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Identifying genetic risk factors for highly heterogeneous disorders like epilepsy remains challenging. Here, we present the largest whole-exome sequencing study of epilepsy to date to investigate rare variants that confer risk for a spectrum of epilepsy syndromes. With an unprecedented sample size of >54,000 human exomes, composed of 20,979 deep-phenotyped patients with epilepsy and 33,444 controls, we replicate previous gene findings at exome-wide significance; using a hypothesis-free approach, we identify potential novel associations. Most discoveries are specific to a particular subtype of epilepsy, highlighting distinct genetic contributions to different epilepsies. Combining evidence from rare single nucleotide/short indel-, copy number-, and common variants, we find convergence of different genetic risk factors at the level of individual genes. Further comparing to other exome-sequencing studies, we implicate shared rare variant risk between epilepsy and other neurodevelopmental disorders. Our study also demonstrates the value of collaborative sequencing and deep-phenotyping efforts, which will continue to unravel the complex genetic architecture underlying the heterogeneity of epilepsy.

Objective: To determine whether the GNAQ R183Q mutation is present in the forme fruste cases of Sturge-Weber syndrome (SWS) to establish a definitive molecular diagnosis. Methods: We used sensitive droplet digital PCR (ddPCR) to detect and quantify the GNAQ mutation in tissues from epilepsy surgery in 4 patients with leptomeningeal angiomatosis; none had ocular or cutaneous manifestations. Results: Low levels of the GNAQ mutation were detected in the brain tissue of all 4 cases - ranging from 0.42% to 7.1% frequency - but not in blood-derived DNA. Molecular evaluation confirmed the diagnosis in 1 case in which the radiologic and pathologic data were equivocal. Conclusions: We detected the mutation at low levels, consistent with mosaicism in the brain or skin (1.0%-18.1%) of classic cases. Our data confirm that the forme fruste is part of the spectrum of SWS, with the same molecular mechanism as the classic disease and that ddPCR is helpful where conventional diagnosis is uncertain.

Supplemental material, sj-docx-1-anp-10.1177_00048674231187312 for Plasma neurofilament light in behavioural variant frontotemporal dementia compared to mood and psychotic disorders by Dhamidhu Eratne, Matthew Kang, Charles Malpas, Steve Simpson-Yap, Courtney Lewis, Christa Dang, Jasleen Grewal, Amy Coe, Hannah Dobson, Michael Keem, Wei-Hsuan Chiu, Tomas Kalincik, Suyi Ooi, David Darby, Amy Brodtmann, Oskar Hansson, Shorena Janelidze, Kaj Blennow, Henrik Zetterberg, Adam Walker, Olivia Dean, Michael Berk, Cassandra Wannan, Christos Pantelis, Samantha M Loi, Mark Walterfang, Samuel F Berkovic, Alexander F Santillo and Dennis Velakoulis in Australian & New Zealand Journal of Psychiatry

Epilepsy is a highly heritable disorder affecting over 50 million people worldwide, of which about one-third are resistant to current treatments. Here, we report a trans-ethnic GWAS including 29,944 cases, stratified into three broad- and seven sub-types of epilepsy, and 52,538 controls. We identify 26 genome-wide significant loci, 19 of which are specific to genetic generalized epilepsy (GGE). We implicate 29 likely causal genes underlying these 26 loci. SNP-based heritability analyses show that common variants substantially close the missing heritability gap for GGE. Subtype analysis revealed markedly different genetic architectures between focal and generalized epilepsies. Gene-set analysis of GGE signals implicate synaptic processes in both excitatory and inhibitory neurons in the brain. Prioritized candidate genes overlap with monogenic epilepsy genes and with targets of current anti-seizure medications. Finally, we leverage our results to identify alternate drugs with predicted efficacy if repurposed for epilepsy treatment.

Hypothalamic hamartomas (HH) are rare, basilar developmental lesions with widespread comorbidities often associated with refractory epilepsy and encephalopathy. Imaging advances allow for early, even prenatal, detection. Genetic studies suggest mutations in GLI3 and other patterning genes are involved in HH pathogenesis. About 50%–80% of children with HH have severe rage and aggression and a majority of patients exhibit externalizing disorders. Behavioral disruption and intellectual disability may predate epilepsy. Neuropsychological, sleep, and endocrine disorders are typical. The purpose of this article is to provide a summary of the current understanding of HH and to highlight opportunities for future research.

EBioMedicine 84, 104244 (2022). doi:10.1016/j.ebiom.2022.104244, Published by Elsevier, Amsterdam [u.a.]

Bott et al. here reports that de novo and biallelic variants in ATP6V0A1 gene affect the ability of the V-ATPase complex to translocate protons and acidify the endolysosomal compartment in neurons, causing a severe neurological phenotype ranging from developmental and epileptic encephalopathy to progressive myoclonus epilepsy. The vacuolar H+-ATPase is a large multi-subunit proton pump, composed of an integral membrane V0 domain, involved in proton translocation, and a peripheral V1 domain, catalysing ATP hydrolysis. This complex is widely distributed on the membrane of various subcellular organelles, such as endosomes and lysosomes, and plays a critical role in cellular processes ranging from autophagy to protein trafficking and endocytosis. Variants in ATP6V0A1, the brain-enriched isoform in the V0 domain, have been recently associated with developmental delay and epilepsy in four individuals. Here, we identified 17 individuals from 14 unrelated families with both with new and previously characterized variants in this gene, representing the largest cohort to date. Five affected subjects with biallelic variants in this gene presented with a phenotype of early-onset progressive myoclonus epilepsy with ataxia, while 12 individuals carried de novo missense variants and showed severe developmental and epileptic encephalopathy. The R740Q mutation, which alone accounts for almost 50% of the mutations identified among our cases, leads to failure of lysosomal hydrolysis by directly impairing acidification of the endolysosomal compartment, causing autophagic dysfunction and severe developmental defect in Caenorhabditis elegans. Altogether, our findings further expand the neurological phenotype associated with variants in this gene and provide a direct link with endolysosomal acidification in the pathophysiology of ATP6V0A1-related conditions.

