Asparagine synthetase deficiency

Mendelian MONDO:0014258 Pathograph 25 Show in embeddings browser Inborn error of metabolism Inborn error of amino acid metabolism

Asparagine synthetase deficiency (ASNSD) is an ultra-rare autosomal recessive neurometabolic disorder caused by biallelic pathogenic variants in ASNS. ASNS catalyzes ATP-dependent synthesis of asparagine from aspartate, using glutamine as the nitrogen donor. The severe end of the spectrum presents congenitally or neonatally with progressive microcephaly, profound developmental impairment, axial hypotonia followed by spastic quadriplegia, early seizures, and cerebral atrophy; later-onset, milder disease is also documented. Plasma and cerebrospinal-fluid asparagine can be low but are not invariably abnormal, so molecular testing is central to diagnosis. Impaired cellular adaptation to limited extracellular asparagine is supported by patient-derived cells. A proposed contribution from cerebral aspartate/glutamate accumulation remains hypothetical and is not treated as an established mechanism.

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1
Mappings
1
Inheritance
7
Pathophys.
12
Phenotypes
2
Hypotheses
25
Pathograph
1
Genes
6
Medical Actions
4
Differentials
13
References
🔗

Mappings

MONDO
MONDO:0014258 congenital microcephaly - severe encephalopathy - progressive cerebral atrophy syndrome
skos:exactMatch MONDO
MONDO exact match for OMIM:615574 and Orphanet:391376, with ASNS as the causal gene.
👪

Inheritance

1
Autosomal recessive HP:0000007
Disease results from biallelic pathogenic or likely pathogenic ASNS variants. Heterozygous carriers are asymptomatic; when both parents are carriers, each pregnancy has a 25% recurrence risk.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:24139043 SUPPORT Human Clinical
"the observed phenotype in all four families can be explained by autosomal recessive deficiency of asparagine synthetase (ASNS)"
The original families establish autosomal recessive inheritance.
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"each sib of an affected individual has at conception a 25% chance of being affected"
Current GeneReviews provides the recurrence-risk counseling statement.
◈

Mechanistic Hypotheses

2
Context-dependent cellular asparagine insufficiency model
asparagine_insufficiency_model CANONICAL
Evidence balance 2 support
Reduced ASNS activity limits de novo asparagine synthesis. Cells in environments with limited extracellular asparagine, especially within the developing nervous system, cannot fully compensate, impairing proliferation and broader metabolism and contributing to abnormal brain growth.
Pathograph links
Biallelic ASNS Functional Deficiency -> Reduced De Novo Asparagine Synthesis DIRECT Reduced ASNS catalytic activity directly lowers capacity for de novo asparagine synthesis.
Reduced De Novo Asparagine Synthesis -> Context-Dependent Cellular Asparagine Insufficiency DIRECT Reduced synthesis becomes limiting when extracellular asparagine availability is low.
Context-Dependent Cellular Asparagine Insufficiency -> Impaired Cortical Development and Brain Growth INDIRECT UNKNOWN INTERMEDIATES A cellular growth defect is proposed to impair neural progenitor expansion and post-mitotic cell survival during brain development.
Impaired Cortical Development and Brain Growth -> Progressive microcephaly DIRECT Reduced prenatal and postnatal brain growth manifests as progressive microcephaly.
Impaired Cortical Development and Brain Growth -> Cerebral atrophy DIRECT Loss of cerebral volume and progressive atrophy are structural consequences of impaired brain growth and injury.
Impaired Cortical Development and Brain Growth -> Global developmental delay INDIRECT UNKNOWN INTERMEDIATES Abnormal cortical development produces severe impairment across developmental domains.
Impaired Cortical Development and Brain Growth -> Axial hypotonia INDIRECT UNKNOWN INTERMEDIATES Central neurologic dysfunction contributes to axial hypotonia.
Impaired Cortical Development and Brain Growth -> Spasticity INDIRECT UNKNOWN INTERMEDIATES Progressive central motor-system dysfunction manifests as appendicular spasticity or spastic quadriplegia.
Impaired Cortical Development and Brain Growth -> Cortical visual impairment INDIRECT UNKNOWN INTERMEDIATES Cerebral visual pathway dysfunction can produce cortical visual impairment.
Impaired Cortical Development and Brain Growth -> Epileptic Network Dysfunction INDIRECT UNKNOWN INTERMEDIATES Abnormal cortical development and progressive structural injury can create epileptogenic networks.
Impaired Cortical Development and Brain Growth -> Neurologic Swallowing and Respiratory Dysfunction INDIRECT UNKNOWN INTERMEDIATES Severe central neurologic impairment can compromise swallowing, airway protection, and respiratory function.
Epileptic Network Dysfunction -> Intractable seizures DIRECT The epileptic network state manifests as recurrent, often refractory seizures.
Epileptic Network Dysfunction -> Status epilepticus DIRECT Severe seizure burden can progress to status epilepticus.
Epileptic Network Dysfunction -> Myoclonus DIRECT Epileptic and nonepileptic network instability can manifest as persistent myoclonus.
Epileptic Network Dysfunction -> Exaggerated startle response INDIRECT UNKNOWN INTERMEDIATES Network hyperexcitability may contribute to the hyperekplexia-like startle phenotype.
Neurologic Swallowing and Respiratory Dysfunction -> Feeding difficulties DIRECT Swallowing and gastroesophageal dysfunction directly impair safe feeding and nutrition.
Neurologic Swallowing and Respiratory Dysfunction -> Respiratory insufficiency DIRECT Apnea, aspiration, and impaired respiratory control can culminate in respiratory insufficiency.
Show evidence (2 references)
PMID:26318253 SUPPORT In Vitro
"there is markedly reduced proliferation of patient fibroblasts when cultured in asparagine-limited growth medium"
Patient fibroblasts directly demonstrate context-dependent cellular vulnerability.
PMID:37111157 SUPPORT In Vitro
"significant decrements in TCA cycle intermediates and anaplerotic substrates in ASNS-deficient cells challenged with Asn deprivation"
Independent patient-derived cell models show wider metabolic consequences during asparagine deprivation.
Proposed cerebral excitatory amino-acid imbalance model
excitatory_amino_acid_model ALTERNATIVE
Evidence balance 2 support
Aspartate and/or glutamate accumulation has been proposed to enhance excitability and neuronal injury. The observation is neither consistent across patients nor directly demonstrated in affected human brain, and glutamate is a reaction product rather than an unused substrate. This model is therefore retained as an alternative hypothesis only.
Pathograph links
Reduced De Novo Asparagine Synthesis -> Proposed Cerebral Excitatory Amino-Acid Imbalance INDIRECT UNKNOWN INTERMEDIATES Altered pathway flux has been proposed to increase excitatory amino acids in brain, but the intermediates and consistency are unresolved.
Proposed Cerebral Excitatory Amino-Acid Imbalance -> Epileptic Network Dysfunction INDIRECT UNKNOWN INTERMEDIATES Putative excitatory amino-acid imbalance could promote seizures, but direct evidence in ASNSD brain is lacking.
Epileptic Network Dysfunction -> Intractable seizures DIRECT The epileptic network state manifests as recurrent, often refractory seizures.
Epileptic Network Dysfunction -> Status epilepticus DIRECT Severe seizure burden can progress to status epilepticus.
Epileptic Network Dysfunction -> Myoclonus DIRECT Epileptic and nonepileptic network instability can manifest as persistent myoclonus.
Epileptic Network Dysfunction -> Exaggerated startle response INDIRECT UNKNOWN INTERMEDIATES Network hyperexcitability may contribute to the hyperekplexia-like startle phenotype.
Show evidence (2 references)
PMID:24139043 SUPPORT Human Clinical
"These features suggest a mechanism that is consistent with the accumulation of aspartate/glutamate in the brain"
The original report explicitly presents accumulation as a suggested mechanism.
PMID:27522229 SUPPORT Human Clinical
"possibly related to cytotoxic glutamate accumulation"
A two-sibling neuropathology report also frames glutamate accumulation as possible, not established.
⚙

