Molecular mechanisms of cognitive and behavioral comorbidities of epilepsy in children

Autism Spectrum Disorder and Epilepsy: Pathogenetic Mechanisms and Therapeutic Implications

The co-occurrence of autism spectrum disorder (ASD) and epilepsy is a complex neurological condition that presents significant challenges for both patients and clinicians. ASD is a group of complex developmental disorders characterized by the following: (1) Social communication difficulties: challenges in understanding and responding to social cues, initiating and maintaining conversations, and developing and maintaining relationships. (2) Repetitive behaviors: engaging in repetitive actions, such as hand-flapping, rocking, or lining up objects. (3) Restricted interests: focusing intensely on specific topics or activities, often to the exclusion of other interests. (4) Sensory sensitivities: over- or under-sensitivity to sensory input, such as sounds, touch, tastes, smells, or sights. These challenges can significantly impact individuals' daily lives and require specialized support and interventions. Early diagnosis and intervention can significantly improve the quality of life for individuals with ASD and their families. Epilepsy is a chronic brain disorder characterized by recurrent unprovoked (≥2) seizures that occur >24 h apart. Single seizures are not considered epileptic seizures. Epilepsy is often idiopathic, but various brain disorders, such as malformations, strokes, and tumors, can cause symptomatic epilepsy. While these two conditions were once considered distinct, growing evidence suggests a substantial overlap in their underlying neurobiology. The prevalence of epilepsy in individuals with ASD is significantly higher than in the general population. This review will explore the epidemiology of this comorbidity, delve into the potential mechanisms linking ASD and epilepsy, and discuss the implications for diagnosis, treatment, and management.

Risk of autism spectrum disorder in children with infantile epileptic spasms syndrome: a retrospective study in a single center in Brazil

OBJECTIVE

This study aimed to investigate the prevalence of autism spectrum disorder and its possible correlations with clinical characteristics in patients with infantile epileptic spasms syndrome in a single center in Brazil.

METHODS

This retrospective cross-sectional study examined 53 children with the diagnosis of infantile epileptic spasms syndrome prior to an autism spectrum disorder assessment. Participants were divided into two groups based on the presence or absence of autism spectrum disorder. Available variables (sex, medications, median age at onset of infantile epileptic spasms syndrome, and presence of comorbidities) were compared using Mann-Whitney U or chi-square tests.

RESULTS

Among the included patients, 12 (23 %) were diagnosed with autism spectrum disorder, corresponding to a relative risk of 0.29 (95 % confidence interval 0.174-0.492). The age at the first seizure ranged from 3 to 15 months, with a mean of 6.65 months. This age significantly differed between participants with autism spectrum disorder (10.58 months) and those without (5.43 months), p<0.001.

CONCLUSION

Children with infantile epileptic spasms syndrome have a higher risk of being diagnosed with autism spectrum disorder. Later age of onset and period of spasm occurrence might be predisposing risk factors.

Traditional and Innovative Anti-seizure Medications Targeting Key Physiopathological Mechanisms: Focus on Neurodevelopment and Neurodegeneration

Despite the wide range of compounds currently available to treat epilepsy, there is still no drug that directly tackles the physiopathological mechanisms underlying its development. Indeed, antiseizure medications attempt to prevent seizures but are inefficacious in counteracting or rescuing the physiopathological phenomena that underlie their onset and recurrence, and hence do not cure epilepsy. Classically, the altered excitation/inhibition balance is postulated as the mechanism underlying epileptogenesis and seizure generation. This oversimplification, however, does not account for deficits in homeostatic plasticity resulting from either insufficient or excessive compensatory mechanisms in response to a change in network activity. In this respect, both neurodevelopmental epilepsies and those associated with neurodegeneration may share common underlying mechanisms that still need to be fully elucidated. The understanding of these molecular mechanisms shed light on the identification of new classes of drugs able not only to suppress seizures, but also to present potential antiepileptogenic effects or "disease-modifying" properties.

Epilepsy and Cognitive Impairment in Childhood and Adolescence: A Mini-Review

Managing epilepsy in people with an intellectual disability remains a therapeutic challenge and must take into account additional issues such as diagnostic difficulties and frequent drug resistance. Advances in genomic technologies improved our understanding of epilepsy and raised the possibility to develop patients-tailored treatments acting on the key molecular mechanisms involved in the development of the disease. In addition to conventional antiseizure medications (ASMs), ketogenic diet, hormone therapy and epilepsy surgery play an important role, especially in cases of drugresistance. This review aims to provide a comprehensive overview of the mainfactors influencing cognition in children and adolescents with epilepsy and the main therapeutic options available for the epilepsies associated with intellectual disability.

Shared Etiology in Autism Spectrum Disorder and Epilepsy with Functional Disability

Autism spectrum disorders and epilepsies are heterogeneous human disorders that have miscellaneous etiologies and pathophysiology. There is considerable risk of frequent epilepsy in autism that facilitates amplified morbidity and mortality. Several biological pathways appear to be involved in disease progression, including gene transcription regulation, cellular growth, synaptic channel function, and maintenance of synaptic structure. Here, abnormalities in excitatory/inhibitory (E/I) balance ratio are reviewed along with part of an epileptiform activity that may drive both overconnectivity and genetic disorders where autism spectrum disorders and epilepsy frequently co-occur. The most current ideas concerning common etiological and molecular mechanisms for co-occurrence of both autism spectrum disorders and epilepsy are discussed along with the powerful pharmacological therapies that protect the cognition and behavior of patients. Better understanding is necessary to identify a biological mechanism that might lead to possible treatments for these neurological disorders.

Learning Deficits and Attenuated Adaptive Stress Response After Early-Life Seizures in Zebrafish

Early-life seizures (ELS) are often associated with the development of cognitive deficits. However, methods to predict and prevent these deficits are lacking. To increase the range of research models available to study cognitive consequences of ELS, we investigated whether seizures in larval zebrafish (Danio rerio) lead to behavioral deficits later in life. We thus modified the existing pentylenetetrazole (PTZ)-induced seizure model in larval zebrafish, exposing zebrafish to PTZ daily from 5 to 7 days post-fertilization (dpf). We then compared later-life learning, social behavior (shoaling), and behavioral and chemical measures of anxiety in the PTZ-exposed zebrafish (PTZ group) to that of naïve clutchmates (untouched controls, UC) and to a second control group (handling control, HC) that experienced the same handling as the PTZ group, but without PTZ exposure. We observed that only the PTZ group displayed a significant deficit in a y-maze learning task, while only the HC group displayed a social deficit of decreased shoaling. HC fish also showed an increased frequency of behavioral freezing and elevated cortisol responses to netting, heightened stress responses not seen in the PTZ fish. Since mild stressors, such as the handling the HC fish experienced, can lead to learned, advantageous responses to stress later in life, we tested escape response in the HC fish using an acoustic startle stimulus. The HC group showed an enhanced startle response, swimming significantly farther than either the PTZ or UC group immediately after being startled. Taken together, these results indicate that seizures in larval zebrafish impair learning and the development of an adaptive, heightened stress response after early-life stress. These findings expand the behavioral characterization of the larval zebrafish seizure model, strengthening the power of this model for ELS research.

