Focal seizures with affective symptoms are a major feature ofPCDH19gene-related epilepsy

Characterizing PCDH19 in human induced pluripotent stem cells (iPSCs) and iPSC-derived developing neurons: emerging role of a protein involved in controlling polarity during neurogenesis

PCDH19 (Protocadherin 19), a member of the cadherin superfamily, is involved in the pathogenic mechanism of an X-linked model of neurological disease. The biological function of PCHD19 in human neurons and during neurogenesis is currently unknown. Therefore, we decided to use the model of the induced pluripotent stem cells (iPSCs) to characterize the location and timing of expression of PCDH19 during cortical neuronal differentiation. Our data show that PCDH19 is expressed in pluripotent cells before differentiation in a homogeneous pattern, despite its localization is often limited to one pole of the cell. During neuronal differentiation, positional information on the progenitor cells assumes an important role in acquiring polarization. The proper control of the cell orientation ensures a fine balancing between symmetric (giving rise to two progenitor sister cells) versus asymmetric (giving rise to one progenitor cell and one newborn neuron) division. This process results in the polar organization of the neural tube with a lumen indicating the basal part of the polarized neuronal progenitor cell; in the iPSC model the cells are organized in the ‘neural rosette’ and interestingly, PCDH19 is located at the center of the rosette, with other well-known markers of the lumen (N-cadherin and ZO-1). These data suggest that PCDH19 has a role in instructing the apico-basal polarity of the progenitor cells, thus regulating the development of a properly organized human brain.

Autism spectrum disorder phenotype and intellectual disability in females with epilepsy and PCDH-19 mutations

INTRODUCTION

Autism features and various degrees of cognitive deficit are reported in patients with PCDH-19 mutations and epilepsy. Autism spectrum disorder (ASD) and, often, cognitive profile are usually assessed clinically. We studied autism phenotype and cognitive outcome in a series of patients using standardized tools for development and ASD. We aimed to describe the phenotype of ASD in this series and to understand whether ASD is strictly linked to intellectual disability (ID) or is present as a comorbidity.

METHODS

Eight females aged 5 to 17years old with PCDH-19 mutations and epilepsy were recruited. For ASD diagnosis, the Autism Diagnostic Interview - Revised (ADI-R) and the Autism Diagnosis Observation Schedule (ADOS) were administered. Patients underwent a neuropsychological examination with tests measuring global intellectual efficiency (WPPSI-III and WISC-IV), language, and executive and social cognition abilities. Parental adaptive behavioral questionnaires were also obtained (VABS, CBCL, and BRIEF).

RESULTS

Six out of eight patients presented with ASD and ID. Two patients had neither ASD nor ID, and both had the latest age of onset for their epilepsy. All cognitive functions were deficient, but theory-of-mind abilities compared to other cognitive features were even impaired. Features of ASD lacked major repetitive and stereotyped behaviors and show some differences with the classical ASD features related to ID.

CONCLUSION

Our results show a large spectrum of ID and a very high rate of ASD in patients with epilepsy and PCDH-19 mutations. Autism spectrum disorder seems to be a genuine comorbidity, more than a consequence of ID. It highlights the importance of standardized psychiatric and cognitive evaluation in order to establish a tailored rehabilitation program.

PCDH19-related epilepsy in two mosaic male patients

PCDH19 gene mutations have been recently associated with an epileptic syndrome characterized by focal and generalized seizures. The PCDH19 gene (Xq22.1) has an unusual X-linked inheritance with a selective involvement for female subjects. A cellular interference mechanism has been hypothesized and male patients can manifest epilepsy only in the case of a mosaicism. So far about 100 female patients, and only one symptomatic male have been described. Using targeted next generation sequencing (NGS) approach we found a PCDH19 point mutation in two male patients with a clinical picture suggestive of PCDH19-related epilepsy. The system allowed us to verify that the two c.1352 C>T; p.(Pro451Leu) and c.918C>G; p.(Tyr306*) variants occurred in mosaic status. Mutations were confirmed by Sanger sequencing and quantified by real-time polymerase chain reaction (PCR). Up to now, the traditional molecular screening for PCDH19-related epilepsy has been targeted to all females with early onset epilepsy with or without cognitive impairment. Male patients were generally excluded. We describe for the first time two mosaic PCDH19 point mutations in two male patients with a clinical picture suggestive of PCDH19-related epilepsy. This finding opens new opportunities for the molecular diagnoses in patients with a peculiar type of epilepsy that remains undiagnosed in male patients.

