GLUT1 Deficiency Syndrome

Mendelian MONDO:0000188 Pathograph 42 Show in embeddings browser Inborn Error of Metabolism Inborn Carbohydrate Metabolic Disorder Metabolic Epilepsy Epilepsy Movement Disorder

Glucose transporter type 1 (GLUT1) deficiency syndrome (Glut1DS) is a disorder of brain energy metabolism caused by heterozygous (rarely biallelic) pathogenic variants in SLC2A1, which encodes the GLUT1 facilitative glucose transporter responsible for transporting glucose across the endothelial cells of the blood-brain barrier and into erythrocytes. Reduced GLUT1 function starves the brain of its principal metabolic fuel, producing a cerebral energy deficit that manifests as an infantile-onset, often pharmacoresistant epileptic encephalopathy with acquired microcephaly, developmental delay, and a complex movement disorder (ataxia, dystonia, spasticity) in the classic severe form. Milder and later-onset presentations exist across a phenotypic spectrum, including paroxysmal exertion-induced dyskinesia (GLUT1 deficiency syndrome 2 / DYT18) and episodic choreoathetosis with spasticity (dystonia 9 / DYT9). The diagnostic hallmark is hypoglycorrhachia (low CSF glucose) with a low CSF:blood glucose ratio in the setting of normoglycemia. The ketogenic diet, which supplies ketone bodies as an alternative cerebral fuel bypassing the GLUT1 transport defect, is first-line disease-specific therapy.

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Inheritance

Autosomal Dominant HP:0000006

Glut1DS is most commonly caused by a heterozygous SLC2A1 pathogenic variant inherited in an autosomal dominant manner. About 90% of individuals have the disorder as the result of a de novo SLC2A1 pathogenic variant; about 10% have a variant inherited from a parent, whose degree of impairment may be mild or nonexistent (possible parental somatic mosaicism). Rare biallelic (autosomal recessive) inheritance has also been reported.

Autosomal dominant inheritance Penetrance: INCOMPLETE Expressivity: VARIABLE De novo rate: About 90% de novo; about 10% inherited from a parent (GeneReviews)

Show evidence (3 references)

PMID:20301603 SUPPORT Human Clinical

"Glut1DS is most commonly caused by a heterozygous SLC2A1 pathogenic variant and inherited in an autosomal dominant manner. About 90% of individuals with Glut1DS have the disorder as the result of a de novo SLC2A1 pathogenic variant; about 10% of individuals have the disorder as the result of a..."

GeneReviews genetic counseling section directly documents autosomal dominant inheritance, predominantly de novo, with a minority of inherited cases.

PMID:11136715 SUPPORT Human Clinical

"This is the first report of autosomal dominant transmission of GLUT1 deficiency, confirming that this condition is the result of haploinsufficiency."

Father-to-child transmission in two separate marriages established dominant inheritance and the haploinsufficiency mechanism.

PMID:20301603 SUPPORT Human Clinical

"The degree of impairment in the transmitting parent may be mild or nonexistent; parental somatic mosaicism for the SLC2A1 pathogenic variant may explain this observation."

Supports incomplete penetrance / variable expressivity in transmitting parents.

Autosomal Recessive HP:0000007

Rarely, biallelic SLC2A1 variants (compound heterozygous or homozygous) inherited from asymptomatic heterozygous parents produce Glut1DS as an autosomal recessive trait. The clinical inheritance pattern is determined by the relative pathogenicity of each allele and the resulting degree of GLUT1 haploinsufficiency, measured as residual erythrocyte glucose uptake.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:20687207 SUPPORT Human Clinical

"These cases demonstrate that Glut1 DS may present as an autosomal recessive trait. The clinical pattern of inheritance is determined by the relative pathogenicity of the mutation and the resulting degree of haploinsufficiency."

Two families with biallelic SLC2A1 variants and asymptomatic heterozygous parents define the recessive presentation.

PMID:20301603 SUPPORT Human Clinical

"Autosomal recessive inheritance has been reported in two families to date."

GeneReviews confirms recessive inheritance is rare (two families).

◆

Subtypes

Classic (Severe, Infantile-Onset) GLUT1 Deficiency Syndrome MONDO:0011724

SLC2A1 hgnc:11005

The most common and severe presentation, with onset in infancy to early childhood. Predominant clinical findings are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay, followed by complex movement disorders and intellectual disability ranging from mild to severe.

Show evidence (1 reference)

PMID:20301603 SUPPORT Human Clinical

"When first diagnosed in infancy to early childhood, the predominant clinical findings of Glut1DS are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay."

GeneReviews describes the classic infantile-onset presentation as the most common and severe form of Glut1DS.

GLUT1 Deficiency Syndrome 2 (DYT18 / Paroxysmal Exercise-Induced Dyskinesia, including DYT9 / episodic choreoathetosis with spasticity) MONDO:0012805

SLC2A1 hgnc:11005

A milder, later-onset (childhood) form dominated by paroxysmal dystonic attacks of the extremities triggered by prolonged physical exertion, with or without epilepsy or hemolytic anemia. Corresponds to OMIM PS612126 / MONDO childhood-onset GLUT1 deficiency syndrome 2 (DYT18). This subtype also covers the presentation formerly designated dystonia 9 (DYT9, OMIM 601042, MONDO:0010983, episodic choreoathetosis with spasticity), in which the same exertion-induced dyskinesia is accompanied by slowly progressive spastic paraparesis: the German/Dutch DYT9 pedigree was shown to carry a causative SLC2A1 mutation, making DYT9 and DYT18 allelic rather than distinct entities.

Show evidence (4 references)

PMID:21649651 SUPPORT Human Clinical

"This paper also shows phenotypical parallels between GLUT1DS and paroxysmal exertion-induced dyskinesia."

Directly documents the milder paroxysmal exertion-induced dyskinesia phenotype as part of the GLUT1DS spectrum.

PMID:18577546 SUPPORT Human Clinical

"co-occurring PED and epilepsy can be due to autosomal dominant heterozygous SLC2A1 mutations, expanding the phenotypic spectrum associated with GLUT1 deficiency"

Five-generation family plus three nuclear families establish PED with epilepsy as an SLC2A1 phenotype.

PMID:18451999 SUPPORT Human Clinical

"Their PED was accompanied by epilepsy, mild developmental delay, reduced CSF glucose levels, hemolytic anemia with echinocytosis, and altered erythrocyte ion concentrations."

Three-generation PED family documents the hemolytic-anemia variant of the GLUT1DS2 presentation.

+ 1 more reference

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Mechanistic Hypotheses

Blood-brain-barrier glucose transport failure causes cerebral energy deficit

canonical_glut1_energy_deficit CANONICAL

Evidence balance 2 support

Haploinsufficient GLUT1 at the brain endothelium limits glucose delivery, producing hypoglycorrhachia and a chronic brain energy deficit that is greatest when developmental glucose demand peaks; the deficit drives cortical hyperexcitability, impaired neurodevelopment and, under exertion or fasting, episodic basal ganglia failure. Ketogenic diet therapy works by supplying ketone bodies that bypass the transporter.

Pathograph links

SLC2A1 Loss-of-Function Variant -> Reduced GLUT1 Transporter Function at the Blood-Brain Barrier DIRECT Loss-of-function SLC2A1 variants reduce the density or activity of GLUT1 transporters expressed on brain microvascular endothelial cells.

Reduced GLUT1 Transporter Function at the Blood-Brain Barrier -> Cerebral Glucose Energy Deficit DIRECT Insufficient transendothelial glucose flux starves brain tissue of its principal metabolic substrate, independent of normal peripheral blood glucose levels.

Cerebral Glucose Energy Deficit -> Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure DIRECT When energy demand rises (sustained exertion) or substrate supply falls (fasting), the marginal glucose supply to metabolically expensive basal ganglia circuits is transiently exceeded.

Cerebral Glucose Energy Deficit -> Neuronal Hyperexcitability and Hypersynchrony INDIRECT KNOWN INTERMEDIATES Energy-deficient neurons and cortical circuits become hyperexcitable and hypersynchronous, generating the pharmacoresistant seizures characteristic of Glut1DS.

Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure -> Paroxysmal Exercise/Exertion-Induced Dyskinesia DIRECT

Show evidence (2 references)

PMID:32913944 SUPPORT Other

"Glut1 deficiency syndrome (Glut1DS) is a brain energy failure syndrome caused by impaired glucose transport across brain tissue barriers."

Consensus definition of the canonical mechanism.

PMID:9462754 SUPPORT Human Clinical

"These symptoms suggested the existence of a defect in glucose transport across the blood brain barrier."

The founding formulation of the hypothesis, confirmed by the mutations reported in the same paper.

GLUT1 deficiency arrests cerebral angiogenesis, adding a structural microvascular deficit

microvascular_developmental_defect EMERGING

Evidence balance 2 support

Beyond its fuel-transport role, endothelial GLUT1 is required for postnatal cerebral angiogenesis; in model mice low GLUT1 arrests microvessel growth and early, but not late, repletion averts disease. The consensus statement has adopted impaired microvascular development as a complication of delayed treatment, but the human contribution is unmeasured, and this model may partly explain why fuel substitution rescues seizures more completely than cognition.

Pathograph links

Reduced GLUT1 Transporter Function at the Blood-Brain Barrier -> Arrested Cerebral Angiogenesis and Microvascular Diminution DIRECT Beyond fuel delivery, endothelial GLUT1 is required for postnatal cerebral angiogenesis; low GLUT1 arrests microvessel expansion in model mice.

Arrested Cerebral Angiogenesis and Microvascular Diminution -> Impaired Neurodevelopment and Movement Disorder INDIRECT UNKNOWN INTERMEDIATES A diminished microvascular bed is proposed to compound the fuel deficit and contribute to cognitive dysfunction; the human contribution is unquantified.

Show evidence (2 references)

PMID:28106060 SUPPORT Model Organism

"We used model mice to demonstrate that low Glut1 protein arrests cerebral angiogenesis, resulting in a profound diminution of the brain microvasculature without compromising the blood-brain barrier."

Primary mouse evidence for the hypothesis.

PMID:40405536 SUPPORT Other

"Research reaches beyond the concept of brain energy depletion by impaired GLUT1-mediated glucose transfer across the blood-brain barrier."

2025 review frames non-fuel mechanisms as an active, still-emerging area.

Pore-region GLUT1 alleles cause hemolysis through a cation leak

erythrocyte_cation_leak_hemolysis EMERGING GLUT1 DS with Paroxysmal Exertion-Induced Dyskinesia

Evidence balance 1 support

Specific pore-region SLC2A1 alleles render the mutant transporter permeable to sodium, potassium and calcium; the resulting erythrocyte electrolyte disturbance produces echinocytosis and hemolytic anemia. Alleles that only reduce transport do not cause hemolysis, so this is an allele-specific gain of an abnormal function layered on haploinsufficiency, established in one family plus heterologous expression.

Pathograph links

Erythrocyte GLUT1 Dysfunction -> Hemolytic anemia DIRECT Restricted to alleles that create a cation leak (e.g. Q282_S285del); alleles that only reduce transport (A275T, G314S) do not cause hemolysis.

Show evidence (1 reference)

PMID:18451999 SUPPORT In Vitro

"the hemolysis with echinocytosis may result from alterations in intracellular electrolytes caused by a cation leak through mutant GLUT1"

The authors' mechanistic proposal from oocyte and erythrocyte studies.

Discussions and Knowledge Gaps

Which cellular intermediate translates chronic cerebral glucose under-supply into the specific pattern of neuronal hyperexcitability and hypersynchrony seen in Glut1DS — failure of the astrocyte-neuron lactate shuttle, selective energy vulnerability of fast-spiking GABAergic interneurons, disturbed adenosine/thalamocortical signaling, or a combination?

KNOWLEDGE GAP OPEN gap_glut1_energy_deficit_to_hyperexcitability_intermediate

Attached to

pathophysiology#Cerebral Glucose Energy Deficit pathophysiology#Neuronal Hyperexcitability and Hypersynchrony

The causal edge from "Cerebral Glucose Energy Deficit" to "Neuronal Hyperexcitability and Hypersynchrony" is curated as INDIRECT_KNOWN_INTERMEDIATES, but the identity of that intermediate is not actually established. Glucose reaches the brain almost exclusively through GLUT1, yet why a global fuel shortfall produces the particular Glut1DS electroclinical signature (including 2.5-4 Hz generalized spike-wave and absence-like seizures) rather than diffuse depression is unresolved. Candidate mechanisms — astrocytic lactate-supply failure, preferential ATP starvation of parvalbumin interneurons whose high firing rates make them metabolically expensive, and adenosine-mediated network effects — carry different therapeutic implications, so resolving the intermediate would materially sharpen the mechanism model.

Proposed experiments

Cell-type-resolved metabolic-to-excitability mapping in Glut1 haploinsufficiency

cell-type-resolved metabolic and excitability mapping experiment

exp_glut1_celltype_metabolic_intermediate

In GLUT-1+/- mice and patient-derived iPSC neuron-astrocyte co-cultures, simultaneously measure astrocytic lactate output, interneuron-specific ATP/metabolic stress, and network excitability, then test whether interneuron-targeted metabolic rescue (or lactate supplementation) normalizes hypersynchrony independently of restoring bulk neuronal glucose.

Perturbations

Interneuron-selective metabolic rescue

pathophysiology#Cerebral Glucose Energy Deficit

Selectively supply alternative fuel (lactate/ketone) or restore GLUT1 in astrocytes vs interneurons vs principal neurons to identify the rate-limiting compartment.

Readouts

Network hyperexcitability

pathophysiology#Neuronal Hyperexcitability and Hypersynchrony

multielectrode array recording electroencephalography

Direction: POSITIVE

Controls

Wild-type co-cultures

GLUT1-normal neuron-astrocyte co-cultures under matched glucose conditions.

Decision criterion

An intermediate is supported if rescuing a single cell compartment (e.g., astrocytic lactate supply or interneuron energetics) normalizes network excitability while leaving bulk neuronal glucose uptake unchanged.

Would support

pathophysiology#Neuronal Hyperexcitability and Hypersynchrony

Show evidence (2 references)

PMID:20301603 SUPPORT Human Clinical

"Glucose, the essential metabolic fuel for the brain, is transported into the brain exclusively by the protein glucose transporter type 1 (Glut1) across the endothelial cells forming the blood-brain barrier (BBB)."

Establishes the exclusive GLUT1 route for cerebral glucose, framing why the deficit is global; the open question is which cell type first converts that global shortfall into focal-onset hyperexcitability.

PMID:16497725 SUPPORT Model Organism

"GLUT-1+/- mice have epileptiform discharges on electroencephalography (EEG), impaired motor activity, incoordination, hypoglycorrhachia, microencephaly, decreased brain glucose uptake as measured by positron emission tomography (PET) scan and decreased brain Glut-1 expression by western blot (66%)."

Provides a tractable in vivo system in which the epileptiform phenotype is reproduced, i.e., a model where the missing cellular intermediate could be dissected with cell-type-specific readouts.

Why does ketone-based fuel substitution robustly control seizures in Glut1DS yet only partially rescue the movement disorder and cognitive impairment — is the residual deficit a missed developmental window, regional or functional under-supply of ketone-derived fuel, or a non-fuel role of glucose that ketones cannot replace?

KNOWLEDGE GAP OPEN gap_glut1_ketogenic_seizure_vs_neurodevelopment_dissociation

Attached to

pathophysiology#Cerebral Glucose Energy Deficit pathophysiology#Impaired Neurodevelopment and Movement Disorder pathophysiology#Recurrent Pharmacoresistant Seizures

Ketogenic diet therapy is the mainstay treatment and supplies ketone bodies as an alternative cerebral fuel that bypasses the GLUT1 transport defect. In practice it controls seizures far more completely than it reverses the paroxysmal movement disorder, ataxia/dystonia, or cognitive outcome, and outcomes are consistently better with earlier treatment. Whether the residual, seizure-independent morbidity reflects irreversible injury incurred before diagnosis (a developmental-window effect), inadequate ketone delivery to specific circuits, or a role of glucose beyond bulk fuel (e.g., biosynthetic/pentose-phosphate demands) is unresolved — and it determines whether earlier or supplemental (e.g., anaplerotic) therapy could close the gap.

Proposed experiments

Treatment-timing dissociation of seizure vs neurodevelopmental endpoints

treatment-timing endpoint dissociation experiment

exp_glut1_treatment_timing_endpoint_dissociation

In GLUT-1+/- mice, initiate ketogenic therapy or GLUT1 repletion across a graded set of ages and measure seizure/EEG control separately from motor coordination, brain growth, and cognitive-behavioral endpoints, testing whether the neurodevelopmental endpoints have an earlier closing window than the seizure endpoint.

Perturbations

Age-graded ketogenic/repletion therapy

pathophysiology#Cerebral Glucose Energy Deficit

Start fuel substitution or GLUT1 repletion at several developmental ages.

Readouts

Seizure control

pathophysiology#Recurrent Pharmacoresistant Seizures

electroencephalography

Direction: NEGATIVE

Motor and neurodevelopmental outcome

pathophysiology#Impaired Neurodevelopment and Movement Disorder

behavioral assay

Direction: POSITIVE

Controls

Untreated mutants and wild-type

Matched untreated GLUT-1+/- and wild-type animals.

Decision criterion

A developmental-window explanation is supported if neurodevelopmental endpoints lose responsiveness at an earlier treatment age than seizure control does; a fuel-limitation explanation is supported if both endpoints respond equally whenever adequate alternative fuel is supplied.

Would support

pathophysiology#Impaired Neurodevelopment and Movement Disorder

Show evidence (5 references)

PMID:20301603 SUPPORT Human Clinical

"Targeted therapy: Age-specific KDTs primarily provide a supplemental fuel, namely, ketone bodies, for brain energy metabolism."

Establishes that ketogenic therapy acts by fuel substitution, framing the question of why fuel substitution rescues seizures more completely than neurodevelopmental outcomes.

PMID:20301603 SUPPORT Human Clinical

"Typically, the earlier the treatment the better the long-term clinical outcome."

Documents the developmental-window dependence of outcome, one of the competing explanations for the residual neurodevelopmental deficit.

PMID:28106060 SUPPORT Model Organism

"Restoring the protein to 2-week old mutants, in which certain disease characteristics are readily apparent, is less effective in shaping normal brain microvasculature."

Model-organism evidence that later restoration incompletely reverses structural brain defects, supporting a developmental-window contribution to residual, seizure-independent morbidity.

+ 2 more references

Does the GLUT-1+/- mouse faithfully model the full human Glut1DS phenotype — in particular the paroxysmal features (paroxysmal eye-head movements, exercise-induced dyskinesia) and the spectrum extending to early-onset absence epilepsy and movement-disorder-predominant presentations — or does it capture mainly the core seizure/hypoglycorrhachia/microcephaly triad?

HUMAN MODEL MISMATCH OPEN gap_glut1_mouse_model_paroxysmal_phenotype_fidelity

Attached to

pathophysiology#Neuronal Hyperexcitability and Hypersynchrony pathophysiology#Impaired Neurodevelopment and Movement Disorder

The GLUT-1+/- mouse reproduces epileptiform EEG, motor impairment, hypoglycorrhachia and microencephaly and is described as mimicking the classical human presentation, making it the workhorse model for Glut1DS. But the human disorder is defined as much by paroxysmal, activity- and fasting-triggered phenomena and by a wide phenotypic spectrum (paroxysmal exercise-induced dyskinesia, early-onset absence epilepsy, isolated movement disorder) that depend on human-specific behavioral repertoire and developmental glucose-demand timing. Whether these paroxysmal and spectrum-defining features are recapitulated — and thus whether the model can validate therapies aimed at them — is the open translational question, distinct from a claim that evidence is simply absent.

Proposed experiments

Provocation phenotyping of paroxysmal features in Glut1 models

provocation phenotyping experiment

exp_glut1_paroxysmal_phenotype_provocation

Deep-phenotype GLUT-1+/- mice and patient-derived neuronal/BBB models under physiological provocations (fasting, exertion, post-prandial state) to test for movement-triggered dyskinesia-like events and absence-like spike-wave, comparing directly against the documented human paroxysmal spectrum.

Readouts

Paroxysmal movement and absence-like events

pathophysiology#Impaired Neurodevelopment and Movement Disorder

behavioral assay electroencephalography

Direction: POSITIVE

Controls

Wild-type littermates under identical provocation

Matched wild-type animals exposed to the same fasting/exertion protocols.

Decision criterion

Human fidelity for the paroxysmal spectrum is supported if physiological provocations reproducibly elicit movement-triggered dyskinesia-like events and absence-like discharges in mutants but not controls; absence of such events flags a genuine human/model mismatch for these features.

Would support

pathophysiology#Impaired Neurodevelopment and Movement Disorder

Show evidence (1 reference)

PMID:16497725 SUPPORT Model Organism

"The GLUT-1+/- murine phenotype mimics the classical human presentation of Glut-1 DS."

Documents fidelity to the classical core phenotype; the open question is whether the paroxysmal and spectrum-defining human features are also captured.

Does SLC2A1 variant class (truncating or deletion versus missense) predict clinical severity in Glut1DS, or is severity set only by residual transporter activity irrespective of variant class?

CONTROVERSY OPEN controversy_glut1_genotype_phenotype_correlation

Attached to

pathophysiology#SLC2A1 Loss-of-Function Variant genetic#SLC2A1 has_subtypes#

The largest laboratory series reported that mutation type was related to the severity of intellectual disability and to the presence of complex movement disorders, whereas the Columbia series of 16 new patients and the 2007 review of 84 published cases found no correlation between genotype, phenotype and biochemical measures, and the French national cohort found overlapping phenotypes that resist genotype-phenotype assignment. What does correlate across series is residual erythrocyte glucose uptake, which even determines whether a family presents as dominant or recessive. The resolution matters for counselling and for how the has_subtypes entries are read: they are phenotype clusters on a continuum, not variant-defined entities.

Show evidence (5 references)

PMID:20129935 SUPPORT Human Clinical

"Type of mutation was related to the severity of mental retardation and the presence of complex movement disorders."

Supports the claim that variant class predicts severity, in 57 genetically confirmed patients.

PMID:15622525 REFUTE Human Clinical

"There were no obvious correlations between phenotype, genotype, or biochemical measures."

Refutes the claim in an independent series of 16 patients.

PMID:17718830 REFUTE Human Clinical

"Autosomal dominant transmission and several mutational hot spots have been identified, but phenotype-genotype correlations are not yet apparent."

Review of 84 published cases found no apparent correlation.

+ 2 more references

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Pathophysiology

SLC2A1 Loss-of-Function Variant

Mechanism confidence: Established

Heterozygous (rarely biallelic) pathogenic variants in SLC2A1 reduce the amount or function of the GLUT1 facilitative glucose transporter protein, typically through haploinsufficiency.

Blood-brain-barrier glucose transport failure causes cerebral energy deficit

SLC2A1 hgnc:11005

D-glucose transmembrane transporter activity GO:0055056 ↓ DECREASED

Animal models

Glut1 haploinsufficient (GLUT-1+/-) mouse Mouse recapitulates The heterozygous null allele reproduces the haploinsufficient state, with brain Glut1 reduced to 66%.

Downstream

Reduced GLUT1 Transporter Function at the Blood-Brain Barrier Loss-of-function SLC2A1 variants reduce the density or activity of GLUT1 transporters expressed on brain microvascular endothelial cells.

Erythrocyte GLUT1 Dysfunction The same haploinsufficient transporter is expressed on erythrocytes, so red-cell hexose uptake falls in parallel with brain transport and serves as the accessible functional surrogate of the lesion.

Show evidence (6 references)

PMID:20301603 SUPPORT Human Clinical

"The diagnosis of Glut1DS is established in a proband with suggestive clinical findings, hypoglycorrhachia documented by lumbar puncture, and a (usually) heterozygous pathogenic variant in SLC2A1 identified by molecular genetic testing."

GeneReviews establishes heterozygous SLC2A1 pathogenic variants as the molecular cause of Glut1DS.

PMID:12029447 SUPPORT Human Clinical

"Several heterozygous mutations resulting in GLUT1 haploinsufficiency have been identified."

Review paper documents the haploinsufficiency mechanism underlying heterozygous SLC2A1 mutations.

PMID:9462754 SUPPORT Human Clinical

"We now report two distinct classes of mutations as the molecular basis for the functional defect of glucose transport: hemizygosity of GLUT1 and nonsense mutations resulting in truncation of the GLUT-1 protein."

The founding molecular study identifies whole-gene hemizygosity and truncating nonsense alleles as the first two classes of causal SLC2A1 lesion.

+ 3 more references

Reduced GLUT1 Transporter Function at the Blood-Brain Barrier

Mechanism confidence: Established

GLUT1 is the transporter responsible for facilitated glucose diffusion across the endothelial cells that form the blood-brain barrier, as well as glucose uptake into erythrocytes. Reduced GLUT1 activity impairs the rate at which glucose can be delivered from blood to brain, independent of blood glucose concentration.

Blood-brain-barrier glucose transport failure causes cerebral energy deficit GLUT1 deficiency arrests cerebral angiogenesis, adding a structural microvascular deficit

Brain Microvascular Endothelial Cell CL:2000044

D-glucose transmembrane transport GO:1904659 ↓ DECREASED

D-glucose transmembrane transporter activity GO:0055056 ↓ DECREASED

blood-brain barrier UBERON:0000120

Animal models

Glut1 haploinsufficient (GLUT-1+/-) mouse Mouse recapitulates Reduced brain glucose uptake and hypoglycorrhachia reproduce the barrier transport failure.

Downstream

Cerebral Glucose Energy Deficit Insufficient transendothelial glucose flux starves brain tissue of its principal metabolic substrate, independent of normal peripheral blood glucose levels.

Hypoglycorrhachia (low CSF glucose) Reduced endothelial glucose flux lowers glucose in the CSF and brain interstitium while blood glucose stays normal, so the CSF:blood glucose ratio falls.

Arrested Cerebral Angiogenesis and Microvascular Diminution Beyond fuel delivery, endothelial GLUT1 is required for postnatal cerebral angiogenesis; low GLUT1 arrests microvessel expansion in model mice.

Show evidence (2 references)

PMID:20301603 SUPPORT Human Clinical

GeneReviews defines the core defect as insufficient GLUT1-mediated glucose transfer across the blood-brain barrier.

PMID:32913944 SUPPORT Other

"Glut1 deficiency syndrome (Glut1DS) is a brain energy failure syndrome caused by impaired glucose transport across brain tissue barriers."

International consensus statement (expert consensus, hence OTHER) restates the barrier-transport lesion as the disease-defining step.

Cerebral Glucose Energy Deficit

Mechanism confidence: Established

Chronic under-supply of glucose to neurons and glia produces a state of cerebral energy insufficiency during the period of childhood brain development when glucose demand is highest, driving neuronal hyperexcitability, impaired neurodevelopment, and deceleration of brain (and hence head) growth.

Blood-brain-barrier glucose transport failure causes cerebral energy deficit

Neuron CL:0000540 Astrocyte CL:0000127

Generation of Precursor Metabolites and Energy GO:0006091 ↓ DECREASED

brain UBERON:0000955

Animal models

Glut1 Rgsc200 ENU missense mouse Mouse recapitulates Reduced brain glucose transport with compensatory hexokinase upregulation reproduces the supply-limited energy state.

Downstream

Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure When energy demand rises (sustained exertion) or substrate supply falls (fasting), the marginal glucose supply to metabolically expensive basal ganglia circuits is transiently exceeded.

Reduced CSF lactate Lower glycolytic substrate delivery is the presumed reason CSF lactate is low-to-normal rather than raised; the intermediate steps are inferred, and the finding distinguishes Glut1DS from mitochondrial disease.

Paroxysmal eye-head movements Paroxysmal eye-head movements are among the earliest signs of the infantile energy deficit; the circuit through which they arise is not established.

Neuronal Hyperexcitability and Hypersynchrony Energy-deficient neurons and cortical circuits become hyperexcitable and hypersynchronous, generating the pharmacoresistant seizures characteristic of Glut1DS.

