorder with overgrowth (CHD8-NDD; MONDO:0014017,
  OMIM 615032, also catalogued as "intellectual developmental disorder with autism
  and macrocephaly"/IDDAM) is an autosomal dominant, highly penetrant monogenic
  neurodevelopmental syndrome caused by heterozygous loss-of-function variants in
  CHD8 (HGNC:20153) at 14q11.2. CHD8 encodes chromodomain helicase DNA-binding
  protein 8, an ATP-dependent chromatin remodeller that binds the promoters of a
  large network of neurodevelopmental and autism risk genes. Haploinsufficiency
  produces a recognisable clinical gestalt: generalised overgrowth with macrocephaly
  (usually apparent in infancy) and tall stature (usually emerging around puberty),
  developmental delay with disproportionate speech and motor delay, intellectual
  disability that is most often mild to moderate, autism spectrum disorder, a
  characteristic facies (broad forehead with prominent supraorbital ridges,
  hypertelorism/widely spaced eyes, depressed nasal bridge, long philtrum, large
  ears), sleep disturbance affecting both sleep initiation and maintenance, and
  gastrointestinal dysfunction dominated by constipation. Less frequent features
  include hypotonia (about 30%), seizures (10%-15%), and rarely dystonia and Chiari I
  malformation. Most probands carry a de novo variant, but inherited variants with
  markedly variable expressivity are documented.

