Delineating the phenotype of PNPLA8-related mitochondriopathies.

Pathogenic variants in PNPLA8 have been described either with congenital onset displaying congenital microcephaly, early onset epileptic encephalopathy and early lethality or childhood neurodegeneration with progressive microcephaly. Moreover, a phenotype comprising adulthood onset cerebellar ataxia and peripheral neuropathy was also reported. To our knowledge, only six patients with biallelic variants in PNPLA8 have been reported so far. Here, we report the clinical and molecular characterizations of three additional patients in whom exome sequencing identified a loss of function variant (c.1231C>T, p.Arg411Ter) in Family I and a missense variant (c.1559T>A, p.Val520Asp) in Family II in PNPLA8. Patient 1 presented with the congenital form of the disease while Patients 2 and 3 showed progressive microcephaly, infantile onset seizures, progressive cortical atrophy, white matter loss, bilateral degeneration of basal ganglia, and cystic encephalomalacia. Therefore, our results add the infantile onset as a new distinct phenotype of the disease and suggest that the site of the variant rather than its type is strongly correlated with the disease onset. In addition, these conditions demonstrate some overlapping features representing a spectrum with clinical features always aligning with different age of onset.

Functional analysis of a novel de novo SCN2A variant in a patient with seizures refractory to oxcarbazepine.

Objective: We admitted a female patient with infantile onset epilepsy (<3-month-old). The use of oxcarbazepine exacerbated epileptic seizures in the patient. In the present study, we aimed to identify the genetic basis of the infantile onset epilepsy in the patient, and determine the correlations among genotype, phenotype, and clinical drug response. Methods: We described the clinical characteristics of an infant with refractory epilepsy. Whole exome sequencing (WES) was used to screen for the pathogenic variant. Whole-cell patch-clamp was performed to determine functional outcomes of the variant. Results: WES identified a novel de novo SCN2A variant (c.468 G > C, p.K156N) in the patient. In comparison with wildtype, electrophysiology revealed that SCN2A-K156N variant in transfected cells demonstrated reduced sodium current density, delayed activation and accelerated inactivation process of Na+ channel, all of which suggested a loss-of-function (LOF) of Nav1.2 channel. Conclusion: We showed the importance of functional analysis for a SCN2A variant with unknown significance to determine pathogenicity, drug reactions, and genotype-phenotype correlations. For patients suffering from early infantile epilepsies, the use of oxcarbazepine in some SCN2A-related epilepsies requires vigilance to assess the possibility of epilepsy worsening.

Skeletal anomaly and opisthotonus in early-onset epileptic encephalopathy with KCNQ2 abnormality.

BACKGROUND: Heterozygous KCNQ2 variants cause benign familial neonatal seizures and early-onset epileptic encephalopathy in an autosomal dominant manner; the latter is called KCNQ2 encephalopathy. No case of KCNQ2 encephalopathy with arthrogryposis multiplex congenita has been reported. Furthermore, early-onset scoliosis and opisthotonus have not been documented as characteristics of KCNQ2 encephalopathy. CASE REPORT: A male infant born with scoliosis and arthrogryposis multiplex congenita developed intractable epilepsy on the second day of life. At 4 months of age, he developed opisthotonus. The opisthotonus was refractory to medication in the beginning, and it spontaneously disappeared at 8 months of age. Whole-exome sequencing revealed a novel de novo heterozygous variant in KCNQ2, NM_172107.4:c.839A > C, p.(Tyr280Ser). CONCLUSIONS: Early-onset scoliosis, arthrogryposis multiplex congenita, and opisthotonus may be related to KCNQ2 encephalopathy.

Developmental and Epileptic Encephalopathy 76: Case Report and Review of Literature.

