Brain morphometry of Dravet syndrome

Fenfluramine increases survival and reduces markers of neurodegeneration in a mouse model of Dravet syndrome

OBJECTIVE

In patients with Dravet syndrome (DS), fenfluramine reduced convulsive seizure frequency and provided clinical benefit in nonseizure endpoints (e.g., executive function, survival). In zebrafish mutant scn1 DS models, chronic fenfluramine treatment preserved neuronal cytoarchitecture prior to seizure onset and prevented gliosis; here, we extend these findings to a mammalian model of DS (Scn1a+/- mice) by evaluating the effects of fenfluramine on neuroinflammation (degenerated myelin, activated microglia) and survival.

METHODS

Scn1a+/- DS mice were treated subcutaneously once daily with fenfluramine (15 mg/kg) or vehicle from postnatal day (PND) 7 until 35-37. Sagittal brain sections were processed for immunohistochemistry using antibodies to degraded myelin basic protein (D-MBP) for degenerated myelin, or CD11b for activated (inflammatory) microglia; sections were scored semi-quantitatively. Apoptotic nuclei were quantified by TUNEL assay. Statistical significance was evaluated by 1-way ANOVA with post-hoc Dunnett's test (D-MBP, CD11b, and TUNEL) or Logrank Mantel-Cox (survival).

RESULTS

Quantitation of D-MBP immunostaining per 0.1 mm2 unit area of the parietal cortex and hippocampus CA3 yielded significantly higher spheroidal and punctate myelin debris counts in vehicle-treated DS mice than in wild-type mice. Fenfluramine treatment in DS mice significantly reduced these counts. Activated CD11b + microglia were more abundant in DS mouse corpus callosum and hippocampus than in wild-type controls. Fenfluramine treatment of DS mice resulted in significantly fewer activated CD11b + microglia than vehicle-treated DS mice in these brain regions. TUNEL staining in corpus callosum was increased in DS mice relative to wild-type controls. Fenfluramine treatment in DS mice lowered TUNEL staining relative to vehicle-treated DS mice. By PND 35-37, 55% of control DS mice had died, compared with 24% of DS mice receiving fenfluramine treatment (P = 0.0291).

SIGNIFICANCE

This is the first report of anti-neuroinflammation and pro-survival after fenfluramine treatment in a mammalian DS model. These results corroborate prior data in humans and animal models and suggest important pharmacological activities for fenfluramine beyond seizure reduction.

PLAIN LANGUAGE SUMMARY

Dravet syndrome is a severe epilepsy disorder that impairs learning and causes premature death. Clinical studies in patients with Dravet syndrome show that fenfluramine reduces convulsive seizures. Additional studies suggest that fenfluramine may have benefits beyond seizures, including promoting survival and improving control over emotions and behavior. Our study is the first to use a Dravet mouse model to investigate nonseizure outcomes of fenfluramine. Results showed that fenfluramine treatment of Dravet mice reduced neuroinflammation significantly more than saline treatment. Fenfluramine-treated Dravet mice also lived longer than saline-treated mice. These results support clinical observations that fenfluramine may have benefits beyond seizures.

Clinical and Genetic Features of Dravet Syndrome: A Prime Example of the Role of Precision Medicine in Genetic Epilepsy

Dravet syndrome (DS), also known as severe myoclonic epilepsy of infancy, is a rare and drug-resistant form of developmental and epileptic encephalopathies, which is both debilitating and challenging to manage, typically arising during the first year of life, with seizures often triggered by fever, infections, or vaccinations. It is characterized by frequent and prolonged seizures, developmental delays, and various other neurological and behavioral impairments. Most cases result from pathogenic mutations in the sodium voltage-gated channel alpha subunit 1 (SCN1A) gene, which encodes a critical voltage-gated sodium channel subunit involved in neuronal excitability. Precision medicine offers significant potential for improving DS diagnosis and treatment. Early genetic testing enables timely and accurate diagnosis. Advances in our understanding of DS's underlying genetic mechanisms and neurobiology have enabled the development of targeted therapies, such as gene therapy, offering more effective and less invasive treatment options for patients with DS. Targeted and gene therapies provide hope for more effective and personalized treatments. However, research into novel approaches remains in its early stages, and their clinical application remains to be seen. This review addresses the current understanding of clinical DS features, genetic involvement in DS development, and outcomes of novel DS therapies.

