CURE Discovery: New Genetic Models of Epileptic Encephalopathies Deepen Our Understanding

This research is generously supported by a grant from Jen Scott and Pierre-Gilles Henry, PhD, in honor of Felix Henry.

Key Points

  • CURE grantee Dr. Mingshan Xue created mice modeling the features of STXBP1-related epileptic encephalopathy (EE) to explore why not having enough STXBP1 activity can cause epilepsy.
  • The team found that inhibitory brain signaling was diminished in the models, causing excessive neuronal excitation, seizures, and other neurological features seen in humans with EE.
  • The long-term goal of the team’s project is to understand the mechanisms that cause EEs and use this knowledge to develop new therapies.

Deep Dive

Reduced activity of a gene called STXBP1 is one of the most common causes of epileptic encephalopathy (EE),1a group of severe pediatric epilepsies which includes Ohtahara Syndrome, West Syndrome, and Dravet Syndrome. Patients with EE often have aggressive, treatment-resistant seizures, developmental delays, behavioral deficits, and intellectual disability among other clinical features. There is an urgent need to better understand these syndromes and develop new therapies for them.

CURE grantee Dr. Mingshan Xue and his colleagues at the Baylor College of Medicine created mouse models with reduced STXBP1 activity to study epilepsy associated with this genetic variant. Through extensive testing, they determined these mice accurately represented EE clinical features such as seizures, behavioral, and cognitive deficits.2

For their CURE-funded work, the team used these models to determine how not having enough STXBP1 activity could cause EE. The team previously observed high levels of neuronal excitation in the brains of mice with low STXBP1. Thus, Dr. Xue’s team hypothesized that not having enough STXBP1 must prevent inhibitory neuronal signaling, causing an imbalance between excitation and inhibition in the brain.

To test this, the team recorded the electrical activity of neurons in the model with reduced STXBP1 activity. They found that inhibitory brain signaling was indeed diminished in these mice while excitatory signaling was not affected, resulting in excessive excitation, seizures, and other neurological features of EE. Further testing revealed that mice with reduced STXBP1 activity specifically in inhibitory neurons had higher anxiety, impaired motor skills, and reduced cognitive function – all features that are seen in humans with EE.

EEs are typically hard to treat with currently available options. The team’s long-term goal is to understand the mechanisms that cause EEs and use this knowledge to develop new therapies. Since completing their CURE-funded grant, Dr. Xue and his co-investigator have received a National Institutes of Health grant, as well as an American Epilepsy Society postdoctoral fellowship to continue this important work.

Bridging the Gap Between STXBP1 Researchers and Families

We are honored to sponsor and attend the first ever STXBP1 Investigators and Family Meeting (SIFM) on June 21, 2019 and June 22, 2019 in Philadelphia. This conference is hosted by STXBP1 Foundation and the Center for Cellular and Molecular Therapeutics (CCMT).

The need for developing community and driving more research on this group of EEs is clear. The inaugural SIFM will bring together researchers and families of individuals with STXBP1 encephalopathies to foster community development and accelerate the search for a cure. This conference is designed to encourage interaction and in-depth discussions among researchers and clinicians to further research and innovation in this field.

You can find out more information about this conference here.

1 Carvill GL et.al. Nat Genet. 2013 Jul;45(7):825-30. doi: 10.1038/ng.2646
2 Wu Chen et.al., Apr 29, 2019, https://www.biorxiv.org/content/10.1101/621516v1

Clinical Study Finds Two Types of SCN8A-Related Epilepsy: Slowly Emerging or Sudden Onset of Epilepsy

Objective: To describe the mode of onset of SCN8A-related severe epilepsy in order to facilitate early recognition, and eventually early treatment with sodium channel blockers.

Methods: Researchers reviewed the phenotype of patients carrying a mutation in the SCN8A gene, among a multicentric cohort of 638 patients prospectively followed by several pediatric neurologists. The study focused on the way clinicians made the diagnosis of epileptic encephalopathy, the very first symptoms, electroencephalography (EEG) findings, and seizure types. The team made genotypic/phenotypic correlation based on epilepsy-associated missense variant localization over the protein.

