High-resolution molecular genomic autopsy reveals complex sudden unexpected death in epilepsy risk profile

Exome-based analysis of cardiac arrhythmia, respiratory control, and epilepsy genes in sudden unexpected death in epilepsy

OBJECTIVE

The leading cause of epilepsy-related premature mortality is sudden unexpected death in epilepsy (SUDEP). The cause of SUDEP remains unknown. To search for genetic risk factors in SUDEP cases, we performed an exome-based analysis of rare variants.

METHODS

Demographic and clinical information of 61 SUDEP cases were collected. Exome sequencing and rare variant collapsing analysis with 2,936 control exomes were performed to test for genes enriched with damaging variants. Additionally, cardiac arrhythmia, respiratory control, and epilepsy genes were screened for variants with frequency of <0.1% and predicted to be pathogenic with multiple in silico tools.

RESULTS

The 61 SUDEP cases were categorized as definite SUDEP (n = 54), probable SUDEP (n = 5), and definite SUDEP plus (n = 2). We identified de novo mutations, previously reported pathogenic mutations, or candidate pathogenic variants in 28 of 61 (46%) cases. Four SUDEP cases (7%) had mutations in common genes responsible for the cardiac arrhythmia disease, long QT syndrome (LQTS). Nine cases (15%) had candidate pathogenic variants in dominant cardiac arrhythmia genes. Fifteen cases (25%) had mutations or candidate pathogenic variants in dominant epilepsy genes. No gene reached genome-wide significance with rare variant collapsing analysis; however, DEPDC5 (p = 0.00015) and KCNH2 (p = 0.0037) were among the top 30 genes, genome-wide.

INTERPRETATION

A sizeable proportion of SUDEP cases have clinically relevant mutations in cardiac arrhythmia and epilepsy genes. In cases with an LQTS gene mutation, SUDEP may occur as a result of a predictable and preventable cause. Understanding the genetic basis of SUDEP may inform cascade testing of at-risk family members.

Single-Gene Determinants of Epilepsy Comorbidity

Common somatic conditions are bound to occur by chance in individuals with neurological disorders as prevalent as epilepsy, but when biological links underlying the comorbidity can be uncovered, the relationship may provide clues into the origin and mechanisms of both. The expanding list of monogenic epilepsies and their associated clinical features offer a remarkable opportunity to mine the epilepsy genome for coordinate neurodevelopmental phenotypes and examine their pathogenic mechanisms. Defined single-gene-linked epilepsy syndromes identified to date include all of the most frequently cited comorbidities, such as cognitive disorders, autism, migraine, mood disorders, late-onset dementia, and even premature lethality. Gene-linked comorbidities may be aggravated by, or independent of, seizure history. Mutations in these genes establish clear biological links between abnormal neuronal synchronization and a variety of neurobehavioral disorders, and critically substantiate the definition of epilepsy as a complex spectrum disorder. Mapping the neural circuitry of epilepsy comorbidities and understanding their single-gene risk should substantially clarify this challenging aspect of clinical epilepsy management.

Sudden unexpected death in epilepsy: Identifying risk and preventing mortality

Premature death among individuals with epilepsy is higher than in the general population, and sudden unexpected death is the most common cause of this mortality. A new multisite collaborative research consortium, the Center for sudden unexpected death in epilepsy (SUDEP) Research (CSR), has received major funding from the National Institutes of Health (NIH) to examine the possible biologic mechanisms underlying this potentially preventable comorbidity and develop predictive biomarkers for interventions that could lower SUDEP incidence. This inaugural report describes the structure of the CSR, its priorities for human and experimental research, and the strategic collaborations and advanced tools under development to reduce this catastrophic outcome of epilepsy. The CSR Partners Program will work closely with committed volunteer agencies, industry, and academic institutions to accelerate and communicate these advances to the professional and lay community.

