Neurodevelopmental outcomes in a cohort of Australian families with self-limited familial epilepsy of neonatal/infantile onset

OBJECTIVES

To determine: i) seizure recurrence; ii) developmental disability; iii) co-morbidities and risk factors in self-limited familial neonatal and/or infantile epilepsy (SeLFE) in a multigenerational study.

METHODS

Families were retrospectively recruited from epilepsy databases (2021-2022) in 2 paediatric hospitals, Sydney, Australia. Eligible families had 2 first degree relatives with seizures and underwent genetic testing. Demographics/clinical data were collected from interviews and medical records. Vineland Adaptive Behaviour Scales-Third Edition measured adaptive function.

RESULTS

Fifteen families participated. Fourteen had a genetic diagnosis (93%): 11 pathogenic; PRRT2 (n=4), KCNQ2 (n=3), SCN2A (n=4), 3 likely pathogenic; KCNQ2 (n=1), SCN8A (n=2). Seizures affected 73 individuals (ages 1-76 years); 30 children and 20 adults had in-depth phenotyping. Ten of 50 individuals (20%) had seizure recurrence, aged 8-65 years. Median time from last neonatal/infantile seizure was 11.8/12.8 years. Predictors of recurrence were high seizure number (p=0.05) and longer treatment duration (p=0.03). Seven children had global developmental delay (GDD): mild (n=4), moderate (n=1) and severe (n=2). Vineland-3 identified 3 had low-average and 3 had mild-moderately impaired functioning. The majority (82%) were average. GDD was associated with older age at last seizure (p=0.03), longer epilepsy duration (p=0.02), and higher number of anti-seizure medications (p=0.05). Four children had speech delay, 5 (10%) had Autism Spectrum Disorder. Paroxysmal kinesiogenic dyskinesia (n=5) occurred in 4 families and hemiplegic migraine (n=8) in 3 families.

CONCLUSIONS

Individuals with SeLFE have a small risk of recurrent seizures (20%) and neurodevelopmental disability. Significant predictors are higher seizure number and longer epilepsy duration. Developmental surveillance is imperative.

KCNQ2-Related Epilepsy: Genotype-Phenotype Relationship with Tailored Antiseizure Medication (ASM)-A Systematic Review

BACKGROUND

Autosomal dominant mutations of the KCNQ2 gene can cause two epileptic disorders: benign familial neonatal seizures (BFNS) and developmental epileptic encephalopathy (DEE). This systematic review aims to identify the best reported therapy for these patients, relating to phenotype, neurodevelopmental outcome, and an eventual correlation between phenotype and genotype.

METHODS

We searched on PubMed using the search terms "KCNQ2" AND "therapy" and "KCNQ2" AND "treatment"; we found 304 articles. Of these, 29 met our criteria. We collected the data from 194 patients. All 29 articles were retrospective studies.

RESULTS

In all, 104 patients were classified as DEE and 90 as BFNS. After treatment began, 95% of BFNS patients became seizure free, whereas the seizures stopped only in 73% of those with DEE. Phenobarbital and sodium channel blockers were the most used treatment in BFNS. Most of the DEE patients (95%) needed polytherapy for seizure control and even that did not prevent subsequent developmental impairment (77%).Missense mutations were discovered in 96% of DEE patients; these were less common in BFNS (50%), followed by large deletion (16%), truncation (16%), splice donor site (10%), and frameshift (7%).

CONCLUSION

Phenobarbital or carbamazepine appears to be the most effective antiseizure medication for children with a "benign" variant. On the contrary, polytherapy is often needed for DEE patients, even if it does not seem to improve neurological outcomes. In DEE patients, most mutations were located in S4 and S6 helix, which could serve as a potential target for the development of more specific treatment in the future.

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.

Peri-ictal EEG in infants with PRRT2-related self-limited infantile epilepsy

OBJECTIVE

Pathogenic PRRT2 variants cause self-limited (familial) infantile epilepsy (SeLIE), which is responsive to sodium channel blocking antiseizure medications. The interictal EEG is typically normal. We describe a cohort of infants with PRRT2-related SeLIE with striking peri-ictal EEG abnormalities.

METHODS

We included all infants diagnosed with PRRT2-related SeLIE during July 2020 to November 2021 at the Royal Children's Hospital, Melbourne. Clinical features and results of aetiologic investigations were collected from electronic medical records. All EEGs were reviewed independently by two epileptologists.

RESULTS

Ten infants presented with focal seizures at a median age of 5 months (range: 3-6 months). Eight had a family history of epilepsy, paroxysmal kinesigenic dyskinesia (PKD) or hemiplegic migraine. Seven of the eight infants with an EEG performed within 24 h of the most recent seizure had epileptiform discharges. Their EEGs showed focal sharp waves, spikes, polyspikes or fast activity independently over the left and right temporo-occipital regions. Conversely, the two infants with last known seizure greater than 24 h prior to their EEG had no epileptiform discharges. Oxcarbazepine was commenced in two infants and was effective. Eight infants were initially treated with levetiracetam, and all were subsequently switched to oxcarbazepine due to ongoing seizures or side effects.

SIGNIFICANCE

Posterior polymorphic focal epileptiform discharges on a peri-ictal EEG recording are a feature of PRRT2-related SeLIE. This finding, particularly in the presence of a family history of infantile epilepsy, PKD or hemiplegic migraine, suggests a diagnosis of PRRT2-related SeLIE and has important treatment implications.

Phenotypic Spectrum in a Family Sharing a Heterozygous KCNQ3 Variant

BACKGROUND AND PURPOSE

Mutations in KCNQ3 have classically been associated with benign familial neonatal and infantile seizures and more recently identified in patients with neurodevelopmental disorders and abnormal electroencephalogram (EEG) findings. We present 4 affected patients from a family with a pathogenic mutation in KCNQ3 with a unique constellation of clinical findings.

METHODS

A family of 3 affected siblings and mother sharing a KCNQ3 pathogenic variant are described, including clinical history, genetic results, and EEG and magnetic resonance imaging (MRI) findings.

RESULTS

This family shows a variety of clinical manifestations, including neonatal seizures, developmental delays, autism spectrum disorder, and anxiety. One child developed absence epilepsy, 2 children have infrequent convulsive seizures that have persisted into childhood, and their parent developed adult-onset epilepsy. An underlying c.1091G>A (R364H) variant in KCNQ3 was found in all affected individuals.

CONCLUSIONS

The phenotypic variability of KCNQ3 channelopathies continues to expand as more individuals and families are described, and the variant identified in this family adds to the understanding of the manifestations of KCNQ3-related disorders.

[Clinical and genetic analysis of a Chinese pedigree affected with benign familial neonatal convulsion]

OBJECTIVE

To analyze the clinical phenotype and genetic variant in a Chinese pedigree affected with benign familial neonatal convulsion (BFNC).