The epilepsy-autism spectrum disorder phenotype in the era of molecular genetics and precision therapy

Autism spectrum disorder (ASD) is frequently associated with infants with epileptic encephalopathy, and early interventions targeting social and cognitive deficits can have positive effects on developmental outcome. However, early diagnosis of ASD among infants with epilepsy is complicated by variability in clinical phenotypes. Commonality in both biological and molecular mechanisms have been suggested between ASD and epilepsy, such as occurs with tuberous sclerosis complex. This review summarizes the current understanding of causal mechanisms between epilepsy and ASD, with a particularly genetic focus. Hypothetical explanations to support the conjugation of the two conditions include abnormalities in synaptic growth, imbalance in neuronal excitation/inhibition, and abnormal synaptic plasticity. Investigation of the probable genetic basis has implemented many genes, although the main risk supports existing hypotheses in that these cluster to abnormalities in ion channels, synaptic function and structure, and transcription regulators, with the mammalian target of rapamycin (mTOR) pathway and "mTORpathies" having been a notable research focus. Experimental models not only have a crucial role in determining gene functions but are also useful instruments for tracing disease trajectory. Precision medicine from gene therapy remains a theoretical possibility, but more contemporary developments continue in molecular tests to aid earlier diagnoses and better therapeutic targeting.

Reduced hippocampal inhibition and enhanced autism-epilepsy comorbidity in mice lacking neuropilin 2

The neuropilin receptors and their secreted semaphorin ligands play key roles in brain circuit development by regulating numerous crucial neuronal processes, including the maturation of synapses and migration of GABAergic interneurons. Consistent with its developmental roles, the neuropilin 2 (Nrp2) locus contains polymorphisms in patients with autism spectrum disorder (ASD). Nrp2-deficient mice show autism-like behavioral deficits and propensity to develop seizures. In order to determine the pathophysiology in Nrp2 deficiency, we examined the hippocampal numbers of interneuron subtypes and inhibitory regulation of hippocampal CA1 pyramidal neurons in mice lacking one or both copies of Nrp2. Immunostaining for interneuron subtypes revealed that Nrp2^-/- mice have a reduced number of parvalbumin, somatostatin, and neuropeptide Y cells, mainly in CA1. Whole-cell recordings identified reduced firing and hyperpolarized shift in resting membrane potential in CA1 pyramidal neurons from Nrp2^+/- and Nrp2^-/- mice compared to age-matched wild-type controls indicating decrease in intrinsic excitability. Simultaneously, the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) are reduced in Nrp2-deficient mice. A convulsive dose of kainic acid evoked electrographic and behavioral seizures with significantly shorter latency, longer duration, and higher severity in Nrp2^-/- compared to Nrp2^+/+ animals. Finally, Nrp2^+/- and Nrp2^-/- but not Nrp2^+/+, mice have impaired cognitive flexibility demonstrated by reward-based reversal learning, a task associated with hippocampal circuit function. Together these data demonstrate a broad reduction in interneuron subtypes and compromised inhibition in CA1 of Nrp2^-/- mice, which could contribute to the heightened seizure susceptibility and behavioral deficits consistent with an ASD/epilepsy phenotype.

Hyperactive behaviour in Angelman syndrome: the association with sleep problems and age of epilepsy onset

BACKGROUND

Sleep problems are common in many neurodevelopmental disorders, but little is known about how sleep is related to behavioural symptoms in Angelman syndrome (AS) or other genetic disorders. Hyperactive behaviour, sleep problems and epilepsy seem to be more common in AS than in other genetic conditions associated with severe intellectual disability. We hypothesised that both more sleep problems and earlier onset of epileptic seizures would predict more symptoms of hyperactivity. Hence, the aim of the project was to explore the association between hyperactive behaviour, sleep problems and age of epilepsy onset in individuals with AS.

METHOD

All known parents/guardians (n = 115) of individuals with AS in Norway were invited to participate in this descriptive correlational study. Fifty-six individuals (49%) responded, and 42 people (25 male and 17 female; mean age 18.5 years, range 2-57 years) with genetically verified AS were included. Scores for 'hyperactivity' and 'sleep problems' were derived from questionnaire data. Information on epilepsy was obtained from medical records.

RESULTS

'Hyperactivity' was positively correlated with 'total sleep problems' (r = 0.46, P = 0.002) and negatively correlated with 'age of epilepsy onset' (r = -0.47, P = 0.01). 'Age of epilepsy onset' was not correlated with 'total sleep problems'. An overall multiple regression model with 'hyperactivity' as the dependent variable and 'age of epilepsy onset' and 'total sleep problems' as covariates was significant (R²  = 0.39, F = 8.16, P = 0.002). Hence, hyperactivity in AS could be predicted from both age of epilepsy onset and current sleep problems.

CONCLUSIONS

Sleep problems may increase hyperactivity symptoms in individuals with AS. The association between hyperactivity and sleep problems in AS indicates that both should be investigated together as part of routine clinical assessment and intervention for either area of difficulty. Younger age of epilepsy onset was associated with more hyperactivity in AS, which may be related to encephalopathic effects of seizures and epilepsy.

Diagnostic Yield and Cost-Effectiveness of "Dynamic" Exome Analysis in Epilepsy with Neurodevelopmental Disorders: A Tertiary-Center Experience in Northern Italy

Background: The advent of next-generation sequencing (NGS) techniques in clinical practice led to a significant advance in gene discovery. We aimed to describe diagnostic yields of a “dynamic” exome-based approach in a cohort of patients with epilepsy associated with neurodevelopmental disorders. Methods: We conducted a retrospective, observational study on 72 probands. All patients underwent a first diagnostic level of a 135 gene panel, a second of 297 genes for inconclusive cases, and finally, a whole-exome sequencing for negative cases. Diagnostic yields at each step and cost-effectiveness were the objects of statistical analysis. Results: Overall diagnostic yield in our cohort was 37.5%: 29% of diagnoses derived from the first step analysis, 5.5% from the second step, and 3% from the third. A significant difference emerged between the three diagnostic steps (p < 0.01), between the first and second (p = 0.001), and the first and third (p << 0.001). The cost-effectiveness plane indicated that our exome-based “dynamic” approach was better in terms of cost savings and higher diagnostic rate. Conclusions: Our findings suggested that “dynamic” NGS techniques applied to well-phenotyped individuals can save both time and resources. In patients with unexplained epilepsy comorbid with NDDs, our approach might maximize the number of diagnoses achieved.