Previous studies have suggested that the ACTL6B monoallelic variant is responsible for an autosomal dominant inherited intellectual developmental disorder with severe speech and ambulation deficits. The clinical phenotype of developmental and epileptic encephalopathy type 76 (DEE76) due to ACTL6B biallelic variants was first reported in 2019, with an autosomal recessive mode of inheritance. In this paper, we report on a child in China with DEE76 caused by a compound heterozygous variant of the ACTL6B gene, and we review the literature on ACTL6B gene variants causing DEE76 with complete clinical information. Including our case 1, the genotype and phenotypic characteristics of 18 children from 14 families are summarized. All 18 cases are autosomal recessive, including 12 with homozygous variants and six with compound heterozygous variants. A total of 17 variants have been reported so far, including 14 variants of the loss function. We summarize the clinical features using Human Phenotype Ontology (HPO) terms. We find that DEE76, caused by the ACTL6B biallelic variant, is an early-onset drug-refractory epilepsy with global developmental delayHP:0001263, hypertoniaHP:0001276, and microcephalyHP:0000252, and imaging is characterized by brain delayed myelinationHP:0012448. Our case of DEE76 had not been reported when the patient underwent genetic testing in 2018, and the diagnosis was clarified by the reanalysis of the data 2 years later, being the first reported Chinese patient and the only one in which the application of a ketogenic diet for antiepileptic treatment may have been effective.

A novel de novo heterozygous variant of the KCNQ2 gene: Contribution to early­onset epileptic encephalopathy in a female infant.

Early­onset epileptic encephalopathy (EOEE) represents one of the most severe epilepsies, characterized by recurrent seizures during early infancy, electroencephalogram (EEG) abnormalities and varying degrees of neurodevelopmental delay. The KCNQ2 gene has been reported to have a major role in EOEE. In the present study, a 3­month­old female infant from the Chinese Lisu minority with EOEE was analyzed. Detailed clinical evaluations and next­generation sequencing were performed to investigate the clinical and genetic characteristics of this patient, respectively. Furthermore, the three­dimensional structure of the mutant protein was predicted by SWISS­Model and the expression of KCNQ2 protein in the patient was assessed by flow cytometry. It was observed that the patient presented with typical clinical features of EOEE, including repeated non­febrile seizures and significant EEG abnormalities. A novel heterozygous missense variant c.431G>C (p.R144P) in KCNQ2 was identified in the patient and the genotyping of KCNQ2 in the patient's parents suggested that this variant was de novo. Subsequently, the breakage of hydrogen bonds between certain amino acids was predicted by structural analysis of the mutant protein. Flow cytometric analysis detected a significant reduction buts not complete loss of native KCNQ2 protein expression in the patient (25.1%). In conclusion, a novel variant in KCNQ2 was confirmed as the genetic cause for EOEE in this patient. The present study expanded the pathogenic mutation spectrum of KCNQ2, enhanced the understanding of the molecular pathogenesis of EOEE and provided novel clues for research on the genotype­phenotype correlation in this disease.

Case report of early-onset epileptic encephalopathy caused by compound heterozygous mutation of the WWOX gene / 中华实用儿科临床杂志

Clinical data of a case with early-onset epileptic encephalopathy admitted in the Department of Neuroendocrinology, Jinan Children′s Hospital in April 2020 were retrospectively analyzed.A 1-month-old male patient was hospitalized for convulsion for 4 days.The child had repeated seizures in the form of tonic and tonic-spasm seizures, accompanied by feeding difficulties, slow weight gain, and overall developmental delay.Electroencephalogram showed multifocal discharge, atypical hypsarrhythmia, and brain magnetic resonance imaging showed delayed myelination.The whole exome sequencing showed compound heterozygous mutation of the WWOX gene.Topiramate, Levetiracetam and Valporate were ineffective to this case.Genetic testing should be performed timely in patients with early-onset epileptic encephalopathy and overall developmental delay to make a clear etiology and prognosis, thus guiding prenatal diagnostics and genetic counseling.

