A founder event causing a dominant childhood epilepsy survives 800 years through weak selective pressure.

Genetic epilepsy with febrile seizures plus (GEFS+) is an autosomal dominant familial epilepsy syndrome characterized by distinctive phenotypic heterogeneity within families. The SCN1B c.363C>G (p.Cys121Trp) variant has been identified in independent, multi-generational families with GEFS+. Although the variant is present in population databases (at very low frequency), there is strong clinical, genetic, and functional evidence to support pathogenicity. Recurrent variants may be due to a founder event in which the variant has been inherited from a common ancestor. Here, we report evidence of a single founder event giving rise to the SCN1B c.363C>G variant in 14 independent families with epilepsy. A common haplotype was observed in all families, and the age of the most recent common ancestor was estimated to be approximately 800 years ago. Analysis of UK Biobank whole-exome-sequencing data identified 74 individuals with the same variant. All individuals carried haplotypes matching the epilepsy-affected families, suggesting all instances of the variant derive from a single mutational event. This unusual finding of a variant causing an autosomal dominant, early-onset disease in an outbred population that has persisted over many generations can be attributed to the relatively mild phenotype in most carriers and incomplete penetrance. Founder events are well established in autosomal recessive and late-onset disorders but are rarely observed in early-onset, autosomal dominant diseases. These findings suggest variants present in the population at low frequencies should be considered potentially pathogenic in mild phenotypes with incomplete penetrance and may be more important contributors to the genetic landscape than previously thought.

Sporadic hypothalamic hamartoma is a ciliopathy with somatic and bi-allelic contributions.

Hypothalamic hamartoma with gelastic seizures is a well-established cause of drug-resistant epilepsy in early life. The development of novel surgical techniques has permitted the genomic interrogation of hypothalamic hamartoma tissue. This has revealed causative mosaic variants within GLI3, OFD1 and other key regulators of the sonic-hedgehog pathway in a minority of cases. Sonic-hedgehog signalling proteins localize to the cellular organelle primary cilia. We therefore explored the hypothesis that cilia gene variants may underlie hitherto unsolved cases of sporadic hypothalamic hamartoma. We performed high-depth exome sequencing and chromosomal microarray on surgically resected hypothalamic hamartoma tissue and paired leukocyte-derived DNA from 27 patients. We searched for both germline and somatic variants under both dominant and bi-allelic genetic models. In hamartoma-derived DNA of seven patients we identified bi-allelic (one germline, one somatic) variants within one of four cilia genes-DYNC2I1, DYNC2H1, IFT140 or SMO. In eight patients, we identified single somatic variants in the previously established hypothalamic hamartoma disease genes GLI3 or OFD1. Overall, we established a plausible molecular cause for 15/27 (56%) patients. Here, we expand the genetic architecture beyond single variants within dominant disease genes that cause sporadic hypothalamic hamartoma to bi-allelic (one germline/one somatic) variants, implicate three novel cilia genes and reconceptualize the disorder as a ciliopathy.

Progressive myoclonus epilepsies-Residual unsolved cases have marked genetic heterogeneity including dolichol-dependent protein glycosylation pathway genes.

Progressive myoclonus epilepsies (PMEs) comprise a group of clinically and genetically heterogeneous rare diseases. Over 70% of PME cases can now be molecularly solved. Known PME genes encode a variety of proteins, many involved in lysosomal and endosomal function. We performed whole-exome sequencing (WES) in 84 (78 unrelated) unsolved PME-affected individuals, with or without additional family members, to discover novel causes. We identified likely disease-causing variants in 24 out of 78 (31%) unrelated individuals, despite previous genetic analyses. The diagnostic yield was significantly higher for individuals studied as trios or families (14/28) versus singletons (10/50) (OR = 3.9, p value = 0.01, Fisher's exact test). The 24 likely solved cases of PME involved 18 genes. First, we found and functionally validated five heterozygous variants in NUS1 and DHDDS and a homozygous variant in ALG10, with no previous disease associations. All three genes are involved in dolichol-dependent protein glycosylation, a pathway not previously implicated in PME. Second, we independently validate SEMA6B as a dominant PME gene in two unrelated individuals. Third, in five families, we identified variants in established PME genes; three with intronic or copy-number changes (CLN6, GBA, NEU1) and two very rare causes (ASAH1, CERS1). Fourth, we found a group of genes usually associated with developmental and epileptic encephalopathies, but here, remarkably, presenting as PME, with or without prior developmental delay. Our systematic analysis of these cases suggests that the small residuum of unsolved cases will most likely be a collection of very rare, genetically heterogeneous etiologies.

