Sporadic infantile epileptic encephalopathy caused by mutations in PCDH19 resembles Dravet syndrome but mainly affects females

Genetic testing, another important tool in presurgical evaluation of focal epilepsies in childhood

Epilepsy surgery may be a curative therapy for patients with drug-resistant epilepsies when focal lesions or foci are identified. Genetic testing is not yet routinely included in many presurgical evaluation programs although recent evidence support that finding a germline genetic mutation could help to better delineate the patient candidacy to surgery and provide valuable information on the expected surgery outcome. In this study, we report nine patients presenting drug-resistant focal epilepsy enrolled in presurgical evaluation. We show how the identification of genetic pathogenic variant in epilepsy known genes led to the interruption of the presurgical work-up and ruled out surgery in 7 of them. We observed that the co-existence of some recurrent clinical characteristics as early seizures' onset, frequent precipitating factors including fever, and developmental delay or intellectual disability may be useful markers for germline genetic pathogenic variants. In this group, genetic assessment should be mandatory during presurgical work up, mainly in patients with negative magnetic resonance imaging (MRI) or doubtful structural lesions. The integration of next generation targeted sequencing into the presurgical evaluation can improve the selection of candidates for resective surgery and fosters a personalized medicine approach with a better outcome. PLAINE LANGUAGE ABSTRACT: Genetic testing is not yet systematically included in the pre-surgical assessment of patients with drug-resistant focal epilepsies. In this study, through the description of nine patients, we underline how the integration of genomics into the presurgical work up can help in evaluating the patient candidacy to surgery and provide valuable information on expected surgery outcome.

Multicenter retrospective study of patients with PCDH19-related epilepsy: The first Hungarian cohort

OBJECTIVE

PCDH19-related epilepsy occurs predominantly in girls and is caused by pathogenic variant of the protocadherin-19 gene. The initial seizures usually develop in association with fever, begin on average at 15 months of age, and often occur in clusters. Autistic symptoms, intellectual disability, and sleep disturbance are often associated.

METHODS

In our retrospective, multicenter study, we reviewed clinical data of nine children with epilepsy genetically confirmed to be associated with PCDH19.

RESULTS

In the Hungarian patient population aged 0-18 years, the prevalence of PCDH19-related epilepsy was found to be lower (1/100000 live births in females) than the reported international data (4-5/100000 live births in females). Four of our nine patients had positive family history of epilepsy (cousins, sister, and mother). We assessed brain anomalies in three patients (in one patient focal cortical dysplasia and left anterior cingulate dysgenesis, and in two children right or left hippocampal sclerosis) and in another three cases incidentally identified benign alterations on brain MRI were found. The first seizure presented as a cluster in seven out of nine children. In seven out of nine cases occurred status epilepticus. Six out of nine children had autistic symptoms and only one child had normal intellectual development. Seven of our patients were seizure free with combined antiseizure medication (ASM). The most effective ASMs were levetiracetam, valproate, and clobazam.

SIGNIFICANCE

The prevalence of PCDH19-related epilepsy is presumably underestimated because of the lack of widely performed molecular genetic evaluations. Molecular genetic testing including PCDH19 pathogenic variants is recommended for female patients with an onset of seizures before the age of 3 years.

Proteomic analysis of the developing mammalian brain links PCDH19 to the Wnt/β-catenin signalling pathway

Clustering Epilepsy (CE) is a neurological disorder caused by pathogenic variants of the Protocadherin 19 (PCDH19) gene. PCDH19 encodes a protein involved in cell adhesion and Estrogen Receptor α mediated-gene regulation. To gain further insights into the molecular role of PCDH19 in the brain, we investigated the PCDH19 interactome in the developing mouse hippocampus and cortex. Combined with a meta-analysis of all reported PCDH19 interacting proteins, our results show that PCDH19 interacts with proteins involved in actin, microtubule, and gene regulation. We report CAPZA1, αN-catenin and, importantly, β-catenin as novel PCDH19 interacting proteins. Furthermore, we show that PCDH19 is a regulator of β-catenin transcriptional activity, and that this pathway is disrupted in CE individuals. Overall, our results support the involvement of PCDH19 in the cytoskeletal network and point to signalling pathways where PCDH19 plays critical roles.

Neuronal network activity and connectivity are impaired in a conditional knockout mouse model with PCDH19 mosaic expression

Mutations in PCDH19 gene, which encodes protocadherin-19 (PCDH19), cause Developmental and Epileptic Encephalopathy 9 (DEE9). Heterogeneous loss of PCDH19 expression in neurons is considered a key determinant of the disorder; however, how PCDH19 mosaic expression affects neuronal network activity and circuits is largely unclear. Here, we show that the hippocampus of Pcdh19 mosaic mice is characterized by structural and functional synaptic defects and by the presence of PCDH19-negative hyperexcitable neurons. Furthermore, global reduction of network firing rate and increased neuronal synchronization have been observed in different limbic system areas. Finally, network activity analysis in freely behaving mice revealed a decrease in excitatory/inhibitory ratio and functional hyperconnectivity within the limbic system of Pcdh19 mosaic mice. Altogether, these results indicate that altered PCDH19 expression profoundly affects circuit wiring and functioning, and provide new key to interpret DEE9 pathogenesis.

Seizure course of PCDH19 clustering epilepsy in female children: A multicentre cohort study in China

AIM

To investigate the seizure course of PCDH19 clustering epilepsy (PCDH19-CE) in a cohort of female children in China.

METHOD

This ambidirectional cohort study examined 113 female patients with PCDH19-CE through multicentre collaboration. Prognostic factors for seizure freedom were evaluated by multivariate Cox regression analysis.

RESULTS

The median seizure course period from seizure onset was 6 years 6 months. Of 113 patients, 78% and 56% experienced seizure freedom for at least 1 year and at least 2 years respectively. In patients younger than 5 years (n = 30), 5 to 10 years (n = 52), and older than 10 years (n = 31), 57%, 81%, and 94% experienced at least 1 year of seizure freedom, and 32%, 52%, and 84% experienced at least 2 years of seizure freedom, respectively. However, 58% (65 out of 113) relapsed at least once after more than 1 year of seizure freedom without trigger exposure (40%) or because of common triggers, including fever (43%) and antiseizure medication (ASM) reduction (29%). There was an 84% risk of seizure relapse after ASM reduction attempts. The likelihood of seizure freedom decreased with early age at seizure onset and developmental delay.

INTERPRETATION

Patients with PCDH19-CE exhibit increasing seizure freedom with age, but there is a risk of relapse. ASM reduction in children younger than 10 years old requires caution. Patients with early seizure onset and developmental delay have a reduced chance of seizure freedom.

WHAT THIS PAPER ADDS

The seizure freedom rate in PCDH19 clustering epilepsy gradually increases with age. The disease course is characterized by relapsing-remitting seizures. Antiseizure medication reduction requires caution for patients younger than 10 years of age. Patients with early seizure onset and developmental delay are less likely to achieve seizure freedom.

Mosaicism-independent mechanisms contribute to Pcdh19-related epilepsy and repetitive behaviors in Xenopus

Protocadherin19 (PCDH19)-related epilepsy syndrome is a rare disorder characterized by early-onset epilepsy, intellectual disability, and autistic behaviors. PCDH19 is located on the X chromosome and encodes a calcium-dependent single-pass transmembrane protein, which regulates cell-to-cell adhesion through homophilic binding. In human, 90% of heterozygous females, containing PCDH19 wild-type and mutant cells due to random X inactivation, are affected, whereas mutant males, containing only mutant cells, are typically not. The current view, the cellular interference, is that the altered interactions between wild-type and mutant cells during development, rather than loss of function itself, are responsible. However, studies using Pcdh19 knockout mice showed that the complete loss of function also causes autism-like behaviors both in males and females, suggesting that other functions of PCDH19 may also contribute to pathogenesis. To address whether mosaicism is required for PCDH19-related epilepsy, we generated Xenopus tropicalis tadpoles with complete or mosaic loss of function by injecting antisense morpholino oligonucleotides into the blastomeres of neural lineage at different stages of development. We found that either mosaic or complete knockdown results in seizure-like behaviors, which could be rescued by antiseizure medication, and repetitive behaviors. Our results suggest that the loss of PCDH19 function itself, in addition to cellular interference, may also contribute to PCDH19-related epilepsy.

