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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, with >54,000 human exomes, comprising 20,979 deeply phenotyped patients from multiple genetic ancestry groups with diverse epilepsy subtypes and 33,444 controls, to investigate rare variants that confer disease risk. These analyses implicate seven individual genes, three gene sets, and four copy number variants at exome-wide significance. Genes encoding ion channels show strong association with multiple epilepsy subtypes, including epileptic encephalopathies, generalized and focal epilepsies, while most other gene discoveries are subtype-specific, highlighting distinct genetic contributions to different epilepsies. Combining results from rare single nucleotide/short indel-, copy number-, and common variants, we offer an expanded view of the genetic architecture of epilepsy, with growing evidence of convergence among different genetic risk loci on the same genes. Top candidate genes are enriched for roles in synaptic transmission and neuronal excitability, particularly postnatally and in the neocortex. We also identify shared rare variant risk between epilepsy and other neurodevelopmental disorders. Our data can be accessed via an interactive browser, hopefully facilitating diagnostic efforts and accelerating the development of follow-up studies., Competing Interests: Competing Interests B.M.N is a member of the scientific advisory board at Deep Genomics and Neumora. No other authors have competing interests to declare

Objective: Infantile seizures cause great concern for both doctors and parents. In addition to modern neuroimaging and genetics, clinical tools helpful in predicting the course of the disease are needed. We prospectively studied the incidence, electroclinical characteristics and etiologies of epilepsy syndromes with onset before the age of 12 months and looked for prognostic determinants of outcome by age 24 months., Methods: From February 2017 through May 2019, we recruited all eligible infants diagnosed with epilepsy at our unit. Data on electroclinical studies, genetic investigations and drug response were gathered prospectively. The infants were given a structured neurological examination (Hammersmith Infantile Neurological examination [HINE] and Griffiths scales) at predetermined intervals until age 24 months at which age neurocognitive evaluation with Bayley scales was performed., Results: Included were 60 infants (27 female). The mean onset age of epilepsy was 5.3 (±2.5 standard deviation) months. The incidence of epilepsy in the population-based cohort was 131 (95% confidence interval 99-172)/100 000. Epilepsy syndrome was identified in 80% and etiology in 58% of infants. Self-limited infantile epilepsy was the second most common syndrome (incidence 18/100 000) after infantile epileptic spasms syndrome. PRRT2 was the most common monogenic cause. At age 24 months, 37% of the infants had drug-resistant epilepsy (DRE) and half had a global developmental delay (GDD). Abnormal first HINE was the strongest predictor of GDD, followed by DRE and identified etiology. DRE was associated with structural etiology and GDD. Those with normal first HINE and good response to treatment had favorable outcomes, irrespective of the identified etiology., Significance: Our results support a high incidence of self-limited epilepsy in infancy and PRRT2 as the genetic cause in the first year of life. Notwithstanding the advances in etiological discovery, we want to highlight the importance of clinical evaluation as standardized neurological examination with HINE proved a valuable tool in prognostication., Plain Language Summary: One in every 700-800 babies develop epilepsy within the first year after birth. Our study identified an epilepsy syndrome in 80% and the cause of epilepsy in 60% of the participants. By age 2 years, over one-third of the children still experienced seizures, and almost half faced significant developmental delay. Structural brain abnormalities increased the likelihood of difficult epilepsy and developmental challenges. Babies whose epilepsy was caused by a gene defect varied widely in development and response to medications. Babies with normal neurological examination at first visit, especially if their seizures stopped quickly, had favorable development., (© 2024 The Author(s). Epilepsia Open published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Anoctamins are a family of Ca 2+ -activated proteins that may act as ion channels and/or phospholipid scramblases with limited understanding of function and disease association. Here, we identified five de novo and two inherited missense variants in ANO4 (alias TMEM16D) as a cause of fever-sensitive developmental and epileptic or epileptic encephalopathy (DEE/EE) and generalized epilepsy with febrile seizures plus (GEFS+) or temporal lobe epilepsy. In