Glut1 Deficiency Syndrome 1
A number sign (#) is used with this entry because GLUT1 deficiency syndrome-1 (GLUT1DS1) is caused by heterozygous mutation in the gene encoding the GLUT1 transporter (SLC2A1; 138140) on chromosome 1p34. Rare cases of GLUT1 deficiency caused by homozygous or compound heterozygous mutation in the SLC2A1 gene have been reported.
Allelic disorders with overlapping features include GLUT1 deficiency syndrome with pseudohyperkalemia and hemolysis (608885), GLUT1 deficiency syndrome-2 (GLUT1DS2; 612126), dystonia-9 (DYT9; 601042), and idiopathic generalized epilepsy-12 (EIG12; 614847).
DescriptionGLUT1 deficiency syndrome-1 is a neurologic disorder showing wide phenotypic variability. The most severe 'classic' phenotype comprises infantile-onset epileptic encephalopathy associated with delayed development, acquired microcephaly, motor incoordination, and spasticity. Onset of seizures, usually characterized by apneic episodes, staring spells, and episodic eye movements, occurs within the first 4 months of life. Other paroxysmal findings include intermittent ataxia, confusion, lethargy, sleep disturbance, and headache. Varying degrees of cognitive impairment can occur, ranging from learning disabilities to severe mental retardation. Hypoglycorrhachia (low CSF glucose, less than 40 mg/dl) and low CSF lactate are essentially diagnostic for the disorder. As more cases with GLUT1 deficiency syndrome were described, the phenotype was broadened to include individuals with ataxia and mental retardation but without seizures, individuals with dystonia and choreoathetosis, and rare individuals with absence seizures and no movement disorder. The disorder, which results from a defect in the GLUT1 glucose transporter causing decreased glucose concentration in the central nervous system, is part of a spectrum of neurologic phenotypes resulting from GLUT1 deficiency. GLUT deficiency syndrome-2 (612126) represents the less severe end of the phenotypic spectrum and is associated with paroxysmal exercise-induced dystonia with or without seizures. Correct diagnosis of GLUT1 deficiency is important because a ketogenic diet often results in marked clinical improvement of the motor and seizure symptoms (reviews by Pascual et al., 2004 and Brockmann, 2009).
Clinical FeaturesDe Vivo et al. (1991) described 2 patients with infantile seizures, delayed development, and acquired microcephaly who had normal circulating blood sugar, low to normal cerebrospinal fluid lactate, but persistent hypoglycorrhachia and diminished transport of hexose into isolated red blood cells. These symptoms suggested the existence of a defect in glucose transport across the blood-brain barrier.
Wang et al. (2000) used the designation GLUT1 deficiency syndrome for the disorder observed in 15 children who presented with infantile seizures, acquired microcephaly, and developmental delay and were found to have heterozygous mutations in the GLUT1 gene. The deficiency in the transporter resulted in reduced cerebrospinal fluid glucose concentrations and reduced erythrocyte glucose transporter activities in the patients. Rotstein et al. (2010) provided further details of a patient with autosomal recessive GLUT1 deficiency syndrome reported by Wang et al. (2000). He developed recurrent limb stiffening and cyanosis at age 6 weeks. Seizures included tonic eye deviation, staring spells, myoclonic jerks, and prolonged and refractory generalized tonic-clonic seizures. He had delayed psychomotor development and progressive microcephaly. CSF showed hypoglycorrhachia. A ketogenic diet was helpful with seizure control, but at age 6 years, his developmental quotient was 42. He had axial hypotonia, limb spasticity and dystonia, and severe ataxia.
Brockmann et al. (2001) reported a family in which GLUT1 deficiency presented in certain members with mild to severe seizures, developmental delay, ataxia, hypoglycorrhachia, and decreased erythrocyte uptake of 3-O-methyl-D-glucose. Seizure frequency and severity were aggravated by fasting, and responded to a carbohydrate load. Ultimately, however, the seizures and motor disability in the patients responded best to a ketogenic diet (Brockmann, 2009).
Klepper and Voit (2002) provided a detailed review of GLUT1 deficiency, including clinical features, a diagnostic algorithm, and effective treatment strategies.
Wang et al. (2005) found that 13 (81%) of 16 patients with GLUT1 deficiency syndrome-1 had the most common 'classic' phenotype, a developmental encephalopathy with infantile seizures, acquired microcephaly, and spasticity. Seizure type varied and included generalized tonic or clonic, myoclonic, atypical absence, atonic, and unclassified. Seizures were unresponsive to typical anticonvulsant medication, but responded rapidly to a ketogenic diet. Patients with the classic phenotype also experienced other variable paroxysmal events, including confusion, lethargy, hemiparesis, ataxia, sleep disturbances, and headaches. Cognitive impairment ranged from learning disabilities to severe mental retardation; some patients had impaired speech and language development. Neurologic signs showed variable involvement of the pyramidal, extrapyramidal, and cerebellar systems.