METHODS

Clinical data and peripheral blood samples of the pedigree were obtained with informed consent. Whole exome sequencing (WES) was carried out for the proband. Candidate variants were verified by Sanger sequencing.

RESULTS

The pedigree comprised 9 individuals, among whom 4 were affected, including 3 males and 1 female. All patients had developed seizures during the neonatal period, which had ceased in 4 to 6 months. One patient had recurrence in between 1 and 2 years old. Genetic testing has identified a novel nonsense c.810G>A (p.W270X) variant in exon 5 of the KCNQ2 gene, which has co-separated with the BFNC phenotype in the pedigree.

CONCLUSION

The patients from this pedigree have conformed to the diagnosis of BFNC with good prognosis, which was in keeping with previously reported cases. The heterozygous c.810G>A (p.W270X) nonsense variant of the KCNQ2 gene probably underlay the pathogenesis of BFNC in this pedigree, which has expanded the mutational spectrum of the disease.

Penetrance estimation of PRRT2 variants in paroxysmal kinesigenic dyskinesia and infantile convulsions

Proline-rich transmembrane protein 2 (PRRT2) is the leading cause of paroxysmal kinesigenic dyskinesia (PKD), benign familial infantile epilepsy (BFIE), and infantile convulsions with choreoathetosis (ICCA). Reduced penetrance of PRRT2 has been observed in previous studies, whereas the exact penetrance has not been evaluated well. The objective of this study was to estimate the penetrance of PRRT2 and determine its influencing factors. We screened 222 PKD index patients and their available relatives, identified 39 families with pathogenic or likely pathogenic (P/LP) PRRT2 variants via Sanger sequencing, and obtained 184 PKD/BFIE/ICCA families with P/LP PRRT2 variants from the literature. Penetrance was estimated as the proportion of affected variant carriers. PRRT2 penetrance estimate was 77.6% (95% confidence interval (CI) 74.5%-80.7%) in relatives and 74.5% (95% CI 70.2%-78.8%) in obligate carriers. In addition, we first observed that penetrance was higher in truncated than in non-truncated variants (75.8% versus 50.0%, P = 0.01), higher in Asian than in Caucasian carriers (81.5% versus 68.5%, P = 0.004), and exhibited no difference in gender or parental transmission. Our results are meaningful for genetic counseling, implying that approximately three-quarters of PRRT2 variant carriers will develop PRRT2-related disorders, with patients from Asia or carrying truncated variants at a higher risk.

Early initial video-electro-encephalography combined with variant location predict prognosis of KCNQ2-related disorder

BACKGROUND

The clinical features of KCNQ2-related disorders range from benign familial neonatal seizures 1 to early infantile epileptic encephalopathy 7. The genotype-phenotypic association is difficult to establish.

OBJECTIVE

To explore potential factors in neonatal period that can predict the prognosis of neonates with KCNQ2-related disorder.

METHODS

Infants with KCNQ2-related disorder were retrospectively enrolled in our study in Children's Hospital of Fudan University in China from Jan 2015 to Mar 2020. All infants were older than age of 12 months at time of follow-up, and assessed by Bayley Scales of Infant and Toddler Development-Third Edition (BSID-III) or Wechsler preschool and primary scale of intelligence-fourth edition (WPPSI-IV), then divided into three groups based on scores of BSID-III or WPPSI-IV: normal group, mild impairment group, encephalopathy group. We collected demographic variables, clinical characteristics, neuroimaging data. Considered variables include gender, gestational age, birth weight, age of the initial seizures, early interictal VEEG, variant location, delivery type. Variables predicting prognosis were identified using multivariate ordinal logistic regression analysis.

RESULTS

A total of 52 infants were selected in this study. Early interictal video-electro-encephalography (VEEG) (β = 2.77, 1.20 to 4.34, P = 0.001), and variant location (β = 2.77, 0.03 to 5.5, P = 0.048) were independent risk factors for prognosis. The worse the early interictal VEEG, the worse the prognosis. Patients with variants located in the pore-lining domain or S4 segment are more likely to have a poor prognosis.

CONCLUSIONS

The integration of early initial VEEG and variant location can predict prognosis. An individual whose KCNQ2 variant located in voltage sensor, the pore domain, with worse early initial VEEG background, often had an adverse outcome.

A novel de novo KCNQ2 mutation in a child with treatmentresistant early-onset epileptic encephalopathy

Benetou C, Papailiou S, Maritsi D, Anagnostopoulou K, Kontos H, Vartzelis G. A novel de novo KCNQ2 mutation in a child with treatmentresistant early-onset epileptic encephalopathy. Turk J Pediatr 2019; 61: 279-281. Mutations in KCNQ2 gene, encoding for voltage-gated K+ channel subunit, may result in a wide spectrum of early-onset epileptic disorders. The phenotype of the disease varies from `benign familial neonatal seizures` to `severe epileptic encephalopathies`. In this report, we present a novel mutation [namely: c.683A > G (p.His228Arg)], as a presumable cause of severe infantile-onset neonatal seizures, in a 3-month old boy. The seizures have been poorly responsive to various pharmacological treatments, with phenytoin and carbamazepine presenting with the most favourable results so far. The study of our patient could help to further clarify the clinical manifestations of KCNQ2 mutations, revealing a previously unreported mutation.

Opposing Effects on NaV1.2 Function Underlie Differences Between SCN2A Variants Observed in Individuals With Autism Spectrum Disorder or Infantile Seizures

BACKGROUND

Variants in the SCN2A gene that disrupt the encoded neuronal sodium channel NaV1.2 are important risk factors for autism spectrum disorder (ASD), developmental delay, and infantile seizures. Variants observed in infantile seizures are predominantly missense, leading to a gain of function and increased neuronal excitability. How variants associated with ASD affect NaV1.2 function and neuronal excitability are unclear.

METHODS

We examined the properties of 11 ASD-associated SCN2A variants in heterologous expression systems using whole-cell voltage-clamp electrophysiology and immunohistochemistry. Resultant data were incorporated into computational models of developing and mature cortical pyramidal cells that express NaV1.2.

RESULTS

In contrast to gain of function variants that contribute to seizure, we found that all ASD-associated variants dampened or eliminated channel function. Incorporating these electrophysiological results into a compartmental model of developing excitatory neurons demonstrated that all ASD variants, regardless of their mechanism of action, resulted in deficits in neuronal excitability. Corresponding analysis of mature neurons predicted minimal change in neuronal excitability.

CONCLUSIONS

This functional characterization thus identifies SCN2A mutation and NaV1.2 dysfunction as the most frequently observed ASD risk factor detectable by exome sequencing and suggests that associated changes in neuronal excitability, particularly in developing neurons, may contribute to ASD etiology.