Impaired Neurodevelopment and Movement Disorder Sustained cerebral energy insufficiency during critical developmental windows impairs neurodevelopment and produces a complex movement disorder combining ataxia, dystonia, and spasticity, together with deceleration of head growth (acquired/progressive microcephaly).

Show evidence (4 references)

PMID:20301603 SUPPORT Human Clinical

"The needs of the brain for glucose increase rapidly after birth, peaking in early childhood, remaining high until about age 10 years, then gradually decreasing throughout adolescence and plateauing in early adulthood."

GeneReviews explains why the cerebral energy deficit is most severe in infancy/early childhood when brain glucose demand peaks, framing the developmental basis of the classic phenotype.

PMID:26536893 SUPPORT Human Clinical

"Furthermore, brain energy metabolism normalised with triheptanoin, that is, increased Pi/PCr ratio during brain activation compared to the recovery phase (p = 0.021), and deteriorated when triheptanoin was withdrawn."

31P-NMR spectroscopy in patients shows an abnormal activation-dependent brain energy profile that normalises with substrate supplementation, a direct in vivo measure of the cerebral energy deficit.

PMID:31399478 SUPPORT Model Organism

"glucose transportation was reduced, whereas hexokinase activity and glucose metabolism were enhanced"

FDG-PET kinetics in a missense mouse model separate the transport-limited supply step from a compensatory rise in downstream hexokinase flux.

+ 1 more reference

Neuronal Hyperexcitability and Hypersynchrony

Cortical and subcortical neuronal networks deprived of adequate glucose fuel become hyperexcitable, producing hypersynchronous discharges that manifest as pharmacoresistant seizures of varying semiology. This node conforms to the shared epilepsy excitation-inhibition-imbalance final common pathway, substituting a metabolic (energy-deficit) upstream driver rather than a primary ion-channel lesion.

Neuron CL:0000540

cerebral cortex UBERON:0000956

Animal models

Glut1 haploinsufficient (GLUT-1+/-) mouse Mouse recapitulates Spontaneous epileptiform EEG discharges reproduce the hyperexcitable network state.

Glut1 Rgsc200 ENU missense mouse Mouse partially recapitulates Spontaneous EEG abnormalities and seizure-like behaviour both occur, but were not observed concurrently.

Downstream

Recurrent Pharmacoresistant Seizures Hyperexcitable, hypersynchronous cortical networks manifest clinically as recurrent seizures.

Generalized 2.5-4 Hz spike-wave EEG The interictal electrographic signature of the hypersynchronous network, most prominent from about two years of age.

Show evidence (4 references)

PMID:20301603 SUPPORT Human Clinical

"the predominant clinical findings of Glut1DS are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay."

GeneReviews documents pharmacoresistant seizures as the predominant early clinical finding reflecting cortical hyperexcitability.

PMID:12752470 SUPPORT Human Clinical

"During 24-h EEGs, background activity showed generalized 2.5- to 4-Hz spike-wave discharges (41%), generalized slowing or attenuation (34%), no abnormalities (34%), focal epileptiform discharges (13%), or focal slowing or attenuation (9%)."

24-hour EEG in 20 children quantifies the hypersynchronous generalized spike-wave and focal epileptiform signatures of the network state.

PMID:17718830 SUPPORT Human Clinical

"Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake."

The food-responsive EEG ties the hypersynchronous discharge directly to the fuel state of the cortex.

+ 1 more reference

Impaired Neurodevelopment and Movement Disorder

Chronic cerebral energy deficit produces a complex, often paroxysmal movement disorder (ataxia, dystonia, spasticity), speech difficulty, and intellectual disability that can present alone or alongside epilepsy, reflecting the breadth of the GLUT1DS phenotypic spectrum.

Neuron CL:0000540

brain development GO:0007420 ↓ DECREASED

Animal models

Glut1 haploinsufficient (GLUT-1+/-) mouse Mouse partially recapitulates Microencephaly, impaired motor activity and incoordination reproduce the growth and motor consequences.

Downstream

Progressive (Acquired) Microcephaly Reduced postnatal brain growth is expressed as deceleration of head growth.

Global Developmental Delay

Intellectual disability

Ataxia

Dystonia

Spasticity

Hypotonia

Speech Difficulty

Gait disturbance Gait disturbance is the functional composite of ataxia, dystonia and spasticity.

Show evidence (4 references)

PMID:20301603 SUPPORT Human Clinical

"the predominant clinical findings of Glut1DS are usually complex paroxysmal movement disorders, spasticity, ataxia, dystonia, speech difficulty, and intellectual disability."

GeneReviews describes the later-onset movement-disorder-predominant clinical picture directly arising from the same energy-deficit mechanism.

PMID:17718830 SUPPORT Human Clinical

"Hypotonic, ataxic, and dystonic features are most prominent. Speech is often severely affected. Some patients develop spasticity and secondary microcephaly."

Review of 84 published cases summarises the motor, speech and head-growth consequences of the developmental energy deficit.

PMID:24789115 SUPPORT Human Clinical

"Epilepsy dominated infancy and improved during childhood. Dystonia emerged during childhood or adolescence."

Longitudinal follow-up (mean 14 years) shows the movement disorder emerging as the dominant later manifestation.

+ 1 more reference

Recurrent Pharmacoresistant Seizures

The clinical endpoint of cortical hyperexcitability is recurrent, typically pharmacoresistant, epileptic seizures of varying types beginning in infancy or early childhood.

Neuron CL:0000540

Downstream

Pharmacoresistant Seizures

Absence seizures

Myoclonic seizures

Generalized tonic-clonic seizures

Focal seizures

Show evidence (3 references)

PMID:25487684 SUPPORT Human Clinical

"The initial symptom was convulsive seizures, which occurred in 15 cases, and was followed by abnormal eye movements in 7 cases and apneic or cyanotic attacks in 4 cases."

Nationwide Japanese survey documents convulsive seizures as the most frequent presenting symptom.

PMID:17718830 SUPPORT Human Clinical

"Patients present with an early-onset epilepsy resistant to anticonvulsants, developmental delay, and a complex movement disorder."

Review of 84 cases confirms early-onset, anticonvulsant-resistant epilepsy as the presenting endpoint.

PMID:12752470 SUPPORT Human Clinical

"Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."

Chart review of 20 children enumerates the seizure semiologies that make up the endpoint.

Erythrocyte GLUT1 Dysfunction

Mechanism confidence: Established

Erythrocytes express the same GLUT1 transporter as the brain endothelium, so the haploinsufficient state is measurable outside the brain as reduced 3-O-methyl-D-glucose uptake (typically about half of control Vmax with an unchanged Km) and, with flow cytometry, as reduced surface GLUT1. Residual uptake tracks clinical severity. Certain pore-region alleles additionally render the mutant transporter leaky to cations, disturbing red-cell sodium, potassium and calcium and producing echinocytosis and hemolysis. This node is chiefly a diagnostic surrogate of the primary lesion; only the cation leak branch is itself pathogenic.

Pore-region GLUT1 alleles cause hemolysis through a cation leak

Erythrocyte CL:0000232

D-glucose transmembrane transport GO:1904659 ↓ DECREASED

Downstream

Hemolytic anemia Restricted to alleles that create a cation leak (e.g. Q282_S285del); alleles that only reduce transport (A275T, G314S) do not cause hemolysis.

Show evidence (3 references)

PMID:15622525 SUPPORT In Vitro

"The mean V(max) for the 3-O-methyl-D-glucose uptake into erythrocytes was 996 fmol/10(6) red blood cells per second, significantly less (54 +/- 11%; t test, p < 0.05) than the mean control value of 1,847. The mean Km value for the patient group (1.4 +/- 0.5mM) was similar to the control group..."

Kinetic assay in 16 patients shows roughly half-normal transport capacity with unchanged affinity, the erythrocyte signature of haploinsufficiency.

PMID:22190371 SUPPORT Human Clinical

"We also noted a significant correlation between the mean erythrocyte 3-OMG uptake and clinical severity (R(2) = 0.94)."

In 109 suspected cases, residual erythrocyte uptake correlates tightly with clinical severity.

PMID:18451999 SUPPORT In Vitro

"the hemolysis with echinocytosis may result from alterations in intracellular electrolytes caused by a cation leak through mutant GLUT1."

Identifies the cation-leak branch by which a pore-region GLUT1 allele damages the erythrocyte itself.

Arrested Cerebral Angiogenesis and Microvascular Diminution

Mechanism confidence: Provisional

In Glut1-deficient mice, low endothelial GLUT1 arrests postnatal cerebral angiogenesis and leaves a profoundly reduced brain microvasculature while barrier integrity is preserved. Pre-symptomatic AAV9-mediated GLUT1 repletion averts the vascular defect and the disease; late (adult) repletion does not. The 2020 consensus statement adopts impaired microvascular development as a complication of delayed treatment, but direct human vascular data are lacking, so this node is provisional and is the structural basis of an emerging, non-fuel mechanism.

GLUT1 deficiency arrests cerebral angiogenesis, adding a structural microvascular deficit

Brain Microvascular Endothelial Cell CL:2000044

cerebral angiogenesis GO:0001525 ↓ DECREASED

brain UBERON:0000955

Animal models

Glut1-deficient mouse with AAV9-mediated Glut1 repletion Mouse recapitulates The vascular phenotype is defined in this model; the human counterpart has not been measured.

Glut1-deficient mouse with AAV9-mediated Glut1 repletion Mouse rescues Early AAV9-Glut1 repletion restores the microvasculature; adult repletion does not.

Downstream

Impaired Neurodevelopment and Movement Disorder A diminished microvascular bed is proposed to compound the fuel deficit and contribute to cognitive dysfunction; the human contribution is unquantified.

Show evidence (2 references)

PMID:28106060 SUPPORT Model Organism

"Studies to define the temporal requirements for Glut1 reveal that pre-symptomatic, AAV9-mediated repletion of the protein averts brain microvasculature defects and prevents disease, whereas augmenting the protein late, during adulthood, is devoid of benefit."

Temporal rescue experiments show the microvascular defect is GLUT1-dependent and has a developmental window.

PMID:32913944 SUPPORT Other

"Impaired development of the brain microvasculature is one such complication of delayed Glut1DS treatment in the postnatal period."

The consensus statement carries the mouse finding into the clinical framing of untreated early disease; it is expert opinion, not human vascular measurement.

Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure

Mechanism confidence: Provisional

Under sustained exertion or fasting, the marginal glucose supply of the energy-deficient brain is transiently overwhelmed in corticostriatal circuits, producing episodes of choreoathetosis or dystonia affecting mainly the legs (paroxysmal exercise-induced dyskinesia). The same triggers aggravate seizures and paroxysmal ataxia. Functional imaging in PED families implicates altered glucose metabolism in the corticostriate pathways; the exertion-induced energy-deficit model is proposed rather than directly measured in the basal ganglia.

Blood-brain-barrier glucose transport failure causes cerebral energy deficit

Neuron CL:0000540

Generation of Precursor Metabolites and Energy GO:0006091 ↓ DECREASED

basal ganglia UBERON:0002420

Downstream

Paroxysmal Exercise/Exertion-Induced Dyskinesia

Show evidence (3 references)

PMID:18577546 SUPPORT Human Clinical

"Functional imaging studies implicated alterations in glucose metabolism in the corticostriate pathways in the pathophysiology of PED and in the frontal lobe cortex in the pathophysiology of epileptic seizures."

Imaging in SLC2A1 PED families localises the metabolic disturbance behind dyskinesia to corticostriatal circuits.

PMID:26193382 SUPPORT Human Clinical

"Sensitivity to fasting or exertion in combination with those 3 main symptoms were the main differences between mutated and negative patients (p < 0.001)."

In a national laboratory cohort, trigger sensitivity to fasting and exertion discriminates SLC2A1-positive from negative patients.

PMID:23443458 SUPPORT Human Clinical

"A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise."

Review confirms fasting and exercise as the characteristic provocations of the paroxysmal phenotype.

⬡

Pathograph

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

●

Phenotypes

Blood 1

Hemolytic anemia HP:0001878

Show evidence (1 reference)

PMID:18451999 SUPPORT Human Clinical

"Their PED was accompanied by epilepsy, mild developmental delay, reduced CSF glucose levels, hemolytic anemia with echinocytosis, and altered erythrocyte ion concentrations."

Three-generation family with the Q282_S285del pore-region allele documents the hemolytic phenotype.

Eye 1

Paroxysmal eye-head movements Paroxysmal involuntary eye movements HP:0007704

Show evidence (2 references)

PMID:20301603 SUPPORT Human Clinical

GeneReviews lists paroxysmal eye-head movements first among infantile findings.

PMID:25487684 SUPPORT Human Clinical

"The initial symptom was convulsive seizures, which occurred in 15 cases, and was followed by abnormal eye movements in 7 cases and apneic or cyanotic attacks in 4 cases."

Abnormal eye movements were the presenting symptom in 7 of 33 nationwide cases.

Head and Neck 1

Progressive (Acquired) Microcephaly Secondary microcephaly HP:0005484

Course: PROGRESSIVE

Re-bound from HP:0000253 (Progressive microcephaly) to HP:0005484 (Secondary microcephaly, synonym "acquired microcephaly") because the defining feature is a normal head circumference at birth followed by postnatal deceleration; the clinical_course qualifier carries the progressive aspect.

Show evidence (3 references)

PMID:20301603 SUPPORT Human Clinical

"the predominant clinical findings of Glut1DS are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay."

GeneReviews lists deceleration of head growth as a predominant early clinical finding.

PMID:15622525 SUPPORT Human Clinical

"characterized by infantile seizures, developmental delay, acquired microcephaly, spasticity, ataxia, and hypoglycorrhachia"

Names the microcephaly as acquired, i.e. postnatal.

PMID:17718830 SUPPORT Human Clinical

"Some patients develop spasticity and secondary microcephaly."

Review of 84 cases classifies it as secondary microcephaly and as occurring in some rather than all patients, so no frequency band is asserted.

Metabolism 2

Hypoglycorrhachia (low CSF glucose) VERY_FREQUENT HP:0011972

Show evidence (3 references)

PMID:20129935 SUPPORT Human Clinical

"Cerebrospinal fluid glucose was below 2.5 mmol/l (range 0.9-2.4 mmol/l) in all patients and cerebrospinal fluid : blood glucose ratio was below 0.50 in all but one patient (range 0.19-0.52)."

All 57 genetically confirmed patients had hypoglycorrhachia, supporting VERY_FREQUENT.

PMID:23999624 SUPPORT Human Clinical

"The CSF glucose levels ranged from 16.2 to 50.5 mg/dL and were at or below the 10th percentile for all 147 patients."

Systematic review of 147 genetically proven patients confirms universally low CSF glucose against age-specific percentiles.

PMID:17718830 SUPPORT Human Clinical

"The essential biochemical finding is a low glucose concentration in the cerebrospinal fluid"

Gives the pooled mean CSF glucose across 84 published cases.

Reduced CSF lactate VERY_FREQUENT HP:0030086

Show evidence (3 references)

PMID:23999624 SUPPORT Human Clinical

"The CSF lactate levels ranged from 5.4 to 13.5 mg/dL and were at or below the 10th percentile for 59 of 73 patients (81%)."

81% of patients with reported values had low CSF lactate, supporting VERY_FREQUENT.

PMID:15622525 SUPPORT Human Clinical

"The mean cerebrospinal fluid lactate concentration was 1.0 +/- 0.3mM, which was less than the normal mean value of 1.63mM."

Mean CSF lactate in 16 new patients was below the normal mean.

PMID:17718830 SUPPORT Human Clinical

"in the setting of normoglycaemia. CSF lactate is normal."

The 2007 review reports CSF lactate as normal rather than reduced; the value is low-to-normal, never elevated, which is the diagnostically useful point.

Musculoskeletal 2

Spasticity FREQUENT HP:0001257

Show evidence (1 reference)

PMID:25487684 SUPPORT Human Clinical

"Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."

Nationwide cohort documents spastic paralysis as a common neurological finding.

Hypotonia FREQUENT HP:0001252

Show evidence (1 reference)

PMID:25487684 SUPPORT Human Clinical

"Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."

Nationwide cohort documents muscle hypotonia as a common neurological finding.

Nervous System 13

Pharmacoresistant Seizures VERY_FREQUENT HP:0001250

Temporal: RECURRENT

Show evidence (3 references)

PMID:25487684 SUPPORT Human Clinical

"Thirty-two patients (97%) exhibited some type of epileptic seizure."

Nationwide cohort of 33 confirmed GLUT1DS patients documents seizures in 97% of individuals, directly supporting VERY_FREQUENT.

PMID:20129935 SUPPORT Human Clinical

"Three different phenotypes were recognized: (i) the classical phenotype (84%), subdivided into early-onset (<2 years) (65%) and late-onset (18%); (ii) a non-classical phenotype, with mental retardation and movement disorder, without epilepsy (15%)"

In 57 genetically confirmed patients, 84% had the epilepsy-containing classical phenotype and 15% had no epilepsy, keeping seizures in the VERY_FREQUENT band while documenting the epilepsy-free minority.

PMID:17718830 SUPPORT Human Clinical

"Patients present with an early-onset epilepsy resistant to anticonvulsants, developmental delay, and a complex movement disorder."

Supports the pharmacoresistance qualifier.

Context-specific annotations (1)

Onset: INFANTILE; mean 0.4y (range 0.08-1.5y)

Show evidence (1 reference)

PMID:12752470 SUPPORT Human Clinical

"Age at seizure diagnosis was between 4 weeks and 18 months (mean, 5 months)."

Quantifies infantile seizure onset.

Global Developmental Delay VERY_FREQUENT HP:0001263

Show evidence (1 reference)

PMID:25487684 SUPPORT Human Clinical

"Mild to severe mental retardation was detected in all 33 cases."

Nationwide cohort documents developmental/cognitive impairment in all 33 confirmed cases.

Ataxia FREQUENT HP:0001251

Show evidence (1 reference)

PMID:25487684 SUPPORT Human Clinical

"Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."

Nationwide cohort documents cerebellar ataxia as a common neurological finding in most patients.

Dystonia FREQUENT HP:0001332

Show evidence (2 references)

PMID:25487684 SUPPORT Human Clinical

"Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."

Nationwide cohort documents dystonia as a common neurological finding.

PMID:17718830 SUPPORT Human Clinical

"Hypotonic, ataxic, and dystonic features are most prominent."

Review of 84 published cases ranks dystonic features among the most prominent motor findings.

Context-specific annotations (1)

Onset: CHILDHOOD

Show evidence (1 reference)

PMID:24789115 SUPPORT Human Clinical

"Dystonia emerged during childhood or adolescence."

Longitudinal cohort places dystonia onset after the infantile epilepsy phase.

Paroxysmal Exercise/Exertion-Induced Dyskinesia OCCASIONAL Paroxysmal dyskinesia HP:0007166

Temporal: RECURRENT

Show evidence (4 references)

PMID:25487684 SUPPORT Human Clinical

"Furthermore, paroxysmal episodes of ataxia, dystonia/dyskinesia, and motor paralysis were described in approximately 1/3 of all patients. The factors that frequently aggravated these events were hunger, exercise, fever, and fatigue, in that order."

Nationwide cohort quantifies paroxysmal dyskinetic episodes in about a third of patients and identifies exertion/hunger/fever/fatigue as triggers.

PMID:18577546 SUPPORT Human Clinical

"PED was characterized by choreoathetosis, dystonia or both, affecting mainly the legs."

Defines the semiology of PED in SLC2A1 families.

PMID:24789115 SUPPORT Human Clinical

"The 6-Minute Walk Test captured gait disturbances and triggered paroxysmal exertional dyskinesia."

A standardised exertion test reproducibly provokes the episodes in long-term follow-up.

+ 1 more reference

Speech Difficulty Dysarthria HP:0001260

Show evidence (1 reference)

PMID:20301603 SUPPORT Human Clinical

"the predominant clinical findings of Glut1DS are usually complex paroxysmal movement disorders, spasticity, ataxia, dystonia, speech difficulty, and intellectual disability."

GeneReviews lists speech difficulty among predominant clinical findings in the later-onset presentation.

Intellectual disability VERY_FREQUENT HP:0001249

Show evidence (3 references)

PMID:20301603 SUPPORT Human Clinical

"Subsequently children develop complex movement disorders and intellectual disability ranging from mild to severe."

GeneReviews documents intellectual disability across a mild-to-severe range.

PMID:25487684 SUPPORT Human Clinical

"Mild to severe mental retardation was detected in all 33 cases."

All 33 confirmed cases had cognitive impairment, supporting VERY_FREQUENT.

PMID:26193382 SUPPORT Human Clinical

"Most patients (87.5%) exhibited classic phenotype with intellectual deficiency (41.7%), epilepsy (75%) or movement disorder (29%) as initial symptoms at a medium age of 7.5 months"

French cohort shows intellectual deficiency as the presenting symptom in 41.7%.

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

Show evidence (3 references)

PMID:12752470 SUPPORT Human Clinical

"Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."

Absence seizures in 10 of 20 children with Glut1DS.

PMID:26537434 SUPPORT Human Clinical

"Mutations in SLC2A1 were detected in 5 (10%) of 50 patients with absence epilepsy"

Shows the converse association, that absence epilepsy is a recognised Glut1DS presentation.

PMID:23443458 SUPPORT Human Clinical

"Absence epilepsy and other idiopathic generalized epilepsy syndromes may occur with seizure onset in childhood or adulthood."

Review places absence epilepsy within the milder end of the spectrum.

Myoclonic seizures HP:0032794

Show evidence (2 references)

PMID:12752470 SUPPORT Human Clinical

"Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."

Myoclonic seizures in 6 of 20 children.

PMID:26193382 SUPPORT Human Clinical

"Patients with myoclonic seizures (52%) evolved with more severe intellectual deficiency and movement disorders compared with those with Early Onset Absence Epilepsy (38%)."

Myoclonic seizures identify a more severe subgroup.

Generalized tonic-clonic seizures Bilateral tonic-clonic seizure HP:0002069

Show evidence (1 reference)

PMID:12752470 SUPPORT Human Clinical

"Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."

Generalized tonic or clonic seizures in 14 of 20 children.

Focal seizures Focal-onset seizure HP:0007359

Show evidence (1 reference)

PMID:12752470 SUPPORT Human Clinical

"Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."

Partial seizures in 9 of 20 children.

Generalized 2.5-4 Hz spike-wave EEG EEG with spike-wave complexes HP:0010850

Show evidence (2 references)

PMID:12752470 SUPPORT Human Clinical

"In all ages, a normal interictal EEG was the most common EEG finding. When abnormalities occurred, focal slowing or epileptiform discharges were more prevalent in the infant. In older children (2 years or older), a generalized 2.5- to 4-Hz spike-wave pattern emerged."

Defines the age-dependent EEG signature and its low sensitivity.

PMID:17718830 SUPPORT Human Clinical

"Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake."

Documents the food-responsive property of the discharge.

Gait disturbance HP:0001288

Show evidence (1 reference)

PMID:24789115 SUPPORT Human Clinical

"Percent-predicted 6-Minute Walk Test distance correlated significantly with Columbia Neurological Scores."

Walking performance is a quantitative correlate of neurological burden in long-term follow-up.

🧬

Genetic Associations

SLC2A1 (Causative)

Gene: SLC2A1 hgnc:11005 gene page relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (5 references)

PMID:20301603 SUPPORT Human Clinical

GeneReviews genetic counseling section quantifies the de novo versus inherited variant origin split.

PMID:25487684 SUPPORT Human Clinical

"Pathological mutations in the SLC2A1 gene were identified in 28 out of 32 cases (87.5%)."

Nationwide Japanese cohort documents the molecular diagnostic yield of SLC2A1 testing among clinically suspected patients.

PMID:20129935 SUPPORT Human Clinical

"In these 57 patients we identified 49 different mutations, including six multiple exon deletions, six known mutations and 37 novel mutations (13 missense, five nonsense, 13 frame shift, four splice site and two translation initiation mutations)."

Largest single-laboratory series enumerates the allelic spectrum, including multi-exon deletions detectable only by MLPA.

+ 2 more references

💊

Medical Actions

Ketogenic Diet Therapy

Category: Therapeutic Action: ketogenic diet intake Ontology label: Ketogenic Diet NCIT:C173168

Platform: Behavioral / lifestyle

Age-specific ketogenic diet therapies (KDTs) supply ketone bodies as an alternative fuel for brain energy metabolism, bypassing the GLUT1 transport defect. Earlier initiation, ideally in infancy, is associated with better seizure control and long-term neurologic outcome. Effective for both seizure control and the movement disorder.

Mechanism Target:

BYPASSES Cerebral Glucose Energy Deficit

Show evidence (1 reference)

PMID:20301603 SUPPORT Human Clinical

"Targeted therapy: Age-specific KDTs primarily provide a supplemental fuel, namely, ketone bodies, for brain energy metabolism."

GeneReviews describes the ketogenic diet mechanism of action as supplying an alternative cerebral fuel that bypasses the GLUT1 transport defect.

Target Phenotypes: Seizure HP:0001250 Paroxysmal dyskinesia HP:0007166

Show evidence (7 references)

PMID:36303089 SUPPORT Human Clinical

"All patients were seizure-free within a month of receiving the diet therapy. All patients were followed up for six months, three were followed up for 12 months after the treatment, and there was no recurrence of epilepsy during this period."

Retrospective single-center cohort of SLC2A1-mutation patients demonstrates rapid and durable seizure control with ketogenic diet therapy.

PMID:20301603 SUPPORT Human Clinical

"Typically, the earlier the treatment the better the long-term clinical outcome."

GeneReviews documents that earlier ketogenic diet initiation yields better long-term neurologic outcome.

PMID:20129935 SUPPORT Human Clinical

"a ketogenic diet was effective in most of the patients with epilepsy (86%) and also reduced movement disorders in 48% of the patients with a classical phenotype and 71% of the patients with a non-classical phenotype."

Quantifies response of both seizures and movement disorder in 57 confirmed patients.

+ 4 more references

Modified Atkins Diet and other ketogenic dietary variants

Category: Therapeutic Action: modified Atkins and other ketogenic dietary therapies Ontology label: Dietary Intervention NCIT:C15447

Platform: Behavioral / lifestyle

Less restrictive ketogenic dietary therapies (modified Atkins diet, medium-chain-triglyceride diet, low-glycaemic-index treatment) are used, particularly in older children and adults, and in a large family survey gave seizure-freedom rates comparable to the classic 4:1 diet. They act by the same ketone-supply mechanism as the classic diet.

Mechanism Target:

BYPASSES Cerebral Glucose Energy Deficit — Supplies ketone bodies as an alternative cerebral fuel, as the classic ketogenic diet does.

Show evidence (2 references)

PMID:26803281 SUPPORT Human Clinical

"Diets used were extremely varied: 59 were treated with the classic ketogenic diet (KD), 29 with the Modified Atkins Diet (MAD), 4 with the Medium-chain Triglyceride (MCT) Diet and 2 with the low glycemic index treatment."

Documents real-world use of the dietary variants.

PMID:26803281 SUPPORT Human Clinical

"There was an equal percentage of children seizure-free receiving the KD/MCT Diets compared to the MAD/Low Glycemic Index Treatment (74% vs. 63%, p=0.30)."

No significant difference in seizure freedom between classic and less restrictive diets in this parent-reported survey.

Triheptanoin

Category: Therapeutic Action: Pharmacotherapy NCIT:C15986

Agent: Triheptanoin CHEBI:757060

Platform: Small molecule

Triheptanoin is an anaplerotic odd-chain (C7) medium-chain triglyceride that provides Krebs-cycle substrates and an alternative brain fuel independent of GLUT1. An open-label study reported marked reduction of non-epileptic paroxysmal manifestations and normalized brain bioenergetics, but a subsequent randomized placebo-controlled trial did not show a significant reduction in seizure frequency in patients not on a ketogenic diet, leaving its efficacy for the epilepsy phenotype unproven.

