Bi-allelic GAD1 variants cause a neonatal onset syndromic developmental and epileptic encephalopathy.

Developmental and epileptic encephalopathies are a heterogeneous group of early-onset epilepsy syndromes dramatically impairing neurodevelopment. Modern genomic technologies have revealed a number of monogenic origins and opened the door to therapeutic hopes. Here we describe a new syndromic developmental and epileptic encephalopathy caused by bi-allelic loss-of-function variants in GAD1, as presented by 11 patients from six independent consanguineous families. Seizure onset occurred in the first 2 months of life in all patients. All 10 patients, from whom early disease history was available, presented with seizure onset in the first month of life, mainly consisting of epileptic spasms or myoclonic seizures. Early EEG showed suppression-burst or pattern of burst attenuation or hypsarrhythmia if only recorded in the post-neonatal period. Eight patients had joint contractures and/or pes equinovarus. Seven patients presented a cleft palate and two also had an omphalocele, reproducing the phenotype of the knockout Gad1-/- mouse model. Four patients died before 4 years of age. GAD1 encodes the glutamate decarboxylase enzyme GAD67, a critical actor of the γ-aminobutyric acid (GABA) metabolism as it catalyses the decarboxylation of glutamic acid to form GABA. Our findings evoke a novel syndrome related to GAD67 deficiency, characterized by the unique association of developmental and epileptic encephalopathies, cleft palate, joint contractures and/or omphalocele.

Testing association of rare genetic variants with resistance to three common antiseizure medications.

OBJECTIVE: Drug resistance is a major concern in the treatment of individuals with epilepsy. No genetic markers for resistance to individual antiseizure medication (ASM) have yet been identified. We aimed to identify the role of rare genetic variants in drug resistance for three common ASMs: levetiracetam (LEV), lamotrigine (LTG), and valproic acid (VPA). METHODS: A cohort of 1622 individuals of European descent with epilepsy was deeply phenotyped and underwent whole exome sequencing (WES), comprising 575 taking LEV, 826 LTG, and 782 VPA. We performed gene- and gene set-based collapsing analyses comparing responders and nonresponders to the three drugs to determine the burden of different categories of rare genetic variants. RESULTS: We observed a marginally significant enrichment of rare missense, truncating, and splice region variants in individuals who were resistant to VPA compared to VPA responders for genes involved in VPA pharmacokinetics. We also found a borderline significant enrichment of truncating and splice region variants in the synaptic vesicle glycoprotein (SV2) gene family in nonresponders compared to responders to LEV. We did not see any significant enrichment using a gene-based approach. SIGNIFICANCE: In our pharmacogenetic study, we identified a slightly increased burden of damaging variants in gene groups related to drug kinetics or targeting in individuals presenting with drug resistance to VPA or LEV. Such variants could thus determine a genetic contribution to drug resistance.

Neuronal mechanisms of mutations in SCN8A causing epilepsy or intellectual disability.

Ion channel mutations can cause distinct neuropsychiatric diseases. We first studied the biophysical and neurophysiological consequences of four mutations in the human Na+ channel gene SCN8A causing either mild (E1483K) or severe epilepsy (R1872W), or intellectual disability and autism without epilepsy (R1620L, A1622D). Only combined electrophysiological recordings of transfected wild-type or mutant channels in both neuroblastoma cells and primary cultured neurons revealed clear genotype-phenotype correlations. The E1483K mutation causing mild epilepsy showed no significant biophysical changes, whereas the R1872W mutation causing severe epilepsy induced clear gain-of-function biophysical changes in neuroblastoma cells. However, both mutations increased neuronal firing in primary neuronal cultures. In contrast, the R1620L mutation associated with intellectual disability and autism-but not epilepsy-reduced Na+ current density in neuroblastoma cells and expectedly decreased neuronal firing. Interestingly, for the fourth mutation, A1622D, causing severe intellectual disability and autism without epilepsy, we observed a dramatic slowing of fast inactivation in neuroblastoma cells, which induced a depolarization block in neurons with a reduction of neuronal firing. This latter finding was corroborated by computational modelling. In a second series of experiments, we recorded three more mutations (G1475R, M1760I, G964R, causing intermediate or severe epilepsy, or intellectual disability without epilepsy, respectively) that revealed similar results confirming clear genotype-phenotype relationships. We found intermediate or severe gain-of-function biophysical changes and increases in neuronal firing for the two epilepsy-causing mutations and decreased firing for the loss-of-function mutation causing intellectual disability. We conclude that studies in neurons are crucial to understand disease mechanisms, which here indicate that increased or decreased neuronal firing is responsible for distinct clinical phenotypes.

