PCDH19-related epilepsy is associated with a broad neurodevelopmental spectrum

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.

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.

NGS-Based Identification of Two Novel PCDH19 Mutations in Female Patients with Early-Onset Epilepsy

Developmental and epileptic encephalopathy-9 (DEE9) is characterized by seizure onset in infancy, mild to severe intellectual impairment, and psychiatric features and is caused by a mutation in the PCDH19 gene on chromosome Xq22. The rare, unusual X-linked type of disorder affects heterozygous females and mosaic males; transmitting males are unaffected. In our study, 165 patients with epilepsy were tested by Next Generation Sequencing (NGS)-based panel and exome sequencing using Illumina technology. PCDH19 screening identified three point mutations, one indel, and one 29 bp-long deletion in five unrelated female probands. Two novel mutations, c.1152_1180del (p.Gln385Serfs*6) and c.830_831delinsAA (p.Phe277*), were identified and found to be de novo pathogenic. Moreover, among the three inherited mutations, two originated from asymptomatic mothers and one from an affected father. The PCDH19 c.1682C>T and c.1711G>T mutations were present in the DNA samples of asymptomatic mothers. After targeted parental testing, X chromosome inactivation tests and Sanger sequencing were carried out for mosaicism examination on maternal saliva samples in the two asymptomatic PCDH19 mutation carrier subjects. Tissue mosaicism and X-inactivation tests were negative. Our results support the opportunity for reduced penetrance in DEE9 and contribute to expanding the genotype-phenotype spectrum of PCDH19-related epilepsy.

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.

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.

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.

Peri-ictal EEG in infants with PRRT2-related self-limited infantile epilepsy

OBJECTIVE

Pathogenic PRRT2 variants cause self-limited (familial) infantile epilepsy (SeLIE), which is responsive to sodium channel blocking antiseizure medications. The interictal EEG is typically normal. We describe a cohort of infants with PRRT2-related SeLIE with striking peri-ictal EEG abnormalities.

METHODS

We included all infants diagnosed with PRRT2-related SeLIE during July 2020 to November 2021 at the Royal Children's Hospital, Melbourne. Clinical features and results of aetiologic investigations were collected from electronic medical records. All EEGs were reviewed independently by two epileptologists.

RESULTS

Ten infants presented with focal seizures at a median age of 5 months (range: 3-6 months). Eight had a family history of epilepsy, paroxysmal kinesigenic dyskinesia (PKD) or hemiplegic migraine. Seven of the eight infants with an EEG performed within 24 h of the most recent seizure had epileptiform discharges. Their EEGs showed focal sharp waves, spikes, polyspikes or fast activity independently over the left and right temporo-occipital regions. Conversely, the two infants with last known seizure greater than 24 h prior to their EEG had no epileptiform discharges. Oxcarbazepine was commenced in two infants and was effective. Eight infants were initially treated with levetiracetam, and all were subsequently switched to oxcarbazepine due to ongoing seizures or side effects.

SIGNIFICANCE

Posterior polymorphic focal epileptiform discharges on a peri-ictal EEG recording are a feature of PRRT2-related SeLIE. This finding, particularly in the presence of a family history of infantile epilepsy, PKD or hemiplegic migraine, suggests a diagnosis of PRRT2-related SeLIE and has important treatment implications.

Novel variants in established epilepsy genes in focal epilepsy

INTRODUCTION

Next generation sequencing (NGS) has greatly expanded our understanding of genetic contributors in multiple epilepsy syndromes, including focal epilepsy. Describing the genetic architecture of common syndromes promises to facilitate the diagnostic process as well as aid in the identification of patients who stand to benefit from genetic testing, but most studies to date have been limited to examining children or adults with intellectual disability. Our aim was to determine the yield of targeted sequencing of 5 established epilepsy genes (DEPDC5, LGI1, SCN1A, GRIN2A, and PCHD19) in an extensively phenotyped cohort of focal epilepsy patients with normal intellectual function or mild intellectual disability, as well as describe novel variants and determine the characteristics of variant carriers.

PATIENTS AND METHODS

Targeted panel sequencing was performed on 96 patients with a strong clinical suspicion of genetic focal epilepsy. Patients had previously gone through a comprehensive diagnostic epilepsy evaluation in The Neurology Clinic, University Clinical Center of Serbia. Variants of interest (VOI) were classified using the American College of Medical Genetics and the Association for Molecular Pathology criteria.

RESULTS

Six VOI in eight (8/96, 8.3%) patients were found in our cohort. Four likely pathogenic VOI were determined in six (6/96, 6.2%) patients, two DEPDC5 variants in two patients, one SCN1A variant in two patients and one PCDH19 variant in two patients. One variant of unknown significance (VUS) was found in GRIN2A in one (1/96, 1.0%) patient. Only one VOI in GRIN2A was classified as likely benign. No VOI were detected in LGI1.

CONCLUSION

Sequencing of only five known epilepsy genes yielded a diagnostic result in 6.2% of our cohort and revealed multiple novel variants. Further research is necessary for a better understanding of the genetic basis in common epilepsy syndromes in patients with normal intellectual function or mild intellectual disability.

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.

PCDH19 in Males: Are Hemizygous Variants Linked to Autism?