Objective: De novo missense variants in KCNQ5, encoding the voltage gated K+ channel KV7.5, have been described as a cause of developmental and epileptic encephalopathy (DEE) or intellectual disability (ID). We set out to identify disease-related KCNQ5 variants in genetic generalized epilepsy (GGE) and their underlying mechanisms. Methods: 1292 families with GGE were studied by next-generation sequencing. Whole-cell patch-clamp recordings, biotinylation and phospholipid overlay assays were performed in mammalian cells combined with docking and homology modeling. Results: We identified three deleterious heterozygous missense variants, one truncation and one splice site alteration in five independent families with GGE with predominant absence seizures, two variants were also associated with mild to moderate ID. All three missense variants displayed a strongly decreased current density indicating a loss-of-function (LOF). When mutant channels were co-expressed with wild-type (WT) KV7.5 or KV7.5 and KV7.3 channels, three variants also revealed a significant dominant-negative effect on WT channels. Other gating parameters were unchanged. Biotinylation assays indicated a normal surface expression of the variants. The p.Arg359Cys variant altered PI(4,5)P2-interaction, presumably in the non-conducting preopen-closed state. Interpretation: Our study indicates that specific deleterious KCNQ5 variants are associated with GGE, partially combined with mild to moderate ID. The disease mechanism is a LOF partially with dominant-negative effects through functional, rather than trafficking deficits. LOF of KV7.5 channels will reduce the M-current, likely resulting in increased excitability of KV7.5-expressing neurons. Further studies on a network level are necessary to understand which circuits are affected and how the variants induce generalized seizures.

Objective To delineate the epileptology, a key part of the SYNGAP1 phenotypic spectrum, in a large patient cohort. Methods Patients were recruited via investigators' practices or social media. We included patients with (likely) pathogenic SYNGAP1 variants or chromosome 6p21.32 microdeletions incorporating SYNGAP1. We analyzed patients' phenotypes using a standardized epilepsy questionnaire, medical records, EEG, MRI, and seizure videos. Results We included 57 patients (53% male, median age 8 years) with SYNGAP1 mutations (n = 53) or microdeletions (n = 4). Of the 57 patients, 56 had epilepsy: generalized in 55, with focal seizures in 7 and infantile spasms in 1. Median seizure onset age was 2 years. A novel type of drop attack was identified comprising eyelid myoclonia evolving to a myoclonic-atonic (n = 5) or atonic (n = 8) seizure. Seizure types included eyelid myoclonia with absences (65%), myoclonic seizures (34%), atypical (20%) and typical (18%) absences, and atonic seizures (14%), triggered by eating in 25%. Developmental delay preceded seizure onset in 54 of 56 (96%) patients for whom early developmental history was available. Developmental plateauing or regression occurred with seizures in 56 in the context of a developmental and epileptic encephalopathy (DEE). Fifty-five of 57 patients had intellectual disability, which was moderate to severe in 50. Other common features included behavioral problems (73%); high pain threshold (72%); eating problems, including oral aversion (68%); hypotonia (67%); sleeping problems (62%); autism spectrum disorder (54%); and ataxia or gait abnormalities (51%). Conclusions SYNGAP1 mutations cause a generalized DEE with a distinctive syndrome combining epilepsy with eyelid myoclonia with absences and myoclonic-atonic seizures, as well as a predilection to seizures triggered by eating.

Additional file 2: Poster. Methodology to develop guidelines for the management of patients with CLN2 disease.

Supplemental material, sj-pdf-1-anp-10.1177_00048674211058684 for Plasma neurofilament light chain protein is not increased in treatment-resistant schizophrenia and first-degree relatives by Dhamidhu Eratne, Shorena Janelidze, Charles B Malpas, Samantha Loi, Mark Walterfang, Antonia Merritt, Ibrahima Diouf, Kaj Blennow, Henrik Zetterberg, Brandon Cilia, Cassandra Wannan, Chad Bousman, Ian Everall, Andrew Zalesky, Mahesh Jayaram, Naveen Thomas, Samuel F Berkovic, Oskar Hansson, Dennis Velakoulis, Christos Pantelis and Alexander Santillo in Australian & New Zealand Journal of Psychiatry

Additional file 1: Appendices. Appendices 1–9.

Variants in RORB have been reported in eight individuals with epilepsy, with phenotypes ranging from eyelid myoclonia with absence epilepsy to developmental and epileptic encephalopathies. We identified novel RORB variants in 11 affected individuals from four families. One was from whole genome sequencing and three were from RORB screening of three epilepsy cohorts: developmental and epileptic encephalopathies (n = 1021), overlap of generalized and occipital epilepsy (n = 84), and photosensitivity (n = 123). Following interviews and review of medical records, individuals' seizure and epilepsy syndromes were classified. Three novel missense variants and one exon 3 deletion were predicted to be pathogenic by in silico tools, not found in population databases, and located in key evolutionary conserved domains. Median age at seizure onset was 3.5 years (0.5-10 years). Generalized, predominantly absence and myoclonic, and occipital seizures were seen in all families, often within the same individual (6/11). All individuals with epilepsy were photosensitive, and seven of 11 had cognitive abnormalities. Electroencephalograms showed generalized spike and wave and/or polyspike and wave. Here we show a striking RORB phenotype of overlap of photosensitive generalized and occipital epilepsy in both individuals and families. This is the first report of a gene associated with this overlap of epilepsy syndromes.

Cytogenic testing is routinely applied in most neurological centres for severe paediatric epilepsies. However, which characteristics of copy number variants (CNVs) confer most epilepsy risk and which epilepsy subtypes carry the most CNV burden, have not been explored on a genome-wide scale. Here, we present the largest CNV investigation in epilepsy to date with 10 712 European epilepsy cases and 6746 ancestry-matched controls. Patients with genetic generalized epilepsy, lesional focal epilepsy, non-acquired focal epilepsy, and developmental and epileptic encephalopathy were included. All samples were processed with the same technology and analysis pipeline. All investigated epilepsy types, including lesional focal epilepsy patients, showed an increase in CNV burden in at least one tested category compared to controls. However, we observed striking differences in CNV burden across epilepsy types and investigated CNV categories. Genetic generalized epilepsy patients have the highest CNV burden in all categories tested, followed by developmental and epileptic encephalopathy patients. Both epilepsy types also show association for deletions covering genes intolerant for truncating variants. Genome-wide CNV breakpoint association showed not only significant loci for genetic generalized and developmental and epileptic encephalopathy patients but also for lesional focal epilepsy patients. With a 34-fold risk for developing genetic generalized epilepsy, we show for the first time that the established epilepsy-associated 15q13.3 deletion represents the strongest risk CNV for genetic generalized epilepsy across the whole genome. Using the human interactome, we examined the largest connected component of the genes overlapped by CNVs in the four epilepsy types. We observed that genetic generalized epilepsy and non-acquired focal epilepsy formed disease modules. In summary, we show that in all common epilepsy types, 1.5–3% of patients carry epilepsy-associated CNVs. The characteristics of risk CNVs vary tremendously across and within epilepsy types. Thus, we advocate genome-wide genomic testing to identify all disease-associated types of CNVs.