  Entity scope (NEC boundary, see `discussions` and `differential_diagnoses`): this
  entry is the MONOGENIC CHD8 haploinsufficiency syndrome anchored on
  MONDO:0014017 / OMIM:615032 / RO:0004003 HGNC:20153. It is deliberately kept
  distinct from (i) broad multifactorial autism spectrum disorder, in which CHD8 is
  merely one of many risk genes recovered by large-scale exome studies - that
  polygenic/multifactorial entity is curated separately and must not be conflated
  with this syndrome; and (ii) the CHD paralogue disorders that are the most common
  sources of citation confusion - CHD7 (CHARGE syndrome), CHD2 (developmental and
  epileptic encephalopathy), and CHD4 (Sifrim-Hitz-Weiss syndrome). Large-scale
  autism exome-sequencing cohorts are cited here only for gene discovery and
  gene-level burden, never for CHD8-specific phenotype frequencies; those come from
  the GeneReviews chapter and CHD8-ascertained clinical series.
disease_term:
  preferred_term: intellectual developmental disorder with autism and macrocephaly
  term:
    id: MONDO:0014017
    label: intellectual developmental disorder with autism and macrocephaly
parents:
- Neurodevelopmental Disorder
- Genetic Disease
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    notes: >-
      The core manifestations - developmental delay, intellectual disability,
      autism, hypotonia, seizures, dystonia and structural brain anomalies - are
      neurologic.
    evidence:
    - reference: PMID:36302072
      reference_title: CHD8-Related Neurodevelopmental Disorder with Overgrowth.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        CHD8-related neurodevelopmental disorder with overgrowth (CHD8-NDD) is characterized by generalized overgrowth, developmental delay / intellectual disability (DD/ID), autism spectrum disorder (ASD), neuropsychiatric issues, neurologic problems, sleep disturbance, and gastrointestinal issues
      explanation: >-
        GeneReviews defines the condition as a neurodevelopmental disorder with
        neurologic and neuropsychiatric problems at its core.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      Autosomal dominant Mendelian disorder caused by heterozygous loss-of-function
      CHD8 variants acting through haploinsufficiency.
    evidence:
    - reference: PMID:30670789
      reference_title: A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        confirms our suggestion that this is a syndromic disorder caused by haploinsufficiency or heterozygous loss of function of CHD8
      explanation: >-
        Establishes the Mendelian haploinsufficiency genetic basis of the syndrome.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0014017
      label: intellectual developmental disorder with autism and macrocephaly
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0014017 carries OMIM:615032 as an xref, asserts a causal gene
      relationship (RO:0004003) to HGNC:20153 (CHD8), and lists "CHD8 overgrowth
      syndrome" (Orphanet:642675) and AUTS18 among its synonyms. All three anchors
      were verified with OAK before curation began; this is the NEC anchor for the
      entry.
inheritance:
- name: Autosomal dominant inheritance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    CHD8-NDD segregates as an autosomal dominant trait. The great majority of
    reported probands carry a de novo CHD8 pathogenic variant, but transmitted
    variants occur and can be associated with strikingly milder parental
    presentations, indicating variable expressivity.
  expressivity: VARIABLE
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CHD8-NDD is inherited in an autosomal dominant fashion. However, most probands reported to date whose parents have undergone molecular genetic testing have the disorder as the result of a de novo CHD8 pathogenic variant.
    explanation: >-
      GeneReviews states autosomal dominant inheritance with a predominance of de
      novo variants.
  - reference: PMID:41407309
    reference_title: "Phenotypic Variability and Paternal Inheritance of a CHD8 Variant Causing Intellectual Developmental Disorder With Autism and Macrocephaly Confirmed by Epigenetic and Structural Analyses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We describe the case of IDDAM caused by a paternally inherited CHD8 variant. Our findings highlight the importance of considering parental inheritance in IDDAM diagnoses
    explanation: >-
      Documents transmitted (non-de novo) inheritance with variable expressivity in
      an IDDAM family.
pathophysiology:
- name: CHD8 Haploinsufficiency
  biological_scale: MOLECULAR
  role: TRIGGER
  description: >-
    A heterozygous loss-of-function variant in CHD8 (nonsense, frameshift, splice,
    or a whole-gene 14q11.2 deletion) reduces functional chromodomain helicase
    DNA-binding protein 8 to roughly half of the normal dose. CHD8 is the root
    molecular lesion of the syndrome; the disorder is a dosage disease rather than a
    dominant-negative or gain-of-function condition, and truncating variants are
    essentially absent from population controls.
  gene:
    preferred_term: CHD8
    term:
      id: hgnc:20153
      label: CHD8
  molecular_functions:
  - preferred_term: ATP-dependent chromatin remodelling activity
    term:
      id: GO:0008094
      label: ATP-dependent activity, acting on DNA
    modifier: DECREASED
  - preferred_term: chromatin binding
    term:
      id: GO:0003682
      label: chromatin binding
    modifier: DECREASED
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of CHD8-NDD is established in a proband by identification of a heterozygous pathogenic (or likely pathogenic) variant in CHD8 by molecular genetic testing.
    explanation: Establishes the heterozygous CHD8 variant as the defining molecular lesion.
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we resequenced the ASD-associated gene CHD8 in 3,730 children with developmental delay or ASD. We identified a total of 15 independent mutations; no truncating events were identified in 8,792 controls, including 2,289 unaffected siblings.
    explanation: >-
      Complete absence of truncating CHD8 events in 8,792 controls supports
      loss-of-function/haploinsufficiency as the disease mechanism.
  - reference: PMID:30670789
    reference_title: "A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      confirms our suggestion that this is a syndromic disorder caused by haploinsufficiency or heterozygous loss of function of CHD8
    explanation: States haploinsufficiency explicitly as the mechanism.
  downstream:
  - target: Failure of Chromatin Remodelling at CHD8 Target Promoters
    causal_link_type: DIRECT
    description: >-
      Halving CHD8 protein reduces occupancy and remodelling activity at the
      thousands of promoters CHD8 normally binds.
    evidence:
    - reference: PMID:25294932
      reference_title: "CHD8 regulates neurodevelopmental pathways associated with autism spectrum disorder in neural progenitors."
      supports: PARTIAL
      evidence_source: IN_VITRO
      snippet: >-
        CHD8 showed widespread binding to chromatin, with 7,324 replicated sites that marked 5,658 genes.
      explanation: >-
        Establishes that CHD8 dose is applied at thousands of chromatin sites, so a halving of protein acts at the promoter-occupancy step.
- name: Failure of Chromatin Remodelling at CHD8 Target Promoters
  biological_scale: MOLECULAR
  description: >-
    CHD8 binds chromatin very widely - thousands of replicated promoter-proximal
    sites in neural progenitors - and its target set is strongly enriched for other
    autism risk genes and for chromatin-modification and transcription-regulation
    genes. Reduced CHD8 dose therefore acts as a hub lesion: a limited set of direct
    binding-site effects is amplified into a far larger secondary transcriptional
    network.
  biological_processes:
  - preferred_term: chromatin remodeling
    term:
      id: GO:0006338
      label: chromatin remodeling
    modifier: DECREASED
  - preferred_term: regulation of transcription by RNA polymerase II
    term:
      id: GO:0006357
      label: regulation of transcription by RNA polymerase II
    modifier: ABNORMAL
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  evidence:
  - reference: PMID:25294932
    reference_title: "CHD8 regulates neurodevelopmental pathways associated with autism spectrum disorder in neural progenitors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      CHD8 showed widespread binding to chromatin, with 7,324 replicated sites that marked 5,658 genes.
    explanation: >-
      Quantifies the breadth of CHD8 chromatin occupancy in human neural progenitor
      cells.
  - reference: PMID:25752243
    reference_title: "The autism-associated chromatin modifier CHD8 regulates other autism risk genes during human neurodevelopment."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      CHD8 targets are strongly enriched for other ASD risk genes in both human and mouse neurodevelopment, and converge in ASD-associated co-expression networks in human midfetal cortex.
    explanation: >-
      Shows the CHD8 target set is an autism risk-gene regulatory hub during human
      neurodevelopment.
  downstream:
  - target: Dysregulation of Neurodevelopmental Gene Networks
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:25294932
      reference_title: "CHD8 regulates neurodevelopmental pathways associated with autism spectrum disorder in neural progenitors."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Integration of these data suggests that a limited array of direct regulatory effects of CHD8 produced a much larger network of secondary expression changes.
      explanation: >-
        Directly states the amplification step from a limited set of direct chromatin effects to a much larger dysregulated network.
- name: Dysregulation of Neurodevelopmental Gene Networks
  biological_scale: MOLECULAR
  description: >-
    Reducing CHD8 to single-allele levels perturbs the expression of well over a
    thousand genes. Directly bound genes are dominated by chromatin and
    transcriptional regulators, while the indirectly down-regulated secondary
    network is dominated by brain-development programmes - synapse formation, neuron
    differentiation, cell adhesion, and axon guidance. This secondary network, not
    any single target, is the proximate cause of the neurodevelopmental phenotype.
  biological_processes:
  - preferred_term: synapse assembly
    term:
      id: GO:0007416
      label: synapse assembly
    modifier: DECREASED
  - preferred_term: axon guidance
    term:
      id: GO:0007411
      label: axon guidance
    modifier: DECREASED
  - preferred_term: brain development
    term:
      id: GO:0007420
      label: brain development
    modifier: ABNORMAL
  evidence:
  - reference: PMID:25294932
    reference_title: "CHD8 regulates neurodevelopmental pathways associated with autism spectrum disorder in neural progenitors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Suppressing CHD8 to levels comparable with the loss of a single allele caused altered expression of 1,756 genes, 64.9% of which were up-regulated.
    explanation: >-
      Establishes the scale and directionality of transcriptional dysregulation at a
      haploinsufficient CHD8 dose.
  - reference: PMID:25294932
    reference_title: "CHD8 regulates neurodevelopmental pathways associated with autism spectrum disorder in neural progenitors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Genes indirectly down-regulated (i.e., without CHD8-binding sites) reflect pathways involved in brain development, including synapse formation, neuron differentiation, cell adhesion, and axon guidance, whereas CHD8-bound genes are strongly associated with chromatin modification and transcriptional regulation.
    explanation: >-
      Identifies the specific neurodevelopmental programmes carried by the secondary
      network.
  - reference: PMID:29668850
    reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Genes involved in cell adhesion and axon guidance are particularly prominent amongst the downregulated transcripts.
    explanation: >-
      Independent replication in the postnatal neocortex of Chd8 heterozygous mice.
  downstream:
  - target: Impaired Wnt/beta-Catenin Signal Transduction
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27694995
      reference_title: "Chd8 mediates cortical neurogenesis via transcriptional regulation of cell cycle and Wnt signaling."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        knockdown of Chd8 disrupts the expression of key transducers of Wnt signaling
      explanation: >-
        Places Wnt transducer expression among the genes dysregulated by reduced Chd8.
  - target: REST-Mediated Repression of Neuronal Genes
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27602517
      reference_title: "CHD8 haploinsufficiency results in autistic-like phenotypes in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        CHD8 was found to interact physically with REST in the mouse brain
      explanation: >-
        A physical CHD8-REST interaction supports a direct edge from the CHD8 regulatory lesion to REST-mediated repression.
  - target: Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27694995
      reference_title: "Chd8 mediates cortical neurogenesis via transcriptional regulation of cell cycle and Wnt signaling."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Chd8 knockdown during cortical development results in defective neural progenitor proliferation and differentiation
      explanation: >-
        Directly links reduced Chd8 and its transcriptional consequences to the progenitor proliferation and differentiation defect.
  - target: Glial and Serotonergic Disruption of Sleep Architecture
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Glial CHD8/kismet-dependent transcriptional programme at the blood-brain barrier
    - Developmental elevation of serotonin
    evidence:
    - reference: PMID:34088660
      reference_title: "The CHD8/CHD7/Kismet family links blood-brain barrier glia and serotonin to ASD-associated sleep defects."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our findings provide fundamental insights into glial regulation of sleep and propose a causal mechanistic link between the CHD8/CHD7/Kismet family, developmental hyperserotonemia, and autism-associated sleep disturbances.
      explanation: >-
        Asserts the causal link from the CHD8/CHD7/Kismet family to
        autism-associated sleep disturbance via glia and developmental serotonin.
  - target: Striatal Circuit Dysfunction
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Brain-region-specific transcriptional dysregulation of chromatin, Wnt and cell-cycle programmes
    evidence:
    - reference: PMID:28402856
      reference_title: "Chd8 Mutation Leads to Autistic-like Behaviors and Impaired Striatal Circuits."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Chd8+/- mice display a broad, brain-region-specific dysregulation of major regulatory and cellular processes, most notably histone and chromatin modification, mRNA and protein processing, Wnt signaling, and cell-cycle regulation.
      explanation: >-
        Establishes that the transcriptional lesion is expressed region-specifically,
        the intermediate step to a striatal circuit phenotype.
  - target: Enteric Neural Crest and Gut Epithelial Dysfunction
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Tissue-specific CHD8 target programmes in vagal neural crest and intestinal epithelium
    evidence:
    - reference: PMID:36375841
      reference_title: "Loss of autism-candidate CHD8 perturbs neural crest development and intestinal homeostatic balance."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our findings propose a causal developmental link between chd8, NCC development, intestinal homeostasis, and autism-associated gastrointestinal complaints.
      explanation: >-
        Asserts the causal developmental link from chd8 to neural crest and intestinal homeostasis; typed indirect because the intervening tissue-specific target programmes are unresolved.
- name: Impaired Wnt/beta-Catenin Signal Transduction
  biological_scale: MOLECULAR
  description: >-
    CHD8 interacts with beta-catenin and regulates the expression of key transducers
    of the Wnt pathway. Chd8 knockdown disrupts Wnt signalling during cortical
    development, and restoring Wnt signalling rescues the resulting transcriptional
    and behavioural deficits, making this a mechanistically load-bearing branch
    rather than a correlate. Wnt/chromatin-remodelling connectivity is also the
    network into which the most disruptive de novo autism mutations fall.
  biological_processes:
  - preferred_term: canonical Wnt signaling pathway
    term:
      id: GO:0060070
      label: canonical Wnt signaling pathway
    modifier: ABNORMAL
  evidence:
  - reference: PMID:27694995
    reference_title: "Chd8 mediates cortical neurogenesis via transcriptional regulation of cell cycle and Wnt signaling."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      knockdown of Chd8 disrupts the expression of key transducers of Wnt signaling, and enhancing Wnt signaling rescues the transcriptional and behavioral deficits caused by Chd8 knockdown
    explanation: >-
      Rescue by Wnt enhancement establishes the causal role of the Wnt branch.
  - reference: PMID:22495309
    reference_title: "Sporadic autism exomes reveal a highly interconnected protein network of de novo mutations."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      39% (49 of 126) of the most severe or disruptive de novo mutations map to a highly interconnected β-catenin/chromatin remodelling protein network ranked significantly for autism candidate genes
    explanation: >-
      Places CHD8 within the beta-catenin/chromatin-remodelling network at the level
      of autism genetics; PARTIAL because this is cohort-level network evidence, not
      a CHD8-specific functional assay.
  downstream:
  - target: Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27694995
      reference_title: "Chd8 mediates cortical neurogenesis via transcriptional regulation of cell cycle and Wnt signaling."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        enhancing Wnt signaling rescues the transcriptional and behavioral deficits caused by Chd8 knockdown
      explanation: >-
        Rescue by Wnt enhancement establishes this edge as causal rather than correlative.
- name: REST-Mediated Repression of Neuronal Genes
  biological_scale: MOLECULAR
  description: >-
    CHD8 physically interacts with the RE-1 silencing transcription factor (REST).
    When CHD8 is reduced, REST is abnormally activated and represses the
    transcription of many neuronal genes, providing one route by which a chromatin
    dosage lesion is converted into a global delay of the neuronal differentiation
    programme. REST activation has also been observed in autism brain tissue.
  biological_processes:
  - preferred_term: negative regulation of transcription by RNA polymerase II
    term:
      id: GO:0000122
      label: negative regulation of transcription by RNA polymerase II
    modifier: INCREASED
  evidence:
  - reference: PMID:27602517
    reference_title: "CHD8 haploinsufficiency results in autistic-like phenotypes in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      reduced expression of CHD8 was associated with abnormal activation of RE-1 silencing transcription factor (REST), which suppresses the transcription of many neuronal genes
    explanation: >-
      Identifies REST derepression of the neuronal programme as a CHD8-dosage
      consequence.
  downstream:
  - target: Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27602517
      reference_title: "CHD8 haploinsufficiency results in autistic-like phenotypes in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Gene set enrichment analysis revealed that neurodevelopment was delayed in the mutant mouse embryos.
      explanation: >-
        REST-driven repression of the neuronal programme is accompanied by a measurable delay in neurodevelopment in the same model.
- name: Altered Neural Progenitor Proliferation and Delayed Neuronal Differentiation
  biological_scale: CELLULAR
  description: >-
    The convergent cellular consequence of the transcriptional lesion. CHD8
    normally stimulates cell-cycle gene transcription while restraining premature
    induction of neural-specific genes; at reduced dose the balance between
    progenitor proliferation and differentiation is disturbed and neurodevelopment
    is globally delayed. In mouse models the effect is dosage-graded: heterozygous
    and mildly hypomorphic animals show increased proliferation of intermediate
    progenitors and brain hyperplasia, whereas severe depletion flips the phenotype
    to p53-driven apoptosis and brain hypoplasia.
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  - preferred_term: radial glial cell
    term:
      id: CL:0000681
      label: radial glial cell
  biological_processes:
  - preferred_term: neural precursor cell proliferation
    term:
      id: GO:0061351
      label: neural precursor cell proliferation
    modifier: INCREASED
  - preferred_term: neuron differentiation
    term:
      id: GO:0030182
      label: neuron differentiation
    modifier: DECREASED
  - preferred_term: cell cycle
    term:
      id: GO:0007049
      label: cell cycle
    modifier: ABNORMAL
  evidence:
  - reference: PMID:27694995
    reference_title: "Chd8 mediates cortical neurogenesis via transcriptional regulation of cell cycle and Wnt signaling."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here we report that Chd8 knockdown during cortical development results in defective neural progenitor proliferation and differentiation that ultimately manifests in abnormal neuronal morphology and behaviors in adult mice.
    explanation: >-
      Directly demonstrates the progenitor proliferation/differentiation defect and
      its behavioural consequence.
  - reference: PMID:33627187
    reference_title: "Distinct, dosage-sensitive requirements for the autism-associated factor CHD8 during cortical development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We identify increased proliferation of non-ventricular zone TBR2+ intermediate progenitors as one potential cause of brain hyperplasia in these mutants.
    explanation: >-
      Identifies the specific progenitor population whose excess proliferation
      drives brain overgrowth in a dosage-graded Chd8 allelic series.
  - reference: PMID:27602517
    reference_title: "CHD8 haploinsufficiency results in autistic-like phenotypes in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Gene set enrichment analysis revealed that neurodevelopment was delayed in the mutant mouse embryos.
    explanation: Supports global delay of the neurodevelopmental programme.
  downstream:
  - target: Brain Overgrowth and Megalencephaly
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:33627187
      reference_title: "Distinct, dosage-sensitive requirements for the autism-associated factor CHD8 during cortical development."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        We identify increased proliferation of non-ventricular zone TBR2+ intermediate progenitors as one potential cause of brain hyperplasia in these mutants.
      explanation: >-
        Names excess intermediate-progenitor proliferation as a cause of brain hyperplasia, which is exactly this edge.
  - target: Excitatory-Inhibitory Neuronal Trajectory Imbalance
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:35385734
      reference_title: "CHD8 haploinsufficiency links autism to transient alterations in excitatory and inhibitory trajectories."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Our results define cell-type-specific CHD8-dependent molecular defects related to an abnormal program of proliferation and alternative splicing.
      explanation: >-
        Ties the abnormal proliferation programme to the cell-type-specific excitatory versus inhibitory defect.
  - target: Increased Gliogenesis and White Matter Expansion
    causal_link_type: DIRECT
    description: >-
      In primates the same progenitor-level lesion is expressed predominantly as
      excess glial rather than excess neuronal output.
    evidence:
    - reference: PMID:36878905
      reference_title: "CHD8 mutations increase gliogenesis to enlarge brain size in the nonhuman primate."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Disrupting CHD8 in the fetal monkey brain prior to gliogenesis increased the number of glial cells in newborn monkeys.
      explanation: >-
        Places the glial expansion downstream of a CHD8 lesion acting on fetal
        progenitors before the gliogenic switch.
- name: Brain Overgrowth and Megalencephaly
  biological_scale: TISSUE
  description: >-
    Expansion of the progenitor pool translates into increased brain size, which is
    the tissue-level substrate of the clinical macrocephaly. This is one of the most
    robustly cross-validated nodes in the entry: chd8 suppression enlarges the
    forebrain/midbrain in zebrafish, Chd8 heterozygous mice have increased brain
    size, and CHD8-haploinsufficient human cerebral organoids are enlarged.
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  biological_processes:
  - preferred_term: brain development
    term:
      id: GO:0007420
      label: brain development
    modifier: ABNORMAL
  evidence:
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      chd8 disruption in zebrafish recapitulates features of the human phenotype, including increased head size as a result of expansion of the forebrain/midbrain and impairment of gastrointestinal motility due to a reduction in postmitotic enteric neurons.
    explanation: >-
      Model-organism recapitulation of both the head-size and the gastrointestinal
      arms of the human phenotype.
  - reference: PMID:29668850
    reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here, we report that Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli.
    explanation: Mouse heterozygote recapitulates brain overgrowth and hypertelorism.
  - reference: PMID:35385734
    reference_title: "CHD8 haploinsufficiency links autism to transient alterations in excitatory and inhibitory trajectories."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      This imbalance is consistent with an enlargement of cerebral organoids as an in vitro correlate of patients' macrocephaly.
    explanation: >-
      Human cerebral organoid model links the cellular imbalance to enlargement,
      the in vitro correlate of macrocephaly.
  downstream:
  - target: Autistic, Cognitive and Neuropsychiatric Phenotype
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Macrocephaly and the autism/cognitive phenotype co-segregate in CHD8-NDD, but
      whether brain overgrowth is itself causal for the behavioural phenotype or is
      a parallel consequence of the same progenitor lesion is not established.
- name: Excitatory-Inhibitory Neuronal Trajectory Imbalance
  biological_scale: CELLULAR
  description: >-
    In isogenic human cerebral organoids, CHD8 haploinsufficiency accelerates
    generation of inhibitory neurons and delays generation of excitatory neurons,
    producing symmetrically opposite, time-dependent distortions of their
    proportions. The effect is cell-autonomous and reflects abnormal proliferation
    and alternative-splicing programmes rather than a static shift in cell identity.
  cell_types:
  - preferred_term: GABAergic (inhibitory) neuron
    term:
      id: CL:0000617
      label: GABAergic neuron
    modifier: INCREASED
  - preferred_term: glutamatergic (excitatory) neuron
    term:
      id: CL:0000679
      label: glutamatergic neuron
    modifier: DECREASED
  biological_processes:
  - preferred_term: cerebral cortex neuron differentiation
    term:
      id: GO:0021895
      label: cerebral cortex neuron differentiation
    modifier: ABNORMAL
  evidence:
  - reference: PMID:35385734
    reference_title: "CHD8 haploinsufficiency links autism to transient alterations in excitatory and inhibitory trajectories."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      we find that CHD8 haploinsufficiency disrupted neurodevelopmental trajectories with an accelerated and delayed generation of, respectively, inhibitory and excitatory neurons that yields, at days 60 and 120, symmetrically opposite expansions in their proportions.
    explanation: >-
      Directly demonstrates the excitatory-inhibitory trajectory imbalance in a
      human isogenic model of CHD8 haploinsufficiency.
  downstream:
  - target: Aberrant Long-Range Functional Connectivity
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Downregulation of cell-adhesion and axon-guidance genes required for long-range wiring
    evidence:
    - reference: PMID:29668850
      reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        altered brain growth and diminished expression of important neurodevelopmental genes that regulate long-range brain wiring are followed by distinctive anomalies in functional brain connectivity in Chd8+/- mice
      explanation: >-
        States the sequence from altered growth and wiring-gene expression to functional connectivity anomalies.
- name: Aberrant Long-Range Functional Connectivity
  biological_scale: TISSUE
  description: >-
    Downregulation of the cell-adhesion and axon-guidance programme that builds
    long-range projections is followed by measurable changes in functional brain
    connectivity. Resting-state fMRI in Chd8 heterozygous mice shows increased
    synchronised activity in cortico-hippocampal and auditory-parietal networks,
    suggesting that CHD8-NDD is a subtype of autism characterised by long-range
    OVER-connectivity, in contrast to the under-connectivity more often reported in
    idiopathic autism.
  biological_processes:
  - preferred_term: axon guidance
    term:
      id: GO:0007411
      label: axon guidance
    modifier: DECREASED
  evidence:
  - reference: PMID:29668850
    reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Resting-state functional MRI identified increased synchronized activity in cortico-hippocampal and auditory-parietal networks in Chd8 heterozygous mutant mice, implicating altered connectivity as a potential mechanism underlying the behavioral phenotypes.
    explanation: >-
      Provides the functional-imaging evidence for altered long-range connectivity.
  - reference: PMID:29668850
    reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Our data suggest that CHD8 haploinsufficiency represents a specific subtype of ASD where neuropsychiatric symptoms are underpinned by long-range over-connectivity.
    explanation: >-
      States the over-connectivity interpretation that distinguishes this subtype.
  downstream:
  - target: Autistic, Cognitive and Neuropsychiatric Phenotype
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:29668850
      reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
      supports: PARTIAL
      evidence_source: MODEL_ORGANISM
      snippet: >-
        implicating altered connectivity as a potential mechanism underlying the behavioral phenotypes
      explanation: >-
        Connectivity is offered only as a potential mechanism for the behavioural phenotype; PARTIAL and indirect because causality is not demonstrated.
- name: Autistic, Cognitive and Neuropsychiatric Phenotype
  biological_scale: ORGANISM
  role: OUTCOME
  description: >-
    The organism-level neurobehavioural endpoint: autism spectrum disorder,
    developmental delay with disproportionate speech and motor involvement,
    intellectual disability usually in the mild-to-moderate range, and
    neuropsychiatric comorbidity including anxiety, ADHD, and aggressive or
    self-injurious behaviour. Chd8 heterozygous mice recapitulate the behavioural
    domain with increased anxiety, repetitive behaviour and altered social
    behaviour.
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays. When present, ID is most often in the mild-to-moderate range.
    explanation: >-
      GeneReviews description of the cognitive/developmental endpoint.
