Benign familial infantile seizures

A Girl with PRRT2 Mutation Presenting with Benign Familial Infantile Seizures Followed by Autistic Regression

Benign familial infantile seizure (BFIS) is an autosomal dominant infantile-onset epilepsy syndrome with a typically benign prognosis. It is commonly associated with heterozygous mutations of the PRRT2 gene located on chromosome 16p11.2. The frameshift heterozygous mutation (c.649dupC, p.Arg217Profs∗8) in PRRT2 is responsible for the majority of BFIS cases. In this report, we present a rare case of a girl with a confirmed clinical and genetic diagnosis of BFIS due to a frameshift heterozygous mutation in PRRT2 (c.649dupC). She exhibited typical neurodevelopment until 15 months of age, followed by an unexpected severe autistic regression. In addition to BFIS, PRRT2 mutations are also associated with paroxysmal kinesigenic dyskinesia (PKD) and infantile convulsions and paroxysmal choreoathetosis (ICCA), indicating a complex genotype-phenotype heterogeneity in PRRT2 mutations. This clinical observation highlights the possibility that BFIS patients with PRRT2 mutations may not always have a benign neurodevelopmental prognosis, emphasizing the need for long-term clinical follow-up.

ILAE Genetic Literacy Series: Self-limited familial epilepsy syndromes with onset in neonatal age and infancy

The self-limited (familial) epilepsies with onset in neonates or infants, formerly called benign familial neonatal and/or infantile epilepsies, are autosomal dominant disorders characterized by neonatal- or infantile-onset focal motor seizures and the absence of neurodevelopmental complications. Seizures tend to remit during infancy or early childhood and are therefore called "self-limited". A positive family history for epilepsy usually suggests the genetic etiology, but incomplete penetrance and de novo inheritance occur. Here, we review the phenotypic spectrum and the genetic architecture of self-limited (familial) epilepsies with onset in neonates or infants. Using an illustrative case study, we describe important clues in recognition of these syndromes, diagnostic steps including genetic testing, management, and genetic counseling.

Clinical and genetic analysis of benign familial infantile epilepsy caused by PRRT2 gene variant

OBJECTIVE

This study presents the clinical phenotypes and genetic analysis of seven patients with benign familial infantile epilepsy (BFIE) diagnosed by whole-exome sequencing.

METHODS

The clinical data of seven children with BFIE diagnosed at the Department of Neurology, Children's Hospital Affiliated to Zhengzhou University between December 2017 and April 2022 were retrospectively analyzed. Whole-exome sequencing was used to identify the genetic causes, and the variants were verified by Sanger sequencing in other family members.

RESULTS

The seven patients with BFIE included two males and five females ranging in age between 3 and 7 months old. The main clinical phenotype of the seven affected children was the presence of focal or generalized tonic-clonic seizures, which was well controlled by anti-seizure medication. Cases 1 and 5 exhibited predominantly generalized tonic-clonic seizures accompanied by focal seizures while cases 2, 3, and 7 displayed generalized tonic-clonic seizures, and cases 4 and 6 had focal seizures. The grandmother and father of cases 2, 6, and 7 had histories of seizures. However, there was no family history of seizures in the remaining cases. Case 1 carried a de novo frameshift variant c.397delG (p.E133Nfs*43) in the proline-rich transmembrane protein 2 (PRRT2) gene while case 2 had a nonsense variant c.46G > T (p.Glu16*) inherited from the father, and cases 3-7 carried a heterozygous frameshift variant c.649dup (p.R217Pfs*8) in the same gene. In cases 3 and 4, the frameshift variant was de novo, while in cases 5-7, the variant was paternally inherited. The c.397delG (p.E133Nfs*43) variant is previously unreported.

CONCLUSION

This study demonstrated the effectiveness of whole-exome sequencing in the diagnosis of BFIE. Moreover, our findings revealed a novel pathogenic variant c.397delG (p.E133Nfs*43) in the PRRT2 gene that causes BFIE, expanding the mutation spectrum of PRRT2.

PRRT2 benign familial infantile seizures (BFIS) with atypical evolution to encephalopathy related to status epilepticus during sleep (ESES)

PURPOSE

Heterozygous variants in PRRT2 are mostly associated with benign phenotypes, being the major genetic cause of benign familial infantile seizures (BFIS), as well as in paroxysmal disorders. We report two children from unrelated families with BFIS that evolved to encephalopathy related to status epilepticus during sleep (ESES).

METHODS AND RESULTS

Two probands presented with focal motor seizures at 3 months of age, with a limited course. Both children presented, at around 5 years of age, with centro-temporal interictal epileptiform discharges with a source in the frontal operculum, markedly activated by sleep, and associated with stagnation on neuropsychological development. Whole-exome sequencing and co-segregation analysis revealed a frameshift mutation c.649dupC in the proline-rich transmembrane protein 2 (PRRT2) in both probands and all affected family members.

CONCLUSION

The mechanism leading to epilepsy and the phenotypic variability of PRRT2 variants remain poorly understood. However, its wide cortical and subcortical expression, in particular in the thalamus, could partially explain both the focal EEG pattern and the evolution to ESES. No variants in the PRRT2 gene have been previously reported in patients with ESES. Due to the rarity of this phenotype, other possible causative cofactors are likely contributing to the more severe course of BFIS in our probands.