PCDH19-clustering epilepsy, pathophysiology and clinical significance

PCDH19 clustering epilepsy (PCDH19-CE) is an X-linked epilepsy disorder associated with intellectual disability (ID) and behavioral disturbances, which is caused by PCDH19 gene variants. PCDH19 pathogenic variant leads to epilepsy in heterozygous females, not in hemizygous males and the inheritance pattern is unusual. The hypothesis of cellular interference was described as a key pathogenic mechanism. According to that, males do not develop the disease because of the uniform expression of PCDH19 (variant or wild type) unless they have a somatic variation. We conducted a literature review on PCDH19-CE pathophysiology and concluded that other significant mechanisms could contribute to pathogenesis including: asymmetric cell division and heterochrony, female-related allopregnanolone deficiency, altered steroid gene expression, decreased Gamma-aminobutyric acid receptor A (GABAA) function, and blood-brain barrier (BBB) dysfunction. Being aware of these mechanisms helps us when we should decide which therapeutic option is more suitable for which patient.

Abnormal cell sorting and altered early neurogenesis in a human cortical organoid model of Protocadherin-19 clustering epilepsy

Introduction

Protocadherin-19 (PCDH19)-Clustering Epilepsy (PCE) is a developmental and epileptic encephalopathy caused by loss-of-function variants of the PCDH19 gene on the X-chromosome. PCE affects females and mosaic males while male carriers are largely spared. Mosaic expression of the cell adhesion molecule PCDH19 due to random X-chromosome inactivation is thought to impair cell-cell interactions between mutant and wild type PCDH19-expressing cells to produce the disease. Progress has been made in understanding PCE using rodent models or patient induced pluripotent stem cells (iPSCs). However, rodents do not faithfully model key aspects of human brain development, and patient iPSC models are limited by issues with random X-chromosome inactivation.

Methods

To overcome these challenges and model mosaic PCDH19 expression in vitro, we generated isogenic female human embryonic stem cells with either HA-FLAG-tagged PCDH19 (WT) or homozygous PCDH19 knockout (KO) using genome editing. We then mixed GFP-labeled WT and RFP-labeled KO cells and generated human cortical organoids (hCOs).

Results

We found that PCDH19 is highly expressed in early (days 20-35) WT neural rosettes where it co-localizes with N-Cadherin in ventricular zone (VZ)-like regions. Mosaic PCE hCOs displayed abnormal cell sorting in the VZ with KO and WT cells completely segregated. This segregation remained robust when WT:KO cells were mixed at 2:1 or 1:2 ratios. PCE hCOs also exhibited altered expression of PCDH19 (in WT cells) and N-Cadherin, and abnormal deep layer neurogenesis. None of these abnormalities were observed in hCOs generated by mixing only WT or only KO (modeling male carrier) cells.

Discussion

Our results using the mosaic PCE hCO model suggest that PCDH19 plays a critical role in human VZ radial glial organization and early cortical development. This model should offer a key platform for exploring mechanisms underlying PCE-related cortical hyperexcitability and testing of potential precision therapies.

Mapping combinatorial expression of non-clustered protocadherins in the developing brain identifies novel PCDH19-mediated cell adhesion properties

Non-clustered protocadherins (ncPcdhs) are adhesive molecules with spatio-temporally regulated overlapping expression in the developing nervous system. Although their unique role in neurogenesis has been widely studied, their combinatorial role in brain physiology and pathology is poorly understood. Using probabilistic cell typing by in situ sequencing, we demonstrate combinatorial inter- and intra-familial expression of ncPcdhs in the developing mouse cortex and hippocampus, at single-cell resolution. We discovered the combinatorial expression of Protocadherin-19 (Pcdh19), a protein involved in PCDH19-clustering epilepsy, with Pcdh1, Pcdh9 or Cadherin 13 (Cdh13) in excitatory neurons. Using aggregation assays, we demonstrate a code-specific adhesion function of PCDH19; mosaic PCDH19 absence in PCDH19+9 and PCDH19 + CDH13, but not in PCDH19+1 codes, alters cell-cell interaction. Interestingly, we found that PCDH19 as a dominant protein in two heterophilic adhesion codes could promote trans-interaction between them. In addition, we discovered increased CDH13-mediated cell adhesion in the presence of PCDH19, suggesting a potential role of PCDH19 as an adhesion mediator of CDH13. Finally, we demonstrated novel cis-interactions between PCDH19 and PCDH1, PCDH9 and CDH13. These observations suggest that there is a unique combinatorial code with a cell- and region-specific characteristic where a single molecule defines the heterophilic cell-cell adhesion properties of each code.

A Male Child with Infantile Epilepsy due to a Mosaic Missense Variant of PCDH19

Background

Pathogenic variants of PCDH19, located on the X-chromosome (Xq22.1), cause a rare epileptic encephalopathy with speech and development delay, seizures, behavioral and psychiatric problems. The specific underlying pathogenic mechanism is known as "cellular interference" that results in affected heterozygous females, normal hemizygous males and affected mosaic males but its functioning is not yet clear.

Objectives

Reporting new cases of affected males is considered useful to a deeper insight.

Subject and Method

We present the case of a three-year-old boy with early-onset seizures at 3 months of age, mild cognitive impairment, partial control of seizures with levetiracetam, normal brain imaging.

Results

The patient has a mosaic pathogenic variant c.698A>G (p.Asp233Gly) in PCDH19 assessed by Next Generation Sequencing analysis. We have compared his characteristics with the genotypes and phenotypes of 34 PCDH19 mosaic males earlier reported in the literature. Finally, we have summarized today's knowledge about phenotype-genotype correlation and pharmacological response in these patients.

Conclusions

Our report confirms that the clinical picture of mosaic affected males, resembling that of females, can show a wide variability in severity of disease and underlines a stringent need to improve therapeutic approaches and to collect data on long-term follow-up.

Effect of PCDH19 missense mutations on cell-to-cell proximity and neuronal development under heterotypic conditions

The mutation of the X-linked protocadherin (PCDH) 19 gene in heterozygous females causes epilepsy. However, because of the erosion of X-chromosome inactivation (XCI) in female human pluripotent stem cells, precise disease modeling often leads to failure. In this study, using a mathematical approach and induced pluripotent stem cells retaining XCI derived from patients with PCDH19 missense mutations, we found that heterotypic conditions, which are composed of wild-type and missense PCDH19, led to significant cell-to-cell proximity and impaired neuronal differentiation, accompanied by the aberrant accumulation of doublecortin, a microtubule-associated protein. Our findings suggest that ease of adhesion between cells expressing either wild-type or missense PCDH19 might lead to aberrant cell aggregation in early embryonic phases, causing poor neuronal development.

Overcoming genetic and cellular complexity to study the pathophysiology of X-linked intellectual disabilities

X-linked genetic causes of intellectual disability (ID) account for a substantial proportion of cases and remain poorly understood, in part due to the heterogeneous expression of X-linked genes in females. This is because most genes on the X chromosome are subject to random X chromosome inactivation (XCI) during early embryonic development, which results in a mosaic pattern of gene expression for a given X-linked mutant allele. This mosaic expression produces substantial complexity, especially when attempting to study the already complicated neural circuits that underly behavior, thus impeding the understanding of disease-related pathophysiology and the development of therapeutics. Here, we review a few selected X-linked forms of ID that predominantly affect heterozygous females and the current obstacles for developing effective therapies for such disorders. We also propose a genetic strategy to overcome the complexity presented by mosaicism in heterozygous females and highlight specific tools for studying synaptic and circuit mechanisms, many of which could be shared across multiple forms of intellectual disability.

Heterozygous Nexmif female mice demonstrate mosaic NEXMIF expression, autism-like behaviors, and abnormalities in dendritic arborization and synaptogenesis

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a strong genetic basis. ASDs are commonly characterized by impairments in language, restrictive and repetitive behaviors, and deficits in social interactions. Although ASD is a highly heterogeneous disease with many different genes implicated in its etiology, many ASD-associated genes converge on common cellular defects, such as aberrant neuronal morphology and synapse dysregulation. Our previous work revealed that, in mice, complete loss of the ASD-associated X-linked gene NEXMIF results in a reduction in dendritic complexity, a decrease in spine and synapse density, altered synaptic transmission, and ASD-like behaviors. Interestingly, human females of NEXMIF haploinsufficiency have recently been reported to demonstrate autistic features; however, the cellular and molecular basis for this haploinsufficiency-caused ASD remains unclear. Here we report that in the brains of Nexmif± female mice, NEXMIF shows a mosaic pattern in its expression in neurons. Heterozygous female mice demonstrate behavioral impairments similar to those of knockout male mice. In the mosaic mixture of neurons from Nexmif± mice, cells that lack NEXMIF have impairments in dendritic arborization and spine development. Remarkably, the NEXMIF-expressing neurons from Nexmif± mice also demonstrate similar defects in dendritic growth and spine formation. These findings establish a novel mouse model of NEXMIF haploinsufficiency and provide new insights into the pathogenesis of NEXMIF-dependent ASD.