A single early-life seizure results in long-term behavioral changes in the adult Fmr1 knockout mouse

Fragile X syndrome (FXS) is the leading cause of inherited intellectual disability and a significant genetic contributor to Autism spectrum disorder. In addition to autistic-like phenotypes, individuals with FXS are subject to developing numerous comorbidities, one of the most prevalent being seizures. In the present study, we investigated how a single early-life seizure superimposed on a genetic condition impacts the autistic-like behavioral phenotype of the mouse. We induced status epilepticus (SE) on postnatal day (PD) 10 in Fmr1 wild type (WT) and knockout (KO) mice. We then tested the mice in a battery of behavioral tests during adulthood (PD90) to examine the long-term impact of an early-life seizure. Our findings replicated prior work that reported a single instance of SE results in behavioral deficits, including increases in repetitive behavior, enhanced hippocampal-dependent learning, and reduced sociability and prepulse inhibition (p <  0.05). We also observed genotypic differences characteristic of the FXS phenotype in Fmr1 KO mice, such as enhanced prepulse inhibition and repetitive behavior, hyperactivity, and reduced startle responses (p <  0.05). Superimposing a seizure on deletion of Fmr1 significantly impacted repetitive behavior in a nosepoke task. Specifically, a single early-life seizure increased consecutive nose poking behavior in the task in WT mice (p <  0.05), yet seizures did not exacerbate the elevated stereotypy observed in Fmr1 KO mice (p >  0.05). Overall, these findings help to elucidate how seizures in a critical period of development can impact long-term behavioral manifestations caused by underlying gene mutations in Fmr1. Utilizing double-hit models, such as superimposing seizures on the Fmr1 mutation, can help to enhance our understanding of comorbidities in disease models.

Transcriptome Analysis Identifies Multifaceted Regulatory Mechanisms Dictating a Genetic Switch from Neuronal Network Establishment to Maintenance During Postnatal Prefrontal Cortex Development

The prefrontal cortex (PFC) is one of the latest brain regions to mature, which allows the acquisition of complex cognitive abilities through experience. To unravel the underlying gene expression changes during postnatal development, we performed RNA-sequencing (RNA-seq) in the rat medial PFC (mPFC) at five developmental time points from infancy to adulthood, and analyzed the differential expression of protein-coding genes, long intergenic noncoding RNAs (lincRNAs), and alternative exons. We showed that most expression changes occur in infancy, and that the number of differentially expressed genes reduces toward adulthood. We observed 137 differentially expressed lincRNAs and 796 genes showing alternative exon usage during postnatal development. Importantly, we detected a genetic switch from neuronal network establishment in infancy to maintenance of neural networks in adulthood based on gene expression dynamics, involving changes in protein-coding and lincRNA gene expression as well as alternative exon usage. Our gene expression datasets provide insights into the multifaceted transcriptional regulation of the developing PFC. They can be used to study the basic developmental processes of the mPFC and to understand the mechanisms of neurodevelopmental and neuropsychiatric disorders. Our study provides an important contribution to the ongoing efforts to complete the "brain map", and to the understanding of PFC development.

Rho GTPases in Intellectual Disability: From Genetics to Therapeutic Opportunities

Rho-class small GTPases are implicated in basic cellular processes at nearly all brain developmental steps, from neurogenesis and migration to axon guidance and synaptic plasticity. GTPases are key signal transducing enzymes that link extracellular cues to the neuronal responses required for the construction of neuronal networks, as well as for synaptic function and plasticity. Rho GTPases are highly regulated by a complex set of activating (GEFs) and inactivating (GAPs) partners, via protein:protein interactions (PPI). Misregulated RhoA, Rac1/Rac3 and cdc42 activity has been linked with intellectual disability (ID) and other neurodevelopmental conditions that comprise ID. All genetic evidences indicate that in these disorders the RhoA pathway is hyperactive while the Rac1 and cdc42 pathways are consistently hypoactive. Adopting cultured neurons for in vitro testing and specific animal models of ID for in vivo examination, the endophenotypes associated with these conditions are emerging and include altered neuronal networking, unbalanced excitation/inhibition and altered synaptic activity and plasticity. As we approach a clearer definition of these phenotype(s) and the role of hyper- and hypo-active GTPases in the construction of neuronal networks, there is an increasing possibility that selective inhibitors and activators might be designed via PPI, or identified by screening, that counteract the misregulation of small GTPases and result in alleviation of the cognitive condition. Here we review all knowledge in support of this possibility.

Autistic traits in epilepsy models: Why, when and how?

Autism spectrum disorder (ASD) is a common comorbidity of epilepsy and seizures and/or epileptiform activity are observed in a significant proportion of ASD patients. Current research also implies that autistic traits can be observed to a various degree in mice and rats with seizures. This suggests that there are shared mechanisms in both ASD and epilepsy syndromes. Here, we first review the standard, validated methods used to assess autistic traits in animal models as well as their limitations with regards to epilepsy models. We then discuss two of the potential pathological processes that could be shared between ASD and epilepsy. We first focus on functional implications of neuroinflammation including changes to excitable networks mediated by inflammatory regulators. Finally we examine mechanisms at the cellular and network level involved in neuronal excitability, timing and network coordination that may directly lead to behavioral disturbances present in both epilepsy and ASD. This mini-review summarizes the work first presented at an Investigators Workshop at the 2016 American Epilepsy Society meeting.

Regulation of seizure-induced MeCP2 Ser421 phosphorylation in the developing brain

Neonatal seizures disrupt normal synaptic maturation and often lead to later-life epilepsy and cognitive deficits. During early life, the brain exhibits heightened synaptic plasticity, in part due to a developmental overabundance of Ca_V1.2 L-type voltage gated calcium (Ca²⁺) channels (LT-VGCCs) and Ca²⁺-permeable AMPARs (CP-AMPARs) lacking GluA2 subunits. We hypothesized that early-life seizures overactivate these channels, in turn dysregulating Ca²⁺-dependent signaling pathways including that of methyl CPG binding protein 2 (MeCP2), a transcription factor implicated in the autism spectrum disorder (ASD) Rett Syndrome. Here, we show that in vivo hypoxia-induced seizures (HS) in postnatal day (P)10 rats acutely induced phosphorylation of the neuronal-specific target of activity-dependent MeCP2 phosphorylation, S421, as well as its upstream activator CaMKII T286. We next identified mechanisms by which activity-dependent Ca²⁺ influx induced MeCP2 phosphorylation using in vitro cortical and hippocampal neuronal cultures at embryonic day (E)18 + 10 days in vitro (DIV). In contrast to the prevalent role of NMDARs in the adult brain, we found that both CP-AMPARs and LT-VGCCs mediated MeCP2 S421 and CaMKII T286 phosphorylation induced by kainic acid (KA) or high potassium chloride (KCl) stimulation. Furthermore, in vivo post-seizure treatment with the broad-spectrum AMPAR antagonist NBQX, the CP-AMPAR blocker IEM-1460, or the LT-VGCC antagonist nimodipine blocked seizure-induced MeCP2 phosphorylation. Collectively, these results demonstrate that early-life seizures dysregulate critical activity-dependent developmental signaling pathways, in part via CP-AMPAR and LT-VGCC activation, providing novel age-specific therapeutic targets for convergent pathways underlying epilepsy and ASDs.

