GLUT1-deficiency: barbiturates potentiate haploinsufficiency in vitro

Barbiturates are known to inhibit glucose transport mediated by the facilitative sugar transporter GLUTI. We have studied such inhibition in children with GLUT1-deficiency. Zero-trans influx of 14C-labeled 3-O-methyl glucose (3OMG) into erythrocytes of patients (n = 3) was 35% of controls (n = 6). Preincubation with 10 mM phenobarbital or pentobarbital reduced patients' 30MG influx to 17%. In patients and controls, preincubation with barbiturates significantly decreased Vmax in a dose-dependent manner (for pentobarbital, IC50 = 0.84 mM, patient 2). The apparent Km in individuals remained largely unchanged. Three-OMG influx without preincubation resulted in a stronger inhibition at lower barbiturate concentrations. The patients' data are discussed in the light of individual missense mutations (patient 1: R126L and K256V; patient 2: T310I; patient 3: S66F) in the GLUTI gene. In conclusion, in controls and patients with GLUT1-deficiency barbiturates interact with GLUT1, lowering its intrinsic activity. The use of barbiturates in this condition for anesthesia or as anticonvulsants could therefore potentially aggravate the existing glucose transport defect and may put these patients at increased risk.     

Glucose transporter type 1 deficiency syndrome (Glut1DS): methylxanthines potentiate GLUT1 haploinsufficiency in vitro

Methylxanthines such as caffeine and theophylline are known to inhibit glucose transport. We have studied such inhibition in the glucose transporter type 1 deficiency syndrome (Glut1DS) by erythrocyte glucose transport assays. Data from four patients with individual mutations in the GLUT1 gene are discussed: patient 1 (hemizygosity), 3 (S66F), 15 (368Ins23), and 17 (R333W). Zero-trans influx of (14)C-labeled 3-O-methyl glucose (3-OMG) into erythrocytes of patients is reduced (patient 1, 51%; 3, 45%; 15, 31%; 17, 52%) compared with maternal controls. Inhibition studies on patients 1, 3, 17, and maternal controls show an IC(50) for caffeine of approximately 1.5 mM both in controls (n = 3) and patients (n = 3) at 5 mM 3-OMG concentration. In the same two groups, kinetic studies show that 3 mM caffeine significantly decreases V(max) (p < 0.005), whereas the decrease in K(m) is significant (p < 0.01) only in the three controls and one patient (patient 3). Kinetic data from individual patients permit us to speculate that the interactions between caffeine and Glut1 are influenced by the mutation. Three mM caffeine also inhibits the transport of dehydroascorbic acid (DHA), another substrate for Glut1. The combined effects of caffeine (3 mM) and phenobarbital (10 mM) on glucose transport, as determined in patient 15 and the maternal control, show no additive or synergistic inhibition. These data indicate that caffeine and phenobarbital have similar Glut1 inhibitory properties in these two subjects. Our study suggests that Glut1DS patients may have a reduced safety margin for methylxanthines. Consumption of methylxanthine-containing products may aggravate the neurologic symptoms associated with the Glut1DS.     

Glut1 deficiency: When to suspect and how to diagnose?

Impaired glucose transport across the blood-brain barrier results in GLUT1 deficiency syndrome (GLUT1-DS), characterized by infantile seizures, developmental delay, acquired microcephaly, spasticity, ataxia, and hypoglycorrhachia. A part from this classic phenotype, clinical conditions associated with a deficiency of GLUT1 are highly variable and several atypical variants have been described; in particular, patients with movement disorders, but without seizures, with paroxysmal exertion-induced dyskinesia, have been reported.Most patients carry heterozygous de novo mutations in the GLUT1-gene but autosomal dominant and recessive transmission has been identified.Diagnosis is based on low cerebrospinal fluid glucose, in the absence of hypoglycemia, and it is confirmed by molecular analysis of the GLUT1-gene and by glucose uptake studies and immunoreactivity in human erythrocytes. Treatment with a ketogenic diet results in marked improvement of seizures and movement disorders.This review summarizes recent advances in understanding of GLUT1-DS and highlights the diagnostic and therapeutic approach to GLUT1-DS.     

