Importance of genetic factors in the occurrence of epilepsy syndrome type: a twin study

Charting the Progress of Epilepsy Classification: Navigating a Shifting Landscape

Epilepsy, a neurological disorder characterized by recurrent seizures, has witnessed a remarkable transformation in its classification paradigm, driven by advances in clinical understanding, neuroimaging, and molecular genetics. This narrative review navigates the dynamic landscape of epilepsy classification, offering insights into recent developments, challenges, and the promising horizon. Historically, epilepsy classification relied heavily on clinical observations, categorizing seizures based on their phenomenology and presumed etiology. However, the field has profoundly shifted from a symptom-based approach to a more refined, multidimensional system. One pivotal aspect of this evolution is the integration of neuroimaging techniques, particularly magnetic resonance imaging (MRI) and functional imaging modalities. These tools have unveiled the intricate neural networks implicated in epilepsy, facilitating the identification of distinct brain abnormalities and the categorization of epilepsy subtypes based on structural and functional findings. Furthermore, the role of genetics has become increasingly prominent in epilepsy classification. Genetic discoveries have not only unraveled the molecular underpinnings of various epileptic syndromes but have also provided valuable diagnostic and prognostic insights. This narrative review delves into the expanding realm of genetic testing and its impact on tailoring treatment strategies to individual patients. As the classification landscape evolves, there are accompanying challenges. The narrative review underscores the transformative potential of artificial intelligence and machine learning in epilepsy classification. These technologies hold promise in automating the analysis of complex neuroimaging and genetic data, offering enhanced accuracy and efficiency in epilepsy diagnosis and classification. In conclusion, navigating the shifting landscape of epilepsy classification is a journey marked by progress, complexity, and the prospect of improved patient care. We are charting a course toward more precise diagnoses and tailored treatments by embracing advanced neuroimaging, genetics, and innovative technologies. As the field continues to evolve, collaborative efforts and a holistic understanding of epilepsy's diverse manifestations will be instrumental in harnessing the full potential of this dynamic landscape.

Epilepsy and Attention Deficit Hyperactivity Disorder: Connection, Chance, and Challenges

Comorbidities are common in children with epilepsy, with nearly half of the patients having at least one comorbidity. Attention deficit hyperactivity disorder (ADHD) is a psychiatric disorder characterized by hyperactivity and inattentiveness level disproportional to the child’s developmental stage. The burden of ADHD in children with epilepsy is high and can adversely affect the patients’ clinical outcomes, psychosocial aspects, and quality of life. Several hypotheses were proposed to explain the high burden of ADHD in childhood epilepsy; the well-established bidirectional connection and shared genetic/non-genetic factors between epilepsy and comorbid ADHD largely rule out the possibility of a chance in this association. Stimulants are effective in children with comorbid ADHD, and the current body of evidence supports their safety within the approved dose. Nonetheless, safety data should be further studied in randomized, double-blinded, placebo-controlled trials. Comorbid ADHD is still under-recognized in clinical practice. Early identification and management of comorbid ADHD are crucial to optimize the prognosis and reduce the risk of adverse long-term neurodevelopmental outcomes. The identification of the shared genetic background of epilepsy and ADHD can open the gate for tailoring treatment options for these patients through precision medicine.

ILAE definition of the Idiopathic Generalized Epilepsy Syndromes: Position statement by the ILAE Task Force on Nosology and Definitions

In 2017, the International League Against Epilepsy (ILAE) Classification of Epilepsies described the "genetic generalized epilepsies" (GGEs), which contained the "idiopathic generalized epilepsies" (IGEs). The goal of this paper is to delineate the four syndromes comprising the IGEs, namely childhood absence epilepsy, juvenile absence epilepsy, juvenile myoclonic epilepsy, and epilepsy with generalized tonic-clonic seizures alone. We provide updated diagnostic criteria for these IGE syndromes determined by the expert consensus opinion of the ILAE's Task Force on Nosology and Definitions (2017-2021) and international external experts outside our Task Force. We incorporate current knowledge from recent advances in genetic, imaging, and electroencephalographic studies, together with current terminology and classification of seizures and epilepsies. Patients that do not fulfill criteria for one of these syndromes, but that have one, or a combination, of the following generalized seizure types: absence, myoclonic, tonic-clonic and myoclonic-tonic-clonic seizures, with 2.5-5.5 Hz generalized spike-wave should be classified as having GGE. Recognizing these four IGE syndromes as a special grouping among the GGEs is helpful, as they carry prognostic and therapeutic implications.

A systems-level analysis highlights microglial activation as a modifying factor in common epilepsies

AIMS

The causes of distinct patterns of reduced cortical thickness in the common human epilepsies, detectable on neuroimaging and with important clinical consequences, are unknown. We investigated the underlying mechanisms of cortical thinning using a systems-level analysis.