Objective To map functional MRI (fMRI) connectivity within and between the somatosensory cortex, putamen, and ventral thalamus in individuals from a family with a GABAergic deficit segregating with febrile seizures and genetic generalized epilepsy. Methods We studied 5 adults from a family with early-onset absence epilepsy and/or febrile seizures and a GABAA receptor subunit gamma2 pathogenic variant (GABRG2[R43Q]) vs 5 age-matched controls. We infer differences between participants with the GABRG2 pathogenic variant and controls in resting-state fMRI connectivity within and between the somatosensory cortex, putamen, and ventral thalamus. Results We observed increased fMRI connectivity within the somatosensory cortex and between the putamen and ventral thalamus in all individuals with the GABRG2 pathogenic variant compared with controls. Post hoc analysis showed less pronounced changes in fMRI connectivity within and between the primary visual cortex and precuneus. Conclusions Although our sample size was small, this preliminary study suggests that individuals with a GABRG2 pathogenic variant, raising risk of febrile seizures and generalized epilepsy, display underlying increased functional connectivity both within the somatosensory cortex and in striatothalamic networks. This human network model aligns with rodent research and should be further validated in larger cohorts, including other individuals with generalized epilepsy with and without known GABA pathogenic variants.

Adverse drug reactions are a leading cause of treatment failure with antiepileptic drugs. Adverse drug reactions are also a major source of morbidity and mortality, and a substantial burden on the use and costs of health care. Recent pharmacogenetic studies have shown that some adverse drug reactions are associated with genetic variants, which has changed how we select antiepileptic drugs for individual patients. This article, beginning with a case of an adverse drug reaction induced by carbamazepine, will answer four key questions about pharmacogenetics of adverse drug reactions: (1) What types of adverse drug reactions can be caused by antiepileptic drugs? (2) What is pharmacogenetics? (3) How does pharmacogenetics play a role in the adverse drug reactions of antiepileptic drugs? and (4) How do we apply pharmacogenetic testing in clinical practice? Our goal is to increase awareness of the contributions of genetic variation to adverse drug reactions of antiepileptic drugs.

Photosensitivity in epilepsy is common and has high heritability, but its genetic basis remains uncertain. Galizia et al. reveal an overrepresentation of unique variants of CHD2 — which encodes the transcriptional regulator ‘chromodomain helicase DNA-binding protein 2’ — in photosensitive epilepsies, and show that chd2 knockdown in zebrafish causes photosensitivity., Photosensitivity is a heritable abnormal cortical response to flickering light, manifesting as particular electroencephalographic changes, with or without seizures. Photosensitivity is prominent in a very rare epileptic encephalopathy due to de novo CHD2 mutations, but is also seen in epileptic encephalopathies due to other gene mutations. We determined whether CHD2 variation underlies photosensitivity in common epilepsies, specific photosensitive epilepsies and individuals with photosensitivity without seizures. We studied 580 individuals with epilepsy and either photosensitive seizures or abnormal photoparoxysmal response on electroencephalography, or both, and 55 individuals with photoparoxysmal response but no seizures. We compared CHD2 sequence data to publicly available data from 34 427 individuals, not enriched for epilepsy. We investigated the role of unique variants seen only once in the entire data set. We sought CHD2 variants in 238 exomes from familial genetic generalized epilepsies, and in other public exome data sets. We identified 11 unique variants in the 580 individuals with photosensitive epilepsies and 128 unique variants in the 34 427 controls: unique CHD2 variation is over-represented in cases overall (P = 2·17 × 10−5). Among epilepsy syndromes, there was over-representation of unique CHD2 variants (3/36 cases) in the archetypal photosensitive epilepsy syndrome, eyelid myoclonia with absences (P = 3·50 × 10−4). CHD2 variation was not over-represented in photoparoxysmal response without seizures. Zebrafish larvae with chd2 knockdown were tested for photosensitivity. Chd2 knockdown markedly enhanced mild innate zebrafish larval photosensitivity. CHD2 mutation is the first identified cause of the archetypal generalized photosensitive epilepsy syndrome, eyelid myoclonia with absences. Unique CHD2 variants are also associated with photosensitivity in common epilepsies. CHD2 does not encode an ion channel, opening new avenues for research into human cortical excitability.

Objective: To evaluate the phenotypic spectrum associated with mutations in TBC1D24.Methods: We acquired new clinical, EEG, and neuroimaging data of 11 previously unreported and 37 published patients. TBC1D24 mutations, identified through various sequencing methods, can be found online (http://lovd.nl/TBC1D24).Results: Forty-eight patients were included (28 men, 20 women, average age 21 years) from 30 independent families. Eighteen patients (38%) had myoclonic epilepsies. The other patients carried diagnoses of focal (25%), multifocal (2%), generalized (4%), and unclassified epilepsy (6%), and early-onset epileptic encephalopathy (25%). Most patients had drug-resistant epilepsy. We detail EEG, neuroimaging, developmental, and cognitive features, treatment responsiveness, and physical examination. In silico evaluation revealed 7 different highly conserved motifs, with the most common pathogenic mutation located in the first. Neuronal outgrowth assays showed that some TBC1D24 mutations, associated with the most severe TBC1D24-associated disorders, are not necessarily the most disruptive to this gene function.Conclusions: TBC1D24-related epilepsy syndromes show marked phenotypic pleiotropy, with multisystem involvement and severity spectrum ranging from isolated deafness (not studied here), benign myoclonic epilepsy restricted to childhood with complete seizure control and normal intellect, to early-onset epileptic encephalopathy with severe developmental delay and early death. There is no distinct correlation with mutation type or location yet, but patterns are emerging. Given the phenotypic breadth observed, TBC1D24 mutation screening is indicated in a wide variety of epilepsies. A TBC1D24 consortium was formed to develop further research on this gene and its associated phenotypes.