Facilitated glucose transporter protein type 1 (GLUT1) deficiency syndrome: impaired glucose transport into brain – a review

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. It is caused by a defect in glucose transport into brain, mediated by the facilitative glucose transporter GLUT1. Since 1991, more than 70 patients have been identified. 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). Clinical features are variable and include seizures, developmental delay, acquired microcephaly, hypotonia, and a complex motor disorder with elements of ataxia, dystonia, and spasticity. The GLUT1 defect can be confirmed in erythrocytes by glucose uptake studies and GLUT1 immunoreactivity, and by molecular analysis of the GLUT1 gene. Several heterozygous mutations resulting in GLUT1 haploinsufficiency have been identified. An effective treatment is available by means of a ketogenic diet as ketone bodies serve as an alternative fuel for the developing brain. CONCLUSION: this treatable condition should be suspected in children with unexplained neurological disorders associated with epilepsy and developmental delay and confirmed by a lumbar puncture.     

Transient regional cerebral hypoperfusion during a paroxysmal hemiplegic event in GLUT1 deficiency syndrome

GLUT1 deficiency syndrome (GLUT1DS) is a well described neurometabolic disorder that results from impaired glucose transport into the central nervous system. GLUT1DS classically presents with infantile-onset epilepsy, progressive microcephaly, developmental delay, ataxia, dystonia, and spasticity, but a minority of patients may manifest with paroxysmal non-epileptic phenomena including hemiparesis (Wang et al., 2002). We report for the first time cerebral perfusion changes during an acute episode of hemiparesis in a 9 year old child with GLUT1DS. The patient presented as a code stroke with her second episode of acute-onset left hemiparesis and altered mental status. Emergency MRI of brain demonstrated normal diffusion-weighted imaging, but arterial spin label perfusion weighted imaging (ASL-PWI) showed regional hypoperfusion of the right cerebral hemisphere and magnetic resonance angiography (MRA) revealed distally restricted flow related enhancement in the right MCA. The patient's deficits resolved entirely within several hours from onset. Repeat MRI one month later was normal. Our report suggests that GLUT1DS-related hemiplegic events are associated with transient lateralized cerebrovascular hypoperfusion similar to that described in hemiplegic migraine and other pediatric stroke mimics. The underlying pathophysiology for this phenomenon in GLUT1DS is not known, but may relate to cortical energy failure or abnormal cerebral microvasculature.     

Acute effectors of GLUT1 glucose transporter subcellular targeting in CIT3 mouse mammary epithelial cells

Lactogenic hormones cause intracellular targeting of glucose transporter 1 (GLUT1) for transport of glucose to the site of lactose synthesis in mammary glands. Our aim was to study the intracellular trafficking mechanisms involved in GLUT1 targeting and recycling in CIT3 mouse mammary epithelial cells. Fusion proteins of GLUT1 and enhanced green fluorescent protein (EGFP) were expressed in CIT3 cells maintained in growth medium (GM), or exposed to secretion medium (SM), containing prolactin. Agents acting on Golgi and related subcellular compartments and on GLUT1 and GLUT4 targeting in muscle and fat cells were studied. Wortmannin and staurosporine effects on internalization of GLUT1 were not specific, supporting a basal constitutive GLUT1 membrane-recycling pathway between an intracellular pool and the cell surface in CIT3 cells, which targets most GLUT1 to the plasma membrane in GM. Upon exposure to prolactin in SM, GLUT1 was specifically targeted intracellularly to a brefeldin A-sensitive compartment. Arrest of endosomal acidification by bafilomycin A1 disrupted this prolactin-induced GLUT1 intracellular trafficking with central coalescence of GLUT1-EGFP signal, suggesting that it is via endosomal pathways. This machinery offers another level of regulation of lactose synthesis by altering GLUT1 targeting within minutes to hours.     