A Method to Culture GABAergic Interneurons Derived from the Medial Ganglionic Eminence

Understanding the mechanisms guiding interneuron development is a central aspect of the current research on cortical/hippocampal interneurons, which is highly relevant to brain function and pathology. In this methodological study we have addressed the setup of protocols for the reproducible culture of dissociated cells from murine medial ganglionic eminences (MGEs), to provide a culture system for the analysis of interneurons in vitro. This study includes the detailed protocols for the preparation of the dissociated cells, and for their culture on optimal substrates for cell migration or differentiation. These cultures enriched in interneurons may allow the investigation of the migratory behavior of interneuron precursors and their differentiation in vitro, up to the formation of morphologically identifiable GABAergic synapses. Live imaging of MGE-derived cells plated on proper substrates shows that they are useful to study the migratory behavior of the precursors, as well as the behavior of growth cones during the development of neurites. Most MGE-derived precursors develop into polarized GABAergic interneurons as determined by axonal, dendritic, and GABAergic markers. We present also a comparison of cells from WT and mutant mice as a proof of principle for the use of these cultures for the analysis of the migration and differentiation of GABAergic cells with different genetic backgrounds. The culture enriched in interneurons described here represents a useful experimental system to examine in a relatively easy and fast way the morpho-functional properties of these cells under physiological or pathological conditions, providing a powerful tool to complement the studies in vivo.

Effect of epilepsy on autism symptoms in Angelman syndrome

Background

Autism spectrum disorder and epilepsy often co-occur; however, the extent to which the association between autism symptoms and epilepsy is due to shared aetiology or to the direct effects of seizures is a topic of ongoing debate. Angelman syndrome (AS) is presented as a suitable disease model to explore this association.

Methods

Data from medical records and questionnaires were used to examine the association between age of epilepsy onset, autism symptoms, genetic aberration and communication level. Forty-eight participants had genetically verified AS (median age 14.5 years; range 1–57 years). A measure of autism symptoms (the Social Communication Questionnaire; SCQ) was completed for 38 individuals aged ≥ 4 years. Genetic cause was subgrouped into deletion and other genetic aberrations of the 15q11-q13 area. The number of signs used to communicate (< 20 sign and ≥ 20 signs) was used as a measure of nonverbal communication.

Results

Mean age of epilepsy onset was 3.0 years (range 3 months–7.8 years). Mean SCQ score for individuals without epilepsy was 13.6 (SD = 6.7) and with epilepsy 17.0 (SD = 5.6; p = 0.17); 58% used fewer than 20 signs to communicate. There were no age differences between groups according to presence of epilepsy, level of nonverbal communication or type of genetic aberration. SCQ scores were higher in individuals with the deletion than in those with other genetic aberrations (18.7 vs 10.8 p = 0.008) and higher in the group who used < 20 signs to communicate (19.4 vs 14.1 p = 0.007). Age of epilepsy onset was correlated with SCQ (r = − 0.61, p < 0.001). Multiple regression showed that age of seizure onset was significantly related to SCQ score (β = − 0.90; p = 0.006), even when the type of genetic abnormality was controlled (R² = 0.53; F = 10.7; p = 0.001).

Conclusions

The study provides support for the notion that seizures themselves contribute more to autism symptoms than expected from the underlying genetic pathology alone. The study demonstrates how a rare genetic syndrome such as Angelman syndrome may be used to study the relation between epilepsy and autism symptomatology.

High Rate of Recurrent De Novo Mutations in Developmental and Epileptic Encephalopathies

Developmental and epileptic encephalopathy (DEE) is a group of conditions characterized by the co-occurrence of epilepsy and intellectual disability (ID), typically with developmental plateauing or regression associated with frequent epileptiform activity. The cause of DEE remains unknown in the majority of cases. We performed whole-genome sequencing (WGS) in 197 individuals with unexplained DEE and pharmaco-resistant seizures and in their unaffected parents. We focused our attention on de novo mutations (DNMs) and identified candidate genes containing such variants. We sought to identify additional subjects with DNMs in these genes by performing targeted sequencing in another series of individuals with DEE and by mining various sequencing datasets. We also performed meta-analyses to document enrichment of DNMs in candidate genes by leveraging our WGS dataset with those of several DEE and ID series. By combining these strategies, we were able to provide a causal link between DEE and the following genes: NTRK2, GABRB2, CLTC, DHDDS, NUS1, RAB11A, GABBR2, and SNAP25. Overall, we established a molecular diagnosis in 63/197 (32%) individuals in our WGS series. The main cause of DEE in these individuals was de novo point mutations (53/63 solved cases), followed by inherited mutations (6/63 solved cases) and de novo CNVs (4/63 solved cases). De novo missense variants explained a larger proportion of individuals in our series than in other series that were primarily ascertained because of ID. Moreover, these DNMs were more frequently recurrent than those identified in ID series. These observations indicate that the genetic landscape of DEE might be different from that of ID without epilepsy.

What is the Relationship Between Autism Spectrum Disorders and Epilepsy?

The association of epilepsy and autism spectrum disorders (ASD) is best understood by examining the relationship between social cognition, nonsocial cognition, and epilepsy. The relationship between ASD and epilepsy is bidirectional and is strongly linked to intellectual disability (ID). The risk of developing ASD in children with epilepsy is highest in children with early onset seizures, with a high prevalence in children with infantile spasms. The risk of developing epilepsy in children first diagnosed with ASD is highest in those with ID. The prevalence of seizures in ASD increases with age. When epilepsy and ASD coexist, they share common pathophysiological mechanisms. In epilepsy with and without ID, social-cognitive deficits are an important determinant of neurodevelopmental outcomes. Early recognition of social deficits is an important aspect of the comprehensive management of children with epilepsy. Treating the seizures in individuals with epilepsy and ASD is crucial but interventions that address social-cognitive deficits are necessary to maximize neurodevelopmental outcomes.

Neurocognitive Comorbidities in Pediatric Epilepsy: Lessons in the Laboratory and Clinical Profile

Children with epilepsy are at risk for a variety of neurocognitive comorbidities. Animal models have increased our understanding about the neurobiological mechanisms underlying the association between seizures and these comorbidities. This article starts with an overview of the current data on animal model research, studying the influence of early-life seizures, followed by a summary of potential cellular and molecular mechanisms by which seizures can affect cognitive development. We then describe specific abnormal neuropsychological profiles that accompany specific pediatric epilepsy syndromes. Finally, we offer a potential guideline to the treatment and management of children with epilepsy and its neurocognitive comorbidities.

Identification of a Protein Network Driving Neuritogenesis of MGE-Derived GABAergic Interneurons

Interneurons are essential modulators of brain activity and their abnormal maturation may lead to neural and intellectual disabilities. Here we show that cultures derived from murine medial ganglionic eminences (MGEs) produce virtually pure, polarized γ-aminobutyric acid (GABA)-ergic interneurons that can form morphologically identifiable inhibitory synapses. We show that Rac GTPases and a protein complex including the GIT family scaffold proteins are expressed during maturation in vitro, and are required for the normal development of neurites. GIT1 promotes neurite extension in a conformation-dependent manner, while affecting its interaction with specific partners reduces neurite branching. Proteins of the GIT network are concentrated at growth cones, and interaction mutants may affect growth cone behavior. Our findings identify the PIX/GIT1/liprin-α1/ERC1 network as critical for the regulation of interneuron neurite differentiation in vitro, and show that these cultures represent a valuable system to identify the molecular mechanisms driving the maturation of cortical/hippocampal interneurons.