  - reference: PMID:27602517
    reference_title: "CHD8 haploinsufficiency results in autistic-like phenotypes in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here we show that mice heterozygous for Chd8 mutations manifest ASD-like behavioural characteristics including increased anxiety, repetitive behaviour, and altered social behaviour.
    explanation: >-
      Model-organism recapitulation of the autistic and anxiety phenotype at the
      same gene dosage as the human disorder.
- name: Enteric Neural Crest and Gut Epithelial Dysfunction
  biological_scale: TISSUE
  description: >-
    CHD8 is also required outside the CNS. In zebrafish, chd8 loss reduces the
    number of vagal neural crest cells and enteric neural/glial progenitors
    emigrating from the neural tube and impairs their early migration, later
    yielding fewer serotonergic enteric neurons and enterochromaffin cells, a
    thinner intestinal epithelium and fewer goblet cells. In mice, Chd8L
    haploinsufficiency increases intestinal permeability and reduces tuft and goblet
    cell counts. This is the mechanistic basis of the gastrointestinal arm of the
    syndrome, which is not explained by the CNS phenotype.
  cell_types:
  - preferred_term: enteric neuron
    term:
      id: CL:0007011
      label: enteric neuron
    modifier: DECREASED
  - preferred_term: intestinal goblet cell
    term:
      id: CL:0000160
      label: goblet cell
    modifier: DECREASED
  - preferred_term: intestinal tuft cell
    term:
      id: CL:0019032
      label: intestinal tuft cell
    modifier: DECREASED
  biological_processes:
  - preferred_term: enteric nervous system development
    term:
      id: GO:0048484
      label: enteric nervous system development
    modifier: ABNORMAL
  evidence:
  - reference: PMID:36375841
    reference_title: "Loss of autism-candidate CHD8 perturbs neural crest development and intestinal homeostatic balance."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      we found that the loss of chd8 leads to a reduced number of vagal neural crest cells (NCCs), enteric neural and glial progenitors, emigrating from the neural tube, and that their early migration capability was altered.
    explanation: >-
      Establishes the enteric neural crest developmental defect downstream of chd8
      loss.
  - reference: PMID:36375841
    reference_title: "Loss of autism-candidate CHD8 perturbs neural crest development and intestinal homeostatic balance."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The tissue examination of chd8 mutants revealed a thinner intestinal epithelium accompanied by an accumulation of neutrophils and the decreased numbers of goblet cells and eosinophils.
    explanation: Documents the intestinal epithelial and immune-balance component.
  - reference: PMID:37783686
    reference_title: "CHD8 regulates gut epithelial cell function and affects autism-related behaviors through the gut-brain axis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The current study found that mice haploinsufficient for the large isoform of Chd8 (Chd8L) exhibited increased intestinal permeability, transcriptomic dysregulation in gut epithelial cells, reduced tuft cell and goblet cell counts in the gut, and an overall increase in microbial load.
    explanation: >-
      Mammalian replication of the gut epithelial defect at a haploinsufficient
      Chd8 dose.
  downstream:
  - target: Gastrointestinal Dysmotility and Barrier Dysfunction
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24998929
      reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        impairment of gastrointestinal motility due to a reduction in postmitotic enteric neurons
      explanation: >-
        Attributes the motility defect specifically to the reduction in enteric neurons, which is this edge.
- name: Gastrointestinal Dysmotility and Barrier Dysfunction
  biological_scale: ORGANISM
  role: OUTCOME
  description: >-
    The clinical gastrointestinal endpoint: impaired gut motility (clinically,
    constipation with or without diarrhoea) attributable to reduced postmitotic
    enteric innervation, together with barrier compromise and altered microbial
    load. Gut-restricted manipulations in mice show this arm also feeds back on
    behaviour, though that gut-brain link remains a model-organism finding.
  locations:
  - preferred_term: intestine
    term:
      id: UBERON:0000160
      label: intestine
  evidence:
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      impairment of gastrointestinal motility due to a reduction in postmitotic enteric neurons
    explanation: >-
      Links reduced enteric innervation to the motility defect in the zebrafish
      model of the human phenotype.
  - reference: PMID:37783686
    reference_title: "CHD8 regulates gut epithelial cell function and affects autism-related behaviors through the gut-brain axis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Antibiotic treatment of Chd8L haploinsufficient mice attenuated social behavioral deficits.
    explanation: >-
      Supports a gut-to-brain contribution to behaviour in the mouse model; not yet
      demonstrated in humans.
- name: Increased Gliogenesis and White Matter Expansion
  biological_scale: CELLULAR
  description: >-
    A primate-specific arm of the overgrowth mechanism. CRISPR/Cas9 disruption of
    CHD8 in cynomolgus monkey embryos increases gliogenesis and the number of glial
    cells in newborn monkeys, and knockdown in organotypic newborn-monkey brain
    slices enhances glial proliferation. Because rodent studies gave inconsistent
    accounts of how CHD8 loss enlarges the brain - and because mouse cortex is
    enlarged without a proportionate increase in neuron number - glial expansion
    rather than neuronal excess may be the dominant driver of megalencephaly in
    primates, including humans. This node is retained deliberately as a parallel,
    species-qualified route into brain overgrowth; see the HUMAN_MODEL_MISMATCH
    discussion.
  cell_types:
  - preferred_term: glial cell
    term:
      id: CL:0000125
      label: glial cell
    modifier: INCREASED
  biological_processes:
  - preferred_term: gliogenesis
    term:
      id: GO:0042063
      label: gliogenesis
    modifier: INCREASED
  locations:
  - preferred_term: white matter
    term:
      id: UBERON:0002316
      label: white matter
  evidence:
  - reference: PMID:36878905
    reference_title: "CHD8 mutations increase gliogenesis to enlarge brain size in the nonhuman primate."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      we found that CRISPR/Cas9-mediated CHD8 mutations in the embryos of cynomolgus monkeys led to increased gliogenesis to cause macrocephaly in cynomolgus monkeys
    explanation: >-
      Establishes increased gliogenesis as the route from CHD8 disruption to
      macrocephaly in a non-human primate.
  - reference: PMID:36878905
    reference_title: "CHD8 mutations increase gliogenesis to enlarge brain size in the nonhuman primate."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      However, studies of small animal models showed inconsistent findings about the mechanisms for CHD8 deficiency-mediated autism symptoms and macrocephaly.
    explanation: >-
      States the rodent inconsistency that motivates treating the primate glial
      mechanism as a distinct, better-supported route in primates.
  downstream:
  - target: Brain Overgrowth and Megalencephaly
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:36878905
      reference_title: "CHD8 mutations increase gliogenesis to enlarge brain size in the nonhuman primate."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our findings suggest that gliogenesis is critical for brain size in primates and that abnormal gliogenesis may contribute to ASD.
      explanation: >-
        Directly asserts gliogenesis as a determinant of primate brain size.
- name: Glial and Serotonergic Disruption of Sleep Architecture
  biological_scale: TISSUE
  description: >-
    A mechanistically distinct arm accounting for the sleep phenotype. In
    Drosophila, the single CHD8/CHD7 ortholog kismet is required in glia -
    specifically the subperineurial glia that constitute the blood-brain barrier -
    for both developmental and adult sleep architecture, and the sleep disturbance
    is caused by elevated serotonin during development. Critically, despite this
    developmental origin the defect is reversible in adulthood by a behavioural
    regime resembling human sleep restriction therapy, which supplies a mechanistic
    rationale for the behavioural sleep interventions GeneReviews already
    recommends empirically.
  cell_types:
  - preferred_term: blood-brain-barrier glia (Drosophila subperineurial glia)
    term:
      id: CL:0000125
      label: glial cell
  chemical_entities:
  - preferred_term: serotonin
    term:
      id: CHEBI:28790
      label: serotonin
    modifier: INCREASED
  evidence:
  - reference: PMID:34088660
    reference_title: "The CHD8/CHD7/Kismet family links blood-brain barrier glia and serotonin to ASD-associated sleep defects."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We show that Kismet is required in glia for early developmental and adult sleep architecture. This role localizes to subperineurial glia constituting the blood-brain barrier.
    explanation: >-
      Localises the sleep requirement to blood-brain-barrier glia in the sole
      CHD8/CHD7 ortholog.
  - reference: PMID:34088660
    reference_title: "The CHD8/CHD7/Kismet family links blood-brain barrier glia and serotonin to ASD-associated sleep defects."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We demonstrate that Kismet-related sleep disturbances are caused by high serotonin during development, paralleling a well-established but genetically unsolved autism endophenotype.
    explanation: >-
      Identifies developmental hyperserotonemia as the mediator of the sleep defect.
  - reference: PMID:34088660
    reference_title: "The CHD8/CHD7/Kismet family links blood-brain barrier glia and serotonin to ASD-associated sleep defects."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Despite their developmental origin, Kismet's sleep architecture defects can be reversed in adulthood by a behavioral regime resembling human sleep restriction therapy.
    explanation: >-
      Shows the sleep phenotype is reversible in adulthood in the fly. Marked PARTIAL
      because reversibility has not been demonstrated in humans with CHD8-NDD; the
      claim supports the plausibility of behavioural sleep intervention, not its
      proven efficacy in this disorder.
  downstream:
  - target: Autistic, Cognitive and Neuropsychiatric Phenotype
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Disrupted sleep architecture is a component of the organism-level
      neurobehavioural burden; whether it also worsens the cognitive and behavioural
      phenotype in CHD8-NDD is untested.
- name: Striatal Circuit Dysfunction
  biological_scale: TISSUE
  description: >-
    Chd8 heterozygous mice show brain-region-specific dysregulation of chromatin
    modification, mRNA/protein processing, Wnt signalling and cell-cycle
    regulation, together with altered synaptic physiology in medium spiny neurons
    of the nucleus accumbens. Perturbing Chd8 in adult mice reproduces an altered
    motor-learning phenotype, indicating an ongoing adult striatal requirement for
    CHD8 rather than a purely developmental one.
  locations:
  - preferred_term: striatum
    term:
      id: UBERON:0002435
      label: striatum
  cell_types:
  - preferred_term: medium spiny neuron of the nucleus accumbens
    term:
      id: CL:1001474
      label: medium spiny neuron
  evidence:
  - reference: PMID:28402856
    reference_title: "Chd8 Mutation Leads to Autistic-like Behaviors and Impaired Striatal Circuits."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We also find altered synaptic physiology in medium spiny neurons of the nucleus accumbens. Perturbation of Chd8 in adult mice recapitulates improved acquired motor learning behavior found in Chd8+/- animals, suggesting a role for CHD8 in adult striatal circuits.
    explanation: >-
      Establishes the striatal synaptic phenotype and an adult (post-developmental)
      CHD8 requirement.
  downstream:
  - target: Autistic, Cognitive and Neuropsychiatric Phenotype
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
mechanistic_hypotheses:
- hypothesis_group_id: chd8_canonical_haploinsufficiency
  hypothesis_label: Canonical CHD8 haploinsufficiency
  status: CANONICAL
  description: >-
    The mainstream model: a heterozygous loss-of-function variant halves CHD8
    protein, reducing ATP-dependent chromatin remodelling at CHD8-bound promoters
    and dysregulating a large secondary network of neurodevelopmental and autism
    risk genes. Supported by the complete absence of truncating CHD8 variants in
    8,792 controls, by the DNA-methylation episignature associated with CHD8
    haploinsufficiency, and by dose-matched heterozygous animal models. This is the
    model the main pathophysiology chain in this entry represents.
- hypothesis_group_id: chd8_remodeling_independent_missense
  hypothesis_label: Remodelling-independent mechanism for a subset of missense alleles
  status: EMERGING
  description: >-
    A minority model with real support: not every CHD8 missense variant found in
    autism patients is causal, and among those that are, some act by a mechanism
    that does NOT involve loss of chromatin-remodelling function. Independently, one
    individual in the largest cohort showed a possible gain-of-function methylation
    signature rather than the expected haploinsufficiency signature. Together these
    imply that "haploinsufficiency" is an incomplete description of the molecular
    etiology and that the pathophysiology graph should not be read as forcing every
    pathogenic allele through the single remodelling node.
  evidence:
  - reference: PMID:38438524
    reference_title: "The complex etiology of autism spectrum disorder due to missense mutations of CHD8."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Furthermore, we found that mutations with high scores cause ASD by mechanisms either dependent on or independent of loss of chromatin-remodeling function.
    explanation: >-
      Direct functional demonstration that some pathogenic CHD8 missense alleles act
      independently of chromatin-remodelling loss.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      one analysis was inconclusive, and one showing a possible gain-of-function signature instead of the expected haploinsufficiency signature was observed
    explanation: >-
      A single human episignature observation consistent with a non-haploinsufficiency
      mechanism; PARTIAL because it is one individual and the signature is described
      only as "possible".
phenotypes:
- category: Growth
  name: Macrocephaly
  description: >-
    Increased occipitofrontal head circumference, most often developing during
    infancy. Macrocephaly plus autism is the single most recognisable pairing that
    should prompt CHD8 testing, and it is reproduced by chd8 disruption in
    zebrafish and by Chd8 heterozygosity in mice.
  phenotype_term:
    preferred_term: Macrocephaly
    term:
      id: HP:0000256
      label: Macrocephaly
  frequency: FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common findings are the development of macrocephaly (most often during infancy) and tall stature (most typically during puberty), which is often accompanied by ASD and/or DD/ID.
    explanation: >-
      GeneReviews names macrocephaly as one of the two most common findings of the
      syndrome.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a pattern of common features: macrocephaly (62.5%), tall stature (47%), developmental delay and/or intellectual disability (81%), ASDs (84%), sleep difficulties (50%), gastrointestinal problems (40%), and distinct facial features
    explanation: >-
      Quantifies macrocephaly at 62.5% in a 25-person CHD8 protein-truncating-variant cohort. This is the quantitative basis for the FREQUENT (30-79%) band; VERY_FREQUENT is deliberately NOT used because cohort figures range from about 52% to 80% depending on ascertainment (see the phenotype description and the frequency-ascertainment discussion).
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In addition to a high likelihood of an ASD diagnosis among patients bearing CHD8 mutations, characteristics enriched in this group included macrocephaly, distinct faces, and gastrointestinal complaints.
    explanation: >-
      Independent CHD8-ascertained cohort confirming macrocephaly enrichment.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      macrocephaly is a striking feature that was common, at birth (53%, 8/15) and at the age of examination (52%, 46/88)
    explanation: >-
      The largest assembled cohort quantifies macrocephaly at 52% (46/88) at
      examination, the lower of the two directly quantified series and the reason
      the band is FREQUENT rather than VERY_FREQUENT. The 53% at-birth figure has a
      denominator of only 15 and is not used for banding.
- category: Growth
  name: Tall Stature and Generalized Overgrowth
  description: >-
    Generalised overgrowth, with tall stature typically emerging around puberty.
    Overgrowth spans weight, height and head circumference, and is most pronounced
    for variants affecting the helicase-C (HELIC) domain.
  phenotype_term:
    preferred_term: Tall stature
    term:
      id: HP:0000098
      label: Tall stature
  frequency: FREQUENT
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common findings are the development of macrocephaly (most often during infancy) and tall stature (most typically during puberty), which is often accompanied by ASD and/or DD/ID.
    explanation: >-
      GeneReviews identifies tall stature as one of the two most common findings,
      qualified by pubertal timing.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a pattern of common features: macrocephaly (62.5%), tall stature (47%), developmental delay and/or intellectual disability (81%), ASDs (84%), sleep difficulties (50%), gastrointestinal problems (40%), and distinct facial features
    explanation: >-
      Quantifies tall stature at 47%, within the FREQUENT (30-79%) band.
  - reference: PMID:31721432
    reference_title: "The CHD8 overgrowth syndrome: A detailed evaluation of an emerging overgrowth phenotype in 27 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      85% had a height and/or head circumference >=2 standard deviations above the mean, meeting our clinical criteria for overgrowth
    explanation: >-
      The overgrowth-ascertained cohort shows that when height and head circumference are considered together, 85% meet formal overgrowth criteria - the generalised (not head-only) nature of the overgrowth is the discriminating feature versus other autism-with-macrocephaly conditions.
  - reference: PMID:31980904
    reference_title: "De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      HELIC domain mutations were associated with a severe phenotype defined by a greater number of clinical features, lower verbal IQ, and a prominent, consistent pattern of overgrowth as measured by weight, height and head circumference.
    explanation: >-
      Documents the overgrowth pattern and its genotype (HELIC domain) correlate.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      as well as tall stature (50%, 39/78)
    explanation: >-
      The largest assembled cohort quantifies tall stature at 50% (39/78),
      independently reproducing the 47% figure from PMID:31001818 and placing the
      FREQUENT band on two concordant denominators rather than on one.
- category: Growth
  name: Overweight
  description: >-
    Increased body weight is part of the generalised overgrowth, distinct from the
    head-only macrocephaly seen in other autism-with-macrocephaly conditions. It is
    clinically actionable: weight is the one modifiable axis of the overgrowth, and
    a baseline excess is worth knowing about before any weight-gaining psychotropic
    is considered for the behavioural phenotype. No CHD8-specific source addresses
    that interaction, so no treatment or avoidance claim is made from it here.
  phenotype_term:
    preferred_term: Overweight
    term:
      id: HP:0025502
      label: Overweight
  frequency: FREQUENT
  evidence:
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      being overweight (34%, 24/71)
    explanation: >-
      The largest assembled cohort (n=106) reports overweight in 34% (24/71) of
      individuals with a recorded weight; 24/71 = 33.8%, which falls in the
      FREQUENT (30-79%) band. The denominator (71 of 106) reflects incomplete
      weight reporting rather than selective assessment, so unlike the
      forehead/dental figures discussed in note (4) this proportion is
      interpretable as a frequency.
  - reference: PMID:31980904
    reference_title: "De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a prominent, consistent pattern of overgrowth as measured by weight, height and head circumference
    explanation: >-
      Independent confirmation that weight is one of the three axes on which the
      overgrowth is expressed; this series does not quantify overweight separately,
      so it contributes no figure to the band.
- category: Neurologic
  name: Global Developmental Delay
  description: >-
    Delayed acquisition of developmental milestones in most or all affected
    individuals, most conspicuously in the speech and motor domains.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays.
    explanation: >-
      "Most, if not all" maps to VERY_FREQUENT in the project's prose-to-enum table.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      developmental delay and/or intellectual disability (81%)
    explanation: >-
      Independent cohort quantification of developmental delay and/or intellectual disability at 81%, supporting the VERY_FREQUENT band.
- category: Neurologic
  name: Delayed Speech and Language Development
  description: >-
    Speech and language delay is the most commonly reported developmental domain in
    CHD8-NDD, and language disability is a defining component of the severe
    HELIC-domain phenotype.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays.
    explanation: >-
      GeneReviews identifies speech delay as one of the two most common developmental
      domains within a near-universal developmental delay.
- category: Neurologic
  name: Motor Delay
  description: Delayed motor milestones, frequently accompanied by hypotonia.
  phenotype_term:
    preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most, if not all, affected individuals have some degree of DD, most commonly speech and motor delays.
    explanation: >-
      GeneReviews identifies motor delay as one of the two most common developmental
      domains within a near-universal developmental delay.
  - reference: PMID:29668850
    reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here, we report that Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli.
    explanation: Motor delay is recapitulated in the Chd8 heterozygous mouse.
- category: Neurologic
  name: Intellectual Disability
  description: >-
    Intellectual disability, when present, is most often in the mild-to-moderate
    range; severity correlates with variant location, with HELIC-domain variants
    associated with lower verbal IQ.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
    severity: MODERATE
  frequency: FREQUENT
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      When present, ID is most often in the mild-to-moderate range.
    explanation: >-
      GeneReviews qualifies ID as present in a subset ("when present") with
      mild-to-moderate severity, so the band is set below the near-universal
      developmental delay.
  - reference: PMID:30670789
    reference_title: "A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Children with the disorder present with developmental delay, intellectual disability, and/or autism spectrum disorder in addition to characteristic facies.
    explanation: Independent clinical series confirming intellectual disability.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Many neurological abnormalities, like intellectual disability (68%) and hypotonia (29%) were observed, as well as a wide variety of behavioural abnormalities (88%).
    explanation: >-
      The largest assembled cohort (n=106) quantifies intellectual disability at 68%, within the FREQUENT (30-79%) band.
  - reference: PMID:31721432
    reference_title: "The CHD8 overgrowth syndrome: A detailed evaluation of an emerging overgrowth phenotype in 27 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients presented with intellectual disability, with 85% in the mild or moderate range
    explanation: >-
      Supports the mild-to-moderate severity characterisation. Note this cohort was ascertained through overgrowth clinics, so the 100% ID figure reflects ascertainment and is not used for the frequency band.
- category: Behavioral
  name: Autism Spectrum Disorder
  description: >-
    Autism spectrum disorder is a core and highly penetrant feature. CHD8
    disruption defines one of the most reproducible genetically-defined autism
    subtypes; the autism here is a monogenic consequence of CHD8 haploinsufficiency,
    not the multifactorial autism of the general population.
  phenotype_term:
    preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  frequency: FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings indicate that CHD8 disruptions define a distinct ASD subtype and reveal unexpected comorbidities between brain development and enteric innervation.
    explanation: >-
      Establishes CHD8 disruption as defining a distinct, monogenic autism subtype.
  - reference: PMID:33627187
    reference_title: "Distinct, dosage-sensitive requirements for the autism-associated factor CHD8 during cortical development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CHD8 haploinsufficiency causes autism and macrocephaly with high penetrance in the human population.
    explanation: >-
      States the high penetrance of the autism-plus-macrocephaly phenotype.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most frequently observed behavioural problems included autism spectrum disorder (76%), short attention span (32%), abnormal social behaviour (31%), sleep disturbance (29%) and impaired social interactions (28%).
    explanation: >-
      The largest cohort (n=106) puts autism spectrum disorder at 76%, inside the FREQUENT (30-79%) band. FREQUENT rather than VERY_FREQUENT is used because the two largest quantified series bracket the 80% threshold (76% here, 84% in PMID:31001818) rather than clearing it.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ASDs (84%)
    explanation: >-
      The second-largest protein-truncating-variant cohort reports 84%, just above the band boundary. The lower, larger-cohort figure is used for the band.
- category: Behavioral
  name: Sleep Disturbance
  description: >-
    Sleep disturbance affecting both initiation (delayed sleep onset) and
    maintenance (frequent night awakenings) of sleep; a prominent and
    management-relevant feature of the syndrome.
  phenotype_term:
    preferred_term: Sleep disturbance
    term:
      id: HP:0002360
      label: Sleep disturbance
  frequency: FREQUENT
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sleep disturbance is characterized by difficulty with both initiation (delayed sleep onset) and maintenance (frequent night awakenings) of sleep.
    explanation: >-
      GeneReviews characterises the sleep phenotype qualitatively (initiation and
      maintenance) but does not quantify it; the FREQUENT band comes from the 50%
      figure in PMID:31001818 below, not from this source.
  - reference: PMID:30670789
    reference_title: "A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Gastrointestinal and sleep problems are notable.
    explanation: Independent clinical series flagging sleep problems as notable.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      sleep difficulties (50%)
    explanation: >-
      Quantifies sleep difficulties at 50%, the basis for the FREQUENT band.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      sleep disturbance (29%)
    explanation: >-
      The largest cohort reports a substantially lower figure (29%). This retrospective HPO-coded aggregation almost certainly undercounts sleep problems relative to prospectively questioned cohorts; the discrepancy is recorded rather than hidden. See the frequency-ascertainment discussion.
- category: Gastrointestinal
  name: Constipation
  description: >-
    Constipation, with or without intervening periods of diarrhoea, is the most
    common gastrointestinal problem in CHD8-NDD. It is mechanistically linked to
    reduced enteric innervation rather than being an incidental comorbidity.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
  frequency: FREQUENT
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common gastrointestinal issue is constipation with or without periods of diarrhea.
    explanation: >-
      GeneReviews identifies constipation as the most common GI issue in a disorder
      in which GI issues are a listed core domain; "most common" maps to FREQUENT.
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      characteristics enriched in this group included macrocephaly, distinct faces, and gastrointestinal complaints
    explanation: Independent cohort evidence for enrichment of GI complaints.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      gastrointestinal problems (40%)
    explanation: >-
      Quantifies gastrointestinal problems at 40%, inside the FREQUENT band.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Furthermore, abnormalities in the digestive (53%), musculoskeletal (79%) and genitourinary systems (18%) were noted.
    explanation: >-
      Independent quantification of digestive-system involvement at 53% in the largest cohort.
- category: Gastrointestinal
  name: Diarrhea
  description: >-
    Periods of diarrhoea may alternate with constipation in affected individuals.
  phenotype_term:
    preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common gastrointestinal issue is constipation with or without periods of diarrhea.
    explanation: >-
      GeneReviews records diarrhoea as an intermittent accompaniment; no frequency is
      stated, so none is asserted.
- category: Neurologic
  name: Hypotonia
  description: Decreased muscle tone, reported in roughly 30% of affected individuals.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare).
    explanation: >-
      GeneReviews gives an approximate 30% figure, sitting exactly on the
      OCCASIONAL/FREQUENT boundary.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Many neurological abnormalities, like intellectual disability (68%) and hypotonia (29%) were observed
    explanation: >-
      Largest cohort reports 29%.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      some had regression of speech (37%), seizures (27%) and hypotonia (27%)
    explanation: >-
      Second independent cohort reports 27%. Two independent quantified cohorts both fall below 30%, so the OCCASIONAL (5-29%) band is used rather than rounding GeneReviews' "about 30%" upward.
- category: Neurologic
  name: Seizures
  description: >-
    Epileptic seizures occur in a minority of affected individuals (10%-15%).
    Seizures are not a defining feature and their presence should not by itself
    redirect testing towards the epilepsy-associated CHD paralogue CHD2.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare).
    explanation: >-
      GeneReviews gives 10%-15%, which falls in the 5-29% OCCASIONAL band.
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      some had regression of speech (37%), seizures (27%) and hypotonia (27%)
    explanation: >-
      An independent cohort reports 27%, at the upper end of but still within the OCCASIONAL band.
  - reference: PMID:31526516