Somatic mosaicism in focal epilepsies.

PURPOSE OF REVIEW: Over the past decade, it has become clear that brain somatic mosaicism is an important contributor to many focal epilepsies. The number of cases and the range of underlying pathologies with somatic mosaicism are rapidly increasing. This growth in somatic variant discovery is revealing dysfunction in distinct molecular pathways in different focal epilepsies. RECENT FINDINGS: We briefly summarize the current diagnostic yield of pathogenic somatic variants across all types of focal epilepsy where somatic mosaicism has been implicated and outline the specific molecular pathways affected by these variants. We will highlight the recent findings that have increased diagnostic yields such as the discovery of pathogenic somatic variants in novel genes, and new techniques that allow the discovery of somatic variants at much lower variant allele fractions. SUMMARY: A major focus will be on the emerging evidence that somatic mosaicism may contribute to some of the more common focal epilepsies such as temporal lobe epilepsy with hippocampal sclerosis, which could lead to it being re-conceptualized as a genetic disorder.

Familial Mesial Temporal Lobe Epilepsy: Clinical Spectrum and Genetic Evidence for a Polygenic Architecture.

OBJECTIVE: Familial mesial temporal lobe epilepsy (FMTLE) is an important focal epilepsy syndrome; its molecular genetic basis is unknown. Clinical descriptions of FMTLE vary between a mild syndrome with prominent déjà vu to a more severe phenotype with febrile seizures and hippocampal sclerosis. We aimed to refine the phenotype of FMTLE by analyzing a large cohort of patients and asked whether common risk variants for focal epilepsy and/or febrile seizures, measured by polygenic risk scores (PRS), are enriched in individuals with FMTLE. METHODS: We studied 134 families with ≥ 2 first or second-degree relatives with temporal lobe epilepsy, with clear mesial ictal semiology required in at least one individual. PRS were calculated for 227 FMTLE cases, 124 unaffected relatives, and 16,077 population controls. RESULTS: The age of patients with FMTLE onset ranged from 2.5 to 70 years (median = 18, interquartile range = 13-28 years). The most common focal seizure symptom was déjà vu (62% of cases), followed by epigastric rising sensation (34%), and fear or anxiety (22%). The clinical spectrum included rare cases with drug-resistance and/or hippocampal sclerosis. FMTLE cases had a higher mean focal epilepsy PRS than population controls (odds ratio = 1.24, 95% confidence interval = 1.06, 1.46, p = 0.007); in contrast, no enrichment for the febrile seizure PRS was observed. INTERPRETATION: FMTLE is a generally mild drug-responsive syndrome with déjà vu being the commonest symptom. In contrast to dominant monogenic focal epilepsy syndromes, our molecular data support a polygenic basis for FMTLE. Furthermore, the PRS data suggest that sub-genome-wide significant focal epilepsy genome-wide association study single nucleotide polymorphisms are important risk variants for FMTLE. ANN NEUROL 2023;94:825-835.

Familial aggregation of seizure outcomes in four familial epilepsy cohorts.

OBJECTIVE: To assess the possible effects of genetics on seizure outcome by estimating the familial aggregation of three outcome measures: seizure remission, history of ≥4 tonic-clonic seizures, and seizure control for individuals taking antiseizure medication. METHODS: We analyzed families containing multiple persons with epilepsy in four previously collected retrospective cohorts. Seizure remission was defined as being 5 and 10 years seizure-free at last observation. Total number of tonic-clonic seizures was dichotomized at <4 and ≥4 seizures. Seizure control in patients taking antiseizure medication was defined as no seizures for 1, 2, and 3 years. We used Bayesian generalized linear mixed-effects model (GLMM) to estimate the intraclass correlation coefficient (ICC) of the family-specific random effect, controlling for epilepsy type, age at epilepsy onset, and age at last data collection as fixed effects. We analyzed each cohort separately and performed meta-analysis using GLMMs. RESULTS: The combined cohorts included 3644 individuals with epilepsy from 1463 families. A history of ≥4 tonic-clonic seizures showed strong familial aggregation in three separate cohorts and meta-analysis (ICC .28, 95% confidence interval [CI] .21-.35, Bayes factor 8 × 1016). Meta-analyses did not reveal significant familial aggregation of seizure remission (ICC .08, 95% CI .01-.17, Bayes factor 1.46) or seizure control for individuals taking antiseizure medication (ICC .13, 95% CI 0-.35, Bayes factor 0.94), with heterogeneity among cohorts. SIGNIFICANCE: A history of ≥4 tonic-clonic seizures aggregated strongly in families, suggesting a genetic influence, whereas seizure remission and seizure control for individuals taking antiseizure medications did not aggregate consistently in families. Different seizure outcomes may have different underlying biology and risk factors. These findings should inform the future molecular genetic studies of seizure outcomes.