Towards Zebrafish Models of CNS Channelopathies

Channelopathies are a large group of systemic disorders whose pathogenesis is associated with dysfunctional ion channels. Aberrant transmembrane transport of K⁺, Na⁺, Ca²⁺ and Cl^- by these channels in the brain induces central nervous system (CNS) channelopathies, most commonly including epilepsy, but also migraine, as well as various movement and psychiatric disorders. Animal models are a useful tool for studying pathogenesis of a wide range of brain disorders, including channelopathies. Complementing multiple well-established rodent models, the zebrafish (Danio rerio) has become a popular translational model organism for neurobiology, psychopharmacology and toxicology research, and for probing mechanisms underlying CNS pathogenesis. Here, we discuss current prospects and challenges of developing genetic, pharmacological and other experimental models of major CNS channelopathies based on zebrafish.

ILAE classification and definition of epilepsy syndromes with onset in neonates and infants: Position statement by the ILAE Task Force on Nosology and Definitions

The International League Against Epilepsy (ILAE) Task Force on Nosology and Definitions proposes a classification and definition of epilepsy syndromes in the neonate and infant with seizure onset up to 2 years of age. The incidence of epilepsy is high in this age group and epilepsy is frequently associated with significant comorbidities and mortality. The licensing of syndrome specific antiseizure medications following randomized controlled trials and the development of precision, gene-related therapies are two of the drivers defining the electroclinical phenotypes of syndromes with onset in infancy. The principal aim of this proposal, consistent with the 2017 ILAE Classification of the Epilepsies, is to support epilepsy diagnosis and emphasize the importance of classifying epilepsy in an individual both by syndrome and etiology. For each syndrome, we report epidemiology, clinical course, seizure types, electroencephalography (EEG), neuroimaging, genetics, and differential diagnosis. Syndromes are separated into self-limited syndromes, where there is likely to be spontaneous remission and developmental and epileptic encephalopathies, diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. The emerging class of etiology-specific epilepsy syndromes, where there is a specific etiology for the epilepsy that is associated with a clearly defined, relatively uniform, and distinct clinical phenotype in most affected individuals as well as consistent EEG, neuroimaging, and/or genetic correlates, is presented. The number of etiology-defined syndromes will continue to increase, and these newly described syndromes will in time be incorporated into this classification. The tables summarize mandatory features, cautionary alerts, and exclusionary features for the common syndromes. Guidance is given on the criteria for syndrome diagnosis in resource-limited regions where laboratory confirmation, including EEG, MRI, and genetic testing, might not be available.

Genetic Epilepsy Syndromes

PURPOSE OF REVIEW

This article reviews the clinical features, typical EEG findings, treatment, prognosis, and underlying molecular etiologies of the more common genetic epilepsy syndromes. Genetic generalized epilepsy, self-limited focal epilepsy of childhood, self-limited neonatal and infantile epilepsy, select developmental and epileptic encephalopathies, progressive myoclonus epilepsies, sleep-related hypermotor epilepsy, photosensitive occipital lobe epilepsy, and focal epilepsy with auditory features are discussed. Also reviewed are two familial epilepsy syndromes: genetic epilepsy with febrile seizures plus and familial focal epilepsy with variable foci.

RECENT FINDINGS

Recent years have seen considerable advances in our understanding of the genetic factors underlying genetic epilepsy syndromes. New therapies are emerging for some of these conditions; in some cases, these precision medicine approaches may dramatically improve the prognosis.

SUMMARY

Many recognizable genetic epilepsy syndromes exist, the identification of which is a crucial skill for neurologists, particularly those who work with children. Proper diagnosis of the electroclinical syndrome allows for appropriate treatment choices and counseling regarding prognosis and possible comorbidities.

Characteristics of infantile convulsions and choreoathetosis syndrome caused by PRRT2 mutation

Importance

Infantile convulsions and choreoathetosis (ICCA) is a rare neurological disorder. Many affected patients are either misdiagnosed or prescribed multiple antiepileptic drugs.

Objective

To explore therapeutic drug treatments and dosages for ICCA in children.

Methods

Detailed clinical features (e.g., past medical history and family history), genetic features, and treatment outcomes were collected from the records of six patients with ICCA.

Results

Mean age at paroxysmal kinesigenic dyskinesia (PKD) onset was 8 years 8 months (range, 3-12 years); the clinical presentation was characterized by daily short paroxysmal episodes of dystonia/dyskinesia. All patients had infantile convulsions at less than 1 year of age, and the mean onset age was 5.5 months (range, 4-7 months). Two patients had a family history of ICCA, PKD, or benign familial infantile epilepsy. Whole exome sequencing identified the c.649-650insC mutation in PRRT2 in six patients; three mutations were inherited and three were de novo. All patients were prescribed low-dose carbamazepine and showed dramatic improvement with the complete disappearance of dyskinetic episodes after 3 days. They attended follow-up for 5-17 months and were attack-free until the final follow-up.

Interpretation

PRRT2 mutations are the primary cause of ICCA. Low-dose carbamazepine monotherapy is effective and well-tolerated in children.

Uncommon epileptic syndromes in children: a review

Epileptic syndromes are well-defined conditions comprising particular clinical features [seizure types, age of onset, response to treatment] and characteristic electroencephalographic changes, while their etiology and subsequent prognosis may vary. The recognition of these syndromes is fundamental for pediatric neurology practice, representing an essential learning topic in this field. Nevertheless, many epileptic syndromes are still quite unfamiliar to students, residents and even neurologists, because of their low incidence and their minimal representation in the literature. This narrative review discusses the concept of epileptic syndromes and revisits seven lesser-known or uncommon syndromes in order to summarize their core clinical features, which can become important clues for daily neurological practice, namely epilepsy of infancy with migrating focal seizures, myoclonic epilepsy of infancy, self-limited infantile epilepsy, myoclonic encephalopathy in nonprogressive disorders, Jeavons syndrome, and epilepsy with myoclonic absences.

