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ObjectivePathogenic SLC6A1 variants were recently described in patients with myoclonic atonic epilepsy (MAE) and intellectual disability (ID). We set out to define the phenotypic spectrum in a larger cohort of SCL6A1-mutated patients.MethodsWe collected 24 SLC6A1 probands and 6 affected family members. Four previously published cases were included for further electroclinical description. In total, we reviewed the electroclinical data of 34 subjects.ResultsCognitive development was impaired in 33/34 (97%) subjects; 28/34 had mild to moderate ID, with language impairment being the most common feature. Epilepsy was diagnosed in 31/34 cases with mean onset at 3.7 years. Cognitive assessment before epilepsy onset was available in 24/31 subjects and was normal in 25% (6/24), and consistent with mild ID in 46% (11/24) or moderate ID in 17% (4/24). Two patients had speech delay only, and 1 had severe ID. After epilepsy onset, cognition deteriorated in 46% (11/24) of cases. The most common seizure types were absence, myoclonic, and atonic seizures. Sixteen cases fulfilled the diagnostic criteria for MAE. Seven further patients had different forms of generalized epilepsy and 2 had focal epilepsy. Twenty of 31 patients became seizure-free, with valproic acid being the most effective drug. There was no clear-cut correlation between seizure control and cognitive outcome. Electroencephalography (EEG) findings were available in 27/31 patients showing irregular bursts of diffuse 2.5-3.5 Hz spikes/polyspikes-and-slow waves in 25/31. Two patients developed an EEG pattern resembling electrical status epilepticus during sleep. Ataxia was observed in 7/34 cases. We describe 7 truncating and 18 missense variants, including 4 recurrent variants (Gly232Val, Ala288Val, Val342Met, and Gly362Arg).SignificanceMost patients carrying pathogenic SLC6A1 variants have an MAE phenotype with language delay and mild/moderate ID before epilepsy onset. However, ID alone or associated with focal epilepsy can also be observed.

Epileptic encephalopathies (EEs) are the most clinically important group of severe early-onset epilepsies. Next-generation sequencing has highlighted the crucial contribution of de novo mutations to the genetic architecture of EEs as well as to their underlying genetic heterogeneity. Our previous whole-exome sequencing study of 264 parent-child trios revealed more than 290 candidate genes in which only a single individual had a de novo variant. We sought to identify additional pathogenic variants in a subset (n = 27) of these genes via targeted sequencing in an unsolved cohort of 531 individuals with a diverse range of EEs. We report 17 individuals with pathogenic variants in seven of the 27 genes, defining a genetic etiology in 3.2% of this unsolved cohort. Our results provide definitive evidence that de novo mutations in SLC1A2 and CACNA1A cause specific EEs and expand the compendium of clinically relevant genotypes for GABRB3. We also identified EEs caused by genetic variants in ALG13, DNM1, and GNAO1 and report a mutation in IQSEC2. Notably, recurrent mutations accounted for 7/17 of the pathogenic variants identified. As a result of high-depth coverage, parental mosaicism was identified in two out of 14 cases tested with mutant allelic fractions of 5%-6% in the unaffected parents, carrying significant reproductive counseling implications. These results confirm that dysregulation in diverse cellular neuronal pathways causes EEs, and they will inform the diagnosis and management of individuals with these devastating disorders.

Developmental and epileptic encephalopathies (DEEs) describe a subset of neurodevelopmental disorders categorized by refractory epilepsy that is often associated with intellectual disability and autism spectrum disorder. The majority of DEEs are now known to have a genetic basis with de novo coding variants accounting for the majority of cases. More recently, a small number of individuals have been identified with intronic SCN1A variants that result in alternative splicing events that lead to ectopic inclusion of poison exons (PEs). PEs are short highly conserved exons that contain a premature truncation codon, and when spliced into the transcript, lead to premature truncation and subsequent degradation by nonsense-mediated decay. The reason for the inclusion/exclusion of these PEs is not entirely clear, but research suggests an autoregulatory role in gene expression and protein abundance. This is seen in proteins such as RNA-binding proteins and serine/arginine-rich proteins. Recent studies have focused on targeting these PEs as a method for therapeutic intervention. Targeting PEs using antisense oligonucleotides (ASOs) has shown to be effective in modulating alternative splicing events by decreasing the amount of transcripts harboring PEs, thus increasing the abundance of full-length transcripts and thereby the amount of protein in haploinsufficient genes implicated in DEE. In the age of personalized medicine, cellular and animal models of the genetic epilepsies have become essential in developing and testing novel precision therapeutics, including PE-targeting ASOs in a subset of DEEs. [ABSTRACT FROM AUTHOR]

