Expanding Phenotype of Poirier–Bienvenu Syndrome: New Evidence from an Italian Multicentrical Cohort of Patients

Casein Kinase 2 Affects Epilepsy by Regulating Ion Channels: A Potential Mechanism

Epilepsy, characterized by recurrent seizures and abnormal brain discharges, is the third most common chronic disorder of the Central Nervous System (CNS). Although significant progress has been made in the research on antiepileptic drugs (AEDs), approximately one-third of patients with epilepsy are refractory to these drugs. Thus, research on the pathogenesis of epilepsy is ongoing to find more effective treatments. Many pathological mechanisms are involved in epilepsy, including neuronal apoptosis, mossy fiber sprouting, neuroinflammation, and dysfunction of neuronal ion channels, leading to abnormal neuronal excitatory networks in the brain. CK2 (Casein kinase 2), which plays a critical role in modulating neuronal excitability and synaptic transmission, has been shown to be associated with epilepsy. However, there is limited research on the mechanisms involved. Recent studies have suggested that CK2 is involved in regulating the function of neuronal ion channels by directly phosphorylating them or their binding partners. Therefore, in this review, we will summarize recent research advances regarding the potential role of CK2 regulating ion channels in epilepsy, aiming to provide more evidence for future studies.

Genetic analysis and literature review of a Poirier-Bienvenu neurodevelopmental syndrome family line caused by a de novo frameshift variant in CSNK2B

BACKGROUND

Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) is a rare autosomal dominant neurologic disorder caused by a heterozygous variant of CSNK2B, which is characterized by early onset epilepsy, hypotonia, varying degrees of intellectual disability (ID), developmental delay (DD), and facial dysmorphism. This study clarifies the molecular diagnosis and causative factors of a Chinese boy with POBINDS.

METHODS

The clinical phenotypes and ancillary laboratory tests were collected and analyzed by trio whole exome sequencing (WES) and copy number variant sequencing (CNV-seq) in the follow-up proband's families. The candidate variant was validated by Sanger sequencing and bioinformatics software was used to further explore the effect of the de novo frameshift variant on the protein structure.

RESULTS

The proband carries a de novo frameshift variant c.453_c.454insAC (p.H152fs*76) in CSNK2B. According to the ACMG genetic variant classification criteria and guidelines, the locus is a pathogenic variant (PVS1+PS2+PM2) and the associated disease was POBINDS. Protein structure prediction suggests significant differences in amino acid sequences before and after mutation.

CONCLUSION

A rare case of POBINDS caused by a novel frameshift variant in CSNK2B was diagnosed. The novel variant extends the variation spectrum of CSNK2B, which provides guidance for early clinical diagnosis, genetic counseling and treatment of this family. A review of the currently reported cases of POBINDS further enriches and summarizes the relationship between genotype and phenotype of POBINDS.

Refining of the electroclinical phenotype in familial and sporadic cases of CSNK2B-related Neurodevelopmental Syndrome

CSNK2B encodes a regulatory subunit of casein kinase II, which is highly expressed in the brain. Heterozygous pathogenic variants in CSNK2B are associated with Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) (OMIM #618732), characterized by facial dysmorphisms, seizures, intellectual disability, and behavioral disturbances. We report ten new patients with CSNK2B-related Neurodevelopmental Syndrome associated with heterozygous variants of CSNK2B. In three patients, a pathogenic variant was inherited from an affected parent. We describe both molecular and clinical features, focusing on epileptic and neurodevelopmental phenotypes. The median age at follow-up was 8.5 years (range 21 months-42 years). All patients had epilepsy, with onset at a median age of 10.5 months range 6 days-10 years). Seizures were both focal and generalized and were resistant to anti-seizure medications in two out of ten patients. Six patients had mild to moderate cognitive delays, whereas four patients had no cognitive disability. Although all previously reported patients had a de novo CSNK2B pathogenic variant, here we report, for the first time, two familial cases of CSNK2B-related Neurodevelopmental Syndrome. We confirmed the highly variable expressivity of the disease among both interfamilial and intrafamilial cases. Furthermore, this study provides information about the long-term outcome in adult patients and underlines the importance of detailed family history collection before performing genetic testing in patients with epilepsy and neurodevelopmental disorders.