METHODS

Imaging-based cortical structural maps from a large-scale epilepsy neuroimaging study were overlaid with highly spatially resolved human brain gene expression data from the Allen Human Brain Atlas. Cell-type deconvolution, differential expression analysis and cell-type enrichment analyses were used to identify differences in cell-type distribution. These differences were followed up in post-mortem brain tissue from humans with epilepsy using Iba1 immunolabelling. Furthermore, to investigate a causal effect in cortical thinning, cell-type-specific depletion was used in a murine model of acquired epilepsy.

RESULTS

We identified elevated fractions of microglia and endothelial cells in regions of reduced cortical thickness. Differentially expressed genes showed enrichment for microglial markers and, in particular, activated microglial states. Analysis of post-mortem brain tissue from humans with epilepsy confirmed excess activated microglia. In the murine model, transient depletion of activated microglia during the early phase of the disease development prevented cortical thinning and neuronal cell loss in the temporal cortex. Although the development of chronic seizures was unaffected, the epileptic mice with early depletion of activated microglia did not develop deficits in a non-spatial memory test seen in epileptic mice not depleted of microglia.

CONCLUSIONS

These convergent data strongly implicate activated microglia in cortical thinning, representing a new dimension for concern and disease modification in the epilepsies, potentially distinct from seizure control.

[Twin research in Germany]

Nach dem Zweiten Weltkrieg wurden weltweit Zwillingskohorten aufgebaut, die inzwischen ca. 1,5 Mio. Zwillinge umfassen und zwischen 1950 und 2012 über 2748 Zwillingsstudien hervorgebracht haben. Diese Zahl steigt jedes Jahr um weitere 500 bis 1000. Die Unterrepräsentanz deutscher Zwillingsstudien in diesen Datenbanken lässt sich nicht allein durch den Missbrauch medizinischer Forschung im Nationalsozialismus erklären. Entwicklung und Ausbau großer Zwillingskohorten sind ethisch und datenschutzrechtlich eine Herausforderung. Zwillingskohorten ermöglichen jedoch die Langzeit- und Echtzeiterforschung vieler medizinischer Fragestellungen; und die Zwillingsstudien tragen auch nach der Entschlüsselung des Humangenoms erheblich zur Beantwortung der Frage nach Anlage oder Umwelt als mögliche Erkrankungsauslöser bei.

Derzeit gibt es 2 deutsche Zwillingskohorten: die biomedizinische Kohorte HealthTwiSt mit ca. 1500 Zwillingspaaren und TwinLife, eine soziologisch-psychologische Kohorte mit ca. 4000 Zwillingspaaren. Daneben gibt es krankheitsspezifische Kohorten. 2016 startete das TwinHealth-Konsortium der Medizinischen Fakultät der Universität Tübingen mit dem Ziel, eine forschungsoffene und nachhaltige Zwillingsforschung am Standort Tübingen zur Bearbeitung unterschiedlicher Fragestellungen zu etablieren.

Der Artikel bietet mithilfe einer systematischen Literaturrecherche und einer medizinhistorischen Betrachtung einen Überblick über die weltweite und nationale Entwicklung von Zwillingsstudien und -datenbanken der letzten 100 Jahre. Anhand der Tübinger TwinHealth-Initiative beleuchtet er den Aufbau eines Zwillingskollektivs und dessen juristische, ethische und Datenschutzaspekte.

New avenues in molecular genetics for the diagnosis and application of therapeutics to the epilepsies

Genetic epidemiology studies have shown that most epilepsies involve some genetic cause. In addition, twin studies have helped strengthen the hypothesis that in most patients with epilepsy, a complex inheritance is involved. More recently, with the development of high-density single-nucleotide polymorphism (SNP) microarrays and next-generation sequencing (NGS) technologies, the discovery of genes related to the epilepsies has accelerated tremendously. Especially, the use of whole exome sequencing (WES) has had a considerable impact on the identification of rare genetic variants with large effect sizes, including inherited or de novo mutations in severe forms of childhood epilepsies. The identification of pathogenic variants in patients with these childhood epilepsies provides many benefits for patients and families, such as the confirmation of the genetic nature of the diseases. This process will allow for better genetic counseling, more accurate therapy decisions, and a significant positive emotional impact. However, to study the genetic component of the more common forms of epilepsy, the use of high-density SNP arrays in genome-wide association studies (GWAS) seems to be the strategy of choice. As such, researchers can identify loci containing genetic variants associated with the common forms of epilepsy. The knowledge generated over the past two decades about the effects of the mutations that cause the monogenic epilepsy is tremendous; however, the scientific community is just starting to apply this information in order to generate better target treatments.

