GLUT1 deficiency

Glucose transporter type 1 deficiency syndrome is a rare inherited neurometabolic disorder in which glucose cannot cross the blood-brain barrier efficiently, leaving the brain chronically short of its main fuel despite normal blood glucose.

It typically presents in infancy with seizures, developmental delay and a low cerebrospinal fluid glucose concentration, and it is one of the few treatable genetic epilepsies because a ketogenic diet can supply the brain with an alternative fuel.

Terminology and classification

• The standard name is glucose transporter type 1 deficiency syndrome, abbreviated GLUT1-DS, and the eponym De Vivo disease honours the neurologist who first described the syndrome in 1991.
• ICD-10 places it under E74.8, other specified disorders of carbohydrate metabolism, and ICD-11 assigns the specific code 5C61.5 within the disorders of glucose transport group.
• Other identifiers are OMIM 606777, Orphanet ORPHA:71277, MONDO:0011724, GARD 0009265, UMLS C1847501, GeneReviews NBK1430 and Wikidata Q1485893.
• Classic GLUT1-DS combines early epilepsy, cognitive impairment and movement disorder, whereas milder allelic phenotypes include paroxysmal exercise-induced dyskinesia and isolated eye-head movements.
• The disorder is classified as a metabolic epilepsy rather than a structural or autoimmune epilepsy, and it belongs to the broader group of blood-brain barrier transport defects.
• The term Glut1DS2 is sometimes used for the paroxysmal dyskinesia phenotype without epilepsy, which can remain undiagnosed for years because cognition and imaging are normal.

History

• De Vivo and colleagues reported the first two patients in 1991 in the New England Journal of Medicine, describing persistent hypoglycorrhachia with seizures and developmental delay and naming the defect a failure of glucose transport across the blood-brain barrier.^[1]
• The causative gene, SLC2A1 on chromosome 1p34.2, was identified later in the 1990s, and haploinsufficiency of the GLUT1 protein became the accepted mechanism.
• During the 2000s the ketogenic diet moved from a desperate option to first-line therapy, and prospective series showed that early treatment improved seizures and development.
• Recognition of paroxysmal exercise-induced dyskinesia and of paroxysmal eye-head movements widened the phenotype beyond epilepsy and showed that normal cognition does not exclude the diagnosis.^[2]
• In 2020 the international Glut1DS study group published state-of-the-art recommendations covering diagnosis, diet composition, monitoring and transition to adult care, which are now the main reference for practice.^[3]
• A randomized phase 3 trial of triheptanoin reported no benefit over placebo for paroxysmal movement events, and the open-label extension was closed early for lack of effectiveness.^[4]

Epidemiology

• Estimated birth incidence ranges from about 1 in 90,000 to 1 in 24,300, and the corresponding United States prevalence estimate is 3,000 to 7,000 people.
• Orphanet records a prevalence class of 1 to 9 per 1,000,000, which is lower than the incidence-based estimate because mild phenotypes are under-ascertained.
• About 90 percent of patients carry a de novo SLC2A1 variant, and the remainder inherit the variant from an affected or mosaic parent in an autosomal dominant pattern.
• No pathogenic variant is detected in roughly 10 to 15 percent of clinically typical patients, a group in which intronic, regulatory or copy-number changes may be missed by standard testing.
• The disorder affects both sexes equally and has been reported in every major ancestral population, with no founder effect.
• Because the phenotype overlaps with cerebral palsy, intractable childhood epilepsy and mitochondrial disease, the true prevalence is probably higher than clinic-based series suggest.
• A 2024 global modelling study estimated about 105,000 affected people worldwide and an incidence of 1.65 to 2.2 per 100,000 live births, higher than earlier clinic-based estimates.
• The GLUT1 Deficiency Foundation states that true prevalence is at least 1 in 24,000, implying that most affected children remain undiagnosed and that adult neurologists should consider the disorder in unexplained paroxysmal symptoms.

Pathophysiology

• GLUT1 is a twelve-transmembrane glucose transporter encoded by SLC2A1 and is the principal carrier that moves glucose from blood into brain across the endothelial cells of the blood-brain barrier.
• The brain depends on a continuous glucose supply, and the concentration of glucose in cerebrospinal fluid normally tracks about 60 percent of the plasma value, which is why a low spinal fluid glucose is the biochemical signature of the disease.
• Loss-of-function variants reduce transporter number at the barrier, producing chronic energy failure that is most damaging during the rapid brain growth of infancy.
• Missense variants may allow residual transport activity and are associated with later onset and paroxysmal dyskinesia, whereas truncating and non-missense variants tend to cause earlier and more severe disease.^[5]
• Chronic fuel deprivation impairs protein synthesis and myelination, which explains microcephaly, cognitive delay, ataxia and the non-epileptic movement disorder.
• Ketone bodies bypass the block because they enter the brain through monocarboxylate transporters, so ketosis restores the energy supply that glucose can no longer provide.