The efficacy and safety of first-line anti-seizure medications as substitution therapy for children with drug-resistant epilepsy: a randomized controlled trial protocol

Although many anti-seizure medications (ASMs) are available, treatment failure, known as drug-resistant epilepsy (DRE), still occurs in around 30% of children with epilepsy. Second-line ASMs are usually used as substitution therapy in DRE to control seizures, although international consensus is not available yet. Previous studies focus on comparing the ASMs, whether as add-on or substitution therapy, mainly conducted in newly diagnosed epilepsy. However, the study that investigated first-line ASMs as substitution therapy compared to second-line ones, particularly among DRE children, is still lacking. A randomized controlled trial (RCT) enrolling 102 participants, aged 1-18, at three referral hospitals in Indonesia will be conducted, dividing them into intervention and control groups. The intervention group will be treated with first-line ASMs as the substitution therapy, while the other in the control group will get second-line ASMs. The primary outcome measure is the proportion difference of responders between groups who get first-line and second-line ASMs in 14 weeks of intervention. Clinical trial registration: ClinicalTrials.gov, identifier NCT05697614.

Haploinsufficiency as a Foreground Pathomechanism of Poirer-Bienvenu Syndrome and Novel Insights Underlying the Phenotypic Continuum of CSNK2B-Associated Disorders

CSNK2B encodes for the regulatory subunit of the casein kinase II, a serine/threonine kinase that is highly expressed in the brain and implicated in development, neuritogenesis, synaptic transmission and plasticity. De novo variants in this gene have been identified as the cause of the Poirier-Bienvenu Neurodevelopmental Syndrome (POBINDS) characterized by seizures and variably impaired intellectual development. More than sixty mutations have been described so far. However, data clarifying their functional impact and the possible pathomechanism are still scarce. Recently, a subset of CSNK2B missense variants affecting the Asp32 in the KEN box-like domain were proposed as the cause of a new intellectual disability-craniodigital syndrome (IDCS). In this study, we combined predictive functional and structural analysis and in vitro experiments to investigate the effect of two CSNK2B mutations, p.Leu39Arg and p.Met132LeufsTer110, identified by WES in two children with POBINDS. Our data prove that loss of the CK2beta protein, due to the instability of mutant CSNK2B mRNA and protein, resulting in a reduced amount of CK2 complex and affecting its kinase activity, may underlie the POBINDS phenotype. In addition, the deep reverse phenotyping of the patient carrying p.Leu39Arg, with an analysis of the available literature for individuals with either POBINDS or IDCS and a mutation in the KEN box-like motif, might suggest the existence of a continuous spectrum of CSNK2B-associated phenotypes rather than a sharp distinction between them.

Case report: Two cases of Poirier-Bienvenu neurodevelopmental syndrome and review of literature

The Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) is a rare disease caused by mutations in the CSNK2B gene, which is characterized by intellectual disability and early-onset epilepsy. Mosaicism has not been previously reported in CSNK2B gene. POBINDS is autosomal dominant and almost all reported cases were de novo variants. Here, we report two patients were diagnosed with POBINDS. Using Whole Exome Sequencing (WES), we detected two novel CSNK2B variants in the two unrelated individuals: c.634_635del (p.Lys212AspfsTer33) and c.142C > T (p.Gln48Ter) respectively. Both of them showed mild developmental delay with early-onset and clustered seizures. The patient with c.634_635del(p.Lys212AspfsTer33) variant was mutant mosaicism, and the proportion of alleles in peripheral blood DNA was 28%. Further, the literature of patients with a de novo mutation of the CSNK2B gene was reviewed, particularly seizure semiology and genotype-phenotype correlations.

Updates on the diagnostic evaluation, genotype-phenotype correlation, and treatments of genetic epilepsies

PURPOSE OF REVIEW

This article reviews the latest publications in genetic epilepsies, with an eye on publications that have had a translational impact. This review is both timely and relevant as translational discoveries in genetic epilepsies are becoming so frequent that it is difficult for the general pediatrician and even the general child neurologist to keep up.

RECENT FINDINGS

We divide these publications from 2021 and 2022 into three categories: diagnostic testing, genotype-phenotype correlation, and therapies. We also summarize ongoing and upcoming clinical trials.

SUMMARY

Two meta-analyses and systematic reviews suggest that exome and genome sequencing offer higher diagnostic yield than gene panels. Genotype-phenotype correlation studies continue to increase our knowledge of the clinical evolution of genetic epilepsy syndromes, particularly with regards to sudden death, auditory dysfunction, neonatal presentation, and magnetoencephalographic manifestations. Pyridoxine supplementation may be helpful in seizure management for various genetic epilepsies. There has been interest in using the neurosteroid ganaxolone for various genetic epilepsy syndromes, with clear efficacy in certain trials. Triheptanoin for epilepsy secondary to glucose transporter 1 ( GLUT1 ) deficiency syndrome is not clearly effective but further studies will be needed.