silico modeling of the ANO4 structure predicted that all identified variants lead to destabilization of the ANO4 structure. Four variants are localized close to the Ca 2+ binding sites of ANO4, suggesting impaired protein function. Variant mapping to the protein topology suggests a preliminary genotype-phenotype correlation. Moreover, the observation of a heterozygous ANO4 deletion in a healthy individual suggests a dysfunctional protein as disease mechanism rather than haploinsufficiency. To test this hypothesis, we examined mutant ANO4 functional properties in a heterologous expression system by patch-clamp recordings, immunocytochemistry, and surface expression of annexin A5 as a measure of phosphatidylserine scramblase activity. All ANO4 variants showed severe loss of ion channel function and DEE/EE associated variants presented mild loss of surface expression due to impaired plasma membrane trafficking. Increased levels of Ca 2+ -independent annexin A5 at the cell surface suggested an increased apoptosis rate in DEE-mutant expressing cells, but no changes in Ca 2+ -dependent scramblase activity were observed. Co-transfection with ANO4 wild-type suggested a dominant-negative effect. In summary, we expand the genetic base for both encephalopathic sporadic and inherited fever-sensitive epilepsies and link germline variants in ANO4 to a hereditary disease., Competing Interests: Declaration of interests K.H. is currently employed by Janssen Research & Development, Janssen Pharmaceutica N.V., Turnhoutseweg 30, Beerse B-2340, Belgium., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: Variants in SCN8A are associated with a spectrum of epilepsies and neurodevelopmental disorders. Ataxia as a predominant symptom of SCN8A variation has not been well studied. We set out to investigate disease mechanisms and genotype-phenotype correlations of SCN8A-related ataxia., Methods: We collected genetic and electro-clinical data of ten individuals from nine unrelated families carrying novel SCN8A variants associated with chronic progressive or episodic ataxia. Electrophysiological characterizations of these variants were performed in ND7/23 cells and cultured neurons., Findings: Variants associated with chronic progressive ataxia either decreased Na + current densities and shifted activation curves towards more depolarized potentials (p.Asn995Asp, p.Lys1498Glu and p.Trp1266Cys) or resulted in a premature stop codon (p.Trp937Ter). Three variants (p.Arg847Gln and biallelic p.Arg191Trp/p.Asp1525Tyr) were associated with episodic ataxia causing loss-of-function by decreasing Na + current densities or a hyperpolarizing shift of the inactivation curve. Two additional episodic ataxia-associated variants caused mixed gain- and loss-of function effects in ND7/23 cells and were further examined in primary murine hippocampal neuronal cultures. Neuronal firing in excitatory neurons was increased by p.Arg1629His, but decreased by p.Glu1201Lys. Neuronal firing in inhibitory neurons was decreased for both variants. No functional effect was observed for p.Arg1913Trp. In four individuals, treatment with sodium channel blockers exacerbated symptoms., Interpretation: We identified episodic or chronic ataxia as predominant phenotypes caused by variants in SCN8A. Genotype-phenotype correlations revealed a more pronounced loss-of-function effect for variants causing chronic ataxia. Sodium channel blockers should be avoided under these conditions., Funding: BMBF, DFG, the Italian Ministry of Health, University of Tuebingen., Competing Interests: Declaration of interests MK reports a doctoral grant from DAAD. JDOE is coordinator of the Chorea and Huntington Disease Group (ERN-RND). EB has received funding from the Dutch Epilepsy Foundation, on behalf of the Dravet syndrome Foundation Netherlands/Flanders, the JANIVO foundation and the K.F. Hein Foundation. LS declares grants from the German Research Foundation, German Ministry of Heath, European Commission, and Innovationsfond, and has received consulting fees from Vico Therapeutics and Novartis. RSM has received consulting and speaker fees from UCB and Orion and speaker fees from EISAI and Angelini Pharma. All other authors report no competing interests., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Introduction: Phenotypic spectrum of SLC6A1 -related neurodevelopmental disorders ( SLC6A1 -NDD) includes intellectual disability (ID), autistic spectrum disorders (ASD), epilepsy, developmental delay, beginning from early infancy or after seizure onset, and other neurological features such as hypotonia and movement disorders. Data on familial phenotypic heterogeneity have been rarely reported, thus in our study we aimed to investigate intrafamilial phenotypic variability in families with SLC6A1 variants., Methods: We collected clinical, laboratory and genetic data on 39 individuals, including 17 