Familial Focal Epilepsy Research Articles

Clinical and genetic analysis of a Chinese pedigree affected with Familial focal epilepsy with variable foci due to variant of NPRL3 gene

To explore the clinical manifestations and genetic etiology of a Chinese pedigree affected with Familial focal epilepsy with variable foci (FFEVF). A FFEVF pedigree presented at the Department of Medical Genetics of Linyi Maternal and Child Health Care Hospital on March 14, 2023 was selected as the study subject. The proband was subjected to whole exome sequencing (WES). Candidate variants were verified by Sanger sequencing of the proband and other affected members and bioinformatic analysis. This study was approved by the Linyi Maternal and Child Health Care Hospital (Ethics No. QTL-YXLL-2023048). WES revealed that the proband has harbored a heterozygous c.1642C>T (p.Arg548Cys) missense variant in exon 15 of the NPRL3 gene. Sanger sequencing confirmed that the variant was inherited from the proband's father, and multiple members of the pedigree had also harbored the same variant. Based on guidelines from the American College of Medical Genetics and Genomics (ACMG), the variant was classified as variant of unknown significance (PM2_supporting + PP3). The clinical phenotype of FFEVF patients caused by variants of NPRL3 gene is extensive, and the patients may present with neurological abnormality of autism spectrum disorder in addition to seizures.

Familial mesial temporal lobe epilepsy phenotype is associated with novel LGI1 variants: A report of two families

ObjectiveTo expand the clinical phenotype and mutation spectrum of familial mesial temporal lobe epilepsy (FMTLE) and provide a new perspective for exploring the pathological mechanisms of epilepsy caused by leucine-rich glioma inactivated 1 (LGI1) variants. MethodsWe reported clinical data from two families with FMTLE and screened patients for variants in the LGI1 gene using Whole-exome sequencing and Sanger sequencing. The clinical features of FMTLE were analysed. The pathogenicity of the causative loci was assessed according to the American College of Medical Genetics and Genomics guidelines, and potential pathogenic mechanisms were predicted through multiple bioinformatics and molecular dynamics software. ResultsWe identified two novel LGI1 truncating variants within two large families with FMTLE: LGI1 (c.1174C>T, p.Q392X) and LGI1 (c.703C>T, p.Q235X). Compared to previous reports, we found that focal to bilateral tonic-clonic seizures are a common type of seizure in FMTLE. The clinical phenotypes of patients with FMTLE caused by LGI1 variants were relatively mild, and all patients responded well to valproic acid. Bioinformatics analyses and molecular dynamics simulations showed that protein structure and interactions were considerably weakened or damaged as a result of both variants. ConclusionThis study presents the first report identifying LGI1 as a potential novel pathogenic gene within FMTLE families, thereby broadening the mutation spectrum associated with FMTLE. The findings of this study offer novel insights and avenues for understanding the intricate molecular mechanisms underlying LGI1 variants and their correlations with patient phenotypes. This study proposes the possibility of familial focal epilepsy syndromes overlapping.

The role of copy number variants in the genetic architecture of common familial epilepsies.

Copy number variants (CNVs) contribute to genetic risk and genetic etiology of both rare and common epilepsies. Whereas many studies have explored the role of CNVs in sporadic or severe cases, fewer have been done in familial generalized and focal epilepsies. We analyzed exome sequence data from 267 multiplex families and 859 first-degree relative pairs with a diagnosis of genetic generalized epilepsies or nonacquired focal epilepsies to predict CNVs. Validation and segregation studies were performed using an orthogonal method when possible. We identified CNVs likely to contribute to epilepsy risk or etiology in the probands of 43 of 1116 (3.9%) families, including known recurrent CNVs (16p13.11 deletion, 15q13.3 deletion, 15q11.2 deletion, 16p11.2 duplication, 1q21.1 duplication, and 5-Mb duplication of 15q11q13). We also identified CNVs affecting monogenic epilepsy genes, including four families with CNVs disrupting the DEPDC5 gene, and a de novo deletion of HNRNPU in one affected individual from a multiplex family. Several large CNVs (>500 kb) of uncertain clinical significance were identified, including a deletion in 18q, a large duplication encompassing the SCN1A gene, and a 15q13.3 duplication (BP4-BP5). The overall CNV landscape in common familial epilepsies is similar to that of sporadic epilepsies, with large recurrent deletions at 15q11, 15q13, and 16p13 contributing in 2.5%-3% of families. CNVs that interrupt known epilepsy genes and rare, large CNVs were also identified. Multiple etiologies were found in a subset of families, emphasizing the importance of genetic testing for multiple affected family members. Rare CNVs found in a single proband remain difficult to interpret and require larger cohorts to confirm their potential role in disease. Overall, our work indicates that CNVs contribute to the complex genetic architecture of familial generalized and focal epilepsies, supporting the role for clinical testing in affected individuals.