Plasma neurofilament light in behavioural variant frontotemporal dementia compared to mood and psychotic disorders.

OBJECTIVE: Blood biomarkers of neuronal injury such as neurofilament light (NfL) show promise to improve diagnosis of neurodegenerative disorders and distinguish neurodegenerative from primary psychiatric disorders (PPD). This study investigated the diagnostic utility of plasma NfL to differentiate behavioural variant frontotemporal dementia (bvFTD, a neurodegenerative disorder commonly misdiagnosed initially as PPD), from PPD, and performance of large normative/reference data sets and models. METHODS: Plasma NfL was analysed in major depressive disorder (MDD, n = 42), bipolar affective disorder (BPAD, n = 121), treatment-resistant schizophrenia (TRS, n = 82), bvFTD (n = 22), and compared to the reference cohort (Control Group 2, n = 1926, using GAMLSS modelling), and age-matched controls (Control Group 1, n = 96, using general linear models). RESULTS: Large differences were seen between bvFTD (mean NfL 34.9 pg/mL) and all PPDs and controls (all < 11 pg/mL). NfL distinguished bvFTD from PPD with high accuracy, sensitivity (86%), and specificity (88%). GAMLSS models using reference Control Group 2 facilitated precision interpretation of individual levels, while performing equally to or outperforming models using local controls. Slightly higher NfL levels were found in BPAD, compared to controls and TRS. CONCLUSIONS: This study adds further evidence on the diagnostic utility of NfL to distinguish bvFTD from PPD of high clinical relevance to a bvFTD differential diagnosis, and includes the largest cohort of BPAD to date. Using large reference cohorts, GAMLSS modelling and the interactive Internet-based application we developed, may have important implications for future research and clinical translation. Studies are underway investigating utility of plasma NfL in diverse neurodegenerative and primary psychiatric conditions in real-world clinical settings.

Cerebrospinal fluid neurofilament light predicts longitudinal diagnostic change in patients with psychiatric and neurodegenerative disorders.

OBJECTIVE: People with neuropsychiatric symptoms often experience delay in accurate diagnosis. Although cerebrospinal fluid neurofilament light (CSF NfL) shows promise in distinguishing neurodegenerative disorders (ND) from psychiatric disorders (PSY), its accuracy in a diagnostically challenging cohort longitudinally is unknown. METHODS: We collected longitudinal diagnostic information (mean = 36 months) from patients assessed at a neuropsychiatry service, categorising diagnoses as ND/mild cognitive impairment/other neurological disorders (ND/MCI/other) and PSY. We pre-specified NfL > 582 pg/mL as indicative of ND/MCI/other. RESULTS: Diagnostic category changed from initial to final diagnosis for 23% (49/212) of patients. NfL predicted the final diagnostic category for 92% (22/24) of these and predicted final diagnostic category overall (ND/MCI/other vs. PSY) in 88% (187/212), compared to 77% (163/212) with clinical assessment alone. CONCLUSIONS: CSF NfL improved diagnostic accuracy, with potential to have led to earlier, accurate diagnosis in a real-world setting using a pre-specified cut-off, adding weight to translation of NfL into clinical practice.

Brain mosaicism of hedgehog signalling and other cilia genes in hypothalamic hamartoma.

Hypothalamic hamartoma (HH) is a rare benign developmental brain lesion commonly associated with a well characterized epilepsy phenotype. Most individuals with HH are non-syndromic without additional developmental anomalies nor a family history of disease. Nonetheless, HH is a feature of Pallister-Hall (PHS) and Oro-Facial-Digital Type VI (OFD VI) syndromes, both characterized by additional developmental anomalies. Initial genetic of analysis HH began with syndromic HH, where germline inherited or de novo variants in GLI3, encoding a central transcription factor in the sonic hedgehog (Shh) signalling pathway, were identified in most individuals with PHS. Following these discoveries in syndromic HH, the hypothesis that post-zygotic mosaicism in related genes may underly non-syndromic HH was tested. We discuss the identified mosaic variants within individuals with non-syndromic HH, review the analytical methodologies and diagnostic yields, and explore understanding of the functional role of the implicated genes with respect to Shh signalling, and cilia development and function. We also outline future challenges in studying non-syndromic HH and suggest potential novel strategies to interrogate brain mosaicism in HH.

