Alternating hemiplegia of childhood: no mutations in the glutamate transporter EAAT1

Alternating hemiplegia of childhood (AHC) is a severe brain disorder, mainly characterised by episodes of hemiplegia, progressive mental retardation, and other severe paroxysmal and permanent neurological symptoms. Clinically and genetically, there is some overlap with sporadic (SHM) and familial (FHM) hemiplegic migraine, a severe monogenic subtype of migraine. Although no mutations were detected in the FHM1 CACNA1A and FHM2 ATP1A2 genes in sporadic AHC patients, a mutation was found in the FHM2 ATP1A2 gene in a family with AHC. Recently, a missense mutation was found in the SLC1A3 gene that encodes the glutamate transporter EAAT1, in a patient with alternating hemiplegia, episodic ataxia, seizures, and headache. Because of the remarkable clinical similarities and the potential role of glutamate in AHC, we analysed six sporadic patients with AHC for mutations in the SLC1A3 gene. No mutations were found. The SLC1A3 EAAT1 glutamate transporter gene does not seem to be involved in the pathogenesis of AHC.     

Alternating hemiplegia of childhood: no mutations in the second familial hemiplegic migraine gene ATP1A2

Alternating hemiplegia of childhood (AHC) is a rare disorder mainly characterised by attacks of hemiplegia and mental retardation. AHC has often been associated with migraine. Previously, we have excluded the involvement of the familial hemiplegic migraine (FHM) CACNA1A gene in four patients with AHC. A second gene for FHM was discovered recently: the ATP1A2 gene on chromosome 1q23, coding for the alpha 2 subunit of Na+,K+-ATPase. We performed a mutation analysis of the ATP1A2 gene in six patients, using direct sequencing, but found no mutations in any of the 23 exons. Other cerebral ion channel genes remain candidate genes for AHC.     

Alternating Hemiplegia of Childhood With a de Novo Mutation in ATP1A3 and Changes in SLC2A1 Responsive to a Ketogenic Diet

BackgroundAlternating hemiplegia of childhood (AHC) is a rare condition characterized by an early onset of hemiplegic episodes and other paroxysmal or permanent neurological dysfunctions. Recently, mutations in the ATP1A3 gene have been identified as the causal mechanism of AHC. Regarding the differential diagnosis of AHC, glucose transporter 1 deficiency syndrome may be considered because these two disorders share some paroxystic and nonparoxystic features.Patient and resultsWe report a typical case of AHC harboring a de novo mutation in the ATP1A3 gene, together with a duplication and insertion in the SLC2A1 gene who exhibited marked clinical improvement following ketogenic diet.ConclusionBecause the contribution of the SLC2A1 mutation to the clinical phenotype cannot be definitely demonstrated, the remarkable clinical response after ketogenic diet led us to the hypothesis that ketogenic diet might be effective in AHC as it provides an alternative energy source for the brain.     

Klinisches Spektrum des Glucosetransporter-Typ-1-Defizienz-Syndroms

Glucose transport protein type 1 (GLUT1) facilitates transport of glucose from the blood across the blood-brain barrier to the central nervous system. Disruption of this transport results in cerebral energy failure and a clinical condition termed GLUT1 deficiency syndrome (GLUT1-DS) caused by heterozygous mutations in the SLC2A1 gene which encodes for GLUT1. These mutations occur de novo in most patients and are rarely inherited as an autosomal dominant trait. The classic clinical phenotype includes developmental delay, infantile onset epilepsy, deceleration of head growth, and a mixed movement disorder with ataxia, dystonia, and spasticity. Over the past years the variability of signs and symptoms in GLUT1-DS and a spectrum of milder phenotypes have been recognized. Absence epilepsy and other generalized epilepsies with infantile onset or onset in adult age, predominant movement disorder without seizures, and paroxysmal exertion-induced dyskinesia have been described. A common laboratory indication for the diagnosis of all phenotypes is a lowered glucose concentration in cerebrospinal fluid (CSF) with reduced CSF-to-blood glucose ratio. Treatment with a ketogenic diet improves seizures and movement disorders.     