CACNA1H genetic variants were originally reported in a childhood absence epilepsy cohort. Subsequently, genetic testing for CACNA1H became available and is currently offered by commercial laboratories. However, the current status of CACNA1H as a monogenic cause of epilepsy is controversial, highlighted by ClinGen's recent reclassification of CACNA1H as disputed. We analyzed published CACNA1H variants and those reported in ClinVar and found none would be classified as pathogenic or likely pathogenic per the American College of Medical Genetics classification criteria. Moreover, Cacna1h did not modify survival in a Dravet Syndrome mouse model. We observed a mild increase in susceptibility to hyperthermia‐induced seizures in mice with reduced Cacna1h expression. Overall, we conclude that there is limited evidence that CACNA1H is a monogenic cause of epilepsy in humans and that this gene should be removed from commercial genetic testing panels to reduce the burden of variants of uncertain significance for healthcare providers, families and patients with epilepsy. [ABSTRACT FROM AUTHOR]

Developmental and epileptic encephalopathies (DEEs) can be primarily attributed to genetic causes. The genetic landscape of DEEs has been largely shaped by the rise of high-throughput sequencing, which led to the discovery of new DEE-associated genes and helped identify de novo pathogenic variants. We discuss briefly the contribution of de novo variants to DEE and also focus on alternative inheritance models that contribute to DEE. First, autosomal recessive inheritance in outbred populations may have a larger contribution than previously appreciated, accounting for up to 13% of DEEs. A small subset of genes that typically harbor de novo variants have been associated with recessive inheritance, and often these individuals have more severe clinical presentations. Additionally, pathogenic variants in X-linked genes have been identified in both affected males and females, possibly due to a lack of X-chromosome inactivation skewing. Collectively, exome sequencing has resulted in a molecular diagnosis for many individuals with DEE, but this still leaves many cases unsolved. Multiple factors contribute to the missing etiology, including nonexonic variants, mosaicism, epigenetics, and oligogenic inheritance. Here, we focus on the first 2 factors. We discuss the promises and challenges of genome sequencing, which allows for a more comprehensive analysis of the genome, including interpretation of structural and noncoding variants and also yields a high number of de novo variants for interpretation. We also consider the contribution of genetic mosaicism, both what it means for a molecular diagnosis in mosaic individuals and the important implications for genetic counseling. [ABSTRACT FROM AUTHOR]

The technological advancement of next-generation sequencing has greatly accelerated the pace of variant discovery in epilepsy. Despite an initial focus on autosomal dominant epilepsy due to the tractable nature of variant discovery with trios under a de novo model, more and more variants are being reported in families with epilepsies consistent with autosomal recessive (AR) inheritance. In this review, we touch on the classical AR epilepsy variants such as the inborn errors of metabolism and malformations of cortical development. However, we also highlight recently reported genes that are being identified by next-generation sequencing approaches and online 'matchmaking' platforms. Syndromes mainly characterized by seizures and complex neurodevelopmental disorders comorbid with epilepsy are discussed as an example of the wide phenotypic spectrum associated with the AR epilepsies. We conclude with a foray into the future, from the application of whole-genome sequencing to identify elusive epilepsy variants, to the promise of precision medicine initiatives to provide novel targeted therapeutics specific to the individual based on their clinical genetic testing. [ABSTRACT FROM AUTHOR]

Ultrarare Genetic Variation in the Epilepsies: A Whole-Exome Sequencing Study of 17 606 Individuals Epi25 Collaborative. Am J Hum Genet. 2019;105(2):267-282. doi: 10.1016/j.ajhg.2019.05.020. Sequencing-based studies have identified novel risk genes associated with severe epilepsies and revealed an excess of rare deleterious variation in less-severe forms of epilepsy. To identify the shared and distinct ultrarare genetic risk factors for different types of epilepsies, we performed a whole-exome sequencing (WES) analysis of 9170 epilepsy-affected individuals and 8436 controls of European ancestry. We focused on 3 phenotypic groups: severe developmental and epileptic encephalopathies (DEEs), genetic generalized epilepsy (GGE), and nonacquired focal epilepsy (NAFE). We observed that compared to controls, individuals with any type of epilepsy carried an excess of ultrarare, deleterious variants in constrained genes and in genes previously associated with epilepsy; we saw the strongest enrichment in individuals with DEEs and the least strong in individuals with NAFE. Moreover, we found that inhibitory GABAA receptor genes were enriched for missense variants across all 3 classes of epilepsy, whereas no enrichment was seen in excitatory receptor genes. The larger gene groups for the GABAergic pathway or cation channels also showed a significant mutational burden in DEEs and GGE. Although no single gene surpassed exome-wide significance among individuals with GGE or NAFE, highly constrained genes and genes encoding ion channels were among the lead associations; such genes included CACNA1G, EEF1A2, and GABRG2 for GGE and LGI1, TRIM3, and GABRG2 for NAFE, respectively. Our study, the largest epilepsy WES study to date, confirms a convergence in the genetics of severe and less-severe epilepsies associated with ultrarare coding variation, and it highlights a ubiquitous role for GABAergic inhibition in epilepsy etiology. [ABSTRACT FROM AUTHOR]

