Identification of susceptibility variants to benign childhood epilepsy with centro-temporal spikes (BECTS) in Chinese Han population

BACKGROUND

Benign Childhood Epilepsy with Centro-temporal Spikes (BECTS) is the most common form of idiopathic epilepsy in children, accounting for up to 23% of pediatric epilepsy. The pathogenesis of BECTS is unknown, but it is thought that genetic factors play a role in susceptibility to the disease.

METHODS

To investigate the role of common genetic variants in BECTS pathogenesis, a 2-stage genome-wide association study (GWAS) was performed in 1,800 Chinese Han BECTS patients, and 7,090 healthy controls. Genetic findings were used in a Mendelian Randomization study in the UK Biobank dataset to investigate the potential role of smoking in BECTS.

FINDINGS

Definitive evidence of a role for common-variant heritability was demonstrated, with heritability of BECTS of >10% observed even with conservative disease prevalence assumptions. Although no individual locus achieved genome-wide significance, twelve loci achieved suggestive evidence of association (5 × 10^-8<P<10^-5). Using combined genetic and brain tissue gene expression data analyzed by Summary-data-based Mendelian Randomization (SMR), causative association of BECTS was demonstrated with SNP rs1948 and the CHRNA5 t3603436 transcript (P_eqtl = 2·10 × 10^-12, P_smr = 7·9 × 10^-5). This finding indicates rs1948 is significantly associated with BECTS through effects on expression of CHRNA5 in brain tissue. The identification of novel loci suggests involvements of KALRN and the CHRNA5-A3-B4 cluster in BECTS. Using a generalized SMR approach we demonstrate that maternal smoking around birth is significantly associated with increased risk of BECTS (odds ratio = 3·90, P = 0·0099).

INTERPRETATION

This study shows that BECTS risk is at least partially heritable and due to common genetic variants. Additionally, we demonstrate that BECTS risk is substantially increased by maternal smoking around birth.

Rare gene deletions in genetic generalized and Rolandic epilepsies

Genetic Generalized Epilepsy (GGE) and benign epilepsy with centro-temporal spikes or Rolandic Epilepsy (RE) are common forms of genetic epilepsies. Rare copy number variants have been recognized as important risk factors in brain disorders. We performed a systematic survey of rare deletions affecting protein-coding genes derived from exome data of patients with common forms of genetic epilepsies. We analysed exomes from 390 European patients (196 GGE and 194 RE) and 572 population controls to identify low-frequency genic deletions. We found that 75 (32 GGE and 43 RE) patients out of 390, i.e. ~19%, carried rare genic deletions. In particular, large deletions (>400 kb) represent a higher burden in both GGE and RE syndromes as compared to controls. The detected low-frequency deletions (1) share genes with brain-expressed exons that are under negative selection, (2) overlap with known autism and epilepsy-associated candidate genes, (3) are enriched for CNV intolerant genes recorded by the Exome Aggregation Consortium (ExAC) and (4) coincide with likely disruptive de novo mutations from the NPdenovo database. Employing several knowledge databases, we discuss the most prominent epilepsy candidate genes and their protein-protein networks for GGE and RE.

KANSL1 variation is not a major contributing factor in self-limited focal epilepsy syndromes of childhood

Background

KANSL1 haploinsufficiency causes Koolen-de Vries syndrome (KdVS), characterized by dysmorphic features and intellectual disability; amiable personality, congenital malformations and seizures also commonly occur. The epilepsy phenotypic spectrum in KdVS is broad, but most individuals have focal seizures with some having a phenotype resembling the self-limited focal epilepsies of childhood (SFEC). We hypothesized that variants in KANSL1 contribute to pathogenesis of SFEC.

Materials and methods

We screened KANSL1 for single nucleotide variants in 90 patients with SFEC. We then screened a cohort of 208 patients with two specific SFEC syndromes, childhood epilepsy with centrotemporal spikes (CECTS) and atypical childhood epilepsy with centrotemporal spikes (ACECTS) for KANSL1 variants. The second cohort was also used to evaluate minor allelic variants that appeared overrepresented in the initial cohort.

Results

One variant, p.Lys104Thr, was predicted damaging and appeared overrepresented in our 90-patient cohort compared to Genome Aggregation Database (gnomAD) allele frequency (0.217 to 0.116, with no homozygotes in gnomAD). However, there was no difference in p.Lys104Thr allele frequency in the follow-up CECTS/ACECTS cohort and controls. Four rare KANSL1 variants of uncertain significance were identified in the CECTS/ACECTS cohort.

Discussion

Our data do not support a major role for KANSL1 variants in pathogenesis of SFEC.

Progress in unraveling the genetic etiology of rolandic epilepsy

Rolandic epilepsy (RE), or benign epilepsy of childhood with centrotemporal spikes (BECT), is the most frequent idiopathic partial epilepsy syndrome of childhood, where the "idiopathic" implies a genetic predisposition. Although RE has long been presumed to have a genetic component, clinical and genetic studies have shown a complex inheritance pattern. Furthermore, the underlying major genetic influence in RE has been challenged by recent reports of twin studies. Meanwhile, many genes or loci have been shown to be associated the RE/atypical RE (ARE) spectrum, with a higher frequency of causative variants in ARE. However, a full understanding of the genetic basis in the more common forms of the RE spectrum remains elusive.