Usefulness of diagnostic tools in a GLUT1 deficiency syndrome patient with 2 inherited mutations

In some patients with GLUT1 deficiency syndrome (GLUT1-DS), the diagnosis can be difficult to reach. We report a child with 2 inherited mutations suggesting an autosomal recessive transmission of SLC2A1 mutations.MethodsThe child and her parents were explored with erythrocyte 3-O-methyl-d-Glucose uptake, glucose uptake in oocytes expressing GLUT1 with the gene mutations and measure of the expression of GLUT1 at the surface of the circulating red blood cells by flow cytometry (METAglut1™ test).ResultsBoth erythrocyte glucose uptake and glucose uptake in oocyte with the patient’s mutations did not support the diagnosis of a mild GLUT1-DS phenotype with autosomal recessive transmission of SLC2A1 mutations. Instead, GLUT-1 expression at the surface of the erythrocytes appeared to better correlate with the clinical phenotypes in this family.ConclusionThe diagnostic value of these functional/expression tools need to be further studied with a focus on mild phenotype of GLUT1-DS.     

The expanding phenotype of GLUT1-deficiency syndrome

Transport of glucose from the bloodstream across the blood–brain barrier to the central nervous system is facilitated by glucose transport protein type 1 (GLUT1), the first member of the solute carrier family 2 (SLC2). Heterozygous mutations in the GLUT1/SLC2A1 gene, occurring de novo or inherited as an autosomal dominant trait, result in cerebral energy failure and a clinical condition termed GLUT1-deficiency syndrome (GLUT1-DS). Clinical features usually comprise motor and mental developmental delay, seizures with infantile onset, deceleration of head growth often resulting in acquired microcephaly, and a movement disorder with ataxia, dystonia, and spasticity. Subsequent to the delineation of this classic phenotype the variability of signs and symptoms in GLUT1-DS is being recognized. Patients with (i) carbohydrate-responsive symptoms, with (ii) predominant ataxia or dystonia, but without seizures, and with (iii) paroxysmal exertion-induced dyskinesia and seizures have been reported. Common laboratory hallmark in all phenotypes is the reduced glucose level in cerebrospinal fluid with lowered CSF-to-blood glucose ratio. Treatment with a ketogenic diet results in marked improvement of seizures and movement disorders.     

The role of SLC2A1 mutations in myoclonic astatic epilepsy and absence epilepsy,and the estimated frequency of GLUT1 deficiency syndrome

The first mutations identified in SLC2A1, encoding the glucose transporter type 1 (GLUT1) protein of the blood–brain barrier, were associated with severe epileptic encephalopathy. Recently, dominant SLC2A1 mutations were found in rare autosomal dominant families with various forms of epilepsy including early onset absence epilepsy (EOAE), myoclonic astatic epilepsy (MAE), and genetic generalized epilepsy (GGE). Our study aimed to investigate the possible role of SLC2A1 in various forms of epilepsy including MAE and absence epilepsy with early onset. We also aimed to estimate the frequency of GLUT1 deficiency syndrome in the Danish population. One hundred twenty patients with MAE, 50 patients with absence epilepsy, and 37 patients with unselected epilepsies, intellectual disability (ID), and/or various movement disorders were screened for mutations in SLC2A1. 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. None of the 120 MAE patients harbored SLC2A1 mutations. We estimated the frequency of SLC2A1 mutations in the Danish population to be approximately 1:83,000. Our study confirmed the role of SLC2A1 mutations in absence epilepsy with early onset. However, our study failed to support the notion that SLC2A1 aberrations are a cause of MAE without associated features such as movement disorders.     