Failure of ketogenic diet therapy in GLUT1 deficiency syndrome

PurposeEpilepsy in GLUT1 deficiency syndrome is generally drug-resistant; ketogenic diet (KD) therapy is the mainstay of therapy, as production of ketones provides the brain with an alternative energy source, bypassing the defect in GLUT1. Failure of KD therapy and risk factors for failure have been sparsely published.MethodsWe performed a retrospective study of GLUT1DS patients with refractory epilepsy failing on KD therapy, to identify their clinical characteristics.ResultsFailure of the ketogenic diet was due to KD inefficacy (poor effect despite adequate ketosis), as well as intolerance and an inability to attain ketosis. Our cohort of seven patients in whom KD therapy failed stood out for their advanced age at seizure onset, i.e. almost 4 years vs 8 months in large series, female sex, as well as their advanced age at diagnosis and initiation of KD therapy. EEG recordings during KD therapy can aid in the assessment of effectiveness of the KD therapy.ConclusionsGLUT1DS is generally described as a treatable disorder and existing case series do not provide details of treatment failure. In select patients with GLUT1DS, KD therapy fails, rendering GLUT1DS an essentially untreatable disorder. Failure of the ketogenic diet was due to KD inefficacy (poor effect despite adequate ketosis), as well as intolerance and an inability to attain ketosis. Failure to reduce seizure frequency with deterioration of the EEG findings should lead to consideration of cessation of KD therapy.     

Symptomatic West Syndrome Secondary to Glucose Transporter-1(GLUT1) Deficiency with Complete Response to 4:1 Ketogenic Diet

Glucose transporter type 1 (GLUT-1) deficiency is a rare cause of preventable intellectual disability. Intellectual disability is due to refractory seizures in infancy and reduced supply of glucose to the brain. The authors report a third born male child of consanguineous parentage who presented with infantile spasms. Initially, he had refractory convulsions of focal, generalised, and myoclonic jerks, not responding to multiple anticonvulsants. He also had choreoathetoid movements. On examination he had microcephaly. MRI of brain was normal and EEG showing diffuse slowing. CSF glucose was low compared to blood glucose, with normal lactate and without any cells, hence diagnosed as Glucose transporter-1 deficiency and started on ketogenic diet. With ketogenic diet, child was seizure free, anticonvulsants decreased to 2 from 5, and improvements in development were noted.     

Seizures, ataxia, developmental delay and the general paediatrician: glucose transporter 1 deficiency syndrome

AIM: Glucose transporter 1 deficiency syndrome (GLUT1-DS) is an important condition for the general paediatrician's differential armamentarium. We describe a case series of eight patients in order to raise awareness of this treatable neurometabolic condition. The diagnosis of GLUT1-DS is suggested by a decreased absolute cerebrospinal fluid (CSF) glucose value (<2.2 mmol/L) or lowered CSF: plasma glucose ratio (<0.4). METHODS: This is a review of eight Queensland patients with GLUT1-DS. The clinical presentation, clinical course, laboratory investigations and treatment outcomes are discussed. RESULTS: The clinical features noted in our patient cohort include combinations of ataxia, developmental delay and a severe seizure disorder that is refractory to anticonvulsant medications. Seizures are the most common clinical manifestation and may be exacerbated by phenobarbitone. The paired CSF: plasma glucose results ranged from 0.2 to 0.39 (normal <0.6) with an average of 0.33. 3-O-Methyl-D-Glucose uptake and GLUT1 Genotyping analysis have been performed on five patients thus far. Rapid and impressive seizure control was observed in 100% of our patients once the ketogenic diet was instituted, with half of the cohort being able to wean completely from anticonvulsants. CONCLUSION: Children presenting with a clinical phenotype consisting of a refractory seizure disorder, ataxia and developmental delay should prompt the consideration of Glucose transporter 1 deficiency syndrome. While the diagnostic test of lumbar puncture is an invasive manoeuvre, the diagnosis provides a viable treatment option, the ketogenic diet. GLUT1-DS displays clinical heterogeneity, but the value of early diagnosis and treatment is demonstrated by our patient cohort.     