Background: Autism spectrum disorder (ASD) is a complex developmental disability that impairs the social communication and interaction of affected individuals and leads to restricted or repetitive behaviors or interests. ASD is genetically heterogeneous, with inheritable and de novo genetic variants in more than hundreds of genes contributing to the disease. However, these account for only around 20% of cases, while the molecular basis of the majority of cases remains unelucidated as of yet. Material and methods: Two unrelated Lebanese patients, a 7-year-old boy (patient A) and a 4-year-old boy (patient B), presenting with ASD were included in this study. Whole-exome sequencing (WES) was carried out for these patients to identify the molecular cause of their diseases. Results: WES analysis revealed hemizygous variants in PCDH19 (NM_001184880.1) as being the candidate causative variants: p.Arg787Leu was detected in patient A and p.Asp1024Asn in patient B. PCDH19, located on chromosome X, encodes a membrane glycoprotein belonging to the protocadherin family. Heterozygous PCDH19 variants have been linked to epilepsy in females with mental retardation (EFMR), while mosaic PCDH19 mutations in males are responsible for treatment-resistant epilepsy presenting similarly to EFMR, with some reported cases of comorbid intellectual disability and autism. Interestingly, a hemizygous PCDH19 variant affecting the same amino acid that is altered in patient A was previously reported in a male patient with ASD. Conclusion: Here, we report hemizygous PCDH19 variants in two males with autism without epilepsy. Reporting further PCDH19 variants in male patients with ASD is important to assess the possible involvement of this gene in autism.

FOXG1 drives transcriptomic networks to specify principal neuron subtypes during the development of the medial pallium

The medial pallium (MP) is the major forebrain region underlying learning and memory, spatial navigation, and emotion; however, the mechanisms underlying the specification of its principal neuron subtypes remain largely unexplored. Here, by postmitotic deletion of FOXG1 (a transcription factor linked to autism spectrum disorders and FOXG1 syndrome) and single-cell RNA sequencing of E17.5 MP in mice, we found that FOXG1 controls the specification of upper-layer retrosplenial cortical pyramidal neurons [RSC-PyNs (UL)], subiculum PyNs (SubC-PyNs), CA1-PyNs, CA3-PyNs, and dentate gyrus granule cells (DG-GCs) in the MP. We uncovered subtype-specific and subtype-shared FOXG1-regulated transcriptomic networks orchestrating MP neuron specification. We further demonstrated that FOXG1 transcriptionally represses Zbtb20, Prox1, and Epha4 to prevent CA3-PyN and DG-GC identities during the specification of RSC-PyNs (UL) and SubC-PyNs; FOXG1 directly activates Nr4a2 to promote SubC-PyN identity. We showed that TBR1, controlled by FOXG1 during CA1-PyN specification, was down-regulated. Thus, our study illuminates MP principal neuron subtype specification and related neuropathogenesis.

Learnings in developmental and epileptic encephalopathies: what do we know?

INTRODUCTION

Developmental and Epileptic Encephalopathies (DEEs) encompass a group of neurological disorders caused by either abnormal neuronal development and white matter maturation or even by weak synaptic plasticity. Hitherto, patients commonly have epileptic seizures featuring cognitive dysfunction, such as neurosensory disorders, difficulties in learning, behavioral disturbances, or speech delay.

AREAS COVERED

This paper provides a comprehensive review of the current knowledge of DEEs and cognition. Medline/Pubmed database was screened for in-English articles published between 1967-2022 dealing with the topic of DEEs and cognitive development. Two authors independently screened the title and abstract of each record and reviewed the selected articles. Reviews, randomized clinical trials, and case reports were selected.

EXPERT OPINION

Scientific literature has never explicitly dealt with the early neuro-psychomotor rehabilitation and neuropsychological assessment of patients with DEEs. Targeted intervention and environmental stimuli can influence the maturation of neuronal circuits and shape changes in physical and mental development based on neuronal plasticity, particularly if applied in 'critical periods' liable to heightened sensitivity. Thus, 'early neurorehabilitation interventions' are worthy of being more and more applied to clinical practice to improve the quality of life and reduce the psychosocial burden on families and caregivers.

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.

Somatic variants in diverse genes leads to a spectrum of focal cortical malformations

Post-zygotically acquired genetic variants, or somatic variants, that arise during cortical development have emerged as important causes of focal epilepsies, particularly those due to malformations of cortical development. Pathogenic somatic variants have been identified in many genes within the PI3K-AKT-mTOR-signalling pathway in individuals with hemimegalencephaly and focal cortical dysplasia (type II), and more recently in SLC35A2 in individuals with focal cortical dysplasia (type I) or non-dysplastic epileptic cortex. Given the expanding role of somatic variants across different brain malformations, we sought to delineate the landscape of somatic variants in a large cohort of patients who underwent epilepsy surgery with hemimegalencephaly or focal cortical dysplasia. We evaluated samples from 123 children with hemimegalencephaly (n = 16), focal cortical dysplasia type I and related phenotypes (n = 48), focal cortical dysplasia type II (n = 44), or focal cortical dysplasia type III (n = 15). We performed high-depth exome sequencing in brain tissue-derived DNA from each case and identified somatic single nucleotide, indel and large copy number variants. In 75% of individuals with hemimegalencephaly and 29% with focal cortical dysplasia type II, we identified pathogenic variants in PI3K-AKT-mTOR pathway genes. Four of 48 cases with focal cortical dysplasia type I (8%) had a likely pathogenic variant in SLC35A2. While no other gene had multiple disease-causing somatic variants across the focal cortical dysplasia type I cohort, four individuals in this group had a single pathogenic or likely pathogenic somatic variant in CASK, KRAS, NF1 and NIPBL, genes previously associated with neurodevelopmental disorders. No rare pathogenic or likely pathogenic somatic variants in any neurological disease genes like those identified in the focal cortical dysplasia type I cohort were found in 63 neurologically normal controls (P = 0.017), suggesting a role for these novel variants. We also identified a somatic loss-of-function variant in the known epilepsy gene, PCDH19, present in a small number of alleles in the dysplastic tissue from a female patient with focal cortical dysplasia IIIa with hippocampal sclerosis. In contrast to focal cortical dysplasia type II, neither focal cortical dysplasia type I nor III had somatic variants in genes that converge on a unifying biological pathway, suggesting greater genetic heterogeneity compared to type II. Importantly, we demonstrate that focal cortical dysplasia types I, II and III are associated with somatic gene variants across a broad range of genes, many associated with epilepsy in clinical syndromes caused by germline variants, as well as including some not previously associated with radiographically evident cortical brain malformations.