Extending the use of stiripentol to other epileptic syndromes: a case of PCDH19-related epilepsy

Stiripentol is an antiepileptic drug (AED) approved by the European Medicines Agency for the treatment of Dravet Syndrome (DS) as adjunct treatment with valproate and clobazam. PCDH19-related epilepsy is an emerging epileptic syndrome characterized by the occurrence of epilepsy in female patients associated with mental retardation and autistic features in most cases. It shares many features with DS: age of onset, normal development before the onset, fever sensitivity, cognitive impairment during the time, drug-resistance. Basing on the numerous similarities between DS and PCDH19-related epilepsy, we tried stiripentol in a nine and half year old female patient with PCDH19-related resistant epilepsy, as add-on treatment to valproate and clobazam. It had a surprising efficacy as the patient had a two years and ten months seizure free period, as never in her epilepsy history. Up to date, clinical trials of stiripentol have been always focused on DS. The delineation of new epileptic syndromes, as PCDH19-related epilepsy, opens new scenarios to the utilization of this AED. This case report is suggestive of a good response of PCDH19-related Epilepsy to stiripentol. However further cases and above all clinical trials are necessary to confirm this result.

Immediate suppression of seizure clusters by corticosteroids in PCDH19 female epilepsy

PURPOSE

The pathomechanism and treatment of PCDH19 female epilepsy (PCDH19-FE) remain unclear. Here, we report that corticosteroids are effective for control of the seizure clusters or other acute symptoms of PCDH19-FE and argue for the possible involvement of a compromised blood-brain barrier (BBB) in its pathogenesis.

METHODS

The efficacy of corticosteroids was retrospectively reviewed in five Japanese patients with PCDH19-FE. The results of antibody assays against the N-methyl-d-aspartate-type glutamate receptor (abs-NR) in serum/cerebrospinal fluid were also compiled.

RESULTS

Corticosteroid treatments significantly improved the acute symptoms, including seizure clusters, in all cases, most often immediately after the initial administration. However, the effect was transient, and some seizures recurred within a few weeks, especially in association with fever. Serum and/or cerebrospinal fluid abs-NR were detected in all patients. Target sequences of the detected antibodies were multiple, and the titers tended to decrease over time. In one patient, immunohistochemical analysis using rat hippocampal slices also revealed serum antibodies targeting an unknown epitope in neuronal cytoplasm.

CONCLUSION

Our findings imply an involvement of inflammatory processes in the pathogenesis of PCDH19-FE and therapeutic utility for corticosteroids as an adjunctive option in acute treatment. PCDH19 is well expressed in brain microvascular endothelial cells and thus its impairment may cause BBB vulnerability, which may be ameliorated by corticosteroids. The abs-NR detected in our patients may not indicate an autoimmune pathomechanism, but may rather represent non-specific sensitization to degraded neuronal components entering the general circulation, the latter process facilitated by the BBB vulnerability.

Cognitive development in females with PCDH19 gene-related epilepsy

Mutations in the PCDH19 gene are now recognized to cause epilepsy in females and are claiming increasing interest in the scientific world. Clinical features and seizure semiology have been described as heterogeneous. Intellectual disability might be present, ranging from mild to severe; behavioral and psychiatric problems are a common feature of the disorder, including aggressiveness, depressed mood, and psychotic traits. The purpose of our study was to describe the cognitive development in 11 girls with a de novo mutation in PCDH19 and early-onset epilepsy. Six patients had average mental development or mild intellectual disability regardless of persistence of seizures in clusters. Five patients presented moderate or severe intellectual disability and autistic features. In younger patients, we found that despite an average developmental quotient, they all presented a delay of expressive language acquisition and lower scores at follow-up testing completed at older ages, underlining that subtle dysfunctions might be present. Larger cohort and long-term follow-up might be useful in defining cognitive features and in improving the care of patients with PCDH19.