Early-onset epileptic encephalopathy caused by the UBA5 gene mutation: a case report and literature review / 中华实用儿科临床杂志

Objective:To explore the clinical and genetic characteristics of a case of early-onset epileptic encephalopathy caused by the UBA5 gene mutation and to review relevant literatures. Methods:The clinical characte-ristics and genetic data of a child with the UBA5 gene mutation in the Department of Pediatrics, the Third Affiliated Hospital of Zhengzhou University in June 2020 were retrospectively analyzed.Clinical characteristics and gene variation characteristics of the disease were reviewed in the domestic and foreign databases. Results:(1) The female patient presented infantile spasms at the age of 4 months.Electroencephalogram(EEG) suggested hypsarrhythmia and she was not responsive to a variety of anti-epileptic drugs.Besides, the patient showed severe cognitive and motor development delay, hypotonia, and microcephaly.The results of whole exome sequencing showed that the compound heterozygous mutation of UBA5 gene: exon 3 c. 214C>T (p.R72C) and exon 9 c. 844_c.845 insA (p.Y282Xfs*1), her father carries c. 214C>T mutation and her mother carries c. 844_c.845 INSA mutation.(2) To December 2020, a total of 15 cases of early-onset epileptic encephalopathy caused by the UBA5 gene mutation have been reported abroad.The main clinical manifestations were uncontrollable spasms, abnormal EEG findings, hypotonia, severe cognitive and movement disorders, microcephaly, and brain atrophy.A total of 11 mutation sites of the UBA5 gene were found, all belonging to the autosomal recessive inheritance, of which c. 1111G>A was the most common. Conclusions:The UBA5 gene mutation can lead to early-onset epileptic encephalopathy, which belongs to the autosomal recessive inheritance.It is featured by the early onset, uncontrollable seizures and poor long-term prognosis.

Clinical features and genetic analysis of the early-onset epileptic encephalopathy caused by sodium channel mutations / 中华实用儿科临床杂志

Objective:To explore the clinical phenotype characteristics of early-onset epileptic encephalopathy (EOEE) caused by sodium channel mutations.Methods:A retrospective study was used.A total of 52 EOEE patients treated in the Department of Neurology, Children′s Hospital of Fudan University and Department of Neurology, Wuhan Children′s Hospital, Tongji Medical College, Huazhong University of Science & Technology from June 2016 to June 2019 were recruited.Peripheral blood samples of 52 patients and their parents were collected for analyzing pathogenic mutations by the next generation sequencing and copy number variations of whole exons in family. Chi- square test was used to compare seizure control data among different voltage-gated sodium channel α1 subunit ( SCN1A) mutation types. Results:A total of 35/52 cases (67.3%) were diagnosed as Dravet syndrome, 3/52 cases (5.8%) were West syndrome, and 14/52 cases (26.9%) were non-symptomatic EOEE.The electroencephalogram (EEG) findings showed a large number of multifocal spikes, spike-slow waves, sharp waves, and sharp-slow waves.A total of 45/52 cases (86.5%) showed normal brain magnetic resonance imaging(MRI), 1 case had slightly widened bilateral frontal sulcus, 1 case had widened bilateral temporal pole and frontal top subarachnoid space, and the remaining 5 cases had widened extracerebral space and slightly larger ventricles.Thirteen cases were re-examined with brain MRI, and 3 cases had mild brain atrophy.A total of 43/52 cases (82.7%) were examined with SCN1A gene mutations, of which 28/52 cases (53.8%) were missense mutations, 5/52 cases (9.6%) were nonsense mutations, 7/52 cases (13.5%) were frameshift mutations and 3/52 cases (5.8%) were splice site mutations.A total of 3/52 cases (5.8%) had SCN2A mutations, of which 2/52 cases (3.8%) were missense mutations, and 1/52 case (1.9%) was a frameshift mutation, 1/52 cases (1.9%) carrying the missense mutation of the SCN3A gene.A total of 5/52 cases (9.6%) had missense mutations of the SCN8A gene.After an average of 1-year follow-up, a total of 13/52 cases (25.0%) had more than 1-year control of seizure, of which 6/52 cases (11.5%) with seizure control for more than 2 years, and 4/52 cases (7.7%) with more than 3-year control.Children carrying SCN1A missense mutations were relatively easier to be controlled for seizures than those carrying SCN1A truncation mutations (nonsense mutations+ frameshift mutations) ( P<0.05). In 5 children carrying SCN8A mutations, 2 cases of them had seizures control for more than 1 year after adding Oxcarbazepine, but the improvement of mental motor function was not obvious. Conclusions:In children with EOEE associated with sodium channel gene mutations, SCN1A, SCN2A, SCN3A, and SCN8A mutations were pathogenic factors.Among them, SCN1A was the most common pathogenic gene for EOEE, with the mutation rate of 82.7%.Dravet syndrome was the most common clinical phenotype of EOEE associated with sodium channel gene mutations.Epileptic seizures in children carrying SCN1A missense mutations were easier to be controlled than those with truncated mutation (nonsense mutations + frameshift mutations), suggesting that the gene mutation type was related to the degree of seizures control.Oxcarbazepine was effective in the treatment of EOEE with SCN8A gene mutations, indicating that the combination therapy using anti-epilepsy drugs can be applied to EOEE patients according to the type of gene function.