Variable Expression of GABAA Receptor Subunit Gamma 2 Mutation in a Nuclear Family Displaying Developmental and Encephalopathic Phenotype

Mutations in GABA_A receptor subunit genes (GABRs) are a major etiology for developmental and epileptic encephalopathies (DEEs). This article reports a case of a genetic abnormality in GABRG2 and updates the pathophysiology and treatment development for mutations in DEEs based on recent advances. Mutations in GABRs, especially in GABRA1, GABRB2, GABRB3, and GABRG2, impair GABAergic signaling and are frequently associated with DEEs such as Dravet syndrome and Lennox-Gastaut syndrome, as GABAergic signaling is critical for early brain development. We here present a novel association of a microdeletion of GABRG2 with a diagnosed DEE phenotype. We characterized the clinical phenotype and underlying mechanisms, including molecular genetics, EEGs, and MRI. We then compiled an update of molecular mechanisms of GABR mutations, especially the mutations in GABRB3 and GABRG2 attributed to DEEs. Genetic therapy is also discussed as a new avenue for treatment of DEEs through employing antisense oligonucleotide techniques. There is an urgent need to define treatment targets and explore new treatment paradigms for the DEEs, as early deployment could alleviate long-term disabilities and improve quality of life for patients. This study highlights biomolecular targets for future therapeutic interventions, including via both pharmacological and genetic approaches.

Mosaic and non-mosaic protocadherin 19 mutation leads to neuronal hyperexcitability in zebrafish

Epilepsy is one of the most common neurological disorders. The X-linked gene PCDH19 is associated with sporadic and familial epilepsy in humans, typically with early-onset clustering seizures and intellectual disability in females but not in so-called 'carrier' males, suggesting that mosaic PCDH19 expression is required to produce epilepsy. To characterize the role of loss of PCDH19 function in epilepsy, we generated zebrafish with truncating pcdh19 variants. Evaluating zebrafish larvae for electrophysiological abnormalities, we observed hyperexcitability phenotypes in both mosaic and non-mosaic pcdh19^+/- and pcdh19^-/- mutant larvae. Thus, we demonstrate that the key feature of epilepsy-network hyperexcitability-can be modeled effectively in zebrafish, even though overt spontaneous seizure-like swim patterns were not observed. Further, zebrafish with non-mosaic pcdh19 mutation displayed reduced numbers of inhibitory interneurons suggesting a potential cellular basis for the observed hyperexcitability. Our findings in both mosaic and non-mosaic pcdh19 mutant zebrafish challenge the prevailing theory that mosaicism governs all PCDH19-related phenotypes and point to interneuron-mediated mechanisms underlying these phenotypes.

Perturbation of Cortical Excitability in a Conditional Model of PCDH19 Disorder

PCDH19 epilepsy (DEE9) is an X-linked syndrome associated with cognitive and behavioral disturbances. Since heterozygous females are affected, while mutant males are spared, it is likely that DEE9 pathogenesis is related to disturbed cell-to-cell communication associated with mosaicism. However, the effects of mosaic PCDH19 expression on cortical networks are unknown. We mimicked the pathology of DEE9 by introducing a patch of mosaic protein expression in one hemisphere of the cortex of conditional PCDH19 knockout mice one day after birth. In the contralateral area, PCDH19 expression was unaffected, thus providing an internal control. In this model, we characterized the physiology of the disrupted network using local field recordings and two photon Ca²⁺ imaging in urethane anesthetized mice. We found transient episodes of hyperexcitability in the form of brief hypersynchronous spikes or bursts of field potential oscillations in the 9–25 Hz range. Furthermore, we observed a strong disruption of slow wave activity, a crucial component of NREM sleep. This phenotype was present also when PCDH19 loss occurred in adult mice, demonstrating that PCDH19 exerts a function on cortical circuitry outside of early development. Our results indicate that a focal mosaic mutation of PCDH19 disrupts cortical networks and broaden our understanding of DEE9.

Regulation of Inhibitory Signaling at the Receptor and Cellular Level; Advances in Our Understanding of GABAergic Neurotransmission and the Mechanisms by Which It Is Disrupted in Epilepsy

Inhibitory signaling in the brain organizes the neural circuits that orchestrate how living creatures interact with the world around them and how they build representations of objects and ideas. Without tight control at multiple points of cellular engagement, the brain’s inhibitory systems would run down and the ability to extract meaningful information from excitatory events would be lost leaving behind a system vulnerable to seizures and to cognitive decline. In this review, we will cover many of the salient features that have emerged regarding the dynamic regulation of inhibitory signaling seen through the lens of cell biology with an emphasis on the major building blocks, the ligand-gated ion channel receptors that are the first transduction point when the neurotransmitter GABA is released into the synapse. Epilepsy association will be used to indicate importance of key proteins and their pathways to brain function and to introduce novel areas for therapeutic intervention.

Understanding Protein Protocadherin-19 (PCDH19) Syndrome: A Literature Review of the Pathophysiology

PCDH19 syndrome is a monogenic epilepsy related to the protein protocadherin-19 (PCDH19) gene, which encodes for a protein important for brain development. The protein also seems to regulate gamma-aminobutyric acid type A receptors (GABA(A)(R)). The disease presents with refractory epilepsy that is characterized by seizures occurring in clusters. Till now, the pathophysiology of the disease is mainly unknown, so we conducted a literature review to elucidate the pathophysiology of PCDH19-related epilepsy. We used two databases to investigate this literature review (Google Scholar and PubMed). We selected full-text papers that are published in the English language and published after the year 2000. We selected initially 64 papers and ended up with 29 to conduct this literature review. We found four main theories for the pathophysiology of PCDH19-related epilepsy: GABA(A)(R) dysregulation, blood-brain barrier (BBB) dysfunction, cellular interference, and the AKR1C1-3 gene product deficiency.