probands, belonging to 13 families harboring inherited variants of SLC6A1 . Data were collected through an international network of Epilepsy and Genetic Centers., Results: Main clinical findings in the whole cohort of 39 subjects were: (a) epilepsy, mainly presenting with generalized seizures, reported in 71% of probands and 36% of siblings or first/second-degree relatives. Within a family, the same epilepsy type (generalized or focal) was observed; (b) ID reported in 100% and in 13% of probands and siblings or first/second-degree relatives, respectively; (c) learning disabilities detected in 28% of the SLC6A1 carriers, all of them were relatives of a proband; (d) around 51% of the whole cohort presented with psychiatric symptoms or behavioral disorders, including 82% of the probands. Out of the 19 patients with psychiatric symptoms, ASD were diagnosed in 40% of them; (e) neurological findings (primarily tremor and speech difficulties) were observed 38.5% of the whole cohort, including 10 probands. Our families harbored 12 different SLC6A1 variants, one was a frameshift, two stop-gain, while the remaining were missense. No genotype-phenotype associations were identified., Discussion: Our study showed that first-or second-degree relatives presented with a less severe phenotype, featuring mainly mild intellectual and/or learning disabilities, at variance with the probands who suffered from moderate to severe ID, generalized, sometimes intractable, epileptic seizures, behavioral and psychiatric disorders. These findings may suggest that a proportion of individuals with mild SLC6A1 -NDD might be missed, in particular those with an older age where genetic testing is not performed. Further studies on intrafamilial phenotypic variability are needed to confirm our results and possibly to expand the phenotypic spectrum of these disorders and benefit genetic counseling., Competing Interests: KG has consulted for Taysha Gene Therapy, Jaguar Gene Therapy, Astellas Gene Therapy, and all Stripes for unrelated work. She also serves as co-chair of the Clinical Advisory Board (unpaid) for the non-profit COMBINEDBrain, which involves collaborations on SLC6A1-NDD. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Kassabian, Fenger, Willems, Aledo-Serrano, Linnankivi, McDonnell, Lusk, Jepsen, Bayat, Kattentidt, Vidal, Valero-Lopez, Alarcon-Martinez, Goodspeed, van Slegtenhorst, Barakat, Møller, Johannesen and Rubboli.)

Epilepsy in infancy links to a significant risk of neurodevelopmental delay, calling for a better understanding of its underlying mechanisms. Here, we studied cortical activity networks in infants with early-onset epilepsy to identify network properties that could pre-empt infants' neurodevelopmental course. We studied high-density (64 channel) electroencephalogram during non-rapid eye movement (N2) sleep in n = 49 infants at 1 year of age after being diagnosed with epilepsy during their first year of life. We computed frequency-specific networks in the cortical source space for two intrinsic brain modes: amplitude-amplitude and phase-phase correlations. Cortical activity networks of all frequency bands and connectivity modes were compared between the syndrome groups as well as between the three categories of neurocognitive development. The group differences were studied at three spatial levels: global, regional, and individual connections. Cortical mechanisms related to infant epilepsy were further compared with physiological networks using an automatic spindle detection algorithm. Our results show that global connectivity does not significantly differ between epilepsy syndromes; however, it co-varies with neurocognitive development. The largest network differences were observed at the lowest (<1 Hz) and mid-range (10-15 Hz) frequency bands. An algorithmic removal of sleep spindles from the data partially reduced the mid-range frequency network's strength. The centrocentral and frontocentral networks at the spindle frequencies were found to be strongest in infants with a persistent age-typical neurocognitive performance, while their low-frequency (< 1 Hz) networks were weaker for both amplitude-amplitude [ P = 0.008, effect size = 0.61] and phase-phase correlations ( P = 0.02, effect size = 0.54) at low (< 1 Hz). However, subjects with persistent mild neurocognitive delay from 1 to 2 years of age had higher amplitude-amplitude ( P = 0.02, effect size = 0.73) and phase-phase ( P = 0.06, effect size = 0.59) at low frequencies than those that deteriorated from mild to severely delayed from 1 to 2 years of age. Our findings suggest that cortical activity networks reflect the underlying clinical course of infants' epilepsy, and measures of spectrally and spatially resolved networks might become useful in better understanding infantile epilepsy as a network disease., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Guarantors of Brain.)

