SLC1A2-Related Developmental and Epileptic Encephalopathy

Mendelian MONDO:0014916 Pathograph 13 Show in embeddings browser Epilepsy Neurodevelopmental Disorder

A severe, early-onset developmental and epileptic encephalopathy (DEE41) caused by recurrent de novo heterozygous missense variants in SLC1A2, which encodes EAAT2/GLT-1, the astrocytic and presynaptic transporter that carries out the bulk of L-glutamate clearance from the synaptic cleft in the mammalian brain. The three recurrent variants (p.Gly82Arg, p.Leu85Pro, p.Pro289Arg) all fall in the trimerization domain of the trimeric transporter and act through a dominant negative mechanism that reduces - but does not eliminate - wild-type EAAT2 localization and function, placing carriers below a critical dosage of functional transporter. Two mechanistically distinct consequences have been demonstrated: loss of glutamate uptake, and, for the pore-lining Gly82Arg and Leu85Pro substitutions, enlargement of the EAAT anion pore so that mutant transporters become L-glutamate EFFLUX pathways. Both routes raise extracellular glutamate, driving excitotoxicity, glutamatergic excitation-inhibition imbalance, and refractory neonatal-onset multifocal seizures with severe global developmental delay and progressive MRI abnormalities. A rare, milder recessive form is also reported. This gene- and mechanism-anchored entry is distinct from the phenotype-level Epilepsy entry and from the generic DEE label.

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1
Mappings
2
Inheritance
11
Pathophys.
17
Phenotypes
3
Hypotheses
2
Gaps
13
Pathograph
1
Genes
4
Medical Actions
1
Differentials
7
References
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Mappings

MONDO
MONDO:0014916 developmental and epileptic encephalopathy, 41
skos:exactMatch MONDO
MONDO:0014916 is the gene-anchored disease concept for this entity - its definition states it is "Any early infantile epileptic encephalopathy in which the cause of the disease is a mutation in the SLC1A2 gene", it carries an RO:0004003 (has material basis in germline mutation in) relationship to HGNC:10940 SLC1A2, and it is equivalent to OMIM:617105. This entry therefore sits at exactly the same altitude as the MONDO term.
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Inheritance

2
Autosomal Dominant (De Novo, Dominant-Negative) HP:0000006
The severe, classical form arises from a recurrent de novo heterozygous SLC1A2 missense variant acting in a dominant negative fashion on the trimeric transporter. Because simple heterozygous SLC1A2 deletion is not epileptogenic in humans or mice, the mode of inheritance here is dominant only by virtue of the dominant-negative protein effect, not by haploinsufficiency. Parental mosaicism at low allelic fraction has been documented in the Epi4K cohort and carries recurrence-risk counseling implications.
Autosomal dominant inheritance
Show evidence (2 references)
PMID:30937933 SUPPORT Human Clinical
"Recurrent de novo SLC1A2 missense variants cause a severe, early onset developmental and epileptic encephalopathy via an unclear mechanism."
Establishes the recurrent de novo heterozygous missense origin of the severe form of the disorder.
PMID:27476654 SUPPORT Human Clinical
"As a result of high-depth coverage, parental mosaicism was identified in two out of 14 cases tested with mutant allelic fractions of 5%-6% in the unaffected parents, carrying significant reproductive counseling implications."
Documents low-level parental mosaicism in this de novo DEE cohort, which modifies recurrence-risk counseling for apparently de novo variants.
Autosomal Recessive (Rare, Milder) HP:0000007
A rare recessive form of SLC1A2-related epilepsy has been reported and is clinically milder than the de novo dominant form, with later seizure onset, monotherapy-responsive seizures, and only mild developmental delay. The severity difference is attributed to a greater amount of residual functional EAAT2 protein than the dominant-negative alleles permit.
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Of note, the case of recessive SLC1A2-related epilepsy appears milder, with seizure onset at 2 years of age that was controlled with a single medication and mild developmental delay."
Documents the existence and milder clinical course of the recessive form, justifying a second inheritance block.
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Mechanistic Hypotheses

3
Dominant-Negative Transport Loss-of-Function Model
transport_loss_of_function_model CANONICAL
Evidence balance 3 support
The canonical model holds that trimerization-domain variants reduce EAAT2 glutamate uptake both directly and by dominant-negative suppression of co-assembled wild-type subunits, driving carriers below a critical threshold of functional transporter and allowing extracellular glutamate to accumulate. It is supported by direct uptake and surface-expression assays for all three recurrent variants, by the quantified dominant-negative effect on wild-type protein, and by the seizure phenotype of GLT-1 null mice and eaat2a-null zebrafish. Under this model the rational therapy is to increase functional transporter.
Pathograph links
Dominant-Negative Suppression of Wild-Type EAAT2 -> Impaired Astrocytic Glutamate Clearance DIRECT
Impaired Astrocytic Glutamate Clearance -> Extracellular Glutamate Accumulation and Excitotoxicity DIRECT
Show evidence (3 references)
PMID:36543780 SUPPORT In Vitro
"we reported that these disease-linked mutants significantly decrease glutamate uptake, cell membrane expression of the glutamate transporter, and glutamate-elicited current"
Provides the core uptake-loss measurement across all three recurrent variants that this model rests on.
PMID:30937933 SUPPORT In Vitro
"the Leu85Pro variant acts via a dominant negative mechanism to reduce, but not eliminate, wild-type SLC1A2 protein localization and function"
Supplies the dominant-negative component that distinguishes this model from simple haploinsufficiency.
PMID:36543780 SUPPORT Other
"Therefore, GLT-1 is a promising and reliable therapeutic target for epilepsy interventions."
States the therapeutic corollary of this model - boosting transporter function - which the anion-pore model would not predict.
Widened EAAT Anion Pore / Glutamate Efflux Gain-of-Function Model
anion_pore_glutamate_efflux_model ALTERNATIVE
Evidence balance 4 support
A mechanistically distinct account, not merely a restatement of transport loss: because EAAT2 is also an anion channel, the pore-lining Gly82Arg and Leu85Pro substitutions widen the anion pore enough for L-glutamate itself to permeate, so the mutant transporter actively EXPORTS glutamate rather than only failing to import it. This is a gain of function and predicts a different therapy - selective EAAT anion-channel antagonists - whereas the canonical model predicts benefit from increasing transporter expression. The two models are not mutually exclusive and may operate in parallel for different variants; Pro289Arg shows the split directly, losing uptake while gaining anion current. Discriminating them clinically matters, because an uptake-enhancing agent would increase expression of a variant transporter that, under this model, leaks glutamate. An independent 18-patient, 13-variant cohort has since corroborated the model at the clinical level: individuals carrying Gly82Arg, Leu85Pro, Pro289Arg, or the further recurrent pore-lining variant Leu85Arg (all classified as "mixed loss-of-transport/gain-of-anion-channel function") had systematically more severe disease than individuals whose variants caused pure transport loss-of-function with no anion-current change, directly supporting anion-channel gain of function as a distinct, clinically material pathogenic contribution rather than a redundant description of transport loss.
Pathograph links
SLC1A2 Trimerization-Domain Missense Variant -> Mutant EAAT2 Anion Pore Glutamate Efflux DIRECT
Mutant EAAT2 Anion Pore Glutamate Efflux -> Extracellular Glutamate Accumulation and Excitotoxicity DIRECT
Show evidence (4 references)
PMID:34961934 SUPPORT In Vitro
"It does not only function as a secondary active glutamate transporter, but also as an anion channel."
Establishes the dual transporter/anion-channel nature of EAAT2 on which this alternative model depends.
PMID:34961934 SUPPORT In Vitro
"l-glutamate permeability of the EAAT anion pore is an unexpected functional consequence of naturally occurring single amino acid substitutions."
States the novel gain-of-function finding that differentiates this model from the canonical uptake-loss account.
PMID:34961934 SUPPORT In Vitro
"Antagonists that selectively suppress the EAAT anion channel function could serve as therapeutic agents in the future."
Captures the divergent therapeutic prediction that makes discriminating the two models clinically consequential.
+ 1 more reference
STIM1/Orai1 Store-Operated Calcium Entry Disruption Arm
soce_disruption_model EMERGING
Evidence balance 1 support
An emerging arm proposing that disease variants additionally perturb STIM1/Orai1-mediated store-operated calcium entry, with GLT-1 acting as a partner of the SOCE machinery. This would introduce a calcium-signaling contribution independent of extracellular glutamate handling. The source reports it in hedged terms and it has not been independently replicated, so it is curated as EMERGING and is deliberately kept off the canonical causal chain.
Pathograph links
SLC1A2 Trimerization-Domain Missense Variant -> Disturbed Store-Operated Calcium Entry INDIRECT UNKNOWN INTERMEDIATES
Disturbed Store-Operated Calcium Entry -> Excitation-Inhibition Imbalance and Neuronal Hyperexcitability INDIRECT UNKNOWN INTERMEDIATES
Show evidence (1 reference)
PMID:36543780 SUPPORT INDIRECT In Vitro
"in which GLT-1 may be a new partner of SOCE"
The originating observation for this arm. Marked INDIRECT because the source itself states the interaction only as a possibility rather than a demonstrated finding.
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Discussions and Knowledge Gaps

2
Why do heterozygous Slc1a2-null mice and humans with heterozygous SLC1A2 deletion have essentially no epilepsy phenotype, while humans heterozygous for a trimerization-domain missense allele have a lethal-grade developmental and epileptic encephalopathy - and does that make the available null models unsuitable for testing therapies aimed at this disorder?
HUMAN MODEL MISMATCH OPEN mismatch_slc1a2_heterozygous_null_models
Attached to
pathophysiology#Dominant-Negative Suppression of Wild-Type EAAT2 pathophysiology#SLC1A2 Trimerization-Domain Missense Variant
The workhorse model for this pathway is the GLT-1 knockout mouse, which faithfully shows lethal spontaneous seizures from elevated brain glutamate - but only in the HOMOZYGOUS state. Heterozygous Slc1a2-deletion mice have no apparent clinical phenotype, and heterozygous SLC1A2 deletion in humans (WAGR syndrome) is only rarely epileptogenic. The human disease, by contrast, is heterozygous. The reconciling proposal is a critical dosage threshold between 0 and 50 percent of wild-type transporter that a deletion does not cross but a dominant-negative missense allele does. That proposal is inferred rather than measured, and it has a direct translational consequence: a homozygous-null mouse models an allelic state no patient has, so a therapy that rescues it may not rescue a mixed wild-type/dominant-negative trimer population, and vice versa. Variant knock-in mice exist but their reported readout is a "hyperactive phenotype", not the human refractory multifocal epilepsy, so phenotypic fidelity at the disease level remains unestablished.
Proposed experiments
Allele-matched dosage-threshold titration
allele-matched in vivo dosage titration Relation: this experiment is of type this experiment type This experiment is of type allele-matched in vivo dosage titration.
exp_slc1a2_dominant_negative_dosage_threshold
Titrate the ratio of functional to dominant-negative EAAT2 in an allele-matched in vivo model (variant knock-in rather than null) and determine the residual-transporter fraction at which epileptiform activity appears, testing directly whether the proposed 0-50 percent critical threshold is real and whether heterozygous knock-in animals reproduce the human seizure phenotype rather than only hyperactivity.
Perturbations
Graded dominant-negative EAAT2 expression
pathophysiology#Dominant-Negative Suppression of Wild-Type EAAT2
Vary the dose of the Leu85Pro allele relative to wild-type SLC1A2 across an allelic series in vivo.
SLC1A2 hgnc:10940 HUGO Gene Nomenclature Committee (hgnc) Relation: this perturbation targets this gene This perturbation targets SLC1A2 (hgnc:10940). hgnc:10940 is a gene from the HUGO Gene Nomenclature Committee.
Readouts
Residual glutamate uptake and epileptiform activity
pathophysiology#Impaired Astrocytic Glutamate Clearance
glutamate reuptake GO:0051935 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on glutamate reuptake (GO:0051935). GO:0051935 is a biological process from the Gene Ontology.
Show evidence (3 references)
PMID:30937933 SUPPORT Model Organism
"Despite the severe epilepsy phenotype of homozygous Slc1a2 knockout mice, mice heterozygote for the Slc1a2 deletion demonstrate no apparent clinical phenotype"
States the core mismatch: the mouse model reproduces the phenotype only in a zygosity that does not correspond to the human disease.
PMID:30937933 SUPPORT Human Clinical
"heterozygous deletion of SLC1A2 in humans (as is frequently seen in the WAGR deletion syndrome) is only rarely associated with epilepsy"
Confirms the same dissociation in humans, ruling out simple haploinsufficiency as the human mechanism.
PMID:36543780 SUPPORT INDIRECT Model Organism
"Furthermore, knock-in mice with disease-associated variants showed a hyperactive phenotype accompanied by reduced glutamate transporter expression."
The closest allele-matched model. Marked INDIRECT because the reported readout is hyperactivity rather than the human refractory epileptic encephalopathy.
Should therapy for SLC1A2-related DEE aim to INCREASE transporter expression or to BLOCK the mutant transporter's anion channel - and does the negative ceftriaxone trial discriminate between the two mechanisms, or merely reflect treating too late?
KNOWLEDGE GAP OPEN gap_slc1a2_uptake_enhancer_versus_anion_channel_blocker
Attached to
pathophysiology#Impaired Astrocytic Glutamate Clearance pathophysiology#Mutant EAAT2 Anion Pore Glutamate Efflux
The two curated mechanistic models make opposite therapeutic predictions. The canonical transport-loss model says to raise EAAT2 expression; the anion-pore efflux model says raising expression of a glutamate-leaking mutant transporter could be neutral or harmful, and that a selective EAAT anion-channel antagonist is the rational agent. The only human therapeutic datum is a single 14-day ceftriaxone trial in one 20-month-old with Leu85Pro, which showed no change in spasm frequency. That result is consistent with the anion-pore model but is equally consistent with the authors' own alternative reading - that cumulative excitotoxic damage had already accrued by 20 months and that earlier initiation might succeed. With n=1, one variant, and a 14-day exposure, the trial cannot separate "wrong mechanism" from "right mechanism, too late". No EAAT anion-channel antagonist has been tested in this disorder at all.
Proposed experiments
Anion-channel antagonist versus uptake enhancer, head to head
comparative pharmacological intervention study Relation: this experiment is of type this experiment type This experiment is of type comparative pharmacological intervention study.
exp_slc1a2_anion_channel_antagonist
Compare a selective EAAT anion-channel antagonist against an EAAT2 expression enhancer in variant-matched cellular and in vivo models, stratified by variant class (pore-lining Gly82Arg/Leu85Pro versus Pro289Arg), with treatment initiated both before and after the onset of excitotoxic structural change, so that mechanism and timing are separated.
Perturbations
EAAT anion-channel blockade versus transporter upregulation
pathophysiology#Mutant EAAT2 Anion Pore Glutamate Efflux
Apply a selective EAAT anion-channel antagonist or an EAAT2-upregulating agent to variant-matched models at early and late time points.
Readouts
Extracellular glutamate and seizure burden
pathophysiology#Extracellular Glutamate Accumulation and Excitotoxicity
L-glutamate transmembrane transport GO:0015813 Gene Ontology (GO) Relation: this readout reports on this biological process This readout reports on L-glutamate transmembrane transport (GO:0015813). GO:0015813 is a biological process from the Gene Ontology.
Show evidence (3 references)
PMID:30937933 SUPPORT Human Clinical
"Ceftriaxone therapy did not result in a significant change in the daily spasm count"
The single negative human therapeutic result that motivates this gap.
PMID:30937933 SUPPORT Other
"earlier initiation of SLC1A2-modulating agents may be efficacious to overcome the cumulative dominant negative effects of the variant SLC1A2 allele"
States the competing timing explanation that the trial design cannot exclude.
PMID:34961934 SUPPORT In Vitro
"Antagonists that selectively suppress the EAAT anion channel function could serve as therapeutic agents in the future."
States the untested alternative therapeutic strategy implied by the anion-pore model.
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Pathophysiology

