Review: Current Knowledge of SLC6A1-Related Neurodevelopmental Disorders

Abstract, originally published in Brain Communications

Advances in gene discovery have identified genetic variants in the solute carrier family 6 member 1 (SLC6A1) gene as a monogenic cause of neurodevelopmental disorders, including epilepsy with myoclonic atonic seizures, autism spectrum disorder, and intellectual disability. The SLC6A1 gene encodes for the GABA transporter protein type 1 (GAT1), which is responsible for the reuptake of the neurotransmitter GABA, the primary inhibitory neurotransmitter in the central nervous system, from the extracellular space. GABAergic inhibition is essential to counterbalance neuronal excitation, and when significantly disrupted, it negatively impacts brain development leading to developmental differences and seizures. Aggregation of patient variants and observed clinical manifestations expand understanding of the genotypic and phenotypic spectrum of this disorder. Here, we assess genetic and phenotypic features in 116 individuals with SLC6A1 variants, the vast majority of which are likely to lead to GAT1 loss-of-function. The knowledge acquired will guide therapeutic decisions and the development of targeted therapies that selectively enhance transporter function and may improve symptoms. We analyzed the longitudinal and cell type-specific expression of SLC6A1 in humans and localization of patient and control missense variants in a novel GAT1 protein structure model. In this update, we discuss the progress made in understanding and treating SLC6A1-related disorders thus far, through the concerted efforts of clinicians, scientists, and family support groups.

Does the Accumulated Antiepileptic Drug Load in Chronic Epilepsy Reflect Disease Severity?

Abstract, originally published in Epilepsia

Objective: To ascertain factors that are related to the antiepileptic drug load in epilepsy.

Methods: In this cross-sectional study, we analyzed a large cohort of conservatively treated patients with epilepsy (n = 1135) and a smaller homogeneous group of presurgical patients with neuropathologically confirmed unilateral hippocampal sclerosis (n = 91). Considered clinical variables comprised (1) presence of an underlying cerebral lesion, (2) onset and (3) duration of epilepsy, (4) seizure frequency, (5) generalized or focal to bilateral tonic-clonic seizures, (6) ictal impairment of awareness, and (7) a history of convulsive status epilepticus. In the presurgical sample, we additionally considered (8) the degree of pathology (hippocampal neuronal cell densities) instead of (1) presence of a cerebral lesion and (9) an overall rating of epilepsy severity (GASE scale). Drug load was quantified as (a) the number of concomitant antiepileptic drugs (AEDs) and (b) the total defined daily dose (DDD).

Results: Analyses disclosed only small correlations between clinical variables and drug load indices. In the conservatively treated cohort, the multiple regression analyses revealed that epilepsy onset, cerebral lesion, history of convulsive status epilepticus, and seizure frequency combined explained only 6%–10% of variance in drug load. Nearly the same variance (5%–8%) could be explained by duration of epilepsy alone. Degree of hippocampal pathology and the epilepsy severity ratings were not related to drug load indices.

Significance: Clinical markers of epilepsy severity were only marginally associated with drug load. Findings rather indicate that patients seem to accumulate drugs due to the chronicity of epilepsy. Overall, the drug load remained largely unexplained. The findings nevertheless call for scrutinizing multidrug therapies in patients with long-lasting epilepsies.

Certain EEG Patterns, Febrile Seizures and Juvenile Myoclonic Epilepsy Associated With Worse Long-Term Outcomes for Individuals With Generalized Genetic Epilepsy

Abstract, originally published in Epilepsia

Objective: To assess prognostic patterns and investigate clinical and electroencephalography (EEG) variables associated with persistent treatment resistance in a population of genetic generalized epilepsy (GGE) patients with a long-term follow-up.

Methods: Data from GGE patients followed from 1975 to 2019 were reviewed retrospectively. Subjects with a follow-up >10 years, starting from epilepsy diagnosis, were included. Persistent treatment resistance was defined as the absence of any period of remission ≥1 year despite treatment with two appropriate and adequate antiepileptic drugs (AEDs).