Crises fébriles chez l’enfant : à propos d’une histoire familiale

Les crises fébriles (CF) sont les crises convulsives les plus fréquentes prises en charge dans les services d’urgence dans la population des moins de cinq ans. Elles sont une crise accompagnée de fièvre, sans infection du système nerveux central, se produisant chez les enfants entre six mois et cinq ans. Les critères utilisés et enseignés pour classer les crises en simples ou complexes n’ont pas la même signification en pratique clinique pour prendre la décision d’effectuer une ponction lombaire et/ou une imagerie cérébrale, et pour l’indication de la prescription d’un antiépileptique de recours ou de fond. Certains facteurs sont prédictifs de la récurrence fébrile, tandis que d’autres sont prédictifs d’une épilepsie. À partir de deux cas cliniques de CF complexes, nous proposons une démarche de prise en charge et de faire une revue des syndromes épileptiques survenant au décours des CF chez le jeune nourrisson.

The Genotype and Phenotype of Proline-Rich Transmembrane Protein 2 Associated Disorders in Chinese Children

Objectives: To study the genetic and clinical characteristics of Chinese children with pathogenic proline-rich transmembrane protein 2 (PRRT2) gene-associated disorders. Methods: Targeted next generation sequencing (NGS) was used to identify pathogenic PRRT2 variations in Chinese children with epilepsy and/or kinesigenic dyskinesia. Patients with confirmed PRRT2-associated disorders were monitored and their clinical data were analyzed. Results: Forty-four patients with pathogenic PRRT2 variants were recruited. Thirty-five of them (79.5%) had heterozygous mutations, including 30 frameshifts, three missenses, one nonsense, and one splice site variant. The c.649dupC was the most common variant (56.8%). Eight patients (18.2%) showed whole gene deletions, and one patient (2.3%) had 16p11.2 microdeletion. Thirty-four cases (97.1%) were inherited and one case (2.9%) was de novo. Forty patients were diagnosed with benign familial infantile epilepsy (BFIE), two patients had paroxysmal kinesigenic dyskinesia (PKD) and two had infantile convulsions and choreoathetosis (ICCA). Patients with whole gene deletions had a later remission than patients with heterozygous mutations (13.9 vs. 7.1 months, P = 0.001). Forty-two patients were treated with antiseizure medications (ASMs). At last follow-up, 35 patients, including one who did not receive therapy, were asymptomatic, and one patient without ASMs died of status epilepticus at 12 months of age. One patient developed autism, and one patient showed mild developmental delay/intellectual disability. Conclusion: Our data suggested that patients with whole gene deletions could have more severe manifestations in PRRT2-associated disorders. Conventional ASMs, especially Oxcarbazepine, showed a good treatment response.

Benign familial infantile epilepsy associated with KCNQ3 mutation: a rare occurrence or an underestimated event?

Benign familial infantile epilepsy (BFIE) is the most genetically heterogeneous phenotype among early-onset familial infantile epilepsies. It has an autosomal dominant inheritance pattern with incomplete penetrance. Although PRRT2 is the most mutated gene detected in families with BFIE, other mutations in KCNQ2, SCN2A, and GABRA6 genes have also been described. To date, KCNQ3 mutations have been detected in only four patients with BFIE. Here, we describe the clinical pattern and course of an additional individual with BFIE associated with a novel missense heterozygous KCNQ3 c.1850G>C variant inherited by his unaffected father. The incidence of KCNQ3 mutations among BFIE patients is reported to be low in the literature, however, whether this is underestimated is unclear as not all current epilepsy gene panels include KCNQ3.

The clinical and genetic spectrum in infants with (an) unprovoked cluster(s) of focal seizures

BACKGROUND

Self-limited (familial) infantile epilepsy (S(F)IE), formerly known as benign (familial) infantile convulsions (B(F)IC), is an infantile cluster epilepsy with in rule a complete recovery. This form of epilepsy is most often caused by variations in the PRRT2 gene (OMIM #605751).

AIM

To describe the clinical and genetic spectrum of sudden onset clusters of focal seizures in infancy.

METHODS

We retrospectively reviewed all individuals, who presented with unprovoked infantile seizures and selected all infants who had unprovoked clustered focal seizures between 1 and 20 months of age. We described the clinical and genetic spectrum of this cohort.

RESULTS

The data of 23 patients from 21 families were collected. All had an initial diagnosis of S(F)IE which was adjusted in 5 individuals. In 12 individuals a pathogenic variation in PRRT2 gene or complete deletion was identified. Pathogenic variants in PCDH19 and KCNQ2 were found in respectively 3 and 1 individuals. One individual had a non-pathogenic variant in ATP1A3 and in 6 others no variants were identified. The mean cluster duration was 2.9 days (range 1-13) (see Table 1). Twelve infants had only one cluster. All patients had focal motor or non-motor seizures, in 12 (52%) followed by bilateral (tonic)clonic seizures. Positive family history was present in 74% of individuals. In 11/12 (92%) tested families, ≥1 family member carried the pathogenic PRRT2 variant. Age of seizure onset (ASO) averaged 6.2 months (range 2-20 months). Age of latest seizure averaged 16 months (range 2-92). In several interictal EEG (electroencephalogram) recordings multifocal spikes or spike-wave abnormalities were detected. Ictal EEG recordings detected primary focal abnormalities.

CONCLUSION

We described 23 individuals with unprovoked cluster(s) of focal seizures at infancy. It appears to be a heterogeneous group. Half of them had a pathogenic variation in PRRT2 gene. Most had only one cluster of seizures. When clusters reoccur frequently, when seizures are more therapy-resistant and when seizures persist beyond the age of 2 years, another diagnosis or causative gene is likely.