11
SLC1A2 Trimerization-Domain Missense Variant
The initiating lesion is a heterozygous de novo missense substitution in SLC1A2, which encodes the trimeric glutamate transporter EAAT2 (GLT-1). All three recurrent disease variants - p.Gly82Arg, p.Leu85Pro and p.Pro289Arg - localize to the trimerization domain of the transporter rather than to the transport domain, so the primary molecular event is a defect of subunit assembly and trafficking within the obligate trimer rather than a simple catalytic-site lesion. This node captures the single molecular trigger.
STIM1/Orai1 Store-Operated Calcium Entry Disruption Arm Widened EAAT Anion Pore / Glutamate Efflux Gain-of-Function Model
SLC1A2 hgnc:10940 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves SLC1A2 (hgnc:10940). hgnc:10940 is a gene from the HUGO Gene Nomenclature Committee.
protein homooligomerization GO:0051260 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal protein homooligomerization (GO:0051260). GO:0051260 is a biological process from the Gene Ontology. ⚠ ABNORMAL
L-glutamate transmembrane transporter activity GO:0005313 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased L-glutamate transmembrane transporter activity (GO:0005313). GO:0005313 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Dominant-Negative Suppression of Wild-Type EAAT2
Mutant EAAT2 Anion Pore Glutamate Efflux Widened EAAT Anion Pore / Glutamate Efflux Gain-of-Function Model
Disturbed Store-Operated Calcium Entry STIM1/Orai1 Store-Operated Calcium Entry Disruption Arm
Show evidence (3 references)
PMID:30937933 SUPPORT In Vitro
"We demonstrate that all 3 variants implicated in this condition localize to the trimerization domain of SLC1A2"
Establishes that the recurrent disease variants cluster in the trimerization domain, the structural basis for this trigger node.
PMID:30937933 SUPPORT Other
"SLC1A2 is a trimeric transporter essential for clearing glutamate from neuronal synapses."
Establishes the trimeric architecture and synaptic glutamate-clearance role of the affected protein.
PMID:27476654 SUPPORT Human Clinical
"Our results provide definitive evidence that de novo mutations in SLC1A2 and CACNA1A cause specific EEs"
Provides the human genetic evidence that de novo SLC1A2 variants are a definitive cause of epileptic encephalopathy.
Dominant-Negative Suppression of Wild-Type EAAT2
Because EAAT2 functions as an obligate trimer, a trimerization-domain variant subunit co-assembles with wild-type subunits into mixed trimers and suppresses their function. The Leu85Pro variant reduces - but does not eliminate - wild-type SLC1A2 protein localization and transport activity, cutting glutamate transport by roughly a third relative to wild-type alone. This explains the central genotype paradox of the disorder: simple heterozygous loss of one SLC1A2 allele is not epileptogenic, so the dominant-negative effect is what pushes carriers below a critical threshold of functional transporter (inferred to lie somewhere between 0 and 50 percent of wild-type).
Dominant-Negative Transport Loss-of-Function Model
L-glutamate transmembrane transporter activity GO:0005313 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased L-glutamate transmembrane transporter activity (GO:0005313). GO:0005313 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Impaired Astrocytic Glutamate Clearance Dominant-Negative Transport Loss-of-Function Model
Show evidence (3 references)
PMID:30937933 SUPPORT In Vitro
"the Leu85Pro variant acts via a dominant negative mechanism to reduce, but not eliminate, wild-type SLC1A2 protein localization and function"
Directly establishes the dominant-negative suppression of wild-type transporter that defines this node.
PMID:30937933 SUPPORT In Vitro
"glutamate transport activity in cells expressing both SLC1A2wt and SLC1A2L85P was reduced by 33% compared to cells expressing only SLC1A2wt"
Quantifies the magnitude of dominant-negative suppression of wild-type transporter activity.
PMID:30937933 SUPPORT Other
"it appears that there is a critical dosage of functional SLC1A2 protein (somewhere between 0 and 50% of wild-type) under which seizures develop"
States the critical-dosage threshold model that reconciles the non-epileptogenic heterozygous deletion with the severe missense phenotype.
Impaired Astrocytic Glutamate Clearance
EAAT2 is expressed in astrocytes and presynaptic nerve terminals and is the principal L-glutamate uptake carrier of the mammalian brain; together with EAAT1/SLC1A3 it mediates the bulk of glutamate clearance from the synaptic cleft. Disease-linked variants significantly decrease glutamate uptake, cell surface expression of the transporter, and glutamate-elicited transport current, so synaptically released glutamate is no longer removed at the normal rate. This is the central effector of the canonical mechanism.
Dominant-Negative Transport Loss-of-Function Model
astrocyte CL:0000127 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves astrocyte (CL:0000127). CL:0000127 is a cell type from the Cell Ontology. glutamatergic neuron CL:0000679 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves glutamatergic neuron (CL:0000679). CL:0000679 is a cell type from the Cell Ontology.
glutamate reuptake GO:0051935 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased glutamate reuptake (GO:0051935). GO:0051935 is a biological process from the Gene Ontology. ↓ DECREASED
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
Extracellular Glutamate Accumulation and Excitotoxicity Dominant-Negative Transport Loss-of-Function Model
Show evidence (3 references)
PMID:34961934 SUPPORT Other
"EAAT2 is expressed in glial cells and presynaptic nerve terminals and represents the main l-glutamate uptake carrier in the mammalian brain."
Establishes EAAT2 as the dominant glutamate uptake carrier whose loss defines this node, and its astrocytic/presynaptic localization.
PMID:36543780 SUPPORT In Vitro
"we reported that these disease-linked mutants significantly decrease glutamate uptake, cell membrane expression of the glutamate transporter, and glutamate-elicited current"
Provides direct functional evidence that the three disease variants reduce glutamate uptake and surface transporter expression.
PMID:36543780 SUPPORT Other
"Astrocytic glutamate transporter GLT-1 is responsible for preventing excitotoxicity via clearing extracellular accumulated glutamate."
States the anti-excitotoxic clearance function whose failure links this node to the downstream excitotoxicity node.
Mutant EAAT2 Anion Pore Glutamate Efflux
EAAT2 is not only a secondary active transporter but also an anion channel. The pore-lining Gly82Arg and Leu85Pro substitutions enlarge the anion pore enough to permit passage of L-glutamate itself, converting the mutant transporter into a glutamate EFFLUX pathway - a gain of function that adds to, rather than merely subtracts from, the uptake defect. Pro289Arg instead decreases uptake while increasing anion current. This arm predicts that selective EAAT anion-channel antagonists, not uptake enhancers, would be the rational therapy, and is modeled as a distinct mechanistic hypothesis.
Widened EAAT Anion Pore / Glutamate Efflux Gain-of-Function Model
L-glutamate transmembrane transport GO:0015813 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal L-glutamate transmembrane transport (GO:0015813). GO:0015813 is a biological process from the Gene Ontology. ⚠ ABNORMAL
L-glutamate transmembrane transporter activity GO:0005313 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves abnormal L-glutamate transmembrane transporter activity (GO:0005313). GO:0005313 is a molecular function from the Gene Ontology. ⚠ ABNORMAL
Downstream
Extracellular Glutamate Accumulation and Excitotoxicity Widened EAAT Anion Pore / Glutamate Efflux Gain-of-Function Model
Show evidence (2 references)
PMID:34961934 SUPPORT In Vitro
"G82R and L85P exchange amino acid residues that contribute to the formation of the EAAT anion pore. They enlarge the pore diameter sufficiently to permit the passage of l-glutamate and thus function as l-glutamate efflux pathways."
Directly establishes the anion-pore enlargement and resulting glutamate efflux that define this node.
PMID:34961934 SUPPORT In Vitro
"The mutation P289R decreases l-glutamate uptake, but increases anion currents despite a lower membrane expression."
Shows the variant-specific split between the uptake-loss and anion-current arms, justifying modeling them as separate mechanisms.
Disturbed Store-Operated Calcium Entry
An emerging, less-established arm: the three disease variants appear to disturb STIM1/Orai1-mediated store-operated calcium entry at the endoplasmic reticulum, with GLT-1 proposed as a new partner of the SOCE machinery. If confirmed, this would add a calcium-signaling component to the disorder that is independent of extracellular glutamate handling. It is curated as an EMERGING hypothesis rather than part of the canonical chain.
STIM1/Orai1 Store-Operated Calcium Entry Disruption Arm
store-operated calcium entry GO:0002115 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal store-operated calcium entry (GO:0002115). GO:0002115 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Excitation-Inhibition Imbalance and Neuronal Hyperexcitability STIM1/Orai1 Store-Operated Calcium Entry Disruption Arm
Show evidence (1 reference)
PMID:36543780 SUPPORT In Vitro
"in which GLT-1 may be a new partner of SOCE"
Reports the proposed GLT-1/SOCE interaction underlying this emerging arm; the hedged wording in the source is why it is curated as EMERGING.
Extracellular Glutamate Accumulation and Excitotoxicity
Whether by failed uptake or by efflux through the widened anion pore, the net result is elevated extracellular glutamate in the synaptic cleft and interstitial space. Excessive activation of glutamate receptors produces excitotoxic injury. The causal sufficiency of this step is established in model organisms: GLT-1 null mice show lethal spontaneous seizures attributable to elevated residual brain glutamate, and eaat2a-null zebrafish show recurrent seizures coinciding with an abrupt rise in extracellular glutamate.
glutamatergic neuron CL:0000679 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves glutamatergic neuron (CL:0000679). CL:0000679 is a cell type from the Cell Ontology. astrocyte CL:0000127 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves astrocyte (CL:0000127). CL:0000127 is a cell type from the Cell Ontology.
excitatory postsynaptic potential GO:0060079 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased excitatory postsynaptic potential (GO:0060079). GO:0060079 is a biological process from the Gene Ontology. ↑ INCREASED
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
Excitation-Inhibition Imbalance and Neuronal Hyperexcitability
Progressive Excitotoxic Neuronal and White Matter Injury
Show evidence (4 references)
PMID:34961934 SUPPORT Other
"l-glutamate efflux through mutant EAAT2 anion channels will cause glutamate excitotoxicity and neuronal hyperexcitability in affected patients."
Links the molecular arms of the disorder to glutamate excitotoxicity and hyperexcitability, this node and the next.
PMID:9180080 SUPPORT Model Organism
"Homozygous mice deficient in GLT-1, a widely distributed astrocytic glutamate transporter, show lethal spontaneous seizures and increased susceptibility to acute cortical injury."
Model-organism evidence that loss of GLT-1 is sufficient to produce spontaneous seizures and heightened excitotoxic injury.
PMID:9180080 SUPPORT Model Organism
"These effects can be attributed to elevated levels of residual glutamate in the brains of these mice."
Attributes the seizure and injury phenotype specifically to elevated extracellular glutamate, the substance of this node.
+ 1 more reference
Excitation-Inhibition Imbalance and Neuronal Hyperexcitability
Sustained elevation of extracellular glutamate shifts cortical networks toward net excitation, prolonging and broadening neuronal excitation because the duration and extent of glutamatergic signaling is normally terminated by EAAT2 uptake. The resulting hyperexcitable, hypersynchronous state is the substrate for the multifocal and generalized epileptiform discharges seen on EEG. Notably, animal models show that this hyperexcitability coexists with reduced BASAL network activity, so the disorder is a dysregulation of excitability rather than a uniform increase.
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.
chemical synaptic transmission GO:0007268 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal chemical synaptic transmission (GO:0007268). GO:0007268 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Seizure Generation and Epileptogenesis
Show evidence (3 references)
PMID:34716961 SUPPORT Model Organism
"Astroglial excitatory amino acid transporter 2 (EAAT2, GLT-1, and SLC1A2) regulates the duration and extent of neuronal excitation by removing glutamate from the synaptic cleft."
States the normal function - termination of neuronal excitation - whose loss produces the hyperexcitable state modeled here.
PMID:34716961 SUPPORT Model Organism
"In stark contrast to this hyperexcitability, basal neuronal and astroglial activity was surprisingly reduced in eaat2a-/- mutant animals, which manifested in decreased overall locomotion."
Documents the coexisting basal hypoactivity that qualifies a naive "pure hyperexcitability" reading of this node.
PMID:36543780 SUPPORT Model Organism
"Furthermore, knock-in mice with disease-associated variants showed a hyperactive phenotype accompanied by reduced glutamate transporter expression."
Variant-specific knock-in mouse evidence connecting reduced transporter expression to an altered-excitability behavioural phenotype.
Seizure Generation and Epileptogenesis
The hyperexcitable neuronal state increases the propensity for seizure generation and epileptogenesis. In this disorder, that shared epilepsy effector step links glutamate-driven network hyperexcitability to the recurrent neonatal-onset seizure syndrome modeled downstream, without conflating the generic network process with its specific clinical phenotype.
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.
Downstream
Refractory Neonatal-Onset Multifocal Epilepsy
Show evidence (1 reference)
PMID:30764523 SUPPORT Other
"increased excitation, decreased inhibition, or both favor a hyperexcitable state and an increased propensity for seizure generation and epileptogenesis."
A pediatric epilepsy review directly links a hyperexcitable state to seizure generation and epileptogenesis, supporting this shared-module bridge between the upstream cellular state and the disease-specific seizure phenotype.
Progressive Excitotoxic Neuronal and White Matter Injury
Cumulative neuronal damage from excessive glutamate-receptor activation accrues over time and is visible on serial neuroimaging. Brain MRI is normal for the first several months of life and only from around five months begins to show delayed myelination, thinning of the corpus callosum, and cerebral cortical atrophy. The initially normal imaging is mechanistically important: it argues that the structural abnormality is an acquired consequence of ongoing excitotoxicity rather than a primary malformation, and it defines a therapeutic window before injury accumulates.
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.
myelination GO:0042552 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased myelination (GO:0042552). GO:0042552 is a biological process from the Gene Ontology. ↓ DECREASED
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
Developmental and Epileptic Encephalopathy
Show evidence (2 references)
PMID:30937933 SUPPORT Human Clinical
"Brain MRIs were all normal for the first several months of life, but around 5 months of life began to show evidence of delayed myelination, thinning of the corpus callosum, and cerebral cortical atrophy."
Establishes the acquired, progressive nature and the specific imaging substrate of this node.
PMID:30937933 SUPPORT Other
"It is likely, based on progressive neuroimaging abnormalities in this disorder, that there is cumulative neuronal damage over time from excessive activation of glutamate receptors."
States the excitotoxic interpretation of the progressive imaging findings that this node models.
Refractory Neonatal-Onset Multifocal Epilepsy
Seizures begin between two days and six weeks of life, typically as focal motor events (often tonic or myoclonic) and progress to multiple seizure types including epileptic spasms, myoclonic seizures, focal and generalized tonic seizures, and tonic-clonic seizures. Seizures are systematically refractory to multiple antiseizure medications, and EEG shows multifocal and generalized epileptiform discharges on an abnormal background, including modified and classic hypsarrhythmia.
Downstream
Developmental and Epileptic Encephalopathy
Show evidence (3 references)
PMID:30937933 SUPPORT Human Clinical
"All six de novo dominant cases developed early onset epilepsy with symptom onset between 2 days and 6 weeks of life"
Establishes the neonatal-to-early-infantile onset window of the seizure phenotype.
PMID:30937933 SUPPORT Human Clinical
"Seizures typically presented as focal motor events (often tonic or myoclonic), and progressed to multiple seizure types including epileptic spasms, myoclonic seizures, focal and generalized tonic seizures, and tonic-clonic seizures."
Documents the evolving multifocal seizure semiology modeled by this node.
PMID:30937933 SUPPORT Human Clinical
"Seizures were systematically refractory to multiple medications."
Establishes pharmacoresistance as a defining feature of the seizure phenotype.
Developmental and Epileptic Encephalopathy
The convergent organism-level outcome: severe global developmental delay in essentially all affected individuals, with cortical visual impairment, axial hypotonia, spasticity and/or joint contractures, and kyphoscoliosis. Both the ongoing epileptic activity and the underlying excitotoxic injury contribute to the developmental impairment, which is the defining feature of a developmental AND epileptic encephalopathy as opposed to a pure epilepsy.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Common clinical features included severe global developmental delay (6/6 cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases), spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6 cases)."
Enumerates the organism-level features and their frequencies in the reported dominant cohort.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for SLC1A2-Related Developmental and Epileptic Encephalopathy Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