GABA(A)(R) dysfunction and expression cause decreased effective inhibitory currents predisposing patients to epilepsy. BBB dysfunction allows the passage of methyl-D-aspartate (NMDA)-type glutamate receptor antibodies (abs-NR) through the BBB susceptible membrane. The cellular interference hypothesis establishes that the mutant and non-mutant cells interfere with each other’s communication within the same tissue. Women are more susceptible to being affected by this hypothesis as men only have one copy of the x gene and interference is mediated by this gene, meaning that it cannot occur in them. Finally, downregulation and deficiency of the AKR1C3/AKR1C2 products lead to decreasing levels of allopregnanolone, which diminish the regulation of GABA(A)(R).

Child Neurology: Initial Presentation of PCDH19-Related Epilepsy with New Onset Refractory Status Epilepticus and Treatment with Anakinra

PCDH19-

related epilepsy is a developmental and epileptic encephalopathy typically presenting with epilepsy and varying degrees of intellectual disability. Seizures typically present in clusters of focal or generalized seizures, sometimes in the setting of fever. We present the case of a 7-month-old girl presenting with new-onset refractory status epilepticus (NORSE) that followed routine vaccine administration and ensuing cytokine storm. She was diagnosed with a pathogenic variant in PCDH19. The patient required five anti-seizure medications and pentobarbital-induced burst suppression for control of seizures. She was noted to have elevated serum cytokine levels (IL-2, IL-4, IL-10, IL-13, IL-17, IL-1 IL-1β, and IL-8) and CSF cytokine levels (IL-6 and IL-13). Anakinra was initiated and titrated based on serial cytokine levels, with doses ranging from 5-20 mg/kg/day resulting in reduction in cytokine levels and seizure reduction. By 14 months of age, she was able to be maintained on three active anti-seizure medications and with ketogenic diet for seizure control.

A rat model of a focal mosaic expression of PCDH19 replicates human brain developmental abnormalities and behaviors

Protocadherin 19 gene-related epilepsy or protocadherin 19 clustering epilepsy is an infantile-onset epilepsy syndrome characterized by psychiatric (including autism-related), sensory, and cognitive impairment of varying degrees. Protocadherin 19 clustering epilepsy is caused by X-linked protocadherin 19 protein loss of function. Due to random X-chromosome inactivation, protocadherin 19 clustering epilepsy-affected females present a mosaic population of healthy and protocadherin 19-mutant cells. Unfortunately, to date, no current mouse model can fully recapitulate both the brain histological and behavioural deficits present in people with protocadherin 19 clustering epilepsy. Thus, the search for a proper understanding of the disease and possible future treatment is hampered. By inducing a focal mosaicism of protocadherin 19 expression using in utero electroporation in rats, we found here that protocadherin 19 signalling in specific brain areas is implicated in neuronal migration, heat-induced epileptic seizures, core/comorbid behaviours related to autism and cognitive function.

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.

Parent-Reported Sleep Profile of Children With Early-Life Epilepsies

BACKGROUND

Sleep comorbidities are common, and sometimes severe, for children with early-life epilepsies (ELEs). Yet, there is a paucity of data regarding the profile of these sleep disturbances and their complications.

METHODS

Participants registered with the Rare Epilepsy Network (REN) were queried about sleep via online questionnaires. Descriptive statistics and logistic regression were performed.

RESULTS

Median age of the 356 children was 56 months (interquartile range 30 to 99), 56% were female, and 53% (188/356) endorsed a sleep concern. Frequent nighttime awakenings (157 of 350; 45%), difficulty falling asleep (133 of 350; 38%), and very restless sleep (118 of 345; 34%) were most endorsed. Nocturnal seizures were associated with sleep concerns and were reported in 75% (268 of 356) of children. Of the children with nocturnal seizures, 56% (118 of 268) had sleep concerns. Of the children without nocturnal seizures, 43% (38 of 88) had sleep concerns. Sleep concerns were most common in dup15q syndrome (16 of 19; 84%). Children aged 4 to ≤10 years (adjusted odds ratio [aOR] 16.1; 95% confidence interval [CI] 2.0, 131.0) and 10 to <13 years (aOR 22.2; 95% CI 2.6, 188.6) had a greater odds of having a sleep concern compared with children aged ≤6 months. Female sex appeared protective for sleep concerns (aOR 0.6; 95% CI 0.4, 0.9). The association between sleep concerns and nocturnal seizures was weaker when adjusted for sex and age category in a logistic regression model.

CONCLUSIONS

Reported sleep concerns are highly prevalent in children with ELEs and persist with age, in contrast to what is expected in healthy children. There may be unmet sleep-related clinical needs in children with ELEs.

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.

Epilepsy surgery in PCDH 19 related developmental and epileptic encephalopathy: A case report

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PCDH19 pathogenic variants may be associated with DEE in females.

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Epilepsy Surgery may be an option for PCDH19 related drug-resistant epilepsy.

We report a female child with PCDH19 related developmental and epileptic encephalopathy with drug-resistant seizures, cognitive and language impairment, autism spectrum disorder and sleep dysfunction. Her seizures, which started at 10 months of age, were resistant to multiple anti-seizure medications. Developmental stagnation followed by regression occurred after the onset of recurrent seizures. Her ictal EEGS suggested left temporal lobe origin for her recorded seizures. MRI upon expert re-review showed a subtle abnormality in the left temporal lobe.

In view of the severe nature and frequency of her seizures, a left temporal lobectomy was undertaken at the age of 2 years and 3 months. Though her seizure outcome was Engel class 3, her seizure frequency and severity were significantly reduced. She has been seizure-free for 10 months at her last outpatient assessment when she was 4 years and 8 months of age (2 years and 5 months after epilepsy surgery). However she recently had an admission for COVID19 infection, with a breakthrough cluster of seizures. Her developmental trajectory changed, though she is making good progress with her cognitive and language skills.

Late-onset cluster seizures and intellectual disability associated with a novel truncation variant in SMC1A

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Epilepsy due to truncating SMC1A variants can present with onset in later childhood.

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People with to truncating SMC1A variants can have normal development prior to presentation.