Pathophysiology

7
Biallelic ASNS Functional Deficiency
Mechanism confidence: Established
Biallelic pathogenic ASNS variants reduce protein abundance, catalytic performance, or both. The initiating lesion is deficient glutamine-dependent asparagine synthetase activity rather than a uniform complete absence of enzyme in every genotype.
Context-dependent cellular asparagine insufficiency model
ASNS hgnc:753 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves ASNS (hgnc:753). hgnc:753 is a gene from the HUGO Gene Nomenclature Committee.
asparagine synthase (glutamine-hydrolyzing) activity GO:0004066 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased asparagine synthase (glutamine-hydrolyzing) activity (GO:0004066). GO:0004066 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Reduced De Novo Asparagine Synthesis Reduced ASNS catalytic activity directly lowers capacity for de novo asparagine synthesis. Context-dependent cellular asparagine insufficiency model
Show evidence (1 reference)
PMID:24139043 SUPPORT In Vitro
"these mutations impaired ASNS gene function by either reducing protein expression (p.A6E or p.F362V) or reducing functional performance (p.R550C)"
Variant assays distinguish reduced abundance from reduced functional performance.
Reduced De Novo Asparagine Synthesis
Mechanism confidence: Established
Deficient ASNS activity lowers the capacity to synthesize asparagine from aspartate and glutamine. Low asparagine has been measured in some patients, but plasma and CSF results can be normal; this node denotes reduced synthetic capacity rather than obligate hypaasparaginemia in every sample.
Context-dependent cellular asparagine insufficiency model Proposed cerebral excitatory amino-acid imbalance model
L-asparagine biosynthetic process GO:0070981 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased L-asparagine biosynthetic process (GO:0070981). GO:0070981 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Context-Dependent Cellular Asparagine Insufficiency Reduced synthesis becomes limiting when extracellular asparagine availability is low. Context-dependent cellular asparagine insufficiency model
Proposed Cerebral Excitatory Amino-Acid Imbalance Altered pathway flux has been proposed to increase excitatory amino acids in brain, but the intermediates and consistency are unresolved. Proposed cerebral excitatory amino-acid imbalance model
Show evidence (2 references)
PMID:24139043 SUPPORT Human Clinical
"the levels of asparagine were decreased in at least two affected individuals"
The original report measured reduced asparagine in a subset of patients.
PMID:25227173 SUPPORT Human Clinical
"Plasma amino acids were normal, including the aspargine level."
A molecularly diagnosed case demonstrates that plasma asparagine can be normal.
Context-Dependent Cellular Asparagine Insufficiency
Mechanism confidence: Provisional
ASNS-deficient patient fibroblasts and lymphoblastoid cells become vulnerable when extracellular asparagine is limited. Reported consequences include impaired proliferation and broad metabolomic disruption, including lower TCA-cycle intermediates and anaplerotic substrates. These are disease-relevant cell-culture observations, not direct measurements in developing human brain.
Context-dependent cellular asparagine insufficiency model
cell population proliferation GO:0008283 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cell population proliferation (GO:0008283). GO:0008283 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Impaired Cortical Development and Brain Growth A cellular growth defect is proposed to impair neural progenitor expansion and post-mitotic cell survival during brain development. Context-dependent cellular asparagine insufficiency model
Show evidence (2 references)
PMID:26318253 SUPPORT In Vitro
"markedly reduced proliferation of patient fibroblasts when cultured in asparagine-limited growth medium"
Patient fibroblasts directly support the proliferation defect.
PMID:37111157 SUPPORT In Vitro
"Asn deprivation in ASNS-deficient cells led to disruptions across a wide range of metabolites."
Metabolomics in two patient-derived cell models supports broader metabolic disruption.
Proposed Cerebral Excitatory Amino-Acid Imbalance
Mechanism confidence: Hypothetical
Aspartate and glutamate excess in brain has been proposed as a contributor to hyperexcitability and neuronal injury. Mild precursor elevations were reported in selected patients, but concentrations have not been consistently abnormal, the affected brain compartment was not directly measured, and glutamate is generated by the ASNS reaction rather than being an unused substrate.
Proposed cerebral excitatory amino-acid imbalance model
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
brain UBERON:0000955 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in brain (UBERON:0000955). UBERON:0000955 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Epileptic Network Dysfunction Putative excitatory amino-acid imbalance could promote seizures, but direct evidence in ASNSD brain is lacking. Proposed cerebral excitatory amino-acid imbalance model
Show evidence (2 references)
PMID:24139043 SUPPORT Human Clinical
"glutamine and aspartic acid, both precursors in the ASNS-catalyzed synthesis of asparagine, were mildly elevated in the patients from family B"
Mild elevations in one family are compatible with, but do not establish, cerebral excitotoxicity.
PMID:27522229 SUPPORT Human Clinical
"possibly related to cytotoxic glutamate accumulation"
The neuropathology report retains this as a possibility.
Impaired Cortical Development and Brain Growth
Mechanism confidence: Provisional
ASNS is expressed in cortical-plate neurons and ventricular/subventricular neural progenitor zones. A hypomorphic Asns gene-trap mouse has reduced cortical thickness and area with enlarged ventricles. Together with human imaging, these findings support abnormal cortical development and growth, while the exact affected cellular process remains unresolved.
Context-dependent cellular asparagine insufficiency model
neural progenitor cell CL:0011020 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neural progenitor cell (CL:0011020). CL:0011020 is a cell type from the Cell Ontology.
cerebral cortex development GO:0021987 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cerebral cortex development (GO:0021987). GO:0021987 is a biological process from the Gene Ontology. ↓ DECREASED
cerebral cortex UBERON:0000956 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in cerebral cortex (UBERON:0000956). UBERON:0000956 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Progressive microcephaly Reduced prenatal and postnatal brain growth manifests as progressive microcephaly. Context-dependent cellular asparagine insufficiency model
Cerebral atrophy Loss of cerebral volume and progressive atrophy are structural consequences of impaired brain growth and injury. Context-dependent cellular asparagine insufficiency model
Global developmental delay Abnormal cortical development produces severe impairment across developmental domains. Context-dependent cellular asparagine insufficiency model
Axial hypotonia Central neurologic dysfunction contributes to axial hypotonia. Context-dependent cellular asparagine insufficiency model
Spasticity Progressive central motor-system dysfunction manifests as appendicular spasticity or spastic quadriplegia. Context-dependent cellular asparagine insufficiency model
Cortical visual impairment Cerebral visual pathway dysfunction can produce cortical visual impairment. Context-dependent cellular asparagine insufficiency model
Epileptic Network Dysfunction Abnormal cortical development and progressive structural injury can create epileptogenic networks. Context-dependent cellular asparagine insufficiency model
Neurologic Swallowing and Respiratory Dysfunction Severe central neurologic impairment can compromise swallowing, airway protection, and respiratory function. Context-dependent cellular asparagine insufficiency model
Show evidence (2 references)
PMID:24139043 SUPPORT Model Organism
"the cortical thickness and area of the Asns−/− brains were on average, ~14% thinner and ~5% smaller than their control littermates"
The hypomorphic mouse directly demonstrates reduced cortical growth.
PMID:24139043 SUPPORT Model Organism
"This expression pattern is similar to that of known microcephaly genes"
Developmental expression supports, but does not prove, the affected cellular pathway.
Epileptic Network Dysfunction
Mechanism confidence: Provisional
ASNSD commonly produces early multifocal or generalized epileptic activity, medically refractory seizures, and sometimes status epilepticus or myoclonus. This node captures the convergent epileptic state without choosing between structural and excitatory-amino-acid mechanisms.
Context-dependent cellular asparagine insufficiency model Proposed cerebral excitatory amino-acid imbalance model
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
brain UBERON:0000955 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in brain (UBERON:0000955). UBERON:0000955 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Intractable seizures The epileptic network state manifests as recurrent, often refractory seizures. Context-dependent cellular asparagine insufficiency model Proposed cerebral excitatory amino-acid imbalance model
Status epilepticus Severe seizure burden can progress to status epilepticus. Context-dependent cellular asparagine insufficiency model Proposed cerebral excitatory amino-acid imbalance model
Myoclonus Epileptic and nonepileptic network instability can manifest as persistent myoclonus. Context-dependent cellular asparagine insufficiency model Proposed cerebral excitatory amino-acid imbalance model
Exaggerated startle response Network hyperexcitability may contribute to the hyperekplexia-like startle phenotype. Context-dependent cellular asparagine insufficiency model Proposed cerebral excitatory amino-acid imbalance model
Show evidence (1 reference)
PMID:27522229 SUPPORT Human Clinical
"Electroencephalogram initially showed multifocal spikes that evolved into modified hypsarrhythmia and then discontinuous activity"
Serial EEG directly demonstrates severe evolving epileptic network dysfunction.
Neurologic Swallowing and Respiratory Dysfunction
Mechanism confidence: Provisional
Severe neurologic impairment can lead to dysphagia, aspiration risk, apnea, and respiratory insufficiency. This is a clinically supported complication branch, but its precise neuroanatomic and neuromuscular intermediates have not been established in ASNSD.
Context-dependent cellular asparagine insufficiency model
Downstream
Feeding difficulties Swallowing and gastroesophageal dysfunction directly impair safe feeding and nutrition. Context-dependent cellular asparagine insufficiency model
Respiratory insufficiency Apnea, aspiration, and impaired respiratory control can culminate in respiratory insufficiency. Context-dependent cellular asparagine insufficiency model
Show evidence (2 references)
PMID:30234940 SUPPORT Other
"swallowing dysfunction"
Current clinical guidance identifies swallowing dysfunction as a major feeding problem.
PMID:30234940 SUPPORT Other
"mechanical ventilation may be required for apnea"
Current management guidance documents severe respiratory compromise.
⬡

Pathograph

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

12
Digestive 1
Feeding difficulties HP:0011968 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Feeding difficulties (HP:0011968). HP:0011968 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30234940 SUPPORT Other
"Feeding difficulties"
Current clinical summary describes feeding difficulties as a major problem.
Eye 1
Cortical visual impairment FREQUENT Cerebral visual impairment HP:0100704 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral visual impairment (HP:0100704). HP:0100704 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"A majority have cortical blindness."
Current GeneReviews identifies cortical blindness as common and places visual impairment in the frequent band.
Head and Neck 1
Progressive microcephaly OBLIGATE HP:0000253 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Progressive microcephaly (HP:0000253), qualified as course progressive. HP:0000253 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"Congenital and progressive microcephaly"
Current GeneReviews identifies congenital, progressive microcephaly as a cardinal feature and reports it in all summarized individuals.
Musculoskeletal 2
Axial hypotonia FREQUENT HP:0008936 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Axial hypotonia (HP:0008936). HP:0008936 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"Hypotonia followed by spastic quadriplegia, seizures, jitteriness, and hyperekplexia"
Current GeneReviews identifies hypotonia as a cardinal feature and places it in the frequent band.
Spasticity VERY_FREQUENT HP:0001257 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Spasticity (HP:0001257). HP:0001257 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"Hypotonia followed by spastic quadriplegia, seizures, jitteriness, and hyperekplexia"
Current GeneReviews identifies spastic quadriplegia as characteristic and places spasticity in the very-frequent band.
Nervous System 6
Cerebral atrophy OBLIGATE HP:0002059 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral atrophy (HP:0002059), qualified as course progressive. HP:0002059 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"generalized brain atrophy (100%)"
Current GeneReviews reports generalized brain atrophy in all summarized imaging cases.
Global developmental delay OBLIGATE HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"Severe global developmental delay is reported in all affected individuals"
Current GeneReviews reports developmental delay in all summarized individuals.
Intractable seizures VERY_FREQUENT HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"seizures occur soon after birth"
The current summary reports seizures in most individuals and places them in the very-frequent band.
Status epilepticus HP:0002133 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Status epilepticus (HP:0002133). HP:0002133 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:27522229 SUPPORT Human Clinical
"Focal clonic seizures, status epilepticus, and infantile spasms appeared later"
Status epilepticus occurred in the reported sibling pair.
Myoclonus HP:0001336 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Myoclonus (HP:0001336). HP:0001336 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:27522229 SUPPORT Human Clinical
"permanent erratic myoclonus since birth"
Persistent neonatal-onset myoclonus was directly observed.
Exaggerated startle response FREQUENT HP:0002267 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Exaggerated startle response (HP:0002267). HP:0002267 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"Hypotonia followed by spastic quadriplegia, seizures, jitteriness, and hyperekplexia"
Current GeneReviews identifies hyperekplexia as characteristic and places it in the frequent band.
Respiratory 1
Respiratory insufficiency HP:0002093 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Respiratory insufficiency (HP:0002093). HP:0002093 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:25227173 SUPPORT Human Clinical
"feeding difficulties and respiratory insufficiency"
Respiratory insufficiency is documented among severe complications.
🧬

