SLC6A1 encodes GAT-1 (GABA transporter 1), the principal sodium- and chloride-dependent GABA transporter in the central nervous system. GAT-1 is responsible for reuptake of GABA from the synaptic cleft and extrasynaptic space, terminating GABAergic signaling and maintaining GABA homeostasis. Pathogenic variants in SLC6A1 cause a spectrum of epilepsy phenotypes, most commonly myoclonic-atonic epilepsy (MAE) and related generalized epilepsy syndromes.
SLC6A1 is one of the few monogenic epilepsy genes where the mechanism is clearly understood (loss of GABA reuptake → reduced inhibition → hyperexcitability) and where a natural small-molecule therapeutic exists: tiagabine, which inhibits GAT-1, partially compensating for the reduced endogenous transporter function.
| Property |
Value |
| Gene Symbol |
SLC6A1 |
| Chromosomal Location |
3p25.3 |
| Genomic Coordinates |
chr3:11,000,000-11,200,000 (GRCh38) |
| Gene Length |
~65 kb |
| Number of Exons |
16 coding exons |
| Protein Length |
599 amino acids |
| Protein Class |
Sodium/chloride-dependent GABA transporter (SLC6 family) |
| Expression |
Brain (neurons and astrocytes), peripheral tissues at low levels |
| Inheritance |
Autosomal dominant (de novo in most cases) |
| OMIM |
137165 |
| UniProt |
P30531 |
¶ Structure and Function
GAT-1 is a 12-transmembrane domain transporter belonging to the SLC6 family (sodium-coupled transporters):
- N-terminal extracellular domain: contains N-glycosylation sites
- Transmembrane domains 1-12: form the pore and substrate binding site
- Large extracellular loop between TM3 and TM4: contains glycosylation sites
- C-terminal intracellular domain: regulatory interactions
GAT-1 uses the sodium gradient to drive GABA transport:
- Na+ binding: Two sodium ions bind to the outward-facing conformation
- GABA binding: GABA binds with the sodium ions
- Conformational change: The transporter switches to inward-facing state
- Release: GABA and Na+ are released into the cytoplasm
- Reset: The empty transporter resets to outward-facing conformation
One Cl- ion is also transported per cycle, contributing to the overall electrochemical driving force.
¶ GABA Clearance and Inhibition
GAT-1 is the primary mechanism for terminating GABAergic transmission:
- Reuptake of synaptic GABA into presynaptic neurons (70-80% of clearance)
- Uptake into astrocytes (remaining clearance)
- Regulation of extracellular GABA concentrations
- Prevention of GABA spillover to adjacent synapses
Loss of GAT-1 function leads to:
- Prolonged GABA receptor activation
- Desensitization of GABA receptors
- Reduced GABA synthesis (less GABA recycled)
- Network hyperexcitability
All pathogenic SLC6A1 variants cause loss of GABA transporter function:
- Missense variants (~50%): reduce transporter expression, trafficking, or function
- Nonsense/frameshift variants (~30%): premature truncation, absent protein
- Splice variants (~15%): abnormal mRNA, reduced functional protein
- Copy number variants (~5%): deletions/duplications affecting dosage
The key consequence: reduced GABA reuptake → prolonged GABAergic inhibition followed by receptor desensitization → net disinhibition at the circuit level.
SLC6A1-related epilepsy likely involves:
- Impaired GABA clearance leading to altered synaptic timing
- Desensitization of GABA-A receptors from excessive activation
- Compensatory downregulation of GABA-A receptor expression
- Network-level hyperexcitability from disrupted inhibition
SLC6A1 variants associate with a range of epilepsy phenotypes:
- Myoclonic-atonic epilepsy (MAE): most common; onset 1-5 years
- Childhood absence epilepsy (CAE): some patients present with pure absences
- Epilepsy with generalized tonic-clonic seizures: overlap with GGE
- Autism spectrum disorder: some patients have ASD features without epilepsy
- Developmental delay/intellectual disability: variable; may be primary or secondary
| Disorder |
Variant Type |
Key Features |
| Myoclonic-atonic epilepsy (MAE / Doose syndrome) |
Missense, truncating |
Onset 1-5 years; myoclonic, atonic, absence seizures; variable outcome |
| Childhood absence epilepsy |
Missense |
Typical absence seizures with 3 Hz spike-wave |
| Generalized epilepsy with febrile seizures plus |
Missense |
Febrile + other generalized seizures |
| Autism spectrum disorder |
Missense, truncating |
ASD without epilepsy in some patients |
| Non-syndromic intellectual disability |
Missense |
ID as primary feature |
Standard ASMs are used, with variable efficacy:
- Valproic acid: broad-spectrum, often first-line
- Ethosuximide: effective for absence component
- Clobazam: adjunct for myoclonic seizures
- Avoid: tiagabine itself (GAT-1 inhibitor — would worsen condition)
Interestingly, tiagabine (GAT-1 inhibitor used to treat focal epilepsy) would worsen SLC6A1-related epilepsy by further reducing GABA reuptake. However, the principle of compensating for reduced transporter function through other mechanisms is valid.
SB-001 (formerly TX-004) (Takeda/Shinobi/Recode): AAV-based gene therapy delivering functional SLC6A1 (GAT-1) to neurons. The approach:
- Delivers wild-type SLC6A1 coding sequence (~1.8 kb — fits easily in AAV)
- Uses neuronal-specific promoter (e.g., synapsin or MECP2)
- Targets neurons to restore GABA reuptake capacity
- Delivered via ICV or intrathecal administration
Preclinical studies in Slc6a1 knockout mice demonstrated:
- Partial restoration of GABA uptake activity
- Reduced seizure susceptibility
- Improved behavioral outcomes
See therapeutics hub page for more on the SLC6A1 preclinical program.
- ASOs to increase SLC6A1 expression: Upregulate the remaining wild-type allele
- Small molecule correctors: Enhance trafficking/function of missense variants
- GABA-A receptor modulators: Compensate at the receptor level (but limited by receptor desensitization)
¶ Research and Open Questions
- Genotype-phenotype correlation — why do some variants cause MAE while others cause pure absence epilepsy?
- GAT-1 vs. GAT-2/3 compensation — are other GABA transporters upregulated as compensation?
- Astrocyte vs. neuronal contribution — what is the relative importance of neuronal vs. astrocytic GAT-1?
- Therapeutic window — when must SLC6A1 function be restored to prevent permanent circuit changes?
- Biomarkers — what pharmacodynamic markers indicate successful GAT-1 restoration?
- Dosing requirements — what level of GAT-1 expression is needed for clinical benefit?
- [@slc6a1_2015] SLC6A1 myoclonic-atonic epilepsy: clinical and genetic characterization
- [@slc6a1_2018] GAT-1 dysfunction and epilepsy: insights from SLC6A1 variants