Aim: To investigate the prevalence of vigabatrin-attributed visual field defect (VAVFD) in infantile spasms and the utility of optical coherence tomography (OCT) in detecting vigabatrin-related damage., Method: We examined visual fields by Goldmann or Octopus perimetry and the thickness of peripapillary retinal nerve fiber layer (RNFL) with spectral-domain OCT at school age or adolescence., Results: Out of 88 patients (38 females, mean age at study 15y, SD 4y 3mo, range 6y 4mo-23y 3mo [n=65] or deceased [n=21] or moved abroad [n=2]) exposed to vigabatrin in infancy, 28 were able to perform formal visual field testing. Two had visual field defect from structural causes. We found mild VAVFD in four patients and severe VAVFD in one patient. Median vigabatrin treatment duration for those with normal visual field was 11 months compared to 19 months for those with VAVFD (p=0.04). OCT showed concomitant attenuated RNFL in three children with VAVFD, and was normal in one. The temporal half of the peripapillary RNFL was significantly thinner in the VAVFD group compared to the normal visual field group., Interpretation: The overall prevalence of VAVFD is lower after exposure in infancy compared to 52% which has been reported after exposure in adulthood. The risk increases with longer treatment duration. Further studies should identify infants particularly susceptible to VAVFD and clarify the role of OCT., (© 2021 Mac Keith Press.)

The genetics of autosomal recessive intellectual disability (ARID) has mainly been studied in consanguineous families, however, founder populations may also be of interest to study intellectual disability (ID) and the contribution of ARID. Here, we used a genotype-driven approach to study the genetic landscape of ID in the founder population of Finland. A total of 39 families with syndromic and non-syndromic ID were analyzed using exome sequencing, which revealed a variant in a known ID gene in 27 families. Notably, 75% of these variants in known ID genes were de novo or suspected de novo (64% autosomal dominant; 11% X-linked) and 25% were inherited (14% autosomal recessive; 7% X-linked; and 4% autosomal dominant). A dual molecular diagnosis was suggested in two families (5%). Via additional analysis and molecular testing, we identified three cases with an abnormal molecular karyotype, including chr21q22.12q22.2 uniparental disomy with a mosaic interstitial 2.7 Mb deletion covering DYRK1A and KCNJ6. Overall, a pathogenic or likely pathogenic variant was identified in 64% (25/39) of the families. Last, we report an alternate inheritance model for 3 known ID genes (UBA7, DDX47, DHX58) and discuss potential candidate genes for ID, including SYPL1 and ERGIC3 with homozygous founder variants and de novo variants in POLR2F and DNAH3. In summary, similar to other European populations, de novo variants were the most common variants underlying ID in the studied Finnish population, with limited contribution of ARID to ID etiology, though mainly driven by founder and potential founder variation in the latter case.

Background: Mutations in the X-linked gene WDR45 cause neurodegeneration with brain iron accumulation type 5. Global developmental delay occurs at an early age with slow progression to dystonia, parkinsonism, and dementia due to progressive iron accumulation in the brain., Methods: We present 17 new cases and reviewed 106 reported cases of neurodegeneration with brain iron accumulation type 5. Detailed information related to developmental history and key time to event measures was collected., Results: Within this cohort, there were 19 males. Most individuals were molecularly diagnosed by whole-exome testing. Overall 10 novel variants were identified across 11 subjects. All individuals were affected by developmental delay, most prominently in verbal skills. Most individuals experienced a decline in motor and cognitive skills. Although most individuals were affected by seizures, the spectrum ranged from provoked seizures to intractable epilepsy. The imaging findings varied as well, often evolving over time. The classic iron accumulation in the globus pallidus and substantia nigra was noted in half of our cohort and was associated with older age of image acquisition, whereas myelination abnormalities were associated with younger age., Conclusions: WDR45 mutations lead to a progressive and evolving disorder whose diagnosis is often delayed. Developmental delay and seizures predominate in early childhood, followed by a progressive decline of neurological function. There is variable expressivity in the clinical phenotypes of individuals with WDR45 mutations, suggesting that this gene should be considered in the diagnostic evaluation of children with myelination abnormalities, iron deposition, developmental delay, and epilepsy