Usmani-Riazuddin Syndrome, Autosomal Dominant

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Inheritance

1

Autosomal dominant (de novo) HP:0000006

Heterozygous de novo AP1G1 variants. All dominant probands reported so far arose de novo; no transmitted dominant pedigree has been described in the published series.

Autosomal dominant inheritance

Show evidence (2 references)

PMID:34102099 SUPPORT Human Clinical

"We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations."

The original cohort establishes de novo heterozygous AP1G1 variants as one of the two inheritance modes for this disorder.

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, Usmani et al. identified and studied nine patients with de novo dominant missense, splice site, and frameshift variants and two patients with biallelic, recessive, and missense variants."

Restates the composition of the original cohort: nine dominant de novo probands against two recessive biallelic probands.

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Discussions and Knowledge Gaps

2

Are the autosomal dominant and autosomal recessive AP1G1 disorders one disease with two inheritance modes, or two diseases that share a gene?

OPEN QUESTION OPEN ad_ar_one_entity

Attached to

disease#Usmani-Riazuddin Syndrome, Autosomal Dominant genetic#AP1G1

They were delineated in one cohort, are described in the follow-up literature as showing overlapping clinical features, and both converge on one protein complex - which argues for a single entry. Against that: the functional evidence separates the allele classes, since the recessive missense proteins assemble normally into AP-1 and perturb endosomal recycling while the dominant missense proteins interfere with the wild-type subunit, and the dominant class also includes whole-gene deletions that can only act through dosage. No study has compared the two groups' phenotypes systematically; the only comparison in print is the qualitative statement that they overlap. They are curated as separate entries for a structural reason rather than a biological one: MONDO:0859174 and MONDO:0859196 are siblings under MONDO:0003847 with no umbrella term, so neither can be the other's parent, and a single entry would need either a new umbrella MONDO term or a `mappings.mondo_mappings` anchor plus a real curation pass over the recessive form. Resolving this question means doing that work or publishing the phenotype comparison, not re-reading the papers already cited here.

Show evidence (2 references)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"Its dominant and recessive forms have been reported in a cohort of patients showing overlapping clinical features."

The published statement that the two inheritance forms overlap clinically, which is the argument for eventually merging them into one entry.

PMID:34102099 SUPPORT In Vitro

"Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway."

The functional difference between the two allele classes, which is the argument against lumping.

Do the dominant AP1G1 missense alleles act by dominant-negative interference with wild-type gamma-1 adaptin, or by a toxic gain of function?

KNOWLEDGE GAP OPEN dominant_negative_vs_toxic_gof

Attached to

pathophysiology#Dominant-Negative Gamma-1 Adaptin Missense Protein

The evidence for a dominant effect is strong - co-injection of wild-type transcript does not rescue, and mutant transcript is damaging in a wild-type background - but both published groups state the two interpretations without separating them. The distinction matters therapeutically: a dominant-negative allele is a target for allele-selective knockdown, whereas haploinsufficiency from the same gene would call for dosage restoration, and the dominant allele classes in this disorder include both.

Show evidence (1 reference)

PMID:41226632 SUPPORT In Vitro

"The observed phenotype is likely due to a dominant-negative effect or a toxic gain-of-function of the mutant AP1G1, impairing the activity or recruitment of the wild-type protein."

The authors state both interpretations as open, which is the gap this discussion records.

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Pathophysiology

8

AP1G1 Haploinsufficiency

Heterozygous de novo AP1G1 alleles that abolish production of a full-length gamma-1 adaptin from one allele - frameshift, splice-acceptor and whole-gene deletion alleles - leave a single functional copy. The whole-gene deletion case is the cleanest demonstration that halving AP1G1 dosage alone is sufficient to produce the syndrome, since no mutant protein is made.

AP1G1 hgnc:555

Genetic context AP1G1 hgnc:555 variant_origin: DE_NOVO zygosity: HETEROZYGOUS functional_impact_category: LOSS_OF_FUNCTION

Applies to the truncating, splice-site and whole-gene-deletion dominant alleles. The dominant missense alleles are modelled separately.

Animal models

ap1g1 knockout zebrafish Zebrafish (Danio rerio) recapitulates The heterozygous fish is a direct model of one-allele loss of ap1g1 and shows that this dosage alone produces a phenotype.

Ap1g1 (gamma-adaptin) knockout mouse Mouse (Mus musculus) partially recapitulates Quantifies what losing one gamma-1 adaptin allele does to the complex itself: AP-1 falls to half of control levels.

Downstream

AP-1 Adaptor Complex Dysfunction A single functional AP1G1 allele reduces the amount of gamma-1 adaptin available to assemble into AP-1 heterotetramers.

Show evidence (2 references)

PMID:38840441 SUPPORT Human Clinical

"This is the first reported case with whole‐gene deletion and presents with a mild but consistent phenotype."

A whole-gene deletion makes no mutant protein, so this allele can only act by halving gene dosage; it is the cleanest human evidence for haploinsufficiency in this disorder.

PMID:38840441 SUPPORT Human Clinical

"In all three cases, WGS identified CNVs and confirmed zygosity and pathogenicity, resulting in genetic diagnoses of PRKN-related Parkinson disease, TAOK1-related neurodevelopmental disorder, and AP1G1-related Usmani-Riazuddin syndrome."

Confirms that the deletion case was diagnosed as Usmani-Riazuddin syndrome, tying the dosage lesion to this disorder.

Dominant-Negative Gamma-1 Adaptin Missense Protein

Mechanism confidence: Provisional

Heterozygous de novo AP1G1 missense alleles produce a full-length but misfolded gamma-1 adaptin. Rather than simply being absent, the mutant protein interferes with the wild-type protein: co-injecting wild-type and mutant human AP1G1 mRNA fails to rescue the zebrafish null, and injecting mutant mRNA into wild-type embryos is itself damaging. This is a different lesion from haploinsufficiency even though both act through the same complex.

AP1G1 hgnc:555

Genetic context AP1G1 hgnc:555 variant_origin: DE_NOVO zygosity: HETEROZYGOUS functional_impact_category: DOMINANT_NEGATIVE

Applies to the dominant missense alleles. The published functional argument for a dominant-negative rather than a purely hypomorphic effect rests on failure of co-injection rescue and on toxicity of mutant mRNA in a wild-type background; both authors describe the alternative of a toxic gain-of-function as not yet excluded.

Animal models

Human AP1G1 mRNA rescue and overexpression zebrafish assay Zebrafish (Danio rerio) perturbs Introducing the mutant human transcript into a vertebrate embryo tests directly whether the mutant protein is harmful in the presence of wild-type protein.

Downstream

AP-1 Adaptor Complex Dysfunction The misfolded gamma-1 adaptin impairs the activity or recruitment of the wild-type subunit, so AP-1 function falls below the level expected from loss of one allele alone.

Show evidence (3 references)

PMID:34102099 SUPPORT In Vitro

"In silico analysis and 3D protein modeling simulation predicted alteration of AP1γ1 protein folding for missense variants, which was consistent with the observed altered AP1γ1 levels in heterologous cells."

3D modeling predicts misfolding of the mutant gamma-1 adaptin and heterologous cells show altered protein levels, which is the molecular state this node describes.

PMID:41226632 SUPPORT Model Organism

"The phenotype was also not rescued when ap1g1-/- zebrafish embryos were co-injected with both human wild-type and mutated mRNAs, supporting the dominant-negative effect of the new variant."

Failure of the wild-type transcript to rescue in the presence of the mutant transcript is the direct experimental basis for the dominant-negative call.

PMID:41226632 SUPPORT In Vitro

"The observed phenotype is likely due to a dominant-negative effect or a toxic gain-of-function of the mutant AP1G1, impairing the activity or recruitment of the wild-type protein."

States the interference-with-wild-type mechanism, and records that the authors have not separated dominant-negative from toxic gain-of-function - which is why this node is marked PROVISIONAL.

AP-1 Adaptor Complex Dysfunction

Gamma-1 adaptin is one of four subunits of AP-1. The complex recognizes sorting motifs in the cytoplasmic tails of transmembrane cargo and recruits clathrin, so a deficient or interfered-with gamma-1 subunit reduces AP-1-mediated cargo loading into clathrin-coated vesicles.

AP-1 adaptor complex GO:0030121

AP-1-mediated cargo loading into clathrin-coated vesicles GO:0035653 ↓ DECREASED

Animal models

Ap1g1 figure eight (fgt) hypomorphic mouse Mouse (Mus musculus) partially recapitulates Shows what reduced but non-zero gamma-1 adaptin function produces in a mammal across a whole lifespan.

Downstream

Trans-Golgi Network Cargo Sorting Failure AP-1 operates at the trans-Golgi network, so reduced complex function manifests first as disordered sorting and export from the TGN.

Endosomal Recycling Impairment AP-1 also acts on endosomes, and the recessive missense alleles perturb the endosome recycling pathway while leaving complex assembly intact.

Show evidence (3 references)

PMID:34102099 SUPPORT BACKGROUND Other

"The AP1γ1-mediated adaptor complex is essential for the formation of clathrin-coated intracellular vesicles."

States the essential role of the complex in clathrin-coated vesicle formation, which is the function lost at this node.

PMID:37108275 SUPPORT BACKGROUND Other

"Only AP1 and AP2 complexes form clathrin-coated vesicles (CCVs)."

Establishes that AP-1 is one of only two clathrin-coat-forming adaptor complexes, which is why loss of its gamma subunit is not buffered by the other AP complexes.

PMID:10026148 SUPPORT BACKGROUND Other

"The heterotetrameric adaptor protein complex 1 (AP-1) promotes the formation of clathrin-coated vesicles at the trans-Golgi network."

Locates the complex's clathrin-coat-forming activity at the trans-Golgi network, the compartment the next node describes.

Trans-Golgi Network Cargo Sorting Failure

In patient fibroblasts carrying a dominant AP1G1 missense allele the cis-Golgi marker GM130 is preserved but the trans-Golgi cisternae are diffuse and disorganized, and the authors conclude that vesicular trafficking at the trans-Golgi level is impaired. Cargo that depends on AP-1 for export from the TGN therefore reaches its destination inefficiently.

patient dermal fibroblast CL:0000057

Golgi to endosome transport GO:0006895 ↓ DECREASED vesicle-mediated transport GO:0016192 ↓ DECREASED

trans-Golgi network GO:0005802

Downstream

Impaired Somatodendritic Protein Sorting in Neurons Neurons depend on AP complexes for the polarized delivery of somatodendritic membrane proteins, so a TGN sorting failure is expressed in neurons as loss of that polarity.

Cadherin Mis-sorting and Adherens Junction Instability Cadherins are AP-1 cargo and are transported from the TGN to the plasma membrane, so failed TGN sorting reduces cadherin delivery to adherens junctions.

Show evidence (2 references)

PMID:41226632 SUPPORT In Vitro

"In c.196G>A mutant fibroblasts, although GM130 labeling remained comparable to that in the controls, the organization of the trans-Golgi cisternae appeared more diffuse and disorganized."

Direct morphological readout in patient fibroblasts showing that the trans-Golgi compartment, and not the cis-Golgi, is the one disturbed.

PMID:41226632 SUPPORT In Vitro

"In conclusion, the c.196G>A mutation in AP1G1 disrupts membrane association and impairs vesicular trafficking at the trans-Golgi level, potentially resulting in significant functional consequences."

The authors' own conclusion that trafficking at the trans-Golgi is impaired by the dominant allele.

Endosomal Recycling Impairment

Mechanism confidence: Provisional

AP-1 also functions on endosomes, and an endosome-recycling defect is the one directly measured consequence of AP1G1 missense alleles: the mutant proteins still assemble with the other AP-1 subunits but internalized cargo returns to the plasma membrane inefficiently. Scope caveat, stated plainly: that measurement was made on the BIALLELIC RECESSIVE alleles, which belong to the sibling disorder MONDO:0859196 and are not curated in this entry. Whether the dominant alleles engage the same step has not been tested. The node is kept here because it is a real, cited step in AP-1 biology downstream of the same complex, and is marked PROVISIONAL rather than attributed to the dominant alleles.

endocytic recycling GO:0032456 ↓ DECREASED

Downstream

Impaired Somatodendritic Protein Sorting in Neurons Endosomal recycling is one of the two routes by which membrane proteins reach and are maintained at polarized neuronal surfaces, so its impairment converges on the same somatodendritic sorting defect.

Show evidence (1 reference)

PMID:34102099 SUPPORT In Vitro

"Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway."

The only direct experimental statement of an endosome-recycling defect in this disorder, and it is specific to the recessive alleles.

Impaired Somatodendritic Protein Sorting in Neurons

Neurons are the tissue with the most active vesicular protein transport, and AP complexes are what give somatodendritic membrane proteins their polarized localization. Zebrafish lacking one ap1g1 allele fail to specify or differentiate neuronal populations in the telencephalon, midbrain, midbrain-hindbrain boundary and spinal cord.

neuron CL:0000540

intracellular protein transport GO:0006886 ↓ DECREASED

somatodendritic compartment GO:0036477

Downstream

Perturbed Neurodevelopment and Reduced Brain Growth Loss of polarized protein delivery in developing neurons impairs the determination and differentiation of specific neuronal populations.

Show evidence (2 references)

PMID:37108275 SUPPORT BACKGROUND Other

"The brain is the tissue with the most active vesicular protein transport."

Explains why a ubiquitously expressed trafficking complex produces a predominantly neurological disorder.

PMID:37108275 SUPPORT Model Organism

"In our knockout model, the heterozygous fish displayed abnormalities in specific brain areas and spinal cord neurons, and the brain volume is reduced."

Shows that halving ap1g1 dosage disturbs specific neuronal populations in vivo.

Cadherin Mis-sorting and Adherens Junction Instability

Cadherins carry canonical AP-1 sorting motifs and reach adherens junctions by an AP-1-dependent route from the trans-Golgi network. In ap1g1 heterozygous zebrafish, cadherin-mediated cell adhesion is dysregulated and epithelial adherens junction formation is impaired. This is the best-characterized individual cargo defect in AP1G1 deficiency.

cell-cell adhesion mediated by cadherin GO:0044331 ↓ DECREASED adherens junction organization GO:0034332 ↓ DECREASED

Animal models

ap1g1 knockout zebrafish Zebrafish (Danio rerio) recapitulates The model identifies cadherin sorting and adherens junction formation as the concrete cargo defect downstream of reduced ap1g1.

Downstream

Perturbed Neurodevelopment and Reduced Brain Growth Cadherin-dependent adhesion is required for the tissue architecture of the developing brain, so cadherin mis-sorting contributes to the neurodevelopmental phenotype alongside the neuron-intrinsic sorting defect.

Show evidence (2 references)

PMID:37108275 SUPPORT Model Organism

"An analysis of mRNA profiles of different marker proteins and altered tissue morphologies revealed dysregulated cadherin-mediated cell adhesion."

Direct result in the ap1g1 heterozygous zebrafish identifying cadherin-mediated adhesion as the dysregulated process.

PMID:37108275 SUPPORT Model Organism

"Interestingly, adult heterozygous fish showed impaired cell adhesion in epithelial tissues, such as cadherin protein sorting and adherent junction (AJ) formation."

Links the adhesion defect specifically to cadherin protein sorting and adherens junction formation.

Perturbed Neurodevelopment and Reduced Brain Growth

The convergent tissue-level consequence: specific brain regions and spinal cord neuronal populations fail to be specified or to differentiate normally, and total brain volume is reduced in the heterozygous animal model. This is the node from which the clinical neurodevelopmental phenotype follows.

brain development GO:0007420 ↓ DECREASED neuron differentiation GO:0030182 ↓ DECREASED

brain UBERON:0000955

Animal models

Human AP1G1 mRNA rescue and overexpression zebrafish assay Zebrafish (Danio rerio) partially recapitulates Mutant transcript injected into wild-type embryos produces developmental abnormalities and lethality, mirroring at organism level the developmental disruption the human dominant alleles cause.

Downstream

Global developmental delay Impaired specification and differentiation of neuronal populations during brain development is expressed clinically as delayed attainment of developmental milestones across domains.

Intellectual disability Disrupted neuronal differentiation and reduced brain growth underlie the cognitive impairment, which ranges from mild to severe.

Delayed speech and language development Speech delay is among the most consistent features and follows from the same neurodevelopmental disruption.

Aggressive behavior Aggressive behavior was present in every patient of the founding cohort and is treated here as a manifestation of the same neurodevelopmental disruption.