Crises fébriles chez l’enfant : à propos d’une histoire familiale

Les crises fébriles (CF) sont les crises convulsives les plus fréquentes prises en charge dans les services d’urgence dans la population des moins de cinq ans. Elles sont une crise accompagnée de fièvre, sans infection du système nerveux central, se produisant chez les enfants entre six mois et cinq ans. Les critères utilisés et enseignés pour classer les crises en simples ou complexes n’ont pas la même signification en pratique clinique pour prendre la décision d’effectuer une ponction lombaire et/ou une imagerie cérébrale, et pour l’indication de la prescription d’un antiépileptique de recours ou de fond. Certains facteurs sont prédictifs de la récurrence fébrile, tandis que d’autres sont prédictifs d’une épilepsie. À partir de deux cas cliniques de CF complexes, nous proposons une démarche de prise en charge et de faire une revue des syndromes épileptiques survenant au décours des CF chez le jeune nourrisson.

The role of EEG in the diagnosis and classification of the epilepsy syndromes: a tool for clinical practice by the ILAE Neurophysiology Task Force (Part 2)

The concept of epilepsy syndromes, introduced in 1989, was defined as "clusters of signs and symptoms customarily occurring together". Definition of epilepsy syndromes based on electro-clinical features facilitated clinical practice and, whenever possible, clinical research in homogeneous groups of patients with epilepsies. Progress in the fields of neuroimaging and genetics made it rapidly clear that, although crucial, the electro-clinical description of epilepsy syndromes was not sufficient to allow much needed development of targeted therapies and a better understanding of the underlying pathophysiological mechanisms of seizures. The 2017 ILAE position paper on Classification of the Epilepsies recognized that "as a critical tool for the practicing clinician, epilepsy classification must be relevant and dynamic to changes in thinking". The concept of "epilepsy syndromes" evolved, incorporating issues related to aetiologies and comorbidities. A comprehensive update (and revision where necessary) of the EEG diagnostic criteria in the light of the 2017 revised terminology and concepts was deemed necessary. Part 2 covers the neonatal and paediatric syndromes in accordance with the age of onset. [Published with educational EEG plates at www.epilepticdisorders.com].

Genetic analysis of benign familial epilepsies in the first year of life in a Chinese cohort

Benign familial epilepsies that present themselves in the first year of life include benign familial neonatal epilepsy (BFNE), benign familial neonatal-infantile epilepsy (BFNIE) and benign familial infantile epilepsy (BFIE). We used Sanger sequencing and targeted next-generation sequencing to detect gene mutations in a Chinese cohort of patients with these three disorders. A total of 79 families were collected, including 4 BFNE, 7 BFNIE, and 68 BFIE. Genetic testing led to the identification of gene mutations in 60 families (60 out of 79, 75.9%). A total of 42 families had PRRT2 mutations, 9 had KCNQ2 mutations, 8 had SCN2A mutations, and 1 had a GABRA6 mutation. In total three of four BFNE families were detected with KCNQ2 mutations. Mutations were detected in all BFNIE families, including 3 KCNQ2 mutations, 3 SCN2A mutations, and 1 PRRT2 mutation. Gene mutations were identified in 50 out of 68 BFIE families (73.5%), including 41 PRRT2 mutations (41 out of 68, 60.3%), 5 SCN2A mutations, 3 KCNQ2 mutations, and 1 GABRA6 mutation. Our results confirmed that mutations in KCNQ2, SCN2A, and PRRT2 are major genetic causes of benign familial epilepsy in the first year of life in the Chinese population. KCNQ2 is the major gene related to BFNE. PRRT2 is the main gene responsible for BFIE.

Genetic basis of pediatric epilepsy syndromes

Childhood epilepsy affects ~0.5-1% in the general population worldwide. Early-onset epileptic encephalopathies are considered to be severe neurological disorders, which lead to impaired motor, cognitive, and sensory development due to recurrence of seizures. Many of the observed epilepsy phenotypes are associated with specific chromosomal imbalances and thus display gene dosage effects, and also specific mutations of a variety of genes ranging from ion channels to transcription factors. High throughput sequencing technologies and whole exome sequencing have led to the recognition of several new candidate genes with a possible role in the pathogenesis of epileptic encephalopathies. The mutations causing channelopathies can be either a gain or a loss of ion channel function and contribute to the pathogenesis of epilepsy syndrome. Nearly 300 mutations of SCN1A gene coding for the Nav1.1 channel protein have been identified that contribute to the pathology of epilepsy. Besides Na, potassium and calcium channels are also implicated in epileptic encephalopathies. Therapeutic management of epileptic encephalopathies has been challenging as the majority of the medications are not efficient and often have many undesirable side effects. A better understanding of the molecular nature of epilepsy in an individual is important to design a personalized medication, considering the number of possible genetic mutations that can contribute to epileptic encephalopathies.