Siblings with MAN1B1-CDG Showing Novel Biochemical Profiles.

Congenital disorders of glycosylation (CDG), inherited metabolic diseases caused by defects in glycosylation, are characterized by a high frequency of intellectual disability (ID) and various clinical manifestations. Two siblings with ID, dysmorphic features, and epilepsy were examined using mass spectrometry of serum transferrin, which revealed a CDG type 2 pattern. Whole-exome sequencing showed that both patients were homozygous for a novel pathogenic variant of MAN1B1 (NM_016219.4:c.1837del) inherited from their healthy parents. We conducted a HPLC analysis of sialylated N-linked glycans released from total plasma proteins and characterized the α1,2-mannosidase I activity of the lymphocyte microsome fraction. The accumulation of monosialoglycans was observed in MAN1B1-deficient patients, indicating N-glycan-processing defects. The enzymatic activity of MAN1B1 was compromised in patient-derived lymphocytes. The present patients exhibited unique manifestations including early-onset epileptic encephalopathy and cerebral infarction. They also showed coagulation abnormalities and hypertransaminasemia. Neither sibling had truncal obesity, which is one of the characteristic features of MAN1B1-CDG.

A de novo nonsense mutation of STXBP1 causes early-onset epileptic encephalopathy.

Mutations in syntaxin-binding protein 1, STXBP1 (also known as MUNC18-1), are linked to multiple neurodevelopmental disorders, including severe early-onset epileptic encephalopathies (EOEEs). A de novo nonsense mutation of STXBP1 (c. 863G > A, p. W288X) was found in a patient diagnosed with EOEE at the age of 17 days. The electroencephalogram (EEG) showed sharp waves and spikes, while brain magnetic resonance imaging was normal. We generated a zebrafish EOEE model by overexpressing mutant STXBP1(W288X) and studied the behavioral changes further to understand the mechanism of W288X mutation in epileptogenesis. In addition, effective antiepileptic drugs were screened in the zebrafish model. Zebrafish STXBP1 homologs were highly conserved and prominently expressed in the larval zebrafish brain. The Tg(hSTXBP1W288X) zebrafish larvae exhibited hyperactivity compared with the wild-type (WT) controls. The expression of STXBP1 decreased during the development course from 1 to 5 days post fertilization. Spontaneous seizures and increased c-fos expression were observed in the mutant zebrafish larvae. The susceptibility of Tg(hSTXBP1W288X) zebrafish to pentylenetetrazol challenge also dramatically increased. Levetiracetam, clonazepam, and topiramate showed antiepileptic effects in the Tg(hSTXBP1W288X) larvae to different extents. Our findings in the newly generated mutant line of zebrafish suggested that zebrafish recapitulated clinical phenotypes associated with human STXBP1 mutation, which provided an appropriate in vivo model for epilepsy research.