Genetic Associations

1
Biallelic pathogenic ASNS variants
Gene: ASNS hgnc:753 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is ASNS (hgnc:753). hgnc:753 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (2 references)
PMID:24139043 SUPPORT Human Clinical
"Critically, in all four families there is complete cosegregation of the identified ASNS mutations/genotypes with disease"
Complete cosegregation in the original four families supports causation.
PMID:30234940 SUPPORT Other
"biallelic pathogenic variants in ASNS identified by molecular genetic testing"
Current GeneReviews defines the molecular criterion for diagnosis.
💊

Medical Actions

6
Multidisciplinary supportive care
Category: Therapeutic Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
No curative or established disease-modifying therapy exists. Management is individualized and supportive, including developmental therapies, management of tone and contractures, vision services, nutrition and airway assessment, respiratory support, and psychosocial support.
Show evidence (1 reference)
PMID:30234940 SUPPORT Other
"Supportive developmental therapies"
Current GeneReviews identifies supportive developmental therapy as standard care.
Anticonvulsant therapy
Category: Therapeutic Action: anticonvulsant agent therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is anticonvulsant agent therapy, annotated with Anticonvulsant Therapy (NCIT:C64172). NCIT:C64172 is a clinical intervention from the NCI Thesaurus. Ontology label: Anticonvulsant Therapy NCIT:C64172
Seizures are treated according to standard epilepsy practice by an experienced neurologist. No antiseizure medication has demonstrated ASNSD-specific superiority, and polytherapy may be required.
Mechanism Target:
MODULATES Epileptic Network Dysfunction — Symptomatic anticonvulsant therapy targets the epileptic network state without correcting the upstream ASNS deficiency.
Show evidence (1 reference)
PMID:30234940 SUPPORT Other
"standard treatment for seizures"
GeneReviews supports symptomatic seizure treatment in ASNSD.
Target Phenotypes: Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology. Status epilepticus HP:0002133 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Status epilepticus (HP:0002133). HP:0002133 is a phenotype from the Human Phenotype Ontology. Myoclonus HP:0001336 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Myoclonus (HP:0001336). HP:0001336 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30234940 SUPPORT Other
"standard treatment for seizures"
Current GeneReviews recommends standard seizure management.
Feeding and enteral-nutrition support
Category: Therapeutic Action: feeding therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is feeding therapy, annotated with Swallowing Therapy (NCIT:C156237). NCIT:C156237 is a clinical intervention from the NCI Thesaurus. Ontology label: Swallowing Therapy NCIT:C156237
Feeding therapy, assessment of swallowing safety, and nasogastric or gastrostomy feeding can be used when oral intake is unsafe or insufficient; aspiration and respiratory status require parallel assessment.
Target Phenotypes: Feeding difficulties HP:0011968 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Feeding difficulties (HP:0011968). HP:0011968 is a phenotype from the Human Phenotype Ontology. Respiratory insufficiency HP:0002093 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Respiratory insufficiency (HP:0002093). HP:0002093 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30234940 SUPPORT Other
"feeding therapy and/or nasogastric or gastrostomy tube to support nutrition"
Current GeneReviews directly supports feeding therapy and enteral access.
Oral L-asparagine supplementation, experimental
Category: Therapeutic Action: amino acid supplementationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is amino acid supplementation, annotated with Nutritional Supplementation (NCIT:C15425). NCIT:C15425 is a clinical intervention from the NCI Thesaurus. Ontology label: Nutritional Supplementation NCIT:C15425
Oral L-asparagine is not an established treatment. One child developed irritability, sleep disturbance, and worsening seizures that required discontinuation; two siblings later tolerated 24 months without seizure improvement and with only limited developmental observations. These uncontrolled and conflicting reports do not establish efficacy and document potential harm.
Show evidence (2 references)
PMID:27268761 SUPPORT Human Clinical
"experienced worsening seizures, requiring discontinuation of the asparagine supplements"
The first documented treatment attempt showed clinically important worsening.
PMID:31123592 SUPPORT Human Clinical
"Asparagine supplementation was well tolerated"
Two later cases support tolerability only; they do not establish efficacy.
Ketogenic diet for drug-resistant epilepsy, case-level evidence
Category: Therapeutic Action: ketogenic diet intakeNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is ketogenic diet intake, annotated with Ketogenic Diet (NCIT:C173168). NCIT:C173168 is a clinical intervention from the NCI Thesaurus. Ontology label: Ketogenic Diet NCIT:C173168
A ketogenic diet was associated with marked seizure improvement and mild cognitive improvement in one child with drug-resistant epilepsy. This first case report provides no controlled or generalizable ASNSD-specific efficacy estimate, so candidacy requires specialist epilepsy and metabolic oversight.
Mechanism Target:
MODULATES Epileptic Network Dysfunction — The diet is linked only to the observed epileptic network phenotype; its molecular mechanism in ASNSD remains unestablished.
Show evidence (1 reference)
PMID:37167844 SUPPORT Human Clinical
"our case is the first report describing significant improvement with a ketogenic diet"
The single case supports an observed antiseizure effect without establishing mechanism or general efficacy.
Target Phenotypes: Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37167844 SUPPORT Human Clinical
"our case is the first report describing significant improvement with a ketogenic diet"
The source is explicitly a first single-case report.
Genetic counseling
Category: Counseling / Informational Action: genetic counselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is genetic counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. Ontology label: Genetic Counseling NCIT:C15240
Counseling should cover autosomal recessive inheritance, carrier testing for at-risk relatives, a 25% recurrence risk when both parents carry an ASNS pathogenic variant, and reproductive testing options once familial variants are known.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"carrier testing for at-risk relatives"
Current GeneReviews directly supports carrier and reproductive-risk counseling.
🔬

Biochemical Markers

2
Cerebrospinal-fluid asparagine (DECREASED)
Context: CSF asparagine is typically low or undetectable, but a normal result does not exclude ASNSD. In a 13-family Saudi cohort, proposed CSF biochemical analysis had 83% sensitivity and 98% specificity.
Pathograph Readouts
Readout Of Reduced De Novo Asparagine Synthesis Negative Diagnostic
Low CSF asparagine is a supportive readout of reduced synthetic capacity, not an obligatory finding.
Show evidence (1 reference)
PMID:32741967 SUPPORT Human Clinical
"clinical sensitivity and specificity of the proposed biochemical analysis of cerebrospinal fluid (CSF) for the detection of patients with ASNSD were 83% and 98%"
The largest biochemical cohort quantifies the test's imperfect sensitivity.
Show evidence (1 reference)
PMID:32741967 SUPPORT Human Clinical
"clinical sensitivity and specificity of the proposed biochemical analysis of cerebrospinal fluid (CSF) for the detection of patients with ASNSD were 83% and 98%"
Cohort performance supports a useful but non-exclusionary CSF biomarker.
Plasma asparagine (VARIABLE)
Context: Plasma asparagine is low in only about half of affected individuals and can be normal in molecularly confirmed disease. Plasma testing is less sensitive than CSF testing and cannot exclude ASNSD.
Pathograph Readouts
Readout Of Reduced De Novo Asparagine Synthesis Negative Diagnostic
A low value supports the biochemical defect, whereas a normal value is nondiagnostic.
Show evidence (1 reference)
PMID:25227173 SUPPORT Human Clinical
"Plasma amino acids were normal, including the aspargine level."
Molecularly diagnosed disease occurred despite normal plasma asparagine.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"is low in about half of affected individuals and is not as sensitive as CSF asparagine concentration"
Current GeneReviews establishes the limited sensitivity of plasma testing.
🔬