The PRRT2 knockout mouse recapitulates the neurological diseases associated with PRRT2 mutations

Heterozygous and rare homozygous mutations in PRoline-Rich Transmembrane protein 2 (PRRT2) underlie a group of paroxysmal disorders including epilepsy, kinesigenic dyskinesia episodic ataxia and migraine. Most of the mutations lead to impaired PRRT2 expression and/or function. Recently, an important role for PRTT2 in the neurotransmitter release machinery, brain development and synapse formation has been uncovered. In this work, we have characterized the phenotype of a mouse in which the PRRT2 gene has been constitutively inactivated (PRRT2 KO). β-galactosidase staining allowed to map the regional expression of PRRT2 that was more intense in the cerebellum, hindbrain and spinal cord, while it was localized to restricted areas in the forebrain. PRRT2 KO mice are normal at birth, but display paroxysmal movements at the onset of locomotion that persist in the adulthood. In addition, adult PRRT2 KO mice present abnormal motor behaviors characterized by wild running and jumping in response to audiogenic stimuli that are ineffective in wild type mice and an increased sensitivity to the convulsive effects of pentylentetrazol. Patch-clamp electrophysiology in hippocampal and cerebellar slices revealed specific effects in the cerebellum, where PRRT2 is highly expressed, consisting in a higher excitatory strength at parallel fiber-Purkinje cell synapses during high frequency stimulation. The results show that the PRRT2 KO mouse reproduces the motor paroxysms present in the human PRRT2-linked pathology and can be proposed as an experimental model for the study of the pathogenesis of the disease as well as for testing personalized therapeutic approaches.

•

PRRT2 is intensely expressed in cerebellum and in restricted areas of the forebrain.

•

PRRT2 KO mice display paroxysmal movements at the onset of locomotion.

•

PRRT2 KO mice present abnormal motor behaviors in response to audiogenic stimuli.

•

PRRT2 KO mice are more sensitive to the convulsive effects of pentylentetrazol.

•

PRRT2 KO mice display an altered synaptic transmission in the cerebellar cortex.

Genetics of pediatric epilepsy

As the genetic etiologies of an expanding number of epilepsy syndromes are revealed, the complexity of the phenotype genotype correlation increases. As our review will show, multiple gene mutations cause different epilepsy syndromes, making identification of the specific mutation increasingly more important for prognostication and often more directed treatment. Examples of that include the need to avoid specific drugs in Dravet syndrome and the ongoing investigations of the potential use of new directed therapies such as retigabine in KCNQ2-related epilepsies, quinidine in KCNT1-related epilepsies, and memantine in GRIN2A-related epilepsies.

Evaluation of clinical course and neurocognition in children with self-limited infantile epilepsy in a Turkish cohort study

The outcome of children with self-limited infantile epilepsy was reported to be normal psychosocial and cognitive development as a characteristic criterion. We aimed to investigate the clinical course and neurocognitive outcome in children with self-limited infantile epilepsy in a Turkish cohort. The clinical course, electroencephalographic (EEG) characteristics, neuroimaging, treatment, and outcome of children with self-limited infantile epilepsy were retrospectively analyzed. All infants were reevaluated with the Denver Developmental Screening Test in addition to neurologic examination. Of 44 patients, self-limited familial infantile epilepsy was diagnosed in 8 infants (18.2%) and self-limited nonfamilial infantile epilepsy in 28 (63.6%). Interictal EEGs and neurologic examinations were normal in all cases. Fine motor and gross motor skills, language, adaptive personal/social skills were near-normal in all patients with self-limited familial infantile epilepsy. Delay in language parameters was observed in 2 infants with self-limited nonfamilial infantile epilepsy. Language skills should be thoroughly evaluated with detailed neurocognitive screening tests in patients with self-limited infantile epilepsy.

Genetic epilepsy syndromes without structural brain abnormalities: clinical features and experimental models

Research in genetics of epilepsy represents an area of great interest both for clinical purposes and for understanding the basic mechanisms of epilepsy. Most mutations in epilepsies without structural brain abnormalities have been identified in ion channel genes, but an increasing number of genes involved in a diversity of functional and developmental processes are being recognized through whole exome or genome sequencing. Targeted molecular diagnosis is now available for different forms of epilepsy. The identification of epileptogenic mutations in patients before epilepsy onset and the possibility of developing therapeutic strategies tested in experimental models may facilitate experimental approaches that prevent epilepsy or decrease its severity. Functional analysis is essential for better understanding pathogenic mechanisms and gene interactions. In vitro experimental systems are either cells that usually do not express the protein of interest or neurons in primary cultures. In vivo/ex vivo systems are organisms or preparations obtained from them (e.g., brain slices), which should better model the complexity of brain circuits and actual pathophysiological conditions. Neurons differentiated from induced pluripotent stem cells generated from the skin fibroblasts of patients have recently allowed the study of mutations in human neurons having the genetic background of a given patient. However, there is remarkable complexity underlying epileptogenesis in the clinical dimension, as reflected by the fact that experimental models have not provided yet results having clinical translation and that, with a few exceptions concerning rare conditions, no new curative treatment has emerged from any genetic finding in epilepsy.

The kick-in system: a novel rapid knock-in strategy

Knock-in mouse models have contributed tremendously to our understanding of human disorders. However, generation of knock-in animals requires a significant investment of time and effort. We addressed this problem by developing a novel knock-in system that circumvents several traditional challenges by establishing stem cells with acceptor elements enveloping a particular genomic target. Once established, these acceptor embryonic stem (ES) cells are efficient at directionally incorporating mutated target DNA using modified Cre/lox technology. This is advantageous, because knock-ins are not restricted to one a priori selected variation. Rather, it is possible to generate several mutant animal lines harboring desired alterations in the targeted area. Acceptor ES cell generation is the rate-limiting step, lasting approximately 2 months. Subsequent manipulations toward animal production require an additional 8 weeks, but this delimits the full period from conception of the genetic alteration to its animal incorporation. We call this system a “kick-in” to emphasize its unique characteristics of speed and convenience. To demonstrate the functionality of the kick-in methodology, we generated two mouse lines with separate mutant versions of the voltage-dependent potassium channel K_v7.2 (Kcnq2): p.Tyr284Cys (Y284C) and p.Ala306Thr (A306T); both variations have been associated with benign familial neonatal epilepsy. Adult mice homozygous for Y284C, heretofore unexamined in animals, presented with spontaneous seizures, whereas A306T homozygotes died early. Heterozygous mice of both lines showed increased sensitivity to pentylenetetrazole, possibly due to a reduction in M-current in CA1 hippocampal pyramidal neurons. Our observations for the A306T animals match those obtained with traditional knock-in technology, demonstrating that the kick-in system can readily generate mice bearing various mutations, making it a suitable feeder technology toward streamlined phenotyping.