Results: One hundred ninety-nine patients were included. The median age was 39.5 years (interquartile range [IQR] 30-49) and the median follow-up was 27 years (IQR 18-35). The most common syndrome was juvenile myoclonic epilepsy (JME), diagnosed in 44.2% of patients. During follow-up, 163 subjects (81.9%) experienced 3-year remission from any seizure type, whereas 5- and 10-year remission occurred in 141 (70.8%) and 92 (46.2%) cases, respectively. The most common prognostic pattern was a relapsing-remitting course, observed in 80 patients (40.2%), whereas 29 (14.6%) displayed persistent treatment resistance. According to multivariable logistic regression analysis, febrile seizures (FS), specific EEG patterns (namely generalized paroxysmal fast activity, GPFA) and valproate (VPA) resistance were the only variables significantly associated with persistent treatment resistance. JME was the only epilepsy syndrome statistically associated with persistent treatment resistance in univariable logistic regression analysis.

Significance: Persistent treatment resistance was observed in almost 15% of genetic generalized epilepsy patients followed in a tertiary epilepsy center. A worse outcome was associated with specific clinical variables (juvenile myoclonic epilepsy, febrile seizures) and EEG patterns (generalized paroxysmal fast activity).

Enduring Language Deficits in Children of Women With Epilepsy and the Potential Role of Intrauterine Exposure to Antiepileptic Drugs

Abstract, originally published in Epilepsia

Objective: Exposure to certain intrauterine antiepileptic drugs (AEDs) can negatively influence the language skills and intelligence of young children. It remains unanswered whether these deficits are transient or persist as children grow up. This study aims to evaluate the language function of children of women with epilepsy (CWE) aged 9-13 years in comparison with their peers, and its relationship with intrauterine AED exposure.

Methods: We included 191 CWE in our study from the Kerala Registry of Epilepsy and Pregnancy. Children in the same age group (n = 144) and without maternal epilepsy or antenatal AED exposure served as controls. We used Clinical Examination for Language Function version IV to assess language in both groups. Relevant data related to maternal epilepsy and AED use were obtained from the registry records.

Results: The average Core Language Scaled Score (CLSS) was significantly lower in CWE as compared to controls (83.19 vs 90.18, P = .001). Similarly, the mean scaled scores in other language parameters were also significantly lower in CWE. In the multivariate analysis, compared to control children, the average CLSS in CWE was 4.5 units lower (95% confidence interval [CI] = -8.8 to -0.2, P = .04) with AED monotherapy exposure and 7.3 units lower with exposure to AED polytherapy (95% CI = -13.8 to -0.8, P = .03). Intrauterine exposure to phenobarbitone (n = 61) and valproate (n = 55) as either monotherapy or polytherapy showed a negative effect on CLSS in CWE as compared to control children. However, carbamazepine (n = 75) and phenytoin (n = 37) use was not associated with significant variation of CLSS. In head-to-head comparisons between AED monotherapies in CWE, phenobarbitone showed a negative effect on CLSS (-14.7, 95% CI = -23.1 to -6.4, P = .001) as compared to carbamazepine.

Significance: Intrauterine exposure to phenobarbitone and valproate impairs language development in children with epilepsy, with effects persisting into the second decade.

College of Medicine Researcher Makes Novel Discoveries in Preventing Epileptic Seizures

Article, originally published by Florida State University News

A team of researchers from the Florida State University College of Medicine has found that an amino acid produced by the brain could play a crucial role in preventing a type of epileptic seizure.

Temporal lobe epileptic seizures are debilitating and can cause lasting damage in patients, including neuronal death and loss of neuron function.

Sanjay Kumar, an associate professor in the College of Medicine’s Department of Biomedical Sciences, and his team are paving the way toward finding effective therapies for this disease.

The research team found a mechanism in the brain responsible for triggering epileptic seizures. Their research indicates that an amino acid known as D-serine could work with the mechanism to help prevent epileptic seizures, thereby also preventing the death of neural cells that accompanies them.

The team’s findings were published in the journal Nature Communications.

Machine Learning From Wristband Sensor Data for Wearable, Noninvasive Seizure Forecasting

Abstract, originally published in Epilepsia

Objective: Seizure forecasting may provide patients with timely warnings to adapt their daily activities and help clinicians deliver more objective, personalized treatments. Although recent work has convincingly demonstrated that seizure risk assessment is in principle possible, these early approaches relied largely on complex, often invasive setups including intracranial electrocorticography, implanted devices, and multichannel electroencephalography, and required patient-specific adaptation or learning to perform optimally, all of which limit translation to broad clinical application. To facilitate broader adaptation of seizure forecasting in clinical practice, noninvasive, easily applicable techniques that reliably assess seizure risk without much prior tuning are crucial. Wristbands that continuously record physiological parameters, including electrodermal activity, body temperature, blood volume pulse, and actigraphy, may afford monitoring of autonomous nervous system function and movement relevant for such a task, hence minimizing potential complications associated with invasive monitoring and avoiding stigma associated with bulky external monitoring devices on the head.