depending on the age at evaluation., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objective: Pathogenic variants in SCN8A have been associated with a wide spectrum of epilepsy phenotypes, ranging from benign familial infantile seizures (BFIS) to epileptic encephalopathies with variable severity. Furthermore, a few patients with intellectual disability (ID) or movement disorders without epilepsy have been reported. The vast majority of the published SCN8A patients suffer from severe developmental and epileptic encephalopathy (DEE). In this study, we aimed to provide further insight on the spectrum of milder SCN8A-related epilepsies., Methods: A cohort of 1095 patients were screened using a next generation sequencing panel. Further patients were ascertained from a network of epilepsy genetics clinics. Patients with severe DEE and BFIS were excluded from the study., Results: We found 36 probands who presented with an SCN8A-related epilepsy and normal intellect (33%) or mild (61%) to moderate ID (6%). All patients presented with epilepsy between age 1.5 months and 7 years (mean = 13.6 months), and 58% of these became seizure-free, two-thirds on monotherapy. Neurological disturbances included ataxia (28%) and hypotonia (19%) as the most prominent features. Interictal electroencephalogram was normal in 41%. Several recurrent variants were observed, including Ile763Val, Val891Met, Gly1475Arg, Gly1483Lys, Phe1588Leu, Arg1617Gln, Ala1650Val/Thr, Arg1872Gln, and Asn1877Ser., Significance: With this study, we explore the electroclinical features of an intermediate SCN8A-related epilepsy with mild cognitive impairment, which is for the majority a treatable epilepsy., (Wiley Periodicals, Inc. © 2019 International League Against Epilepsy.)

Objective: Pathogenic 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., Methods: We 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., Results: Cognitive 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)., Significance: Most 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., (Wiley Periodicals, Inc. © 2018 International League Against Epilepsy.)

Background: We aimed for a comprehensive delineation of genetic, functional and phenotypic aspects of GRIN2B encephalopathy and explored potential prospects of personalised medicine., Methods: Data of 48 individuals with de novo GRIN2B variants were collected from several diagnostic and research cohorts, as well as from 43 patients from the literature. Functional consequences and response to memantine treatment were investigated in vitro and eventually translated into patient care., Results: Overall, de novo variants in 86 patients were classified as pathogenic/likely pathogenic. Patients presented with neurodevelopmental disorders and a spectrum of hypotonia, movement disorder, cortical visual impairment, cerebral volume loss and epilepsy. Six patients presented with a consistent malformation of cortical development (MCD) intermediate between tubulinopathies and polymicrogyria. Missense variants cluster in transmembrane segments and ligand-binding sites. Functional consequences of variants were diverse, revealing various potential gain-of-function and loss-of-function mechanisms and a retained sensitivity to the use-dependent blocker memantine. However, an objectifiable beneficial treatment response in the respective patients still remains to be demonstrated., Conclusions: In addition to previously known features of intellectual disability, epilepsy and autism, we found evidence that GRIN2B encephalopathy is also frequently associated with movement disorder, cortical visual impairment and MCD revealing novel phenotypic consequences of channelopathies., Competing Interests: Competing interests: SFT is a consultant of Janssen Pharmaceuticals, Inc., Pfizer Inc., Boehringer Ingelheim Pharma GmbH & Co. KG, and co-founder of NeurOp Inc., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

The ubiquitin fold modifier 1 (UFM1) cascade is a recently identified evolutionarily conserved ubiquitin-like modification system whose function and link to human disease have remained largely uncharacterized. By using exome sequencing in Finnish individuals with severe epileptic syndromes, we identified pathogenic compound heterozygous variants in UBA5, encoding an activating enzyme for UFM1, in two unrelated families. Two additional individuals with biallelic UBA5 variants were identified from the UK-based Deciphering Developmental Disorders study and one from the Northern Finland Intellectual Disability cohort. The affected individuals (n = 9) presented in early infancy with severe irritability, followed by dystonia and stagnation of development. Furthermore, the majority of individuals display postnatal microcephaly and epilepsy and develop spasticity. The affected