PRRT2 phenotypic spectrum includes sporadic and fever-related infantile seizures

OBJECTIVE

Benign familial infantile epilepsy (BFIE) is an autosomal dominant epilepsy syndrome characterized by afebrile seizures beginning at about 6 months of age. Mutations in PRRT2, encoding the proline-rich transmembrane protein 2 gene, have recently been identified in the majority of families with BFIE and the associated syndrome of infantile convulsions and choreoathetosis (ICCA). We asked whether the phenotypic spectrum of PRRT2 was broader than initially recognized by studying patients with sporadic benign infantile seizures and non-BFIE familial infantile seizures for PRRT2 mutations.

METHODS

Forty-four probands with infantile-onset seizures, infantile convulsions with mild gastroenteritis, and benign neonatal seizures underwent detailed phenotyping and PRRT2 sequencing. The familial segregation of mutations identified in probands was studied.

RESULTS

The PRRT2 mutation c.649-650insC (p.R217fsX224) was identified in 11 probands. Nine probands had a family history of BFIE or ICCA. Two probands had no family history of infantile seizures or paroxysmal kinesigenic dyskinesia and had de novo PRRT2 mutations. Febrile seizures with or without afebrile seizures were observed in 2 families with PRRT2 mutations.

CONCLUSIONS

PRRT2 mutations are present in >80% of BFIE and >90% ICCA families, but are not a common cause of other forms of infantile epilepsy. De novo mutations of PRRT2 can cause sporadic benign infantile seizures. Seizures with fever may occur in BFIE such that it may be difficult to distinguish BFIE from febrile seizures and febrile seizures plus in small families.

Pediatric epilepsy syndromes

Epilepsy syndromes denote specific constellations of clinical seizure type(s), EEG findings, and other characteristic clinical features. Most syndromes recognized in epilepsy are genetic and developmental disorders that begin in the pediatric years. Epilepsy syndromes are divided into idiopathic (primary) types, in which the presumed etiology is genetic, versus symptomatic (secondary) types, in which there is either an underlying etiology that is known or presumed based on other evidence of brain dysfunction. Epilepsies are also classified by those with generalized seizures and those with localization-related seizures. Identification of a specific syndrome is important to define the best treatment and accurately prognosticate long-term outcome for children with epilepsy. In this chapter, clinical and electrographic features as well as inheritance patterns of common pediatric epilepsy syndromes are discussed.

Paroxysmal kinesigenic dyskinesia: cortical or non-cortical origin

Paroxysmal kinesigenic dyskinesia (PKD) is characterized by involuntary dystonia and/or chorea triggered by a sudden movement. Cases are usually familial with an autosomal dominant inheritance. Hypotheses regarding the pathogenesis of PKD focus on the controversy whether PKD has a cortical or non-cortical origin. A combined familial trait of PKD and benign familial infantile seizures has been reported as the infantile convulsions and paroxysmal choreoathetosis (ICCA) syndrome. Here, we report a family diagnosed with ICCA syndrome with an Arg217STOP mutation. The index patient showed interictal EEG focal changes compatible with paroxysmal dystonic movements of his contralateral leg. This might support cortical involvement in PKD.

Mutation detection in candidate genes for benign familial infantile seizures on a novel locus

Benign familial infantile seizures (BFIS) is an autosomal dominant epileptic syndrome characterized by afebrile partial seizures with or without secondary generalized tonic-clonic seizures beginning at three to ten months of age. Genetic studies have revealed three susceptibility chromosomal loci on 19q12-q13.1, 16p12-q12 and 2q24. Previously we described the novel locus on 1p36.12-p35.1 for a Chinese family affected with BFIS, and below is a subsequent mutation analysis of candidate genes for the mapped chromosome region. Forty-five genes were selected and subjected to mutation analysis. Thirty-six nucleotide variants were found, none of which led to pathogenic changes, thereby were identified as nucleotide polymorphisms. The analyses suggest those candidate genes that were detected might not be involved in the epileptogenesis of pure BFIS, at least in the Chinese family we studied.

What's new in: "genetics in childhood epilepsy"

In recent years, different mutations in genes that control the excitability of neurons have been described in idiopathic childhood epilepsies. Most commonly, sodium/potassium channelopathies and GABA-receptor mutations are involved. Major progress has been made in the field of idiopathic generalised epilepsies associated with febrile seizures (GEFS+). It now is becoming clear that mutations should not only be looked for in familial cases, but also in sporadic cases, especially in infants and young children with unexplained severe epileptic encephalopathies. Many studies also define 'epilepsy susceptibility genes', which contribute to one's individual genetic vulnerability to develop epilepsy. It should be realized, however, that in the most common idiopathic benign childhood epilepsies (benign rolandic and occipital epilepsies), major breakthroughs are still awaited. In addition, a better clinical description of the epileptic phenotypes is needed to explain more precisely the genotypic and phenotypic heterogeneity. Genetic studies are nowadays becoming a necessary diagnostic step in the evaluation of idiopathic childhood epilepsies, not only in familial cases, but also in sporadic cases.

