SLC6A1-Related Neurodevelopmental Disorder

🔗

Mappings

MONDO

MONDO:0014633 epilepsy with myoclonic atonic seizures

MONDO:0014633 is equivalentTo OMIM:616421, whose definition states the disorder "has material basis in heterozygous mutation in the SLC6A1 gene on chromosome 3p25" - i.e. this is the gene-anchored SLC6A1 disease concept, not merely the phenotype label. No separate SLC6A1-specific neurodevelopmental-disorder MONDO term exists at the time of curation. The phenotype-level, genetically heterogeneous Epilepsy with Myoclonic-Atonic Seizures (Doose syndrome) entry maps to the same MONDO term at the clinical syndrome altitude; this entry uses it at the gene/mechanism altitude.

👪

Inheritance

1

Autosomal Dominant (De Novo) HP:0000006

SLC6A1-NDD is an autosomal dominant disorder typically caused by a de novo heterozygous SLC6A1 variant; rarely the variant is inherited from a heterozygous parent. A single loss-of-function allele is sufficient to cause disease.

Autosomal dominant inheritance

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"SLC6A1-NDD is an autosomal dominant disorder typically caused by a de novo pathogenic variant."

The GeneReviews genetic-counseling section establishes autosomal dominant inheritance arising typically from a de novo pathogenic variant.

◈

Mechanistic Hypotheses

2

Excess Tonic Extrasynaptic GABA-A Inhibition / Thalamocortical Absence Model

excess_tonic_extrasynaptic_gaba_inhibition_absence_model CANONICAL

Evidence balance 3 support

The absence-seizure mechanism of SLC6A1-NDD is paradoxical: loss of GAT-1 reuptake does not simply disinhibit the cortex but instead raises ambient extrasynaptic GABA, INCREASING tonic GABA-A receptor inhibition of thalamocortical relay neurons. The resulting sustained hyperpolarization de-inactivates low-threshold T-type calcium channels and promotes rhythmic thalamocortical burst-firing, generating the generalized spike-wave discharges that underlie absence seizures. This excess-tonic-inhibition model, established across genetic and pharmacological absence-epilepsy models and in Gat1-deficient mice, is the canonical explanation for the absence phenotype and clarifies why a GABA-clearance defect produces seizures rather than pure disinhibition.

Pathograph links

Thalamocortical Excitation-Inhibition Imbalance and Generalized Seizures -> Absence Seizures DIRECT

Show evidence (3 references)

PMID:19966779 SUPPORT Model Organism

"extrasynaptic GABA(A) receptor-dependent 'tonic' inhibition is increased in thalamocortical neurons from diverse genetic and pharmacological models of absence seizures."

Establishes that tonic extrasynaptic GABA-A inhibition of thalamocortical neurons is increased across absence-epilepsy models, the core of this hypothesis.

PMID:19966779 SUPPORT Model Organism

"Increased tonic inhibition is due to compromised GABA uptake by the GABA transporter GAT-1 in the genetic models tested, and GAT-1 is crucial in governing seizure genesis."

Directly attributes the increased tonic inhibition to compromised GAT-1 uptake and identifies GAT-1 as governing seizure genesis, linking SLC6A1/GAT-1 loss to the absence mechanism.

PMID:29315614 SUPPORT Model Organism

"GAT-1 knockout mice exhibit spontaneous spike-wave discharges (SWDs) and absence seizures."

Confirms in the GAT-1 knockout model the spike-wave and absence phenotype that the tonic-inhibition mechanism generates.

Reduced Phasic GABAergic Synaptic Inhibition Arm

reduced_phasic_gabaergic_synaptic_inhibition_model ALTERNATIVE

Evidence balance 1 support

A complementary arm holds that impaired GAT-1 reuptake degrades the timing and fidelity of fast phasic GABAergic synaptic transmission, reducing effective synaptic inhibition and contributing to cortical network hyperexcitability and the myoclonic-atonic seizure component. This is the intuitive loss-of-inhibition arm; it complements rather than replaces the excess-tonic-inhibition model, which better accounts for the absence phenotype.

Pathograph links

Thalamocortical Excitation-Inhibition Imbalance and Generalized Seizures -> Generalized Myoclonic-Atonic Seizures DIRECT

Show evidence (1 reference)

PMID:25865495 SUPPORT Human Clinical

"all of which most likely lead to loss of function of GAT-1 and thus reduced GABA re-uptake from the synapse."

Supports reduced synaptic GABA reuptake as the phasic loss-of-inhibition arm accompanying the tonic-increase mechanism.

?

Discussions and Knowledge Gaps

2

Does restoring GAT-1 function - by genetic dose restoration (e.g. antisense or gene-based upregulation) or by pharmacological/chaperone rescue of misfolded, ER-retained transporter - translate from patient iPSC-derived astrocytes and neurons into clinical benefit in humans with SLC6A1-NDD?

HUMAN MODEL MISMATCH OPEN gap_slc6a1_gat1_rescue_human_translation

Attached to

pathophysiology#SLC6A1 Variant and GAT-1 Loss of Function pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis

In vitro model evidence exists: patient iPSC-derived astrocytes and neurons show that reduced GABA uptake is caused by misfolding, ER retention, and degradation of variant GAT-1, and the authors conclude that boosting transporter function by genetic or pharmacological approaches would be beneficial. The open question is translational fidelity - whether restoring surface GAT-1 in cultured patient cells predicts clinical improvement in seizures and, especially, in the seizure-independent neurodevelopmental features, which may depend on early developmental windows that a mature-cell rescue cannot recapitulate. Whether haploinsufficiency versus a misfolding-driven dominant effect predominates also gates which strategy (dose restoration versus chaperone/proteostasis) is optimal.

Proposed experiments

GAT-1 rescue translation from iPSC models to in vivo readouts

cross-model therapeutic rescue experiment

exp_slc6a1_gat1_rescue_translation

Test whether genetic dose restoration and chemical-chaperone rescue that restore surface GAT-1 and GABA uptake in patient iPSC-derived astrocytes and neurons also correct network inhibition and seizure/behavioral phenotypes in an SLC6A1 haploinsufficient in vivo model, and whether efficacy depends on the developmental timing of the intervention.

Perturbations

GAT-1 dose restoration and chaperone rescue

pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis

Apply genetic upregulation and chemical-chaperone treatment to patient iPSC-derived cells and to an SLC6A1 haploinsufficient in vivo model at different developmental time points.

SLC6A1 hgnc:11042

Readouts

Surface GAT-1, GABA uptake, and network inhibition

pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis

gamma-aminobutyric acid transport GO:0015812 ↑ INCREASED

radiolabeled GABA uptake assay electroencephalography

Direction: POSITIVE

Controls

Wild-type and isogenic-corrected cells

Wild-type and CRISPR-corrected isogenic lines as references.

Vehicle versus chaperone

Matched untreated versus chemical-chaperone-treated conditions.

Decision criterion

Translation is supported if rescue that restores surface GAT-1 and GABA uptake in patient cells also improves in vivo inhibition and seizure/behavioral phenotypes; a mismatch is supported if cellular rescue fails to translate or is effective only within a narrow developmental window.

Would support

pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis

Show evidence (2 references)

PMID:34028503 SUPPORT In Vitro

"This study provides critical insight into therapeutic developments for SLC6A1 variant-mediated disorders and implicates that boosting transporter function by either genetic or pharmacological approaches would be beneficial."

Establishes the iPSC-model-derived therapeutic rationale (GAT-1 boosting) whose translation to human clinical benefit is the open question.

PMID:34028503 SUPPORT In Vitro

"the loss of GABA uptake function and endoplasmic reticulum retention is consistent across induced pluripotent stem cell-derived cell types, including astrocytes and neurons, for the surveyed variants."

Documents the iPSC-derived cellular model in which GAT-1 loss and ER retention - and thus candidate rescue - are demonstrated.

Is SLC6A1-NDD a pure loss-of-dose (haploinsufficiency) disorder, or do misfolded, ER-retained missense GAT-1 mutants additionally act dominant-negatively by co-assembling with and retaining wild-type GAT-1 below hemizygous levels, and does the answer differ by variant class with consequences for therapy choice?

OPEN QUESTION OPEN gap_slc6a1_haploinsufficiency_vs_dominant_negative

Attached to

pathophysiology#SLC6A1 Variant and GAT-1 Loss of Function

Truncating SLC6A1 variants plausibly act through simple haploinsufficiency, but most disease variants are missense, and functional studies show they misfold and are retained in the endoplasmic reticulum - a route that, as seen for GABAA-receptor subunits, can co-deplete wild-type protein and produce a dominant-negative effect exceeding loss of one allele. Whether this occurs for GAT-1, and how strongly it varies by variant, is unresolved and directly gates therapy: pure haploinsufficiency favors dose-restoration (e.g. antisense upregulation of the wild-type allele), whereas a dominant-negative misfolding mechanism favors chaperone/proteostasis rescue or allele-selective approaches.