17
Eye 1
Cerebral Visual Impairment FREQUENT 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)
PMID:30937933 SUPPORT Human Clinical
"cortical visual impairment (3/6 cases)"
3/6 (50%) of reported dominant cases falls in the FREQUENT band (30-79%).
Musculoskeletal 4
Axial Hypotonia VERY_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)
PMID:30937933 SUPPORT Human Clinical
"Common clinical features included severe global developmental delay (6/6 cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases), spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6 cases)."
6/6 (100%) of reported dominant cases supports a VERY_FREQUENT band.
Spasticity 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)
PMID:30937933 SUPPORT Human Clinical
"spasticity and/or joint contractures (5/6 cases)"
Supports the association with spasticity only. No separate frequency is asserted because the source pools spasticity with joint contractures in a disjunctive count.
Flexion Contracture HP:0001371 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Flexion contracture (HP:0001371). HP:0001371 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"spasticity and/or joint contractures (5/6 cases)"
Documents joint contractures. No separate frequency is asserted because the source pools contractures with spasticity in a single count.
Kyphoscoliosis HP:0002751 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Kyphoscoliosis (HP:0002751). HP:0002751 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Common clinical features included severe global developmental delay (6/6 cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases), spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6 cases)."
Documents kyphoscoliosis in 2/6 reported dominant cases. No frequency band is asserted because the estimate comes from only six cases.
Nervous System 12
Epileptic Encephalopathy HP:0200134 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Epileptic encephalopathy (HP:0200134), qualified as neonatal onset, up to 0.12y. HP:0200134 is a phenotype from the Human Phenotype Ontology.
Onset: NEONATAL; up to 0.12y
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Recurrent de novo SLC1A2 missense variants cause a severe, early onset developmental and epileptic encephalopathy via an unclear mechanism."
Establishes the developmental and epileptic encephalopathy phenotype as the disease-defining presentation.
Focal Motor Seizure HP:0011153 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Focal motor seizure (HP:0011153). HP:0011153 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Seizures typically presented as focal motor events (often tonic or myoclonic), and progressed to multiple seizure types including epileptic spasms, myoclonic seizures, focal and generalized tonic seizures, and tonic-clonic seizures."
Establishes focal motor events as the typical presenting seizure type; the qualitative word "typically" does not justify a quantitative frequency band.
Epileptic Spasms HP:0011097 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Epileptic spasm (HP:0011097). HP:0011097 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"progressed to multiple seizure types including epileptic spasms, myoclonic seizures, focal and generalized tonic seizures, and tonic-clonic seizures"
Documents epileptic spasms within the evolving seizure repertoire.
Generalized Myoclonic Seizure HP:0002123 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Generalized myoclonic seizure (HP:0002123). HP:0002123 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"progressed to multiple seizure types including epileptic spasms, myoclonic seizures, focal and generalized tonic seizures, and tonic-clonic seizures"
Lists myoclonic seizures among the seizure types observed.
Generalized Tonic Seizure HP:0010818 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Generalized tonic seizure (HP:0010818). HP:0010818 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"progressed to multiple seizure types including epileptic spasms, myoclonic seizures, focal and generalized tonic seizures, and tonic-clonic seizures"
Lists generalized tonic seizures among the seizure types observed.
Bilateral Tonic-Clonic Seizure HP:0002069 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bilateral tonic-clonic seizure (HP:0002069). HP:0002069 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"progressed to multiple seizure types including epileptic spasms, myoclonic seizures, focal and generalized tonic seizures, and tonic-clonic seizures"
Lists tonic-clonic seizures among the seizure types observed.
Multifocal Epileptiform Discharges HP:0010841 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Multifocal epileptiform discharges (HP:0010841). HP:0010841 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"EEG patterns demonstrated multifocal and generalized epileptiform discharges with abnormal background activity, including modified and classic hypsarrhythmia."
Directly documents the multifocal and generalized epileptiform EEG pattern.
Hypsarrhythmia HP:0002521 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypsarrhythmia (HP:0002521). HP:0002521 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"including modified and classic hypsarrhythmia"
Documents hypsarrhythmia in the reported EEG phenotype.
Severe Global Developmental Delay VERY_FREQUENT HP:0011344 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Severe global developmental delay (HP:0011344). HP:0011344 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Common clinical features included severe global developmental delay (6/6 cases)"
6/6 (100%) of reported dominant cases supports a VERY_FREQUENT band.
Delayed Myelination HP:0012448 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Delayed myelination (HP:0012448), qualified as course progressive. HP:0012448 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"around 5 months of life began to show evidence of delayed myelination, thinning of the corpus callosum, and cerebral cortical atrophy"
Documents delayed myelination and its delayed, progressive appearance.
Thin Corpus Callosum HP:0033725 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Thin corpus callosum (HP:0033725), qualified as course progressive. HP:0033725 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"around 5 months of life began to show evidence of delayed myelination, thinning of the corpus callosum, and cerebral cortical atrophy"
Documents progressive corpus callosum thinning.
Cerebral Cortical Atrophy HP:0002120 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral cortical atrophy (HP:0002120), qualified as course progressive. HP:0002120 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"around 5 months of life began to show evidence of delayed myelination, thinning of the corpus callosum, and cerebral cortical atrophy"
Documents progressive cerebral cortical atrophy.
🧬

Genetic Associations

1
SLC1A2 (Recurrent De Novo Trimerization-Domain Missense Variants)
Gene: SLC1A2 hgnc:10940 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is SLC1A2 (hgnc:10940). hgnc:10940 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Autosomal Dominant (De Novo, Dominant-Negative)
Show evidence (4 references)
PMID:30937933 SUPPORT Human Clinical
"Singleton whole exome sequencing (Prevention Genetics, Marshfield, WI) revealed a pathogenic heterozygous c.254T>C (p.Leu85Pro) variant in the SLC1A2 gene"
Documents the specific recurrent Leu85Pro allele and its identification by exome sequencing.
PMID:30937933 SUPPORT Human Clinical
"heterozygous deletion of SLC1A2 in humans (as is frequently seen in the WAGR deletion syndrome) is only rarely associated with epilepsy"
Establishes that SLC1A2 haploinsufficiency alone is not epileptogenic in humans, the key variant-interpretation caveat recorded in the notes.
PMID:34961934 SUPPORT In Vitro
"we studied the functional consequences of three disease-associated mutations, which predict amino acid exchanges p.Gly82Arg (G82R), p.Leu85Pro (L85P), and p.Pro289Arg (P289R)"
Enumerates the three recurrent disease alleles that define the allelic spectrum of this entry.
+ 1 more reference
💊