[Cognitive deficits are underestimated in children with benign epilepsy with centro-temporal spikes]

Benign epilepsy with centro-temporal spikes (BECTS) is, as the name suggests, usually considered benign. However, there is a growing awareness that this is not the case in all instances. Many of the children with BECTS have neuropsychological and linguistic dysfunctions, even after remission of the disease. In patients with classic BECTS, an association with GRIN2A-mutations is reported by several groups, suggesting a possible placement of BECTS at the mild end of an epileptic-aphasia spectrum. Awareness of the possible neuropsychological consequences of BECTS should be considered when treating these children.

Prioritizing rare variants with conditional likelihood ratios

BACKGROUND

Prioritizing individual rare variants within associated genes or regions often consists of an ad hoc combination of statistical and biological considerations. From the statistical perspective, rare variants are often ranked using Fisher's exact p values, which can lead to different rankings of the same set of variants depending on whether 1- or 2-sided p values are used.

RESULTS

We propose a likelihood ratio-based measure, maxLRc, for the statistical component of ranking rare variants under a case-control study design that avoids the hypothesis-testing paradigm. We prove analytically that the maxLRc is always well-defined, even when the data has zero cell counts in the 2×2 disease-variant table. Via simulation, we show that the maxLRc outperforms Fisher's exact p values in most practical scenarios considered. Using next-generation sequence data from 27 rolandic epilepsy cases and 200 controls in a region previously shown to be linked to and associated with rolandic epilepsy, we demonstrate that rankings assigned by the maxLRc and exact p values can differ substantially.

CONCLUSION

The maxLRc provides reliable statistical prioritization of rare variants using only the observed data, avoiding the need to specify parameters associated with hypothesis testing that can result in ranking discrepancies across p value procedures; and it is applicable to common variant prioritization.

Modify or die?--RNA modification defects in metazoans

Chemical RNA modifications are present in all kingdoms of life and many of these post-transcriptional modifications are conserved throughout evolution. However, most of the research has been performed on single cell organisms, whereas little is known about how RNA modifications contribute to the development of metazoans. In recent years, the identification of RNA modification genes in genome wide association studies (GWAS) has sparked new interest in previously neglected genes. In this review, we summarize recent findings that connect RNA modification defects and phenotypes in higher eukaryotes. Furthermore, we discuss the implications of aberrant tRNA modification in various human diseases including metabolic defects, mitochondrial dysfunctions, neurological disorders, and cancer. As the molecular mechanisms of these diseases are being elucidated, we will gain first insights into the functions of RNA modifications in higher eukaryotes and finally understand their roles during development.

RBFOX1 and RBFOX3 mutations in rolandic epilepsy

Partial deletions of the gene encoding the neuronal splicing regulator RBFOX1 have been reported in a range of neurodevelopmental diseases, including idiopathic generalized epilepsy. The RBFOX1 protein and its homologues (RBFOX2 and RBFOX3) regulate alternative splicing of many neuronal transcripts involved in the homeostatic control of neuronal excitability. In this study, we explored if structural microdeletions and exonic sequence variations in RBFOX1, RBFOX2, RBFOX3 confer susceptibility to rolandic epilepsy (RE), a common idiopathic focal childhood epilepsy. By high-density SNP array screening of 289 unrelated RE patients, we identified two hemizygous deletions, a 365 kb deletion affecting two untranslated 5′-terminal exons of RBFOX1 and a 43 kb deletion spanning exon 3 of RBFOX3. Exome sequencing of 242 RE patients revealed two novel probably deleterious variants in RBFOX1, a frameshift mutation (p.A233Vfs*74) and a hexanucleotide deletion (p.A299_A300del), and a novel nonsense mutation in RBFOX3 (p.Y287*). Although the three variants were inherited from unaffected parents, they were present in all family members exhibiting the RE trait clinically or electroencephalographically with only one exception. In contrast, no deleterious mutations of RBFOX1 and RBFOX3 were found in the exomes of 6503 non-RE subjects deposited in the Exome Variant Server database. The observed RBFOX3 exon 3 deletion and nonsense mutation suggest that RBFOX3 represents a novel risk factor for RE, indicating that exon deletions and truncating mutations of RBFOX1 and RBFOX3 contribute to the genetic variance of partial and generalized idiopathic epilepsy syndromes.

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.

The genetics of reading disability in an often excluded sample: novel loci suggested for reading disability in Rolandic epilepsy

BACKGROUND

Reading disability (RD) is a common neurodevelopmental disorder with genetic basis established in families segregating "pure" dyslexia. RD commonly occurs in neurodevelopmental disorders including Rolandic Epilepsy (RE), a complex genetic disorder. We performed genomewide linkage analysis of RD in RE families, testing the hypotheses that RD in RE families is genetically heterogenenous to pure dyslexia, and shares genetic influences with other sub-phenotypes of RE.

METHODS

We initially performed genome-wide linkage analysis using 1000 STR markers in 38 US families ascertained through a RE proband; most of these families were multiplex for RD. We analyzed the data by two-point and multipoint parametric LOD score methods. We then confirmed the linkage evidence in a second US dataset of 20 RE families. We also resequenced the SEMA3C gene at the 7q21 linkage locus in members of one multiplex RE/RD pedigree and the DISC1 gene in affected pedigrees at the 1q42 locus.

RESULTS

In the discovery dataset there was suggestive evidence of linkage for RD to chromosome 7q21 (two-point LOD score 3.05, multipoint LOD 3.08) and at 1q42 (two-point LOD 2.87, multipoint LOD 3.03). Much of the linkage evidence at 7q21 derived from families of French-Canadian origin, whereas the linkage evidence at 1q42 was well distributed across all the families. There was little evidence for linkage at known dyslexia loci. Combining the discovery and confirmation datasets increased the evidence at 1q42 (two-point LOD = 3.49, multipoint HLOD = 4.70), but decreased evidence at 7q21 (two-point LOD = 2.28, multipoint HLOD  = 1.81), possibly because the replication sample did not have French Canadian representation.