Resting-state EEG theta activity reflects degree of genetic determination of the major epilepsy syndromes

OBJECTIVE

To explore relationship between EEG theta activity and clinical data that imply the degree of genetic determination of epilepsy.

METHODS

Clinical data of interest were epilepsy diagnosis and positive / negative family history of epilepsy. Study groups were: idiopathic generalized epilepsy (IGE), focal epilepsy (FE); FE of unknown etiology (FEUNK), FE of postnatal-acquired etiology (FEPA); all patients with positive / negative family history of epilepsy (FAPALL, FANALL, respectively), disregarding of the syndrome; FAP patients with 1st degree affected relative (FAP1) and those with 2nd degree epileptic relative only (FAP2). Quantitative EEG analysis assessed amount of theta (3.5-7.0 Hz) activity in 180 seconds of artifact-free waking EEG background activity for each patient and group. Group comparison was carried out by nonparametric statistics.

RESULTS

Differences of theta activity were: FAPALL > FANALL (p = 0.01); FAP1 > FAP2 (p = 0.2752). IGE > FE (p = 0.02); FEUNK > FEPA (p = 0.07).

CONCLUSIONS

This was the first attempt to explore and quantitatively ascertain relationship between an EEG variable and clinical data that imply greater or lesser degree of genetic determination in epilepsy.

SIGNIFICANCE

Theta activity is endophenotype that bridges the gap between epilepsy susceptibility genes and clinical phenotypes. Amount of theta activity is indicative of degree of genetic determination of the epilepsies.

The Genetics of Epilepsy

Epilepsy encompasses a group of heterogeneous brain diseases that affect more than 50 million people worldwide. Epilepsy may have discernible structural, infectious, metabolic, and immune etiologies; however, in most people with epilepsy, no obvious cause is identifiable. Based initially on family studies and later on advances in gene sequencing technologies and computational approaches, as well as the establishment of large collaborative initiatives, we now know that genetics plays a much greater role in epilepsy than was previously appreciated. Here, we review the progress in the field of epilepsy genetics and highlight molecular discoveries in the most important epilepsy groups, including those that have been long considered to have a nongenetic cause. We discuss where the field of epilepsy genetics is moving as it enters a new era in which the genetic architecture of common epilepsies is starting to be unraveled.

Impaired Cognitive Abilities in Siblings of Patients with Temporal Lobe Epilepsy

PURPOSE

Patients with temporal lobe epilepsy (TLE) are at high risk of cognitive impairment. In addition to persistent seizures and antiepileptic drugs (AEDs), genetic factors also play an important role in the progression of cognitive deficits in TLE patients. Defining a cognitive endophenotype for TLE can provide information on the risk of cognitive impairment in patients. This study investigated the cognitive endophenotype of TLE by comparing neuropsychological function between patients with TLE, their unaffected siblings, and healthy control subjects.

PATIENTS AND METHODS

A total of 46 patients with TLE, 26 siblings, and 33 control subjects were recruited. Cognitive function (ie, general cognition, short- and long-term memory, attention, visuospatial and executive functions, and working memory) was assessed with a battery of neuropsychological tests. Differences between groups were evaluated by analysis of covariance, with age and years of education as covariates. The Kruskal-Wallis test was used to evaluate data that did not satisfy the homogeneity of variance assumption. Pairwise comparisons were adjusted by Bonferroni correction, with a significance threshold of P<0.05.

RESULTS

Patients with TLE showed deficits in the information test (P<0.001), arithmetic test (P=0.003), digit symbol substitution test (P=0.001), block design test (BDT; P=0.005), and backward digit span test (P=0.001) and took a longer time to complete the Hayling test Part A (P=0.011) compared to controls. Left TLE patients tended to have worse executive function test scores than right TLE patients. The siblings of TLE patients showed deficits in the BDT (P=0.006, Bonferroni-corrected) relative to controls.

CONCLUSION

Patients with TLE exhibit cognitive impairment. Executive function is worse in patients with left TLE than in those with right TLE. Siblings show impaired visuospatial function relative to controls. Thus, cognitive deficits in TLE patients have a genetic component and are independent of seizures or AED use.

Autism and social anxiety in children with sex chromosome trisomies: an observational study

Background: Recent studies suggest that an extra sex chromosome increases the risk of both autism and social anxiety, but it unclear whether these risks are specific to particular karyotypes.

Methods: We considered diagnostic data from an online psychiatric assessment (DAWBA – The Development and Well-Being Assessment) and questionnaire responses completed by parents of children with 47,XXX (N = 29), 47,XXY (N = 28) and 47,XYY (N = 32) karyotypes. Analysis focused mainly on 54 children who were diagnosed prenatally or on the basis of other medical concerns in childhood (Low Bias subgroup), to minimise ascertainment bias.