Show evidence (1 reference)

PMID:34028503 SUPPORT In Vitro

"Our results resemble findings from pathogenic variants in other genes affecting the GABA pathway, such as GABAA receptors."

Draws the parallel to GABAA-receptor variants, for which misfolding and wild-type co-retention (a dominant-negative route) are established, framing the open haploinsufficiency-versus-dominant-negative question for GAT-1.

⚙

Pathophysiology

4

SLC6A1 Variant and GAT-1 Loss of Function

Heterozygous SLC6A1 variants impair GAT-1, the major sodium/chloride-dependent GABA transporter of the brain. Truncating variants (nonsense, frameshift, splice-site) reduce functional GAT-1 dose through haploinsufficiency, while most disease missense variants misfold and are retained in the endoplasmic reticulum with subsequent degradation, lowering cell-surface transporter expression. Both routes converge on partial or complete loss of GAT-1 function. This node captures the single molecular trigger - the variant and the resulting transporter loss of function.

GABAergic neuron CL:0000617 astrocyte CL:0000127

SLC6A1 hgnc:11042

GAT-1-mediated GABA neurotransmitter transport GO:0006836 ↓ DECREASED

brain UBERON:0000955

Downstream

Impaired GABA Reuptake and Disrupted GABA Homeostasis

Show evidence (4 references)

PMID:25865495 SUPPORT Human Clinical

"GAT-1, encoded by SLC6A1, is one of the major gamma-aminobutyric acid (GABA) transporters in the brain and is responsible for re-uptake of GABA from the synapse."

Establishes GAT-1/SLC6A1 as a principal brain GABA transporter mediating synaptic GABA reuptake, the function lost in this disorder.

PMID:25865495 SUPPORT Human Clinical

"all of which most likely lead to loss of function of GAT-1 and thus reduced GABA re-uptake from the synapse."

Identifies loss of GAT-1 function and reduced GABA reuptake as the direct consequence of the identified SLC6A1 variants.

PMID:34028503 SUPPORT In Vitro

"The reduced GABA uptake appears to be due to reduced cell surface expression of the variant transporter caused by variant protein misfolding, endoplasmic reticulum retention, and subsequent degradation."

Defines the molecular route to loss of function for missense variants - misfolding, ER retention, and degradation reducing surface GAT-1.

+ 1 more reference

Impaired GABA Reuptake and Disrupted GABA Homeostasis

Loss of surface GAT-1 reduces clearance of synaptic and extrasynaptic GABA by both presynaptic GABAergic neurons and surrounding astrocytes, dysregulating GABA homeostasis. Because neuronal GAT-1 reuptake cannot be compensated by other GABA transporters (astrocytic GAT-1 is only partly covered by GAT-3), the net effect is a disturbance of the timing and tonic level of GABAergic inhibition. This node captures the single functional consequence - impaired GABA reuptake and disrupted GABA homeostasis.

astrocyte CL:0000127 GABAergic neuron CL:0000617

neurotransmitter reuptake GO:0098810 ↓ DECREASED gamma-aminobutyric acid transport GO:0015812 ↓ DECREASED

brain UBERON:0000955

Downstream

Thalamocortical Excitation-Inhibition Imbalance and Generalized Seizures

Impaired GABAergic Signaling in Neurodevelopment

Show evidence (3 references)

PMID:34028503 SUPPORT In Vitro

"Its encoded GABA transporter 1 (GAT-1) is responsible for the reuptake of GABA into presynaptic neurons and glia, thereby modulating neurotransmission."

Establishes GAT-1-mediated GABA reuptake into neurons and glia as the step that modulates neurotransmission and is impaired in the disorder.

PMID:34028503 SUPPORT In Vitro

"GAT-1 is expressed globally in the brain, in both astrocytes and neurons."

Supports the dual astrocytic and neuronal localization of GAT-1 whose loss disrupts GABA homeostasis at both compartments.

PMID:34028503 SUPPORT In Vitro

"The GABA uptake function of GAT-1 in neurons cannot be compensated for by other GABA transporters, while the function in glia can be partially replaced by GABA transporter 3."

Explains why neuronal GAT-1 loss is non-redundant, so impaired reuptake directly disrupts inhibitory GABA homeostasis.

Thalamocortical Excitation-Inhibition Imbalance and Generalized Seizures

Loss of GAT-1-mediated GABA clearance disrupts thalamocortical GABAergic signaling through two opposing arms. In the seizure-generating arm, reduced GABA reuptake raises ambient extrasynaptic GABA and paradoxically INCREASES tonic extrasynaptic GABA-A receptor inhibition of thalamocortical relay neurons; the resulting sustained hyperpolarization de-inactivates low-threshold T-type calcium channels and drives the rhythmic thalamocortical burst-firing that generates generalized spike-wave discharges and absence seizures - the mechanism established in Gat1-deficient mice and other absence models. In a parallel synaptic arm, impaired reuptake also degrades the timing and fidelity of fast phasic GABAergic synaptic transmission, contributing to cortical network hyperexcitability and the myoclonic-atonic component. Individuals with SLC6A1 variants share electrophysiological features with Gat1-deficient mice, including spontaneous spike-wave discharges. The two arms are curated as disease-level mechanistic_hypotheses.

Excess Tonic Extrasynaptic GABA-A Inhibition / Thalamocortical Absence Model Reduced Phasic GABAergic Synaptic Inhibition Arm

GABAergic neuron CL:0000617

Tonic extrasynaptic GABA-A receptor inhibition GO:0007214 ↑ INCREASED GABAergic synaptic transmission GO:0051932 ↓ DECREASED chemical synaptic transmission GO:0007268 ⚠ ABNORMAL

cerebral cortex UBERON:0000956 thalamus UBERON:0001897

Downstream

Generalized Myoclonic-Atonic Seizures

Absence Seizures

Show evidence (1 reference)

PMID:25865495 SUPPORT Model Organism

"These individuals share many of the electrophysiological properties of Gat1-deficient mice, including spontaneous spike-wave discharges."

Links reduced GAT-1 function to the generalized spike-wave hyperexcitability seen in the Gat1-deficient mouse and shared by patients.

Impaired GABAergic Signaling in Neurodevelopment

SLC6A1 is expressed in the developing brain even before the CNS is fully formed, and GABAergic signaling has trophic, developmental roles beyond fast inhibition. Impaired GAT-1 function therefore perturbs GABAergic signaling during neurodevelopment, contributing to the broad, seizure-independent neurodevelopmental phenotype - developmental delay/intellectual disability and autism spectrum disorder. This node captures the single developmental consequence of disrupted GABAergic signaling.

GABAergic neuron CL:0000617

gamma-aminobutyric acid signaling pathway GO:0007214 ⚠ ABNORMAL nervous system development GO:0007399 ⚠ ABNORMAL

brain UBERON:0000955

Downstream

Global Developmental Delay

Intellectual Disability

Autism Spectrum Disorder

Show evidence (2 references)

PMID:34028503 SUPPORT In Vitro

"Solute carrier family 6 member 1 (SLC6A1) is abundantly expressed in the developing brain even before the CNS is formed."

Supports an early developmental role for SLC6A1/GAT-1, consistent with a neurodevelopmental phenotype arising from disrupted GABAergic signaling.

PMID:35761184 SUPPORT Human Clinical

"the phenotypic spectrum is broad and includes developmental delay, epilepsy, and autism or autistic traits."

Documents the broad neurodevelopmental phenotype (developmental delay, autism) that accompanies the epilepsy in SLC6A1-related disorder.

⬡

Pathograph

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

●

Phenotypes

15

Digestive 2

Constipation HP:0002019

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"Gastrointestinal manifestations (e.g., constipation, diarrhea) are also common."

Lists constipation among the common gastrointestinal manifestations of SLC6A1-NDD.

Diarrhea HP:0002014

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"Gastrointestinal manifestations (e.g., constipation, diarrhea) are also common."

Lists diarrhea among the common gastrointestinal manifestations of SLC6A1-NDD.

Musculoskeletal 1

Hypotonia HP:0001252

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"developmental delay and/or intellectual disability, hypotonia, epilepsy"

Lists hypotonia among the core clinical characteristics of SLC6A1-NDD.

Nervous System 10

Absence Seizures Generalized non-motor (absence) seizure HP:0002121

Show evidence (1 reference)

PMID:34028503 SUPPORT Other

"including myoclonic atonic epilepsy, childhood absence epilepsy, autism, and intellectual disability"

Documents childhood absence epilepsy within the reported SLC6A1 epilepsy and neurodevelopmental spectrum.

Epilepsy Seizure HP:0001250

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"developmental delay and/or intellectual disability, hypotonia, epilepsy, movement disorders"

Lists epilepsy among the core clinical characteristics of SLC6A1-NDD.

Global Developmental Delay HP:0001263

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"SLC6A1-NDD) is characterized by mild-to-severe developmental delay and/or intellectual disability"

Establishes mild-to-severe developmental delay as a defining feature of SLC6A1-NDD.