Diagnosis

3
Molecular confirmation of biallelic ASNS variants
The diagnosis is established by biallelic pathogenic or likely pathogenic ASNS variants, identified by single-gene sequencing, a relevant multigene panel, exome sequencing, or genome sequencing. Biallelic variants of uncertain significance do not establish or exclude the diagnosis.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Results: Biallelic pathogenic or likely pathogenic ASNS variants establish the molecular diagnosis.
Show evidence (2 references)
PMID:30234940 SUPPORT Other
"biallelic pathogenic variants in ASNS identified by molecular genetic testing"
Current GeneReviews directly defines the molecular diagnostic criterion.
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"does not establish or rule out the diagnosis."
Current GeneReviews cautions that VUS-only findings are not diagnostic.
CSF and plasma amino-acid analysis
Amino-acid analysis can show low or undetectable CSF asparagine and sometimes low plasma asparagine. Normal results do not rule out disease, so biochemical testing is supportive rather than definitive.
diagnostic procedure NCIT:C18020 NCI Thesaurus (NCIT)
Markers: Asparagine in cerebrospinal fluid and plasma
Results: Low CSF asparagine supports ASNSD; a normal CSF or plasma value does not exclude it.
Show evidence (1 reference)
PMID:32741967 SUPPORT Human Clinical
"suboptimal sensitivity of biochemical screening"
The largest biochemical cohort warns against using biochemical screening to exclude ASNSD.
Brain MRI
MRI commonly shows generalized atrophy, delayed myelination, gyral simplification, a small pons, or corpus-callosum thinning. These findings support the phenotype but are nonspecific.
MRI of the brain NCIT:C16809 NCI Thesaurus (NCIT)
Results: A compatible pattern supports suspicion of ASNSD but does not establish the diagnosis.
Show evidence (1 reference)
PMID:30234940 SUPPORT Other
"Brain MRI findings are nonspecific but may include generalized atrophy and simplified gyral pattern."
Current clinical summary directly characterizes the MRI findings as nonspecific.
🩻

Imaging Findings

4
Generalized cerebral atrophy on brain MRI OBLIGATE
Generalized cerebral atrophy is the most consistently reported imaging finding but is nonspecific.
Mri Diffuse
brain UBERON:0000955 Uberon multi-species anatomy ontology (UBERON) Cerebral atrophy HP:0002059 Human Phenotype Ontology (HP)
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"generalized brain atrophy (100%)"
Current GeneReviews reports generalized atrophy in all summarized imaging cases.
Delayed myelination on brain MRI FREQUENT
Delayed myelination is common but not specific to ASNSD.
Mri Diffuse
brain UBERON:0000955 Uberon multi-species anatomy ontology (UBERON) Delayed myelination HP:0012448 Human Phenotype Ontology (HP)
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"delayed myelination (75%)"
Current GeneReviews places delayed myelination in the frequent band.
Simplified gyral pattern on brain MRI FREQUENT
Gyral simplification supports abnormal cortical development but is nonspecific.
Mri Diffuse
cerebral cortex UBERON:0000956 Uberon multi-species anatomy ontology (UBERON) Simplified gyral pattern HP:0009879 Human Phenotype Ontology (HP)
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"gyral simplification pattern (62%)"
Current GeneReviews places gyral simplification in the frequent band.
Thin corpus callosum on brain MRI FREQUENT
A thin or hypoplastic corpus callosum occurs in about half of reported imaging cases.
Mri Focal
corpus callosum UBERON:0002336 Uberon multi-species anatomy ontology (UBERON) Hypoplasia of the corpus callosum HP:0002079 Human Phenotype Ontology (HP)
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"thin corpus callosum (55%)"
Current GeneReviews places a thin corpus callosum in the frequent band.
📈

Progression

2
Severe congenital or neonatal presentation
Age: Prenatal development through early infancy
Congenital microcephaly can be followed within days or months by seizures, profound developmental impairment, worsening spasticity, feeding and respiratory complications, and progressive cerebral atrophy. Published mortality is high, but ascertainment of the most severe cases may inflate the apparent first-year mortality.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"median age of onset: 1 day; range: 1 day to 9 months"
Current GeneReviews summarizes the early age-of-onset distribution.
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"because fewer than 100 affected individuals have been reported, it is possible that this represents the more severe end"
The prognosis summary explicitly cautions about severe-spectrum ascertainment.
Later-onset or attenuated presentation
Age: Infancy through childhood
Some individuals have a period of apparently normal early development before seizures and regression, and may retain motor or cognitive skills not seen at the severe end of the spectrum.
Show evidence (1 reference)
PMID:29279279 SUPPORT Human Clinical
"Both siblings had a period of normal development before onset of seizures, and development regression."
Two siblings with p.Arg49Gln expand the phenotype to later-onset disease.
📊

Prevalence

1
Worldwide
Point Prevalence <1 in 1,000,000
Orphadata gives a validated class-only worldwide point-prevalence estimate below one per million. This is a prevalence band, not a precise rate or a current count of published patients.
Show evidence (1 reference)
url:https://api.orphadata.com/rd-epidemiology/orphacodes/391376 SUPPORT Other
""PrevalenceClass": "<1 / 1 000 000","
Orphadata reports the validated worldwide point-prevalence class.
🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Asparagine synthetase deficiency:

Autosomal recessive primary microcephaly MONDO:0016660
Overlapping Features Primary microcephaly overlaps in congenital microcephaly and developmental impairment, but ASNSD more characteristically adds progressive microcephaly, spastic quadriplegia, severe early epilepsy, and potentially low CSF asparagine.
Distinguishing Features
  • Normal CSF asparagine concentration in primary microcephaly
  • Absence of spastic quadriplegia in typical primary microcephaly
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"Normal CSF asparagine concentration"
Current GeneReviews uses CSF asparagine and spastic quadriplegia to distinguish these disorders.
Lissencephaly spectrum disorder MONDO:0018838
Overlapping Features Lissencephaly and tubulinopathies can share simplified gyration, microcephaly, cerebellar hypoplasia, and spasticity. Frank lissencephaly or generalized polymicrogyria with normal CSF asparagine favors that spectrum.
Distinguishing Features
  • Lissencephaly or generalized polymicrogyria
  • Normal CSF asparagine concentration
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"generalized polymicrogyria"
Current GeneReviews identifies these malformations as distinguishing findings.
Inborn serine deficiency
Overlapping Features Serine-biosynthesis disorders also cause congenital microcephaly, neonatal seizures, developmental delay, and spasticity. Low CSF serine and glycine, rather than the ASNS molecular defect, distinguish them.
Distinguishing Features
  • Low CSF serine and glycine
  • Cataract or nystagmus in some serine deficiency disorders
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/ SUPPORT Other
"Low CSF serine"
Current GeneReviews directly identifies the distinguishing biochemical pattern.
{ }