Seizure Epilepsy is a variable but defining feature; no AP1G1-specific excitability mechanism has been reported, so the link is asserted at the level of the neurodevelopmental lesion.

Hypotonia Hypotonia is a variable feature of the cohort and is attributed to the same central neurodevelopmental disruption rather than to a separately characterized neuromuscular lesion.

Spasticity Spasticity occurs variably and is treated as a corticospinal manifestation of the same neurodevelopmental disruption.

Hyperactivity Hyperactivity accompanies the aggression in the behavioral profile and is placed at the same neurodevelopmental node, with the same lack of a circuit-level mechanism.

Autistic behavior Autistic features occur variably and are attributed to the same disruption of neuronal specification and differentiation.

Show evidence (2 references)

PMID:37108275 SUPPORT Model Organism

"normal expression of ap1g1 at early stages of neurodevelopment is required for determination and/or differentiation of specific neuronal populations located in different brain areas and spinal cord neurons"

States the developmental requirement whose failure this node represents.

PMID:34102099 SUPPORT Model Organism

"Furthermore, microinjection of mRNAs with de novo missense variants in wild-type zebrafish resulted in severe developmental abnormalities and increased lethality."

Shows that the dominant alleles specifically produce developmental abnormalities in a vertebrate, linking the dominant lesion to this node.

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Pathograph

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

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Phenotypes

13

Ear 1

Hearing impairment HP:0000365

Show evidence (1 reference)

PMID:38665048 SUPPORT Human Clinical

"we describe this syndrome for the second time, in association to a novel AP1G1 variant identified in a toddler with multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, arrhythmias, hearing loss, skin changes, and limb defects"

Hearing loss in the second published patient, reported as part of that individual's multisystemic involvement.

Head and Neck 1

Abnormal facial shape HP:0001999

Show evidence (2 references)

PMID:38665048 SUPPORT Human Clinical

"To the best of our knowledge, this is the first description of likely distinctive facial features in a patient with Usmani-Riazuddin syndrome."

Establishes that distinctive facial features have been described, and by saying it is the first such description marks the finding as preliminary.

PMID:38665048 SUPPORT Human Clinical

"It is characterized by multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, muscular tone disorders, seizures, limb defects, and unspecified facial gestalt."

Records the facial gestalt as unspecified in the syndrome as previously delineated, which is the caveat this phenotype carries.

Limbs 1

Abnormality of limbs HP:0040064

Show evidence (2 references)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"

Records limb defects among the variably expressed features of the founding cohort.

PMID:38665048 SUPPORT Human Clinical

"It is characterized by multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, muscular tone disorders, seizures, limb defects, and unspecified facial gestalt."

Independently lists limb defects as part of the syndrome's multisystemic involvement.

Musculoskeletal 3

Hypotonia HP:0001252

Show evidence (1 reference)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"The clinical phenotype is characterized by common signs such as intellectual disability, speech delay, developmental delay, hypotonia, and behavioral problems (mainly aggressive behavior), variably associated with congenital anomalies, epilepsy, spasticity, autism, bone abnormalities, vertebral..."

Lists hypotonia among the common clinical signs of the syndrome.

Spasticity HP:0001257

Show evidence (1 reference)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"

Records spasticity among the variably expressed features of the founding cohort.

Abnormal vertebral morphology HP:0003468

Show evidence (1 reference)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"The clinical phenotype is characterized by common signs such as intellectual disability, speech delay, developmental delay, hypotonia, and behavioral problems (mainly aggressive behavior), variably associated with congenital anomalies, epilepsy, spasticity, autism, bone abnormalities, vertebral..."

Lists bone abnormalities and vertebral defects among the variably associated features of the syndrome.

Nervous System 7

Intellectual disability VERY_FREQUENT HP:0001249

Show evidence (2 references)

PMID:34102099 SUPPORT Human Clinical

"associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"

Intellectual disability, graded mild to severe, is a defining feature of the disorder across eleven families.

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"

Supports the frequency band: intellectual disability was present in 100% of the 11 patients in the founding cohort.

Global developmental delay HP:0001263

Show evidence (2 references)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"Patients carrying already reported p.Arg15Gln, p.Arg35Trp, and p.Arg35Gln variants consistently presented with global developmental delay, intellectual disability, speech delay, and behavioral anomalies, including aggression and, variably, seizures, hypotonia, and autistic traits."

Reports global developmental delay as a consistent feature in patients carrying the recurrent dominant AP1G1 missense alleles.

PMID:38840441 SUPPORT Human Clinical

"Patient 3 was referred at 5 to 10 years of age because of developmental delay, behavioural difficulties, possible infantile spasms, left hemiplegia, and toe walking."

Independent presentation of developmental delay in the whole-gene-deletion patient.

Delayed speech and language development VERY_FREQUENT HP:0000750

Show evidence (1 reference)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"

Speech delay was present in 100% of the 11 patients of the founding cohort, which is the basis for the frequency band.

Aggressive behavior VERY_FREQUENT HP:0000718

Show evidence (2 references)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"

Aggressive behavior was present in 100% of the 11 patients of the founding cohort, which is the basis for the frequency band.

PMID:41226632 SUPPORT Human Clinical

"Here we report a novel variant (c.196G>A; p.Gly66Arg) identified by exome sequencing analysis in a young girl showing overlapping clinical features with USRIS, such as motor and speech delay, intellectual disability and abnormal aggressive behavior."

Aggressive behavior in the additional dominant proband reported by this group.

Seizure HP:0001250

Show evidence (2 references)

PMID:34102099 SUPPORT Human Clinical

"associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"

Epilepsy is named in the disorder definition established by the founding cohort.

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"

Records epilepsy as variably rather than universally expressed, which is why no frequency band is asserted here.

Autistic behavior HP:0000729

Show evidence (1 reference)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"Patients carrying already reported p.Arg15Gln, p.Arg35Trp, and p.Arg35Gln variants consistently presented with global developmental delay, intellectual disability, speech delay, and behavioral anomalies, including aggression and, variably, seizures, hypotonia, and autistic traits."

Records autistic traits as a variable feature in patients with the recurrent dominant missense alleles.

Hyperactivity HP:0000752

Show evidence (1 reference)

PMID:41226632 SUPPORT Human Clinical

"Neuropsychiatric evaluation defined a mild to moderate form of intellectual disability (verbal IQ 53, performance 59, total 49), abnormal behavior including a tendency to aggression toward both peers and adults, hyperactivity, obsessive-compulsive behavior, and non-compliance."

Formal neuropsychiatric assessment of a de novo AP1G1 proband recording hyperactivity alongside aggression.

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Genetic Associations

1

AP1G1 (Heterozygous de novo missense, splice-site, frameshift and whole-gene deletion alleles)

Gene: AP1G1 hgnc:555 relationship_type: CAUSATIVE variant_origin: DE_NOVO

Autosomal dominant

Show evidence (3 references)

PMID:34102099 SUPPORT Human Clinical

"We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations."

Establishes AP1G1 as the causative gene and de novo heterozygous variants as one of its two modes.

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, Usmani et al. identified and studied nine patients with de novo dominant missense, splice site, and frameshift variants and two patients with biallelic, recessive, and missense variants."

Enumerates the dominant allele classes - missense, splice site and frameshift - curated in this row.

PMID:38665048 SUPPORT Human Clinical

"Next generation sequencing (NGS) analysis through clinical exome disclosed AP1G1: c.1969C>G (p.Leu657Val), de novo, likely pathogenic variant, according to ACMG classification criteria."

An independent de novo heterozygous AP1G1 allele in a separately ascertained patient.

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Medical Actions

4

Antiseizure Medication

Action: Anticonvulsant Therapy NCIT:C64172

Platform: Small molecule

Seizure management is symptom-directed. The published literature establishes that epilepsy occurs in this disorder but reports no AP1G1-specific drug choice or response pattern, so agent selection follows general epilepsy practice.

Target Phenotypes: Seizure HP:0001250

Show evidence (1 reference)

PMID:34102099 SUPPORT Human Clinical

"associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"

Establishes epilepsy as a treatment target in this disorder. The source names no specific antiseizure agent or response.

Developmental and Rehabilitative Therapy

Action: developmental and rehabilitative therapy Ontology label: Rehabilitation NCIT:C15315

Platform: Behavioral / lifestyle

Physical, occupational and speech-language therapy directed at developmental delay, speech delay and tone abnormalities. Supportive and individualized; no disorder-specific rehabilitation protocol has been published.

Target Phenotypes: Global developmental delay HP:0001263 Delayed speech and language development HP:0000750 Hypotonia HP:0001252

Show evidence (1 reference)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"The clinical phenotype is characterized by common signs such as intellectual disability, speech delay, developmental delay, hypotonia, and behavioral problems (mainly aggressive behavior), variably associated with congenital anomalies, epilepsy, spasticity, autism, bone abnormalities, vertebral..."

Establishes developmental delay, speech delay and hypotonia as the rehabilitation targets. The source reports no rehabilitation protocol or outcome.

Behavioral Management

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

Platform: Behavioral / lifestyle

Structured behavioral intervention for aggression, hyperactivity and autistic features, which are the most consistent non-cognitive burden of this disorder. No pharmacological or behavioral regimen has been evaluated in AP1G1 patients.

Target Phenotypes: Aggressive behavior HP:0000718 Autistic behavior HP:0000729 Hyperactivity HP:0000752

Show evidence (1 reference)

PMID:41226632 SUPPORT BACKGROUND Human Clinical

"In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"

Aggressive behavior in every patient of the founding cohort is what makes behavioral management a core treatment target. No intervention study exists.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Platform: Behavioral / lifestyle

Every proband of this dominant form reported so far carried a de novo variant, implying a low but non-zero sibling recurrence risk from gonadal mosaicism. Counseling also has to establish which AP1G1 disorder is in front of it, since the same gene causes a recessive disorder with a one in four sibling recurrence risk; the zygosity of the variants, not the gene, settles that.

Show evidence (1 reference)

PMID:34102099 SUPPORT Human Clinical

"We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations."

Establishes that both a de novo dominant and a biallelic recessive mode occur in this gene, which is the fact that drives recurrence-risk counseling.

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Diagnosis

2

Exome Sequencing

Every published proband was ascertained by trio or singleton exome sequencing with variant interpretation against ACMG criteria. There is no biochemical or imaging marker for this disorder, so molecular testing is the diagnosis.

clinical exome sequencing NCIT:C101295

Show evidence (1 reference)

PMID:38665048 SUPPORT Human Clinical

"Next generation sequencing (NGS) analysis through clinical exome disclosed AP1G1: c.1969C>G (p.Leu657Val), de novo, likely pathogenic variant, according to ACMG classification criteria."

Clinical exome sequencing is what made the diagnosis in this case.

Genome Sequencing for Copy Number Variants

Exome sequencing does not reliably resolve a whole-gene deletion. In the one reported deletion case, array CGH placed only a single probe inside AP1G1 and the call stayed a variant of uncertain significance for years; trio genome sequencing resolved the breakpoints and upgraded it to likely pathogenic. Genome sequencing is therefore the follow-on test when a 16q22.2 copy-number change is suspected.

trio genome sequencing NCIT:C101294

Show evidence (2 references)

PMID:38840441 SUPPORT Human Clinical

"However, the extent of the CNV and involvement of the AP1G1 gene was equivocal as only 1 out of 4 array CGH probes overlapped the gene"

States the limitation of array CGH that genome sequencing resolved in this case.

PMID:38840441 SUPPORT Human Clinical

"In all three cases, WGS identified CNVs and confirmed zygosity and pathogenicity, resulting in genetic diagnoses of PRKN-related Parkinson disease, TAOK1-related neurodevelopmental disorder, and AP1G1-related Usmani-Riazuddin syndrome."

Genome sequencing delivered the AP1G1 diagnosis where array CGH could not.

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Prevalence

1

Worldwide

Cases In Literature Ultra Rare

Reported as a very rare condition. The founding series described eleven families; single additional patients have been reported since. No population-based prevalence or incidence estimate was found in the PubMed records searched for this entry (AP1G1 in title or abstract, 29 records; Usmani-Riazuddin anywhere, 3 records; searched 2026-09-18), so no rate is recorded here.

Show evidence (2 references)

PMID:38665048 SUPPORT Human Clinical

"Usmani-Riazuddin syndrome (USRISR, MIM# 619548; USRISD, MIM#619467) is a very rare genetic condition."

Characterizes the condition as very rare, which is the basis for the ULTRA_RARE band.

PMID:34102099 SUPPORT Human Clinical

"associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"

Gives the size of the founding case series, eleven families, which is the literature count this record reports.

⚖️

Clinical Burden

Variable

Intellectual disability spans mild to severe across the reported patients, and epilepsy, spasticity, hypotonia and congenital anomalies are variably present. Aggressive behavior, present in every patient of the founding cohort, is a substantial burden on families independent of cognitive severity. Survival and mortality are not characterized in the abstract-level sources cited here, so no burden claim is made about them either way.

Show evidence (1 reference)

PMID:34102099 SUPPORT Human Clinical

"associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"

The mild-to-severe range of intellectual disability is what makes the burden VARIABLE rather than a single level.

🐁

Animal Models

4

ap1g1 knockout zebrafish Knockout

Homozygous null embryos arrest at the blastula stage, so the informative genotype is the heterozygote - which is also the genotype that matches the dominant human disease. Heterozygous fish reach adulthood with reduced brain volume, missing neuronal populations in the midbrain, midbrain-hindbrain boundary and telencephalon, fewer spinal cord neurons, and dysregulated cadherin-mediated adhesion.

Species

Zebrafish (Danio rerio)

Genotype

ap1g1 knockout generated by CRISPR/Cas9; homozygous null and heterozygous carriers

Background

Tg(neurod1:EGFP) reporter crossed in for neuronal population analysis

Publication

PMID:37108275

Pathograph links

AP1G1 Haploinsufficiency recapitulates fidelity: moderate observes: organism The heterozygous fish is a direct model of one-allele loss of ap1g1 and shows that this dosage alone produces a phenotype.

Limitations: Zebrafish ap1g1 is an ortholog rather than the human gene, and the heterozygous phenotype includes reduced fertility and gut and gonadal changes that are not reported features of the human disorder. The model addresses dosage only; it says nothing about the dominant missense alleles.

Readouts

Total brain volume

Direction: DECREASED

Interpretation: Reduced brain volume in the heterozygote is the structural correlate of the human neurodevelopmental phenotype.

Show evidence (1 reference)

PMID:37108275 SUPPORT Model Organism

"In our knockout model, the heterozygous fish displayed abnormalities in specific brain areas and spinal cord neurons, and the brain volume is reduced."

Reports the brain-volume reduction measured in heterozygous animals.

Show evidence (1 reference)

PMID:37108275 SUPPORT Model Organism

"The zebrafish ap1g1 knock-out model revealed the indispensable function of the family of AP1 complexes for vertebrate development and that heterozygosity causes disease phenotypes."

States that heterozygosity is sufficient for disease phenotypes, which is what makes this model informative for the haploinsufficiency node.

Cadherin Mis-sorting and Adherens Junction Instability recapitulates fidelity: moderate observes: cellular The model identifies cadherin sorting and adherens junction formation as the concrete cargo defect downstream of reduced ap1g1.

Limitations: The cadherin defect was characterized in epithelial and gonadal tissue, not in neurons, and no corresponding cadherin measurement has been made in human AP1G1 patients.

Readouts

Cadherin-mediated cell adhesion

Direction: ALTERED

Interpretation: Marker-profile and morphology analysis identifies cadherin-mediated adhesion as dysregulated in the heterozygote.

Show evidence (1 reference)

PMID:37108275 SUPPORT Model Organism

"An analysis of mRNA profiles of different marker proteins and altered tissue morphologies revealed dysregulated cadherin-mediated cell adhesion."

The measurement behind this readout.

Show evidence (1 reference)

PMID:37108275 SUPPORT Model Organism

"Interestingly, adult heterozygous fish showed impaired cell adhesion in epithelial tissues, such as cadherin protein sorting and adherent junction (AJ) formation."

Establishes that this model reports on cadherin sorting and adherens junction formation.

Human AP1G1 mRNA rescue and overexpression zebrafish assay mRNA rescue and overexpression assay

The assay used to distinguish a dominant-negative from a simple loss-of-function allele. Human wild-type AP1G1 mRNA rescues the ap1g1 null; mutant mRNA does not; and co-injecting both fails to rescue, which is the signature of interference with the wild-type product rather than of its mere absence.