Methods: Here, we applied deep learning on multimodal wristband sensor data from 69 patients with epilepsy (total duration > 2311 hours, 452 seizures) to assess its capability to forecast seizures in a statistically significant way.

Results: Using a leave-one-subject-out cross-validation approach, we identified better-than-chance predictability in 43% of the patients. Time-matched seizure surrogate data analyses indicated forecasting not to be driven simply by time of day or vigilance state. Prediction performance peaked when all sensor modalities were used, and did not differ between generalized and focal seizure types, but generally increased with the size of the training dataset, indicating potential further improvement with larger datasets in the future.

Significance: Collectively, these results show that statistically significant seizure risk assessments are feasible from easy-to-use, noninvasive wearable devices without the need of patient-specific training or parameter optimization.

Epilepsy Research News: October 2020

This month’s research news features two studies advancing Dravet syndrome research, both utilizing mouse models mimicking the disorder. One study, featuring the work of former CURE Grantee Dr. Lori Isom, tested a new type of drug and found that it decreased the frequency of Sudden Unexplained Death in Epilepsy (SUDEP) in these mice.

In other news, a recent study has increased our understanding of the unique way epilepsy can affect women, showing that women who have seizures that increase in frequency during their menstrual cycle are also more likely to have drug-resistant epilepsy.

Finally, research has helped pinpoint individuals with epilepsy who may be at risk for obstructive sleep apnea, a finding that may help physicians identify who is most at risk and who would likely benefit from treatment.

Summaries of these research discoveries and more are below.

Research Discoveries

Dravet Syndrome (Featuring the work of former CURE Grantee, Dr. Lori Isom)
A new treatment curbs deadly seizures in a mouse model of Dravet syndrome, a severe form of epilepsy, according to a new study. This new drug counteracts the effects of mutations in a gene known as SCN1A, which cause Dravet syndrome. In this study, the drug significantly decreased the overall frequency of SUDEP, lowering the likelihood of a fatal seizure. A clinical trial is evaluating the drug’s safety in children with the syndrome.

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Dravet Syndrome
A study has utilized a gene therapy technique to reduce seizures and improve behaviors in a mouse model of Dravet syndrome. Researchers used the technique to activate the SCN1A gene, a gene with decreased activity in individuals with Dravet syndrome. The authors note that although more work must be done before the technique can be tested in people, the study supports a potential new approach to treating this cause of epilepsy.

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Epilepsy Genetics
Researchers have identified a critical new step in how brain cells function in people with one of the most common forms of epilepsy. Using mice, researchers found certain changes in gene activity and regulation in an area of the brain important in temporal lobe epilepsy. The researchers note that the study could eventually lead to targeted treatments that prevent a person from developing epilepsy.

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Epilepsy and Fetal Alcohol Spectrum Disorder
A study has found a much higher prevalence of epilepsy or history of seizures in individuals with fetal alcohol spectrum disorder (FASD), a disorder that refers to a range of developmental problems that result from maternal drinking during pregnancy. Although more research is needed to establish a direct cause-effect relationship between FASD and epilepsy, the study, which examined the medical histories of individuals from two FASD clinics, supports the link between maternal drinking during pregnancy and a wide array of health impacts to the child.

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Drug Resistant Epilepsy and Women
More frequent seizures during the menstrual cycle in women with genetic generalized epilepsy have been linked for the first time to drug-resistant epilepsy. Women with catamenial epilepsy, a generalized epilepsy characterized by increased seizure frequency during the menstrual cycle, were nearly four times more likely to have drug-resistant epilepsy than women who experience no changes in frequency.

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Epilepsy and Sleep Apnea
People with generalized epilepsy who have seizures arising from both sides of the brain simultaneously have a higher risk of obstructive sleep apnea than those who have focal epilepsy where seizures emanate from one area of the brain, according to a new study. These findings may help physicians better understand who is most at risk for obstructive sleep apnea and, therefore, who will benefit most from treatment.