Multiomic analysis implicates nuclear hormone receptor signalling in clustering epilepsy

Clustering Epilepsy (CE) is an epileptic disorder with neurological comorbidities caused by heterozygous variants of the X chromosome gene Protocadherin 19 (PCDH19). Recent studies have implicated dysregulation of the Nuclear Hormone Receptor (NHR) pathway in CE pathogenesis. To obtain a comprehensive overview of the impact and mechanisms of loss of PCDH19 function in CE pathogenesis, we have performed epigenomic, transcriptomic and proteomic analysis of CE relevant models. Our studies identified differential regulation and expression of Androgen Receptor (AR) and its targets in CE patient skin fibroblasts. Furthermore, our cell culture assays revealed the repression of PCDH19 expression mediated through ERα and the co-regulator FOXA1. We also identified a protein-protein interaction between PCDH19 and AR, expanding upon the intrinsic link between PCDH19 and the NHR pathway. Together, these results point to a novel mechanism of NHR signaling in the pathogenesis of CE that can be explored for potential therapeutic options.

Next-generation sequencing testing in children with epilepsy reveals novel clinical, diagnostic and therapeutic implications

Introduction: Epilepsy is one of the commonest diseases in children, characterized by extensive phenotypic and genetic heterogeneity. This study was conducted to determine the diagnostic utility and to identify novel clinical and therapeutic implications of genetic testing in pediatric patients with epilepsy. Methods: Large multigene panel and/or exome sequencing was performed in 127 unrelated Polish and Ukrainian patients with suspected monogenic epilepsy. Diagnostic yields were presented for five phenotypic subgroups, distinguished by seizure type, electroencephalographic abnormalities, anti-seizure treatment response, and neurodevelopmental deficits. Results: A definite molecular diagnosis was established in 46 out of 127 cases (36%). Alterations in six genes were detected in more than one patient: SCN1A, MECP2, KCNT1, KCNA2, PCDH19, SLC6A1, STXBP1, and TPP1, accounting for 48% of positive cases. 4/46 cases (8.7%) were mosaic for the variant. Although the highest rates of positive diagnoses were identified in children with developmental delay and generalized seizures (17/41, 41%) and in developmental end epileptic encephalopathies (16/40, 40%), a monogenic etiology was also frequently detected in patients with solely focal seizures (10/28, 36%). Molecular diagnosis directly influenced anti-seizure management in 15/46 cases. Conclusion: This study demonstrates the high diagnostic and therapeutic utility of large panel testing in childhood epilepsies irrespective of seizure types. Copy number variations and somatic mosaic variants are important disease-causing factors, pointing the need for comprehensive genetic testing in all unexplained cases. Pleiotropy is a common phenomenon contributing to the growing phenotypic complexity of single-gene epilepsies.

Prenatal diagnosis of developmental and epileptic encephalopathy 9 with a 10.05-Mb microdeletion at Xq21.31q22.1 inherited from mother: A case report and literature review

BACKGROUND

Developmental and epileptic encephalopathy 9 (DEE9) is characterized by early infantile seizures and mild-to-severe neuropsychiatric symptoms. Despite being an X-linked dominant disorder, DEE9 mainly affects heterozygous females or mosaic males, while hemizygous males are less affected. PCDH19 gene has been documented as the causative gene.

METHODS

Karyotyping analysis and copy number variation sequencing (CNV-seq) were performed on a pregnant woman with epilepsy, together with her husband, son, and fetus.

RESULTS

A disease-causing microdeletion, seq[GRCh37] del(X)(q21.31q22.1) (90310001-100360000), was identified in the pregnant woman and her female fetus. The microdeletion includes the entire PCDH19 gene and is classified as "pathogenic" according to the American College of Medical Genetics and Genomics guidelines.

CONCLUSION

In this case study, we have not only identified the epilepsy type of the woman as DEE9 but have also made an unfavorable prognosis for her fetus. Our findings from this prenatal case provide valuable clinical resources for prenatal diagnosis and genetic counseling, while also implying the potential of CNV-seq as a viable method for uncovering PCDH19-related epilepsy.

[Epilepsy with PCDH19 mutation: polypharmacy as a consequence of the complexity and diversity of pathogenesis mechanisms]

Mutations in the human PCDH19 gene lead to epileptic encephalopathy of early childhood. It is characterized by the early onset of serial seizures, cognitive impairment and behavioral disorders (including autistic personality traits). In most cases, difficulties arise in selecting therapy due to pharmacoresistance. The pathogenesis of the disease is complex. The data available to us at the moment from numerous studies present the pathogenesis of «PCDH19 syndrome» as multi-level, affecting both the epigenetic support of cell life, and development of stem cells and progenitor cells in the process of neuroontogenesis, and the influence on the neurotransmitter mechanisms of the brain, and disruption of the formation of neural networks with an inevitable increase in the excitability of the cerebral cortex as a whole, and local changes in the highly labile regulatory structures of the hippocampal region. And it is not surprising that all these changes entail not only (and perhaps not so much) epileptization, but a profound disruption of the regulation of brain activity, accompanied by autism spectrum disorders, more profound disorders in the form of schizophrenia or cyclothymia, and the formation of delayed psychomotor development. A «side branch» of these pathogenetic processes can also be considered the participation of PCDH19 dysfunctions in certain variants of oncogenesis. The need for polypharmacy (in most cases) confirms the diversity of mechanisms involved in the pathogenesis of the disease and makes the prospects for the development of effective and rational treatment regimens very vague. Cautious optimism is caused only by attempts at relatively specific treatment with ganaxolone.

Epileptic seizures worsen the gait and motor abnormalities in adult patients with Dravet syndrome (with a case report and literature review)

Dravet syndrome (DS), previously known as severe myoclonic epilepsy in infancy (SMEI), is considered the most serious "epileptic encephalopathy." Here, we present a man with a de novo SCN1A mutation who was diagnosed with DS at the age of 29. In addition to pharmaco-resistant seizures and cognitive delay, he also developed moderate to severe motor and gait problems, such as crouching gait and Pisa syndrome. Moreover, it deteriorated significantly following an epileptic seizure. The patient presented with severe flexion of the head and trunk in the sagittal plane and fulfilled the diagnostic criteria for camptocormia and antecollis. After a week, it spontaneously alleviated partially. We applied levodopa to the patient and had a good response. Functional Gait Assessment (FGA) was assessed at three different times: 4 days after the seizure, 1 week after the seizure, and after taking levodopa for 2 years. The results were 4, 12, and 19 points, respectively. We postulated that: (1) gait and motor deficits are somehow influenced by recurrent epileptic episodes;(2) the nigrostriatal dopamine system is involved. To our knowledge, we were the ones who first reported this phenomenon.

Customized targeted massively parallel sequencing enables the identification of novel pathogenic variants in Tunisian patients with developmental and epileptic encephalopathy

OBJECTIVE

To develop a high-throughput sequencing panel for the diagnosis of developmental and epileptic encephalopathy in Tunisia and to clarify the frequency of disease-causing genes in this region.

METHODS

We developed a custom panel for next-generation sequencing of the coding sequences of 116 genes in individuals with developmental and epileptic encephalopathy from the Tunisian population. Segregation analyses and in silico studies have been conducted to assess the identified variants' pathogenicity.

RESULTS

We report 12 pathogenic variants in SCN1A, CHD2, CDKL5, SZT2, KCNT1, GNAO1, PCDH19, MECP2, GRIN2A, and SYNGAP1 in patients with developmental and epileptic encephalopathy. Five of these variants are novel: "c.149delA, p.(Asn50MetfsTer26)" in CDKL5; "c.3616C > T, p.(Arg1206Ter)" in SZT2; "c.111_113del, p.(Leu39del)" in GNAO1; "c.1435G>C, p.(Asp479His)" in PCDH19; and "c.2143delC, p.(Arg716GlyfsTer10)" in SYNGAP1. Additionally, for four of our patients, the genetic result facilitated the choice of the appropriate treatment.