DISCUSSION

Reading disability in rolandic epilepsy has a genetic basis and may be influenced by loci at 1q42 and, in some populations, at 7q21; there is little evidence of a role for known DYX loci discovered in "pure" dyslexia pedigrees. 1q42 and 7q21 are candidate novel dyslexia loci.

Seizure in benign epilepsy with centro-temporal spikes

Rolandic epilepsy is frequent in children but seizures are rarely seen by the physician or captured by video-EEG monitoring. In most children the attacks are few and sporadic and generally occur at night. Also, a high percentage of children with benign epilepsy with centro-temporal spikes (BECTS) have characteristic centro-temporal spikes based on routine EEG monitoring and therefore do not require further tests such as telemetry or sleep studies. We report a video-EEG recording of a seizure in a patient with rolandic epilepsy which may be useful for educational purposes.

High risk of reading disability and speech sound disorder in rolandic epilepsy families: case-control study

PURPOSE

Associations between rolandic epilepsy (RE) with reading disability (RD) and speech sound disorder (SSD) have not been tested in a controlled study. We conducted a case-control study to determine whether (1) RD and SSD odds are higher in RE probands than controls and (2) an RE proband predicts a family member with RD or SSD, hence suggesting a shared genetic etiology for RE, RD, and SSD.

METHODS

Unmatched case-control study with 55 stringently defined RE cases, 150 controls in the same age range lacking a primary brain disorder diagnosis, and their siblings and parents. Odds ratios (OR) were calculated by multiple logistic regression, adjusted for sex and age, and for relatives, also adjusted for comorbidity of RD and SSD in the proband.

RESULTS

RD was strongly associated with RE after adjustment for sex and age: OR 5.78 (95% CI: 2.86-11.69). An RE proband predicts RD in family members: OR 2.84 (95% CI: 1.38-5.84), but not independently of the RE proband's RD status: OR 1.30 (95% CI: 0.55-12.79). SSD was also comorbid with RE: adjusted OR 2.47 (95%CI: 1.22-4.97). An RE proband predicts SSD in relatives, even after controlling for sex, age and proband SSD comorbidity: OR 4.44 (95% CI: 1.93-10.22).

CONCLUSIONS

RE is strongly comorbid with RD and SSD. Both RD and SSD are likely to be genetically influenced and may contribute to the complex genetic etiology of the RE syndrome. Siblings of RE patients are at high risk of RD and SSD and both RE patients and their younger siblings should be screened early.

Autosomal dominant inheritance of centrotemporal sharp waves in rolandic epilepsy families

PURPOSE

Centrotemporal sharp (CTS) waves, the electroencephalogram (EEG) hallmark of rolandic epilepsy, are found in approximately 4% of the childhood population. The inheritance of CTS is presumed autosomal dominant but this is controversial. Previous studies have varied considerably in methodology, especially in the control of bias and confounding. We aimed to test the hypothesis of autosomal dominant inheritance of CTS in a well-designed family segregation analysis study.

METHODS

Probands with rolandic epilepsy were collected through unambiguous single ascertainment. Siblings in the age range 4-16 years underwent sleep-deprived EEG; observations from those who remained awake were omitted. CTS were rated as present or absent by two independent observers blinded to the study hypothesis and subject identities. We computed the segregation ratio of CTS, corrected for ascertainment. We tested the segregation ratio estimate for consistency with dominant and recessive modes of inheritance, and compared the observed sex ratio of those affected with CTS for consistency with sex linkage.

RESULTS

Thirty siblings from 23 families underwent EEG examination. Twenty-three showed evidence of sleep in their EEG recordings. Eleven of 23 recordings demonstrated CTS, yielding a corrected segregation ratio of 0.48 (95% CI: 0.27-0.69). The male to female ratio of CTS affectedness was approximately equal.

CONCLUSIONS

The segregation ratio of CTS in rolandic epilepsy families is consistent with a highly penetrant autosomal dominant inheritance, with equal sex ratio. Autosomal recessive and X-linked inheritance are rejected. The CTS locus might act in combination with one or more loci to produce the phenotype of rolandic epilepsy.

Coexistence of Idiopathic Rolandic Epilepsy and CSWS in Two Families

PURPOSE

To report two families combining benign childhood epilepsy with centrotemporal spikes (BCECS) and cryptogenic epilepsy with continuous spike-waves during sleep (CSWS) in first-degree relatives.

METHODS

Clinical, EEG, and cerebral imaging data are described.

RESULTS

FAMILY 1: The proband was 3 years old at epilepsy onset. First seizures were convulsive, with centrotemporal spikes on EEG. At age 5 years, he had complex partial seizures, psychomotor regression, and centrotemporal CSWS. [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) showed left parietal hypermetabolism. After several antiepileptic drug (AED) trials, valproate (VPA) and ethosuximide (ESM) induced seizure remission, CSWS disappearance, and psychomotor improvement. Learning disabilities, however, persisted. Family history was remarkable for BCECS in his father. FAMILY 2: The proband was 2 years old at epilepsy onset. First seizures were convulsive, with centrotemporal CSWS on EEG. Despite several AED trials including corticosteroids, focal negative myoclonia, atypical absences, and psychomotor regression occurred, leading to severe mental retardation. FDG-PET showed bilateral parietal hypermetabolism. Vagus nerve stimulator was implanted. Her family history was remarkable for BCECS in her father and febrile convulsions in infancy in her mother.