Mechanism Target:

BYPASSES Cerebral Glucose Energy Deficit

Show evidence (1 reference)

PMID:26536893 SUPPORT Human Clinical

"Treatment with triheptanoin resulted in a 90% clinical improvement in non-epileptic paroxysmal manifestations and a normalised brain bioenergetics profile in patients with GLUT1-DS."

Open-label study demonstrates triheptanoin supplies anaplerotic Krebs-cycle substrates that bypass the GLUT1 defect and normalize brain energy metabolism.

Show evidence (2 references)

PMID:26536893 SUPPORT Human Clinical

"Treatment with triheptanoin resulted in a 90% clinical improvement in non-epileptic paroxysmal manifestations and a normalised brain bioenergetics profile in patients with GLUT1-DS."

Open-label pilot study supports triheptanoin efficacy against the non-epileptic paroxysmal (movement-disorder) manifestations of GLUT1DS.

PMID:35441706 REFUTE Human Clinical

"Triheptanoin did not significantly reduce seizure frequency in patients with Glut1DS not on the ketogenic diet."

Randomized double-blind placebo-controlled trial qualifies the treatment claim by showing no significant seizure-frequency benefit for the epilepsy phenotype.

Anti-Seizure Medications to Avoid

In individuals on ketogenic diet therapy, valproic acid should be avoided because it increases the risk of a Reye-like illness and may also inhibit glucose transport; phenobarbital, acetazolamide, topiramate, and zonisamide may be relatively contraindicated as adjunctive treatment. This is a "circumstance to avoid" (GeneReviews Agents/Circumstances to Avoid section) rather than a recommended treatment; retained here as a treatment-adjacent drug-safety note.

Show evidence (1 reference)

PMID:20301603 SUPPORT Human Clinical

"Agents/circumstances to avoid: In individuals on KDTs: (1) avoidance of treatment of seizures with valproic acid, because it increases the risk of a Reye-like illness and may also inhibit glucose transport; (2) other anti-seizure medications (ASMs) including phenobarbital, acetazolamide,..."

GeneReviews Agents/Circumstances to Avoid section directly documents these drug-safety warnings for GLUT1DS patients on ketogenic diet therapy.

Multidisciplinary Supportive Care

Action: Supportive Care NCIT:C15747

Physical medicine and rehabilitation, physical therapy, occupational therapy, speech and language therapy, educational programs, and clinical genetics/genetic counseling, alongside routine neurology follow-up to monitor response to ketogenic diet therapy and identify new manifestations.

Show evidence (1 reference)

PMID:20301603 SUPPORT Human Clinical

"Supportive care: In addition to educational programs to address the individual's needs, multidisciplinary care by specialists in neurology familiar with KDTs, physical medicine and rehabilitation, physical therapy, occupational therapy, speech and therapy, and clinical genetics and genetic counseling."

GeneReviews management section documents the multidisciplinary supportive care regimen recommended alongside ketogenic diet therapy.

Genetic Counseling

Category: Counseling / Informational Action: Genetic Counseling NCIT:C15240

Each child of an individual with autosomal dominant Glut1DS has a 50% chance of inheriting the SLC2A1 variant; because about 90% of cases are de novo and transmitting parents may be mildly affected or unaffected (possible mosaicism), parental testing is informative. Prenatal and preimplantation testing are possible once the familial variant is known.

Show evidence (2 references)

PMID:20301603 SUPPORT Human Clinical

"Each child of an individual with autosomal dominant Glut1DS has a 50% chance of inheriting the SLC2A1 pathogenic variant and being clinically affected."

Recurrence risk for offspring of an affected individual.

PMID:20301603 SUPPORT Human Clinical

"Once the SLC2A1 pathogenic variant(s) have been identified in an affected family member, prenatal and preimplantation genetic testing for Glut1DS are possible."

Reproductive options.

Evaluation of At-Risk Relatives and Early Treatment

Category: Screening Action: targeted SLC2A1 variant testing of at-risk relatives Ontology label: Molecular Analysis NCIT:C19770

Because early ketogenic diet therapy improves seizure control and long-term neurological outcome, at-risk newborns, infants and other relatives of a proband should be tested for the familial SLC2A1 variant so that treatment can begin before or at the first manifestations.

Show evidence (2 references)

PMID:20301603 SUPPORT Human Clinical

"It is appropriate to evaluate at-risk newborns, infants, and other relatives of a proband to identify as early as possible those who would benefit from initiation of treatment and preventive measures."

GeneReviews recommendation to evaluate relatives at risk.

PMID:20301603 SUPPORT Human Clinical

"Early initiation of KDTs, ideally in infancy, results in better seizure control and improves long-term neurologic outcome."

The rationale for presymptomatic identification.

Neurological Surveillance

Category: Monitoring Action: scheduled neurological re-evaluation Ontology label: Diagnostic Procedure NCIT:C18020

Routinely scheduled neurology review to judge response to ketogenic diet therapy and to detect new manifestations, especially the movement disorder that emerges in later childhood and adolescence, with follow-up by the treating physical, occupational and speech-language therapists.

Show evidence (1 reference)

PMID:20301603 SUPPORT Human Clinical

"Surveillance: Routinely scheduled evaluations with a neurologist (to determine response to KDTs and identify any new manifestations) as well as follow up per treating physical therapists, occupational therapists, and speech-language therapists."

GeneReviews surveillance recommendation.

AAV9-Mediated GLUT1 Gene Replacement (Experimental)

Category: Therapeutic Action: AAV9 SLC2A1 gene replacement Ontology label: Gene Therapy NCIT:C15238

Platform: Gene therapy

Experimental, preclinical only. In Glut1-deficient mice, pre-symptomatic AAV9-mediated repletion of GLUT1 averts the brain microvascular defect and prevents disease, and repletion in early-symptomatic animals still restores the microvasculature and ameliorates disease, whereas adult repletion gives no benefit. The 2020 consensus notes that interventions to restore GLUT1 protein content and function are in development. No human trial of GLUT1 gene replacement is cited here.

Mechanism Target:

RESTORES SLC2A1 Loss-of-Function Variant — Vector-delivered SLC2A1 restores GLUT1 protein content in the deficient brain.

Show evidence (1 reference)

PMID:32913944 SUPPORT Other

"Ongoing research has identified future interventions to restore Glut1 protein content and function."

Consensus statement records protein-restoring interventions as the direction of therapeutic research.

RESTORES Arrested Cerebral Angiogenesis and Microvascular Diminution — Early GLUT1 repletion restores the cerebral microvasculature in model mice.

Show evidence (1 reference)

PMID:28106060 SUPPORT Model Organism

"Glut1 repletion in early-symptomatic mutants that have experienced sustained periods of low brain glucose nevertheless restores the cerebral microvasculature and ameliorates disease."

Direct rescue of the vascular node by gene replacement in symptomatic mice.

Show evidence (1 reference)

PMID:28106060 SUPPORT Model Organism

"Timely Glut1 repletion may thus constitute an effective treatment for Glut1 DS."

The authors' conclusion from the temporal rescue series; preclinical.

🌍

Environmental Factors

Prolonged or strenuous exercise

Sustained physical exertion is the defining trigger of paroxysmal exercise-induced dyskinesia and also aggravates paroxysmal ataxia, weakness and seizures. A standardised 6-Minute Walk Test reproducibly provokes episodes in long-term follow-up, and exertion sensitivity discriminates SLC2A1-positive from SLC2A1-negative patients.

Show evidence (2 references)

PMID:24789115 SUPPORT Human Clinical

"The 6-Minute Walk Test captured gait disturbances and triggered paroxysmal exertional dyskinesia."

A standardised exertion protocol provokes the episodes.

PMID:25487684 SUPPORT Human Clinical

"The factors that frequently aggravated these events were hunger, exercise, fever, and fatigue, in that order."

Exercise ranked second among aggravating factors in the nationwide cohort.

Mechanism Target:

TRIGGERS Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure — Sustained muscular activity raises whole-body and cerebral glucose demand beyond what the haploinsufficient transporter can deliver to corticostriatal circuits.

Show evidence (1 reference)

PMID:18451999 SUPPORT Human Clinical

"we propose that the dyskinesias result from an exertion-induced energy deficit that may cause episodic dysfunction of the basal ganglia"

The proposed mechanism by which exertion acts on this node.

Fasting and hunger

Deliberately left unbound. An ECTO search for fasting, food deprivation and starvation returned no exposure term, and the XCO candidates are experimental-condition terms rather than exposure events, so no term beats a wrong one. Bind when ECTO adds a fasting exposure.

Fasting or hunger lowers substrate supply to an already glucose-limited brain. Hunger was the most frequent aggravating factor for paroxysmal events in the Japanese nationwide cohort, fasting sensitivity discriminates SLC2A1-positive patients, and pre-prandial EEG abnormalities improve after feeding.

Show evidence (2 references)

PMID:25487684 SUPPORT Human Clinical

"The factors that frequently aggravated these events were hunger, exercise, fever, and fatigue, in that order."

Hunger was the leading aggravating factor.

PMID:26193382 SUPPORT Human Clinical

"Sensitivity to fasting or exertion in combination with those 3 main symptoms were the main differences between mutated and negative patients (p < 0.001)."

Fasting sensitivity is a discriminating clinical feature of SLC2A1-positive patients.

Mechanism Target:

EXACERBATES Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure — Reduced blood glucose availability lowers an already marginal cerebral supply.

Show evidence (1 reference)

PMID:23443458 SUPPORT Human Clinical

"A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise."

Fasting as a trigger of the paroxysmal events produced by this node.

EXACERBATES Neuronal Hyperexcitability and Hypersynchrony — Pre-prandial worsening and post-prandial improvement of spike-wave discharges tie network hyperexcitability to the fuel state.

Show evidence (1 reference)

PMID:17718830 SUPPORT Human Clinical

"Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake."

Feeding reverses the electrographic abnormality.

🔬

Biochemical Markers

Hypoglycorrhachia (Decreased)

Context: Low CSF glucose relative to blood glucose (CSF:blood glucose ratio typically below 0.4) in the setting of normoglycemia is the classic diagnostic biochemical signature of GLUT1DS, reflecting impaired GLUT1-mediated glucose transport across the blood-brain barrier.

Pathograph Readouts

Readout Of Reduced GLUT1 Transporter Function at the Blood-Brain Barrier Negative Diagnostic

A low CSF:blood glucose ratio reports reduced GLUT1-mediated glucose transport across the blood-brain barrier independent of systemic glucose levels.

Show evidence (1 reference)

PMID:21649651 SUPPORT Human Clinical

"the presence of normoglycaemia with a CSF/blood glucose ratio of less than 0.4."

Directly defines the diagnostic CSF:blood glucose ratio cutoff used clinically.

Show evidence (5 references)

PMID:25487684 SUPPORT Human Clinical

"The mean CSF/blood glucose ratio was 0.36 (0.28-0.48)."

Nationwide cohort of confirmed cases reports the empirical mean and range of the diagnostic CSF:blood glucose ratio.

PMID:12029447 SUPPORT Human Clinical

"The hallmark of the disease is a low glucose concentration in the CSF (hypoglycorrhachia) in the presence of normoglycaemia (CSF/blood glucose ratio <0.4)."

Review confirms hypoglycorrhachia with CSF:blood glucose ratio below 0.4 as the diagnostic hallmark.

PMID:20129935 SUPPORT Human Clinical

"Cerebrospinal fluid glucose was below 2.5 mmol/l (range 0.9-2.4 mmol/l) in all patients and cerebrospinal fluid : blood glucose ratio was below 0.50 in all but one patient (range 0.19-0.52)."

The ratio cut-off of 0.4 is not absolute; in 57 confirmed patients the ratio ranged up to 0.52, so a ratio below 0.5 with an absolute CSF glucose below 2.5 mmol/L is the practical screen.

+ 2 more references

CSF lactate (Low-to-normal)

Context: CSF lactate is low-to-normal (mean about 1.0 mmol/L versus a normal mean of 1.63 mmol/L; at or below the 10th percentile in 81% of reported patients) and is never elevated. Because raised CSF lactate is expected in mitochondrial encephalopathies, a low CSF lactate alongside low CSF glucose points to a transport rather than an oxidative defect.

Show evidence (2 references)

PMID:15622525 SUPPORT Human Clinical

"The mean cerebrospinal fluid lactate concentration was 1.0 +/- 0.3mM, which was less than the normal mean value of 1.63mM."

Quantifies the lowered CSF lactate in 16 patients.

PMID:23999624 SUPPORT Human Clinical

"We conclude that if age-specific reference values are applied, CSF glucose and lactate levels are adequate biomarkers in the diagnostic workup of GLUT1 deficiency syndrome."

Systematic review endorses CSF lactate, with glucose, as a diagnostic biomarker when age-specific references are used.

Erythrocyte 3-O-methyl-D-glucose uptake (Decreased)

Context: Zero-trans uptake of the non-metabolisable glucose analogue 3-O-methyl-D-glucose into freshly isolated erythrocytes is reduced to about half of control Vmax with an unchanged Km. A cut-off of 74% of control uptake gives 99% sensitivity and 100% specificity against molecular confirmation, and residual uptake correlates with clinical severity, making it both a confirmatory functional test and a surrogate of the degree of haploinsufficiency.

Pathograph Readouts

Readout Of Erythrocyte GLUT1 Dysfunction Negative Diagnostic

Reduced uptake reports the transport capacity of the haploinsufficient GLUT1 population on the erythrocyte membrane.

Show evidence (1 reference)

PMID:22190371 SUPPORT Human Clinical

"These findings validate the erythrocyte glucose uptake assay as a confirmatory functional test for Glut1 DS and as a surrogate marker for GLUT1 haploinsufficiency."

Establishes the assay as a surrogate of the transporter lesion.

Show evidence (2 references)

PMID:22190371 SUPPORT Human Clinical

"The cut-off for an abnormally low uptake value was increased from 60% to 74% with a corresponding sensitivity of 99% and specificity of 100%."

Diagnostic performance of the uptake assay in 109 suspected cases.

PMID:15622525 SUPPORT In Vitro

Kinetic quantification of the roughly 50% reduction in transport capacity.

Erythrocyte surface GLUT1 (METAglut1) (Decreased)

Context: Flow-cytometric quantification of GLUT1 on the erythrocyte surface (METAglut1) is a noninvasive blood test that is 80% sensitive and more than 99% specific for Glut1DS against lumbar puncture plus SLC2A1 analysis, and in one family with two inherited variants tracked the clinical phenotype better than functional uptake assays.

Pathograph Readouts

Readout Of Erythrocyte GLUT1 Dysfunction Negative Diagnostic

Reduced surface GLUT1 reports the reduced transporter content of the erythrocyte membrane.

Show evidence (1 reference)

PMID:37076312 SUPPORT Human Clinical

"We wished to validate the diagnostic performance of METAglut1, a simple blood test that quantifies GLUT1 on the erythrocyte surface."

Defines what the test measures.

Show evidence (2 references)

PMID:37076312 SUPPORT Human Clinical

"METAglut1 was 80% sensitive and >99% specific for the diagnosis of Glut1DS."

Prospective multicentre validation (428 prospective and 67 retrospective patients).

PMID:31196579 SUPPORT Human Clinical

"Instead, GLUT-1 expression at the surface of the erythrocytes appeared to better correlate with the clinical phenotypes in this family."

Single-family report in which surface expression, not uptake, tracked phenotype; a case-level observation, not a validation study.

🔬

Diagnosis

Lumbar Puncture with Paired CSF and Blood Glucose

Fasting lumbar puncture with simultaneous blood glucose measurement to demonstrate hypoglycorrhachia and calculate the CSF:blood glucose ratio, the key diagnostic biochemical test. CSF lactate should be measured on the same sample. Age-specific reference values, not a single ratio cut-off, should be applied.

lumbar puncture with paired CSF and blood glucose NCIT:C15327

Markers: CSF glucose, CSF:blood glucose ratio, CSF lactate

Results: CSF glucose typically below 2.5 mmol/L with a CSF:blood ratio below 0.5 and low-to-normal CSF lactate in the presence of normoglycemia.

Show evidence (4 references)

PMID:20129935 SUPPORT Human Clinical

"Our study demonstrates that a lumbar puncture provides the diagnostic clue to glucose transporter-1 deficiency syndrome and can thereby dramatically reduce diagnostic delay to allow early start of the ketogenic diet."

Series of 57 patients with a mean diagnostic delay of 6.6 years shows lumbar puncture as the step that shortens it.

PMID:32913944 SUPPORT Other

"Diagnosis is confirmed by the presence of these clinical signs, hypoglycorrhachia documented by lumbar puncture, and genetic analysis showing pathogenic SLC2A1 variants."

Consensus diagnostic triad.

PMID:23999624 SUPPORT Human Clinical

"A typical CSF profile for GLUT1 deficiency syndrome, which is defined as a CSF glucose level at or below the 10th percentile, a CSF to blood glucose ratio at or below the 25th percentile, and a CSF lactate level at or below the 10th percentile, was found in only 35 of 4099 CSF samples (0.9%)..."

Specificity of the full CSF profile against a 4,099-sample database of other diagnoses.

+ 1 more reference

SLC2A1 Molecular Genetic Testing

Sequence analysis (and, if negative, gene-targeted deletion/duplication analysis such as MLPA) of SLC2A1 to identify the causative pathogenic variant. In the largest laboratory series 41% of referred requests were positive, and multi-exon deletions accounted for 6 of 49 distinct alleles, so deletion analysis is not optional.

SLC2A1 sequence and deletion/duplication analysis NCIT:C19770

Markers: SLC2A1 pathogenic variant (heterozygous; rarely biallelic)

Show evidence (2 references)

PMID:20129935 SUPPORT Human Clinical

"From 2004-2008, 132 requests for mutational analysis of the SLC2A1 gene were studied by automated Sanger sequencing and multiplex ligation-dependent probe amplification. Mutations in the SLC2A1 gene were detected in 54 patients (41%) and subsequently in three clinically affected family members."

Defines the two-tier testing method and its yield in referred patients.

PMID:25487684 SUPPORT Human Clinical

"Pathological mutations in the SLC2A1 gene were identified in 28 out of 32 cases (87.5%)."

Nationwide cohort demonstrates the diagnostic yield of SLC2A1 molecular testing in clinically suspected cases.

Erythrocyte GLUT1 Function Assay

The GLUT1 defect can be confirmed in erythrocytes by 3-O-methyl-D-glucose uptake studies and GLUT1 immunoreactivity, providing a functional confirmatory test alongside molecular genetic testing; at a 74%-of-control cut-off the uptake assay is 99% sensitive and 100% specific.

erythrocyte 3-O-methyl-D-glucose uptake assay NCIT:C18020

Markers: Erythrocyte 3-O-methyl-D-glucose uptake (% of control)

Show evidence (2 references)

PMID:22190371 SUPPORT Human Clinical

"The cut-off for an abnormally low uptake value was increased from 60% to 74% with a corresponding sensitivity of 99% and specificity of 100%."

Validation of the uptake assay's diagnostic performance in 109 suspected cases.

PMID:12029447 SUPPORT Human Clinical

"The GLUT1 defect can be confirmed in erythrocytes by glucose uptake studies and GLUT1 immunoreactivity, and by molecular analysis of the GLUT1 gene."

Review documents erythrocyte glucose uptake and GLUT1 immunoreactivity as confirmatory functional diagnostic assays.

METAglut1 Erythrocyte Surface GLUT1 Blood Test

METAglut1 is a simple, noninvasive flow-cytometry blood test that quantifies GLUT1 protein on the surface of circulating erythrocytes, prospectively validated as a diagnostic test for GLUT1 deficiency syndrome and an alternative or complement to lumbar puncture. It can detect patients with SLC2A1 mosaicism and variants of unknown significance.

METAglut1 erythrocyte surface GLUT1 flow cytometry NCIT:C18020

Markers: Erythrocyte surface GLUT1 (flow cytometry)

Show evidence (2 references)

PMID:37076312 SUPPORT Human Clinical

"METAglut1 was 80% sensitive and >99% specific for the diagnosis of Glut1DS."

Prospective multicenter validation reports the diagnostic sensitivity and specificity of the METAglut1 erythrocyte-surface GLUT1 blood test.

PMID:37076312 SUPPORT Human Clinical

"METAglut1 succeeded to identify patients with Glut1DS with SCL2A1 mosaicism and variants of unknown significance."

The blood test detects diagnostically challenging cases including SLC2A1 mosaicism and variants of unknown significance.

Electroencephalography

Routine and 24-hour EEG characterise seizure types and interictal discharges, but a normal interictal EEG is the most common finding at all ages, so EEG cannot exclude the diagnosis. A pre-prandial recording that improves after feeding is a supportive clue.

electroencephalography NCIT:C38054

Results: Normal interictal EEG most often; focal slowing or discharges in infants; generalized 2.5-4 Hz spike-wave from about 2 years, improving with food.

Show evidence (1 reference)

PMID:12752470 SUPPORT Human Clinical

"In all ages, a normal interictal EEG was the most common EEG finding."

32 continuous 24-hour EEG sessions and 42 routine EEGs establish the low sensitivity of EEG.

🩻

Imaging Findings

Normal or nonspecific brain MRI

Structural neuroimaging is uninformative in Glut1DS. MRI is used to exclude structural lesions and other neurometabolic encephalopathies rather than to establish the diagnosis.

Mri

Show evidence (1 reference)

PMID:17718830 SUPPORT Human Clinical

"Neuroimaging is uninformative. Most patients carry heterozygous de novo mutations in the GLUT1 gene"

Review of 84 published cases states that neuroimaging does not contribute to diagnosis.

📈

Progression

Infancy, epilepsy-dominant phase

Age: First months of life to early childhood

Seizures with a mean onset around 5 months, paroxysmal eye-head movements, developmental delay and deceleration of head growth dominate; 65% of classical patients present before 2 years. Seizures improve through childhood, particularly on ketogenic diet therapy.

Show evidence (2 references)

PMID:24789115 SUPPORT Human Clinical

"Epilepsy dominated infancy and improved during childhood."

Longitudinal cohort defines the infantile epilepsy-dominant phase.

PMID:20129935 SUPPORT Human Clinical

"the classical phenotype (84%), subdivided into early-onset (<2 years) (65%) and late-onset (18%)"

Quantifies early versus late onset within the classical phenotype.

Childhood to adulthood, movement-disorder-dominant phase

Age: Later childhood, adolescence and adult life

Dystonia and paroxysmal exertion-induced dyskinesia emerge and become the dominant manifestations, with ataxia, spasticity, speech difficulty and intellectual disability persisting. Longitudinal neurological and neuropsychological measures remain stable rather than deteriorating, so the condition is chronic but not degenerative, and some individuals shift from a classic childhood phenotype to a movement-disorder-predominant adult one.

Show evidence (3 references)

PMID:24789115 SUPPORT Human Clinical

"We conclude that Glut1 deficiency syndrome is a chronic condition, dominated by epilepsy in infancy and by movement disorders thereafter."

Defines the biphasic natural history.

PMID:24789115 SUPPORT Human Clinical

"All longitudinal outcomes remained stable over time."

Stability across a mean of 14.2 years of follow-up.

PMID:26193382 SUPPORT Human Clinical

"Three patients evolved from a classic phenotype during early childhood to a movement disorder predominant phenotype at a late childhood/adulthood."

Documents the phenotype shift occurring within individuals.

📊

Prevalence

Danish population (SLC2A1 mutation carriers)

Point Prevalence 1.2 per 100,000 1–9 per 100,000

Estimated frequency of SLC2A1 mutations in the Danish population of approximately 1:83,000 (100000/83000 = 1.2 per 100,000), derived from mutation screening of absence-epilepsy and other cohorts; the authors call it an estimate of the frequency of GLUT1 deficiency syndrome and it is likely an underestimate given underdiagnosis.

Show evidence (1 reference)

PMID:26537434 SUPPORT Human Clinical

"We estimated the frequency of SLC2A1 mutations in the Danish population to be approximately 1:83,000."

Population-level frequency estimate.

Scotland, children presenting with seizures before age 3 (live births)

Birth Prevalence 4.13 per 100,000 (1.07–7.19) 1–9 per 100,000 (births)

Minimum incidence of SLC2A1-related epilepsy of 1 per 24,300 live births (4.13 per 100,000; 95% CI 1.07-7.19) in a prospective national cohort of childhood-onset epilepsy; captures only the epilepsy-presenting fraction of Glut1DS diagnosed by age 3, so it is a floor for the birth prevalence of the syndrome as a whole.

Show evidence (1 reference)

PMID:31302675 SUPPORT Human Clinical

"KCNQ2: 1 per 17 000 (5.89/100 000; 95% confidence interval 2.24-9.56) and SLC2A1: 1 per 24 300 (4.13/100 000; 95% confidence interval 1.07-7.19)."

Prospective population-based incidence of SLC2A1-related childhood epilepsy.

Japan (nationwide survey of board-certified pediatric neurologists)

Cases In Literature Rare

National case-ascertainment count (57 reported patients, 33 with detailed data), informative for rarity but not a normalised rate; likely an underestimate due to underdiagnosis.

Show evidence (1 reference)

PMID:25487684 SUPPORT Human Clinical

"A questionnaire to survey the number of genetically and clinically confirmed cases of GLUT-1DS was sent to 1018 board-certified pediatric neurologists, which resulted in 57 patients being reported."

Nationwide Japanese survey ascertained 57 genetically/clinically confirmed cases nationally, informative for rarity but not directly convertible to a per-100,000 rate without further population denominators.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from GLUT1 Deficiency Syndrome:

Mitochondrial encephalopathies and other causes of low CSF glucose

Overlapping Features Low CSF glucose is more often seen acutely in CNS infection or malignancy than in a chronic neurological disorder, and in that chronic setting it is the diagnostic marker of Glut1DS. Mitochondrial encephalopathies can share seizures, movement disorder and developmental delay but characteristically raise CSF lactate, whereas in Glut1DS lactate is low-to-normal and blood glucose is normal.

Distinguishing Features

Low CSF glucose with normal blood glucose and low-to-normal CSF lactate favours Glut1DS.
Raised CSF lactate favours a mitochondrial encephalopathy.
Acute presentation with pleocytosis or malignant cells points to infectious or neoplastic causes of low CSF glucose.

Show evidence (2 references)

PMID:24323444 SUPPORT Human Clinical

"We present a practical overview on the differential diagnosis of a low CSF glucose and stress the importance of recognizing a low CSF glucose as the diagnostic marker for GLUT1 deficiency syndrome, a treatable neurometabolic disorder."

Frames low CSF glucose in chronic neurological disease as the Glut1DS marker to be separated from its other causes.

PMID:17718830 SUPPORT Human Clinical

"in the setting of normoglycaemia. CSF lactate is normal."

Normal (never raised) CSF lactate is the discriminating feature from mitochondrial disease.

Childhood absence epilepsy and other early-onset absence epilepsies

Overlapping Features Early-onset absence epilepsy without other features can be the sole presentation of an SLC2A1 variant; a Danish screen found SLC2A1 variants in 10% of absence-epilepsy patients, so Glut1DS should be excluded in absence epilepsy beginning before age four, especially with fasting or exertion sensitivity, developmental concerns or a movement disorder.

Distinguishing Features

Onset of absences before age 4, drug resistance, developmental concerns, movement disorder or fasting/exertion sensitivity favour SLC2A1 testing.
Hypoglycorrhachia on lumbar puncture separates Glut1DS from idiopathic absence epilepsy.

Show evidence (1 reference)

PMID:26537434 SUPPORT Human Clinical

"Mutations in SLC2A1 were detected in 5 (10%) of 50 patients with absence epilepsy, and in one (2.7%) of 37 patient with unselected epilepsies, ID, and/or various movement disorders."

Quantifies the overlap between absence epilepsy and Glut1DS.

Epilepsy with myoclonic-atonic seizures (Doose syndrome)

Overlapping Features Myoclonic-astatic epilepsy shares early-onset generalized seizures with Glut1DS, but a screen of 120 patients with myoclonic astatic epilepsy without associated movement disorder found no SLC2A1 variants.