Results: Children with symptoms of autism who fell short of meeting the Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV criteria were coded as cases of Pervasive Developmental Disorder Not Otherwise Specified (PDDNOS). The odds ratio of autism or PDDNOS in the Low Bias group was computed relative to gender-specific population norms. This gave log odds ratio (95% confidence interval) of 5.56 (4.25 - 6.88) for XXX girls; 4.00 (2.66 - 5.33) for XXY boys; and 4.60 (3.46 - 5.74) for XYY boys. Despite this elevated risk, most children had no autistic features. A diagnosis of DSM-IV Social Phobia was rare, though, in line with prediction, all three Low Bias cases with this diagnosis had 47,XXY karyotype. All three trisomy groups showed increased risk of milder symptoms of social anxiety.

Conclusions: An increased risk of autism was found in girls with 47,XXX karyotype, as well as in boys with 47,XXY or 47,XYY. Symptoms of social anxiety were increased in all three karyotypes. There was wide variation in psychiatric status of children with the same karyotype, suggesting that an extra sex chromosome affects developmental stability in a non-specific way, with a diverse range of possible phenotypes.

An overview of structurally diversified anticonvulsant agents

There are several limited approaches to treat epilepsy in hospitals, for example, using medicines, surgery, electrical stimulation and dietary interventions. Despite the availability of all these new and old approaches, seizure is particularly difficult to manage. The quest for new antiepileptic molecules with more specificity and less CNS toxicity continues for medicinal chemists until a new and ideal drug arrives. This review covers new antiseizure molecules of different chemical classes, the exact mode of action of which is still unidentified. Newer agents include sulfonamides, thiadiazoles, semi- and thiosemicarbazones, pyrrolidine-2,5-diones, imidazoles, benzothiazoles and amino acid deriva tives. These new chemical entities can be useful for the design and development of forthcoming antiseizure agents.

Abnormal hippocampal structure and function in juvenile myoclonic epilepsy and unaffected siblings

Juvenile myoclonic epilepsy is the most common genetic generalized epilepsy syndrome, characterized by a complex polygenetic aetiology. Structural and functional MRI studies demonstrated mesial or lateral frontal cortical derangements and impaired fronto-cortico-subcortical connectivity in patients and their unaffected siblings. The presence of hippocampal abnormalities and associated memory deficits is controversial, and functional MRI studies in juvenile myoclonic epilepsy have not tested hippocampal activation. In this observational study, we implemented multi-modal MRI and neuropsychological data to investigate hippocampal structure and function in 37 patients with juvenile myoclonic epilepsy, 16 unaffected siblings and 20 healthy controls, comparable for age, gender, handedness and hemispheric dominance as assessed with language laterality indices. Automated hippocampal volumetry was complemented by validated qualitative and quantitative morphological criteria to detect hippocampal malrotation, assumed to represent a neurodevelopmental marker. Neuropsychological measures of verbal and visuo-spatial learning and an event-related verbal and visual memory functional MRI paradigm addressed mesiotemporal function. We detected a reduction of mean left hippocampal volume in patients and their siblings compared with controls (P < 0.01). Unilateral or bilateral hippocampal malrotation was identified in 51% of patients and 50% of siblings, against 15% of controls (P < 0.05). For bilateral hippocampi, quantitative markers of verticalization had significantly larger values in patients and siblings compared with controls (P < 0.05). In the patient subgroup, there was no relationship between structural measures and age at disease onset or degree of seizure control. No overt impairment of verbal and visual memory was identified with neuropsychological tests. Functional mapping highlighted atypical patterns of hippocampal activation, pointing to abnormal recruitment during verbal encoding in patients and their siblings [P < 0.05, familywise error (FWE)-corrected]. Subgroup analyses indicated distinct profiles of hypoactivation along the hippocampal long axis in juvenile myoclonic epilepsy patients with and without malrotation; patients with malrotation also exhibited reduced frontal recruitment for verbal memory, and more pronounced left posterior hippocampal involvement for visual memory. Linear models across the entire study cohort indicated significant associations between morphological markers of hippocampal positioning and hippocampal activation for verbal items (all P < 0.05, FWE-corrected). We demonstrate abnormalities of hippocampal volume, shape and positioning in patients with juvenile myoclonic epilepsy and their siblings, which are associated with reorganization of function and imply an underlying neurodevelopmental mechanism with expression during the prenatal stage. Co-segregation of abnormal hippocampal morphology in patients and their siblings is suggestive of a genetic imaging phenotype, independent of disease activity, and can be construed as a novel endophenotype of juvenile myoclonic epilepsy.