A novel variation in DEPDC5 causing familial focal epilepsy with variable foci.

Disheveled, EGL-10, and pleckstrin (DEP) domain-containing protein 5 (DEPDC5) is a component of GTPase-activating protein (GAP) activity toward the RAG complex 1 (GATOR1) protein, which is an inhibitor of the amino acid-sensing branch of the mammalian target of rapamycin complex 1 (mTORC1) pathway. GATOR1 complex variations were reported to correlate with familial focal epilepsy with variable foci (FFEVF). With the wide application of whole exome sequencing (WES), more and more variations in DEPDC5 were uncovered in FFEVF families. A family with a proband diagnosed with familial focal epilepsy with variable foci (FFEVF) was involved in this study. Whole exome sequencing (WES) was performed in the proband, and Sanger sequencing was used to confirm the variation carrying status of the family members. Mini-gene splicing assay was performed to validate the effect on the alternative splicing of the variation. A novel variant, c.1217 + 2T>A, in DEPDC5 was identified by WES in the proband. This splicing variant that occurred at the 5' end of intron 17 was confirmed by mini-gene splicing assays, which impacted alternative splicing and led to the inclusion of an intron fragment. The analysis of the transcribed mRNA sequence indicates that the translation of the protein is terminated prematurely, which is very likely to result in the loss of function of the protein and lead to the occurrence of FFEVF. The results suggest that c.1217 + 2T>A variations in DEPDC5 might be the genetic etiology for FFEVF in this pedigree. This finding expands the genotype spectrum of FFEVF and provides new etiological information for FFEVF.

Varijante u GATOR1 genima u fokalnoj epilepsiji

Significant genetic contributions to focal epilepsy have only recently been recognized, despite the well-established hereditary nature of other epilepsy syndromes. In 2013, the significant role of the DEPDC5 gene in a rare familial focal epilepsy syndrome was described, followed by the discovery of variants in NPRL2 and NPRL3 genes in patients with similar clinical features three years later. The genes listed above code the three subunits that comprise the GTPase-activating protein (GAP) activity towards Rags 1 (GATOR1) complex, a negative regulator of the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1). Loss of function of GATOR1 leads to constitutive mTORC1 activation that is linked to various malformations of cortical development (MCD), most notoriously focal cortical dysplasia (FCD), but has also been linked to epilepsy in the absence of overt MCD. Variants in GATOR1 genes have been detected in multiplex families with rare familial focal epilepsy syndromes where they demonstrate an autosomal dominant inheritance pattern with reduced penetrance. More recently, they have also been defined as major contributors in common nonacquired focal epilepsy in which they are detected in 3% of familial and 0.2% of sporadic cases and are particularly common in familial epilepsy associated with FCD where up to 11% of affected subjects carry gene variants. Clinical features of carriers include a propensity for nocturnal seizures, a poor response to antiseizure medication as well and an increased risk of sudden unexpected death in epilepsy, which is why other forms of treatment have been explored, including epilepsy surgery after which GATOR1 gene variant carriers have similar outcomes to other patients with focal epilepsy. A particularly promising avenue of exploration is the utilization of mTOR inhibitors like everolimus in epilepsy treatment, but further investigation into this option is warranted.