Early‐onset absence epilepsy caused by mutations in the glucose transporter GLUT1

Absence epilepsies of childhood are heterogeneous with most cases following complex inheritance. Those cases with onset before 4 years of age represent a poorly studied subset. We screened 34 patients with early‐onset absence epilepsy for mutations in SLC2A1, the gene encoding the GLUT1 glucose transporter. Mutations leading to reduced protein function were found in 12% (4/34) of patients. Two mutations arose de novo, and two were familial. These findings suggest GLUT1 deficiency underlies a significant proportion of early‐onset absence epilepsy, which has both genetic counseling and treatment implications because the ketogenic diet is effective in GLUT1 deficiency. Ann Neurol 2009;66:415–419     

GLUT1 deficiency syndrome 2013: Current state of the art

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is the result of impaired glucose transport into the brain. The “classic” GLUT1DS patient presents with infantile seizures (resistant to traditional seizure medications), developmental delay, acquired microcephaly, hypotonia, spasticity, and a complex movement disorder consisting of ataxia and dystonia. However, over the years, other clinical manifestations have been described, such as paroxysmal exertion-induced dystonia with or without seizures, choreoathetosis, alternating hemiplegia, and other paroxysmal events, such as intermittent ataxia, dystonia, and migraine.At the current state of the art in understanding of GLUT1DS, classifying the disease phenotype as “classical” or “non-classical” seems to be of limited clinical utility. It seems more appropriate to think in terms of a broad clinical spectrum in which we can observe intellectual impairment, acquired microcephaly, epilepsy, and movement disorders characterized by different clinical manifestations and degrees of severity.Lumbar puncture, a simple investigation, should be considered the first diagnostic step that, moreover, is feasible worldwide. Thereafter, mutational analysis of the solute carrier family 2 (facilitated glucose transporter) member 1 (SLC2A1) gene should be performed in patients with highly suggestive clinical findings and low cerebrospinal fluid glucose (<50 mg/dl or ratio <0.60).Early diagnosis is critical because it allows prompt initiation of treatment with a ketogenic diet (KD). Childhood is the critical period for treatment of GLUT1DS: early diagnosis is crucial for an effective etiological therapy. KD treatment can be useful in adulthood too. Compliance has been found to be much better in GLUT1DS than in the other conditions for which KD treatment is indicated.     

Estudio de pacientes pediátricos con fenotipo clínico y bioquímico de síndrome de déficit de transportador de glucosa cerebral (GLUT-1)

IntroductionGlucose transporter type 1 (GLUT1) deficiency syndrome may present a range of phenotypes, including epilepsy, intellectual disability, and movement disorders. The majority of patients present low CSF glucose levels and/or defects in the SLC2A1 gene; however, some patients do not present low CSF glucose or SLC2A1 mutations, and may have other mutations in other genes with compatible phenotypes.AimsWe describe the clinical, biochemical, and genetic characteristics of the disease and perform a univariate analysis of a group of patients with clinical and biochemical phenotype of GLUT1 deficiency syndrome, with or without SLC2A1 mutations.Material and methodsThe study included 13 patients meeting clinical and biochemical criteria for GLUT1 deficiency syndrome. SLC2A1 sequencing and multiplex ligation-dependent probe amplification were performed; exome sequencing was performed for patients with negative results.ResultsSix patients presented the classic phenotype; 2 paroxysmal dyskinesia, 2 complex movement disorders, 2 early-onset absence seizures, and one presented drug-resistant childhood absence epilepsy. Six patients were positive for SLC2A1 mutations; in the other 5, another genetic defect was identified. No significant differences were observed between the 2 groups for age of onset, clinical presentation, microcephaly, intellectual disability, or response to ketogenic diet. Patients with SLC2A1 mutations presented more clinical changes in relation to diet (66.7% vs. 28.6% in the SLC2A1-negative group) and greater persistence of motor symptoms (66% vs. 28.6%); these differences were not statistically significant. Significant differences were observed for CSF glucose level (34.5 vs. 46 mg/dL, P = .04) and CSF/serum glucose ratio (0.4 vs. 0.48, P < .05).ConclusionsGLUT1 deficiency syndrome may be caused by mutations to genes other than SLC2A1 in patients with compatible phenotype, low CSF glucose level, and good response to the ketogenic diet.     