Distinguishing Features

Absence of a movement disorder and normal CSF glucose argue against Glut1DS in myoclonic-atonic epilepsy.

Show evidence (1 reference)

PMID:26537434 SUPPORT Human Clinical

"None of the 120 MAE patients harbored SLC2A1 mutations."

Negative screen separates typical MAE from Glut1DS.

🔬

Clinical Trials

NCT02014883 PHASE_II COMPLETED

Open-label phase II study of triheptanoin oil in eight patients with Glut1DS aged 7 to 47 years who declined or did not tolerate ketogenic diets, with baseline, treatment and withdrawal phases of two months each. It reported a 90% reduction in non-epileptic paroxysmal manifestations and a normalised brain bioenergetic profile on 31P-NMR. Completion is taken from the published results paper rather than from the registry summary.

Target Phenotypes: Paroxysmal dyskinesia HP:0007166

Show evidence (2 references)

clinicaltrials:NCT02014883 SUPPORT Human Clinical

"The purpose of this project is to study the efficacy of triheptanoin oil in patients with GLUT1 deficiency syndrome."

Registry statement of the trial's objective.

PMID:26536893 SUPPORT Human Clinical

"We performed an open-label pilot study with three phases of 2 months each (baseline, treatment and withdrawal) in eight patients with GLUT1-DS (7-47 years old) with non-epileptic paroxysmal manifestations."

The results paper, which registers this NCT number, describes the trial design and population summarised here.

🐁

Animal Models

Glut1 haploinsufficient (GLUT-1+/-) mouse Genetically engineered

The first mouse model of Glut1DS: heterozygous disruption of the Glut1 promoter and exon 1 reduces brain Glut1 to 66% of wild type and produces epileptiform EEG discharges, impaired motor activity and incoordination, hypoglycorrhachia, microencephaly and reduced brain glucose uptake on PET, mimicking the classical human presentation.

Species

Mouse

Genotype

Slc2a1 heterozygous null, targeted disruption of the promoter and exon 1

Genes

SLC2A1 hgnc:11005

Publication

PMID:16497725

Pathograph links

SLC2A1 Loss-of-Function Variant recapitulates fidelity: high observes: molecular The heterozygous null allele reproduces the haploinsufficient state, with brain Glut1 reduced to 66%.

Readouts

Brain Glut1 protein by western blot

Direction: DECREASED

Interpretation: 66% of wild-type brain Glut1 quantifies the haploinsufficiency the model carries.

Show evidence (1 reference)

PMID:16497725 SUPPORT Model Organism

"decreased brain Glut-1 expression by western blot (66%)"

Reports the measurement.

Show evidence (1 reference)

PMID:16497725 SUPPORT Model Organism

"We generated a heterozygous haploinsufficient mouse model by targeted disruption of the promoter and exon 1 regions of the mouse GLUT-1 gene."

Defines the allele as a haploinsufficiency model.

Reduced GLUT1 Transporter Function at the Blood-Brain Barrier recapitulates fidelity: high observes: tissue Reduced brain glucose uptake and hypoglycorrhachia reproduce the barrier transport failure.

Readouts

Brain glucose uptake by FDG-PET

Direction: DECREASED

Interpretation: Whole-brain PET uptake reports transendothelial glucose delivery in vivo.

CSF glucose concentration

Direction: DECREASED

Interpretation: Hypoglycorrhachia in the mouse mirrors the human diagnostic finding.

Show evidence (1 reference)

PMID:16497725 SUPPORT Model Organism

"hypoglycorrhachia, microencephaly, decreased brain glucose uptake as measured by positron emission tomography (PET) scan"

Reports both readouts.

Neuronal Hyperexcitability and Hypersynchrony recapitulates fidelity: moderate observes: tissue Spontaneous epileptiform EEG discharges reproduce the hyperexcitable network state.

Limitations: Discharges are reported, not the human electroclinical syndrome; whether the mouse shows absence-like 2.5-4 Hz spike-wave or a food-responsive EEG is not stated in the abstract.

Readouts

Epileptiform EEG discharges

Direction: INCREASED

Interpretation: Electrographic evidence of cortical hypersynchrony in the mutant.

Show evidence (1 reference)

PMID:16497725 SUPPORT Model Organism

"GLUT-1+/- mice have epileptiform discharges on electroencephalography (EEG)"

Reports the EEG finding.

Impaired Neurodevelopment and Movement Disorder partially recapitulates fidelity: moderate observes: organism Microencephaly, impaired motor activity and incoordination reproduce the growth and motor consequences.

Limitations: Mouse motor impairment does not reproduce human dystonia, spasticity or paroxysmal exertion-induced dyskinesia, and rodent learning measures differ in kind from human intellectual disability; see the HUMAN_MODEL_MISMATCH discussion on paroxysmal phenotype fidelity.

Readouts

Brain size, microencephaly

Direction: DECREASED

Interpretation: Reduced brain growth parallels human acquired microcephaly.

Motor activity and coordination

Direction: DECREASED

Interpretation: Impaired motor activity and incoordination parallel the human motor disorder.

Show evidence (1 reference)

PMID:16497725 SUPPORT Model Organism

"The GLUT-1+/- murine phenotype mimics the classical human presentation of Glut-1 DS."

The authors' fidelity claim, made for the classical rather than the paroxysmal phenotype.

Show evidence (1 reference)

PMID:16497725 SUPPORT Model Organism

"This GLUT-1+/- mouse model creates an opportunity to investigate Glut-1 function, to examine the pathophysiology of Glut-1 DS in vivo and to evaluate new treatment strategies."

The authors state the model's intended use for studying Glut1DS pathophysiology and testing treatments.

Glut1 Rgsc200 ENU missense mouse Chemically induced by ENU mutagenesis

An ENU-induced missense allele at residue 324 of Glut1. Heterozygotes show decreased CSF glucose, contextual learning deficits, reduced body size, seizure-like behaviour, spontaneous EEG abnormalities and a longer wake and shorter NREM sleep pattern; FDG-PET kinetics show reduced glucose transport with enhanced hexokinase activity. Homozygotes die in utero, paralleling the presumed lethality of complete GLUT1 loss in humans.

Species

Mouse

Genotype

Slc2a1 Rgsc200 heterozygous missense at residue 324; homozygotes embryonic lethal

Genes

SLC2A1 hgnc:11005

Publication

PMID:31399478

Pathograph links

Cerebral Glucose Energy Deficit recapitulates fidelity: moderate observes: tissue Reduced brain glucose transport with compensatory hexokinase upregulation reproduces the supply-limited energy state.

Limitations: A missense allele of unknown residual transport, so the depth of the deficit is not calibrated against the human haploinsufficient range, and the enhanced hexokinase activity is a mouse observation not yet shown in patients.

Readouts

Brain glucose transport by FDG-PET kinetics

Direction: DECREASED

Interpretation: The reduced transport constant reports the supply limitation.

Cerebrospinal fluid glucose

Direction: DECREASED

Interpretation: Hypoglycorrhachia in the mutant.

Show evidence (1 reference)

PMID:31399478 SUPPORT Model Organism

"revealed that glucose transportation was reduced, whereas hexokinase activity and glucose metabolism were enhanced"

Reports the PET kinetic result.

Neuronal Hyperexcitability and Hypersynchrony partially recapitulates fidelity: low observes: organism Spontaneous EEG abnormalities and seizure-like behaviour both occur, but were not observed concurrently.

Limitations: EEG abnormality and seizure-like behaviour were dissociated in time, so electroclinical seizures were not demonstrated in this model.

Readouts

Spontaneous EEG abnormality

Direction: INCREASED

Interpretation: Electrographic hyperexcitability without confirmed concurrent behavioural seizures.

Show evidence (1 reference)

PMID:31399478 SUPPORT Model Organism

"During EEG recording, the abnormality occurred spontaneously, whereas the seizure-like phenotypes were not observed at the same time."

Reports the dissociation that limits fidelity.

Show evidence (1 reference)

PMID:31399478 SUPPORT Model Organism

"These results indicate that a Glut1Rgsc200 mutant is a useful tool for elucidating the molecular mechanisms of GLUT1DS."

The authors' conclusion that this ENU allele is an informative model of GLUT1DS.

Glut1-deficient mouse with AAV9-mediated Glut1 repletion Genetically engineered with gene-replacement rescue

Glut1-deficient model mice used to show that low Glut1 arrests cerebral angiogenesis and diminishes the brain microvasculature without breaching the blood-brain barrier, and that pre-symptomatic or early-symptomatic AAV9-mediated Glut1 repletion restores the microvasculature and prevents or ameliorates disease, whereas adult repletion does not.

Species

Mouse

Genotype

Slc2a1-deficient model mice, with or without AAV9-mediated Glut1 repletion at defined ages

Genes

SLC2A1 hgnc:11005

Publication

PMID:28106060

Pathograph links

Arrested Cerebral Angiogenesis and Microvascular Diminution recapitulates fidelity: unknown observes: tissue The vascular phenotype is defined in this model; the human counterpart has not been measured.

Limitations: Fidelity cannot be graded because no human cerebral microvascular data exist for comparison, which is itself the subject of an open HUMAN_MODEL_MISMATCH question.

Readouts

Cerebral microvascular density

Direction: DECREASED

Interpretation: Profound diminution of the brain microvasculature in mutants.

Show evidence (1 reference)

PMID:28106060 SUPPORT Model Organism

"low Glut1 protein arrests cerebral angiogenesis, resulting in a profound diminution of the brain microvasculature without compromising the blood-brain barrier"

Defines the vascular phenotype.

Arrested Cerebral Angiogenesis and Microvascular Diminution rescues fidelity: unknown observes: tissue Early AAV9-Glut1 repletion restores the microvasculature; adult repletion does not.

Readouts

Cerebral microvascular density after AAV9-Glut1 repletion

Direction: RESTORED

Interpretation: Restoration is age-dependent, defining a treatment window.

Show evidence (1 reference)

PMID:28106060 SUPPORT Model Organism

"pre-symptomatic, AAV9-mediated repletion of the protein averts brain microvasculature defects and prevents disease, whereas augmenting the protein late, during adulthood, is devoid of benefit"

Reports the rescue and its temporal window.

Show evidence (1 reference)

PMID:28106060 SUPPORT Model Organism

"Timely Glut1 repletion may thus constitute an effective treatment for Glut1 DS."

The authors' translational conclusion from this rescue model, which is why the model is recorded here.