Medical Actions

4
Antiseizure Medication
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Platform: Small molecule
Standard antiseizure medication is the mainstay but performs poorly: seizures in the de novo dominant form were systematically refractory to multiple medications. Seizures in the rare recessive form, by contrast, were controlled with a single medication, so pharmacoresponsiveness tracks residual EAAT2 function rather than drug choice.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Seizures were systematically refractory to multiple medications."
Supports the claim that standard antiseizure medication performs poorly in the de novo dominant form, documenting refractoriness rather than benefit.
Ceftriaxone (Investigational EAAT2-Modulating Agent)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: ceftriaxone CHEBI:29007 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses ceftriaxone (CHEBI:29007). CHEBI:29007 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Ceftriaxone is a blood-brain-barrier-penetrant beta-lactam that increases SLC1A2 expression and function in neural tissue, making it the most obvious mechanism-matched repurposing candidate under the transport-loss-of-function model. It has been trialled once, under an IRB-approved innovative-therapy protocol, in a 20-month-old with the Leu85Pro variant at 80 mg/kg/day intravenously for 14 days with continuous video-EEG spasm counting. It did NOT significantly change daily spasm frequency, though it was well tolerated. This is a negative n-of-1 result, not an established therapy, and is curated here because the negative result is mechanistically informative - it is exactly what the anion-pore efflux model would predict, since raising expression of a leaky mutant transporter should not help. Positive allosteric modulation of EAAT2 is a distinct pharmacological strategy under general development for epilepsy that increases transport activity directly rather than via transcriptional upregulation; it has not been reported as tested in SLC1A2-related DEE41 specifically, but is mechanistically relevant as an alternative route to the same transport-loss-of-function target.
Mechanism Target:
INHIBITS Impaired Astrocytic Glutamate Clearance — Ceftriaxone was given to oppose the pathological clearance impairment by increasing EAAT2 expression and restoring astrocytic glutamate clearance.
Show evidence (4 references)
PMID:30937933 SUPPORT Other
"Ceftriaxone is an FDA-approved antibiotic that crosses the blood-brain barrier and increases SLC1A2 expression and function within several days in neural tissue"
Establishes the mechanistic rationale for using ceftriaxone as an EAAT2-modulating agent.
PMID:33507976 SUPPORT INDIRECT Model Organism
"Ceftriaxone administration in epileptic animals led to a reduction of glutamate along with elevation of the level of glutamine synthetase activity and GLT-1 expression in the acute phase."
Independent rodent temporal-lobe-epilepsy model supporting the same ceftriaxone/GLT-1-upregulation rationale used here; INDIRECT because it is an acquired-epilepsy model, not the SLC1A2 dominant-negative genotype, and so cannot speak to why the DEE41 trial itself failed.
PMID:30937933 REFUTE Human Clinical
"Ceftriaxone therapy did not result in a significant change in the daily spasm count"
Refutes short-term clinical efficacy of ceftriaxone in this n-of-1 trial; recorded as REFUTE so the negative result is not read as support.
+ 1 more reference
Supportive and Rehabilitative Care
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. NCIT:C15747
Platform: Behavioral / lifestyle
Management of severe global developmental delay, axial hypotonia, spasticity and contractures, kyphoscoliosis, and cerebral visual impairment requires multidisciplinary supportive care, physical therapy and orthopaedic surveillance.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Common clinical features included severe global developmental delay (6/6 cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases), spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6 cases)."
Enumerates the comorbidities that define the supportive-care needs.
Genetic Counseling
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. NCIT:C15240
Platform: Behavioral / lifestyle
Counseling covers the typically de novo origin of the dominant variants and the specific possibility of low-level parental mosaicism, which has been detected at 5-6% allelic fraction in unaffected parents in this cohort and raises recurrence risk above the baseline assumed for a de novo event.
Show evidence (1 reference)
PMID:27476654 SUPPORT Human Clinical
"parental mosaicism was identified in two out of 14 cases tested with mutant allelic fractions of 5%-6% in the unaffected parents, carrying significant reproductive counseling implications"
Directly supports the mosaicism-focused counseling content of this entry.
🔬

Diagnosis

2
SLC1A2 Molecular Diagnosis
Diagnosis rests on identification of a heterozygous pathogenic SLC1A2 missense variant, typically de novo, in an infant with neonatal-onset refractory multifocal epilepsy. Because the pathogenic alleles are recurrent and confined to the trimerization domain, exome or epilepsy gene-panel sequencing is the practical route. Deep coverage of parental samples is worthwhile: low-level parental mosaicism has been detected at 5-6% allelic fraction in apparently de novo DEE cases and changes recurrence-risk counseling.
Show evidence (1 reference)
PMID:27476654 SUPPORT Human Clinical
"We sought to identify additional pathogenic variants in a subset (n = 27) of these genes via targeted sequencing in an unsolved cohort of 531 individuals with a diverse range of EEs."
Describes the targeted-sequencing route by which SLC1A2 pathogenic variants are identified in unsolved epileptic encephalopathy.
EEG and Neuroimaging Phenotyping
EEG shows multifocal and generalized epileptiform discharges on an abnormal background, with modified or classic hypsarrhythmia. Serial MRI is important for staging rather than diagnosis: imaging is normal for the first several months and only later shows delayed myelination, corpus callosum thinning and cortical atrophy, so a normal early MRI does not argue against the diagnosis.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"Brain MRIs were all normal for the first several months of life"
Supports the caveat that early normal neuroimaging does not exclude the diagnosis.
📈

Progression

1
Neonatal onset through infancy
Seizures begin between two days and six weeks of life as focal motor events and broaden into a multi-seizure-type refractory epilepsy. Brain MRI is normal for the first several months, with delayed myelination, corpus callosum thinning and cortical atrophy appearing from around five months. Severe global developmental delay is established in essentially all dominant cases. The recessive form follows a substantially milder course with onset at two years, monotherapy-controlled seizures, and mild delay.
Show evidence (2 references)
PMID:30937933 SUPPORT Human Clinical
"All six de novo dominant cases developed early onset epilepsy with symptom onset between 2 days and 6 weeks of life"
Anchors the onset window of the progression narrative.
PMID:30937933 SUPPORT Human Clinical
"Of note, the case of recessive SLC1A2-related epilepsy appears milder, with seizure onset at 2 years of age that was controlled with a single medication and mild developmental delay."
Contrasts the milder recessive trajectory with the dominant course.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
An ultra-rare disorder. The expanded phenotype description in 2019 was based on seven independent cases in total (six de novo dominant, one recessive). No population prevalence estimate exists.
Show evidence (1 reference)
PMID:30937933 SUPPORT Human Clinical
"We present an expanded clinical phenotype of SLC1A2-related epilepsy based on seven independent cases, including: one new de novo dominant case; five previously reported de novo dominant cases"
Establishes the very small number of reported cases underpinning the ULTRA_RARE class and CASES_IN_LITERATURE measure.
🔀

Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from SLC1A2-Related Developmental and Epileptic Encephalopathy:

Other genetic developmental and epileptic encephalopathies
Overlapping Features Neonatal-onset refractory multifocal epilepsy with severe developmental delay is genetically heterogeneous. In the same targeted-sequencing study that established SLC1A2, pathogenic variants in CACNA1A, GABRB3, ALG13, DNM1, GNAO1 and IQSEC2 were also identified in individuals with epileptic encephalopathy, and these are the practical differential on a gene panel. Distinguishing features favouring SLC1A2 are the recurrent trimerization-domain missense alleles and the initially normal MRI that later acquires delayed myelination and cortical atrophy.
Show evidence (1 reference)
PMID:27476654 SUPPORT Human Clinical
"We also identified EEs caused by genetic variants in ALG13, DNM1, and GNAO1 and report a mutation in IQSEC2."
Enumerates the co-identified genetic causes of epileptic encephalopathy that constitute the differential.
{ }