Alternating hemiplegia of childhood or familial hemiplegic migraine?: A novel ATP1A2 mutation

Alternating hemiplegia of childhood (AHC) is typically distinguished from familial hemiplegic migraine (FHM) by infantile onset of the characteristic symptoms and high prevalence of associated neurological deficits that become increasingly obvious with age. Expansion of the clinical spectrum in FHM recently has begun to blur the distinction between these disorders. We report a novel ATP1A2 mutation in a kindred with features that bridge the phenotypic spectrum between AHC and FHM syndromes, supporting a possible common pathogenesis in a subset of such cases. Mutation analysis in classic sporadic AHC patients and in an additional five kindreds in which linkage to the ATP1A2 locus could not be excluded failed to identify additional mutations.     

Early onset absence epilepsy: 1 in 10 cases is caused by GLUT1 deficiency

Glucose transporter 1 (GLUT1) deficiency caused by mutations of SLC2A1 is an increasingly recognized cause of genetic generalized epilepsy. We previously reported that >10% (4 of 34) of a cohort with early onset absence epilepsy (EOAE) had GLUT1 deficiency. This study uses a new cohort of 55 patients with EOAE to confirm that finding. Patients with typical absence seizures beginning before 4 years of age were screened for solute carrier family 2 (facilitated glucose transporter), member 1 (SLC2A1) mutations or deletions. All had generalized spike‐waves on electroencephalography (EEG). Those with tonic and/or atonic seizures were excluded. Mutations were found in 7 (13%) of 55 cases, including five missense mutations, an in‐frame deletion leading to loss of a single amino acid, and a deletion spanning two exons. Over both studies, 11 (12%) of 89 probands with EOAE have GLUT1 deficiency. Given the major treatment and genetic counseling implications, this study confirms that SLC2A1 mutational analysis should be strongly considered in EOAE.     

Pseudohyperkalemia due to cryohydrocytosis in GLUT1 deficiency syndrome. A case report and literature review

Cryohydrocytosis is a form of stomatocytosis characterized by the leakage of sodium and potassium from red blood cells at low temperatures, characterized by pseudohyperkalemia. Stomatin-deficient cryohydrocytosis is an extremely rare variant that only recently has been related to pathogenic variants in the SLC2A1 gene, encoding the main glucose transporter of the blood–brain barrier and red blood cells, GLUT1. It follows that GLUT1 deficiency syndrome, a rare but significant cause of metabolic epilepsy, may present with stomatin-deficient cryohydrocytosis, although this correlation has only been reported in a few instances. We present the case of a patient carrying a novel de novo SLC2A1 pathogenic variant presenting with GLUT1 deficiency syndrome, pseudohyperkalemia, and splenomegaly consistent with cryohydrocytosis. We also review the previously reported cases of stomatin-deficient cryohydrocytosis in the literature. As highlighted by our case, elevated potassium levels are a cause of concern, and GLUT1 deficiency syndrome patients are thus at risk of being subjected to unnecessary examinations; pseudohyperkalemia may be underrecognized in clinical practice.     

Mild adolescent/adult onset epilepsy and paroxysmal exercise-induced dyskinesia due to GLUT1 deficiency

Paroxysmal exercise-induced dyskinesia (PED) and epilepsy without intellectual disability have recently been recognized as manifestations of deficiency of the glucose transporter GLUT1, due to mutations in the gene SLC2A1. We describe a family with six definitely affected members in two generations. Two had PED, three had epilepsy, and one had both. A missense mutation in SLC2A1 (c.950A>C; p.N317T) was detected in five living affected members, but absent in three nonaffected first-degree members and in one subject believed to be a phenocopy. The clinical picture of mild epilepsy with onset in adolescence or early adulthood plus PED should raise a suspicion of GLUT1 deficiency.     

First report of GLUT1 deficiency syndrome in Chinese patients with novel and hot spot mutations in SLC2A1 gene

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is increasingly recognized as a cause of various neurological disorders but a high index of suspicion is important to make the diagnosis. We report two Chinese patients with GLUT1DS, one of which had a novel mutation in the SLC2A1 gene.     