{ }

Source YAML

click to show

name: GLUT1 Deficiency Syndrome
creation_date: "2026-07-06T00:00:00Z"
category: Mendelian
description: >-
  Glucose transporter type 1 (GLUT1) deficiency syndrome (Glut1DS) is a disorder
  of brain energy metabolism caused by heterozygous (rarely biallelic) pathogenic
  variants in SLC2A1, which encodes the GLUT1 facilitative glucose transporter
  responsible for transporting glucose across the endothelial cells of the
  blood-brain barrier and into erythrocytes. Reduced GLUT1 function starves the
  brain of its principal metabolic fuel, producing a cerebral energy deficit that
  manifests as an infantile-onset, often pharmacoresistant epileptic
  encephalopathy with acquired microcephaly, developmental delay, and a complex
  movement disorder (ataxia, dystonia, spasticity) in the classic severe form.
  Milder and later-onset presentations exist across a phenotypic spectrum,
  including paroxysmal exertion-induced dyskinesia (GLUT1 deficiency syndrome 2 /
  DYT18) and episodic choreoathetosis with spasticity (dystonia 9 / DYT9). The
  diagnostic hallmark is hypoglycorrhachia (low CSF glucose) with a low CSF:blood
  glucose ratio in the setting of normoglycemia. The ketogenic diet, which
  supplies ketone bodies as an alternative cerebral fuel bypassing the GLUT1
  transport defect, is first-line disease-specific therapy.
synonyms:
- Glut1DS
- GLUT1DS
- GLUT1 DS
- De Vivo Disease
- Glucose Transporter Type 1 Deficiency Syndrome
- SLC2A1-related GLUT1 deficiency syndrome
- Encephalopathy due to GLUT1 Deficiency
disease_term:
  preferred_term: GLUT1 deficiency syndrome
  term:
    id: MONDO:0000188
    label: GLUT1 deficiency syndrome
references:
- reference: PMID:20301603
  title: "Glucose Transporter Type 1 Deficiency Syndrome."
  tags:
  - GeneReviews
  findings: []
- reference: PMID:9462754
  title: "GLUT-1 deficiency syndrome caused by haploinsufficiency of the blood-brain barrier hexose carrier."
- reference: PMID:11136715
  title: "Autosomal dominant transmission of GLUT1 deficiency."
- reference: PMID:20687207
  title: "Glut1 deficiency: inheritance pattern determined by haploinsufficiency."
- reference: PMID:18451999
  title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
- reference: PMID:18577546
  title: "Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1."
- reference: PMID:20129935
  title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
- reference: PMID:17718830
  title: "GLUT1 deficiency syndrome--2007 update."
- reference: PMID:32913944
  title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
- reference: PMID:15622525
  title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
- reference: PMID:12752470
  title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
- reference: PMID:24789115
  title: "Long-term clinical course of Glut1 deficiency syndrome."
- reference: PMID:22190371
  title: "Glut1 deficiency syndrome and erythrocyte glucose uptake assay."
- reference: PMID:23443458
  title: "Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)."
- reference: PMID:23999624
  title: "Cerebrospinal fluid analysis in the workup of GLUT1 deficiency syndrome: a systematic review."
- reference: PMID:24323444
  title: "Child neurology: differential diagnosis of a low CSF glucose in children and young adults."
- reference: PMID:26803281
  title: "Use of dietary therapies amongst patients with GLUT1 deficiency syndrome."
- reference: PMID:26193382
  title: "From splitting GLUT1 deficiency syndromes to overlapping phenotypes."
- reference: PMID:26537434
  title: "The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy, and the estimated frequency of GLUT1 deficiency syndrome."
- reference: PMID:31302675
  title: "Incidence and phenotypes of childhood-onset genetic epilepsies: a prospective population-based national cohort."
- reference: PMID:31399478
  title: "A new mouse model of GLUT1 deficiency syndrome exhibits abnormal sleep-wake patterns and alterations of glucose kinetics in the brain."
- reference: PMID:40405536
  title: "Glut1 Deficiency Syndrome: Novel Pathomechanisms, Current Concepts, and Challenges."
- reference: PMID:16497725
  title: "A mouse model for Glut-1 haploinsufficiency."
- reference: PMID:28106060
  title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
- reference: PMID:31196579
  title: "Usefulness of diagnostic tools in a GLUT1 deficiency syndrome patient with 2 inherited mutations."
- reference: PMID:25487684
  title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
- reference: PMID:12029447
  title: "Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain-- a review."
- reference: PMID:21649651
  title: "Milder phenotypes of glucose transporter type 1 deficiency syndrome."
- reference: PMID:36303089
  title: "Ketogenic diet therapy in children with epilepsy caused by SLC2A1 mutations: a single-center single-arm retrospective study."
- reference: PMID:35441706
  title: "A randomized, double-blind trial of triheptanoin for drug-resistant epilepsy in glucose transporter 1 deficiency syndrome."
- reference: PMID:37076312
  title: "Prospective Multicenter Validation of a Simple Blood Test for the Diagnosis of Glut1 Deficiency Syndrome."
- reference: PMID:26536893
  title: "Triheptanoin dramatically reduces paroxysmal motor disorder in patients with GLUT1 deficiency."
- reference: clinicaltrials:NCT02014883
  title: "Phase II Open Label Study Using Triheptanoin in Patients With Glucose Type 1 Transporter Deficiency GLUT1-DS"
parents:
- Inborn Error of Metabolism
- Inborn Carbohydrate Metabolic Disorder
- Metabolic Epilepsy
- Epilepsy
- Movement Disorder
has_subtypes:
- name: Classic GLUT1 Deficiency Syndrome
  display_name: Classic (Severe, Infantile-Onset) GLUT1 Deficiency Syndrome
  subtype_term:
    preferred_term: encephalopathy due to GLUT1 deficiency
    term:
      id: MONDO:0011724
      label: encephalopathy due to GLUT1 deficiency
  description: >-
    The most common and severe presentation, with onset in infancy to early
    childhood. Predominant clinical findings are paroxysmal eye-head movements,
    pharmacoresistant seizures of varying types, deceleration of head growth,
    and developmental delay, followed by complex movement disorders and
    intellectual disability ranging from mild to severe.
  genes:
  - preferred_term: SLC2A1
    term:
      id: hgnc:11005
      label: SLC2A1
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "When first diagnosed in infancy to early childhood, the predominant clinical findings of Glut1DS are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay."
    explanation: GeneReviews describes the classic infantile-onset presentation as the most common and severe form of Glut1DS.
- name: GLUT1 DS with Paroxysmal Exertion-Induced Dyskinesia
  display_name: GLUT1 Deficiency Syndrome 2 (DYT18 / Paroxysmal Exercise-Induced Dyskinesia,
    including DYT9 / episodic choreoathetosis with spasticity)
  subtype_term:
    preferred_term: childhood onset GLUT1 deficiency syndrome 2
    term:
      id: MONDO:0012805
      label: childhood onset GLUT1 deficiency syndrome 2
  description: >-
    A milder, later-onset (childhood) form dominated by paroxysmal dystonic
    attacks of the extremities triggered by prolonged physical exertion, with or
    without epilepsy or hemolytic anemia. Corresponds to OMIM PS612126 / MONDO
    childhood-onset GLUT1 deficiency syndrome 2 (DYT18). This subtype also
    covers the presentation formerly designated dystonia 9 (DYT9, OMIM 601042,
    MONDO:0010983, episodic choreoathetosis with spasticity), in which the same
    exertion-induced dyskinesia is accompanied by slowly progressive spastic
    paraparesis: the German/Dutch DYT9 pedigree was shown to carry a causative
    SLC2A1 mutation, making DYT9 and DYT18 allelic rather than distinct
    entities.
  genes:
  - preferred_term: SLC2A1
    term:
      id: hgnc:11005
      label: SLC2A1
  evidence:
  - reference: PMID:21649651
    reference_title: "Milder phenotypes of glucose transporter type 1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This paper also shows phenotypical parallels between GLUT1DS and paroxysmal exertion-induced dyskinesia."
    explanation: Directly documents the milder paroxysmal exertion-induced dyskinesia phenotype as part of the GLUT1DS spectrum.
  - reference: PMID:18577546
    reference_title: "Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "co-occurring PED and epilepsy can be due to autosomal dominant heterozygous SLC2A1 mutations, expanding the phenotypic spectrum associated with GLUT1 deficiency"
    explanation: Five-generation family plus three nuclear families establish PED with epilepsy as an SLC2A1 phenotype.
  - reference: PMID:18451999
    reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Their PED was accompanied by epilepsy, mild developmental delay, reduced CSF glucose levels, hemolytic anemia with echinocytosis, and altered erythrocyte ion concentrations."
    explanation: Three-generation PED family documents the hemolytic-anemia variant of the GLUT1DS2 presentation.
  - reference: PMID:21832227
    reference_title: "Paroxysmal choreoathetosis/spasticity (DYT9) is caused by a GLUT1 defect."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study shows that DYT9 and DYT18 are allelic disorders and enlarges the spectrum of GLUT1 phenotypes, now also including slowly progressive spastic paraparesis combined with PED."
    explanation: Establishes that the formerly separate DYT9 designation names the same SLC2A1 entity as DYT18, which is why the two are curated as one subtype rather than as siblings.
inheritance:
- name: Autosomal Dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    Glut1DS is most commonly caused by a heterozygous SLC2A1 pathogenic variant
    inherited in an autosomal dominant manner. About 90% of individuals have the
    disorder as the result of a de novo SLC2A1 pathogenic variant; about 10%
    have a variant inherited from a parent, whose degree of impairment may be
    mild or nonexistent (possible parental somatic mosaicism). Rare biallelic
    (autosomal recessive) inheritance has also been reported.
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Glut1DS is most commonly caused by a heterozygous SLC2A1 pathogenic variant and inherited in an autosomal dominant manner. About 90% of individuals with Glut1DS have the disorder as the result of a de novo SLC2A1 pathogenic variant; about 10% of individuals have the disorder as the result of a pathogenic variant inherited from a parent."
    explanation: GeneReviews genetic counseling section directly documents autosomal dominant inheritance, predominantly de novo, with a minority of inherited cases.
  - reference: PMID:11136715
    reference_title: "Autosomal dominant transmission of GLUT1 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the first report of autosomal dominant transmission of GLUT1 deficiency, confirming that this condition is the result of haploinsufficiency."
    explanation: Father-to-child transmission in two separate marriages established dominant inheritance and the haploinsufficiency mechanism.
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The degree of impairment in the transmitting parent may be mild or nonexistent; parental somatic mosaicism for the SLC2A1 pathogenic variant may explain this observation."
    explanation: Supports incomplete penetrance / variable expressivity in transmitting parents.
  de_novo_rate: "About 90% de novo; about 10% inherited from a parent (GeneReviews)"
  penetrance: INCOMPLETE
  expressivity: VARIABLE
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Rarely, biallelic SLC2A1 variants (compound heterozygous or homozygous)
    inherited from asymptomatic heterozygous parents produce Glut1DS as an
    autosomal recessive trait. The clinical inheritance pattern is determined by
    the relative pathogenicity of each allele and the resulting degree of GLUT1
    haploinsufficiency, measured as residual erythrocyte glucose uptake.
  evidence:
  - reference: PMID:20687207
    reference_title: "Glut1 deficiency: inheritance pattern determined by haploinsufficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These cases demonstrate that Glut1 DS may present as an autosomal recessive trait. The clinical pattern of inheritance is determined by the relative pathogenicity of the mutation and the resulting degree of haploinsufficiency."
    explanation: Two families with biallelic SLC2A1 variants and asymptomatic heterozygous parents define the recessive presentation.
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Autosomal recessive inheritance has been reported in two families to date."
    explanation: GeneReviews confirms recessive inheritance is rare (two families).
pathophysiology:
- name: SLC2A1 Loss-of-Function Variant
  description: >-
    Heterozygous (rarely biallelic) pathogenic variants in SLC2A1 reduce the
    amount or function of the GLUT1 facilitative glucose transporter protein,
    typically through haploinsufficiency.
  gene:
    preferred_term: SLC2A1
    term:
      id: hgnc:11005
      label: SLC2A1
  role: trigger
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  molecular_functions:
  - preferred_term: D-glucose transmembrane transporter activity
    term:
      id: GO:0055056
      label: D-glucose transmembrane transporter activity
    modifier: DECREASED
  notes: >-
    Variant classes span the whole loss-of-function spectrum. The founding
    molecular report identified hemizygosity (whole-gene deletion) and nonsense
    truncations; large series add missense, frameshift, splice-site,
    translation-initiation and multi-exon deletion alleles. Missense alleles can
    leave immunoreactive protein at the membrane while abolishing transport
    (Gly91Asp), and pore-region alleles (Q282_S285del) additionally create an
    erythrocyte cation leak. The degree of residual transport, not the variant
    class per se, sets clinical severity and even the apparent inheritance
    pattern.
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of Glut1DS is established in a proband with suggestive clinical findings, hypoglycorrhachia documented by lumbar puncture, and a (usually) heterozygous pathogenic variant in SLC2A1 identified by molecular genetic testing."
    explanation: GeneReviews establishes heterozygous SLC2A1 pathogenic variants as the molecular cause of Glut1DS.
  - reference: PMID:12029447
    reference_title: "Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain-- a review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Several heterozygous mutations resulting in GLUT1 haploinsufficiency have been identified."
    explanation: Review paper documents the haploinsufficiency mechanism underlying heterozygous SLC2A1 mutations.
  - reference: PMID:9462754
    reference_title: "GLUT-1 deficiency syndrome caused by haploinsufficiency of the blood-brain barrier hexose carrier."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We now report two distinct classes of mutations as the molecular basis for the functional defect of glucose transport: hemizygosity of GLUT1 and nonsense mutations resulting in truncation of the GLUT-1 protein."
    explanation: The founding molecular study identifies whole-gene hemizygosity and truncating nonsense alleles as the first two classes of causal SLC2A1 lesion.
  - reference: PMID:11136715
    reference_title: "Autosomal dominant transmission of GLUT1 deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "GLUT1 immunoreactivity was normal, but 3-O-methyl-D-glucose uptake into erythrocytes was significantly reduced, suggesting a quantitatively normal, but functionally impaired, GLUT1 protein at the cell membrane."
    explanation: A missense allele (Gly91Asp) shows that loss of transport function, not only loss of protein, produces the haploinsufficient state.
  - reference: PMID:18451999
    reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies in Xenopus oocytes and human erythrocytes revealed that this mutation decreased glucose transport and caused a cation leak that alters intracellular concentrations of sodium, potassium, and calcium."
    explanation: Heterologous expression confirms that PED-associated SLC2A1 alleles are loss-of-function for glucose transport, with an additional cation-leak gain in the pore-region deletion.
  - reference: PMID:20687207
    reference_title: "Glut1 deficiency: inheritance pattern determined by haploinsufficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Red blood cell glucose uptake residual activity, a surrogate of haploinsufficiency, correlated with the clinical severity."
    explanation: The degree of residual transporter activity, rather than the variant class, scales the clinical phenotype.
  downstream:
  - target: Reduced GLUT1 Transporter Function at the Blood-Brain Barrier
    causal_link_type: DIRECT
    description: >-
      Loss-of-function SLC2A1 variants reduce the density or activity of GLUT1
      transporters expressed on brain microvascular endothelial cells.
    hypothesis_groups:
    - canonical_glut1_energy_deficit
    evidence:
    - reference: PMID:12029447
      reference_title: "Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain-- a review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "It is caused by a defect in glucose transport into brain, mediated by the facilitative glucose transporter GLUT1."
      explanation: Directly links the SLC2A1/GLUT1 defect to impaired glucose transport into the brain.
    - reference: PMID:9462754
      reference_title: "GLUT-1 deficiency syndrome caused by haploinsufficiency of the blood-brain barrier hexose carrier."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "GLUT-1, whose sequence was originally deduced from cDNAs cloned from human hepatoma and rat brain, is present at high levels in primate erythrocytes and brain endothelial cells."
      explanation: Places the mutated carrier at the brain endothelium, the site where the transport lesion acts.
  - target: Erythrocyte GLUT1 Dysfunction
    causal_link_type: DIRECT
    description: >-
      The same haploinsufficient transporter is expressed on erythrocytes, so
      red-cell hexose uptake falls in parallel with brain transport and serves
      as the accessible functional surrogate of the lesion.
    evidence:
    - reference: PMID:22190371
      reference_title: "Glut1 deficiency syndrome and erythrocyte glucose uptake assay."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "These findings validate the erythrocyte glucose uptake assay as a confirmatory functional test for Glut1 DS and as a surrogate marker for GLUT1 haploinsufficiency."
      explanation: Establishes reduced erythrocyte uptake as a direct read-out of the same haploinsufficient transporter.
- name: Reduced GLUT1 Transporter Function at the Blood-Brain Barrier
  description: >-
    GLUT1 is the transporter responsible for facilitated glucose diffusion
    across the endothelial cells that form the blood-brain barrier, as well as
    glucose uptake into erythrocytes. Reduced GLUT1 activity impairs the rate at
    which glucose can be delivered from blood to brain, independent of blood
    glucose concentration.
  role: mediator
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  locations:
  - preferred_term: blood-brain barrier
    term:
      id: UBERON:0000120
      label: blood brain barrier
  cell_types:
  - preferred_term: Brain Microvascular Endothelial Cell
    term:
      id: CL:2000044
      label: brain microvascular endothelial cell
  molecular_functions:
  - preferred_term: D-glucose transmembrane transporter activity
    term:
      id: GO:0055056
      label: D-glucose transmembrane transporter activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: D-glucose transmembrane transport
    term:
      id: GO:1904659
      label: D-glucose transmembrane transport
    modifier: DECREASED
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Glucose, the essential metabolic fuel for the brain, is transported into the brain exclusively by the protein glucose transporter type 1 (Glut1) across the endothelial cells forming the blood-brain barrier (BBB). Glut1DS results from the inability of Glut1 to transfer sufficient glucose across the BBB to meet the glucose demands of the brain."
    explanation: GeneReviews defines the core defect as insufficient GLUT1-mediated glucose transfer across the blood-brain barrier.
  - reference: PMID:32913944
    reference_title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Glut1 deficiency syndrome (Glut1DS) is a brain energy failure syndrome caused by impaired glucose transport across brain tissue barriers."
    explanation: International consensus statement (expert consensus, hence OTHER) restates the barrier-transport lesion as the disease-defining step.
  downstream:
  - target: Cerebral Glucose Energy Deficit
    causal_link_type: DIRECT
    description: >-
      Insufficient transendothelial glucose flux starves brain tissue of its
      principal metabolic substrate, independent of normal peripheral blood
      glucose levels.
    hypothesis_groups:
    - canonical_glut1_energy_deficit
    evidence:
    - reference: PMID:12029447
      reference_title: "Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain-- a review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome (MIM 138140) defines a prototype of a novel group of disorders resulting from impaired glucose transport across blood-tissue barriers."
      explanation: Review frames Glut1DS as the prototypic disorder of impaired glucose transport across blood-tissue barriers, i.e., a cerebral energy-deficit disease.
    - reference: PMID:11136715
      reference_title: "Autosomal dominant transmission of GLUT1 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Impaired glucose transport across brain tissue barriers is reflected by hypoglycorrhachia and results in an epileptic encephalopathy with developmental delay and motor disorders."
      explanation: States the causal step from barrier transport failure to the low-CSF-glucose, energy-deprived brain.
  - target: Hypoglycorrhachia (low CSF glucose)
    causal_link_type: DIRECT
    description: >-
      Reduced endothelial glucose flux lowers glucose in the CSF and brain
      interstitium while blood glucose stays normal, so the CSF:blood glucose
      ratio falls.
    evidence:
    - reference: PMID:17718830
      reference_title: "GLUT1 deficiency syndrome--2007 update."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The essential biochemical finding is a low glucose concentration in the cerebrospinal fluid"
      explanation: Low CSF glucose with normal blood glucose is the direct biochemical signature of the barrier transport defect.
  - target: Arrested Cerebral Angiogenesis and Microvascular Diminution
    causal_link_type: DIRECT
    description: >-
      Beyond fuel delivery, endothelial GLUT1 is required for postnatal cerebral
      angiogenesis; low GLUT1 arrests microvessel expansion in model mice.
    hypothesis_groups:
    - microvascular_developmental_defect
    evidence:
    - reference: PMID:28106060
      reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We used model mice to demonstrate that low Glut1 protein arrests cerebral angiogenesis, resulting in a profound diminution of the brain microvasculature without compromising the blood-brain barrier."
      explanation: Mouse evidence that low GLUT1 itself, independent of barrier integrity, arrests cerebral angiogenesis.
- name: Cerebral Glucose Energy Deficit
  description: >-
    Chronic under-supply of glucose to neurons and glia produces a state of
    cerebral energy insufficiency during the period of childhood brain
    development when glucose demand is highest, driving neuronal
    hyperexcitability, impaired neurodevelopment, and deceleration of brain (and
    hence head) growth.
  role: mediator
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: Astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: Generation of Precursor Metabolites and Energy
    term:
      id: GO:0006091
      label: generation of precursor metabolites and energy
    modifier: DECREASED
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The needs of the brain for glucose increase rapidly after birth, peaking in early childhood, remaining high until about age 10 years, then gradually decreasing throughout adolescence and plateauing in early adulthood."
    explanation: GeneReviews explains why the cerebral energy deficit is most severe in infancy/early childhood when brain glucose demand peaks, framing the developmental basis of the classic phenotype.
  - reference: PMID:26536893
    reference_title: "Triheptanoin dramatically reduces paroxysmal motor disorder in patients with GLUT1 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, brain energy metabolism normalised with triheptanoin, that is, increased Pi/PCr ratio during brain activation compared to the recovery phase (p = 0.021), and deteriorated when triheptanoin was withdrawn."
    explanation: 31P-NMR spectroscopy in patients shows an abnormal activation-dependent brain energy profile that normalises with substrate supplementation, a direct in vivo measure of the cerebral energy deficit.
  - reference: PMID:31399478
    reference_title: "A new mouse model of GLUT1 deficiency syndrome exhibits abnormal sleep-wake patterns and alterations of glucose kinetics in the brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "glucose transportation was reduced, whereas hexokinase activity and glucose metabolism were enhanced"
    explanation: FDG-PET kinetics in a missense mouse model separate the transport-limited supply step from a compensatory rise in downstream hexokinase flux.
  - reference: PMID:40405536
    reference_title: "Glut1 Deficiency Syndrome: Novel Pathomechanisms, Current Concepts, and Challenges."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Research reaches beyond the concept of brain energy depletion by impaired GLUT1-mediated glucose transfer across the blood-brain barrier. Novel concepts investigate alternative substrates, transport mechanisms, and metabolic interactions of different brain cell types."
    explanation: Recent review frames energy depletion as the canonical model while flagging that astrocyte-neuron metabolic interactions are an active refinement of it.
  downstream:
  - target: Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure
    causal_link_type: DIRECT
    description: >-
      When energy demand rises (sustained exertion) or substrate supply falls
      (fasting), the marginal glucose supply to metabolically expensive basal
      ganglia circuits is transiently exceeded.
    hypothesis_groups:
    - canonical_glut1_energy_deficit
    evidence:
    - reference: PMID:18451999
      reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "we propose that the dyskinesias result from an exertion-induced energy deficit that may cause episodic dysfunction of the basal ganglia"
      explanation: Proposes, from combined genetic, functional and brain-imaging data, that exertion converts the chronic deficit into episodic basal ganglia failure.
  - target: Reduced CSF lactate
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Lower glycolytic substrate delivery is the presumed reason CSF lactate is
      low-to-normal rather than raised; the intermediate steps are inferred, and
      the finding distinguishes Glut1DS from mitochondrial disease.
  - target: Paroxysmal eye-head movements
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Paroxysmal eye-head movements are among the earliest signs of the
      infantile energy deficit; the circuit through which they arise is not
      established.
    evidence:
    - reference: PMID:32913944
      reference_title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Key clinical features signaling the onset of Glut1DS are eye-head movement abnormalities, seizures, neurodevelopmental impairment, deceleration of head growth, and movement disorders."
      explanation: Consensus statement lists eye-head movement abnormalities among the earliest onset features of the energy-deficient brain.
  - target: Neuronal Hyperexcitability and Hypersynchrony
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Energy-deficient neurons and cortical circuits become hyperexcitable and
      hypersynchronous, generating the pharmacoresistant seizures characteristic
      of Glut1DS.
    hypothesis_groups:
    - canonical_glut1_energy_deficit
    evidence:
    - reference: PMID:25487684
      reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Thirty-two patients (97%) exhibited some type of epileptic seizure."
      explanation: Nationwide cohort documents near-universal seizure occurrence, the clinical readout of energy-deficit-driven cortical hyperexcitability.
  - target: Impaired Neurodevelopment and Movement Disorder
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Sustained cerebral energy insufficiency during critical developmental
      windows impairs neurodevelopment and produces a complex movement disorder
      combining ataxia, dystonia, and spasticity, together with deceleration of
      head growth (acquired/progressive microcephaly).
    evidence:
    - reference: PMID:20301603
      reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Subsequently children develop complex movement disorders and intellectual disability ranging from mild to severe."
      explanation: GeneReviews documents the progression from early seizures/developmental delay to complex movement disorder and intellectual disability.
- name: Neuronal Hyperexcitability and Hypersynchrony
  description: >-
    Cortical and subcortical neuronal networks deprived of adequate glucose fuel
    become hyperexcitable, producing hypersynchronous discharges that manifest
    as pharmacoresistant seizures of varying semiology. This node conforms to
    the shared epilepsy excitation-inhibition-imbalance final common pathway,
    substituting a metabolic (energy-deficit) upstream driver rather than a
    primary ion-channel lesion.
  role: central_effector
  biological_scale: TISSUE
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Neuronal Hyperexcitability and Hypersynchrony"
  locations:
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the predominant clinical findings of Glut1DS are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay."
    explanation: GeneReviews documents pharmacoresistant seizures as the predominant early clinical finding reflecting cortical hyperexcitability.
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "During 24-h EEGs, background activity showed generalized 2.5- to 4-Hz spike-wave discharges (41%), generalized slowing or attenuation (34%), no abnormalities (34%), focal epileptiform discharges (13%), or focal slowing or attenuation (9%)."
    explanation: 24-hour EEG in 20 children quantifies the hypersynchronous generalized spike-wave and focal epileptiform signatures of the network state.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake."
    explanation: The food-responsive EEG ties the hypersynchronous discharge directly to the fuel state of the cortex.
  - reference: PMID:16497725
    reference_title: "A mouse model for Glut-1 haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "GLUT-1+/- mice have epileptiform discharges on electroencephalography (EEG), impaired motor activity, incoordination, hypoglycorrhachia, microencephaly, decreased brain glucose uptake as measured by positron emission tomography (PET) scan and decreased brain Glut-1 expression by western blot (66%)."
    explanation: Haploinsufficient mice reproduce epileptiform discharges, showing that a 34% loss of brain GLUT1 is sufficient for network hyperexcitability.
  downstream:
  - target: Recurrent Pharmacoresistant Seizures
    causal_link_type: DIRECT
    description: Hyperexcitable, hypersynchronous cortical networks manifest clinically as recurrent seizures.
    evidence:
    - reference: PMID:25487684
      reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Thirty-two patients (97%) exhibited some type of epileptic seizure."
      explanation: Nationwide cohort documents near-universal seizure occurrence as the clinical manifestation of cortical hyperexcitability.
  - target: Generalized 2.5-4 Hz spike-wave EEG
    causal_link_type: DIRECT
    description: >-
      The interictal electrographic signature of the hypersynchronous network,
      most prominent from about two years of age.
    evidence:
    - reference: PMID:12752470
      reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In older children (2 years or older), a generalized 2.5- to 4-Hz spike-wave pattern emerged."
      explanation: Documents the age-dependent emergence of the generalized spike-wave pattern.
- name: Impaired Neurodevelopment and Movement Disorder
  description: >-
    Chronic cerebral energy deficit produces a complex, often paroxysmal
    movement disorder (ataxia, dystonia, spasticity), speech difficulty, and
    intellectual disability that can present alone or alongside epilepsy,
    reflecting the breadth of the GLUT1DS phenotypic spectrum.
  role: effector
  biological_scale: TISSUE
  biological_processes:
  - preferred_term: brain development
    term:
      id: GO:0007420
      label: brain development
    modifier: DECREASED
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the predominant clinical findings of Glut1DS are usually complex paroxysmal movement disorders, spasticity, ataxia, dystonia, speech difficulty, and intellectual disability."
    explanation: GeneReviews describes the later-onset movement-disorder-predominant clinical picture directly arising from the same energy-deficit mechanism.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hypotonic, ataxic, and dystonic features are most prominent. Speech is often severely affected. Some patients develop spasticity and secondary microcephaly."
    explanation: Review of 84 published cases summarises the motor, speech and head-growth consequences of the developmental energy deficit.
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Epilepsy dominated infancy and improved during childhood. Dystonia emerged during childhood or adolescence."
    explanation: Longitudinal follow-up (mean 14 years) shows the movement disorder emerging as the dominant later manifestation.
  - reference: PMID:16497725
    reference_title: "A mouse model for Glut-1 haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The GLUT-1+/- murine phenotype mimics the classical human presentation of Glut-1 DS."
    explanation: Haploinsufficient mice with microencephaly and incoordination recapitulate the developmental and motor consequences.
  downstream:
  - target: Progressive (Acquired) Microcephaly
    causal_link_type: DIRECT
    description: Reduced postnatal brain growth is expressed as deceleration of head growth.
    evidence:
    - reference: PMID:16497725
      reference_title: "A mouse model for Glut-1 haploinsufficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Glut-1 deficiency syndrome (Glut-1 DS, OMIM #606777) is characterized by infantile seizures, developmental delay, acquired microcephaly and hypoglycorrhachia."
      explanation: Acquired microcephaly is a defining consequence in both the human syndrome and the haploinsufficient mouse (microencephaly).
  - target: Global Developmental Delay
    causal_link_type: DIRECT
  - target: Intellectual disability
    causal_link_type: DIRECT
  - target: Ataxia
    causal_link_type: DIRECT
  - target: Dystonia
    causal_link_type: DIRECT
  - target: Spasticity
    causal_link_type: DIRECT
  - target: Hypotonia
    causal_link_type: DIRECT
  - target: Speech Difficulty
    causal_link_type: DIRECT
  - target: Gait disturbance
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: Gait disturbance is the functional composite of ataxia, dystonia and spasticity.
- name: Recurrent Pharmacoresistant Seizures
  description: >-
    The clinical endpoint of cortical hyperexcitability is recurrent,
    typically pharmacoresistant, epileptic seizures of varying types beginning
    in infancy or early childhood.
  role: consequence
  conforms_to: "epilepsy_excitation_inhibition_imbalance#Recurrent Unprovoked Seizures"
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The initial symptom was convulsive seizures, which occurred in 15 cases, and was followed by abnormal eye movements in 7 cases and apneic or cyanotic attacks in 4 cases."
    explanation: Nationwide Japanese survey documents convulsive seizures as the most frequent presenting symptom.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients present with an early-onset epilepsy resistant to anticonvulsants, developmental delay, and a complex movement disorder."
    explanation: Review of 84 cases confirms early-onset, anticonvulsant-resistant epilepsy as the presenting endpoint.
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."
    explanation: Chart review of 20 children enumerates the seizure semiologies that make up the endpoint.
  biological_scale: ORGANISM
  downstream:
  - target: Pharmacoresistant Seizures
    causal_link_type: DIRECT
  - target: Absence seizures
    causal_link_type: DIRECT
  - target: Myoclonic seizures
    causal_link_type: DIRECT
  - target: Generalized tonic-clonic seizures
    causal_link_type: DIRECT
  - target: Focal seizures
    causal_link_type: DIRECT
- name: Erythrocyte GLUT1 Dysfunction
  description: >-
    Erythrocytes express the same GLUT1 transporter as the brain endothelium, so
    the haploinsufficient state is measurable outside the brain as reduced
    3-O-methyl-D-glucose uptake (typically about half of control Vmax with an
    unchanged Km) and, with flow cytometry, as reduced surface GLUT1. Residual
    uptake tracks clinical severity. Certain pore-region alleles additionally
    render the mutant transporter leaky to cations, disturbing red-cell sodium,
    potassium and calcium and producing echinocytosis and hemolysis. This node
    is chiefly a diagnostic surrogate of the primary lesion; only the cation
    leak branch is itself pathogenic.
  role: mediator
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  cell_types:
  - preferred_term: Erythrocyte
    term:
      id: CL:0000232
      label: erythrocyte
  biological_processes:
  - preferred_term: D-glucose transmembrane transport
    term:
      id: GO:1904659
      label: D-glucose transmembrane transport
    modifier: DECREASED
  evidence:
  - reference: PMID:15622525
    reference_title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The mean V(max) for the 3-O-methyl-D-glucose uptake into erythrocytes was 996 fmol/10(6) red blood cells per second, significantly less (54 +/- 11%; t test, p < 0.05) than the mean control value of 1,847. The mean Km value for the patient group (1.4 +/- 0.5mM) was similar to the control group (1.7 +/- 0.5mM; t test, p > 0.05)."
    explanation: Kinetic assay in 16 patients shows roughly half-normal transport capacity with unchanged affinity, the erythrocyte signature of haploinsufficiency.
  - reference: PMID:22190371
    reference_title: "Glut1 deficiency syndrome and erythrocyte glucose uptake assay."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We also noted a significant correlation between the mean erythrocyte 3-OMG uptake and clinical severity (R(2) = 0.94)."
    explanation: In 109 suspected cases, residual erythrocyte uptake correlates tightly with clinical severity.
  - reference: PMID:18451999
    reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the hemolysis with echinocytosis may result from alterations in intracellular electrolytes caused by a cation leak through mutant GLUT1."
    explanation: Identifies the cation-leak branch by which a pore-region GLUT1 allele damages the erythrocyte itself.
  downstream:
  - target: Hemolytic anemia
    causal_link_type: DIRECT
    description: >-
      Restricted to alleles that create a cation leak (e.g. Q282_S285del);
      alleles that only reduce transport (A275T, G314S) do not cause hemolysis.
    hypothesis_groups:
    - erythrocyte_cation_leak_hemolysis
    evidence:
    - reference: PMID:18451999
      reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We screened 4 additional families, in which PED is combined with epilepsy, developmental delay, or migraine, but not with hemolysis or echinocytosis, and identified 2 additional GLUT1 mutations (A275T, G314S) that decreased glucose transport but did not affect cation permeability."
      explanation: Allele-level dissociation shows hemolysis follows the cation leak, not the transport loss per se.
- name: Arrested Cerebral Angiogenesis and Microvascular Diminution
  description: >-
    In Glut1-deficient mice, low endothelial GLUT1 arrests postnatal cerebral
    angiogenesis and leaves a profoundly reduced brain microvasculature while
    barrier integrity is preserved. Pre-symptomatic AAV9-mediated GLUT1
    repletion averts the vascular defect and the disease; late (adult) repletion
    does not. The 2020 consensus statement adopts impaired microvascular
    development as a complication of delayed treatment, but direct human
    vascular data are lacking, so this node is provisional and is the
    structural basis of an emerging, non-fuel mechanism.
  role: mediator
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  cell_types:
  - preferred_term: Brain Microvascular Endothelial Cell
    term:
      id: CL:2000044
      label: brain microvascular endothelial cell
  biological_processes:
  - preferred_term: cerebral angiogenesis
    term:
      id: GO:0001525
      label: angiogenesis
    modifier: DECREASED
  evidence:
  - reference: PMID:28106060
    reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Studies to define the temporal requirements for Glut1 reveal that pre-symptomatic, AAV9-mediated repletion of the protein averts brain microvasculature defects and prevents disease, whereas augmenting the protein late, during adulthood, is devoid of benefit."
    explanation: Temporal rescue experiments show the microvascular defect is GLUT1-dependent and has a developmental window.
  - reference: PMID:32913944
    reference_title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Impaired development of the brain microvasculature is one such complication of delayed Glut1DS treatment in the postnatal period."
    explanation: The consensus statement carries the mouse finding into the clinical framing of untreated early disease; it is expert opinion, not human vascular measurement.
  downstream:
  - target: Impaired Neurodevelopment and Movement Disorder
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      A diminished microvascular bed is proposed to compound the fuel deficit
      and contribute to cognitive dysfunction; the human contribution is
      unquantified.
    hypothesis_groups:
    - microvascular_developmental_defect
    evidence:
    - reference: PMID:28106060
      reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Glut1 repletion in early-symptomatic mutants that have experienced sustained periods of low brain glucose nevertheless restores the cerebral microvasculature and ameliorates disease."
      explanation: Restoring the microvasculature ameliorates disease in symptomatic mutants, linking the vascular node to the neurodevelopmental outcome.
- name: Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure
  description: >-
    Under sustained exertion or fasting, the marginal glucose supply of the
    energy-deficient brain is transiently overwhelmed in corticostriatal
    circuits, producing episodes of choreoathetosis or dystonia affecting mainly
    the legs (paroxysmal exercise-induced dyskinesia). The same triggers
    aggravate seizures and paroxysmal ataxia. Functional imaging in PED
    families implicates altered glucose metabolism in the corticostriate
    pathways; the exertion-induced energy-deficit model is proposed rather than
    directly measured in the basal ganglia.
  role: mediator
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  locations:
  - preferred_term: basal ganglia
    term:
      id: UBERON:0002420
      label: basal ganglion
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: Generation of Precursor Metabolites and Energy
    term:
      id: GO:0006091
      label: generation of precursor metabolites and energy
    modifier: DECREASED
  evidence:
  - reference: PMID:18577546
    reference_title: "Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Functional imaging studies implicated alterations in glucose metabolism in the corticostriate pathways in the pathophysiology of PED and in the frontal lobe cortex in the pathophysiology of epileptic seizures."
    explanation: Imaging in SLC2A1 PED families localises the metabolic disturbance behind dyskinesia to corticostriatal circuits.
  - reference: PMID:26193382
    reference_title: "From splitting GLUT1 deficiency syndromes to overlapping phenotypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sensitivity to fasting or exertion in combination with those 3 main symptoms were the main differences between mutated and negative patients (p < 0.001)."
    explanation: In a national laboratory cohort, trigger sensitivity to fasting and exertion discriminates SLC2A1-positive from negative patients.
  - reference: PMID:23443458
    reference_title: "Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise."
    explanation: Review confirms fasting and exercise as the characteristic provocations of the paroxysmal phenotype.
  downstream:
  - target: Paroxysmal Exercise/Exertion-Induced Dyskinesia
    causal_link_type: DIRECT
    hypothesis_groups:
    - canonical_glut1_energy_deficit
    evidence:
    - reference: PMID:18577546
      reference_title: "Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "PED was characterized by choreoathetosis, dystonia or both, affecting mainly the legs."
      explanation: Describes the clinical form of the exertion-triggered episodes produced by this mechanism.
phenotypes:
- name: Pharmacoresistant Seizures
  description: >-
    Seizures of varying types (often including absence, myoclonic, or
    generalized tonic-clonic seizures), typically beginning in infancy and
    frequently resistant to conventional anti-seizure medications, but
    responsive to ketogenic diet therapy.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
    temporality: RECURRENT
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty-two patients (97%) exhibited some type of epileptic seizure."
    explanation: Nationwide cohort of 33 confirmed GLUT1DS patients documents seizures in 97% of individuals, directly supporting VERY_FREQUENT.
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three different phenotypes were recognized: (i) the classical phenotype (84%), subdivided into early-onset (<2 years) (65%) and late-onset (18%); (ii) a non-classical phenotype, with mental retardation and movement disorder, without epilepsy (15%)"
    explanation: In 57 genetically confirmed patients, 84% had the epilepsy-containing classical phenotype and 15% had no epilepsy, keeping seizures in the VERY_FREQUENT band while documenting the epilepsy-free minority.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients present with an early-onset epilepsy resistant to anticonvulsants, developmental delay, and a complex movement disorder."
    explanation: Supports the pharmacoresistance qualifier.
  phenotype_contexts:
  - onset:
      onset_category: INFANTILE
      mean_age_years: 0.4
      min_age_years: 0.08
      max_age_years: 1.5
      notes: Seizure diagnosis between 4 weeks and 18 months, mean 5 months, in the 20-child EEG series.
    evidence:
    - reference: PMID:12752470
      reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Age at seizure diagnosis was between 4 weeks and 18 months (mean, 5 months)."
      explanation: Quantifies infantile seizure onset.
- name: Global Developmental Delay
  description: >-
    Delayed acquisition of motor and cognitive milestones, typically apparent
    from infancy, with mild-to-severe intellectual disability persisting into
    later childhood and adulthood.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mild to severe mental retardation was detected in all 33 cases."
    explanation: Nationwide cohort documents developmental/cognitive impairment in all 33 confirmed cases.
- name: Progressive (Acquired) Microcephaly
  description: >-
    Deceleration of head growth after a normal birth head circumference,
    reflecting impaired postnatal brain growth from the underlying cerebral
    energy deficit.
  notes: >-
    Re-bound from HP:0000253 (Progressive microcephaly) to HP:0005484
    (Secondary microcephaly, synonym "acquired microcephaly") because the
    defining feature is a normal head circumference at birth followed by
    postnatal deceleration; the clinical_course qualifier carries the
    progressive aspect.
  phenotype_term:
    preferred_term: Acquired (postnatal) microcephaly
    term:
      id: HP:0005484
      label: Secondary microcephaly
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the predominant clinical findings of Glut1DS are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay."
    explanation: GeneReviews lists deceleration of head growth as a predominant early clinical finding.
  - reference: PMID:15622525
    reference_title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterized by infantile seizures, developmental delay, acquired microcephaly, spasticity, ataxia, and hypoglycorrhachia"
    explanation: Names the microcephaly as acquired, i.e. postnatal.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Some patients develop spasticity and secondary microcephaly."
    explanation: Review of 84 cases classifies it as secondary microcephaly and as occurring in some rather than all patients, so no frequency band is asserted.
- name: Ataxia
  description: >-
    Impaired coordination of voluntary movement, part of the complex movement
    disorder that emerges as GLUT1DS progresses.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  frequency: FREQUENT
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."
    explanation: Nationwide cohort documents cerebellar ataxia as a common neurological finding in most patients.
- name: Dystonia
  description: >-
    Sustained or intermittent muscle contractions causing abnormal, often
    repetitive movements or postures; part of the complex movement disorder of
    GLUT1DS and the dominant feature of the paroxysmal-dyskinesia-predominant
    subtype.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  frequency: FREQUENT
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."
    explanation: Nationwide cohort documents dystonia as a common neurological finding.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hypotonic, ataxic, and dystonic features are most prominent."
    explanation: Review of 84 published cases ranks dystonic features among the most prominent motor findings.
  phenotype_contexts:
  - onset:
      onset_category: CHILDHOOD
      notes: Dystonia emerged during childhood or adolescence in the 13-patient longitudinal series.
    evidence:
    - reference: PMID:24789115
      reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Dystonia emerged during childhood or adolescence."
      explanation: Longitudinal cohort places dystonia onset after the infantile epilepsy phase.
- name: Spasticity
  description: Increased muscle tone contributing to the complex movement disorder of GLUT1DS.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  frequency: FREQUENT
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."
    explanation: Nationwide cohort documents spastic paralysis as a common neurological finding.
- name: Paroxysmal Exercise/Exertion-Induced Dyskinesia
  description: >-
    Episodic dystonic or dyskinetic attacks of the extremities triggered by
    prolonged physical exertion, hunger, fever, or fatigue; the dominant
    presenting feature of the milder GLUT1DS2/DYT18 phenotype but also reported
    in classic disease.
  phenotype_term:
    preferred_term: Paroxysmal dyskinesia
    term:
      id: HP:0007166
      label: Paroxysmal dyskinesia
    temporality: RECURRENT
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, paroxysmal episodes of ataxia, dystonia/dyskinesia, and motor paralysis were described in approximately 1/3 of all patients. The factors that frequently aggravated these events were hunger, exercise, fever, and fatigue, in that order."
    explanation: Nationwide cohort quantifies paroxysmal dyskinetic episodes in about a third of patients and identifies exertion/hunger/fever/fatigue as triggers.
  - reference: PMID:18577546
    reference_title: "Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PED was characterized by choreoathetosis, dystonia or both, affecting mainly the legs."
    explanation: Defines the semiology of PED in SLC2A1 families.
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The 6-Minute Walk Test captured gait disturbances and triggered paroxysmal exertional dyskinesia."
    explanation: A standardised exertion test reproducibly provokes the episodes in long-term follow-up.
  - reference: PMID:23443458
    reference_title: "Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In particular, paroxysmal exertional dyskinesia is now a well-documented clinical feature that occurs in individuals with Glut1 DS."
    explanation: Review establishes PED as a recognised feature across the spectrum, not only in GLUT1DS2.
- name: Speech Difficulty
  description: >-
    Dysarthria and other speech production difficulties associated with the
    movement disorder and developmental impairment of GLUT1DS.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the predominant clinical findings of Glut1DS are usually complex paroxysmal movement disorders, spasticity, ataxia, dystonia, speech difficulty, and intellectual disability."
    explanation: GeneReviews lists speech difficulty among predominant clinical findings in the later-onset presentation.
- name: Hypotonia
  description: Reduced muscle tone, frequently observed alongside ataxia and dystonia.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  frequency: FREQUENT
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological findings revealed that most patients had muscle hypotonia, cerebellar ataxia, dystonia, and spastic paralysis."
    explanation: Nationwide cohort documents muscle hypotonia as a common neurological finding.
- category: Neurological
  name: Intellectual disability
  description: >-
    Cognitive impairment ranging from mild learning difficulty to severe
    intellectual disability, present in essentially all classic cases and in
    the non-classical movement-disorder phenotype; it was the initial symptom
    in over 40% of a French national cohort.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Subsequently children develop complex movement disorders and intellectual disability ranging from mild to severe."
    explanation: GeneReviews documents intellectual disability across a mild-to-severe range.
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mild to severe mental retardation was detected in all 33 cases."
    explanation: All 33 confirmed cases had cognitive impairment, supporting VERY_FREQUENT.
  - reference: PMID:26193382
    reference_title: "From splitting GLUT1 deficiency syndromes to overlapping phenotypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most patients (87.5%) exhibited classic phenotype with intellectual deficiency (41.7%), epilepsy (75%) or movement disorder (29%) as initial symptoms at a medium age of 7.5 months"
    explanation: French cohort shows intellectual deficiency as the presenting symptom in 41.7%.
- category: Neurological
  name: Absence seizures
  description: >-
    Absence seizures, including early-onset absence epilepsy beginning before