Source YAML

click to show 
name: SLC1A2-Related Developmental and Epileptic Encephalopathy
creation_date: "2026-08-05T00:00:00Z"
description: >-
  A severe, early-onset developmental and epileptic encephalopathy (DEE41) caused
  by recurrent de novo heterozygous missense variants in SLC1A2, which encodes
  EAAT2/GLT-1, the astrocytic and presynaptic transporter that carries out the
  bulk of L-glutamate clearance from the synaptic cleft in the mammalian brain.
  The three recurrent variants (p.Gly82Arg, p.Leu85Pro, p.Pro289Arg) all fall in
  the trimerization domain of the trimeric transporter and act through a dominant
  negative mechanism that reduces - but does not eliminate - wild-type EAAT2
  localization and function, placing carriers below a critical dosage of
  functional transporter. Two mechanistically distinct consequences have been
  demonstrated: loss of glutamate uptake, and, for the pore-lining Gly82Arg and
  Leu85Pro substitutions, enlargement of the EAAT anion pore so that mutant
  transporters become L-glutamate EFFLUX pathways. Both routes raise extracellular
  glutamate, driving excitotoxicity, glutamatergic excitation-inhibition
  imbalance, and refractory neonatal-onset multifocal seizures with severe global
  developmental delay and progressive MRI abnormalities. A rare, milder recessive
  form is also reported. This gene- and mechanism-anchored entry is distinct from
  the phenotype-level Epilepsy entry and from the generic DEE label.
category: Mendelian
parents:
- Epilepsy
- Neurodevelopmental Disorder
synonyms:
- DEE41
- EIEE41
- Developmental and epileptic encephalopathy 41
- Epileptic encephalopathy, early infantile, 41
- SLC1A2-related epilepsy
- EAAT2 encephalopathy
- GLT-1 encephalopathy
disease_term:
  preferred_term: SLC1A2-related developmental and epileptic encephalopathy
  term:
    id: MONDO:0014916
    label: developmental and epileptic encephalopathy, 41
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0014916
      label: developmental and epileptic encephalopathy, 41
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0014916 is the gene-anchored disease concept for this entity - its
      definition states it is "Any early infantile epileptic encephalopathy in
      which the cause of the disease is a mutation in the SLC1A2 gene", it carries
      an RO:0004003 (has material basis in germline mutation in) relationship to
      HGNC:10940 SLC1A2, and it is equivalent to OMIM:617105. This entry therefore
      sits at exactly the same altitude as the MONDO term.
inheritance:
- name: Autosomal Dominant (De Novo, Dominant-Negative)
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    The severe, classical form arises from a recurrent de novo heterozygous
    SLC1A2 missense variant acting in a dominant negative fashion on the trimeric
    transporter. Because simple heterozygous SLC1A2 deletion is not epileptogenic
    in humans or mice, the mode of inheritance here is dominant only by virtue of
    the dominant-negative protein effect, not by haploinsufficiency. Parental
    mosaicism at low allelic fraction has been documented in the Epi4K cohort and
    carries recurrence-risk counseling implications.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recurrent de novo SLC1A2 missense variants cause a severe, early onset
      developmental and epileptic encephalopathy via an unclear mechanism.
    explanation: >-
      Establishes the recurrent de novo heterozygous missense origin of the severe
      form of the disorder.
  - reference: PMID:27476654
    reference_title: "De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      As a result of high-depth coverage, parental mosaicism was identified in two
      out of 14 cases tested with mutant allelic fractions of 5%-6% in the
      unaffected parents, carrying significant reproductive counseling
      implications.
    explanation: >-
      Documents low-level parental mosaicism in this de novo DEE cohort, which
      modifies recurrence-risk counseling for apparently de novo variants.
- name: Autosomal Recessive (Rare, Milder)
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    A rare recessive form of SLC1A2-related epilepsy has been reported and is
    clinically milder than the de novo dominant form, with later seizure onset,
    monotherapy-responsive seizures, and only mild developmental delay. The
    severity difference is attributed to a greater amount of residual functional
    EAAT2 protein than the dominant-negative alleles permit.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of note, the case of recessive SLC1A2-related epilepsy appears milder, with
      seizure onset at 2 years of age that was controlled with a single medication
      and mild developmental delay.
    explanation: >-
      Documents the existence and milder clinical course of the recessive form,
      justifying a second inheritance block.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    An ultra-rare disorder. The expanded phenotype description in 2019 was based
    on seven independent cases in total (six de novo dominant, one recessive). No
    population prevalence estimate exists.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We present an expanded clinical phenotype of SLC1A2-related epilepsy based
      on seven independent cases, including: one new de novo dominant case; five
      previously reported de novo dominant cases
    explanation: >-
      Establishes the very small number of reported cases underpinning the
      ULTRA_RARE class and CASES_IN_LITERATURE measure.
references:
- reference: PMID:27476654
  title: "De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies."
- reference: PMID:30764523
  title: "Pediatric Epilepsy Mechanisms: Expanding the Paradigm of Excitation/Inhibition Imbalance."
- reference: PMID:30937933
  title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
- reference: PMID:34961934
  title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
- reference: PMID:36543780
  title: "Functional investigation of SLC1A2 variants associated with epilepsy."
- reference: PMID:9180080
  title: "Epilepsy and exacerbation of brain injury in mice lacking the glutamate transporter GLT-1."
- reference: PMID:34716961
  title: "Loss of glutamate transporter eaat2a leads to aberrant neuronal excitability, recurrent epileptic seizures, and basal hypoactivity."
pathophysiology:
- name: SLC1A2 Trimerization-Domain Missense Variant
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Ion Channel and Synaptic Dysfunction"
  biological_scale: MOLECULAR
  description: >-
    The initiating lesion is a heterozygous de novo missense substitution in
    SLC1A2, which encodes the trimeric glutamate transporter EAAT2 (GLT-1). All
    three recurrent disease variants - p.Gly82Arg, p.Leu85Pro and p.Pro289Arg -
    localize to the trimerization domain of the transporter rather than to the
    transport domain, so the primary molecular event is a defect of subunit
    assembly and trafficking within the obligate trimer rather than a simple
    catalytic-site lesion. This node captures the single molecular trigger.
  role: trigger
  gene:
    preferred_term: SLC1A2
    term:
      id: hgnc:10940
      label: SLC1A2
  molecular_functions:
  - preferred_term: L-glutamate transmembrane transporter activity
    term:
      id: GO:0005313
      label: L-glutamate transmembrane transporter activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: protein homooligomerization
    term:
      id: GO:0051260
      label: protein homooligomerization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We demonstrate that all 3 variants implicated in this condition localize to
      the trimerization domain of SLC1A2
    explanation: >-
      Establishes that the recurrent disease variants cluster in the trimerization
      domain, the structural basis for this trigger node.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      SLC1A2 is a trimeric transporter essential for clearing glutamate from
      neuronal synapses.
    explanation: >-
      Establishes the trimeric architecture and synaptic glutamate-clearance role
      of the affected protein.
  - reference: PMID:27476654
    reference_title: "De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our results provide definitive evidence that de novo mutations in SLC1A2 and
      CACNA1A cause specific EEs
    explanation: >-
      Provides the human genetic evidence that de novo SLC1A2 variants are a
      definitive cause of epileptic encephalopathy.
  downstream:
  - target: Dominant-Negative Suppression of Wild-Type EAAT2
    causal_link_type: DIRECT
  - target: Mutant EAAT2 Anion Pore Glutamate Efflux
    causal_link_type: DIRECT
    hypothesis_groups:
    - anion_pore_glutamate_efflux_model
  - target: Disturbed Store-Operated Calcium Entry
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - soce_disruption_model
- name: Dominant-Negative Suppression of Wild-Type EAAT2
  biological_scale: MOLECULAR
  description: >-
    Because EAAT2 functions as an obligate trimer, a trimerization-domain variant
    subunit co-assembles with wild-type subunits into mixed trimers and suppresses
    their function. The Leu85Pro variant reduces - but does not eliminate -
    wild-type SLC1A2 protein localization and transport activity, cutting
    glutamate transport by roughly a third relative to wild-type alone. This
    explains the central genotype paradox of the disorder: simple heterozygous
    loss of one SLC1A2 allele is not epileptogenic, so the dominant-negative
    effect is what pushes carriers below a critical threshold of functional
    transporter (inferred to lie somewhere between 0 and 50 percent of wild-type).
  role: amplifier
  molecular_functions:
  - preferred_term: L-glutamate transmembrane transporter activity
    term:
      id: GO:0005313
      label: L-glutamate transmembrane transporter activity
    modifier: DECREASED
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the Leu85Pro variant acts via a dominant negative mechanism to reduce, but
      not eliminate, wild-type SLC1A2 protein localization and function
    explanation: >-
      Directly establishes the dominant-negative suppression of wild-type
      transporter that defines this node.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      glutamate transport activity in cells expressing both SLC1A2wt and
      SLC1A2L85P was reduced by 33% compared to cells expressing only SLC1A2wt
    explanation: >-
      Quantifies the magnitude of dominant-negative suppression of wild-type
      transporter activity.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      it appears that there is a critical dosage of functional SLC1A2 protein
      (somewhere between 0 and 50% of wild-type) under which seizures develop
    explanation: >-
      States the critical-dosage threshold model that reconciles the
      non-epileptogenic heterozygous deletion with the severe missense phenotype.
  downstream:
  - target: Impaired Astrocytic Glutamate Clearance
    causal_link_type: DIRECT
    hypothesis_groups:
    - transport_loss_of_function_model
- name: Impaired Astrocytic Glutamate Clearance
  biological_scale: CELLULAR
  description: >-
    EAAT2 is expressed in astrocytes and presynaptic nerve terminals and is the
    principal L-glutamate uptake carrier of the mammalian brain; together with
    EAAT1/SLC1A3 it mediates the bulk of glutamate clearance from the synaptic
    cleft. Disease-linked variants significantly decrease glutamate uptake, cell
    surface expression of the transporter, and glutamate-elicited transport
    current, so synaptically released glutamate is no longer removed at the
    normal rate. This is the central effector of the canonical mechanism.
  role: central_effector
  cell_types:
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  - preferred_term: glutamatergic neuron
    term:
      id: CL:0000679
      label: glutamatergic neuron
  biological_processes:
  - preferred_term: glutamate reuptake
    term:
      id: GO:0051935
      label: glutamate reuptake
    modifier: DECREASED
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      EAAT2 is expressed in glial cells and presynaptic nerve terminals and
      represents the main l-glutamate uptake carrier in the mammalian brain.
    explanation: >-
      Establishes EAAT2 as the dominant glutamate uptake carrier whose loss
      defines this node, and its astrocytic/presynaptic localization.
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      we reported that these disease-linked mutants significantly decrease
      glutamate uptake, cell membrane expression of the glutamate transporter, and
      glutamate-elicited current
    explanation: >-
      Provides direct functional evidence that the three disease variants reduce
      glutamate uptake and surface transporter expression.
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Astrocytic glutamate transporter GLT-1 is responsible for preventing
      excitotoxicity via clearing extracellular accumulated glutamate.
    explanation: >-
      States the anti-excitotoxic clearance function whose failure links this node
      to the downstream excitotoxicity node.
  downstream:
  - target: Extracellular Glutamate Accumulation and Excitotoxicity
    causal_link_type: DIRECT
    hypothesis_groups:
    - transport_loss_of_function_model
- name: Mutant EAAT2 Anion Pore Glutamate Efflux
  biological_scale: MOLECULAR
  description: >-
    EAAT2 is not only a secondary active transporter but also an anion channel.
    The pore-lining Gly82Arg and Leu85Pro substitutions enlarge the anion pore
    enough to permit passage of L-glutamate itself, converting the mutant
    transporter into a glutamate EFFLUX pathway - a gain of function that adds to,
    rather than merely subtracts from, the uptake defect. Pro289Arg instead
    decreases uptake while increasing anion current. This arm predicts that
    selective EAAT anion-channel antagonists, not uptake enhancers, would be the
    rational therapy, and is modeled as a distinct mechanistic hypothesis.
  role: amplifier
  molecular_functions:
  - preferred_term: L-glutamate transmembrane transporter activity
    term:
      id: GO:0005313
      label: L-glutamate transmembrane transporter activity
    modifier: ABNORMAL
  biological_processes:
  - preferred_term: L-glutamate transmembrane transport
    term:
      id: GO:0015813
      label: L-glutamate transmembrane transport
    modifier: ABNORMAL
  evidence:
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      G82R and L85P exchange amino acid residues that contribute to the formation
      of the EAAT anion pore. They enlarge the pore diameter sufficiently to permit
      the passage of l-glutamate and thus function as l-glutamate efflux pathways.
    explanation: >-
      Directly establishes the anion-pore enlargement and resulting glutamate
      efflux that define this node.
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The mutation P289R decreases l-glutamate uptake, but increases anion
      currents despite a lower membrane expression.
    explanation: >-
      Shows the variant-specific split between the uptake-loss and anion-current
      arms, justifying modeling them as separate mechanisms.
  downstream:
  - target: Extracellular Glutamate Accumulation and Excitotoxicity
    causal_link_type: DIRECT
    hypothesis_groups:
    - anion_pore_glutamate_efflux_model
- name: Disturbed Store-Operated Calcium Entry
  biological_scale: MOLECULAR
  description: >-
    An emerging, less-established arm: the three disease variants appear to
    disturb STIM1/Orai1-mediated store-operated calcium entry at the endoplasmic
    reticulum, with GLT-1 proposed as a new partner of the SOCE machinery. If
    confirmed, this would add a calcium-signaling component to the disorder that
    is independent of extracellular glutamate handling. It is curated as an
    EMERGING hypothesis rather than part of the canonical chain.
  role: modifier
  biological_processes:
  - preferred_term: store-operated calcium entry
    term:
      id: GO:0002115
      label: store-operated calcium entry
    modifier: ABNORMAL
  evidence:
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      in which GLT-1 may be a new partner of SOCE
    explanation: >-
      Reports the proposed GLT-1/SOCE interaction underlying this emerging arm;
      the hedged wording in the source is why it is curated as EMERGING.
  downstream:
  - target: Excitation-Inhibition Imbalance and Neuronal Hyperexcitability
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - soce_disruption_model
- name: Extracellular Glutamate Accumulation and Excitotoxicity
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Excitation-Inhibition Imbalance"