Dystonia and Contractures are Potential Early Signs of CACNA1E-Related Epileptic Encephalopathy.

Epileptic encephalopathy related to CACNA1E has been described as a severe neurodevelopmental disorder presenting with early-onset refractory seizures, hypotonia, macrocephaly, hyperkinetic movements, and contractures and is associated with an autosomal dominant inheritance pattern. Most pathogenic variants described to date are missense variants with a gain of function effect, and the role of haploinsufficiency has yet to be clarified. We describe 2 cases of CACNA1E encephalopathy. Notable findings include congenital contractures and movement disorders predating onset of epilepsy, particularly dystonia. We further compared the key phenotypic features depending on variant location. In conclusion, the appearance of congenital contractures, areflexia, and movement disorders before the onset of epilepsy may provide key guidance in the diagnosis of epileptic CACNA1E encephalopathy. A genotype-phenotype correlation was found between the presence of movement disorders and severe intellectual disability and the location of the variant in the CACNA1E gene.

Ketogenic Diet in Infants with Early-Onset Epileptic Encephalopathy and SCN2A Mutation.

Research has shown mutations in the voltage-gated sodium channel gene SCN2A to be associated with developmental delays and infantile seizures in patients with early-onset epileptic encephalopathies (EOEEs). Here, we report the case of an infant with a de novo SCN2A mutation with EOEE who had medically refractory seizures that improved with a ketogenic diet (KD) implemented at an age less than 2 months. On the day of his birth, the infant presented with a pattern of convulsions with dozens of episodes per day. An initial video electroencephalogram revealed poor reactivity of background activity, with multiple partial episodes starting from the right temporal region, and abnormal electrical activity in the right hemisphere. The seizures previously were not controlled with successive therapy with phenobarbital, topiramate, and levetiracetam. Genetic testing revealed the presence of a mutation in the SCN2A gene (c.4425C>G, p.Asn1475Lys). The infant's seizures decreased significantly with a combination of KD and medication. The present case exemplifies the potential for personalized genomics in identifying the etiology of an illness. Furthermore, the KD appears to feasible in infants younger than 2 months and might elicit good responses to EOEE associated with SCN2A mutation.

Association of early-onset epileptic encephalopathy with involuntary movements - Case series and literature review.

Epileptic-dyskinetic encephalopathies are rare epilepsies characterized by early-onset epileptic encephalopathies (EOEEs) with involuntary movement. Herein, we investigated the impact of gene variants in epileptic-dyskinetic encephalopathies. Four independent patients from four families who exhibited involuntary movements were recruited from Tokyo Metropolitan Neurological Hospital. The inclusion criteria were as follows: onset within 1 year after birth, frequent seizures, severe developmental delay and accompanying involuntary movements. We detected four genetic mutations, including STXBP1, GNAO1, CYFIP2, and SCN8A variants. The involuntary movements were drug-resistant. However, pallidal electrocoagulation followed by gabapentin were partially effective in treating chorea and ballismus of the extremities in patients with GNAO1 variants, and perampanel partially suppressed seizures and involuntary movements in one patient with a SCN8A variant. Movement disorders are common to many neurodevelopmental disorders, including a variety of EOEEs. Although we could not establish a definitive correlation using genetic variants in patients with EOEE and movement disorders, involuntary movements in patients with EOEEs may be a key diagnostic finding. The usage of genetic variants could prove beneficial in the future as more patients are investigated with epileptic-dyskinetic encephalopathies.

Early-Onset Developmental and Epileptic Encephalopathies of Infancy: An Overview of the Genetic Basis and Clinical Features.