    age four, are a characteristic seizure type; SLC2A1 variants account for
    about one in ten cases of absence epilepsy screened in a Danish series.
  phenotype_term:
    preferred_term: Absence seizure
    term:
      id: HP:0002121
      label: Generalized non-motor (absence) seizure
  evidence:
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."
    explanation: Absence seizures in 10 of 20 children with Glut1DS.
  - reference: PMID:26537434
    reference_title: "The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy, and the estimated frequency of GLUT1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in SLC2A1 were detected in 5 (10%) of 50 patients with absence epilepsy"
    explanation: Shows the converse association, that absence epilepsy is a recognised Glut1DS presentation.
  - reference: PMID:23443458
    reference_title: "Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Absence epilepsy and other idiopathic generalized epilepsy syndromes may occur with seizure onset in childhood or adulthood."
    explanation: Review places absence epilepsy within the milder end of the spectrum.
- category: Neurological
  name: Myoclonic seizures
  description: >-
    Myoclonic seizures occur in a substantial minority and mark the more severe
    end of the spectrum, with worse intellectual and motor outcome than
    early-onset absence epilepsy in the French national cohort.
  phenotype_term:
    preferred_term: Myoclonic seizure
    term:
      id: HP:0032794
      label: Myoclonic seizure
  evidence:
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."
    explanation: Myoclonic seizures in 6 of 20 children.
  - reference: PMID:26193382
    reference_title: "From splitting GLUT1 deficiency syndromes to overlapping phenotypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with myoclonic seizures (52%) evolved with more severe intellectual deficiency and movement disorders compared with those with Early Onset Absence Epilepsy (38%)."
    explanation: Myoclonic seizures identify a more severe subgroup.
- category: Neurological
  name: Generalized tonic-clonic seizures
  description: Generalized tonic or clonic seizures were the most frequent seizure type in a 20-child series.
  phenotype_term:
    preferred_term: Generalized tonic-clonic seizure
    term:
      id: HP:0002069
      label: Bilateral tonic-clonic seizure
  evidence:
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."
    explanation: Generalized tonic or clonic seizures in 14 of 20 children.
- category: Neurological
  name: Focal seizures
  description: Partial (focal-onset) seizures occur alongside the generalized seizure types, particularly in infancy.
  phenotype_term:
    preferred_term: Focal-onset seizure
    term:
      id: HP:0007359
      label: Focal-onset seizure
  evidence:
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seizure types were generalized tonic or clonic (14), absence (10), partial (nine), myoclonic (six), or astatic (four)."
    explanation: Partial seizures in 9 of 20 children.
- category: Neurological
  name: Generalized 2.5-4 Hz spike-wave EEG
  description: >-
    Interictal EEG is most often normal, but when abnormal the characteristic
    finding from about two years of age is generalized 2.5-4 Hz spike-wave
    discharges, which improve after food intake; focal discharges and slowing
    predominate in infants.
  phenotype_term:
    preferred_term: Generalized 2.5-4 Hz spike-wave discharges
    term:
      id: HP:0010850
      label: EEG with spike-wave complexes
  electrophysiology:
    electrophysiology_modality: EEG
    ictal_state: INTERICTAL
  evidence:
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In all ages, a normal interictal EEG was the most common EEG finding. When abnormalities occurred, focal slowing or epileptiform discharges were more prevalent in the infant. In older children (2 years or older), a generalized 2.5- to 4-Hz spike-wave pattern emerged."
    explanation: Defines the age-dependent EEG signature and its low sensitivity.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake."
    explanation: Documents the food-responsive property of the discharge.
- category: Neurological
  name: Paroxysmal eye-head movements
  description: >-
    Paroxysmal, often multidirectional eye movements accompanied by head
    movements in the same direction are among the earliest signs in infancy and
    are frequently misread as seizures.
  phenotype_term:
    preferred_term: Paroxysmal eye-head movements
    term:
      id: HP:0007704
      label: Paroxysmal involuntary eye movements
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "When first diagnosed in infancy to early childhood, the predominant clinical findings of Glut1DS are paroxysmal eye-head movements, pharmacoresistant seizures of varying types, deceleration of head growth, and developmental delay."
    explanation: GeneReviews lists paroxysmal eye-head movements first among infantile findings.
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The initial symptom was convulsive seizures, which occurred in 15 cases, and was followed by abnormal eye movements in 7 cases and apneic or cyanotic attacks in 4 cases."
    explanation: Abnormal eye movements were the presenting symptom in 7 of 33 nationwide cases.
- category: Neurological
  name: Gait disturbance
  description: >-
    Gait disturbance reflecting the combined ataxia, dystonia and spasticity;
    percent-predicted 6-Minute Walk distance tracks overall neurological
    severity.
  phenotype_term:
    preferred_term: Gait disturbance
    term:
      id: HP:0001288
      label: Gait disturbance
  evidence:
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Percent-predicted 6-Minute Walk Test distance correlated significantly with Columbia Neurological Scores."
    explanation: Walking performance is a quantitative correlate of neurological burden in long-term follow-up.
- category: Laboratory
  name: Hypoglycorrhachia (low CSF glucose)
  description: >-
    Low CSF glucose (typically below 2.5 mmol/L, mean about 1.7 mmol/L) with a
    CSF:blood glucose ratio usually below 0.5 in the presence of normal blood
    glucose. Present in essentially all genetically confirmed patients when
    age-specific reference values are applied, so it is the diagnostic
    laboratory phenotype; rare reports of apparently normal CSF glucose exist.
  phenotype_term:
    preferred_term: Hypoglycorrhachia
    term:
      id: HP:0011972
      label: Hypoglycorrhachia
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cerebrospinal fluid glucose was below 2.5 mmol/l (range 0.9-2.4 mmol/l) in all patients and cerebrospinal fluid : blood glucose ratio was below 0.50 in all but one patient (range 0.19-0.52)."
    explanation: All 57 genetically confirmed patients had hypoglycorrhachia, supporting VERY_FREQUENT.
  - reference: PMID:23999624
    reference_title: "Cerebrospinal fluid analysis in the workup of GLUT1 deficiency syndrome: a systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The CSF glucose levels ranged from 16.2 to 50.5 mg/dL and were at or below the 10th percentile for all 147 patients."
    explanation: Systematic review of 147 genetically proven patients confirms universally low CSF glucose against age-specific percentiles.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The essential biochemical finding is a low glucose concentration in the cerebrospinal fluid"
    explanation: Gives the pooled mean CSF glucose across 84 published cases.
- category: Laboratory
  name: Reduced CSF lactate
  description: >-
    CSF lactate is low-to-normal, at or below the 10th percentile in about 80%
    of patients with reported values, in contrast to the raised CSF lactate of
    mitochondrial encephalopathies; this helps separate a transport defect from
    an oxidative one.
  phenotype_term:
    preferred_term: Low-to-normal CSF lactate
    term:
      id: HP:0030086
      label: Reduced CSF lactate
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:23999624
    reference_title: "Cerebrospinal fluid analysis in the workup of GLUT1 deficiency syndrome: a systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The CSF lactate levels ranged from 5.4 to 13.5 mg/dL and were at or below the 10th percentile for 59 of 73 patients (81%)."
    explanation: 81% of patients with reported values had low CSF lactate, supporting VERY_FREQUENT.
  - reference: PMID:15622525
    reference_title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean cerebrospinal fluid lactate concentration was 1.0 +/- 0.3mM, which was less than the normal mean value of 1.63mM."
    explanation: Mean CSF lactate in 16 new patients was below the normal mean.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in the setting of normoglycaemia. CSF lactate is normal."
    explanation: The 2007 review reports CSF lactate as normal rather than reduced; the value is low-to-normal, never elevated, which is the diagnostically useful point.
- category: Hematologic
  name: Hemolytic anemia
  description: >-
    Hemolytic anemia with echinocytosis and altered erythrocyte ion
    concentrations occurs in the subset of families whose SLC2A1 allele creates
    a cation leak through the mutant transporter; it is absent with alleles
    that only reduce glucose transport.
  phenotype_term:
    preferred_term: Hemolytic anemia with echinocytosis
    term:
      id: HP:0001878
      label: Hemolytic anemia
  evidence:
  - reference: PMID:18451999
    reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Their PED was accompanied by epilepsy, mild developmental delay, reduced CSF glucose levels, hemolytic anemia with echinocytosis, and altered erythrocyte ion concentrations."
    explanation: Three-generation family with the Q282_S285del pore-region allele documents the hemolytic phenotype.
genetic:
- name: SLC2A1
  gene_term:
    preferred_term: SLC2A1
    term:
      id: hgnc:11005
      label: SLC2A1
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  frequency: "About 90% de novo; about 10% inherited from a parent"
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Glut1DS is most commonly caused by a heterozygous SLC2A1 pathogenic variant and inherited in an autosomal dominant manner. About 90% of individuals with Glut1DS have the disorder as the result of a de novo SLC2A1 pathogenic variant; about 10% of individuals have the disorder as the result of a pathogenic variant inherited from a parent."
    explanation: GeneReviews genetic counseling section quantifies the de novo versus inherited variant origin split.
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pathological mutations in the SLC2A1 gene were identified in 28 out of 32 cases (87.5%)."
    explanation: Nationwide Japanese cohort documents the molecular diagnostic yield of SLC2A1 testing among clinically suspected patients.
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In these 57 patients we identified 49 different mutations, including six multiple exon deletions, six known mutations and 37 novel mutations (13 missense, five nonsense, 13 frame shift, four splice site and two translation initiation mutations)."
    explanation: Largest single-laboratory series enumerates the allelic spectrum, including multi-exon deletions detectable only by MLPA.
  - reference: PMID:9462754
    reference_title: "GLUT-1 deficiency syndrome caused by haploinsufficiency of the blood-brain barrier hexose carrier."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We now report two distinct classes of mutations as the molecular basis for the functional defect of glucose transport: hemizygosity of GLUT1 and nonsense mutations resulting in truncation of the GLUT-1 protein."
    explanation: Founding gene-discovery report.
  - reference: PMID:15622525
    reference_title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified 16 rearrangements, including seven missense, one nonsense, one insertion, and seven deletion mutations. Fourteen were novel mutations. There were no obvious correlations between phenotype, genotype, or biochemical measures."
    explanation: Adds the deletion-heavy spectrum of a further 16 patients and the absence of genotype-phenotype correlation in that series.
  notes: >-
    Allelic spectrum: whole-gene hemizygosity, nonsense, frameshift, splice-site,
    translation-initiation, multi-exon deletion and missense alleles, all
    converging on haploinsufficiency of transport. Biallelic (compound
    heterozygous or homozygous) genotypes with asymptomatic heterozygous parents
    account for the rare recessive families. Whether variant class predicts
    severity is contested (see the genotype-phenotype discussion).
biochemical:
- name: Hypoglycorrhachia
  presence: Decreased
  context: >-
    Low CSF glucose relative to blood glucose (CSF:blood glucose ratio typically
    below 0.4) in the setting of normoglycemia is the classic diagnostic
    biochemical signature of GLUT1DS, reflecting impaired GLUT1-mediated glucose
    transport across the blood-brain barrier.
  biomarker_term:
    preferred_term: Hypoglycorrhachia
    term:
      id: HP:0011972
      label: Hypoglycorrhachia
  readouts:
  - target: Reduced GLUT1 Transporter Function at the Blood-Brain Barrier
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      A low CSF:blood glucose ratio reports reduced GLUT1-mediated glucose
      transport across the blood-brain barrier independent of systemic glucose
      levels.
    evidence:
    - reference: PMID:21649651
      reference_title: "Milder phenotypes of glucose transporter type 1 deficiency syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the presence of normoglycaemia with a CSF/blood glucose ratio of less than 0.4."
      explanation: Directly defines the diagnostic CSF:blood glucose ratio cutoff used clinically.
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean CSF/blood glucose ratio was 0.36 (0.28-0.48)."
    explanation: Nationwide cohort of confirmed cases reports the empirical mean and range of the diagnostic CSF:blood glucose ratio.
  - reference: PMID:12029447
    reference_title: "Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain-- a review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The hallmark of the disease is a low glucose concentration in the CSF (hypoglycorrhachia) in the presence of normoglycaemia (CSF/blood glucose ratio <0.4)."
    explanation: Review confirms hypoglycorrhachia with CSF:blood glucose ratio below 0.4 as the diagnostic hallmark.
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cerebrospinal fluid glucose was below 2.5 mmol/l (range 0.9-2.4 mmol/l) in all patients and cerebrospinal fluid : blood glucose ratio was below 0.50 in all but one patient (range 0.19-0.52)."
    explanation: The ratio cut-off of 0.4 is not absolute; in 57 confirmed patients the ratio ranged up to 0.52, so a ratio below 0.5 with an absolute CSF glucose below 2.5 mmol/L is the practical screen.
  - reference: PMID:23999624
    reference_title: "Cerebrospinal fluid analysis in the workup of GLUT1 deficiency syndrome: a systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The CSF to blood glucose ratios ranged from 0.19 to 0.59 and were at or below the 10th percentile for 139 of 152 patients (91%), but they could be within the normal range as well."
    explanation: Systematic review shows the ratio alone misses about 9% of genetically proven patients, so age-specific absolute CSF glucose percentiles should be used alongside it.
  - reference: PMID:18577546
    reference_title: "Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, encoding the glucose transporter GLUT1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A median CSF/blood glucose ratio of 0.52 (normal >0.60) in the patients and a reduced glucose uptake by mutated transporters compared with the wild-type as determined in Xenopus oocytes confirmed a pathogenic role of these mutations."
    explanation: In the milder PED phenotype the ratio is only modestly reduced (median 0.52), illustrating the graded relationship between residual transport and CSF glucose.
- name: CSF lactate
  presence: Low-to-normal
  context: >-
    CSF lactate is low-to-normal (mean about 1.0 mmol/L versus a normal mean of
    1.63 mmol/L; at or below the 10th percentile in 81% of reported patients)
    and is never elevated. Because raised CSF lactate is expected in
    mitochondrial encephalopathies, a low CSF lactate alongside low CSF glucose
    points to a transport rather than an oxidative defect.
  biomarker_term:
    preferred_term: Reduced CSF lactate
    term:
      id: HP:0030086
      label: Reduced CSF lactate
  evidence:
  - reference: PMID:15622525
    reference_title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean cerebrospinal fluid lactate concentration was 1.0 +/- 0.3mM, which was less than the normal mean value of 1.63mM."
    explanation: Quantifies the lowered CSF lactate in 16 patients.
  - reference: PMID:23999624
    reference_title: "Cerebrospinal fluid analysis in the workup of GLUT1 deficiency syndrome: a systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that if age-specific reference values are applied, CSF glucose and lactate levels are adequate biomarkers in the diagnostic workup of GLUT1 deficiency syndrome."
    explanation: Systematic review endorses CSF lactate, with glucose, as a diagnostic biomarker when age-specific references are used.
- name: Erythrocyte 3-O-methyl-D-glucose uptake
  presence: Decreased
  context: >-
    Zero-trans uptake of the non-metabolisable glucose analogue
    3-O-methyl-D-glucose into freshly isolated erythrocytes is reduced to about
    half of control Vmax with an unchanged Km. A cut-off of 74% of control
    uptake gives 99% sensitivity and 100% specificity against molecular
    confirmation, and residual uptake correlates with clinical severity, making
    it both a confirmatory functional test and a surrogate of the degree of
    haploinsufficiency.
  readouts:
  - target: Erythrocyte GLUT1 Dysfunction
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Reduced uptake reports the transport capacity of the haploinsufficient
      GLUT1 population on the erythrocyte membrane.
    evidence:
    - reference: PMID:22190371
      reference_title: "Glut1 deficiency syndrome and erythrocyte glucose uptake assay."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "These findings validate the erythrocyte glucose uptake assay as a confirmatory functional test for Glut1 DS and as a surrogate marker for GLUT1 haploinsufficiency."
      explanation: Establishes the assay as a surrogate of the transporter lesion.
  evidence:
  - reference: PMID:22190371
    reference_title: "Glut1 deficiency syndrome and erythrocyte glucose uptake assay."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The cut-off for an abnormally low uptake value was increased from 60% to 74% with a corresponding sensitivity of 99% and specificity of 100%."
    explanation: Diagnostic performance of the uptake assay in 109 suspected cases.
  - reference: PMID:15622525
    reference_title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The mean V(max) for the 3-O-methyl-D-glucose uptake into erythrocytes was 996 fmol/10(6) red blood cells per second, significantly less (54 +/- 11%; t test, p < 0.05) than the mean control value of 1,847."
    explanation: Kinetic quantification of the roughly 50% reduction in transport capacity.
- name: Erythrocyte surface GLUT1 (METAglut1)
  presence: Decreased
  context: >-
    Flow-cytometric quantification of GLUT1 on the erythrocyte surface
    (METAglut1) is a noninvasive blood test that is 80% sensitive and more than
    99% specific for Glut1DS against lumbar puncture plus SLC2A1 analysis, and
    in one family with two inherited variants tracked the clinical phenotype
    better than functional uptake assays.
  readouts:
  - target: Erythrocyte GLUT1 Dysfunction
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Reduced surface GLUT1 reports the reduced transporter content of the erythrocyte membrane.
    evidence:
    - reference: PMID:37076312
      reference_title: "Prospective Multicenter Validation of a Simple Blood Test for the Diagnosis of Glut1 Deficiency Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We wished to validate the diagnostic performance of METAglut1, a simple blood test that quantifies GLUT1 on the erythrocyte surface."
      explanation: Defines what the test measures.
  evidence:
  - reference: PMID:37076312
    reference_title: "Prospective Multicenter Validation of a Simple Blood Test for the Diagnosis of Glut1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "METAglut1 was 80% sensitive and >99% specific for the diagnosis of Glut1DS."
    explanation: Prospective multicentre validation (428 prospective and 67 retrospective patients).
  - reference: PMID:31196579
    reference_title: "Usefulness of diagnostic tools in a GLUT1 deficiency syndrome patient with 2 inherited mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Instead, GLUT-1 expression at the surface of the erythrocytes appeared to better correlate with the clinical phenotypes in this family."
    explanation: Single-family report in which surface expression, not uptake, tracked phenotype; a case-level observation, not a validation study.
diagnosis:
- name: Lumbar Puncture with Paired CSF and Blood Glucose
  description: >-
    Fasting lumbar puncture with simultaneous blood glucose measurement to
    demonstrate hypoglycorrhachia and calculate the CSF:blood glucose ratio,
    the key diagnostic biochemical test. CSF lactate should be measured on the
    same sample. Age-specific reference values, not a single ratio cut-off,
    should be applied.
  diagnosis_term:
    preferred_term: lumbar puncture with paired CSF and blood glucose
    term:
      id: NCIT:C15327
      label: Lumbar Puncture
  markers: CSF glucose, CSF:blood glucose ratio, CSF lactate
  results: >-
    CSF glucose typically below 2.5 mmol/L with a CSF:blood ratio below 0.5 and
    low-to-normal CSF lactate in the presence of normoglycemia.
  evidence:
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our study demonstrates that a lumbar puncture provides the diagnostic clue to glucose transporter-1 deficiency syndrome and can thereby dramatically reduce diagnostic delay to allow early start of the ketogenic diet."
    explanation: Series of 57 patients with a mean diagnostic delay of 6.6 years shows lumbar puncture as the step that shortens it.
  - reference: PMID:32913944
    reference_title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Diagnosis is confirmed by the presence of these clinical signs, hypoglycorrhachia documented by lumbar puncture, and genetic analysis showing pathogenic SLC2A1 variants."
    explanation: Consensus diagnostic triad.
  - reference: PMID:23999624
    reference_title: "Cerebrospinal fluid analysis in the workup of GLUT1 deficiency syndrome: a systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A typical CSF profile for GLUT1 deficiency syndrome, which is defined as a CSF glucose level at or below the 10th percentile, a CSF to blood glucose ratio at or below the 25th percentile, and a CSF lactate level at or below the 10th percentile, was found in only 35 of 4099 CSF samples (0.9%) present in our CSF database of patients who received a diagnosis other than GLUT1 deficiency syndrome."
    explanation: Specificity of the full CSF profile against a 4,099-sample database of other diagnoses.
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of Glut1DS is established in a proband with suggestive clinical findings, hypoglycorrhachia documented by lumbar puncture, and a (usually) heterozygous pathogenic variant in SLC2A1 identified by molecular genetic testing."
    explanation: GeneReviews establishes lumbar puncture-documented hypoglycorrhachia as a core diagnostic criterion.
- name: SLC2A1 Molecular Genetic Testing
  description: >-
    Sequence analysis (and, if negative, gene-targeted deletion/duplication
    analysis such as MLPA) of SLC2A1 to identify the causative pathogenic
    variant. In the largest laboratory series 41% of referred requests were
    positive, and multi-exon deletions accounted for 6 of 49 distinct alleles,
    so deletion analysis is not optional.
  diagnosis_term:
    preferred_term: SLC2A1 sequence and deletion/duplication analysis
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  markers: SLC2A1 pathogenic variant (heterozygous; rarely biallelic)
  evidence:
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "From 2004-2008, 132 requests for mutational analysis of the SLC2A1 gene were studied by automated Sanger sequencing and multiplex ligation-dependent probe amplification. Mutations in the SLC2A1 gene were detected in 54 patients (41%) and subsequently in three clinically affected family members."
    explanation: Defines the two-tier testing method and its yield in referred patients.
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pathological mutations in the SLC2A1 gene were identified in 28 out of 32 cases (87.5%)."
    explanation: Nationwide cohort demonstrates the diagnostic yield of SLC2A1 molecular testing in clinically suspected cases.
- name: Erythrocyte GLUT1 Function Assay
  description: >-
    The GLUT1 defect can be confirmed in erythrocytes by 3-O-methyl-D-glucose
    uptake studies and GLUT1 immunoreactivity, providing a functional
    confirmatory test alongside molecular genetic testing; at a 74%-of-control
    cut-off the uptake assay is 99% sensitive and 100% specific.
  diagnosis_term:
    preferred_term: erythrocyte 3-O-methyl-D-glucose uptake assay
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  markers: Erythrocyte 3-O-methyl-D-glucose uptake (% of control)
  evidence:
  - reference: PMID:22190371
    reference_title: "Glut1 deficiency syndrome and erythrocyte glucose uptake assay."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The cut-off for an abnormally low uptake value was increased from 60% to 74% with a corresponding sensitivity of 99% and specificity of 100%."
    explanation: Validation of the uptake assay's diagnostic performance in 109 suspected cases.
  - reference: PMID:12029447
    reference_title: "Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain-- a review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The GLUT1 defect can be confirmed in erythrocytes by glucose uptake studies and GLUT1 immunoreactivity, and by molecular analysis of the GLUT1 gene."
    explanation: Review documents erythrocyte glucose uptake and GLUT1 immunoreactivity as confirmatory functional diagnostic assays.
- name: METAglut1 Erythrocyte Surface GLUT1 Blood Test
  diagnosis_term:
    preferred_term: METAglut1 erythrocyte surface GLUT1 flow cytometry
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  markers: Erythrocyte surface GLUT1 (flow cytometry)
  description: >-
    METAglut1 is a simple, noninvasive flow-cytometry blood test that
    quantifies GLUT1 protein on the surface of circulating erythrocytes,
    prospectively validated as a diagnostic test for GLUT1 deficiency syndrome
    and an alternative or complement to lumbar puncture. It can detect patients
    with SLC2A1 mosaicism and variants of unknown significance.
  evidence:
  - reference: PMID:37076312
    reference_title: "Prospective Multicenter Validation of a Simple Blood Test for the Diagnosis of Glut1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "METAglut1 was 80% sensitive and >99% specific for the diagnosis of Glut1DS."
    explanation: Prospective multicenter validation reports the diagnostic sensitivity and specificity of the METAglut1 erythrocyte-surface GLUT1 blood test.
  - reference: PMID:37076312
    reference_title: "Prospective Multicenter Validation of a Simple Blood Test for the Diagnosis of Glut1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "METAglut1 succeeded to identify patients with Glut1DS with SCL2A1 mosaicism and variants of unknown significance."
    explanation: The blood test detects diagnostically challenging cases including SLC2A1 mosaicism and variants of unknown significance.
- name: Electroencephalography
  description: >-
    Routine and 24-hour EEG characterise seizure types and interictal
    discharges, but a normal interictal EEG is the most common finding at all
    ages, so EEG cannot exclude the diagnosis. A pre-prandial recording that
    improves after feeding is a supportive clue.
  diagnosis_term:
    preferred_term: electroencephalography
    term:
      id: NCIT:C38054
      label: Electroencephalography
  results: >-
    Normal interictal EEG most often; focal slowing or discharges in infants;
    generalized 2.5-4 Hz spike-wave from about 2 years, improving with food.
  evidence:
  - reference: PMID:12752470
    reference_title: "Seizure characterization and electroencephalographic features in Glut-1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In all ages, a normal interictal EEG was the most common EEG finding."
    explanation: 32 continuous 24-hour EEG sessions and 42 routine EEGs establish the low sensitivity of EEG.
differential_diagnoses:
- name: Mitochondrial encephalopathies and other causes of low CSF glucose
  description: >-
    Low CSF glucose is more often seen acutely in CNS infection or malignancy
    than in a chronic neurological disorder, and in that chronic setting it is
    the diagnostic marker of Glut1DS. Mitochondrial encephalopathies can share
    seizures, movement disorder and developmental delay but characteristically
    raise CSF lactate, whereas in Glut1DS lactate is low-to-normal and blood
    glucose is normal.
  distinguishing_features:
  - Low CSF glucose with normal blood glucose and low-to-normal CSF lactate favours Glut1DS.
  - Raised CSF lactate favours a mitochondrial encephalopathy.
  - Acute presentation with pleocytosis or malignant cells points to infectious or neoplastic causes of low CSF glucose.
  evidence:
  - reference: PMID:24323444
    reference_title: "Child neurology: differential diagnosis of a low CSF glucose in children and young adults."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present a practical overview on the differential diagnosis of a low CSF glucose and stress the importance of recognizing a low CSF glucose as the diagnostic marker for GLUT1 deficiency syndrome, a treatable neurometabolic disorder."
    explanation: Frames low CSF glucose in chronic neurological disease as the Glut1DS marker to be separated from its other causes.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in the setting of normoglycaemia. CSF lactate is normal."
    explanation: Normal (never raised) CSF lactate is the discriminating feature from mitochondrial disease.
- name: Childhood absence epilepsy and other early-onset absence epilepsies
  description: >-
    Early-onset absence epilepsy without other features can be the sole
    presentation of an SLC2A1 variant; a Danish screen found SLC2A1 variants
    in 10% of absence-epilepsy patients, so Glut1DS should be excluded in
    absence epilepsy beginning before age four, especially with fasting or
    exertion sensitivity, developmental concerns or a movement disorder.
  distinguishing_features:
  - Onset of absences before age 4, drug resistance, developmental concerns, movement disorder or fasting/exertion sensitivity favour SLC2A1 testing.
  - Hypoglycorrhachia on lumbar puncture separates Glut1DS from idiopathic absence epilepsy.
  evidence:
  - reference: PMID:26537434
    reference_title: "The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy, and the estimated frequency of GLUT1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in SLC2A1 were detected in 5 (10%) of 50 patients with absence epilepsy, and in one (2.7%) of 37 patient with unselected epilepsies, ID, and/or various movement disorders."
    explanation: Quantifies the overlap between absence epilepsy and Glut1DS.
- name: Epilepsy with myoclonic-atonic seizures (Doose syndrome)
  description: >-
    Myoclonic-astatic epilepsy shares early-onset generalized seizures with
    Glut1DS, but a screen of 120 patients with myoclonic astatic epilepsy
    without associated movement disorder found no SLC2A1 variants.
  distinguishing_features:
  - Absence of a movement disorder and normal CSF glucose argue against Glut1DS in myoclonic-atonic epilepsy.
  evidence:
  - reference: PMID:26537434
    reference_title: "The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy, and the estimated frequency of GLUT1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "None of the 120 MAE patients harbored SLC2A1 mutations."
    explanation: Negative screen separates typical MAE from Glut1DS.
- name: Other paroxysmal dyskinesias (PRRT2-related kinesigenic and non-kinesigenic dyskinesias)
  description: >-
    Paroxysmal dyskinesias are classified by trigger; the exertion-induced
    (PED) form, provoked by prolonged exercise or fasting rather than sudden
    movement, is the one most likely to be Glut1DS, and a fasting or exercise
    trigger is the diagnostic clue.
  distinguishing_features:
  - Episodes provoked by prolonged exertion or fasting, lasting minutes to an hour and affecting mainly the legs, favour SLC2A1-related PED.
  - Brief attacks provoked by sudden movement favour PRRT2-related kinesigenic dyskinesia.
  - A reduced CSF:blood glucose ratio (median about 0.5 in PED families) supports Glut1DS.
  evidence:
  - reference: PMID:23443458
    reference_title: "Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise."
    explanation: Trigger profile as the discriminating clinical feature.
  - reference: PMID:18451999
    reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Paroxysmal dyskinesias are episodic movement disorders that can be inherited or are sporadic in nature."
    explanation: Places SLC2A1-related PED within the broader paroxysmal dyskinesia group from which it must be distinguished.
treatments:
- name: Ketogenic Diet Therapy
  description: >-
    Age-specific ketogenic diet therapies (KDTs) supply ketone bodies as an
    alternative fuel for brain energy metabolism, bypassing the GLUT1 transport
    defect. Earlier initiation, ideally in infancy, is associated with better
    seizure control and long-term neurologic outcome. Effective for both
    seizure control and the movement disorder.
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: ketogenic diet intake
    term:
      id: NCIT:C173168
      label: Ketogenic Diet
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  - preferred_term: Paroxysmal dyskinesia
    term:
      id: HP:0007166
      label: Paroxysmal dyskinesia
  target_mechanisms:
  - target: Cerebral Glucose Energy Deficit
    treatment_effect: BYPASSES
    evidence:
    - reference: PMID:20301603
      reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Targeted therapy: Age-specific KDTs primarily provide a supplemental fuel, namely, ketone bodies, for brain energy metabolism."
      explanation: GeneReviews describes the ketogenic diet mechanism of action as supplying an alternative cerebral fuel that bypasses the GLUT1 transport defect.
  evidence:
  - reference: PMID:36303089
    reference_title: "Ketogenic diet therapy in children with epilepsy caused by SLC2A1 mutations: a single-center single-arm retrospective study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients were seizure-free within a month of receiving the diet therapy. All patients were followed up for six months, three were followed up for 12 months after the treatment, and there was no recurrence of epilepsy during this period."
    explanation: Retrospective single-center cohort of SLC2A1-mutation patients demonstrates rapid and durable seizure control with ketogenic diet therapy.
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Typically, the earlier the treatment the better the long-term clinical outcome."
    explanation: GeneReviews documents that earlier ketogenic diet initiation yields better long-term neurologic outcome.
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a ketogenic diet was effective in most of the patients with epilepsy (86%) and also reduced movement disorders in 48% of the patients with a classical phenotype and 71% of the patients with a non-classical phenotype."
    explanation: Quantifies response of both seizures and movement disorder in 57 confirmed patients.
  - reference: PMID:26803281
    reference_title: "Use of dietary therapies amongst patients with GLUT1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of those with seizures, 95% of the children had >50% seizure reduction and 80% had >90% seizure reduction."
    explanation: Largest (92-family, parent-reported) series of dietary therapy in Glut1DS.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The ketogenic diet is the treatment of choice as it provides an alternative fuel to the brain. It should be introduced early and maintained into puberty. Seizures are effectively controlled with the onset of ketosis, but might recur and require comedication."
    explanation: Review of 84 cases states duration guidance and the possibility of seizure recurrence needing co-medication.
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Earlier introduction of the ketogenic diet correlated with better long-term outcomes on some measures."
    explanation: Longitudinal cohort (mean 14 years) supports the early-treatment claim with outcome data rather than expert statement.
  - reference: PMID:32913944
    reference_title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "KDT represent standard choices with Glut1DS-specific recommendations regarding duration, composition, and management."
    explanation: International consensus designates KDT as standard of care.
- name: Modified Atkins Diet and other ketogenic dietary variants
  description: >-
    Less restrictive ketogenic dietary therapies (modified Atkins diet,
    medium-chain-triglyceride diet, low-glycaemic-index treatment) are used,
    particularly in older children and adults, and in a large family survey
    gave seizure-freedom rates comparable to the classic 4:1 diet. They act by
    the same ketone-supply mechanism as the classic diet.
  action_category: THERAPEUTIC
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: modified Atkins and other ketogenic dietary therapies
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_mechanisms:
  - target: Cerebral Glucose Energy Deficit
    treatment_effect: BYPASSES
    description: Supplies ketone bodies as an alternative cerebral fuel, as the classic ketogenic diet does.
  evidence:
  - reference: PMID:26803281
    reference_title: "Use of dietary therapies amongst patients with GLUT1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diets used were extremely varied: 59 were treated with the classic ketogenic diet (KD), 29 with the Modified Atkins Diet (MAD), 4 with the Medium-chain Triglyceride (MCT) Diet and 2 with the low glycemic index treatment."
    explanation: Documents real-world use of the dietary variants.
  - reference: PMID:26803281
    reference_title: "Use of dietary therapies amongst patients with GLUT1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was an equal percentage of children seizure-free receiving the KD/MCT Diets compared to the MAD/Low Glycemic Index Treatment (74% vs. 63%, p=0.30)."
    explanation: No significant difference in seizure freedom between classic and less restrictive diets in this parent-reported survey.
- name: Triheptanoin
  description: >-
    Triheptanoin is an anaplerotic odd-chain (C7) medium-chain triglyceride
    that provides Krebs-cycle substrates and an alternative brain fuel
    independent of GLUT1. An open-label study reported marked reduction of
    non-epileptic paroxysmal manifestations and normalized brain bioenergetics,
    but a subsequent randomized placebo-controlled trial did not show a
    significant reduction in seizure frequency in patients not on a ketogenic
    diet, leaving its efficacy for the epilepsy phenotype unproven.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Triheptanoin
      term:
        id: CHEBI:757060
        label: triheptanoin
  action_category: THERAPEUTIC
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Cerebral Glucose Energy Deficit
    treatment_effect: BYPASSES
    evidence:
    - reference: PMID:26536893
      reference_title: "Triheptanoin dramatically reduces paroxysmal motor disorder in patients with GLUT1 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Treatment with triheptanoin resulted in a 90% clinical improvement in non-epileptic paroxysmal manifestations and a normalised brain bioenergetics profile in patients with GLUT1-DS."
      explanation: Open-label study demonstrates triheptanoin supplies anaplerotic Krebs-cycle substrates that bypass the GLUT1 defect and normalize brain energy metabolism.
  evidence:
  - reference: PMID:26536893
    reference_title: "Triheptanoin dramatically reduces paroxysmal motor disorder in patients with GLUT1 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with triheptanoin resulted in a 90% clinical improvement in non-epileptic paroxysmal manifestations and a normalised brain bioenergetics profile in patients with GLUT1-DS."
    explanation: Open-label pilot study supports triheptanoin efficacy against the non-epileptic paroxysmal (movement-disorder) manifestations of GLUT1DS.
  - reference: PMID:35441706
    reference_title: "A randomized, double-blind trial of triheptanoin for drug-resistant epilepsy in glucose transporter 1 deficiency syndrome."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Triheptanoin did not significantly reduce seizure frequency in patients with Glut1DS not on the ketogenic diet."
    explanation: Randomized double-blind placebo-controlled trial qualifies the treatment claim by showing no significant seizure-frequency benefit for the epilepsy phenotype.
- name: Anti-Seizure Medications to Avoid
  description: >-
    In individuals on ketogenic diet therapy, valproic acid should be avoided
    because it increases the risk of a Reye-like illness and may also inhibit
    glucose transport; phenobarbital, acetazolamide, topiramate, and zonisamide
    may be relatively contraindicated as adjunctive treatment. This is a
    "circumstance to avoid" (GeneReviews Agents/Circumstances to Avoid section)
    rather than a recommended treatment; retained here as a treatment-adjacent
    drug-safety note.
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Agents/circumstances to avoid: In individuals on KDTs: (1) avoidance of treatment of seizures with valproic acid, because it increases the risk of a Reye-like illness and may also inhibit glucose transport; (2) other anti-seizure medications (ASMs) including phenobarbital, acetazolamide, topiramate, and zonisamide may be relatively contraindicated as adjunctive treatment."
    explanation: GeneReviews Agents/Circumstances to Avoid section directly documents these drug-safety warnings for GLUT1DS patients on ketogenic diet therapy.
- name: Multidisciplinary Supportive Care
  description: >-
    Physical medicine and rehabilitation, physical therapy, occupational
    therapy, speech and language therapy, educational programs, and clinical
    genetics/genetic counseling, alongside routine neurology follow-up to
    monitor response to ketogenic diet therapy and identify new manifestations.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Supportive care: In addition to educational programs to address the individual's needs, multidisciplinary care by specialists in neurology familiar with KDTs, physical medicine and rehabilitation, physical therapy, occupational therapy, speech and therapy, and clinical genetics and genetic counseling."
    explanation: GeneReviews management section documents the multidisciplinary supportive care regimen recommended alongside ketogenic diet therapy.
- name: Genetic Counseling
  description: >-
    Each child of an individual with autosomal dominant Glut1DS has a 50% chance
    of inheriting the SLC2A1 variant; because about 90% of cases are de novo
    and transmitting parents may be mildly affected or unaffected (possible
    mosaicism), parental testing is informative. Prenatal and preimplantation
    testing are possible once the familial variant is known.
  action_category: COUNSELING_INFORMATIONAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Each child of an individual with autosomal dominant Glut1DS has a 50% chance of inheriting the SLC2A1 pathogenic variant and being clinically affected."
    explanation: Recurrence risk for offspring of an affected individual.
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Once the SLC2A1 pathogenic variant(s) have been identified in an affected family member, prenatal and preimplantation genetic testing for Glut1DS are possible."
    explanation: Reproductive options.
- name: Evaluation of At-Risk Relatives and Early Treatment
  description: >-
    Because early ketogenic diet therapy improves seizure control and long-term
    neurological outcome, at-risk newborns, infants and other relatives of a
    proband should be tested for the familial SLC2A1 variant so that treatment
    can begin before or at the first manifestations.
  action_category: SCREENING
  treatment_term:
    preferred_term: targeted SLC2A1 variant testing of at-risk relatives
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is appropriate to evaluate at-risk newborns, infants, and other relatives of a proband to identify as early as possible those who would benefit from initiation of treatment and preventive measures."
    explanation: GeneReviews recommendation to evaluate relatives at risk.
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Early initiation of KDTs, ideally in infancy, results in better seizure control and improves long-term neurologic outcome."
    explanation: The rationale for presymptomatic identification.
- name: Neurological Surveillance
  description: >-
    Routinely scheduled neurology review to judge response to ketogenic diet
    therapy and to detect new manifestations, especially the movement disorder
    that emerges in later childhood and adolescence, with follow-up by the
    treating physical, occupational and speech-language therapists.
  action_category: MONITORING
  treatment_term:
    preferred_term: scheduled neurological re-evaluation
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Surveillance: Routinely scheduled evaluations with a neurologist (to determine response to KDTs and identify any new manifestations) as well as follow up per treating physical therapists, occupational therapists, and speech-language therapists."
    explanation: GeneReviews surveillance recommendation.
- name: AAV9-Mediated GLUT1 Gene Replacement (Experimental)
  description: >-
    Experimental, preclinical only. In Glut1-deficient mice, pre-symptomatic
    AAV9-mediated repletion of GLUT1 averts the brain microvascular defect and
    prevents disease, and repletion in early-symptomatic animals still
    restores the microvasculature and ameliorates disease, whereas adult
    repletion gives no benefit. The 2020 consensus notes that interventions to
    restore GLUT1 protein content and function are in development. No human
    trial of GLUT1 gene replacement is cited here.
  action_category: THERAPEUTIC
  therapeutic_modality: GENE_THERAPY
  treatment_term:
    preferred_term: AAV9 SLC2A1 gene replacement
    term:
      id: NCIT:C15238
      label: Gene Therapy
  target_mechanisms:
  - target: SLC2A1 Loss-of-Function Variant
    treatment_effect: RESTORES
    description: Vector-delivered SLC2A1 restores GLUT1 protein content in the deficient brain.
    evidence:
    - reference: PMID:32913944
      reference_title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Ongoing research has identified future interventions to restore Glut1 protein content and function."
      explanation: Consensus statement records protein-restoring interventions as the direction of therapeutic research.
  - target: Arrested Cerebral Angiogenesis and Microvascular Diminution
    treatment_effect: RESTORES
    description: Early GLUT1 repletion restores the cerebral microvasculature in model mice.
    evidence:
    - reference: PMID:28106060
      reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Glut1 repletion in early-symptomatic mutants that have experienced sustained periods of low brain glucose nevertheless restores the cerebral microvasculature and ameliorates disease."
      explanation: Direct rescue of the vascular node by gene replacement in symptomatic mice.
  evidence:
  - reference: PMID:28106060
    reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Timely Glut1 repletion may thus constitute an effective treatment for Glut1 DS."
    explanation: The authors' conclusion from the temporal rescue series; preclinical.
prevalence:
- population: Danish population (SLC2A1 mutation carriers)
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 1.2
  notes: >-
    Estimated frequency of SLC2A1 mutations in the Danish population of
    approximately 1:83,000 (100000/83000 = 1.2 per 100,000), derived from
    mutation screening of absence-epilepsy and other cohorts; the authors call
    it an estimate of the frequency of GLUT1 deficiency syndrome and it is
    likely an underestimate given underdiagnosis.
  evidence:
  - reference: PMID:26537434
    reference_title: "The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy, and the estimated frequency of GLUT1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We estimated the frequency of SLC2A1 mutations in the Danish population to be approximately 1:83,000."
    explanation: Population-level frequency estimate.
- population: Scotland, children presenting with seizures before age 3 (live births)
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 4.13
  rate_low: 1.07
  rate_high: 7.19
  notes: >-
    Minimum incidence of SLC2A1-related epilepsy of 1 per 24,300 live births
    (4.13 per 100,000; 95% CI 1.07-7.19) in a prospective national cohort of
    childhood-onset epilepsy; captures only the epilepsy-presenting fraction
    of Glut1DS diagnosed by age 3, so it is a floor for the birth prevalence
    of the syndrome as a whole.
  evidence:
  - reference: PMID:31302675
    reference_title: "Incidence and phenotypes of childhood-onset genetic epilepsies: a prospective population-based national cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "KCNQ2: 1 per 17 000 (5.89/100 000; 95% confidence interval 2.24-9.56) and SLC2A1: 1 per 24 300 (4.13/100 000; 95% confidence interval 1.07-7.19)."
    explanation: Prospective population-based incidence of SLC2A1-related childhood epilepsy.
- population: Japan (nationwide survey of board-certified pediatric neurologists)
  measure_type: CASES_IN_LITERATURE
  prevalence_class: RARE
  notes: >-
    National case-ascertainment count (57 reported patients, 33 with detailed
    data), informative for rarity but not a normalised rate; likely an
    underestimate due to underdiagnosis.
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A questionnaire to survey the number of genetically and clinically confirmed cases of GLUT-1DS was sent to 1018 board-certified pediatric neurologists, which resulted in 57 patients being reported."
    explanation: Nationwide Japanese survey ascertained 57 genetically/clinically confirmed cases nationally, informative for rarity but not directly convertible to a per-100,000 rate without further population denominators.
datasets: []
discussions:
- discussion_id: gap_glut1_energy_deficit_to_hyperexcitability_intermediate
  prompt: >-
    Which cellular intermediate translates chronic cerebral glucose
    under-supply into the specific pattern of neuronal hyperexcitability and
    hypersynchrony seen in Glut1DS — failure of the astrocyte-neuron lactate
    shuttle, selective energy vulnerability of fast-spiking GABAergic
    interneurons, disturbed adenosine/thalamocortical signaling, or a
    combination?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Cerebral Glucose Energy Deficit
  - pathophysiology#Neuronal Hyperexcitability and Hypersynchrony
  rationale: >-
    The causal edge from "Cerebral Glucose Energy Deficit" to "Neuronal
    Hyperexcitability and Hypersynchrony" is curated as
    INDIRECT_KNOWN_INTERMEDIATES, but the identity of that intermediate is not
    actually established. Glucose reaches the brain almost exclusively through
    GLUT1, yet why a global fuel shortfall produces the particular Glut1DS
    electroclinical signature (including 2.5-4 Hz generalized spike-wave and
    absence-like seizures) rather than diffuse depression is unresolved.
    Candidate mechanisms — astrocytic lactate-supply failure, preferential ATP
    starvation of parvalbumin interneurons whose high firing rates make them
    metabolically expensive, and adenosine-mediated network effects — carry
    different therapeutic implications, so resolving the intermediate would
    materially sharpen the mechanism model.
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Glucose, the essential metabolic fuel for the brain, is transported into the brain exclusively by the protein glucose transporter type 1 (Glut1) across the endothelial cells forming the blood-brain barrier (BBB)."
    explanation: >-
      Establishes the exclusive GLUT1 route for cerebral glucose, framing why
      the deficit is global; the open question is which cell type first
      converts that global shortfall into focal-onset hyperexcitability.
  - reference: PMID:16497725
    reference_title: "A mouse model for Glut-1 haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "GLUT-1+/- mice have epileptiform discharges on electroencephalography (EEG), impaired motor activity, incoordination, hypoglycorrhachia, microencephaly, decreased brain glucose uptake as measured by positron emission tomography (PET) scan and decreased brain Glut-1 expression by western blot (66%)."
    explanation: >-
      Provides a tractable in vivo system in which the epileptiform phenotype is
      reproduced, i.e., a model where the missing cellular intermediate could be
      dissected with cell-type-specific readouts.
  proposed_experiments:
  - experiment_id: exp_glut1_celltype_metabolic_intermediate
    name: Cell-type-resolved metabolic-to-excitability mapping in Glut1 haploinsufficiency
    description: >-
      In GLUT-1+/- mice and patient-derived iPSC neuron-astrocyte co-cultures,
      simultaneously measure astrocytic lactate output, interneuron-specific
      ATP/metabolic stress, and network excitability, then test whether
      interneuron-targeted metabolic rescue (or lactate supplementation)
      normalizes hypersynchrony independently of restoring bulk neuronal
      glucose.
    experiment_type:
      preferred_term: cell-type-resolved metabolic and excitability mapping experiment
    perturbations:
    - name: Interneuron-selective metabolic rescue
      target: pathophysiology#Cerebral Glucose Energy Deficit
      description: >-
        Selectively supply alternative fuel (lactate/ketone) or restore GLUT1 in
        astrocytes vs interneurons vs principal neurons to identify the
        rate-limiting compartment.
    readouts:
    - name: Network hyperexcitability
      target: pathophysiology#Neuronal Hyperexcitability and Hypersynchrony
      assays:
      - preferred_term: multielectrode array recording
      - preferred_term: electroencephalography
      direction: POSITIVE
    controls:
    - name: Wild-type co-cultures
      description: GLUT1-normal neuron-astrocyte co-cultures under matched glucose conditions.
    decision_criterion: >-
      An intermediate is supported if rescuing a single cell compartment (e.g.,
      astrocytic lactate supply or interneuron energetics) normalizes network
      excitability while leaving bulk neuronal glucose uptake unchanged.
    would_support:
    - pathophysiology#Neuronal Hyperexcitability and Hypersynchrony