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Seizures occur periodically in clusters and are poorly responsive to antiseizure medications.

SMC1A variants are known to cause Cornelia de Lange Syndrome (CdLS) which encompasses a clinical spectrum of intellectual disability, dysmorphic features (long or thick eyebrows, a hypomorphic philtrum and small nose) and, in some cases, epilepsy. More recently, SMC1A truncating variants have been described as the cause of a neurodevelopmental disorder with early-childhood onset drug-resistant epilepsy with seizures that occur in clusters, similar to that seen in PCDH19-related epilepsy, but without the classical features of CdLS. Here, we report the case of a 28-year-old woman with a de novo heterozygous truncating variant in SMC1A who unusually presented with seizures at the late age of 12 years and had normal development into adulthood.

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.

Rett Syndrome Spectrum in Monogenic Developmental-Epileptic Encephalopathies and Epilepsies: A Review

INTRODUCTION

Progress in the clinical application of next-generation-sequencing-based techniques has resulted in a dramatic increase in the recognized genetic heterogeneity of the Rett syndrome spectrum (RSS). Our awareness of the considerable overlap with pediatric-onset epilepsies and epileptic/developmental encephalopathies (EE/DE) genes is also growing, and the presence of variable clinical features inside a general frame of commonalities has drawn renewed attention into deep phenotyping.

METHODS

We decided to review the medical literature on atypical Rett syndrome and "Rett-like" phenotypes, with special emphasis on described cases with pediatric-onset epilepsies and/or EE-DE, evaluating Neul's criteria for Rett syndrome and associated movement disorders and notable stereotypies.

RESULTS

"Rett-like" features were described in syndromic and non-syndromic monogenic epilepsy- and DE/EE-related genes, in "intellectual disability plus epilepsy"-related genes and in neurodegenerative disorders. Additionally, prominent stereotypies can be observed in monogenic complex neurodevelopmental disorders featuring epilepsy with or without autistic features outside of the RSS.

CONCLUSIONS

Patients share a complex neurodevelopmental and neurological phenotype (developmental delay, movement disorder) with impaired gait, abnormal tone and hand stereotypies. However, the presence and characteristics of regression and loss of language and functional hand use can differ. Finally, the frequency of additional supportive criteria and their distribution also vary widely.

[Early identification and diagnosis of epilepsy related to fever sensitivity]

Febrile seizures are the most common nervous system disease in childhood, and most children have a good prognosis. However, some epilepsy cases are easily induced by fever and are characterized by "fever sensitivity", and it is difficult to differentiate such cases from febrile seizures. Epilepsy related to fever sensitivity includes hereditary epilepsy with febrile seizures plus, Dravet syndrome, and PCDH19 gene-related epilepsy. This article mainly describes the clinical manifestations of these three types of epilepsy and summarizes their clinical features in the early stage of disease onset, so as to achieve early identification, early diagnosis, and early intervention to improve prognosis.

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.

PCDH19-Related Epilepsies

Protocadherin-19 (PCDH19) is considered one of the most relevant genes related to epilepsy. To date, more than 150 mutations have been identified as causative for PCDH19-female epilepsy (also known as early infantile epileptic encephalopathy-9, EIEE9), which is characterized by early onset epilepsy, intellectual disabilities, and behavioral disturbances. More recently, mosaic-males (i.e., exhibiting the variants in less than 25% of their cells) have been described as affected by infant-onset epilepsy associated with intellectual disability, as well as compulsive or aggressive behavior and autistic features. Although little is known about the physiological role of PCDH19 protein and the pathogenic mechanisms that lead to EIEE9, many reports and clinical observation seem to suggest a relevant role of this protein in the development of cellular hyperexcitability. However, a genotype–phenotype correlation is difficult to establish. The main feature of EIEE9 consists in early onset of seizures, which generally occur in clusters lasting 1 to 5 minutes and repeating up to 10 times a day for several days. Seizures tend to present during febrile episodes, similarly to the first phases of Dravet syndrome and PCDH19 variants have been found in ∼25% of females who present with features of Dravet syndrome and testing negative for SCN1A variants. There is no “standardized” treatment for PCDH19-related epilepsy and most of the patients receiving a combination of several drugs. In this review, we focus on the latest researches on these aspects, with regard to protein expression, its known functions, and the mechanisms by which the protein acts. The clinical phenotypes related to PCDH19 mutations are also discussed.

Developmental and epileptic encephalopathies: what we do and do not know

Developmental encephalopathies, including intellectual disability and autistic spectrum disorder, are frequently associated with infant epilepsy. Epileptic encephalopathy is used to describe an assumed causal relationship between epilepsy and developmental delay. Developmental encephalopathies pathogenesis more independent from epilepsy is supported by the identification of several gene variants associated with both developmental encephalopathies and epilepsy, the possibility for gene-associated developmental encephalopathies without epilepsy, and the continued development of developmental encephalopathies even when seizures are controlled. Hence, 'developmental and epileptic encephalopathy' may be a more appropriate term than epileptic encephalopathy. This update considers the best studied 'developmental and epileptic encephalopathy' gene variants for illustrative support for 'developmental and epileptic encephalopathy' over epileptic encephalopathy. Moreover, the interaction between epilepsy and developmental encephalopathies is considered with respect to influence on treatment decisions. Continued research in genetic testing will increase access to clinical tests, earlier diagnosis, better application of current treatments, and potentially provide new molecular-investigated treatments.

Seizure Clusters: Morbidity and Mortality

Seizure clusters, an intermediate between single seizure and status epilepticus, are associated with morbidity, impaired quality of life, and premature mortality. The relationship between seizure clusters and sudden unexplained death in epilepsy (SUDEP) is poorly understood. Here, we define seizure clusters; review comorbid psychiatric disorders and memory deficits associated with seizure clusters; and review cases of witnessed SUDEP for which seizure frequency prior to death is available. Patients with a history of seizure clusters have a 2.5 fold increased risk for SUDEP, and one third of patients with monitored in hospital SUDEP experienced a cluster of generalized tonic clonic seizures prior to death. Understanding the effects of seizure frequency and duration on SUDEP risk could yield new insights in SUDEP pathophysiology and new targets for intervention.