<i>DEPDC5</i>-related familial focal epilepsy

Focal epilepsy is the most common type of epilepsy accounting for 60–70% of all cases of this pathology. We present two familial cases of focal epilepsy associated with a nucleotide sequence variant in DEPDC5 gene. Clinical and ancestry examination was performed by using instrumental (magnetic resonance imaging, video-electroencephalography) and genetic testing methods. The nucleotide sequence variants in DEPDC5 gene were found in two probands and paired fathers with epilepsy. Focal cortical dysplasia was detected only in the father of Proband 1 as well as Proband 2 with resistant epilepsy and severe cognitive deficit. Hence, such clinical cases confirm that pathogenic variants in DEPDC5 gene are related with familial focal epilepsy, which clinical manifestation may depend on the type of identified mutation. The study of genotype-phenotype correlations is necessary to apply proper therapy. Before surgical treatment of epilepsy, the genetic testing by whole exome or whole genome sequencing should be performed.

Expanding the spectrum of gene-associated reflex seizures: A case report of a “bidet-induced” reflex epilepsy

In this case report, we present the case of a 20-month-old girl who manifested paroxysmal “bidet-induced” episodes characterized by impaired awareness, pallor, and hypotonia, with a duration of less than a minute. Initial neurological examination yielded unremarkable results, prompting further investigation. A video-electroencephalogram recording documented the epileptic nature of these episodes, revealing an ictal discharge originating from the right central-temporal region. A brain magnetic resonance imaging exhibited a sulcal/gyral asymmetry within the central sulci, along with the presence of the “power button sign” within the right central sulcus. These findings were indicative of a focal cortical dysplasia type-2. Subsequent genetic analysis through a gene panel identified the presence of an NPRL2 variant. Mutations affecting this particular gene are known to disrupt the normal functioning of the GATOR1 complex, potentially causing focal cortical dysplasia and various forms of epilepsy, including familial focal epilepsy with variable foci. On the diagnosis, the patient received levetiracetam, and the ictal episodes promptly ceased. At the most recent follow-up (at 4 years old), the patient remained free of seizures without the need for any treatment, and her neurodevelopment so far had exhibited no abnormalities. Considering the landscape of epilepsy-related GATOR1 variants, it is conceivable that this gene family may play a significant role in the pathogenesis of benign forms of focal reflex seizures, including bathing epilepsy.

The clinical, imaging, pathological and genetic landscape of bottom-of-sulcus dysplasia.

Bottom-of-sulcus dysplasia (BOSD) is increasingly recognized as a cause of drug-resistant, surgically-remediable, focal epilepsy, often in seemingly MRI-negative patients. We describe the clinical manifestations, morphological features, localization patterns and genetics of BOSD, with the aims of improving management and understanding pathogenesis. We studied 85 patients with BOSD diagnosed between 2005-2022. Presenting seizure and EEG characteristics, clinical course, genetic findings and treatment response were obtained from medical records. MRI (3 T) and 18F-FDG-PET scans were reviewed systematically for BOSD morphology and metabolism. Histopathological analysis and tissue genetic testing were performed in 64 operated patients. BOSD locations were transposed to common imaging space to study anatomical location, functional network localization and relationship to normal MTOR gene expression. All patients presented with stereotyped focal seizures with rapidly escalating frequency, prompting hospitalization in 48%. Despite 42% patients having seizure remissions, usually with sodium channel blocking medications, most eventually became drug-resistant and underwent surgery (86% seizure-free). Prior developmental delay was uncommon but intellectual, language and executive dysfunction were present in 24%, 48% and 29% when assessed preoperatively, low intellect being associated with greater epilepsy duration. BOSDs were missed on initial MRI in 68%, being ultimately recognized following repeat MRI, 18F-FDG-PET or image postprocessing. MRI features were grey-white junction blurring (100%), cortical thickening (91%), transmantle band (62%), increased cortical T1 signal (46%) and increased subcortical FLAIR signal (26%). BOSD hypometabolism was present on 18F-FDG-PET in 99%. Additional areas of cortical malformation or grey matter heterotopia were present in eight patients. BOSDs predominated in frontal and pericentral cortex and related functional networks, mostly sparing temporal and occipital cortex, and limbic and visual networks. Genetic testing yielded pathogenic mTOR pathway variants in 63% patients, including somatic MTOR variants in 47% operated patients and germline DEPDC5 or NPRL3 variants in 73% patients with familial focal epilepsy. BOSDs tended to occur in regions where the healthy brain normally shows lower MTOR expression, suggesting these regions may be more vulnerable to upregulation of MTOR activity. Consistent with the existing literature, these results highlight (i) clinical features raising suspicion of BOSD; (ii) the role of somatic and germline mTOR pathway variants in patients with sporadic and familial focal epilepsy associated with BOSD; and (iii) the role of 18F-FDG-PET alongside high-field MRI in detecting subtle BOSD. The anatomical and functional distribution of BOSDs likely explain their seizure, EEG and cognitive manifestations and may relate to relative MTOR expression.