- discussion_id: gap_glut1_ketogenic_seizure_vs_neurodevelopment_dissociation
  prompt: >-
    Why does ketone-based fuel substitution robustly control seizures in Glut1DS
    yet only partially rescue the movement disorder and cognitive impairment —
    is the residual deficit a missed developmental window, regional or
    functional under-supply of ketone-derived fuel, or a non-fuel role of
    glucose that ketones cannot replace?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Cerebral Glucose Energy Deficit
  - pathophysiology#Impaired Neurodevelopment and Movement Disorder
  - pathophysiology#Recurrent Pharmacoresistant Seizures
  rationale: >-
    Ketogenic diet therapy is the mainstay treatment and supplies ketone bodies
    as an alternative cerebral fuel that bypasses the GLUT1 transport defect. In
    practice it controls seizures far more completely than it reverses the
    paroxysmal movement disorder, ataxia/dystonia, or cognitive outcome, and
    outcomes are consistently better with earlier treatment. Whether the
    residual, seizure-independent morbidity reflects irreversible injury
    incurred before diagnosis (a developmental-window effect), inadequate
    ketone delivery to specific circuits, or a role of glucose beyond bulk fuel
    (e.g., biosynthetic/pentose-phosphate demands) is unresolved — and it
    determines whether earlier or supplemental (e.g., anaplerotic) therapy could
    close the gap.
  evidence:
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Targeted therapy: Age-specific KDTs primarily provide a supplemental fuel, namely, ketone bodies, for brain energy metabolism."
    explanation: >-
      Establishes that ketogenic therapy acts by fuel substitution, framing the
      question of why fuel substitution rescues seizures more completely than
      neurodevelopmental outcomes.
  - reference: PMID:20301603
    reference_title: "Glucose Transporter Type 1 Deficiency Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Typically, the earlier the treatment the better the long-term clinical outcome."
    explanation: >-
      Documents the developmental-window dependence of outcome, one of the
      competing explanations for the residual neurodevelopmental deficit.
  - reference: PMID:28106060
    reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Restoring the protein to 2-week old mutants, in which certain disease characteristics are readily apparent, is less effective in shaping normal brain microvasculature."
    explanation: >-
      Model-organism evidence that later restoration incompletely reverses
      structural brain defects, supporting a developmental-window contribution
      to residual, seizure-independent morbidity.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The effect on neurodevelopment appears less impressive."
    explanation: >-
      Review of 84 cases records the seizure-versus-neurodevelopment
      dissociation that this gap is about.
  - reference: PMID:40405536
    reference_title: "Glut1 Deficiency Syndrome: Novel Pathomechanisms, Current Concepts, and Challenges."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "KDT are ineffective in some patients for reasons yet unknown."
    explanation: >-
      2025 review states that the determinants of KDT non-response are unknown,
      confirming the gap remains open.
  proposed_experiments:
  - experiment_id: exp_glut1_treatment_timing_endpoint_dissociation
    name: Treatment-timing dissociation of seizure vs neurodevelopmental endpoints
    description: >-
      In GLUT-1+/- mice, initiate ketogenic therapy or GLUT1 repletion across a
      graded set of ages and measure seizure/EEG control separately from motor
      coordination, brain growth, and cognitive-behavioral endpoints, testing
      whether the neurodevelopmental endpoints have an earlier closing window
      than the seizure endpoint.
    experiment_type:
      preferred_term: treatment-timing endpoint dissociation experiment
    perturbations:
    - name: Age-graded ketogenic/repletion therapy
      target: pathophysiology#Cerebral Glucose Energy Deficit
      description: Start fuel substitution or GLUT1 repletion at several developmental ages.
    readouts:
    - name: Seizure control
      target: pathophysiology#Recurrent Pharmacoresistant Seizures
      assays:
      - preferred_term: electroencephalography
      direction: NEGATIVE
    - name: Motor and neurodevelopmental outcome
      target: pathophysiology#Impaired Neurodevelopment and Movement Disorder
      assays:
      - preferred_term: behavioral assay
      direction: POSITIVE
    controls:
    - name: Untreated mutants and wild-type
      description: Matched untreated GLUT-1+/- and wild-type animals.
    decision_criterion: >-
      A developmental-window explanation is supported if neurodevelopmental
      endpoints lose responsiveness at an earlier treatment age than seizure
      control does; a fuel-limitation explanation is supported if both endpoints
      respond equally whenever adequate alternative fuel is supplied.
    would_support:
    - pathophysiology#Impaired Neurodevelopment and Movement Disorder

- discussion_id: gap_glut1_mouse_model_paroxysmal_phenotype_fidelity
  prompt: >-
    Does the GLUT-1+/- mouse faithfully model the full human Glut1DS phenotype —
    in particular the paroxysmal features (paroxysmal eye-head movements,
    exercise-induced dyskinesia) and the spectrum extending to early-onset
    absence epilepsy and movement-disorder-predominant presentations — or does
    it capture mainly the core seizure/hypoglycorrhachia/microcephaly triad?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Neuronal Hyperexcitability and Hypersynchrony
  - pathophysiology#Impaired Neurodevelopment and Movement Disorder
  rationale: >-
    The GLUT-1+/- mouse reproduces epileptiform EEG, motor impairment,
    hypoglycorrhachia and microencephaly and is described as mimicking the
    classical human presentation, making it the workhorse model for Glut1DS.
    But the human disorder is defined as much by paroxysmal, activity- and
    fasting-triggered phenomena and by a wide phenotypic spectrum (paroxysmal
    exercise-induced dyskinesia, early-onset absence epilepsy, isolated
    movement disorder) that depend on human-specific behavioral repertoire and
    developmental glucose-demand timing. Whether these paroxysmal and
    spectrum-defining features are recapitulated — and thus whether the model
    can validate therapies aimed at them — is the open translational question,
    distinct from a claim that evidence is simply absent.
  evidence:
  - reference: PMID:16497725
    reference_title: "A mouse model for Glut-1 haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The GLUT-1+/- murine phenotype mimics the classical human presentation of Glut-1 DS."
    explanation: >-
      Documents fidelity to the classical core phenotype; the open question is
      whether the paroxysmal and spectrum-defining human features are also
      captured.
  proposed_experiments:
  - experiment_id: exp_glut1_paroxysmal_phenotype_provocation
    name: Provocation phenotyping of paroxysmal features in Glut1 models
    description: >-
      Deep-phenotype GLUT-1+/- mice and patient-derived neuronal/BBB models
      under physiological provocations (fasting, exertion, post-prandial state)
      to test for movement-triggered dyskinesia-like events and absence-like
      spike-wave, comparing directly against the documented human paroxysmal
      spectrum.
    experiment_type:
      preferred_term: provocation phenotyping experiment
    readouts:
    - name: Paroxysmal movement and absence-like events
      target: pathophysiology#Impaired Neurodevelopment and Movement Disorder
      assays:
      - preferred_term: behavioral assay
      - preferred_term: electroencephalography
      direction: POSITIVE
    controls:
    - name: Wild-type littermates under identical provocation
      description: Matched wild-type animals exposed to the same fasting/exertion protocols.
    decision_criterion: >-
      Human fidelity for the paroxysmal spectrum is supported if physiological
      provocations reproducibly elicit movement-triggered dyskinesia-like events
      and absence-like discharges in mutants but not controls; absence of such
      events flags a genuine human/model mismatch for these features.
    would_support:
    - pathophysiology#Impaired Neurodevelopment and Movement Disorder