    reference_title: "Clinical Phenotypes of Carriers of Mutations in CHD8 or Its Conserved Target Genes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      less severe adaptive deficits in communication skills, similar functional language, more social motivation challenges in those with ASD, larger head circumference, higher weight, and lower seizure prevalence relative to the other gene group
    explanation: >-
      CHD8 carriers have LOWER seizure prevalence than other autism-risk-gene carriers, reinforcing that epilepsy is not a defining feature of this disorder.
- category: Neurologic
  name: Dystonia
  description: >-
    Young-onset dystonia is a rare but validated part of the CHD8-NDD phenotypic
    spectrum. Reported dystonic presentations are heterogeneous, ranging from focal,
    exercise-dependent and apparently isolated forms to generalised permanent
    phenotypes with spasticity and tremor, and can occur with minimal or absent
    cognitive and autistic features - so dystonia may be the presenting complaint.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  frequency: VERY_RARE
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare).
    explanation: >-
      GeneReviews describes dystonia as rare, mapping to the VERY_RARE band.
  - reference: PMID:38441608
    reference_title: "CHD8-related disorders redefined: an expanding spectrum of dystonic phenotypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This work validates our previous observation that dystonia is part of the phenotypic spectrum of CHD8-related
    explanation: >-
      Dedicated case series validating dystonia as part of the CHD8-NDD spectrum.
  - reference: PMID:34415117
    reference_title: "Childhood-onset progressive dystonia associated with pathogenic truncating variants in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We further expand the CHD8-related phenotype with the description of two unrelated patients who presented with childhood-onset progressive dystonia.
    explanation: >-
      The original report establishing childhood-onset progressive dystonia as a CHD8 presentation. Note this is the one phenotype in the entry described as progressive.
- category: Neurologic
  name: Chiari Type I Malformation
  description: >-
    Chiari I malformation is a rare structural finding in CHD8-NDD. GeneReviews
    recommends assessing for signs of cerebrospinal fluid obstruction and spinal
    cord dysfunction, and considering serial imaging when a Chiari I malformation is
    known.
  phenotype_term:
    preferred_term: Chiari type I malformation
    term:
      id: HP:0007099
      label: Chiari type I malformation
  frequency: VERY_RARE
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare).
    explanation: >-
      GeneReviews describes Chiari I malformation as rare, mapping to VERY_RARE.
- category: Behavioral
  name: Anxiety
  description: >-
    Anxiety is one of the neuropsychiatric manifestations GeneReviews recommends
    monitoring for at every visit; increased anxiety is also the most consistent
    behavioural readout in Chd8 heterozygous mice. In a genotype-first comparison
    against two other monogenic neurodevelopmental conditions, anxiety is
    the psychiatric feature that most distinguishes CHD8 from ADNP and DYRK1A, and
    anxiety features rose with age across that pooled sample - which is why
    anxiety is treated here as a recurring surveillance target rather than a
    one-off developmental finding.
  phenotype_term:
    preferred_term: Anxiety
    term:
      id: HP:0000739
      label: Anxiety
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      monitor for signs and symptoms of anxiety, attention-deficit/hyperactivity disorder, and aggressive or self-injurious behavior
    explanation: >-
      GeneReviews surveillance guidance identifies anxiety as an expected
      manifestation; no frequency is given, so none is asserted.
  - reference: PMID:27602517
    reference_title: "CHD8 haploinsufficiency results in autistic-like phenotypes in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      mice heterozygous for Chd8 mutations manifest ASD-like behavioural characteristics including increased anxiety, repetitive behaviour, and altered social behaviour
    explanation: Anxiety is recapitulated at the same gene dosage in mice.
  - reference: PMID:38622540
    reference_title: "Shared and divergent mental health characteristics of ADNP-, CHD8- and DYRK1A-related neurodevelopmental conditions."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patterns of mental health features varied by group, with anxiety most prominent for CHD8
    explanation: >-
      Genotype-first CBCL comparison across ADNP, CHD8 and DYRK1A identifies anxiety
      as the psychiatric feature most characteristic of CHD8 specifically. The CHD8
      subgroup is n=18, so this establishes the qualitative profile, not a frequency.
  - reference: PMID:38622540
    reference_title: "Shared and divergent mental health characteristics of ADNP-, CHD8- and DYRK1A-related neurodevelopmental conditions."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For the full sample, age was positively associated with anxiety features, such that elevations in anxiety relative to same-age and same-sex peers may worsen with increasing age.
    explanation: >-
      Reports an age-related increase in anxiety, which is the basis for treating
      anxiety as an ongoing surveillance target. No `clinical_course: PROGRESSIVE`
      qualifier is asserted from this: the association was estimated across the full
      three-gene sample (N=65) rather than within the CHD8 subgroup, is stated
      hedged ("may worsen"), and comes from a cross-sectional design that cannot
      distinguish worsening within individuals from cohort effects. Marked PARTIAL
      for the same reason.
- category: Behavioral
  name: Attention Deficit Hyperactivity Disorder
  description: >-
    ADHD is an expected neuropsychiatric comorbidity, and ADHD-like traits have been
    the sole manifestation in a mildly affected transmitting parent.
  phenotype_term:
    preferred_term: Attention deficit hyperactivity disorder
    term:
      id: HP:0007018
      label: Attention deficit hyperactivity disorder
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      monitor for signs and symptoms of anxiety, attention-deficit/hyperactivity disorder, and aggressive or self-injurious behavior
    explanation: >-
      GeneReviews surveillance guidance identifies ADHD as an expected manifestation.
  - reference: PMID:41407309
    reference_title: "Phenotypic Variability and Paternal Inheritance of a CHD8 Variant Causing Intellectual Developmental Disorder With Autism and Macrocephaly Confirmed by Epigenetic and Structural Analyses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      who exhibited a subtle feature, including traits consistent with attention-deficit/hyperactivity disorder
    explanation: >-
      Illustrates ADHD traits as the minimal expression in a transmitting parent.
- category: Behavioral
  name: Aggressive and Self-Injurious Behavior
  description: >-
    Aggressive or self-injurious behaviour is an expected behavioural manifestation
    requiring active surveillance.
  phenotype_term:
    preferred_term: Self-injurious behavior
    term:
      id: HP:0100716
      label: Self-injurious behavior
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      monitor for signs and symptoms of anxiety, attention-deficit/hyperactivity disorder, and aggressive or self-injurious behavior
    explanation: >-
      GeneReviews surveillance guidance identifies aggressive/self-injurious
      behaviour as an expected manifestation.
  - reference: PMID:33175317
    reference_title: "Brief Report: Associations Between Self-injurious Behaviors and Abdominal Pain Among Individuals with ASD-Associated Disruptive Mutations."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      History of severe abdominal pain predicted higher rates of SIB and SIB severity after controlling for age and adaptive behavior; individuals with a history of severe abdominal pain were eight times more likely to exhibit SIB than those with no history.
    explanation: >-
      In carriers of disruptive autism-risk-gene mutations, self-injury is strongly associated with severe abdominal pain, suggesting some challenging behaviour in this disorder is a pain signal from the gastrointestinal phenotype rather than a primary behavioural phenotype. Marked PARTIAL because the cohort spans multiple autism-risk genes and is not CHD8-specific.
- category: Craniofacial
  name: Hypertelorism
  description: >-
    Widely spaced eyes are part of the recognisable CHD8 facies and are reproduced
    in Chd8 heterozygous mice.
  phenotype_term:
    preferred_term: Hypertelorism
    term:
      id: HP:0000316
      label: Hypertelorism
  evidence:
  - reference: PMID:30670789
    reference_title: "A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      similar dysmorphic features, including widely-spaced eyes, short nose with flat nasal bridge, long philtrum, prominent Cupid's bow of the upper lip, full lower lip, and auricular anomalies
    explanation: Clinical series describing widely spaced eyes in the CHD8 facies.
  - reference: PMID:29668850
    reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli
    explanation: Hypertelorism is recapitulated in the mouse heterozygote.
- category: Craniofacial
  name: Broad Forehead with Prominent Supraorbital Ridges
  description: >-
    A broad forehead with prominent supraorbital ridges is a recurring element of
    the CHD8 facial gestalt.
  phenotype_term:
    preferred_term: Broad forehead
    term:
      id: HP:0000337
      label: Broad forehead
  evidence:
  - reference: PMID:31980904
    reference_title: "De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      dysmorphic features, including broad forehead with prominent supraorbital ridges, flat nasal bridge, telecanthus and large ears
    explanation: Clinical series describing the forehead and supraorbital features.
- category: Craniofacial
  name: Prominent Supraorbital Ridges
  description: >-
    Prominent supraorbital ridges accompany the broad forehead in the CHD8 facies.
  phenotype_term:
    preferred_term: Prominent supraorbital ridges
    term:
      id: HP:0000336
      label: Prominent supraorbital ridges
  evidence:
  - reference: PMID:31980904
    reference_title: "De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      dysmorphic features, including broad forehead with prominent supraorbital ridges, flat nasal bridge, telecanthus and large ears
    explanation: Clinical series naming prominent supraorbital ridges.
- category: Craniofacial
  name: Depressed Nasal Bridge
  description: A flat or depressed nasal bridge, often with a short nose.
  phenotype_term:
    preferred_term: Depressed nasal bridge
    term:
      id: HP:0005280
      label: Depressed nasal bridge
  evidence:
  - reference: PMID:30670789
    reference_title: "A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      similar dysmorphic features, including widely-spaced eyes, short nose with flat nasal bridge, long philtrum, prominent Cupid's bow of the upper lip, full lower lip, and auricular anomalies
    explanation: Clinical series describing the flat nasal bridge.
- category: Craniofacial
  name: Long Philtrum
  description: A long philtrum, frequently with a prominent Cupid's bow and full lower lip.
  phenotype_term:
    preferred_term: Long philtrum
    term:
      id: HP:0000343
      label: Long philtrum
  evidence:
  - reference: PMID:30670789
    reference_title: "A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      similar dysmorphic features, including widely-spaced eyes, short nose with flat nasal bridge, long philtrum, prominent Cupid's bow of the upper lip, full lower lip, and auricular anomalies
    explanation: Clinical series describing the long philtrum.
- category: Craniofacial
  name: Large Ears
  description: Large ears and other auricular anomalies are part of the CHD8 facies.
  phenotype_term:
    preferred_term: Macrotia
    term:
      id: HP:0000400
      label: Macrotia
  evidence:
  - reference: PMID:31980904
    reference_title: "De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      dysmorphic features, including broad forehead with prominent supraorbital ridges, flat nasal bridge, telecanthus and large ears
    explanation: Clinical series naming large ears.
- category: Craniofacial
  name: Downslanted Palpebral Fissures
  description: >-
    Downslanting of the palpebral fissures accompanies the wide-set eyes in the
    CHD8 facial gestalt.
  phenotype_term:
    preferred_term: Downslanted palpebral fissures
    term:
      id: HP:0000494
      label: Downslanted palpebral fissures
  evidence:
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      wide-set eyes with down slanted palpebral ﬁssures
    explanation: >-
      Named as a typical dysmorphic feature of the entity. This sentence summarises
      the prior literature in the introduction of the largest cohort paper rather
      than reporting that cohort's own counts, so no frequency is asserted.
- category: Craniofacial
  name: Pointed Chin
  description: A pointed chin completes the lower-face element of the CHD8 gestalt.
  phenotype_term:
    preferred_term: Pointed chin
    term:
      id: HP:0000307
      label: Pointed chin
  evidence:
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a broad nose with full nasal tip, and a pointed chin
    explanation: >-
      Named as a typical dysmorphic feature of the entity. As above, this is a
      literature-summary sentence, so no frequency is asserted.
- category: Behavioral
  name: Behavioral Abnormality
  description: >-
    Behavioural problems taken as a whole are the single most frequent
    manifestation of CHD8-NDD, more frequent than any individual behavioural
    diagnosis. The composite includes autism spectrum disorder, short attention
    span, abnormal social behaviour, impaired social interaction, stereotypy and
    aggression.
  phenotype_term:
    preferred_term: Atypical behavior
    term:
      id: HP:0000708
      label: Atypical behavior
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Many neurological abnormalities, like intellectual disability (68%) and hypotonia (29%) were observed, as well as a wide variety of behavioural abnormalities (88%).
    explanation: >-
      Quantifies composite behavioural abnormality at 88% in the largest cohort,
      supporting the VERY_FREQUENT (80-100%) band.
  - reference: PMID:31721432
    reference_title: "The CHD8 overgrowth syndrome: A detailed evaluation of an emerging overgrowth phenotype in 27 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Behavioral problems were reported in the majority of patients (78%), with over half (56%) either formally diagnosed with an autistic spectrum disorder or described as having autistic traits.
    explanation: >-
      Independent cohort reporting behavioural problems in 78%.
- category: Neurologic
  name: Developmental Regression
  description: >-
    Loss of previously acquired skills - most often speech, but also social and
    motor skills - occurring in infancy and early childhood. Regression is a
    distinctive and under-recognised element of the CHD8-NDD course, and it is one
    reason the disorder cannot be described as a purely static encephalopathy.
  phenotype_term:
    preferred_term: Developmental regression
    term:
      id: HP:0002376
      label: Developmental regression
  frequency: FREQUENT
  evidence:
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      some had regression of speech (37%), seizures (27%) and hypotonia (27%)
    explanation: >-
      Quantifies speech regression at 37%, inside the FREQUENT (30-79%) band. Note
      the source measures regression of speech specifically; regression of social and
      motor skills is described qualitatively elsewhere and is not separately banded.
- category: Musculoskeletal
  name: Musculoskeletal Abnormality
  description: >-
    A broad category of skeletal and limb findings reported in the majority of
    systematically examined individuals, including pes planus, scoliosis and fifth
    finger clinodactyly. No single musculoskeletal feature is individually common;
    the burden is in the aggregate.
  phenotype_term:
    preferred_term: Abnormality of the musculoskeletal system
    term:
      id: HP:0033127
      label: Abnormality of the musculoskeletal system
  frequency: FREQUENT
  evidence:
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Furthermore, abnormalities in the digestive (53%), musculoskeletal (79%) and genitourinary systems (18%) were noted.
    explanation: >-
      Quantifies composite musculoskeletal involvement at 79%, the top of the
      FREQUENT band.
  - reference: PMID:31721432
    reference_title: "The CHD8 overgrowth syndrome: A detailed evaluation of an emerging overgrowth phenotype in 27 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Additional clinical features included neonatal hypotonia (33%), and less frequently seizures, pes planus, scoliosis, fifth finger clinodactyly, umbilical hernia, and glabellar hemangioma
    explanation: >-
      Enumerates the individual musculoskeletal findings that make up the composite,
      each individually uncommon.
genetic:
- name: CHD8
  gene_term:
    preferred_term: CHD8
    term:
      id: hgnc:20153
      label: CHD8
  relationship_type: CAUSATIVE
  variant_origin: DE_NOVO
  notes: >-
    Heterozygous loss-of-function variants in CHD8 at 14q11.2 - nonsense, frameshift
    and splice-site variants, and whole-gene deletions within the recurrent 14q11.2
    microdeletion - cause CHD8-NDD by haploinsufficiency. Missense variants also
    occur; the helicase-C (HELIC) domain is a genotype-phenotype hotspot associated
    with a more severe phenotype. CHD8 is the gene most frequently hit by de novo
    disruptive variants in autism exome studies, and truncating events are absent
    from large control cohorts. The MONDO entity used as this entry's anchor asserts
    RO:0004003 to HGNC:20153, verified with OAK.
  evidence:
  - reference: PMID:22495309
    reference_title: "Sporadic autism exomes reveal a highly interconnected protein network of de novo mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In proband exomes, recurrent protein-altering mutations were observed in two genes: CHD8 and NTNG1.
    explanation: >-
      Gene-discovery evidence: the original sporadic-autism exome study that
      identified recurrent de novo CHD8 mutations. Cited for discovery only, not for
      CHD8-specific phenotype frequencies.
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we resequenced the ASD-associated gene CHD8 in 3,730 children with developmental delay or ASD. We identified a total of 15 independent mutations; no truncating events were identified in 8,792 controls, including 2,289 unaffected siblings.
    explanation: >-
      Establishes the mutational burden and the absence of truncating CHD8 events in
      controls.
  - reference: PMID:31980904
    reference_title: "De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      HELIC domain mutations were associated with a severe phenotype defined by a greater number of clinical features, lower verbal IQ, and a prominent, consistent pattern of overgrowth as measured by weight, height and head circumference.
    explanation: Documents the HELIC-domain genotype-phenotype correlation.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified 29 unique nonsense, 25 frameshift, 24 missense, and 12 splice site variants. Furthermore, two unique inframe deletions, one larger deletion (exons 26-28), and one translocation were observed.
    explanation: >-
      Defines the variant spectrum across the largest assembled cohort: truncating
      classes dominate, but missense variants are the second most numerous class.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Although no significant difference in severity was observed between males and females, individuals with a missense variant were less severely affected.
    explanation: >-
      Reports a modest missense-versus-truncating severity difference and no sex
      difference in severity. PARTIAL because the missense finding is borderline,
      unreplicated, and confounded by the demonstration (PMID:38438524) that some
      CHD8 missense variants in autism patients are not causal at all - which would
      by itself dilute apparent severity in a missense group.
  - reference: PMID:25257502
    reference_title: "Recurrent \u223c100 Kb microdeletion in the chromosomal region 14q11.2, involving CHD8 gene, is associated with autism and macrocephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The minimal critical region, considering present and previous cases, contains the SUPT16H and CHD8 genes.
    explanation: >-
      Recurrent 14q11.2 microdeletion route to CHD8 haploinsufficiency; note the
      minimal region also contains SUPT16H, so deletion cases are not a pure CHD8
      lesion.
variants:
- name: CHD8 helicase-C (HELIC) domain truncating and missense variants
  gene:
    preferred_term: CHD8
    term:
      id: hgnc:20153
      label: CHD8
  description: >-
    Constitutive truncating variants in the helicase-C domain of CHD8 are seen in
    individuals with autism (and, somatically, in cancer) but not in the general
    population, and are associated with the most severe end of the CHD8-NDD
    phenotypic spectrum, including lower verbal IQ and a consistent overgrowth
    pattern.
  evidence:
  - reference: PMID:31980904
    reference_title: "De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we compiled a comprehensive list of CHD8 variants from the literature and databases, which revealed constitutive and somatic truncating variants in the HELIC (Helicase-C) domain in ASD and in cancer patients, respectively, but not in the general population.
    explanation: >-
      Documents the HELIC-domain variant class and its absence from the general
      population.
- name: CHD8 missense variants of uncertain causality
  gene:
    preferred_term: CHD8
    term:
      id: hgnc:20153
      label: CHD8
  description: >-
    Missense variants are the most common non-truncating CHD8 change reported in
    autism, and they are the principal variant-interpretation problem in this
    disorder. Functional testing across biochemical activity, embryonic stem cell
    neural differentiation and mouse behaviour showed that only high-prediction-score
    missense alleles produce autism-like phenotypes, so a CHD8 missense variant must
    not be assumed pathogenic without in silico support and, ideally, functional or
    episignature data.
  evidence:
  - reference: PMID:38438524
    reference_title: "The complex etiology of autism spectrum disorder due to missense mutations of CHD8."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Only mutations with high prediction scores gave rise to ASD-like phenotypes in mice, suggesting that not all CHD8 missense mutations detected in ASD patients are directly responsible for the development of ASD.
    explanation: >-
      Direct functional evidence that a subset of CHD8 missense variants found in
      autism patients are not causal.
diagnosis:
- name: Molecular Genetic Diagnosis of CHD8-NDD
  description: >-
    The diagnosis is molecular: identification of a heterozygous pathogenic or
    likely pathogenic CHD8 variant in a proband with a consistent phenotype
    (macrocephaly and/or tall stature with developmental delay and/or autism).
    Chromosomal microarray will detect the 14q11.2 whole-gene deletion route.
    For variants of uncertain significance, DNA methylation episignature testing
    and structural modelling have been used as adjunctive reclassification tools.
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of CHD8-NDD is established in a proband by identification of a heterozygous pathogenic (or likely pathogenic) variant in CHD8 by molecular genetic testing.
    explanation: GeneReviews diagnostic criterion.
  - reference: PMID:41407309
    reference_title: "Phenotypic Variability and Paternal Inheritance of a CHD8 Variant Causing Intellectual Developmental Disorder With Autism and Macrocephaly Confirmed by Epigenetic and Structural Analyses."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pathogenicity was confirmed through epigenetic signature testing (EpiSign), demonstrating characteristic methylation patterns and structural biology analysis, predicting significant protein destabilization.
    explanation: >-
      Illustrates episignature and structural modelling as VUS-reclassification
      adjuncts in this disorder.
  - reference: PMID:36182950
    reference_title: "The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Methylation analysis was performed for 13 patients, 11 of which showed the previously established episignature for IDDAM (85%) associated with CHD8 haploinsufficiency
    explanation: >-
      Establishes the CHD8/IDDAM peripheral-blood DNA methylation episignature and
      quantifies its sensitivity at 85% - so a negative episignature does not
      exclude the diagnosis.
treatments:
- name: Sleep Disturbance Management
  description: >-
    GeneReviews recommends addressing sleep disturbance through behavioural
    interventions and/or pharmacologic treatment. Sleep is a high-yield target
    because the disturbance affects both sleep onset and maintenance and is a major
    driver of daytime behavioural burden. No CHD8-specific agent is established;
    management follows general neurodevelopmental-disorder practice.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: behavioral counseling
    term:
      id: NCIT:C181743
      label: Behavioral Counseling
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sleep disturbance may be addressed through behavioral interventions and/or pharmacologic treatment
    explanation: GeneReviews management recommendation for sleep disturbance.
- name: Management of Bowel Dysfunction
  description: >-
    Standard treatment for bowel dysfunction, principally constipation. Because the
    constipation in CHD8-NDD is linked to reduced enteric innervation rather than
    to diet alone, it commonly requires sustained rather than episodic management,
    and GeneReviews recommends ongoing monitoring for constipation at surveillance
    visits.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Gastrointestinal Dysmotility and Barrier Dysfunction
    treatment_effect: INHIBITS
    description: >-
      Symptomatic management of the clinical endpoint of the enteric arm of the
      mechanism graph.
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      standard treatment for DD/ID, seizures, and bowel dysfunction
    explanation: GeneReviews management recommendation for bowel dysfunction.
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      monitor for constipation
    explanation: GeneReviews surveillance recommendation.
- name: Developmental and Educational Intervention
  description: >-
    Standard treatment for developmental delay and intellectual disability, with
    assessment of developmental progress and educational needs at each visit. Given
    the disproportionate speech and language involvement, speech-language therapy is
    a particular priority.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech and language therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      standard treatment for DD/ID, seizures, and bowel dysfunction
    explanation: GeneReviews management recommendation for DD/ID.
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      assessment of developmental progress and educational needs
    explanation: GeneReviews surveillance recommendation for developmental progress.
- name: Antiseizure Pharmacotherapy
  description: >-
    Standard antiseizure treatment for the 10%-15% of affected individuals who
    develop seizures. No CHD8-specific antiseizure medication preference is
    established.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      standard treatment for DD/ID, seizures, and bowel dysfunction
    explanation: GeneReviews management recommendation for seizures.
- name: Surgical Treatment of Chiari I Malformation
  description: >-
    When a Chiari I malformation is present, surgical treatment may be required.
    Serial imaging may be considered for asymptomatic or minimally symptomatic
    Chiari I malformation as clinically indicated.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      if Chiari I malformation is present, surgical treatment may be required
    explanation: GeneReviews management recommendation for Chiari I malformation.
- name: Growth and Neurologic Surveillance
  description: >-
    Structured surveillance at each visit: measurement of growth parameters
    including head circumference; assessment of developmental progress and
    educational needs; monitoring for anxiety, ADHD and aggressive or self-injurious
    behaviour; assessment for new manifestations such as seizures, tone changes, and
    signs of cerebrospinal fluid obstruction or spinal cord dysfunction; screening
    for sleep disturbance; and monitoring for constipation.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At each visit: measurement of growth parameters (including head circumference); assessment of developmental progress and educational needs
    explanation: GeneReviews surveillance schedule.
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      assess for new manifestations, such as seizures, changes in tone, and signs/symptoms of cerebrospinal fluid obstruction and/or spinal cord dysfunction
    explanation: GeneReviews surveillance for new neurologic manifestations.
- name: Deep Brain Stimulation for Refractory Dystonia
  description: >-
    In the rare subgroup presenting with childhood-onset progressive dystonia, deep
    brain stimulation produced clinical improvement in both reported cases. This is
    the best-evidenced targeted intervention in the disorder, although the evidence
    base is two patients. Pharmacologic options tried in the dystonic subgroup
    (levodopa, tizanidine, botulinum toxin) have given inconsistent results, with
    levodopa ineffective in one individual and partially effective in another.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: deep brain stimulation
    term:
      id: NCIT:C21024
      label: Deep Brain Stimulation
  target_phenotypes:
  - preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:34415117
    reference_title: "Childhood-onset progressive dystonia associated with pathogenic truncating variants in CHD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Deep brain stimulation led to clinical improvement in both cases.
    explanation: >-
      Both reported individuals with CHD8-related progressive dystonia improved with
      deep brain stimulation.
- name: Genetic Counseling
  description: >-
    Autosomal dominant counselling: each child of an affected individual has a 50%
    chance of inheriting the variant. Because most probands have a de novo variant,
    parental testing informs recurrence-risk estimates - and, as transmitted
    variants with very mild parental expression are documented, apparently
    unaffected parents should still be tested before recurrence risk is quoted as
    low. Once the familial variant is known, prenatal and preimplantation genetic
    testing are possible.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each child of an individual with CHD8-NDD has a 50% chance of inheriting the CHD8 pathogenic variant. Once the CHD8 pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible.
    explanation: GeneReviews genetic counselling guidance.
animal_models:
- species: Mus musculus
  genotype: Chd8+/- (heterozygous loss-of-function)
  category: GENETIC
  description: >-
    Constitutive Chd8 heterozygous mice are the closest dosage match to the human
    disorder and recapitulate brain overgrowth, hypertelorism, motor delay, altered
    social responses, increased anxiety and repetitive behaviour, together with
    long-range functional over-connectivity on resting-state fMRI.
  evidence:
  - reference: PMID:27602517