individuals were compound heterozygous for a missense substitution, c.1111G>A (p.Ala371Thr; allele frequency of 0.28% in Europeans), and a nonsense variant or c.164G>A that encodes an amino acid substitution p.Arg55His, but also affects splicing by facilitating exon 2 skipping, thus also being in effect a loss-of-function allele. Using an in vitro thioester formation assay and cellular analyses, we show that the p.Ala371Thr variant is hypomorphic with attenuated ability to transfer the activated UFM1 to UFC1. Finally, we show that the CNS-specific knockout of Ufm1 in mice causes neonatal death accompanied by microcephaly and apoptosis in specific neurons, further suggesting that the UFM1 system is essential for CNS development and function. Taken together, our data imply that the combination of a hypomorphic p.Ala371Thr variant in trans with a loss-of-function allele in UBA5 underlies a severe infantile-onset encephalopathy., (Copyright © 2016 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Mitochondrial aminoacyl-tRNA synthetases are an important group of disease genes typically underlying either a disorder affecting an isolated tissue or a distinct syndrome. Missense mutations in the mitochondrial seryl-tRNA synthetase gene, SARS2, have been identified in HUPRA syndrome (hyperuricemia, pulmonary hypertension, renal failure in infancy, and alkalosis). We report here a homozygous splicing mutation in SARS2 in a patient with progressive spastic paresis. We show that the mutation leads to diminished levels of the synthetase in patient's fibroblasts. This has a destabilizing effect on the tRNASer(AGY) isoacceptor, but to a lesser degree than in HUPRA syndrome patients. tRNASer(UCN) is largely unaffected in both phenotypes. In conclusion, the level of tRNASer(AGY) instability may be a factor in determining tissue manifestation in patients with SARS2 mutations. This finding exemplifies the sensitivity of the nervous system to partially reduced aminoacylation, which is sufficient in other tissues to maintain respiratory chain function., (© 2016 WILEY PERIODICALS, INC.)

Objective: We aimed to decipher the molecular genetic basis of disease in a cohort of children with a uniform clinical presentation of neonatal irritability, spastic or dystonic quadriplegia, virtually absent psychomotor development, axonal neuropathy, and elevated blood/CSF lactate., Methods: We performed whole-exome sequencing of blood DNA from the index patients. Detected compound heterozygous mutations were confirmed by Sanger sequencing. Structural predictions and a bacterial activity assay were performed to evaluate the functional consequences of the mutations. Mass spectrometry, Western blotting, and protein oxidation detection were used to analyze the effects of selenoprotein deficiency., Results: Neuropathology indicated laminar necrosis and severe loss of myelin, with neuron loss and astrogliosis. In 3 families, we identified a missense (p.Thr325Ser) and a nonsense (p.Tyr429*) mutation in SEPSECS, encoding the O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase, which was previously associated with progressive cerebellocerebral atrophy. We show that the mutations do not completely abolish the activity of SEPSECS, but lead to decreased selenoprotein levels, with demonstrated increase in oxidative protein damage in the patient brain., Conclusions: These results extend the phenotypes caused by defective selenocysteine biosynthesis, and suggest SEPSECS as a candidate gene for progressive encephalopathies with lactate elevation., (© 2015 American Academy of Neurology.)

Epileptic encephalopathies are a phenotypically and genetically heterogeneous group of severe epilepsies accompanied by intellectual disability and other neurodevelopmental features. Using next-generation sequencing, we identified four different de novo mutations in KCNA2, encoding the potassium channel KV1.2, in six isolated patients with epileptic encephalopathy (one mutation recurred three times independently). Four individuals presented with febrile and multiple afebrile, often focal seizure types, multifocal epileptiform discharges strongly activated by sleep, mild to moderate intellectual disability, delayed speech development and sometimes ataxia. Functional studies of the two mutations associated with this phenotype showed almost complete loss of function with a dominant-negative effect. Two further individuals presented with a different and more severe epileptic encephalopathy phenotype. They carried mutations inducing a drastic gain-of-function effect leading to permanently open channels. These results establish KCNA2 as a new gene involved in human neurodevelopmental disorders through two different mechanisms, predicting either hyperexcitability or electrical silencing of KV1.2-expressing neurons.