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Risk of Stroke After New-Onset Seizures

Article, originally published in Seizure – European Journal of Epilepsy

Researchers quantified the risk of stroke following epileptic seizures in this case-control analysis based on Swedish national registers. From the Swedish Stroke Register, they selected cases ≤100 years of age with a first-ever stroke from 2001-2009. They used the Population Register to identify stroke-free controls (matched for age and gender). This study involved a total of 123,105 stroke cases and 250,506 controls. Epileptic seizures prior to index stroke date were detected in 1,559 (1.27%) cases and 1,806 (0.72%) controls. An elevated risk of subsequent stroke was observed in relation to a history of epileptic seizures. The risk appeared to be especially high in the first year after seizure diagnosis; this finding lends support to the notion that unexplained late-onset seizures may merit prompt evaluation of vascular risk profile. Further inquiry is needed for the nature of stroke prevention.

Efficacy and Safety of Fenfluramine Hydrochloride (Fintepla®) for the Treatment of Seizures in Dravet Syndrome: A Real-world Study

Abstract, originally published in Epilepsia

Objective: Dravet syndrome (DS) is a drug-resistant, infantile onset epilepsy syndrome with multiple seizure types and developmental delay. In recently published randomized controlled trials, fenfluramine (FFA) proved to be safe and effective in DS.

Methods: DS patients were treated with FFA in the Zogenix Early Access Program at four Italian pediatric epilepsy centers. FFA was administered as add-on, twice daily at an initial dose of 0.2 mg/kg/d up to 0.7 mg/kg/d. Seizures were recorded in a diary. Adverse events and cardiac safety (with Doppler echocardiography) were investigated every 3 to 6 months.

Results: Fifty-two patients were enrolled, with a median age of 8.6 years (interquartile range [IQR] = 4.1-13.9). Forty-five (86.5%) patients completed the efficacy analysis. The median follow-up was 9.0 months (IQR = 3.2-9.5). At last follow-up visit, there was a 77.4% median reduction in convulsive seizures. Thirty-two patients (71.1%) had a ≥ 50% reduction of convulsive seizures, 24 (53.3%) had a ≥ 75% reduction, and five (11.1%) were seizure-free. The most common adverse event was decreased appetite (n = 7, 13.4%). No echocardiographic signs of cardiac valvulopathy or pulmonary hypertension were observed. There was no correlation between type of genetic variants and response to FFA.

Significance: In this real-world study, fenfluramine provided a clinically meaningful reduction in convulsive seizure frequency in the majority of patients with DS and was well tolerated.

Study Examines the Potential Role of Next-Generation Sequencing for Genetic Diagnoses of Epilepsy Presenting in the First 2 Years of Life

Abstract, originally published in Epilepsia

Objective: Population?based data on epilepsy syndromes and etiologies in early onset epilepsy are scarce. The use of next?generation sequencing (NGS) has hitherto not been reported in this context. The aim of this study is to describe children with epilepsy onset before 2 years of age, and to explore to what degree whole exome and whole genome sequencing (WES/WGS) can help reveal a molecular genetic diagnosis.

Methods: Children presenting with a first unprovoked epileptic seizure before age 2 years and registered in the Stockholm Incidence Registry of Epilepsy (SIRE) between September 1, 2001 and December 31, 2006, were retrieved and their medical records up to age 7 years reviewed. Children who met the epilepsy criteria were included in the study cohort. WES/WGS was offered in cases of suspected genetic etiology regardless of whether a structural or metabolic diagnosis had been established.

Results: One hundred sixteen children were included, of which 88 had seizure onset during the first year of life and 28 during the second, corresponding to incidences of 139 and 42/100 000 person?years, respectively. An epilepsy syndrome could be diagnosed in 54% of cases, corresponding to a birth prevalence of 1/1100. Structural etiology was revealed in 34% of cases, a genetic cause in 20%, and altogether etiology was known in 65% of children. The highest diagnostic yield was seen in magnetic resonance imaging (MRI) with 65% revealing an etiology. WES/WGS was performed in 26/116 cases (22%), with a diagnostic yield of 58%.

Significance: Epilepsy syndromes can be diagnosed and etiologies revealed in a majority of early onset cases. Next-generation sequencing can identify a molecular diagnosis in a substantial number of children, and should be included in the work?up, especially in cases of epileptic encephalopathy, cerebral malformation, or metabolic disease without molecular diagnosis. A genetic diagnosis is essential to genetic counselling, prenatal diagnostics, and precision therapy.