Audit of practice in sudden unexpected death in epilepsy (SUDEP) post mortems and neuropathological findings

AIMS

Sudden unexpected death in epilepsy (SUDEP) is one of the leading causes of death in people with epilepsy. For classification of definite SUDEP, a post mortem (PM), including anatomical and toxicological examination, is mandatory to exclude other causes of death. We audited PM practice as well as the value of brain examination in SUDEP.

METHODS

We reviewed 145 PM reports in SUDEP cases from four UK neuropathology centres. Data were extracted for clinical epilepsy details, circumstances of death and neuropathological findings.

RESULTS

Macroscopic brain abnormalities were identified in 52% of cases. Mild brain swelling was present in 28%, and microscopic pathologies relevant to cause or effect of seizures were seen in 89%. Examination based on whole fixed brains (76.6% of all PMs), and systematic regional sampling was associated with higher detection rates of underlying pathology (P < 0.01). Information was more frequently recorded regarding circumstances of death and body position/location than clinical epilepsy history and investigations.

CONCLUSION

Our findings support the contribution of examination of the whole fixed brain in SUDEP, with high rates of detection of relevant pathology. Availability of full clinical epilepsy-related information at the time of PM could potentially further improve detection through targeted tissue sampling. Apart from confirmation of SUDEP, complete neuropathological examination contributes to evaluation of risk factors as well as helping to direct future research into underlying causes.

Cardiac and autonomic mechanisms contributing to SUDEP

Sudden unexpected death in epilepsy is likely caused by a cascade of events affecting the vegetative nervous system leading to cardiorespiratory failure and death. Multiple genetic, electrophysiological, neurochemical, and pharmacological cardiac alterations have been associated with epilepsy, which can affect autonomic regulation of the heart and predispose patients to sudden unexpected death in epilepsy. These cardiac and autonomic changes are more frequently seen in patients with longstanding and medication refractory epilepsy and may be a prerequisite for sudden unexpected death in epilepsy. Cardiac changes are also observed within the immediate periictal period in patients with and without preexisting cardiac pathology and could be the tipping point in the cascade of events compromising autonomic, respiratory, and cardiac function during an epileptic convulsion. Better understanding if and how these cardiac alterations can make a particular individual with epilepsy more susceptible to sudden unexpected death in epilepsy will hopefully lead us to more effective preventative strategies.

Spontaneous seizures in Kcna1-null mice lacking voltage-gated Kv1.1 channels activate Fos expression in select limbic circuits

Mice lacking voltage-gated Kv1.1 channels as a result of deletion of the Kcna1 gene are an extensively utilized genetic model of human epilepsy and sudden unexpected death in epilepsy because of their frequent seizures and genotypic-phenotypic similarity to the human condition. Ictal behaviors, electrophysiological recordings, and gene expression studies suggest limbic circuits are critical for epilepsy in Kcna1-null mice, but the exact brain networks recruited by seizures remain unknown. In this study, Fos protein expression patterns were used to map limbic brain regions with increased neuronal activity at baseline and during spontaneous seizures in Kcna1-null mice by comparing seizing and non-seizing knockouts and wild-type controls. Basal Fos levels were unchanged in non-seizing knockout mice compared to wild types for all brain regions examined except the dentate gyrus granule cell layer which exhibited a significant decrease in Fos-positive cells. Following seizures, Kcna1-null brains exhibited significantly increased Fos labeling in the basolateral amygdala and the dentate hilus region, but not in other principal cell layers of the hippocampal formation. The selective Fos activation in the amygdala following seizures suggests that extra hippocampal limbic circuits may be critically involved with seizure generation or spread in Kcna1-null mice. Fos protein expression patterns were analyzed using immunohistochemistry to provide the first map of brain regions recruited by spontaneous seizures in mice lacking Kv1.1 channels, an extensively used genetic model of epilepsy. Seizures significantly increased Fos expression in the amygdala and hilus by about fourfold, suggesting an important contribution by extrahippocampal networks to epilepsy in this model.