Intellectual Disability HP:0001249

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"mild-to-severe developmental delay and/or intellectual disability"

Documents intellectual disability across a mild-to-severe range in SLC6A1-NDD.

Autism Spectrum Disorder Autistic behavior HP:0000729

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"neurobehavioral and/or psychiatric manifestations (e.g., autism spectrum disorder, attention-deficit/hyperactivity disorder"

Lists autism spectrum disorder among the neurobehavioral manifestations of SLC6A1-NDD.

Attention-Deficit/Hyperactivity Disorder HP:0007018

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"autism spectrum disorder, attention-deficit/hyperactivity disorder, aggression, anxiety, and/or sleep disturbances"

Lists attention-deficit/hyperactivity disorder among the neurobehavioral manifestations of SLC6A1-NDD.

Tremor HP:0001337

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"movement disorders (e.g., tremor, stereotypies, ataxia)"

Lists tremor among the movement disorders characterizing SLC6A1-NDD.

Ataxia HP:0001251

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"movement disorders (e.g., tremor, stereotypies, ataxia)"

Lists ataxia among the movement disorders characterizing SLC6A1-NDD.

Delayed Speech and Language Development HP:0000750

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"Language skills, particularly expressive language, are often more significantly affected than motor development."

Documents disproportionate expressive-language impairment in SLC6A1-NDD.

Developmental Regression HP:0002376

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"Developmental regression has been reported."

Documents developmental regression as a reported feature of SLC6A1-NDD.

Other 2

Generalized Myoclonic-Atonic Seizures HP:0011170

Show evidence (1 reference)

PMID:25865495 SUPPORT Human Clinical

"six SLC6A1 mutations in seven individuals, all of whom have epilepsy with myoclonic-atonic seizures (MAE)."

Establishes epilepsy with myoclonic-atonic seizures as the defining phenotype of the SLC6A1 discovery cohort.

Motor Stereotypies Motor stereotypy HP:0000733

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"movement disorders (e.g., tremor, stereotypies, ataxia)"

Lists stereotypies among the movement disorders characterizing SLC6A1-NDD.

🧬

Genetic Associations

1

SLC6A1 (Loss-of-Function Variants)

Gene: SLC6A1 hgnc:11042 variant_origin: GERMLINE

Autosomal Dominant (De Novo)

Show evidence (3 references)

PMID:37647852 SUPPORT Human Clinical

"For variants with complete loss of in vitro GABA uptake, we found a 4.6-fold enrichment in patients having severe disease versus non-severe disease"

Quantifies the genotype-severity correlation, linking complete loss of GAT-1 GABA-uptake function to severe disease.

PMID:25865495 SUPPORT Human Clinical

"targeted resequencing of 644 individuals with epileptic encephalopathies led to the identification of six SLC6A1 mutations in seven individuals"

Original identification of heterozygous SLC6A1 variants as a cause of epileptic encephalopathy with myoclonic-atonic seizures.

PMID:35761184 SUPPORT Human Clinical

"Carriers in Searchlight had 83 unique pathogenic or likely pathogenic variants in SLC6A1, which were predominantly missense or nonsense variants."

Documents the predominantly missense/nonsense SLC6A1 variant spectrum in a standardized patient registry.

💊

Medical Actions

6

Antiseizure Medication

Action: Pharmacotherapy NCIT:C15986

Agent: levetiracetam CHEBI:6437

Seizures are managed with antiseizure medications, generally broad-spectrum agents appropriate for generalized epilepsy, with valproate the most effective and usual first-line choice. Levetiracetam is frequently used but is poorly tolerated in SLC6A1-NDD because of behavioral side effects at higher rates than in the general population, so alternatives are often considered. Tiagabine, a selective GAT-1 inhibitor, is mechanistically contraindicated: pharmacologically blocking the residual transporter would further raise extrasynaptic GABA and is expected to aggravate tonic-inhibition-driven absence seizures.

Show evidence (2 references)

PMID:36780407 SUPPORT Human Clinical

"anti-seizure medications are often needed to control seizures"

The GeneReviews management section establishes antiseizure medication as the mainstay of seizure control.

PMID:36780407 SUPPORT Human Clinical

"Individuals with SLC6A1-NDD have intolerable behavioral side effects with levetiracetam at higher rates than reported in the general population."

Documents the levetiracetam behavioral-tolerability caution specific to SLC6A1-NDD.

Valproate (Valproic Acid)

Action: Pharmacotherapy NCIT:C15986

Agent: valproic acid CHEBI:39867

Valproate is the most effective and generally first-line antiseizure medication for the generalized seizures of SLC6A1-NDD, controlling myoclonic-atonic and absence seizures as monotherapy or in combination.

Show evidence (1 reference)

PMID:29315614 SUPPORT Human Clinical

"seizure-free, with valproic acid being the most effective drug."

In the SLC6A1 patient cohort, valproic acid was the most effective antiseizure drug, supporting its first-line role.

4-Phenylbutyrate Pharmacochaperone

Action: Pharmacotherapy NCIT:C15986

Agent: 4-phenylbutyric acid CHEBI:41500

4-Phenylbutyrate is a small-molecule chemical chaperone under clinical investigation as a disease-modifying therapy for SLC6A1-NDD: by promoting proper folding and endoplasmic-reticulum export of misfolded missense GAT-1, it aims to restore cell-surface transporter expression and GABA reuptake rather than only suppressing seizures.

Show evidence (1 reference)

PMID:34028503 SUPPORT In Vitro

"This study provides critical insight into therapeutic developments for SLC6A1 variant-mediated disorders and implicates that boosting transporter function by either genetic or pharmacological approaches would be beneficial."

Provides the iPSC-model rationale for pharmacological (chaperone) rescue of misfolded GAT-1 as a disease-modifying approach.

AAV9 SLC6A1 Gene Therapy

Action: gene therapy Ontology label: Gene Therapy NCIT:C15238

Gene-replacement therapy delivering a functional SLC6A1/GAT-1 transgene by an AAV9 vector is in early-phase clinical development as a disease-modifying treatment aimed at restoring GAT-1 dose in the CNS - the genetic-restoration counterpart to pharmacological chaperone rescue.

Show evidence (1 reference)

PMID:34028503 SUPPORT In Vitro

"This study provides critical insight into therapeutic developments for SLC6A1 variant-mediated disorders and implicates that boosting transporter function by either genetic or pharmacological approaches would be beneficial."

Provides the iPSC-model rationale for genetic dose restoration of GAT-1 as a disease-modifying approach.

Developmental and Educational Support

Action: Supportive Care NCIT:C15747

Multidisciplinary developmental and educational support, including therapies for language and motor delay and management of behavioral and sleep problems, is a mainstay of care.

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"Developmental and educational support"

The GeneReviews management section lists developmental and educational support as core treatment of manifestations.

Genetic Counseling

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

Genetic counseling addresses the autosomal dominant, typically de novo mechanism, the 50% transmission risk from an affected individual, and the availability of prenatal and preimplantation genetic testing once the variant is known.

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"Each child of an individual with SLC6A1-NDD has a 50% chance of inheriting the pathogenic variant."

Supports the genetic-counseling content on autosomal dominant transmission risk.

🔬

Diagnosis

2

SLC6A1 Molecular Diagnosis

The diagnosis of SLC6A1-NDD is established in a proband with suggestive findings and a heterozygous pathogenic or likely pathogenic SLC6A1 variant identified by molecular genetic testing, typically de novo.

molecular genetic testing NCIT:C19770

Results: A heterozygous pathogenic SLC6A1 variant establishes the diagnosis.

Show evidence (1 reference)

PMID:36780407 SUPPORT Human Clinical

"The diagnosis of SLC6A1-NDD is established in a proband with suggestive findings and a heterozygous pathogenic variant in SLC6A1 identified by molecular genetic testing."

The GeneReviews chapter defines the molecular-genetic-testing basis for establishing the diagnosis.

EEG and Seizure Phenotyping

EEG documents the generalized epilepsy - typically generalized spike-and-wave activity - and characterizes the myoclonic-atonic and absence seizure types, guiding antiseizure treatment.

electroencephalography NCIT:C38054

Results: Generalized spike-and-wave discharges support the generalized epilepsy.

📈

Progression

2

Early childhood

Onset is typically in early childhood with generalized seizures (myoclonic-atonic and absence) in a child with emerging developmental delay, hypotonia, and language delay.

Show evidence (1 reference)

PMID:25865495 SUPPORT Human Clinical

"all of whom have epilepsy with myoclonic-atonic seizures (MAE)."

Anchors the early-childhood myoclonic-atonic epilepsy presentation of the disorder.

Later childhood to adulthood

Seizures may improve over time in some individuals, while the neurodevelopmental features - intellectual disability, autism spectrum disorder, and behavioral difficulties - persist as the dominant long-term burden.

Show evidence (1 reference)

PMID:35761184 SUPPORT Human Clinical

"the phenotypic spectrum is broad and includes developmental delay, epilepsy, and autism or autistic traits."

Documents the persistent neurodevelopmental features that dominate the long-term course.