OBJECTIVE: To evaluate the phenotypic spectrum associated with mutations in TBC1D24.METHODS: We acquired new clinical, EEG, and neuroimaging data of 11 previously unreported and 37 published patients. TBC1D24 mutations, identified through various sequencing methods, can be found online (http://lovd.nl/TBC1D24).RESULTS: Forty-eight patients were included (28 men, 20 women, average age 21 years) from 30 independent families. Eighteen patients (38%) had myoclonic epilepsies. The other patients carried diagnoses of focal (25%), multifocal (2%), generalized (4%), and unclassified epilepsy (6%), and early-onset epileptic encephalopathy (25%). Most patients had drug-resistant epilepsy. We detail EEG, neuroimaging, developmental, and cognitive features, treatment responsiveness, and physical examination. In silico evaluation revealed 7 different highly conserved motifs, with the most common pathogenic mutation located in the first. Neuronal outgrowth assays showed that some TBC1D24 mutations, associated with the most severe TBC1D24-associated disorders, are not necessarily the most disruptive to this gene function.CONCLUSIONS: TBC1D24-related epilepsy syndromes show marked phenotypic pleiotropy, with multisystem involvement and severity spectrum ranging from isolated deafness (not studied here), benign myoclonic epilepsy restricted to childhood with complete seizure control and normal intellect, to early-onset epileptic encephalopathy with severe developmental delay and early death. There is no distinct correlation with mutation type or location yet, but patterns are emerging. Given the phenotypic breadth observed, TBC1D24 mutation screening is indicated in a wide variety of epilepsies. A TBC1D24 consortium was formed to develop further research on this gene and its associated phenotypes.

Objective: To critically re-evaluate cases diagnosed as adult neuronal ceroid lipofuscinosis (ANCL) in order to aid clinicopathologic diagnosis as a route to further gene discovery.Methods: Through establishment of an international consortium we pooled 47 unsolved cases regarded by referring centers as ANCL. Clinical and neuropathologic experts within the Consortium established diagnostic criteria for ANCL based on the literature to assess each case. A panel of 3 neuropathologists independently reviewed source pathologic data. Cases were given a final clinicopathologic classification of definite ANCL, probable ANCL, possible ANCL, or not ANCL.Results: Of the 47 cases, only 16 fulfilled the Consortium's criteria of ANCL (5 definite, 2 probable, 9 possible). Definitive alternate diagnoses were made in 10, including Huntington disease, early-onset Alzheimer disease, Niemann-Pick disease, neuroserpinopathy, prion disease, and neurodegeneration with brain iron accumulation. Six cases had features suggesting an alternate diagnosis, but no specific condition was identified; in 15, the data were inadequate for classification. Misinterpretation of normal lipofuscin as abnormal storage material was the commonest cause of misdiagnosis.Conclusions: Diagnosis of ANCL remains challenging; expert pathologic analysis and recent molecular genetic advances revealed misdiagnoses in >1/3 of cases. We now have a refined group of cases that will facilitate identification of new causative genes.

Rolandic epilepsy (RE) is the most common idiopathic focal childhood epilepsy. Its molecular basis is largely unknown and a complex genetic etiology is assumed in the majority of affected individuals. The present study tested whether six large recurrent copy number variants at 1q21, 15q11.2, 15q13.3, 16p11.2, 16p13.11 and 22q11.2 previously associated with neurodevelopmental disorders also increase risk of RE. Our association analyses revealed a significant excess of the 600 kb genomic duplication at the 16p11.2 locus (chr16: 29.5-30.1 Mb) in 393 unrelated patients with typical (n = 339) and atypical (ARE; n = 54) RE compared with the prevalence in 65 046 European population controls (5/393 cases versus 32/65 046 controls; Fisher's exact test P = 2.83 × 10−6, odds ratio = 26.2, 95% confidence interval: 7.9-68.2). In contrast, the 16p11.2 duplication was not detected in 1738 European epilepsy patients with either temporal lobe epilepsy (n = 330) and genetic generalized epilepsies (n = 1408), suggesting a selective enrichment of the 16p11.2 duplication in idiopathic focal childhood epilepsies (Fisher's exact test P = 2.1 × 10−4). In a subsequent screen among children carrying the 16p11.2 600 kb rearrangement we identified three patients with RE-spectrum epilepsies in 117 duplication carriers (2.6%) but none in 202 carriers of the reciprocal deletion. Our results suggest that the 16p11.2 duplication represents a significant genetic risk factor for typical and atypical RE

Objective: To assist the interpretation of genomic data for common epilepsies, we asked whether variants implicated in mild epilepsies in autosomal dominant families are present in the general population. Methods: We studied 12 genes for the milder epilepsies and identified published variants with strong segregation support (de novo germline mutation or ≥4 affected family members). These variants were checked in the Exome Aggregation Consortium (ExAC), a database of genetic variation in over 60,000 individuals. We subsequently evaluated variants in these epilepsy genes that lacked strong segregation support. To determine whether the findings in epilepsies were representative of other diseases, we also assessed the presence of variants in other dominant neurologic disorders (e.g., CADASIL). Results: Published epilepsy variants with strong segregation support (n = 65) were absent (n = 61) or present once (n = 4) in ExAC. By contrast, of 46 published epilepsy variants without strong segregation support, 8 occurred recurrently (2–186 times). Similarly, none of the 45 disease-associated variants from other neurologic disorders with strong segregation support occurred more than once in ExAC. Reanalysis using the larger ExAC V2 plus gnomAD reference cohort showed consistent results. Conclusions: Variants causing autosomal dominant epilepsies are ultra-rare in the general population. Variants observed more than once in ExAC were only found among reports without strong segregation support, suggesting that they may be benign. Clinicians are increasingly faced with the interpretation of genetic variants of unknown significance. These data illustrate that variants present more than once in ExAC are less likely to be pathogenic, reinforcing the valuable clinical role of ExAC.