Challenging Occam’s Razor: Dual Molecular Diagnoses Explain Entangled Clinical Pictures

Dual molecular diagnoses are defined as the presence of pathogenic variants at two distinct and independently segregating loci that cause two different Mendelian conditions. In this study, we report the identification of double genetic disorders in a series of patients with complex clinical features. In the last 24 months, 342 syndromic patients have been recruited and clinically characterised. Whole Exome Sequencing analysis has been performed on the proband and on both parents and identified seven patients affected by a dual molecular diagnosis. Upon a detailed evaluation of both their clinical and molecular features, subjects are able to be divided into two groups: (A) five patients who present distinct phenotypes, due to each of the two different underlying genetic diseases; (B) two patients with overlapping clinical features that may be underpinned by both the identified genetic variations. Notably, only in one case a multilocus genomic variation was already suspected during the clinical evaluation. Overall, our findings highlight how dual molecular diagnoses represent a challenging model of complex inheritance that should always be considered whenever a patient shows atypical clinical features. Indeed, an accurate genetic characterisation is of the utmost importance to provide patients with a personalised and safe clinical management.

De Novo CSNK2B Mutations in Five Cases of Poirier–Bienvenu Neurodevelopmental Syndrome

The Poirier–Bienvenu neurodevelopmental syndrome is an autosomal dominant disorder characterized by intellectual disability and epilepsy. The disease is caused by mutations in the CSNK2B gene, which encodes the beta subunit of casein kinase II, and it has important roles in neuron development and synaptic transmission. In this study, five Chinese patients were diagnosed with Poirier–Bienvenu neurodevelopmental syndrome caused by CSNK2B mutations by whole exome sequencing. We detected four different de novo variants of the CSNK2B gene in these five unrelated Chinese patients: two novel mutations, namely, c.100delT (p.Phe34fs^*16) and c.158_159insA (p.Asp55fs^*4), and two recurrent mutations, namely, c.1A>G (p.Met1?) and c.332 G >C (p.R111P). All five patients showed mild-to-profound intellectual disabilities/or learning disabilities and developmental delays, with or without seizures. Although intellectual disability/developmental delay and epilepsy are the most common manifestations of CSNK2B deficiency, the clinical phenotypes of probands are highly variable, and there is no significant correlation between genotype and phenotype. An abnormal stature may be another common manifestation of CSNK2B deficiency. Here, we report the effects of growth hormone (GH) therapy on the patients' linear height. In conclusion, Poirier–Bienvenu neurodevelopmental syndrome is a highly heterogeneous disease caused by mutations in the CSNK2B gene. The phenotype was highly variable, and no significant correlation of genotype and phenotype was found. Patients with short-stature and CSNK2B deficiency may benefit from GH therapy. The identification and characterization of these novel variants will expand the genotypic and phenotypic spectrum of Poirier–Bienvenu neurodevelopmental syndrome.

The Genetic Diagnosis of Ultrarare DEEs: An Ongoing Challenge

Epileptic encephalopathies (EEs) and developmental and epileptic encephalopathies (DEEs) are a group of severe early-onset neurodevelopmental disorders (NDDs). In recent years, next-generation equencing (NGS) technologies enabled the discovery of numerous genes involved in these conditions. However, more than 50% of patients remained undiagnosed. A major obstacle lies in the high degree of genetic heterogeneity and the wide phenotypic variability that has characterized these disorders. Interpreting a large amount of NGS data is also a crucial challenge. This study describes a dynamic diagnostic procedure used to investigate 17 patients with DEE or EE with previous negative or inconclusive genetic testing by whole-exome sequencing (WES), leading to a definite diagnosis in about 59% of participants. Biallelic mutations caused most of the diagnosed cases (50%), and a pathogenic somatic mutation resulted in 10% of the subjects. The high diagnostic yield reached highlights the relevance of the scientific approach, the importance of the reverse phenotyping strategy, and the involvement of a dedicated multidisciplinary team. The study emphasizes the role of recessive and somatic variants, new genetic mechanisms, and the complexity of genotype–phenotype associations. In older patients, WES results could end invasive diagnostic procedures and allow a more accurate transition. Finally, an early pursued diagnosis is essential for comprehensive care of patients, precision approach, knowledge of prognosis, patient and family planning, and quality of life.