Our current knowledge of genetically determined forms of epilepsy has shortened the diagnostic pathway usually experienced by the families of infants diagnosed with early-onset developmental and epileptic encephalopathies. Genetic causes can be found in up to 80% of infants presenting with early-onset developmental and epileptic encephalopathies, often in the context of an uneventful perinatal history and with no clear underlying brain abnormalities. Although current disease-specific therapies remain limited and patient outcomes are often guarded, a genetic diagnosis may lead to early therapeutic intervention using new and/or repurposed therapies. In this review, an overview of epilepsy genetics, the indications for genetic testing in infants, the advantages and limitations of each test, and the challenges and ethical implications of genetic testing are discussed. In addition, the following causative genes associated with early-onset developmental and epileptic encephalopathies are discussed in detail: KCNT1, KCNQ2, KCNA2, SCN2A, SCN8A, STXBP1, CDKL5, PIGA, SPTAN1, and GNAO1. The epilepsy phenotypes, comorbidities, electroencephalgraphic findings, neuroimaging findings, and potential targeted therapies for each gene are reviewed.

[Early onset epileptic encephalopathy caused by mitochondrial arginyl-tRNA synthetase gene deficiency: report of two cases and literature review].

Objective: To summarize the clinical features of two early onset epileptic encephalopathy (EOEE) patients with arginyl-tRNA synthetase (RARS2) gene variations and to review related literature. Methods: The clinical data and genetic features of two pontocerebellar hypoplasia type 6 (PCH6) patients with RARS2 variation diagnosed by the Department of Neurology, Beijing Children's Hospital from January 2017 to December 2018 were analyzed retrospectively. A literature search with "RARS2" "pontocerebellar hypoplasia type 6" and "early onset epileptic encephalopathy" as key words was conducted at China national knowledge infrastructure (CNKI), Wanfang Data Knowledge Service Platform and PubMed (up to May 2020), literature about RARS2 gene variation patients and their complete clinical data were chosen and reviewed. Results: The onset age of the two cases (1 male, 1 female) were 2 months and 29 days respectively and the early onset symptom of them was epileptic encephalopathy. The main symptoms included seizures, development delay, microcephaly and lactic acidosis. In addition to these symptoms, the female also had dyspnea, hypoglycemia and metabolic acidosis after birth. Brain magnetic resonance imaging (MRI) of the two patients were normal at first. Follow up at four-month (case 1) and eight-month (case 2) MRI showed atrophy of cerebral and cerebellar, but the pons was not affected. All four heterozygous variations in RARS2 gene revealed by whole-exome sequencing (p.Arg560His and p.Arg6His from case 1, p.Arg254Trp and p.Phe5Ser from case 2) were novel. No eligible reports were found in Chinese journals, while 17 reports were found in English literature. Excluded cases with incomplete data together with these two cases, a total of 34 patients from 20 families were found. All patients had developmental delay while 94% (32/34) patients showed the initial symptoms within 3 months, 93% (28/30) patients were diagnosed as epilepsy, 89% (25/28) patients had progressively microcephaly and 52% (16/31) cases did not show the pons atrophy on brain MRI. Twenty of 28 cases (71%) were refractory epilepsy. There were 31 types of gene variations and most of them were missense variations (21/31, 68%). Conclusions: The majority of PCH6 cases caused by RARS2 gene variation show the initial symptoms within 3 months, characterized by EOEE, most of them are refractory epilepsy, accompanied by developmental delay, microcephaly and increased lactic acid. Brain MRI indicates progressive cerebral or pontocerebellar atrophy.

De novo CACNA1G variants in developmental delay and early-onset epileptic encephalopathies.

