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

The role of molecular analysis of SLC2A1 in the diagnostic workup of glucose transporter 1 deficiency syndrome

The study aimed to investigate the role of molecular analysis of SLC2A1 in the diagnostic workup of glucose transporter 1 deficiency syndrome (Glut1DS). During 2006-2020, we received 100 requests for SLC2A1 variant analysis of patients clinically suspected for Glut1DS. Pathogenic variants were detected in 37 patients, among whom 11 were familial cases. Most patients presented with epilepsy (n = 31; 84%), movement disorders (MD) (n = 28; 76%), and intellectual disabilities (ID) (n = 29; 78%). Moreover, paroxysmal dyskinesias (PD) (n = 10; 27%) were more frequently seen in familial cases (55%) than in sporadic cases (15%) (p < .05). The Glut1DS patients with ID typically had either epilepsy or MD. The presence of MD, particularly when associated with epilepsy or ID, indicated Glut1DS (p < .05). The cerebrospinal fluid (CSF) glucose levels were at or below the 10th percentile in all 32 SLC2A1-positive patients but only in 16 of 52 (31%) SLC2A1-negative patients (p < .05). Thus, CSF analysis is an essential tool in the diagnostic workup of Glut1DS. SLC2A1 molecular analysis should be performed in patients with a family history of Glut1DS or with at least one of the following clinical features, such as epilepsy, MD, and PD with or without ID, and low CSF glucose level. This would help in precise molecular diagnosis of the disease and facilitate effective treatment and appropriate genetic counseling.

Electromyographic and Joint Kinematic Patterns in Runner's Dystonia

Runner’s dystonia (RD) is a task-specific focal dystonia of the lower limbs that occurs when running. In this retrospective case series, we present surface electromyography (EMG) and joint kinematic data from thirteen patients with RD who underwent instrumented gait analysis (IGA) at the Functional and Biomechanics Laboratory at the National Institutes of Health. Four cases of RD are described in greater detail to demonstrate the potential utility of EMG with kinematic studies to identify dystonic muscle groups in RD. In these cases, the methodology for muscle selection for botulinum toxin therapy and the therapeutic response is discussed. Lateral heel whip, a proposed novel presentation of lower-limb dystonia, is also described.

Paroxysmal movement disorders: An update

Paroxysmal movement disorders comprise both paroxysmal dyskinesia, characterized by attacks of dystonic and/or choreic movements, and episodic ataxia, defined by attacks of cerebellar ataxia. They may be primary (familial or sporadic) or secondary to an underlying cause. They can be classified according to their phenomenology (kinesigenic, non-kinesigenic or exercise-induced) or their genetic cause. The main genes involved in primary paroxysmal movement disorders include PRRT2, PNKD, SLC2A1, ATP1A3, GCH1, PARK2, ADCY5, CACNA1A and KCNA1. Many cases remain genetically undiagnosed, thereby suggesting that additional culprit genes remain to be discovered. The present report is a general overview that aims to help clinicians diagnose and treat patients with paroxysmal movement disorders.

Epilepsy genetics: the ongoing revolution

Epilepsies have long remained refractory to gene identification due to several obstacles, including a highly variable inter- and intrafamilial expressivity of the phenotypes, a high frequency of phenocopies, and a huge genetic heterogeneity. Recent technological breakthroughs, such as array comparative genomic hybridization and next generation sequencing, have been leading, in the past few years, to the identification of an increasing number of genomic regions and genes in which mutations or copy-number variations cause various epileptic disorders, revealing an enormous diversity of pathophysiological mechanisms. The field that has undergone the most striking revolution is that of epileptic encephalopathies, for which most of causing genes have been discovered since the year 2012. Some examples are the continuous spike-and-waves during slow-wave sleep and Landau-Kleffner syndromes for which the recent discovery of the role of GRIN2A mutations has finally confirmed the genetic bases. These new technologies begin to be used for diagnostic applications, and the main challenge now resides in the interpretation of the huge mass of variants detected by these methods. The identification of causative mutations in epilepsies provides definitive confirmation of the clinical diagnosis, allows accurate genetic counselling, and sometimes permits the development of new appropriate and specific antiepileptic therapies. Future challenges include the identification of the genetic or environmental factors that modify the epileptic phenotypes caused by mutations in a given gene and the understanding of the role of somatic mutations in sporadic epilepsies.