Source YAML

click to show 
name: Asparagine synthetase deficiency
creation_date: "2026-07-11T00:00:00Z"
category: Mendelian
synonyms:
- ASNSD
- ASNS deficiency
- Congenital microcephaly-severe encephalopathy-progressive cerebral atrophy syndrome
description: >-
  Asparagine synthetase deficiency (ASNSD) is an ultra-rare autosomal
  recessive neurometabolic disorder caused by biallelic pathogenic variants in
  ASNS. ASNS catalyzes ATP-dependent synthesis of asparagine from aspartate,
  using glutamine as the nitrogen donor. The severe end of the spectrum
  presents congenitally or neonatally with progressive microcephaly, profound
  developmental impairment, axial hypotonia followed by spastic quadriplegia,
  early seizures, and cerebral atrophy; later-onset, milder disease is also
  documented. Plasma and cerebrospinal-fluid asparagine can be low but are not
  invariably abnormal, so molecular testing is central to diagnosis. Impaired
  cellular adaptation to limited extracellular asparagine is supported by
  patient-derived cells. A proposed contribution from cerebral
  aspartate/glutamate accumulation remains hypothetical and is not treated as
  an established mechanism.
disease_term:
  preferred_term: asparagine synthetase deficiency
  term:
    id: MONDO:0014258
    label: congenital microcephaly - severe encephalopathy - progressive cerebral atrophy syndrome
parents:
- Inborn error of metabolism
- Inborn error of amino acid metabolism
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0014258
      label: congenital microcephaly - severe encephalopathy - progressive cerebral atrophy syndrome
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO exact match for OMIM:615574 and Orphanet:391376, with ASNS as the
      causal gene.
references:
- reference: PMID:24139043
  title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
- reference: PMID:25227173
  title: "Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay."
- reference: PMID:26318253
  title: Asparagine Synthetase Deficiency causes reduced proliferation of cells under conditions of limited asparagine.
- reference: PMID:27268761
  title: Worsening of Seizures After Asparagine Supplementation in a Child with Asparagine Synthetase Deficiency.
- reference: PMID:27522229
  title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
- reference: PMID:29279279
  title: Characterization of a novel variant in siblings with Asparagine Synthetase Deficiency.
- reference: PMID:30234940
  title: Asparagine Synthetase Deficiency.
  tags:
  - GeneReviews
- reference: PMID:31123592
  title: "Clinical outcomes of two patients with a novel pathogenic variant in ASNS: response to asparagine supplementation and review of the literature."
- reference: PMID:32741967
  title: "Clinical, molecular, and biochemical delineation of asparagine synthetase deficiency in Saudi cohort."
- reference: PMID:37111157
  title: Metabolomic Profiling of Asparagine Deprivation in Asparagine Synthetase Deficiency Patient-Derived Cells.
- reference: PMID:37167844
  title: Ketogenic diet-responsive drug-resistant epilepsy in a case of asparagine synthetase deficiency with a novel compound heterozygous missense variant.
- reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
  title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
  tags:
  - GeneReviews
- reference: url:https://api.orphadata.com/rd-epidemiology/orphacodes/391376
  title: "https://api.orphadata.com/rd-epidemiology/orphacodes/391376"
prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: BELOW_1_IN_1000000
  notes: >-
    Orphadata gives a validated class-only worldwide point-prevalence estimate
    below one per million. This is a prevalence band, not a precise rate or a
    current count of published patients.
  evidence:
  - reference: url:https://api.orphadata.com/rd-epidemiology/orphacodes/391376
    reference_title: "https://api.orphadata.com/rd-epidemiology/orphacodes/391376"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: '"PrevalenceClass": "<1 / 1 000 000",'
    explanation: Orphadata reports the validated worldwide point-prevalence class.
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Disease results from biallelic pathogenic or likely pathogenic ASNS
    variants. Heterozygous carriers are asymptomatic; when both parents are
    carriers, each pregnancy has a 25% recurrence risk.
  evidence:
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the observed phenotype in all four families can be explained by autosomal recessive deficiency of asparagine synthetase (ASNS)"
    explanation: The original families establish autosomal recessive inheritance.
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "each sib of an affected individual has at conception a 25% chance of being affected"
    explanation: Current GeneReviews provides the recurrence-risk counseling statement.
genetic:
- name: Biallelic pathogenic ASNS variants
  gene_term:
    preferred_term: ASNS
    term:
      id: hgnc:753
      label: ASNS
  relationship_type: CAUSATIVE
  notes: >-
    Pathogenic alleles include missense, truncating, splice-altering, and rare
    copy-number variants. Functional severity varies; the entry therefore does
    not label every disease-associated allele as a complete null.
  evidence:
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Critically, in all four families there is complete cosegregation of the identified ASNS mutations/genotypes with disease"
    explanation: Complete cosegregation in the original four families supports causation.
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "biallelic pathogenic variants in ASNS identified by molecular genetic testing"
    explanation: Current GeneReviews defines the molecular criterion for diagnosis.
progression:
- phase: Severe congenital or neonatal presentation
  age_range: Prenatal development through early infancy
  notes: >-
    Congenital microcephaly can be followed within days or months by seizures,
    profound developmental impairment, worsening spasticity, feeding and
    respiratory complications, and progressive cerebral atrophy. Published
    mortality is high, but ascertainment of the most severe cases may inflate
    the apparent first-year mortality.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "median age of onset: 1 day; range: 1 day to 9 months"
    explanation: Current GeneReviews summarizes the early age-of-onset distribution.
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "because fewer than 100 affected individuals have been reported, it is possible that this represents the more severe end"
    explanation: The prognosis summary explicitly cautions about severe-spectrum ascertainment.
- phase: Later-onset or attenuated presentation
  age_range: Infancy through childhood
  notes: >-
    Some individuals have a period of apparently normal early development
    before seizures and regression, and may retain motor or cognitive skills
    not seen at the severe end of the spectrum.
  evidence:
  - reference: PMID:29279279
    reference_title: Characterization of a novel variant in siblings with Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both siblings had a period of normal development before onset of seizures, and development regression."
    explanation: Two siblings with p.Arg49Gln expand the phenotype to later-onset disease.
mechanistic_hypotheses:
- hypothesis_group_id: asparagine_insufficiency_model
  hypothesis_label: Context-dependent cellular asparagine insufficiency model
  status: CANONICAL
  description: >-
    Reduced ASNS activity limits de novo asparagine synthesis. Cells in
    environments with limited extracellular asparagine, especially within the
    developing nervous system, cannot fully compensate, impairing proliferation
    and broader metabolism and contributing to abnormal brain growth.
  evidence:
  - reference: PMID:26318253
    reference_title: Asparagine Synthetase Deficiency causes reduced proliferation of cells under conditions of limited asparagine.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "there is markedly reduced proliferation of patient fibroblasts when cultured in asparagine-limited growth medium"
    explanation: Patient fibroblasts directly demonstrate context-dependent cellular vulnerability.
  - reference: PMID:37111157
    reference_title: Metabolomic Profiling of Asparagine Deprivation in Asparagine Synthetase Deficiency Patient-Derived Cells.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "significant decrements in TCA cycle intermediates and anaplerotic substrates in ASNS-deficient cells challenged with Asn deprivation"
    explanation: Independent patient-derived cell models show wider metabolic consequences during asparagine deprivation.
- hypothesis_group_id: excitatory_amino_acid_model
  hypothesis_label: Proposed cerebral excitatory amino-acid imbalance model
  status: ALTERNATIVE
  description: >-
    Aspartate and/or glutamate accumulation has been proposed to enhance
    excitability and neuronal injury. The observation is neither consistent
    across patients nor directly demonstrated in affected human brain, and
    glutamate is a reaction product rather than an unused substrate. This model
    is therefore retained as an alternative hypothesis only.
  evidence:
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These features suggest a mechanism that is consistent with the accumulation of aspartate/glutamate in the brain"
    explanation: The original report explicitly presents accumulation as a suggested mechanism.
  - reference: PMID:27522229
    reference_title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "possibly related to cytotoxic glutamate accumulation"
    explanation: A two-sibling neuropathology report also frames glutamate accumulation as possible, not established.
pathophysiology:
- name: Biallelic ASNS Functional Deficiency
  description: >-
    Biallelic pathogenic ASNS variants reduce protein abundance, catalytic
    performance, or both. The initiating lesion is deficient
    glutamine-dependent asparagine synthetase activity rather than a uniform
    complete absence of enzyme in every genotype.
  mechanism_confidence: ESTABLISHED
  biological_scale: MOLECULAR
  genes:
  - preferred_term: ASNS
    term:
      id: hgnc:753
      label: ASNS
  molecular_functions:
  - preferred_term: asparagine synthase (glutamine-hydrolyzing) activity
    term:
      id: GO:0004066
      label: asparagine synthase (glutamine-hydrolyzing) activity
    modifier: DECREASED
  evidence:
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "these mutations impaired ASNS gene function by either reducing protein expression (p.A6E or p.F362V) or reducing functional performance (p.R550C)"
    explanation: Variant assays distinguish reduced abundance from reduced functional performance.
  downstream:
  - target: Reduced De Novo Asparagine Synthesis
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Reduced ASNS catalytic activity directly lowers capacity for de novo asparagine synthesis.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "ASNS encodes the glutamine-dependent asparagine synthetase enzyme"
      explanation: ASNS is the enzyme responsible for the affected synthesis reaction.
- name: Reduced De Novo Asparagine Synthesis
  description: >-
    Deficient ASNS activity lowers the capacity to synthesize asparagine from
    aspartate and glutamine. Low asparagine has been measured in some patients,
    but plasma and CSF results can be normal; this node denotes reduced
    synthetic capacity rather than obligate hypaasparaginemia in every sample.
  mechanism_confidence: ESTABLISHED
  biological_scale: MOLECULAR
  biological_processes:
  - preferred_term: L-asparagine biosynthetic process
    term:
      id: GO:0070981
      label: L-asparagine biosynthetic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: L-asparagine
    term:
      id: CHEBI:17196
      label: L-asparagine
    modifier: DECREASED
  evidence:
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the levels of asparagine were decreased in at least two affected individuals"
    explanation: The original report measured reduced asparagine in a subset of patients.
  - reference: PMID:25227173
    reference_title: "Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma amino acids were normal, including the aspargine level."
    explanation: A molecularly diagnosed case demonstrates that plasma asparagine can be normal.
  downstream:
  - target: Context-Dependent Cellular Asparagine Insufficiency
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Reduced synthesis becomes limiting when extracellular asparagine availability is low.
    evidence:
    - reference: PMID:26318253
      reference_title: Asparagine Synthetase Deficiency causes reduced proliferation of cells under conditions of limited asparagine.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "markedly reduced proliferation of patient fibroblasts when cultured in asparagine-limited growth medium"
      explanation: The cellular defect appears specifically under limited extracellular asparagine.
  - target: Proposed Cerebral Excitatory Amino-Acid Imbalance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - excitatory_amino_acid_model
    description: Altered pathway flux has been proposed to increase excitatory amino acids in brain, but the intermediates and consistency are unresolved.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "accumulation of aspartate/glutamate in the brain, resulting in enhanced excitability and neuronal damage"
      explanation: This supports only the authors' proposed, unconfirmed pathway.
- name: Context-Dependent Cellular Asparagine Insufficiency
  description: >-
    ASNS-deficient patient fibroblasts and lymphoblastoid cells become
    vulnerable when extracellular asparagine is limited. Reported consequences
    include impaired proliferation and broad metabolomic disruption, including
    lower TCA-cycle intermediates and anaplerotic substrates. These are
    disease-relevant cell-culture observations, not direct measurements in
    developing human brain.
  mechanism_confidence: PROVISIONAL
  biological_scale: CELLULAR
  biological_processes:
  - preferred_term: cell population proliferation
    term:
      id: GO:0008283
      label: cell population proliferation
    modifier: DECREASED
  chemical_entities:
  - preferred_term: L-asparagine
    term:
      id: CHEBI:17196
      label: L-asparagine
    modifier: DECREASED
  evidence:
  - reference: PMID:26318253
    reference_title: Asparagine Synthetase Deficiency causes reduced proliferation of cells under conditions of limited asparagine.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "markedly reduced proliferation of patient fibroblasts when cultured in asparagine-limited growth medium"
    explanation: Patient fibroblasts directly support the proliferation defect.
  - reference: PMID:37111157
    reference_title: Metabolomic Profiling of Asparagine Deprivation in Asparagine Synthetase Deficiency Patient-Derived Cells.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Asn deprivation in ASNS-deficient cells led to disruptions across a wide range of metabolites."
    explanation: Metabolomics in two patient-derived cell models supports broader metabolic disruption.
  downstream:
  - target: Impaired Cortical Development and Brain Growth
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: A cellular growth defect is proposed to impair neural progenitor expansion and post-mitotic cell survival during brain development.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "These structural abnormalities could be caused in part by aberrations in neural progenitor proliferation during development"
      explanation: The original study explicitly identifies this bridge as a possible explanation.
- name: Proposed Cerebral Excitatory Amino-Acid Imbalance
  description: >-
    Aspartate and glutamate excess in brain has been proposed as a contributor
    to hyperexcitability and neuronal injury. Mild precursor elevations were
    reported in selected patients, but concentrations have not been
    consistently abnormal, the affected brain compartment was not directly
    measured, and glutamate is generated by the ASNS reaction rather than being
    an unused substrate.
  mechanism_confidence: HYPOTHETICAL
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  chemical_entities:
  - preferred_term: L-aspartic acid
    term:
      id: CHEBI:17053
      label: L-aspartic acid
    modifier: INCREASED
  - preferred_term: L-glutamic acid
    term:
      id: CHEBI:16015
      label: L-glutamic acid
    modifier: INCREASED
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "glutamine and aspartic acid, both precursors in the ASNS-catalyzed synthesis of asparagine, were mildly elevated in the patients from family B"