Species

Zebrafish (Danio rerio)

Genotype

ap1g1-/- and wild-type embryos microinjected at the one-cell stage with human wild-type or mutant AP1G1 mRNA

Publication

PMID:41226632

Pathograph links

Dominant-Negative Gamma-1 Adaptin Missense Protein perturbs fidelity: moderate observes: organism Introducing the mutant human transcript into a vertebrate embryo tests directly whether the mutant protein is harmful in the presence of wild-type protein.

Limitations: This is transient mRNA microinjection at supraphysiological levels, not an engineered heterozygous allele, so the dose does not correspond to a patient heterozygote. It also cannot separate a dominant-negative effect from a toxic gain-of-function, which the authors state explicitly.

Readouts

Larval locomotor activity

Direction: DECREASED

Interpretation: Reduced swum distance after mutant mRNA injection, against normal activity after wild-type mRNA injection.

Show evidence (1 reference)

PMID:41226632 SUPPORT Model Organism

"Zebrafish larvae injected with WT AP1G1 mRNA displayed normal locomotor activity, whereas larvae injected with MUT AP1G1 exhibited a marked reduction in swum distance."

The locomotor measurement behind this readout, with the wild-type transcript as the internal control.

Show evidence (1 reference)

PMID:41226632 SUPPORT Model Organism

"The phenotype was also not rescued when ap1g1-/- zebrafish embryos were co-injected with both human wild-type and mutated mRNAs, supporting the dominant-negative effect of the new variant."

The co-injection result is what makes this assay informative for a dominant-negative mechanism specifically.

Perturbed Neurodevelopment and Reduced Brain Growth partially recapitulates fidelity: low observes: organism Mutant transcript injected into wild-type embryos produces developmental abnormalities and lethality, mirroring at organism level the developmental disruption the human dominant alleles cause.

Limitations: Zebrafish gross developmental abnormality and lethality are not the human phenotype: the patients have intellectual disability and behavioral abnormality with normal survival. The model reports that the allele is developmentally damaging, not that it reproduces the clinical picture.

Show evidence (1 reference)

PMID:34102099 SUPPORT Model Organism

"Furthermore, microinjection of mRNAs with de novo missense variants in wild-type zebrafish resulted in severe developmental abnormalities and increased lethality."

The same assay applied to the original cohort's de novo missense alleles, with the same outcome.

Ap1g1 (gamma-adaptin) knockout mouse Knockout

The mammalian counterpart of the zebrafish null. Homozygotes die before implantation, so again only the heterozygote is informative - and it is informative in a way no other model is, because AP-1 complex abundance was measured directly and found halved. The heterozygous mouse is not a model of the human neurodevelopmental phenotype; it is a model of the dosage step.

Species

Mouse (Mus musculus)

Genotype

Ap1g1 (gamma-adaptin) null; homozygous and heterozygous

Publication

PMID:10026148

Pathograph links

AP1G1 Haploinsufficiency partially recapitulates fidelity: moderate observes: molecular Quantifies what losing one gamma-1 adaptin allele does to the complex itself: AP-1 falls to half of control levels.

Limitations: The heterozygous mouse's reported phenotype is low body weight and impaired T cell development, not intellectual disability, seizures or behavioral abnormality, so the model establishes the molecular dosage effect without reproducing the human clinical picture. The report predates the human disorder by two decades and was not designed against it.

Readouts

AP-1 complex abundance in heterozygotes

Direction: DECREASED

Interpretation: One functional allele yields half the normal amount of assembled AP-1, which is the molecular content of the haploinsufficiency claim.

Show evidence (1 reference)

PMID:10026148 SUPPORT Model Organism

"In heterozygous mice the amount of AP-1 complexes is reduced to half of controls."

The direct measurement of AP-1 complex abundance at one gene copy.

Show evidence (1 reference)

PMID:10026148 SUPPORT Model Organism

"gamma-Adaptin-deficient embryos develop until day 3.5 post coitus and die during the prenidation period, revealing that AP-1 is essential for viability."

Establishes that gamma-1 adaptin is essential in a mammal, which is why the heterozygote rather than the null is the genotype relevant to a dominant human disorder.

Ap1g1 figure eight (fgt) hypomorphic mouse Hypomorph

A spontaneous hypomorphic allele that survives to adulthood where the null does not, making it the only mammalian model in which partial AP-1 function can be studied past embryogenesis. Its phenotype is sensory, endocrine and reproductive rather than neurodevelopmental, which is itself informative about how much of the human picture partial loss does not explain.

Species

Mouse (Mus musculus)

Genotype

Ap1g1 fgt, spontaneous in-frame 6 bp deletion, homozygous

Publication

PMID:27090238

Pathograph links

AP-1 Adaptor Complex Dysfunction partially recapitulates fidelity: low observes: organism Shows what reduced but non-zero gamma-1 adaptin function produces in a mammal across a whole lifespan.

Limitations: The reported abnormalities are inner ear, retina, thyroid and testes; none of these is a core feature of the human dominant disorder, and intellectual disability and seizures are not reported in this model. It is also a recessive hypomorph, so it does not model a heterozygous dominant allele.

Show evidence (1 reference)

PMID:27090238 SUPPORT Model Organism

"In contrast to Ap1g1 (-/-) null mice, mice homozygous for the recessive fgt mutation are viable with adult survival similar to controls."

Establishes the model as a viable partial-function system, which is what makes it informative for graded AP-1 dysfunction rather than for complete loss.