Zorzi et al. (2008) reported 3 unrelated Italian females with GLUT1 deficiency associated with paroxysmal movement disorders diagnosed in early adulthood. None had a positive family history. All had global developmental delay noted in infancy, and 2 had seizures beginning in the first 6 months of life (myoclonic absence and complex partial seizures, respectively). All had microcephaly, dysarthria, spasticity, and moderate mental retardation. Paroxysmal movements included myoclonic jerks, stiffening, and dystonic posturing. The phenotype in the 2 patients with early-onset seizures was consistent with GLUT1DS1; the other patient did not have seizures, but had ataxia, spasticity, dystonia, and dysarthria, more similar to the phenotype observed in GLUT1 syndrome-2 (612126). Genetic analysis identified a different heterozygous mutation in the GLUT1 gene in each patient (see, e.g., 138140.0014). Zorzi et al. (2008) noted that the abnormal movements were consistent with paroxysmal dyskinesia, thus expanding the phenotype associated with GLUT1 deficiency.
Hully et al. (2015) reported 58 French patients with SLC2A1 mutations identified in a large population-based study. Detailed retrospective clinical information was available for 24 patients. The patients came to medical attention at a median age of 7.5 months (range, 6 weeks to 5 years) for a combination of seizures (75%) with developmental delay or hypotonia (42%). Movement disorders were less prominent (29%) at disease onset. Seizures started between 1.5 months and 11 years, and usually included several types, the most common being focal seizures (52%) and atypical absence (87%). Other types included myoclonic (48%), generalized tonic-clonic (22%), and febrile (17%). Sensitivity to fasting or exertion was a prominent feature. Seizures tended to be refractory to medical therapy, but 79% of patients responded favorably to a ketogenic diet. Patients with myoclonic seizures had more severe intellectual disability. All patients had some sort of movement disorder, including dystonia (83%), chorea (25%), and ataxia (88%) with cerebellar kinetic syndrome (75%). Many movements affected the buccofacial area and eye movements. Almost all patients (92%) had both cognitive and motor impairment with variable intellectual disability; most had a friendly disposition. The phenotype tended change over time: epilepsy tended to decrease with age, while movement disorders and paroxysmal exercise-induced dystonia and dyskinesias worsened with age. Missense mutations were associated with a less severe phenotype.
Clinical Variability
Mullen et al. (2011) found that 4 (5%) of 84 probands with myoclonic astatic epilepsy (MAE) had a mutation in the SLC2A1 gene, consistent with GLUT1 deficiency. Three of the patients fulfilled the narrow definition of MAE, and 1 fit a broader definition. The first 3 patients had onset of multiple seizure types, including myoclonic-atonic seizures, by age 3 years, and subsequent cognitive decline, resulting in severe intellectual disability in patients 1 and 3. Patient 2, who was treated early with a ketogenic diet, had mild intellectual disability. The patient with the broader definition of MAE had onset at age 4 years of atonic and absence seizures, followed by a progressive epileptic encephalopathy and mild intellectual disability. Two of the patients also developed paroxysmal exertional dyskinesia in childhood. The findings were important because GLUT1 deficient patients can be treated with a ketogenic diet. Mullen et al. (2011) suggested that patients with MAE should be tested for GLUT1 deficiency.
DiagnosisYang et al. (2011) performed an erythrocyte glucose uptake assay in 109 patients with suspected GLUT1 deficiency. There were 2 groups of patients: 74 had decreased glucose uptake (mean of about 55% compared to controls) and 35 had normal uptake. The ROC curve defined a new cutoff of 74%, which was increased from the previously accepted cutoff of 60%. The 74% cutoff increased the specificity and sensitivity of the assay to 100% and 99%, respectively. Pathogenic SLC2A1 mutations were found in 95% of patients with decreased uptake and in only 1 patient with normal uptake. Among those with defects, there was a significant inverse correlation between median values of uptake and clinical severity. The findings validated the erythrocyte glucose uptake assay as a confirmatory functional test for GLUT1 deficiency and as a surrogate marker for GLUT1 haploinsufficiency.
Diagnostic Criteria
In a review, Klepper and Leiendecker (2007) proposed diagnostic criteria for GLUT1 deficiency syndrome: seizures, developmental delay, complex movement disorder, and fasting EEG changes that improve postprandially. Laboratory criteria for the disorder include hypoglycorrhachia, low CSF/blood glucose ratio, low to normal CSF lactate, and reduced erythrocyte glucose uptake and/or decreased GLUT1 immunoreactivity in erythrocyte membranes.
PathogenesisPascual et al. (2007) compared the clinical phenotype of 2 unrelated patients with neuroglycopenia in infancy: a 16-year-old boy who had GLUT1 deficiency confirmed by genetic analysis and a 23-year-old woman who had early infantile chronic hypoglycemia due to hyperinsulinism and pancreatic nesidioblastosis (see, e.g., 256450). The woman had an unaffected twin sister who served as a control. Both patients had residual encephalopathy with hypertonicity, dysarthria, hyperreflexia, ataxia, mental retardation, and microcephaly. Neuropsychologic testing revealed decreased IQ, articulation difficulties, and friendly demeanor in both patients. Pascual et al. (2007) concluded that a persistent decrease in glucose in the developing brain is the unifying pathogenic mechanism in both of these disorders, which can be classified as infantile neuroglycopenia. The authors hypothesized that glucose serves a dual capacity in the developing brain, acting both as a fuel and as a signaling molecule.