Autosomal dominant SCN8A mutation with an unusually mild phenotype

BACKGROUND

Mutations in SCN8A, coding for the voltage-gated sodium channel Nav 1.6, have been described in relation to infantile onset epilepsy with developmental delay and cognitive impairment, in particular early onset epileptic encephalopathy (EIEE) type 13.

CASE REPORT

Here we report an infant and his father with early onset focal epileptic seizures but without cognitive or neurological impairment in whom next generation sequence analysis identified a heterozygous mutation (c.5630A > G, p. (Asn1877Ser)) in the SCN8A gene. This mutation, confirmed by Sanger sequence analysis, affects a highly conserved amino acid and in silico tools predicts that it may be pathogenic. The reported infant has a normal developmental profile at 16-month follow-up. His father also had normal development and has no cognitive impairment at 42 years. This is the second known SCN8A mutation associated with a phenotype of benign familial infantile epilepsy. Good seizure control was achieved in our patients with sodium channel blockers.

CONCLUSION

Based on our proband and a recently described group of families with benign familial infantile epilepsy and SCN8A variant we suggest expanding testing to patients with infantile epilepsy and no cognitive impairment. In addition, the same SCN8A variant (c.5630A > G, p. (Asn1877Ser)) is also found in patients with epilepsy and developmental delay highlighting the phenotypic variability and the possible role of other protective genetic factors.

[Phenotypes and PRRT2 mutation analysis in families with benign familial infantile epilepsy]

OBJECTIVE

To study the phenotypes and proline-rich transmembrane protein 2 (PRRT2) mutations in families with benign familial infantile epilepsy (BFIE).

METHOD

Data of all BFIE probands and their family members were collected from Peking University First Hospital between September 2006 and August 2013. Clinical phenotypes of affected members were analyzed. Genomic DNA was extracted from peripheral blood samples with standard protocol. Mutations in PRRT2 were screened using PCR amplification and Sanger sequencing.

RESULT

Twenty-nine BFIE families were recruited in this study. In total, 110 family members were affected. The age of seizure onset of these affected members was between 2 and 12 months (median: 4.5 months). All probands presented with clusters of seizures. Two probands had one seizure induced by diarrhea respectively at 25 months and 31 months. In four BFIE families, four family members had a history of febrile seizures. PRRT2 mutations were found in 17 of the 29 (58.6%) BFIE families. Mutation c.649_650insC was detected in 12 of the 17 families with PRRT2 mutations. Mutation c.649delC (p.R217EfsX12) was identified in three families. Mutation c.323_324delCA (p. T108SfsX25) and c.904_ 905insG (p. D302GfsX39) were detected in one family, respectively.

CONCLUSION

The minimum seizure onset age of affected members in BFIE families was 2 months of age. The seizures often occur in clusters. PRRT2 is the major causative gene of BFIE in Chinese families. Mutation c.649_650insC is the hotspot mutation of PRRT2. A novel mutation c.323_324delCA was first reported in BFIE family. Few affected members with PRRT2 mutation presented with febrile seizures phenotype.

Benign infantile convulsion as a diagnostic clue of paroxysmal kinesigenic dyskinesia: a case series

INTRODUCTION

Paroxysmal kinesigenic dyskinesia is characterized by sudden attacks of involuntary movements. It is often misdiagnosed clinically as psychogenic illness, which distresses the patients to a great extent. A correct diagnosis will improve the quality of life in patients with paroxysmal kinesigenic dyskinesia because treatment with low doses of anticonvulsants is effective for eliminating the clinical manifestations. Paroxysmal kinesigenic dyskinesia can occur independently of or concurrently with benign infantile convulsion. Identification of PRRT2 as the causative gene of benign infantile convulsion and paroxysmal kinesigenic dyskinesia allows genetic confirmation of the clinical diagnosis.

CASE PRESENTATION

We describe the clinical features of a Japanese family with either paroxysmal kinesigenic dyskinesia or benign infantile convulsion. A PRRT2 missense mutation (c.981C > G, p.Ile327Met) was identified in two patients with benign infantile convulsion and three patients with paroxysmal kinesigenic dyskinesia as well as in two unaffected individuals. Allowing incomplete penetrance in the mutation carriers, this mutation co-segregated completely with the phenotype. The patients with paroxysmal kinesigenic dyskinesia had been misdiagnosed with psychogenic illness for many years. They were correctly diagnosed with paroxysmal kinesigenic dyskinesia when their children visited a pediatrician for benign infantile convulsion. Treatment with carbamazepine controlled their involuntary movements completely.

CONCLUSIONS

Paroxysmal kinesigenic dyskinesia is a treatable movement disorder that is often misdiagnosed clinically as psychogenic illness. It is important to note that two clinically distinct disorders, benign infantile convulsion and paroxysmal kinesigenic dyskinesia, are allelic conditions caused by PRRT2 mutations. Paroxysmal kinesigenic dyskinesia should be suspected in families with a child with benign infantile convulsion.

SLC25A22 is a novel gene for migrating partial seizures in infancy

OBJECTIVE

To identify a genetic cause for migrating partial seizures in infancy (MPSI).

METHODS

We characterized a consanguineous pedigree with MPSI and obtained DNA from affected and unaffected family members. We analyzed single nucleotide polymorphism 500K data to identify regions with evidence of linkage. We performed whole exome sequencing and analyzed homozygous variants in regions of linkage to identify a candidate gene and performed functional studies of the candidate gene SLC25A22.

RESULTS

In a consanguineous pedigree with 2 individuals with MPSI, we identified 2 regions of linkage, chromosome 4p16.1-p16.3 and chromosome 11p15.4-pter. Using whole exome sequencing, we identified 8 novel homozygous variants in genes in these regions. Only 1 variant, SLC25A22 c.G328C, results in a change of a highly conserved amino acid (p.G110R) and was not present in control samples. SLC25A22 encodes a glutamate transporter with strong expression in the developing brain. We show that the specific G110R mutation, located in a transmembrane domain of the protein, disrupts mitochondrial glutamate transport.

INTERPRETATION

We have shown that MPSI can be inherited and have identified a novel homozygous mutation in SLC25A22 in the affected individuals. Our data strongly suggest that SLC25A22 is responsible for MPSI, a severe condition with few known etiologies. We have demonstrated that a combination of linkage analysis and whole exome sequencing can be used for disease gene discovery. Finally, as SLC25A22 had been implicated in the distinct syndrome of neonatal epilepsy with suppression bursts on electroencephalogram, we have expanded the phenotypic spectrum associated with SLC25A22.

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.

Genetic analysis of PRRT2 for benign infantile epilepsy, infantile convulsions with choreoathetosis syndrome, and benign convulsions with mild gastroenteritis

PURPOSE

PRRT2 mutations were recently identified in benign familial infantile epilepsy (BFIE) and infantile convulsions with paroxysmal choreoathetosis (ICCA) but no abnormalities have so far been identified in their phenotypically similar seizure disorder of benign convulsions with mild gastroenteritis (CwG), while mutations in KCNQ2 and KCNQ3 have been recognized in benign familial neonatal epilepsy (BFNE). The aim of this study was to identify PRRT2 mutations in infantile convulsions in Asian families with BFIE and ICCA, CwG and BFNE.