CONCLUSIONS

These data suggest the existence of a common genetic basis between BCECS and cryptogenic epilepsies with CSWS. The higher expression in patients with CSWS could be related to other genetic or acquired factors. These data suggest that these epileptic syndromes constitute edges of a continuum.

Analyzing the etiology of benign rolandic epilepsy: a multicenter twin collaboration

PURPOSE

Benign rolandic epilepsy (BRE) is considered a genetically determined idiopathic partial epilepsy. We analyzed a large sample of twins from four international twin registers to probe the genetics of BRE. We also aim to synthesize the apparently conflicting family and twin data into a model of BRE etiology.

METHODS

Large population-based twin registries of epilepsies from Odense (Denmark), Richmond, Virginia (United States), and Oslo (Norway) were reviewed for BRE cases and added to our Australian twin data. Diagnosis of classic BRE was based on electroclinical criteria with normal neurologic development. Cases with a compatible electroclinical picture but abnormal neurologic development were termed non-classic BRE.

RESULTS

Eighteen twin pairs were identified (10 monozygous; eight dizygous) of whom at least one twin was diagnosed with classic BRE among a total sample of 1,952 twin pairs validated for seizures, and all were discordant for BRE. The estimated monozygous pairwise concordance for BRE in this sample was 0.0 [95% confidence interval (CI), 0.0-0.3). Four twin pairs (one monozygous, three dizygous) had non-classic BRE, and all co-twins had seizures.

CONCLUSIONS

The twin data showing an absence of any concordant twin pairs with classic BRE suggest that noninherited factors are of major importance in BRE. Modelling the data shows that the familial occurrence of centrotemporal spikes makes only a minor contribution to the familial aggregation of BRE. Genetic factors are probably more important in non-classic BRE. The etiology and mode(s) of inheritance of BRE are much more complicated than initially conceptualized.

SRPX2 mutations in disorders of language cortex and cognition

The rolandic and sylvian fissures divide the human cerebral hemispheres and the adjacent areas participate in speech processing. The relationship of rolandic (sylvian) seizure disorders with speech and cognitive impairments is well known, albeit poorly understood. We have identified the Xq22 gene SRPX2 as being responsible for rolandic seizures (RSs) associated with oral and speech dyspraxia and mental retardation (MR). SRPX2 is a secreted sushi-repeat containing protein expressed in neurons of the human adult brain, including the rolandic area. The disease-causing mutation (N327S) resulted in gain-of-glycosylation of the secreted mutant protein. A second mutation (Y72S) was identified within the first sushi domain of SRPX2 in a male with RSs and bilateral perisylvian polymicrogyria and his female relatives with mild MR or unaffected carrier status. In cultured cells, both mutations were associated with altered patterns of intracellular processing, suggesting protein misfolding. In the murine brain, Srpx2 protein expression appeared in neurons at birth. The involvement of SRPX2 in these disorders suggests an important role for SRPX2 in the perisylvian region critical for language and cognitive development.

Síndrome peri-sylviana: estudo de uma família brasileira com ênfase na modalidade de transmissão genética e espectro clínico

Síndrome peri-sylviana (SP) refere-se a diversas manifestações clínicas que podem acompanhar lesões que comprometem a região peri-sylviana ou opercular, podendo ser adquirida, como em acidentes vasculares cerebrais ou encefalites virais, ou ser congênita. A SP congênita pode se manifestar com grande variação clínica e em idades precoces. Com o advento da ressonância magnética (RM) foi possível observar a presença de polimicrogiria (PMG) na região da fissura de Sylvius em diversos pacientes com quadro clínico de SP. O objetivo do presente estudo é analisar e divulgar essa entidade raramente diagnosticada por meio da descrição de uma família. A família em questão compõe-se de cinco indivíduos acometidos, sendo o distúrbio de linguagem a manifestação mais prevalente, ou seja, presente em todos eles. Epilepsia, déficit motor e sinais pseudobulbares (como sialorréia) foram evidenciados no paciente que mostrou maior alteração à RM (PMG difusa). A paciente com PMG parietal posterior e os outros três com RM normais tiveram manifestações clínicas mais sutis. Apesar da maioria das famílias descritas até o momento apresentar transmissão ligada ao cromossomo X, a nossa família sugere transmissão autossômica dominante, já que dois meninos afetados são filhos de homens também acometidos. Os nossos dados reforçam a idéia de que a SP apresenta heterogeneidade genética.

Benigne epilepsietypische Potentiale des Kindesalters (Rolando-Spikes) - neurobiologische und neuropsychologische Befunde und ihre klinische Bedeutung in der Kinder- und Jugendpsychiatrie