  biological_scale: TISSUE
  description: >-
    Whether by failed uptake or by efflux through the widened anion pore, the net
    result is elevated extracellular glutamate in the synaptic cleft and
    interstitial space. Excessive activation of glutamate receptors produces
    excitotoxic injury. The causal sufficiency of this step is established in
    model organisms: GLT-1 null mice show lethal spontaneous seizures attributable
    to elevated residual brain glutamate, and eaat2a-null zebrafish show recurrent
    seizures coinciding with an abrupt rise in extracellular glutamate.
  role: central_effector
  cell_types:
  - preferred_term: glutamatergic neuron
    term:
      id: CL:0000679
      label: glutamatergic neuron
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: excitatory postsynaptic potential
    term:
      id: GO:0060079
      label: excitatory postsynaptic potential
    modifier: INCREASED
  locations:
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  evidence:
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      l-glutamate efflux through mutant EAAT2 anion channels will cause glutamate
      excitotoxicity and neuronal hyperexcitability in affected patients.
    explanation: >-
      Links the molecular arms of the disorder to glutamate excitotoxicity and
      hyperexcitability, this node and the next.
  - reference: PMID:9180080
    reference_title: "Epilepsy and exacerbation of brain injury in mice lacking the glutamate transporter GLT-1."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Homozygous mice deficient in GLT-1, a widely distributed astrocytic
      glutamate transporter, show lethal spontaneous seizures and increased
      susceptibility to acute cortical injury.
    explanation: >-
      Model-organism evidence that loss of GLT-1 is sufficient to produce
      spontaneous seizures and heightened excitotoxic injury.
  - reference: PMID:9180080
    reference_title: "Epilepsy and exacerbation of brain injury in mice lacking the glutamate transporter GLT-1."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These effects can be attributed to elevated levels of residual glutamate in
      the brains of these mice.
    explanation: >-
      Attributes the seizure and injury phenotype specifically to elevated
      extracellular glutamate, the substance of this node.
  - reference: PMID:34716961
    reference_title: "Loss of glutamate transporter eaat2a leads to aberrant neuronal excitability, recurrent epileptic seizures, and basal hypoactivity."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We observed that eaat2a-/- mutant zebrafish larvae display recurrent
      spontaneous and light-induced seizures in neurons and astroglia, which
      coincide with an abrupt increase in extracellular glutamate levels.
    explanation: >-
      Independent model-organism confirmation that EAAT2 loss raises extracellular
      glutamate in temporal register with seizure events.
  downstream:
  - target: Excitation-Inhibition Imbalance and Neuronal Hyperexcitability
    causal_link_type: DIRECT
  - target: Progressive Excitotoxic Neuronal and White Matter Injury
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Cumulative excessive activation of postsynaptic glutamate receptors.
- name: Excitation-Inhibition Imbalance and Neuronal Hyperexcitability
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Neuronal Hyperexcitability and Hypersynchrony"
  biological_scale: CELLULAR
  description: >-
    Sustained elevation of extracellular glutamate shifts cortical networks toward
    net excitation, prolonging and broadening neuronal excitation because the
    duration and extent of glutamatergic signaling is normally terminated by EAAT2
    uptake. The resulting hyperexcitable, hypersynchronous state is the substrate
    for the multifocal and generalized epileptiform discharges seen on EEG.
    Notably, animal models show that this hyperexcitability coexists with reduced
    BASAL network activity, so the disorder is a dysregulation of excitability
    rather than a uniform increase.
  role: amplifier
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: chemical synaptic transmission
    term:
      id: GO:0007268
      label: chemical synaptic transmission
    modifier: ABNORMAL
  evidence:
  - reference: PMID:34716961
    reference_title: "Loss of glutamate transporter eaat2a leads to aberrant neuronal excitability, recurrent epileptic seizures, and basal hypoactivity."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Astroglial excitatory amino acid transporter 2 (EAAT2, GLT-1, and SLC1A2)
      regulates the duration and extent of neuronal excitation by removing
      glutamate from the synaptic cleft.
    explanation: >-
      States the normal function - termination of neuronal excitation - whose loss
      produces the hyperexcitable state modeled here.
  - reference: PMID:34716961
    reference_title: "Loss of glutamate transporter eaat2a leads to aberrant neuronal excitability, recurrent epileptic seizures, and basal hypoactivity."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In stark contrast to this hyperexcitability, basal neuronal and astroglial
      activity was surprisingly reduced in eaat2a-/- mutant animals, which
      manifested in decreased overall locomotion.
    explanation: >-
      Documents the coexisting basal hypoactivity that qualifies a naive
      "pure hyperexcitability" reading of this node.
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Furthermore, knock-in mice with disease-associated variants showed a
      hyperactive phenotype accompanied by reduced glutamate transporter
      expression.
    explanation: >-
      Variant-specific knock-in mouse evidence connecting reduced transporter
      expression to an altered-excitability behavioural phenotype.
  downstream:
  - target: Seizure Generation and Epileptogenesis
    causal_link_type: DIRECT
- name: Seizure Generation and Epileptogenesis
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Seizure Generation and Epileptogenesis"
  biological_scale: CELLULAR
  description: >-
    The hyperexcitable neuronal state increases the propensity for seizure
    generation and epileptogenesis. In this disorder, that shared epilepsy
    effector step links glutamate-driven network hyperexcitability to the
    recurrent neonatal-onset seizure syndrome modeled downstream, without
    conflating the generic network process with its specific clinical phenotype.
  role: effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:30764523
    reference_title: "Pediatric Epilepsy Mechanisms: Expanding the Paradigm of Excitation/Inhibition Imbalance."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      increased excitation, decreased inhibition, or both favor a hyperexcitable
      state and an increased propensity for seizure generation and
      epileptogenesis.
    explanation: >-
      A pediatric epilepsy review directly links a hyperexcitable state to
      seizure generation and epileptogenesis, supporting this shared-module
      bridge between the upstream cellular state and the disease-specific
      seizure phenotype.
  downstream:
  - target: Refractory Neonatal-Onset Multifocal Epilepsy
    causal_link_type: DIRECT
- name: Progressive Excitotoxic Neuronal and White Matter Injury
  biological_scale: TISSUE
  description: >-
    Cumulative neuronal damage from excessive glutamate-receptor activation
    accrues over time and is visible on serial neuroimaging. Brain MRI is normal
    for the first several months of life and only from around five months begins
    to show delayed myelination, thinning of the corpus callosum, and cerebral
    cortical atrophy. The initially normal imaging is mechanistically important:
    it argues that the structural abnormality is an acquired consequence of
    ongoing excitotoxicity rather than a primary malformation, and it defines a
    therapeutic window before injury accumulates.
  role: effector
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: myelination
    term:
      id: GO:0042552
      label: myelination
    modifier: DECREASED
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain MRIs were all normal for the first several months of life, but around
      5 months of life began to show evidence of delayed myelination, thinning of
      the corpus callosum, and cerebral cortical atrophy.
    explanation: >-
      Establishes the acquired, progressive nature and the specific imaging
      substrate of this node.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      It is likely, based on progressive neuroimaging abnormalities in this
      disorder, that there is cumulative neuronal damage over time from excessive
      activation of glutamate receptors.
    explanation: >-
      States the excitotoxic interpretation of the progressive imaging findings
      that this node models.
  downstream:
  - target: Developmental and Epileptic Encephalopathy
    causal_link_type: DIRECT
- name: Refractory Neonatal-Onset Multifocal Epilepsy
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Recurrent Unprovoked Seizures"
  biological_scale: ORGANISM
  description: >-
    Seizures begin between two days and six weeks of life, typically as focal
    motor events (often tonic or myoclonic) and progress to multiple seizure types
    including epileptic spasms, myoclonic seizures, focal and generalized tonic
    seizures, and tonic-clonic seizures. Seizures are systematically refractory to
    multiple antiseizure medications, and EEG shows multifocal and generalized
    epileptiform discharges on an abnormal background, including modified and
    classic hypsarrhythmia.
  role: effector
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All six de novo dominant cases developed early onset epilepsy with symptom
      onset between 2 days and 6 weeks of life
    explanation: >-
      Establishes the neonatal-to-early-infantile onset window of the seizure
      phenotype.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Seizures typically presented as focal motor events (often tonic or
      myoclonic), and progressed to multiple seizure types including epileptic
      spasms, myoclonic seizures, focal and generalized tonic seizures, and
      tonic-clonic seizures.
    explanation: >-
      Documents the evolving multifocal seizure semiology modeled by this node.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Seizures were systematically refractory to multiple medications.
    explanation: >-
      Establishes pharmacoresistance as a defining feature of the seizure
      phenotype.
  downstream:
  - target: Developmental and Epileptic Encephalopathy
    causal_link_type: DIRECT
- name: Developmental and Epileptic Encephalopathy
  biological_scale: ORGANISM
  description: >-
    The convergent organism-level outcome: severe global developmental delay in
    essentially all affected individuals, with cortical visual impairment, axial
    hypotonia, spasticity and/or joint contractures, and kyphoscoliosis. Both the
    ongoing epileptic activity and the underlying excitotoxic injury contribute to
    the developmental impairment, which is the defining feature of a
    developmental AND epileptic encephalopathy as opposed to a pure epilepsy.
  role: outcome
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common clinical features included severe global developmental delay (6/6
      cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases),
      spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6
      cases).
    explanation: >-
      Enumerates the organism-level features and their frequencies in the reported
      dominant cohort.
mechanistic_hypotheses:
- hypothesis_group_id: transport_loss_of_function_model
  hypothesis_label: Dominant-Negative Transport Loss-of-Function Model
  status: CANONICAL
  description: >-
    The canonical model holds that trimerization-domain variants reduce EAAT2
    glutamate uptake both directly and by dominant-negative suppression of
    co-assembled wild-type subunits, driving carriers below a critical threshold
    of functional transporter and allowing extracellular glutamate to accumulate.
    It is supported by direct uptake and surface-expression assays for all three
    recurrent variants, by the quantified dominant-negative effect on wild-type
    protein, and by the seizure phenotype of GLT-1 null mice and eaat2a-null
    zebrafish. Under this model the rational therapy is to increase functional
    transporter.
  evidence:
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      we reported that these disease-linked mutants significantly decrease
      glutamate uptake, cell membrane expression of the glutamate transporter, and
      glutamate-elicited current
    explanation: >-
      Provides the core uptake-loss measurement across all three recurrent
      variants that this model rests on.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the Leu85Pro variant acts via a dominant negative mechanism to reduce, but
      not eliminate, wild-type SLC1A2 protein localization and function
    explanation: >-
      Supplies the dominant-negative component that distinguishes this model from
      simple haploinsufficiency.
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Therefore, GLT-1 is a promising and reliable therapeutic target for epilepsy
      interventions.
    explanation: >-
      States the therapeutic corollary of this model - boosting transporter
      function - which the anion-pore model would not predict.
- hypothesis_group_id: anion_pore_glutamate_efflux_model
  hypothesis_label: Widened EAAT Anion Pore / Glutamate Efflux Gain-of-Function Model
  status: ALTERNATIVE
  description: >-
    A mechanistically distinct account, not merely a restatement of transport
    loss: because EAAT2 is also an anion channel, the pore-lining Gly82Arg and
    Leu85Pro substitutions widen the anion pore enough for L-glutamate itself to
    permeate, so the mutant transporter actively EXPORTS glutamate rather than
    only failing to import it. This is a gain of function and predicts a different
    therapy - selective EAAT anion-channel antagonists - whereas the canonical
    model predicts benefit from increasing transporter expression. The two models
    are not mutually exclusive and may operate in parallel for different variants;
    Pro289Arg shows the split directly, losing uptake while gaining anion current.
    Discriminating them clinically matters, because an uptake-enhancing agent
    would increase expression of a variant transporter that, under this model,
    leaks glutamate. An independent 18-patient, 13-variant cohort has since
    corroborated the model at the clinical level: individuals carrying Gly82Arg,
    Leu85Pro, Pro289Arg, or the further recurrent pore-lining variant Leu85Arg
    (all classified as "mixed loss-of-transport/gain-of-anion-channel function")
    had systematically more severe disease than individuals whose variants caused
    pure transport loss-of-function with no anion-current change, directly
    supporting anion-channel gain of function as a distinct, clinically material
    pathogenic contribution rather than a redundant description of transport loss.
  evidence:
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      It does not only function as a secondary active glutamate transporter, but
      also as an anion channel.
    explanation: >-
      Establishes the dual transporter/anion-channel nature of EAAT2 on which this
      alternative model depends.
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      l-glutamate permeability of the EAAT anion pore is an unexpected functional
      consequence of naturally occurring single amino acid substitutions.
    explanation: >-
      States the novel gain-of-function finding that differentiates this model
      from the canonical uptake-loss account.
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Antagonists that selectively suppress the EAAT anion channel function could
      serve as therapeutic agents in the future.
    explanation: >-
      Captures the divergent therapeutic prediction that makes discriminating the
      two models clinically consequential.
  - reference: PMID:40174554
    reference_title: "The severity of SLC1A2-associated neurodevelopmental disorders correlates with transporter dysfunction."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Individuals harbouring the heterozygous G82R, L85P, L85R or P289R variants
      inducing the “mixed loss-of-transport/gain-of-anion-channel function”
      molecular phenotype presented with by far the most severe clinical outcomes
      (early infantile DEE, profound intellectual disability, non-ambulant and
      nonverbal) in our cohort.