METHODS

We recruited 26 unrelated Japanese affected with either BFIE or non-familial benign infantile seizures and their families, including three families with ICCA. A total of 17 Japanese and Taiwanese with CwG, 50 Japanese with BFNE and 96 healthy volunteers were also recruited. Mutations of PRRT2 were sought using direct sequencing.

RESULTS

Heterozygous truncation mutation (c.649dupC) was identified in 15 of 26 individuals with benign infantile epilepsy (52.1%). All three families of ICCA harbored the same mutation (100%). Another novel mutation (c.1012+2dupT) was found in the proband of a family with BFIE. However, no PRRT2 mutation was found in either CwG or BFNE.

CONCLUSIONS

The results confirm that c.649dupC, a truncating mutation of PRRT2, is a hotspot mutation resulting in BFIE or ICCA regardless of the ethnic background. In contrast, PRRT2 mutations do not seem to be associated with CwG or BFNE. Screening for PRRT2 mutation might be useful in early-stage differentiation of BFIE from CwG.

Benign familial neonatal convulsions caused by mutation in KCNQ3, exon 6: a European case

Benign familial neonatal convulsions (BFNC) is a rare, clinically and genetically heterogenous epileptic disorder. Two voltage gated potassium genes, KCNQ2 and KCNQ3, have been identified as genes responsible for BFNC1 and BFNC2 respectively. While as many as 73 mutations of KCNQ2 have been described up to date, only 4 mutations in KCNQ3, 3 of them appearing in exon 5, have been identified. Mutation in exon 6 was found for the first time in a Chinese family, and here we report the same missense mutation of KCNQ3 within exon 6 in a Caucasian family, whose history and clinical picture were in accordance with BFNC.

PRRT2-related disorders: further PKD and ICCA cases and review of the literature

Recent studies reported mutations in the gene encoding the proline-rich transmembrane protein 2 (PRRT2) to be causative for paroxysmal kinesigenic dyskinesia (PKD), PKD combined with infantile seizures (ICCA), and benign familial infantile seizures (BFIS). PRRT2 is a presynaptic protein which seems to play an important role in exocytosis and neurotransmitter release. PKD is the most common form of paroxysmal movement disorder characterized by recurrent brief involuntary hyperkinesias triggered by sudden movements. Here, we sequenced PRRT2 in 14 sporadic and 8 familial PKD and ICCA cases of Caucasian origin and identified three novel mutations (c.919C>T/p.Gln307, c.388delG/p.Ala130Profs 46, c.884G>A/p.Arg295Gln) predicting two truncated proteins and one probably damaging point mutation. A review of all published cases is also included. PRRT2 mutations occur more frequently in familial forms of PRRT2-related syndromes (80-100 %) than in sporadic cases (33-46 %) suggesting further heterogeneity in the latter. PRRT2 mutations were rarely described in other forms of paroxysmal dyskinesias deviating from classical PKD, as we report here in one ICCA family without kinesigenic triggers. Mutations are exclusively found in two exons of the PRRT2 gene at a high rate across all syndromes and with one major mutation (c.649dupC) in a mutational hotspot of nine cytosines, which is responsible for 57 % of all cases in all phenotypes. We therefore propose that genetic analysis rapidly performed in early stages of the disease is highly cost-effective and can help to avoid further unnecessary diagnostic and therapeutic interventions.

KCNQ2 abnormality in BECTS: benign childhood epilepsy with centrotemporal spikes following benign neonatal seizures resulting from a mutation of KCNQ2

The molecular pathogenesis of benign childhood epilepsy with centrotemporal spikes (BECTS) remains unclear whereas mutations of the KCNQ2 and KCNQ3 genes have been identified as causes of benign familial neonatal convulsions. We report here a girl with benign neonatal convulsions followed by BECTS, for whom a mutation of KCNQ2 was identified. This case may provide the clue to the understanding of the molecular pathogenesis of BECTS.

[Site-directed mutagenesis and protein expression of KCNQ2 gene associated with neonatal convulsions]

OBJECTIVE

To study the protocol of construction of a KCNQ2-c.812G>T mutant and it's eukaryotic expression vector, the c.812G>T (p.G271V) mutation which was detected in a Chinese pedigree of benign familial infantile convulsions, and to examine the expression of mutant protein in human embyonic kidney (HEK) 293 cells.

METHODS

A KCNQ2 mutation c.812G>T was engineered on KCNQ2 cDNAs cloned into pcDNA3.0 by sequence overlap extension PCR and restriction enzymes. HEK293 cells were co-transfected with pRK5-GFP and KCNQ2 plasmid (the wild type or mutant) using lipofectamine and then subjected to confocal microscopy. The transfected cells were immunostained to visualize the intracellular expression of the mutant molecules.

RESULTS

Direct sequence analysis revealed a G to T transition at position 812. The c.812G>T mutation was correctly combined to eukaryotic expressive vector pcDNA3.0 and expressed in HEK293 cells. Immunostaining of transfected cells showed the expression of both the wild type and mutant molecules on the plasma membrane, which suggested that the c.812G>T mutation at the pore forming region of KCNQ2 channel did not impair normal protein expression in HEK293 cells.

CONCLUSIONS

Successful construction of mutant KCNQ2 eukaryotic expression vector and expression of KCNQ2 protein in HEK293 cells provide a basis for further study on the functional effects of convulsion-causing KCNQ2 mutations and for understanding the molecular pathogenesis of epilepsy.

The first Korean case of KCNQ2 mutation in a family with benign familial neonatal convulsions

Neonatal seizures represent a heterogeneous group of disorders with vastly different etiologies and outcomes. Benign familial neonatal convulsions (BFNC) are a distinctive epileptic syndrome of autosomal dominant inheritance with a favorable prognosis, characterized by the occurrence of unprovoked partial or generalized clonic seizures in the neonatal period or early infancy. Recently, mutations in two potassium channel genes, KCNQ2 and KCNQ3, have been described in this disorder. In this report, we describe a family with BFNC due to a KCNQ2 mutation, the first such family to be described in the Korean population. The diagnosis of BFNC can be made based on clinical suspicion and careful history taking with special emphasis on the familial nature of the disorder. KCNQ2 mutations may be associated with BFNC in a number of different races, as has been reported in other ethnic groups.

[Linkage analysis and gene mapping of one Chinese family with benign familial infantile convulsions]

OBJECTIVE

The present study performed linkage analysis and gene mapping to find the possible chromosome locus harboring in one family with benign familial infantile convulsions (BFIC) and investigate the possible molecular pathogenesis of BFIC.