📊

Prevalence

1

Worldwide

Unknown Rare

SLC6A1-NDD is a rare, recently delineated single-gene neurodevelopmental disorder; a precise population prevalence has not been established. In the discovery cohort, pathogenic SLC6A1 variants accounted for about 4% of otherwise unsolved myoclonic-atonic epilepsy cases.

Show evidence (1 reference)

PMID:25865495 SUPPORT Human Clinical

"pathogenic mutations occurred in 6/160 individuals with MAE, accounting for ~4% of unsolved MAE cases."

Quantifies the SLC6A1 contribution to myoclonic-atonic epilepsy in the discovery cohort, supporting the disorder's rarity.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from SLC6A1-Related Neurodevelopmental Disorder:

Epilepsy with Myoclonic-Atonic Seizures (Doose syndrome), other genetic causes

Overlapping Features Epilepsy with myoclonic-atonic seizures (Doose syndrome) is a genetically heterogeneous clinical syndrome for which SLC6A1 is the best-established single gene; other cases involve SCN1A, SCN1B, GABRG2 and the GEFS+ spectrum or have complex/polygenic architecture. This SLC6A1 gene-anchored entry is one molecular cause of that clinical syndrome.

Distinguishing Features

A heterozygous loss-of-function SLC6A1 variant favors SLC6A1-NDD.
Absence of an SLC6A1 variant, or a variant in another epilepsy gene, favors a non-SLC6A1 cause of the Doose-syndrome phenotype.

Show evidence (1 reference)

PMID:25865495 SUPPORT Human Clinical

"pathogenic mutations occurred in 6/160 individuals with MAE, accounting for ~4% of unsolved MAE cases."

Shows SLC6A1 accounts for a minority of myoclonic-atonic epilepsy cases, so the Doose-syndrome phenotype has other genetic causes.

Other GABAergic-pathway developmental and epileptic encephalopathies

Overlapping Features Developmental and epileptic encephalopathies caused by other GABA-pathway genes (e.g. GABRA1, GABRB3, GABRG2 encoding GABAA-receptor subunits) share impaired GABAergic inhibition and overlapping generalized epilepsy and are distinguished by molecular testing.

Distinguishing Features

An SLC6A1 variant favors this disorder.
A GABAA-receptor-subunit gene variant favors the corresponding channelopathy.

🔬

Clinical Trials

2

NCT04937062 PHASE_I ACTIVE_NOT_RECRUITING

Trial of glycerol phenylbutyrate as a pharmacochaperone for monogenic developmental and epileptic encephalopathies including SLC6A1-NDD, testing safety and tolerability of boosting residual transporter/protein function.

Target Phenotypes: Seizure HP:0001250 Global developmental delay HP:0001263

Show evidence (1 reference)

clinicaltrials:NCT04937062 SUPPORT Human Clinical

"It is possible that a medication called phenylbutyrate may help the the remaining proteins work better for STXBP1, SLC6A1, and/or other similar DEEs caused by single genes"

The trial tests phenylbutyrate as a chaperone to improve residual GAT-1 protein function in SLC6A1-NDD.

NCT07173153 PHASE_I ENROLLING_BY_INVITATION

Phase I/II intrathecal gene-delivery trial of scAAV9.P546.SLC6A1, an AAV9 vector carrying the SLC6A1 gene, for SLC6A1 neurodevelopmental disorder.

Target Phenotypes: Seizure HP:0001250 Global developmental delay HP:0001263

Show evidence (1 reference)

clinicaltrials:NCT07173153 SUPPORT Human Clinical

"This is gene therapy study of an AAV9 vector carrying the SLCA1 gene for SLC6A1 neurodevelopmental disorder."

First-in-human AAV9 gene-replacement trial for SLC6A1-NDD, supporting gene therapy as a disease-modifying strategy.