Epileptic syndromes in infancy and childhood

PURPOSE OF REVIEW

The aim of this article is to review new epilepsy syndromes, acquire a new understanding of older ones and emphasize the impact of this concept on basic research regarding aetiology and treatment.

RECENT FINDINGS

In addition to those included in the classification of the International League Against Epilepsy, new epilepsy syndromes comprise febrile seizures plus, benign familial neonatal-infantile seizures (BFNIS), benign infantile focal epilepsy with midline spikes and waves during sleep (BFIS), malignant migrating partial seizures in infancy, devastating epilepsy in school age children and late onset cryptogenic spasms. Genetics played a central role in identifying some new entities (BFNIS, BFIS with choreoathetosis), to delineate older syndromes (Dravet syndrome and myoclonic astatic epilepsy) and determine their mechanisms (infantile spasms, pyridoxine dependent seizures, neonatal encephalopathy with suppression bursts).

SUMMARY

A significant number of children, mainly infants, do not fit in any of the described epilepsy syndromes. Still many patients with infantile epilepsy require the identification of cause or recognition of an epilepsy syndrome.

Ictal EEG in benign partial epilepsy in infancy

The aim of this study is to further clarify ictal electroencephalographic findings of patients with benign partial epilepsy in infancy in order to better understand its neurophysiologic features. The study group consisted of 13 infants with definite benign partial epilepsy in infancy, in whom ictal electroencephalograms were recorded and its benignity was confirmed at 8 years or more. The seizure manifestation was reviewed on the basis of video findings in eight patients in whom simultaneous video-electroencephalography recording was available. In the other five patients, the seizure manifestations were determined according to the observations of physicians, nurses, or technicians. Thirteen seizures from eight patients were complex partial, and six seizures from six patients were secondarily generalized ones. Ictal discharges at the onset of a seizure were focal in all seizures. The site of the origin of seizures was in the temporal area in 10 of 13 complex partial seizures, whereas it was in the parietal or occipital area in all 6 secondarily generalized seizures. Among 13 complex partial seizures, paroxysmal discharges remained focal throughout the seizures in 6 seizures, whereas they spread to one hemisphere in the other 7 seizures. Motion arrest or decreased responsiveness was uniformly observed. Lateral eye deviation was commonly recognized in complex partial seizures, whereas head rotation was observed only in seizures in which hemispheric propagation of ictal discharges was observed. Ictal electroencephalographic findings of patients with benign partial epilepsy in infancy were relatively uniform, suggesting the homogeneity of patients with benign partial epilepsy in infancy.

The spectrum of benign infantile seizures

Benign epilepsies during infancy are a wide topic, which needs both clinical and nosological clarifications. Already in 1963 Fukuyama reported patients with seizures during infancy with a benign outcome. In the late 80s and early 90s, Watanabe reported series of infants with complex partial seizures or partial seizures with secondary generalization, with a normal development before onset and a benign outcome. In the same years Vigevano focused on familial cases: he described several families with seizures with onset around the 6-month of age, and autosomal dominant mode of inheritance. To define this condition, he coined the term "benign familial infantile seizures" (BFIS). Afterwards, studying families with this phenotype, loci on chromosomes 19, 16 and 2 responsible for BFIS were detected. Similar loci were found in families affected by BFIS and subsequent choreoathetosis, and BFIS associated with familial hemiplegic migraine. In most recent years a new form of benign epilepsy has been proposed, with an intermediate onset between the neonatal and infantile age, which was defined with the term benign familial neonatal-infantile seizures (BFNIS). This condition could have some clinical and genetic features overlapping with BFIS. Seizures with a benign outcome have been reported also in infants during episode of mild gastroenteritis (BIS with MG) frequently with positive Rotavirus antigen. Lastly, sleep EEG abnormalities have been reported in children with a peculiar form of epilepsy by Capovilla, who defined this condition as benign infantile focal epilepsy with midline spikes and waves during sleep (BIMSE). Some of these entities have been included in the last classification proposed by the ILAE and have been differentiated in familial and non-familial forms. The aim of this review is to describe these entities, discuss their nosological aspects, pointing out the similarities and differences with benign neonatal seizures and benign focal epilepsies appearing later in life such as early-onset benign occipital seizure susceptibility syndrome (EBOSS), or benign epilepsy of childhood with centro-temporal spikes (BECTS).

Benign partial epilepsy in infancy long-term outcome and marginal syndromes

Benign partial epilepsy in infancy (BPEI) is an infantile epilepsy with excellent seizure and developmental outcome proposed by Watanabe et al. Our telephone interview survey revealed that the long-term outcome of patients with BPEI was also excellent over 8 years of age. Six of 39 patients did not fulfill the criteria of BPEI by the last follow-up. Two patients had a recurrence of unprovoked seizure beyond 2 years of age, three had cognitive problems (mild mental retardation in two and Asperger syndrome in one) and the other had both a recurrence of seizure and mild mental retardation. These results indicates that a large majority of patients diagnosed as possible BPEI at 2 years of age did not have a recurrence of unprovoked seizures and mental problems beyond 8 years of age. Our study also suggested a presence of some marginal syndromes of BPEI. An association of paroxysmal kinesigenic choreoathetosis was observed in three patients. Another three patients had experienced seizures with mild gastroenteritis. The seizure outcome of three patients with mild cognitive problems was quite excellent. These patients can be grouped as a marginal syndrome of BPEI.