Results: The study found 19 patients carrying a de novo mutation of SCN8A, representing 3% of our cohort, with 9 mutations being novel. Age at onset of epilepsy was 1 day to 16 months. The team also found two modes of onset: 12 patients had slowly emerging onset with rare and/or subtle seizures and normal interictal EEG (group 1). The first event was either acute generalized tonic-clonic seizure (GTCS; Group  1a, n = 6) or episodes of myoclonic jerks that were often mistaken for sleep-related movements or other movement disorders (Group 1b, n = 6). Seven patients had a sudden onset of frequent tonic seizures or epileptic spasms with abnormal interictal EEG leading to rapid diagnosis of epileptic encephalopathy. Sodium channel blockers were effective or nonaggravating in most cases.

Significance: SCN8A is the third most prevalent early onset epileptic encephalopathy gene and is associated with two modes of onset of epilepsy.

Epilepsy Research Findings: May 2019

In this month’s research news, treatments, genetic analysis, and preclinical work offer hope to those impacted by hard-to-treat or difficult-to-diagnose forms of epilepsy.

Exciting treatment developments include a positive Phase 3 clinical trial outcomefor the cannabidiol-based drug EPIDIOLEX® for the treatment of seizures associated with tuberous sclerosis complex. In addition, an improved treatment regimen targeting the severe, prolonged seizures that make up status epilepticus has been created.

In promising genetics news, a report from CURE’s own Epilepsy Genetics Initiativeunderscores the value of continued reanalysis of genetic information from people with epilepsy to increase their chances of obtaining a genetic diagnosis for their epilepsy.

Additionally, important preclinical work led by CURE Grantees Dr. Chris Dulla and Dr. Janice Naegele uncovers a potential drug to treat post-traumatic epilepsy and a way to restore the balance of brain activity and reduce seizures in temporal lobe epilepsy, respectively.

Summaries of all highlighted studies follow below. I’ve organized the findings into four categories: Treatment Advances, Diagnostic Advances, Research Discoveries, and Also Notable.

Treatment Advances

GW Pharmaceuticals Reports Reduction in Seizure Frequency for EPIDIOLEX® (cannabidiol) Oral Solution in Patients with Seizures Associated With Tuberous Sclerosis Complex
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GW Pharmaceuticals and Greenwich Biosciences announced positive top-line results of a Phase 3 clinical trial of EPIDIOLEX® (cannabidiol or CBD) in the treatment of seizures associated with Tuberous Sclerosis Complex (TSC). TSC is a rare and severe form of childhood-onset epilepsy. In this trial, EPIDIOLEX met its primary endpoint, which was a reduction in seizure frequency in the group given EPIDIOLEX compared to the placebo group.

Breakthrough for Children with Serious Epileptic Seizures
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A new treatment regimen of administering levetiracetam and phenytoin one after the other has given emergency medicine doctors a better way to treat severe, prolonged epileptic seizures in children. These treatment modifications will lower the chances of intubation and intensive care, as well as increase the chances of children recovering more quickly.

Diagnostic Advances

The Epilepsy Genetics Initiative: Systematic Reanalysis of Diagnostic Exomes Increases Yield
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Featuring CURE’s Epilepsy Genetics Initiative

Results from CURE’s Epilepsy Genetics Initiative (EGI) show that when the genetic information of a person with epilepsy is systematically reanalyzed, there is an increase in the return of a genetic diagnosis. Eight new diagnoses were made as a result of updated annotations or the discovery of novel epilepsy genes after the initial diagnostic analysis was performed. One novel epilepsy gene was discovered through dual interrogation of research and clinically generated whole-exome sequencing. According to this recently-published report, EGI’s contributions to gene discovery underscore the importance of data sharing and the value of collaborative enterprises.

Research Discoveries

Using a Drug that Mimics the Ketogenic Diet to Help Prevent Epilepsy after Traumatic Brain Injury
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Featuring the work of CURE Grantee Dr. Chris Dulla

Neuroscientists led by CURE Grantee Dr. Chris Dulla at Tufts University School of Medicine prevented the development of epileptic activity in mice after traumatic brain injury by using a drug that mimics the metabolic effects of the ketogenic diet.