The classic epileptic encephalopathies, including infantile spasms (IS) and Lennox-Gastaut syndrome (LGS), are severe seizure disorders that usually arise sporadically. De novo variants in genes mainly encoding ion channel and synaptic proteins have been found to account for over 15% of patients with IS or LGS. The contribution of autosomal recessive genetic variation, however, is less well understood. We implemented a rare variant transmission disequilibrium test (TDT) to search for autosomal recessive epileptic encephalopathy genes in a cohort of 320 outbred patient-parent trios that were generally prescreened for rare metabolic disorders. In the current sample, our rare variant transmission disequilibrium test did not identify individual genes with significantly distorted transmission over expectation after correcting for the multiple tests. While the rare variant transmission disequilibrium test did not find evidence of a role for individual autosomal recessive genes, our current sample is insufficiently powered to assess the overall role of autosomal recessive genotypes in an outbred epileptic encephalopathy population.

(The American Journal of Human Genetics 95, 360–370; October 2, 2014) In the list of consortium members for the Epilepsy Phenome/Genome Project, member Dina Amrom's name was misspelled as Amron. The authors regret the error.

The classic epileptic encephalopathies, including infantile spasms (IS) and Lennox-Gastaut syndrome (LGS), are severe seizure disorders that usually arise sporadically. De novo variants in genes mainly encoding ion channel and synaptic proteins have been found to account for over 15% of patients with IS or LGS. The contribution of autosomal recessive genetic variation, however, is less well understood. We implemented a rare variant transmission disequilibrium test (TDT) to search for autosomal recessive epileptic encephalopathy genes in a cohort of 320 outbred patient-parent trios that were generally prescreened for rare metabolic disorders. In the current sample, our rare variant transmission disequilibrium test did not identify individual genes with significantly distorted transmission over expectation after correcting for the multiple tests. While the rare variant transmission disequilibrium test did not find evidence of a role for individual autosomal recessive genes, our current sample is insufficiently powered to assess the overall role of autosomal recessive genotypes in an outbred epileptic encephalopathy population.

We recently identified DEPDC5 as the gene for familial focal epilepsy with variable foci and found mutations in >10% of small families with nonlesional focal epilepsy. Here we show that DEPDC5 mutations are associated with both lesional and nonlesional epilepsies, even within the same family. DEPDC5-associated malformations include bottom-of-the-sulcus dysplasia (3 members from 2 families), and focal band heterotopia (1 individual). DEPDC5 negatively regulates the mammalian target of rapamycin (mTOR) pathway, which plays a key role in cell growth. The clinicoradiological phenotypes associated with DEPDC5 mutations share features with the archetypal mTORopathy, tuberous sclerosis, raising the possibility of therapies targeted to this pathway.

Objective: To evaluate the phenotypic spectrum associated with mutations in TBC1D24. Methods: We acquired new clinical, EEG, and neuroimaging data of 11 previously unreported and 37 published patients. TBC1D24 mutations, identified through various sequencing methods, can be found online (http://lovd.nl/TBC1D24). Results: Forty-eight patients were included (28 men, 20 women, average age 21 years) from 30 independent families. Eighteen patients (38%) had myoclonic epilepsies. The other patients carried diagnoses of focal (25%), multifocal (2%), generalized (4%), and unclassified epilepsy (6%), and early-onset epileptic encephalopathy (25%). Most patients had drug-resistant epilepsy. We detail EEG, neuroimaging, developmental, and cognitive features, treatment responsiveness, and physical examination. In silico evaluation revealed 7 different highly conserved motifs, with the most common pathogenic mutation located in the first. Neuronal outgrowth assays showed that some TBC1D24 mutations, associated with the most severe TBC1D24-associated disorders, are not necessarily the most disruptive to this gene function. Conclusions: TBC1D24-related epilepsy syndromes show marked phenotypic pleiotropy, with multisystem involvement and severity spectrum ranging from isolated deafness (not studied here), benign myoclonic epilepsy restricted to childhood with complete seizure control and normal intellect, to early-onset epileptic encephalopathy with severe developmental delay and early death. There is no distinct correlation with mutation type or location yet, but patterns are emerging. Given the phenotypic breadth observed, TBC1D24 mutation screening is indicated in a wide variety of epilepsies. A TBC1D24 consortium was formed to develop further research on this gene and its associated phenotypes.

The epileptic encephalopathies (EEs) are a devastating group of epilepsies in which epileptic activity and seizures contribute to cognitive impairment or regression.1 Most EEs begin in infancy or early childhood and are associated with poor developmental outcome. Although the cause is unknown in the majority of cases, recent studies confirm that de novo mutations and copy number variants (CNVs) play an important role.2, 3 We recently reported exome sequencing data in 264 parent–proband trios with infantile spasms (n = 149) or Lennox–Gastaut syndrome (LGS; n = 115) without syndromic features or magnetic resonance imaging (MRI) abnormalities from the Epilepsy Phenome/Genome Project (EPGP) cohort, identifying likely pathogenic, de novo sequence changes in >10% of patients.2 Here we report results of copy number analysis derived from the exome data of this cohort and 85 additional patients to further elucidate the genetic architecture of these paradigmatic EEs. Our exome‐based CNV calling yields similar results to array‐based studies for confirmed, de novo, likely pathogenic CNVs.

Genetics should now be part of everyday clinical epilepsy practice. Good data exist to provide empiric risks based on epilepsy syndrome diagnosis. Investigation of the molecular basis of some epilepsies is now a practical clinical task and is of clear value to the patient and family. In some cases, specific therapeutic decisions can now be made based on genetic findings, and this scenario of precision therapy is likely to increase in the coming years.