Summary: Heterozygous de novo variants in the autophagy gene, WDR45, are found in beta‐propeller protein‐associated neurodegeneration (BPAN). BPAN is characterized by adolescent onset dementia and dystonia; 66% patients have seizures. We asked whether WDR45 was associated with developmental and epileptic encephalopathy (DEE). We performed next generation sequencing of WDR45 in 655 patients with developmental and epileptic encephalopathies. We identified 3/655 patients with DEE plus 4 additional patients with de novo WDR45 pathogenic variants (6 truncations, 1 missense); all were female. Six presented with DEE and 1 with early onset focal seizures and profound regression. Median seizure onset was 12 months, 6 had multiple seizure types, and 5/7 had focal seizures. Three patients had magnetic resonance susceptibility‐weighted imaging; blooming was noted in the globus pallidi and substantia nigra in the 2 older children aged 4 and 9 years, consistent with iron accumulation. We show that de novo pathogenic variants are associated with a range of developmental and epileptic encephalopathies with profound developmental consequences. [ABSTRACT FROM AUTHOR]

Background Sanger sequencing, still the standard technique for genetic testing in most diagnostic laboratories and until recently widely used in research, is gradually being complemented by next-generation sequencing ( NGS). No single mutation detection technique is however perfect in identifying all mutations. Therefore, we wondered to what extent inconsistencies between Sanger sequencing and NGS affect the molecular diagnosis of patients. Since mutations in SCN1A, the major gene implicated in epilepsy, are found in the majority of Dravet syndrome ( DS) patients, we focused on missed SCN1A mutations. Methods We sent out a survey to 16 genetic centers performing SCN1A testing. Results We collected data on 28 mutations initially missed using Sanger sequencing. All patients were falsely reported as SCN1A mutation-negative, both due to technical limitations and human errors. Conclusion We illustrate the pitfalls of Sanger sequencing and most importantly provide evidence that SCN1A mutations are an even more frequent cause of DS than already anticipated. [ABSTRACT FROM AUTHOR]

The epilepsies are a complex group of disorders that can be caused by a myriad of genetic and acquired factors. As such, identifying interventions that will prevent development of epilepsy, as well as cure the disorder once established, will require a multifaceted approach. Here we discuss the progress in scientific discovery propelling us towards this goal, including identification of genetic risk factors and big data approaches that integrate clinical and molecular 'omics' datasets to identify common pathophysiological signatures and biomarkers. We discuss the many animal and cellular models of epilepsy, what they have taught us about pathophysiology, and the cutting edge cellular, optogenetic, chemogenetic and anti-seizure drug screening approaches that are being used to find new cures in these models. Finally, we reflect on the work that still needs to be done towards identify at-risk individuals early, targeting and stopping epileptogenesis, and optimizing promising treatment approaches. Ultimately, developing and implementing cures for epilepsy will require a coordinated and immense effort from clinicians and basic scientists, as well as industry, and should always be guided by the needs of individuals affected by epilepsy and their families. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century – From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'. • Basic research has increased our understanding of epilepsy. • 1/3 of patients still have seizures resistant to current therapies. • We are making significant progress in understanding the biological basis of epilepsy. • Exciting new technologies and insights put new therapies in our sights. • Basic research is essential for the development of effective treatments over the long term. [ABSTRACT FROM AUTHOR]

Dystonia is a debilitating hyperkinetic movement disorder, which can be transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense, and missense variants in TSPOAP1, which encodes the active-zone RIM-binding protein 1 (RIMBP1), as a genetic cause of autosomal recessive dystonia in 7 subjects from 3 unrelated families. Subjects carrying loss-of-function variants presented with juvenile-onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between dysfunction of the presynaptic active zone and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis. [ABSTRACT FROM AUTHOR]