Two novel PCDH19 mutations in Russian patients with epilepsy with intellectual disability limited to females: a case report

Background

Epilepsy with intellectual disability limited to females (Epileptic encephalopathy, early infantile, 9; EIEE9) is a rare early infantile epileptic encephalopathy characterized by an unusual X-linked inheritance: females with heterozygous mutations are affected, while hemizygous males are not.

Case presentation

We describe the clinical and molecular characteristics of 2 Russian patients with EIEE9 (females, ages 3 years and 7 years). In these patients seizures developed at the age of 3 years. Additionally, for our patients and for cases described in the literature we searched for a possible relationship between the type and localization of the mutation and the EIEE9 clinical phenotype.

Conclusions

We identified two novel PCDH19 mutations in EIEE9 patients: a missense mutation in exon 1 (c.1236C > A, p.Asp412Glu) and a frameshift in exon 3 (c.2386_2387insGTCT, p.Thr796fs). We conclude that the age of seizure onset and the presence of intellectual disability may depend not on the type and localization of PCDH19 mutations, but on the X-inactivation status. The study also highlights the need to screen for EIEE9 among young female epilepsy patients.

The Epilepsy-Related Protein PCDH19 Regulates Tonic Inhibition, GABAAR Kinetics, and the Intrinsic Excitability of Hippocampal Neurons

PCDH19 encodes for protocadherin-19 (PCDH19), a cell-adhesion molecule of the cadherin superfamily preferentially expressed in the brain. PCDH19 mutations cause a neurodevelopmental syndrome named epileptic encephalopathy, early infantile, 9 (EIEE9) characterized by seizures associated with cognitive and behavioral deficits. We recently reported that PCDH19 binds the alpha subunits of GABA_A receptors (GABA_ARs), modulating their surface availability and miniature inhibitory postsynaptic currents (mIPSCs). Here, we investigated whether PCDH19 regulatory function on GABA_ARs extends to the extrasynaptic receptor pool that mediates tonic current. In fact, the latter shapes neuronal excitability and network properties at the base of information processing. By combining patch-clamp recordings in whole-cell and cell-attached configurations, we provided a functional characterization of primary hippocampal neurons from embryonic rats of either sex expressing a specific PCDH19 short hairpin (sh)RNA. We first demonstrated that PCDH19 downregulation reduces GABA_AR-mediated tonic current, evaluated by current shift and baseline noise analysis. Next, by single-channel recordings, we showed that PCDH19 regulates GABA_ARs kinetics without altering their conductance. In particular, GABA_ARs of shRNA-expressing neurons preferentially exhibit brief openings at the expense of long ones, thus displaying a flickering behavior. Finally, we showed that PCDH19 downregulation reduces the rheobase and increases the frequency of action potential firing, thus indicating neuronal hyperexcitability. These findings establish PCDH19 as a critical determinant of GABA_AR-mediated tonic transmission and GABA_ARs gating, and provide the first mechanistic insights into PCDH19-related hyperexcitability and comorbidities.

Disentangling the paradox of the PCDH19 clustering epilepsy, a disorder of cellular mosaics

PCDH19 Clustering Epilepsy (CE) is an intriguing early-onset seizure, autism and neurocognitive disorder with unique inheritance. The causative gene, PCDH19, is on the X-chromosome and encodes a cell-cell adhesion protein with restricted expression during brain development. Unlike other X-linked disorders, PCDH19-CE manifests in heterozygous females. Strikingly, hemizygous males are not affected. However, males with postzygotic somatic mutation in PCDH19 are affected and clinically similar to the affected females. PCDH19-CE is a disorder of cellular mosaicism. The coexistence of two different, but otherwise 'normal' cells in a PCDH19-CE individual, that is the wild type and the variant PCDH19 cells, has been proposed as the driving force of the disorder. This 'cellular interference' hypothesis could and has now been tested using sophisticated mouse models.

Integrative structural, functional, and transcriptomic analyses of sex-biased brain organization in humans

Humans display reproducible sex differences in cognition and behavior, which may partly reflect intrinsic sex differences in regional brain organization. However, the consistency, causes and consequences of sex differences in the human brain are poorly characterized and hotly debated. In contrast, recent studies in mice-a major model organism for studying neurobiological sex differences-have established: 1) highly consistent sex biases in regional gray matter volume (GMV) involving the cortex and classical subcortical foci, 2) a preponderance of regional GMV sex differences in brain circuits for social and reproductive behavior, and 3) a spatial coupling between regional GMV sex biases and brain expression of sex chromosome genes in adulthood. Here, we directly test translatability of rodent findings to humans. First, using two independent structural-neuroimaging datasets (n > 2,000), we find that the spatial map of sex-biased GMV in humans is highly reproducible (r > 0.8 within and across cohorts). Relative GMV is female biased in prefrontal and superior parietal cortices, and male biased in ventral occipitotemporal, and distributed subcortical regions. Second, through systematic comparison with functional neuroimaging meta-analyses, we establish a statistically significant concentration of human GMV sex differences within brain regions that subserve face processing. Finally, by imaging-transcriptomic analyses, we show that GMV sex differences in human adulthood are specifically and significantly coupled to regional expression of sex-chromosome (vs. autosomal) genes and enriched for distinct cell-type signatures. These findings establish conserved aspects of sex-biased brain development in humans and mice, and shed light on the consistency, candidate causes, and potential functional corollaries of sex-biased brain anatomy in humans.

Antiseizure medication withdrawal in seizure-free patients with PCDH19-related epilepsy: A multinational cohort survey

PURPOSE

PCDH19-related epilepsy is usually refractory to current antiseizure medications (ASM), but seizures are easier to control especially after the second decade of life. Nonetheless, there is no evidence regarding the withdrawal of ASM in this clinical scenario. We aimed to evaluate the outcomes of attempts to discontinue ASM in seizure-free patients with PCDH19-related epilepsy.