Epilepsy in children and adolescents: Disease concepts, practical knowledge, and coping

PROBLEM

Children suffering from epilepsy face severe difficulties in daily life. However, data about the self-assessment of children are scarce.

METHODS

From October 2013 to February 2014, patients aged 6-18years suffering from epilepsy were consecutively invited (i) to take part in a structured interview and (ii) to draw a picture about their self-assessment of epilepsy.

RESULTS

Eighty-four children and their parents agreed to participate: (i) 63/84 (75%) of the children named their disease correctly; contagiousness was assumed by 8/84 (10%); 81/84 (96%) knew whether they have to take medication; 36/69 (52%) of the children taking long-term medication reported the name(s) of their medication; 8/69 (12%) believed that their medication will cure their disease; 45/84 (54%) named specific precautions to prevent harm from seizures; 6/84 (7%) believed that nonadherence to safety precautions would cause new seizures; and 23/84 (27%) believed that they are worse off than healthy children. (ii) 67/84 (80%) drew a picture titled "This is how I feel when I have a seizure". Specific symptoms [17/67 (25%)] and the interaction between child and environment [12/67 (18%)] were the most common subjects.

CONCLUSION

Most children with epilepsy had rather good knowledge about medication; half of the children knew specific safety precautions. The children were often able to describe their seizures well. Pictures drawn by patients can give an insight into their experiences. Teaching programs should, among others, address the fear of contagiousness of epilepsy in some children and the fact that children with epilepsy might feel disadvantaged.

Surgical versus medical treatment for children with epileptic encephalopathy in infancy and early childhood: Results of an international multicenter cohort study in Far-East Asia (the FACE study)

OBJECTIVE

To compare the seizure and developmental outcomes in infants and young children with epileptic encephalopathy who have undergone surgical and medical treatments.

METHODS

An international, multicenter, observational cohort study was undertaken. A total of 317 children aged <6 years, who had frequent disabling seizures despite intensive medical treatments, were registered. Among the enrolled children, 250 were treated medically (medical group), 31 underwent resective surgery (resective group), and 36 underwent palliative surgery [callosotomy (n=30) or vagal nerve stimulation (n=6); palliative group] on admission. Seizure and developmental outcomes were obtained for 230 children during the 3-year follow-up period. Cox proportional hazard model was used to adjust for clinical backgrounds among treatment groups when comparing the seizure-free survival rates.

RESULTS

At the 3-year follow-up, seizure-free survival was 15.7%, 32.1%, and 52.4% in the medical, palliative, and resective groups, respectively. The adjusted hazard ratios for seizure recurrence in the resective and palliative groups versus the medical group were 0.43 (95% CI, 0.21-0.87, P=0.019) and 0.82 (95% CI, 0.46-1.46, P=0.50), respectively; the former was statistically significant. Regarding the developmental outcome, the mean DQs in the resective group increased significantly compared to those in the medical group during the follow-up (P<0.01). As for subgroup analysis, better seizure and development outcomes were demonstrated in the resective group compared to the medical group in children with nonsyndromic epilepsies (those to which no known epilepsy syndromes were applicable).

SIGNIFICANCE

These results suggest that surgical treatments, particularly resective surgeries, are associated with better seizure and developmental outcomes compared with successive medical treatment. The present observations may facilitate the identification of infants and young children with epileptic encephalopathy who could benefit from surgery.

Loss of Either Rac1 or Rac3 GTPase Differentially Affects the Behavior of Mutant Mice and the Development of Functional GABAergic Networks

Rac GTPases regulate the development of cortical/hippocampal GABAergic interneurons by affecting the early development and migration of GABAergic precursors. We have addressed the function of Rac1 and Rac3 proteins during the late maturation of hippocampal interneurons. We observed specific phenotypic differences between conditional Rac1 and full Rac3 knockout mice. Rac1 deletion caused greater generalized hyperactivity and cognitive impairment compared with Rac3 deletion. This phenotype matched with a more evident functional impairment of the inhibitory circuits in Rac1 mutants, showing higher excitability and reduced spontaneous inhibitory currents in the CA hippocampal pyramidal neurons. Morphological analysis confirmed a differential modification of the inhibitory circuits: deletion of either Rac caused a similar reduction of parvalbumin-positive inhibitory terminals in the pyramidal layer. Intriguingly, cannabinoid receptor-1-positive terminals were strongly increased only in the CA1 of Rac1-depleted mice. This increase may underlie the stronger electrophysiological defects in this mutant. Accordingly, incubation with an antagonist for cannabinoid receptors partially rescued the reduction of spontaneous inhibitory currents in the pyramidal cells of Rac1 mutants. Our results show that Rac1 and Rac3 have independent roles in the formation of GABAergic circuits, as highlighted by the differential effects of their deletion on the late maturation of specific populations of interneurons.

Third International Congress on Epilepsy, Brain, and Mind: Part 2

Epilepsy is both a disease of the brain and the mind. Here, we present the second of two papers with extended summaries of selected presentations of the Third International Congress on Epilepsy, Brain and Mind (April 3-5, 2014; Brno, Czech Republic). Humanistic, biologic, and therapeutic aspects of epilepsy, particularly those related to the mind, were discussed. The extended summaries provide current overviews of epilepsy, cognitive impairment, and treatment, including brain functional connectivity and functional organization; juvenile myoclonic epilepsy; cognitive problems in newly diagnosed epilepsy; SUDEP including studies on prevention and involvement of the serotoninergic system; aggression and antiepileptic drugs; body, mind, and brain, including pain, orientation, the "self-location", Gourmand syndrome, and obesity; euphoria, obsessions, and compulsions; and circumstantiality and psychiatric comorbidities.

Molecular underpinnings of prefrontal cortex development in rodents provide insights into the etiology of neurodevelopmental disorders

The prefrontal cortex (PFC), seat of the highest-order cognitive functions, constitutes a conglomerate of highly specialized brain areas and has been implicated to have a role in the onset and installation of various neurodevelopmental disorders. The development of a properly functioning PFC is directed by transcription factors, guidance cues and other regulatory molecules and requires the intricate and temporal orchestration of a number of developmental processes. Disturbance or failure of any of these processes causing neurodevelopmental abnormalities within the PFC may contribute to several of the cognitive deficits seen in patients with neurodevelopmental disorders. In this review, we elaborate on the specific processes underlying prefrontal development, such as induction and patterning of the prefrontal area, proliferation, migration and axonal guidance of medial prefrontal progenitors, and their eventual efferent and afferent connections. We furthermore integrate for the first time the available knowledge from genome-wide studies that have revealed genes linked to neurodevelopmental disorders with experimental molecular evidence in rodents. The integrated data suggest that the pathogenic variants in the neurodevelopmental disorder-associated genes induce prefrontal cytoarchitectonical impairments. This enhances our understanding of the molecular mechanisms of prefrontal (mis)development underlying the four major neurodevelopmental disorders in humans, that is, intellectual disability, autism spectrum disorders, attention deficit hyperactivity disorder and schizophrenia, and may thus provide clues for the development of novel therapies.