    reference_title: "CHD8 haploinsufficiency results in autistic-like phenotypes in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here we show that mice heterozygous for Chd8 mutations manifest ASD-like behavioural characteristics including increased anxiety, repetitive behaviour, and altered social behaviour.
    explanation: Behavioural recapitulation in the mouse heterozygote.
  - reference: PMID:29668850
    reference_title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here, we report that Chd8 heterozygous mice display increased brain size, motor delay, hypertelorism, pronounced hypoactivity, and anomalous responses to social stimuli.
    explanation: Somatic and behavioural recapitulation in the mouse heterozygote.
  - reference: PMID:36738737
    reference_title: "Mouse population genetics phenocopies heterogeneity of human Chd8 haploinsufficiency."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Trait disruptions mimicked those seen clinically, with robust strain and sex differences. Some strains exhibited large effect-size trait disruptions, sometimes in opposite directions, and-remarkably-others expressed resilience.
    explanation: >-
      Crossing the Chd8 lesion across 33 mouse strains shows genetic background is a
      powerful modifier, producing opposite-direction effects and outright
      resilience. This reframes the well-known behavioural inconsistency between
      published Chd8 mouse lines as background-dependent biology rather than
      experimental noise, and is the main reason any single-strain mouse result here
      is weighted cautiously. PARTIAL because it qualifies rather than directly
      supports the model's fidelity.
- species: Danio rerio
  genotype: chd8 loss of function (morpholino suppression and stable constitutive mutant)
  category: GENETIC
  description: >-
    Zebrafish chd8 loss of function reproduces the two most distinctive arms of the
    human syndrome simultaneously - increased head size from forebrain/midbrain
    expansion, and impaired gastrointestinal motility from reduced enteric
    innervation - and further localises the GI defect to vagal neural crest
    development and intestinal epithelial homeostasis.
  evidence:
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      chd8 disruption in zebrafish recapitulates features of the human phenotype, including increased head size as a result of expansion of the forebrain/midbrain and impairment of gastrointestinal motility due to a reduction in postmitotic enteric neurons.
    explanation: Dual recapitulation of the head-size and GI arms of the phenotype.
  - reference: PMID:36375841
    reference_title: "Loss of autism-candidate CHD8 perturbs neural crest development and intestinal homeostatic balance."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Our findings propose a causal developmental link between chd8, NCC development, intestinal homeostasis, and autism-associated gastrointestinal complaints.
    explanation: Localises the GI arm to neural crest and intestinal homeostasis.
- species: Macaca fascicularis
  genotype: CRISPR/Cas9-mediated CHD8 mutation (embryo editing)
  category: GENETIC
  description: >-
    Cynomolgus monkey CHD8 mutants are the only non-human primate model and are
    uniquely informative because they resolve a question rodents could not: they
    show that macrocephaly in a primate arises through increased gliogenesis rather
    than excess neuronal production. Limitations are small n, cost, mosaic founders
    and limited behavioural phenotyping.
  evidence:
  - reference: PMID:36878905
    reference_title: "CHD8 mutations increase gliogenesis to enlarge brain size in the nonhuman primate."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Moreover, knocking down CHD8 via CRISPR/Cas9 in organotypic monkey brain slices from newborn monkeys also enhanced the proliferation of glial cells.
    explanation: >-
      Independent slice-culture confirmation of the glial proliferation phenotype in
      primate tissue.
experimental_models:
- name: CHD8 heterozygous human cerebral organoids
  description: >-
    Isogenic CRISPR/Cas9 CHD8+/- iPSC-derived cerebral organoids model CHD8
    haploinsufficiency in a human genetic background. They show enlargement, an
    accelerated/delayed split in inhibitory versus excitatory neurogenesis, and
    cell-autonomous, patient-mutation-specific molecular defects in proliferation
    and alternative splicing.
  evidence:
  - reference: PMID:35385734
    reference_title: "CHD8 haploinsufficiency links autism to transient alterations in excitatory and inhibitory trajectories."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Through an isogenic design of patient-specific mutations and mosaic organoids, we define genotype-phenotype relationships and uncover their cell-autonomous nature.
    explanation: Describes the isogenic organoid design and its cell-autonomous readout.
  - reference: PMID:28321286
    reference_title: "CRISPR/Cas9-mediated heterozygous knockout of the autism gene CHD8 and characterization of its transcriptional networks in cerebral organoids derived from iPS cells."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      CRISPR/Cas9-mediated heterozygous knockout of the autism gene CHD8 and characterization of its transcriptional networks in cerebral organoids derived from iPS cells.
    explanation: Establishes the heterozygous CHD8 organoid model system.
differential_diagnoses:
- name: Autism Spectrum Disorder (multifactorial)
  disease_term:
    preferred_term: autism spectrum disorder
    term:
      id: MONDO:0005258
      label: autism spectrum disorder
  description: >-
    The single most important boundary for this entry. Broad, multifactorial autism
    spectrum disorder lists CHD8 among many risk genes recovered by large-scale
    exome sequencing, and dismech curates it as a separate, polygenic entity. This
    entry is NOT that entity: here CHD8 haploinsufficiency is the sufficient
    monogenic cause of a syndromic, highly penetrant phenotype with overgrowth,
    macrocephaly, dysmorphism, sleep and gastrointestinal involvement.
  distinguishing_features:
  - >-
      Presence of a heterozygous pathogenic CHD8 variant; macrocephaly and tall
      stature; recognisable facies; prominent sleep and gastrointestinal involvement;
      autosomal dominant transmission with 50% recurrence risk to offspring. Broad ASD
      has no single sufficient genetic cause and no consistent overgrowth phenotype.
  evidence:
  - reference: PMID:24998929
    reference_title: "Disruptive CHD8 mutations define a subtype of autism early in development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings indicate that CHD8 disruptions define a distinct ASD subtype and reveal unexpected comorbidities between brain development and enteric innervation.
    explanation: >-
      Explicitly frames CHD8 disruption as defining a distinct subtype separable
      from autism at large.
- name: CHARGE Syndrome (CHD7)
  disease_term:
    preferred_term: CHARGE syndrome
    term:
      id: MONDO:0008965
      label: CHARGE syndrome
  description: >-
    Caused by the CHD paralogue CHD7, not CHD8. Cited here as an explicit
    named-entity-confusion guard: CHD7 and CHD8 are adjacent in the CHD family and
    are readily transposed in literature searches, but the diseases are distinct.
  distinguishing_features:
  - >-
      CHARGE syndrome is characterised by coloboma, choanal atresia, cranial nerve
      dysfunction, characteristic external and inner ear anomalies with semicircular
      canal hypoplasia, and heart defects; growth retardation rather than overgrowth
      is typical. CHD8-NDD has none of these as core features.
- name: CHD2-Related Developmental and Epileptic Encephalopathy
  disease_term:
    preferred_term: CHD2-related developmental and epileptic encephalopathy
    term:
      id: MONDO:0014150
      label: developmental and epileptic encephalopathy 94
  description: >-
    Caused by the CHD paralogue CHD2. A second explicit NEC guard: CHD2 is an
    epilepsy gene, and seizures also occur in a minority of CHD8-NDD, so the
    combination of a "CHD" gene plus seizures is a known route to
    misattribution.
  distinguishing_features:
  - >-
      CHD2-related disease is dominated by early-onset, often photosensitive
      myoclonic epilepsy and epileptic encephalopathy with developmental regression.
      In CHD8-NDD seizures occur in only 10%-15%, are not the defining feature, and
      overgrowth/macrocephaly dominates the presentation.
  evidence:
  - reference: PMID:36302072
    reference_title: "CHD8-Related Neurodevelopmental Disorder with Overgrowth."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Less common features are hypotonia (about 30% of affected individuals), seizures (10%-15%), dystonia (rare), and Chiari I malformation (rare).
    explanation: >-
      Quantifies seizures as a minority feature in CHD8-NDD, distinguishing it from
      a primary epilepsy gene.
- name: Sifrim-Hitz-Weiss Syndrome (CHD4)
  disease_term:
    preferred_term: Sifrim-Hitz-Weiss syndrome
    term:
      id: MONDO:0014946
      label: Sifrim-Hitz-Weiss syndrome
  description: >-
    Caused by the CHD paralogue CHD4. A third NEC guard within the CHD family;
    CHD4-related disease also involves developmental delay and macrocephaly, making
    it the closest phenotypic neighbour among the paralogues.
  distinguishing_features:
  - >-
      CHD4-related Sifrim-Hitz-Weiss syndrome is typically caused by missense
      (largely gain-of-function-like) variants and features hearing loss, congenital
      heart defects, skeletal and genital anomalies, and ventriculomegaly. CHD8-NDD
      is a loss-of-function/haploinsufficiency disorder without that visceral
      malformation profile.
- name: 14q11.2 Microdeletion Syndrome
  description: >-
    A contiguous-gene deletion encompassing CHD8 and neighbouring genes. Deletion
    cases share the CHD8-NDD core phenotype, and the minimal critical region has
    been narrowed to SUPT16H and CHD8, but a deletion is not a pure CHD8 lesion.
  distinguishing_features:
  - >-
      Detected by chromosomal microarray rather than sequencing; additional deleted
      genes (notably SUPT16H) may modify the phenotype, so deletion cases are held
      adjacent to, not inside, the intragenic-variant entity.
  evidence:
  - reference: PMID:25257502
    reference_title: "Recurrent \u223c100 Kb microdeletion in the chromosomal region 14q11.2, involving CHD8 gene, is associated with autism and macrocephaly."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The minimal critical region, considering present and previous cases, contains the SUPT16H and CHD8 genes.
    explanation: >-
      Defines the minimal critical region and shows it is not CHD8 alone.
- name: 14q11.2 Microduplication (CHD8-SUPT16H) Syndrome
  disease_term:
    preferred_term: 14q11.2 microduplication syndrome
    term:
      id: MONDO:0016835
      label: 14q11.2 microduplication syndrome
  description: >-
    The reciprocal dosage disorder. Duplication of the same 14q11.2 segment
    containing CHD8 and SUPT16H also produces a neurodevelopmental phenotype, which
    is why CHD8 is described as requiring tight dosage control in both directions.
    Duplication cases are a separate entity and must not be folded into this entry.
  distinguishing_features:
  - >-
    Detected as a copy-number GAIN on chromosomal microarray rather than a
    loss-of-function sequence variant; neurodevelopmental severity is variable and
    at least one reported individual had normal intelligence; the duplication also
    spans SUPT16H so single-gene CHD8 triplosensitivity is not established.
  evidence:
  - reference: PMID:31823155
    reference_title: "Neurodevelopmental phenotype associated with CHD8-SUPT16H duplication."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recently, a 14q11.2 microduplication syndrome, encompassing CHD8 and SUPT16H, has been described, highlighting the importance of a tight control of at least CHD8 gene-dosage for a normal development.
    explanation: >-
      Establishes the duplication entity and the bidirectional dosage sensitivity.
  - reference: PMID:31823155
    reference_title: "Neurodevelopmental phenotype associated with CHD8-SUPT16H duplication."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report on two patients with 14q11.2 microduplication encompassing CHD8 and SUPT16H, one of whom had normal intelligence.
    explanation: >-
      Documents the milder end of the duplication phenotype, distinguishing it from
      the deletion/loss-of-function disorder.
- name: PTEN Hamartoma Tumor Syndrome
  disease_term:
    preferred_term: PTEN hamartoma tumor syndrome
    term:
      id: MONDO:0017623
      label: PTEN hamartoma tumor syndrome
  description: >-
    The most important not-to-miss alternative in the macrocephaly-plus-autism
    presentation, because unlike CHD8-NDD it carries a defined cancer risk that
    changes surveillance.
  distinguishing_features:
  - >-
    In PTEN hamartoma tumor syndrome the macrocephaly is disproportionate to height,
    whereas CHD8-NDD overgrowth is generalised (height and head circumference
    together). Hamartomas and a defined malignancy risk are features of PTEN
    disease and are not established in CHD8-NDD, where tumour surveillance is
    explicitly not recommended.
- name: Other Overgrowth-with-Intellectual-Disability Syndromes
  description: >-
    Sotos syndrome (NSD1), Weaver syndrome (EZH2), Tatton-Brown-Rahman syndrome
    (DNMT3A), Malan syndrome (NFIX) and Beckwith-Wiedemann syndrome share the
    overgrowth-plus-developmental-impairment presentation and are the differential
    within which CHD8-NDD was originally delineated.
  distinguishing_features:
  - >-
    Most of these conditions - including CHD8-NDD itself - have distinct DNA
    methylation episignatures, so a single episignature array can discriminate much
    of this differential simultaneously. Beckwith-Wiedemann syndrome is further
    distinguished by asymmetric/lateralised overgrowth and embryonal tumour risk.
  evidence:
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CHD8 is one of the causative genes for OGID (overgrowth and ID)
    explanation: >-
      Places CHD8 explicitly within the overgrowth-and-intellectual-disability
      disease group that constitutes this differential.
discussions:
- discussion_id: chd8_nec_boundary_vs_multifactorial_asd
  kind: INTERPRETATION
  prompt: >-
    Where exactly is the boundary between this monogenic CHD8 entity and the broad
    multifactorial autism spectrum disorder entry that also lists CHD8 as a risk
    gene?
  rationale: >-
    kb/disorders/Autism_Spectrum_Disorder.yaml lists CHD8 among many autism risk
    genes. That entry models the polygenic/multifactorial disease. This entry models
    the syndromic, autosomal dominant, highly penetrant disorder in which a single
    heterozygous CHD8 loss-of-function variant is sufficient. The two must not be
    merged, and evidence should not be moved between them: large-scale autism exome
    cohorts (e.g. PMID:22495309) belong in both as gene-discovery evidence, but
    CHD8-ascertained phenotype frequencies (macrocephaly, overgrowth, GI, sleep)
    belong only here. Practical rule applied during curation: any claim sourced from
    a cohort that was NOT ascertained on CHD8 genotype is admissible here only for
    gene-level statements.
- discussion_id: chd8_brain_overgrowth_causality_for_behaviour
  kind: KNOWLEDGE_GAP
  prompt: >-
    Is brain overgrowth causally upstream of the autistic and cognitive phenotype in
    CHD8-NDD, or are the two parallel consequences of the same progenitor lesion?
  attaches_to:
  - pathophysiology#Brain Overgrowth and Megalencephaly
  rationale: >-
    Macrocephaly and autism co-segregate tightly in CHD8-NDD, and both are
    downstream of altered progenitor proliferation, but no experiment separates
    them. The edge from Brain Overgrowth and Megalencephaly to the behavioural
    outcome is therefore modelled as INDIRECT_UNKNOWN_INTERMEDIATES rather than as
    a supported direct cause.
  proposed_experiments:
  - experiment_id: chd8_exp_brain_size_vs_behaviour_rescue
    name: Temporally restricted CHD8 restoration in a Chd8+/- mouse that normalises brain size after the neurogenic window, testing whether behaviour is rescued independently of size.
  - experiment_id: chd8_exp_imaging_genetics_ohc_vs_severity
    name: Human imaging-genetics comparison of CHD8 variant carriers stratified by head circumference against behavioural severity.
- discussion_id: chd8_gut_brain_axis_human_translation
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Does the gut-to-brain contribution to behaviour demonstrated in Chd8
    haploinsufficient mice operate in humans with CHD8-NDD?
  attaches_to:
  - pathophysiology#Gastrointestinal Dysmotility and Barrier Dysfunction
  rationale: >-
    In mice, gut-epithelial-restricted Chd8 haploinsufficiency alters anxiety-related
    behaviour and antibiotic treatment attenuates social deficits, implying a
    microbiota-dependent gut-to-brain arm. Nothing equivalent has been shown in
    humans, and the human GI phenotype is documented clinically (constipation)
    without any demonstrated behavioural consequence. Evidence exists in the model
    but its translational validity is the open question, so this is a
    HUMAN_MODEL_MISMATCH rather than a plain knowledge gap.
  proposed_experiments:
  - experiment_id: chd8_exp_human_gut_brain_cohort
    name: Prospective characterisation of GI symptom burden, intestinal permeability and microbiome composition in a CHD8-NDD cohort with paired behavioural measures.
- discussion_id: chd8_dystonia_female_preponderance
  kind: KNOWLEDGE_GAP
  prompt: >-
    Why do the reported CHD8-related dystonia cases show an apparent female
    preponderance, and how frequent is dystonia in unselected CHD8-NDD cohorts?
  rationale: >-
    Every reported CHD8-related young-onset dystonia case to date has been female,
    and these individuals had minimal or absent cognitive and autistic features -
    the opposite of the classical presentation. Because the observation comes from
    small case series with obvious ascertainment bias, both the sex skew and the
    true frequency of dystonia remain unresolved; the frequency band here is taken
    from the GeneReviews "rare" descriptor, not from these series.
  evidence:
  - reference: PMID:38441608
    reference_title: "CHD8-related disorders redefined: an expanding spectrum of dystonic phenotypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This work validates our previous observation that dystonia is part of the phenotypic spectrum of CHD8-related
    explanation: Source of the dystonia observation and the female-preponderance suggestion.
- discussion_id: chd8_megalencephaly_rodent_vs_primate_mechanism
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Is CHD8-related brain overgrowth in humans driven mainly by excess glial
    production, as the non-human primate data indicate, or by excess neural
    progenitor/neuronal output, as the rodent models are usually read to show?
  attaches_to:
  - pathophysiology#Increased Gliogenesis and White Matter Expansion
  - pathophysiology#Brain Overgrowth and Megalencephaly
  rationale: >-
    Rodent models produced inconsistent accounts of the macrocephaly mechanism, and
    mouse cortex is enlarged without a proportionate increase in neuron number. In
    cynomolgus monkey, CHD8 disruption before the gliogenic switch increases glial
    number and enlarges the brain. Because primate brains have a far larger glial
    complement and a much more protracted gliogenic period than rodent brains, this
    is plausibly a real species difference rather than a technical discrepancy - so
    the question is not whether the mouse result is reproducible but whether it
    translates. That is a translational-validity question about existing model
    evidence, which is why this is a HUMAN_MODEL_MISMATCH rather than a plain
    knowledge gap. Practical consequence: the entry keeps both the
    progenitor-proliferation route and the gliogenesis route as parallel edges
    into brain
    overgrowth rather than committing to one.
  proposed_experiments:
  - experiment_id: chd8_exp_human_postmortem_glia_neuron_ratio
    name: Cell-type-resolved quantification (single-nucleus RNA-seq or stereology) of glial versus neuronal number in post-mortem cortex from CHD8 variant carriers versus matched controls.
  - experiment_id: chd8_exp_human_white_matter_imaging
    name: Systematic volumetric and white-matter MRI characterisation of a CHD8-NDD cohort, testing whether white-matter expansion accounts for the increased head circumference as it does in the monkey.
  evidence:
  - reference: PMID:36878905
    reference_title: "CHD8 mutations increase gliogenesis to enlarge brain size in the nonhuman primate."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      However, studies of small animal models showed inconsistent findings about the mechanisms for CHD8 deficiency-mediated autism symptoms and macrocephaly.
    explanation: >-
      States the rodent inconsistency that the primate work was designed to resolve.
- discussion_id: chd8_frequency_ascertainment_discrepancy
  kind: INTERPRETATION
  prompt: >-
    Which phenotype frequencies should this entry assert, given that CHD8 cohorts
    were ascertained in systematically different ways and report materially
    different numbers for the same features?
  rationale: >-
    The published cohorts disagree in a patterned, non-random way. Cohorts recruited
    through overgrowth clinics report near-universal overgrowth and intellectual
    disability; cohorts recruited through autism cohorts report high autism rates;
    the largest series is a literature aggregation across both and regresses toward
    lower values. Concretely: macrocephaly is 62.5% in the truncating-variant series
    and about 80% in GeneReviews; sleep disturbance is 50% versus 29%; hypotonia is
    27%-29% across two cohorts versus "about 30%" in GeneReviews. The convention
    applied in this entry is to band on the figure defensible across sources rather
    than the highest available one, to cite the quantitative statement itself as
    evidence for each band per the project's frequency-evidence guidelines, and to
    record the disagreeing figure alongside it rather than suppress it. Where the
    sources cannot be reconciled into a band at all, `frequency:` is omitted.
  evidence:
  - reference: PMID:31001818
    reference_title: "The clinical presentation caused by truncating CHD8 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a pattern of common features: macrocephaly (62.5%), tall stature (47%), developmental delay and/or intellectual disability (81%), ASDs (84%), sleep difficulties (50%), gastrointestinal problems (40%), and distinct facial features
    explanation: >-
      The protein-truncating-variant cohort figures used as the primary quantitative
      anchor for several bands in this entry.
- discussion_id: chd8_neoplasia_not_established
  kind: KNOWLEDGE_GAP
  prompt: >-
    Does CHD8-NDD carry an increased tumour risk, and should tumour surveillance be
    recommended?
  rationale: >-
    Two separate literatures could be mistaken for one. Somatic CHD8 alterations
    occur in sporadic microsatellite-instability-high gastric and colorectal
    cancers, and a retrospective aggregation of CHD8-NDD individuals recorded
    neoplasia in a minority. Neither establishes a germline tumour predisposition:
    the tumour types, comparison to population baseline, and causality are not
    established, and the GeneReviews management section - which would be expected to
    flag a tumour risk - does not recommend tumour surveillance. This entry
    therefore asserts no tumour phenotype and no surveillance recommendation. The
    point matters clinically because two conditions in this entry's differential
    (PTEN hamartoma tumor syndrome and Beckwith-Wiedemann syndrome) do carry defined
    tumour risk, so conflating them with CHD8-NDD in either direction would be
    harmful.
  proposed_experiments:
  - experiment_id: chd8_exp_cancer_incidence_registry_linkage
    name: Registry linkage of a molecularly confirmed CHD8-NDD cohort to national cancer registries, with age- and sex-standardised incidence ratios against population baseline.
- discussion_id: chd8_genetic_background_modifier
  kind: OPEN_QUESTION
  prompt: >-
    Is the marked clinical variability of CHD8-NDD - which extends from severe
    intellectual disability with autism to an isolated adult focal dystonia in a
    cognitively intact individual - driven by genetic background rather than chance?
  rationale: >-
    Crossing a Chd8 mutation across a mouse genetic reference panel produced strain-
    and sex-dependent trait disruptions, including effects in opposite directions on
    different backgrounds and frank resilience on others. That is a designed
    experiment rather than a post-hoc observation, and it makes modifier-driven
    variability a serious hypothesis for the human disorder. No human modifier locus
    has been mapped, so no MODIFIER-typed gene record is asserted in the `genetic:`
    section. The practical implication for counselling is that intrafamilial
    variability should be expected, as the documented paternal-transmission case
    shows.
  proposed_experiments:
  - experiment_id: chd8_exp_human_polygenic_modifier_analysis
    name: Polygenic background and rare-variant modifier analysis within a molecularly confirmed CHD8-NDD cohort phenotyped on a common severity instrument.
  evidence:
  - reference: PMID:36738737
    reference_title: "Mouse population genetics phenocopies heterogeneity of human Chd8 haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Some strains exhibited large effect-size trait disruptions, sometimes in opposite directions, and-remarkably-others expressed resilience.
    explanation: >-
      Demonstrates background-dependent modification of the same Chd8 lesion,
      including resilience.
clinical_trials:
- name: NCT01238250
  status: RECRUITING
  description: >-
    Simons Searchlight - an observational, online, international registry for
    families with rare genetic variants causing neurodevelopmental disorders,
    including CHD8. It is the principal longitudinal natural-history data source for
    this disorder. There is no interventional trial for CHD8-NDD.
  target_phenotypes:
  - preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: clinicaltrials:NCT01238250
    reference_title: "Online Study of People Who Have Genetic Changes and Features of Autism: Simons Searchlight"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Simons Searchlight is an observational, online, international research program for families with rare genetic variants that cause neurodevelopmental disorders and may be associated with autism.
    explanation: >-
      Describes the registry that provides longitudinal natural-history data for
      CHD8 variant carriers.
references:
- reference: PMID:36302072
  title: CHD8-Related Neurodevelopmental Disorder with Overgrowth.
  tags:
  - GeneReviews
- reference: PMID:24998929
  title: Disruptive CHD8 mutations define a subtype of autism early in development.
- reference: PMID:30670789
  title: A distinct neurodevelopmental syndrome with intellectual disability, autism spectrum disorder, characteristic facies, and macrocephaly is caused by defects in CHD8.
- reference: PMID:31980904
  title: De novo variants in the Helicase-C domain of CHD8 are associated with severe phenotypes including autism, language disability and overgrowth.
- reference: PMID:38441608
  title: "CHD8-related disorders redefined: an expanding spectrum of dystonic phenotypes."
- reference: PMID:41407309
  title: Phenotypic Variability and Paternal Inheritance of a CHD8 Variant Causing Intellectual Developmental Disorder With Autism and Macrocephaly Confirmed by Epigenetic and Structural Analyses.
- reference: PMID:25257502
  title: Recurrent ~100 Kb microdeletion in the chromosomal region 14q11.2, involving CHD8 gene, is associated with autism and macrocephaly.
- reference: PMID:22495309
  title: Sporadic autism exomes reveal a highly interconnected protein network of de novo mutations.
- reference: PMID:25294932
  title: CHD8 regulates neurodevelopmental pathways associated with autism spectrum disorder in neural progenitors.
- reference: PMID:25752243
  title: The autism-associated chromatin modifier CHD8 regulates other autism risk genes during human neurodevelopment.
- reference: PMID:27602517
  title: CHD8 haploinsufficiency results in autistic-like phenotypes in mice.
- reference: PMID:27694995
  title: Chd8 mediates cortical neurogenesis via transcriptional regulation of cell cycle and Wnt signaling.
- reference: PMID:29668850
  title: "Altered Neocortical Gene Expression, Brain Overgrowth and Functional Over-Connectivity in Chd8 Haploinsufficient Mice."
- reference: PMID:33627187
  title: "Distinct, dosage-sensitive requirements for the autism-associated factor CHD8 during cortical development."
- reference: PMID:35385734
  title: CHD8 haploinsufficiency links autism to transient alterations in excitatory and inhibitory trajectories.
- reference: PMID:28321286
  title: CRISPR/Cas9-mediated heterozygous knockout of the autism gene CHD8 and characterization of its transcriptional networks in cerebral organoids derived from iPS cells.
- reference: PMID:37783686
  title: CHD8 regulates gut epithelial cell function and affects autism-related behaviors through the gut-brain axis.
- reference: PMID:36375841
  title: Loss of autism-candidate CHD8 perturbs neural crest development and intestinal homeostatic balance.
- reference: PMID:36182950
  title: The phenotypic spectrum and genotype-phenotype correlations in 106 patients with variants in major autism gene CHD8.
- reference: PMID:31721432
  title: "The CHD8 overgrowth syndrome: A detailed evaluation of an emerging overgrowth phenotype in 27 patients."
- reference: PMID:31001818
  title: The clinical presentation caused by truncating CHD8 variants.
- reference: PMID:31526516
  title: Clinical Phenotypes of Carriers of Mutations in CHD8 or Its Conserved Target Genes.
- reference: PMID:34415117
  title: Childhood-onset progressive dystonia associated with pathogenic truncating variants in CHD8.
- reference: PMID:38438524
  title: The complex etiology of autism spectrum disorder due to missense mutations of CHD8.
- reference: PMID:36878905
  title: CHD8 mutations increase gliogenesis to enlarge brain size in the nonhuman primate.
- reference: PMID:36738737
  title: Mouse population genetics phenocopies heterogeneity of human Chd8 haploinsufficiency.
- reference: PMID:34088660
  title: "The CHD8/CHD7/Kismet family links blood-brain barrier glia and serotonin to ASD-associated sleep defects."
- reference: PMID:28402856
  title: Chd8 Mutation Leads to Autistic-like Behaviors and Impaired Striatal Circuits.
- reference: PMID:31823155
  title: Neurodevelopmental phenotype associated with CHD8-SUPT16H duplication.
- reference: PMID:33175317
  title: "Brief Report: Associations Between Self-injurious Behaviors and Abdominal Pain Among Individuals with ASD-Associated Disruptive Mutations."
- reference: PMID:38622540
  title: "Shared and divergent mental health characteristics of ADNP-, CHD8- and DYRK1A-related neurodevelopmental conditions."
- reference: clinicaltrials:NCT01238250
  title: "Online Study of People Who Have Genetic Changes and Features of Autism: Simons Searchlight"
notes: >-
  Provenance. Deep research was run with the `claude_code` provider
  (`just research-disorder claude_code CHD8-Related_Neurodevelopmental_Disorder_with_Overgrowth`;
  report at research/CHD8-Related_Neurodevelopmental_Disorder_with_Overgrowth-deep-research-claude_code.md,
  1,602 lines, 29 web searches, 78 turns). The report itself warns that its quoted
  snippets are model-summarised rather than verbatim; accordingly EVERY PMID cited
  in this entry was independently fetched with `just fetch-reference` and every
  snippet was copy-pasted from the cached abstract and verified by
  `just validate-references`. Several claims present in the research report were
  dropped because the cached abstract did not contain a quotable sentence for them
  (see items 1 and 2 below).