METHODS

A four-generation family with BFIC was investigated. The family was genotyped using eight hypervariable microsatellite markers covering four loci: D19S245 and D19S250 for the 19q12-13.1 region, D16S3131 and D16S3133 for the 16p12-q12 region, D2S156 and D2S286 for the 2q24 region, and D20S480 and D20S481 for the 20q13.3 region. Polymorphism fragments were amplified using polymerase chain reaction (PCR) method. PCR products for the markers were subjected to electrophoresis on 8% denatured polyacrylamide gel and silver staining for length judgment of amplification fragment. Linkage analysis was performed by use of MLINK in the LINKAGE computer package. Two-point LOD scores were calculated to estimate the linkage relationship.

RESULTS

The two-point LOD scores were less than -2.0 for the genetic markers at chromosomes 19q12-13.1, 16p12-q12 and 2q24 at the recombination rate between 0.000 and 0.01. The two-point LOD scores for D20S481 at the 20q13.3 region were 0.3 and 0.25 at the recombination rate of 0.000 and 0.01, respectively.

CONCLUSIONS

There is no evidence that this family with BFIC is linked to one of the following loci: 19q12-13.1, 16p12-q12 and 2q24, but a possible linkage with 20q13.3 region cannot be excluded.

[Convulsions in neonatal period and infancy with rare etiology (neurogenetic disease)]

Authors summarized the etiology of convulsions in neonatal period and infancy (hypoxia, intracranial hemorrhage, infections of central nervous system, metabolic background, chromosomal abnormalities, brain developmental abnormalities, benign neonatal convulsions, benign neonatal familial convulsions, drug withdrawal, inborn error of metabolism). They suggest screening examinations after convulsion, summarized the basic principle of tandem examination and review a proposal at suspicion of inborn error of enzyme defects (aminoacidemias, defects of fatty acid oxidation, organic acidemias). They present case history of two patients suffered in extraordinary inborn error of enzyme defect (SCO2 gene mutation, propionic acidemia). Diagnosis originated in Helm P61 Hospital (settlement Madarász Hospital) with a Hungarian and international cooperation.

Impaired NaV1.2 function and reduced cell surface expression in benign familial neonatal-infantile seizures

PURPOSE

Mutations in SCN2A, the gene encoding the brain voltage-gated sodium channel alpha-subunit Na(V)1.2, are associated with inherited epilepsies including benign familial neonatal-infantile seizures (BFNIS). Functional characterization of three BFNIS mutations was performed to identify defects in channel function that underlie this disease.

METHODS

We examined three BFNIS mutations (R1319Q, L1330F, and L1563V) using whole-cell patch-clamp recording of heterologously expressed human Na(V)1.2. Membrane biotinylation was employed to examine the cell surface protein expression of the four Na(V)1.2 alleles.

RESULTS

R1319Q displayed mixed effects on activation and fast inactivation gating, consistent with a net loss of channel function. L1563V exhibited impaired fast inactivation predicting a net gain of channel function. The L1330F mutation significantly decreased overall channel availability during repetitive stimulation. Patch-clamp analysis also revealed that cells expressing BFNIS mutants exhibited lower levels of sodium current compared to wild type (WT) Na(V)1.2. Biochemical experiments demonstrated that all three BFNIS mutations exhibited a significant reduction in cell surface expression compared to WT.

DISCUSSION

Our findings indicate that BFNIS is associated with a range of biophysical defects accompanied by reduced levels of channel protein at the plasma membrane.

Nervous system KV7 disorders: breakdown of a subthreshold brake

Voltage-gated K+channels of the K(V)7 (KCNQ) family have been identified in the last 10-15 years by discovering the causative genes for three autosomal dominant diseases: cardiac arrhythmia (long QT syndrome) with or without congenital deafness (KCNQ1), a neonatal epilepsy (KCNQ2 and KCNQ3) and progressive deafness alone (KCNQ4). A fifth member of this gene family (KCNQ5) is not affected in a disease so far. Four genes (KCNQ2-5) are expressed in the nervous system. This review is focused on recent findings on the neuronal K(V)7 channelopathies, in particular on benign familial neonatal seizures (BFNS) and peripheral nerve hyperexcitability (PNH, neuromyotonia, myokymia) caused by KCNQ2 mutations. The phenotypic spectrum associated with KCNQ2 mutations is probably broader than initially thought, as patients with severe epilepsies and developmental delay, or with Rolando epilepsy have been described. With regard to the underlying molecular pathophysiology, it has been shown that mutations with very subtle changes restricted to subthreshold voltages can cause BFNS thereby proving in a human disease model that this is the relevant voltage range for these channels to modulate neuronal firing. The two mutations associated with PNH induce much more severe channel dysfunction with a dominant negative effect on wild type (WT) channels. Finally, K(V)7 channels present interesting targets for new therapeutic approaches to diseases caused by neuronal hyperexcitability, such as epilepsy, neuropathic pain, and migraine. The molecular mechanism of K(V)7 activation by retigabine, which is in phase III clinical testing to treat pharmacoresistant focal epilepsies, has been recently elucidated as a stabilization of the open conformation by binding to the pore region.

A novel missense mutation (N258S) in the KCNQ2 gene in a Turkish family afflicted with benign familial neonatal convulsions (BFNC)

Benign familial neonatal convulsions (BFNC) is a rare monogenic subtype of idiopathic epilepsy exhibiting autosomal dominant mode of inheritance. The disease is caused by mutations in the two homologous genes KCNQ2 and KCNQ3 that encode the subunits of the voltage-gated potassium channel. Most KCNQ2 mutations are found in the pore region and the cytoplasmic C domain. These mutations are either deletions/insertions that result in frameshift or truncation of the protein product, splice-site variants or missense mutations. This study reveals a novel missense mutation (N258S) in the KCNQ2 gene between the S5 domain and the pore of the potassium channel in two BFNC patients in a Turkish family. The absence of the mutation both in the healthy members of the family and in a control group, and the lack of any other change in the KCNQ2 gene of the patients indicate that N258S substitution is a pathogenic mutation leading to epileptic seizures in this family.

Deletions or duplications in KCNQ2 can cause benign familial neonatal seizures

BACKGROUND

Benign familial neonatal seizures are most often caused by mutations in the voltage-gated potassium channel subunit gene KCNQ2. More than 60 mutations have been described in BFNS families, approximately half of which lead to protein truncation. The hypothesis of this study was that deletion or duplication of >or=1 exons of KCNQ2 could cause BFNS in cases without coding or splicing mutations.

METHODS

Multiplex ligation-dependent probe amplification (MLPA) was used to test a group of 21 unrelated patients with clinical features consistent with either BFNS, benign familial neonatal-infantile seizures or sporadic neonatal seizures, for exonic deletions and duplications.