METHODS

This survey was a cross-sectional study of patients with PCDH19-related epilepsy open between June 2019 and February 2020 and implemented in collaboration with international patient advocacy groups. Caregivers or patients were asked to fill out an anonymous questionnaire of clinical data about the attempts of ASM reduction.

RESULTS

The survey received 42 unique responses with collected data of 77 attempts of ASM withdrawal. Median age at the ASM reduction was 10 years and mean duration of the previous seizure-free period was 35.8 months. Overall, 88.3 % had seizure recurrence (p < 0.001). After seizure recurrence, the medication had to be increased above the previous ASM dose in 36.5 % and come back to the previous one in 25.4 % cases. 5.2 % did not become seizure-free again. Only 2.6 % cases had their ASM totally withdrawn. Patients without seizure recurrence were significantly older and showed longer seizure-free period (p < 0.001).

CONCLUSION

This pilot study in PCDH19-related epilepsy shows that the withdrawal of ASM seems to be associated with a high risk of seizure recurrence. Despite this novel methodology is useful for rare diseases, it has some limitations and biases. Additional studies are warranted in more extensive samples.

The Humanistic and Economic Burden of Pediatric Focal Seizures in the United States

OBJECTIVE

To better understand the humanistic and economic burden of focal seizures in children 2-12 years old.

METHODS

We conducted a targeted literature review by searching MEDLINE for English-language publications reporting on children 2-12 years old with focal seizures published in the United States since 2008.

RESULTS

Thirty-five publications were included. Incidence of focal seizures was 23.2 to 47.1 per 100,000 children per year; prevalence was 2.0 per 1,000 children, and ranged from 1.6 - 2.6 per 1,000 in patients of any age. Life expectancy was 47.3-61.8 years among children 3-12 years old. Patients took several antiepileptic drugs and experienced frequent seizures, sleep disorders, mood disorders, migraine, and seizure-related injuries (eg, bone fractures, sprains, open wounds). Children with focal seizures scored below average on cognitive assessments and up to 42%, 16%, and 19% had depression, anxiety, and attention-deficit disorder, respectively. Patients of any age had about 10 outpatient visits (2 epilepsy-related), 2 inpatient visits (less than 1 epilepsy-related), and 24 procedures (1 epilepsy-related) per year. Medication adherence was low: only half of pediatric patients maintained ≥90% adherence over 6 months. Annual total health care costs among patients of any age ranged from $18,369 - 38,549; first-year total health care costs for children were $19,883.

CONCLUSIONS

Incidence and prevalence of focal seizures is high and the humanistic and economic burdens are significant. Future studies focused exclusively on children with focal seizures are needed to more precisely describe the burden. We also suggest further research and implementation of methods to improve medication adherence as an approach to lessen burden on these young patients.

Quantitative MRI-Based Analysis Identifies Developmental Limbic Abnormalities in PCDH19 Encephalopathy

Protocadherin-19 (PCDH19) is a calcium dependent cell-adhesion molecule involved in neuronal circuit formation with prevalent expression in the limbic structures. PCDH19-gene mutations cause a developmental encephalopathy with prominent infantile onset focal seizures, variably associated with intellectual disability and autistic features. Diagnostic neuroimaging is usually unrevealing. We used quantitative MRI to investigate the cortex and white matter in a group of 20 PCDH19-mutated patients. By a statistical comparison between quantitative features in PCDH19 brains and in a group of age and sex matched controls, we found that patients exhibited bilateral reductions of local gyrification index (lGI) in limbic cortical areas, including the parahippocampal and entorhinal cortex and the fusiform and lingual gyri, and altered diffusivity features in the underlying white matter. In patients with an earlier onset of seizures, worse psychiatric manifestations and cognitive impairment, reductions of lGI and diffusivity abnormalities in the limbic areas were more pronounced. Developmental abnormalities involving the limbic structures likely represent a measurable anatomic counterpart of the reduced contribution of the PCDH19 protein to local cortical folding and white matter organization and are functionally reflected in the phenotypic features involving cognitive and communicative skills as well as local epileptogenesis.

A standardized patient-centered characterization of the phenotypic spectrum of PCDH19 girls clustering epilepsy

Protocadherin-19 (PCDH19) pathogenic variants cause an early-onset seizure disorder called girls clustering epilepsy (GCE). GCE is an X-chromosome disorder that affects heterozygous females and mosaic males, however hemizygous ("transmitting") males are spared. We aimed to define the neuropsychiatric profile associated with PCDH19 pathogenic variants and determine if a clinical profile exists for transmitting males. We also examined genotype- and phenotype-phenotype associations. We developed an online PCDH19 survey comprising the following standardized assessments: The Behavior Rating Inventory of Executive Function; the Social Responsiveness Scale, 2nd edition; the Strengths and Difficulties Questionnaire; and the Dimensional Obsessive-Compulsive Scale. Genetic, seizure, and developmental information were also collected. The survey was completed by patients or by caregivers on behalf of patients. Of the 112 individuals represented (15 males), there were 70 unique variants. Thirty-five variants were novel and included a newly identified recurrent variant Ile781Asnfs*3. There were no significant differences in phenotypic outcomes between published and unpublished cases. Seizures occurred in clusters in 94% of individuals, with seizures resolving in 28% at an average age of 17.5 years. Developmental delay prior to seizure onset occurred in 18% of our cohort. Executive dysfunction and autism spectrum disorder (ASD) occurred in approximately 60% of individuals. The ASD profile included features of attention-deficit hyperactivity disorder. In addition, 21% of individuals met criteria for obsessive-compulsive disorder that appeared to be distinct from ASD. There were no phenotypic differences between heterozygous females and mosaic males. We describe a mosaic male and two hemizygous males with atypical clinical profiles. Earlier seizure onset age and increased number of seizures within a cluster were associated with more severe ASD symptoms (p = 0.001), with seizure onset also predictive of executive dysfunction (p = 4.69 × 10^-4) and prosocial behavior (p = 0.040). No clinical profile was observed for transmitting males. This is the first patient-derived standardized assessment of the neuropsychiatric profile of GCE. These phenotypic insights will inform diagnosis, management, and prognostic and genetic counseling.