No evidence for a BRD2 promoter hypermethylation in blood leukocytes of Europeans with juvenile myoclonic epilepsy.

Juvenile myoclonic epilepsy (JME) is a common syndrome of genetic generalized epilepsies (GGEs). Linkage and association studies suggest that the gene encoding the bromodomain-containing protein 2 (BRD2) may increase risk of JME. The present methylation and association study followed up a recent report highlighting that the BRD2 promoter CpG island (CpG76) is differentially hypermethylated in lymphoblastoid cells from Caucasian patients with JME compared to patients with other GGE subtypes and unaffected relatives. In contrast, we found a uniform low average percentage of methylation (<4.5%) for 13 CpG76-CpGs in whole blood cells from 782 unrelated European Caucasians, including 116 JME patients, 196 patients with genetic absence epilepsies, and 470 control subjects. We also failed to confirm an allelic association of the BRD2 promoter single nucleotide polymorphism (SNP) rs3918149 with JME (Armitage trend test, P = 0.98), and we did not detect a substantial impact of SNP rs3918149 on CpG76 methylation in either 116 JME patients (methylation quantitative trait loci [meQTL], P = 0.29) or 470 German control subjects (meQTL, P = 0.55). Our results do not support the previous observation that a high DNA methylation level of the BRD2 promoter CpG76 island is a prevalent epigenetic motif associated with JME in Caucasians.

Rare GABRA3 variants are associated with epileptic seizures, encephalopathy and dysmorphic features.

Genetic epilepsies are caused by mutations in a range of different genes, many of them encoding ion channels, receptors or transporters. While the number of detected variants and genes increased dramatically in the recent years, pleiotropic effects have also been recognized, revealing that clinical syndromes with various degrees of severity arise from a single gene, a single mutation, or from different mutations showing similar functional defects. Accordingly, several genes coding for GABAA receptor subunits have been linked to a spectrum of benign to severe epileptic disorders and it was shown that a loss of function presents the major correlated pathomechanism. Here, we identified six variants in GABRA3 encoding the α3-subunit of the GABAA receptor. This gene is located on chromosome Xq28 and has not been previously associated with human disease. Five missense variants and one microduplication were detected in four families and two sporadic cases presenting with a range of epileptic seizure types, a varying degree of intellectual disability and developmental delay, sometimes with dysmorphic features or nystagmus. The variants co-segregated mostly but not completely with the phenotype in the families, indicating in some cases incomplete penetrance, involvement of other genes, or presence of phenocopies. Overall, males were more severely affected and there were three asymptomatic female mutation carriers compared to only one male without a clinical phenotype. X-chromosome inactivation studies could not explain the phenotypic variability in females. Three detected missense variants are localized in the extracellular GABA-binding NH2-terminus, one in the M2-M3 linker and one in the M4 transmembrane segment of the α3-subunit. Functional studies in Xenopus laevis oocytes revealed a variable but significant reduction of GABA-evoked anion currents for all mutants compared to wild-type receptors. The degree of current reduction correlated partially with the phenotype. The microduplication disrupted GABRA3 expression in fibroblasts of the affected patient. In summary, our results reveal that rare loss-of-function variants in GABRA3 increase the risk for a varying combination of epilepsy, intellectual disability/developmental delay and dysmorphic features, presenting in some pedigrees with an X-linked inheritance pattern.

Galanin pathogenic mutations in temporal lobe epilepsy.