Neural Stem Cell Transplantation May Reduce Abnormal Increases in New Cells in the Brains of Mice with Temporal Lobe Epilepsy
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Featuring the work of CURE Grantee Dr. Janice Naegele

According to a new, CURE-funded study featuring the work of grantee Dr. Janice Naegele, the transplantation of inhibitory cells into the brains of mice with temporal lobe epilepsy may reduce the abnormal growth of new neurons in an area of the brain called the hippocampus. This in turn could reduce brain hyperexcitability that leads to seizures.

Stimulating the Epileptic Brain Breaks Up Neural Networks to Prevent Seizures
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Responsive neurostimulation treats epilepsy by detecting seizures and intervening with a jolt of electric current. Over time, most patients find their seizures become fewer and further between. New evidence suggests responsive neurostimulation can remodel the brain to be less susceptible to seizures.

Scientists Discover Trigger Region for Absence Epileptic Seizures
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Scientists have discovered a neurological origin for absence seizures – a type of seizure characterized by very short periods of lost consciousness in which people appear to stare blankly at nothing. Using a mouse model of childhood epilepsy, a group of scientists has shown that absence epilepsy can be triggered by impaired communication between two brain regions: the cortex and the striatum.

Autism-Related Memory and Seizures Improved through Gene Repair in Adults
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Scientists have shown that correcting the protein deficiency caused by a genetic form of autism spectrum disorder in adult mice can improve behavioral and electrophysiological measures of both memory and seizure. The evidence suggests this is true even when the treatment is carried out well past what has traditionally been thought of as the critical window of early brain development.

Drug Used to Treat Multiple Sclerosis May Be Beneficial for Individuals with Epilepsy 
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A drug commonly used to treat multiple sclerosis may, after necessary modifications, one day be used to treat patients with epilepsy, according to research from the laboratory of Dr. Inna Slutsky.

Study Reveals How Glial Cells May Play Key Epilepsy Role
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A study provides potential new targets for treating epilepsy and novel fundamental insights into the relationship between neurons and their glial “helper” cells. This study reports finding a key sequence of molecular events in which the genetic mutation in a fruit fly model of epilepsy leaves neurons vulnerable to becoming hyper-activated by stress, leading to seizures.

Ketogenic Diet May Reduce Sudden Unexpected Deaths in Epilepsy, Mouse Study Suggests
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Sudden unexpected death in epilepsy (SUDEP) occurs more frequently during the early evening and is significantly prevented by prolonged use of the ketogenic diet, research in a mouse model of Dravet syndrome suggests. The reasons why this happens are unclear and should be examined in more depth by future studies, but these findings may be useful to understand why most SUDEP episodes happen at night and how certain diets can benefit people with epilepsy, especially those with Dravet syndrome, researchers say.

Attention, Behavioral Problems Common in New, Recent-Onset Juvenile Myoclonic Epilepsy
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Children with new recent-onset juvenile myoclonic epilepsy are more likely to have difficulty with executive, attention, and verbal faculties than their healthy peers and are also more likely to use a greater number of academic services, researchers found.

Also Notable

Zogenix Receives Refusal to File Letter from FDA for FINTEPLA® New Drug Application
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Zogenix announced that it received a Refusal to File letter from the FDA regarding its New Drug Application (NDA) for FINTEPLA® for the treatment of seizures associated with Dravet syndrome. Upon its preliminary review, the FDA determined that the NDA was not sufficiently complete to permit a substantive review.

Is Targeting of Compensatory Ion Channel Gene Expression a Viable Therapeutic Strategy for Dravet Syndrome?

Loss of function in the Scn1a gene leads to a severe epileptic encephalopathy called Dravet syndrome (DS). Reduced excitability in cortical inhibitory neurons is thought to be the major cause of DS seizures. Here, in contrast, researchers show enhanced excitability in thalamic inhibitory neurons that promotes the nonconvulsive seizures that are a prominent yet poorly understood feature of DS. In a mouse model of DS with a loss of function in Scn1a, reticular thalamic cells exhibited abnormally long bursts of firing caused by the downregulation of calcium-activated potassium SK channels.

The authors claim that this study supports a mechanism in which loss of potassium SK channel activity causes the reticular thalamic neurons to become hyperexcitable and promote nonconvulsive seizures in DS. They propose that reduced excitability of inhibitory neurons is not global in Dravet syndrome and that non-GABAergic mechanisms such as SK channels may be important targets for treatment.