SIGNIFICANCE

This is the first report of a custom gene panel to identify genetic variants implicated in developmental and epileptic encephalopathy in the Tunisian population as well as the North African region (Tunisia, Egypt, Libya, Algeria, Morocco) with a diagnostic rate of 30%. This high-throughput sequencing panel has considerably improved the rate of positive diagnosis of developmental and epileptic encephalopathy in the Tunisian population, which was less than 15% using Sanger sequencing. The benefit of genetic testing in these patients was approved by both physicians and parents.

Genetic and clinical landscape of ARR3-associated MYP26: the most common cause of Mendelian early-onset high myopia with a unique inheritance

AIMS

To elucidate genetic background of early-onset high myopia (eoHM) and characteristics of ARR3-associated MYP26.

METHODS

Variants in 14 genes reported to contribute to eoHM, including ARR3, were selected from exome sequencing data set and classified into different categories following American College of Medical Genetics and Genomics guidelines based on in silico prediction, associated phenotypes, confirmation and cosegregation analysis. The available clinical data of individuals were summarised.

RESULTS

Pathogenic and likely pathogenic variants in three of 14 genes were identified in 52 of 928 families with eoHM, including 29 in ARR3, 22 in OPN1LW and 1 in LRPAP1. For ARR3, 24 pathogenic variants (16 truncation and 8 missense) were identified in 66 women and 12 men, in whom 64 women and 4 men had eoHM by X-linked female-limited inheritance. Refraction ranged from -5.00 to -28.75 diopter (-12.58±4.83). Mild-to-moderately reduced cone responses were recorded in 76.9% (10/13) of patients with electroretinogram recordings. Most patients (75.9%, 41/54) had mild myopic fundus changes (C0 to C1). Genotype-phenotype analysis suggested that the myopic retinopathy degree was correlated with age and the variant's nature. Peripheral retinal degeneration was observed in 38.5% (5/13) patients using wide-field examinations.

CONCLUSION

This study reveals ARR3 as the most frequently implicated gene for Mendelian eoHM. Truncations and highly scored missense variants in ARR3 are pathogenic. Myopia due to ARR3 mutations is transmitted in X-linked female-limited inheritance, manifests with mild cone impairment and slowly progresses to pathologic myopia. Identification of the most common cause for Mendelian eoHM provides a valuable starting point into the molecular mechanism of myopia.

Exposure to SARS-CoV-2 and Infantile Diseases

Background and Aim  Immune response against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in newborns and children after prophylactic immunization is currently a relevant research topic. The present study analyzes the issue by examining the possibility that the anti-SARS-CoV-2 immune responses are not uniquely directed against the virus but can-via molecular mimicry and the consequent cross-reactivity-also hit human proteins involved in infantile diseases. Methods  Human proteins that-if altered-associate with infantile disorders were searched for minimal immune pentapeptide determinants shared with SARS-CoV-2 spike glycoprotein (gp). Then, the shared pentapeptides were analyzed for immunologic potential and immunologic imprinting phenomena. Results  Comparative sequence analysis shows that: (1) numerous pentapeptides (namely, 54) are common to SARS-CoV-2 spike gp and human proteins that, when altered, are linked to infantile diseases; (2) all the shared peptides have an immunologic potential since they are present in experimentally validated SARS-CoV-2 spike gp-derived epitopes; and (3) many of the shared peptides are also hosted in infectious pathogens to which children can have already been exposed, thus making immunologic imprint phenomena feasible. Conclusion  Molecular mimicry and the consequent cross-reactivity can represent the mechanism that connects exposure to SARS-CoV-2 and various pediatric diseases, with a fundamental role of the immunologic memory and the history of the child's infections in determining and specifying the immune response and the pathologic autoimmune sequela.

Molecular analysis and prenatal diagnosis of seven Chinese families with genetic epilepsy

Introduction

Genetic epilepsy is a large group of clinically and genetically heterogeneous neurological disorders characterized by recurrent seizures, which have a clear association with genetic defects. In this study, we have recruited seven families from China with neurodevelopmental abnormalities in which epilepsy was a predominant manifestation, aiming to elucidate the underlying causes and make a precise diagnosis for the cases.

Methods

Whole-exome sequencing (WES) combined with Sanger sequencing was used to identify the causative variants associated with the diseases in addition to essential imaging and biomedical examination.

Results

A gross intragenic deletion detected in MFSD8 was investigated via gap-polymerase chain reaction (PCR), real-time quantitative PCR (qPCR), and mRNA sequence analysis. We identified 11 variants in seven genes (ALDH7A1, CDKL5, PCDH19, QARS1, POLG, GRIN2A, and MFSD8) responsible for genetic epilepsy in the seven families, respectively. A total of six variants (c.1408T>G in ALDH7A1, c.1994_1997del in CDKL5, c.794G>A in QARS1, c.2453C>T in GRIN2A, and c.217dup and c.863+995_998+1480del in MFSD8) have not yet been reported to be associated with diseases and were all evaluated to be pathogenic or likely pathogenic according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

Methods

Based on the molecular findings, we have associated the intragenic deletion in MFSD8 with the mutagenesis mechanism of Alu-mediated genomic rearrangements for the first time and provided genetic counseling, medical suggestions, and prenatal diagnosis for the families. In conclusion, molecular diagnosis is crucial to obtain improved medical outcomes and recurrence risk evaluation for genetic epilepsy.

Modelling PCDH19 clustering epilepsy by Neurogenin 2 induction of patient-derived induced pluripotent stem cells

BACKGROUND

Loss of function mutations in PCDH19 gene cause an X-linked, infant-onset clustering epilepsy, associated with intellectual disability and autistic features. The unique pattern of inheritance includes random X-chromosome inactivation, which leads to pathological tissue mosaicism. Females carrying PCDH19 mutations are affected, while males have normal phenotype. No cure is presently available for this disease.

METHODS

Fibroblasts from a female patient carrying frameshift mutation were reprogrammed into human induced pluripotent stem cells (hiPSC). To create a cell model of PCDH19-clustering epilepsy (PCDH19-CE) where both cell populations co-exist, we created mosaic neurons by mixing wild-type (WT) and mutated (mut) human iPSC clones, and differentiated them into mature neurons with overexpression of the transcriptional factor Neurogenin 2.

RESULTS

We generated functional neurons from patient-derived iPSC using a rapid and efficient method of differentiation through overexpression of Neurogenin 2. Was revealed an accelerated maturation and higher arborisation in the mutated neurons, while the mosaic neurons showed the highest frequency of action potential firing and hyperexcitability features, compared to mutated and WT neurons.

CONCLUSIONS

Our findings provide evidence that PCDH19 c.2133delG mutation affects proper metaphases with increased numbers of centrosomes in stem cells and accelerates neuronal maturation in premature cells. PCDH19 mosaic neurons showed an elevated excitability, representing the situation in PCDH19-CE brain. We suggest an Ngn-2 hiPSC-derived PCDH19 neurons as an informative experimental tool for understanding the pathogenesis of PCDH19-CE and a suitable approach for use in targeted drug screening strategies.

Structure and function in artificial, zebrafish and human neural networks

Network science provides a set of tools for the characterization of the structure and functional behavior of complex systems. Yet a major problem is to quantify how the structural domain is related to the dynamical one. In other words, how the diversity of dynamical states of a system can be predicted from the static network structure? Or the reverse problem: starting from a set of signals derived from experimental recordings, how can one discover the network connections or the causal relations behind the observed dynamics? Despite the advances achieved over the last two decades, many challenges remain concerning the study of the structure-dynamics interplay of complex systems. In neuroscience, progress is typically constrained by the low spatio-temporal resolution of experiments and by the lack of a universal inferring framework for empirical systems. To address these issues, applications of network science and artificial intelligence to neural data have been rapidly growing. In this article, we review important recent applications of methods from those fields to the study of the interplay between structure and functional dynamics of human and zebrafish brain. We cover the selection of topological features for the characterization of brain networks, inference of functional connections, dynamical modeling, and close with applications to both the human and zebrafish brain. This review is intended to neuroscientists who want to become acquainted with techniques from network science, as well as to researchers from the latter field who are interested in exploring novel application scenarios in neuroscience.