Temporal lobe epilepsy (TLE) is a common epilepsy syndrome with a complex etiology. Despite evidence for the participation of genetic factors, the genetic basis of TLE remains largely unknown. A role for the galanin neuropeptide in the regulation of epileptic seizures has been established in animal models more than two decades ago. However, until now there was no report of pathogenic mutations in GAL, the galanin-encoding gene, and therefore its role in human epilepsy was not established. Here, we studied a family with a pair of monozygotic twins affected by TLE and two unaffected siblings born to healthy parents. Exome sequencing revealed that both twins carried a novel de novo mutation (p.A39E) in the GAL gene. Functional analysis revealed that the p.A39E mutant showed antagonistic activity against galanin receptor 1 (GalR1)-mediated response, and decreased binding affinity and reduced agonist properties for GalR2. These findings suggest that the p.A39E mutant could impair galanin signaling in the hippocampus, leading to increased glutamatergic excitation and ultimately to TLE. In a cohort of 582 cases, we did not observe any pathogenic mutations indicating that mutations in GAL are a rare cause of TLE. The identification of a novel de novo mutation in a biologically-relevant candidate gene, coupled with functional evidence that the mutant protein disrupts galanin signaling, strongly supports GAL as the causal gene for the TLE in this family. Given the availability of galanin agonists which inhibit seizures, our findings could potentially have direct implications for the development of anti-epileptic treatment.

Benign infantile seizures and paroxysmal dyskinesia caused by an SCN8A mutation.

OBJECTIVE: Benign familial infantile seizures (BFIS), paroxysmal kinesigenic dyskinesia (PKD), and their combination-known as infantile convulsions and paroxysmal choreoathetosis (ICCA)-are related autosomal dominant diseases. PRRT2 (proline-rich transmembrane protein 2 gene) has been identified as the major gene in all 3 conditions, found to be mutated in 80 to 90% of familial and 30 to 35% of sporadic cases. METHODS: We searched for the genetic defect in PRRT2-negative, unrelated families with BFIS or ICCA using whole exome or targeted gene panel sequencing, and performed a detailed cliniconeurophysiological workup. RESULTS: In 3 families with a total of 16 affected members, we identified the same, cosegregating heterozygous missense mutation (c.4447G>A; p.E1483K) in SCN8A, encoding a voltage-gated sodium channel. A founder effect was excluded by linkage analysis. All individuals except 1 had normal cognitive and motor milestones, neuroimaging, and interictal neurological status. Fifteen affected members presented with afebrile focal or generalized tonic-clonic seizures during the first to second year of life; 5 of them experienced single unprovoked seizures later on. One patient had seizures only at school age. All patients stayed otherwise seizure-free, most without medication. Interictal electroencephalogram (EEG) was normal in all cases but 2. Five of 16 patients developed additional brief paroxysmal episodes in puberty, either dystonic/dyskinetic or "shivering" attacks, triggered by stretching, motor initiation, or emotional stimuli. In 1 case, we recorded typical PKD spells by video-EEG-polygraphy, documenting a cortical involvement. INTERPRETATION: Our study establishes SCN8A as a novel gene in which a recurrent mutation causes BFIS/ICCA, expanding the clinical-genetic spectrum of combined epileptic and dyskinetic syndromes.

Comparative effectiveness of antiepileptic drugs in patients with mesial temporal lobe epilepsy with hippocampal sclerosis.

OBJECTIVE: Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) is a common epilepsy syndrome that is often poorly controlled by antiepileptic drug (AED) treatment. Comparative AED effectiveness studies in this condition are lacking. We report retention, efficacy, and tolerability in a cohort of patients with MTLE-HS. METHODS: Clinical data were collected from a European database of patients with epilepsy. We estimated retention, 12-month seizure freedom, and adverse drug reaction (ADR) rates for the 10 most commonly used AEDs in patients with MTLE-HS. RESULTS: Seven hundred sixty-seven patients with a total of 3,249 AED trials were included. The highest 12-month retention rates were observed with carbamazepine (85.9%), valproate (85%), and clobazam (79%). Twelve-month seizure freedom rates varied from 1.2% for gabapentin and vigabatrin to 11% for carbamazepine. Response rates were highest for AEDs that were prescribed as initial treatment and lowest for AEDs that were used in a third or higher instance. ADRs were reported in 47.6% of patients, with the highest rates observed with oxcarbazepine (35.7%), topiramate (30.9%), and pregabalin (27.4%), and the lowest rates with clobazam (6.5%), gabapentin (8.9%), and lamotrigine (16.6%). The most commonly reported ADRs were lethargy and drowsiness, dizziness, vertigo and ataxia, and blurred vision and diplopia. SIGNIFICANCE: Our results did not demonstrate any clear advantage of newer versus older AEDs. Our results provide useful insights into AED retention, efficacy, and ADR rates in patients with MTLE-HS.