Autism-Related Memory and Seizures Improved through Gene Repair in Adult Animals

Scientists in the US have shown that correcting the protein deficiency caused by a genetic form of autism spectrum disorder (ASD) in adult mice can improve some of the characteristic symptoms, even though the treatment is carried out well past what has traditionally been thought of as the critical window of early brain development. The studies, carried out in a mouse model of human ASD caused by defects in the SYNGAP1 gene, found that restoring normal SynGAP protein levels in adult animals improved behavioral and electrophysiological measures of both memory and seizure. The authors suggest that future gene therapies for genetic causes of neurodevelopmental disorders (NDDs) such as ASD, intellectual disability (ID), and epilepsy, may also be effective in adult patients.

“Our findings in mice suggest that neurodevelopmental disorders’ disease course can be altered in adult patients,” said research lead Gavin Rumbaugh, PhD, an associate professor in the department of neuroscience at Scripps Research in Florida. “We can correct brain dysfunction related to seizure as well as memory impairments after restoring SynGAP protein levels in the adult animals.”

Rumbaugh’s team, together with colleagues at the University of Texas at Austin, and the Jan and Dan Duncan Neurological Research Institute and department of pediatrics at Baylor College of Medicine, report their results in eLife, in a paper titled, “Re-expression of SynGAP Protein in Adulthood Improves Translatable Measures of Brain Function and Behavior.”

Novel Variants and Phenotypes Widen the Phenotypic Spectrum of GABRG2-Related Disorders

PURPOSE: Next-generation sequencing (NGS) has made genetic testing of patients with epileptic encephalopathies easier – novel variants are discovered and new phenotypes described. Variants in the same gene – even the same variant – can cause different types of epilepsy and neurodevelopmental disorders. The aim of this study was to identify the genetic causes of epileptic encephalopathies in pediatric patients with complex phenotypes.

METHODS: NGS was carried out for three patients with epileptic encephalopathies. Detailed clinical features, brain magnetic resonance imaging and electroencephalography were analysed. Researchers searched the Human Gene Mutation Database for the published GABRG2 variants with clinical description of patients and composed a summary of the variants and their phenotypic features.

RESULTS: Researchers identified two novel de novo GABRG2 variants, p.P282T and p.S306F, with new phenotypes including neuroradiological evidence of neurodegeneration and epilepsy of infancy with migrating focal seizures (EIMFS). One patient carried previously reported p.P83S variant with autism spectrum disorder (ASD) phenotype that has not yet been described related to GABRG2 disorders and a more severe epilepsy phenotype than reported earlier. In all, the literature search yielded twenty-two articles describing 27 different variants that were divided into two categories: those with self-limiting epilepsies and febrile seizures and those with more severe drug-resistant epileptic encephalopathies.

CONCLUSION: This study further expands the genotypic and phenotypic spectrum of epilepsies associated with GABRG2 variants. More knowledge is still needed about the influence of the environment, genetic background and other epilepsy susceptibility genes on the phenotype of the specific GABRG2 variants.

Epilepsy and Seizures in Young People with 22q11.2 Deletion Syndrome: Prevalence and Links with Other Neurodevelopmental Disorders

Objective: The true prevalence of epileptic seizures and epilepsy in 22q11.2 deletion syndrome (22q11.2DS) is unknown, because previous studies have relied on historical medical record review. Associations of epilepsy with other neurodevelopmental manifestations (eg, specific psychiatric diagnoses) remain unexplored.

Methods: The primary caregivers of 108 deletion carriers (mean age 13.6 years) and 60 control siblings (mean age 13.1 years) completed a validated epilepsy screening questionnaire. A subsample (n = 44) underwent a second assessment with interview, prolonged electroencephalography (EEG), and medical record and epileptologist review. Intelligence quotient (IQ), psychopathology, and other neurodevelopmental problems were examined using neurocognitive assessment and questionnaire/interview.