Glucose transporter type 1 deficiency: a study of two cases with video-EEG

Glucose transporter type 1 (GLUT1) deficiency is an inborn error of glucose transport. Clinical manifestations are presumed secondary to reduced glucose transport across the blood brain barrier, and include seizures, abnormal tone, developmental delay and hypoglycorrhachia. A high index of suspicion is important as GLUT1 deficiency is a potentially treatable cause of mental retardation. We studied two affected children by continuous video-EEG in order to better understand the cause of the clinical manifestations and improvement on a ketogenic diet. The EEG was characterized by generalized paroxysmal 2–2.5 Hz spike-wave discharges, although normal EEGs were also obtained. Atypical absence seizures were the most prominent clinical seizure. Epileptiform activity and clinical seizures occurred in both children while acutely ketotic and non-ketotic, but were markedly more frequent in one child when non-ketotic. Discharges were not associated with a reduction in substrate for brain metabolism in the blood at that time. Conclusion Atypical absence seizures are common in glucose transporter type 1 deficiency and should alert the clinician to the possibility of this treatable disorder when present in a young child with developmental delay. Our data suggest that the therapeutic mechanism of the ketogenic diet in this disorder is more complicated than simply delivering ketones as an alternative substrate for brain metabolism. Received: 28 September 1998 / Accepted: 12 May 1999     

Adolescents with clinical type 1 diabetes display reduced red blood cell glucose transporter isoform 1 (GLUT1)

Type 1 diabetic (T1D) adolescent children on insulin therapy suffer episodes of both hyper‐ and hypoglycemic episodes. Glucose transporter isoform GLUT1 expressed in blood–brain barrier (BBB) and red blood cells (RBC) compensates for perturbed circulating glucose toward protecting the supply to brain and RBCs. We hypothesized that RBC‐GLUT1 concentration, as a surrogate for BBB‐GLUT1, is altered in T1D children. To test this hypothesis, we measured RBC‐GLUT1 by enzyme‐linked immunosorbent assay (ELISA) in T1D children (n = 72; mean age 15.3 ± 0.2 yr) and control children (CON; n = 11; mean age 15.6 ± 0.9 yr) after 12 h of euglycemia and during a hyperinsulinemic–hypoglycemic clamp with a nadir blood glucose of ?3.3 mmol/L for 90 min (clamp I) or ?3 mmol/L for 45 min (clamp II). Reduced baseline RBC‐GLUT1 was observed in T1D (2.4 ± 0.17 ng/ng membrane protein); vs. CON (4.2 ± 0.61 ng/ng protein) (p < 0.0001). Additionally, baseline RBC‐GLUT1 in T1D negatively correlated with hemoglobin A1c (HbA1c) (R = ?0.23, p < 0.05) but not in CON (R = 0.06, p < 0.9). Acute decline in serum glucose to 3.3 mmol/L (90 min) or 3 mmol/L (45 min) did not change baseline RBC‐GLUT1 in T1D or CON children. We conclude that reduced RBC‐GLUT1 encountered in T1D, with no ability to compensate by increasing during acute hypoglycemia over the durations examined, may demonstrate a vulnerability of impaired RBC glucose transport (serving as a surrogate for BBB), especially in those with the worst control. We speculate that this may contribute to the perturbed cognition seen in T1D adolescents.     

Questionnaire survey on the current status of ketogenic diet therapy in patients with glucose transporter 1 deficiency syndrome (GLUT1DS) in Japan

Objectives

We conducted a questionnaire survey on the efficacy and side effects of ketogenic diet (KD) therapy in patients with glucose transporter 1 deficiency syndrome (GLUT1DS) as well as issues associated with long-term KD therapy from the viewpoint of patients' families.