Sudden Unexpected Death in Epilepsy and Respiratory Defects in a Mouse Model of DEPDC5-Related Epilepsy.

DEPDC5 is a common causative gene in familial focal epilepsy with or without malformations of cortical development. Its pathogenic variants also confer a significantly higher risk for sudden unexpected death in epilepsy (SUDEP), providing opportunities to investigate the pathophysiology intersecting neurodevelopment, epilepsy, and cardiorespiratory function. There is an urgent need to gain a mechanistic understanding of DEPDC5-related epilepsy and SUDEP, identify biomarkers for patients at high risk, and develop preventive interventions. Depdc5 was specifically deleted in excitatory or inhibitory neurons in the mouse brain to determine neuronal subtypes that drive epileptogenesis and SUDEP. Electroencephalogram (EEG), cardiac, and respiratory recordings were performed to determine cardiorespiratory phenotypes associated with SUDEP. Baseline respiratory function and the response to hypoxia challenge were also studied in these mice. Depdc5 deletion in excitatory neurons in cortical layer 5 and dentate gyrus caused frequent generalized tonic-clonic seizures and SUDEP in young adult mice, but Depdc5 deletion in cortical interneurons did not. EEG suppression immediately following ictal offset was observed in fatal and non-fatal seizures, but low amplitude rhythmic theta frequency activity was lost only in fatal seizures. In addition, these mice developed baseline respiratory dysfunction prior to SUDEP, during which ictal apnea occurred long before terminal cardiac asystole. Depdc5 deletion in excitatory neurons is sufficient to cause DEPDC5-related epilepsy and SUDEP. Ictal apnea and respiratory dysregulation play critical roles in SUDEP. Our study also provides a novel mouse model to investigate the underlying mechanisms of DEPDC5-related epilepsy and SUDEP. ANN NEUROL 2023;94:812-824.

Generation of a human iPSC line CIPi003-A from a patient with focal epilepsy harboring a heterozygous mutation in DEPDC5 gene

The DEPDC5 gene (OMIM 614191) has been proven to be a frequent cause of familial and sporadic focal epilepsy. A human induced pluripotent stem cell (iPSC) line was generated from a child diagnosed with focal epilepsy, which was caused by DEDPC5 mutation. The iPSC line expresses high pluripotency markers, carries the DEDPC5 mutation, and can differentiate into three germ layers in vitro. The iPSC lines offer a promising technique for studying the pathogenesis and conducting drug screening of DEDPC5-related epilepsy.

Hemimegalencephaly and intractable focal seizures related to NPRL3 mutation with variable familial expressivity treated with anatomic hemispherectomy

AbstractIntroductionHemimegalencephaly is a syndrome of dysplastic cortical formation, with hamartomatous overgrowth of a cerebral hemisphere, classically associated with intractable focal epilepsy, hemiparesis, and hemianopia. While often cryptogenic, associations with various proliferative syndromes have been implicated, such as in our patients.Patient DescriptionWe present a newborn with intractable focal epilepsy due to hemimegalencephaly caused by an inherited mutation in nitrogen permease regulator‐like 3 (NPRL3). He underwent anatomic hemispherectomy. His phenotype was more severe than that of other family member, which is consistent with recent studies suggesting that NPRL3 and other genes implicated in familial focal epilepsy with variable foci (FFEVF) produce a phenotypic range.ConclusionsHemimegalencephaly can produce intractable focal epilepsy and has been associated with various genetic causes, including NPRL3 mutations. We describe the fifth patient with hemimegalencephaly secondary to NPRL3 and the only one to undergo anatomic hemispherectomy. Given the small number of documented patients, more research is needed to elucidate the role of interventions such as sirolimus and palliative surgical procedures such as hemispherectomy.