    explanation: Mild elevations in one family are compatible with, but do not establish, cerebral excitotoxicity.
  - reference: PMID:27522229
    reference_title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "possibly related to cytotoxic glutamate accumulation"
    explanation: The neuropathology report retains this as a possibility.
  downstream:
  - target: Epileptic Network Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - excitatory_amino_acid_model
    description: Putative excitatory amino-acid imbalance could promote seizures, but direct evidence in ASNSD brain is lacking.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "seizures in the patients could reflect enhanced excitability, these could also be secondary to the structural effects of altered proliferation"
      explanation: The source explicitly preserves both alternatives.
- name: Impaired Cortical Development and Brain Growth
  description: >-
    ASNS is expressed in cortical-plate neurons and ventricular/subventricular
    neural progenitor zones. A hypomorphic Asns gene-trap mouse has reduced
    cortical thickness and area with enlarged ventricles. Together with human
    imaging, these findings support abnormal cortical development and growth,
    while the exact affected cellular process remains unresolved.
  mechanism_confidence: PROVISIONAL
  biological_scale: TISSUE
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  biological_processes:
  - preferred_term: cerebral cortex development
    term:
      id: GO:0021987
      label: cerebral cortex development
    modifier: DECREASED
  locations:
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  evidence:
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "the cortical thickness and area of the Asns−/− brains were on average, ~14% thinner and ~5% smaller than their control littermates"
    explanation: The hypomorphic mouse directly demonstrates reduced cortical growth.
  - reference: PMID:24139043
    reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "This expression pattern is similar to that of known microcephaly genes"
    explanation: Developmental expression supports, but does not prove, the affected cellular pathway.
  downstream:
  - target: Progressive microcephaly
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Reduced prenatal and postnatal brain growth manifests as progressive microcephaly.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "These children were born with a small head circumference and showed progressive microcephaly."
      explanation: Human observations directly connect impaired brain growth to the phenotype.
  - target: Cerebral atrophy
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Loss of cerebral volume and progressive atrophy are structural consequences of impaired brain growth and injury.
    evidence:
    - reference: PMID:26318253
      reference_title: Asparagine Synthetase Deficiency causes reduced proliferation of cells under conditions of limited asparagine.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "marked progressive cerebral atrophy"
      explanation: >-
        The paper's clinical-background statement anchors its cell findings to
        the defining progressive atrophy; the quoted text is not an in-vitro
        result.
  - target: Global developmental delay
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Abnormal cortical development produces severe impairment across developmental domains.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
      reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Severe global developmental delay"
      explanation: Current GeneReviews identifies severe global delay as a cardinal feature.
  - target: Axial hypotonia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Central neurologic dysfunction contributes to axial hypotonia.
    evidence:
    - reference: PMID:30234940
      reference_title: Asparagine Synthetase Deficiency.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "axial hypotonia followed by spastic quadriplegia"
      explanation: Current clinical summary documents the characteristic tone sequence.
  - target: Spasticity
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Progressive central motor-system dysfunction manifests as appendicular spasticity or spastic quadriplegia.
    evidence:
    - reference: PMID:30234940
      reference_title: Asparagine Synthetase Deficiency.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "axial hypotonia followed by spastic quadriplegia"
      explanation: Current clinical summary supports the progression to spasticity.
  - target: Cortical visual impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Cerebral visual pathway dysfunction can produce cortical visual impairment.
    evidence:
    - reference: PMID:30234940
      reference_title: Asparagine Synthetase Deficiency.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "A majority have cortical blindness."
      explanation: Current clinical summary identifies cortical blindness as common.
  - target: Epileptic Network Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Abnormal cortical development and progressive structural injury can create epileptogenic networks.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "seizures in the patients could reflect enhanced excitability, these could also be secondary to the structural effects of altered proliferation"
      explanation: The original report explicitly considers structural disease as a seizure mechanism.
  - target: Neurologic Swallowing and Respiratory Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Severe central neurologic impairment can compromise swallowing, airway protection, and respiratory function.
    evidence:
    - reference: PMID:25227173
      reference_title: "Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "feeding difficulties and respiratory insufficiency"
      explanation: These complications co-occur with the severe neurologic phenotype, while the precise intermediate is unresolved.
- name: Epileptic Network Dysfunction
  description: >-
    ASNSD commonly produces early multifocal or generalized epileptic activity,
    medically refractory seizures, and sometimes status epilepticus or
    myoclonus. This node captures the convergent epileptic state without
    choosing between structural and excitatory-amino-acid mechanisms.
  mechanism_confidence: PROVISIONAL
  biological_scale: TISSUE
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:27522229
    reference_title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electroencephalogram initially showed multifocal spikes that evolved into modified hypsarrhythmia and then discontinuous activity"
    explanation: Serial EEG directly demonstrates severe evolving epileptic network dysfunction.
  downstream:
  - target: Intractable seizures
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    - excitatory_amino_acid_model
    description: The epileptic network state manifests as recurrent, often refractory seizures.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "early-onset intractable seizures"
      explanation: The original series directly documents the seizure phenotype.
  - target: Status epilepticus
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    - excitatory_amino_acid_model
    description: Severe seizure burden can progress to status epilepticus.
    evidence:
    - reference: PMID:27522229
      reference_title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Focal clonic seizures, status epilepticus, and infantile spasms appeared later"
      explanation: Status epilepticus was observed in the affected siblings.
  - target: Myoclonus
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    - excitatory_amino_acid_model
    description: Epileptic and nonepileptic network instability can manifest as persistent myoclonus.
    evidence:
    - reference: PMID:27522229
      reference_title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "permanent erratic myoclonus since birth"
      explanation: Persistent myoclonus was directly documented in two siblings.
  - target: Exaggerated startle response
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - asparagine_insufficiency_model
    - excitatory_amino_acid_model
    description: Network hyperexcitability may contribute to the hyperekplexia-like startle phenotype.
    evidence:
    - reference: PMID:24139043
      reference_title: Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "excessive startle reflex, mimicking hyperekplexia"
      explanation: The phenotype is documented, while its mechanistic connection remains uncertain.
- name: Neurologic Swallowing and Respiratory Dysfunction
  description: >-
    Severe neurologic impairment can lead to dysphagia, aspiration risk, apnea,
    and respiratory insufficiency. This is a clinically supported complication
    branch, but its precise neuroanatomic and neuromuscular intermediates have
    not been established in ASNSD.
  mechanism_confidence: PROVISIONAL
  biological_scale: ORGANISM
  evidence:
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "swallowing dysfunction"
    explanation: Current clinical guidance identifies swallowing dysfunction as a major feeding problem.
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "mechanical ventilation may be required for apnea"
    explanation: Current management guidance documents severe respiratory compromise.
  downstream:
  - target: Feeding difficulties
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Swallowing and gastroesophageal dysfunction directly impair safe feeding and nutrition.
    evidence:
    - reference: PMID:30234940
      reference_title: Asparagine Synthetase Deficiency.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Feeding difficulties"
      explanation: Current clinical summary identifies feeding difficulties as a significant problem.
  - target: Respiratory insufficiency
    causal_link_type: DIRECT
    hypothesis_groups:
    - asparagine_insufficiency_model
    description: Apnea, aspiration, and impaired respiratory control can culminate in respiratory insufficiency.
    evidence:
    - reference: PMID:25227173
      reference_title: "Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "feeding difficulties and respiratory insufficiency"
      explanation: Respiratory insufficiency is documented among severe clinical complications.
phenotypes:
- name: Progressive microcephaly
  category: Neurologic
  frequency: OBLIGATE
  description: Microcephaly is usually congenital and becomes more marked with age.
  phenotype_term:
    preferred_term: Progressive microcephaly
    term:
      id: HP:0000253
      label: Progressive microcephaly
    clinical_course: PROGRESSIVE
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Congenital and progressive microcephaly"
    explanation: Current GeneReviews identifies congenital, progressive microcephaly as a cardinal feature and reports it in all summarized individuals.
- name: Cerebral atrophy
  category: Neurologic
  frequency: OBLIGATE
  description: Generalized or cortical cerebral atrophy is a consistent imaging feature and may progress.
  phenotype_term:
    preferred_term: Cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "generalized brain atrophy (100%)"
    explanation: Current GeneReviews reports generalized brain atrophy in all summarized imaging cases.
- name: Global developmental delay
  category: Neurologic
  frequency: OBLIGATE
  description: Developmental impairment is usually severe or profound, although attenuated cases retain more skills.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Severe global developmental delay is reported in all affected individuals"
    explanation: Current GeneReviews reports developmental delay in all summarized individuals.
- name: Intractable seizures
  category: Neurologic
  frequency: VERY_FREQUENT
  description: Seizures are usually early and often medically refractory, but type and severity vary.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "seizures occur soon after birth"
    explanation: The current summary reports seizures in most individuals and places them in the very-frequent band.
- name: Status epilepticus
  category: Neurologic
  description: Status epilepticus is a severe complication in some affected individuals.
  phenotype_term:
    preferred_term: Status epilepticus
    term:
      id: HP:0002133
      label: Status epilepticus
  evidence:
  - reference: PMID:27522229
    reference_title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Focal clonic seizures, status epilepticus, and infantile spasms appeared later"
    explanation: Status epilepticus occurred in the reported sibling pair.
- name: Myoclonus
  category: Neurologic
  description: Erratic myoclonus can begin at birth and persist.
  phenotype_term:
    preferred_term: Myoclonus
    term:
      id: HP:0001336
      label: Myoclonus
  evidence:
  - reference: PMID:27522229
    reference_title: Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "permanent erratic myoclonus since birth"
    explanation: Persistent neonatal-onset myoclonus was directly observed.
- name: Axial hypotonia
  category: Neurologic
  frequency: FREQUENT
  description: Central axial hypotonia often precedes or coexists with appendicular spasticity.
  phenotype_term:
    preferred_term: Axial hypotonia
    term:
      id: HP:0008936
      label: Axial hypotonia
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Hypotonia followed by spastic quadriplegia, seizures, jitteriness, and hyperekplexia"
    explanation: Current GeneReviews identifies hypotonia as a cardinal feature and places it in the frequent band.
- name: Spasticity
  category: Neurologic
  frequency: VERY_FREQUENT
  description: Appendicular spasticity can progress to spastic quadriplegia with contractures and scoliosis.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Hypotonia followed by spastic quadriplegia, seizures, jitteriness, and hyperekplexia"
    explanation: Current GeneReviews identifies spastic quadriplegia as characteristic and places spasticity in the very-frequent band.
- name: Exaggerated startle response
  category: Neurologic
  frequency: FREQUENT
  description: A hyperekplexia-like excessive startle response occurs in a substantial subset.
  phenotype_term:
    preferred_term: Exaggerated startle response
    term:
      id: HP:0002267
      label: Exaggerated startle response
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Hypotonia followed by spastic quadriplegia, seizures, jitteriness, and hyperekplexia"
    explanation: Current GeneReviews identifies hyperekplexia as characteristic and places it in the frequent band.
- name: Cortical visual impairment
  category: Neurologic
  frequency: FREQUENT
  description: Cerebral visual impairment or cortical blindness is reported.
  phenotype_term:
    preferred_term: Cerebral visual impairment
    term:
      id: HP:0100704
      label: Cerebral visual impairment
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "A majority have cortical blindness."
    explanation: Current GeneReviews identifies cortical blindness as common and places visual impairment in the frequent band.
- name: Feeding difficulties
  category: Gastrointestinal
  description: Dysphagia, vomiting, reflux, and gastroesophageal incoordination can compromise nutrition and airway safety.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Feeding difficulties"
    explanation: Current clinical summary describes feeding difficulties as a major problem.
- name: Respiratory insufficiency
  category: Respiratory
  description: Apnea, aspiration, or severe neurologic respiratory dysfunction may require ventilatory support.
  phenotype_term:
    preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
  evidence:
  - reference: PMID:25227173
    reference_title: "Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "feeding difficulties and respiratory insufficiency"
    explanation: Respiratory insufficiency is documented among severe complications.
imaging_findings:
- name: Generalized cerebral atrophy on brain MRI
  modality: MRI
  phenotype_term:
    preferred_term: Cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
  located_in:
    preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  spatial_extent: DIFFUSE
  frequency: OBLIGATE
  diagnostic: false
  description: Generalized cerebral atrophy is the most consistently reported imaging finding but is nonspecific.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "generalized brain atrophy (100%)"
    explanation: Current GeneReviews reports generalized atrophy in all summarized imaging cases.