{ }

Source YAML

click to show

name: SLC6A1-Related Neurodevelopmental Disorder
creation_date: "2026-07-25T00:00:00Z"
description: >-
  A gene-anchored, autosomal dominant neurodevelopmental disorder caused by
  heterozygous loss-of-function variants in SLC6A1, which encodes GAT-1, the
  sodium- and chloride-dependent GABA transporter 1 responsible for reuptake of
  the inhibitory neurotransmitter GABA from the synapse into presynaptic neurons
  and surrounding astrocytes. Most pathogenic missense variants misfold and are
  retained in the endoplasmic reticulum, reducing GAT-1 cell-surface expression
  and GABA reuptake; truncating variants act through haploinsufficiency. The
  resulting disturbance of GABA homeostasis and inhibitory neurotransmission
  produces a characteristic generalized epilepsy - classically epilepsy with
  myoclonic-atonic seizures (Doose-like) and childhood absence epilepsy -
  together with developmental delay/intellectual disability, autism spectrum
  disorder, hypotonia, and movement abnormalities (tremor, ataxia,
  stereotypies). This entry models the SLC6A1/GAT-1 gene-specific mechanism and
  is distinct from the phenotype-level, genetically heterogeneous Epilepsy with
  Myoclonic-Atonic Seizures (Doose syndrome) entry, of which SLC6A1 is the
  best-established single-gene cause.
category: Mendelian
parents:
- Neurodevelopmental Disorder
- Epilepsy
synonyms:
- SLC6A1-related disorder
- SLC6A1-NDD
- SLC6A1-related epilepsy
- GAT-1 encephalopathy
- Myoclonic-atonic epilepsy, SLC6A1-related
disease_term:
  preferred_term: SLC6A1-related neurodevelopmental disorder
  term:
    id: MONDO:0014633
    label: epilepsy with myoclonic atonic seizures
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0014633
      label: epilepsy with myoclonic atonic seizures
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0014633 is equivalentTo OMIM:616421, whose definition states the
      disorder "has material basis in heterozygous mutation in the SLC6A1 gene
      on chromosome 3p25" - i.e. this is the gene-anchored SLC6A1 disease
      concept, not merely the phenotype label. No separate SLC6A1-specific
      neurodevelopmental-disorder MONDO term exists at the time of curation. The
      phenotype-level, genetically heterogeneous Epilepsy with Myoclonic-Atonic
      Seizures (Doose syndrome) entry maps to the same MONDO term at the clinical
      syndrome altitude; this entry uses it at the gene/mechanism altitude.
inheritance:
- name: Autosomal Dominant (De Novo)
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    SLC6A1-NDD is an autosomal dominant disorder typically caused by a de novo
    heterozygous SLC6A1 variant; rarely the variant is inherited from a
    heterozygous parent. A single loss-of-function allele is sufficient to cause
    disease.
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SLC6A1-NDD is an autosomal dominant disorder typically caused by a de novo
      pathogenic variant.
    explanation: >-
      The GeneReviews genetic-counseling section establishes autosomal dominant
      inheritance arising typically from a de novo pathogenic variant.
prevalence:
- population: Worldwide
  measure_type: UNKNOWN
  prevalence_class: RARE
  notes: >-
    SLC6A1-NDD is a rare, recently delineated single-gene neurodevelopmental
    disorder; a precise population prevalence has not been established. In the
    discovery cohort, pathogenic SLC6A1 variants accounted for about 4% of
    otherwise unsolved myoclonic-atonic epilepsy cases.
  evidence:
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      pathogenic mutations occurred in 6/160 individuals with MAE, accounting for
      ~4% of unsolved MAE cases.
    explanation: >-
      Quantifies the SLC6A1 contribution to myoclonic-atonic epilepsy in the
      discovery cohort, supporting the disorder's rarity.
references:
- reference: PMID:25865495
  title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
- reference: PMID:34028503
  title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
- reference: PMID:35761184
  title: "Consistency of parent-report SLC6A1 data in Simons Searchlight with Provider-Based Publications."
- reference: PMID:36780407
  title: "SLC6A1-Related Neurodevelopmental Disorder."
  tags:
  - GeneReviews
pathophysiology:
- name: SLC6A1 Variant and GAT-1 Loss of Function
  description: >-
    Heterozygous SLC6A1 variants impair GAT-1, the major sodium/chloride-dependent
    GABA transporter of the brain. Truncating variants (nonsense, frameshift,
    splice-site) reduce functional GAT-1 dose through haploinsufficiency, while
    most disease missense variants misfold and are retained in the endoplasmic
    reticulum with subsequent degradation, lowering cell-surface transporter
    expression. Both routes converge on partial or complete loss of GAT-1
    function. This node captures the single molecular trigger - the variant and
    the resulting transporter loss of function.
  role: trigger
  gene:
    preferred_term: SLC6A1
    term:
      id: hgnc:11042
      label: SLC6A1
  cell_types:
  - preferred_term: GABAergic neuron
    term:
      id: CL:0000617
      label: GABAergic neuron
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: GAT-1-mediated GABA neurotransmitter transport
    term:
      id: GO:0006836
      label: neurotransmitter transport
    modifier: DECREASED
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GAT-1, encoded by SLC6A1, is one of the major gamma-aminobutyric acid
      (GABA) transporters in the brain and is responsible for re-uptake of GABA
      from the synapse.
    explanation: >-
      Establishes GAT-1/SLC6A1 as a principal brain GABA transporter mediating
      synaptic GABA reuptake, the function lost in this disorder.
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      all of which most likely lead to loss of function of GAT-1 and thus reduced
      GABA re-uptake from the synapse.
    explanation: >-
      Identifies loss of GAT-1 function and reduced GABA reuptake as the direct
      consequence of the identified SLC6A1 variants.
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The reduced GABA uptake appears to be due to reduced cell surface expression
      of the variant transporter caused by variant protein misfolding, endoplasmic
      reticulum retention, and subsequent degradation.
    explanation: >-
      Defines the molecular route to loss of function for missense variants -
      misfolding, ER retention, and degradation reducing surface GAT-1.
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We found that a partial or complete loss-of-function represents a common
      disease mechanism, although the extent of GABA uptake reduction is variable.
    explanation: >-
      Confirms partial-to-complete GAT-1 loss of function as the shared mechanism
      across SLC6A1 variants in patient-derived cells.
  downstream:
  - target: Impaired GABA Reuptake and Disrupted GABA Homeostasis
    causal_link_type: DIRECT
- name: Impaired GABA Reuptake and Disrupted GABA Homeostasis
  description: >-
    Loss of surface GAT-1 reduces clearance of synaptic and extrasynaptic GABA by
    both presynaptic GABAergic neurons and surrounding astrocytes, dysregulating
    GABA homeostasis. Because neuronal GAT-1 reuptake cannot be compensated by
    other GABA transporters (astrocytic GAT-1 is only partly covered by GAT-3),
    the net effect is a disturbance of the timing and tonic level of GABAergic
    inhibition. This node captures the single functional consequence - impaired
    GABA reuptake and disrupted GABA homeostasis.
  role: central_effector
  cell_types:
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  - preferred_term: GABAergic neuron
    term:
      id: CL:0000617
      label: GABAergic neuron
  biological_processes:
  - preferred_term: neurotransmitter reuptake
    term:
      id: GO:0098810
      label: neurotransmitter reuptake
    modifier: DECREASED
  - preferred_term: gamma-aminobutyric acid transport
    term:
      id: GO:0015812
      label: gamma-aminobutyric acid transport
    modifier: DECREASED
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Its encoded GABA transporter 1 (GAT-1) is responsible for the reuptake of
      GABA into presynaptic neurons and glia, thereby modulating neurotransmission.
    explanation: >-
      Establishes GAT-1-mediated GABA reuptake into neurons and glia as the step
      that modulates neurotransmission and is impaired in the disorder.
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      GAT-1 is expressed globally in the brain, in both astrocytes and neurons.
    explanation: >-
      Supports the dual astrocytic and neuronal localization of GAT-1 whose loss
      disrupts GABA homeostasis at both compartments.
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The GABA uptake function of GAT-1 in neurons cannot be compensated for by
      other GABA transporters, while the function in glia can be partially replaced
      by GABA transporter 3.
    explanation: >-
      Explains why neuronal GAT-1 loss is non-redundant, so impaired reuptake
      directly disrupts inhibitory GABA homeostasis.
  downstream:
  - target: Thalamocortical Excitation-Inhibition Imbalance and Generalized Seizures
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Dysregulated tonic and phasic GABAergic inhibition.
  - target: Impaired GABAergic Signaling in Neurodevelopment
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Altered GABAergic signaling during critical developmental windows.
- name: Thalamocortical Excitation-Inhibition Imbalance and Generalized Seizures
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Neuronal Hyperexcitability and Hypersynchrony"
  description: >-
    Loss of GAT-1-mediated GABA clearance disrupts thalamocortical GABAergic
    signaling through two opposing arms. In the seizure-generating arm, reduced
    GABA reuptake raises ambient extrasynaptic GABA and paradoxically INCREASES
    tonic extrasynaptic GABA-A receptor inhibition of thalamocortical relay
    neurons; the resulting sustained hyperpolarization de-inactivates
    low-threshold T-type calcium channels and drives the rhythmic thalamocortical
    burst-firing that generates generalized spike-wave discharges and absence
    seizures - the mechanism established in Gat1-deficient mice and other absence
    models. In a parallel synaptic arm, impaired reuptake also degrades the timing
    and fidelity of fast phasic GABAergic synaptic transmission, contributing to
    cortical network hyperexcitability and the myoclonic-atonic component.
    Individuals with SLC6A1 variants share electrophysiological features with
    Gat1-deficient mice, including spontaneous spike-wave discharges. The two arms
    are curated as disease-level mechanistic_hypotheses.
  role: amplifier
  cell_types:
  - preferred_term: GABAergic neuron
    term:
      id: CL:0000617
      label: GABAergic neuron
  biological_processes:
  - preferred_term: Tonic extrasynaptic GABA-A receptor inhibition
    term:
      id: GO:0007214
      label: gamma-aminobutyric acid signaling pathway
    modifier: INCREASED
  - preferred_term: GABAergic synaptic transmission
    term:
      id: GO:0051932
      label: synaptic transmission, GABAergic
    modifier: DECREASED
  - preferred_term: chemical synaptic transmission
    term:
      id: GO:0007268
      label: chemical synaptic transmission
    modifier: ABNORMAL
  locations:
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  - preferred_term: thalamus
    term:
      id: UBERON:0001897