Morphometry and network-based atrophy patterns in SCN1A-related Dravet syndrome

Mutations of the voltage-gated sodium channel SCN1A gene (MIM#182389) are among the most clinically relevant epilepsy-related genetic mutations and present variable phenotypes, from the milder genetic epilepsy with febrile seizures plus to Dravet syndrome, a severe developmental and epileptic encephalopathy. Qualitative neuroimaging studies have identified malformations of cortical development in some patients and mild atrophic changes, partially confirmed by quantitative studies. Precise correlations between MRI findings and clinical variables have not been addressed. We used morphometric methods and network-based models to detect abnormal brain structural patterns in 34 patients with SCN1A-related epilepsy, including 22 with Dravet syndrome. By measuring the morphometric characteristics of the cortical mantle and volume of subcortical structures, we found bilateral atrophic changes in the hippocampus, amygdala, and the temporo-limbic cortex (P-value < 0.05). By correlating atrophic patterns with brain connectivity profiles, we found the region of the hippocampal formation as the epicenter of the structural changes. We also observed that Dravet syndrome was associated with more severe atrophy patterns with respect to the genetic epilepsy with febrile seizures plus phenotype (r = -0.0613, P-value = 0.03), thus suggesting that both the underlying mutation and seizure severity contribute to determine atrophic changes.

Epileptic Mechanisms Shared by Alzheimer's Disease: Viewed via the Unique Lens of Genetic Epilepsy

Our recent work on genetic epilepsy (GE) has identified common mechanisms between GE and neurodegenerative diseases including Alzheimer's disease (AD). Although both disorders are seemingly unrelated and occur at opposite ends of the age spectrum, it is likely there are shared mechanisms and studies on GE could provide unique insights into AD pathogenesis. Neurodegenerative diseases are typically late-onset disorders, but the underlying pathology may have already occurred long before the clinical symptoms emerge. Pathophysiology in the early phase of these diseases is understudied but critical for developing mechanism-based treatment. In AD, increased seizure susceptibility and silent epileptiform activity due to disrupted excitatory/inhibitory (E/I) balance has been identified much earlier than cognition deficit. Increased epileptiform activity is likely a main pathology in the early phase that directly contributes to impaired cognition. It is an enormous challenge to model the early phase of pathology with conventional AD mouse models due to the chronic disease course, let alone the complex interplay between subclinical nonconvulsive epileptiform activity, AD pathology, and cognition deficit. We have extensively studied GE, especially with gene mutations that affect the GABA pathway such as mutations in GABA_A receptors and GABA transporter 1. We believe that some mouse models developed for studying GE and insights gained from GE could provide unique opportunity to understand AD. These include the pathology in early phase of AD, endoplasmic reticulum (ER) stress, and E/I imbalance as well as the contribution to cognitive deficit. In this review, we will focus on the overlapping mechanisms between GE and AD, the insights from mutations affecting GABA_A receptors, and GABA transporter 1. We will detail mechanisms of E/I imbalance and the toxic epileptiform generation in AD, and the complex interplay between ER stress, impaired membrane protein trafficking, and synaptic physiology in both GE and AD.

Head circumferences of patients with Dravet syndrome show growth slowdown

The measurement of head circumference (HC) represents a useful and reliable tool to monitor brain growth. Many genetic conditions are associated with an abnormal pattern of head growth, but no specific pattern has been described in Dravet Syndrome (DS). To investigate the head growth trajectories in a pediatric population with DS, a retrospective analysis of medical records of patients with DS was performed in 2 epilepsy centers. Quantitative data were compared with z-score growth curve of standard population, and an independent samples t-test was performed using 6-month ranges. A total of 137 subjects aged less than 18 years were included, with a total of 529 HC values and a mean of 3.9 measures per patient. From birth until 24 months of life, HC values were almost equally distributed around the mean trajectory of the reference population from each side of the curve. This trend line deflects from the mean curve after 24 months showing a head growth slowdown reaching a statistical significance (p < .05) from 48 months for males and 60 for females. Future prospective studies are needed to assess factors that can impact head growth and explore possible phenotype-genotype correlation with HC.

Adolescent behavioral abnormalities in a Scn1a+/- mouse model of Dravet syndrome

Dravet syndrome is an intractable pediatric epilepsy associated with SCN1A mutations. In addition to having a large seizure burden and a reduced lifespan, patients with Dravet syndrome also exhibit delays in reaching normal developmental milestones in attentional, emotional, and cognitive function. These developmental delays manifest in autistic-like social withdrawal and compulsive behavior. Additionally, cognitive impairments including deficits in sensorimotor processing and memory function are present. Several mouse models utilizing heterozygous deletion of Scn1a (Scn1a^+/- mice) have been generated that recapitulate many aspects of Dravet syndrome. Studies in these mouse models of Dravet syndrome have characterized behavioral phenotypes in adult mice. In the present study, we characterized the behavioral phenotype of Scn1a^+/- mice generated by targeted deletion of Scn1a exon 1 (Scn1a^tm1Kea) during adolescence. Identifying behavioral deficits in adolescent mice would more closely model the early onset of attentional, emotional, and cognitive delays observed in patients with Dravet syndrome. The behaviors of adolescent Scn1a^+/- and wildtype (WT) mice were compared across several behavioral domains. We assessed motor function (open-field test), sociability and social recognition memory (three-chambered social preference and social interaction tests), memory function (novel object recognition, Barnes maze, fear conditioning paradigm), anxiety-related behavior (elevated plus maze and open-field thigmotaxis), startle reflex and sensorimotor gating (prepulse inhibition of startle (PPI) tests), and repetitive compulsive behavior (marble burying test). Adolescent Scn1a^+/- mice exhibited normal locomotor activity, marble burying behavior, sociability, and sensorimotor gating. However, adolescent Scn1a^+/- mice displayed increased anxiety-related thigmotactic behavior, atypical fear expression, blunted acoustic startle responses, and impaired social recognition and spatial memory. Our results show that Scn1a^+/- mice display various behavioral impairments during adolescence, which provides a foundation for testing early intervention therapies targeting developmental delays modeled in Dravet syndrome mice.