Zusammenfassung: Einleitung: Die Rolando-Epilepsie ist das häufigste Epilepsie-Syndrom im Kindesalter. Sie ist elektroenzephalographisch charakterisiert durch das Auftreten von fokalen epilepsietypischen Potentialen, den sog. Rolando-Spikes (benigne epilepsietypische Potentiale des Kindesalters, BEPK). BEPK treten mit einer Häufigkeit von etwa 1,5 bis 2,4% bei Kindern auf; nur ein Zehntel erleidet epileptische Anfälle. Methoden: Diese Arbeit gibt einen Überblick über genetische, epidemiologische, radiologische, neurophysiologische, metabolische und neuropsychologische Befunde bei Kindern mit BEPK. Resultate: Der epileptologische Verlauf ist günstig, eventuell auftretende Anfälle sistieren spätestens mit der Pubertät; die epilepsietypischen Potentiale sind dann nicht mehr nachweisbar. Entgegen früherer Annahmen erstreckt sich das Symptomenspektrum über seltene Anfälle hinaus auf neuropsychologische Beeinträchtigungen und Verhaltensauffälligkeiten, auch bei Kindern ohne manifeste Anfälle. Der Einfluss der Rolando-Spikes auf die Entwicklung betroffener Kinder und ihr Verhalten ist unklar. Durch zwei Modelle wird versucht, den Zusammenhang von paroxysmaler EEG-Aktivität und neuropsychologischen Auffälligkeiten zu erklären. Das erste betrachtet die beobachtbaren Defizite als vorübergehende kognitive Beeinträchtigung infolge der epileptischen Aktivität; das zweite sieht als Ursache eine genetisch bedingte zerebrale Reifungsstörung mit enger Verwandtschaft zu Teilleistungsstörungen. Schlussfolgerung: Die Behandlungsnotwendigkeit neuropsychiatrischer Symptome bei Kindern mit BEPK ohne manifeste Anfälle wird derzeit kontrovers diskutiert.

Is benign rolandic epilepsy genetically determined?

Benign rolandic epilepsy (BRE) is considered to be a genetically determined idiopathic partial epilepsy. We studied twins with BRE and compared the concordance with a twin sample of idiopathic generalized epilepsy (IGE). All eight BRE pairs (six monozygous [MZ], two dizygous [DZ]) were discordant. MZ pairwise concordance was 0 (95% confidence interval [CI], 0-0.4) for BRE compared with 0.7 (95% CI, 0.5-0.9) for 26 IGE MZ pairs. Our data suggest that conventional genetic influences in BRE are considerably less than for IGE, and other mechanisms need to be explored.

Genetic identifiers of epilepsy

Epilepsy affects >0.5% of the world's population and has a large genetic component. The most common human genetic epilepsies display a complex pattern of inheritance, and the identity of the susceptibility genes is largely unknown despite recent advances in molecular biology. However, genetic identifiers of certain types of epilepsy with neurodegenerative characteristics and of a small number of familial idiopathic epilepsies have been uncovered to date. This article reviews recent progress made in molecular genetics of epilepsy, focusing mostly on idiopathic epilepsy together with our own discovery of novel mutations in the genes of autosomal dominant nocturnal frontal lobe epilepsy and benign familial neonatal convulsions (BFNCs), and the genetic locus of benign adult familial myoclonic epilepsy. Pathogenesis of epilepsy as a channelopathy and of BFNC also is discussed.

A Rett patient with a typical Angelman EEG

PURPOSE

To draw attention to the phenomenon that EEG characteristics of both Angelman syndrome (AS) and Rett syndrome (RS) can be found in the same patient, as evidenced by the description of one case. There are specific EEG patterns in AS patients, in which the most frequently occurring EEG characteristics are rhythmic triphasic 2- to 3-Hz, high-voltage (200-500 microV) activity, mixed with spikes or sharp waves, with a maximum over the frontal regions. EEG changes in RS patients are less specific and can show multifocal, mostly central or centrotemporal epileptiform discharges in combination with slow background activity.

METHODS

A 6-year-old girl with RS and a proven MECP2 mutation was described.

RESULTS

She had an EEG pattern at age 2 years comparable with the clinical diagnosis of RS, and an EEG at age 6 years comparable with an AS EEG.

CONCLUSIONS

We wish to draw attention to this phenomenon, although there is as yet no evident explanation for it. We advise MECP2 examination in AS patients of unknown genetic etiology whose EEG examinations are/were pathognomonic for AS to exclude RS.

Epilepsy in fragile X syndrome

Epilepsy is reported to occur in 10 to 20% of individuals with fragile X syndrome (FXS). A frequent seizure/EEG pattern in FXS appears to resemble that of benign focal epilepsy of childhood (BFEC, benign rolandic epilepsy). To evaluate seizure frequency and type in a Chicago FXS cohort, data regarding potential seizure history were reviewed for 136 individuals with FXS (age range 2 to 51 years: 113 males and 23 females). Seizures occurred in 15 males (13.3%) and one female (4.8%): of these, 12 had partial seizures. EEG findings were available for 35 individuals (13 of 16 with seizures and 22 of 120 without seizures) and showed an epileptiform abnormality in 10 (77%) individuals with seizures and five (23%) individuals without seizures--the most common epileptiform pattern being centrotemporal spikes. Seizures were easily controlled in 14 of the 16 individuals with seizures. Many individuals, including all with centrotemporal spikes, had remission of seizures in childhood. The most common seizure syndrome resembled BFEC and this pattern had the best prognosis for epilepsy remission. Deficiency of FMRP (fragile X mental retardation protein) appears to lead to increased neuronal excitability and susceptibility to epilepsy, but particularly seems to facilitate mechanisms leading to the BFEC pattern.

Autosomal dominant rolandic epilepsy with speech dyspraxia

Autosomal Dominant Rolandic Epilepsy with Speech Dyspraxia (ADRESD) is a rare disorder which highlights the relationship between Benign Rolandic Epilepsy (BRE) and speech and language disorders. Subtle speech and language disorders have recently been well characterised in BRE. ADRESD is associated with long term, more severe speech and language difficulties. The time course of rolandic epilepsy in ADRESD is typical of that of BRE. ADRESD is inherited in an autosomal dominant manner with anticipation. It is postulated that the anticipation may be due to an, as yet unidentified, triplet repeat expansion in a gene for rolandic epilepsy. BRE follows complex inheritance but it is possible that ADRESD may hold some valuable clues to the pathogenesis of BRE.