      label: dorsal plus ventral thalamus
  evidence:
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These individuals share many of the electrophysiological properties of
      Gat1-deficient mice, including spontaneous spike-wave discharges.
    explanation: >-
      Links reduced GAT-1 function to the generalized spike-wave hyperexcitability
      seen in the Gat1-deficient mouse and shared by patients.
  downstream:
  - target: Generalized Myoclonic-Atonic Seizures
    causal_link_type: DIRECT
    hypothesis_groups:
    - reduced_phasic_gabaergic_synaptic_inhibition_model
  - target: Absence Seizures
    causal_link_type: DIRECT
    hypothesis_groups:
    - excess_tonic_extrasynaptic_gaba_inhibition_absence_model
- name: Impaired GABAergic Signaling in Neurodevelopment
  description: >-
    SLC6A1 is expressed in the developing brain even before the CNS is fully
    formed, and GABAergic signaling has trophic, developmental roles beyond fast
    inhibition. Impaired GAT-1 function therefore perturbs GABAergic signaling
    during neurodevelopment, contributing to the broad, seizure-independent
    neurodevelopmental phenotype - developmental delay/intellectual disability and
    autism spectrum disorder. This node captures the single developmental
    consequence of disrupted GABAergic signaling.
  role: effector
  cell_types:
  - preferred_term: GABAergic neuron
    term:
      id: CL:0000617
      label: GABAergic neuron
  biological_processes:
  - preferred_term: gamma-aminobutyric acid signaling pathway
    term:
      id: GO:0007214
      label: gamma-aminobutyric acid signaling pathway
    modifier: ABNORMAL
  - preferred_term: nervous system development
    term:
      id: GO:0007399
      label: nervous system development
    modifier: ABNORMAL
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Solute carrier family 6 member 1 (SLC6A1) is abundantly expressed in the
      developing brain even before the CNS is formed.
    explanation: >-
      Supports an early developmental role for SLC6A1/GAT-1, consistent with a
      neurodevelopmental phenotype arising from disrupted GABAergic signaling.
  - reference: PMID:35761184
    reference_title: "Consistency of parent-report SLC6A1 data in Simons Searchlight with Provider-Based Publications."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the phenotypic spectrum is broad and includes developmental delay, epilepsy,
      and autism or autistic traits.
    explanation: >-
      Documents the broad neurodevelopmental phenotype (developmental delay,
      autism) that accompanies the epilepsy in SLC6A1-related disorder.
  downstream:
  - target: Global Developmental Delay
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Intellectual Disability
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Autism Spectrum Disorder
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
mechanistic_hypotheses:
- hypothesis_group_id: excess_tonic_extrasynaptic_gaba_inhibition_absence_model
  hypothesis_label: Excess Tonic Extrasynaptic GABA-A Inhibition / Thalamocortical Absence Model
  status: CANONICAL
  description: >-
    The absence-seizure mechanism of SLC6A1-NDD is paradoxical: loss of GAT-1
    reuptake does not simply disinhibit the cortex but instead raises ambient
    extrasynaptic GABA, INCREASING tonic GABA-A receptor inhibition of
    thalamocortical relay neurons. The resulting sustained hyperpolarization
    de-inactivates low-threshold T-type calcium channels and promotes rhythmic
    thalamocortical burst-firing, generating the generalized spike-wave discharges
    that underlie absence seizures. This excess-tonic-inhibition model, established
    across genetic and pharmacological absence-epilepsy models and in
    Gat1-deficient mice, is the canonical explanation for the absence phenotype
    and clarifies why a GABA-clearance defect produces seizures rather than pure
    disinhibition.
  evidence:
  - reference: PMID:19966779
    reference_title: "Enhanced tonic GABAA inhibition in typical absence epilepsy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      extrasynaptic GABA(A) receptor-dependent 'tonic' inhibition is increased in
      thalamocortical neurons from diverse genetic and pharmacological models of
      absence seizures.
    explanation: >-
      Establishes that tonic extrasynaptic GABA-A inhibition of thalamocortical
      neurons is increased across absence-epilepsy models, the core of this
      hypothesis.
  - reference: PMID:19966779
    reference_title: "Enhanced tonic GABAA inhibition in typical absence epilepsy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Increased tonic inhibition is due to compromised GABA uptake by the GABA
      transporter GAT-1 in the genetic models tested, and GAT-1 is crucial in
      governing seizure genesis.
    explanation: >-
      Directly attributes the increased tonic inhibition to compromised GAT-1
      uptake and identifies GAT-1 as governing seizure genesis, linking SLC6A1/GAT-1
      loss to the absence mechanism.
  - reference: PMID:29315614
    reference_title: "Defining the phenotypic spectrum of SLC6A1 mutations."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      GAT-1 knockout mice exhibit spontaneous spike-wave discharges (SWDs) and
      absence seizures.
    explanation: >-
      Confirms in the GAT-1 knockout model the spike-wave and absence phenotype
      that the tonic-inhibition mechanism generates.
- hypothesis_group_id: reduced_phasic_gabaergic_synaptic_inhibition_model
  hypothesis_label: Reduced Phasic GABAergic Synaptic Inhibition Arm
  status: ALTERNATIVE
  description: >-
    A complementary arm holds that impaired GAT-1 reuptake degrades the timing and
    fidelity of fast phasic GABAergic synaptic transmission, reducing effective
    synaptic inhibition and contributing to cortical network hyperexcitability and
    the myoclonic-atonic seizure component. This is the intuitive
    loss-of-inhibition arm; it complements rather than replaces the
    excess-tonic-inhibition model, which better accounts for the absence phenotype.
  evidence:
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      all of which most likely lead to loss of function of GAT-1 and thus reduced
      GABA re-uptake from the synapse.
    explanation: >-
      Supports reduced synaptic GABA reuptake as the phasic loss-of-inhibition arm
      accompanying the tonic-increase mechanism.
phenotypes:
- name: Generalized Myoclonic-Atonic Seizures
  category: Clinical
  description: >-
    Myoclonic-atonic (myoclonic-astatic) seizures - a brief myoclonic jerk
    followed by loss of tone - are the classic seizure type, defining the
    epilepsy with myoclonic-atonic seizures (Doose-like) presentation in which
    SLC6A1 was first identified.
  diagnostic: true
  phenotype_term:
    preferred_term: Generalized myoclonic-atonic seizure
    term:
      id: HP:0011170
      label: Generalized myoclonic-atonic seizure
  evidence:
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      six SLC6A1 mutations in seven individuals, all of whom have epilepsy with
      myoclonic-atonic seizures (MAE).
    explanation: >-
      Establishes epilepsy with myoclonic-atonic seizures as the defining
      phenotype of the SLC6A1 discovery cohort.
- name: Absence Seizures
  category: Clinical
  description: >-
    Generalized non-motor (absence) seizures, including a childhood absence
    epilepsy presentation, are part of the SLC6A1 epilepsy spectrum.
  phenotype_term:
    preferred_term: Absence seizure
    term:
      id: HP:0002121
      label: Generalized non-motor (absence) seizure
  evidence:
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      including myoclonic atonic epilepsy, childhood absence epilepsy, autism, and
      intellectual disability
    explanation: >-
      Documents childhood absence epilepsy within the reported SLC6A1 epilepsy and
      neurodevelopmental spectrum.
- name: Epilepsy
  category: Clinical
  description: >-
    Epilepsy is a core feature of SLC6A1-NDD, generally a genetic generalized
    epilepsy with onset in early childhood.
  diagnostic: true
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      developmental delay and/or intellectual disability, hypotonia, epilepsy,
      movement disorders
    explanation: >-
      Lists epilepsy among the core clinical characteristics of SLC6A1-NDD.
- name: Global Developmental Delay
  category: Clinical
  description: >-
    Mild-to-severe developmental delay is a core feature, with language -
    particularly expressive language - often more affected than motor development.
  diagnostic: true
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SLC6A1-NDD) is characterized by mild-to-severe developmental delay and/or
      intellectual disability
    explanation: >-
      Establishes mild-to-severe developmental delay as a defining feature of
      SLC6A1-NDD.
- name: Intellectual Disability
  category: Clinical
  description: >-
    Intellectual disability, ranging from mild to severe, is a core feature of
    SLC6A1-NDD.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      mild-to-severe developmental delay and/or intellectual disability
    explanation: >-
      Documents intellectual disability across a mild-to-severe range in
      SLC6A1-NDD.
- name: Autism Spectrum Disorder
  category: Clinical
  description: >-
    Autism spectrum disorder is a frequent neurobehavioral manifestation of
    SLC6A1-NDD.
  phenotype_term:
    preferred_term: Autism spectrum disorder
    term:
      id: HP:0000729
      label: Autistic behavior
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      neurobehavioral and/or psychiatric manifestations (e.g., autism spectrum
      disorder, attention-deficit/hyperactivity disorder
    explanation: >-
      Lists autism spectrum disorder among the neurobehavioral manifestations of
      SLC6A1-NDD.
- name: Attention-Deficit/Hyperactivity Disorder
  category: Clinical
  description: >-
    Attention-deficit/hyperactivity disorder is a recognized neurobehavioral
    manifestation of SLC6A1-NDD.
  phenotype_term:
    preferred_term: Attention deficit hyperactivity disorder
    term:
      id: HP:0007018
      label: Attention deficit hyperactivity disorder
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      autism spectrum disorder, attention-deficit/hyperactivity disorder,
      aggression, anxiety, and/or sleep disturbances
    explanation: >-
      Lists attention-deficit/hyperactivity disorder among the neurobehavioral
      manifestations of SLC6A1-NDD.
- name: Hypotonia
  category: Clinical
  description: >-
    Hypotonia is a common feature of SLC6A1-NDD and is frequently reported by
    caregivers.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      developmental delay and/or intellectual disability, hypotonia, epilepsy
    explanation: >-
      Lists hypotonia among the core clinical characteristics of SLC6A1-NDD.
- name: Tremor
  category: Clinical
  description: >-
    Tremor is part of the movement-disorder spectrum in SLC6A1-NDD.
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      movement disorders (e.g., tremor, stereotypies, ataxia)
    explanation: >-
      Lists tremor among the movement disorders characterizing SLC6A1-NDD.
- name: Ataxia
  category: Clinical
  description: >-
    Ataxia and gait disturbance are part of the movement-disorder spectrum in
    SLC6A1-NDD.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      movement disorders (e.g., tremor, stereotypies, ataxia)
    explanation: >-
      Lists ataxia among the movement disorders characterizing SLC6A1-NDD.
