Glut1 deficiency syndrome (Glut1DS) is a brain energy failure syndrome caused by impaired glucose transport across brain tissue barriers. Glucose diffusion across tissue barriers is facilitated by a family of proteins including glucose transporter type 1 (Glut1). Patients are treated effectively with ketogenic diet therapies (KDT) that provide a supplemental fuel, namely ketone bodies, for brain energy metabolism. The increasing complexity of Glut1DS, since its original description in 1991, now demands an international consensus statement regarding diagnosis and treatment. International experts (n = 23) developed a consensus statement utilizing their collective professional experience, responses to a standardized questionnaire, and serial discussions of wide‐ranging issues related to Glut1DS. Key clinical features signaling the onset of Glut1DS are eye‐head movement abnormalities, seizures, neurodevelopmental impairment, deceleration of head growth, and movement disorders. Diagnosis is confirmed by the presence of these clinical signs, hypoglycorrhachia documented by lumbar puncture, and genetic analysis showing pathogenic SLC2A1 variants. KDT represent standard choices with Glut1DS‐specific recommendations regarding duration, composition, and management. Ongoing research has identified future interventions to restore Glut1 protein content and function. Clinical manifestations are influenced by patient age, genetic complexity, and novel therapeutic interventions. All clinical phenotypes will benefit from a better understanding of Glut1DS natural history throughout the life cycle and from improved guidelines facilitating early diagnosis and prompt treatment. Often, the presenting seizures are treated initially with antiseizure drugs before the cause of the epilepsy is ascertained and appropriate KDT are initiated. Initial drug treatment fails to treat the underlying metabolic disturbance during early brain development, contributing to the long‐term disease burden. Impaired development of the brain microvasculature is one such complication of delayed Glut1DS treatment in the postnatal period. This international consensus statement should facilitate prompt diagnosis and guide best standard of care for Glut1DS throughout the life cycle.

Glut1 Deficiency (Glut1D) is caused by impaired glucose transport into brain. The resulting epileptic encephalopathy and movement disorders can be treated effectively by high-fat carbohydrate-restricted ketogenic diet therapies (KDT) mimicking fasting and providing ketones as an alternative cerebral fuel. Recently 6-24 months follow-ups of epileptic patients reported elevated blood lipids and intima thickening of the carotid artery raising concerns about potential cardiovascular risks by KDT. To clarify potential cardiovascular risks we performed a prospective 10 year follow up of 10 Glut1D patients. Between August 2001 and January 2016 we enrolled Glut1D patients on KDT at two hospitals in Germany in this prospective, multicenter case series. The minimal follow up was 10 years. Standard deviation scores (SDS) of body mass index (BMI), total cholesterol (TC), HDL-/LDL cholesterol, and triglycerides (TG) before initiation of KDT were compared with respective values at 6 months, 2, 5 years, and 10 years after initiation. After 10 years on KDT cardiovascular risk, assessed by BMI, carotid intima-media thickness (CIMT) measurement, and blood pressure, was compared to a healthy reference population (n = 550). Baseline and 10 year follow-up investigations were available for 10 individuals with Glut1D on KDT. After two years on KDT BMI increased significantly, while total cholesterol, HDL-cholesterol, and LDL-cholesterol decreased. Within 3-5 years on KDT these differences disappeared, and after 10 years blood lipid parameters reflected the situation at initiation of KDT. Prior to KDT one child had dyslipidaemia, but no child after 10 years on KDT. No significant differences were observed with respect to BMI SDS (p = 0.26), CIMT (p = 0.63) or systolic and diastolic blood pressure (SDS p = 0.11 and p = 0.37, respectively) in Glut1D children treated with KDT for at least 10 years compared to healthy controls. In contrast to previous short-term reports on adverse effects of KDT, 10-year follow-up did not identify cardiovascular risks of dietary treatment for Glut1D.

Glut1 Deficiency Syndrome (Glut1DS) has emerged as a treatable, but complex entity. Increasing data on pathogenic mechanisms, phenotype, genotype, and ketogenic dietary therapies (KDT) are available, as summarized in this review. Many challenges remain: novel symptoms emerge and vary with age. In Glut1DS, KDT in pregnancy and the clinical features in neonates and adults are poorly understood. KDT are ineffective in some patients for reasons yet unknown. 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. Future, yet currently unavailable prospects are neonatal screening for Glut1DS, reliable biomarkers, predictors for outcome, and alternative therapies, along with and beyond KDT.

View Supplementary Video 1 View Supplementary Video 2 View Supplementary Video 3Movement disorders are a major feature of Glut1 deficiency. As recently identified in adults with paroxysmal exercise‐induced dystonia, similar events were reported in pediatric Glut1 deficiency. In a case series, parent videos of regular motor state and paroxysmal events were requested from children with Glut1 deficiency on clinical follow‐up. A questionnaire was sent out to 60 families. Videos of nonparoxysmal/paroxysmal states in 3 children illustrated the ataxic‐dystonic, choreatiform, and dyskinetic‐dystonic nature of paroxysmal events. Fifty‐six evaluated questionnaires confirmed this observation in 73% of patients. Events appeared to increase with age, were triggered by low ketosis, sleep deprivation, and physical exercise, and unrelated to sex, hypoglycorrhachia, SLC2A1 mutations, or type of ketogenic diet. We conclude that paroxysmal events are a major clinical feature in Glut1 deficieny, linking the pediatric disease to adult Glut1D‐associated exercise‐induced paroxysmal dyskinesias.

Glucose transporter type 1 deficiency syndrome (GLUT1DS) commonly presents with early‐onset epilepsy that often resists conventional pharmacological treatment. Ketogenic diet therapy (KDT) is the preferred approach to address the underlying metabolic anomaly. However, a subset of GLUT1DS patients presents resistance to KDT, with the causes remaining elusive. This comprehensive literature review aims to explore the characteristics of KDT failure in GLUT1DS and identify risk factors within this population. Our goal is to improve counseling and prognostication for these patients. So, we conducted a comprehensive literature review on PubMed, focusing on studies documenting pediatric GLUT1DS patients with drug‐resistant epilepsy unresponsive to KDT. We identified five cases of KDT failure in female GLUT1DS patients, aged 10 days to 13 years at diagnosis. Predominant seizure types were absence seizures, with a few cases of clonic, tonic, or myoclonic seizures. EEG consistently revealed 2–3.5 Hz generalized spike‐and‐wave discharges. Genetic investigations revealed point mutations and deletions in two cases each. Despite an in‐depth search, no specific features were found to reliably distinguish KDT non‐responders from responders, underscoring the need for further research. In cases of KDT ineffectiveness for seizure control in GLUT1DS patients, exploring alternative therapeutic strategies becomes imperative to managing symptoms while maintaining quality of life. Large‐scale multicenter studies, facilitated through international collaborations like the European Network for Therapy in Rare Epilepsies (NETRE), hold promise in elucidating the complexities of this patient population and developing personalized therapeutic approaches.Plain Language Summary: Glucose transporter type 1 deficiency syndrome often causes difficult‐to‐treat epilepsy. The ketogenic diet works for many patients, but some do not respond. This review investigated cases of diet failure but could not identify common features among poor responders. Further research is needed to understand these cases and explore alternative treatments.