The genetics of rolandic epilepsy

Focal spikes and sharp waves with predominantly centrotemporal localization are the electroencephalograhic hallmark of Rolandic epilepsy (or BECTS). This EEG trait, but not BECTS itself, has been reported to follow an autosomal dominant mode of inheritance with incomplete penetrance and age dependency. CTS therefore may represent a neurobiological marker for the increased risk of developing BECTS. Several linkage studies exploring candidate loci have rendered negative results. The first positive evidence for linkage in families with centrotemporal spikes was found on chromosome 15q14.

Mutation analysis of the potassium chloride cotransporter KCC3 (SLC12A6) in rolandic and idiopathic generalized epilepsy

Genetic predisposition plays a major role in the etiology of idiopathic epilepsies. The common epilepsy syndromes display a complex pattern of inheritance, with an unknown number of genes contributing to seizure susceptibility. During the last decade linkage studies have narrowed down several candidate regions for susceptibility loci of idiopathic epilepsies. Several lines of evidence point to the existence of an epilepsy susceptibility gene on chromosome 15q14. Evidence for linkage to this region has thus been reported for juvenile myoclonic epilepsy, common subtypes of idiopathic generalized epilepsy (IGE), in addition to the EEG trait 'centrotemporal spikes' in families with rolandic epilepsy. The chromosomal region 15q14 harbours several candidate genes that are involved in the regulation of neuronal excitability. One of the most promising candidate genes is the brain-expressed potassium chloride cotransporter KCC3, given that this class of ion transporter has been implicated in the regulation of neuronal chloride activity. We therefore performed a mutation analysis of KCC3 in the index patients of 23 IGE-families as well as of 16 families with rolandic epilepsy which where selected by positive evidence for linkage to D15S165. Four novel single nucleotide exchanges (SNPs) were identified, none of which change the coding sequence. These results do not support a major role for KCC3 in the etiology of rolandic epilepsy or common subtypes of IGE.

Atypical "benign" partial epilepsy of childhood or pseudo-lennox syndrome. Part II: family study

Atypical benign partial epilepsy of childhood (ABPE = Pseudo-Lennox syndrome) shows semiologic parallels to Lennox-Gastaut syndrome, however--besides the lack of tonic seizures--it has an entirely different etiology and prognosis. Recently Hahn et al [17] investigated the long-term evolution of 43 cases with ABPE. Symptomatology, EEG findings, and course were found to overlap with Rolandic epilepsy, Landau-Kleffner syndrome and ESES. The incidence of seizures in relatives was determined in the whole series investigated by Hahn et al [17]. Five of 56 siblings suffered from seizures (3 Rolandic seizures; one febrile convulsions; one unclassified). Three fathers reported grand mal. In 29 families of the series of Hahn et al EEG recordings were performed: 22 brothers, 19 sisters and 16 pairs of parents. In 29% of the siblings a sharp wave focus was demonstrable. The rate rose to 40% when only siblings investigated at the age of maximum expression (3 to 10 years) were considered. Sharp wave foci were mostly multifocal and indistinguishable from those observed in siblings of children with Rolandic epilepsy. Photoparoxysmal response and generalized spikes and waves during rest and hyperventilation were also found to be significantly elevated (26% and 13% respectively). We conclude that ABPE is a subgroup of idiopathic partial epilepsy of childhood (representing a less benign part of a spectrum) that has to be ranked in a continuum with Rolandic epilepsy. The different clinical phenotype might be caused by a higher expressivity of the identical genetic trait, possibly facilitated by other genetic or acquired factors. Genetic heterogeneity represents another possibility.

Familial paroxysmal exercise-induced dyskinesia and benign epilepsy: a clinical and neurophysiological study of an uncommon disorder

We report a family with 6 members affected by a long-lasting paroxysmal exertion-induced dyskinesia. Fasting and stress were precipitating factors. All the patients of this family had also epileptic seizures mainly of generalised type with a favourable outcome. All patients were submitted to a neurophysiological study which included somatosensory evoked potentials by median nerve stimulation (MN-SEPs), somatosensory evoked potentials by posterior tibial nerve stimulation (PTN-SEPs), brainstem auditory evoked potentials (BAEPs), visual evoked potentials (VEPs), motor evoked potentials (MEPs) by magnetic transcranial cortical stimulation (TCS) and electromyography (EMG). The neurophysiological findings suggest a hyperexcitability at the muscular and brain membrane levels, probably due to an ion channel disorder.

Can protrusion of the tongue stop seizures in Rolandic epilepsy?

We report the case of a child with benign partial epilepsy with centro-temporal spikes (BECT) in whom protrusion of the tongue stopped the interictal abnormalities, and describe the polygraphic EEG recording of a seizure which terminated upon voluntary protrusion of the tongue. We mention the close link between the post-central (somatosensory) cortex and pre-central (motor) cortex, and how the primary sensory area has direct access to the motor cortex. We also examine how a tactile stimulus may provoke the inhibition of an epileptic discharge.

[Opercular epileptic syndrome: an unusual form of benign partial epilepsy in childhood]

INTRODUCTION

Functional opercular syndrome in childhood is an exceptional form of presentation of benign partial epilepsy with centro-temporal rolandic spikes (BECRS).