- name: Motor Stereotypies
  category: Clinical
  description: >-
    Motor stereotypies are part of the movement-disorder spectrum in SLC6A1-NDD.
  phenotype_term:
    preferred_term: Motor stereotypy
    term:
      id: HP:0000733
      label: Motor stereotypy
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      movement disorders (e.g., tremor, stereotypies, ataxia)
    explanation: >-
      Lists stereotypies among the movement disorders characterizing SLC6A1-NDD.
- name: Delayed Speech and Language Development
  category: Clinical
  description: >-
    Language skills, particularly expressive language, are often more severely
    affected than motor development in SLC6A1-NDD.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Language skills, particularly expressive language, are often more
      significantly affected than motor development.
    explanation: >-
      Documents disproportionate expressive-language impairment in SLC6A1-NDD.
- name: Developmental Regression
  category: Clinical
  description: >-
    Developmental regression has been reported in some individuals with
    SLC6A1-NDD.
  phenotype_term:
    preferred_term: Developmental regression
    term:
      id: HP:0002376
      label: Developmental regression
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Developmental regression has been reported.
    explanation: >-
      Documents developmental regression as a reported feature of SLC6A1-NDD.
- name: Constipation
  category: Clinical
  description: >-
    Gastrointestinal manifestations, including constipation, are common in
    SLC6A1-NDD.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Gastrointestinal manifestations (e.g., constipation, diarrhea) are also
      common.
    explanation: >-
      Lists constipation among the common gastrointestinal manifestations of
      SLC6A1-NDD.
- name: Diarrhea
  category: Clinical
  description: >-
    Gastrointestinal manifestations, including diarrhea, are common in SLC6A1-NDD.
  phenotype_term:
    preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Gastrointestinal manifestations (e.g., constipation, diarrhea) are also
      common.
    explanation: >-
      Lists diarrhea among the common gastrointestinal manifestations of
      SLC6A1-NDD.
genetic:
- name: SLC6A1
  gene_term:
    preferred_term: SLC6A1
    term:
      id: hgnc:11042
      label: SLC6A1
  association: Loss-of-Function Variants
  presence: Positive
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal Dominant (De Novo)
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
  notes: >-
    Heterozygous SLC6A1 variants cause disease through loss of GAT-1 function.
    The spectrum includes truncating variants (nonsense, frameshift, splice-site)
    acting via haploinsufficiency and predominantly missense variants that misfold
    and are retained in the endoplasmic reticulum, reducing surface transporter
    expression. In the Simons Searchlight registry, carriers had predominantly
    missense or nonsense variants. Residual GAT-1 transporter function is a
    determinant of severity: variants causing complete loss of in vitro GABA
    uptake are enriched in individuals with severe disease, a genotype-severity
    correlation that informs variant interpretation.
  evidence:
  - reference: PMID:37647852
    reference_title: "SLC6A1 variant pathogenicity, molecular function and phenotype: a genetic and clinical analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For variants with complete loss of in vitro GABA uptake, we found a 4.6-fold
      enrichment in patients having severe disease versus non-severe disease
    explanation: >-
      Quantifies the genotype-severity correlation, linking complete loss of GAT-1
      GABA-uptake function to severe disease.
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      targeted resequencing of 644 individuals with epileptic encephalopathies led
      to the identification of six SLC6A1 mutations in seven individuals
    explanation: >-
      Original identification of heterozygous SLC6A1 variants as a cause of
      epileptic encephalopathy with myoclonic-atonic seizures.
  - reference: PMID:35761184
    reference_title: "Consistency of parent-report SLC6A1 data in Simons Searchlight with Provider-Based Publications."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Carriers in Searchlight had 83 unique pathogenic or likely pathogenic
      variants in SLC6A1, which were predominantly missense or nonsense variants.
    explanation: >-
      Documents the predominantly missense/nonsense SLC6A1 variant spectrum in a
      standardized patient registry.
diagnosis:
- name: SLC6A1 Molecular Diagnosis
  description: >-
    The diagnosis of SLC6A1-NDD is established in a proband with suggestive
    findings and a heterozygous pathogenic or likely pathogenic SLC6A1 variant
    identified by molecular genetic testing, typically de novo.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
    qualifiers:
    - predicate:
        preferred_term: has participant
        term:
          id: RO:0000057
          label: has participant
      value:
        preferred_term: SLC6A1
        term:
          id: hgnc:11042
          label: SLC6A1
  results: A heterozygous pathogenic SLC6A1 variant establishes the diagnosis.
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of SLC6A1-NDD is established in a proband with suggestive
      findings and a heterozygous pathogenic variant in SLC6A1 identified by
      molecular genetic testing.
    explanation: >-
      The GeneReviews chapter defines the molecular-genetic-testing basis for
      establishing the diagnosis.
- name: EEG and Seizure Phenotyping
  description: >-
    EEG documents the generalized epilepsy - typically generalized spike-and-wave
    activity - and characterizes the myoclonic-atonic and absence seizure types,
    guiding antiseizure treatment.
  diagnosis_term:
    preferred_term: electroencephalography
    term:
      id: NCIT:C38054
      label: Electroencephalography
  results: Generalized spike-and-wave discharges support the generalized epilepsy.
differential_diagnoses:
- name: Epilepsy with Myoclonic-Atonic Seizures (Doose syndrome), other genetic causes
  description: >-
    Epilepsy with myoclonic-atonic seizures (Doose syndrome) is a genetically
    heterogeneous clinical syndrome for which SLC6A1 is the best-established single
    gene; other cases involve SCN1A, SCN1B, GABRG2 and the GEFS+ spectrum or have
    complex/polygenic architecture. This SLC6A1 gene-anchored entry is one
    molecular cause of that clinical syndrome.
  distinguishing_features:
  - A heterozygous loss-of-function SLC6A1 variant favors SLC6A1-NDD.
  - Absence of an SLC6A1 variant, or a variant in another epilepsy gene, favors a
    non-SLC6A1 cause of the Doose-syndrome phenotype.
  evidence:
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      pathogenic mutations occurred in 6/160 individuals with MAE, accounting for
      ~4% of unsolved MAE cases.
    explanation: >-
      Shows SLC6A1 accounts for a minority of myoclonic-atonic epilepsy cases, so
      the Doose-syndrome phenotype has other genetic causes.
- name: Other GABAergic-pathway developmental and epileptic encephalopathies
  description: >-
    Developmental and epileptic encephalopathies caused by other GABA-pathway
    genes (e.g. GABRA1, GABRB3, GABRG2 encoding GABAA-receptor subunits) share
    impaired GABAergic inhibition and overlapping generalized epilepsy and are
    distinguished by molecular testing.
  distinguishing_features:
  - An SLC6A1 variant favors this disorder.
  - A GABAA-receptor-subunit gene variant favors the corresponding channelopathy.
progression:
- phase: Early childhood
  notes: >-
    Onset is typically in early childhood with generalized seizures
    (myoclonic-atonic and absence) in a child with emerging developmental delay, hypotonia,
    and language delay.
  evidence:
  - reference: PMID:25865495
    reference_title: "Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      all of whom have epilepsy with myoclonic-atonic seizures (MAE).
    explanation: >-
      Anchors the early-childhood myoclonic-atonic epilepsy presentation of the
      disorder.
- phase: Later childhood to adulthood
  notes: >-
    Seizures may improve over time in some individuals, while the
    neurodevelopmental features - intellectual disability, autism spectrum
    disorder, and behavioral difficulties - persist as the dominant long-term
    burden.
  evidence:
  - reference: PMID:35761184
    reference_title: "Consistency of parent-report SLC6A1 data in Simons Searchlight with Provider-Based Publications."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the phenotypic spectrum is broad and includes developmental delay, epilepsy,
      and autism or autistic traits.
    explanation: >-
      Documents the persistent neurodevelopmental features that dominate the
      long-term course.
treatments:
- name: Antiseizure Medication
  description: >-
    Seizures are managed with antiseizure medications, generally broad-spectrum
    agents appropriate for generalized epilepsy, with valproate the most effective
    and usual first-line choice. Levetiracetam is frequently used but is poorly
    tolerated in SLC6A1-NDD because of behavioral side effects at higher rates than
    in the general population, so alternatives are often considered. Tiagabine, a
    selective GAT-1 inhibitor, is mechanistically contraindicated: pharmacologically
    blocking the residual transporter would further raise extrasynaptic GABA and is
    expected to aggravate tonic-inhibition-driven absence seizures.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: levetiracetam
      term:
        id: CHEBI:6437
        label: levetiracetam
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      anti-seizure medications are often needed to control seizures
    explanation: >-
      The GeneReviews management section establishes antiseizure medication as the
      mainstay of seizure control.
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Individuals with SLC6A1-NDD have intolerable behavioral side effects with
      levetiracetam at higher rates than reported in the general population.
    explanation: >-
      Documents the levetiracetam behavioral-tolerability caution specific to
      SLC6A1-NDD.
- name: Valproate (Valproic Acid)
  description: >-
    Valproate is the most effective and generally first-line antiseizure
    medication for the generalized seizures of SLC6A1-NDD, controlling
    myoclonic-atonic and absence seizures as monotherapy or in combination.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: valproic acid
      term:
        id: CHEBI:39867
        label: valproic acid
  evidence:
  - reference: PMID:29315614
    reference_title: "Defining the phenotypic spectrum of SLC6A1 mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      seizure-free, with valproic acid being the most effective drug.
    explanation: >-
      In the SLC6A1 patient cohort, valproic acid was the most effective
      antiseizure drug, supporting its first-line role.
- name: 4-Phenylbutyrate Pharmacochaperone
  description: >-
    4-Phenylbutyrate is a small-molecule chemical chaperone under clinical
    investigation as a disease-modifying therapy for SLC6A1-NDD: by promoting
    proper folding and endoplasmic-reticulum export of misfolded missense GAT-1,
    it aims to restore cell-surface transporter expression and GABA reuptake
    rather than only suppressing seizures.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: 4-phenylbutyric acid