Independent Neuronal Origin of Seizures and Behavioral Comorbidities in an Animal Model of a Severe Childhood Genetic Epileptic Encephalopathy

The childhood epileptic encephalopathies (EE’s) are seizure disorders that broadly impact development including cognitive, sensory and motor progress with severe consequences and comorbidities. Recently, mutations in DNM1 (dynamin 1) have been implicated in two EE syndromes, Lennox-Gastaut Syndrome and Infantile Spasms. Dnm1 encodes dynamin 1, a large multimeric GTPase necessary for activity-dependent membrane recycling in neurons, including synaptic vesicle endocytosis. Dnm1^Ftfl or “fitful” mice carry a spontaneous mutation in the mouse ortholog of DNM1 and recapitulate many of the disease features associated with human DNM1 patients, providing a relevant disease model of human EE’s. In order to examine the cellular etiology of seizures and behavioral and neurological comorbidities, we engineered a conditional Dnm1^Ftfl mouse model of DNM1 EE. Observations of Dnm1^Ftfl/flox mice in combination with various neuronal subpopulation specific cre strains demonstrate unique seizure phenotypes and clear separation of major neurobehavioral comorbidities from severe seizures associated with the germline model. This demonstration of pleiotropy suggests that treating seizures per se may not prevent severe comorbidity observed in EE associated with dynamin-1 mutations, and is likely to have implications for other genetic forms of EE.

Childhood epilepsy syndromes, such as the early epileptic encephalopathies (EE’s) encompass seizure disorders that manifest early and negatively impact or completely block developmental progression. Recently, mutations in DNM1 (dynamin 1) have been implicated in two EE syndromes, Lennox-Gastaut Syndrome and Infantile Spasms. Dynamin 1 is a large multimeric protein that is critical for electro-chemical communication between neurons. To understand the relationship between severe seizures and the cognitive and behavioral developmental outcomes in DNM1 patients, we focus on “fitful” mice that carry a mutation in the dynamin 1 gene. Fitful mice have an EE disorder that is highly reminiscent of the documented human patients. Here, we describe genetic manipulations in the mice that allow us to determine that the seizure activity has independent cellular origins from the developmental and behavioral consequences. This separation confirms that the seizures do not cause the severe developmental delay and abnormal behaviors in this animal model and further suggests that any treatments aimed at controlling the seizures per se may not be effective for some of the most acute neurobehavioral symptoms in these patients.

Cognitive development in females with PCDH19 gene-related epilepsy

Mutations in the PCDH19 gene are now recognized to cause epilepsy in females and are claiming increasing interest in the scientific world. Clinical features and seizure semiology have been described as heterogeneous. Intellectual disability might be present, ranging from mild to severe; behavioral and psychiatric problems are a common feature of the disorder, including aggressiveness, depressed mood, and psychotic traits. The purpose of our study was to describe the cognitive development in 11 girls with a de novo mutation in PCDH19 and early-onset epilepsy. Six patients had average mental development or mild intellectual disability regardless of persistence of seizures in clusters. Five patients presented moderate or severe intellectual disability and autistic features. In younger patients, we found that despite an average developmental quotient, they all presented a delay of expressive language acquisition and lower scores at follow-up testing completed at older ages, underlining that subtle dysfunctions might be present. Larger cohort and long-term follow-up might be useful in defining cognitive features and in improving the care of patients with PCDH19.

EEG abnormalities and seizures in genetically diagnosed Fragile X syndrome

We describe the seizure and EEG characteristics in a population of children with known Fragile X. The medical records of 135 genetically confirmed FXS patients receiving care in a Fragile X clinic and their available EEG reports were reviewed. The mean age was 5.94 years old including 18 males and 1 female. The mean age was 4-9 years old with an age range of 15 months to 13 years old. Twenty-two patients (16.3%) in the series had parent-reported behavior suspicious of seizures. Sixteen patients (14.1%, 1 female) had at least one EEG recorded for evaluation of clinical events suspicious for seizure, and three patients (2.2%) had an EEG in the context of a polysomnography for diagnosing sleep apnea. The mean age at EEG evaluation was 6.0 years (standard deviation 3.8 years). EEG findings included slowing of background rhythm (n=9) and epileptiform discharges (n=7). Four patients had normal EEGs (n=4). Six patients (4.4% of the sample population) were diagnosed with epilepsy by both clinical seizure semiology and documented EEG abnormalities. Thirteen patients (68.4% of total) had episodes of staring and behavioral arrest with no EEG correlate, indicating non-epileptic events. Of the eight patients who underwent a repeat EEG, five patients had showed normalization in the posterior dominant rhythm over time, two patients had unchanged findings and one patient had worsening of his EEG. Our data warrant further prospective validation.

A variant of KCC2 from patients with febrile seizures impairs neuronal Cl- extrusion and dendritic spine formation

Genetic variation in SLC12A5 which encodes KCC2, the neuron-specific cation-chloride cotransporter that is essential for hyperpolarizing GABAergic signaling and formation of cortical dendritic spines, has not been reported in human disease. Screening of SLC12A5 revealed a co-segregating variant (KCC2-R952H) in an Australian family with febrile seizures. We show that KCC2-R952H reduces neuronal Cl(-) extrusion and has a compromised ability to induce dendritic spines in vivo and in vitro. Biochemical analyses indicate a reduced surface expression of KCC2-R952H which likely contributes to the functional deficits. Our data suggest that KCC2-R952H is a bona fide susceptibility variant for febrile seizures.

Developmental dyscalculia in children and adolescents with idiopathic epilepsies in a Brazilian sample

Epilepsy is one of the most prevalent chronic disorders of childhood which can threaten child development and mental health. Among cognitive disorders, dyscalculia is one of the most important. In this study, 39 children and adolescents with idiopathic epilepsy underwent clinical and neuropsychological assessment to determine the intellectual level, math skills, reading and writing performance and neuropsychological profile. It was observed that the mathematical ability was below schooling expectations in a higher frequency than expected. There were no significant differences in mathematical performance among groups divided by number of antiepileptic drugs used, duration of disease and types and frequency of seizures. There was a positive correlation with intelligence quotient and attentional and reading level. These results suggest the existence not only of dyscalculia, but the concurrence of attentional and reading problems for the poor mathematical performance in this population.

Does epilepsy in multiplex autism pedigrees define a different subgroup in terms of clinical characteristics and genetic risk?