The Genetics of Epilepsy.

Epilepsy encompasses a group of heterogeneous brain diseases that affect more than 50 million people worldwide. Epilepsy may have discernible structural, infectious, metabolic, and immune etiologies; however, in most people with epilepsy, no obvious cause is identifiable. Based initially on family studies and later on advances in gene sequencing technologies and computational approaches, as well as the establishment of large collaborative initiatives, we now know that genetics plays a much greater role in epilepsy than was previously appreciated. Here, we review the progress in the field of epilepsy genetics and highlight molecular discoveries in the most important epilepsy groups, including those that have been long considered to have a nongenetic cause. We discuss where the field of epilepsy genetics is moving as it enters a new era in which the genetic architecture of common epilepsies is starting to be unraveled.

Rare Genetic Variation and Outcome of Surgery for Mesial Temporal Lobe Epilepsy.

OBJECTIVE: Genetic factors have long been debated as a cause of failure of surgery for mesial temporal lobe epilepsy (MTLE). We investigated whether rare genetic variation influences seizure outcomes of MTLE surgery. METHODS: We performed an international, multicenter, whole exome sequencing study of patients who underwent surgery for drug-resistant, unilateral MTLE with normal magnetic resonance imaging (MRI) or MRI evidence of hippocampal sclerosis and ≥2-year postsurgical follow-up. Patients with either sustained seizure freedom (favorable outcome) or ongoing uncontrolled seizures since surgery (unfavorable outcome) were included. Exomes of controls without epilepsy were also included. Gene set burden analyses were carried out to identify genes with significant enrichment of rare deleterious variants in patients compared to controls. RESULTS: Nine centers from 3 continents contributed 206 patients operated for drug-resistant unilateral MTLE, of whom 196 (149 with favorable outcome and 47 with unfavorable outcome) were included after stringent quality control. Compared to 8,718 controls, MTLE cases carried a higher burden of ultrarare missense variants in constrained genes that are intolerant to loss-of-function (LoF) variants (odds ratio [OR] = 2.6, 95% confidence interval [CI] = 1.9-3.5, p = 1.3E-09) and in genes encoding voltage-gated cation channels (OR = 2.4, 95% CI = 1.4-3.8, p = 2.7E-04). Proportions of subjects with such variants were comparable between patients with favorable outcome and those with unfavorable outcome, with no significant between-group differences. INTERPRETATION: Rare variation contributes to the genetic architecture of MTLE, but does not appear to have a major role in failure of MTLE surgery. These findings can be incorporated into presurgical decision-making and counseling. ANN NEUROL 2022.

History of familial adult myoclonus epilepsy/benign adult familial myoclonic epilepsy around the world.

Familial adult myoclonus epilepsy/benign adult familial myoclonic epilepsy (FAME/BAFME) has emerged as a specific and recognizable epilepsy syndrome with autosomal dominant inheritance found around the world. Here, we trace the history of this syndrome. Initially, it was likely conflated with other familial myoclonus epilepsies, especially the progressive myoclonus epilepsies. As the progressive myoclonus epilepsies became better understood clinically and genetically, this group began to stand out and was first recognized as such in Japan. Subsequently, families were recognized around the world and there was debate as to whether they represented one or multiple disorders. Clarification came with the identification of pentanucleotide repeats in Japanese families, and FAME/BAFME was quickly shown to be due to pentanucleotide expansions in at least six genes. These have geographic predilections and appear to have been caused by historically ancient initial mutations. Within and between families, there is some variation in the phenotype, explained in large part by expansion size, but whether there are features specific to individual genes remains uncertain.

Extended follow-up after anterior temporal lobectomy demonstrates seizure recurrence 20+ years postsurgery.