Paroxysmal dyskinesias revisited: a review of 500 genetically proven cases and a new classification

Paroxysmal movement disorders are a heterogeneous group of conditions manifesting as episodic dyskinesia with sudden onset and lasting a variable duration. Based on the difference of precipitating factors, three forms are clearly recognized, namely, paroxysmal kinesigenic (PKD), non-kinesigenic (PNKD), and exercise induced (PED). The elucidation of the genetic cause of various forms of paroxysmal dyskinesia has led to better clinical definitions based on genotype-phenotype correlations in the familial forms. However, it has been increasingly recognized that (1) there is a marked pleiotropy of mutations in such genes with still expanding clinical spectra; and (2) not all patients clinically presenting with either PKD, PNKD, or PED have mutations in these genes. We aimed to review the clinical features of 500 genetically proven cases published to date. Based on our results, it is clear that there is not a complete phenotypic-genotypic correlation, and therefore we suggest an algorithm to lead the genetic analyses. Given the fact that the reliability of current clinical categorization is not entirely valid, we further propose a novel classification for paroxysmal dyskinesias, which takes into account the recent genetic discoveries in this field.

Crystal structure of the human glucose transporter GLUT1

The glucose transporter GLUT1 catalyses facilitative diffusion of glucose into erythrocytes and is responsible for glucose supply to the brain and other organs. Dysfunctional mutations may lead to GLUT1 deficiency syndrome, whereas overexpression of GLUT1 is a prognostic indicator for cancer. Despite decades of investigation, the structure of GLUT1 remains unknown. Here we report the crystal structure of human GLUT1 at 3.2 Å resolution. The full-length protein, which has a canonical major facilitator superfamily fold, is captured in an inward-open conformation. This structure allows accurate mapping and potential mechanistic interpretation of disease-associated mutations in GLUT1. Structure-based analysis of these mutations provides an insight into the alternating access mechanism of GLUT1 and other members of the sugar porter subfamily. Structural comparison of the uniporter GLUT1 with its bacterial homologue XylE, a proton-coupled xylose symporter, allows examination of the transport mechanisms of both passive facilitators and active transporters.

GLUT1 deficiency syndrome into adulthood: a follow-up study

GLUT1 deficiency syndrome (GLUT1DS) is a treatable neurometabolic disorder in which glucose transport into the brain is disturbed. Besides the classic phenotype of intellectual disability, epilepsy, and movement disorders, other phenotypes are increasingly recognized. These include, for example, idiopathic generalized epilepsy and paroxysmal exercise-induced dyskinesia. Since the disorder has only been recognized for two decades and is mostly diagnosed in children, little is known about the disease course. Our purpose was to investigate the disease course of GLUT1DS patients with the classic, complex phenotype from infancy into adulthood. We performed a systematic literature review as well as a cohort study, including GLUT1DS patients aged 18 years and older. The literature search yielded a total of 91 adult GLUT1DS patients, of which 33 patients (one-third) had a complex phenotype. The cohort study included seven GLUT1DS patients with a complex phenotype who were prospectively followed up in our clinic from childhood into adulthood. Our results show that epilepsy is a prominent feature during childhood in classic GLUT1DS patients. During adolescence, however, epilepsy diminishes or even disappears, but new paroxysmal movement disorders, especially paroxysmal exercise-induced dyskinesia, either appear or worsen if already present in childhood. Intellectual disability was not systematically assessed, but cognitive functions appeared to be stabile throughout life. Like children, adolescents may benefit from a ketogenic diet or variants thereof.

GLUT1 deficiency syndrome: an update

INTRODUCTION

Glucose transporter type 1 deficiency syndrome is caused by heterozygous, mostly de novo, mutations in the SLC2A1 gene encoding the glucose transporter GLUT1. Mutations in this gene limit brain glucose availability and lead to cerebral energy deficiency.