Genome-wide Polygenic Burden of Rare Deleterious Variants in Sudden Unexpected Death in Epilepsy

Sudden unexpected death in epilepsy (SUDEP) represents the most severe degree of the spectrum of epilepsy severity and is the commonest cause of epilepsy-related premature mortality. The precise pathophysiology and the genetic architecture of SUDEP remain elusive. Aiming to elucidate the genetic basis of SUDEP, we analysed rare, protein-changing variants from whole-exome sequences of 18 people who died of SUDEP, 87 living people with epilepsy and 1479 non-epilepsy disease controls. Association analysis revealed a significantly increased genome-wide polygenic burden per individual in the SUDEP cohort when compared to epilepsy (P = 5.7 × 10(- 3)) and non-epilepsy disease controls (P = 1.2 × 10(- 3)). The polygenic burden was driven both by the number of variants per individual, and over-representation of variants likely to be deleterious in the SUDEP cohort. As determined by this study, more than a thousand genes contribute to the observed polygenic burden within the framework of this study. Subsequent gene-based association analysis revealed five possible candidate genes significantly associated with SUDEP or epilepsy, but no one single gene emerges as common to the SUDEP cases. Our findings provide further evidence for a genetic susceptibility to SUDEP, and suggest an extensive polygenic contribution to SUDEP causation. Thus, an overall increased burden of deleterious variants in a highly polygenic background might be important in rendering a given individual more susceptible to SUDEP. Our findings suggest that exome sequencing in people with epilepsy might eventually contribute to generating SUDEP risk estimates, promoting stratified medicine in epilepsy, with the eventual aim of reducing an individual patient's risk of SUDEP.

Sudden infant death syndrome, sleep, and seizures

benign febrile seizures seen in 7% of infants before 6 months play a role in the terminal pathway in a subset of sudden infant death syndrome victims. Supporting evidence: (1) lack of 5-hydroxitryptamine, one consistent finding in sudden infant death syndrome that Kinney et al coined a developmental serotonopathy, is consistent with risk for seizures. (2) Non-rapid eye movement sleep increasing during the age of highest risk for sudden infant death syndrome facilitates some seizures (seizure gate). (3) Sudden unexpected death in epilepsy is associated with severe hypoxemia and hypercapnia during postictal generalized electroencephalographic (EEG) suppression. In toddlers, sudden unexplained deaths are associated with hippocampal abnormalities and some seizures. (4) The sudden nature of both deaths warrants an exploration of similarities in the terminal pathway. Moreover, sudden infant death syndrome, febrile seizures, sudden unexplained death in childhood, and sudden unexpected death in epilepsy share some of the following risk factors: prone sleeping, infections, hyperthermia, preterm birth, male gender, maternal smoking, and mutations in genes that regulate sodium channels. State-of-the-art molecular studies can be exploited to test this hypothesis.

Mechanisms of sudden unexplained death in epilepsy

PURPOSE OF REVIEW

Human and experimental research has identified cardioautonomic and respiratory dysfunction as a frequent accompaniment in human and animal model events of sudden unexpected death in epilepsy (SUDEP). This review aims to provide an overview of the scientific evidence behind the currently accepted risk factors and working hypotheses regarding SUDEP pathophysiology.

RECENT FINDINGS

Epidemiological analysis of public health burden of SUDEP has shown that it rates second only to stroke in the years of potential life lost. Clinical and experimental studies uncovered the dynamic cardiorespiratory dysfunction interictally and imminently to SUDEP, and model systems have facilitated discoveries in SUDEP mechanistic understanding and application of pilot therapeutic interventions. Pilot molecular profiling of human SUDEP has uncovered complex genomic structure in the candidate gene network.

SUMMARY

Extensive clinical and experimental work has established a rationale for the conceptual thinking about SUDEP mechanisms. The application of the global molecular profiling will be invaluable in unraveling the individually unique genomic complexities and interactions that underlie the physiological signature of each patient. At the same time, sophisticated model systems will be critical in the iterative translation of human genetics, physiology, pharmacological interventions, and in testing preventive interventions.