OBJECTIVE: Anterior temporal lobectomy (ATL) for medication-resistant localized epilepsy results in ablation or reduction of seizures for most patients. However, some individuals who attain an initial extended period of postsurgical seizure freedom will experience a later seizure recurrence. In this study, we examined the prevalence and some risk factors for late recurrence in an ATL cohort with extensive regular follow-up. METHODS: Included were 449 patients who underwent ATL at Austin Health, Australia, from 1978 to 2008. Postsurgical follow-up was undertaken 2-3 yearly. Seizure recurrence was tested using Kaplan-Meier analysis, log-rank test, and Cox regression. Late recurrence was qualified as a first disabling seizure >2 years postsurgery. We examined risks within the ATL cohort according to broad pathology groups and tested whether late recurrence differed for the ATL cohort compared to patients who had resections outside the temporal lobe (n = 98). RESULTS: Median post-ATL follow-up was 22 years (range = .1-38.6), 6% were lost to follow-up, and 12% had died. Probabilities for remaining completely seizure-free after surgery were 51% (95% confidence interval [CI] = 53-63) at 2 postoperative years, 36% (95% CI = 32-41) at 10 years, 32% (95% CI = 27-36) at 20 years, and 30% (95% CI = 25-34) at 25 years. Recurrences were reported up to 23 years postoperatively. Late seizures occurred in all major ATL pathology groups, with increased risk in the "normal" and "distant lesion" groups (p ≤ .03). Comparison between the ATL cohort and patients who underwent extratemporal resection demonstrated similar patterns of late recurrence (p = .74). SIGNIFICANCE: Some first recurrences were very late, reported decades after ATL. Late recurrences were not unique to any broad ATL pathology group and did not differ according to whether resections were ATL or extratemporal. Reports of these events by patients with residual pathology suggest that potentially epileptogenic abnormalities outside the area of resection may be implicated as one of several possible underlying mechanisms.

Genes4Epilepsy: An epilepsy gene resource.

OBJECTIVE: "How many epilepsy genes are there?" is a frequently asked question. We sought to (1) provide a curated list of genes that cause monogenic epilepsies, and (2) compare and contrast epilepsy gene panels from multiple sources. METHODS: We compared genes included on the epilepsy panels (as of July 29, 2022) of four clinical diagnostic providers: Invitae, GeneDx, Fulgent Genetics, and Blueprint Genetics; and two research resources: PanelApp Australia and ClinGen. A master list of all unique genes was supplemented by additional genes identified via PubMed searches up until August 15, 2022, using the search terms "genetics" AND/OR "epilepsy" AND/OR "seizures". Evidence supporting a monogenic role for all genes was manually reviewed; those with limited or disputed evidence were excluded. All genes were annotated according to inheritance pattern and broad epilepsy phenotype. RESULTS: The comparison of genes included on epilepsy clinical panels revealed high heterogeneity in both number of genes (range: 144-511) and content. Just 111 genes (15.5%) were included on all four clinical panels. Subsequent manual curation of all "epilepsy genes" identified >900 monogenic etiologies. Almost 90% of genes were associated with developmental and epileptic encephalopathies. By comparison only 5% of genes were associated with monogenic causes of "common epilepsies" (i.e., generalized and focal epilepsy syndromes). Autosomal recessive genes were most frequent (56% of genes); however, this varied according to the associated epilepsy phenotype(s). Genes associated with common epilepsy syndromes were more likely to be dominantly inherited and associated with multiple epilepsy types. SIGNIFICANCE: Our curated list of monogenic epilepsy genes is publicly available: github.com/bahlolab/genes4epilepsy and will be regularly updated. This gene resource can be utilized to target genes beyond those included on clinical gene panels, for gene enrichment methods and candidate gene prioritization. We invite ongoing feedback and contributions from the scientific community via genes4-epilepsy@unimelb.edu.au.

IRF2BPL: A new genotype for progressive myoclonus epilepsies.

The progressive myoclonus epilepsies (PMEs) are a heterogeneous group of neurodegenerative disorders, typically presenting in late childhood. An etiologic diagnosis is achieved in about 80% of patients with PME, and genome-wide molecular studies on remaining, well-selected, undiagnosed cases can further dissect the underlying genetic heterogeneity. Through whole-exome sequencing (WES), we identified pathogenic truncating variants in the IRF2BPL gene in two, unrelated patients presenting with PME. IRF2BPL belongs to the transcriptional regulators family and it is expressed in multiple human tissues, including the brain. Recently missense and nonsense mutations in IRF2BPL were found in patients presenting with developmental delay and epileptic encephalopathy, ataxia, and movement disorders, but none with clear PME. We identified 13 other patients in the literature with myoclonic seizures and IRF2BPL variants. There was no clear genotype-phenotype correlation. With the description of these cases, the IRF2BPL gene should be considered in the list of genes to be tested in the presence of PME, in addition to patients with neurodevelopmental or movement disorders.