INTRODUCTION: Variants of CACNA1G, which encodes CaV3.1, have been reported to be associated with various neurological disorders. METHODS: Whole-exome sequencing of genomic DNA from 348 Japanese patients with neurodevelopmental disorders and their parents was conducted, and de novo variants of CACNA1G were extracted. The electrophysiological properties of each mutant channel were investigated by voltage-clamp and current-clamp analyses of HEK293T cells overexpressing these channels. RESULTS: Two patients diagnosed with Rett syndrome and West syndrome were found to have known pathological CACNA1G mutations reported in cerebellar ataxia cohorts: c.2881G > A, p.Ala961Thr and c.4591A > G, p.Met1531Val, respectively. One patient with Lennox-Gastaut syndrome was revealed to harbor a previously unreported heterozygous variant: c.3817A > T, p.Ile1273Phe. Clinical symptoms of the two patients with known mutations included severe developmental delay without acquisition of the ability to walk independently. The patient with a potentially novel mutation showed developmental delay, intractable seizures, and mild cerebral atrophy on MRI, but the severity of symptoms was milder than in the former two cases. Electrophysiological study using HEK293T cells demonstrated significant changes of T-type Ca2+ currents by p.Ala961Thr and p.Met1531Val SNVs, which were likely to enhance oscillation of membrane potential at low frequencies. In contrast, p.Ile1273Phe showed no significant effects in our electrophysiological evaluations, with its pathogenesis remaining undetermined. CONCLUSION: De novo variants of CACNA1G explain some neurodevelopmental disorders. Our study further provides information to understand the genotype-phenotype correlations of patients with CACNA1G mutations.

Effect of total callosotomy on KCNQ2-related intractable epilepsy.

AIM: To describe beneficial effects of callosotomy on KCNQ2-related intractable epilepsy. CASE REPORT: Our patient was a 10-year-old girl who had developed epilepsy during the neonatal period, accompanied by a suppression-burst pattern on the electroencephalography (EEG). The patient showed profound psychomotor developmental delay since early infancy. Daily seizures of versive posturing and ocular deviation were transiently controlled by carbamazepine and valproate at the age of 1 year; however, the seizures gradually increased to up to 50 times per day. Ictal EEG and positron emission tomography revealed an epileptic focus in the left frontal lobe at age 5 years. Total callosotomy resulted in marked reduction of epileptic seizures thereafter, as well as improved responses to external auditory and visual stimuli. Whole exome sequencing at age 9 identified a de novo missense variant in KCNQ2 (NM_172107.3:c.563A > C:p.(Gln188Pro)). CONCLUSION: This case supports that epilepsy surgery could benefit children with epileptic encephalopathy, even with the etiology of channelopathy.

GABAA receptor ß3 subunit mutation D120N causes Lennox-Gastaut syndrome in knock-in mice.

The Lennox-Gastaut syndrome is a devastating early-onset epileptic encephalopathy, associated with severe behavioural abnormalities. Its pathophysiology, however, is largely unknown. A de novo mutation (c.G358A, p.D120N) in the human GABA type-A receptor ß3 subunit gene (GABRB3) has been identified in a patient with Lennox-Gastaut syndrome. To determine whether the mutation causes Lennox-Gastaut syndrome in vivo in mice and to elucidate its mechanistic effects, we generated the heterozygous Gabrb3+/D120N knock-in mouse and found that it had frequent spontaneous atypical absence seizures, as well as less frequent tonic, myoclonic, atonic and generalized tonic-clonic seizures. Each of these seizure types had a unique and characteristic ictal EEG. In addition, knock-in mice displayed abnormal behaviours seen in patients with Lennox-Gastaut syndrome including impaired learning and memory, hyperactivity, impaired social interactions and increased anxiety. This Gabrb3 mutation did not alter GABA type-A receptor trafficking or expression in knock-in mice. However, cortical neurons in thalamocortical slices from knock-in mice had reduced miniature inhibitory post-synaptic current amplitude and prolonged spontaneous thalamocortical oscillations. Thus, the Gabrb3+/D120N knock-in mouse recapitulated human Lennox-Gastaut syndrome seizure types and behavioural abnormalities and was caused by impaired inhibitory GABAergic signalling in the thalamocortical loop. In addition, treatment with antiepileptic drugs and cannabinoids ameliorated atypical absence seizures in knock-in mice. This congenic knock-in mouse demonstrates that a single-point mutation in a single gene can cause development of multiple types of seizures and multiple behavioural abnormalities. The knock-in mouse will be useful for further investigation of the mechanisms of Lennox-Gastaut syndrome development and for the development of new antiepileptic drugs and treatments.