- discussion_id: controversy_glut1_genotype_phenotype_correlation
  prompt: >-
    Does SLC2A1 variant class (truncating or deletion versus missense) predict
    clinical severity in Glut1DS, or is severity set only by residual
    transporter activity irrespective of variant class?
  kind: CONTROVERSY
  status: OPEN
  attaches_to:
  - pathophysiology#SLC2A1 Loss-of-Function Variant
  - genetic#SLC2A1
  - has_subtypes#
  rationale: >-
    The largest laboratory series reported that mutation type was related to
    the severity of intellectual disability and to the presence of complex
    movement disorders, whereas the Columbia series of 16 new patients and the
    2007 review of 84 published cases found no correlation between genotype,
    phenotype and biochemical measures, and the French national cohort found
    overlapping phenotypes that resist genotype-phenotype assignment. What
    does correlate across series is residual erythrocyte glucose uptake, which
    even determines whether a family presents as dominant or recessive. The
    resolution matters for counselling and for how the has_subtypes entries are
    read: they are phenotype clusters on a continuum, not variant-defined
    entities.
  evidence:
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Type of mutation was related to the severity of mental retardation and the presence of complex movement disorders."
    explanation: Supports the claim that variant class predicts severity, in 57 genetically confirmed patients.
  - reference: PMID:15622525
    reference_title: "Glut-1 deficiency syndrome: clinical, genetic, and therapeutic aspects."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "There were no obvious correlations between phenotype, genotype, or biochemical measures."
    explanation: Refutes the claim in an independent series of 16 patients.
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Autosomal dominant transmission and several mutational hot spots have been identified, but phenotype-genotype correlations are not yet apparent."
    explanation: Review of 84 published cases found no apparent correlation.
  - reference: PMID:26193382
    reference_title: "From splitting GLUT1 deficiency syndromes to overlapping phenotypes."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "thus making it difficult to identify definite genotype-phenotype correlations"
    explanation: French national cohort argues phenotypes overlap along a continuum rather than segregating by genotype.
  - reference: PMID:22190371
    reference_title: "Glut1 deficiency syndrome and erythrocyte glucose uptake assay."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We also noted a significant correlation between the mean erythrocyte 3-OMG uptake and clinical severity (R(2) = 0.94)."
    explanation: Supports the alternative position that residual transporter function, rather than variant class, predicts severity.
mechanistic_hypotheses:
- hypothesis_group_id: canonical_glut1_energy_deficit
  hypothesis_label: Blood-brain-barrier glucose transport failure causes cerebral energy deficit
  status: CANONICAL
  description: >-
    Haploinsufficient GLUT1 at the brain endothelium limits glucose delivery,
    producing hypoglycorrhachia and a chronic brain energy deficit that is
    greatest when developmental glucose demand peaks; the deficit drives
    cortical hyperexcitability, impaired neurodevelopment and, under exertion
    or fasting, episodic basal ganglia failure. Ketogenic diet therapy works by
    supplying ketone bodies that bypass the transporter.
  evidence:
  - reference: PMID:32913944
    reference_title: "Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Glut1 deficiency syndrome (Glut1DS) is a brain energy failure syndrome caused by impaired glucose transport across brain tissue barriers."
    explanation: Consensus definition of the canonical mechanism.
  - reference: PMID:9462754
    reference_title: "GLUT-1 deficiency syndrome caused by haploinsufficiency of the blood-brain barrier hexose carrier."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These symptoms suggested the existence of a defect in glucose transport across the blood brain barrier."
    explanation: The founding formulation of the hypothesis, confirmed by the mutations reported in the same paper.
- hypothesis_group_id: microvascular_developmental_defect
  hypothesis_label: GLUT1 deficiency arrests cerebral angiogenesis, adding a structural microvascular deficit
  status: EMERGING
  description: >-
    Beyond its fuel-transport role, endothelial GLUT1 is required for postnatal
    cerebral angiogenesis; in model mice low GLUT1 arrests microvessel growth
    and early, but not late, repletion averts disease. The consensus statement
    has adopted impaired microvascular development as a complication of delayed
    treatment, but the human contribution is unmeasured, and this model may
    partly explain why fuel substitution rescues seizures more completely than
    cognition.
  evidence:
  - reference: PMID:28106060
    reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We used model mice to demonstrate that low Glut1 protein arrests cerebral angiogenesis, resulting in a profound diminution of the brain microvasculature without compromising the blood-brain barrier."
    explanation: Primary mouse evidence for the hypothesis.
  - reference: PMID:40405536
    reference_title: "Glut1 Deficiency Syndrome: Novel Pathomechanisms, Current Concepts, and Challenges."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Research reaches beyond the concept of brain energy depletion by impaired GLUT1-mediated glucose transfer across the blood-brain barrier."
    explanation: 2025 review frames non-fuel mechanisms as an active, still-emerging area.
- hypothesis_group_id: erythrocyte_cation_leak_hemolysis
  hypothesis_label: Pore-region GLUT1 alleles cause hemolysis through a cation leak
  status: EMERGING
  description: >-
    Specific pore-region SLC2A1 alleles render the mutant transporter permeable
    to sodium, potassium and calcium; the resulting erythrocyte electrolyte
    disturbance produces echinocytosis and hemolytic anemia. Alleles that only
    reduce transport do not cause hemolysis, so this is an allele-specific gain
    of an abnormal function layered on haploinsufficiency, established in one
    family plus heterologous expression.
  applies_to_subtypes:
  - GLUT1 DS with Paroxysmal Exertion-Induced Dyskinesia
  evidence:
  - reference: PMID:18451999
    reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the hemolysis with echinocytosis may result from alterations in intracellular electrolytes caused by a cation leak through mutant GLUT1"
    explanation: The authors' mechanistic proposal from oocyte and erythrocyte studies.
animal_models:
- name: Glut1 haploinsufficient (GLUT-1+/-) mouse
  species: Mouse
  genotype: Slc2a1 heterozygous null, targeted disruption of the promoter and exon 1
  category: Genetically engineered
  genes:
  - preferred_term: SLC2A1
    term:
      id: hgnc:11005
      label: SLC2A1
  publication: PMID:16497725
  description: >-
    The first mouse model of Glut1DS: heterozygous disruption of the Glut1
    promoter and exon 1 reduces brain Glut1 to 66% of wild type and produces
    epileptiform EEG discharges, impaired motor activity and incoordination,
    hypoglycorrhachia, microencephaly and reduced brain glucose uptake on PET,
    mimicking the classical human presentation.
  evidence:
  - reference: PMID:16497725
    reference_title: "A mouse model for Glut-1 haploinsufficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "This GLUT-1+/- mouse model creates an opportunity to investigate Glut-1 function, to examine the pathophysiology of Glut-1 DS in vivo and to evaluate new treatment strategies."
    explanation: The authors state the model's intended use for studying Glut1DS pathophysiology and testing treatments.
  associated_phenotypes:
  - Epileptiform EEG discharges
  - Hypoglycorrhachia
  - Microencephaly
  - Impaired motor activity and incoordination
  - Decreased brain glucose uptake on PET
  modeled_mechanisms:
  - target: SLC2A1 Loss-of-Function Variant
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: MOLECULAR
    description: The heterozygous null allele reproduces the haploinsufficient state, with brain Glut1 reduced to 66%.
    readouts:
    - name: Brain Glut1 protein by western blot
      target: SLC2A1 Loss-of-Function Variant
      direction: DECREASED
      interpretation: 66% of wild-type brain Glut1 quantifies the haploinsufficiency the model carries.
      evidence:
      - reference: PMID:16497725
        reference_title: "A mouse model for Glut-1 haploinsufficiency."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "decreased brain Glut-1 expression by western blot (66%)"
        explanation: Reports the measurement.
    evidence:
    - reference: PMID:16497725
      reference_title: "A mouse model for Glut-1 haploinsufficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We generated a heterozygous haploinsufficient mouse model by targeted disruption of the promoter and exon 1 regions of the mouse GLUT-1 gene."
      explanation: Defines the allele as a haploinsufficiency model.
  - target: Reduced GLUT1 Transporter Function at the Blood-Brain Barrier
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: TISSUE
    description: Reduced brain glucose uptake and hypoglycorrhachia reproduce the barrier transport failure.
    readouts:
    - name: Brain glucose uptake by FDG-PET
      target: Reduced GLUT1 Transporter Function at the Blood-Brain Barrier
      direction: DECREASED
      interpretation: Whole-brain PET uptake reports transendothelial glucose delivery in vivo.
    - name: CSF glucose concentration
      target: Reduced GLUT1 Transporter Function at the Blood-Brain Barrier
      direction: DECREASED
      interpretation: Hypoglycorrhachia in the mouse mirrors the human diagnostic finding.
    evidence:
    - reference: PMID:16497725
      reference_title: "A mouse model for Glut-1 haploinsufficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "hypoglycorrhachia, microencephaly, decreased brain glucose uptake as measured by positron emission tomography (PET) scan"
      explanation: Reports both readouts.
  - target: Neuronal Hyperexcitability and Hypersynchrony
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: Spontaneous epileptiform EEG discharges reproduce the hyperexcitable network state.
    limitations: >-
      Discharges are reported, not the human electroclinical syndrome; whether
      the mouse shows absence-like 2.5-4 Hz spike-wave or a food-responsive EEG
      is not stated in the abstract.
    readouts:
    - name: Epileptiform EEG discharges
      target: Neuronal Hyperexcitability and Hypersynchrony
      direction: INCREASED
      interpretation: Electrographic evidence of cortical hypersynchrony in the mutant.
    evidence:
    - reference: PMID:16497725
      reference_title: "A mouse model for Glut-1 haploinsufficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "GLUT-1+/- mice have epileptiform discharges on electroencephalography (EEG)"
      explanation: Reports the EEG finding.
  - target: Impaired Neurodevelopment and Movement Disorder
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: Microencephaly, impaired motor activity and incoordination reproduce the growth and motor consequences.
    limitations: >-
      Mouse motor impairment does not reproduce human dystonia, spasticity or
      paroxysmal exertion-induced dyskinesia, and rodent learning measures
      differ in kind from human intellectual disability; see the
      HUMAN_MODEL_MISMATCH discussion on paroxysmal phenotype fidelity.
    readouts:
    - name: Brain size, microencephaly
      target: Impaired Neurodevelopment and Movement Disorder
      direction: DECREASED
      interpretation: Reduced brain growth parallels human acquired microcephaly.
    - name: Motor activity and coordination
      target: Impaired Neurodevelopment and Movement Disorder
      direction: DECREASED
      interpretation: Impaired motor activity and incoordination parallel the human motor disorder.
    evidence:
    - reference: PMID:16497725
      reference_title: "A mouse model for Glut-1 haploinsufficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The GLUT-1+/- murine phenotype mimics the classical human presentation of Glut-1 DS."
      explanation: The authors' fidelity claim, made for the classical rather than the paroxysmal phenotype.
- name: Glut1 Rgsc200 ENU missense mouse
  species: Mouse
  genotype: Slc2a1 Rgsc200 heterozygous missense at residue 324; homozygotes embryonic lethal
  category: Chemically induced by ENU mutagenesis
  genes:
  - preferred_term: SLC2A1
    term:
      id: hgnc:11005
      label: SLC2A1
  publication: PMID:31399478
  description: >-
    An ENU-induced missense allele at residue 324 of Glut1. Heterozygotes show
    decreased CSF glucose, contextual learning deficits, reduced body size,
    seizure-like behaviour, spontaneous EEG abnormalities and a longer wake and
    shorter NREM sleep pattern; FDG-PET kinetics show reduced glucose transport
    with enhanced hexokinase activity. Homozygotes die in utero, paralleling
    the presumed lethality of complete GLUT1 loss in humans.
  evidence:
  - reference: PMID:31399478
    reference_title: "A new mouse model of GLUT1 deficiency syndrome exhibits abnormal sleep-wake patterns and alterations of glucose kinetics in the brain."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These results indicate that a Glut1Rgsc200 mutant is a useful tool for elucidating the molecular mechanisms of GLUT1DS."
    explanation: The authors' conclusion that this ENU allele is an informative model of GLUT1DS.
  associated_phenotypes:
  - Decreased cerebrospinal fluid glucose
  - Seizure-like behaviour and abnormal EEG
  - Contextual learning deficit
  - Reduced body size
  - Prolonged wake and shortened NREM sleep
  - Embryonic lethality of homozygotes
  modeled_mechanisms:
  - target: Cerebral Glucose Energy Deficit
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: Reduced brain glucose transport with compensatory hexokinase upregulation reproduces the supply-limited energy state.
    limitations: >-
      A missense allele of unknown residual transport, so the depth of the
      deficit is not calibrated against the human haploinsufficient range, and
      the enhanced hexokinase activity is a mouse observation not yet shown in
      patients.
    readouts:
    - name: Brain glucose transport by FDG-PET kinetics
      target: Cerebral Glucose Energy Deficit
      direction: DECREASED
      interpretation: The reduced transport constant reports the supply limitation.
    - name: Cerebrospinal fluid glucose
      target: Cerebral Glucose Energy Deficit
      direction: DECREASED
      interpretation: Hypoglycorrhachia in the mutant.
    evidence:
    - reference: PMID:31399478
      reference_title: "A new mouse model of GLUT1 deficiency syndrome exhibits abnormal sleep-wake patterns and alterations of glucose kinetics in the brain."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "revealed that glucose transportation was reduced, whereas hexokinase activity and glucose metabolism were enhanced"
      explanation: Reports the PET kinetic result.
  - target: Neuronal Hyperexcitability and Hypersynchrony
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: ORGANISM
    description: Spontaneous EEG abnormalities and seizure-like behaviour both occur, but were not observed concurrently.
    limitations: >-
      EEG abnormality and seizure-like behaviour were dissociated in time, so
      electroclinical seizures were not demonstrated in this model.
    readouts:
    - name: Spontaneous EEG abnormality
      target: Neuronal Hyperexcitability and Hypersynchrony
      direction: INCREASED
      interpretation: Electrographic hyperexcitability without confirmed concurrent behavioural seizures.
    evidence:
    - reference: PMID:31399478
      reference_title: "A new mouse model of GLUT1 deficiency syndrome exhibits abnormal sleep-wake patterns and alterations of glucose kinetics in the brain."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "During EEG recording, the abnormality occurred spontaneously, whereas the seizure-like phenotypes were not observed at the same time."
      explanation: Reports the dissociation that limits fidelity.
- name: Glut1-deficient mouse with AAV9-mediated Glut1 repletion
  species: Mouse
  genotype: Slc2a1-deficient model mice, with or without AAV9-mediated Glut1 repletion at defined ages
  category: Genetically engineered with gene-replacement rescue
  genes:
  - preferred_term: SLC2A1
    term:
      id: hgnc:11005
      label: SLC2A1
  publication: PMID:28106060
  description: >-
    Glut1-deficient model mice used to show that low Glut1 arrests cerebral
    angiogenesis and diminishes the brain microvasculature without breaching
    the blood-brain barrier, and that pre-symptomatic or early-symptomatic
    AAV9-mediated Glut1 repletion restores the microvasculature and prevents or
    ameliorates disease, whereas adult repletion does not.
  evidence:
  - reference: PMID:28106060
    reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Timely Glut1 repletion may thus constitute an effective treatment for Glut1 DS."
    explanation: The authors' translational conclusion from this rescue model, which is why the model is recorded here.
  associated_phenotypes:
  - Arrested cerebral angiogenesis and reduced brain microvasculature
  - Preserved blood-brain barrier integrity
  - Disease prevention after pre-symptomatic Glut1 repletion
  modeled_mechanisms:
  - target: Arrested Cerebral Angiogenesis and Microvascular Diminution
    relationship: RECAPITULATES
    fidelity: UNKNOWN
    model_scale: TISSUE
    description: The vascular phenotype is defined in this model; the human counterpart has not been measured.
    limitations: >-
      Fidelity cannot be graded because no human cerebral microvascular data
      exist for comparison, which is itself the subject of an open
      HUMAN_MODEL_MISMATCH question.
    readouts:
    - name: Cerebral microvascular density
      target: Arrested Cerebral Angiogenesis and Microvascular Diminution
      direction: DECREASED
      interpretation: Profound diminution of the brain microvasculature in mutants.
    evidence:
    - reference: PMID:28106060
      reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "low Glut1 protein arrests cerebral angiogenesis, resulting in a profound diminution of the brain microvasculature without compromising the blood-brain barrier"
      explanation: Defines the vascular phenotype.
  - target: Arrested Cerebral Angiogenesis and Microvascular Diminution
    relationship: RESCUES
    fidelity: UNKNOWN
    model_scale: TISSUE
    description: Early AAV9-Glut1 repletion restores the microvasculature; adult repletion does not.
    readouts:
    - name: Cerebral microvascular density after AAV9-Glut1 repletion
      target: Arrested Cerebral Angiogenesis and Microvascular Diminution
      direction: RESTORED
      interpretation: Restoration is age-dependent, defining a treatment window.
    evidence:
    - reference: PMID:28106060
      reference_title: "Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "pre-symptomatic, AAV9-mediated repletion of the protein averts brain microvasculature defects and prevents disease, whereas augmenting the protein late, during adulthood, is devoid of benefit"
      explanation: Reports the rescue and its temporal window.
environmental:
- name: Prolonged or strenuous exercise
  description: >-
    Sustained physical exertion is the defining trigger of paroxysmal
    exercise-induced dyskinesia and also aggravates paroxysmal ataxia, weakness
    and seizures. A standardised 6-Minute Walk Test reproducibly provokes
    episodes in long-term follow-up, and exertion sensitivity discriminates
    SLC2A1-positive from SLC2A1-negative patients.
  effect: Triggers paroxysmal dyskinesia and aggravates other paroxysmal events
  exposure_term:
    preferred_term: exposure to prolonged or strenuous exercise
    term:
      id: ECTO:6000031
      label: exposure to strenuous exercise
  evidence:
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The 6-Minute Walk Test captured gait disturbances and triggered paroxysmal exertional dyskinesia."
    explanation: A standardised exertion protocol provokes the episodes.
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The factors that frequently aggravated these events were hunger, exercise, fever, and fatigue, in that order."
    explanation: Exercise ranked second among aggravating factors in the nationwide cohort.
  influences_mechanisms:
  - target: Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Sustained muscular activity raises whole-body and cerebral glucose demand
      beyond what the haploinsufficient transporter can deliver to
      corticostriatal circuits.
    evidence:
    - reference: PMID:18451999
      reference_title: "GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "we propose that the dyskinesias result from an exertion-induced energy deficit that may cause episodic dysfunction of the basal ganglia"
      explanation: The proposed mechanism by which exertion acts on this node.
- name: Fasting and hunger
  description: >-
    Fasting or hunger lowers substrate supply to an already glucose-limited
    brain. Hunger was the most frequent aggravating factor for paroxysmal
    events in the Japanese nationwide cohort, fasting sensitivity discriminates
    SLC2A1-positive patients, and pre-prandial EEG abnormalities improve after
    feeding.
  effect: Exacerbates paroxysmal dyskinesia, seizures and EEG abnormalities
  exposure_term:
    preferred_term: fasting
  notes: >-
    Deliberately left unbound. An ECTO search for fasting, food deprivation and
    starvation returned no exposure term, and the XCO candidates are
    experimental-condition terms rather than exposure events, so no term beats
    a wrong one. Bind when ECTO adds a fasting exposure.
  evidence:
  - reference: PMID:25487684
    reference_title: "Nationwide survey of glucose transporter-1 deficiency syndrome (GLUT-1DS) in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The factors that frequently aggravated these events were hunger, exercise, fever, and fatigue, in that order."
    explanation: Hunger was the leading aggravating factor.
  - reference: PMID:26193382
    reference_title: "From splitting GLUT1 deficiency syndromes to overlapping phenotypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sensitivity to fasting or exertion in combination with those 3 main symptoms were the main differences between mutated and negative patients (p < 0.001)."
    explanation: Fasting sensitivity is a discriminating clinical feature of SLC2A1-positive patients.
  influences_mechanisms:
  - target: Exertion- and Fasting-Sensitive Basal Ganglia Energy Failure
    environmental_effect: EXACERBATES
    causal_link_type: DIRECT
    description: Reduced blood glucose availability lowers an already marginal cerebral supply.
    evidence:
    - reference: PMID:23443458
      reference_title: "Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise."
      explanation: Fasting as a trigger of the paroxysmal events produced by this node.
  - target: Neuronal Hyperexcitability and Hypersynchrony
    environmental_effect: EXACERBATES
    causal_link_type: DIRECT
    description: Pre-prandial worsening and post-prandial improvement of spike-wave discharges tie network hyperexcitability to the fuel state.
    evidence:
    - reference: PMID:17718830
      reference_title: "GLUT1 deficiency syndrome--2007 update."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Electroencephalography (EEG) may show 2.5-4Hz spike-waves improving on food intake."
      explanation: Feeding reverses the electrographic abnormality.
clinical_trials:
- name: NCT02014883
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Open-label phase II study of triheptanoin oil in eight patients with
    Glut1DS aged 7 to 47 years who declined or did not tolerate ketogenic
    diets, with baseline, treatment and withdrawal phases of two months each.
    It reported a 90% reduction in non-epileptic paroxysmal manifestations and
    a normalised brain bioenergetic profile on 31P-NMR. Completion is taken
    from the published results paper rather than from the registry summary.
  target_phenotypes:
  - preferred_term: Paroxysmal dyskinesia
    term:
      id: HP:0007166
      label: Paroxysmal dyskinesia
  evidence:
  - reference: clinicaltrials:NCT02014883
    reference_title: "Phase II Open Label Study Using Triheptanoin in Patients With Glucose Type 1 Transporter Deficiency GLUT1-DS"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The purpose of this project is to study the efficacy of triheptanoin oil in patients with GLUT1 deficiency syndrome."
    explanation: Registry statement of the trial's objective.
  - reference: PMID:26536893
    reference_title: "Triheptanoin dramatically reduces paroxysmal motor disorder in patients with GLUT1 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We performed an open-label pilot study with three phases of 2 months each (baseline, treatment and withdrawal) in eight patients with GLUT1-DS (7-47 years old) with non-epileptic paroxysmal manifestations."
    explanation: The results paper, which registers this NCT number, describes the trial design and population summarised here.
progression:
- phase: Infancy, epilepsy-dominant phase
  age_range: First months of life to early childhood
  notes: >-
    Seizures with a mean onset around 5 months, paroxysmal eye-head movements,
    developmental delay and deceleration of head growth dominate; 65% of
    classical patients present before 2 years. Seizures improve through
    childhood, particularly on ketogenic diet therapy.
  evidence:
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Epilepsy dominated infancy and improved during childhood."
    explanation: Longitudinal cohort defines the infantile epilepsy-dominant phase.
  - reference: PMID:20129935
    reference_title: "Glucose transporter-1 deficiency syndrome: the expanding clinical and genetic spectrum of a treatable disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the classical phenotype (84%), subdivided into early-onset (<2 years) (65%) and late-onset (18%)"
    explanation: Quantifies early versus late onset within the classical phenotype.
- phase: Childhood to adulthood, movement-disorder-dominant phase
  age_range: Later childhood, adolescence and adult life
  notes: >-
    Dystonia and paroxysmal exertion-induced dyskinesia emerge and become the
    dominant manifestations, with ataxia, spasticity, speech difficulty and
    intellectual disability persisting. Longitudinal neurological and
    neuropsychological measures remain stable rather than deteriorating, so the
    condition is chronic but not degenerative, and some individuals shift from
    a classic childhood phenotype to a movement-disorder-predominant adult one.
  evidence:
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We conclude that Glut1 deficiency syndrome is a chronic condition, dominated by epilepsy in infancy and by movement disorders thereafter."
    explanation: Defines the biphasic natural history.
  - reference: PMID:24789115
    reference_title: "Long-term clinical course of Glut1 deficiency syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All longitudinal outcomes remained stable over time."
    explanation: Stability across a mean of 14.2 years of follow-up.
  - reference: PMID:26193382
    reference_title: "From splitting GLUT1 deficiency syndromes to overlapping phenotypes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three patients evolved from a classic phenotype during early childhood to a movement disorder predominant phenotype at a late childhood/adulthood."
    explanation: Documents the phenotype shift occurring within individuals.
imaging_findings:
- name: Normal or nonspecific brain MRI
  modality: MRI
  description: >-
    Structural neuroimaging is uninformative in Glut1DS. MRI is used to exclude
    structural lesions and other neurometabolic encephalopathies rather than to
    establish the diagnosis.
  diagnostic: false
  evidence:
  - reference: PMID:17718830
    reference_title: "GLUT1 deficiency syndrome--2007 update."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging is uninformative. Most patients carry heterozygous de novo mutations in the GLUT1 gene"
    explanation: Review of 84 published cases states that neuroimaging does not contribute to diagnosis.
notes: >-
  Lump/split decision (2026-09-05 revision, claim issue #11080). This entry is
  the single Disease record for the SLC2A1 haploinsufficiency spectrum and is
  now anchored to the umbrella term MONDO:0000188, GLUT1 deficiency syndrome.
  Its two MONDO descendants, MONDO:0011724 (encephalopathy due to GLUT1
  deficiency, the classic infantile form) and MONDO:0012805 (childhood-onset
  GLUT1 deficiency syndrome 2, paroxysmal exercise-induced dyskinesia), are
  modelled as has_subtypes rather than as separate entries, because they share
  one molecular lesion and one mechanism chain and differ only in residual
  transporter activity and hence severity; the French national cohort documents
  individual patients crossing between them over time. The earlier version of
  this entry, created 2026-07-06, anchored disease_term to MONDO:0011724, which
  left the umbrella concept uncurated; the re-anchoring retires
  stubs/GLUT1_Deficiency_Syndrome.yaml. Dystonia 9 (DYT9, MONDO:0010983,
  OMIM 601042) was initially listed as a third subtype for completeness of the
  OMIM phenotypic series. It has been folded into the paroxysmal
  exertion-induced dyskinesia subtype instead, because Weber and colleagues
  sequenced SLC2A1 in the original German/Dutch DYT9 pedigree and concluded
  that DYT9 and DYT18 are allelic disorders; listing both as sibling subtypes
  would double-count one concept. MONDO:0010983 is therefore deliberately not
  bound as a subtype_term, and the DYT9 presentation is described within the
  DYT18 subtype, whose description records the additional spastic paraparesis.
  Evidence-policy notes for this pass. PMID:1714544, De Vivo 1991 in the New
  England Journal of Medicine, is the original clinical description but has no
  abstract in PubMed, so it cannot carry a snippet-verified evidence item and
  is acknowledged here rather than cited. PMID:20830593, an acetazolamide
  response letter, likewise has no cached content, so acetazolamide is not
  listed as a treatment; note that GeneReviews lists acetazolamide among the
  anti-seizure medications relatively contraindicated during ketogenic diet
  therapy. Orphanet ORPHA:71277 is not reachable through the structured-source
  cache, so no Orphanet frequency rows are cited. Two PMIDs supplied in the
  curation brief were wrong and were replaced after PubMed verification: Seidner
  1998 was given as 9620772, which is an EXT1 paper, and is actually
  PMID:9462754; Tang 2017 was given as 28211455, which is a physics paper, and
  is actually PMID:28106060. Five HP CURIEs offered by the Perplexity report
  were mislabelled and were not used, namely HP:0011610, HP:0007295, HP:0001942,
  HP:0002211 and HP:0001252 for paroxysmal dyskinesia, exercise-induced
  dyskinesia, hypoglycorrhachia, decreased CSF lactate and epileptic
  encephalopathy; the correct bindings used here are HP:0007166, HP:0011972 and
  HP:0030086. Caffeine avoidance, often mentioned clinically, is not in the
  GeneReviews abstract and is therefore not asserted. Evidence taken from the
  2020 international consensus statement and the 2025 narrative review is
  graded evidence_source OTHER rather than HUMAN_CLINICAL, because those
  documents report expert consensus and synthesis rather than a study cohort.

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