Phase 2, placebo-controlled clinical study of oral ganaxolone in PCDH19-clustering epilepsy

INTRODUCTION

Protocadherin-19 (PCDH19)-clustering epilepsy is a distinct developmental and epileptic encephalopathy characterized by early-onset seizures that are often treatment refractory. Caused by a mutation of the PCDH19 gene on the X chromosome, this rare epilepsy syndrome primarily affects females with seizure onset commonly in the first year of life. A global, randomized, double-blind, placebo-controlled, phase 2 trial was conducted to evaluate the efficacy, safety, and tolerability of ganaxolone compared with placebo as adjunctive therapy to a standard antiseizure medication regimen in patients with PCDH19-clustering epilepsy (VIOLET; NCT03865732).

METHODS

Females aged 1-17 years with a molecularly confirmed pathogenic or likely pathogenic PCDH19 variant who were experiencing ≥12 seizures during a 12-week screening period were stratified by baseline allopregnanolone sulfate (Allo-S) levels (low: ≤2.5 ng/mL; high: >2.5 ng/mL) at screening and randomized 1:1 within each strata to receive ganaxolone (maximum daily dose of 63 mg/kg/day if ≤28 kg or 1800 mg/day if >28 kg) or matching placebo in addition to their standard antiseizure treatment for the 17-week double-blind phase. The primary efficacy endpoint was the median percentage change in 28-day seizure frequency from baseline to the 17-week double-blind phase. Treatment-emergent adverse events (TEAEs) were tabulated by overall, system organ class, and preferred term.

RESULTS

Of the 29 patients screened, 21 (median age, 7.0 years; IQR, 5.0-10.0 years) were randomized to receive either ganaxolone (n = 10) or placebo (n = 11). After the 17-week double-blind phase, the median (IQR) percentage change in 28-day seizure frequency from baseline was - 61.5% (-95.9% to -33.4%) among patients in the ganaxolone group and - 24.0% (-88.2% to -4.9%) among patients in the placebo group (Wilcoxon rank-sum test, p = 0.17). TEAEs were reported by 7 of 10 (70.0%) patients in the ganaxolone group and 11 of 11 (100%) patients in the placebo group. Somnolence was the most common TEAE (40.0% ganaxolone vs 27.3% placebo); serious TEAEs were more common in the placebo group (10.0% ganaxolone vs 45.5% placebo); and 1 (10.0%) patient in the ganaxolone group discontinued the study versus none in the placebo group.

CONCLUSIONS

Ganaxolone was generally well tolerated and led to a greater reduction in the frequency of PCDH19-clustering seizures compared to placebo; however, the trend did not reach statistical significance. Novel trial designs are likely needed to evaluate the effectiveness of antiseizure treatments for PCDH19-clustering epilepsy.

Genetic variants and phenotype analysis in a five-generation Chinese pedigree with PCDH19 female-limited epilepsy

Objective

Albeit the gene of PCDH19-FE was ascertained, the correlation of gene mutation, PCDH19 protein structure, and phenotype heterogeneity remained obscure. This study aimed to report a five-generation pedigree of seven female patients of PCDH19-FE and tried to explore whether two variants were correlated with PCDH19 protein structure and function alteration, and PCDH19-FE phenotype.

Methods

We analyzed the clinical data and genetic variants of a PCDH19-FE pedigree, to explore the phenotype heterogeneity of PCDH19-FE and underlying mechanisms. In addition to the clinical information of family members, next-generation sequencing was adopted to detect the variant sites of probands with validation by sanger sequencing. And the sanger sequencing was conducted in other patients in this pedigree. The biological conservation analysis and population polymorphism analysis of variants were also performed subsequently. The structure alteration of mutated PCDH19 protein was predicted by AlphaFold2.

Results

Based on a five-generation pedigree of PCDH19-FE, missense variants of c.695A>G and c.2760T>A in the PCDH19 gene were found in the heterozygous proband (V:1), which resulted in the change of amino acid 232 from Asn to Ser (p.Asn232Ser) and amino acid 920 from Asp to Glu (p.Asp920Glu) influencing PCDH19 function. The other six females in the pedigree (II:6, II:8, IV:3, IV:4, IV:5, IV:11) exhibited different clinical phenotypes but shared the same variant. Two males with the same variant have no clinical manifestations (III:3, III:10). The biological conservation analysis and population polymorphism analysis demonstrated the highly conservative characteristics of these two variants. AlphaFold2 predicted that the variant, p.Asp920Glu, led to the disappearance of the hydrogen bond between Asp at position 920 and His at position 919. Furthermore, the hydrogen bond between Asp920 and His919 also disappeared when the Asn amino acid mutated to Ser at position 232.

Conclusion

A strong genotype-phenotype heterogeneity was observed among female patients with the same genotype in our PCDH19-FE pedigree. And two missense variants, c.695A > G and c.2760T>A in the PCDH19 gene, have been identified in our pedigree. The c.2760T>A variant was a novel variant site probably related to the PCDH19-FE.

PCDH19-related epilepsy in mosaic males: The phenotypic implication of genotype and variant allele frequency

OBJECTIVE

To analyze the genotypes and phenotypes of mosaic male patients with PCDH19-related epilepsy (PCDH19-RE) and explore the correlation between genotype, variant allele frequency (VAF), and phenotypic severity.

METHODS

Clinical data and peripheral blood samples of 11 male mosaic patients were collected and analyzed in our study. The VAF of the PCDH19 gene from peripheral blood was quantified using amplicon-based deep sequencing. Additional 20 mosaic male patients with PCDH19-RE were collected from the published literature, with 10 patients whose VAFs of the PCDH19 gene were available for analytic purposes.

RESULTS

In our cohort of 11 patients, 10 variants were identified, and four were novel. The VAF of the PCDH19 gene from peripheral blood ranged from 27 to 90%. The median seizure onset age was 6 months (range: 4-9 months). Clinical manifestations included cluster seizures (100%), fever sensitivity (73%), focal seizures (91%), developmental delay/intellectual disability (DD/ID, 82%), and autistic features (45%). Thirty-one mosaic male patients collected from our cohort and the literature developed seizures mostly (87%) within one year of age. Variant types included missense variants (42%), truncating variants (52%), splice variants (3%), and whole PCDH19 deletion (3%). Among 21 patients with a definite VAF from our cohort and the literature, nine had a low VAF ( ≤ 50%) and 12 had a high VAF (> 50%). Seventy-five percent of variants from the high VAF group were missense, whereas 89% of those from the low VAF group were truncations. The median seizure onset age was 6 months in the low VAF group and 9 months in the high VAF group (p = 0.018). Forty-four percent (4/9) of patients from the low VAF group achieved seizure-free for ≥1 year, whereas none of the 12 patients from the high VAF group did (p = 0.021). DD/ID was present in 83% (10/12) of the high VAF group and 56% (5/9) of the low VAF group (p = 0.331).

CONCLUSION

The predominant variant types were truncating and missense variants. Missense variants tended to have higher VAFs. Patients with a high VAF were more likely to have a more severe epileptic phenotype. Our findings shed light on the phenotypic implications of VAF in mosaic males with PCDH19-RE.

Case report: A novel mosaic nonsense mutation of PCDH19 in a Chinese male with febrile epilepsy

The clinical features of the PCDH19 gene mutation include febrile epilepsy ranging from mild to severe, with or without intellectual disability, cognitive impairment, and psych-behavioral disorders, but there has been little research on males with the mosaic mutation of PCDH19. This study reported a novel, de novo, and mosaic PCDH19 nonsense mutation (NM_001184880: c.840C > A, p. Tyr280^*) from a Chinese male in early middle childhood by trio whole-exome sequence (Trio-WES) and confirmed by Sanger sequence. The proportion of the mosaic mutation (c.840C > A, p. Tyr280^*) in PCDH19 was 27.9% in, buccal mucosal cells, 48.3% in exfoliated cells in the urine, and 50.6% in peripheral blood of proband. He had the first onset of seizures in toddlerhood with febrile epilepsy, mild impaired cognitive psychological, and behavioral abnormalities. The electroencephalography (EEG) exhibited sharp waves and sharp slow complex waves in the bilateral parietal, occipital, and posterior temporal regions during the interictal period. Pinpoint white matter lesions in the periventricular white matter and slightly bulging bilateral ventricles appeared on cranial magnetic resonance imaging (MRI). With Depakine and Keppra he gained good control over his epilepsy. This study might expand the genotypes and broaden the spectrums.

Genetic causes of rare and common epilepsies: What should the epileptologist know?