Recognition and epileptology of protracted CLN3 disease.

OBJECTIVE: This study was undertaken to analyze phenotypic features of a cohort of patients with protracted CLN3 disease to improve recognition of the disorder. METHODS: We analyzed phenotypic data of 10 patients from six families with protracted CLN3 disease. Haplotype analysis was performed in three reportedly unrelated families. RESULTS: Visual impairment was the initial symptom, with onset at 5-9 years, similar to classic CLN3 disease. Mean time from onset of visual impairment to seizures was 12 years (range = 6-41 years). Various seizure types were reported, most commonly generalized tonic-clonic seizures; focal seizures were present in four patients. Progressive myoclonus epilepsy was not seen. Interictal electroencephalogram revealed mild background slowing and 2.5-3.5-Hz spontaneous generalized spike-wave discharges. Additional interictal focal epileptiform discharges were noted in some patients. Age at death for the three deceased patients was 31, 31, and 52 years. Molecular testing revealed five individuals were homozygous for c.461-280_677 + 382del966, the "common 1-kb" CLN3 deletion. The remaining individuals were compound heterozygous for various combinations of recurrent pathogenic CLN3 variants. Haplotype analysis demonstrated evidence of a common founder for the common 1-kb deletion. Dating analysis suggested the deletion arose approximately 1500 years ago and thus did not represent cryptic familial relationship in this Australian cohort. SIGNIFICANCE: We highlight the protracted phenotype of a disease generally associated with death in adolescence, which is a combined focal and generalized epilepsy syndrome with progressive neurological deterioration. The disorder should be suspected in an adolescent or adult patient presenting with generalized or focal seizures preceded by progressive visual loss. The common 1-kb deletion has been typically associated with classic CLN3 disease, and the protracted phenotype has not previously been reported with this genotype. This suggests that modifying genetic factors may be important in determining this somewhat milder phenotype and identification of these factors should be the subject of future research.

Defective lipid signalling caused by mutations in PIK3C2B underlies focal epilepsy.

Epilepsy is one of the most frequent neurological diseases, with focal epilepsy accounting for the largest number of cases. The genetic alterations involved in focal epilepsy are far from being fully elucidated. Here, we show that defective lipid signalling caused by heterozygous ultra-rare variants in PIK3C2B, encoding for the class II phosphatidylinositol 3-kinase PI3K-C2ß, underlie focal epilepsy in humans. We demonstrate that patients' variants act as loss-of-function alleles, leading to impaired synthesis of the rare signalling lipid phosphatidylinositol 3,4-bisphosphate, resulting in mTORC1 hyperactivation. In vivo, mutant Pik3c2b alleles caused dose-dependent neuronal hyperexcitability and increased seizure susceptibility, indicating haploinsufficiency as a key driver of disease. Moreover, acute mTORC1 inhibition in mutant mice prevented experimentally induced seizures, providing a potential therapeutic option for a selective group of patients with focal epilepsy. Our findings reveal an unexpected role for class II PI3K-mediated lipid signalling in regulating mTORC1-dependent neuronal excitability in mice and humans.

Genome-wide association study of febrile seizures implicates fever response and neuronal excitability genes.

Febrile seizures represent the most common type of pathological brain activity in young children and are influenced by genetic, environmental and developmental factors. In a minority of cases, febrile seizures precede later development of epilepsy. We conducted a genome-wide association study of febrile seizures in 7635 cases and 83 966 controls identifying and replicating seven new loci, all with P < 5 × 10-10. Variants at two loci were functionally related to altered expression of the fever response genes PTGER3 and IL10, and four other loci harboured genes (BSN, ERC2, GABRG2, HERC1) influencing neuronal excitability by regulating neurotransmitter release and binding, vesicular transport or membrane trafficking at the synapse. Four previously reported loci (SCN1A, SCN2A, ANO3 and 12q21.33) were all confirmed. Collectively, the seven novel and four previously reported loci explained 2.8% of the variance in liability to febrile seizures, and the single nucleotide polymorphism heritability based on all common autosomal single nucleotide polymorphisms was 10.8%. GABRG2, SCN1A and SCN2A are well-established epilepsy genes and, overall, we found positive genetic correlations with epilepsies (rg = 0.39, P = 1.68 × 10-4). Further, we found that higher polygenic risk scores for febrile seizures were associated with epilepsy and with history of hospital admission for febrile seizures. Finally, we found that polygenic risk of febrile seizures was lower in febrile seizure patients with neuropsychiatric disease compared to febrile seizure patients in a general population sample. In conclusion, this largest genetic investigation of febrile seizures to date implicates central fever response genes as well as genes affecting neuronal excitability, including several known epilepsy genes. Further functional and genetic studies based on these findings will provide important insights into the complex pathophysiological processes of seizures with and without fever.