Clinical Course May Be Independent from Neuroimaging in DEPDC-5-Related Epilepsy.

DEPDC5 is an upstream repressor of the mechanistic target of rapamycin pathway via the GATOR-1 complex. Pathogenic variants causing loss of function typically result in familial focal epilepsy with variable foci. Neuroimaging may either be normal or show brain malformations. Lesional and nonlesional cases may be present within the same family. Here, we describe a parent-child dyad affected by a truncating DEPDC5 pathogenic variant (c.727C > T; p.Arg243*), analyze the epilepsy clinical course, and describe neuroimaging characteristics from a 3T brain magnetic resonance imaging. Despite sharing the same variant, patients diverged both in terms of epilepsy severity and neuroimaging features. Surprisingly, the mother is still suffering from drug-resistant seizures and has normal neuroimaging, while the child has been experiencing prolonged seizure freedom notwithstanding a bottom-of-sulcus focal cortical dysplasia. An increasing gradient of severity has been proposed for families with GATOR1-related epilepsies. We confirm clinical and neuroradiological expressivities are variable and also suggest the prognostication of epilepsy outcome may be particularly difficult. The epilepsy outcome could partially be independent from brain structural abnormalities.

The clinical features of familial focal epilepsy with variable foci and NPRL3 gene variant.

Familial focal epilepsy with variable foci (FFEVF) is a rare type of focal epilepsy syndrome; it is associated with NPRL3 variant. However, relevant reports are rare in China. We aimed to analyze the clinical features of Chinese patients with FFEVF to understand further the differences between various NPRL3 variants and explored the effect of NPRL3 variant on mRNA. We ran a full workup on a family with FFEVF (four patients, one healthy member): an inquiry of medical history, cranial magnetic resonance imaging (MRI), electroencephalogram (EEG), and whole exon sequencing. Their clinical features were compared with those of other FFEVF patients in published reports. The mRNA splicing changes were analyzed quantitatively and qualitatively using real-time quantitative-polymerase chain reaction (q-PCR) and reverse transcription (RT)-PCR and compared between our patients and healthy individuals. Patients with NPRL3: c.1137dupT variant had a wide range of onset age (4 months to 31 years), diverse seizure types, variable foci (frontal lobe/temporal lobe), different seizure times (day/night) and frequencies (monthly/seldom/every day), different therapeutic effects (refractory epilepsy/almost seizure free), normal MRI, and abnormal EEG (epileptiform discharge, slow wave). The phenotypic spectrum with different NPRL3 variants was either similar or different. Significantly different relative quantities of mRNA were found between patients and healthy individuals in real-time qPCR. Abnormal splicing was observed in patients compared with healthy individual in RT-PCR. Despite having the same gene variant, different family members had different mRNA splicing, possibly causing different phenotypes. The clinical features of FFEVF varied, and auxiliary inspection was atypical. NPRL3: c.1137dupT could change the relative quantity of mRNA and cause abnormal splicing, which might produce different phenotypes in different family members.

Identification of two rare NPRL3 variants in two Chinese families with familial focal epilepsy with variable foci 3: NGS analysis with literature review.