      term:
        id: CHEBI:41500
        label: 4-phenylbutyric acid
  evidence:
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      This study provides critical insight into therapeutic developments for
      SLC6A1 variant-mediated disorders and implicates that boosting transporter
      function by either genetic or pharmacological approaches would be beneficial.
    explanation: >-
      Provides the iPSC-model rationale for pharmacological (chaperone) rescue of
      misfolded GAT-1 as a disease-modifying approach.
- name: AAV9 SLC6A1 Gene Therapy
  description: >-
    Gene-replacement therapy delivering a functional SLC6A1/GAT-1 transgene by an
    AAV9 vector is in early-phase clinical development as a disease-modifying
    treatment aimed at restoring GAT-1 dose in the CNS - the genetic-restoration
    counterpart to pharmacological chaperone rescue.
  therapeutic_modality: GENE_THERAPY
  treatment_term:
    preferred_term: gene therapy
    term:
      id: NCIT:C15238
      label: Gene Therapy
  evidence:
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      This study provides critical insight into therapeutic developments for
      SLC6A1 variant-mediated disorders and implicates that boosting transporter
      function by either genetic or pharmacological approaches would be beneficial.
    explanation: >-
      Provides the iPSC-model rationale for genetic dose restoration of GAT-1 as a
      disease-modifying approach.
- name: Developmental and Educational Support
  description: >-
    Multidisciplinary developmental and educational support, including therapies
    for language and motor delay and management of behavioral and sleep problems,
    is a mainstay of care.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Developmental and educational support
    explanation: >-
      The GeneReviews management section lists developmental and educational
      support as core treatment of manifestations.
- name: Genetic Counseling
  description: >-
    Genetic counseling addresses the autosomal dominant, typically de novo
    mechanism, the 50% transmission risk from an affected individual, and the
    availability of prenatal and preimplantation genetic testing once the variant
    is known.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:36780407
    reference_title: "SLC6A1-Related Neurodevelopmental Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each child of an individual with SLC6A1-NDD has a 50% chance of inheriting
      the pathogenic variant.
    explanation: >-
      Supports the genetic-counseling content on autosomal dominant transmission
      risk.
clinical_trials:
- name: NCT04937062
  phase: PHASE_I
  status: ACTIVE_NOT_RECRUITING
  description: >-
    Trial of glycerol phenylbutyrate as a pharmacochaperone for monogenic
    developmental and epileptic encephalopathies including SLC6A1-NDD, testing
    safety and tolerability of boosting residual transporter/protein function.
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: clinicaltrials:NCT04937062
    reference_title: "Phenylbutyrate for Monogenetic Developmental and Epileptic Encephalopathy"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is possible that a medication called phenylbutyrate may help the the
      remaining proteins work better for STXBP1, SLC6A1, and/or other similar
      DEEs caused by single genes
    explanation: >-
      The trial tests phenylbutyrate as a chaperone to improve residual GAT-1
      protein function in SLC6A1-NDD.
- name: NCT07173153
  phase: PHASE_I
  status: ENROLLING_BY_INVITATION
  description: >-
    Phase I/II intrathecal gene-delivery trial of scAAV9.P546.SLC6A1, an AAV9
    vector carrying the SLC6A1 gene, for SLC6A1 neurodevelopmental disorder.
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: clinicaltrials:NCT07173153
    reference_title: "Phase I/II Intrathecal Gene Delivery Clinical Trial of scAAV9.P546.SLC6A1 for SLC6A1 Neurodevelopmental Disorder"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This is gene therapy study of an AAV9 vector carrying the SLCA1 gene for
      SLC6A1 neurodevelopmental disorder.
    explanation: >-
      First-in-human AAV9 gene-replacement trial for SLC6A1-NDD, supporting gene
      therapy as a disease-modifying strategy.
discussions:
- discussion_id: gap_slc6a1_gat1_rescue_human_translation
  prompt: >-
    Does restoring GAT-1 function - by genetic dose restoration (e.g. antisense
    or gene-based upregulation) or by pharmacological/chaperone rescue of
    misfolded, ER-retained transporter - translate from patient iPSC-derived
    astrocytes and neurons into clinical benefit in humans with SLC6A1-NDD?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#SLC6A1 Variant and GAT-1 Loss of Function
  - pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis
  rationale: >-
    In vitro model evidence exists: patient iPSC-derived astrocytes and neurons
    show that reduced GABA uptake is caused by misfolding, ER retention, and
    degradation of variant GAT-1, and the authors conclude that boosting
    transporter function by genetic or pharmacological approaches would be
    beneficial. The open question is translational fidelity - whether restoring
    surface GAT-1 in cultured patient cells predicts clinical improvement in
    seizures and, especially, in the seizure-independent neurodevelopmental
    features, which may depend on early developmental windows that a mature-cell
    rescue cannot recapitulate. Whether haploinsufficiency versus a
    misfolding-driven dominant effect predominates also gates which strategy
    (dose restoration versus chaperone/proteostasis) is optimal.
  evidence:
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      This study provides critical insight into therapeutic developments for
      SLC6A1 variant-mediated disorders and implicates that boosting transporter
      function by either genetic or pharmacological approaches would be beneficial.
    explanation: >-
      Establishes the iPSC-model-derived therapeutic rationale (GAT-1 boosting)
      whose translation to human clinical benefit is the open question.
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the loss of GABA uptake function and endoplasmic reticulum retention is
      consistent across induced pluripotent stem cell-derived cell types, including
      astrocytes and neurons, for the surveyed variants.
    explanation: >-
      Documents the iPSC-derived cellular model in which GAT-1 loss and ER
      retention - and thus candidate rescue - are demonstrated.
  proposed_experiments:
  - experiment_id: exp_slc6a1_gat1_rescue_translation
    name: GAT-1 rescue translation from iPSC models to in vivo readouts
    description: >-
      Test whether genetic dose restoration and chemical-chaperone rescue that
      restore surface GAT-1 and GABA uptake in patient iPSC-derived astrocytes and
      neurons also correct network inhibition and seizure/behavioral phenotypes in
      an SLC6A1 haploinsufficient in vivo model, and whether efficacy depends on the
      developmental timing of the intervention.
    experiment_type:
      preferred_term: cross-model therapeutic rescue experiment
    perturbations:
    - name: GAT-1 dose restoration and chaperone rescue
      target: pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis
      genes:
      - preferred_term: SLC6A1
        term:
          id: hgnc:11042
          label: SLC6A1
      description: >-
        Apply genetic upregulation and chemical-chaperone treatment to patient
        iPSC-derived cells and to an SLC6A1 haploinsufficient in vivo model at
        different developmental time points.
    readouts:
    - name: Surface GAT-1, GABA uptake, and network inhibition
      target: pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis
      biological_processes:
      - preferred_term: gamma-aminobutyric acid transport
        term:
          id: GO:0015812
          label: gamma-aminobutyric acid transport
        modifier: INCREASED
      assays:
      - preferred_term: radiolabeled GABA uptake assay
      - preferred_term: electroencephalography
      direction: POSITIVE
    controls:
    - name: Wild-type and isogenic-corrected cells
      description: Wild-type and CRISPR-corrected isogenic lines as references.
    - name: Vehicle versus chaperone
      description: Matched untreated versus chemical-chaperone-treated conditions.
    decision_criterion: >-
      Translation is supported if rescue that restores surface GAT-1 and GABA
      uptake in patient cells also improves in vivo inhibition and
      seizure/behavioral phenotypes; a mismatch is supported if cellular rescue
      fails to translate or is effective only within a narrow developmental window.
    would_support:
    - pathophysiology#Impaired GABA Reuptake and Disrupted GABA Homeostasis
- discussion_id: gap_slc6a1_haploinsufficiency_vs_dominant_negative
  prompt: >-
    Is SLC6A1-NDD a pure loss-of-dose (haploinsufficiency) disorder, or do
    misfolded, ER-retained missense GAT-1 mutants additionally act
    dominant-negatively by co-assembling with and retaining wild-type GAT-1 below
    hemizygous levels, and does the answer differ by variant class with
    consequences for therapy choice?
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - pathophysiology#SLC6A1 Variant and GAT-1 Loss of Function
  rationale: >-
    Truncating SLC6A1 variants plausibly act through simple haploinsufficiency,
    but most disease variants are missense, and functional studies show they
    misfold and are retained in the endoplasmic reticulum - a route that, as seen
    for GABAA-receptor subunits, can co-deplete wild-type protein and produce a
    dominant-negative effect exceeding loss of one allele. Whether this occurs for
    GAT-1, and how strongly it varies by variant, is unresolved and directly gates
    therapy: pure haploinsufficiency favors dose-restoration (e.g. antisense
    upregulation of the wild-type allele), whereas a dominant-negative
    misfolding mechanism favors chaperone/proteostasis rescue or allele-selective
    approaches.
  evidence:
  - reference: PMID:34028503
    reference_title: "Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our results resemble findings from pathogenic variants in other genes
      affecting the GABA pathway, such as GABAA receptors.
    explanation: >-
      Draws the parallel to GABAA-receptor variants, for which misfolding and
      wild-type co-retention (a dominant-negative route) are established, framing
      the open haploinsufficiency-versus-dominant-negative question for GAT-1.

📚

References & Deep Research

References

4

PMID:25865495

Mutations in the GABA Transporter SLC6A1 Cause Epilepsy with Myoclonic-Atonic Seizures.

No top-level findings curated for this source.

PMID:34028503

Common molecular mechanisms of SLC6A1 variant-mediated neurodevelopmental disorders in astrocytes and neurons.

No top-level findings curated for this source.

PMID:35761184

Consistency of parent-report SLC6A1 data in Simons Searchlight with Provider-Based Publications.

No top-level findings curated for this source.

PMID:36780407

SLC6A1-Related Neurodevelopmental Disorder.

No top-level findings curated for this source.

SLC6A1-Related Neurodevelopmental Disorder

Ask OpenScientist

OpenScientist Report

Mappings

Inheritance

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Diagnosis

Progression

Prevalence

Differential Diagnoses

Clinical Trials

Source YAML

References & Deep Research

References