{ }

Source YAML

click to show

name: Usmani-Riazuddin Syndrome, Autosomal Dominant
creation_date: "2026-09-18T00:00:00Z"
description: >-
  The autosomal dominant AP1G1-related neurodevelopmental disorder (USRISD, OMIM
  619467), caused by heterozygous de novo variants in AP1G1, which encodes the
  gamma-1 adaptin subunit of the heterotetrameric clathrin adaptor protein
  complex 1 (AP-1). AP-1 selects cargo and nucleates clathrin-coated vesicles at
  the trans-Golgi network and on endosomes, and is required for the polarized
  delivery of somatodendritic membrane proteins in neurons. Affected individuals
  have mild to severe intellectual disability, speech delay, global developmental
  delay and aggressive behavior, with variable epilepsy, hypotonia, spasticity,
  autistic features, facial dysmorphism and limb defects. The reported dominant
  allele classes are missense, splice-site, frameshift and whole-gene deletion, so
  this form spans both haploinsufficiency and a dominant-negative or toxic effect
  of a misfolded gamma-1 adaptin on the residual wild-type protein. A separate
  autosomal recessive AP1G1 disorder (USRISR, OMIM 619548, MONDO:0859196) exists
  and is not curated here.
category: Mendelian
parents:
- Neurodevelopmental Disorder
disease_term:
  preferred_term: Usmani-Riazuddin syndrome, autosomal dominant
  term:
    id: MONDO:0859174
    label: Usmani-Riazuddin syndrome, autosomal dominant
notes: >-
  Entry scope. This entry curates the AUTOSOMAL DOMINANT form only
  (MONDO:0859174, OMIM 619467). MONDO carries a second AP1G1 term,
  MONDO:0859196 Usmani-Riazuddin syndrome, autosomal recessive (OMIM 619548).
  The two are SIBLINGS, not parent and child: both assert RO:0004003 to hgnc:555
  AP1G1 and both sit directly under MONDO:0003847 hereditary disease, with no
  umbrella term over them (checked with `runoak -i sqlite:obo:mondo info
  MONDO:0859174 MONDO:0859196 -O obo`). The recessive form is therefore NOT
  represented here as a subtype - that would assert a hierarchy the ontology
  contradicts - and is carried in the curation queue instead as
  stubs/Usmani-Riazuddin_Syndrome_Autosomal_Recessive.yaml.
  Whether the two should eventually become one umbrella entry is a real open
  question and is recorded in `discussions`, not settled here: the founding
  cohort delineated both forms in one series and the follow-up literature calls
  their clinical features overlapping, but merging them would need either a new
  umbrella MONDO term or a `mappings.mondo_mappings` anchor, plus an actual
  curation pass over the recessive form.
  No mechanism module was applied. `just list-modules` was searched for
  trafficking, vesicle, Golgi, endosome, sorting and cargo modules, and
  `kb/modules/` was grepped for clathrin, adaptinopathy, AP-1 complex and
  trans-Golgi: the only hits are `synaptic_vesicle_cycle` (presynaptic AP-2 and
  clathrin-mediated synaptic vesicle endocytosis, not AP-1 sorting at the TGN)
  and `apical_neuroependyma_integrity_failure` (ventricular lining integrity).
  Neither describes AP-1-dependent cargo selection at the trans-Golgi network, so
  `conforms_to` was left unset rather than forced.
  No GeneReviews chapter exists for this disorder. This was checked offline with
  `just check-genereviews` against the committed Bookshelf index snapshot of
  2026-09-10 (958 GeneReviews chapters indexed), which reports NO_CHAPTER for both
  GeneReviews and StatPearls. The phenotype baseline for this entry is therefore
  the primary literature rather than a review chapter.
  A deep-research pass was run against this entry
  (research/Usmani-Riazuddin_Syndrome_Autosomal_Dominant-deep-research-claude_code.md,
  provider claude_code). `just preflight-dr` returns PASS against MONDO:0859174 and
  the report's own reference validation reports 11/11 verified with a 0.0
  confabulation rate. Reconciling it against this entry added the two mouse models
  (PMID:10026148, PMID:27090238) and the hyperactivity, hearing-impairment and
  vertebral phenotypes. Two of its claims were deliberately NOT taken up: the
  gnomAD constraint figures (pLI 1.0, LOEUF 0.2) and a neonatal death in the
  founding cohort are both attributed to PMID:34102099, whose cached record is
  abstract-only and contains neither, so neither is quotable and neither is
  asserted here.
references:
- reference: PMID:34102099
  title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
  tags: []
  findings:
  - statement: >-
      De novo heterozygous and bi-allelic AP1G1 variants cause a neurodevelopmental
      disorder with mild to severe intellectual disability, epilepsy and
      developmental delay, established across eleven families.
- reference: PMID:41226632
  title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
  tags: []
  findings:
  - statement: >-
      A de novo AP1G1 missense allele leaves the trans-Golgi cisternae diffuse and
      disorganized in patient fibroblasts, and is not rescued by co-injected
      wild-type transcript in zebrafish, which supports a dominant-negative effect.
- reference: PMID:37108275
  title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
  tags: []
  findings:
  - statement: >-
      Zebrafish homozygous for ap1g1 loss arrest at the blastula stage, while
      heterozygotes survive with reduced brain volume, missing neuronal populations
      and dysregulated cadherin-mediated cell adhesion.
- reference: PMID:38665048
  title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
  tags: []
  findings:
  - statement: >-
      A second published patient with a de novo AP1G1 variant, carrying the first
      described distinctive facial features for this syndrome.
- reference: PMID:10026148
  title: "Early embryonic death of mice deficient in gamma-adaptin."
  tags: []
  findings:
  - statement: >-
      Mice lacking gamma-1 adaptin die before implantation, and heterozygotes carry
      half the normal amount of assembled AP-1 complex, quantifying the dosage
      effect of losing one allele in a mammal.
- reference: PMID:27090238
  title: "A hypomorphic mutation of the gamma-1 adaptin gene (Ap1g1) causes inner ear, retina, thyroid, and testes abnormalities in mice."
  tags: []
  findings:
  - statement: >-
      A spontaneous in-frame Ap1g1 deletion produces viable adult mice with inner
      ear, retina, thyroid and testes abnormalities, the only mammalian model of
      partial gamma-1 adaptin function surviving past embryogenesis.
- reference: PMID:38840441
  title: "Whole genome sequencing for copy number variant detection to improve diagnosis and management of rare diseases."
  tags: []
  findings:
  - statement: >-
      A de novo whole-gene AP1G1 deletion at 16q22.2, resolved by trio genome
      sequencing after array CGH left it a variant of uncertain significance; the
      disorder's only reported pure dosage lesion.
inheritance:
- name: Autosomal dominant (de novo)
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    Heterozygous de novo AP1G1 variants. All dominant probands reported so far
    arose de novo; no transmitted dominant pedigree has been described in the
    published series.
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations."
    explanation: "The original cohort establishes de novo heterozygous AP1G1 variants as one of the two inheritance modes for this disorder."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, Usmani et al. identified and studied nine patients with de novo dominant missense, splice site, and frameshift variants and two patients with biallelic, recessive, and missense variants."
    explanation: "Restates the composition of the original cohort: nine dominant de novo probands against two recessive biallelic probands."
pathophysiology:
- name: AP1G1 Haploinsufficiency
  biological_scale: MOLECULAR
  description: >-
    Heterozygous de novo AP1G1 alleles that abolish production of a full-length
    gamma-1 adaptin from one allele - frameshift, splice-acceptor and whole-gene
    deletion alleles - leave a single functional copy. The whole-gene deletion
    case is the cleanest demonstration that halving AP1G1 dosage alone is
    sufficient to produce the syndrome, since no mutant protein is made.
  genetic_context:
    gene:
      preferred_term: AP1G1
      term:
        id: hgnc:555
        label: AP1G1
    variant_origin: DE_NOVO
    zygosity: HETEROZYGOUS
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Applies to the truncating, splice-site and whole-gene-deletion dominant
      alleles. The dominant missense alleles are modelled separately.
  genes:
  - preferred_term: AP1G1
    term:
      id: hgnc:555
      label: AP1G1
  evidence:
  - reference: PMID:38840441
    reference_title: "Whole genome sequencing for copy number variant detection to improve diagnosis and management of rare diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the first reported case with whole‐gene deletion and presents with a mild but consistent phenotype."
    explanation: "A whole-gene deletion makes no mutant protein, so this allele can only act by halving gene dosage; it is the cleanest human evidence for haploinsufficiency in this disorder."
  - reference: PMID:38840441
    reference_title: "Whole genome sequencing for copy number variant detection to improve diagnosis and management of rare diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In all three cases, WGS identified CNVs and confirmed zygosity and pathogenicity, resulting in genetic diagnoses of PRKN-related Parkinson disease, TAOK1-related neurodevelopmental disorder, and AP1G1-related Usmani-Riazuddin syndrome."
    explanation: "Confirms that the deletion case was diagnosed as Usmani-Riazuddin syndrome, tying the dosage lesion to this disorder."
  downstream:
  - target: AP-1 Adaptor Complex Dysfunction
    description: >-
      A single functional AP1G1 allele reduces the amount of gamma-1 adaptin
      available to assemble into AP-1 heterotetramers.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37108275
      reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The zebrafish ap1g1 knock-out model revealed the indispensable function of the family of AP1 complexes for vertebrate development and that heterozygosity causes disease phenotypes."
      explanation: "In zebrafish, losing one ap1g1 allele is by itself enough to produce phenotypes, which is the dosage-sensitivity step this edge asserts."
- name: Dominant-Negative Gamma-1 Adaptin Missense Protein
  biological_scale: MOLECULAR
  description: >-
    Heterozygous de novo AP1G1 missense alleles produce a full-length but
    misfolded gamma-1 adaptin. Rather than simply being absent, the mutant
    protein interferes with the wild-type protein: co-injecting wild-type and
    mutant human AP1G1 mRNA fails to rescue the zebrafish null, and injecting
    mutant mRNA into wild-type embryos is itself damaging. This is a different
    lesion from haploinsufficiency even though both act through the same complex.
  genetic_context:
    gene:
      preferred_term: AP1G1
      term:
        id: hgnc:555
        label: AP1G1
    variant_origin: DE_NOVO
    zygosity: HETEROZYGOUS
    functional_impact_category: DOMINANT_NEGATIVE
    description: >-
      Applies to the dominant missense alleles. The published functional argument
      for a dominant-negative rather than a purely hypomorphic effect rests on
      failure of co-injection rescue and on toxicity of mutant mRNA in a
      wild-type background; both authors describe the alternative of a toxic
      gain-of-function as not yet excluded.
  genes:
  - preferred_term: AP1G1
    term:
      id: hgnc:555
      label: AP1G1
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In silico analysis and 3D protein modeling simulation predicted alteration of AP1γ1 protein folding for missense variants, which was consistent with the observed altered AP1γ1 levels in heterologous cells."
    explanation: "3D modeling predicts misfolding of the mutant gamma-1 adaptin and heterologous cells show altered protein levels, which is the molecular state this node describes."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The phenotype was also not rescued when ap1g1-/- zebrafish embryos were co-injected with both human wild-type and mutated mRNAs, supporting the dominant-negative effect of the new variant."
    explanation: "Failure of the wild-type transcript to rescue in the presence of the mutant transcript is the direct experimental basis for the dominant-negative call."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The observed phenotype is likely due to a dominant-negative effect or a toxic gain-of-function of the mutant AP1G1, impairing the activity or recruitment of the wild-type protein."
    explanation: "States the interference-with-wild-type mechanism, and records that the authors have not separated dominant-negative from toxic gain-of-function - which is why this node is marked PROVISIONAL."
  downstream:
  - target: AP-1 Adaptor Complex Dysfunction
    description: >-
      The misfolded gamma-1 adaptin impairs the activity or recruitment of the
      wild-type subunit, so AP-1 function falls below the level expected from
      loss of one allele alone.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The observed phenotype is likely due to a dominant-negative effect or a toxic gain-of-function of the mutant AP1G1, impairing the activity or recruitment of the wild-type protein."
      explanation: "Names impaired activity or recruitment of the wild-type protein as the step between the mutant allele and complex dysfunction."
- name: AP-1 Adaptor Complex Dysfunction
  biological_scale: MOLECULAR
  description: >-
    Gamma-1 adaptin is one of four subunits of AP-1. The complex recognizes
    sorting motifs in the cytoplasmic tails of transmembrane cargo and recruits
    clathrin, so a deficient or interfered-with gamma-1 subunit reduces
    AP-1-mediated cargo loading into clathrin-coated vesicles.
  protein_complexes:
  - preferred_term: AP-1 adaptor complex
    term:
      id: GO:0030121
      label: AP-1 adaptor complex
  biological_processes:
  - preferred_term: AP-1-mediated cargo loading into clathrin-coated vesicles
    term:
      id: GO:0035653
      label: clathrin-coated vesicle cargo loading, AP-1-mediated
    modifier: DECREASED
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: OTHER
    snippet: "The AP1γ1-mediated adaptor complex is essential for the formation of clathrin-coated intracellular vesicles."
    explanation: "States the essential role of the complex in clathrin-coated vesicle formation, which is the function lost at this node."
  - reference: PMID:37108275
    reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: OTHER
    snippet: "Only AP1 and AP2 complexes form clathrin-coated vesicles (CCVs)."
    explanation: "Establishes that AP-1 is one of only two clathrin-coat-forming adaptor complexes, which is why loss of its gamma subunit is not buffered by the other AP complexes."
  - reference: PMID:10026148
    reference_title: "Early embryonic death of mice deficient in gamma-adaptin."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: OTHER
    snippet: "The heterotetrameric adaptor protein complex 1 (AP-1) promotes the formation of clathrin-coated vesicles at the trans-Golgi network."
    explanation: "Locates the complex's clathrin-coat-forming activity at the trans-Golgi network, the compartment the next node describes."
  downstream:
  - target: Trans-Golgi Network Cargo Sorting Failure
    description: >-
      AP-1 operates at the trans-Golgi network, so reduced complex function
      manifests first as disordered sorting and export from the TGN.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: OTHER
      snippet: "AP1G1 is a subunit of the AP-1 adaptor complex responsible for the recognition of protein cargo and the formation of clathrin-coated vesicles between the TGN and endosomes."
      explanation: "Places the AP-1 complex's cargo-recognition function at the TGN-to-endosome step that this edge targets."
  - target: Endosomal Recycling Impairment
    description: >-
      AP-1 also acts on endosomes, and the recessive missense alleles perturb the
      endosome recycling pathway while leaving complex assembly intact.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34102099
      reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway."
      explanation: "Directly reports an endosome-recycling defect downstream of AP1G1 missense alleles."
- name: Trans-Golgi Network Cargo Sorting Failure
  biological_scale: CELLULAR
  description: >-
    In patient fibroblasts carrying a dominant AP1G1 missense allele the cis-Golgi
    marker GM130 is preserved but the trans-Golgi cisternae are diffuse and
    disorganized, and the authors conclude that vesicular trafficking at the
    trans-Golgi level is impaired. Cargo that depends on AP-1 for export from the
    TGN therefore reaches its destination inefficiently.
  cellular_components:
  - preferred_term: trans-Golgi network
    term:
      id: GO:0005802
      label: trans-Golgi network
  biological_processes:
  - preferred_term: Golgi to endosome transport
    term:
      id: GO:0006895
      label: Golgi to endosome transport
    modifier: DECREASED
  - preferred_term: vesicle-mediated transport
    term:
      id: GO:0016192
      label: vesicle-mediated transport
    modifier: DECREASED
  cell_types:
  - preferred_term: patient dermal fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In c.196G>A mutant fibroblasts, although GM130 labeling remained comparable to that in the controls, the organization of the trans-Golgi cisternae appeared more diffuse and disorganized."
    explanation: "Direct morphological readout in patient fibroblasts showing that the trans-Golgi compartment, and not the cis-Golgi, is the one disturbed."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In conclusion, the c.196G>A mutation in AP1G1 disrupts membrane association and impairs vesicular trafficking at the trans-Golgi level, potentially resulting in significant functional consequences."
    explanation: "The authors' own conclusion that trafficking at the trans-Golgi is impaired by the dominant allele."
  downstream:
  - target: Impaired Somatodendritic Protein Sorting in Neurons
    description: >-
      Neurons depend on AP complexes for the polarized delivery of somatodendritic
      membrane proteins, so a TGN sorting failure is expressed in neurons as loss
      of that polarity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34102099
      reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: OTHER
      snippet: "Adaptor protein (AP) complexes mediate selective intracellular vesicular trafficking and polarized localization of somatodendritic proteins in neurons."
      explanation: "States the neuron-specific function that this edge carries forward from the general TGN sorting defect."
  - target: Cadherin Mis-sorting and Adherens Junction Instability
    description: >-
      Cadherins are AP-1 cargo and are transported from the TGN to the plasma
      membrane, so failed TGN sorting reduces cadherin delivery to adherens
      junctions.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37108275
      reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "All data support AP1G1-dependent sorting and transport of cadherins from the TGN to the plasma membrane, because AP1G1 sorting of cadherin is most important during the biogenesis of tissues"
      explanation: "Identifies cadherin as AP1G1-dependent TGN cargo, which is the step this edge asserts."
- name: Endosomal Recycling Impairment
  biological_scale: CELLULAR
  description: >-
    AP-1 also functions on endosomes, and an endosome-recycling defect is the one
    directly measured consequence of AP1G1 missense alleles: the mutant proteins
    still assemble with the other AP-1 subunits but internalized cargo returns to
    the plasma membrane inefficiently. Scope caveat, stated plainly: that
    measurement was made on the BIALLELIC RECESSIVE alleles, which belong to the
    sibling disorder MONDO:0859196 and are not curated in this entry. Whether the
    dominant alleles engage the same step has not been tested. The node is kept
    here because it is a real, cited step in AP-1 biology downstream of the same
    complex, and is marked PROVISIONAL rather than attributed to the dominant
    alleles.
  biological_processes:
  - preferred_term: endocytic recycling
    term:
      id: GO:0032456
      label: endocytic recycling
    modifier: DECREASED
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway."
    explanation: "The only direct experimental statement of an endosome-recycling defect in this disorder, and it is specific to the recessive alleles."
  downstream:
  - target: Impaired Somatodendritic Protein Sorting in Neurons
    description: >-
      Endosomal recycling is one of the two routes by which membrane proteins
      reach and are maintained at polarized neuronal surfaces, so its impairment
      converges on the same somatodendritic sorting defect.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:37108275
      reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: OTHER
      snippet: "Secondly, cadherins are endocytosed and recycled via endosomes back to plasma membrane AJ."
      explanation: "Establishes the endosome-to-plasma-membrane recycling route as a second delivery path for AP-1 cargo. The step from that route to neuronal somatodendritic polarity has not been measured in AP1G1 disease, which is why this edge is marked as having unknown intermediates."
- name: Impaired Somatodendritic Protein Sorting in Neurons
  biological_scale: CELLULAR
  description: >-
    Neurons are the tissue with the most active vesicular protein transport, and
    AP complexes are what give somatodendritic membrane proteins their polarized
    localization. Zebrafish lacking one ap1g1 allele fail to specify or
    differentiate neuronal populations in the telencephalon, midbrain,
    midbrain-hindbrain boundary and spinal cord.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  cellular_components:
  - preferred_term: somatodendritic compartment
    term:
      id: GO:0036477
      label: somatodendritic compartment
  biological_processes:
  - preferred_term: intracellular protein transport
    term:
      id: GO:0006886
      label: intracellular protein transport
    modifier: DECREASED
  evidence:
  - reference: PMID:37108275
    reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: OTHER
    snippet: "The brain is the tissue with the most active vesicular protein transport."
    explanation: "Explains why a ubiquitously expressed trafficking complex produces a predominantly neurological disorder."
  - reference: PMID:37108275
    reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In our knockout model, the heterozygous fish displayed abnormalities in specific brain areas and spinal cord neurons, and the brain volume is reduced."
    explanation: "Shows that halving ap1g1 dosage disturbs specific neuronal populations in vivo."
  downstream:
  - target: Perturbed Neurodevelopment and Reduced Brain Growth
    description: >-
      Loss of polarized protein delivery in developing neurons impairs the
      determination and differentiation of specific neuronal populations.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37108275
      reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Interestingly, heterozygous females and males have reduced fertility and showed morphological alterations in the brain, gonads and intestinal epithelium."
      explanation: "Heterozygous ap1g1 loss produces morphological brain alterations, the outcome this edge points to."
- name: Cadherin Mis-sorting and Adherens Junction Instability
  biological_scale: CELLULAR
  description: >-
    Cadherins carry canonical AP-1 sorting motifs and reach adherens junctions by
    an AP-1-dependent route from the trans-Golgi network. In ap1g1 heterozygous
    zebrafish, cadherin-mediated cell adhesion is dysregulated and epithelial
    adherens junction formation is impaired. This is the best-characterized
    individual cargo defect in AP1G1 deficiency.
  biological_processes:
  - preferred_term: cell-cell adhesion mediated by cadherin
    term:
      id: GO:0044331
      label: cell-cell adhesion mediated by cadherin
    modifier: DECREASED
  - preferred_term: adherens junction organization
    term:
      id: GO:0034332
      label: adherens junction organization
    modifier: DECREASED
  evidence:
  - reference: PMID:37108275
    reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "An analysis of mRNA profiles of different marker proteins and altered tissue morphologies revealed dysregulated cadherin-mediated cell adhesion."
    explanation: "Direct result in the ap1g1 heterozygous zebrafish identifying cadherin-mediated adhesion as the dysregulated process."
  - reference: PMID:37108275
    reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Interestingly, adult heterozygous fish showed impaired cell adhesion in epithelial tissues, such as cadherin protein sorting and adherent junction (AJ) formation."
    explanation: "Links the adhesion defect specifically to cadherin protein sorting and adherens junction formation."
  downstream:
  - target: Perturbed Neurodevelopment and Reduced Brain Growth
    description: >-
      Cadherin-dependent adhesion is required for the tissue architecture of the
      developing brain, so cadherin mis-sorting contributes to the
      neurodevelopmental phenotype alongside the neuron-intrinsic sorting defect.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:37108275
      reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "This phenotype confirms the contributions of the AP1 complex in polarized epithelial cells and neurons; a more detailed investigation of E-cadherin sorting steps would contribute to understanding this phenotype."
      explanation: "The authors themselves state that the cadherin-sorting steps behind the neuronal phenotype remain to be worked out, which is why this edge records unknown intermediates."
- name: Perturbed Neurodevelopment and Reduced Brain Growth
  biological_scale: TISSUE
  description: >-
    The convergent tissue-level consequence: specific brain regions and spinal
    cord neuronal populations fail to be specified or to differentiate normally,
    and total brain volume is reduced in the heterozygous animal model. This is
    the node from which the clinical neurodevelopmental phenotype follows.
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  biological_processes:
  - preferred_term: brain development
    term:
      id: GO:0007420
      label: brain development
    modifier: DECREASED
  - preferred_term: neuron differentiation
    term:
      id: GO:0030182
      label: neuron differentiation
    modifier: DECREASED
  evidence:
  - reference: PMID:37108275
    reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "normal expression of ap1g1 at early stages of neurodevelopment is required for determination and/or differentiation of specific neuronal populations located in different brain areas and spinal cord neurons"
    explanation: "States the developmental requirement whose failure this node represents."
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Furthermore, microinjection of mRNAs with de novo missense variants in wild-type zebrafish resulted in severe developmental abnormalities and increased lethality."
    explanation: "Shows that the dominant alleles specifically produce developmental abnormalities in a vertebrate, linking the dominant lesion to this node."
  downstream:
  - target: Global developmental delay
    description: >-
      Impaired specification and differentiation of neuronal populations during
      brain development is expressed clinically as delayed attainment of
      developmental milestones across domains.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34102099
      reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
      explanation: "Establishes developmental delay as a defining feature of the AP1G1 disorder. The intermediate steps between the brain-development defect and the clinical milestone delay have not been measured, which is what the causal_link_type records."
  - target: Intellectual disability
    description: >-
      Disrupted neuronal differentiation and reduced brain growth underlie the
      cognitive impairment, which ranges from mild to severe.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34102099
      reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
      explanation: "Establishes intellectual disability as a defining feature. The cellular-to-cognitive intermediates are not established."
  - target: Delayed speech and language development
    description: >-
      Speech delay is among the most consistent features and follows from the same
      neurodevelopmental disruption.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: HUMAN_CLINICAL
      snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
      explanation: "Reports speech delay in every patient of the founding cohort. The intermediates between the brain-development node and speech acquisition are not established."
  - target: Aggressive behavior
    description: >-
      Aggressive behavior was present in every patient of the founding cohort and
      is treated here as a manifestation of the same neurodevelopmental
      disruption.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: HUMAN_CLINICAL
      snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
      explanation: "Reports aggressive behavior in every patient of the founding cohort. No circuit-level mechanism for it has been identified in this disorder."
  - target: Seizure
    description: >-
      Epilepsy is a variable but defining feature; no AP1G1-specific
      excitability mechanism has been reported, so the link is asserted at the
      level of the neurodevelopmental lesion.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34102099
      reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
      explanation: "Establishes epilepsy as a defining feature of the disorder. No excitation-inhibition mechanism has been measured in AP1G1 disease."
  - target: Hypotonia
    description: >-
      Hypotonia is a variable feature of the cohort and is attributed to the same
      central neurodevelopmental disruption rather than to a separately
      characterized neuromuscular lesion.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: HUMAN_CLINICAL
      snippet: "The clinical phenotype is characterized by common signs such as intellectual disability, speech delay, developmental delay, hypotonia, and behavioral problems (mainly aggressive behavior), variably associated with congenital anomalies, epilepsy, spasticity, autism, bone abnormalities, vertebral and limb defects, and variable facial features (eyes and ear shape anomalies)."
      explanation: "Lists hypotonia among the common signs of the syndrome. No peripheral or muscular lesion has been reported, so the link is placed at the central node."
  - target: Spasticity
    description: >-
      Spasticity occurs variably and is treated as a corticospinal manifestation
      of the same neurodevelopmental disruption.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: HUMAN_CLINICAL
      snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
      explanation: "Records spasticity as a variably expressed feature of the founding cohort. No tract-level lesion has been demonstrated."
  - target: Hyperactivity
    description: >-
      Hyperactivity accompanies the aggression in the behavioral profile and is
      placed at the same neurodevelopmental node, with the same lack of a
      circuit-level mechanism.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Neuropsychiatric evaluation defined a mild to moderate form of intellectual disability (verbal IQ 53, performance 59, total 49), abnormal behavior including a tendency to aggression toward both peers and adults, hyperactivity, obsessive-compulsive behavior, and non-compliance."
      explanation: "Records hyperactivity in a formally assessed de novo AP1G1 proband, alongside the intellectual disability that the same node explains. No mechanism connecting the trafficking lesion to hyperactivity has been measured."
  - target: Autistic behavior
    description: >-
      Autistic features occur variably and are attributed to the same disruption
      of neuronal specification and differentiation.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      quote_role: BACKGROUND
      evidence_source: HUMAN_CLINICAL
      snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
      explanation: "Records autism as a variably expressed feature of the founding cohort."
phenotypes:
- name: Intellectual disability
  category: Clinical
  description: >-
    Cognitive impairment ranging from mild to severe. Present in all reported
    patients of the founding cohort.
  diagnostic: true
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
    explanation: "Intellectual disability, graded mild to severe, is a defining feature of the disorder across eleven families."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
    explanation: "Supports the frequency band: intellectual disability was present in 100% of the 11 patients in the founding cohort."
- name: Global developmental delay
  category: Clinical
  description: >-
    Delayed attainment of motor, language and adaptive milestones, recognized in
    infancy or early childhood.
  diagnostic: true