Background: The GAP Activity Towards Rags 1 (GATOR1) complex, which includes DEPDC5, NPRL2, and NPRL3, plays a key role in epilepsy. It has been reported that focal epilepsy is associated with mutations in the NPRL3 gene in some cases. We report two rare mutations in the NPRL3 gene in two unrelated Chinese families with focal epilepsy in this study. Methods: The proband and her brother in family E1 first experienced seizures at 1.5 and 6years of age, respectively. Despite resection of epileptogenic foci, she still suffered recurrent seizures. The first seizure of a 20-year-old male proband in family E2 occurred when he was 2years old. To identify pathogenic variants in these families, whole-exome sequencing (WES) was performed on genomic DNA from peripheral blood. Results: In family E1, the trio-WES analysis of the proband and her brother without apparent structural brain abnormalities identified a heterozygous variant in the NPRL3 gene (c.954C>A, p.Y318*, NM_001077350.3). In family E2, the proband carried a heterozygous NPRL3 mutation (c.1545-1G>C, NM_001077350.3). Surprisingly, the mothers of the two probands each carried the variants, but neither had an attack. Bioinformatics analysis predicted that the mutation (c.954C>A) was in the highly conserved amino acid residues of NPRL3, which affected the α-helix of NPRL3 protein, leading to a truncated protein. The splice variant (c.1545-1G>C) resulted in the loss of the last exon of the NPRL3 gene. Conclusion: The results of this study provide a foundation for diagnosing NPRL3-related epilepsy by enriching their genotypes and phenotypes and help us identify the genetic etiologies of epilepsy in these two families.

Germline homozygous missense DEPDC5 variants cause severe refractory early-onset epilepsy, macrocephaly and bilateral polymicrogyria.

DEPDC5 (DEP Domain-Containing Protein 5) encodes an inhibitory component of the mammalian target of rapamycin (mTOR) pathway and is commonly implicated in sporadic and familial focal epilepsies, both non-lesional and in association with focal cortical dysplasia. Germline pathogenic variants are typically heterozygous and inactivating. We describe a novel phenotype caused by germline biallelic missense variants in DEPDC5. Cases were identified clinically. Available records, including magnetic resonance imaging and electroencephalography, were reviewed. Genetic testing was performed by whole exome and whole-genome sequencing and cascade screening. In addition, immunohistochemistry was performed on skin biopsy. The phenotype was identified in nine children, eight of which are described in detail herein. Six of the children were of Irish Traveller, two of Tunisian and one of Lebanese origin. The Irish Traveller children shared the same DEPDC5 germline homozygous missense variant (p.Thr337Arg), whereas the Lebanese and Tunisian children shared a different germline homozygous variant (p.Arg806Cys). Consistent phenotypic features included extensive bilateral polymicrogyria, congenital macrocephaly and early-onset refractory epilepsy, in keeping with other mTOR-opathies. Eye and cardiac involvement and severe neutropenia were also observed in one or more patients. Five of the children died in infancy or childhood; the other four are currently aged between 5 months and 6 years. Skin biopsy immunohistochemistry was supportive of hyperactivation of the mTOR pathway. The clinical, histopathological and genetic evidence supports a causal role for the homozygous DEPDC5 variants, expanding our understanding of the biology of this gene.

What is the impact of a novel DEPDC5 variant on an infant with focal epilepsy: a case report

BackgroundVariants in the DEPDC5 have been proved to be main cause of not only various dominant familial focal epilepsies, but also sporadic focal epilepsies. In the present study, a novel variant in DEPDC5 was detected in the patient with focal epilepsy and his healthy father. We aimed to analyze the pathogenic DEPDC5 variant in the small family of three.Case presentationA 5-month-old male infant presented with focal epilepsy. Whole exome sequencing identified a novel heterozygous variant c.1696delC (p.Gln566fs) in DEPDC5, confirmed by Sanger sequencing. The variant was inherited from healthy father.ConclusionsOur study expands the spectrum of DEPDC5 variants. Moreover, We discuss the relation between the low penetrance of DEPDC5 and the relatively high morbidity rate of DEPDC5-related sporadic focal epilepsy. Besides, due to interfamilial phenotypic and genetic heterogeneity, we speculate the prevalence of familial focal epilepsy with variable foci might be underestimated in such small families. We emphasize the importance of gene detection in patients with sporadic epilepsy of unknown etiology, as well as their family members. It can identify causative mutations, thus providing help to clinicians in making a definitive diagnosis.

Genetic Epilepsy Syndromes.