InheritanceKlepper et al. (2001) reported a father and 2 children from separate marriages who were affected by GLUT1 deficiency, and confirmed autosomal dominant transmission by identifying a heterozygous mutation in the GLUT1 gene (G91D; 138140.0006).
In the family reported by Brockmann et al. (2001), the GLUT1 deficiency syndrome affected 5 members over 3 generations. The syndrome behaved as an autosomal dominant, with 1 instance of father-to-son transmission.
Rare cases of autosomal recessive transmission have been reported (Wang et al., 2000; Klepper et al., 2009). The patient reported by Klepper et al. (2009) was a 6-year-old girl born to consanguineous Arab parents from a Bedouin kindred from Qatar. She was noted to have unsteady ataxic gait at age 18 months, as well as paroxysmal choreoathetosis. She also had developmental delay and hypotonia. EEG showed a polymorphic baseline alpha-theta activity with an isolated monomorphic sharp wave focus. Lumbar puncture showed hypoglycorrhachia and decreased CSF lactate. Genetic analysis identified a homozygous mutation in the GLUT1 gene (R468W; 138140.0016). Her asymptomatic 2-year-old sister was also homozygous for the mutation; she was found to have hypoglycorrhachia and decreased CSF lactate. The parents, who were unaffected, were heterozygous for the mutation. Klepper et al. (2009) concluded that the mutation was pathogenic, and suggested that the sister who was homozygous for the mutation was too young for symptom onset. The findings suggested that GLUT1 deficiency can also be inherited in an autosomal recessive pattern.
Clinical ManagementKlepper et al. (2002) used the ketogenic diet to treat 4 patients with seizures and low CSF glucose suggesting GLUT1 deficiency, which was confirmed in 2 of the patients. All 4 were started on a ketogenic diet at 6 to 28 weeks of age. Ketosis developed within 24 hours. 3-Hydroxybutyrate concentrations available at the bedside correlated inversely with the base excess. At glucose levels of 40 mg/dl or less, patients remained asymptomatic in the presence of ketones. The ketogenic formula was tolerated well, parental compliance was good, and all patients remained seizure-free on the diet. One infant developed failure to thrive on medium-chain triglycerides, which was reversed using long-chain triglycerides. Adverse effects of the diet were limited to renal stones in 1 patient. Klepper et al. (2002) concluded that seizure control was effective and adverse effects were limited, but that evaluation of long-term effects was necessary.
Klepper et al. (2003) reported in vitro studies of the effects of preincubation of anticonvulsants and ethanol on GLUT1-mediated glucose transport in erythrocytes from 11 patients and 30 controls. They concluded that ethanol, diazepam, chloralhydrate, phenobarbital, and pentobarbital could exacerbate the effect of GLUT1 deficiency on glucose transport into the brain, whereas phenytoin and carbamazepine had no significant inhibitory effects and might be preferable for use in seizure control. They noted that recommendations should be viewed with caution as the data did not assess cerebral glucose utilization.
Wang et al. (2005) reported that the ketogenic diet effectively controlled seizures and other motor symptoms of GLUT1 deficiency, but was less effective on cognitive symptoms.
Klepper et al. (2005) reported favorable seizure control with a ketogenic diet in 15 patients with GLUT1 deficiency. Two patients had recurrence of seizures after 2.5 years despite adequate ketosis, but were controlled by other medications.
Molecular GeneticsSeidner et al. (1998) demonstrated 2 classes of mutations as the molecular basis for the functional defect of glucose transport: hemizygosity of GLUT1 (138140.0001) and heterozygous nonsense mutations resulting in truncation of the GLUT1 protein (e.g., 138140.0002).
Abnormalities in the GLUT1 gene found by Wang et al. (2000) included 1 large deletion (138140.0001), 5 missense mutations (see, e.g., 138140.0004-138140.0005), 3 small deletions, 3 insertions, 3 splice site mutations, and 1 nonsense mutation. In the family with GLUT1 deficiency syndrome-1 reported by Brockmann et al. (2001), a heterozygous arg126-to-his missense mutation in the GLUT1 gene was identified (138140.0007).
Animal ModelWang et al. (2006) found that mice with targeted heterozygous disruption of the Glut1 gene developed spontaneous epileptiform discharges, impaired motor activity, incoordination, hypoglycorrhachia, decreased brain weight (microencephaly), decreased brain glucose uptake, and decreased expression of Glut1 in the brain (66% of controls). Homozygous mutant mice were embryonic lethal. Wang et al. (2006) suggested that Glut1 +/- mice mimics the classic human presentation of GLUT1 deficiency and can be used as an animal model to examine the pathophysiology of the disorder in vivo.