Clinical and genetic spectrum of SCN2A-associated episodic ataxia

BACKGROUND

Pathogenic variants in SCN2A are associated with various neurological disorders including epilepsy, autism spectrum disorder and intellectual disability. Few reports have recently described SCN2A-associated episodic ataxia (EA). Our study identifies its broader clinical and genetic spectrum, and describes pharmacological approaches.

RESULTS

We report 21 patients with SCN2A-associated EA, of which 9 are unpublished cases. The large majority of patients present with epileptic seizures (18/21, 86%), often starting within the first three months of life (12/18, 67%). In contrast, onset of episodic ataxia ranged from 10 months to 14 years of age. The frequency of EA episodes ranged from brief, daily events up to 1-2 episodes per year each lasting several weeks. Potential triggers include minor head traumas and sleep deprivation. Cognitive outcome is favorable in most patients with normal or mildly impaired cognitive development in 17/21 patients (81%). No clear genotype-phenotype correlations were identified in this cohort. However, two mutational hotspots were identified, i.e. 7/21 patients (33%) harbor the identical pathogenic variant p.A263V, whereas 5/21 (24%) carry pathogenic variants that affect the S4 segment and its cytoplasmic loop within the domain IV. In addition, we identified six novel pathogenic variants in SCN2A. While acetazolamide was previously reported as beneficial in SCN2A-associated EA in one case, our data show a conflicting response in 8 additional patients treated with acetazolamide: three of them profited from acetazolamide treatment, while 5/8 did not.

CONCLUSIONS

Our study describes the heterogeneous clinical spectrum of SCN2A-associated EA, identifies two mutational hotspots and shows positive effects of acetazolamide in about 50%.

Autism and social anxiety in children with sex chromosome trisomies: an observational study

Background: Recent studies suggest that an extra sex chromosome increases the risk of both autism and social anxiety, but it unclear whether these risks are specific to particular karyotypes. Methods: We considered diagnostic data from an online psychiatric assessment (DAWBA – The Development and Well-Being Assessment) and questionnaire responses completed by parents of children with 47,XXX (N = 29), 47,XXY (N = 28) and 47,XYY (N = 32) karyotypes. Analysis focused mainly on 54 children who were diagnosed prenatally or on the basis of other medical concerns in childhood (Low Bias subgroup), to minimise ascertainment bias. Results: Children with symptoms of autism who fell short of meeting the Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV criteria were coded as cases of Pervasive Developmental Disorder Not Otherwise Specified (PDDNOS). The odds ratio of autism or PDDNOS in the Low Bias group was computed relative to gender-specific population norms. This gave log odds ratio (95% confidence interval) of 5.56 (4.25 - 6.88) for XXX girls; 4.00 (2.66 - 5.33) for XXY boys; and 4.60 (3.46 - 5.74) for XYY boys. Despite this elevated risk, most children had no autistic features. A diagnosis of DSM-IV Social Phobia was rare, though, in line with prediction, all three Low Bias cases with this diagnosis had 47,XXY karyotype. All three trisomy groups showed increased risk of milder symptoms of social anxiety. Conclusions: An increased risk of autism was found in girls with 47,XXX karyotype, as well as in boys with 47,XXY or 47,XYY. Symptoms of social anxiety were increased in all three karyotypes. There was wide variation in psychiatric status of children with the same karyotype, suggesting that an extra sex chromosome affects developmental stability in a non-specific way, with a diverse range of possible phenotypes.

Genetics of Focal Epilepsies: What Do We Know and Where Are We Heading?

This article is based on a lecture delivered at the 2017 American Epilepsy Society Annual Meeting and provides an overview of the growing evidence supporting the strong genetic contribution to focal epilepsies. This also discusses how advances in the molecular genetics of focal epilepsies are rapidly translating to routine clinical care.

Long-term negative impact of an inappropriate first antiepileptic medication on the efficacy of a second antiepileptic medication in mice

Childhood absence epilepsy (CAE) is one of the most frequent epilepsies in infancy. The first-line recommended therapy for CAE is based on the prescription of the narrow-spectrum ethosuximide and the broad-spectrum valproic acid, which have similar efficacy in the first 12 months. Nevertheless, some antiepileptic drugs (AEDs) may worsen seizure duration and type in this syndrome. In line with this, we have encountered a case of identical twins with CAE and early exposure to different antiseizure drugs leading to divergent outcomes. From this, we hypothesized that the first AED to treat CAE may determine the long-term prognosis, especially in the developing brain, and that some situations leading to drug resistance may be explained by use of an inappropriate first AED. Therefore, we investigated this hypothesis by using a genetic mouse model of absence epilepsy (BS/Orl). Mice received a first appropriate or inappropriate AED followed by the same appropriate AED. Our data demonstrate that an inappropriate first AED has a negative impact on the long-term efficacy of a second appropriate AED. This work supports the necessity to effectively diagnose epileptic syndromes prior to medication use, particularly in children, in order to prevent the deleterious effects of an inappropriate initial AED.