CLINICAL CASES

We studied the evolution of four patients, three of them followed for more than 15 years. Two were siblings, and their father suffered from BECRS with permanent language problems (verbal dyspraxia) and difficulty of protunding his tongue in adulthood. A third patient suffered benign familial neonatal convulsions (BFNC). In all four patients the actual illness begun as a BECRS with opercular troubles as an ictal phenomena. At about four years of age, the opercular disfunction became evident, with severe drooling, facial hypomobility and speech disturbance which waxed and vanished along weeks, months or years, apparently not ictal. Antiepileptic drugs not only were unable to control this situation but also, some of them, like carbamazepine, even worsened the opercular disfunction, increased the number of seizures and enhanced the neuropsychologic disfunction. Only clobazam could achieve the control on opercular disfunction. After 16 years, no further treatment was needed for all patients. There were some permanent sequelae, as speech and orolingual dyspraxia and different neuropsychologic problems.

CONCLUSION

Of noteworth the best performance was attained by the patient treated with clobazam on monotherapy.

Autistic regression with rolandic spikes

OBJECTIVE

This study was designed to further define the electroencephalographic abnormalities seen in the Landau-Kleffner syndrome variants and the associated clinical features.

BACKGROUND

Landau-Kleffner syndrome is rare, but its putative variants are more common.

METHOD

We report two patients with centro-temporal spikes, autistic epileptiform regression, and variably prominent oro-motor symptoms.

RESULTS

The epileptic aphasia pattern found among patients with prominent Rolandic spikes may more frequently involve expressive language than is seen in the typical Landau-Kleffner syndrome, where verbal auditory agnosia is the rule.

CONCLUSIONS

This clinical difference likely reflects the location of the epileptiform activity (centrotemporal as opposed to anterior or mid-temporal) on buccal-lingual function, vocalization, and language production.

[Diagnosis and treatment of Rolandic epilepsy]

Rolandic epilepsy belongs to the most frequent forms of epilepsy in children. 43 patients aged 2-14 years were observed. Complex neurologic, genealogic, neurophysiologic and neuroradiologic examinations was performed. There was a microfocal symptomatology in the form of ptosis and syndrome of infantile cerebral paralysis. The changes found at neuroradiologic examination were not related to the location of an epileptic focus and didn't influence the prognosis of the disease. In 10 cases electroencephalographic patterns were observed in clinically healthy relatives. In all the patients a remission of the fits was achieved. Administration of low doses (20 mg/kg daily) of valproic acid (depakin) resulted in a remission of the fits.

Autosomal recessive rolandic epilepsy with paroxysmal exercise-induced dystonia and writer's cramp: delineation of the syndrome and gene mapping to chromosome 16p12-11.2

We describe a pedigree in which 3 members in the same generation are affected by Rolandic epilepsy (RE), paroxysmal exercise-induced dystonia (PED), and writer's cramp (WC). Both the seizures and paroxysmal dystonia had a strong age-related expression that peaked during childhood, whereas the WC, also appearing in childhood, has been stable since diagnosis. Genome-wide linkage analysis performed under the assumption of recessive inheritance identified a common homozygous haplotype in a critical region spanning 6 cM between markers D16S3133 and D16S3131 on chromosome 16, cosegregating with the affected phenotype and producing a multipoint LOD score value of 3.68. Although its features are unique, this syndrome presents striking analogies with the autosomal dominant infantile convulsions and paroxysmal coreoathetosis (ICCA) syndrome, linked to a 10 cM region between D16S401 and D16S517, which entirely includes the 6 cM of the RE-PED-WC critical region. The same gene may be responsible for both RE-PED-WC and ICCA, with specific mutations explaining each of these Mendelian disorders. This report shows that idiopathic focal disorders such as epilepsy and dystonia, can be caused by the same genetic abnormality, may have a transient expression, and may be inherited as an autosomal recessive trait.

Centrotemporal spikes in families with rolandic epilepsy: linkage to chromosome 15q14

OBJECTIVE

To localize a gene predisposing to benign epilepsy of childhood with centrotemporal spikes (BECTS).

BACKGROUND

BECTS, or rolandic epilepsy, is the most prevalent idiopathic epilepsy syndrome in childhood. Functional relevant defects in the alpha 4 subunit of the neuronal nicotinic acetylcholine receptor (AChR) have been demonstrated in autosomal dominant nocturnal frontal lobe epilepsy, which, like BECTS, is an idiopathic partial epilepsy.

METHODS

A DNA linkage study was conducted screening all chromosomal regions known to harbor neuronal nicotinic AChR subunit genes. Twenty-two nuclear families with BECTS were analyzed.

RESULTS

In an "affected-only" study, best p values and lod scores were reached between D15S165 and D15S1010 on chromosome 15q14. In multipoint nonparametric linkage analysis a nominal p value of 0.000494 was calculated by GENEHUNTER. Best parametric results were obtained under an autosomal recessive model with heterogeneity (multipoint lod score 3.56 with 70% of families linked to the locus). These markers are localized in direct vicinity to the alpha 7 subunit gene of the AChR.

CONCLUSIONS

We found evidence for linkage of BECTS to a region on chromosome 15q14. Either the alpha 7 AChR subunit gene or a closely linked gene are implicated in pedigrees with BECTS. The disorder is genetically heterogeneous. Surprisingly, the same chromosomal area has been reported to be linked to the phenotype in families with an auditory neurophysiologic deficit as well as in families with juvenile myoclonic epilepsy, another idiopathic but generalized epilepsy syndrome.

Children with focal sharp waves: clinical and genetic aspects

PURPOSE

To investigate the spectrum of clinical manifestations in children with benign focal sharp waves in the EEG to gain further insight into the genetic background of clinical and EEG symptomatology in a family study.