Inhibitory effects of diazoxide or polymyxin B on glucose transport by isolated rat erythrocytes or adipocytes

The inhibitory effects of diazoxide or polymyxin B on 3-O-methylglucose uptake were studied in isolated rat erythrocytes or adipocytes to elucidate the mechanisms of the actions of these agents. One to three mmol/L diazoxide significantly inhibited 3-O-methylglucose uptake into erythrocytes by 11–33% without altering the equilibrium space, while 0.3 mmol/L diazoxide did not. The inhibitory effect was exerted in a dose-dependent manner in this concentration range. To test whether polymyxin B affects the process of insulin action or the glucose transport activity recruited by insulin, adipocytes prestimulated with insulin and exposed to 2 mmol/L potassium cyanide (KCN) were employed since the cells, on which glucose transporters recruited by insulin were located quiescently, were useful to estimate the effect of an agent on glucose transport activity per se. Polymyxin B (100 μg/mL) inhibited the insulin-stimulated uptake activity in this transport system by 22.5% while it inhibited the insulin-stimulated uptake activity in intact adipocytes which were not exposed to KCN by 32.2%. These results suggest that diazoxide inhibits the function of the erythrocyte glucose transporter, GLUT1*** (classified by Bell et al.), and indicate that the inhibition of the glucose transport activity recruited by insulin is the major effect of polymyxin B (100 μg/mL) and the inhibition of the process of insulin action is rather small.     

The ketogenic diet in German-speaking countries: update 2003

BACKGROUND: The ketogenic diet has been used for decades to treat intractable childhood epilepsies. It is also the treatment of choice for GLUT1 deficiency syndrome and pyruvate-dehydrogenase-complex-deficiency. Recent studies have once again confirmed the efficiacy of the diet, but the diet is hardly known in Europe and has never been quite accepted as an effective treatment of childhood epilepsy. PATIENTS: We report retrospective data on 146 children treated with the ketogenic diet in Austria, Switzerland, and Germany. METHOD: In 2000 and 2002, standardized questionaires were sent to 13 neuropediatric departments to evaluate indications, effects and side effects. RESULTS: In children with refractory epilepsy (n = 111), 8 % became seizure-free on the diet. Seizure reduction of > 90 % was achieved in additional 9 % of patients, a seizure reduction of 50-90 % in additional 14 % of patients. There was a great variability between epilepsy departments. All patients with GLUT1 deficiency syndrome (n = 18) and pyruvate-dehydrogenase-complex-deficiency (n = 15) showed clinical improvement. In GLUT1 deficiency syndrome, complete seizure control was achieved in 94 % of patients. Compliance was good in 82 % of all patients regardless of the indication for the diet. CONCLUSION: In contrast to the general restraint towards the ketogenic diet in Europe, our data supports its effectiveness as the treatment of choice for GLUT1-deficiency syndrome und pyruvate-dehydrogenase-complex-deficiency. In children with refractory epilepsy, the ketogenic diet matched the effect of most anticonvulsants and was well tolerated. These data and two workshops resulted in recommendations for the use of the ketogenic diet in children as a basis for a general diagnostic and therapeutic standards to compare and improve the use of the ketogenic diet in Europe.     

Indikation und Anwendung der ketogenen Diät im Kindesalter1. Workshop ketogene Diät am 15. Dezember 2000 in Essen

The ketogenic diet, a high fat, low carbohydrate diet, is the treatment of choice for pyruvate-dehydrogenase-deficiency and GLUT1 deficiency syndrome, and effective in intractable childhood epilepsy. In Germany the diet is hardly used, protocols are not standardized, and German literature is non-existent. 12/2000 physicians and dietitians using the ketogenic diet in Germany met. In 52 patients a good response was seen in pyruvate-dehydrogenase-deficiency (n = 7) and GLUT1 deficiency syndrome (n = 9). In intractable childhood epilepsy (n = 36) the effect of the ketogenic diet was rated as good in 3 patients (8%), moderate in 14 patients (39%), and poor in 19 patients (53%). Compliance was good and few side effects were observed. Standards for the introduction and maintenance of the ketogenic diet were developed and protocols coordinated to ensure quality control and a prospective evaluation of the diet.     