Intestinal Microbiota as an Alternative Therapeutic Target for Epilepsy

Epilepsy is one of the most widespread serious neurological disorders, and an aetiological explanation has not been fully identified. In recent decades, a growing body of evidence has highlighted the influential role of autoimmune mechanisms in the progression of epilepsy. The hygiene hypothesis draws people's attention to the association between gut microbes and the onset of multiple immune disorders. It is also believed that, in addition to influencing digestive system function, symbiotic microbiota can bidirectionally and reversibly impact the programming of extraintestinal pathogenic immune responses during autoimmunity. Herein, we investigate the concept that the diversity of parasitifer sensitivity to commensal microbes and the specific constitution of the intestinal microbiota might impact host susceptibility to epilepsy through promotion of Th17 cell populations in the central nervous system (CNS).

Epilepsy After Febrile Seizures: Twins Suggest Genetic Influence

BACKGROUND

A history of complex febrile seizures can increase the risk of epilepsy, but the role of genetic factors is unclear. This analysis evaluated the relationship between febrile seizures and epilepsy.

METHODS

Information on the history of seizures was obtained by a questionnaire from twin pairs in the Mid-Atlantic, Danish, and Norwegian Twin Registries. The information was verified using medical records and detailed clinical and family interviews. The initial study evaluated the genetic epidemiology of febrile seizures in this population. Further information was analyzed and used to evaluate genetic associations of different febrile seizure subtypes.

RESULTS

Histories of febrile seizures were validated in 1051 twins in 900 pairs. The febrile seizure type was classified as simple, complex, or febrile status epilepticus. There were 61% simple, 12% complex, and 7% febrile status epilepticus. There were 78 twins who developed epilepsy. The highest rate of epilepsy (22.2%) occurred in the febrile status epilepticus group. Concordance was highest in simple group.

CONCLUSION

A twin with febrile status epilepticus is at the highest risk of developing epilepsy, but simple febrile seizures gave the highest risk for the unaffected twin to develop seizures or other neurological issues. These results are consistent with previous findings. There is a subgroup of febrile seizures that can be associated with long-term consequences. This subgroup can be associated with a significant financial and emotional burden. It is currently not possible to accurately identify which children will develop recurrent febrile seizures, epilepsy, or neuropsychological comorbidities.

Parental and comorbid epilepsy in persons with bipolar disorder

BACKGROUND

Population-based studies have demonstrated an overrepresentation of bipolar disorder (BPD) in individuals with epilepsy. However, few studies have examined the reverse association, i.e. comorbid epilepsy in individuals selected based on BPD diagnosis. No previous population-based study having examined the co-occurrence of BPD and epilepsy has adjusted for parental psychopathology. Such an adjustment is motivated by population-based studies reporting an overrepresentation of various types of parental psychiatric disorders in both BPD and epilepsy. Furthermore, an association between epilepsy in first-degree relatives and BPD has previously only been examined and demonstrated in a small clinical sample. The objective of this study is to examine the associations between parental and comorbid epilepsy and BPD, adjusting for parental psychopathology.

METHODS

This nested case-control study identified 1861 cases with BPD, age up to 25 years, 3643 matched controls, and their parents from Finnish national registers. Conditional logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) and two-sided significance limits of p<0.05.

RESULTS

BPD was associated with comorbid epilepsy (adjusted OR 2.53, 95% CI: 1.73-3.70) but not with parental epilepsy. Epilepsy was found in 3.33% of cases versus 1.29% of controls, 2.69% of cases' parents versus 2.53% of controls' parents.

LIMITATIONS

The diagnoses were register-based, not based on standardized procedures with direct ascertainment.

CONCLUSIONS

An association between BPD and comorbid epilepsy persists even after adjusting for parental psychopathology. Lack of familial clustering of BPD and epilepsy would suggest that the elevated co-occurrence of these disorders is influenced by non-genetic factors.

Multisensory integration and cross-modal learning in synaesthesia: A unifying model

Recent research into synaesthesia has highlighted the role of learning, yet synaesthesia is clearly a genetic condition. Here we ask how can the idea that synaesthesia reflects innate, genetic differences be reconciled with models that suggest it is driven by learning. A number of lines of evidence suggest that synaesthesia relies on, or at least interacts with, processes of multisensory integration that are common across all people. These include multisensory activations that arise in early regions of the brain as well as feedback from longer-term cross-modal associations generated in memory. These cognitive processes may interact independently to influence the phenomenology of the synaesthetic experience, as well as the individual differences within particular types of synaesthesia. The theoretical framework presented here is consistent with both an innate difference as the fundamental driver of the condition of synaesthesia, and with experiential and semantic influences on the eventual phenotype that emerges. In particular, it proposes that the internally generated synaesthetic percepts are treated similarly to other sensory information as the brain is learning the multisensory attributes of objects and developing cross-modal associations that merge in the concept of the object.