Pathway-driven discovery of epilepsy genes

Epilepsy genes deliver critical insights into the molecular control of brain synchronization and are revolutionizing our understanding and treatment of the disease. The epilepsy-associated genome is rapidly expanding, and two powerful complementary approaches, isolation of de novo exome variants in patients and targeted mutagenesis in model systems, account for the steep increase. In sheer number, the tally of genes linked to seizures will likely match that of cancer and exceed it in biological diversity. The proteins act within most intracellular compartments and span the molecular determinants of firing and wiring in the developing brain. Every facet of neurotransmission, from dendritic spine to exocytotic machinery, is in play, and defects of synaptic inhibition are over-represented. The contributions of somatic mutations and noncoding microRNAs are also being explored. The functional spectrum of established epilepsy genes and the arrival of rapid, precise technologies for genome editing now provide a robust scaffold to prioritize hypothesis-driven discovery and further populate this genetic proto-map. Although each gene identified offers translational potential to stratify patient care, the complexity of individual variation and covert actions of genetic modifiers may confound single-gene solutions for the clinical disorder. In vivo genetic deconstruction of epileptic networks, ex vivo validation of variant profiles in patient-derived induced pluripotent stem cells, in silico variant modeling and modifier gene discovery, now in their earliest stages, will help clarify individual patterns. Because seizures stand at the crossroads of all neuronal synchronization disorders in the developing and aging brain, the neurobiological analysis of epilepsy-associated genes provides an extraordinary gateway to new insights into higher cortical function.

Cardiac asystole associated with seizures of right hemispheric onset

Ictal asystole is frequently underrecognized despite being a potentially lethal condition. We report two cases of ictal asystole with right hemispheric onset. These cases are unique since previous literature reports that seizures associated with bradyarrhythmias typically arise from left hemispheric foci. These cases further underscore the importance of clinical vigilance and the need of an enhanced diagnostic biomarker.

Genetic and forensic implications in epilepsy and cardiac arrhythmias: a case series

Epilepsy affects approximately 3% of the world's population, and sudden death is a significant cause of death in this population. Sudden unexpected death in epilepsy (SUDEP) accounts for up to 17% of all these cases, which increases the rate of sudden death by 24-fold as compared to the general population. The underlying mechanisms are still not elucidated, but recent studies suggest the possibility that a common genetic channelopathy might contribute to both epilepsy and cardiac disease to increase the incidence of death via a lethal cardiac arrhythmia. We performed genetic testing in a large cohort of individuals with epilepsy and cardiac conduction disorders in order to identify genetic mutations that could play a role in the mechanism of sudden death. Putative pathogenic disease-causing mutations in genes encoding cardiac ion channel were detected in 24% of unrelated individuals with epilepsy. Segregation analysis through genetic screening of the available family members and functional studies are crucial tasks to understand and to prove the possible pathogenicity of the variant, but in our cohort, only two families were available. Despite further research should be performed to clarify the mechanism of coexistence of both clinical conditions, genetic analysis, applied also in post-mortem setting, could be very useful to identify genetic factors that predispose epileptic patients to sudden death, helping to prevent sudden death in patients with epilepsy.

Serotonin and sudden death: differential effects of serotonergic drugs on seizure-induced respiratory arrest in DBA/1 mice

In the DBA/1 mouse model of sudden unexpected death in epilepsy (SUDEP), administration of a selective serotonin (5-HT) reuptake inhibitor (SSRI), fluvoxamine, completely suppressed seizure-induced respiratory arrest (S-IRA) at 30 min after administration (i.p.) in a dose-related manner without blocking audiogenic seizures (AGSz), but another SSRI, paroxetine, reduced S-IRA but with a delayed (24 h) onset and significant toxicity. A serotonin-norepinephrine reuptake inhibitor, venlafaxine, reduced S-IRA incidence, but higher doses were ineffective. A selective 5-HT7 agonist, AS-19, was totally ineffective in reducing S-IRA. In developing DBA/1 mice that had not previously experienced AGSz, administration of a nonselective 5-HT antagonist, cyproheptadine, induced a significantly greater incidence of S-IRA than that of saline. This study confirms that certain drugs that enhance the activation of 5-HT receptors are able to prevent S-IRA, but not all serotonergic drugs are equally effective, which may be relevant to the potential use of these drugs for SUDEP prevention. Serotonergic antagonists may be problematic in patients with epilepsy.