Large-scale structural alteration of brain in epileptic children with SCN1A mutation

Objective

Mutations in SCN1A gene encoding the alpha 1 subunit of the voltage gated sodium channel are associated with several epilepsy syndromes including genetic epilepsy with febrile seizures plus (GEFS +) and severe myoclonic epilepsy of infancy (SMEI). However, in most patients with SCN1A mutation, brain imaging has reported normal or non-specific findings including cerebral or cerebellar atrophy. The aim of this study was to investigate differences in brain morphometry in epileptic children with SCN1A mutation compared to healthy control subjects.

Methods

We obtained cortical morphology (thickness, and surface area) and brain volume (global, subcortical, and regional) measurements using FreeSurfer (version 5.3.0, https://surfer.nmr.mgh.harvard.edu) and compared measurements of children with epilepsy and SCN1A gene mutation (n = 21) with those of age and gender matched healthy controls (n = 42).

Results

Compared to the healthy control group, children with epilepsy and SCN1A gene mutation exhibited smaller total brain, total gray matter and white matter, cerebellar white matter, and subcortical volumes, as well as mean surface area and mean cortical thickness. A regional analysis revealed significantly reduced gray matter volume in the patient group in the bilateral inferior parietal, left lateral orbitofrontal, left precentral, right postcentral, right isthmus cingulate, right middle temporal area with smaller surface area and white matter volume in some of these areas. However, the regional cortical thickness was not significantly different in two groups.

Significance

This study showed large-scale developmental brain changes in patients with epilepsy and SCN1A gene mutation, which may be associated with the core symptoms of the patients. Further longitudinal MRI studies with larger cohorts are required to confirm the effect of SCN1A gene mutation on structural brain development.

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Surface-based morphometry was performed in epileptic children with SCN1A mutation.

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Cortical GM and WM volumes, cerebellar WM volume and surface area are smaller.

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Patients group showed similar age effect on total brain volume and GM volume.

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No significant difference were obtained in regional cortical thickness.

Optimizing the Diagnosis and Management of Dravet Syndrome: Recommendations From a North American Consensus Panel

OBJECTIVES

To establish standards for early, cost-effective, and accurate diagnosis; optimal therapies for seizures; and recommendations for evaluation and management of comorbidities for children and adults with Dravet syndrome, using a modified Delphi process.

METHODS

An expert panel was convened comprising epileptologists with nationally recognized expertise in Dravet syndrome and parents of children with Dravet syndrome, whose experience and understanding was enhanced by their active roles in Dravet syndrome associations. Panelists were asked to base their responses to questions both on their clinical expertise and results of a literature review that was forwarded to each panelist. Three rounds of online questionnaires were conducted to identify areas of consensus and strength of that consensus, as well as areas of contention.

RESULTS

The panel consisted of 13 physicians and five family members. Strong consensus was reached regarding typical clinical presentation of Dravet syndrome, range of electroencephalography and magnetic resonance imaging findings, need for genetic testing, critical information that should be conveyed to families at diagnosis, priorities for seizure control and typical degree of control, seizure triggers and recommendations for avoidance, first- and second-line therapies for seizures, requirement and indications for rescue therapy, specific recommendations for comorbidity screening, and need for family support. Consensus was not as strong regarding later therapies, including vagus nerve stimulation and callosotomy, and for specific therapies of associated comorbidities. Beyond the initial treatment with benzodiazepines and use of valproate, there was no consensus on the optimal in-hospital management of convulsive status epilepticus.

CONCLUSIONS

We were able to identify areas where there was strong consensus that we hope will (1) inform health care providers on optimal diagnosis and management of patients with Dravet syndrome, (2) support reimbursement from insurance companies for genetic testing and Dravet syndrome-specific therapies, and (3) improve quality of life for patients with Dravet syndrome and their families by avoidance of unnecessary testing and provision of an early accurate diagnosis allowing optimal selection of therapeutic strategies.