Results: Eleven percent (12/108) of deletion carriers had an epilepsy diagnosis (controls 0%, P = 0.004). 57 of the remaining 96 deletion carriers (59.4%) had seizures or seizure-like symptoms (controls 13.3%, 8/60, P < 0.001). A febrile seizure was reported for 24.1% (26/107) of cases (controls 0%, P < 0.001). One deletion carrier with a clinical history of epilepsy was diagnosed with an additional type of unprovoked seizure during the second assessment. One deletion carrier was newly diagnosed with epilepsy, and two more with possible nonmotor absence seizures. A positive screen on the epilepsy questionnaire was more likely in deletion carriers with lower performance IQ (odds ratio [OR] 0.96, P = 0.018), attention-deficit/hyperactivity disorder (ADHD) (OR 3.28, P = 0.021), autism symptoms (OR 3.86, P = 0.004), and indicative motor coordination disorder (OR 4.56, P = 0.021).

Significance: Even when accounting for deletion carriers diagnosed with epilepsy, reports of seizures and seizure-like symptoms are common. These may be “true” epileptic seizures in some cases, which are not recognized during routine clinical care. Febrile seizures were far more common in deletion carriers compared to known population risk. A propensity for seizures in 22q11.2DS was associated with cognitive impairment, psychopathology, and motor coordination problems. Future research is required to determine whether this reflects common neurobiologic risk pathways or is a consequence of recurrent seizures.

HCN Ion Channel Function May Play a Major Role in Epilepsy: Genetic Analysis of a Large Cohort of Patients and Review of the Literature

Background: The Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels are highly expressed in the Central Nervous Systems, where they are responsible for the Ih current. Together with specific accessory proteins, these channels finely regulate neuronal excitability and discharge activity. In the last few years, a substantial body of evidence has been gathered showing that modifications of Ih can play an important role in the pathogenesis of epilepsy. However, the extent to which HCN dysfunction is spread among the epileptic population is still unknown.

Aim: The aim of this work is to evaluate the impact of genetic mutations potentially affecting the HCN channels’ activity, using a NGS approach.

Method: Researchers screened a large cohort of patients with epilepsy of unknown etiology for mutations in HCN1, HCN2 and HCN4 and in genes coding for accessory proteins (MiRP1, Filamin A, Caveolin-3, TRIP8b, Tamalin, S-SCAM and Mint2).

Results: Researchers confirmed the presence of specific mutations of HCN genes affecting channel function and predisposing to the development of the disease. They also found several previously unreported additional genetic variants, whose contribution to the phenotype remains to be clarified. According to these results and data from literature, alteration of HCN1 channel function seems to play a major role in epilepsy, but also dysfunctional HCN2 and HCN4 channels can predispose to the development of the disease.

Significance: These findings suggest that inclusion of the genetic screening of HCN channels in diagnostic procedures of epileptic patients should be recommended. This would help pave the way for a better understanding of the role played by Ih dysfunction in the pathogenesis of epilepsy.

The Epilepsy Genetics Initiative: Systematic Reanalysis of Diagnostic Exomes Increases Yield

Featuring CURE’s Epilepsy Genetics Initiative

OBJECTIVE: The Epilepsy Genetics Initiative (EGI) was formed in 2014 to create a centrally managed database of clinically generated exome sequence data. EGI performs systematic research-based reanalysis to identify new molecular diagnoses that were not possible at the time of initial sequencing and to aid in novel gene discovery. Herein researchers report on the efficacy of this approach 3 years after inception.

METHODS: One hundred sixty-six individuals with epilepsy who underwent diagnostic whole exome sequencing (WES) were enrolled, including 139 who had not received a genetic diagnosis. Sequence data were transferred to the EGI and periodically reevaluated on a research basis.

RESULTS: Eight new diagnoses were made as a result of updated annotations or the discovery of novel epilepsy genes after the initial diagnostic analysis was performed. In five additional cases, the team provided new evidence to support or contradict the likelihood of variant pathogenicity reported by the laboratory. One novel epilepsy gene was discovered through dual interrogation of research and clinically generated WES.

SIGNIFICANCE: EGI’s diagnosis rate of 5.8% represents a considerable increase in diagnostic yield and demonstrates the value of periodic reinterrogation of whole exome data. The initiative’s contributions to gene discovery underscore the importance of data sharing and the value of collaborative enterprises.