In past decades, the identification of genes involved in epileptic disorders has grown exponentially. The pace of gene identification in epileptic disorders began to accelerate in the late 2000s, driven by new technologies such as molecular cytogenetics and next-generation sequencing (NGS). These technologies have also been applied to genetic diagnostics, with different configurations, such as gene panels, whole-exome sequencing and whole-genome sequencing. The clinician must be aware that any technology has its limitations and complementary techniques must still be used to establish a diagnosis for specific diseases. In addition, increasing the amount of genetic information available in a larger patient sample also increases the need for rigorous interpretation steps, when taking into account the clinical, electroclinical, and when available, functional data. Local, multidisciplinary discussions have proven valuable in difficult diagnostic situations, especially in cases where precision medicine is being considered. They also serve to improve genetic counseling in complex situations. In this article, we will briefly review the genetic basis of rare and common epilepsies, the current strategies used for molecular diagnosis, including their limitations, and some pitfalls for data interpretation, in the context of etiological diagnosis and genetic counseling.

Phenotypic and Genotypic Spectrum of Early-Onset Developmental and Epileptic Encephalopathies-Data from a Romanian Cohort

Early-onset developmental epileptic encephalopathy (DEE) refers to an age-specific, diverse group of epilepsy syndromes with electroclinical anomalies that are associated with severe cognitive, behavioral, and developmental impairments. Genetic DEEs have heterogeneous etiologies. This study includes 36 Romanian patients referred to the Regional Centre for Medical Genetics Dolj for genetic testing between 2017 and 2020. The patients had been admitted to and clinically evaluated at Doctor Victor Gomoiu Children’s Hospital and Prof. Dr. Alexandru Obregia Psychiatry Hospital in Bucharest. Panel testing was performed using the Illumina® TruSight™ One “clinical exome” (4811 genes), and the analysis focused on the known genes reported in DEEs and clinical concordance. The overall diagnostic rate was 25% (9/36 cases). Seven cases were diagnosed with Dravet syndrome (likely pathogenic/pathogenic variants in SCN1A) and two with Genetic Epilepsy with Febrile Seizures Plus (SCN1B). For the diagnosed patients, seizure onset was <1 year, and the seizure type was generalized tonic-clonic. Four additional plausible variants of unknown significance in SCN2A, SCN9A, and SLC2A1 correlated with the reported phenotype. Overall, we are reporting seven novel variants. Comprehensive clinical phenotyping is crucial for variant interpretation. Genetic assessment of patients with severe early-onset DEE can be a powerful diagnostic tool for clinicians, with implications for the management and counseling of the patients and their families.

ILAE classification and definition of epilepsy syndromes with onset in neonates and infants: Position statement by the ILAE Task Force on Nosology and Definitions

The International League Against Epilepsy (ILAE) Task Force on Nosology and Definitions proposes a classification and definition of epilepsy syndromes in the neonate and infant with seizure onset up to 2 years of age. The incidence of epilepsy is high in this age group and epilepsy is frequently associated with significant comorbidities and mortality. The licensing of syndrome specific antiseizure medications following randomized controlled trials and the development of precision, gene-related therapies are two of the drivers defining the electroclinical phenotypes of syndromes with onset in infancy. The principal aim of this proposal, consistent with the 2017 ILAE Classification of the Epilepsies, is to support epilepsy diagnosis and emphasize the importance of classifying epilepsy in an individual both by syndrome and etiology. For each syndrome, we report epidemiology, clinical course, seizure types, electroencephalography (EEG), neuroimaging, genetics, and differential diagnosis. Syndromes are separated into self-limited syndromes, where there is likely to be spontaneous remission and developmental and epileptic encephalopathies, diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. The emerging class of etiology-specific epilepsy syndromes, where there is a specific etiology for the epilepsy that is associated with a clearly defined, relatively uniform, and distinct clinical phenotype in most affected individuals as well as consistent EEG, neuroimaging, and/or genetic correlates, is presented. The number of etiology-defined syndromes will continue to increase, and these newly described syndromes will in time be incorporated into this classification. The tables summarize mandatory features, cautionary alerts, and exclusionary features for the common syndromes. Guidance is given on the criteria for syndrome diagnosis in resource-limited regions where laboratory confirmation, including EEG, MRI, and genetic testing, might not be available.

Patient with Dravet syndrome: A case report

Dravet syndrome is rare genetic epilepsy syndrome and epileptic encephalopathy. The patient initially has normal developmental profile with plateau or regression that begins after seizure onset. We report a case of two-year-old child diagnosed as dravet syndrome with moderate cerebral atrophy and ventricular dilatation as rare MRI finding.

Modeling PCDH19-CE: From 2D Stem Cell Model to 3D Brain Organoids

PCDH19 clustering epilepsy (PCDH19-CE) is a genetic disease characterized by a heterogeneous phenotypic spectrum ranging from focal epilepsy with rare seizures and normal cognitive development to severe drug-resistant epilepsy associated with intellectual disability and autism. Unfortunately, little is known about the pathogenic mechanism underlying this disease and an effective treatment is lacking. Studies with zebrafish and murine models have provided insights on the function of PCDH19 during brain development and how its altered function causes the disease, but these models fail to reproduce the human phenotype. Induced pluripotent stem cell (iPSC) technology has provided a complementary experimental approach for investigating the pathogenic mechanisms implicated in PCDH19-CE during neurogenesis and studying the pathology in a more physiological three-dimensional (3D) environment through the development of brain organoids. We report on recent progress in the development of human brain organoids with a particular focus on how this 3D model may shed light on the pathomechanisms implicated in PCDH19-CE.

Do All Roads Lead to Rome? Genes Causing Dravet Syndrome and Dravet Syndrome-Like Phenotypes

Background

Dravet syndrome (DS) is a severe epileptic encephalopathy mainly caused by haploinsufficiency of the gene SCN1A, which encodes the voltage-gated sodium channel Na_V1. 1 in the brain. While SCN1A mutations are known to be the primary cause of DS, other genes that may cause DS are poorly understood. Several genes with pathogenic mutations result in DS or DS-like phenotypes, which may require different drug treatment approaches. Therefore, it is urgent for clinicians, especially epilepsy specialists to fully understand these genes involved in DS in addition to SCN1A. Particularly for healthcare providers, a deep understanding of these pathogenic genes is useful in properly selecting and adjusting drugs in a more effective and timely manner.

Objective

The purpose of this study was to identify genes other than SCN1A that may also cause DS or DS-like phenotypes.

Methods

A comprehensive search of relevant Dravet syndrome and severe myoclonic epilepsy in infancy was performed in PubMed, until December 1, 2021. Two independent authors performed the screening for potentially eligible studies. Disagreements were decided by a third, more professional researcher or by all three. The results reported by each study were narratively summarized.

Results

A PubMed search yielded 5,064 items, and other sources search 12 records. A total of 29 studies published between 2009 and 2021 met the inclusion criteria. Regarding the included articles, seven studies on PCDH19, three on SCN2A, two on SCN8A, five on SCN1B, two on GABRA1, three on GABRB3, three on GABRG2, and three on STXBP1 were included. Only one study was recorded for CHD2, CPLX1, HCN1 and KCNA2, respectively. It is worth noting that a few articles reported on more than one epilepsy gene.

Conclusion

DS is not only identified in variants of SCN1A, but other genes such as PCDH19, SCN2A, SCN8A, SCN1B, GABRA1, GABRB3, GABRG2, KCNA2, CHD2, CPLX1, HCN1A, STXBP1 can also be involved in DS or DS-like phenotypes. As genetic testing becomes more widely available, more genes associated with DS and DS-like phenotypes may be identified and gene-based diagnosis of subtypes of phenotypes in this spectrum may improve the management of these diseases in the future.

The Broad Clinical Spectrum of Epilepsies Associated With Protocadherin 19 Gene Mutation

Protocadherin 19 (PCDH19) gene is one of the most common genes involved in epilepsy syndromes. According to literature data PCDH19 is among the 6 genes most involved in genetic epilepsies. PCDH19 is located on chromosome Xq22.1 and is involved in neuronal connections and signal transduction. The most frequent clinical expression of PCDH19 mutation is epilepsy and mental retardation limited to female (EFMR) characterized by epileptic and non-epileptic symptoms affecting mainly females. However, the phenotypic spectrum of these mutations is considerably variable from genetic epilepsy with febrile seizure plus to epileptic encephalopathies. The peculiar exclusive involvement of females seems to be caused by a cellular interference in heterozygosity, however, affected mosaic-males have been reported. Seizure types range from focal seizure to generalized tonic-clonic, tonic, atonic, absences, and myoclonic jerks. Treatment of PCDH19-related epilepsy is limited by drug resistance and by the absence of specific treatment indications. However, seizures become less severe with adolescence and some patients may even become seizure-free. Non-epileptic symptoms represent the main disabilities of adult patients with PCDH19 mutation. This review aims to analyze the highly variable phenotypic expression of PCDH19 gene mutation associated with epilepsy.