Dravet Syndrome: Diagnosis and Long-Term Course

Dravet syndrome is one of the most severe epilepsy syndromes of early childhood, and it comes with very high morbidity and mortality. The typical presentation is characterized by hemiclonic or generalized clonic seizures triggered by fever during the first year of life, followed by myoclonic, absence, focal and generalized tonic-clonic seizures. Non-convulsive status epilepticus and epileptic encephalopathy are common. Development is normal in the first year of life, but most individuals eventually suffer from intellectual impairment. Dravet syndrome is associated with mutations in the sodium channel alpha1 subunit gene (SCN1A) in 70-80% of individuals. SCN1A mutation results in inhibition of the GABAergic inhibitory interneurons, leading to excessive neuronal excitation. The "interneuron hypothesis" is the current most accepted pathophysiological mechanism of Dravet syndrome. The mortality rate is increased significantly in Dravet syndrome. Ataxia, a characteristic crouched gait and Parkinson's symptoms may develop in some individuals. It is likely that Dravet syndrome is underdiagnosed in adults with treatment-resistant epilepsy. Early diagnosis is important to avoid anti-seizure medications that exacerbate seizures.

Dysarthria and broader motor speech deficits in Dravet syndrome

OBJECTIVE

To analyze the oral motor, speech, and language phenotype in 20 children and adults with Dravet syndrome (DS) associated with mutations in SCN1A.

METHODS

Fifteen verbal and 5 minimally verbal DS patients with SCN1A mutations (aged 15 months-28 years) underwent a tailored assessment battery.

RESULTS

Speech was characterized by imprecise articulation, abnormal nasal resonance, voice, and pitch, and prosody errors. Half of verbal patients had moderate to severely impaired conversational speech intelligibility. Oral motor impairment, motor planning/programming difficulties, and poor postural control were typical. Nonverbal individuals had intentional communication. Cognitive skills varied markedly, with intellectual functioning ranging from the low average range to severe intellectual disability. Language impairment was congruent with cognition.

CONCLUSIONS

We describe a distinctive speech, language, and oral motor phenotype in children and adults with DS associated with mutations in SCN1A. Recognizing this phenotype will guide therapeutic intervention in patients with DS.

Anatomic and Functional Connectivity Relationship in Autistic Children During Three Different Experimental Conditions

A group of 21 autistic children were studied for determining the relationship between the anatomic (AC) versus functional (FC) connectivity, considering short-range and long-range brain networks. AC was assessed by the DW-MRI technique and FC by EEG coherence calculation, in three experimental conditions: basal, watching a popular cartoon with audio (V-A), and with muted audio track (VwA). For short-range connections, basal records, statistical significant correlations were found for all EEG bands in the left hemisphere, but no significant correlations were found for fast EEG frequencies in the right hemisphere. For the V-A condition, significant correlations were mainly diminished for the left hemisphere; for the right hemisphere, no significant correlations were found for the fast EEG frequency bands. For the VwA condition, significant correlations for the rapid EEG frequencies mainly disappeared for the right hemisphere. For long-range connections, basal records showed similar correlations for both hemispheres. For the right hemisphere, significant correlations incremented to all EEG bands for the V-A condition, but these significant correlations disappeared for the fast EEG frequencies in the VwA condition. It appears that in a resting-state condition, AC is better associated with functional connectivity for short-range connections in the left hemisphere. The V-A experimental condition enriches the AC and FC association for long-range connections in the right hemisphere. This might be related to an effective connectivity improvement due to full video stimulation (visual and auditory). An impaired audiovisual interaction in the right hemisphere might explain why significant correlations disappeared for the fast EEG frequencies in the VwA experimental condition.

The human epilepsy mutation GABRG2(Q390X) causes chronic subunit accumulation and neurodegeneration

Genetic epilepsy and neurodegenerative diseases are two common neurological disorders conventionally viewed as being unrelated. A subset of patients with severe genetic epilepsies with impaired development and often death respond poorly to anticonvulsant drug therapy, suggesting a need for new therapeutic targets. Previously, we reported that multiple GABA_A receptor epilepsy mutations caused protein misfolding and abnormal receptor trafficking. Here we establish in a novel model of a severe human genetic epileptic encephalopathy, the Gabrg2^+/Q390X knock-in mouse, that in addition to impairing inhibitory neurotransmission, mutant GABA_A receptor γ2(Q390X) subunits accumulated and aggregated intracellularly, activated caspase 3 and caused widespread, age-dependent neurodegeneration. These novel findings suggest that the fundamental protein metabolism and cellular consequences of the epilepsy-associated mutant γ2(Q390X) ion channel subunit are not fundamentally different from those associated with neurodegeneration. The study has far-reaching significance for identification of conserved pathological cascades and mechanism-based therapies that overlap genetic epilepsies and neurodegenerative diseases.