Recessive mutations in SLC13A5 result in a loss of citrate transport and cause neonatal epilepsy, developmental delay and teeth hypoplasia.

The epileptic encephalopathies are a clinically and aetiologically heterogeneous subgroup of epilepsy syndromes. Most epileptic encephalopathies have a genetic cause and patients are often found to carry a heterozygous de novo mutation in one of the genes associated with the disease entity. Occasionally recessive mutations are identified: a recent publication described a distinct neonatal epileptic encephalopathy (MIM 615905) caused by autosomal recessive mutations in the SLC13A5 gene. Here, we report eight additional patients belonging to four different families with autosomal recessive mutations in SLC13A5. SLC13A5 encodes a high affinity sodium-dependent citrate transporter, which is expressed in the brain. Neurons are considered incapable of de novo synthesis of tricarboxylic acid cycle intermediates; therefore they rely on the uptake of intermediates, such as citrate, to maintain their energy status and neurotransmitter production. The effect of all seven identified mutations (two premature stops and five amino acid substitutions) was studied in vitro, using immunocytochemistry, selective western blot and mass spectrometry. We hereby demonstrate that cells expressing mutant sodium-dependent citrate transporter have a complete loss of citrate uptake due to various cellular loss-of-function mechanisms. In addition, we provide independent proof of the involvement of autosomal recessive SLC13A5 mutations in the development of neonatal epileptic encephalopathies, and highlight teeth hypoplasia as a possible indicator for SLC13A5 screening. All three patients who tried the ketogenic diet responded well to this treatment, and future studies will allow us to ascertain whether this is a recurrent feature in this severe disorder.

DEPDC5 mutations in genetic focal epilepsies of childhood.

Recent studies reported DEPDC5 loss-of-function mutations in different focal epilepsy syndromes. Here we identified 1 predicted truncation and 2 missense mutations in 3 children with rolandic epilepsy (3 of 207). In addition, we identified 3 families with unclassified focal childhood epilepsies carrying predicted truncating DEPDC5 mutations (3 of 82). The detected variants were all novel, inherited, and present in all tested affected (n=11) and in 7 unaffected family members, indicating low penetrance. Our findings extend the phenotypic spectrum associated with mutations in DEPDC5 and suggest that rolandic epilepsy, albeit rarely, and other nonlesional childhood epilepsies are among the associated syndromes.

Extending the phenotypic spectrum of RBFOX1 deletions: Sporadic focal epilepsy.

Partial deletions of the RBFOX1 gene encoding the neuronal splicing regulator have been reported in a range of neurodevelopmental diseases including idiopathic/genetic generalized epilepsy (IGE/GGE), childhood focal epilepsy, and self-limited childhood benign epilepsy with centrotemporal spikes (BECTS, rolandic epilepsy), and autism. The protein regulates alternative splicing of many neuronal transcripts involved in the homeostatic control of neuronal excitability. Herein, we examined whether structural deletions affecting RBFOX1 exons confer susceptibility to common forms of juvenile and adult focal epilepsy syndromes. We screened 807 unrelated patients with sporadic focal epilepsy, and we identified seven hemizygous exonic RBFOX1 deletions in patients with sporadic focal epilepsy (0.9%) in comparison to one deletion found in 1,502 controls. The phenotypes of the patients carrying RBFOX1 deletions comprise magnetic resonance imaging (MRI)-negative epilepsy of unknown etiology with frontal and temporal origin (n = 5) and two patients with temporal lobe epilepsy with hippocampal sclerosis. The epilepsies were largely pharmacoresistant but not associated with intellectual disability. Our study extends the phenotypic spectrum of RBFOX1 deletions as a risk factor for focal epilepsy and suggests that exonic RBFOX1 deletions are involved in the broad spectrum of focal and generalized epilepsies.