Clinical features

• Seizures occur in about 90 percent of patients, begin in the first two years of life and are often the presenting feature, with focal, generalized or mixed semiology and frequent status epilepticus.
• Developmental delay, intellectual disability, expressive speech impairment and microcephaly are common and become more evident after the first year.
• Movement disorders include ataxia, dystonia, chorea and paroxysmal exercise-induced dyskinesia, and they were the presenting symptom in about one third of a published movement disorder series.^[5]
• Paroxysmal eye-head movements in infancy, described as rapid multidirectional eye deviations with head version, are a useful early clue and may precede epilepsy.^[2]
• Many patients are described as irritable or sleepy between meals, and prolonged fasting, gastroenteritis or anaesthesia can precipitate seizures, lethargy and hypoglycaemic-like deterioration.
• Adults who survive with late diagnosis often have mild intellectual disability, action tremor, spasticity or scoliosis, and some have no seizures at all.

Diagnosis

• The key test is cerebrospinal fluid glucose measured after a four to six hour fast, and values below 2.2 mmol/L or a cerebrospinal fluid to blood ratio below 0.4 support the diagnosis.
• Cerebrospinal fluid lactate, protein and cell count are normal, which distinguishes the disorder from meningitis, mitochondrial disease and other causes of low spinal fluid glucose.
• Erythrocyte glucose uptake measured with labelled glucose is reduced by about half in most patients and remains a useful functional confirmation in specialized laboratories.
• SLC2A1 sequencing with deletion and duplication analysis is the confirmatory genetic test, and parental testing distinguishes de novo from inherited variants.
• Electroencephalography is often abnormal but nonspecific, and brain magnetic resonance imaging is usually normal or shows mild atrophy, so neither excludes the diagnosis.
• The differential diagnosis includes cerebral palsy, early-onset epileptic encephalopathy, alternating hemiplegia of childhood, mitochondrial disease, glucose-6-phosphatase deficiency and psychogenic paroxysmal events.

Management

• The ketogenic diet is first-line therapy and is usually started at a ratio of 3 to 1 or 4 to 1 grams of fat to carbohydrate plus protein, with gradual titration and close dietitian supervision.
• Most patients achieve substantial seizure reduction and many become seizure-free, and earlier initiation is associated with better cognitive and motor outcomes.
• Monitoring during the diet includes growth, serum lipids, carnitine, electrolytes, renal ultrasound for stones, bone density and essential fatty acid status.
• Acute illness requires avoidance of fasting, early intravenous glucose-containing fluids and a written emergency plan, because infection or dehydration can provoke status epilepticus.
• Triheptanoin is not effective for paroxysmal movement events, diazoxide has been reported to improve symptoms in a single-patient observation and acetazolamide has shown favourable responses in small series.^[6]
• Transition to adult care must address diet adherence, pregnancy, driving, employment and the risk of unrecognised paroxysmal events, and genetic counselling is offered to families planning children.
• The 2020 international recommendations advise a 3 to 1 or 4 to 1 ketogenic ratio in infancy and a lower ratio in adults, with a modified Atkins diet as an alternative when the classic diet is not tolerated.
• Adherence often declines in adolescence, and a structured transition programme involving a dietitian, neurologist and psychologist improves retention in adult care and prevents avoidable metabolic decompensation.

Research and controversies

• The negative triheptanoin trial showed that a plausible alternative fuel does not automatically translate into clinical benefit, and it shifted attention back to ketogenic strategies and to adherence support.^[4]
• Alternative and adjunctive therapies reviewed in 2026 include modified Atkins variants, intravenous sodium lactate, acetazolamide, zonisamide and intermittent glucose, but the evidence base remains small and heterogeneous.^[7]
• Whether adults with mild or late-diagnosed disease benefit from starting a ketogenic diet is uncertain, and retrospective reports describe improvement in movement disorder and fatigue.
• Gene therapy and ketone ester supplementation are under preclinical investigation, and neither has entered routine clinical use.
• Newborn screening is not currently available because no reliable dried-blood-spot biomarker exists, so diagnosis still depends on clinical suspicion and cerebrospinal fluid analysis.
• Long-term data on bone health, cardiac effects of decades of high-fat diet and pregnancy outcomes remain scarce, and international registries are attempting to fill these gaps.