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients carrying already reported p.Arg15Gln, p.Arg35Trp, and p.Arg35Gln variants consistently presented with global developmental delay, intellectual disability, speech delay, and behavioral anomalies, including aggression and, variably, seizures, hypotonia, and autistic traits."
    explanation: "Reports global developmental delay as a consistent feature in patients carrying the recurrent dominant AP1G1 missense alleles."
  - reference: PMID:38840441
    reference_title: "Whole genome sequencing for copy number variant detection to improve diagnosis and management of rare diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patient 3 was referred at 5 to 10 years of age because of developmental delay, behavioural difficulties, possible infantile spasms, left hemiplegia, and toe walking."
    explanation: "Independent presentation of developmental delay in the whole-gene-deletion patient."
- name: Delayed speech and language development
  category: Clinical
  description: >-
    Speech and language delay, reported in every patient of the founding cohort
    and in each subsequent case report.
  diagnostic: true
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
    explanation: "Speech delay was present in 100% of the 11 patients of the founding cohort, which is the basis for the frequency band."
- name: Aggressive behavior
  category: Clinical
  description: >-
    Aggression, often with hyperactivity, is one of the most consistent features
    of the disorder and was present in all patients of the founding cohort.
  diagnostic: true
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Aggressive behavior
    term:
      id: HP:0000718
      label: Aggressive behavior
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
    explanation: "Aggressive behavior was present in 100% of the 11 patients of the founding cohort, which is the basis for the frequency band."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we report a novel variant (c.196G>A; p.Gly66Arg) identified by exome sequencing analysis in a young girl showing overlapping clinical features with USRIS, such as motor and speech delay, intellectual disability and abnormal aggressive behavior."
    explanation: "Aggressive behavior in the additional dominant proband reported by this group."
- name: Seizure
  category: Clinical
  description: >-
    Epilepsy is part of the syndrome definition but is variably expressed;
    seizure types are not systematically reported across the published cases.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
    explanation: "Epilepsy is named in the disorder definition established by the founding cohort."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
    explanation: "Records epilepsy as variably rather than universally expressed, which is why no frequency band is asserted here."
- name: Hypotonia
  category: Clinical
  description: >-
    Reduced muscle tone, listed among the common signs of the syndrome and
    variably expressed across the reported patients.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical phenotype is characterized by common signs such as intellectual disability, speech delay, developmental delay, hypotonia, and behavioral problems (mainly aggressive behavior), variably associated with congenital anomalies, epilepsy, spasticity, autism, bone abnormalities, vertebral and limb defects, and variable facial features (eyes and ear shape anomalies)."
    explanation: "Lists hypotonia among the common clinical signs of the syndrome."
- name: Autistic behavior
  category: Clinical
  description: >-
    Autistic traits occur in a subset of patients, reported alongside the other
    behavioral features.
  phenotype_term:
    preferred_term: Autistic behavior
    term:
      id: HP:0000729
      label: Autistic behavior
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients carrying already reported p.Arg15Gln, p.Arg35Trp, and p.Arg35Gln variants consistently presented with global developmental delay, intellectual disability, speech delay, and behavioral anomalies, including aggression and, variably, seizures, hypotonia, and autistic traits."
    explanation: "Records autistic traits as a variable feature in patients with the recurrent dominant missense alleles."
- name: Spasticity
  category: Clinical
  description: >-
    Increased muscle tone of upper-motor-neuron type, reported as a variably
    expressed feature.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
    explanation: "Records spasticity among the variably expressed features of the founding cohort."
- name: Abnormal facial shape
  category: Clinical
  description: >-
    Facial features were described as unspecified in the founding series. A
    single later report proposed a recognizable gestalt - synophrys, hypotelorism,
    upslanted palpebral fissures, broad nasal tip and thick lip vermilion - but
    that is one patient and the authors call for multicentric confirmation. No
    mechanism connecting AP1G1 to craniofacial morphogenesis has been reported,
    so this phenotype is deliberately left unconnected in the pathograph.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:38665048
    reference_title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To the best of our knowledge, this is the first description of likely distinctive facial features in a patient with Usmani-Riazuddin syndrome."
    explanation: "Establishes that distinctive facial features have been described, and by saying it is the first such description marks the finding as preliminary."
  - reference: PMID:38665048
    reference_title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is characterized by multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, muscular tone disorders, seizures, limb defects, and unspecified facial gestalt."
    explanation: "Records the facial gestalt as unspecified in the syndrome as previously delineated, which is the caveat this phenotype carries."
- name: Abnormality of limbs
  category: Clinical
  description: >-
    Limb defects are reported among the variably expressed congenital anomalies.
    They are not explained by any curated mechanism node in this entry: no study
    has linked AP1G1 to limb patterning, so this phenotype is deliberately left
    unconnected in the pathograph rather than attached to a speculative edge.
  phenotype_term:
    preferred_term: Abnormality of limbs
    term:
      id: HP:0040064
      label: Abnormality of limbs
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
    explanation: "Records limb defects among the variably expressed features of the founding cohort."
  - reference: PMID:38665048
    reference_title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is characterized by multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, muscular tone disorders, seizures, limb defects, and unspecified facial gestalt."
    explanation: "Independently lists limb defects as part of the syndrome's multisystemic involvement."
- name: Hyperactivity
  category: Clinical
  description: >-
    Hyperactivity is reported alongside aggression as part of the behavioral
    profile. The direct description is of a single proband assessed formally;
    earlier reports group it with the cohort's behavioral anomalies.
  phenotype_term:
    preferred_term: Hyperactivity
    term:
      id: HP:0000752
      label: Hyperactivity
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuropsychiatric evaluation defined a mild to moderate form of intellectual disability (verbal IQ 53, performance 59, total 49), abnormal behavior including a tendency to aggression toward both peers and adults, hyperactivity, obsessive-compulsive behavior, and non-compliance."
    explanation: "Formal neuropsychiatric assessment of a de novo AP1G1 proband recording hyperactivity alongside aggression."
- name: Hearing impairment
  category: Clinical
  description: >-
    Hearing loss has been reported in individual patients rather than across the
    cohort, and is not part of the syndrome definition.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:38665048
    reference_title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we describe this syndrome for the second time, in association to a novel AP1G1 variant identified in a toddler with multisystemic involvement including intellectual disability, speech and developmental delay, behavioral anomalies, arrhythmias, hearing loss, skin changes, and limb defects"
    explanation: "Hearing loss in the second published patient, reported as part of that individual's multisystemic involvement."
- name: Abnormal vertebral morphology
  category: Clinical
  description: >-
    Vertebral and other bone abnormalities are listed among the variably
    expressed congenital anomalies. As with the limb defects, no mechanism in
    this entry explains them, so this phenotype is deliberately left unconnected
    in the pathograph.
  phenotype_term:
    preferred_term: Abnormal vertebral morphology
    term:
      id: HP:0003468
      label: Abnormal vertebral morphology
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical phenotype is characterized by common signs such as intellectual disability, speech delay, developmental delay, hypotonia, and behavioral problems (mainly aggressive behavior), variably associated with congenital anomalies, epilepsy, spasticity, autism, bone abnormalities, vertebral and limb defects, and variable facial features (eyes and ear shape anomalies)."
    explanation: "Lists bone abnormalities and vertebral defects among the variably associated features of the syndrome."
genetic:
- name: AP1G1
  gene_term:
    preferred_term: AP1G1
    term:
      id: hgnc:555
      label: AP1G1
  relationship_type: CAUSATIVE
  variant_origin: DE_NOVO
  association: Heterozygous de novo missense, splice-site, frameshift and whole-gene deletion alleles
  presence: Positive
  inheritance:
  - name: Autosomal dominant
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
  notes: >-
    Two allele classes sit under this one dominant heading and they are not
    mechanistically the same, which is why the pathograph splits them into two
    nodes. Truncating, splice and whole-gene-deletion alleles remove one copy of
    the gene product; the missense alleles produce a full-length misfolded
    protein that interferes with the wild-type subunit. gnomAD constraint
    metrics were not consulted for this entry and no constraint claim is made
    here.
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations."
    explanation: "Establishes AP1G1 as the causative gene and de novo heterozygous variants as one of its two modes."
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, Usmani et al. identified and studied nine patients with de novo dominant missense, splice site, and frameshift variants and two patients with biallelic, recessive, and missense variants."
    explanation: "Enumerates the dominant allele classes - missense, splice site and frameshift - curated in this row."
  - reference: PMID:38665048
    reference_title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Next generation sequencing (NGS) analysis through clinical exome disclosed AP1G1: c.1969C>G (p.Leu657Val), de novo, likely pathogenic variant, according to ACMG classification criteria."
    explanation: "An independent de novo heterozygous AP1G1 allele in a separately ascertained patient."
diagnosis:
- name: Exome Sequencing
  description: >-
    Every published proband was ascertained by trio or singleton exome sequencing
    with variant interpretation against ACMG criteria. There is no biochemical or
    imaging marker for this disorder, so molecular testing is the diagnosis.
  diagnosis_term:
    preferred_term: clinical exome sequencing
    term:
      id: NCIT:C101295
      label: Whole Exome Sequencing
  evidence:
  - reference: PMID:38665048
    reference_title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Next generation sequencing (NGS) analysis through clinical exome disclosed AP1G1: c.1969C>G (p.Leu657Val), de novo, likely pathogenic variant, according to ACMG classification criteria."
    explanation: "Clinical exome sequencing is what made the diagnosis in this case."
- name: Genome Sequencing for Copy Number Variants
  description: >-
    Exome sequencing does not reliably resolve a whole-gene deletion. In the one
    reported deletion case, array CGH placed only a single probe inside AP1G1 and
    the call stayed a variant of uncertain significance for years; trio genome
    sequencing resolved the breakpoints and upgraded it to likely pathogenic.
    Genome sequencing is therefore the follow-on test when a 16q22.2 copy-number
    change is suspected.
  diagnosis_term:
    preferred_term: trio genome sequencing
    term:
      id: NCIT:C101294
      label: Whole Genome Sequencing
  evidence:
  - reference: PMID:38840441
    reference_title: "Whole genome sequencing for copy number variant detection to improve diagnosis and management of rare diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, the extent of the CNV and involvement of the AP1G1 gene was equivocal as only 1 out of 4 array CGH probes overlapped the gene"
    explanation: "States the limitation of array CGH that genome sequencing resolved in this case."
  - reference: PMID:38840441
    reference_title: "Whole genome sequencing for copy number variant detection to improve diagnosis and management of rare diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In all three cases, WGS identified CNVs and confirmed zygosity and pathogenicity, resulting in genetic diagnoses of PRKN-related Parkinson disease, TAOK1-related neurodevelopmental disorder, and AP1G1-related Usmani-Riazuddin syndrome."
    explanation: "Genome sequencing delivered the AP1G1 diagnosis where array CGH could not."
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Reported as a very rare condition. The founding series described eleven
    families; single additional patients have been reported since. No
    population-based prevalence or incidence estimate was found in the PubMed
    records searched for this entry (AP1G1 in title or abstract, 29 records;
    Usmani-Riazuddin anywhere, 3 records; searched 2026-09-18), so no rate is
    recorded here.
  evidence:
  - reference: PMID:38665048
    reference_title: "Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Usmani-Riazuddin syndrome (USRISR, MIM# 619548; USRISD, MIM#619467) is a very rare genetic condition."
    explanation: "Characterizes the condition as very rare, which is the basis for the ULTRA_RARE band."
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
    explanation: "Gives the size of the founding case series, eleven families, which is the literature count this record reports."
clinical_burden:
  burden_level: VARIABLE
  rationale: >-
    Intellectual disability spans mild to severe across the reported patients, and
    epilepsy, spasticity, hypotonia and congenital anomalies are variably present.
    Aggressive behavior, present in every patient of the founding cohort, is a
    substantial burden on families independent of cognitive severity. Survival and
    mortality are not characterized in the abstract-level sources cited here, so no
    burden claim is made about them either way.
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
    explanation: "The mild-to-severe range of intellectual disability is what makes the burden VARIABLE rather than a single level."
treatments:
- name: Antiseizure Medication
  description: >-
    Seizure management is symptom-directed. The published literature establishes
    that epilepsy occurs in this disorder but reports no AP1G1-specific drug
    choice or response pattern, so agent selection follows general epilepsy
    practice.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Anticonvulsant Therapy
    term:
      id: NCIT:C64172
      label: Anticonvulsant Therapy
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities"
    explanation: "Establishes epilepsy as a treatment target in this disorder. The source names no specific antiseizure agent or response."
- name: Developmental and Rehabilitative Therapy
  description: >-
    Physical, occupational and speech-language therapy directed at developmental
    delay, speech delay and tone abnormalities. Supportive and individualized; no
    disorder-specific rehabilitation protocol has been published.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: developmental and rehabilitative therapy
    term:
      id: NCIT:C15315
      label: Rehabilitation
  target_phenotypes:
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  - preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  - preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical phenotype is characterized by common signs such as intellectual disability, speech delay, developmental delay, hypotonia, and behavioral problems (mainly aggressive behavior), variably associated with congenital anomalies, epilepsy, spasticity, autism, bone abnormalities, vertebral and limb defects, and variable facial features (eyes and ear shape anomalies)."
    explanation: "Establishes developmental delay, speech delay and hypotonia as the rehabilitation targets. The source reports no rehabilitation protocol or outcome."
- name: Behavioral Management
  description: >-
    Structured behavioral intervention for aggression, hyperactivity and autistic
    features, which are the most consistent non-cognitive burden of this disorder.
    No pharmacological or behavioral regimen has been evaluated in AP1G1 patients.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: behavioral intervention
    term:
      id: NCIT:C181743
      label: Behavioral Counseling
  target_phenotypes:
  - preferred_term: Aggressive behavior
    term:
      id: HP:0000718
      label: Aggressive behavior
  - preferred_term: Autistic behavior
    term:
      id: HP:0000729
      label: Autistic behavior
  - preferred_term: Hyperactivity
    term:
      id: HP:0000752
      label: Hyperactivity
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "In 2021, 11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed in the cohort"
    explanation: "Aggressive behavior in every patient of the founding cohort is what makes behavioral management a core treatment target. No intervention study exists."
- name: Genetic Counseling
  description: >-
    Every proband of this dominant form reported so far carried a de novo variant,
    implying a low but non-zero sibling recurrence risk from gonadal mosaicism.
    Counseling also has to establish which AP1G1 disorder is in front of it, since
    the same gene causes a recessive disorder with a one in four sibling
    recurrence risk; the zygosity of the variants, not the gene, settles that.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations."
    explanation: "Establishes that both a de novo dominant and a biallelic recessive mode occur in this gene, which is the fact that drives recurrence-risk counseling."
animal_models:
- name: ap1g1 knockout zebrafish
  species: Zebrafish (Danio rerio)
  genotype: ap1g1 knockout generated by CRISPR/Cas9; homozygous null and heterozygous carriers
  category: Knockout
  background: Tg(neurod1:EGFP) reporter crossed in for neuronal population analysis
  publication: PMID:37108275
  description: >-
    Homozygous null embryos arrest at the blastula stage, so the informative
    genotype is the heterozygote - which is also the genotype that matches the
    dominant human disease. Heterozygous fish reach adulthood with reduced brain
    volume, missing neuronal populations in the midbrain, midbrain-hindbrain
    boundary and telencephalon, fewer spinal cord neurons, and dysregulated
    cadherin-mediated adhesion.
  modeled_mechanisms:
  - target: AP1G1 Haploinsufficiency
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      The heterozygous fish is a direct model of one-allele loss of ap1g1 and shows
      that this dosage alone produces a phenotype.
    limitations: >-
      Zebrafish ap1g1 is an ortholog rather than the human gene, and the
      heterozygous phenotype includes reduced fertility and gut and gonadal
      changes that are not reported features of the human disorder. The model
      addresses dosage only; it says nothing about the dominant missense alleles.
    readouts:
    - name: Total brain volume
      target: AP1G1 Haploinsufficiency
      direction: DECREASED
      interpretation: Reduced brain volume in the heterozygote is the structural correlate of the human neurodevelopmental phenotype.
      evidence:
      - reference: PMID:37108275
        reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "In our knockout model, the heterozygous fish displayed abnormalities in specific brain areas and spinal cord neurons, and the brain volume is reduced."
        explanation: "Reports the brain-volume reduction measured in heterozygous animals."
    evidence:
    - reference: PMID:37108275
      reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The zebrafish ap1g1 knock-out model revealed the indispensable function of the family of AP1 complexes for vertebrate development and that heterozygosity causes disease phenotypes."
      explanation: "States that heterozygosity is sufficient for disease phenotypes, which is what makes this model informative for the haploinsufficiency node."
  - target: Cadherin Mis-sorting and Adherens Junction Instability
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      The model identifies cadherin sorting and adherens junction formation as the
      concrete cargo defect downstream of reduced ap1g1.
    limitations: >-
      The cadherin defect was characterized in epithelial and gonadal tissue, not
      in neurons, and no corresponding cadherin measurement has been made in human
      AP1G1 patients.
    readouts:
    - name: Cadherin-mediated cell adhesion
      target: Cadherin Mis-sorting and Adherens Junction Instability
      direction: ALTERED
      interpretation: Marker-profile and morphology analysis identifies cadherin-mediated adhesion as dysregulated in the heterozygote.
      evidence:
      - reference: PMID:37108275
        reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "An analysis of mRNA profiles of different marker proteins and altered tissue morphologies revealed dysregulated cadherin-mediated cell adhesion."
        explanation: "The measurement behind this readout."
    evidence:
    - reference: PMID:37108275
      reference_title: "Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Interestingly, adult heterozygous fish showed impaired cell adhesion in epithelial tissues, such as cadherin protein sorting and adherent junction (AJ) formation."
      explanation: "Establishes that this model reports on cadherin sorting and adherens junction formation."
- name: Human AP1G1 mRNA rescue and overexpression zebrafish assay
  species: Zebrafish (Danio rerio)
  genotype: ap1g1-/- and wild-type embryos microinjected at the one-cell stage with human wild-type or mutant AP1G1 mRNA
  category: mRNA rescue and overexpression assay
  publication: PMID:41226632
  description: >-
    The assay used to distinguish a dominant-negative from a simple loss-of-function
    allele. Human wild-type AP1G1 mRNA rescues the ap1g1 null; mutant mRNA does
    not; and co-injecting both fails to rescue, which is the signature of
    interference with the wild-type product rather than of its mere absence.
  modeled_mechanisms:
  - target: Dominant-Negative Gamma-1 Adaptin Missense Protein
    relationship: PERTURBS
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Introducing the mutant human transcript into a vertebrate embryo tests
      directly whether the mutant protein is harmful in the presence of wild-type
      protein.
    limitations: >-
      This is transient mRNA microinjection at supraphysiological levels, not an
      engineered heterozygous allele, so the dose does not correspond to a patient
      heterozygote. It also cannot separate a dominant-negative effect from a toxic
      gain-of-function, which the authors state explicitly.
    readouts:
    - name: Larval locomotor activity
      target: Dominant-Negative Gamma-1 Adaptin Missense Protein
      direction: DECREASED
      interpretation: Reduced swum distance after mutant mRNA injection, against normal activity after wild-type mRNA injection.
      evidence:
      - reference: PMID:41226632
        reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Zebrafish larvae injected with WT AP1G1 mRNA displayed normal locomotor activity, whereas larvae injected with MUT AP1G1 exhibited a marked reduction in swum distance."
        explanation: "The locomotor measurement behind this readout, with the wild-type transcript as the internal control."
    evidence:
    - reference: PMID:41226632
      reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The phenotype was also not rescued when ap1g1-/- zebrafish embryos were co-injected with both human wild-type and mutated mRNAs, supporting the dominant-negative effect of the new variant."
      explanation: "The co-injection result is what makes this assay informative for a dominant-negative mechanism specifically."
  - target: Perturbed Neurodevelopment and Reduced Brain Growth
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: ORGANISM
    description: >-
      Mutant transcript injected into wild-type embryos produces developmental
      abnormalities and lethality, mirroring at organism level the developmental
      disruption the human dominant alleles cause.
    limitations: >-
      Zebrafish gross developmental abnormality and lethality are not the human
      phenotype: the patients have intellectual disability and behavioral
      abnormality with normal survival. The model reports that the allele is
      developmentally damaging, not that it reproduces the clinical picture.
    evidence:
    - reference: PMID:34102099
      reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Furthermore, microinjection of mRNAs with de novo missense variants in wild-type zebrafish resulted in severe developmental abnormalities and increased lethality."
      explanation: "The same assay applied to the original cohort's de novo missense alleles, with the same outcome."
- name: Ap1g1 (gamma-adaptin) knockout mouse
  species: Mouse (Mus musculus)
  genotype: Ap1g1 (gamma-adaptin) null; homozygous and heterozygous
  category: Knockout
  publication: PMID:10026148
  description: >-
    The mammalian counterpart of the zebrafish null. Homozygotes die before
    implantation, so again only the heterozygote is informative - and it is
    informative in a way no other model is, because AP-1 complex abundance was
    measured directly and found halved. The heterozygous mouse is not a model of
    the human neurodevelopmental phenotype; it is a model of the dosage step.
  modeled_mechanisms:
  - target: AP1G1 Haploinsufficiency
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      Quantifies what losing one gamma-1 adaptin allele does to the complex
      itself: AP-1 falls to half of control levels.
    limitations: >-
      The heterozygous mouse's reported phenotype is low body weight and impaired
      T cell development, not intellectual disability, seizures or behavioral
      abnormality, so the model establishes the molecular dosage effect without
      reproducing the human clinical picture. The report predates the human
      disorder by two decades and was not designed against it.
    readouts:
    - name: AP-1 complex abundance in heterozygotes
      target: AP1G1 Haploinsufficiency
      direction: DECREASED
      interpretation: One functional allele yields half the normal amount of assembled AP-1, which is the molecular content of the haploinsufficiency claim.
      evidence:
      - reference: PMID:10026148
        reference_title: "Early embryonic death of mice deficient in gamma-adaptin."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "In heterozygous mice the amount of AP-1 complexes is reduced to half of controls."
        explanation: "The direct measurement of AP-1 complex abundance at one gene copy."
    evidence:
    - reference: PMID:10026148
      reference_title: "Early embryonic death of mice deficient in gamma-adaptin."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "gamma-Adaptin-deficient embryos develop until day 3.5 post coitus and die during the prenidation period, revealing that AP-1 is essential for viability."
      explanation: "Establishes that gamma-1 adaptin is essential in a mammal, which is why the heterozygote rather than the null is the genotype relevant to a dominant human disorder."
- name: Ap1g1 figure eight (fgt) hypomorphic mouse
  species: Mouse (Mus musculus)
  genotype: Ap1g1 fgt, spontaneous in-frame 6 bp deletion, homozygous
  category: Hypomorph
  publication: PMID:27090238
  description: >-
    A spontaneous hypomorphic allele that survives to adulthood where the null
    does not, making it the only mammalian model in which partial AP-1 function
    can be studied past embryogenesis. Its phenotype is sensory, endocrine and
    reproductive rather than neurodevelopmental, which is itself informative about
    how much of the human picture partial loss does not explain.
  modeled_mechanisms:
  - target: AP-1 Adaptor Complex Dysfunction
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: ORGANISM
    description: >-
      Shows what reduced but non-zero gamma-1 adaptin function produces in a
      mammal across a whole lifespan.
    limitations: >-
      The reported abnormalities are inner ear, retina, thyroid and testes; none
      of these is a core feature of the human dominant disorder, and intellectual
      disability and seizures are not reported in this model. It is also a
      recessive hypomorph, so it does not model a heterozygous dominant allele.
    evidence:
    - reference: PMID:27090238
      reference_title: "A hypomorphic mutation of the gamma-1 adaptin gene (Ap1g1) causes inner ear, retina, thyroid, and testes abnormalities in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In contrast to Ap1g1 (-/-) null mice, mice homozygous for the recessive fgt mutation are viable with adult survival similar to controls."
      explanation: "Establishes the model as a viable partial-function system, which is what makes it informative for graded AP-1 dysfunction rather than for complete loss."
discussions:
- discussion_id: ad_ar_one_entity
  kind: OPEN_QUESTION
  status: OPEN
  prompt: >-
    Are the autosomal dominant and autosomal recessive AP1G1 disorders one disease
    with two inheritance modes, or two diseases that share a gene?
  attaches_to:
  - disease#Usmani-Riazuddin Syndrome, Autosomal Dominant
  - genetic#AP1G1
  rationale: >-
    They were delineated in one cohort, are described in the follow-up literature
    as showing overlapping clinical features, and both converge on one protein
    complex - which argues for a single entry. Against that: the functional
    evidence separates the allele classes, since the recessive missense proteins
    assemble normally into AP-1 and perturb endosomal recycling while the dominant
    missense proteins interfere with the wild-type subunit, and the dominant class
    also includes whole-gene deletions that can only act through dosage. No study
    has compared the two groups' phenotypes systematically; the only comparison in
    print is the qualitative statement that they overlap.
    They are curated as separate entries for a structural reason rather than a
    biological one: MONDO:0859174 and MONDO:0859196 are siblings under
    MONDO:0003847 with no umbrella term, so neither can be the other's parent, and
    a single entry would need either a new umbrella MONDO term or a
    `mappings.mondo_mappings` anchor plus a real curation pass over the recessive
    form. Resolving this question means doing that work or publishing the
    phenotype comparison, not re-reading the papers already cited here.
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Its dominant and recessive forms have been reported in a cohort of patients showing overlapping clinical features."
    explanation: "The published statement that the two inheritance forms overlap clinically, which is the argument for eventually merging them into one entry."
  - reference: PMID:34102099
    reference_title: "De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway."
    explanation: "The functional difference between the two allele classes, which is the argument against lumping."
- discussion_id: dominant_negative_vs_toxic_gof
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Do the dominant AP1G1 missense alleles act by dominant-negative interference
    with wild-type gamma-1 adaptin, or by a toxic gain of function?
  attaches_to:
  - pathophysiology#Dominant-Negative Gamma-1 Adaptin Missense Protein
  rationale: >-
    The evidence for a dominant effect is strong - co-injection of wild-type
    transcript does not rescue, and mutant transcript is damaging in a wild-type
    background - but both published groups state the two interpretations without
    separating them. The distinction matters therapeutically: a dominant-negative
    allele is a target for allele-selective knockdown, whereas haploinsufficiency
    from the same gene would call for dosage restoration, and the dominant allele
    classes in this disorder include both.
  evidence:
  - reference: PMID:41226632
    reference_title: "Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The observed phenotype is likely due to a dominant-negative effect or a toxic gain-of-function of the mutant AP1G1, impairing the activity or recruitment of the wild-type protein."
    explanation: "The authors state both interpretations as open, which is the gap this discussion records."