  NEC boundary. The mandatory preflight was re-run before any content was written:
  `uv run runoak -i sqlite:obo:mondo info MONDO:0014017 -O obo` returns
  `relationship: RO:0004003 HGNC:20153 ! CHD8` and `xref: OMIM:615032`, matching the
  target exactly. Every citation in this entry was checked to be about CHD8 and not
  a CHD paralogue; CHD7 (CHARGE), CHD2 (developmental and epileptic encephalopathy)
  and CHD4 (Sifrim-Hitz-Weiss) are recorded as explicit differential diagnoses for
  that reason. The one genuine cross-gene citation, PMID:34088660, studies
  Drosophila `kismet`, which is the SOLE ortholog of both CHD8 and CHD7 - this is
  stated in the node description rather than glossed over, and the node is marked
  MODEL_ORGANISM. PMID:33175317 is a multi-gene autism-risk-gene cohort, not a CHD8
  cohort, and is marked PARTIAL for that reason.

  Deliberate omissions and honest gaps.

  (1) No `prevalence` record is asserted. No population-based prevalence estimate for
  CHD8-NDD exists. The figures in circulation (about 0.2%-0.4% of autism cohorts,
  about 2% of macrocephalic autism probands, 1.7% of
  overgrowth-plus-intellectual-disability) are diagnostic YIELDS within
  ascertained cohorts, not population
  occurrence, and the structured Prevalence class would misrepresent them. Those
  yields also appear only in the GeneReviews chapter body, not in the cached
  structured abstract, so no verified snippet is available for them either.
  Orphanet has a record for this entity (Orphanet:642675, "CHD8 overgrowth
  syndrome") but it is absent from this repository's ORPHA reference cache, so no
  ORPHA-sourced epidemiology row could be quoted.