Epilepsy genetics: the ongoing revolution

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

Motor co-activation in siblings of patients with juvenile myoclonic epilepsy: an imaging endophenotype?

In juvenile myoclonic epilepsy (JME), myoclonic jerks are often triggered by cognitive effort. Wandschneider et al. report co-activation of the motor and prefrontal cognitive networks in unaffected siblings, similar to that previously reported in patients themselves. This co-activation could constitute a heritable marker for further genetic studies of JME.

Juvenile myoclonic epilepsy is a heritable idiopathic generalized epilepsy syndrome, characterized by myoclonic jerks and frequently triggered by cognitive effort. Impairment of frontal lobe cognitive functions has been reported in patients with juvenile myoclonic epilepsy and their unaffected siblings. In a recent functional magnetic resonance imaging study we reported abnormal co-activation of the motor cortex and increased functional connectivity between the motor system and prefrontal cognitive networks during a working memory paradigm, providing an underlying mechanism for cognitively triggered jerks. In this study, we used the same task in 15 unaffected siblings (10 female; age range 18–65 years, median 40) of 11 of those patients with juvenile myoclonic epilepsy (six female; age range 22–54 years, median 35) and compared functional magnetic resonance imaging activations with 20 age- and gender-matched healthy control subjects (12 female; age range 23–46 years, median 30.5). Unaffected siblings showed abnormal primary motor cortex and supplementary motor area co-activation with increasing cognitive load, as well as increased task-related functional connectivity between motor and prefrontal cognitive networks, with a similar pattern to patients (P < 0.001 uncorrected; 20-voxel threshold extent). This finding in unaffected siblings suggests that altered motor system activation and functional connectivity is not medication- or seizure-related, but represents a potential underlying mechanism for impairment of frontal lobe functions in both patients and siblings, and so constitutes an endophenotype of juvenile myoclonic epilepsy.

The role of T-type calcium channel genes in absence seizures

The thalamic relay neurons, reticular thalamic nucleus, and neocortical pyramidal cells form a circuit that sustains oscillatory burst firing, and is regarded as the underlying mechanism of absence seizures. T-type calcium channels play a key role in this circuit. Here, we review the role of T-type calcium channel genes in the development of absence seizures, and emphasize gain or loss of function mutations, and other variations that alter both quantity and quality of transcripts, and methylation status of isoforms of T-type calcium channel proteins might be of equal importance in understanding the pathological mechanism of absence seizures.

Current advances in childhood absence epilepsy

BACKGROUND

Childhood absence epilepsy is an age-dependent, idiopathic, generalized epilepsy with a characteristic seizure appearance. The disorder is likely to be multifactorial, resulting from interactions between genetic and acquired factors, but the debate is still open. We review recent studies on different aspects of childhood absence epilepsy and also to describe new concepts.

METHODS

Data for this review were identified using Medline and PubMed survey to locate studies dealing with childhood absence epilepsy. Searches included articles published between 1924 and 2013.

RESULTS

The diagnosis comprises predominant and associated seizure types associated with other clinical and electroencephalographic characteristics. Many studies have challenged the prevailing concepts, particularly with respect to the pathophysiological mechanisms underlying the electroencephalographic seizure discharges. Childhood absence epilepsy fits the definition of system epilepsy as a condition resulting from the persisting susceptibility of the thalamocortical system as a whole to generate seizures. This syndrome, if properly defined using strict diagnostic criteria, has a good prognosis. In some cases, it may affect multiple cognitive functions determining risk for academic and functional difficulties; the detection of children at risk allows tailored interventions. Childhood absence epilepsy is usually treated with ethosuximide, valproate, lamotrigine, or levetiracetam, but the most efficacious and tolerable initial empirical treatment has not been well defined.

CONCLUSIONS

We review recent studies and new concepts on the electroclinical features and pathophysiological findings of childhood absence epilepsy in order to highlight areas of consensus as well as areas of uncertainty that indicate directions for future research.