Genetic and phenotypic heterogeneity in sporadic and familial forms of paroxysmal dyskinesia

Paroxysmal dyskinesia (PxD) is a group of movement disorders characterized by recurrent episodes of involuntary movements. Familial paroxysmal kinesigenic dyskinesia (PKD) is caused by PRRT2 mutations, but a distinct etiology has been suggested for sporadic PKD. Here we describe a cohort of patients collected from our movement disorders outpatient clinic in the period 1996–2011. Fifteen patients with sporadic PxD and 23 subjects from three pedigrees with familial PKD were screened for mutations in candidate genes. PRRT2 mutations co-segregated with PKD in two families and occurred in two sporadic cases of PKD. No mutations were detected in patients with non-kinesigenic or exertion-induced dyskinesia, and none in other candidate genes including PNKD1 (MR-1) and SLC2A1 (GLUT1). Thus, PRRT2 mutations also cause sporadic PKD as might be expected given the variable expressivity and reduced penetrance observed in familial PKD. Further genetic heterogeneity is suggested by the absence of candidate gene mutations in both sporadic and familial PKD suggesting a contribution of other genes or non-coding regions.     

ATP1A3-related epileptic encephalopathy responding to ketogenic diet

Background

Alternating Hemiplegia of Childhood (AHC) is a rare neurological disease caused by mutations in ATP1A3 gene codifying for alpha3 subunit of Na⁺-K⁺ ATPase pump. Repeated and transient attacks of hemiplegia, usually affecting one side of the body or the other, or both sides of the body at once, are the core features of AHC. Monocular nystagmus, other abnormalities in ocular movements, dystonic posturing and epilepsy are commonly associated to AHC. However, the spectrum of ATP1A3 related diseases is still expanding and new phenotypes have been reported.

Video/EEG recording of myoclonic absences in GLUT1 deficiency syndrome with a hot-spot R126C mutation in the SLC2A1 gene

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is an inborn error of brain energy metabolism characterized by impaired glucose transport into the brain. A classic phenotype comprising epilepsy, mental retardation, an often paroxysmal disorder, and several subtypes has been described. Although typical absences are frequent in GLUT1DS, myoclonic absence seizures are rarely reported. Here we describe a novel Turkish patient with a hot-spot mutation (R126C) in the SLC2A1 gene who presented with unusual myoclonic absence epilepsy and paroxysmal shivering. The case is discussed in view of eight other cases carrying the R126C mutation.     

Long-term follow up of an adult with alternating hemiplegia of childhood and a p.Gly755Ser mutation in the ATP1A3 gene

Alternating hemiplegia of childhood (AHC) is a rare neurological disease mainly caused by mutations in the ATP1A3 gene and showing varied clinical severity according to genotype. Patients with a p.Gly755Ser (p.G755S) mutation, one of minor genotypes for AHC, were recently described as having a mild phenotype, although their long-term outcomes are still unclear due to the lack of long-term follow up. Here, we demonstrate the full clinical course of a 43-year-old female AHC patient with p.G755S mutation. Although her motor dysfunction had been relatively mild into her 30?s, she showed a subsequent severe aggravation of symptoms that left her bedridden, concomitant with a recent recurrence of seizure status. The seizures were refractory to anti-epileptic drugs, but administration of flunarizine improved seizures and the paralysis.Our case suggests that the phenotype of AHC with p.G755S mutation is not necessarily mild, despite such a presentation during the patient’s younger years.     

Alternating hemiplegia of childhood: New diagnostic options

A syndrome of alternating hemiplegia of childhood (AHC) is a rare disorder first presented in 1971. AHC is characterized by transient episodes of hemiplegia affecting either one or both sides of the body. Age of onset is before 18 months and the common earliest manifestations are dystonic or tonic attacks and nystagmus. Hemiplegic episodes last minutes to days and the frequency and duration tend to decrease with time. Motor and intellectual development is affected, deficits may also develop later. Epileptic seizures occur in some patients. Neuroimaging of the brain usually reveals no abnormalities. The variability of individual clinical presentations and evolution of symptoms have made diagnosis difficult. Therefore the problems of misdiagnosis could account for the low prevalence of this syndrome. This paper hopes to present actual data on AHC, especially of the results of genetic research and new diagnostic tools.