  (2) CORRECTED at review (PR #7603). This note previously claimed that figures
  appearing only in a paper's body text were unquotable because the cache holds only
  the abstract. That is wrong for PMID:36182950: its cache is a full-text capture and
  the reference validator matches against the whole cached body, not just the
  abstract. The Dingemans body-text figures are therefore now cited directly -
  macrocephaly at examination 52% (46/88), tall stature 50% (39/78), and overweight
  34% (24/71), the last of which is curated as its own Growth phenotype
  (`HP:0025502`, FREQUENT: 24/71 = 33.8%). The correction does NOT extend to
  GeneReviews: the PMID:36302072 cache is a 92-line structured summary, not the full
  chapter, so the Table 2 percentage grid is genuinely absent from it and remains
  uncited. The distinction is per-reference - each cache must be checked for what it
  actually contains rather than assumed to be abstract-only. Frequency bands
  that still rest on cross-cohort judgement rather than a single figure are explained
  in the `chd8_frequency_ascertainment_discrepancy` discussion.

  (3) Frequency bands were set on the figure defensible across cohorts rather than
  the highest available. Macrocephaly and autism spectrum disorder are banded
  FREQUENT, not VERY_FREQUENT, because the quantified series bracket rather than
  clear the 80% threshold. Hypotonia is banded OCCASIONAL because two independent
  cohorts report 27% and 29% against the GeneReviews "about 30%". Several
  phenotypes carry no band at all - diarrhoea, anxiety, ADHD, self-injurious
  behaviour and every craniofacial feature - because the sources describe them
  qualitatively only.