CURE Discovery: Using Patient-Specific Cardiac Cells to Predict SUDEP Risk

CURE-funded researchers are using a novel technique to discover ways to predict patients at an increased risk of Sudden Unexpected Death in Epilepsy (SUDEP). Dr. Lori Isom, her team, and co-investigator Dr. Jack Parent at the University of Michigan are transforming skin cells from patients with developmental and epileptic encephalopathy (DEE) syndromes into induced pluripotent stem cells (iPSCs). The team then generates cardiac cells from the iPSCs which retain the patients’ exact genetic information. These unique, patient-specific cardiac cells are used as models to understand if DEE-associated genes play a role in causing heart abnormalities which may lead to SUDEP. The team also hopes to develop measurable indicators, known as biomarkers, of SUDEP risk.

Severe DEE syndromes, such as Dravet syndrome, are associated with a high incidence of SUDEP. It is estimated that up to 20% of patients with Dravet syndrome die from SUDEP.1 There is still much to be understood about the mechanisms of SUDEP and how to predict who is at risk for it.

Dravet syndrome and other DEEs are often associated with variants in genes, such as SCN1A, SCN1B, and SCN8A. These genes provide instructions to make sodium ion channels, which are very important proteins that help brain cells transmit electrical signals. The same genes are also expressed in the heart; thus, the team hypothesizes that any variants in these genes that disrupt electrical signaling in the brain would affect normal electrical function of the heart as well. In support of this hypothesis, the investigators’ previous work in mouse models of Dravet syndrome and DEEs showed that these mice exhibited irregular heartbeat, which in some cases preceded SUDEP-like events.2-4

In this CURE-funded project, the investigators expanded upon their previous work by testing their hypothesis in heart muscle cells called cardiac myocytes, generated in the laboratory from skin cells of patients with Dravet syndrome or other DEEs using iPSC technology. This Nobel Prize-winning technology involves obtaining skin or blood cells from patients and converting them to iPSCs. These are stem cells that can be converted into almost any specialized cell type in the body, such as heart, muscle, pancreatic, or neuronal cells. The cells are patient-specific, meaning they retain the unique genetic make-up of the patient they originated from, allowing investigators to study cell types which would otherwise be very difficult or impossible to obtain from a living patient.

Dr. Isom, Dr. Parent, and their colleagues previously used iPSC technology to generate heart muscle cells from four patients with variants in the SCN1A gene and found increased sodium currents and spontaneous contraction rates in these cells, suggesting cardiac electrical dysfunction.5 Cardiac abnormalities were subsequently found in the patient with the highest increase in sodium current.5 These data suggest that iPSC-cardiac cells may be useful models for identifying and developing biomarkers, such as increased sodium current, as indicators of SUDEP risk.

The investigators used the same technique to study variants in the SCN1B and SCN8A genes. The team observed that iPSC-cardiac myocytes derived from a patient with SCN1B Dravet syndrome had increased sodium currents similar to those seen in iPSC-cardiac myocytes from the patient with SCN1A Dravet syndrome, suggesting that variants in these two different genes could cause heart abnormalities through similar mechanisms. Preliminary data in iPSC-cardiac myocytes from patients with DEE caused by variants in SCN8A, suggest that these cells have altered beating rates but no change in sodium current, which is aligned with their observations in a mouse model with a variant in SCN8A.

Taken together, these results reveal mechanisms by which different epilepsy-related genes can affect heart function and SUDEP. Future research will investigate the impact of variants of a specific non-ion channel gene to see if it causes altered cardiac beating. Patient-specific iPSC cardiac myocytes are a very useful model to study SUDEP mechanisms and could be developed as diagnostic biomarkers to identify SUDEP risk in patients.

1 Cooper MS et al. Mortality in Dravet Syndrome. Epilepsy Res. 2016 Dec; 128:43-47.
2 Auerbach DS et al. Altered Cardiac Electrophysiology and SUDEP in a Model of Dravet Syndrome. PLoS One. 2013;8(10).
3 Lopez-Santiago LF et al. Sodium channel Scn1b null mice exhibit prolonged QT and RR intervals. J Mol Cell Cardiol. 2007;43(5):636-47.
4 Frasier CR et al. Cardiac arrhythmia in a mouse model of SCN8A Epileptic Encephalopathy. Proc Natl Acad Sci U S A. 2016; in press.
5 Frasier CR et al. Channelopathy as a SUDEP Biomarker in Dravet Syndrome Patient Derived Cardiac Myocytes. Stem Cell Reports. 2018 Sep 11;11(3):626-634.