Genome-wide association analysis of genetic generalized epilepsies implicates susceptibility loci at 1q43, 2p16.1, 2q22.3 and 17q21.32.

Genetic generalized epilepsies (GGEs) have a lifetime prevalence of 0.3% and account for 20-30% of all epilepsies. Despite their high heritability of 80%, the genetic factors predisposing to GGEs remain elusive. To identify susceptibility variants shared across common GGE syndromes, we carried out a two-stage genome-wide association study (GWAS) including 3020 patients with GGEs and 3954 controls of European ancestry. To dissect out syndrome-related variants, we also explored two distinct GGE subgroups comprising 1434 patients with genetic absence epilepsies (GAEs) and 1134 patients with juvenile myoclonic epilepsy (JME). Joint Stage-1 and 2 analyses revealed genome-wide significant associations for GGEs at 2p16.1 (rs13026414, P(meta) = 2.5 × 10(-9), OR[T] = 0.81) and 17q21.32 (rs72823592, P(meta) = 9.3 × 10(-9), OR[A] = 0.77). The search for syndrome-related susceptibility alleles identified significant associations for GAEs at 2q22.3 (rs10496964, P(meta) = 9.1 × 10(-9), OR[T] = 0.68) and at 1q43 for JME (rs12059546, P(meta) = 4.1 × 10(-8), OR[G] = 1.42). Suggestive evidence for an association with GGEs was found in the region 2q24.3 (rs11890028, P(meta) = 4.0 × 10(-6)) nearby the SCN1A gene, which is currently the gene with the largest number of known epilepsy-related mutations. The associated regions harbor high-ranking candidate genes: CHRM3 at 1q43, VRK2 at 2p16.1, ZEB2 at 2q22.3, SCN1A at 2q24.3 and PNPO at 17q21.32. Further replication efforts are necessary to elucidate whether these positional candidate genes contribute to the heritability of the common GGE syndromes.

Successful use of Fenfluramine in super-refractory status epilepticus in a patient with tuberous sclerosis complex and Lennox-Gastaut syndrome.

A 24-year-old female patient with pre-existing refractory epilepsy caused by tuberous sclerosis (TSC) and electroclinical features of Lennox-Gastaut syndrome (LGS) was referred to our hospital from an external clinic. Upon arrival, she presented with super-refractory status epilepticus (SRSE) since anaesthetics had already been used in the referring clinic. Despite various changes in ASM-treatment and continuous administration of anaesthetics for more than two weeks, SRSE could not be terminated. On treatment day 24, we started Fenfluramin (FFA) which was soon titrated to a dose of 0,7 mg/kg/day. A few days after beginning the treatment with FFA, EEG and clinical situation improved dramatically. The following 6 weeks of treatment went without reported seizures. This case illustrates the successful use of FFA in SRSE in TSC and LGS and, to the best of our knowledge, represents the first report of FFA in this clinical context.

Rare exonic deletions of the RBFOX1 gene increase risk of idiopathic generalized epilepsy.

PURPOSE: Structural variations disrupting the gene encoding the neuron-specific splicing regulator RBFOX1 have been reported in three patients exhibiting epilepsy in comorbidity with other neuropsychiatric disorders. Consistently, the Rbfox1 knockout mouse model showed an increased susceptibility of seizures. The present candidate gene study tested whether exon-disrupting deletions of RBFOX1 increase the risk of idiopathic generalized epilepsies (IGEs), representing the largest group of genetically determined epilepsies. METHODS: Screening of microdeletions (size: >40 kb, coverage >20 markers) affecting the genomic sequence of the RBFOX1 gene was carried out by high-resolution single-nucleotide polymorphism (SNP) arrays in 1,408 European patients with idiopathic generalized epilepsy (IGE) and 2,256 population controls. Validation of RBFOX1 deletions and familial segregation analysis were performed by quantitative polymerase chain reaction (qPCR). KEY FINDINGS: We detected five exon-disrupting RBFOX1 deletions in the IGE patients, whereas none was observed in the controls (p = 0.008, Fisher's exact test). The size of the exonic deletions ranged from 68 to 896 kb and affected the untranslated 5'-terminal RBFOX1 exons. Segregation analysis in four families indicated that the deletions were inherited, display incomplete penetrance, and heterogeneous cosegregation patterns with IGE. SIGNIFICANCE: Rare deletions affecting the untranslated 5'-terminal RBFOX1 exons increase risk of common IGE syndromes. Variable expressivity, incomplete penetrance, and heterogeneous cosegregation patterns suggest that RBFOX1 deletions act as susceptibility factor in a genetically complex etiology, where heterogeneous combinations of genetic factors determine the disease phenotype.