Purpose: To determine clinical phenotypes, evolution and genetic background of a large family with a combination of two unusual forms of reflex epilepsies. Method: Phenotyping was performed in eighteen family members (10 F, 8 M) including standardized EEG recordings with intermittent photic stimulation (IPS). Genetic analyses (linkage scans, Whole Exome Sequencing (WES) and Functional studies) were performed using photoparoxysmal EEG responses (PPRs) as affection status. Results: The proband suffered from speaking induced jaw-jerks and increasing limb jerks evoked by flickering sunlight since about 50 years of age. Three of her family members had the same phenotype. Generalized PPRs were found in seven members (six above 50 years of age) with myoclonus during the PPR. Evolution was typical: Sensitivity to lights with migraine-like complaints around adolescence, followed by jerks evoked by lights and spontaneously with dropping of objects, and strong increase of light sensitivity and onset of talking induced jaw jerks around 50 years. Linkage analysis showed suggestive evidence for linkage to four genomic regions. All photosensitive family members shared a heterozygous R129C mutation in the SCNM1 gene that regulates splicing of voltage gated ion channels. Mutation screening of 134 unrelated PPR patients and 95 healthy controls, did not replicate these findings. Conclusion: This family presents a combination of two rare reflex epilepsies. Genetic analysis favors four genomic regions and points to a shared SCNM1 mutation that was not replicated in a general cohort of photosensitive subjects. Further genetic studies in families with similar combination of features are warranted. (C) 2015 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.

Mutations in KCNT1 have been implicated in autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and epilepsy of infancy with migrating focal seizures (EIMFS). More recently, a whole exome sequencing study of epileptic encephalopathies identified an additional de novo mutation in 1 proband with EIMFS. We aim to investigate the electrophysiological and pharmacological characteristics of hKCNT1 mutations and examine developmental expression levels.Here we use a Xenopus laevis oocyte-based automated 2-electrode voltage clamp assay. The effects of quinidine (100 and 300 μM) are also tested. Using quantitative reverse transcriptase polymerase chain reaction, the relative levels of mouse brain mKcnt1 mRNA expression are determined.We demonstrate that KCNT1 mutations implicated in epilepsy cause a marked increase in function. Importantly, there is a significant group difference in gain of function between mutations associated with ADNFLE and EIMFS. Finally, exposure to quinidine significantly reduces this gain of function for all mutations studied.These results establish direction for a targeted therapy and potentially exemplify a translational paradigm for in vitro studies informing novel therapies in a neuropsychiatric disease.

We identified a small family with autosomal recessive, infantile-onset epilepsy and intellectual disability. Exome sequencing identified a homozygous missense variant in the gene TNK2, encoding a brain-expressed tyrosine kinase. Sequencing of the coding region of TNK2 in 110 patients with a similar phenotype failed to detect further homozygote or compound heterozygote mutations. Pathogenicity of the variant is supported by the results of our functional studies, which demonstrated that the variant abolishes NEDD4 binding to TNK2, preventing its degradation after epidermal growth factor stimulation. Definitive proof of pathogenicity will require confirmation in unrelated patients.

This report is a practical reference guide for genetic testing of SCN1A, the gene encoding the α1 subunit of neuronal voltage-gated sodium channels (protein name: Nav1.1). Mutations in this gene are frequently found in Dravet syndrome (DS), and are sometimes found in genetic epilepsy with febrile seizures plus (GEFS+), migrating partial seizures of infancy (MPSI), other infantile epileptic encephalopathies, and rarely in infantile spasms. Recommendations for testing: (1) Testing is particularly useful for people with suspected DS and sometimes in other early onset infantile epileptic encephalopathies such as MPSI because genetic confirmation of the clinical diagnosis may allow optimization of antiepileptic therapy with the potential to improve seizure control and developmental outcome. In addition, a molecular diagnosis may prevent the need for unnecessary investigations, as well as inform genetic counseling. (2) SCN1A testing should be considered in people with possible DS where the typical initial presentation is of a developmentally normal infant presenting with recurrent, febrile or afebrile prolonged, hemiclonic seizures or generalized status epilepticus. After age 2, the clinical diagnosis of DS becomes more obvious, with the classical evolution of other seizure types and developmental slowing. (3) In contrast to DS, the clinical utility of SCN1A testing for GEFS+ remains questionable. (4) The test is not recommended for children with phenotypes that are not clearly associated with SCN1A mutations such as those characterized by abnormal development or neurologic deficits apparent at birth or structural abnormalities of the brain. Interpreting test results: (1) Mutational testing of SCN1A involves both conventional DNA sequencing of the coding regions and analyses to detect genomic rearrangements within the relevant chromosomal region: 2q24. Interpretation of the test results must always be done in the context of the electroclinical syndrome and often requires the assistance of a medical geneticist, since many genomic variations are possible and it is essential to differentiate benign polymorphisms from pathogenic mutations. (2) Missense variants may have no apparent effect on the phenotype (benign polymorphisms) or may represent mutations underlying DS, MPSI, GEFS+, and related syndromes and can provide a challenge in interpretation. (3) Conventional methods do not detect variations in introns or promoter or regulatory regions; therefore, a negative test does not exclude a pathogenic role of SCN1A in a specific phenotype. (4) It is important to note that a negative test does not rule out the clinical diagnosis of DS or other conditions because genes other than SCN1A may be involved. Obtaining written informed consent and genetic counseling should be considered prior to molecular testing, depending on the clinical situation and local regulations. Fil: Hirose, Shinichi. Fukuoka University; Japón Fil: Scheffer, Ingrid E.. The University of Melbourne; Australia Fil: Marini, Carla. Università degli Studi di Pisa; Italia Fil: De Jonghe, Peter. Universiteit Antwerpen; Bélgica Fil: Andermann, Eva. McGill University. Montreal Neurological Institute and Hospital; Canadá Fil: Goldman, Alica M.. Baylor College of Medicine; Estados Unidos Fil: Kauffman, Marcelo Andres. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos "Ramos Mejía"; Argentina Fil: Tan, Nigel C. K.. National Neuroscience Institute; Singapur Fil: Lowenstein, Daniel H.. University of California; Estados Unidos Fil: Sisodiya, Sanjay M.. University College London; Estados Unidos. Epilepsy Society; Reino Unido Fil: Ottman, Ruth. Columbia University; Estados Unidos Fil: Berkovic, Samuel F.. The University of Melbourne; Australia Fil: The Genetics Commission of the International League Against Epilepsy.

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 typerelated 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.