Identification and Functional Characterization of a Novel Nonsense Variant in ARR3 in a Southern Chinese Family With High Myopia

ARR3 has been associated with X-linked, female-limited, high myopia. However, using exome sequencing (ES), we identified the first high myopia case with hemizygous ARR3-related mutation in a male patient in a Southern Chinese family. This novel truncated mutation (ARR3: c.569C>G, p.S190*) co-segregated with the disease phenotype in affected family members and demonstrated that high myopia caused by ARR3 is not X-linked, female-limited, where a complicated X-linked inheritance pattern may exist. Thus, our case expanded the variant spectrum in ARR3 and provided additional information for genetic counseling, prenatal testing, and diagnosis. Moreover, we characterized the nonsense-mediated decay of the ARR3 mutant mRNA and discussed the possible underlying pathogenic mechanisms.

Novel treatments in epilepsy guided by genetic diagnosis

In recent years, precision medicine has emerged as a new paradigm for improved and more individualized patient care. Its key objective is to provide the right treatment, to the right patient at the right time, by basing medical decisions on individual characteristics, including specific genetic biomarkers. In order to realize this objective researchers and physicians must first identify the underlying genetic cause; over the last 10 years, advances in genetics have made this possible for several monogenic epilepsies. Through next generation techniques, a precise genetic aetiology is attainable in 30-50% of genetic epilepsies beginning in the paediatric age. While committed in such search for novel genes carrying disease-causing variants, progress in the study of experimental models of epilepsy has also provided a better understanding of the mechanisms underlying the condition. Such advances are already being translated into improving care, management and treatment of some patients. Identification of a precise genetic aetiology can already direct physicians to prescribe treatments correcting specific metabolic defects, avoid antiseizure medicines that might aggravate functional consequences of the disease-causing variant or select the drugs that counteract the underlying, genetically determined, functional disturbance. Personalized, tailored treatments should not just focus on how to stop seizures but possibly prevent their onset and cure the disorder, often consisting of seizures and its comorbidities including cognitive, motor and behaviour deficiencies. This review discusses the therapeutic implications following a specific genetic diagnosis and the correlation between genetic findings, pathophysiological mechanisms and tailored seizure treatment, emphasizing the impact on current clinical practice.

Inherited Developmental and Epileptic Encephalopathies

Epileptic encephalopathies often have a genetic etiology. The epileptic activity itself exerts a direct detrimental effect on neurodevelopment, which may add to the cognitive impairment induced by the underlying mutation (“developmental and epileptic encephalopathy”). The focus of this review is on inherited syndromes. The phenotypes of genetic disorders affecting ion channels, metabolic signalling, membrane trafficking and exocytosis, cell adhesion, cell growth and proliferation are discussed. Red flags suggesting family of genes or even specific genes are highlighted. The knowledge of the phenotypical spectrum can indeed prompt the clinician to suspect specific etiologies, expediting the diagnosis.

Clinical next generation sequencing in developmental and epileptic encephalopathies: Diagnostic relevance of data re-analysis and variants re-interpretation

Developmental and epileptic encephalopathies (DEE) are complex pediatric epilepsies, in which heterogeneous pathogenic factors play an important role. Next-generation-sequencing based tools have shown excellent effectiveness. The constant increase in the number of new genotype-phenotype associations suggests the periodic need for re-interpretation and re-analysis of genetic studies without positive results. In this study, we report the diagnostic utility of targeted gene panel sequencing and whole exome sequencing in 55 Argentine subjects with DEE, focusing on the utility of re-interpretation and re-analysis of undetermined and negative genetic diagnoses. The new information in biomedical literature and databases was used for the re-interpretation. For re-analysis, sequencing data processing was repeated using updated bioinformatics tools. Initially, pathogenic variants were detected in 21 subjects (38%). After an average time of 29 months, 25% of the subjects without a genetic diagnosis were re-categorized as diagnosed. Finally, the overall diagnostic yield increased to 53% (29 subjects). In consequence of the re-interpretation and re-analysis, we identified novel variants in the genes: CHD2, COL4A1, FOXG1, GABRA1, GRIN2B, HNRNPU, KCNQ2, MECP2, PCDH19, SCN1A, SCN2A, SCN8A, SLC6A1, STXBP1 and WWOX. Our results expand the diagnostic yield of this subgroup of infantile and childhood seizures and demonstrate the importance of re-evaluation of genetic tests in subjects without an identified causative etiology.

A complete Protocadherin-19 ectodomain model for evaluating epilepsy-causing mutations and potential protein interaction sites

Cadherin superfamily members play a critical role in differential adhesion during neurodevelopment, and their disruption has been linked to several neurodevelopmental disorders. Mutations in protocadherin-19 (PCDH19), a member of the δ-protocadherin subfamily of cadherins, cause a unique form of epilepsy called PCDH19 clustering epilepsy. While PCDH19 and other non-clustered δ-protocadherins form multimers with other members of the cadherin superfamily to alter adhesiveness, the specific protein surfaces responsible for these interactions are unknown. Only portions of the PCDH19 extracellular domain structure had been solved previously. Here, we present a structure of the missing segment from zebrafish Protocadherin-19 (Pcdh19) and create a complete ectodomain model. This model shows the structural environment for 97% of disease-causing missense mutations and reveals two potential surfaces for intermolecular interactions that could modify Pcdh19's adhesive strength and specificity.

The Hidden Side of NCAM Family: NCAM2, a Key Cytoskeleton Organization Molecule Regulating Multiple Neural Functions

Although it has been over 20 years since Neural Cell Adhesion Molecule 2 (NCAM2) was identified as the second member of the NCAM family with a high expression in the nervous system, the knowledge of NCAM2 is still eclipsed by NCAM1. The first studies with NCAM2 focused on the olfactory bulb, where this protein has a key role in axonal projection and axonal/dendritic compartmentalization. In contrast to NCAM1, NCAM2's functions and partners in the brain during development and adulthood have remained largely unknown until not long ago. Recent studies have revealed the importance of NCAM2 in nervous system development. NCAM2 governs neuronal morphogenesis and axodendritic architecture, and controls important neuron-specific processes such as neuronal differentiation, synaptogenesis and memory formation. In the adult brain, NCAM2 is highly expressed in dendritic spines, and it regulates synaptic plasticity and learning processes. NCAM2's functions are related to its ability to adapt to the external inputs of the cell and to modify the cytoskeleton accordingly. Different studies show that NCAM2 interacts with proteins involved in cytoskeleton stability and proteins that regulate calcium influx, which could also modify the cytoskeleton. In this review, we examine the evidence that points to NCAM2 as a crucial cytoskeleton regulation protein during brain development and adulthood. This key function of NCAM2 may offer promising new therapeutic approaches for the treatment of neurodevelopmental diseases and neurodegenerative disorders.

Protocadherin 19 Clustering Epilepsy and Neurosteroids: Opportunities for Intervention

Steroids yield great influence on neurological development through nuclear hormone receptor (NHR)-mediated gene regulation. We recently reported that cell adhesion molecule protocadherin 19 (encoded by the PCDH19 gene) is involved in the coregulation of steroid receptor activity on gene expression. PCDH19 variants cause early-onset developmental epileptic encephalopathy clustering epilepsy (CE), with altered steroidogenesis and NHR-related gene expression being identified in these individuals. The implication of hormonal pathways in CE pathogenesis has led to the investigation of various steroid-based antiepileptic drugs in the treatment of this disorder, with mixed results so far. Therefore, there are many unmet challenges in assessing the antiseizure targets and efficiency of steroid-based therapeutics for CE. We review and assess the evidence for and against the implication of neurosteroids in the pathogenesis of CE and in view of their possible clinical benefit.