STATE OF THE ART

The phenotype is characterized by the variable association of mental retardation, acquired microcephaly, complex motor disorders, and paroxysmal manifestations including seizures and non-epileptic paroxysmal episodes. Clinical severity varies from mild motor dysfunction to severe neurological disability. In patients with mild phenotypes, paroxysmal manifestations may be the sole manifestations of the disease. In particular, the diagnosis should be considered in patients with paroxysmal exercise-induced dyskinesia or with early-onset generalized epilepsy. Low CSF level of glucose, relative to blood level, is the best biochemical clue to the diagnosis although not constantly found. Molecular analysis of the SLC2A1 gene confirms the diagnosis. Ketogenic diet is the cornerstone of the treatment and implicates a close monitoring by a multidisciplinary team including trained dieticians. Non-specific drugs may be used as add-on symptomatic treatments but their effects are often disappointing.

CONCLUSION

Glucose transporter type 1 deficiency syndrome is likely under diagnosed due to its complex and pleiotropic phenotype. Proper identification of the affected patients is important for clinical practice since the disease is treatable.

Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)

Glut1 deficiency syndrome (Glut1 DS) was originally described in 1991 as a developmental encephalopathy characterized by infantile onset refractory epilepsy, cognitive impairment, and mixed motor abnormalities including spasticity, ataxia, and dystonia. The clinical condition is caused by impaired glucose transport across the blood brain barrier. The past 5 years have seen a dramatic expansion in the range of clinical syndromes that are recognized to occur with Glut1 DS. In particular, there has been greater recognition of milder phenotypes. Absence epilepsy and other idiopathic generalized epilepsy syndromes may occur with seizure onset in childhood or adulthood. A number of patients present predominantly with movement disorders, sometimes without any accompanying seizures. In particular, paroxysmal exertional dyskinesia is now a well-documented clinical feature that occurs in individuals with Glut1 DS. A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise. Intellectual impairment may range from severe to very mild. Awareness of the broad range of potential clinical phenotypes associated with Glut1 DS will facilitate earlier diagnosis of this treatable neurologic condition. The ketogenic diet is the mainstay of treatment and nourishes the starving symptomatic brain during development.

Movement disorders in GLUT1 deficiency syndrome respond to the modified Atkins diet

BACKGROUND

Movement disorders are a prominent feature of glucose transporter-1 (GLUT1) deficiency syndrome (GLUT1DS). First-choice treatment is a ketogenic diet, but compliance is poor. We have investigated the effect of the modified Atkins diet as an alternative treatment for movement disorders in GLUT1DS.

METHODS

Four patients with GLUT1DS ages 15 to 30 years who had movement disorders as the most prominent feature were prospectively evaluated after initiation of the modified Atkins diet. Movement disorders included dystonia, ataxia, myoclonus, and spasticity, either continuous or paroxysmal, triggered by action or exercise. Duration of treatment ranged from 3 months to 16 months.

RESULTS

All patients reached mild to moderate ketosis and experienced remarkable improvement in the frequency and severity of paroxysmal movement disorders. Cognitive function also improved subjectively.

CONCLUSIONS

The modified Atkins diet is an effective and feasible alternative to the ketogenic diet for the treatment of GLUT1DS-related paroxysmal movement disorders in adolescence and adulthood.

Should we routinely use modified Atkins diet instead of regular ketogenic diet to treat children with epilepsy?

The modified Atkins diet (MAD) consists of a nearly balanced diet without any age-dependent restriction of recommended daily calorie intake. Recently, there has been a marked increase in the use of the MAD in the treatment of epilepsy. Over the last 8 years, evidence suggesting that the MAD may exhibit similar anticonvulsant properties as the traditional ketogenic diet (KD) has been accumulating. KD is now an 'evidence-based' treatment for refractory epilepsy. Although there are currently no direct comparisons data from the literature suggest that the KD is more efficacious than the MAD. However, the MAD is easier to administer and has better tolerability. This review discusses when to consider each diet. The MAD may be the first diet of choice. In case of insufficient efficacy under the MAD, a switch from the MAD to the KD should be considered.