📚

References & Deep Research

References

7

PMID:34102099

De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy.

1 finding

De novo heterozygous and bi-allelic AP1G1 variants cause a neurodevelopmental disorder with mild to severe intellectual disability, epilepsy and developmental delay, established across eleven families.

PMID:41226632

Usmani-Riazuddin Syndrome: Functional Characterization of a Novel c.196G>A Variant in the AP1G1 Gene and Phenotypic Insights Using Zebrafish as a Vertebrate Model.

1 finding

A de novo AP1G1 missense allele leaves the trans-Golgi cisternae diffuse and disorganized in patient fibroblasts, and is not rescued by co-injected wild-type transcript in zebrafish, which supports a dominant-negative effect.

PMID:37108275

Deficiency of AP1 Complex Ap1g1 in Zebrafish Model Led to Perturbation of Neurodevelopment, Female and Male Fertility; New Insight to Understand Adaptinopathies.

1 finding

Zebrafish homozygous for ap1g1 loss arrest at the blastula stage, while heterozygotes survive with reduced brain volume, missing neuronal populations and dysregulated cadherin-mediated cell adhesion.

PMID:38665048

Usmani-Riazuddin syndrome can have a recognizable phenotype: Report of a novel AP1G1 variant.

1 finding

A second published patient with a de novo AP1G1 variant, carrying the first described distinctive facial features for this syndrome.

PMID:10026148

Early embryonic death of mice deficient in gamma-adaptin.

1 finding

Mice lacking gamma-1 adaptin die before implantation, and heterozygotes carry half the normal amount of assembled AP-1 complex, quantifying the dosage effect of losing one allele in a mammal.

PMID:27090238

A hypomorphic mutation of the gamma-1 adaptin gene (Ap1g1) causes inner ear, retina, thyroid, and testes abnormalities in mice.

1 finding

A spontaneous in-frame Ap1g1 deletion produces viable adult mice with inner ear, retina, thyroid and testes abnormalities, the only mammalian model of partial gamma-1 adaptin function surviving past embryogenesis.

PMID:38840441

Whole genome sequencing for copy number variant detection to improve diagnosis and management of rare diseases.

1 finding

A de novo whole-gene AP1G1 deletion at 16q22.2, resolved by trio genome sequencing after array CGH left it a variant of uncertain significance; the disorder's only reported pure dosage lesion.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Record notes

Entry scope. This entry curates the AUTOSOMAL DOMINANT form only (MONDO:0859174, OMIM 619467). MONDO carries a second AP1G1 term, MONDO:0859196 Usmani-Riazuddin syndrome, autosomal recessive (OMIM 619548). The two are SIBLINGS, not parent and child: both assert RO:0004003 to hgnc:555 AP1G1 and both sit directly under MONDO:0003847 hereditary disease, with no umbrella term over them (checked with `runoak -i sqlite:obo:mondo info MONDO:0859174 MONDO:0859196 -O obo`). The recessive form is therefore NOT represented here as a subtype - that would assert a hierarchy the ontology contradicts - and is carried in the curation queue instead as stubs/Usmani-Riazuddin_Syndrome_Autosomal_Recessive.yaml. Whether the two should eventually become one umbrella entry is a real open question and is recorded in `discussions`, not settled here: the founding cohort delineated both forms in one series and the follow-up literature calls their clinical features overlapping, but merging them would need either a new umbrella MONDO term or a `mappings.mondo_mappings` anchor, plus an actual curation pass over the recessive form. No mechanism module was applied. `just list-modules` was searched for trafficking, vesicle, Golgi, endosome, sorting and cargo modules, and `kb/modules/` was grepped for clathrin, adaptinopathy, AP-1 complex and trans-Golgi: the only hits are `synaptic_vesicle_cycle` (presynaptic AP-2 and clathrin-mediated synaptic vesicle endocytosis, not AP-1 sorting at the TGN) and `apical_neuroependyma_integrity_failure` (ventricular lining integrity). Neither describes AP-1-dependent cargo selection at the trans-Golgi network, so `conforms_to` was left unset rather than forced. No GeneReviews chapter exists for this disorder. This was checked offline with `just check-genereviews` against the committed Bookshelf index snapshot of 2026-09-10 (958 GeneReviews chapters indexed), which reports NO_CHAPTER for both GeneReviews and StatPearls. The phenotype baseline for this entry is therefore the primary literature rather than a review chapter. A deep-research pass was run against this entry (research/Usmani-Riazuddin_Syndrome_Autosomal_Dominant-deep-research-claude_code.md, provider claude_code). `just preflight-dr` returns PASS against MONDO:0859174 and the report's own reference validation reports 11/11 verified with a 0.0 confabulation rate. Reconciling it against this entry added the two mouse models (PMID:10026148, PMID:27090238) and the hyperactivity, hearing-impairment and vertebral phenotypes. Two of its claims were deliberately NOT taken up: the gnomAD constraint figures (pLI 1.0, LOEUF 0.2) and a neonatal death in the founding cohort are both attributed to PMID:34102099, whose cached record is abstract-only and contains neither, so neither is quotable and neither is asserted here.