- name: Delayed myelination on brain MRI
  modality: MRI
  phenotype_term:
    preferred_term: Delayed myelination
    term:
      id: HP:0012448
      label: Delayed myelination
  located_in:
    preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  spatial_extent: DIFFUSE
  frequency: FREQUENT
  diagnostic: false
  description: Delayed myelination is common but not specific to ASNSD.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "delayed myelination (75%)"
    explanation: Current GeneReviews places delayed myelination in the frequent band.
- name: Simplified gyral pattern on brain MRI
  modality: MRI
  phenotype_term:
    preferred_term: Simplified gyral pattern
    term:
      id: HP:0009879
      label: Simplified gyral pattern
  located_in:
    preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  spatial_extent: DIFFUSE
  frequency: FREQUENT
  diagnostic: false
  description: Gyral simplification supports abnormal cortical development but is nonspecific.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "gyral simplification pattern (62%)"
    explanation: Current GeneReviews places gyral simplification in the frequent band.
- name: Thin corpus callosum on brain MRI
  modality: MRI
  phenotype_term:
    preferred_term: Hypoplasia of the corpus callosum
    term:
      id: HP:0002079
      label: Hypoplasia of the corpus callosum
  located_in:
    preferred_term: corpus callosum
    term:
      id: UBERON:0002336
      label: corpus callosum
  spatial_extent: FOCAL
  frequency: FREQUENT
  diagnostic: false
  description: A thin or hypoplastic corpus callosum occurs in about half of reported imaging cases.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "thin corpus callosum (55%)"
    explanation: Current GeneReviews places a thin corpus callosum in the frequent band.
biochemical:
- name: Cerebrospinal-fluid asparagine
  biomarker_term:
    preferred_term: L-asparagine
    term:
      id: CHEBI:17196
      label: L-asparagine
  presence: DECREASED
  frequency: VERY_FREQUENT
  context: >-
    CSF asparagine is typically low or undetectable, but a normal result does
    not exclude ASNSD. In a 13-family Saudi cohort, proposed CSF biochemical
    analysis had 83% sensitivity and 98% specificity.
  readouts:
  - target: Reduced De Novo Asparagine Synthesis
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Low CSF asparagine is a supportive readout of reduced synthetic capacity, not an obligatory finding.
    evidence:
    - reference: PMID:32741967
      reference_title: "Clinical, molecular, and biochemical delineation of asparagine synthetase deficiency in Saudi cohort."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "clinical sensitivity and specificity of the proposed biochemical analysis of cerebrospinal fluid (CSF) for the detection of patients with ASNSD were 83% and 98%"
      explanation: The largest biochemical cohort quantifies the test's imperfect sensitivity.
  evidence:
  - reference: PMID:32741967
    reference_title: "Clinical, molecular, and biochemical delineation of asparagine synthetase deficiency in Saudi cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "clinical sensitivity and specificity of the proposed biochemical analysis of cerebrospinal fluid (CSF) for the detection of patients with ASNSD were 83% and 98%"
    explanation: Cohort performance supports a useful but non-exclusionary CSF biomarker.
- name: Plasma asparagine
  biomarker_term:
    preferred_term: L-asparagine
    term:
      id: CHEBI:17196
      label: L-asparagine
  presence: VARIABLE
  context: >-
    Plasma asparagine is low in only about half of affected individuals and can
    be normal in molecularly confirmed disease. Plasma testing is less
    sensitive than CSF testing and cannot exclude ASNSD.
  readouts:
  - target: Reduced De Novo Asparagine Synthesis
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: A low value supports the biochemical defect, whereas a normal value is nondiagnostic.
    evidence:
    - reference: PMID:25227173
      reference_title: "Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Plasma amino acids were normal, including the aspargine level."
      explanation: Molecularly diagnosed disease occurred despite normal plasma asparagine.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "is low in about half of affected individuals and is not as sensitive as CSF asparagine concentration"
    explanation: Current GeneReviews establishes the limited sensitivity of plasma testing.
diagnosis:
- name: Molecular confirmation of biallelic ASNS variants
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: >-
    The diagnosis is established by biallelic pathogenic or likely pathogenic
    ASNS variants, identified by single-gene sequencing, a relevant multigene
    panel, exome sequencing, or genome sequencing. Biallelic variants of
    uncertain significance do not establish or exclude the diagnosis.
  results: Biallelic pathogenic or likely pathogenic ASNS variants establish the molecular diagnosis.
  evidence:
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "biallelic pathogenic variants in ASNS identified by molecular genetic testing"
    explanation: Current GeneReviews directly defines the molecular diagnostic criterion.
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "does not establish or rule out the diagnosis."
    explanation: Current GeneReviews cautions that VUS-only findings are not diagnostic.
- name: CSF and plasma amino-acid analysis
  diagnosis_term:
    preferred_term: diagnostic procedure
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  description: >-
    Amino-acid analysis can show low or undetectable CSF asparagine and
    sometimes low plasma asparagine. Normal results do not rule out disease, so
    biochemical testing is supportive rather than definitive.
  markers: Asparagine in cerebrospinal fluid and plasma
  results: Low CSF asparagine supports ASNSD; a normal CSF or plasma value does not exclude it.
  evidence:
  - reference: PMID:32741967
    reference_title: "Clinical, molecular, and biochemical delineation of asparagine synthetase deficiency in Saudi cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "suboptimal sensitivity of biochemical screening"
    explanation: The largest biochemical cohort warns against using biochemical screening to exclude ASNSD.
- name: Brain MRI
  diagnosis_term:
    preferred_term: MRI of the brain
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  description: >-
    MRI commonly shows generalized atrophy, delayed myelination, gyral
    simplification, a small pons, or corpus-callosum thinning. These findings
    support the phenotype but are nonspecific.
  results: A compatible pattern supports suspicion of ASNSD but does not establish the diagnosis.
  evidence:
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Brain MRI findings are nonspecific but may include generalized atrophy and simplified gyral pattern."
    explanation: Current clinical summary directly characterizes the MRI findings as nonspecific.
differential_diagnoses:
- name: Autosomal recessive primary microcephaly
  disease_term:
    preferred_term: autosomal recessive primary microcephaly
    term:
      id: MONDO:0016660
      label: autosomal recessive primary microcephaly
  description: >-
    Primary microcephaly overlaps in congenital microcephaly and developmental
    impairment, but ASNSD more characteristically adds progressive
    microcephaly, spastic quadriplegia, severe early epilepsy, and potentially
    low CSF asparagine.
  distinguishing_features:
  - Normal CSF asparagine concentration in primary microcephaly
  - Absence of spastic quadriplegia in typical primary microcephaly
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Normal CSF asparagine concentration"
    explanation: Current GeneReviews uses CSF asparagine and spastic quadriplegia to distinguish these disorders.
- name: Lissencephaly spectrum disorder
  disease_term:
    preferred_term: lissencephaly spectrum disorder
    term:
      id: MONDO:0018838
      label: lissencephaly spectrum disorders
  description: >-
    Lissencephaly and tubulinopathies can share simplified gyration,
    microcephaly, cerebellar hypoplasia, and spasticity. Frank lissencephaly or
    generalized polymicrogyria with normal CSF asparagine favors that spectrum.
  distinguishing_features:
  - Lissencephaly or generalized polymicrogyria
  - Normal CSF asparagine concentration
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "generalized polymicrogyria"
    explanation: Current GeneReviews identifies these malformations as distinguishing findings.
- name: Inborn serine deficiency
  description: >-
    Serine-biosynthesis disorders also cause congenital microcephaly, neonatal
    seizures, developmental delay, and spasticity. Low CSF serine and glycine,
    rather than the ASNS molecular defect, distinguish them.
  distinguishing_features:
  - Low CSF serine and glycine
  - Cataract or nystagmus in some serine deficiency disorders
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Low CSF serine"
    explanation: Current GeneReviews directly identifies the distinguishing biochemical pattern.
- name: WWOX-related developmental and epileptic encephalopathy
  description: >-
    WWOX-related encephalopathy can closely mimic congenital microcephaly,
    severe developmental delay, hypotonia, spastic quadriplegia, thin corpus
    callosum, and delayed myelination. Normal blood and CSF asparagine and
    WWOX molecular findings distinguish it.
  distinguishing_features:
  - Normal blood and CSF asparagine concentrations
  - Biallelic pathogenic WWOX variants rather than ASNS variants
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "CSF asparagine concentrations"
    explanation: Current GeneReviews lists normal asparagine as a distinguishing feature.
treatments:
- name: Multidisciplinary supportive care
  action_category: THERAPEUTIC
  description: >-
    No curative or established disease-modifying therapy exists. Management is
    individualized and supportive, including developmental therapies,
    management of tone and contractures, vision services, nutrition and airway
    assessment, respiratory support, and psychosocial support.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Supportive developmental therapies"
    explanation: Current GeneReviews identifies supportive developmental therapy as standard care.
- name: Anticonvulsant therapy
  action_category: THERAPEUTIC
  description: >-
    Seizures are treated according to standard epilepsy practice by an
    experienced neurologist. No antiseizure medication has demonstrated
    ASNSD-specific superiority, and polytherapy may be required.
  treatment_term:
    preferred_term: anticonvulsant agent therapy
    term:
      id: NCIT:C64172
      label: Anticonvulsant Therapy
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  - preferred_term: Status epilepticus
    term:
      id: HP:0002133
      label: Status epilepticus
  - preferred_term: Myoclonus
    term:
      id: HP:0001336
      label: Myoclonus
  target_mechanisms:
  - target: Epileptic Network Dysfunction
    treatment_effect: MODULATES
    description: >-
      Symptomatic anticonvulsant therapy targets the epileptic network state
      without correcting the upstream ASNS deficiency.
    evidence:
    - reference: PMID:30234940
      reference_title: Asparagine Synthetase Deficiency.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "standard treatment for seizures"
      explanation: GeneReviews supports symptomatic seizure treatment in ASNSD.
  evidence:
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "standard treatment for seizures"
    explanation: Current GeneReviews recommends standard seizure management.
- name: Feeding and enteral-nutrition support
  action_category: THERAPEUTIC
  description: >-
    Feeding therapy, assessment of swallowing safety, and nasogastric or
    gastrostomy feeding can be used when oral intake is unsafe or insufficient;
    aspiration and respiratory status require parallel assessment.
  treatment_term:
    preferred_term: feeding therapy
    term:
      id: NCIT:C156237
      label: Swallowing Therapy
  target_phenotypes:
  - preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  - preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
  evidence:
  - reference: PMID:30234940
    reference_title: Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "feeding therapy and/or nasogastric or gastrostomy tube to support nutrition"
    explanation: Current GeneReviews directly supports feeding therapy and enteral access.
- name: Oral L-asparagine supplementation, experimental
  action_category: THERAPEUTIC
  description: >-
    Oral L-asparagine is not an established treatment. One child developed
    irritability, sleep disturbance, and worsening seizures that required
    discontinuation; two siblings later tolerated 24 months without seizure
    improvement and with only limited developmental observations. These
    uncontrolled and conflicting reports do not establish efficacy and document
    potential harm.
  treatment_term:
    preferred_term: amino acid supplementation
    term:
      id: NCIT:C15425
      label: Nutritional Supplementation
  evidence:
  - reference: PMID:27268761
    reference_title: Worsening of Seizures After Asparagine Supplementation in a Child with Asparagine Synthetase Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "experienced worsening seizures, requiring discontinuation of the asparagine supplements"
    explanation: The first documented treatment attempt showed clinically important worsening.
  - reference: PMID:31123592
    reference_title: "Clinical outcomes of two patients with a novel pathogenic variant in ASNS: response to asparagine supplementation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Asparagine supplementation was well tolerated"
    explanation: Two later cases support tolerability only; they do not establish efficacy.
- name: Ketogenic diet for drug-resistant epilepsy, case-level evidence
  action_category: THERAPEUTIC
  description: >-
    A ketogenic diet was associated with marked seizure improvement and mild
    cognitive improvement in one child with drug-resistant epilepsy. This first
    case report provides no controlled or generalizable ASNSD-specific efficacy
    estimate, so candidacy requires specialist epilepsy and metabolic oversight.
  treatment_term:
    preferred_term: ketogenic diet intake
    term:
      id: NCIT:C173168
      label: Ketogenic Diet
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  target_mechanisms:
  - target: Epileptic Network Dysfunction
    treatment_effect: MODULATES
    description: >-
      The diet is linked only to the observed epileptic network phenotype; its
      molecular mechanism in ASNSD remains unestablished.
    evidence:
    - reference: PMID:37167844
      reference_title: Ketogenic diet-responsive drug-resistant epilepsy in a case of asparagine synthetase deficiency with a novel compound heterozygous missense variant.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "our case is the first report describing significant improvement with a ketogenic diet"
      explanation: The single case supports an observed antiseizure effect without establishing mechanism or general efficacy.
  evidence:
  - reference: PMID:37167844
    reference_title: Ketogenic diet-responsive drug-resistant epilepsy in a case of asparagine synthetase deficiency with a novel compound heterozygous missense variant.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "our case is the first report describing significant improvement with a ketogenic diet"
    explanation: The source is explicitly a first single-case report.
- name: Genetic counseling
  action_category: COUNSELING_INFORMATIONAL
  description: >-
    Counseling should cover autosomal recessive inheritance, carrier testing
    for at-risk relatives, a 25% recurrence risk when both parents carry an
    ASNS pathogenic variant, and reproductive testing options once familial
    variants are known.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
    reference_title: Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "carrier testing for at-risk relatives"
    explanation: Current GeneReviews directly supports carrier and reproductive-risk counseling.
review_notes: >-
  A targeted 2026-07-20 review did not identify ASNSD-specific human, animal,
  or cell evidence for S-adenosylmethionine as a treatment; it was therefore
  not added. This avoids conflating ASNSD with methionine
  S-adenosyltransferase deficiency. The excitatory amino-acid branch and both
  dietary interventions are deliberately qualified at their observed evidence
  levels.
📚