Genetic diagnosis and clinical characteristics by etiological classification in early-onset epileptic encephalopathy with burst suppression pattern.

BACKGROUND: Early-onset epileptic encephalopathies with burst suppression (EOEE-BS) are a group of neonatal epileptic syndromes characterized by intractable epilepsy and severe psychomotor delay with structural and metabolic factors accounting for major etiologies. However, recent advances in gene sequencing have identified that genetic factors might also play a significant role in the development of EOEE-BS. Herein, we used various genetic tests to identify pathogenic genetic variants in EOEE-BS irrespective of structural malformations and analyzed the clinical features associated with each different etiology. METHODS: A total of 48 patients with EOEE-BS were included. Except for patients with severe hypoxic damage, patients with structural malformations were included in our patient cohort. Clinical features of the patients were reviewed, and etiological diagnoses were made based on several genetic tests, metabolic studies, and radiological findings. RESULT: A genetic diagnosis was made in 31 (64.6 %) patients, with the most commonly diagnosed gene being STXBP1 (n = 13, 27.1 %), followed by KCNQ2 (n = 5, 10.4 %), SCN2A (n = 5, 10.4 %), DEPDC5 (n = 3, 6.3 %), CASK (n = 1, 2.1 %), CDKL5 (n = 1, 2.1 %), GNAO1 (n = 1, 2.1 %), SLC6A8 (n = 1, 2.1 %), and LIS1 deletion (n = 1, 2.1 %). Other than the classification of epilepsy syndrome, no clinical features were associated with the genetically diagnosed group. Among eight patients with structural malformations, genetic diagnosis was achieved in five (62.5 %), and those patients had pathogenic mutations in DEPDC5 and CASK or LIS1 deletion, indicating the significance of gene sequencing irrespective of structural abnormalities. Treatment responses to a variety of medications and the ketogenic diet differed by etiology, and surgical resection proved to be effective in patients with cortical dysplasia. CONCLUSION: Genetic etiologies are an important factor in EOEE-BS irrespective of structural malformations and the treatment options may differ by etiology.

Targeted gene panel sequencing in early infantile onset developmental and epileptic encephalopathy.

BACKGROUND: Early-onset developmental and epileptic encephalopathy (DEE) is characterized by repeated seizures beginning within 3 months of birth and severe interictal epileptiform discharge, including burst suppression. This study assessed the utility of targeted gene panel sequencing in the genetic diagnosis of this disease. MATERIALS AND METHODS: Targeted gene panel sequencing was performed in 150 early infantile-onset DEE patients (≤3 months of age), and we extensively reviewed their clinical characteristics, including therapeutic efficacy, according to genotype. RESULTS: Of the early infantile-onset DEE patients, 70 were neonatal-onset DEE and the other 80 patients began experiencing seizures from 1 to 3 months after birth. There were 11 different pathogenic or likely pathogenic variants among 34.7% (52/150) of patients with early infantile-onset DEE, in whom KCNQ2, STXBP1, CDKL5, and SCN1A were the major pathogenic variants. Among the neonatal-onset DEE patients, pathological genes were identified in 42.9% (30/70), indicating a significantly higher diagnostic yield than in 27.5% (22/80) of patients who experienced seizure onset 1 to 3 months after birth (p = 0.048). Among the neonatal-onset DEE group, variants in KCNQ2, STXBP1, and CDKL5 were detected at high frequencies, accounting for 66.7% (20/30) of the pathogenic or likely pathogenic variants found in this study. CONCLUSION: Targeted gene panel sequencing demonstrated a high yield of pathogenic variants in the diagnosis of early-onset epileptic encephalopathy, especially in those with neonatal-onset DEE. Early diagnosis of early-onset epileptic encephalopathy may improve the prognosis of patients by earlier selection of appropriate treatment based on pathogenic variant.