The axon initial segment (AIS) contains the site of action potential initiation and plays a major role in neuronal excitability. AIS function relies on high concentrations of different ion channels and complex regulatory mechanisms that orchestrate molecular microarchitecture. We review recent evidence that a large number of ion channels associated with epilepsy are enriched at the AIS, making it a 'hotspot' for epileptogenesis. Furthermore, we present novel data on the clustering of GABRgamma2 receptors in the AIS of cortical and hippocampal neurons in a knock in mouse model of a human genetic epilepsy. This article highlights the molecular coincidence of epilepsy mutations at the AIS and reviews pathogenic mechanisms converging at the AIS.

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is a nonlesional condition associated with mutation of the gene coding for the α4 nicotinic acetylcholine receptor (nAChR). The nAChR modulates aspects of memory and attention. We examined the neuropsychological phenotype of ADNFLE, with a particular emphasis on understanding the impact on frontal lobe functions. We used standard clinical tests as well as focused measures of frontal lobe function in a well-defined group of patients with ADNFLE. Their performance was compared with that of a group of age-, sex-, and education-matched control participants. Patients with ADNFLE showed impairments on tasks requiring cognitive flexibility against a background of well-preserved intellectual abilities. In accord with existing research, verbal memory impairments were identified in the patient group; the level of impairment on these tasks correlated with disease-related factors. In our study of ADNFLE associated with one mutation, cognitive flexibility appears to be the core cognitive deficit.

P>Paroxysmal exercise-induced dyskinesia (PED) and epilepsy without intellectual disability have recently been recognized as manifestations of deficiency of the glucose transporter GLUT1, due to mutations in the gene SLC2A1. We describe a family with six definitely affected members in two generations. Two had PED, three had epilepsy, and one had both. A missense mutation in SLC2A1 (c.950A > C; p.N317T) was detected in five living affected members, but absent in three nonaffected first-degree members and in one subject believed to be a phenocopy. The clinical picture of mild epilepsy with onset in adolescence or early adulthood plus PED should raise a suspicion of GLUT1 deficiency.

OBJECTIVE: A major goal of epilepsy research is to understand the molecular and functional basis of seizure genesis. A human GABA(A) gamma2 gene mutation (R43Q) is associated with generalized epilepsy. Introduction of this mutation into a mouse by gene targeting recapitulates the human phenotype demonstrating a strong genotype to phenotype link. GABA(A) receptors play a role in the moment-to-moment control of brain function and also on the long-term wiring of the brain by directing neuronal development. Our objective was to determine whether developmental expression of the mutation alters seizure susceptibility later in life. METHODS: A tetracycline-based conditional model for activation of a hypomorphic Q43 disease allele was created and validated. Seizure susceptibility was assessed using the subcutaneous pentylenetetrazole model. RESULTS: Seizure susceptibility was significantly reduced in mice where the Q43 allele was suppressed during development. INTERPRETATION: These results demonstrate that a human epilepsy-causing mutation impacts network stability during a critical developmental period. These data suggest that identification of presymptomatic children may provide a window for therapeutic intervention before overt symptoms are observed, potentially altering the course of epileptogenesis.

ObjectiveWe aimed to identify genes associated with genetic generalized epilepsy (GGE) by combining large cohorts enriched with individuals with a positive family history. Secondarily, we set out to compare the association of genes independently with familial and sporadic GGE.MethodsWe performed a case-control whole exome sequencing study in unrelated individuals of European descent diagnosed with GGE (previously recruited and sequenced through multiple international collaborations) and ancestry-matched controls. The association of ultra-rare variants (URVs; in 18834 protein-coding genes) with epilepsy was examined in 1928 individuals with GGE (vs. 8578 controls), then separately in 945 individuals with familial GGE (vs. 8626 controls), and finally in 1005 individuals with sporadic GGE (vs. 8621 controls). We additionally examined the association of URVs with familial and sporadic GGE in two gene sets important for inhibitory signaling (19genes encoding γ-aminobutyric acid type A [GABAA ] receptors, 113genes representing the GABAergic pathway).ResultsGABRG2 was associated with GGE (p=1.8×10-5 ), approaching study-wide significance in familial GGE (p=3.0×10-6 ), whereas no gene approached a significant association with sporadic GGE. Deleterious URVs in the most intolerant subgenic regions in genes encoding GABAA receptors were associated with familial GGE (odds ratio [OR]=3.9, 95% confidence interval [CI]=1.9-7.8, false discovery rate [FDR]-adjusted p=.0024), whereas their association with sporadic GGE had marginally lower odds (OR=3.1, 95% CI=1.3-6.7, FDR-adjusted p=.022). URVs in GABAergic pathway genes were associated with familial GGE (OR=1.8, 95% CI=1.3-2.5, FDR-adjusted p=.0024) but not with sporadic GGE (OR=1.3, 95% CI=.9-1.9, FDR-adjusted p=.19).SignificanceURVs in GABRG2 are likely an important risk factor for familial GGE. The association of gene sets of GABAergic signaling with familial GGE is more prominent than with sporadic GGE.

© 2019 Elsevier Ltd Treatment of the neuronal ceroid lipofuscinoses, also known as Batten disease, is at the start of a new era because of diagnostic and therapeutic advances relevant to this group of inherited neurodegenerative and life-limiting disorders that affect children. Diagnosis has improved with the use of comprehensive DNA-based tests that simultaneously screen for many genes. The identification of disease-causing mutations in 13 genes provides a basis for understanding the molecular mechanisms underlying neuronal ceroid lipofuscinoses, and for the development of targeted therapies. These targeted therapies include enzyme replacement therapies, gene therapies targeting the brain and the eye, cell therapies, and pharmacological drugs that could modulate defective molecular pathways. Such therapeutic developments have the potential to enable earlier diagnosis and better targeted therapeutic management. The first approved treatment is an intracerebroventricularly administered enzyme for neuronal ceroid lipofuscinosis type 2 disease that delays symptom progression. Efforts are underway to make similar progress for other forms of the disorder.

EBioMedicine 72, 103588 (2021). doi:10.1016/j.ebiom.2021.103588, Published by Elsevier, Amsterdam [u.a.]