References & Deep Research

References

13
PMID:24139043
Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.
No top-level findings curated for this source.
PMID:25227173
Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay.
No top-level findings curated for this source.
PMID:26318253
Asparagine Synthetase Deficiency causes reduced proliferation of cells under conditions of limited asparagine.
No top-level findings curated for this source.
PMID:27268761
Worsening of Seizures After Asparagine Supplementation in a Child with Asparagine Synthetase Deficiency.
No top-level findings curated for this source.
PMID:27522229
Epileptic Phenotype of Two Siblings with Asparagine Synthesis Deficiency Mimics Neonatal Pyridoxine-Dependent Epilepsy.
No top-level findings curated for this source.
PMID:29279279
Characterization of a novel variant in siblings with Asparagine Synthetase Deficiency.
No top-level findings curated for this source.
PMID:30234940
Asparagine Synthetase Deficiency.
No top-level findings curated for this source.
PMID:31123592
Clinical outcomes of two patients with a novel pathogenic variant in ASNS: response to asparagine supplementation and review of the literature.
No top-level findings curated for this source.
PMID:32741967
Clinical, molecular, and biochemical delineation of asparagine synthetase deficiency in Saudi cohort.
No top-level findings curated for this source.
PMID:37111157
Metabolomic Profiling of Asparagine Deprivation in Asparagine Synthetase Deficiency Patient-Derived Cells.
No top-level findings curated for this source.
PMID:37167844
Ketogenic diet-responsive drug-resistant epilepsy in a case of asparagine synthetase deficiency with a novel compound heterozygous missense variant.
No top-level findings curated for this source.
url:https://www.ncbi.nlm.nih.gov/books/NBK525916/
Asparagine Synthetase Deficiency - GeneReviews® - NCBI Bookshelf
No top-level findings curated for this source.
url:https://api.orphadata.com/rd-epidemiology/orphacodes/391376
https://api.orphadata.com/rd-epidemiology/orphacodes/391376
No top-level findings curated for this source.