Cellular and Behavioral Characterization of Pcdh19 Mutant Mice: subtle Molecular Changes, Increased Exploratory Behavior and an Impact of Social Environment

Mutations in the X-linked cell adhesion protein PCDH19 lead to seizures, cognitive impairment, and other behavioral comorbidities when present in a mosaic pattern. Neither the molecular mechanisms underpinning this disorder nor the function of PCDH19 itself are well understood. By combining RNA in situ hybridization with immunohistochemistry and analyzing single-cell RNA sequencing datasets, we reveal Pcdh19 expression in cortical interneurons and provide a first account of the subtypes of neurons expressing Pcdh19/PCDH19, both in the mouse and the human cortex. Our quantitative analysis of the Pcdh19 mutant mouse exposes subtle changes in cortical layer composition, with no major alterations of the main axonal tracts. In addition, Pcdh19 mutant animals, particularly females, display preweaning behavioral changes, including reduced anxiety and increased exploratory behavior. Importantly, our experiments also reveal an effect of the social environment on the behavior of wild-type littermates of Pcdh19 mutant mice, which show alterations when compared with wild-type animals not housed with mutants.

δ-Protocadherins regulate neural progenitor cell division by antagonizing Ryk and Wnt/β-catenin signaling

The division of neural progenitor cells provides the cellular substrate from which the nervous system is sculpted during development. The δ-protocadherin family of homophilic cell adhesion molecules is essential for the development of the vertebrate nervous system and is implicated in an array of neurodevelopmental disorders. We show that lesions in any of six, individual δ-protocadherins increases cell divisions of neural progenitors in the hindbrain. This increase is due to mis-regulation of Wnt/β-catenin signaling, as this pathway is upregulated in δ-protocadherin mutants and inhibition of this pathway blocks the increase in cell division. Furthermore, the δ-protocadherins can be present in complex with the Wnt receptor Ryk, and Ryk is required for the increased proliferation in protocadherin mutants. Thus, δ-protocadherins are novel regulators of Wnt/β-catenin signaling that may control the development of neural circuits by defining a molecular code for the identity of neural progenitor cells and differentially regulating their proliferation.

X-chromosome inactivation and PCDH19-associated epileptic encephalopathy: A novel PCDH19 variant in a Chinese family

BACKGROUND

Developmental and epileptic encephalopathy 9 (DEE9, MIM #300088) is an early onset seizure disorder associated with cognitive impairment and behavioral disturbances. It is caused by mutation in protocadherin 19 with an unusual X-linked inheritance selectively involving heterozygous females or mosaic hemizygous males, while hemizygous males are unaffected. Cellular interference was the postulated mechanism underlying the unusual inheritance pattern.

CASE REPORT

We report a Chinese girl who presented with severe treatment refractory seizures at 26 months of age and was found heterozygous for a novel likely pathogenic missense variant NM_001184880.2:c.488T>A p.(Val163Glu) in PCDH19. Her younger sister, who was also heterozygous for the variant, was asymptomatic with normal development at the time of reporting at 37 months of age. X-chromosome inactivation study by androgen receptor gene methylation assay in DNA from peripheral leukocytes was performed which demonstrated somewhat skewed X-chromosome inactivation in the proband and extremely skewed X-chromosome inactivation in the asymptomatic younger sibling.

CONCLUSION

PCDH19-related seizure disorder has incomplete penetrance and variable expressivity. Further studies are required to determine the potential role of X-chromosome inactivation on the phenotypic variability and patient outcomes. Liberal referral for PCDH19 testing among female patients with early-onset seizures should be considered to enhance case detection.

Regulation of Neural Circuit Development by Cadherin-11 Provides Implications for Autism

Autism spectrum disorder (ASD) is a neurologic condition characterized by alterations in social interaction and communication, and restricted and/or repetitive behaviors. The classical Type II cadherins cadherin-8 (Cdh8, CDH8) and cadherin-11 (Cdh11, CDH11) have been implicated as autism risk gene candidates. To explore the role of cadherins in the etiology of autism, we investigated their expression patterns during mouse brain development and in autism-specific human tissue. In mice, expression of cadherin-8 and cadherin-11 was developmentally regulated and enriched in the cortex, hippocampus, and thalamus/striatum during the peak of dendrite formation and synaptogenesis. Both cadherins were expressed in synaptic compartments but only cadherin-8 associated with the excitatory synaptic marker neuroligin-1. Induced pluripotent stem cell (iPSC)-derived cortical neural precursor cells (NPCs) and cortical organoids generated from individuals with autism showed upregulated CDH8 expression levels, but downregulated CDH11. We used Cdh11 knock-out (KO) mice of both sexes to analyze the function of cadherin-11, which could help explain phenotypes observed in autism. Cdh11-/- hippocampal neurons exhibited increased dendritic complexity along with altered neuronal and synaptic activity. Similar to the expression profiles in human tissue, levels of cadherin-8 were significantly elevated in Cdh11 KO brains. Additionally, excitatory synaptic markers neuroligin-1 and postsynaptic density (PSD)-95 were both increased. Together, these results strongly suggest that cadherin-11 is involved in regulating the development of neuronal circuitry and that alterations in the expression levels of cadherin-11 may contribute to the etiology of autism.

Neuroinflammation: A Signature or a Cause of Epilepsy?

Epilepsy can be both a primary pathology and a secondary effect of many neurological conditions. Many papers show that neuroinflammation is a product of epilepsy, and that in pathological conditions characterized by neuroinflammation, there is a higher probability to develop epilepsy. However, the bidirectional mechanism of the reciprocal interaction between epilepsy and neuroinflammation remains to be fully understood. Here, we attempt to explore and discuss the relationship between epilepsy and inflammation in some paradigmatic neurological and systemic disorders associated with epilepsy. In particular, we have chosen one representative form of epilepsy for each one of its actual known etiologies. A better understanding of the mechanistic link between neuroinflammation and epilepsy would be important to improve subject-based therapies, both for prophylaxis and for the treatment of epilepsy.

Dissecting the Role of PCDH19 in Clustering Epilepsy by Exploiting Patient-Specific Models of Neurogenesis

PCDH19-related epilepsy is a rare genetic disease caused by defective function of PCDH19, a calcium-dependent cell–cell adhesion protein of the cadherin superfamily. This disorder is characterized by a heterogeneous phenotypic spectrum, with partial and generalized febrile convulsions that are gradually increasing in frequency. Developmental regression may occur during disease progression. Patients may present with intellectual disability (ID), behavioral problems, motor and language delay, and a low motor tone. In most cases, seizures are resistant to treatment, but their frequency decreases with age, and some patients may even become seizure-free. ID generally persists after seizure remission, making neurological abnormalities the main clinical issue in affected individuals. An effective treatment is lacking. In vitro studies using patient-derived induced pluripotent stem cells (iPSCs) reported accelerated neural differentiation as a major endophenotype associated with PCDH19 mutations. By using this in vitro model system, we show that accelerated in vitro neurogenesis is associated with a defect in the cell division plane at the neural progenitors stage. We also provide evidence that altered PCDH19 function affects proper mitotic spindle orientation. Our findings identify an altered equilibrium between symmetric versus asymmetric cell division as a previously unrecognized mechanism contributing to the pathogenesis of this rare epileptic encephalopathy.

Integrated in silico and experimental assessment of disease relevance of PCDH19 missense variants

PCDH19 is a nonclustered protocadherin molecule involved in axon bundling, synapse function, and transcriptional coregulation. Pathogenic variants in PCDH19 cause infantile-onset epilepsy known as PCDH19-clustering epilepsy or PCDH19-CE. Recent advances in DNA-sequencing technologies have led to a significant increase in the number of reported PCDH19-CE variants, many of uncertain significance. We aimed to determine the best approaches for assessing the disease relevance of missense variants in PCDH19. The application of the American College of Medical Genetics and Association for Molecular Pathology (ACMG-AMP) guidelines was only 50% accurate. Using a training set of 322 known benign or pathogenic missense variants, we identified MutPred2, MutationAssessor, and GPP as the best performing in silico tools. We generated a protein structural model of the extracellular domain and assessed 24 missense variants. We also assessed 24 variants using an in vitro reporter assay. A combination of these tools was 93% accurate in assessing known pathogenic and benign PCDH19 variants. We increased the accuracy of the ACMG-AMP classification of 45 PCDH19 variants from 50% to 94%, using these tools. In summary, we have developed a robust toolbox for the assessment of PCDH19 variant pathogenicity to improve the accuracy of PCDH19-CE variant classification.