Researching the Aftermath of Slavery in Mainland East Africa: Methodological, Ethical, and Practical Challenges.

This article examines ethical, practical, and methodological challenges in researching the aftermath of slavery in continental East Africa away from the coastal plantation belt. Interest in post-slavery there is recent and inspired by the apparent contrast with West Africa, where the issue is much more salient. The article explains this silence by highlighting politically-motivated avoidance of the issue in colonial sources and the preference of post-colonial historians for 'useful' pasts. Further, it questions the balance of successful integration and continuing marginalization reflected in the apparent obsolescence of slavery. It argues that tracing the trajectories of ex-slaves requires attention to all forms of social inequality and dependency, to the potential status implications for informants of speaking about slavery, and to the variety of terms and fields of meaning relevant to freedom, unfreedom and dependency. Recent research in this vein shows that slave antecedents remain a matter of aibu, shame, and that ex-slaves' disappearance as a social category took lifelong efforts on their part. While the social valence of slave antecedents is relatively limited in mainland East Africa, slavery remains a problematic and painful heritage that demands great circumspection by researchers.

Unified Quantification of Quantum Defects in Small-Diameter Single-Walled Carbon Nanotubes by Raman Spectroscopy.

The covalent functionalization of single-walled carbon nanotubes (SWCNTs) with luminescent quantum defects enables their application as near-infrared single-photon sources, as optical sensors, and for in vivo tissue imaging. Tuning the emission wavelength and defect density is crucial for these applications. While the former can be controlled by different synthetic protocols and is easily measured, defect densities are still determined as relative rather than absolute values, limiting the comparability between different nanotube batches and chiralities. Here, we present an absolute and unified quantification metric for the defect density in SWCNT samples based on Raman spectroscopy. It is applicable to a range of small-diameter semiconducting nanotubes and for arbitrary laser wavelengths. We observe a clear inverse correlation of the D/G+ ratio increase with nanotube diameter, indicating that curvature effects contribute significantly to the defect activation of Raman modes. Correlation of intermediate frequency modes with defect densities further corroborates their activation by defects and provides additional quantitative metrics for the characterization of functionalized SWCNTs.

PRRT2 mutations are the major cause of benign familial infantile seizures.

Mutations in PRRT2 have been described in paroxysmal kinesigenic dyskinesia (PKD) and infantile convulsions with choreoathetosis (PKD with infantile seizures), and recently also in some families with benign familial infantile seizures (BFIS) alone. We analyzed PRRT2 in 49 families and three sporadic cases with BFIS only of Italian, German, Turkish, and Japanese origin and identified the previously described mutation c.649dupC in an unstable series of nine cytosines to occur in 39 of our families and one sporadic case (77% of index cases). Furthermore, three novel mutations were found in three other families, whereas 17% of our index cases did not show PRRT2 mutations, including a large family with late-onset BFIS and febrile seizures. Our study further establishes PRRT2 as the major gene for BFIS alone.

Targeted next generation sequencing as a diagnostic tool in epileptic disorders.