Comorbidities in newly diagnosed epilepsy: Pre-existing health conditions are common and complex across age groups.

OBJECTIVES: People with epilepsy have a higher prevalence of medical and psychiatric comorbidities compared to the general population. Comorbidities are associated with poor epilepsy outcomes, and there have been recommendations for screening and early identification to improve clinical management. Data from 'First Seizure Clinics' (FSCs) with expert epileptological review can inform about disorders already present at the point of diagnosis of epilepsy or unprovoked seizures. Here, we aimed to describe pre-existing conditions with a focus on psychiatric, substance use, cardiac, neurological, and cancer health domains. METHODS: We included 1383 adults who received a new diagnosis of epilepsy or unprovoked seizures at Austin Hospital (AH) or Royal Melbourne Hospital (RMH) (Australia) FSCs from 2000 to 2010. Data were audited from FSC records, primarily detailed interviews undertaken by epileptologists. Logistic regression examined age distribution and other risk factors. RESULTS: The median age at FSC presentation was 37 years (IQR 26-53, range 18-94). Pre-existing conditions were reported by 40 %; from 32 % in the youngest group (18-30 years) to 53 % in the oldest (65+ years). Psychiatric (18 %) and substance use (16 %) disorders were most common, with higher prevalence among patients 18 to 65 years of age compared to those older than 65 years (p < 0.001). Cardiac, neurological, or cancer conditions were reported by 3-6 %, most often amongst those older than 65 years (p < 0.01). Eight percent (n = 112) reported disorders in >1 health domain. The commonest combination was a psychiatric condition with substance use disorder. Of the sixty-two patients reporting this combination, 61 were ≤65 years of age. CONCLUSIONS: Pre-existing health conditions are present in a substantial proportion of patients diagnosed with epilepsy or unprovoked seizures. Disorders are highest amongst elders, but one-third of younger adults also reported positive histories. These are predominantly psychiatric and/or substance use disorders, conditions strongly associated with poor outcomes in the general population. These findings inform post-diagnosis planning and management, as well as research examining post-diagnostic outcomes and associations between comorbidities and epilepsy.

GABA-mediated tonic inhibition differentially modulates gain in functional subtypes of cortical interneurons.

The binding of GABA (γ-aminobutyric acid) to extrasynaptic GABAA receptors generates tonic inhibition that acts as a powerful modulator of cortical network activity. Despite GABA being present throughout the extracellular space of the brain, previous work has shown that GABA may differentially modulate the excitability of neuron subtypes according to variation in chloride gradient. Here, using biophysically detailed neuron models, we predict that tonic inhibition can differentially modulate the excitability of neuron subtypes according to variation in electrophysiological properties. Surprisingly, tonic inhibition increased the responsiveness (or gain) in models with features typical for somatostatin interneurons but decreased gain in models with features typical for parvalbumin interneurons. Patch-clamp recordings from cortical interneurons supported these predictions, and further in silico analysis was then performed to seek a putative mechanism underlying gain modulation. We found that gain modulation in models was dependent upon the magnitude of tonic current generated at depolarized membrane potential-a property associated with outward rectifying GABAA receptors. Furthermore, tonic inhibition produced two biophysical changes in models of relevance to neuronal excitability: 1) enhanced action potential repolarization via increased current flow into the dendritic compartment, and 2) reduced activation of voltage-dependent potassium channels. Finally, we show theoretically that reduced potassium channel activation selectively increases gain in models possessing action potential dynamics typical for somatostatin interneurons. Potassium channels in parvalbumin-type models deactivate rapidly and are unavailable for further modulation. These findings show that GABA can differentially modulate interneuron excitability and suggest a mechanism through which this occurs in silico via differences of intrinsic electrophysiological properties.