葡萄糖转运子1缺陷综合征运动障碍特点和诊疗分析

目的 探讨葡萄糖转运子1缺陷综合征（GLUT1-DS）的临床特征和诊疗方法,分析运动障碍的诊断意义。方法 收集4例GLUT1-DS患儿的临床资料,分析其临床特点和治疗随访情况。结果 4例中男2例、女2例,起病年龄2~15个月。表现为运动障碍、癫癎发作和发育迟缓,均以癫癎发作为首诊原因。4例均有持续性共济失调、肌张力异常和构音障碍,2例有持续性震颤,发作性肢体瘫痪和眼球运动障碍各2例,劳累易诱发发作性症状。4例患儿的脑脊液葡萄糖及其与血糖的比值均降低。4例均检测到SLC2A1基因突变,均接受生酮饮食治疗,生酮比3：1~2：1,发作性症状5周内完全缓解。结论 对于合并多样化运动障碍的智力运动发育迟缓的癫癎患儿需考虑GLUT1-DS,生酮饮食的生酮比维持在3：1~2：1可起效。     

Functional studies of the T295M mutation causing Glut1 deficiency: glucose efflux preferentially affected by T295M

Glucose transporter type 1 (Glut1) deficiency syndrome (Glut1 DS, OMIM: #606777) is characterized by infantile seizures, acquired microcephaly, developmental delay, hypoglycorrhachia (CSF glucose <40 mg/dL), and decreased erythrocyte glucose uptake (56.1 +/- 17% of control). Previously, we reported two patients with a mild Glut1 deficiency phenotype associated with a heterozygous GLUT1 T295M mutation and normal erythrocyte glucose uptake. We assessed the pathogenicity of T295M in the Xenopus laevis oocyte expression system. Under zero-trans influx conditions, the T295M Vmax (590 pmol/min/oocyte) was 79% of the WT value and the Km (14.3 mM) was increased compared with WT (9.6 mM). Under zero-trans efflux conditions, both the Vmax (1216 pmol/min/oocyte) and Km (8.8 mM) in T295M mutant Glut1 were markedly decreased in comparison to the WT values (7443 pmol/min/oocyte and 90.8 mM). Western blot analysis and confocal studies confirmed incorporation of the T295M mutant protein into the plasma membrane. The side chain of M295 is predicted to block the extracellular "gate" for glucose efflux in our Glut-1 molecular model. We conclude that the T295M mutation specifically alters Glut1 conformation and asymmetrically affects glucose flux across the cell by perturbing efflux more than influx. These findings explain the seemingly paradoxical findings of Glut1 DS with hypoglycorrhachia and "normal" erythrocyte glucose uptake.     

Growth hormone deficiency: a possible complication of glucose transporter 1 deficiency?

Glucose transporter 1 deficiency syndrome (GLUT1DS) is an autosomal dominant disorder of brain energy metabolism caused by impaired GLUT1-mediated glucose transport across the blood-brain barrier. Although the clinical spectrum of this disorder is expanding rapidly, the growth patterns and endocrine status of these patients are not well known. We report the case of a boy aged 12 years and 7 months who has GLUT1DS complicated by growth failure. His failure to grow had progressed since birth, and his body height was 125 cm (-3.6 SDS). Growth hormone stimulation tests showed severe growth hormone deficiency (GHD), and we initiated GH replacement therapy. After 2 years of treatment, the boy's growth rate recovered from 1.7 cm/year before treatment, to 7.5 cm/year and 4.3 cm/year after treatment with no adverse effects. We speculate that GHD is a possible complication of GLUT1DS and discuss the underlying causative mechanism. CONCLUSION: GHD may be a possible complication of GLUT1DS.