    explanation: >-
      Independent 18-patient/13-variant cohort corroborates the alternative model
      at the clinical level: the anion-pore-efflux variants (which also include
      the further recurrent Leu85Arg allele) are the most severely affected group,
      arguing that the anion-channel gain of function is a distinct pathogenic
      contribution and not a redundant restatement of transport loss.
- hypothesis_group_id: soce_disruption_model
  hypothesis_label: STIM1/Orai1 Store-Operated Calcium Entry Disruption Arm
  status: EMERGING
  description: >-
    An emerging arm proposing that disease variants additionally perturb
    STIM1/Orai1-mediated store-operated calcium entry, with GLT-1 acting as a
    partner of the SOCE machinery. This would introduce a calcium-signaling
    contribution independent of extracellular glutamate handling. The source
    reports it in hedged terms and it has not been independently replicated, so it
    is curated as EMERGING and is deliberately kept off the canonical causal
    chain.
  evidence:
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: IN_VITRO
    snippet: >-
      in which GLT-1 may be a new partner of SOCE
    explanation: >-
      The originating observation for this arm. Marked INDIRECT because the
      source itself states the interaction only as a possibility rather than a
      demonstrated finding.
phenotypes:
- name: Epileptic Encephalopathy
  category: Clinical
  description: >-
    The defining presentation: refractory early-onset epilepsy in which the
    epileptic activity itself, together with the underlying excitotoxic process,
    contributes to severe developmental impairment.
  diagnostic: true
  phenotype_term:
    preferred_term: Epileptic encephalopathy
    term:
      id: HP:0200134
      label: Epileptic encephalopathy
    onset:
      onset_category: NEONATAL
      max_age_years: 0.12
      notes: >-
        Seizure onset between 2 days and 6 weeks of life across all six reported
        de novo dominant cases.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recurrent de novo SLC1A2 missense variants cause a severe, early onset
      developmental and epileptic encephalopathy via an unclear mechanism.
    explanation: >-
      Establishes the developmental and epileptic encephalopathy phenotype as the
      disease-defining presentation.
- name: Focal Motor Seizure
  category: Clinical
  description: >-
    The typical presenting seizure type in the neonatal period, often tonic or
    myoclonic in semiology, before evolution to multiple seizure types.
  phenotype_term:
    preferred_term: Focal motor seizure
    term:
      id: HP:0011153
      label: Focal motor seizure
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Seizures typically presented as focal motor events (often tonic or
      myoclonic), and progressed to multiple seizure types including epileptic
      spasms, myoclonic seizures, focal and generalized tonic seizures, and
      tonic-clonic seizures.
    explanation: >-
      Establishes focal motor events as the typical presenting seizure type; the
      qualitative word "typically" does not justify a quantitative frequency
      band.
- name: Epileptic Spasms
  category: Clinical
  description: >-
    Epileptic spasms emerge as the seizure phenotype evolves and were the seizure
    type quantified during the ceftriaxone treatment trial.
  phenotype_term:
    preferred_term: Epileptic spasm
    term:
      id: HP:0011097
      label: Epileptic spasm
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      progressed to multiple seizure types including epileptic spasms, myoclonic
      seizures, focal and generalized tonic seizures, and tonic-clonic seizures
    explanation: >-
      Documents epileptic spasms within the evolving seizure repertoire.
- name: Generalized Myoclonic Seizure
  category: Clinical
  phenotype_term:
    preferred_term: Generalized myoclonic seizure
    term:
      id: HP:0002123
      label: Generalized myoclonic seizure
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      progressed to multiple seizure types including epileptic spasms, myoclonic
      seizures, focal and generalized tonic seizures, and tonic-clonic seizures
    explanation: >-
      Lists myoclonic seizures among the seizure types observed.
- name: Generalized Tonic Seizure
  category: Clinical
  phenotype_term:
    preferred_term: Generalized tonic seizure
    term:
      id: HP:0010818
      label: Generalized tonic seizure
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      progressed to multiple seizure types including epileptic spasms, myoclonic
      seizures, focal and generalized tonic seizures, and tonic-clonic seizures
    explanation: >-
      Lists generalized tonic seizures among the seizure types observed.
- name: Bilateral Tonic-Clonic Seizure
  category: Clinical
  phenotype_term:
    preferred_term: Bilateral tonic-clonic seizure
    term:
      id: HP:0002069
      label: Bilateral tonic-clonic seizure
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      progressed to multiple seizure types including epileptic spasms, myoclonic
      seizures, focal and generalized tonic seizures, and tonic-clonic seizures
    explanation: >-
      Lists tonic-clonic seizures among the seizure types observed.
- name: Multifocal Epileptiform Discharges
  category: Clinical
  description: >-
    EEG shows multifocal and generalized epileptiform discharges on an abnormal
    background.
  diagnostic: true
  phenotype_term:
    preferred_term: Multifocal epileptiform discharges
    term:
      id: HP:0010841
      label: Multifocal epileptiform discharges
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      EEG patterns demonstrated multifocal and generalized epileptiform discharges
      with abnormal background activity, including modified and classic
      hypsarrhythmia.
    explanation: >-
      Directly documents the multifocal and generalized epileptiform EEG pattern.
- name: Hypsarrhythmia
  category: Clinical
  description: >-
    Both modified and classic hypsarrhythmia were observed, consistent with the
    epileptic-spasms component of the phenotype.
  phenotype_term:
    preferred_term: Hypsarrhythmia
    term:
      id: HP:0002521
      label: Hypsarrhythmia
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      including modified and classic hypsarrhythmia
    explanation: >-
      Documents hypsarrhythmia in the reported EEG phenotype.
- name: Severe Global Developmental Delay
  category: Clinical
  description: >-
    Present in all six reported de novo dominant cases.
  phenotype_term:
    preferred_term: Severe global developmental delay
    term:
      id: HP:0011344
      label: Severe global developmental delay
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common clinical features included severe global developmental delay (6/6
      cases)
    explanation: >-
      6/6 (100%) of reported dominant cases supports a VERY_FREQUENT band.
- name: Axial Hypotonia
  category: Clinical
  phenotype_term:
    preferred_term: Axial hypotonia
    term:
      id: HP:0008936
      label: Axial hypotonia
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common clinical features included severe global developmental delay (6/6
      cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases),
      spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6
      cases).
    explanation: >-
      6/6 (100%) of reported dominant cases supports a VERY_FREQUENT band.
- name: Cerebral Visual Impairment
  category: Clinical
  phenotype_term:
    preferred_term: Cerebral visual impairment
    term:
      id: HP:0100704
      label: Cerebral visual impairment
  frequency: FREQUENT
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      cortical visual impairment (3/6 cases)
    explanation: >-
      3/6 (50%) of reported dominant cases falls in the FREQUENT band (30-79%).
- name: Spasticity
  category: Clinical
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      spasticity and/or joint contractures (5/6 cases)
    explanation: >-
      Supports the association with spasticity only. No separate frequency is
      asserted because the source pools spasticity with joint contractures in a
      disjunctive count.
- name: Flexion Contracture
  category: Clinical
  phenotype_term:
    preferred_term: Flexion contracture
    term:
      id: HP:0001371
      label: Flexion contracture
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      spasticity and/or joint contractures (5/6 cases)
    explanation: >-
      Documents joint contractures. No separate frequency is asserted because the
      source pools contractures with spasticity in a single count.
- name: Kyphoscoliosis
  category: Clinical
  phenotype_term:
    preferred_term: Kyphoscoliosis
    term:
      id: HP:0002751
      label: Kyphoscoliosis
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common clinical features included severe global developmental delay (6/6
      cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases),
      spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6
      cases).
    explanation: >-
      Documents kyphoscoliosis in 2/6 reported dominant cases. No frequency band
      is asserted because the estimate comes from only six cases.
- name: Delayed Myelination
  category: Clinical
  description: >-
    Absent on early infant MRI and emerging from around five months of life,
    consistent with an acquired rather than malformative process.
  phenotype_term:
    preferred_term: Delayed myelination
    term:
      id: HP:0012448
      label: Delayed myelination
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      around 5 months of life began to show evidence of delayed myelination,
      thinning of the corpus callosum, and cerebral cortical atrophy
    explanation: >-
      Documents delayed myelination and its delayed, progressive appearance.
- name: Thin Corpus Callosum
  category: Clinical
  phenotype_term:
    preferred_term: Thin corpus callosum
    term:
      id: HP:0033725
      label: Thin corpus callosum
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      around 5 months of life began to show evidence of delayed myelination,
      thinning of the corpus callosum, and cerebral cortical atrophy
    explanation: >-
      Documents progressive corpus callosum thinning.
- name: Cerebral Cortical Atrophy
  category: Clinical
  phenotype_term:
    preferred_term: Cerebral cortical atrophy
    term:
      id: HP:0002120
      label: Cerebral cortical atrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      around 5 months of life began to show evidence of delayed myelination,
      thinning of the corpus callosum, and cerebral cortical atrophy
    explanation: >-
      Documents progressive cerebral cortical atrophy.
genetic:
- name: SLC1A2
  gene_term:
    preferred_term: SLC1A2
    term:
      id: hgnc:10940
      label: SLC1A2
  association: Recurrent De Novo Trimerization-Domain Missense Variants
  presence: Positive
  variant_origin: GERMLINE
  relationship_type: CAUSATIVE
  inheritance:
  - name: Autosomal Dominant (De Novo, Dominant-Negative)
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
  notes: >-
    Three recurrent heterozygous missense variants account for the reported
    dominant cases: p.Gly82Arg, p.Leu85Pro (c.254T>C) and p.Pro289Arg. All three
    fall in the trimerization domain. Mechanistically they are not equivalent:
    Gly82Arg and Leu85Pro line the EAAT anion pore and widen it enough to make the
    transporter a glutamate efflux pathway, while Pro289Arg reduces uptake and
    raises anion current without that pore geometry change. Simple heterozygous
    SLC1A2 deletion - as occurs in WAGR syndrome - is only rarely associated with
    epilepsy, so haploinsufficiency alone does not explain the phenotype and
    variant interpretation should not treat SLC1A2 truncating variants as
    equivalent to these missense alleles. An independent multi-center cohort has
    since reported a fourth pore-lining, anion-pore-efflux variant, p.Leu85Arg,
    with the same "mixed loss-of-transport/gain-of-anion-channel function"
    molecular phenotype as Gly82Arg and Leu85Pro, alongside other SLC1A2 variants
    that cause pure loss-of-function or mild gain-of-anion-channel-function
    phenotypes without efflux; those additional variants are not curated here
    individually because case-level phenotype detail comparable to the recurrent
    dominant alleles above is not yet available for them.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Singleton whole exome sequencing (Prevention Genetics, Marshfield, WI)
      revealed a pathogenic heterozygous c.254T>C (p.Leu85Pro) variant in the
      SLC1A2 gene
    explanation: >-
      Documents the specific recurrent Leu85Pro allele and its identification by
      exome sequencing.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      heterozygous deletion of SLC1A2 in humans (as is frequently seen in the WAGR
      deletion syndrome) is only rarely associated with epilepsy
    explanation: >-
      Establishes that SLC1A2 haploinsufficiency alone is not epileptogenic in
      humans, the key variant-interpretation caveat recorded in the notes.
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      we studied the functional consequences of three disease-associated
      mutations, which predict amino acid exchanges p.Gly82Arg (G82R), p.Leu85Pro
      (L85P), and p.Pro289Arg (P289R)
    explanation: >-
      Enumerates the three recurrent disease alleles that define the allelic
      spectrum of this entry.
  - reference: PMID:40174554
    reference_title: "The severity of SLC1A2-associated neurodevelopmental disorders correlates with transporter dysfunction."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      These molecular phenotypes were classified into three categories: overall
      loss-of-function (F249Sfs∗17, A432D, A439V, c.1421+1G>C), mild
      gain-of-anion-channel function (I276S, G360A), and mixed
      loss-of-transport/gain-of-anion-channel function (G82R, L85R, L85P, P289R).
    explanation: >-
      Reports a fourth pore-lining variant, p.Leu85Arg, functionally grouped with
      Gly82Arg/Leu85Pro/Pro289Arg in the same mixed
      loss-of-transport/gain-of-anion-channel-function molecular category.
diagnosis:
- name: SLC1A2 Molecular Diagnosis
  description: >-
    Diagnosis rests on identification of a heterozygous pathogenic SLC1A2
    missense variant, typically de novo, in an infant with neonatal-onset
    refractory multifocal epilepsy. Because the pathogenic alleles are recurrent
    and confined to the trimerization domain, exome or epilepsy gene-panel
    sequencing is the practical route. Deep coverage of parental samples is
    worthwhile: low-level parental mosaicism has been detected at 5-6% allelic
    fraction in apparently de novo DEE cases and changes recurrence-risk
    counseling.
  evidence:
  - reference: PMID:27476654
    reference_title: "De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We sought to identify additional pathogenic variants in a subset (n = 27) of
      these genes via targeted sequencing in an unsolved cohort of 531 individuals
      with a diverse range of EEs.
    explanation: >-
      Describes the targeted-sequencing route by which SLC1A2 pathogenic variants
      are identified in unsolved epileptic encephalopathy.
- name: EEG and Neuroimaging Phenotyping
  description: >-
    EEG shows multifocal and generalized epileptiform discharges on an abnormal
    background, with modified or classic hypsarrhythmia. Serial MRI is important
    for staging rather than diagnosis: imaging is normal for the first several
    months and only later shows delayed myelination, corpus callosum thinning and
    cortical atrophy, so a normal early MRI does not argue against the diagnosis.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain MRIs were all normal for the first several months of life
    explanation: >-
      Supports the caveat that early normal neuroimaging does not exclude the
      diagnosis.
progression:
- phase: Neonatal onset through infancy
  notes: >-
    Seizures begin between two days and six weeks of life as focal motor events
    and broaden into a multi-seizure-type refractory epilepsy. Brain MRI is
    normal for the first several months, with delayed myelination, corpus callosum
    thinning and cortical atrophy appearing from around five months. Severe global
    developmental delay is established in essentially all dominant cases. The
    recessive form follows a substantially milder course with onset at two years,
    monotherapy-controlled seizures, and mild delay.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All six de novo dominant cases developed early onset epilepsy with symptom