RESULTS

Three deletions and one duplication mutation were identified in four familial cases and cascade testing of their available family members showed that the mutations segregated with the phenotype in each family. The junction fragment for one of the deletions was amplified by PCR and sequenced to characterise the breakpoint and verify that a deletion had occurred.

CONCLUSIONS

Submicroscopic deletions or duplications of KCNQ2 are seen in a significant proportion of BFNS families: four of nine (44%) cases previously testing negative for coding or splice site mutation by sequencing KCNQ2 and KCNQ3. MLPA is an efficient second-tier testing strategy for KCNQ2 to identify pathogenic intragenic mutations not detectable by conventional DNA sequencing methods.

K+ M-current regulates the transition to seizures in immature and adult hippocampus

PURPOSE

Loss-of-function mutations in Kv7.2 or Kv7.3 K(+) channel subunits underlies the neonatal epilepsy benign familial neonatal convulsions (BFNC). These two subunits interact to form a functional K(+) channel that underlies the M-current (I(M)), a voltage-dependent noninactivating K(+) current. In BFNC, seizures begin shortly after birth, and spontaneously remit in the first few months of life. The nature of this window of vulnerability is unclear. We address this issue using a hippocampal slice model, to study the effects of I(M) blockade or augmentation on epileptiform activity.

METHODS

We used the Mg(+)(+)-free seizure model in adult and immature (P8-P15) acute rat hippocampal slices. We recorded from both CA1 and CA3 regions using extracellular and intracellular methods.

RESULTS

When M-channels are blocked pharmacologically, the transition from interictal to ictal bursting becomes much more likely, especially in immature brain. We also show augmentation of I(M) is effective in stopping ictal events in immature brain, at the developmental age that approximates a human newborn in cortical development. I(M) appears to counter the sustained N-methyl-D-aspartate (NMDA) receptor-mediated depolarizations needed to trigger an ictal event. The increased likelihood of ictal bursting by I(M) blockade is not shared by other selective K(+) channel blockers that increase hippocampal excitability.

CONCLUSIONS

Voltage-dependent M-channels are activated during interictal bursts and contribute to burst termination. When these channels are compromised, interictal burst duration becomes sufficient to trigger the sustained depolarizations that underlie ictal bursts. This transition to ictal bursts upon I(M) blockade is especially likely to occur in immature hippocampus. This selective function of M-channels likely contributes to the transient window of vulnerability to seizures that occurs with BFNC.

Atypical gating of M-type potassium channels conferred by mutations in uncharged residues in the S4 region of KCNQ2 causing benign familial neonatal convulsions

Heteromeric assembly of KCNQ2 and KCNQ3 subunits underlie the M-current (I(KM)), a slowly activating and noninactivating neuronal K(+) current. Mutations in KCNQ2 and KCNQ3 genes cause benign familial neonatal convulsions (BFNCs), a rare autosomal-dominant epilepsy of the newborn. In the present study, we describe the identification of a novel KCNQ2 heterozygous mutation (c587t) in a BFNC-affected family, leading to an alanine to valine substitution at amino acid position 196 located at the N-terminal end of the voltage-sensing S(4) domain. The consequences on KCNQ2 subunit function prompted by the A196V substitution, as well as by the A196V/L197P mutation previously described in another BFNC-affected family, were investigated by macroscopic and single-channel current measurements in CHO cells transiently transfected with wild-type and mutant subunits. When compared with KCNQ2 channels, homomeric KCNQ2 A196V or A196V/L197P channels showed a 20 mV rightward shift in their activation voltage dependence, with no concomitant change in maximal open probability or single-channel conductance. Furthermore, current activation kinetics of KCNQ2 A196V channels displayed an unusual dependence on the conditioning prepulse voltage, being markedly slower when preceded by prepulses to more depolarized potentials. Heteromeric channels formed by KCNQ2 A196V and KCNQ3 subunits displayed gating changes similar to those of KCNQ2 A196V homomeric channels. Collectively, these results reveal a novel role for noncharged residues in the N-terminal end of S(4) in controlling gating of I(KM) and suggest that gating changes caused by mutations at these residues may decrease I(KM) function, thus causing neuronal hyperexcitability, ultimately leading to neonatal convulsions.

SCN2A mutations and benign familial neonatal-infantile seizures: the phenotypic spectrum

Mutations of the sodium channel subunit gene SCN2A have been described in families with benign familial neonatal-infantile seizure (BFNIS). We describe two large families with BFNIS and novel SCN2A mutations. The families had 12 and 9 affected individuals, respectively, with phenotypes consistent with BFNIS. Two mutations were discovered in SCN2A (E430Q; I1596S). Both families had individuals with neonatal onset but the typical age of onset was in the early infantile period (mean 3.0 months). One mutation positive individual, with an otherwise typical clinical pattern, had seizures beginning at 13 months. Two individuals with SCN2A mutations were identified with seizures in later life. In each family a single individual with infantile seizures was mutation negative and thus represented phenocopies. This study extends the age range of presentation of BFNIS, confirms that neonatal and early infantile onsets are characteristic, and emphasizes the role of molecular diagnosis to confirm the etiology.

Benign familial neonatal convulsions: always benign?

BACKGROUND

Benign familial neonatal convulsions (BFNC) is a rare autosomal dominant seizure disorder usually described to be characterized by a benign course, spontaneous remission and normal psychomotor development. The latter statement had come under consideration when a few case reports of families with less than favorable outcomes were published.

METHODS

Since 1998 a total of 112 families suspected to have BFNC have been referred to our lab for genetic testing. Within this sample we identified private KCNQ2 mutations in 17 BFNC families. For 10 of those 17 families follow up information about the psychomotor development and the outcome were available.

RESULTS

In 4 (40%) of the 10 families at least 1 affected individual showed delayed psychomotor development or mental retardation. Three of the four mutations were familial, while the fourth mutation was de novo. Mutations associated with an unfavorable outcome tended to be located within the functionally critical S5/S6 regions of the KCNQ2 gene.

CONCLUSIONS

Our data raise the question if BFNC can indeed be described as a benign disorder, and which are the genetic and/or environmental factors that influence the outcome.