BACKGROUND

Autism spectrum disorders (ASD) and epilepsy frequently occur together. Prevalence rates are variable, and have been attributed to age, gender, comorbidity, subtype of pervasive developmental disorder (PDD) and risk factors. Recent studies have suggested disparate clinical and genetic settings depending on simplex or multiplex autism. The aim of this study was to assess: 1) the prevalence of epilepsy in multiplex autism and its association with genetic and non-genetic risk factors of major effect, intellectual disability and gender; and 2) whether autism and epilepsy cosegregate within multiplex autism families.

METHODS

We extracted from the Autism Genetic Resource Exchange (AGRE) database (n = 3,818 children from 1,264 families) all families with relevant medical data (n = 664 children from 290 families). The sample included 478 children with ASD and 186 siblings without ASD. We analyzed the following variables: seizures, genetic and non-genetic risk factors, gender, and cognitive functioning as assessed by Raven's Colored Progressive Matrices (RCPM) and Vineland Adaptive Behavior Scales (VABS).

RESULTS

The prevalence of epilepsy was 12.8% in cases with ASD and 2.2% in siblings without ASD (P <10-5). With each RCPM or VABS measure, the risk of epilepsy in multiplex autism was significantly associated with intellectual disability, but not with gender. Identified risk factors (genetic or non-genetic) of autism tended to be significantly associated with epilepsy (P = 0.052). When children with prematurity, pre- or perinatal insult, or cerebral palsy were excluded, a genetic risk factor was reported for 6/59 (10.2%) of children with epilepsy and 12/395 (3.0%) of children without epilepsy (P = 0.002). Finally, using a permutation test, there was significant evidence that the epilepsy phenotype co-segregated within families (P <10-4).

CONCLUSIONS

Epilepsy in multiplex autism may define a different subgroup in terms of clinical characteristics and genetic risk.

NINDS epilepsy and autism spectrum disorders workshop report

The association of epilepsy and autism spectrum disorders (ASD), although well-recognized, is poorly understood. The purpose of this report is to summarize the discussion of a workshop sponsored by the National Institute of Neurological Disorders and Stroke, with support from the National Institute of Child Health and Human Development, Autism Speaks, and Citizens United for Research in Epilepsy, that took place in Bethesda, Maryland, on May 29 and 30, 2012. The goals of this workshop were to highlight the clinical and biological relationships between ASD and epilepsy, to determine both short- and long-term goals that address research and treatment conundrums in individuals with both ASD and epilepsy, and to identify resources that can further both clinical and basic research. Topics discussed included epidemiology, genetics, environmental factors, common mechanisms, neuroimaging, neuropathology, neurophysiology, treatment, and research gaps and challenges in this unique population.

A common susceptibility factor of both autism and epilepsy: functional deficiency of GABA A receptors

Autism and epilepsy are common childhood neurological disorders with a great heterogeneity of clinical phenotypes as well as risk factors. There is a high co-morbidity of autism and epilepsy. The neuropathology of autism and epilepsy has similar histology implicating the processes of neurogenesis, neural migration, programmed cell death, and neurite outgrowth. Genetic advances have identified multiple molecules that participate in neural development, brain network connectivity, and synaptic function which are involved in the pathogenesis of autism and epilepsy. Mutations in GABA(A) receptor subunit have been frequently associated with epilepsy, autism, and other neuropsychiatric disorders. In this paper, we address the hypothesis that functional deficiency of GABAergic signaling is a potential common molecular mechanism underpinning the co-morbidity of autism and epilepsy.

MicroRNAs: new insights into chronic childhood diseases

Chronic diseases are the major cause of morbidity and mortality worldwide and have shown increasing incidence rates among children in the last decades. Chronic illnesses in the pediatric population, even if well managed, affect social, psychological, and physical development and often limit education and active participation and increase the risk for health complications. The significant pediatric morbidity and mortality rates caused by chronic illnesses call for serious efforts toward better understanding of the pathogenesis of these disorders. Recent studies have shown the involvement of microRNAs (miRNAs) in various aspects of major pediatric chronic non-neoplastic diseases. This review focuses on the role of miRNAs in four major pediatric chronic diseases including bronchial asthma, diabetes mellitus, epilepsy and cystic fibrosis. We intend to emphasize the importance of miRNA-based research in combating these major disorders, as we believe this approach will result in novel therapies to aid securing normal development and to prevent disabilities in the pediatric population.

Resilience to audiogenic seizures is associated with p-ERK1/2 dephosphorylation in the subiculum of Fmr1 knockout mice

Young, but not adult, fragile X mental retardation gene (Fmr1) knockout (KO) mice display audiogenic seizures (AGS) that can be prevented by inhibiting extracellular signal-regulated kinases 1/2 (ERK1/2) phosphorylation. In order to identify the cerebral regions involved in these phenomena, we characterized the response to AGS in Fmr1 KO mice and wild type (WT) controls at postnatal day (P) 45 and P90. To characterize the diverse response to AGS in various cerebral regions, we evaluated the activity markers FosB/ΔFosB and phosphorylated ERK1/2 (p-ERK1/2). Wild running (100% of tested mice) followed by clonic/tonic seizures (30%) were observed in P45 Fmr1 KO mice, but not in WT mice. In P90 Fmr1 KO mice, wild running was only present in 25% of tested animals. Basal FosB/ΔFosB immunoreactivity was higher (P < 0.01 vs. WT) in the CA1 and subiculum of P45 Fmr1 KO mice. Following the AGS test, FosB/ΔFosB expression consistently increased in most of the analyzed regions in both groups at P45, but not at P90. Interestingly, FosB/ΔFosB immunoreactivity was significantly higher in P45 Fmr1 KO mice in the medial geniculate body (P < 0.05 vs. WT) and CA3 (P < 0.01). Neurons presenting with immunopositivity to p-ERK1/2 were more abundant in the subiculum of Fmr1 KO mice in control condition (P < 0.05 vs. WT, in both age groups). In this region, p-ERK1/2-immunopositive cells significantly decreased (–75%, P < 0.01) in P90 Fmr1 KO mice exposed to the AGS test, but no changes were found in P45 mice or in other brain regions. In both age groups of WT mice, p-ERK1/2-immunopositive cells increased in the subiculum after exposure to the acoustic test. Our findings illustrate that FosB/ΔFosB markers are overexpressed in the medial geniculate body and CA3 in Fmr1 KO mice experiencing AGS, and that p-ERK1/2 is markedly decreased in the subiculum of Fmr1 KO mice resistant to AGS induction. These findings suggest that resilience to AGS is associated with dephosphorylation of p-ERK1/2 in the subiculum of mature Fmr1 KO mice.

Resource utilization in children with tuberous sclerosis complex and associated seizures: a retrospective chart review study

Seizures are a hallmark manifestation of tuberous sclerosis complex, yet data characterizing resource utilization are lacking. This retrospective chart review was performed to assess the economic burden of tuberous sclerosis complex with neurologic manifestations. Demographic and resource utilization data were collected for 95 patients for up to 5 years after tuberous sclerosis complex diagnosis. Mean age at diagnosis was 3.1 years, with complex partial and infantile spasms as the most common seizure types. In the first 5 years post-diagnosis, 83.2% required hospitalization, 30.5% underwent surgery, and the majority of patients (90.5%) underwent ≥3 testing procedures. In 79 patients with a full 5 years of data, hospitalizations, intensive care unit stays, diagnostic testing, and rehabilitation services decreased over the 5-year period. Resource utilization is cost-intensive in children with tuberous sclerosis complex and associated seizures during the first few years following diagnosis. Improving seizure control and reducing health care costs in this population remain unmet needs.