Familial risk of epilepsy: a population-based study

Almost all previous studies of familial risk of epilepsy have had potentially serious methodological limitations. Our goal was to address these limitations and provide more rigorous estimates of familial risk in a population-based study. We used the unique resources of the Rochester Epidemiology Project to identify all 660 Rochester, Minnesota residents born in 1920 or later with incidence of epilepsy from 1935-94 (probands) and their 2439 first-degree relatives who resided in Olmsted County. We assessed incidence of epilepsy in relatives by comprehensive review of the relatives' medical records, and estimated age-specific cumulative incidence and standardized incidence ratios for epilepsy in relatives compared with the general population, according to proband and relative characteristics. Among relatives of all probands, cumulative incidence of epilepsy to age 40 was 4.7%, and risk was increased 3.3-fold (95% confidence interval 2.75-5.99) compared with population incidence. Risk was increased to the greatest extent in relatives of probands with idiopathic generalized epilepsies (standardized incidence ratio 6.0) and epilepsies associated with intellectual or motor disability presumed present from birth, which we denoted 'prenatal/developmental cause' (standardized incidence ratio 4.3). Among relatives of probands with epilepsy without identified cause (including epilepsies classified as 'idiopathic' or 'unknown cause'), risk was significantly increased for epilepsy of prenatal/developmental cause (standardized incidence ratio 4.1). Similarly, among relatives of probands with prenatal/developmental cause, risk was significantly increased for epilepsies without identified cause (standardized incidence ratio 3.8). In relatives of probands with generalized epilepsy, standardized incidence ratios were 8.3 (95% confidence interval 2.93-15.31) for generalized epilepsy and 2.5 (95% confidence interval 0.92-4.00) for focal epilepsy. In relatives of probands with focal epilepsy, standardized incidence ratios were 1.0 (95% confidence interval 0.00-2.19) for generalized epilepsy and 2.6 (95% confidence interval 1.19-4.26) for focal epilepsy. Epilepsy incidence was greater in offspring of female probands than in offspring of male probands, and this maternal effect was restricted to offspring of probands with focal epilepsy. The results suggest that risks for epilepsies of unknown and prenatal/developmental cause may be influenced by shared genetic mechanisms. They also suggest that some of the genetic influences on generalized and focal epilepsies are distinct. However, the similar increase in risk for focal epilepsy among relatives of probands with either generalized (2.5-fold) or focal epilepsy (2.6-fold) may reflect some coexisting shared genetic influences.

Genetics of febrile seizure subtypes and syndromes: a twin study

PURPOSE

Febrile seizures (FS) are the most common seizure syndrome. A strong genetic component has been well established through family and twin studies; however, such studies have not examined the genetics of different FS types (simple, complex, febrile status epilepticus) and sub-syndromes (true FS, febrile seizures plus (FS+), 'FS with later epilepsy'). Here we used a community-based twin sample to analyze genetic factors within different FS subtypes and FS syndromes.

METHODS

Twin pairs were ascertained from the twin database of the Epilepsy Research Centre. A retrospective chart review was conducted and follow-up attempted for all subjects. Casewise concordance values were calculated for the different subgroups and intra-pair variation was analyzed.

KEY FINDINGS

One hundred and seventy-nine twin pairs with FS were identified. Overall casewise concordance for FS in monozygotic (MZ) twins (0.62) was greater than in dizygotic (DZ) twins (0.16, p<0.0001). A greater concordance amongst MZ pairs than DZ twin pairs was also observed for all FS subtypes and FS sub-syndromes, particularly in twins with FS+. Within concordant MZ pairs, we did not observe the co-occurrence of FS and FS+.

SIGNIFICANCE

These results suggest a strong genetic contribution to different FS subtypes and sub-syndromes. They also support the existence of distinct genetic factors for different FS subtypes and sub-syndromes, especially FS+. This information is important for the strategic planning of next generation sequencing studies of febrile seizures.

The Mid-Atlantic Twin Registry, revisited

The Mid-Atlantic Twin Registry (MATR) is a population-based registry of more than 56,000 twins primarily born or living in Virginia, North Carolina, and South Carolina. The MATR employs several methods of ascertaining twins, and devotes considerable resources to tracking and maintaining communication with MATR participants. Researchers may utilize the MATR for administration of research services including study recruitment, collection of DNA, archival data set creation, as well as data collection through mailed, phone, or online surveys. In addition, the MATR houses the MATR Repository, with over 1,200 blood samples available for researchers interested in DNA genotyping. For over 35 years MATR twins have participated in research studies with investigators from diverse scientific disciplines and various institutions. These studies, which have resulted in numerous publications, have covered a range of topics, including the human microbiome, developmental psychopathology, depression, anxiety, substance use, epigenetics of aging, children of twins, pre-term birth, social attitudes, seizures, eating disorders, as well as sleep homeostasis. Researchers interested in utilizing twins are encouraged to contact the MATR to discuss potential research opportunities.

Advances in epilepsy genetics and genomics

Current and emerging technologies for mutation identification are changing the landscape of genetics and accelerating the pace of discovery. Application of high throughput genomic analysis to epilepsy will advance our understanding of the genetic contribution to common forms of epilepsy and suggest novel therapeutic strategies for improved treatment.