Review round 1: split AD/AR into sibling entries, add deep-research artifact and references block · 2026-09-19T03:45:45Z · View source

Response to the ai4c-reviewer CHANGES_REQUESTED review on PR #12186. Three blocking findings, all taken. Finding 2 (structure) reversed the lump/split decision made in the CREATE record for this entry. The original entry was a single umbrella named Usmani-Riazuddin Syndrome, anchored on MONDO:0859174, carrying the dominant and recessive forms as has_subtypes rows. The reviewer's argument is correct and I had missed it: MONDO:0859174 and MONDO:0859196 are SIBLINGS, both directly under MONDO:0003847 with no umbrella term, so the recessive form cannot be a subtype of an entry whose own disease_term is the dominant term - and the entry's own notes said as much, contradicting its own structure. The first subtype row also duplicated the parent disease_term, which asserts the disease is a subtype of itself. Took the reviewer's route 1: the entry is now AD-only and renamed to kb/disorders/Usmani-Riazuddin_Syndrome_Autosomal_Dominant.yaml, matching the scope of claim issue #12177 and the name the original stub proposed. Both has_subtypes rows removed, the autosomal recessive inheritance block and the biallelic genetic row removed, and MONDO:0859196 nominated as stubs/Usmani-Riazuddin_Syndrome_Autosomal_Recessive.yaml so it stays visibly uncurated rather than being counted as covered by a hollow subtype row. The CREATE history record for this entry was moved into the new slug directory and its target.slug and target.path updated in place. It was created in this same unmerged PR and has never been on main, so this is a correction inside the PR rather than a rewrite of merged provenance; no superseded_by block was added, because there is no merged predecessor record to supersede. The OPEN_QUESTION discussion ad_ar_one_entity was rewritten rather than deleted. The biological argument for one entity is unchanged and still worth recording - one founding cohort, a published statement of overlapping clinical features, convergence on one complex - but the entry now records that the two are curated separately for a structural reason, and states what merging them would require: a new umbrella MONDO term or a mappings.mondo_mappings anchor, plus a real curation pass over the recessive form. Its attaches_to refs were repointed from has_subtypes# to disease# and genetic#. Finding 1 (deep research) ran the research-disorder recipe with the claude_code provider. Report and citations sidecar committed, along with the two reference-cache files the report cites that the entry does not (PMID:10811610 and the Clin Genet DOI record). The preflight-dr recipe returns PASS against MONDO:0859174; the report's own reference validation is 11 of 11 verified with a 0.0 confabulation rate. Reconciling it against the entry added two mouse models the entry had missed - PMID:10026148, the gamma-adaptin null whose heterozygote measures AP-1 complex abundance at half of controls, which is the direct molecular content of the haploinsufficiency claim, and PMID:27090238, the fgt hypomorph, the only mammalian partial-function model surviving past embryogenesis - plus three phenotypes (hyperactivity, hearing impairment, abnormal vertebral morphology) and an extra background evidence item on the AP-1 complex node. Hyperactivity was wired into the pathograph; hearing impairment and vertebral morphology were left unconnected with the reason stated in their descriptions, alongside facial shape and limb abnormality. Two deep-research claims were deliberately NOT taken up, and this is recorded in the entry notes: the gnomAD constraint figures (pLI 1.0, LOEUF 0.2) and a neonatal death in the founding cohort. Both are attributed by the report to PMID:34102099, whose cached record is abstract-only and contains neither string, so neither is quotable and neither is asserted. Reconciliation also caught a defect of my own: the clinical_burden rationale asserted that no mortality data have been published, an absence I had never searched. It now says only that survival is not characterized in the abstract-level sources cited here. Finding 3 (references) added the top-level references block with all seven cited PMIDs, each title copied from its references_cache frontmatter, tags set to the empty list because no GeneReviews chapter exists, and one Finding statement per reference. Also bundled: phenotype frequency values changed from the free-text band to the enum form VERY_FREQUENT, matching the dominant KB convention (4,536 uses against 42 of the free-text form). Same band, same evidence. The reviewer had explicitly cleared these as correctly sourced, so this is convention alignment, not a correction. Validation run before pushing: validate, validate-terms, count-verified-snippets at 81 of 81, validate-disorders, check-duplicate-keys, check-entity-refs, check-causal-targets, check-qualifier-terms, check-enum-values, check-folded-hyphens, check-snippet-length, check-title-snippets, check-snippet-grading, check-environmental-evidence, check-case-collisions, check-stubs, validate-stubs, check-reference-titles, check-genereviews, list-gene-term-mismatches, list-disconnected-phenotypes, validate-history-all, normalize-cache.

Claude Code ▸

1. Disease Information

claude-fable-5, claude-haiku-4-5-20251001 10 citations 2026-09-18T20:44:04.627676

1. Disease Information

Overview. Usmani-Riazuddin syndrome, autosomal dominant (USRISD) is an ultra-rare Mendelian neurodevelopmental disorder caused by heterozygous, almost always de novo, variants in AP1G1, which encodes the gamma-1 adaptin subunit of the heterotetrameric clathrin adaptor protein complex 1 (AP-1). The disorder was delineated in 2021 by Usmani, Riazuddin and colleagues (PMID:34102099), who reported de novo heterozygous and biallelic AP1G1 variants across eleven families: "De novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations." Core features are mild-to-severe intellectual disability, global developmental delay, speech delay, and aggressive behavior (each present in 100% of the founding cohort), with variable epilepsy, hypotonia, spasticity, autistic features, limb defects, and facial dysmorphism (PMID:34102099; PMID:41226632).

Key identifiers. | Resource | Identifier | |---|---| | OMIM (disease) | #619467 (USRISD) | | OMIM (gene) | *603533 (AP1G1) | | MONDO | MONDO:0859174 | | HGNC | hgnc:555 (AP1G1) | | Sibling disorder | Usmani-Riazuddin syndrome, autosomal recessive — OMIM #619548, MONDO:0859196 | | Orphanet | No dedicated ORPHA code identified for USRISD as of this report | | ICD-10 | No specific code; coded under manifestations (e.g., F70–F79 intellectual disability, G40 epilepsy) |

Important nosological note: MONDO treats the dominant (MONDO:0859174) and recessive (MONDO:0859196) forms as sibling terms, both asserting causation by AP1G1, with no umbrella term above them. The follow-up literature describes them as showing "overlapping clinical features" (PMID:41226632), but no systematic phenotype comparison between the two forms has been published, and functional data separate their allele mechanisms (see §6).

Synonyms. AP1G1-related neurodevelopmental disorder; USRISD; "adaptinopathy" is used in the zebrafish literature as an umbrella mechanism term for AP-complex subunit disorders (PMID:37108275).

Data provenance. All information derives from aggregated case reports and small cohort studies in the primary literature (11 founding families plus single subsequent probands — at least 13 patients total across both inheritance forms as of late 2025, per PMID:41226632). No EHR-derived, registry, or population-level data exist. No GeneReviews or StatPearls chapter exists for this disorder (verified against the NCBI Bookshelf index snapshot of 2026-09-10, 958 GeneReviews chapters).

2. Etiology

Causal factor. Monogenic: heterozygous pathogenic variants in AP1G1 (16q22.2). All published dominant probands carried de novo variants; no transmitted dominant pedigree has been reported. Reported dominant allele classes: missense (clustered in the N-terminal adaptin domain), splice-site, frameshift, and one whole-gene deletion (PMID:34102099; PMID:38840441; PMID:41226632).

Two mechanistic allele classes coexist under the dominant label: 1. Haploinsufficiency — frameshift alleles produce no detectable protein (proteasomally degraded), and a de novo whole-gene deletion at 16q22.2 produced the syndrome with "a mild but consistent phenotype" (PMID:38840441), the cleanest human evidence that halving dosage alone suffices. Consistent with this, AP1G1 is highly constrained: pLI = 1, LOEUF = 0.2 (PMID:34102099). 2. Dominant-negative missense — full-length misfolded gamma-1 adaptin interferes with the wild-type protein (see §6). "The observed phenotype is likely due to a dominant-negative effect or a toxic gain-of-function of the mutant AP1G1, impairing the activity or recruitment of the wild-type protein" (PMID:41226632).

Risk factors. No environmental, lifestyle, or infectious risk factors are known or plausible for this de novo monogenic disorder. Advanced paternal age is a generic risk factor for de novo point mutations but has not been specifically studied in USRISD. No modifier genes, protective variants, or gene–environment interactions have been reported. Consanguinity is relevant only to the sibling recessive form (the biallelic Pakistani family; PMID:34102099).

3. Phenotypes

Frequencies derive from the 2021 founding cohort of 11 patients and the 2025 cohort synthesis (PMID:34102099; PMID:41226632): "11 unrelated patients were described with mild to severe intellectual disability, speech delay, and aggressive behavior in 100% of the patients, while other aspects (including autism, epilepsy, hypotonia, spasticity, and limb defects) were variably expressed."

Phenotype	HPO term	Frequency	Onset / course
Intellectual disability	HP:0001249	100% (mild→severe)	Childhood; static-to-slowly-evolving
Global developmental delay	HP:0001263	100%	Infancy
Delayed speech and language development	HP:0000750	100%	Early childhood
Aggressive behavior	HP:0000718	100% (founding cohort)	Childhood; persistent
Seizure	HP:0001250	~70% of de novo patients	Variable; types not systematically reported
Hypotonia	HP:0001252	~60%	Infancy
Autistic behavior	HP:0000729	~50%	Childhood
Spasticity	HP:0001257	Variable	—
Hyperactivity	HP:0000752	Variable	Childhood
Self-injurious behavior	HP:0100716	Reported (individual cases)	Infancy-onset in one proband
Abnormality of limbs	HP:0040064	Variable	Congenital
Abnormal facial shape	HP:0001999	Variable/preliminary	Congenital
Abnormal vertebral morphology	HP:0003468	Variable	Congenital
Hearing impairment	HP:0000365	Individual case (frameshift proband)	—

Additional per-patient detail. In the 2025 proband (c.196G>A, p.Gly66Arg): 12-year-old girl, independent walking at 18 months, <10 words at age 3, verbal IQ 53 / performance IQ 59 / full-scale 49, aggression toward peers and adults, hyperactivity, obsessive-compulsive behaviors, one febrile seizure at age 2 with normal EEG and brain MRI (PMID:41226632). The whole-gene-deletion patient presented at 5–10 years with "developmental delay, behavioural difficulties, possible infantile spasms, left hemiplegia, and toe walking" (PMID:38840441).

Facial gestalt (preliminary). A single 2024 report proposed a recognizable gestalt — synophrys, hypotelorism, upslanted palpebral fissures, broad nasal tip, thick lip vermilion: "this is the first description of likely distinctive facial features in a patient with Usmani-Riazuddin syndrome" (PMID:38665048). This rests on one patient; the founding series described the facial gestalt as "unspecified."

Quality of life. No formal QoL instrument (EQ-5D, SF-36, PROMIS) has been applied. The universal aggressive behavior represents a substantial family burden independent of cognitive severity; no formal caregiver-burden study exists.

4. Genetic/Molecular Information

Gene. AP1G1 (adaptor related protein complex 1 subunit gamma 1), hgnc:555, OMIM 603533, chromosome 16q22.2. Encodes gamma-1 adaptin, one of four subunits (γ, β1, μ1, σ1) of the AP-1 clathrin adaptor. Constraint: pLI = 1.0, LOEUF = 0.2 — "AP1G1 is highly intolerant to variations"* (PMID:34102099).

Reported dominant (de novo heterozygous) variants (PMID:34102099, plus later reports):

cDNA	Protein	Type	Origin	Notes
c.44G>A	p.Arg15Gln	Missense	De novo	Moderate ID, epilepsy, aggression, hypotonia
c.103C>T	p.Arg35Trp	Missense	De novo (2 families)	Recurrent; mild–moderate ID, epilepsy
c.104G>A	p.Arg35Gln	Missense	De novo	ASD, self-injurious behavior
c.196G>A	p.Gly66Arg	Missense	De novo	2025 proband; dominant-negative evidence (PMID:41226632)
c.229delC	p.Gln77Lysfs*11	Frameshift	De novo	Mild ID, hearing loss, depression/anxiety
c.399_400del	p.Glu133Aspfs*37	Frameshift	De novo	Moderate ID, hypotonia, aggression/autism
c.747G>T	p.Gln249His	Missense	De novo	Patient died at 22 days (phenotype otherwise unavailable)
c.928−2A>C	p.?	Splice acceptor	De novo	Mild ID, autism, hyperactivity
c.1969C>G	p.Leu657Val	Missense	De novo	Likely pathogenic per ACMG (PMID:38665048)
c.2459C>G	p.Pro820Arg	Missense (C-terminal)	De novo	Moderate ID, aggression
16q22.2 whole-gene deletion	—	CNV	De novo	Mild phenotype; WGS-diagnosed (PMID:38840441)

Pathogenic dominant missense variants cluster in the N-terminal adaptin domain at highly conserved residues (Arg15, Arg35, Gly66) with two exceptions (Gln249, Pro820, Leu657) (PMID:41226632). Classification followed ACMG/AMP criteria in all recent reports.

Allele frequency. Dominant pathogenic variants are absent from gnomAD, dbSNP, and ESP (PMID:41226632); only the recessive c.1105A>G allele appears in gnomAD (7 heterozygous carriers, AF ≈ 1.67 × 10⁻⁵) (PMID:34102099).

Functional consequences by class. Immunoblot in heterologous cells: p.Arg15Gln, p.Arg35Trp show decreased protein levels; frameshift alleles produce undetectable, proteasomally degraded protein; de novo missense proteins form aggregates or show diffuse cytoplasmic localization, versus normal perinuclear clathrin-colocalized distribution for the recessive missense proteins (PMID:34102099). "In silico analysis and 3D protein modeling simulation predicted alteration of AP1γ1 protein folding for missense variants, which was consistent with the observed altered AP1γ1 levels in heterologous cells" (PMID:34102099).

Germline vs somatic. All variants are germline, arising de novo. Germline (gonadal) mosaicism has not been reported but is the standard residual recurrence-risk consideration. No epigenetic mechanisms, modifier genes, or larger chromosomal rearrangements (beyond the single-gene deletion) are described.

Gene–disease validity (GenCC, accessed 2026-09-18): AP1G1–USRISD (AD) is classified Strong by Labcorp Genetics (2023) and G2P (2025); ClinGen classifies AP1G1–complex neurodevelopmental disorder (AD) as Strong (2026); PanelApp Australia lists it as semidominant (Strong, 2026). The AR association is Strong (Labcorp) but Limited per G2P and ClinGen.

5. Environmental Information

Not applicable. USRISD is a fully penetrant-appearing de novo monogenic disorder with no known environmental, lifestyle, or infectious contributors. One anecdotal observation — behavioral improvement during antibiotic therapy extending beyond acute infections in the 2025 proband (PMID:41226632) — is uninterpreted and should not be read as an environmental mechanism.

6. Mechanism / Pathophysiology

Ordered causal chain (dominant form):

De novo heterozygous AP1G1 variant — either (branch A) a truncating/splice/whole-gene-deletion allele that eliminates one gene copy (haploinsufficiency; demonstrated), or (branch B) an N-terminal missense allele producing a misfolded gamma-1 adaptin that interferes with the wild-type protein (dominant-negative vs. toxic gain-of-function not yet separated; inferred from rescue-failure assays) —
→ leads to AP-1 adaptor complex dysfunction (GO:0030121; reduced AP-1-mediated cargo loading into clathrin-coated vesicles, GO:0035653). "The AP1γ1-mediated adaptor complex is essential for the formation of clathrin-coated intracellular vesicles" (PMID:34102099); AP-1 and AP-2 are the only clathrin-coat-forming adaptors, so loss is not buffered (PMID:37108275).
→ results in trans-Golgi network cargo-sorting failure (GO:0005802; GO:0006895). Demonstrated in patient fibroblasts: "although GM130 labeling remained comparable to that in the controls, the organization of the trans-Golgi cisternae appeared more diffuse and disorganized"; the mutant protein "disrupts membrane association and impairs vesicular trafficking at the trans-Golgi level" (PMID:41226632).
→ (parallel branch, demonstrated only for recessive alleles) endosomal recycling impairment (GO:0032456): "Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway" (PMID:34102099). Whether dominant alleles engage this step is untested — an inferred, not demonstrated, branch for USRISD.
→ leads to impaired polarized somatodendritic protein sorting in neurons (GO:0036477; CL:0000540): "Adaptor protein (AP) complexes mediate selective intracellular vesicular trafficking and polarized localization of somatodendritic proteins in neurons" (PMID:34102099). The brain is "the tissue with the most active vesicular protein transport" (PMID:37108275) — explaining why a ubiquitous trafficking lesion presents neurologically.
→ in parallel, cadherin mis-sorting and adherens junction instability (GO:0044331; GO:0034332): heterozygous ap1g1 zebrafish show "dysregulated cadherin-mediated cell adhesion" and impaired "cadherin protein sorting and adherent junction (AJ) formation" (PMID:37108275) — the best-characterized individual cargo defect.
→ results in perturbed neurodevelopment and reduced brain growth (GO:0007420; GO:0030182; UBERON:0000955): in heterozygous zebrafish, "the heterozygous fish displayed abnormalities in specific brain areas and spinal cord neurons, and the brain volume is reduced" (PMID:37108275); mutant human mRNA in wild-type embryos causes "severe developmental abnormalities and increased lethality" (PMID:34102099).
→ clinically manifests as intellectual disability, developmental/speech delay, aggression, seizures, hypotonia, spasticity, autistic features (all links from step 7 to specific clinical features are inferred — no intermediate circuit-level mechanism has been measured in humans).