Sudden cardiac death is associated both with epilepsy and with use of antiepileptic medications

OBJECTIVE

Epilepsy is associated with increased risk for sudden cardiac death (SCD). We aimed to establish, in a community based study, whether this association is mediated by epilepsy per se, use of antiepileptic medications (AEMs), or both.

METHODS

We studied SCD cases and age/sex matched controls in a case-control study in a large scale general practitioners' research database (n=478 661 patients). SCD risk for symptomatic epilepsy (seizure <2 years before SCD), stable epilepsy (no seizure <2 years before SCD), and use of AEMs (any indication) was determined.

RESULTS

We identified 926 SCD cases and 9832 controls. Fourteen cases had epilepsy. Epilepsy was associated with an increased SCD risk (cases 1.5%, controls 0.5%; adjusted OR 2.8, 95% CI 1.4 to 5.3). SCD risk was increased for symptomatic epilepsy (cases 0.9%, controls 0.1%; adjusted OR 5.8, 95% CI 2.1 to 15.6), but not with stable epilepsy (cases 0.6%, controls 0.4%; adjusted OR 1.6, 95% CI 0.7 to 4.1). AEM use was found in 23 cases and was associated with an increased SCD risk (cases 2.5%, controls 0.8%; adjusted OR overall 2.6, 95% CI 1.5 to 4.3) among symptomatic epilepsy cases (cases 0.9%, controls 0.1%; adjusted OR 6.4, 95% CI 2.4 to 17.4) and non-epilepsy cases (cases 1.0%, controls 0.4%; adjusted OR 2.3, 95% CI 1.01 to 5.2). Increased SCD risk was associated with sodium channel blocking AEMs (cases 1.6%, controls 0.4%; adjusted OR 2.8, 95% CI 1.1 to 7.2), but not with non-sodium channel blocking AEMs. Carbamazepine and gabapentin were associated with increased SCD risk (carbamazepine: cases 1.1%, controls 0.3%; adjusted OR 3.2, 95% CI 1.1 to 9.2; gabapentin: cases 0.3%, controls 0.1%; adjusted OR 5.7, 95% CI 1.2 to 27.9).

CONCLUSIONS

Epilepsy and AEM use are both associated with increased SCD risk in the general population. Poor seizure control contributes to increased SCD risk in epilepsy, while sodium channel blockade contributes to SCD susceptibility in AEM users.

Mechanisms of sudden unexpected death in epilepsy: the pathway to prevention

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy, with an estimated 35% lifetime risk in this patient population. There is a surprising lack of awareness among patients and physicians of this increased risk of sudden death: in a recent survey, only 33% of Canadian paediatricians who treated patients with epilepsy knew the term SUDEP. Controversy prevails over whether cardiac arrhythmia or respiratory arrest is more important as the primary cause of death. Effective preventive strategies in high-risk patients will rely on definition of the mechanisms that lead from seizures to death. Here, we summarize evidence for the mechanisms that cause cardiac, respiratory and arousal abnormalities during the ictal and postictal period. We highlight potential cellular mechanisms underlying these abnormalities, such as a defect in the serotonergic system, ictal adenosine release, and changes in autonomic output. We discuss genetic mutations that cause Dravet and long QT syndromes, both of which are linked with increased risk of sudden death. We then highlight possible preventive interventions that are likely to decrease SUDEP incidence, including respiratory monitoring in epilepsy monitoring units and overnight supervision. Finally, we discuss treatments, such as selective serotonin reuptake inhibitors, that might be personalized to a specific genetic or pathological defect.