METHODS

All 147 children (134 with seizures, 13 without) met the following inclusion criteria: (a) at least one EEG with focal sharp waves characteristic of benign partial epilepsies, and (b) at least 1 sibling investigated by EEG. The families were questioned orally or in writing regarding the occurrence of seizures. Patients' records were evaluated by a standardized scheme.

RESULTS

The following types of seizures occurred: febrile convulsions (FC), afebrile generalized tonic-clonic seizures (GTCS), simple and (rarely) complex partial seizures; and rolandic seizures in the strict sense. Neonatal seizures were overrepresented (6%); there were no indications of lesional causes. FC occurred in 38 children (26%). As compared with unselected cases of FC, complex symptoms were overrepresented. Family data suggested a maternal preponderance in the transmission of FC liability. Affected relatives of FC probands manifested FC more often than did relatives of probands without FC. Families of 32 patients with typical rolandic seizures (24% of the 134 probands with seizures) showed no aggregation of rolandic epilepsy, but did show variable seizure types. In the entire sample, EEG investigations showed focal sharp waves in 11% of siblings aged 2-10 years. No relation existed between clinical symptomatology and sharp wave findings in siblings. In 66% of probands, the EEG disclosed generalized genetic patterns. Siblings with generalized spike-waves (sw) and/or theta rhythm had focal sharp waves more often than those without sw and/or theta rhythm.

CONCLUSIONS

The phenotypic expression of the genetic anomaly underlying focal sharp waves shows considerable variability. The clinical and EEG findings are in agreement with a multifactorial pathogenesis of epilepsies with "benign" focal epileptiform sharp waves.

Benign childhood epilepsy with centrotemporal spikes and electroencephalography trait are not linked to EBN1 and EBN2 of benign neonatal familial convulsions

PURPOSE

The electroencephalographic hallmark of benign childhood epilepsy with centrotemporal spikes (BECTS, or rolandic epilepsy) are characteristically shaped centrotemporal spikes and sharp waves (CTS). This EEG trait, but not BECTS itself, has been reported to follow an autosomal dominant mode of inheritance with incomplete penetrance and age dependence. CTS therefore represents a neurobiologic marker for the increased risk of developing BECTS. Benign neonatal familial convulsions (BNFC) like BECTS is an idiopathic age-dependent epilepsy with a benign course. Observations of benign neonatal seizures and BECTS in the same individual are well documented. Neonatal seizures with benign course were found in increased numbers in a series of CTS carriers. Two genetic loci, EBN1 and EBN2, have been mapped in families with BNFC, making these two loci strong candidates for the CTS trait underlying BECTS. The aim of this study was to determine whether these two epilepsy syndromes are allelic disorders.

METHODS

Linkage analysis was performed in 12 families with probands with BECTS and one or more relatives with CTS in the EEG with or without BECTS by using polymorphic DNA markers.

RESULTS

Assuming an autosomal mode of inheritance with penetrances of 0.9 and 0.45, respectively, both loci were consistently excluded.

CONCLUSIONS

The CTS trait and EBN1 and EBN2 segregate independently. BECTS and BNFC therefore appear to be genetically distinct entities. Benign neonatal seizures may be a underrecognized symptom of the CTS trait itself.

Similarities of EEG and seizures in del(1q) and benign rolandic epilepsy

We studied the seizure disorders manifested by three previously reported children with "de novo" terminal deletions of the long arm of chromosome 1 (46,XX,del(1)(q43)) and similar clinical phenotypes. In late infancy, two of these children developed partial seizures characterized by tonic-clonic movements of the ipsilateral face and arm with occasional involvement of the leg. In both children, the seizure frequency decreased with increasing age. Electroencephalograms of these two children demonstrated centrotemporal spike discharges morphologically similar to rolandic spikes. Although these cases present significant similarities to benign rolandic epilepsy, they also express many manifestations not detected in benign rolandic epilepsy that may reflect the extensive deletion of chromosome 1. Based on the seizure semiology and centrotemporal epileptiform discharges, we suggest that the distal portion of the long arm of chromosome 1 is a potential site for a candidate gene for benign rolandic epilepsy.

Children with benign focal sharp waves in the EEG--developmental disorders and epilepsy

Focal sharp waves (shw) in the childhood EEG with predominantly centrotemporal localization are a diagnostic hallmark of idiopathic partial epilepsy and have been shown to be genetically determined. Absence of neurological and neuropsychological impairment was long considered to be a prerequisite for diagnosis. For years, this diagnostic paradigm obscured the large phenotypic variability of genetically determined focal shw. The purpose of the present review is to survey and critically evaluate the widely dispersed literature on this topic. Two main groups can be distinguished: Idiopathic partial epilepsies and specific developmental disorders such as dysphasia, dyslexia etc. These conditions, however, do not represent clear-cut nosologic entities, but exhibit large symptomatic overlaps. In non-epileptic children, developmental disabilities constitute the main symptoms, in epileptic children-at least in non-selected groups-they are an optional feature. Conversely, epileptic phenomena can dominate the clinical picture or be an optional symptom in developmentally disabled children. The wide spectrum of epileptic and non-epileptic disorders probably represents the multifarious clinical manifestations of a common widespread, genetically determined pathogenetic mechanism. The marked age-dependency of the EEG and clinical symptoms, and the almost regular disappearance of both at puberty appear to justify the hypothesis of a hereditary impairment of brain maturation. The large phenotypic variability can be explained by differences in location and extent of the maturational disturbance as well as by the effect of additional genetic and environmental factors. The nature and cause of the hypothetical maturational disturbance are still unknown.