A single pentylenetetrazole-induced clonic-tonic seizure episode is accompanied by a slowly developing cognitive decline in rats

According to different studies, between 5% and 10% of people suffer a single isolated seizure episode at some time in their life. However, little is known about the effects of a single seizure episode on cognitive function, and clinical investigations of this issue are not easy to perform. In this situation, animal models may be a reasonable choice. The aim of our study was to follow the time course of delayed effects of generalized clonic-tonic convulsions on learning and memory functions in rats. A clonic-tonic seizure episode was induced by a single i.p. injection of pentylenetetrazole (70 mg/kg). Different behavioral tests were performed between days 10 and 100 after the convulsant administration. A single seizure episode resulted in a gradual decline in short-term memory function as assessed by novel object recognition and social recognition tests. The seizure episode induced a quick increase in hippocampal cell proliferation; however, the excessive newly generated cells seemed to be eliminated by the time of obvious cognitive impairment. These observations are indicative of a slowly developing and long-lasting influence of a single seizure episode on cognitive function. A rather long time period between the seizure episode and the manifestations of cognitive decline provides a window for a possible therapeutic intervention, and an elaboration of such "post-conditioning" treatments may be a promising opportunity to prevent subsequent mental impairments in patients.

Epilepsy in four genetically determined syndromes of intellectual disability

BACKGROUND

Epilepsy occurs with increased frequency in people with an intellectual disability (ID) compared to the rest of the population. A variety of research has in recent years shed light on genetic and biochemical aetiologies of epilepsy and, often in a different literature, on syndromes of ID. The aims of this annotation are to review developments in understanding of the pathophysiology of several ID syndromes in which epilepsy is a frequent co-occurrence and to relate these observations to recent advances in understanding of how these pathophysiological disturbances may lead to epilepsy.

METHOD

The ID syndromes selected for review were fragile X (FXS), Rett (RTT) and Angelman syndromes (AS) and tuberous sclerosis complex (TSC). Epilepsy is a significant aspect of these syndromes and relevant research into the genetic and biochemical pathophysiology of these four ID syndromes may be informative in establishing the association between epilepsy and ID. Employing a structured approach the authors initially searched the PubMed database for large case series describing the characteristics of epilepsy as manifested in these ID syndromes. The criteria for inclusion of the case series in the review were a sample size of greater than 50 and the description of several of the characteristic features of epilepsy, namely prevalence of seizures, age of seizure onset, seizure frequency, seizure semiology, severity and treatment. Following this, studies of the genetic and biochemical pathophysiology of these four ID syndromes were reviewed and the potential relevance of this research in understanding the association with epilepsy highlighted. Findings were considered in a focused manner in terms of effects on excitatory and inhibitory neurotransmitter systems and on glial function.

RESULTS

Diverse genetic pathologies underlying several ID syndromes can lead to alterations in the functioning of the glutamatergic and GABAergic neurotransmitter systems. The mechanisms involved include transcriptional regulation in RTT, translational regulation in FXS and TSC, and UBE3A-mediated proteolysis in AS. Expression or functioning of receptor subunits, uptake sites and enzymes involved in neurotransmitter metabolism are often affected by these changes, and may lead to modifications in network excitability and neuronal plasticity that may contribute to epileptogenesis and ID. Dysfunction in astrocytes may also contribute to epileptogenesis and ID in FXS, RTT and TSC with potential mechanisms including failure of astrocytic support functions, glial inflammation and homeostatic disturbances that affect the excitability and architecture of neuronal networks.

CONCLUSIONS

The annotation highlights research describing disturbances in excitatory and inhibitory neurotransmitter systems, neuronal ion channel and glial functions that provide possible explanations for the co-occurrence of seizures within several ID syndromes, in some cases suggesting possible avenues for research into novel therapeutic targets. Phenotypic overlaps between syndromes may also relate to roles for the implicated genes in different disturbances in linked biochemical pathways.

Rac1 and rac3 GTPases control synergistically the development of cortical and hippocampal GABAergic interneurons

The intracellular mechanisms driving postmitotic development of cortical γ-aminobutyric acid (GABA)ergic interneurons are poorly understood. We have addressed the function of Rac GTPases in cortical and hippocampal interneuron development. Developing neurons express both Rac1 and Rac3. Previous work has shown that Rac1 ablation does not affect the development of migrating cortical interneurons. Analysis of mice with double deletion of Rac1 and Rac3 shows that these GTPases are required during postmitotic interneuron development. The number of parvalbumin-positive cells was affected in the hippocampus and cortex of double knockout mice. Rac depletion also influences the maturation of interneurons that reach their destination, with reduction of inhibitory synapses in both hippocampal CA1 and cortical pyramidal cells. The decreased number of cortical migrating interneurons and their altered morphology indicate a role of Rac1 and Rac3 in regulating the motility of cortical interneurons, thus interfering with their final localization. While electrophysiological passive and active properties of pyramidal neurons including membrane capacity, resting potential, and spike amplitude and duration were normal, these cells showed reduced spontaneous inhibitory currents and increased excitability. Our results show that Rac1 and Rac3 contribute synergistically to postmitotic development of specific populations of GABAergic cells, suggesting that these proteins regulate their migration and differentiation.

Epilepsy in Rett syndrome, and CDKL5- and FOXG1-gene-related encephalopathies

Rett syndrome is an X-linked neurodevelopmental disorder that manifests in early childhood with developmental stagnation, and loss of spoken language and hand use, with the development of distinctive hand stereotypies, severe cognitive impairment, and autistic features. About 60% of patients have epilepsy. Seizure onset before the age of 3 years is unlikely, and onset after age 20 is rare. Diagnosis of Rett syndrome is based on key clinical elements that identify "typical" Rett syndrome but also "variant" or "atypical" forms. Diagnostic criteria have been modified only slightly over time, even after discovering that MECP2 gene alterations are present in >90% of patients with typical Rett syndrome but only in 50-70% of atypical cases. Over the last several years, intragenic or genomic alterations of the CDKL5 and FOXG1 genes have been associated with severe cognitive impairment, early onset epilepsy and, often, dyskinetic movement disorders, which have variably been defined as Rett variants. It is now clearly emerging that epilepsy has distinctive characteristics in typical Rett syndrome and in the different syndromes caused by CDKL5 and FOXG1 gene alterations. The progressive parting of CDKL5- and FOXG1-gene-related encephalopathies from the core Rett syndrome is reflected by the effort to produce clearer diagnostic criteria for typical and atypical Rett syndrome. Efforts to characterize the molecular pathology underlying these developmental encephalopathies are pointing to abnormalities of telencephalic development, neuronal morphogenesis, maturation and maintenance, and dendritic arborization.