PURPOSE: Epilepsies have a highly heterogeneous background with a strong genetic contribution. The variety of unspecific and overlapping syndromic and nonsyndromic phenotypes often hampers a clear clinical diagnosis and prevents straightforward genetic testing. Knowing the genetic basis of a patient's epilepsy can be valuable not only for diagnosis but also for guiding treatment and estimating recurrence risks. METHODS: To overcome these diagnostic restrictions, we composed a panel of genes for Next Generation Sequencing containing the most relevant epilepsy genes and covering the most relevant epilepsy phenotypes known so far. With this method, 265 genes were analyzed per patient in a single step. We evaluated this panel on a pilot cohort of 33 index patients with concise epilepsy phenotypes or with a severe but unspecific seizure disorder covering both sporadic and familial cases. KEY FINDINGS: We identified presumed disease-causing mutations in 16 of 33 patients comprising sequence alterations in frequently as well as in less commonly affected genes. The detected aberrations encompassed known and unknown point mutations (SCN1A p.R222X, p. E289V, p.379R, p.R393H; SCN2A p.V208E; STXBP1 p.R122X; KCNJ10 p.L68P, p.I129V; KCTD7 p.L108M; KCNQ3 p.P574S; ARHGEF9 p.R290H; SMS p.F58L; TPP1 p.Q278R, p.Q422H; MFSD8 p.T294K), a putative splice site mutation (SCN1A c.693A> p.T/P231P) and small deletions (SCN1A p.F1330Lfs3X [1 bp]; MFSD8 p.A138Dfs10X [7 bp]). All mutations have been confirmed by conventional Sanger sequencing and, where possible, validated by parental testing and segregation analysis. In three patients with either Dravet syndrome or myoclonic epilepsy, we detected SCN1A mutations (p.R222X, p.P231P, p.R393H), even though other laboratories had previously excluded aberrations of this gene by Sanger sequencing or high-resolution melting analysis. SIGNIFICANCE: We have developed a fast and cost-efficient diagnostic screening method to analyze the genetic basis of epilepsies. We were able to detect mutations in patients with clear and with unspecific epilepsy phenotypes, to uncover the genetic basis of many so far unresolved cases with epilepsy including mutation detection in cases in which previous conventional methods yielded falsely negative results. Our approach thus proved to be a powerful diagnostic tool that may contribute to collecting information on both common and unknown epileptic disorders and in delineating associated phenotypes of less frequently mutated genes.

Genome-wide linkage meta-analysis identifies susceptibility loci at 2q34 and 13q31.3 for genetic generalized epilepsies.

PURPOSE: Genetic generalized epilepsies (GGEs) have a lifetime prevalence of 0.3% with heritability estimates of 80%. A considerable proportion of families with siblings affected by GGEs presumably display an oligogenic inheritance. The present genome-wide linkage meta-analysis aimed to map: (1) susceptibility loci shared by a broad spectrum of GGEs, and (2) seizure type-related genetic factors preferentially predisposing to either typical absence or myoclonic seizures, respectively. METHODS: Meta-analysis of three genome-wide linkage datasets was carried out in 379 GGE-multiplex families of European ancestry including 982 relatives with GGEs. To dissect out seizure type-related susceptibility genes, two family subgroups were stratified comprising 235 families with predominantly genetic absence epilepsies (GAEs) and 118 families with an aggregation of juvenile myoclonic epilepsy (JME). To map shared and seizure type-related susceptibility loci, both nonparametric loci (NPL) and parametric linkage analyses were performed for a broad trait model (GGEs) in the entire set of GGE-multiplex families and a narrow trait model (typical absence or myoclonic seizures) in the subgroups of JME and GAE families. KEY FINDINGS: For the entire set of 379 GGE-multiplex families, linkage analysis revealed six loci achieving suggestive evidence for linkage at 1p36.22, 3p14.2, 5q34, 13q12.12, 13q31.3, and 19q13.42. The linkage finding at 5q34 was consistently supported by both NPL and parametric linkage results across all three family groups. A genome-wide significant nonparametric logarithm of odds score of 3.43 was obtained at 2q34 in 118 JME families. Significant parametric linkage to 13q31.3 was found in 235 GAE families assuming recessive inheritance (heterogeneity logarithm of odds = 5.02). SIGNIFICANCE: Our linkage results support an oligogenic predisposition of familial GGE syndromes. The genetic risk factor at 5q34 confers risk to a broad spectrum of familial GGE syndromes, whereas susceptibility loci at 2q34 and 13q31.3 preferentially predispose to myoclonic seizures or absence seizures, respectively. Phenotype- genotype strategies applying narrow trait definitions in phenotypic homogeneous subgroups of families improve the prospects of disentangling the genetic basis of common familial GGE syndromes.