Effects in neocortical neurons of mutations of the Na(v)1.2 Na+ channel causing benign familial neonatal-infantile seizures

Mutations of voltage-gated Na+ channels are the most common cause of familial epilepsy. Benign familial neonatal-infantile seizures (BFNIS) is an epileptic trait of the early infancy, and it is the only well characterized epileptic syndrome caused exclusively by mutations of Na(V)1.2 Na+ channels, but no functional studies of BFNIS mutations have been done. The comparative study of the functional effects and the elucidation of the pathogenic mechanisms of epileptogenic mutations is essential for designing targeted and effective therapies. However, the functional properties of Na+ channels and the effects of their mutations are very sensitive to the cell background and thus to the expression system used. We investigated the functional effects of four of the six BFNIS mutations identified (L1330F, L1563V, R223Q, and R1319Q) using as expression system transfected pyramidal and bipolar neocortical neurons in short primary cultures, which have small endogenous Na+ current and thus permit the selective study of transfected channels. The mutation L1330F caused a positive shift of the inactivation curve, and the mutation L1563V caused a negative shift of the activation curve, effects that are consistent with neuronal hyperexcitability. The mutations R223Q and R1319Q mainly caused positive shifts of both activation and inactivation curves, effects that cannot be directly associated with a specific modification of excitability. Using physiological stimuli in voltage-clamp experiments, we showed that these mutations increase both subthreshold and action Na+ currents, consistently with hyperexcitability. Thus, the pathogenic mechanism of BFNIS mutations is neuronal hyperexcitability caused by increased Na+ current.

Andreas Rett and benign familial neonatal convulsions revisited

In 1964 Andreas Rett published the first account of a family with benign familial neonatal convulsions (BFNC). The authors retraced Rett's family and report that the clinical and genetic features of this original family fit the currently accepted definitions of BFNC. They also consider the career of Dr. Rett, a researcher and social reformer as well as an advocate for the rights of children with developmental disabilities.

Benign pediatric localization-related epilepsies. Part I. Syndromes in infancy

There is currently increasing interest in identifying and classifying pediatric benign epilepsy syndromes and recently several new syndromes have been recognized. Benign epilepsy syndromes, by definition, occur in children with normal developmental history, respond well to therapy, and remit without sequelae. The large majority of children with benign epilepsy syndromes follow a truly benign course. The concept of benign epilepsy syndromes has, however, been challenged by the minority of patients who continue to have seizures despite therapy, develop new seizures after initial remission, or exhibit neuropsychological abnormalities. Without long-term follow-up, benignity can not be truly ascertained a priori. Thus it may be preferable to use the terms possible and probable before the name of a specific syndrome until such time that the diagnosis of a definite benign syndrome is confirmed on long-term follow-up. In this review of the pediatric benign localization-related epilepsy syndromes, we address the concept of benignity and the process of diagnosis of a benign epilepsy syndrome. In addition we review the epidemiology, clinical manifestations, EEG findings, work-up, diagnostic criteria, differential diagnosis, genetics, management and prognosis of benign infantile familial convulsions, benign partial epilepsy in infancy with complex partial seizures, benign partial epilepsy in infancy with secondarily generalized seizures, benign infantile convulsions associated with mild gastroenteritis, and benign infantile focal epilepsy with midline spikes and waves during sleep.

Subthreshold changes of voltage-dependent activation of the K(V)7.2 channel in neonatal epilepsy

Benign familial neonatal convulsions (BFNC) is an epileptic disorder caused by dominant mutations in the genes KCNQ2 and KCNQ3 encoding the K+ channels K(V)7.2 and K(V)7.3. We identified two novel KCNQ2 mutations in two BFNC families. One mutation predicted a truncated protein (S247X) that lacks the channel's pore region, the other resulted in the amino acid substitution S122L in the S2 segment of K(V)7.2. In comparison to wild-type (WT) K(V)7.2, functional analysis of S122L mutant channels in Xenopus oocytes revealed a significant positive shift and increased slope of the activation curve leading to significant current reduction in the subthreshold range of an action potential (75% reduction at -50 mV). Our results establish an important role of the K(V)7.2 S2 segment in voltage-dependent channel gating and demonstrate in a human disease that subthreshold voltages are likely to represent the physiologically relevant range for this K+ channel to regulate neuronal firing.

[Clinical and mutational analysis of KCNQ3 gene in a Chinese family with benign familial neonatal convulsions]

OBJECTIVE

To study the clinical and genetic characteristics of a Chinese family with benign familial convulsions (BFNC).

METHODS

The clinical data of this family was analyzed. The blood samples were collected from 13 members of this family. By four microsatellite markers which are located in the gene loci of both K+ channel KCNQ2 and KCNQ3, the linkage analysis was performed in the family. With DNA direct sequencing and restriction endonuclease cutting analysis, the mutation analysis of KCNQ3 gene was made for the proband, other 12 family members and 76 unrelated normal individuals.

RESULTS

There were 7 patients with BFNC observed in the three generation of family. The BFNC seizures of all patients disappeared during one month and no recurrence of seizures was found. The linkage analysis suggested the disease gene linked to KCNQ3 gene locus in the family. The mutation 988(C to T) of KCNQ3 gene was found in the proband by DNA-direct sequencing. Cosegregation of this mutation with BFNC was confirmed by restriction endonuclease cutting analysis.

CONCLUSION

Chinese patients with BFNC can be caused by KCNQ3 gene mutation.

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.

[A novel mutation in KCNQ2 gene causes benign familial infantile convulsions (BFIC) in a Chinese family]

OBJECTIVE

Benign familial infantile convulsions (BFIC) is a form of idiopathic epileptic syndrome characterized by onset of afebrile seizures between 3 and 12 months of life, Spontaneous remission after several weeks or months, and autosomal dominant mode of inheritance. Previous linkage analysis in western countries defined three susceptible loci on chromosomes 19q12.0-13.1, 16p12-q12, and 2q23-31, but studies performed in several Chinese families with BFIC got negative results of these previously reported loci. The authors investigated the relation of voltage-gated potassium channel gene KCNQ2 to BFIC in a Chinese family and thus to understand the molecular pathogenesis of BFIC.

METHODS

A four-generation Chinese BFIC family was investigated. All the affected 17 members had similar pattern of seizures starting from 2 to 6 months of age. In 15 of them, the seizures disappeared spontaneously within the first year of life. The phenotype extended beyond infancy only in two patients. Blood sample was collected from the 41 family members and 75 unassociated normal individuals. Polymerase chain reaction (PCR)-DNA direct sequencing was performed to screen all exons and their flanking introns of KCNQ2 gene for mutation analysis. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) was used to ascertain the co-segregation of genotype and phenotype and to exclude polymorphism.

RESULTS

PCR amplification and subsequent direct sequencing of KCNQ2 from the DNA of proband revealed a heterozygous guanine to thymine nucleotide exchange (G812T) in exon 5, leading to the substitution of glycine by valine at amino acid position 271 (G271V) of the predicted protein. The same mutation with a comparable localization has been previously described for KCNQ3 in benign familial neonatal convulsions (BFNC). The glycine at this position (G271) is located in pore region of KCNQ2 protein and is evolutionarily highly conserved. The same SSCP variant as that of the proband was shown in the rest of the affected members of this family but not in the unaffected members enrolled in the study of this family and all the 75 unrelated normal individuals.