OBJECTIVE: To comprehensively describe the new syndrome of myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK), including cellular electrophysiological characterization of observed clinical improvement with fever.METHODS: We analyzed clinical, electroclinical, and neuroimaging data for 20 patients with MEAK due to recurrent KCNC1 p.R320H mutation. In vitro electrophysiological studies were conducted using whole cell patch-clamp to explore biophysical properties of wild-type and mutant KV 3.1 channels.RESULTS: Symptoms began at between 3 and 15 years of age (median = 9.5), with progressively severe myoclonus and rare tonic-clonic seizures. Ataxia was present early, but quickly became overshadowed by myoclonus; 10 patients were wheelchair-bound by their late teenage years. Mild cognitive decline occurred in half. Early death was not observed. Electroencephalogram (EEG) showed generalized spike and polyspike wave discharges, with documented photosensitivity in most. Polygraphic EEG-electromyographic studies demonstrated a cortical origin for myoclonus and striking coactivation of agonist and antagonist muscles. Magnetic resonance imaging revealed symmetrical cerebellar atrophy, which appeared progressive, and a prominent corpus callosum. Unexpectedly, transient clinical improvement with fever was noted in 6 patients. To explore this, we performed high-temperature in vitro recordings. At elevated temperatures, there was a robust leftward shift in activation of wild-type KV 3.1, increasing channel availability.INTERPRETATION: MEAK has a relatively homogeneous presentation, resembling Unverricht-Lundborg disease, despite the genetic and biological basis being quite different. A remarkable improvement with fever may be explained by the temperature-dependent leftward shift in activation of wild-type KV 3.1 subunit-containing channels, which would counter the loss of function observed for mutant channels, highlighting KCNC1 as a potential target for precision therapeutics. Ann Neurol 2017;81:677-689.

The chromosome 15q13.3 region has been implicated in epilepsy, intellectual disability and neuropsychiatric disorders, especially schizophrenia. Deficiency of the acetylcholine receptor gene CHRNA7 and the partial duplication, CHRFAM7A, may contribute to these phenotypes and we sought to comprehensively analyze these genes in genetic generalized epilepsy. We analyzed using DHPLC, Sanger sequencing and long range PCR, 174 probands with genetic generalized epilepsy with or without intellectual disability or psychosis, including 8 with the recurrent 15q13.3 microdeletion. We searched CHRNA7 and CHRFAM7A for single sequence variants, small copy number variants, and the common 2-bp deletion in CHRFAM7A. We identified two novel and one reported missense variants. The common 2-bp deletion was not enriched in patients compared to controls. Our data suggest that missense mutations in CHRNA7 contribute to complex inheritance in genetic generalized epilepsy in a similar fashion to the 15q13.3 microdeletion. They do not support a pathogenic role for the common 2-bp CHRFAM7A deletion. Refereed/Peer-reviewed

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

Knobloch syndrome [OMIM: (KNO1) #267750] is a rare and clinically heterogeneous autosomal recessive disorder caused by mutations in COL18A1. Knobloch syndrome is characterised by abnormalities of the eye and occipital skull defects however the full phenotypic spectrum is yet to be defined. This report describes a family of four affected sisters with polymicrogyria, refractory seizures, and intellectual impairment of varying severity with a Lennox-Gastaut phenotype, and complex eye abnormalities where a syndromic diagnosis was not initially made. Whole exome sequencing of two affected sisters followed by filtering for rare and potentially disease causing variants in all genes identified compound heterozygous variants in NM_030582.3 (COL18A1): c.3690G > A: p.(Trp1230*) and NM_030582.3 (COL18A1): c.4063_4064delCT: p.(Leu1355Valfs*72). The two variants co-segregated with the affected individuals in the family. Identification of COL18A1 mutations in individuals with a Lennox-Gastaut phenotype and anterior polymicrogyria but lacking the classical occipital encephalocele expands the COL18A1 clinical spectrum. Refereed/Peer-reviewed

International audience; Familial adult myoclonus epilepsy (FAME) is a rare autosomal dominant disorder characterized by adult onset, involuntary muscle jerks, cortical myoclonus and occasional seizures. FAME is genetically heterogeneous with more than 70 families reported worldwide and five potential disease loci. The efforts to identify potential causal variants have been unsuccessful in all but three families. To date, linkage analysis has been the main approach to find and narrow FAME critical regions. We propose an alternative method, pedigree free identity-by-descent (IBD) mapping, that infers regions of the genome between individuals that have been inherited from a common ancestor. IBD mapping provides an alternative to linkage analysis in the presence of allelic and locus heterogeneity by detecting clusters of individuals who share a common allele. Succeeding IBD mapping, gene prioritization based on gene co-expression analysis can be used to identify the most promising candidate genes. We performed an IBD analysis using high-density single nucleotide polymorphism (SNP) array data followed by gene prioritization on a FAME cohort of ten European families and one Australian/New Zealander family; eight of which had known disease loci. By identifying IBD regions common to multiple families, we were able to narrow the FAME2 locus to a 9.78 megabase interval within 2p11.2-q11.2. We provide additional evidence of a founder effect in four Italian families and allelic heterogeneity with at least four distinct founders responsible for FAME at the FAME2 locus. In addition, we suggest candidate disease genes using gene prioritization based on gene co-expression analysis.

Aim To show that atypical multifocal Dravet syndrome is a recognizable, electroclinical syndrome associated with sodium channel gene (SCN1A) mutations that readily escapes diagnosis owing to later cognitive decline and tonic seizures. Method Eight patients underwent electroclinical characterization. SCN1A was sequenced and copy number variations sought by multiplex ligation-dependent probe amplification. Results All patients were female (age range at assessment 5–26y) with median seizure onset at 6.5 months (range 4–19mo). The initial seizure was brief in seven and status epilepticus only occurred in one; three were febrile. Focal seizures occurred in four patients and bilateral convulsion in the other four. All patients developed multiple focal seizure types and bilateral convulsions, with seizure clusters in six. The most common focal seizure semiology (six out of eight) comprised unilateral clonic activity. Five also had focal or asymmetric tonic seizures. Rare or transient myoclonic seizures occurred in six individuals, often triggered by specific antiepileptic drugs. Developmental slowing occurred in all: six between 3 years and 8 years, and two around 1 year 6 months. Cognitive outcome varied from severe to mild intellectual disability. Multifocal epileptiform discharges were seen on electroencephalography. Seven out of eight patients had SCN1A mutations. Interpretation Atypical, multifocal Dravet syndrome with SCN1A mutations may not be recognized because of later cognitive decline and frequent tonic seizures.