      onset between 2 days and 6 weeks of life
    explanation: >-
      Anchors the onset window of the progression narrative.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of note, the case of recessive SLC1A2-related epilepsy appears milder, with
      seizure onset at 2 years of age that was controlled with a single medication
      and mild developmental delay.
    explanation: >-
      Contrasts the milder recessive trajectory with the dominant course.
differential_diagnoses:
- name: Other genetic developmental and epileptic encephalopathies
  description: >-
    Neonatal-onset refractory multifocal epilepsy with severe developmental delay
    is genetically heterogeneous. In the same targeted-sequencing study that
    established SLC1A2, pathogenic variants in CACNA1A, GABRB3, ALG13, DNM1,
    GNAO1 and IQSEC2 were also identified in individuals with epileptic
    encephalopathy, and these are the practical differential on a gene panel.
    Distinguishing features favouring SLC1A2 are the recurrent trimerization-domain
    missense alleles and the initially normal MRI that later acquires delayed
    myelination and cortical atrophy.
  evidence:
  - reference: PMID:27476654
    reference_title: "De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We also identified EEs caused by genetic variants in ALG13, DNM1, and GNAO1
      and report a mutation in IQSEC2.
    explanation: >-
      Enumerates the co-identified genetic causes of epileptic encephalopathy that
      constitute the differential.
treatments:
- name: Antiseizure Medication
  description: >-
    Standard antiseizure medication is the mainstay but performs poorly: seizures
    in the de novo dominant form were systematically refractory to multiple
    medications. Seizures in the rare recessive form, by contrast, were controlled
    with a single medication, so pharmacoresponsiveness tracks residual EAAT2
    function rather than drug choice.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Seizures were systematically refractory to multiple medications.
    explanation: >-
      Supports the claim that standard antiseizure medication performs poorly in
      the de novo dominant form, documenting refractoriness rather than benefit.
- name: Ceftriaxone (Investigational EAAT2-Modulating Agent)
  description: >-
    Ceftriaxone is a blood-brain-barrier-penetrant beta-lactam that increases
    SLC1A2 expression and function in neural tissue, making it the most obvious
    mechanism-matched repurposing candidate under the transport-loss-of-function
    model. It has been trialled once, under an IRB-approved innovative-therapy
    protocol, in a 20-month-old with the Leu85Pro variant at 80 mg/kg/day
    intravenously for 14 days with continuous video-EEG spasm counting. It did NOT
    significantly change daily spasm frequency, though it was well tolerated. This
    is a negative n-of-1 result, not an established therapy, and is curated here
    because the negative result is mechanistically informative - it is exactly
    what the anion-pore efflux model would predict, since raising expression of a
    leaky mutant transporter should not help. Positive allosteric modulation of
    EAAT2 is a distinct pharmacological strategy under general development for
    epilepsy that increases transport activity directly rather than via
    transcriptional upregulation; it has not been reported as tested in
    SLC1A2-related DEE41 specifically, but is mechanistically relevant as an
    alternative route to the same transport-loss-of-function target.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ceftriaxone
      term:
        id: CHEBI:29007
        label: ceftriaxone
  target_mechanisms:
  - target: Impaired Astrocytic Glutamate Clearance
    treatment_effect: INHIBITS
    description: >-
      Ceftriaxone was given to oppose the pathological clearance impairment by
      increasing EAAT2 expression and restoring astrocytic glutamate clearance.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Ceftriaxone is an FDA-approved antibiotic that crosses the blood-brain
      barrier and increases SLC1A2 expression and function within several days in
      neural tissue
    explanation: >-
      Establishes the mechanistic rationale for using ceftriaxone as an
      EAAT2-modulating agent.
  - reference: PMID:33507976
    reference_title: "Pharmacological upregulation of GLT-1 alleviates the cognitive impairments in the animal model of temporal lobe epilepsy."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Ceftriaxone administration in epileptic animals led to
      a reduction of glutamate along with elevation of the level of glutamine synthetase activity and
      GLT-1 expression in the acute phase.
    explanation: >-
      Independent rodent temporal-lobe-epilepsy model supporting the same
      ceftriaxone/GLT-1-upregulation rationale used here; INDIRECT because it is
      an acquired-epilepsy model, not the SLC1A2 dominant-negative genotype, and
      so cannot speak to why the DEE41 trial itself failed.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Ceftriaxone therapy did not result in a significant change in the daily
      spasm count
    explanation: >-
      Refutes short-term clinical efficacy of ceftriaxone in this n-of-1 trial;
      recorded as REFUTE so the negative result is not read as support.
  - reference: PMID:34571003
    reference_title: "Role of glutamate excitotoxicity and glutamate transporter EAAT2 in epilepsy: Opportunities for novel therapeutics development."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    snippet: >-
      Another approach to regulate EAAT2 activity is through positive allosteric
      modulation (PAM). Novel PAMs of EAAT2 have recently been identified and are
      under development, representing a promising approach for the advance of
      novel therapeutics for epilepsy.
    explanation: >-
      Supports the existence of a PAM-based alternative to transcriptional EAAT2
      upregulation; INDIRECT because this review is not specific to SLC1A2-DEE41
      and no PAM has been reported as tested in this disease.
- name: Supportive and Rehabilitative Care
  description: >-
    Management of severe global developmental delay, axial hypotonia, spasticity
    and contractures, kyphoscoliosis, and cerebral visual impairment requires
    multidisciplinary supportive care, physical therapy and orthopaedic
    surveillance.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Common clinical features included severe global developmental delay (6/6
      cases), cortical visual impairment (3/6 cases), axial hypotonia (6/6 cases),
      spasticity and/or joint contractures (5/6 cases), and kyphoscoliosis (2/6
      cases).
    explanation: >-
      Enumerates the comorbidities that define the supportive-care needs.
- name: Genetic Counseling
  description: >-
    Counseling covers the typically de novo origin of the dominant variants and
    the specific possibility of low-level parental mosaicism, which has been
    detected at 5-6% allelic fraction in unaffected parents in this cohort and
    raises recurrence risk above the baseline assumed for a de novo event.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:27476654
    reference_title: "De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      parental mosaicism was identified in two out of 14 cases tested with mutant
      allelic fractions of 5%-6% in the unaffected parents, carrying significant
      reproductive counseling implications
    explanation: >-
      Directly supports the mosaicism-focused counseling content of this entry.
discussions:
- discussion_id: mismatch_slc1a2_heterozygous_null_models
  prompt: >-
    Why do heterozygous Slc1a2-null mice and humans with heterozygous SLC1A2
    deletion have essentially no epilepsy phenotype, while humans heterozygous for
    a trimerization-domain missense allele have a lethal-grade developmental and
    epileptic encephalopathy - and does that make the available null models
    unsuitable for testing therapies aimed at this disorder?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Dominant-Negative Suppression of Wild-Type EAAT2
  - pathophysiology#SLC1A2 Trimerization-Domain Missense Variant
  rationale: >-
    The workhorse model for this pathway is the GLT-1 knockout mouse, which
    faithfully shows lethal spontaneous seizures from elevated brain glutamate -
    but only in the HOMOZYGOUS state. Heterozygous Slc1a2-deletion mice have no
    apparent clinical phenotype, and heterozygous SLC1A2 deletion in humans (WAGR
    syndrome) is only rarely epileptogenic. The human disease, by contrast, is
    heterozygous. The reconciling proposal is a critical dosage threshold between
    0 and 50 percent of wild-type transporter that a deletion does not cross but a
    dominant-negative missense allele does. That proposal is inferred rather than
    measured, and it has a direct translational consequence: a homozygous-null
    mouse models an allelic state no patient has, so a therapy that rescues it may
    not rescue a mixed wild-type/dominant-negative trimer population, and vice
    versa. Variant knock-in mice exist but their reported readout is a
    "hyperactive phenotype", not the human refractory multifocal epilepsy, so
    phenotypic fidelity at the disease level remains unestablished.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Despite the severe epilepsy phenotype of homozygous Slc1a2 knockout mice,
      mice heterozygote for the Slc1a2 deletion demonstrate no apparent clinical
      phenotype
    explanation: >-
      States the core mismatch: the mouse model reproduces the phenotype only in a
      zygosity that does not correspond to the human disease.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      heterozygous deletion of SLC1A2 in humans (as is frequently seen in the WAGR
      deletion syndrome) is only rarely associated with epilepsy
    explanation: >-
      Confirms the same dissociation in humans, ruling out simple
      haploinsufficiency as the human mechanism.
  - reference: PMID:36543780
    reference_title: "Functional investigation of SLC1A2 variants associated with epilepsy."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Furthermore, knock-in mice with disease-associated variants showed a
      hyperactive phenotype accompanied by reduced glutamate transporter
      expression.
    explanation: >-
      The closest allele-matched model. Marked INDIRECT because the reported
      readout is hyperactivity rather than the human refractory epileptic
      encephalopathy.
  proposed_experiments:
  - experiment_id: exp_slc1a2_dominant_negative_dosage_threshold
    name: Allele-matched dosage-threshold titration
    description: >-
      Titrate the ratio of functional to dominant-negative EAAT2 in an
      allele-matched in vivo model (variant knock-in rather than null) and
      determine the residual-transporter fraction at which epileptiform activity
      appears, testing directly whether the proposed 0-50 percent critical
      threshold is real and whether heterozygous knock-in animals reproduce the
      human seizure phenotype rather than only hyperactivity.
    experiment_type:
      preferred_term: allele-matched in vivo dosage titration
    perturbations:
    - name: Graded dominant-negative EAAT2 expression
      target: pathophysiology#Dominant-Negative Suppression of Wild-Type EAAT2
      genes:
      - preferred_term: SLC1A2
        term:
          id: hgnc:10940
          label: SLC1A2
      description: >-
        Vary the dose of the Leu85Pro allele relative to wild-type SLC1A2 across
        an allelic series in vivo.
    readouts:
    - name: Residual glutamate uptake and epileptiform activity
      target: pathophysiology#Impaired Astrocytic Glutamate Clearance
      biological_processes:
      - preferred_term: glutamate reuptake
        term:
          id: GO:0051935
          label: glutamate reuptake
- discussion_id: gap_slc1a2_uptake_enhancer_versus_anion_channel_blocker
  prompt: >-
    Should therapy for SLC1A2-related DEE aim to INCREASE transporter expression
    or to BLOCK the mutant transporter's anion channel - and does the negative
    ceftriaxone trial discriminate between the two mechanisms, or merely reflect
    treating too late?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Impaired Astrocytic Glutamate Clearance
  - pathophysiology#Mutant EAAT2 Anion Pore Glutamate Efflux
  rationale: >-
    The two curated mechanistic models make opposite therapeutic predictions. The
    canonical transport-loss model says to raise EAAT2 expression; the anion-pore
    efflux model says raising expression of a glutamate-leaking mutant transporter
    could be neutral or harmful, and that a selective EAAT anion-channel
    antagonist is the rational agent. The only human therapeutic datum is a single
    14-day ceftriaxone trial in one 20-month-old with Leu85Pro, which showed no
    change in spasm frequency. That result is consistent with the anion-pore model
    but is equally consistent with the authors' own alternative reading - that
    cumulative excitotoxic damage had already accrued by 20 months and that
    earlier initiation might succeed. With n=1, one variant, and a 14-day exposure,
    the trial cannot separate "wrong mechanism" from "right mechanism, too late".
    No EAAT anion-channel antagonist has been tested in this disorder at all.
  evidence:
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Ceftriaxone therapy did not result in a significant change in the daily
      spasm count
    explanation: >-
      The single negative human therapeutic result that motivates this gap.
  - reference: PMID:30937933
    reference_title: "Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      earlier initiation of SLC1A2-modulating agents may be efficacious to
      overcome the cumulative dominant negative effects of the variant SLC1A2
      allele
    explanation: >-
      States the competing timing explanation that the trial design cannot exclude.
  - reference: PMID:34961934
    reference_title: "Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Antagonists that selectively suppress the EAAT anion channel function could
      serve as therapeutic agents in the future.
    explanation: >-
      States the untested alternative therapeutic strategy implied by the
      anion-pore model.
  proposed_experiments:
  - experiment_id: exp_slc1a2_anion_channel_antagonist
    name: Anion-channel antagonist versus uptake enhancer, head to head
    description: >-
      Compare a selective EAAT anion-channel antagonist against an EAAT2
      expression enhancer in variant-matched cellular and in vivo models,
      stratified by variant class (pore-lining Gly82Arg/Leu85Pro versus
      Pro289Arg), with treatment initiated both before and after the onset of
      excitotoxic structural change, so that mechanism and timing are separated.
    experiment_type:
      preferred_term: comparative pharmacological intervention study
    perturbations:
    - name: EAAT anion-channel blockade versus transporter upregulation
      target: pathophysiology#Mutant EAAT2 Anion Pore Glutamate Efflux
      description: >-
        Apply a selective EAAT anion-channel antagonist or an EAAT2-upregulating
        agent to variant-matched models at early and late time points.
    readouts:
    - name: Extracellular glutamate and seizure burden
      target: pathophysiology#Extracellular Glutamate Accumulation and Excitotoxicity
      biological_processes:
      - preferred_term: L-glutamate transmembrane transport
        term:
          id: GO:0015813
          label: L-glutamate transmembrane transport
📚

References & Deep Research

References

7
PMID:27476654
De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies.
No top-level findings curated for this source.
PMID:30764523
Pediatric Epilepsy Mechanisms: Expanding the Paradigm of Excitation/Inhibition Imbalance.
No top-level findings curated for this source.
PMID:30937933
Recurrent SLC1A2 variants cause epilepsy via a dominant negative mechanism.
No top-level findings curated for this source.
PMID:34961934
Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function.
No top-level findings curated for this source.
PMID:36543780
Functional investigation of SLC1A2 variants associated with epilepsy.
No top-level findings curated for this source.
PMID:9180080
Epilepsy and exacerbation of brain injury in mice lacking the glutamate transporter GLT-1.
No top-level findings curated for this source.
PMID:34716961
Loss of glutamate transporter eaat2a leads to aberrant neuronal excitability, recurrent epileptic seizures, and basal hypoactivity.
No top-level findings curated for this source.