  (4) The distinctive facial gestalt is curated as individual HPO-bound features
  rather than one "characteristic facies" phenotype, because that is what the
  primary series enumerate. Reported forehead- and dental-abnormality rates near
  90% are not curated: their denominators (18 and 11) reflect assessment only when
  a dysmorphologist examined the patient, which makes them uninterpretable as
  population frequencies.

  (5) No tumour phenotype and no tumour surveillance are asserted, despite an 11%
  neoplasia figure in one retrospective aggregation and a separate somatic
  CHD8-in-cancer literature. See the `chd8_neoplasia_not_established` discussion for
  the full reasoning; this is a deliberate refusal, not an oversight.

  (6) The mechanism graph is single-rooted at CHD8 Haploinsufficiency, with all 15
  nodes reachable from it over 20 causal edges. Terminal edges into the behavioural
  outcome are typed INDIRECT_UNKNOWN_INTERMEDIATES because the causal step from
  brain overgrowth, altered connectivity, striatal dysfunction or disrupted sleep to
  the behavioural phenotype is not experimentally established in humans.

  (7) Much of the mechanistic evidence is MODEL_ORGANISM (mouse, zebrafish,
  cynomolgus monkey, Drosophila) or IN_VITRO (human neural progenitors, cerebral
  organoids); this is flagged per evidence item. Human-clinical evidence is used for
  every phenotype claim. Model evidence supports mechanism nodes and corroborates
  phenotypes but never stands alone for a human phenotype. Model fidelity is itself
  qualified: PMID:36738737 shows the same Chd8 lesion produces opposite-direction
  effects and even resilience on different mouse backgrounds, which is why no single
  mouse result is treated as decisive here.

  (8) Two named agents in the dystonia literature (tizanidine, botulinum toxin) and
  the levodopa trials are described in the deep-research report from the papers'
  case tables, not their abstracts, so no `therapeutic_agent` bindings are asserted
  for them; the dystonia treatment entry cites only the deep brain stimulation
  outcome, which IS in the abstract. Similarly, no melatonin, methylphenidate or
  antipsychotic agent is curated, because no CHD8-specific source names them - the
  sleep and behavioural treatments are kept at the level GeneReviews actually
  states.

  (9) No `conforms_to` module reference is declared. No existing kb/modules/ module
  captures the chromatin-remodeller-dosage-to-neurodevelopment pattern; a future
  "chromatinopathy" module would be the natural home and would also serve SETD5,
  the other CHD paralogue disorders, and the KMT2 disorders.

  (10) A `biochemical` record for the DNA-methylation episignature was considered
  and not created: the episignature is a diagnostic classifier rather than an
  analyte with a reference interval, so it is curated under `diagnosis` instead.

  (11) `clinical_course: PROGRESSIVE` on anxiety was considered at review and NOT
  asserted. PMID:38622540 is now cited for the age-anxiety association, but that
  association is estimated across the pooled three-gene sample (N=65; CHD8 n=18),
  reported hedged as "may worsen with increasing age", and derived from a
  cross-sectional design. GeneReviews names anxiety only as a surveillance target
  and says nothing about its trajectory. The finding is therefore carried in the
  phenotype description and in a PARTIAL evidence row rather than as a structured
  course qualifier.

  (12) A `CGDS:HGNC_20153` ClinGen dosage evidence row was attempted at review and
  could not be produced: `just clingen-dosage-refresh` fails with a checksum
  mismatch against the pinned snapshot in data/clingen-dosage/MANIFEST.yaml, and
  re-pinning that repository-wide snapshot is out of scope for a single disorder
  entry. The haploinsufficiency mechanism remains supported by the primary
  literature already cited.

📚