CONCLUSION

Previously reported mutations of KCNQ2 were mainly identified in BFNC family in which at least one individual had an onset of seizures during the first week of life, a hallmark of the BFNC disorder. The results of the present study suggest the possibility that KCNQ2 mutation exist in patients with BFIC diagnosis. G812T of KCNQ2 gene is a novel mutation found in BFIC and functional expression of KCNQ2 G812T is required for understanding the mechanism of BFIC and other idiopathic epilepsy.

A novel splicing mutation in KCNQ2 in a multigenerational family with BFNC followed for 25 years

PURPOSE

A large multigenerational family with benign familial neonatal convulsions (BFNC) was revisited to identify the disease-causing mutation and to assess long-term outcome.

METHODS

We supplemented the original data with recent clinical and neurophysiologic data on patients and first-degree relatives, including information on seizure recurrence. We conducted linkage analysis at the EBN1 and EBN2 loci, followed by mutation analysis of KCNQ2. We evaluated the qualitative effect of the KCNQ2 mutation at the messenger RNA (mRNA) level by using reverse-transcribed total RNA isolated from leukocytes.

RESULTS

Thirteen relatives had a history of neonatal convulsions, 11 of whom showed remission within 2 months. One patient showed an atypical course of neonatal convulsions, developing photosensitive myoclonic epilepsy at age 13 years. We found suggestive linkage of the BFNC phenotype to the 20q13-EBN1 locus (lod score, 2.03) and an intronic mutation IVS14-6 C>A in KCNQ2 segregating with the trait in all affected members, but absent in 100 unrelated control subjects. This mutation creates a new, preferentially used, splice site. Alternative splicing adds 4 nt containing a premature stop codon to the transcript, resulting in a truncated protein after position R588.

CONCLUSIONS

We detected and characterized a novel splicing mutation in the brain-specific KCNQ2 gene by using easily accessible blood leukocytes. Aberrant splicing cosegregates with BFNC but not with photosensitivity.

Polarized axonal surface expression of neuronal KCNQ channels is mediated by multiple signals in the KCNQ2 and KCNQ3 C-terminal domains

The M channels, important regulators of neuronal excitability, are voltage-gated potassium channels composed of KCNQ2-5 subunits. Mutations in KCNQ2 and KCNQ3 cause benign familial neonatal convulsions (BFNC), dominantly inherited epilepsy and myokymia. Crucial for their functions in controlling neuronal excitability, the M channels must be placed at specific regions of the neuronal membrane. However, the precise distribution of surface KCNQ channels is not known. Here, we show that KCNQ2/KCNQ3 channels are preferentially localized to the surface of axons both at the axonal initial segment and more distally. Whereas axonal initial segment targeting of surface KCNQ channels is mediated by ankyrin-G binding motifs of KCNQ2 and KCNQ3, sequences mediating targeting to more distal portion of the axon reside in the membrane proximal and A domains of the KCNQ2 C-terminal tail. We further show that several BFNC mutations of KCNQ2 and KCNQ3 disrupt surface expression or polarized surface distribution of KCNQ channels, thereby revealing impaired targeting of KCNQ channels to axonal surfaces as a BFNC etiology.

Early pattern of epilepsy in the ring chromosome 20 syndrome

PURPOSE

The characteristics of epilepsy in ring chromosome 20 have been reported in adolescents and adults. The mode of onset most often remains imprecise. To clarify this onset period, we studied the early-onset features in our personal series and in the reported pediatric cases.

METHODS

Our series comprises one child with an onset of epilepsy in the neonatal period and five others with an onset before age 8 years. The cases in the literature with an epilepsy onset before 8 years also were reviewed.

RESULTS

Seizures in the neonatal period were described as motor seizures. Our personal patient with a neonatal onset had severe psychomotor delay. In both infancy and early childhood, the EEG showed no interictal frontal localization of the anomalies, and no long-lasting seizure was recorded. Seizures with terror and hallucinations usually appeared from about age 4 years. It is not before the age of 8 years that the usual interictal EEG pattern appeared of rhythmic theta slow-waves activity with spikes predominating in frontal areas described in adolescence and adulthood. The interictal EEG showed 1- to 2-Hz delta slow waves and spike-and-waves predominating in frontal areas, but no physiologic activity.

CONCLUSIONS

In ring 20 chromosome, specific epilepsy features are lacking in the neonate, but the whole phenotype shows a more severe expression in terms of mental delay. The characteristic frontal EEG pattern and ictal terror do not appear before age 4 to 5 years.

Neonatal epilepsy syndromes and GEFS+: mechanistic considerations

Genetic analyses of familial epilepsies over the past decade have identified mutations in several different ion channel genes that result in neonatal or early-onset seizure disorders, including benign familial neonatal convulsions (BFNC), generalized epilepsy with febrile seizures plus (GEFS+), and severe myoclonic epilepsy of infancy (SMEI). These genes encode voltage-gated Na+ channel subunits (SCN1A, SCN2A, SCN1B), voltage-gated K+ channel subunits (KCNQ2, KCNQ3), and a ligand-gated neurotransmitter receptor subunit (GABRG2). While the opportunity to genotype patients for mutations in these genes can have an immediate and significant impact on our ability to diagnose and provide genetic counseling to patients, the ultimate goal is to use this molecular knowledge to develop effective treatments and cures for each disorder. This will necessitate elucidation of the molecular, cellular, and network mechanisms that translate ion channel defects into specific epilepsy phenotypes. The functional analysis of epileptogenic channel mutations in vitro and in vivo has already provided a vast amount of raw biophysical data, but attempts to interpret these data to explain clinical phenotypes so far appear to raise as many questions as they answer. Nevertheless, patterns are beginning to emerge from these early studies that will help define the full scope of the challenges ahead while simultaneously providing the foundation of future efforts to overcome them. Here, I discuss some of the potential mechanisms that have been uncovered recently linking mutant ion channel genes to neonatal epilepsy syndromes and GEFS+.

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.

No evidence of ATP1A2 involvement in 12 multiplex Italian families with benign familial infantile seizures

A missense mutation in the gene encoding the alpha(2) subunit of the Na(+),K(+) ATPase pump (ATP1A2) was found in a family with both familial hemiplegic migraine (FHM) and Benign Familial Infantile Seizures (BFIC). As it is still unclear whether ATP1A2 is responsible for pure BFIC syndromes, we checked mutations of the ATP1A2 gene in probands of 12 Italian multiplex families with pure BFIC, who were negative for mutations in the SCN2A gene. We screened the ATP1A2 gene by denaturing high performance liquid chromatography (D-HPLC) and direct sequencing of DNA fragments showing an aberrant elution pattern. We found one exonic variant and five intronic variants, none leading to significant amino acid changes or causing a modification of the physiological mRNA maturation. The ATP1A2 gene does not appear to be involved in the ethiopathogenesis of pure BFIC syndromes, at least in the explored Italian multiplex families. It could be either responsible of a minority of cases, or of complex syndromes where BFIC and FHM co-occur.