This article reviews the clinical features, typical EEG findings, treatment, prognosis, and underlying molecular etiologies of the more common genetic epilepsy syndromes. Genetic generalized epilepsy, self-limited focal epilepsy of childhood, self-limited neonatal and infantile epilepsy, select developmental and epileptic encephalopathies, progressive myoclonus epilepsies, sleep-related hypermotor epilepsy, photosensitive occipital lobe epilepsy, and focal epilepsy with auditory features are discussed. Also reviewed are two familial epilepsy syndromes: genetic epilepsy with febrile seizures plus and familial focal epilepsy with variable foci. Recent years have seen considerable advances in our understanding of the genetic factors underlying genetic epilepsy syndromes. New therapies are emerging for some of these conditions; in some cases, these precision medicine approaches may dramatically improve the prognosis. Many recognizable genetic epilepsy syndromes exist, the identification of which is a crucial skill for neurologists, particularly those who work with children. Proper diagnosis of the electroclinical syndrome allows for appropriate treatment choices and counseling regarding prognosis and possible comorbidities.

ILAE Genetic Literacy Series: familial focal epilepsy syndromes.

There are a number of familial focal epilepsy syndromes, each with distinct clinical characteristics. Here, we review the epilepsy phenotypes and the genetic architecture of these syndromes. Using an illustrative clinical case, we describe the important steps in making a diagnosis and ordering appropriate genetic tests. Our discussion on the genetics of the familial focal epilepsies will provide a framework for interpreting the results of genetic testing, and allow us to apply this information to patient management.

NPRL2 Inhibition of mTORC1 Controls Sodium Channel Expression and Brain Amino Acid Homeostasis.

Genetic mutations in nitrogen permease regulator-like 2 (NPRL2) are associated with a wide spectrum of familial focal epilepsies, autism, and sudden unexpected death of epileptics (SUDEP), but the mechanisms by which NPRL2 contributes to these effects are not well known. NPRL2 is a requisite subunit of the GAP activity toward Rags 1 (GATOR1) complex, which functions as a negative regulator of mammalian target of rapamycin complex 1 (mTORC1) kinase when intracellular amino acids are low. Here, we show that loss of NPRL2 expression in mouse excitatory glutamatergic neurons causes seizures before death, consistent with SUDEP in humans with epilepsy. Additionally, the absence of NPRL2 expression increases mTORC1-dependent signal transduction and significantly alters amino acid homeostasis in the brain. Loss of NPRL2 reduces dendritic branching and increases the strength of electrically stimulated action potentials (APs) in neurons. The increased AP strength is consistent with elevated expression of epilepsy-linked, voltage-gated sodium channels in the NPRL2-deficient brain. Targeted deletion of NPRL2 in primary neurons increases the expression of sodium channel Scn1A, whereas treatment with the pharmacological mTORC1 inhibitor called rapamycin prevents Scn1A upregulation. These studies demonstrate a novel role of NPRL2 and mTORC1 signaling in the regulation of sodium channels, which can contribute to seizures and early lethality.

A Novel Loss-of-Function Mutation in the NPRL3 Gene Identified in Chinese Familial Focal Epilepsy with Variable Foci.

Familial focal epilepsy with variable foci is an autosomal dominant disorder characterized by partial epilepsy with variable foci. In this study, we report a six-generation with segregation of the mutation present in four generations Chinese family presenting with focal epilepsy with variable foci. Whole exome sequencing confirms a novel pathogenic mutation in the NPRL3 gene (c316C>T; p. Q106*). PCR, Western blotting, and immunohistochemistry were conducted to analyze the gene transcription, protein expression, and subcellular localization of NPRL3 and related signaling molecules in peripheral blood cells from family members. As compared with healthy family members, both mRNA level and protein expression of NPRL3 are decreased in peripheral blood cells of the mutation carrier. In addition, the expression of downstream molecular Phospho-p70 S6 kinase (P-s6k) are increased consequently. Our findings expand the genotypic and phenotypic spectrum of the NPRL3-associated epilepsy and reveal the mechanisms of mTOR pathway signaling and GATOR1 pathogenesis in focal epilepsies, providing exciting potential for future diagnostic and therapeutic interventions. However, further in vitro and animal experiments are still needed to evaluate the role of NPRL3 loss-of-function mutation in epileptogensis.