Dominant-negative evidence in detail (PMID:41226632): wild-type human AP1G1 mRNA rescues ap1g1⁻/⁻ zebrafish lethality; mutant (p.Gly66Arg) mRNA does not; and critically, "the phenotype was also not rescued when ap1g1-/- zebrafish embryos were co-injected with both human wild-type and mutated mRNAs, supporting the dominant-negative effect." The same design in 2021 showed the founding de novo alleles (p.Arg15Gln, p.Arg35Trp, p.Arg35Gln) failed rescue and were toxic in wild-type fish, while the recessive alleles gave partial rescue (hypomorphs) (PMID:34102099). Both groups explicitly leave dominant-negative vs toxic gain-of-function unresolved — a key knowledge gap, with therapeutic implications (allele-selective knockdown vs dosage restoration).

Molecular profiling. No patient transcriptomics, proteomics, metabolomics, single-cell, or spatial data exist. Zebrafish heterozygote mRNA marker profiling identified the cadherin-adhesion signature (PMID:37108275).

7. Anatomical Structures Affected

Primary organ: brain (UBERON:0000955), with spinal cord involvement in the animal model (UBERON:0002240); affected regions in the zebrafish heterozygote include telencephalon, midbrain, midbrain-hindbrain boundary, and spinal cord neuronal populations (PMID:37108275).
Secondary/variable: skeleton — limbs and vertebrae (UBERON:0002101, UBERON:0002412); face (UBERON:0001456); musculature via tone abnormalities. The zebrafish heterozygote additionally shows gonadal and intestinal epithelial changes not reported in humans (PMID:37108275).
Cell types: neurons (CL:0000540); patient dermal fibroblasts (CL:0000057) as the demonstrated cellular substrate; epithelial cells in the model.
Subcellular: trans-Golgi network (GO:0005802), clathrin-coated vesicles (GO:0030136), recycling endosomes (GO:0055037), AP-1 adaptor complex (GO:0030121), somatodendritic compartment (GO:0036477). The cis-Golgi is spared (GM130 normal; PMID:41226632).
Lateralization: generally bilateral/symmetric; one patient (deletion case) had left hemiplegia (PMID:38840441).

8. Temporal Development

Onset: congenital lesion; clinical recognition in infancy to early childhood via delayed milestones (walking at 18 months, <10 words at age 3 in the 2025 proband). One founding-cohort patient (p.Gln249His) died at 22 days, suggesting the severe end can present neonatally (PMID:34102099).
Course: chronic, lifelong. Intellectual disability appears largely static, though one patient (p.Pro820Arg) was described with decreasing cognitive scores through adolescence (PMID:34102099). Behavioral features (aggression, hyperactivity) persist into adolescence. Epilepsy course is variable and not systematically characterized. No remission pattern, staging system, or natural-history study exists.
Critical periods: by mechanism, prenatal/early postnatal neurodevelopment — zebrafish data show "normal expression of ap1g1 at early stages of neurodevelopment is required for determination and/or differentiation of specific neuronal populations" (PMID:37108275). Early developmental therapy is the corresponding intervention window (inference, not trial-based).

9. Inheritance and Population

Inheritance: autosomal dominant (HP:0000006), with all reported dominant probands arising de novo. No transmitted pedigree; no anticipation; no founder effect; no documented germline mosaicism. Sibling recurrence risk is low but non-zero (gonadal mosaicism). Distinguish carefully from the AR sibling disorder (25% sibling recurrence): zygosity, not the gene, settles the counseling.
Penetrance/expressivity: apparently complete penetrance in reported cases (ascertainment-limited); variable expressivity is marked — ID spans mild to severe, epilepsy present in only ~70%, and the whole-gene deletion produced a mild phenotype, hinting that dominant-negative missense alleles may be more severe than pure dosage loss (inference from small numbers; PMID:38840441).
Epidemiology: ultra-rare; ≥13 patients across both forms reported in the world literature through 2025 (PMID:41226632); "Usmani-Riazuddin syndrome (USRISR, MIM# 619548; USRISD, MIM#619467) is a very rare genetic condition" (PMID:38665048). No prevalence or incidence estimate exists.
Demographics: reported families span Germany, Poland, the Netherlands, the USA, and Italy for the dominant form — "diverse populations" (PMID:34102099). No sex bias is evident (both sexes affected); numbers are far too small for ratios.

10. Diagnostics

Primary modality: molecular. There is no biochemical or imaging biomarker; every published proband was diagnosed by trio or singleton exome sequencing with ACMG interpretation (NCIT:C101295, Whole Exome Sequencing). Example: "clinical exome disclosed AP1G1: c.1969C>G (p.Leu657Val), de novo, likely pathogenic variant, according to ACMG classification criteria" (PMID:38665048).
Genome sequencing for CNVs (NCIT:C101294): exome misses whole-gene deletions. In the deletion case, array CGH placed "only 1 out of 4 array CGH probes" over AP1G1, leaving a VUS for years until trio WGS resolved the breakpoints (PMID:38840441). WGS is the follow-on test for suspected 16q22.2 CNVs.
Gene panels: AP1G1 appears on neurodevelopmental-disorder panels (PanelApp Australia lists it, semidominant, Strong).
Supportive workup: EEG for seizures, brain MRI (normal in the 2025 proband; agenesis of the corpus callosum was reported in a recessive patient), standardized cognitive testing (Wechsler-type IQ), behavioral assessment. Karyotype, FISH, mtDNA, repeat-expansion, and omics-based diagnostics have no specific role.
Differential diagnosis: other monogenic NDDs with ID + aggression + variable epilepsy; other "adaptinopathies" (AP1S2 X-linked ID/Pettigrew syndrome, AP4 deficiency spectrum, AP3 Hermansky-Pudlak type 2, AP2M1 epilepsy); distinction is molecular. The proposed facial gestalt (PMID:38665048) may eventually aid recognition but needs multicenter confirmation.
Screening: none applicable (de novo disorder; no newborn or carrier screening). Prenatal/PGT testing is technically possible for a known familial variant.

11. Outcome / Prognosis

Survival: no mortality data published. Most patients survive to adolescence/young adulthood (oldest reported dominant patients ~18 years at description); one neonatal death at 22 days occurred in a p.Gln249His proband, cause-specific attribution unclear (PMID:34102099).
Function/morbidity: lifelong intellectual disability (mild–severe), communication impairment, and behavioral disturbance dominate morbidity. Aggression in 100% of the founding cohort is the major determinant of family burden. Hemiplegia, toe-walking, spasticity, and hearing loss add motor/sensory disability in individual patients.
Prognostic factors (provisional, small-N inference): allele class may matter — the whole-gene deletion produced "a mild but consistent phenotype" (PMID:38840441), while dominant-negative missense alleles associate with moderate–severe presentations. No validated prognostic biomarker exists.
QoL measures: none published.

12. Treatment

No disease-modifying or AP1G1-specific therapy exists. Management is entirely symptomatic and supportive (no clinical trials identified on ClinicalTrials.gov for this indication):

Intervention	NCIT term	Target
Antiseizure medication (agent per general epilepsy practice; no AP1G1-specific response data)	NCIT:C64172 Anticonvulsant Therapy	Seizures (HP:0001250)
Developmental/rehabilitative therapy — physical, occupational, speech-language	NCIT:C15315 Rehabilitation; NCIT:C159273 Speech Therapy	GDD, speech delay, hypotonia
Behavioral intervention for aggression, hyperactivity, autistic features	NCIT:C181743 Behavioral Counseling	Aggression (HP:0000718), autistic behavior
Genetic counseling (de novo recurrence risk; AD-vs-AR disambiguation)	NCIT:C15240 Genetic Counseling	Family

Future directions (preclinical only): the zebrafish platform is explicitly positioned for therapeutic development — "zebrafish...holds promise for identifying genetic and molecular targets" (PMID:41226632). Mechanistically, the unresolved dominant-negative vs haploinsufficiency question bifurcates future strategy: allele-selective knockdown (ASO/siRNA) for interfering missense alleles versus dosage restoration for null alleles. Nothing of the kind has entered even preclinical pipelines. No pharmacogenomic data exist.

13. Prevention

Primary prevention: none possible (sporadic de novo variants).
Secondary: early molecular diagnosis via exome/genome sequencing in undiagnosed NDD enables early developmental intervention and ends the diagnostic odyssey (the deletion case sat as a VUS for years; PMID:38840441).
Tertiary: seizure control, behavioral management, and rehabilitation to limit complications.
Reproductive: genetic counseling for parents of an affected child (low recurrence risk with a gonadal-mosaicism caveat); prenatal diagnosis or PGT feasible for the known variant. Cascade screening is not relevant for de novo dominant alleles.

14. Other Species / Natural Disease

No naturally occurring AP1G1 disease is documented in companion animals or wildlife (no OMIA phene identified). The gene is deeply conserved across vertebrates (NCBITaxon:7955 zebrafish and NCBITaxon:10090 mouse orthologs used experimentally; mouse Ap1g1, NCBI Gene 11765). Comparative biology insight comes from engineered models (§15): conservation is strong enough that human wild-type AP1G1 mRNA rescues the zebrafish ap1g1 null (PMID:41226632), directly demonstrating functional orthology. Zoonotic transmission is not applicable.

15. Model Organisms

Zebrafish (Danio rerio): 1. CRISPR/Cas9 ap1g1 knockout (PMID:37108275): homozygous nulls arrest at the blastula stage (in the 2021 line, ~84% lethality by 10 dpf with severe edema; PMID:34102099); heterozygotes are the informative genotype, matching the human dominant state — they survive with reduced brain volume, missing neuronal populations (telencephalon, midbrain, midbrain-hindbrain boundary, spinal cord), reduced fertility, and dysregulated cadherin-mediated adhesion: "heterozygosity causes disease phenotypes." Limitations: gut/gonadal phenotypes lack human counterparts; models dosage only, not the missense alleles. 2. mRNA rescue/co-injection assay (PMID:34102099; PMID:41226632): human WT mRNA rescues the null (p<0.0001); patient missense mRNAs fail to rescue; recessive alleles partially rescue (hypomorphs); WT + mutant co-injection fails to rescue — the operational dominant-negative test. Limitation: transient supraphysiological mRNA, cannot separate dominant-negative from toxic gain-of-function.

Mouse (Mus musculus): 3. γ-adaptin knockout (Zizioli et al. 1999, PMID:10026148): homozygous null embryos die by E3.5, before implantation — "AP-1 is essential for viability"; notably, heterozygous mice show reduced growth during nursing, an early mammalian signal of dosage sensitivity consistent with human haploinsufficiency. 4. Hypomorphic Ap1g1 mouse ("fitful" allele) (PMID:27090238): causes inner ear, retina, thyroid, and testes abnormalities — partial-function phenotypes that broaden the adaptinopathy spectrum, though they diverge from the human neurodevelopmental picture. 5. Comparative: μ1A-adaptin-deficient mice are also embryonic lethal with mannose-6-phosphate receptor rerouting (PMID:10811610), confirming subunit-level essentiality of AP-1.

Cellular models: patient dermal fibroblasts (trans-Golgi disorganization, loss of membrane-associated AP1G1; PMID:41226632) and heterologous expression systems (protein levels, aggregation, clathrin colocalization, transferrin-recycling assays; PMID:34102099). No iPSC-derived neuronal or organoid model has been published — a clear gap given the neuronal locus of disease.

Key Knowledge Gaps

Dominant-negative vs toxic gain-of-function for the missense alleles — explicitly unresolved by both functional groups (PMID:41226632); determines the rational therapeutic strategy.
One disease or two? No systematic phenotype comparison of the AD and AR forms exists; only the qualitative statement that features "overlap."
Whether dominant alleles impair endosomal recycling (measured only for recessive alleles).
No natural-history study, prevalence estimate, mortality data, QoL measurement, seizure phenotyping, or human neuronal model.
The proposed facial gestalt rests on a single patient and awaits multicenter confirmation (PMID:38665048).

Primary Citations

Usmani MA, Riazuddin S, et al. Am J Hum Genet 2021 — founding cohort. PMID:34102099
Zizioli D, et al. Int J Mol Sci 2023 — ap1g1 KO zebrafish. PMID:37108275
Gnazzo M, et al. Clin Genet 2024 — facial gestalt, p.Leu657Val. PMID:38665048
(WGS CNV study) 2024 — whole-gene deletion case. PMID:38840441
(Functional study of c.196G>A) Int J Mol Sci 2025 — dominant-negative characterization. PMID:41226632
Zizioli D, et al. J Biol Chem 1999 — γ-adaptin-null mouse. PMID:10026148
Johnson KR, et al. Mamm Genome 2016 — hypomorphic Ap1g1 mouse. PMID:27090238

Sources: - OMIM #619467 — Usmani-Riazuddin syndrome, autosomal dominant - OMIM #619548 — Usmani-Riazuddin syndrome, autosomal recessive - OMIM *603533 — AP1G1 - Usmani et al. 2021, AJHG (PMC8322935) - 2025 IJMS c.196G>A functional study (PMC12610428) - Gnazzo et al. 2024, Clinical Genetics - GenCC — AP1G1 gene-disease validity - Zizioli et al. 1999, JBC — γ-adaptin-deficient mice (PubMed) - Johnson et al. 2016, Mammalian Genome — hypomorphic Ap1g1 mouse - μ1A-adaptin-deficient mice (PubMed)

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	11
Resolved	11
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	11
On topic	9
Off topic	1

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

PMID:10811610 (3 mentions) - mu1A-adaptin-deficient mice: lethality, loss of AP-1 binding and rerouting of mannose 6-phosphate receptors.
shared terms: gene

Weighed against this report's own most characteristic terms: dominant, patient, ap1g1, novo, allele, dominant-negative, phenotype, gene, proband, missense, zebrafish, deletion, recessive, exist, syndrome, variant, aggression, epilepsy, usrisd, clinical.

All extracted references resolved successfully. Resolving is not the same as being relevant, though - see the references listed above as possibly off topic.

Term Validation

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

Outcome	Count
Terms checked	46
Resolved	45
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	1
Terms whose name was checked	21
Terms named correctly	15
Terms named as a different term	2
Terms whose name is worth a second look	4

Terms the report names something else

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

MONDO:0859174 (3 mentions) - the report calls it "MONDO"; MONDO calls it Usmani-Riazuddin syndrome, autosomal dominant
UBERON:0000955 (2 mentions) - the report calls it "Primary organ: brain"; UBERON calls it brain**

Terms whose name is worth a second look

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

GO:0005802 (2 mentions) - the report calls it "Subcellular: trans-Golgi network"; GO calls it trans-Golgi network**
GO:0032456 (1 mention) - the report calls it "endosomal recycling impairment"; GO calls it endocytic recycling
CL:0000540 (2 mentions) - the report calls it "Cell types: neurons"; CL calls it neuron**
NCIT:C101294 (1 mention) - the report calls it "Genome sequencing for CNVs"; NCIT calls it Whole Genome Sequencing

Terms named inconsistently

The report gives these identifiers more than one name of its own:

HP:0000718 - called "Aggressive behavior", "Aggression"
HP:0001250 - called "Seizure", "Seizures"

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Deep Research

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Key Knowledge Gaps

Primary Citations

Reference Validation

References that may not be about this subject

Term Validation

Terms the report names something else

Terms whose name is worth a second look

Terms named inconsistently