A novel PCDH19 missense mutation, c.812G>A (p.Gly271Asp), identified using whole-exome sequencing in a Chinese family with epilepsy female restricted mental retardation syndrome

Background

Epilepsy limited to females with mental retardation (EFMR) is a rare type of epilepsy with an X‐linked mode of inheritance, which affect heterozygous females while the males are not affected. Mutations within the protocadherin 19 (PCDH19) gene have been identified as the direct cause of EFMR. The phenotype of EFMR is characterized by seizure onset in infancy with or without cognitive impairment, intellectual disturbances, and autistic features.

Methods

Whole‐exome sequencing (WES) was performed in the proband to identify the underlying genetic mutations. The candidate genes were confirmed by Sanger sequencing following PCR amplification. In silico analyses were conducted to predict the effect of the novel missense mutation on the function of PCDH19 protein.

Results

We identified three female patients in a family with a novel missense mutation in PCDH19, c.812G>A (p. (Gly271Asp)). The patients III‐1 and III‐2 presented with more severe clinical phenotypes and an earlier age of onset (6 and 11 months, respectively), intellectual disability, and movement disorders. By contrast, patient II‐4 has a later age of onset (23 months), and there was no relapse of seizures without antiepileptic treatment after the age of six. In silico analyses showed that p. (Gly271Asp) in the PCDH19 affects a highly conserved residue.

Conclusions

Our results indicated that patients with the same PCDH19 mutation in a family may show intrafamilial phenotypic variability. Givening the mother of the proband was 18 weeks pregnant and intends to have a prenatal diagnosis, the more reasonable and less harmful strategies for prenatal diagnosis could be chosen based on the results of noninvasive prenatal testing and genetic testing.

PCDH19-Related Epilepsy Syndrome: A Comprehensive Clinical Review

PCDH19-related epilepsy is a distinct childhood-onset epilepsy syndrome characterized by brief clusters of febrile and afebrile seizures with onset primarily before the age of three years, cognitive impairment, autistic traits, and behavioral abnormalities. PCDH19 gene is located in Xq22 and produces nonclustered delta protocadherin. This disorder primarily manifests in heterozygote females due to random X chromosome inactivation leading to somatic mosaicism and abnormal cellular interference between cells with and without delta-protocadherin. This article reviews the clinical features based on a comprehensive literature review (MEDLINE using PubMed and OvidSP vendors with appropriate keywords to incorporate recent evidence), personal practice, and experience. Significant progress has been made in the past 10 years, including identification of the gene responsible for the condition, characterization of clinical phenotypes, and development of animal models. More rigorous studies involving quality-of-life measures as well as standardized neuropsychiatric testing are necessary to understand the full spectrum of the disease. The recent discovery of allopregnanolone deficiency in patients with PCDH19-related epilepsy leads to opportunities in precision therapy. A phase 3 clinical study is currently active to evaluate the efficacy, safety, and tolerability of adjunctive ganaxolone (an allopregnanolone analog) therapy.

Identification of PCDH19 Gene Mutations/Deletions in Patients with Early Onset Epilepsy

Background and Aims:

PCDH19 gene, which encodes protocadherin 19, is associated with epilepsy and intellectual disability, mainly in affected females. The clinical manifestations are heterogeneous and the main features include early onset seizure, generalized or focal seizures sensitive to fever, and brief seizures occurring in clusters. The disorders exhibit a unique and unusual X-linked pattern of expression. We aimed to investigate PCDH19 mutations/deletions in patients with epilepsy and describe the clinical/molecular features.

Methods:

PCDH19 gene was analyzed in 35 Turkish female patients from 34 families with early-onset epilepsy via direct sequencing and multiplex ligation-dependent probe amplification analysis. Additionally, array comparative genomic hybridization analysis was performed in patients with whole gene deletion.

Results:

We identified 2 different heterozygous mutations in 2 unrelated probands (5. 7%) which were located in exon 1. Additionally, whole gene deletions were detected in dizygotic twin girls (5. 7%), who had distinct clinical features and the deletion was inherited from the unaffected father. The second twin suffered more severe clinical manifestations including autistic features, behavioral problems, mild-moderate mental retardation and seizures, which were under control with multidrug regimen when compared with the first twin.

Conclusion:

PCDH19 is a major causative gene in patients with epilepsy and further data is required to gain a better understanding of phenotype-genotype correlation. In addition to gene sequencing, deletion/duplication analysis will improve the molecular diagnosis in patients with clinical findings.

[Clinical and genetic characteristics of epilepsy caused by mutations in the PCDH19 gene (OMIM: 300088)]

AIM

To analyze clinical and genetic characteristics of PCDH19-associated epilepsy in a sample of patients from the Russian population.

MATERIAL AND METHODS

The sample of patients with early epileptic encephalopathies included 16 people aged 10 month to 30 years. All patients underwent neurological examination according to standard methods, exome sequencing and EEG monitoring.

RESULTS

Most of the identified mutations led to a shift in the reading frame or the formation of a termination codon. Six of them were duplications, four were deletions of one nucleotide, and three were nonsense mutations. Consistent with earlier studies, the authors identified the polymorphism of clinical manifestations of seizures that did not depend on the type of mutation and its localization.

CONCLUSION

Based on the study of the clinical and genetic characteristics of the patients, the authors conclude that the so-called 'hot spots' are present in the PCDH19 gene, which are more common in the group of patients with mutations in this gene, and that the clinical picture of early infantile epileptic encephalopathy type 9 is variable.