Linkage analysis and disease models in benign familial infantile seizures: a study of 16 families

PURPOSE

Benign familial infantile seizures (BFIS) is a genetically heterogeneous condition characterized by partial seizures, onset age from 3 to 9 months, and favorable outcome. BFIS loci were identified on chromosomes 19q12-13.1 and 16p12-q12, allelic to infantile convulsions and choreathetosis. The identification of SCN2A mutations in families with only infantile seizures indicated that BFNIS and BFIS may show overlapping clinical features. Infantile seizures also were in a family with familial hemiplegic migraine and mutations in the ATP1A2 gene. We have examined the heterogeneous genetics of BFIS by means of linkage analysis.

METHODS

Sixteen families were examined. Probands underwent neurologic examination, at least one EEG recording, and, when possible, brain CT and MRI. Clinical information about relatives was collected. Families with SCN2A or ATP1A2 mutations were excluded from the study. Chromosome 16p and 19q loci were examined by linkage analysis using two models that differed in penetrance rate. Genetic heterogeneity was evaluated with both models.

RESULTS

Clinical information was available for 124 members of affected families. BFIS was diagnosed in 69 subjects. One patient without BFIS had a single febrile seizure, and another had rare episodes of paroxysmal dystonia. Evidence of linkage was obtained only for chromosome 16. Moreover, the high penetrance allowed the identification of genetic heterogeneity.

CONCLUSIONS

Our data confirm the relevance of the chromosome 16 locus in BFIS and suggest the presence of an additional locus. This study shows that the genetic model used affects the outcome of linkage analysis.

Benign Partial Epilepsy in Infancy: Myth or Reality?

PURPOSE

Benign partial epilepsy in infancy (BPEI) was first described by Watanabe in 1987. The aim of this study is to describe a series of infants from the United States to characterize this entity further.

METHODS

Among patients with the diagnosis of epilepsy followed up at our institution between 2002 and 2004, those satisfying the criteria for BPEI were included in a retrospective study.

RESULTS

Sixteen (10.2%) of 150 patients with new onset of epilepsy younger than 2 years were identified. The mean age at seizure onset was 8 months. Four (25%) infants had a family history of benign seizures. All infants were neurologically and developmentally normal at the onset of seizures. The seizures occurred in clusters in 75% of patients, predominantly in wakefulness. The initial manifestation was behavioral arrest with staring (69%) and apnea with cyanosis or pallor (37.5%). These symptoms were followed by deviation of eyes or head or both (56%), mild clonic movements (31%), or increased limb tone (35%). Secondary generalization was noticed in 37.5% of patients. All infants had normal interictal EEGs and brain MRIs. Ictal EEGs disclosed electrographic seizures in 50% of patients (temporal origin in 62% and central in 38%). Fifteen (94%) patients were treated with AEDs with good response. The mean duration of treatment was 12.4 months. The final developmental assessment of all patients was normal.

CONCLUSIONS

We believe that BPEI exists as a unique entity and should be included in the differential diagnosis of epilepsies in infancy with partial origin.

A novel SCN2A mutation in family with benign familial infantile seizures

Benign familial infantile seizures (BFIS) is a clinical entity characterized by focal seizures with or without secondary generalization, occurring mostly in clusters, and usually first seen between 4 and 8 months of life. Psychomotor development is normal, and seizures usually resolve within the first year of life. BFIS is a genetically heterogenous condition with loci mapped to chromosomes 19 and 16. Mutations in the voltage-gated sodium channel alpha2 subunit (SCN2A) gene on chromosome 2 were recently identified in families affected by neonatal and infantile seizures (benign familial neonatal-infantile seizures, BFNIS) with typical onset before 4 months of life. The identification of SCN2A mutations in families with only infantile seizures indicated that BFNIS and BFIS show overlapping clinical features. We report a pedigree showing three affected individuals over three generations. All subjects experienced clusters of focal seizures with or without secondary generalization and onset between 4 and 12 months of life. Response to antiepileptic drugs and the outcome were good. No subjects had other forms of epilepsy later in the life. Neonatal or febrile seizures did not occur in the family. Genetic study in this family revealed a novel heterozygous mutation c.3003 T>A in the SCN2A gene. Comparative analysis of different sodium channel alpha subunits indicates that the mutated residue is highly conserved throughout the evolution, suggesting an important functional role for this domain. Additional families with the infantile form of benign familial seizures should be investigated to corroborate that BFIS and BFNIS may share the same genetic abnormality.

Long-term Follow-up of Patients with Benign Partial Epilepsy in Infancy

PURPOSE

The aim of this study was to investigate the long-term outcome of children with benign partial epilepsy in infancy (BPEI).

METHODS

A telephone-interview survey using a structured questionnaire was conducted with patients who were diagnosed as having possible BPEI at age 2 years and who were 8 years or older at the time of the survey. The data from 39 of 48 patients were available. The median age at the time of the survey was 11.3 years; 18 boys and 21 girls were included.

RESULTS

Three patients had a recurrence of unprovoked seizure beyond age 2 years. Four patients had cognitive problems (mild mental retardation in three and Asperger syndrome in one). An association of paroxysmal kinesigenic choreoathetosis was observed in three patients, and another three had experienced seizures associated with mild gastroenteritis. Major behavioral problems were not recognized in any patients. Four patients were excluded from having definite BPEI at age 5 years, and another two were excluded for having definite BPEI at the last follow-up. Eventually, 33 of 39 patients were categorized as having definite BPEI beyond 8 years of age.

CONCLUSIONS

A large majority of patients diagnosed as possibly having BPEI at age 2 years did not have a recurrence of unprovoked seizures and cognitive problems beyond 8 years of age.