Epilepsy and mental retardation restricted to females: X-linked epileptic infantile encephalopathy of unusual inheritance

Epilepsy in females with mental retardation (EFMR) is a rare early infantile epileptic encephalopathy (EIEE), phenotypically resembling Dravet syndrome (DS). It is characterised by a variable degree of intellectual deficits and epilepsy. EFMR is caused by heterozygous mutations in the PCDH19 gene (locus Xq22.1) encoding protocadherin-19, a protein that is highly expressed during brain development. The protein is involved in cell adhesion and probably plays an important role in neuronal migration and formation of synaptic connections. EFMR is considered X-linked of variable mutations' penetrance. Mutations in the PCDH19 gene mainly arise de novo, but if inherited, they show a unique pattern of transmission. Females with heterozygous mutations are affected, while hemizygous males are not, regardless of mutation carriage. This singular mode might be explained by cell interference as a pathogenic molecular mechanism leading to neuronal dysfunction. Recently, PCDH19-related EIEE turned out to be more frequent than initially thought, contributing to around 16% of cases (25% in female groups) in the SCN1A-negative DS-like patients. Therefore, the PCDH19 gene is now estimated to be the second, after SCN1A, most clinically relevant gene in epilepsy.

Genetic epilepsy syndromes without structural brain abnormalities: clinical features and experimental models

Research in genetics of epilepsy represents an area of great interest both for clinical purposes and for understanding the basic mechanisms of epilepsy. Most mutations in epilepsies without structural brain abnormalities have been identified in ion channel genes, but an increasing number of genes involved in a diversity of functional and developmental processes are being recognized through whole exome or genome sequencing. Targeted molecular diagnosis is now available for different forms of epilepsy. The identification of epileptogenic mutations in patients before epilepsy onset and the possibility of developing therapeutic strategies tested in experimental models may facilitate experimental approaches that prevent epilepsy or decrease its severity. Functional analysis is essential for better understanding pathogenic mechanisms and gene interactions. In vitro experimental systems are either cells that usually do not express the protein of interest or neurons in primary cultures. In vivo/ex vivo systems are organisms or preparations obtained from them (e.g., brain slices), which should better model the complexity of brain circuits and actual pathophysiological conditions. Neurons differentiated from induced pluripotent stem cells generated from the skin fibroblasts of patients have recently allowed the study of mutations in human neurons having the genetic background of a given patient. However, there is remarkable complexity underlying epileptogenesis in the clinical dimension, as reflected by the fact that experimental models have not provided yet results having clinical translation and that, with a few exceptions concerning rare conditions, no new curative treatment has emerged from any genetic finding in epilepsy.

Clinical and genetic aspects of PCDH19-related epilepsy syndromes and the possible role of PCDH19 mutations in males with autism spectrum disorders

Epilepsy and mental retardation limited to females (EFMR), caused by PCDH19 mutations, has a variable clinical expression that needs further exploration. Onset of epilepsy may be provoked by fever and can resemble Dravet syndrome. Furthermore, transmitting males have no seizures, but are reported to have rigid personalities suggesting possible autism spectrum disorders (ASD). Therefore, this study aimed to determine the phenotypic spectrum associated with PCDH19 mutations in Dravet-like and EFMR female patients and in males with ASD. We screened 120 females suffering from Dravet-like epilepsy, 136 females with EFMR features and 20 males with ASD. Phenotypes and genotypes of the PCDH19 mutation carriers were compared with those of 125 females with EFMR reported in the literature. We report 15 additional patients with a PCDH19 mutation. Review of clinical data of all reported patients showed that the clinical picture of EFMR is heterogeneous, but epilepsy onset in infancy, fever sensitivity and occurrence of seizures in clusters are key features. Seizures remit in the majority of patients during teenage years. Intellectual disability and behavioural disturbances are common. Fifty percent of all mutations are missense mutations, located in the extracellular domains only. Truncating mutations have been identified in all protein domains. One ASD proband carried one missense mutation predicted to have a deleterious effect, suggesting that ASD in males can be associated with PCDH19 mutations.